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LECTURES
ON THE
(Elements  of  Cljemistrp,
DELIVERED
IN THE UNIVERSITY  OF EDINBURGH;
                 BY THE fl,ATE

         JOSEPH BLACK, M. D.

   PROFESSOROF CHEMISTRY IN THAT UNIVERSITY,
PHYSICIAN TO HIS MAJESTY FOR SCOTLAND; MEMBER OF THE ROYAI.
  SQCIF.TY OF EDINBURGH, OF THE ROYAL ACADEMY OF SCIENCES
        A^ PA'RIS, AND THE IMPERIAL ACADEMY OF  .
            -*eiEHSt.t at s-r. PETERSBURG.
PUBLISHED FROM HIS MANUSCRIPTS
       JOHN ROBISON, LL. D.

PROFESSOR OF NATURAL PHILOSOPHY IN THE UNIVERSITY
             OF EDINBURGH.
i-fRST AMERICAN EDITION FROM <THE LAST LONDON EDITJOS
VOL. II.
_______ /.. X (- <> (r  I
          PHILADELPHIA:    ~-
U.INTED * OR MATIIEW CAREY, NO. 122,' MARKET-STREET,
   "Y B/ GRAVES, NO. 40, NORTH FO VRTH*STREET. V
    /          *.....:
               1806. 
l*r>|! 
LECTURES
IS   V^T***''   /.
ON
CHEMISTRY.
THE  CHEMICAL  HISTORY OF  BODIES,
                  INTRODUCTION.

    HAVING acquired some knowledge of  the general
effects of heat and mixture, the great chemical agents in
nature, you are enabled to understand the more particular
doctrines of chemistry.   These comprehend the descrip-
tion of all the great classes of natural substances, and the
peculiarities which are observed,, in the effects  of heat and
mixture upon  each ;  which peculiarities serve as distin-
guishing characters of  each, ascertaining what  may  be
called  their chemical nature, qualities, and powers.   It is
thus that we are able to distinguish gold from  lead.   The
first bears the  most intense heat of our furnaces, and the
action of air, while  thus subjected to heat, without any
'change in its qualities ;  whereas the  same treatment will
quickly change the lead into dross or  glass. These pecu-
liarities, being  constant and  uniform, give  us .certain
marks of distinction,  and also enable us to employ both
substances for very interesting purposes.
   If the peculiar effects of heat and mixture  on  an indi-
vidual body be  altogether .peculiar to itself, the study of
thenv.would be endless.   But there are  certain classes  of 
   t SPLXVLATIOXS.TWtf ELEMENTARY ATOMS.

  natural substances, on which  these agents produce effects
  so similar, that one of them may be taken as the represen-
v  tative. oj . all  the^ rest.   Philosophers  have  taken  much
  pains  to class the substances that we  see around us,  by
  means of those resemblances in  the effects  of heat  and
  mixture that have  been observed;  and have thus obtained a
  chemical arrangement of natural substances, which makes
  the study of their properties  much more expeditious and
  comprehensive.
     In thinking on  a proper method, the one which occurs
  the most readily, and which appears at  first sight the most
  proper, is  to begin with an account  of the  elements, or
  elementary kinds  of matter, of which  all things are  com-
  posed ; and,  after explaining  the powers  and  properties
  ol those elementary  substances,  to  shew  how, by  their
  various combinations with one another, thev give rise  to
  the  various  productions of nature.     nd,  that  there  is
   some foundation for thinking of such an order or system,
   is sufficiently plain.   It  is evident that  there  are in reality
   certain elements,  or elementary substances, which are few
   in number, and of such a nature  as to be exempted from
   decay or change, but capable of being variously compound-
   ed together, and separated again, so as to give origin  to
  the productions which we see daily arise, and to  the per-
   petual changes of one form or state of matter into  ano-
   ther.
     This is evident from the constant regularity and general
   uniformity of the productions of nature.   There is a cer-
   tain succession and rotation of forms which the same mat-
   ter  undergoes, and through which it has repeatedly passed
   with regularity, fiom the beginning, or from the earliest
   account of time,  of which we have  any knowledge.   At
   least, any examples of irregularity that  occur  are so incon-
   siderable i:i number, that thev mav  be overlooked.   The
   water arises in vapours from the ocean,  chiefly to form
   the clouds; these again descend  upon  the dry land  in
   rain,  which,  penetrating the soil, occasions  and  supports
   the vco^ution of plmvs.   The greater number of plants
   serve fo:  ihe nourishment of animals; all of which, with
   the  remaining plants,  are  dissolved  again at  last, and 
    SPFXULATIONS  ABOUT  ELEMENTS.    5

return to the elementary substances from which they were
originally composed, and  from  which similar plants and
animals are to be produced.
   This rotation has continued from the earliest accounts
of time, in  the  most steady and regular manner.   The
productions  of nature have  not only succeeded one ano-
ther in the same  general order ;  but have been from the
beginning,  so far as our knowledge reaches, invariably the
same.  An oak of the present time has the same general
nature, and the same properties, as those of all other oaks
that  have  ever existed.   We find the same texture in its
wood and  bark ;  a  similar  disposition in general in the
root  and branches ;  the leaves have the same form ; the
juices the  same  astringent power ; the  fruit is  moulded
to the same  form of an acorn, and has the same  invaria-
ble property of never producing  any other  tree  than an
oak.
   All this shews that the elements  of bodies are perma-
nent  and  unchangeable.   Had they  been liable to any
gradual change or decay, the oaks of the present times,
 composed  of those changed materials, would not be found
to have the same qualities as  the oaks of remote  ages :
and the order and course of nature, as well as the qualities
 of her productions,  would have been undergoing a gradual
 change, which, so far as our knowledge reaches, has not
 actually taken place.
   Such obvious reflections on the course of nature have, in
 the earliest ages of philosophy of which we have any ac-
 counts,  suggested the supposition of  a certain number of
 unchangeable elements, of which it was imagined all things
 were composed, and on the successive separations and re-
 unions of  which, depended the decay and reproduction of
 the objects which nature  presents to our view.  This was
 the  meaning of the  opinion ascribed  to  Democritus,
 That all things were formed of atoms.  And others of the
 Greeks, in consequence probably  of their intercourse with
 the Egyptian philosophers, began to form and teach a sys-
 tem  upon  this subject.   They  assigned four elements, or
 elementary kinds of matter, viz. tire, or the matter of fire,
 air,  •>;•'.•!<'/•, and <rn:th.   And by the  different combinations 
  6   SPECULATIONS ABOUT ELEMENTS.

  of those elements, they supposed that all the different bo-
  dies in nature were formed.
    These four supposed  elements  were accordingly con-
  sidered, until very lately, as the primary elements  of na-
  tural bodies ; insomuch, that Mr. Macquer, in his System
  of Chemistry, thought it proper to begin by treating- these
  four kinds of matter as  elementary ; and endeavoured to
  explain the nature and qualities of some of the productions
  of nature, which he first describes by assigning the  number
  of these elements which he  imagined entered  into their
 composition.   But it appears from the sequel, that he was
 not fortunate, nor sufficiently considerate, in choosing thi6
 method.
   In the first place, chemistry gave, at  that time, too little
 light into this subject,  to enable him to form a system of
 this kind with any degree of assurance.   On the contrary,
 there were  many reasons for doubting, even at that  time,
 that these four supposed elements were in reality  simple,
 elementary, and unchangeable substances ; and  now, we
 have direct evidence from experiments, that most of them
 are not.
   Atmospheric air has been demonstrated to  be  a  com-
 pound mass of  more than two or  three different kinds of
 matter.
   Water is also believed now to be a compound body.
   And of the  purest and  most simple  earthy matter, six
 or more different kinds are now reckoned, which we cannot
 reduce to greater simplicity by our operations.
   The  truth is, that our knowledge of nature is not yet
 brought to that state of advancement, which  might enable
 us to follow, with propriety, an  order of  this kind.  We
have advanced a considerable  way in our analysis of many
different substances.   But our knowledge of their compo-
 sition and origin is far too imperfect,  to  give solid foun-
dation for  an attempt to arrange them, or 10 explain their
different qualities, by beginning from their ultimate ele-
mentary principles.   We  should certainly be in  danger of
falling into many errors and mistakes by such an attempt.
   To avoid this, therefore, I do not  pre. .nd to determine
what are the ultimate elements' of bodies.  I content  myself
* 
       CONVENIENT ARRANGEMENT.       7

with distinguishing and  dividing the principal  objects of
chemistrv into a number of classes,  each of which compre-'
hends  substances  that bear a remarkable resemblance or
analogy to one another,  in their chemical properties,  and
differ from those comprehended in the other classes.  And
I offer these classes to your consideration in what appears1
to me to be the most convenient order;....I mean the order
in which" the most independent, and I  may say elementary
facts,  are first stated; and  the rest are  described  after-
wards, in that  succession and order in which they can be
 explained and understood, by the  knowledge o£ the facts'
 and doctrines that have been stated before them.
    An attempt  to  form classes, or  assemblages, of the
 objects of chemistry, was made  long since by the elder
 chemists, and their classes were three in number.  They
 chose to give them the  title of kingdoms.   The frst com-
 prehended all animals and animal substances ; the second
 the vegetables ; and the third fossils.   These assemblages
 may appear at  the first view to have some foundation in
 reason, but they are in fact very  improper.   They bring
 together a great number of objects,  which have no simi-
 larity in their chemical properties, and they separate others,
 which, being similar,  or the same in a chemical view of
 them, ought certainly to be assembled and considered to-
 gether.
    In the arrangement which has prevailed for some time
 past among the chemists, and which I have found to be the
  most suitable to our purpose, the  objects of chemistry are
  distinguished into five  classes, which are, 1st, The Salts;
  idly, The Earths ; 3dly, The Inflammable Substances ; 4thly,
  The  Metals ; and 5thly, The Waters.
     These  classes take  in a great  part of  the materials of
  which  the animal and vegetable substances are composed.
  But  yet there are some of  these materials that do  not, on
  a first consideration,  easily find a place in any of  these
  classes.   And beside this,  the animal and vegetable sub-
  stances are compounded in  such a particular manner, that
  they have some chemical qualities peculiar to themselves
  on that  account.  „ne. '■'. For these reasons, it is proper and
< 
 8         OF CHEMICAL  SUBSTANCES.

 necessary to take a chemical view  of the vegetable  and
 animal substances, after the five classes already mentioned
 have been considered:  and this shall accordingly be done
 in the end of this course.
   N. B. It may perhaps be thought that we shall be guilty
 of an omission, if we do not constitute a class of airs or
 gases, as they are now named.  But there is no  necessity
 for constituting such a class, and even the propriety of it
may be called in question.
   These  gases are acknowledged to be various kinds of
 matter,  combined with latent  heat, or the matter of heat,
the calorique of  the French chemists.   And why should
substances of such very different natures be assembled  into
one class ? For this reason alone, that they were combined
with latent heat, and thereby  reduced to a form  or condi-
tion, to which many other bodies can be reduced by it.
We might as well think of classifying the objects of che-
mistry into those that are hot and those that are cold, or
into those that are solid and  those that are fluid,  which
would be  very improper, when it is in our power to make
the same  body hot or cold, or solid or fluid.   It must be
confessed that we have not been able hitherto to deprive
some of the gases of their latent heat, and to reduce them
to  a condensed state,  without combining them with other
matter ;  but this is certainly  in our power with  regard to
others ;  and means may possibly hereafter be discovered
for condensing them all.   But whether this should succeed
or not. there is no reason for assembling into one class sub-
stances, which are, in fact,  more dissimilar in their che-
mical properties than any substances that we know ;  and
resemble  each other only in a quality,  almost purely  me-
chanical (their elastic fluidity) merely because they derive
this nerial form from heat combined  in them.
   But, although it appears improper to form such a class,
 I do not mean to leave these substances unnoticed.  Ver\
convenient opportunities will occur during this course for
bringing them into view, and  I shall not fail to make  vou
thoroughly acquainted with them all.   (See Note  26, at the
end of this Illume. J 
SALTS.
9
   In  prosecution, therefore, of the arrangement that  I
mentioned as peculiarly convenient, I begin with the con-
sideration of CLASS FIRST.
CLASS  I,
                       SALTS.


   THIS class is placed  first because  the knowledge of
 their properties, both general and particular, is almost in-
 dispensably necessary for the investigation of the interest-
 ing properties of all other substances.  They stand in very
 interesting relation to every chemical substance;  and thus
 are  considered as the most general agents in the way of
 mixture.   This, of  itself, raises a  surmise that they are
 of a very simple  nature, and nearly allied to the  elements
 of which all are composed.   This has been a very current
 opinion  and has been supported by specious  arguments.
 But I apprehend, that before we have  gone over the five
 classes of our arrangement,  we shall find the proofs be-
 coming very weak indeed.
   In describing the  salts, I shall first enumerate the quali-
 ties  common to them all, and afterwards take a nearer view
 of their  several kinds.   Moreover, as, in defining chem-
 istry, I said that it  is the study of the effects of heat and
 mixture  on all  bodies; so, in enumerating the  chemical
 qualities  of  salts, and, indeed, of  all bodies of  whatever
 class, I shall first describe the effects of heat on them, and
afterwards,  the  consequences  of mixing  them  with  one
     voi ,11.        ^       B
f 
.10                     SALTS.
another, and with other bodies.   Moreover, in doing this,
I subjeet myself to a rule which I shall endeavour to follow,
with all reasonable strictness, through the whole of this
course, namely, that while I am treating any particular
substance, or class of substances in the way of mixture, 1
shall mix them with those  others only which have been al-
ready described.   If I cannot rigidly  abide by  this rule
on every occasion, I  shall be careful to consider  the mix-
ture with substances  which are as far known to you as the
argument proposed  by the mixture  may require.    No
quality of the other substance shall be employed in the ar-
gument, but such as is known with the fullest evidence,
and understood, as far as I shall employ it in  argument.
The result  of this caution  on my part, will, indeed, be  a
slower progress than may be acceptable to some impatient
minds: but the knowledge which we shall acquire will be
more confident and satisfactory. Sir Isaac Newton said to a
celebrated foreigner, who was complimenting him on his
wonderful discoveries, and the greatness of  his genius,
which was  able to comprehend such vast objects l* Indeed,
" Sir, you are pn a mistake on both points.  The objects
" are, indeed, vast and magnificent; and therefore I made
si a choice fortunate for  my reputation.   But they are
" comprehensible by the most ordinary genius, if he will
" take my method,....never to hurry.   If I have any ad-
u vantages over  other naturalists,  it rs  only  in  a more
" patient thinking,  in  which I  perhaps exceed  many of
" them.  To this I am indebted for all my success."   Let
us imitate the patience of this great man, and hope that we
shall have some portion of his success.
  / In compliance, therefore, with my rule, in the conside-
ration of the saline substances, 1 shall, at present, take no-
tice of such qualities only as they manifest in mixture with
water, and with one another, deferring the effects of mix-
ing  them  with earths, metals, and other bodies, till we
consider those classes themselves. 
11
             OF  SALTS  IN GENERAL.

   In  the definition which is commonly given of a sak, an
 attempt is made to enumerate the qualities by which salts
 are  known to agree  with one another, and to differ  from
 other classes of the objects of chemistry.
   Thus, the salts, in general,  are said to be substances
 easily  melted, or volatilized by heat, soluble in water, not in-
flammable, and sapid, or, when applied to the tongue, pro-
 ducing the sensation of taste.
   Some objections may be offered to this definition ; but it
 is impossible to contrive a definition of them that will  be
 free from all objections : and the same difficulty occurs in
 attempting to define any other assemblage or class of the
 productions of nature.   There are, in reality, no classes in
 nature distinctly defined ; the  productions of nature are so
 very numerous, and so much diversified, and there is  such
 a gradation throughout the whole,  from one to another,
 that it has  been found impossible  to  arrange them  into
 classes precisely limited, and liable to no exceptions.
   I shall not, therefore, be anxious to give an unexception-
 able definition of the  salts. I hope to give you better infor-
 mation of them, by entering into their history, and by  enu-
 merating their .qualities.
   The most pure state in which we can exhibit the salts,
or the state under  which they are the most free from ad-
 mixture with all  other  matter  that is not salt, is the form
 of a white, hard, brittle mass, more or less transparent,  and,
 in some  cases, perfectly transparent.
   The effect of heat on salts is first to produce fusion, with
an appearance like white wax.   All the salts can be meltad
 in this manner, but  they require very different heats to
their fusion.   Most of them require different degrees of
red heat.  When cooled, they return to their former state:
 and it is only by fusion that they are brought to that now
described.
   Salts can also be made to assume the form of vapour,
by heats under our command.   But  they differ still more
widely with respect to the force  of heat necessary to pro- * 
 12      SOLUTION  OF SALTS  IN  WATER.

 duce this effect.  Some require the most violent heats that
 we can raise. Others are so volatile that they are disposed
 to assume the  form of vapour even in the  ordinary heats
 of the  air.   Their differences in this respect shall be men-
 tioned when we are describing the different kinds of the
 salts. And this is all we can say in general of the manner in
 which salts are affected by heat.
   In relating the effects of mixture upon salts, we can only
 mention at present the effects of mixing them with water,
 and  some  of those produced by mixture with one  another.
 Water  is the only body  which, in the way of mixture,
 produces  effects upon  salts  that can be  considered  as
 general, or which are similar in  a  certain degree on all
the different salts.   And  one of these  effects  has been
 mentioned already  in defining salts, when we said they are
 bodies soluble in water.
   All  saline substances, when thrown into water, dissolve
 in it more  or less  readily.  This  is  so  well known and
 familiar a  property of all salts, that it is inseparably con-
 nected  with the idea of salt in the mind of a chemrst.
   There is therefore an attraction between water and salts,
 a disposition to  combine  by chemical union.   The only
 difference  of salts from  one another in this respect, is in
 the force of this attraction,  which is very different in the
 different salts.   It  is in some so powerful, that they attract
 the humidity which is contained in  an imperceptible state
 in common atmospherical air,  and are dissolved by that
 humidity into a  liquid.   Such  salts, therefore, are called
 deliquescent salts, as I remarked formerly: and it requires
 the utmost care  to keep  them  in the solid form.  They
 must be kept in vessels very accurately closed.
  When we dissolve a salt in water, we have an opportunity
 of observing several phenomena :
   I. The  first which occurs, is the  separation of part of
 the air which the water contains, and that which generally
 adheres to the salt. • The moment the salt dissolves in the
 water,  this fluid appears white or turbid.   And  when we
 examine the cause, we find numerous little bubbles of air
 which in a short time rise to the top, and then the solution
 becomes transparent.   This  is an example  of elective at. 
    PHENOMENA  OF  SALINE SOLUTIONS.  13

traction or separation  of two bodies by means of a third.
 (See Note, 27, at the end of the  Volume.)   This separation
 of the air from the water is more sudden and violent, if the
 water be made boiling hot before the salt is added ; a vio-
 lent  momentary ebullition takes  place,  almost like  an
 explosion.
   2.   A  second particular observable when  we dissolve a
 salt in water, is, that the sensible heat of the mixture under-
 goes some change.  In the greatest number of cases, the
 mixture  becomes colder than the  materials were before:
 but.,  in some  cases, it becomes warmer.  Even the same
 salt,  added  in different  states  to water, will increase the
 sensible heat of the water  at one time, and  diminish it at
 another.
   The late  Dr.  Irvine  supposed that the capacity of the
 mixture for heat is changed; and  it appears to be so from
 some late experiments*.
   3.  A third  particular which  comes under our observa-
 tion in dissolving salt, is,  that the  more we dissolve in the
 water, the more slowly it dissolves the further additions of
 salt,  until a certain quantity has been added; after which
 it dissolves  no more.   The water is then said to be  satu-
 rated; and the solution is called a saturated solution.   But
 this proportion of salt, which saturates water, is  found to
 be very different, when we make the  experiment,  either
 with salts of different kinds, or with water of different de-
 grees of heat.   In trying the different salts, we  find that
 each of them differs from almost every other.  Some re-
 quire twenty times their weight, or more, of the  water, to
 dissolve them ;  while others are so soluable, as to dissolve

  * The experiments on this subject were, in general, in this form : the heat
required for changing the temperature of  tl.e materials one degree, was
ascertained ; as also the  heat necessary for changing that of the mixture.
 In several cases,  the last was found greater or less than the  sum of the
two others, according as the mixture produced  cold or  heat.  Hence Dr.
 Irvine was induced to confide more in  the  truth  of his  general principle.
But Mr. Gadolin,  and afterwards  Lavoisier, and De la Place, shewed that
 there was no steady connection between those phenomena, the exceptions
 being equally numerous, if not more so; and the phenomena appear, as yet,
altogether, anomalous  f.oitok. 
 14 SOLUBILITY VARIES WITH THE HEAT.

 perfectly in le3s than an equal weight.   And the greater
 number of those very  soluble salts shew, by other particu-
 lars, that they have a stronger attraction for water  than
 other salts.  Such salts  attract it  from moist air,  and run
 per deliquiunt, becoming perfectly fluid, with a very small
 quantity of water.   Moreover, these salts, without excep-
 tion, retain the water, more strongly than others,  when we
 attempt to separate it by heat. The other salts, which are
 less soluble, or require much water, are not liable to deli-
 quescence,  and are more  easily deprived of  it  by heat.
 But the solubility  of  most salts is greatly affected also by
 the heat of the water.
   This is a curious subject, and the intimate knowledge of
 it requires, and leads to very nice speculations  concern-
 ing the manner of chemical action.   But I find that it will
 be long before we can safely proceed  in this way.  It is
 better for us to be contented with accurate  and extensive
observation of the facts.   It will be no mean service to the
 chemist, to  state, in a number of important cases, the pro-
 portion in which water dissolves salt at different tempera-
 tures.   You will find a considerable collection of  this kind
 by a Mr. Pfa.hler, in Kozier's Journal for 177$, and occa-
 sional observations by almost every chemical writer.
   The  most simple and  unexceptionable form of the expe-
 riment  is to throw into cold  water a  greater  quantity of
 salt than it  can dissolve.   Having made a saturated solu-
 tion  in  that temperature, pour it off into a vessel,  in which
 it may  be made warmer  to any degree.   Pour into this
 solution more salt than it can dissolve in that temperature;
 and pour  off the  saturated solution,  to  be treated in the
 same manner at a higher temperature, and so on.   Having
 noted  the quantity of these solutions,  (by weight)  and
 knowing the strength  of brines of different weights, we
 obtain the degrees of solubility corresponding to  different
 temperatures.   1 he difference in some salts is very great.
 A salt, which you will afterwards know by the name of S.
 de Seignette, requires an ounce of water, of the tempera-
 ture of 50°, to dissolve 37 grains.  But an ounce of boiling
 hot water dissolves 640 grains, nearly 18 times as much as
 the cold water.   Nitre  is about 7 times  more soluble in 
   DR. HUTTON'S  CURIOUS OBSERVTIONS. 15

boiling water, than at 50° : Glauber's salt is about 3* times:
green  vitriol i3 about  8 times, &c. &c.         ,
   My friend  Dr. Hutton engaged in a series of experi-
ments  of this  kind, and conducted them in the form I have
been describing.   He did not content himself with trials
in two extreme  temperatures,  but took three or four for
each salt.  This showed him that the progress of solubility
was not equable in any salt, but  that, in most of them, the
solubility increased faster than the temperature : for, when
he took a temperature half way between the two extremes,
he found that the difference between the quantities  of salt
dissolved in the hottest water, and in that of mean temper-
ature,  was generally greater than  the difference between
this last and the coldest solution.
   Hence it followed, that the  salt contained in a  pint of
the  hottest, and  a pint of the coldest, was more than was
contained in two  pints of the mean temperature, (all three
being  saturated solutions); and, therefore, if the two ex-
treme  solutions were mixed, the  mixture should  not be
able to keep the salt dissolved.   He found, accordingly,
that it did not,  but  made an instantaneous,  and,  some-
times, a copious precipitation.   He also observed consid-
erable  deviations from the temperature which he expected
on mixture.   It were to be wished that he had  prosecuted
these curious  experiments ;  for this general law which he
observed is a  curious and important one.  But his atten-
tion was called off by a most important consequence which
he deduced from it, namely, if  the solubilitv of water in
air  observes  such a law,  it follows, that two saturated
strata  of air, of different temperatures,  cannot mix with-
out precipitation.  On this he has founded his  Theory of
Rain ;  a theory which explains some of the greater changes
in our atmosphere more  perspicuously than any I  know.
(See note 28, at the end of the volume.)
  This observation holds true with respect to most salts.
Perhaps there is  only one which we can say is an excep-
tion, viz. Common Salt.   Macquer says that all deliques-
cent salts are  exceptions ;  but this  is not just.   Besides,
it is not easy to determine  what salts are deliquescent, and
what not. 
16  SALTS UNIFORMLY  DIFFUSED IN A BK.
   From some of the particulars already stated, as obser-
vable in dissolving the salts, you will perceive the founda-
tion of  an opinion of Sir Isaac Newton concerning  those
solutions.   He  supposed that the particles of a  salt dis-
solved in water are equidistant from one another through
the whole of the water, and, therefore, arranged in a regu-
lar order, or, as he expresses it,  in  fank and file.  This
arrangement is, in reality,  a necessary  consequence  of
some of the particulars we observed in the action  of water
upon salt.   We  find that  water has a stronger attraction
for salt, in proportion as it is purer, or contains less salt;
for, in proportion to the quantity of salt it already contains,
it dissolves further additions of salt the more slowly. This is
all the proof that we can desire, that it is acting upon them
with a weaker attraction, or dissolving power, until it have
dissolved a certain quantity, after  which it cannot dissolve
any more.   It is,  therefore, evident, that if, in a solution
of salt,  any part of the water contain less salt than the rest,
that part must have a stronger attraction,  and must draw
some particles of salt from the others into itself, until the
salt be  distributed  through the whole with the  most exact
equality and regularity ; and the particles of it  are, there-
fore, equidistant throughout the liquor.
   When we examine the  solidity of thi» reasoning  by an
experiment, we have the pleasure to find  facts agree  ex-
actly with the theory ;  for, however unequally  the salt be
distributed in the liquor at first, it is sure to spread from.
the parts which contain most, to those which contain lessr
until it is equally diffused  through the whole.
   But it is proper, however, to observe on this occasion,
that when  the  liquor is preserved from  external disturb-
ance, this  progress of the  saline particles through it is-
excessively slow.   This  is  the pro'of of  the assumptions
on the other side, namely, that an internal motion  is neces-
sary.   It  requires so long a time, that an  impatient  and
inconsiderate observer  will perhaps conclude that it does
not take place.   But it is easy to explain why it requires so
much time.   There are two causes of this :  1st, the weight
of the saline particles, which are heavier than those of the
water,  generally about twice as heavy  ; and, 2dly, the very 
          SOLUTION  PROCEEDS SLOWLY.      17

   small distance to which chemical attraction reaches round
   the  particles of bodies.  You will perceive  the effect of
   these two causes,  if you consider with  a little  attention
   what must necessarily happen, in a solution in which the
   salt  is unequally distributed  through the water.   Let us
   suppose, for example, that I put  into  a glass a certain
   quantity of a saturated solution of salt,  and  a quantity of
   pure water, without  mixing  them together  by agitation,
   which will be best done by introducing the saturated solu-
   tion under the water, by means of a funnel and pipe reach-
   ing to the bottom of the glass ;...the solution being poured
s  slowly into the  funnel, will rise quietly  under the water,
   and  they will be separated  by a surface perfectly even.
   The solution of a deep-coloured and heavy salt is the best
   for this purpose.  Blue vitriol answers very well.  It must
   immediately happen, that the lowest part of the pure water,
   which is in contact with the upper surface of the solution,
   while it draws up some particles of salt out  of that upper
   surface, must form an horizontal stratum, or  layer of fluid,
   which will be  less salt  than the saturated  solution,  and
   which will be  interposed between  it and the  pure water.
    No  sooner does this  take  place, than the lowest part of
   this stratum will  draw up  more salt from  the  saturated
   solution upon which  it lies ;  while  at the same time,  the
   pure water will draw up some salt out of the upper sur-
    face of the stratum.   And  thus innumerable strata will be
    produced within a very small space,  and in a very short
    time,...all lying between the pure water and the saturated
    solution ;  the lowest of which will contain less salt than  the
    saturated  solution, and each of  the rest less than the one
    immediately below it.  But when matters are in this condi-
    tion, every two contiguous strata, which (on account of the
    extremely small  distance  to which chemical  attraction
    reaches) are  the  only ones that can act on one another,
    must act  with  an extremely  weak force.  The upper one
    must draw salt from the one under it very weakly, for this
    reason, that they differ very little from one another in salt-
    ness,  and therefore  in  attraction for salt.   And, for  the
    same  reason,  the pure water above will have but a weak
    nower to draw the  salt up from the uppermost and most
        vol..  tf.                 c 
18   PROGRESS OF SOLUTION EXPLAINED.

diluted  stratum.   And now, if we consider that the  par-
ticles of the  salt are heavier than those of the water,  it is
easv to conceive how their  gravitation, together  with the
resistance  they  must meet with  in moving through  the
fluid, must almost  counterbalance' the  force with which
thev are drawn up, so as  to render the motion excessively
slow.
   The slowness with which the equal diffusion of a salt in
water is performed,  when  left to  itself,  is  therefore evi
dentlv a necessary consequence of the very  small and  im- •
perceptible distance  to which chemical attraction reaches,
and  also of tin  greater weight or  gravitation of the   salt
than of the water*.  And I thought it was worth while to give
a clear view of the matter,  once for all, that you may un-
derstand better how to make solutions of salts, for different
purposes,  and the necessity  of employing mechanical agita-
tion to promote  the equal distribution of the salts through
the  whole  of the water,  in a moderate  time.   In some
of the arts,  great mistakes have been committed  some-
times, in consequence of  the ignorance of  this necessity.
In the bleaching of linen, for example, and some other arts,
the  vitriolic acid is employed in part of the process, very
largely diluted with water.  A careless workman may think
it enough to pour in  the proper  quantity '>! acid, not recol-
lecting that its great weight will keep it at the bottom,  and
that if it be not  stirred briskly about, it may be long ere  it
be equably diffused through the water.   When goods are

  * It is, indeed, the clearest proof of the nature of chemical action, and oi
the very small distance to which it extends.  It shews that it does extend to
some distance, otherwise there would be nothing to move a particle out oi
its place.  However %trongly particles attract one another in  absolute fcon-   v
tact, this may cause them to cohere, but will never move a quiescejii particle <'
out of its place.  I must at the same time observe, that some solutfonfiof
saline substances manifest an inequality in their saturation, even aftefc-We
have reason to think them perfectly uniform.  When a strong solution of sal
ammoniac, or of saccharura saturni, has  been made perfectly uniform by agi-
tation, it becomes unequal, in a small degree, by long keeping, the lower strata
containing more salt than the upper.  It is accompanied by a very curious
circumstance.  If the solution be poured into a hollow glass prism, having
the angle downwards, end it be  allowed t"> remain  undisturbed for  some
months, it acquires a double refraction, like roejt ciystal___kditop. 
SEPARATION OF SALTS BY EVAPORATION. IS

put in to be soured, they get  into this very  acid and  cor-
rosive part of the liquor,  and are frequently eaten  into
holes by it.
   Remember, therefore, when you dissolve or dilute salts
in water, to quicken  the equal distribution of the salt by
agitation: and be assured, that if there be enough of water,
the salt will remain for ever after equally diffused through-
out the whole.
   It  is  somewhat surprising  that  the solutions of many
salts begin to  boil with a less  heat than pure water does.
But they soon rise to  a temperature considerably above
that of boiling water, and nearly the same in them all.  I ob-
serve that this first boiling is sudden and transitory; so that
I think it probable that it is the disengagement of air which
adhered to  the salt.   I observe,  that on pouring  boiling
water on a solution of salt, or throwing salt into  boiling
water, there is a sudden puff of  ebullition like an explo-
sion.
   Most of the salts may be separated from  water  by eva-
poration, because the greater  number are  much less  vola-
tile than water, and do not adhere with such great force as
greatly to diminish the volatility of the water.
   But this  evaporation may  be conducted  in two ways,
either briskly and  tin inter rupte'd,  till  all  the water is
dissipated; or partially, and by repeated operations.   The
conse'quence of  the. first method is, that the  salt remains,
forming a  white mass  like chalk, or  hardened lime-mor-
tar, adhering  more or less to  the  vessel in which the  eva-
ration was performed.
   This  is called  evaporation  to  dryness; and is at-
tended,  in most cases,  with  the loss of  some of the salt,
which evaporates with  the  water, in consequence of their
mutual attraction.
   But the second  method is that which is commonly fol-
lowed, at least with regard to a number of salts which are
prepared in large quantities for sale, such as Glauber's salt,
saltpetre, alum, vitriol, and others.  And the consequence
of this method of proceeding  is,  that the salt is obtained
in a different  form.  This method consists in evaporating
a solution to a-certain  degree, so that  though the water 
20              CRYSTALLIZATION.

which remains is still sufficient to retain  all the salt dis-
solved, as  long as it is kept warm over a fire ; it is too lit-
tle, however, to retain it all dissolved when it is cold.    It
it be taken off, therefore, and allowed to cool, a part of the
salt must, and does separate.
  A salt deposited in water in this manner is always  for-
med into angular masses,  having polished surfaces, more
or less of a regular figure, and transparent.  These masses
are called  Crystals, from their resemblance to the natu-
ral stones  of that name.   And one of  the most  curious
particulars belonging to this subject is,  that each distinct
species of  salt has  a figure of its  own, which it affects in
its crystals, not alw.v, s with ex-ict regularity, but with such
a degree of it,  that, upon the whole, a person well accus-
tomed to  view  the crystals of different  salts, will in most
 cases be able to tell, by  the figure  and  appearant e of the
 saline crystals, from what salt they  were produced.  Ne-
 vertheless, a judgment formed in this way is far from being
so sure as  has been  imagined.
   This method  of separating  salts from  water is called
 crystallization, from  its effect:  And as it is practised
 ct:en, you will find in books several directions for perform-
 ing  it  right.  But it is difficult to  give am that will  suit
 all the  different  kinds  of salts;  as they require different
 conduct.   The common direction is to evaporate to a pel-
 licle ; that is, till the surface of  the  solution exhibits u
 thin film,  which glistens when viewed obliquely; ami, when
 narrowly  examined, is  found to consist of minute en s'uls.
  It is f.rmedon the surface, because the  gentle evapora-
  tion goes  on there.  But if yeu proceed so far with  the
 evaporation, few of them will crystallize right;  as too lit-
 tle  water will remain, too much salt will be deposited, and
 the crystals will be small and confused.   In general, it is
 usual to filtrate the solution,  if it be foul ;  because  a parti-
  cle of solid matter any where in the fluid,  becomes u cen-
  tre of crystallization, (as maybe observed in the  thread:
 hung in syrop for the manufacture of sutpr-enndy) and this
  happening all over a solution ehut is (<»ul,inak?;s the  cp's^ils
 small and confused.  We must then evaporate  it to .\ mo-
  derate degree, cool it slowly, ai"! avoid disturb:;.;'e ;  a:i !. 
               CRYSTALLIZATION.             21

pouring off the liquid, we repeat the  same operation on it.
Those who prepare very large quantities  of particular salts
for sale, as Glauber's salt, saltpetre, &c. have better, or at
least larger, crystals, on account of the large quantity, and
slow refrigeration, than can easily be obtained from  small
quantities in the way of experiment.
   But some  of the salts do not afford good crystals by this
method, and agree better with  an uninterrupted, but slow
and insensible evaporation, with a heat like  that  of the
human body, or with  a spontaneous  evaporation, merely
by exposure  to the air.  In this way the water is  dimin-
ished  in so  slow and  gradual  a manner,  that  the saline
particles, in  approaching one another, have full time  and
opportunity to assume  that arrangement and mode of con-
cretion, to which they are naturally disposed. The crystals,
therefore, are  formed more  regular and  fine than by other
processes ; but this method of obtaining crystals is far too
slow for common use.
   I am informed that some  of the trading chemists in
London, who prepare specimens for the  curious,  have
particular secrets  by which they  procure large and fine
crystals  ; and  that these secrets consist  in the addition of
certain  fattv matters,  and  making  the  solution in lime-
water,  and close vessels.    It is certain,  that in the  great
manufactures  of salt-petre, alum,  copperas, borax,  &c.
things of this kind are  used  with success.  Urine is a very
general  addition ; and  I  am assured that fine crystals of
copperas and  borax cannot be had without it.   I have
tried lime-water : and  it certainly gives  most elegant crys-
tals of saltpetre, superior to any that I can  obtain without
it.  But it seems to have no such effect on Glauber's salt,
soda,  or Epsom  salt, the only other  salts on which I have
tried it.
    Some authors  speak much of  the influence of light on
the formation of crystals ; but I observe none*.   Others
say that a mass of crystallized tolt being placed in contact,
  * Chaptal has, I think, proved it  beyond contradiction, in a memoir pre-
sented to the Royal Academy, 1780.  I am certain of its influence in the
crystallization of the  vapours of salt of hartshorn, and of camphor.   Th-.t
iaU.s are also singiiltrV.- af!Vt»d by electricity,   editor. 
CHEMICAL  VEGETATION.
 or even very near the outside of the vessel, greatly affects
 the crystallization.   I am  persuaded that this  is a mere
 fancy.   The directions  I have  already given are the only
 rules that have been generally  successful with me,  and I
 think they are  supported by any little knowledge that we
 have acquired of the internal procedure.
   In evaporating solutions of  salts, especially when the
 evaporation is  verv slow, an accident often occurs, which
 may create surprise,  and  ma)' prove  troublesome  to  a
 person who is not accustomed to  it ;....I mean what is called
 the Efflorescence or Ve^ltation of salts.   This is a
 peculiar concretion of  salts from water.  Wh^n the evapor-
 ation is carried on in a  deep vessel, so as the concretion
 cannot rise so  high as to  get over the  lip, it shoots and
 spreads -sometimes  in the upper  part  of the  glass into
 branched figures, resembling irregular foliage.  And sorae
 of the more enthusiastic chemists have imagined tbat they
 perceived in it  an exact  resemblance  to the leaves and
 ramifications of plants : and, if the salt was obtained fr >m
 a plant, they supposed that it still retained something  of
 the vegetating  nature  of the plant  from which it was pro-
 duced.   But this is an imaginary, and perfectly Groundless
 fancy.   The resemblance  between  such concretions  of
 salts and  vegetation is accidental, like that of the  frozen
 humidity  which is  condensed on the  inside  of g!-is..
 windows in hard frost.  This depends on the same cause
 asfcrystallization.
   This vegetation, as it is  called,  is often troublesome  tu
 the chemist. After reaching the lip of the vessel, it creeps
 down the outside : and as soon as it gets as low_as the sur-
 face of the liquor,  the  whole  becomes an assemblage  of
 syphons,  and our solution runs over and  is lost.   This
 may be prevented by covering  the vessel with a piece  of
 tin plate,  having a round  hole cut out  of  it, about two
inches less  in  diameter than  the rim of the evaporating
 dish.   This prevents  the  evaporation at the edges, and
 even occasions a dew, which will trickle  down the side  of    *
 the dish.   I find this a complete preventive.
  It happens sometimes, in attempting to crystallize some
 salts, that although the liquor be duly evaporated, and then 
         SUDDEN  CRYSTALLIZATION.        23

allowed to cool, it does not crystallize : the whole remains
still liui :.   This happens only with some of the salts, and
only when the saline liquor is ^allowed to cool slowly and
wihout being disturbed.    If we disturb it when it is thus
cooled, it suddenly crystallizes, and at the same time Jttu
comes w  mrr by several degrees.  It is therefore evidafjtj;
that its proti acted  fluidity proceeded from a quantity  of
heat, whi'-h it retained in the form of latent heat, in conse-
quence,  I am  persuaded, of a chemical attraction which
the  materials of the mixture  have for heat  in  that state.
As this  is a curious and  instructive experiment, you will
derive  advantage from  a few  instructions  for  making it
6urceed in the best manner.   Glauber's and Epsom salts
are those  which  exhibit it to most advantage.   Alum and
copperas also do very well.  Take crystals that  have been
formed in a solution carefully filtrated,  that there may  be
no foulness ;  put them into a flask with  distilled water, a
little more than enough  for  dissolving the  whole  with a
boiling heat; set the flask into a pan or tea-kettle  of cold
 water ;  and set the whole on the fir-, and keep it boiling
 till all the salt is dissolved ; take out the flask  from time
 to time to agitate  the  contents,  otherwise  it will consist
 of strata too unequally saturated : now cork  the flask, and
 let it stand in the boiling water for some time. I think that
 this allows a small degree of more saltness towards the bot-
 tom, which 1 believe of service.  Now set the  whole in a
 cool place, where it will not be exposed to the tremor of
 persons walking in  the room, or of carriages in the street.
 It will cool very slowly, and generally remains fluid.' Lift
 the flask, with the  utmost care not to  shake it; pull out  the
 cork, and it shoots  into crystals ; or,  if it do not, drop into
 the liquor the smallest fragment of the salt in crystals, and
 thus it never fails.  A thermometer will  shew the emission
 of latent heat.   There is in this experiment an equilibrium
 in the mixture,  between its chemical attraction for latent
 heat, or the force with which it retains  a certain  quantity
 of heat in that form, and the cohesive attraction which tends
 to make it crystallize.   These two attractions,  the chemi-
 cal  and the cohesive, are always  in  opposition  to  one
 another : and here  they are exactly  balanced,  or  at least 
24    WATERY  FUSION....CALCINATION.

the force of the chemical attraction for the heat, exceeds,
by very little,  the force of the cohesive,  which tends to
crystallization.   A proof of this  is, that if we give a little
advantage to the  cohesive  attraction,  either by sudden
Cfl^ussion of  the fluid matter, or by dropping in ever so
rrlje of the same matter already concreted, the crystalliza-
tion immediately begins, and the latent heat  is expelled ;
the  cohesive  attraction  having  now prevailed over the
chemical  one.   You  will  perceive, therefore,  an exact
■-.imilaritv between this experiment  and  Fahrenheit's ex-
periment with overcooled water*.
   Salts are commonlv exhibited and treated of by chemists
in their crystallized state.   But  this is  not the  most sim-
ple state of saline  matter.  All of them contain water, se-
parable by heat; and it  is.so  copious in some, that they
undergo Watery Fusion, and  spontaneous Calcination,
improperly called  Efflorescence.   Glauber's  salt,  alum,
copperas, and many other salts, when very suddenly heat-
ed, melt,  boil, and foam, emitting much watery  vapour ;
and, in a little, are changed into  a dry spongy mass, much
larger than the salt, but  of much smaller  weight.  After
this they bear  to be heated  red  hot, before they take the
true wax-like  fusion which I described  in the beginning.
This is called the  watery fusion of the saline crystal.   It  is
really a solution again in water which had been  enabled,
by  its combination with the saline matter, to bear a greater
heat  without evaporation.   It therefore dissolves what  it
could not dissolve while  of  a lower temperature.   But  it
is almost instantly raised to  a  temperature in which  even
 this union cannot hinder it  from boiling.   It  therefore

    I doubt much whether this reasoning be conclusive or explicatory. We
can form no notion  of a difference between  a cohesive and a chemical attrac-
fion, viewing them  merely as moving forces ; a conception  absolutely neces-
sary for speaking of opposition and equilibrium.  It will be seen presently,
 hat what is here called a cohesive attraction, is an attraction as truly
ihemical as the attraction for heat; and indeed, in  the  opinion of many
chemists, it is the  only chemical attraction, uniting two bodies of different
kinds, with mutual saturation, and the loss of the-former properties of the
ingredients.  We shall  at leaSt see  that more  happens than the niirc
balancing of two attractions, editor. 
     EFFLORESCENCE...DECREPITATION.  25

froths  up, evaporates by bursting the saline bubbles, and
leaves  them shattered, and the whole a spongy mass.
   But if the same salt be exposed  to a very gentle heat,
and the action of dry air, the water of crystallization eva-
porates from it without  dissolving the salt, and leaves it a
fine meal.   It is this that is called Efflorescence.  The
particles of this dust appear, through  a microscope, to be
fragments of inconceivably thin plates.   In all probability,
a  saline crystal  is made up of ultimate plates of salt and
water.*  In other salts, the water occasions Decrepita-
tion ; that is, the  crystals retain the water with great ob-
stinacy, till red hot, or near it, when it tears them asunder
with a loud crack.   Such, therefore, is the nature of the
crystals of salts,  that  they  must be  considered as com-
pounds of salt and water.
   The  manner  in which  saline  crystals are  produced,
and the remarkable figures they assume,  could not fail to
attract the attention of  chemists and others,  and to occa-
sion attempts to explain how they are formed.
   The most obvious idea, and which first occurred, was,
that the ultimate atoms of salts have similar forms to those
of their crystals, being oblong, or angular, or pointed 5 and
that, when they  unite,  they necessarily form a mass, the
figure of which is somewhat similar to that of the consti-
tuent  particles.  This opinion appeared the more probable,
as. it was thought to explain  the dissolving power of salts,
with regard to earths, metals, and other bodies, which, it
was imagined, they dissolved, or acted upon, in consequence
 of the pointed forms and sharpness of their particles. But
as, when we considered the more general effects of mix:-
 ture, we already found this an insufficient and unsatisfac-
 tory explanation  of  the dissolving power of solvents  in
 general, so  neither will it explain the  crystallization of
 salts.  It is certain, that, in the crystals of salts and saline
 compounds, the saline  atoms do not  touch  one  another.

   * Tins structure is rendered more probable, by remarking that saline crys-
tals are evidently striated transversely, an* many of them have a double
refraction, like some natural crystals, which we know to have a plated struc -
•ure ...EDITOR.
     :.'Oi,. II.                V     -. 
26   THEORIES  OF CRYSTALLIZATION.

This is evident, in the first place, from the  transparency
of those  crystals.   Light passes through  them  in  every
direction.   We have direct  proof that the saline atoms do
not touch one another.  The  crystals of  fossil alkali,
Glauber's salt, Epsom salt, vitriol, alum, and borax, con-
tain a quantity of water more than thrice the bulk of the
saline  matter.   Perfect crystals  of fossil alkali  contain
tW of water, T7&. of fixed air, and &% of alkali. The form
of the crystals, therefore, cannot depend  merely on the
form of the saline atoms.
   Besides, this phenomenon of crystallization is not con-
fined to salts.  They are, of all other substances, the most
easily disposed to crystallization.  But  most other kinds of
matter, when passing from a state of fluidity to  solidity,
shew more or less disposition to  concrete  into  regular
figures.   In mineral veins, we find  many  kinds of stones
and minerals crystallized.    Metals, in congealing, shew a
disposition to crystallize, or to form regular figures.  Pure
water also crystallizes in snow and ice.  Flakes  of snow
are formed of assemblages of small spicular or columnar
crystals, like the crystals of Glauber's salt,  often assem-
bled together without order, but  sometimes  joined  toge-
ther into stars of si?; rays, ckc.    If we suppose, therefore,
che figures of saline  crystals to be a proof that the ultimate
atoms of salts are angular  and pointed, we must allow the
particles of water to be so likewise.
   Another principle was pointed out by Sir Isaac Newton,
to explain  the crystallization of salts; but it is insufjficient.
He supposed it to be a consequence of the regular arrange-
ment of the saline atoms dissolved in water.   This might
explain the  concretion of salts  into a  mass of  uniform
structure,  and perhaps transparent;  but it cannot explain
why there are a number of separate angular masses.
   In the first place, the cause which occasions the particles
of salt to concrete together  in crystallization,is undoubtedly
the attraction of cohesion.  In  a solution  of salt, this
attraction, by which  the particles of the salt have a ten-
dency to unite", is counteracted and overcome by the che-
mical attraction of the water for the particles of  the salt.
But if we  diminish the quantity  of the water by evapora. 
 DIFFERENT BRINES  MIX COMPLETELY.  27

tion,  it will act with less power,  and the saline particles
with more.   (See Note 29, at the end of the Volume.)
   Mr. Baume's opinion is, that crystallization, that is, the
separation of salts by crystallization, depends both on the
attraction of the homogeneous particles for one another,
and on the repulsion of the heterogeneous ones.   And he
thus explains how perfectly neutral crystals are formed in
acid,  or alkaline  solutions ; or clean and transparent crys-
tals in muddy and coloured saline liquors.  And he thinks
he has perceived, by  experiments, both the attraction and
repulsion, acting even at the distance of a foot, by placing
beside a vessel, in  which a solution of Glauber's salt was
set to crystallize, either a vessel containing Glauber's salt,
which occasioned the crystals to be all formed on that side;
or a vessel  containing salt of tartar, which occasioned the
crystals to be formed on the opposite side. But Mr. Lavoi-
sier  has proved that there  is not  the  least  ground  foV
thinking that the attraction and repulsion act  at a sensible
distance.
   Consult,   on  this subject,  the  Crystallographie  of Mr.
Rome de ITsle, edition of 1784 ; and the Essai sur la forma-
tion des Crystaux, par Mr. PAbbe de HaUy.    (Annales de
Chemie, Juni 1793.)   These authors, particularly the last,
shew how,  from a  very small number of simple primitive
forms, may arise a vast variety of figures of crystals.  This
subject is  treated with great  neatness  and  perspicuity,
both  mathematically and philosophically, in a work entitled
Crystallographie des Mineraux, by Dr. Kramp,  of Stras-
burg.  It was printed at  Vienna 1793;  and is,  I think,
the most instructive work on the subject.
   There is  yet another way of separating salts from water,
namely, by  adding  something with which the water is more
disposed to unite.  Thus,  if to a nearly saturated solution
of most salts in water, we pour some strong spirit of wine,
we shall  have an immediate  precipitation of the salt in  a
crystalline  form.  This method is sometimes practised
as the only way of procuring the salt in a state of  great
purity.   It is surely somewhat extraordinary, that by  the
addition of a  substance  more strongly attracted by  the
water, we should produce, in an  instant, the  union of salt 
SALTS, HOW SEPARATED.
 and water in a crvstalline form, so strong in some cases,
 that a red heat cannot separate them.   And this is another
 proof how little we are able to judge of the comparative
 strength of chemical attractions.
   Such  are the general observations which it was proper
 to make on  the relation of salts to water.
   All the different kinds of salt may be  easily mixed in
 the  most intimate  manner, in  consequence of this rela-
 tion,....this  general quality of dissolving in water:  for
 water can dissolve  not  only two kinds of salt at the same
 time, but many different kinds.   And we have learned by
 experience,  that when  it is saturated  with one  salt, this
 does not hinder from dissolving a considemble quantity of
 another, and even of several others.  -'You may see many
 examples of this  collected by  Muschenbroeck, Neuman,
 Watson, and others.    Water will dissolve more saltpetre
afx-r it is saturated with alum  than when pure.
   When different  salts  are  thus mixed  together by being.
 dissolved in the same water, some act immediatelv  one on
 another, and unite together,  so as to remain afterwards
 very strongly combined.   Many others mix without any
 appearance of action, or any  signs of their uniting toge-
tht r.  These can generally be separated from one another
 again without much difficulty.   The others, when we de-
sire  to separate them, require to be disunited by an elec-
 tive attraction.    The  various  cases, where elective  at-
 traction or  exchange is necessary to separate salts which
 are strongly united together, will be fully considered here-
 after.
   But when the mixed salts have no attraction, or after
 that attraction has been  overcome, we separate them by
 one or other of three methods, which will succeed in most
 of these cases.   We take advantage either of their diffe-
 rence of volatility,  if there be any considerable difference
 of this kind between them; or of their different solubility
 in water; or we separate them  by crystallizing them.
   The manner of separating them by  taking advantage of
their diff r< nt volatility, when there is a considerable dif-
 ference  between them in this  respect, is obvious.    It is
to put the saline mixture into a retort, or other such ves- 
    SEPARATION OF SALTS IN A BRINE. 29

sel;  to.join a receiver to this retort;   and then to apply
heat,  which must be very slowly and gradually increased.
Thus the more volatile salt may be raised to  vapour, and
condensed in a separate vessel, while the fixed salt remains
behind.    In no  case does this process produce a com-
plete  separation.   The  volatile salt is always  tainted with
a little of the fixed one,  and this always retains some of the
volatile salt.   We must often repeat the operation two or
three times.
   When the salts which we desire to separate, do not dif-
fer much  in volatility, and this operation cannot be per-
formed, it  happens however in many cases, that they differ
greatly in  solubility ; and this circumstance puts it in our
power to separate them.   Thus, if the one be of the less
soluble salts, and require  a large quantity of  water to dis-
solve it, while the other easily dissolves in a small quantity
of water, we may evaporate the mixed solution till no more
water remain  than is necessary to keep the most  soluble
salt dissolved.  Allowing the solution then to cool, the less
soluble salt will separate in crystals, and may  be taken out,
while the other remains still dissolved.
   Or, if the salts be  mixed together in a dry mass, we may
add as much water as is just sufficient to dissolve the most
soluble,  and  the less  soluble  will remain  undissolved.
When one of those salts has little solubility, and the other
is so very soluble as to be deliquescent, we  can obtain a
more complete and exact  separation by exposing the mixed
mass to the air in a cellar,  or some other damp and cold
place, until the deliquescent salt be liquefied by attracting
the moisture of  the air.   It is found by experience, that
there is no method of dissolving it by which it is so effec-
tually parted from the other.   Sometimes the mixed mass
is thus exposed upon a quantity of bibulous paper, or other
porous absorbed substance,  which sucks in the  deliques-
cent salt as fast as it liquefies : and this is a most effectual
and quick method.
   Besides the difference of  greater or less  solubility in
general, there  is  another  difference of solubility, which is
in some cases  the foundation of separability, (if I may be
 dlowed the term):  I mean a  difference of  solubility in 
JO  SEPARATION OF  SALTS  IN A BRINE.
 hot or in cold water.   Thus, common sea-salt differs from
 perhaps all the rest, by dissolving as readily,  and almost
 as copiously,  in cold water as in hot; and may therefore
 be very conveniently and effectually separated from many
 of them, upon this same principle.   The saltpetre, in its
 native  state, has always a great  quantity of common salt
 mixed  with it. In order to separate it, the whole is dissolved
 in water, and the solution evaporated to a certain degree,
 and then cooled.  A quantity of saltpetre then crystallizes,
 and is taken out.   The same operation is repeated with the
 remaining liquor,  and some more saltpetre is  thus taken
 out before any of the common salt crystallizes, because the
 common salt is generally the least copious of the two; and
 as it is also more soluble, the water must be considerably
 wasted  before it begins to appear.   But when the evapora-
 tion has been repeated a certain  number of times, the re-
 maining water* comes to be saturated with common salt as
 well as  with saltpetre.  And now, the next time we evapo-
 rate, a  part of the common salt will  crystallize,  but in a
 manner quite different from the saltpetre; for it crystallizes
 while the evaporation is going on, and  while the  liquor
 is hot on the fire; for the heat does not much increase its
 solubility,  or prevent it from separating.   But heat has
 this effect very remarkably upon the saltpetre.   It  is dis-
solved in greater quantity by far in hot water than in cold,
 and although the water is greatly diminished, it  still  re-
 mains dissolved as  long as it is  hot.   The common salt
 which has grained, must now be taken  out; and afterwards
 we must allow  the solution to cool.  While  it cools, none
 of the  remaining  common salt separates, or excessively
 little; but a great part of the  saltpetre now concretes in the
 form of crystals.   And if these  are taken out, the same
 operation may  be  repeated with the remaining  solution
 until the whole of these salts are alternately separated from
 the water, and from one another; the one always concreting
 while the fluid evaporates, and the other while it is cooled.
 And the very same operation mav be practised to separate
 sea-salt from a number of the other salts.
   Solubility in spirit of wine is also another foundation of
 separability;  for some  salts are dissolved  by th^t fluid. 
            SEPARATION OF  SALTS.          31

while the rest are not: but of this we shall speak more fully
when we treat of spirit of wine.
  In cases in which none of the methods hitherto  men-
tioned will do, (which, however, are very few), the  only
remaining means is crystallization.  Some of  the former
methods of managing  might be classed under the title of
crystallization, because the separated salts form crystals. But
as the  separation  depends  in reality upon difference of
solubility, we have referred such cases to that head.
   The cases in which the separation  of  salts depends on
crystallization  alone, are those in which the mixed  salts
do not differ considerably, either in volatility or solubility,
and  in which we cannot  have recourse to any of the opera-
tions hitherto mentioned.   All that is left in our power is
to reduce the whole saline matter to  crystals, in the best
manner we  can ;  that is, to give fair crystals, but this is
the  most imperfect mode of any.   (See Note 30,  at the
end of the Volume.)
   To conclude this subject of the  separation of salts in
general, we must  remark, that some of  these  methods of
working do not produce full and exact separation at first:
but by repetition the separation can be made very complete.
   You are  now acquainted with the nature of the salts in
general.  We must next take a view of the different kinds
of them.    To do this in a  proper manner, it is necessary
first to divide them into two principal divisions: the first,
that of the  more simple; the second, that of the compound
salts, which are formed by the  union  of the simpler salts
with one  another.   We shall therefore  consider the sim-
pler salts first, and then shew how by combination they pro-
duce the compound :  each of  which shall be considered
 separately, as well as the means of resolving the compound
 again into its constituent salts.
   Further, the simpler  salts, that they may be considered
 more distinctly, must be divided into two orders, the alka-
 Une, and the acid salts.   You will be fully sensible of the
 propriety of this division as we proceed.    At present we
 are to consider the alkalis. 
32
GENUS   II.
                ILK ALINE SALTS.

   UNDER this general name  are comprehended three
salts, having similar properties,  but,  at tfie  same  time,
other properties which are not interchangeable.
   The only character which I need to  give of them in
common, at present, is, that when they are mixed, though
in exceedingly small quantity, with  infusions of purple or
blue  flowers of  vegetables,  they change the colour gene-
rally  to a  green,  or,  in some few  cases, from purple to
blue.    The spiritous tincture of alkanet root is still more
sensible to  alkalis.   Several other properties besides this
are usually  given to distinguish the  alkalis ;  but it is not
necessary to notice  them at  present,  It is better to delay
the mention of them now.    I  may, however, add, that,
when tasted as dissolved in v/ater,  they affect the tongue
with considerable acrimony and pungency. The particular
taste  is much the same in the three  species.*  They are,
moreover, noted detergents,  and feel greasy to the touch,
because they instantly dissolve the unctuous matters which
adhere to the skin. They shew, indeed, an acrid and corro-
sive nature  with  respect to all animal substances, especially
when we apply to  them these  alkalis in  their purest and
most active state ; in which  condition they dissolve  every

  * This taste has not a name in our language ; nor is it indeed very familiar,
being peculiarly disgusting, and is seldom to be met with, except in what we
are accustomed to consider as offal, or refuse.  But it is a taste as distinct
and characteristic as the acidity which denominates the other class.  Who-
ever touches, with the tip of the tongue, a little potash, or even lime, or lime
water,  will never afterwards  fort^t the disgusting taste of an alkaline sub
stance.....editoh. 
VEGETABLE  ALKALI.            S3
thing into a soapy pulp.   It is a state to which thev are
reduced on some occasions  only,  and to serve particular
purposes.  But it  is  better, for the present, to describe
them in the state in which they are commonly kept for use,
and in  which you will most frequently  see  them in  the
shops.   This is a more convenient and  manageable form
than their purest state.
   I said that there  are three species of them.   These are
tEe vegetable alkali, the fossil alkali, and the volatile alkali.
The last is called  volatile very  properly;  as it is incom-
parably more volatile than the other two, which, with re-
ference to it, are therefore called the two fixed  alkalis.


        SPECIES I....VEGETABLE  ALKALI.

   The first, the vegetable alkali,  or  common potash, has
all the  qualities described as belonging to salts in general.
It requires a red heat to melt it; and in a violent one emits
vapours, and is gradually dissipated,  especially if air be
admitted to  its surface.
   This alkali, in its ordinary state, has a very strong at-
traction for water.    It deliquiates in the air, and is with
great difficulty kept dry.   When thrown into water, it dis-
solves quickly ; and can be dissolved  in  less  than an equal
quantity.   The solution is  generally  accompanied  with
heat.   The  water  is separated again with difficulty, and
requires  a strong  heat;  and it  is not easy to obtain crys-
tals from this salt in its ordinary state.   It  is  not usual,
therefore, to attempt to  crystallize this  alkali, in separat-
ing it from water.   The  common practice is to evaporate
to dryness, which is done in an  iron pot, as it has scarcely
any power to corrode the iron.  Hence it has got the name
of potash.
   When the greater part of the water is boiled away, the
i-emaining matter is much disposed to foam and boil over.
And at last the small portion of water which remains with
the  salt, forms with it a mixture like wet lime or soft mor-
tar.  A strong heat is then required to  evaporate this last
part of the water :  and the salt must be stirred and scraped
      V"OT. it.                  i 
34            VEGETABLE  ALKALI.

from the bottom of the pot incessantly.   If this be omit-
ted, it adheres strongly in the form of a hard white crust,
or indurated mass.
   This alkali has its  origin in  the Ian 1 vegetables, espe-
cially trees, the greater number of which contain, in their
juices, a small quantity of this salt combined with others ;
and it is produced in  the plant by the powers of vegeta-
tion.
   It is extracted, for the most part, by burning the wood
(or whatever plant we  operate on) slowly, to perfect white
ashes, or until all the  inflammable  matter be completely
consumed.  The alkali  remains in these ashes, and is easily
extracted  from them  bv water;  and when refined to a
certain degree, is sold under the name  of Pearl Ashes.
   It is prepared in  this manner chiefly in those  countries
where  wood is exceedingly plenty and cheap.   And  for
many purposes, thev do  not take the trouble to refine this
salt :  but,  taking  the  solution of it which they  have ex-
tracted by water from  the ashes, they add to it a quantity
of fresh ashes, which still contain a salt;  and boil  up the
whole together into  a  coarse and impure  mass,  which is
also called  Potashes,  and from which the alkali is after-
wards  extracted by those who have occasion to use it.
  The reason for selling some of it in this form is, that it
is more easily preserved and transported. The purer alkali,
called pearl ashes, is so deliquescent, that it would be im-
possible to keep it dry and solid, except by packing it  up
in very close and tight  vessels ; whereas the coarser or less
pure kinds of potashes can be more easily preserved and
transported without such expensive package.
  The softer and more succulent vegetables do not con-
tain so much of it as the hard woods.   But some of them
especially ferns and some others, are burnt with great
profit in some places,  on account of the alkali which mav
be had from their ashes.   And such ashe9 are sold under
the name of weed-ashes.
   It is also separated, in a great measure, from  the other
principles of vegetables, when they are completely putre-
fied: and in this way is produced the alkali, which may  be
had from the drains of  dunghills, by a pro.Cis described  by 
              VEGETABLE ALKALI.             j*

Dr. Percival of Manchester, in the Philosophical Transac-
tions for the year 1779 or 1780.
   There is now  such demand for this salt in many manu-
factures  as a detergent, that it is found highly worth while
to recover it from the liquors in which it is mixed with all
the sordes which it has dissolved. The water is boiled off:
and the  impure residuum is burnt to ashe-s ; and the alka-
line salt  extracted from them by water.
   Mr. Margraaf, in some memoirs in the Transactions of
the Berlin  Academy,  on the waters used in  Berlin, says
that he  found  a small quantity  of this alkali in  some of
their well waters.   It probably had the same origin as the
alkali contained  in  the drainings of dunghills ;  and  had
been  extricated from vegetable substances by putrefaction,
and been carried by the surface water into the_ wells.
   The vegetable substance which yields it in the largest
quantity and purest  state, is the vegetable salt sailed tartar
or wine-stone.   And when this alkali has been extracted
from the tartar,  it has been commonly called  Salt of Tar
tar.*
  Sal tartari contains about 70 per  cent, of pure, i. e. caustic
    alkali.
  The best pearl-ashes  contain about    -     55
  Dantzic ashes -----       51
  Ordinary        *-     -     -     "     -    46
   The names, therefore, by which this alkali was formerly
known,  were pot ash,  pearl ash,  weed ash,  salt of tartar,
salt of wormwood,  and some others.  But the names of
the salts have been often changed of late.   In a new set of
names which were lately proposed by the French chemists,
it is called Potasse in French, and Potassa for Latin ; in the
last edition of  the  London Pharmacopoeia, Kali; in the
Edinburgh Pharmacopoeia,  Lixiva.    I  shall take some
notice of  the names, when I have done with the  descrip-
tion of the salts.

  » There are strong reasons, some of which occur in these lectures, for be-
lieving that this salt is formed in the plants, by the powers of vegetation, of
ingredients still more simple....edit or.. 
36               FOSSIL  ALKALI.

    Uses of the vegetable fixed alkali.........It constitutes a
 part <T several compound salts employed in medicine ; and
 is used by  itself to correct acidity in the bowels ; to pro-
 mote the secretion of urine ; and to  give relief from the
 distress occasioned by  gravel or the stone, in the kidneys
 or  bladder ; which relief it very seldom fails to procure,
 when the disease is not of long standing.   It is given for
 this purpose in different states, which I shall describe here-
 after.   It is used also  in large quantities in the  arts, as in
 making soap and glass,  in bleaching, in dying,  8tc.


          SPECIES II.....FOSSIL  ALKALI.

    The other fixed  alkali, the fossil alkali, when examined
 in its  ordinary state,  resembles  the vegetable  alkali  in
 some  particulars ;   but is very different from it  in others.
 It requires the same heat to melt k, and make it evaporate.
 It has the same taste,  but not so acrid.  Its attraction for
 water is not near so strong ; and it is not deliquescent.   It
 dissolves, however, readily in water, but not so quickly as
 the vegetable  alkali does.  And it  requires  five or six
 times its weight of the water to dissolve it, in the tempe-
 rature 50°.
    The fossil  fixed alkali  in solution is easily separated
 from  water  again by  evaporation ;  and  in its ordinary
 state, it is easily crystallized.   Its crystals have generally
 the form of  a thin  oblique  lozenge, the narrow sides  of
 which are reduced  to  an edge by oblique planes, like the
 edge  of a ruler. (See  Rome de  ITsle, No. 43.) Its crystals
 contain a large proportion of water, adhering loosely, nearly
 T«*5,  and  7'/7  of  elastic  matter  in  an  ujielastic  state.
  Hence they are very  liable to watery fusion  and  spon-
 taneous calcination.   The water quickly evaporates,  and
  leaves the  salt a white crusty mass, which may be  dis-
  solved in water, and crystallized again.
     Such are the qualities of this alkali, that can be men-
  tioned with propriety at present.  It remains  only to take
  notice of its origin.   Upon this article we may remark
  *har  it is one of  the salts which have been longest known 
    F0SSIL ALKALI....NATRON....TRONA.   3t

and in use.   It is this salt which is mentioned in several
parts of the Bible by the name of nitre.   It is once men-
tioned as a detergent, and once as making a turbulent or
foaming mixture with vinegar; neither of which properties
agree with the salt now called nitre.   It appears that  the
ancients were  supplied  with this salt from Egypt,  and
some parts of  Persia, where it is found on the surface of
the soil, in particular places, in the form of small impure
crystals, or composing a saline efflorescence, or crust, like
hoar-frost,  which is undoubtedly formed by the  evapora-
tion of water,  which had  dissolved and extracted it from
the soil.
   In the 55th  volume of  the Philosophical Transactions,
there is mention made by Dr. Heberden, of a production
of this  alkali, somewhat  similar to this, in the  island of
Teneriffe.   And we are also informed  by Dr. Donald
Monro, in the  Philosophical  Transactions for  the year
 1771, of another source, from which it is probable  the
 ancients derived in part their supplies of this salt.   It is
 brought yearly to  Tripoli,  in large quantities  from  the
 mountains, and is called  Trona.  From its appearance, he
 concludes that it is found forming veins in the mountains
 of rock salt; for it is always in the form of cakes, of about
 half an inch thick, to one side of which there always ad-
 here incrusted crystals of common salt*.
    There is  no example, however,  in  any part of Europe,
 of its being  found in considerable quantity in any of these
 states.   We have only a saline efflorescence, which is often
 formed on the plastered walls of cellars, and other damp
 places, which is mostly composed of this salt.   We  also
 find a small quantity of  it dissolved in the water of some
 of our springs in Europe; but such spring waters are very
 uncommon.
    Though, on the whole, we but rarely find this alkali ir
 a separate state  in nature, it occurs however,  in grea
 quantities, in a  state of  combination  with  other salts.
 Common salt is a compound salt, of which this fixed alkali

   * It is found in its detached state in all salt water fishes, and in some in coi,
 siderable quantity.  The earth round Ravenna, which is full of the remains-i
 ■sea fishes, and even the stone?, abound in it.....editor 
 38         SODA....BARILLA....KELP.

 composes the half.   And common salt is found solid, in
 immense quantities, in the bowels of  the earth, 'besides
 what is  contained in the waters of the sea, and those of
 innumerable springs in all parts of the world.   You will,
 therefore, understand why it has been called the fossil al-
 kali.    I have reason  to  believe that the fossil  alkali
 that is found on the plastered walls of cellars, and  other
 damp places,  is produced by the decomposition of  com-
 mon salt.
   iiut  the  great quantities of  it which  are made use of
 in different  arts and manufactures in Europe, are procured
 from sea plants, and some particular plants which grow in
 the neighbourhood of  the  sea.   The  plant which affords
 it of the best quality, and is cultivated in Spain, Sicily,
 and Italy, for that purpose, is called Kali and Salsola.   To
 obtain the alkali, these plants are burned to ashes, in which
 the alkali is found.  Such ashes are accordingly prepared
 upon  the coasts of  the Mediterranean, and receive  the
 name of Soda, or  Soude, or  Barilla ashes.   They  form
large and hard lumps, like stones, of a  dark gray or black-
 ish colour.   The hardness is occasioned by a fusion which
these ashes  undergo in  the end of the operation, in conse-
quence of the heat produced by the burning of the vegeta-
 ble. Upon our coasts  also, we burn certain kinds of sea
 plants, and melt the saline ashes of them together into one
 mass, called Kelp, which also contains  a small quantity of
 this alkali.
   The purest fossil  alkali, obtained from the efflorescence
 on plaster walls, contains about 60 per cent, of  its weight
 of alkali in  crystals.
    Alkali manufactured at Liverpool,             49
    Fossil alkali from India,                     28
    Best Alicant Barilla,                        26.J
    Sicilian  Barilla,                              23
    The richest kelp made in Norway,
       the  Orkney  Islands, and Skye,
    The general produce of Scottish kelp,          2*
   The  sea-weed, varech, or wreck, is either taken as it is
 -os^ed  ashore by the storms, or is cut and pulled from the

6j 
VOLATILE ALKALI.             39
 rocks with rakes, at low water.   It is brought ashore, and
 spread on the beach to dry and wither.   As soon as it will
 burn,  it is burned in  little pits  lined with stone, feeding
 the fire scantily with the dry plant.   When the pit is nearly
 full of the ashes, which are but slightly burnt a great quan-
 tity of weed, well dried on purpose, is.thrown  in at once;
 and a very hot fire kept up, and the whole stirred, to bring
 all the charry  matter  to the air, that it may burn.   This
 melts the whole into an impure  heterogeneous  mass, of a
 dark,  dirty, gray colour, containing much common  salt,
 vegetable earth, brimstone, and the alkali.
    It may also be had by decompounding common salt, by
 particular processes to be described hereafter, and some
 of which  are actually practised  in the  way of business  at
 present.
    The names which have been  given to it, therefore, are,
 Natrum  or Nitrumby the ancients, Trona in Africa, Soda
 and Barilla in  the Mediterranean, and Alkali of common
 Salt,  or  Fossil Fixed Alkali.   In France they prefer the
 name of Soda  or Soude:  and  the  same  name has  been
 adopted in the last edition of the Edinburgh  Pharmaco-
 poeia. In the  London Pharmacopoeia,  it is named Natron.
    It  is  employed chiefly in  the composition of  soap, in
 making glass, in bleaching linen, and in other arts.   It is
 also  an article of  the materia medica.   It  has the same
 powers in medicine as potash, or alkali of tartar.


         SPECIES III.—VOLATILE ALKALI.

    The last of these  salts, the volatile alkali, differs more
  from the two former than they do from one another.  It
  shews great  volatility when exposed to  the  most gentle
  heat  : and, even in the ordinary heat  of the air, it is con-
  stantly emitting vapour, not visible, but pungent to the nose,
  and of an urinous smell.   It is commonly known by the
  name of volatile  salts, and salt of harsthorn.   When ex-
 ; posed to heat, it does not melt, but is totally evaporated
'' before it arrives at the melting heat: and when the vapour
  of it is condensed in a receiver, it forms a saline crust. It 
40 VARIOUS NAMES OF VOLATILE  ALKALI.

has a good deal of acrimony and pungency;  and if  con-
fined upon the skin, will certainly inflame and corrode it;
It is easily combined with water, and sometimes crystal-
lizes.   But it is incapable of being separated by evapora-
tion, as other salts, by employing heat.
    With respect to its origin, it is not found in a separate
state in nature, except in putrefying animal or vegetable
substances, or in the air which is  immediately over them.
It is contained in all animal and vegetable substances, and
is extricated from them by putrefaction,  and by a destruc-
tive heat.   There is also a little of  it in fossil coals.
Hence it  appears in the vapours which  arise from these
different substances, when they are destroyed or consumed
by  fire, or by a heat strong enough to  dissipate  all their
volatile parts.   In Lord  Dundonald's process for obtain-
ing a tar from pit-coal, a quantity of water is produced  with
the tar, which water contains some volatile alkali.  Soot,
which is  a matter produced by the condensation of some
of the vapours arising from heated coal or wood, also con-
tains it, combined with some other saline substances, which
repress its volatility to a certain  degree.   It is therefore
extracted in  large  quantity in some manufactures from
soot.  Urine also,  when putrefied  to  a certain degree,
•) ields a good deal of it :  and this is the cause of the  pun-
gent  alkaline odour felt in stables.   Some manufacturers
therefore prepare it from urine: and the  chemists formerly
did so too, and called it salt of urine.   It is this alkali in
putrid urine which makes it detergent.
   There  are also other animal  substances which afford it
in great quantity,  when they are heated and scorched to a
black coal in close vessels.  It is procured most plentifully
in  this way from the horny  parts  and the bones.   For-
merly the horns of the hart were preferred to  other ani-
mal substances: and the volatile alkali which they afforded
was called salt of hartshorn. There is still a volatile alkali
so called  in our shops; but it is prepared from bones of all
kinds  that can be collected.   They are  put into large dis-
tilling vessels of iron, and exposed to an increasing heat,
until all  their  volatile  parts are extracted ;  and  among
rhese is found a volatile alkali, which is  precisely of the 
ITS USES.                    41
same nature with the volatile alkali of hart's horns.  It has a
very foetid odour, proceeding from a burnt and volatile oil,
which  arises from these substances during the process,  and
which cannot afterwards be  completely separated from  the
alkali without too much expence.
  The best way to have this alkali free from such offensive
impurities, is to  extract it from a compound salt called sal
ammoniac, the process for which is to be shewn hereafter.
Thus prepared,  it is called spirit of sal ammoniac, or sal am-
moniacum volatile, or sal volatile.
  The other names that have been given to it are ammonia, in
the London and Edinburgh Pharmacopoey*,  spirit or salt of
urine, spirit or salt of hartshorn, volatile alkali.  The French
now give it the  name of ammoniac. '
  In the course  of our  examination of chemical bodies, we
shall have frequent occasion  to speak to this  alkali, and  will
also be able to  form a more  distinct notion of its origin  and
nature.
  It is much used in medicine, as a powerful and grateful sti-
mulant and diaphoretic of quick operation ; and is reckoned an
antidote  against  the bites  of venomous animals.  It is  also
employed in some of the arts, as in the manufacture of sal  am-
moniac ;  in  the manufacture of alum ; and in cleansing wool,
silk, and other  substances,  to  prepare them  for receiving
colours in the art of dyeing.
vdr.. ik 
*■'
GENUS   II
                   ACID  SALTS.

  YOU must next be made acquainted with the acids, so de-
nominated from their  taste.
  Of the salts belonging to this order, there is a much greater
number than of the alkalif.  But there are three, which, on ac-
count of the eminent and distinct manner in which  they pos-
sess the distinctive properties of acids, claim our chief atten-
tion, and greatly  assist us  in  investigating the properties of
the rest.
  These three have commonly been distinguished by the  title
of Fossil Acids ; and are now specified by the names of the
Sulphuric or Vitriolic, the Nitric, and the Muriatic
Acids.  Their common properties are these :
   1st. They have a  very  strong  attraction for  water ;  and
being at  the same time very volatile, a consequence of these
qualities is, that the only form in which we can have them for
use, is that of watery  fluids, or united with water, which re-
presses their volatility, and renders them manageable.
   We cannot separate the water entirely from them by evapo-
ration, or otherwise.  They  retain it too strongly, and are
themselves too volatile to  admit of this.  But when they are
 much weakened or diluted with water, we can separate a part
 of this water by distillation, and thus strengthen, or, as we say,,.
 concentrate the acid to a certain degree:  and in this  strong-;'-*.■..
 state they are commonly kept for use.   I shall, therefore, de-'"*''
 scribe them as they  appear when in this strong state, or as
 united with as little water as possible. 
ACID  SALTS.                  43
   In this state they have a powerful attraction for more water.
They attract it from  the air more quickly, and in greater
quantity, than  the vegetable fixed  alkali  does.   And when
mixed with water in its ordinary state, they unite with it ra-
pidly with violence, and produce heat.   Upon this account,
it has been thought the more extraordinary, that,  when mixed
with ice or frozen water, they produce a considerable degree
of cold.   But I formerly gave an explication of this phenome-
non, as depending on absorption of heat.
   Although these acids,  therefore, are  always exhibited and
used in the form of fluids, we  may consider their fluidity as
depending upon the water that is mixed  with them, and con-
clude that they are salts dissolved in water: for that the saline
matter which they contain is capable of appearing in the form
of solid salts, is plain from several facts.
   One of these is the solid form which the sulphuric  acid ac-
tually  assumes upon some occasions.   The whole of it con-
geals into a mass resembling ice, which, on account of its ap-
pearance, is called Glacial Vitriolic Acid.
   The  nitric acid  also, when exposed in its strongest state,
to a cold of 40° of Fahrenheit's  scale,  assumed,  in part,  a
solid form. A  considerable part of it crystallized into spicular
crystals.
   With respect to the muriatic acid, the same experiment has
not  been made with it.  But it is  probable that it also  would
crystallize in the same degree of cold, or in a greater *.
   At any rate, there is an easy method by which we can re-
duce these  acids to a solid form, which serves to shew that
they are capable of solidity. The method I mean  is to com-
bine them with the fixed alkalis.  They  are disposed to unite
readily and strongly with the alkalis, and  form with them com-
pound  salts, which can easily be  separated from water, and
made to appear in a solid form, as we shall see hereafter.
   2dly.  A second quality, which the acids are possessed ot in
common, is, that, like the alkalis, they change the colour of
infusions of the purple or blue flowers of vegetables : but

                * It does crvstallize....Ex»iTOB  • 
44 TEST-PAPER.... ACIDS UNITE WITH ALKALIS.

whereas the alkalis change them to a green, or abolish the red,
and deepen the blue ;  the acids, on the contrary, change them
into bright red,  or into a scarlet:  and  an extremely small
quantity is sufficient.   And this effect they produce upon the
same juices, although they have  been previously tinged green
or blue by an alkali:  while the alkali, on the other hand, will
produce a green colour in those juices, although they have
been previously tinged red by an acid.  We can, in this way,
change the colour of the same infusion to a red or  green alter-
nated, for a number of times, by  adding the one or the other
kind of salt.
  The chemists  are, on many occasions,  much interested in
ascertaining the presence of an alkali or an acid ; and keep in
readiness phials  of coloured tinctures of vegetables.   They
also use for this purpose slips of paper stained with those
juices,  called Test-Papers.  These tests must be carefully
kept from the action of the air and the light.
  Different tinctures  have different degrees of sensibility to
acids and alkalis. The tincture or dye called archil, cudbear,
or litn^us, is the most sensible to acids.   The juice of the
scrapings of red  cabbage  and radish  is also very sensible to
acids.   March violet, convolvulus, viola tricolor, and cyanus,
are less affected. Mallow flowers, march violet, convolvulus,
and alkanet, are much more sensible  to the alkalis.
  3dly. A third  quality of  the acids in general is,  that they
readily unite with any of the alkalis:  and if these are in their
ordinary  state,  a  violent effervescence is produced.   This
effervescence was formerly  reckoned a criterion of acids or
alkalis.
  This mixture  is a true chemical combination.   All the
distinguishing  qualities of both  ingredients arc gone.  The
acid or the  alkaline taste is no longer perceived ;  and one dif-
ferent from both is induced.  The mixture makes no  change
in the colour of vegetable infusions.  This gives  us the first
employment for  our tests and test-papers.   By these we dis-  :/
cover the exact saturation of the ingredients, which is another
proof of the chemical combination.  The great attraction for
water is gone:  and the compound is easily separated from ft 
ACID  SALTS.                  45
 by crystallization.  The great volatility of the ingredients is
 also repressed ; and trrfs, in one instance, in a most unaccoun-
 table degree.   The marine  acid, and the volatile  alkali,  in
 their utmost state of purity,  are  so volatile  that we cannot
 condense their vapours.  Yet these vapours, when united,
 instantly form a dry powder, which requires a very consider-
 able heat, approaching to ignition, to convert it into vapour. *
   4thly, and lastly,  The acids are powerful solvents of a
 number of different substances, as chalk,  limestone, marble,
 and metals ;  and they also  shew  a solvent  and destructive
 power, when applied to  animal and  vegetable  substances.
 Taken internally, in their strong state,  they would prove in-
 stant poison.   Applied externally, they immediately occasion
 sharp  and violent pain,  and very  soon destroy the part, as
 burning coal would do.  All this is to be understood of them
 only in their strong state ;  for if they be very greatly diluted,
 they  are not corrosive ;  and their most general effect is then
 to prevent or retard fermentation and putrefaction.   They are
 often taken in this diluted state as medicines,  and are cooling
 and astringent, and impress upon the tongue, in a very distinct
 and lively manner,  the  particular  taste  which their  name
 implies.
   These therefore are the qualities which  these acids have in
 common.  We shall  now consider the peculiar nature of each
 of them separately.


                  VITRIOLIC  ACID.

   The  vitriolic acid has this  name from vitriol, a compound
 in which it is contained,  and from which it was formerly  ex-
 tracted. At present, all that is brought to the market is pre,
 pared from sulphur; for which reason, and others, the French
 chemists have lately proposed  that it  shall be named Acide
Sulfurique, Sulphuric Acid.  And  it must be  acknowledged

   * This almost overturns all our mechanical explanations of chemical
 phenomena....edit p 
46                VITRIOLIC ACID.

that this is a more proper name than the other ; for even the
acid which we find in vitriol has its origin from sulphur.
   When pure, it is a colourless heavy fluid, in specific gravity
to water as  18i to 10.   This great weight gives it some ap-
pearance of sluggishness like  oil;  for which reason,  it has
been common to call it oil of vitriol.
   It is also  much less volatile than water.  It therefore does
not emit any sensible vapours or effluvia, in the ordinary heats
of the air;  nor has  it the smallest perceptible odour.
   It is  congealable by cold, and the more easily as it is
stronger.  It is then called Glacial Oil of Vitriol.   When of
the gravity  1.78,   it congeals  at  32°; and  requires  45° of
Fahrenheit to thaw it.  This shews that  it  is not a  simple
congelation, but,  in some measure, also a crystallization.  If
undisturbed, it will remain fluid below 32°,  and freezes and
emits heat when stirred.  (Phil. Trans. 1787,. Part 2d.)
   When very strong, it shews  the  powerful  attraction, it has
for water, by the violence and  rapidity with  which it mixes
with that fluid ;  in  mixing with which it grows very hot,  and
contracts greatly in bulk.   The heat produced, by suddenly
mixing strong variolic acid  and water,  will split  any thick
glass vessel.  The  mixture should, therefore, be  made gra-
dually,  by small additions,  and agitating the mixture after
each addition ;  otherwise the heavy acid will collect below  and
when you agitate, you will  mix  a great deal,  and produce      i
much heat.  The bleachers often pour the acid carelessly even
into hot water ; and it breaks out into steam, and scatters  the
acid about on the goods.
   The contraction of bulk is very great.   Twenty-eight mea-
sures of  water, mixed with four of acid, make only 29 mea-     A
sures of mixture, instead of 32.                                  *
   Its attraction for water likewise appears from the  quickness
with which  it attracts it from the air, and the quantity it will
attract.   Dr. Gould, Professor at Oxford,  found that three  *
drachms attracted more than a drachm of water in one day       !
and in 55  days, 6^- drachms; the quantity which it attracted  ''■'■
always diminishing.  Newman tells us that one ounce  of it in' ■■•■?'   "'
 » year attracted 6\ ounces of  water.                               ; 
COMBINED WITH  WATER.          47
  When this acid is diluted, or mixed with too much water,
it can be strengthened, tar the superfluous water separated, by
distillation in the retort and receiver.   If the quantity of water
with which it is diluted be considerable, the  first vapours that
arise are pure watery ones, or  little else :  and it does not re-
quire much more heat to raise it than water.   But, as the ope-
ration goes on,  the  water that remains, in proportion as the
quantity is diminished, is more strongly retained by the  acid:
and a  stronger heat  is required  to continue the  distillation,
until  it rise to near  the 600th  degree.  546, or 550, may be
accounted the boiling point of the strongest vitriolic acid that
can  be made.   The  vapour, too,  that arises during the pro-
gress of this operation, is  found to contain the larger propor-
tion of acid, the farther we advance in the distillation, until at
last what distils is as  strong as what remains  in the retort; the
small quantity  of water which it retains being so  strongly at-
tracted by the  acid, that they cannot be separated from one
another by heat, but arise  in equal proportions.
  I may notice,  by the way, that  this operation, by which we
clear a fluid of a volatile ingredient, which we consider  as di-
luting it, is called Concentration.  When we clear a volatile
fluid of a more fixed ingredient, we are not said to concentrate
itt but to rectify  it.   We  concentrate vitriolic acid;  but we
rectify vinous spirits.
  This acid, as first  produced  in the manufactory of it,  is al-
ways much diluted with water.   And it must be concentrated
by distillation, before it can be  carried to the market, or deli-
vered  to those who make use of it.  And the concentration is
always carried  on so far as to bring it up to the specific gravity
I mentioned, viz. 18* to 10.
  Such are the properties of this acid with  regard to water.
But, before we quit it, I find it necessary  to take some notice
of its relation to inflammable substances, the effects of which
upon this, as well as some  other acid salts, must be known be-
fore we can understand the processes by which some of the
compound salts are decompounded.
* The vitriolic acid acts powerfully on most inflammable sub-
stances.If  some olive oil, for example, be poured on vitriolic 
 48   VITRIOLIC ACID....SULPI1URIC  ACID.

 acid in a glass, heat is generally produced,  and the touching
 parts immediately become of a very dark coffee colour.  Fcetid
 steams soon arise, as the mixture goes on, and become at last
 very offensive and suffocating.   The mixture becomes thick
 and black, like tar.  If we mix the acid in the same way with
 oil of turpentine, the mixture is more remarkable, with violent
 heat, and bursts of suffocating steams : and the viscid mixture
 foams and froths over the brim of the vessel.   The oil ac-
 quires a very particular smell; and some of the spongy matter
 becomes hard and charred.
   One phenomenon observable in all these mixtures of vitrio-
lic acid with  common  inflammable  substances,  is the very
dark or black colour produced.  This occasions the brown co-
lour which this acid acquires when kept in a negligent man-
ner.   The acid of vitriol that is to be found in the shops, is of-
ten of a dark brown or black colour, although,  when fresh or
new, it is perfectly colourless and transparent;  and if kept in
close vessels with a glass stopper will remain so.  But if any
dust be allowed to get into it, or if the phial be stopped with a
cork, or other vegetable inflammable matter, the acid dissolves
and corrodes it, and acquires more or less of a brown tinge or
even black colour.   The way to restore a vitriolic acid thus
tainted, is to distil off a small part of it in a retort and receiver,
or boil it in a  matrass  under the vent.   When we do this,
a small part of the acid arises in the form of volatile steams,
which have the suffocating odour of burning sulphur.  The rest
becomes clear, and free from colour or smell.
   When we have had the curiosity to apply heat to such mix-
tures as these, and to subject them to distillation, we have ob-
tained several products :
   1st, A great deal of the acid arises in that volatile and suf-
 focating state which I just now mentioned, in which state we
 call it the  sulphurous acid;  and along with it the water which
 ■vas combined with it at first, and also a quantity which is con.
 tained in the composition of the oil.
   2dly, After this water  and suffocating sulphurous acid have
 arisen in considerable quantity, vapours next arise, which are
 vapours of perfecj sulphur or brimstone ;  a  part of the acid 
       ITS  ACTION ON INFLAMMABLES.     49

being changed into this form by the action of the inflammable
matter and it  on one another.  We also frequently obtain a
dry black powder, which, on examination, is a pure charcoal.
This rises, or at least is brought off from the black mixture
with a very moderate heat, and appears to have been merely
floating in it, having probably been the cause of its blackness.
  A great variety of other inflammable substances may be em-
ployed, as well as these oils, for producing these  changes on
the vitriolic acid.  I shall just mention two instances, which
exhibit classes of appearances somewhat different, and lead the
philosophical chemist to a variety of different conclusions.
  The first is a very simple one.   Dr. Stahl, observing the
sulphurous fumes obtained  in the process which I have just
now described, and the genuine sulphur sometimes produced,
and that this  sulphur did not appear till towards the end of
the prpcess, when the matter in the retort was of a burning heal,
wished to force the acid to bear this heat from the beginning,
while it acted on inflammable bodies.   For this purpose, he
took the acid as it is found combined with another substance
in the form of a salt.   He chose alum, of which it is an ingre-
dient.   He mixed dry alum with powdered charcoal. Apply-
ing a very great heat, he sublimed a quantity of pure sulphur.
a prodigious volume  of air was produced, which could not be
condensed by cold, and would have burst the vessels, if hot al-
lowed to escape.
  The other example is the distillation of the acid from dry
vegetable matter, such as sugar or straw.   If this last be put
into the strongest sulphuric acid,  it is immediately blackened,
aird after some time, dissolved  into a dark brown or black
pulp.  No smell or suffocating fumes are produced in the cold.
If we now dilute with water, a considerable quantity of impal-
pable black powder  is thrown down after a long standing.
This, when examined,  is very pure charcoal or carbone.   It
is remarkable, that this great addition of water to the strong
acid produces but a moderate heat.   It produces, however, a
distinct smell of vinegar.   If we now proceed to distillation,
we obtain real vinegar from it, and a much •= mailer proportion
    VOL. IX.           \ ."    r- 
 so   DR. STAHL'S  THEORY....PHLOGISTON.

 of the sulphurous acid and brimstone than in the process with
 oil.
   We shall return to this process, when we shall have acqul-
'red  a clear knowledge of the agents which are concerned in
 these changes.
   In these processes, therefore, the acid undergoes a most re-
 markable transformation ;. for that it is a part of the acid which
 is thus transformed into sulphur, cannot be doubted a moment.
 When we examine this sulphur,  and make experiments with
 it,  we  find  that it  has every  quality  of common sulphur,
 and among the re&t,  that of being  convertible into vitriolic
 acid by inflammation in the free air.
   I  have been somewhat minute  in the account given of this
 action of vitriolic acid on inflammable  substances, because it
 may be affirmed that it was the observation of these phenomena
 by the celebrated Stahl that first introduced any thing like phi-
 losophical discussion in"' chemistry.  The vague and obscure
 notions of.Geber, Becher, and others, about their sulphur and
 sulphuric principle, do  not deserve such a name.   But Dr.
 Staid founded, on the observations which I have now related
 to vou, a body or system of very precise and perspicuous doc-
 trines, whose influence  connected all the great.and important
 phenomena in chemistry.  Observing that the mixture of vi-
 triolic acid  with every inflammable  substance  produced  the
 same sulphur,  and that the substance was no longer inflamma-
 ble, he inferred, with great propriety, that all inflammables im-
 parted one and the same substance to   the acid.   Moreover,
 as those bodies resembled only in inflammability,  and as none
 but  inflammables produced sulphur with the acid,, he has pro-
 perly concluded that the thing thus imparted was  the cause or
 principle of their inflammability.   He  called it the Phlogis-
 ton.  " Materiam et principium ignis ego phlogiston appellare
 " incepi : ?iempe,primum, igniscibile, inflammabile, direct: at-
 " cue eminenter ad calorem suscipiendum habile, principium"
 Adding this"to any body that attracts it, renders it inflamma-
 ble ; and taking it away, renders it uninflammable.  Inflam-
 mation is its dissipation ; therefore the remains are uninflam-
 mable.   It may also be taken away by another body which at- 
     DR.  STAHL'S THEORY....DOUBTED.       51

tracts it more strongly:  and this transference is not accom-
panied by inflammation.  It is thus that vitriolic  acid takes
it from charcoal.
  Such is the famous doctrine of Stahl.  And its immediate
and  interesting consequences explain all the, operations of
metallurgy.  It was received with great applause.  And Ger-
many became the great school of chemistry.
  Such being the state of our science at the beginning of the
century, all the chemists were  accustomed to conceive and
explain these phenomena according  to the doctrine  of Dr.
Stahl, by supposing the volatile suffocating acid, which arises
before the sulphur, to be a part  of the vitriolic acid,  com-
bined with a certain proportion of their supposed phlogiston
or principle  of inflammability;  and the  sulphur, which  is
formed afterwards,  to be the rest  of the acid, combined more
perfectly, or saturated with a larger  proportion of the  same
principle.  The effect of this is to make it  assume the form
of an inflammable substance, namely sulphur; which sulphur
may be inflamed and burned, so as to dissipate its principle
of inflammability,  and thus to give us the  acid again in its
pure state.   This, I say, was the manner in which the chemists
were accustomed, until lately, to understand the facts I have
narrated. *
  But a great number of important discoveries, which have
been made of late, have occasioned these  facts to be- now
viewed in a  different light.  It has been  discovered,  that
while the vitriolic  acid  undergoes these  changes into suffo-
cating acid and sulphur, there is extricated from the materials
a very great  quantity of air, or elastic aerial matter: and, on
the other hand, when sulphur is changed again into acid by-
inflammation, a quantity of  air,  without which it cannot be
burned, is absorbed,  so as to enter  into the  composition of
the  acid, and  make  up apart of it;  the  quantity of vitri-
olic  acid obtained being, in fact, of much greater weight than
the quantity of the sulphur burnt,  nearly 2{..
  It is therefore concluded now, that the vitriolic acid !s a
compound of sulphur  and air;  and  that, when the  acid is
mixed with inflaoim^.hle  substances,  and, by  being distilled 
STAHL'S THEORY DOUBTED.
with these, is converted into sulphurous acid and sulphur,
these changes are not produced by the addition of any mattei
which  it receives from the  inflammable body:  but that,  on
the contrary, by  a  decomposition which it suffers, a great
quantity of its air being separated from it by  the superior at-
traction of the inflammable body  for that air;  and that part
of the acid which has lost a portion only of its air, becomes, by
its redundancy in sulphur, sulphurous acid,  or volatile suffo
eating vitriolic acid ; while that portion which loses the whole
of its air, becomes perfect sulphur.
   On the other hand,  when  sulphur is set on fire and made
to burn, and by inflammation is converted into acid, it unites
with a part of the air which  is in contact with its  flame,  and
which is necessary to the inflammation ;  and  by uniting with,
or attracting to itself, this air, it becomes vitriolic  acid again,
or a compound of sulphur and air.
   That a quantity of air is absorbed.by  sulphur,  when con-
verted  into acid  by inflammation,  is  now acknowledged by
every chemist.   The most direct  proof of this is had by burn-
ing sulphur in a known quantity of air, in the following man-
ner:....^ a cistern of water, or mercury, setup a stand, rising
some inches above the water ; and on the top of it put a small
quantity of sulphur ;  have ready  a glass  jar, and  having kin-
dled the sulphur, instantly  cover  it with the jar, whose mouth
must dip an inch or two in the water.  The heat will expand
the  air a little at first, and the water will be pressed  down:
but  by and by the water will rise in the  jar ; and, when the
brimstone ceases to burn,  and the whole has grown cold, the
water will have risen considerably in the jar; that is, air has
been absorbed.   By attending to all the circumstances which
affect the result, it is found that the weight of the air absorbed
 is equal to that gained by the sulphur consumed by inflamma-
 tion.
   It is also completely proved that a great quantity of air  is
 extricated, when wc convert the  acid into sulphur by the
 action of inflammable substances.  Of this you had an exam-
 ple  in the process lately shewn with alum and charcoal.  P'or
 unless an  exit be allowed, the vessels will be burst.   And if 
    UNION  OF SULPHUR WITH  ALKALI.     5 >

the vapour be collected in another vessel,  it will be found
aerial,  that is, incondensable by  cold.  It is, therefore, no
longer disputed that the acid is a compound substance, hav-
ing air, or the basis of  air, for one of its component parts.
But some of the chemists still  maintain that  sulphur also is a
compounded substance, as well as the acid:  that there is a
specific matter  in sulphur,  which matter,  when  combined
with air,  forms vitriolic acid,  and when  combined with  the
principle of inflammability,  forms sulphur;  and that while
this specific matter unites with  air, it loses the principle of in-
flammability ;  and that when  it  unites with the principle of
 inflammability, it loses its air.   This opinion, however, is not
supported by  direct experiments as the other is.  And until
those who maintain it can shew this specific  matter in a sepa-
rate state, and make  us acquainted with its  nature and pro-
perties, there is reason to suspect that their opinion proceeds
rather from the old habits of thinking, than that it is  founded
 on fact.   They think  it is necessary to suppose a principle of
 inflammability in sulphur, in order to account for the light and
 heat  which it gives in burning.   But, by the French theory,
 this light and heat are  supposed to proceed from the latent
 and specific heat, the  cabrique, as they call it, which is sepa-
 rated from the air, while this air is condensed by the attraction
 of the sulphur.
    From the whole of the facts, it is manifest that sulphur and
 the vitriolic acid are very nearly allied.  Each of them  it
 easily convertible into the other:  and yet their properties and
 powers are very different.  The  acid is  extremely acrid  and
 corrosive with  respect  to animal and vegetable  substances:
 sulphur, or the contrary, is mild and harmless.  The acid
 has a strong attraction for water: sulphur has not the least.
 The acid mixed with alkalis unites quickly and violently, and
 is strongly combined,  and difficultly separated : sulphur added
 to alkalis does not exhibit any  such phenomena.   Sulphur,
 however, has a considerable degree of attraction for alkaline
 salts, and is disposed to unite  with them. To see this,  how-
 ever, and make them actually unite, it is not enough that we
 mix them together in the form of dry powders.  In this case, 
 54      HEPAR SULPHURIS ABSORBS AIR.

 as in most others, it is necessary that one of the bodies, the
 alkali or the sulphur, be fluid, before they will act on one ano-
 ther, or unite.   But this fluidity may be obtained in two ways,
 either by using water to dissolve the alkali, or by applying
 heat to melt the sulphur.  In the language of chemists, the
 one is called the dry way, and the other the humid.
   1. Sulphur,  in the form of a dry powder, being mixed with
 an equal weight of vegetable alkali, must be exposed in a cru-
 cible to  a heat gradually increased.  This melts the sulphur,
 which then unites with the alkali, forming a compound, fusible
 in heat, and soluble in water.  When it cools, its colour great-
 ly resembles  that of liver.   Hence  it has been called Liver
 of sulphur, Hepab  sulphuris. This is the compound pre-
 pared, via sicca.
   2. A strong solution in water  of vegetable fixed alkali in Its
 purest active state, will dissolve powdered sulphur, with the
 assistance of a moderate heat.   This is  the preparation of
 liver of sulphur, via humidd.
   This combination of sulphur and alkali emits a most  disa-
 greeable smell, thought to resemble that of rotten eggs.   But
 it has nothing  putrid  or cadaverous.   It perfectly resembles
 what you perceive in  the washings  or scourings of a fowling
 piece :  and this smell is really occasioned by hepar sulphuris.
   The sulphur, when thus combined with an alkali, by either
 of these processes, and dissolved in water, shews a  much
 greater disposition to unite with air,  and to be changed  into
 an acid by the action of the air,  than  when it  is pure.   Wc
 need only to expose it to the air  of the atmosphere for a  few
 weeks.   Thus, by an imperceptible  action-of the air upon it,
.the  sulphur is gradually changed into acid, which however
 remains combined with the  alkali: and we have at last a com-
 pound salt in place of the hepar sulphuris which we exposed.
   This conversion oi  hepar sulphuris, a deep coloured, strong
 rmelling compound, into a pure white inodorous salt, by the
 simple exposition to the air, is  a curious fact, and  naturallv
 excited the attention of the chemists.  When the experiment
 is made  in closed vessels, that is, in a vessel set under a jar
 inViT'ed in a cistern of water, we discover that the change i<j 
 SCHEELE»S DR. PRIESTLEY'S DISCOVERIES.  55

 effected, or at least is accompanied, by the absorption of a
 quantity of air;  for the water of the cistern will gradually rise
 into the jar.   We shall find that about one fourth part of the
 air inclosed  with the hepar sulphuris can  be thus absorbed.
 Whatever quantity of hepar is thus exposed to  a given quan-
 tity of air, no more air can be absorbed : and the quantity of
 salt produced is thus limited.
   We learn  by these experiments that the air of our atmos-
 phere is not homogeneous ;  that there is only a  certain part of
 it disposed to unite with sulphur, a little more than the fourth
 part.  The rest has not the least disposition to unite with sul-
 phur, either when exposed to it in the form of heparsulphuris,
 or when we attempt to fire the sulphur in it. We cannot either
 inflame the sulphur, or change it into an acid, or perceive that
 any of the air is absorbed.
   We owe this most important experiment, and  the conclusion
 deduced from it, to Mr. Scheele, of Koping,  in Sweden, one
 of the most penetrating, judicious, and accurate chemists of
 the present age.  It is to be seen in detail in his Publications
 on Air  and  Fire,  and in the Memoirs of the Academy of
 Stockholm.
   Much about the same time, and without any knowledge of
 the other, Dr. Priestley had discovered this elastic fluid, which
 appeared to Dr. Scheele as a residuum of atmospheric air.
 The train of Dr. Priestley's experiments led him to form a
 very different opinion of it.  He conceived it to be atmosphe-
 ric air combined and saturated with the.principle of inflam-
 mability or phlogiston : and therefore he called it phhgisticated
 air. Scheele called it foul air, which we should translate, not
tainted, put putrid, corrupted.   It is now named by the Ger-
man chemists stick-stofl]  i. e.  suffoeating or choking air.
When Dr. Priestley learned Scheele's method of obtaining it,
he was confirmed in his opinion, and said that the  phlogiston,
 which had quitted the vitriolic acid, had united  with air. But
however specious  and perspicuous this explanation  is, and
although the opinion was adopted by the most intelligent che-
mists of Europe, it  is now found to be a mistake.   The spe-
 ..fic gravity  of  this  phlogistirated air was  ascertained by 
56
DEPHLOGISTICATED  AIRS.
w
 several chemists.  And when this was compared with the di-
 minution of bulk, it was observed that the absolute weight of
 the air had been diminished as much as its bulk.  This seems
 incompatible with the notion of the remainder being a com-
 pound of the whole original air and phlogiston. Few chemists
 could admit phlogiston to be a substance which  diminishes
 the weight of the substances with which it unites.  Moreover,
 experiments were afterwards made, which completely refuted
 Dr. Priestley's opinion.   Dr. Priestley and Dr. Scheele  had
 discovered  a method of purifying air from every  thing  that
 could be  supposed phlogiston: and  Dr. Priestley therefore
 called it aephlogisticated air.  It was  indeed his greatest  dis-
 covery ; and has  produced a total and extensive change in the
 chief doctrines of chemistry, as you will very soon see. Now,
 if this experiment of Scheele's be made with depblogisticated
 air, that is,  if the jar in which the hepar sulphuris is exposed,
 be filled with this instead of atmospheric  air, the separation
 of the sulphur and alkali is effected with great rapidity:  and
 the dephlogisticated air is completely absorbed,  and disappears.
 Here there is no longer room for  doubt: and it is perfectly
 agreeable  to Scheele's view of the matter.  There is no foul
 air in the  beginning, and therefore none can remain.
   These  experiments succeed exactly in the same manner
 when we make  use of the fossil alkali in its purest state. And
 sulphur is also capable of being joined to the  volatile alkali,
 bat by a very different process, of which we shall speak here-
 after.
   From the experiments you have now seen, you have  gotten
 some knowledge ofphe nature of sulphur, and of the origin of
 the vitriolic acid,  and  you see the propriety of the new names.
 Sulphuric  denotes  its origin : and sulphurous (sulphurosus
 denotes a  redundancy of sulphur in  the  volatile  suffocating
 acid.
   Of this  last, it is proper to remark, that it is much less emi-
nently acid^  and when combined with sulphur  to the utmost
has little sourness of taste.   Its attraction for water and  for
alkalis,  is  also  prodigiously diminished.   It even seems to
unite  with water reluctantly : and exposure to  air takes a\va\ 
*    SULPHURIC AND SULPHUROUS ACIDS. 57

the  peculiar smell, and gives  us simple sulphuric acid.
There are  even some  curious  experiments,  where  the
suffocating vapour  is made to  deposit the sulphur it con-
tains  in  a snow-white dry powder.  The weakest  acids
dislodge it from an alkali.
   The change of sulphur into acid  is performed by the
chemical artists as a manufacture.  It may be effected by
different  processes:  but only one of them  produces the
acid in its most perfect and most active state.  This pro-
cess consists in an inflammation of the sulphur.  A pro-
cess for  this# purpose  was  prescribed formerly in  our
Pharmacopoeias, under the title of Spiritus  Sulphuris pet
Campanam;   and  had this name from the apparatus em-
ployed, which was a large glass bell hung over a wide dish,
in the  middle of which stood a small vessel with burning
sulphur.   By this process, however, a small quantity only
of the  acid was obtained.  By  far the greater part arose
fnom the flame of the sulphur in  the form of the sulphu-
rous acid, which was very difficultly condensed; and when
condensed,  afforded an  acid liquor, which  continued  to
have the same suffocating odour, and was very different in
several respects from the strong vitriolic acid.
   It is evident that this proceeded from an imperfect in-
flammation, and incomplete change. Processes have since
been contrived, by which the inflammation is made more
complete, and the sulphur is changed into  a large quantity
of perfect vitriolic acid.  I shall mention the  manner of
doing this hereafter.
   This much is  sufficient at present with respect to sul-
phur, of which it was necessary to take some  notice, on
account of its connection with vitriolic acid.   We are to
take farther notice of it hereafter, in treating of inflam-
mables.
  Let  us next turn our attention  to the natural  history of
this acid.  Some time ago, it was very generally supposed
among the chemists,.that this  acid abounds in the air,  or at
least that there is some of it always mixed with common
air.  It was called the Acidum vagum A'ereum. Nay,  some
of the most eminent chemists conceived it to  be the primi-
tive acid, and called it Acidum Primigenium, affirming that
   VOL.  TI.                  H 
58        ORIGIN OF VITRIOLIC ACID.

it made the basis of  all  acids.  But the experiments to
prove  these  points are not satisfactory:  and there are
others which are incompatible with them.
   The place in which  this acid is in reality found,  is the
interior parts of the earth.   Sometimes, if we may credit
observers, it is found combined with water alone, in some
mineral waters.  But this I think very doubtful.  The bad
air, or vapour, by which miners have been sometimes suf-
focated, has also been supposed by some to be  vitriolic
acid, on account of the steams  of burning sulphur  being
also  suffocating.   But  all accounts of those vapours shew
them to be a very different matter; of which hereafter.
  Upon  the  whole, we have no  clear evidence that this
acid ever occurs in a separate state,  except in the steams
and smoke of volcanoes and volcanic ground; which steams
are said often to have  a very perceptible  and suffocating
odour of burning sulphur.   But it is found in great quan-
tity combined with other matter;  as in gypsum combined
with lime ; in bitter purging salt combined with magnesia;
in alum  and aluminous stones or clays ;  and in vitriol,
green,  blue, and white; the origin of  all which, and the
processes for obtaining the acid from them, shall be> con*
sidered as we proceed.
  Uses.........This acid  is itself employed as a medicine,
and is necessary in the preparation of a great number.   It*
is used in the arts;  in the process of making aquafortis; in
separating copper from gold; also in the bleaching of linen,
the tanning of leather, and the art of dying. The sulphurous
acid  is used for whitening woollen stuffs and silks, &c.  &c.
And vitriolic acid has been the great instrument in the
hands of the chemist for detecting other acids, by dislodg-
ing  them from the compounds in which they were  con-
tained.

                 SPECIES  III.....

        NITROUS AN,D MURIATIC ACIDS.

   The nitrous and muriatic acids derive their names from
the nitre and sea-salt, from which they are commonly ob- 
       NITROUS AND MURIATIC ACIDS.     -59

tained.   In their strongest state, they are not so heavy as
the vitriolic acid;  and are therefore supposed to contain
less  saline matter and more water.  The salt which they
contain appears to be of itself very volatile, and to have its
volatility repressed by the water with which it is joined.
This appears when we attempt to prepare those acids of ex-
traordinary strength.  They arise in the  form of fumes,
which cannot be  condensed, except we apply a receiver
with some water,  by which the acid particles are strongly
attracted  and condensed, and brought into the form of a
fluid, more or less manageable, according to the quantity
of water with which the acid  is combined.   If the quantity
of  water  be  moderate,  it will not be sufficient for totally
repressing the volatility of the acid,  some of which is
always disposed to fly off in vapour whenever the fluid is
exposed to the air.   But if much  more water be added,
the disposition to smoke in that manner will be diminished,
until it is entirely taken away; the greater quantity of water
having more power  and effect  in suppresing the volatility
of the acid.
   But it is proper to  observe  here, that both of them ap-
pear sometimes in a  more  volatile, sometimes in a less
volatile state ; the causes of which shall be explained here-
after.
   When they are diluted with  a large quantity of  w*tejg,
we can distil off part of this water, and render the acid again
moderately strong.  For it is very  remarkable, that when
they are moderately diluted only, they compose, with the
water, a fluid that is rather less volatile than either the wa-
ter or the acid particles in their  separate state.   If we
therefore  subject them  to diatillation  in a largely diluted
state, a part of the water distils over at first by itself, or
with very  little acid, and  the  acid in  the retort becomes
stronger.   But they can be strengthened in this manner to
a certain  degree only, which falls considerably short of the
strength to which vitriolic acid may be  brought by this ope-
ration.   This proceeds from their being more volatile than
that acid.
   What  has been said  so far,  therefore,  is, applicable to
both these acids.   But we must consider more particularly
Ahe nature of each bv itself. 
60
                  NITROUS  ACID.

   First, therefore, the nitrous acid, when very strong,
smokes if exposed to the air ; and emits ruddy fumes, ot
a  highly disagreeable suffocating smell, which tinge the
air in the phial in which it is kept, with a deep orange co-
lour, but perfectly transparent.  When this vapour gets
out, and mixes with the air, it forms a dense cloud  of ruddy
mist, sometimes as red as blood. The acid may be cleared
of these fumes,  by distilling off a small quantity, and is
now called Nitric Acid.   What remains is equally, per-
haps more acid  than  before, but does not smoke.  Yet if
this acid be exposed to  the light of die  sun, in a phial
close  shut by a glass stopper, it immediately begins to
tinge the air above it, and to produce the same fumes.
   The most  eminent and distinguishing property of this
 acid is the strong action which it exhibits on inflammable
 bodies, ajid the violent effects which  it produces, when
 mixed with  a  number of  those substances.   They are
 among the most surprising phenomena that chemistry ex-
 hibits.  You have a good  example in its  action on  the
 aromatic oils.  If one of these, such as oil of caraways, or
 even oil of turpentine, be put in a  small  dish or cup,  and
 about two  ounces of the strongest smoking nitrous acid
 (usually called  Glauber's spirit of nitre) be poured  into
 the middle  of  it, the  mixture  immediately grows  hot,
 smokes,  boils,  or froths up, and bursts out into a  bright
 flame.  The experiment is attended  with  some risk of
 being bespattered with the burning stuff, and should there-
 fore be performed in a particular  way.  Some  little  cir-
 cumstances must also be attended to for  insuring success.
 Let the oil be in a dish, in form of a cup ; and put the
 acid into a three-ounce phial, of which the neck is cut off;
 this must be  fastened to the end of a long stick  as a  han-
 dle.   The quantity of the acid should Lx- about half of
 the oil.   Pour  in about two thirds of it;  and as soon as
 the violent boiling begins, pour in the rest, where the boil-
 ing stuff appears blackest and driest.  The oil of  turpentine
 should either be thick by long keeping, or  be thickened a   V< 
NITROUS ACID.
61
little by some turpentine.   Mixing about a third  part of
the strongest vitriolic acid with the nitrous acid is thought
to make the success more certaip.
   This surprising experiment was first published by Dr.
Hoffman, with respect to one kind of oil.  But others have
since shewn that the nitrous acid produces the same effect
upon a great number of the oils, and even upon charcoal;
when  finely levigated,  it fires it instantly; only, that with
some of  those oils the  mixture must be made in a parti-
cular manner;  and,  in general, the acid must be used as
strong as possible.
    As the vitriolic acid is blackened,  and made to yield
suffocating vapours, by the smallest addition of inflammable
substances;   so such addition to the  nitric acid causes it
to assume the orange colour, and give out  those ruddy
fumes;  and it is then  in the state called Nitrous Acid.
    From  the late  discoveries in chemistry, there is reason
to conclude, that  this power of the nitric acid to act with
 such violence on the inflammable substances, depends on its
 containing a large quantity of  the same sort of  air which
 makes a part of the vitriolic  acid,....a particular kind of
 air which I shall soon make known to you.   In the nitric
 acid it is more loose and active than  in the vitriolie acid;
 and there is a strong attraction between this air  and the
 inflammable  substances.   The nitric acid,  therefore,  in
 acting on some of them, produces elastic fluids, and violent
 explosions, and very bright and rapid inflammations.  All
 these particulars, in the constitution of the nitric acid, and
 their  relation to  the phenomena of combustion,  will open
 upon  us  by degrees, as we proceed in our examination of
 chemical bodies.
    This acid mixes with water, producing heat, ebullition,
 red fumes, and a green of blue colour, which, by adding
 more water, is  weakened, and  disappears.   This  blue
 colour, also appears  to be owing to the action of inflamma-
 ble substances;  for, when it is  diluted, and has lost  its
 blue colour, it may be restored by a single drop of spirit of
 wine  added to several ounces of the diluted acid.   N.  P>
 This  diluted acid is the aquafortis of the shops. 
62               MURIATIC ACID.

   You may remember that, on another occasion,  I men-
tioned the remarkable  effect of this acid on water,  in the
form of ice or snow, especially the last.   It  melts them
into an acid brine, and the liquefaction is accompanied with
most intense cold.   But I then explained the cause of this
sudden disappearance of heat.   It is  no way inconsistent
with the  production of heat by the  mixture of the acid
with water.   Vitriolic acid produces the same  effects : but
the cold is  inconsiderable. ;  because  the freezing or crys-
tallizing temperature of the acid is not very low ; whereas
the nitric acid has never yet been congealed by cold, when
moderately strong.
  Natural History.........All the nitric  acid  we have  is
extracted from a compound salt, namely,  common nitre
or saltpetre; with the natural history of which I shall soon
make you acquainted.   There  is also unquestionable evi-
dence, by experiments of  Mr. Kirwan, MiJner, Berthollet,
and others,  that it may be  produced by mixing air with
pure volatile alkali.   You will see,  as we  proceed,  how
this may happen, although neither of those vapours contain
this acid.
   This acid is employed in pharmacy, in preparing a num-
ber of the articles of the materia medica ; and  is necessary
or useful in many other arts, as parting of gold and silver,
etching, scarlet dye,  and others.


        SPECIES  III.....MURIATIC ACID.

   1 he muriatic acid, in its ordinary state, is a light yel-
low, or citron-coloured fluid, which, being exposed to the
air, emits fumes that do not tinge the air, but are colourless
and transparent in the phial; and when allowed to exhale,
and  mix with the air of a chamber,  they render it misty.
These fumes  also are noxious to the lungs of those who
are  much exposed to them.   But their smell is  very dif-
ferent from that of  the nitrous acid,  and is  thought  by
some to resemble the smell of saffron.
   These are  the characters of this acid in its more fixed
 mte.  But I must not omit t6 inform you, that it is alsc 
MURIATIC ACID.                63
liable to great difference in the degree of its volatility.  As
obtained by the process usually prescribed for preparing
it strong, it is of a paler colour, and sometimes has hardly
any tinge of yellow.   It is  then  in a much  more fuming
state ; and the  fumes  are  much more disagreeable  and
suffocating.   Yet with all these appearances,  it is not, as
an acid, so strong as when less fuming.   If we distil away
the half, the fuming,  or most volatile  part,  comes over,
while  the  stronger and more fixed remains  in the retort.
This more fuming state seems to  depend upon the same
cause as in the nitric acid: but we cannot  demonstrate this
so clearly  by extemporaneous experiments*.
   In mixing with water, it does not produce  so  much heat
as the former two  fossil acids ;  and  its colour is only-
diluted,  and the fumes suppressed.
   It has very little attraction for inflammable substances.
It acts upon them but very slowly and weakly, never  pro-
ducing heat or ebullition.  Its action is best observed when
it is digested with them.  It is then found to darken in its
colour, and thicken in its consistence.
   Origin.........Margraaf observed that a minute quantity
of it exists in the air;  but  it is found  no where else  in a
separate state.   Great abundance of  it, however, is found
in a state  of combination.   Common salt, which,  as we
observed  before, is formed in such great  quantities  in
the earth,  as well as in the  sea, and one half of which is
composed  of fossil alkali, has this acid for its other half,
and  from it this acid is always obtained.


   The preceding observations may suffice for giving you
a  preparatory knowledge of the general characters of the
mineral acids,  as far as is  necessary  for understanding
their manner of acting on certain  great classes of chemical
bodies.  In the consideration of those bodies, and of the

  * I confess that the two cases seem to me  to  be remarkably different.
The vitriolic  and nitric acids are most  eminently  acid, when they have no
redundancy in their distinguishing ingredient.  The  muriatic acid is most
eminently acid, when it  has the greatest proportion of its distinguishing
ingredient. This anomaly still remains a mystery.....editor 
64               ACETOUS ACID.
way they arc affected by their union with these acids, we
shall learn by degrees much  more  concerning the nature
and constitution of the acids themselves.
   I observed before, that there are many more acids than
these : I do not propose, however, to take notice of them
all at present; but will confine myself to the description of
three of  them,  of more frequent occurrence.   Thev  are
distinguished from the former, or mineral acids, by being
much less powerful as acids,  and  less perfect as salts.
  These three  are called,
  The Acetous Acid ;
  The Acid of Tartar; and           ,
  The Sedative Salt, or Acid of Borax.
   The acetous acid, and  acid of  tartar,  are called  the
vegetable acids, on account of their being obtained from
vegetables only.  The acetous is got from fermentable
vegetable substances, by fermenting them in a particular
manner ; and it seems to be formed  by  the fermentation.
The acid of tartar also is obtained chiefly from fermented
vegetable juices ; but appears to exist  in the  vegetable
matter before the fermentation, which does  not form this
acid, but only extricates it.   The nature of  fermentation,
and the  particular kinds of  it by which these  acids  are
obtained,  shall be considered on another occasion.  At
present we shall attend to the properties of these two acids
thus obtained.

         SPECIES IV.....ACETOUS  ACID.

   The Acetous Acid, or Vinegar, is of all the acids the
most commonly known, and from it  even the fossil acids
derived their name.   It resembles them in several particu-
lars>   Like  them, it is a watery  fluid; and, in its  original
state,  is always unavoidably diluted with  a very great
quantity of water ; so that if we compare its strength with
that of the fossil acids, we shall find that it has hardly equal
acidity to  a mixture of  these with 40 or 50 times their
weight of water.  It is,  in fact, a  mixture of the true
 saline matter and water, in the same manner as the fossil
 acids.   It may be freed from a very considerable portion 
AjJETOUS ACID.               65
of the water by freezing. The ice which is formed scarcely
retails any of the acid..  Having done this by a moderate
frost, the liquor which remains, and which contains almost!
the whole acid, may be exposed  to a more intense cold*
which will separate still more water, and leave  the  acid
of very great strength, not less than ten  times its former
strength. However, this method cannot be practised except
in the coldest climates.  But you  will learn other methods
by  which it may be freed from  a great portion of this
superfluous water, and  made equal in acidity to  some of
the mineral acids.
   But besides this great proportion of water in which it
is diffused, we find it mixed with a quantity of mucilaginous
and inflammable  matter,  and some other saline bodies
beside our acid.   When we desire to render it purer  for
chemical purposes, we separate these impurities by distil-
lation, the  purer acid being so volatile  as to rise  by a
moderate heat, very little exceeding that  of boiling water;
while the other matters, which are not disposed to rise at
this heat, remain.   It is then called distilled vinegar.   By
the same operation too we can free it of  some part of  its
water: that is, having first separated it by dist'dlation from
those  extraneous  .matters  which  are  less  volatile,   we
separate  some  of the  water that  dilutes  it, by another
distillation,  in  which the  dephlegmated  acid  remains in
the  retort.   By  this method, the acid is pretty  well
separated  from  the slimy, tartarous,   and  other fixed
matters.  But the  separation of the water, or the  dephleg-
mation or  concentration  of vinegar, as  it is  called,  can
be  carried only to  a very  imperfect length by distillation
alone, on account of the small difference in point of volatility
between the acid and the water.   Other  ways, therefore,
have  been  attempted,  1st,  By   freezing,  as has  been
already mentioned ;  2d, By joining some fixed substance,
which diminishes  its attraction for water,  and fixes it so
as it  can be reduced to a dry mass ; and then it may be
separated by heat alone, if it be not too strongly retained,
or with the assistance of some addition, such as  charcoa!
VOL. II.
r 
 66               ACETOUS ACID.

 dust*.  At present, I can only notice the general principle
 on which  those additions  are  made,  namely, to force the
 acid to bear a considerable heat.  But .this alone would not
 be enough.   It only comes in aid of elective attractions,
 which of themselves are too weak.  The particular modifi-
 cation of each of these additions not  being yet familiar to
 you, I need not name them at present.  They will occur
 in course.                              •
   Thus jt may be made as strong as the fossil acids;  for
 though it  is more easily elevated by heat applied, it is not
 so elastic  as the nitric and  muriatic acids.   In this very-
 concentrated state, the acetous  acid crystallizes, and  its
 vapours are  inflammable, as also the acid itself,  if made
 pretty warm.   Tht3 operation, however, is not necessary
 to prepare the acid for the common uses to  which it is
 applied.   For  common uses,  it is only purified by distil-
 lation: and it is then known by the name oi distilled vinegar.
 It resembles  the fossil acids by effervescing with alkalis in
 their ordinary  state, and  by uniting with them, and with
 absorbent  earths, and some metals, though weakly.   Like
 those  acids, it  changes vegetable  colours to red.   But it
 has little effect upon  inflammable bodies ; though it may
 be combined with  them ;  nor is it so acrid and corrosive,
 even when equal in strength.
   But there is  another remarkable particular by which it
 differs from the fossil acids, viz. by being easily destructi-
 ble by the action of heat, if the heat to which it is exposed
 ever rises  to the point of ignition.   We may observe the
 effects of this heat upon it, by joining to it some fixed sub-
 stance that can retain it, and repress its volatility with pro-
 per force,  such as a fixed alkali;-   If it be united to  one of
 these, and the compound exposed to heat in close vessels,

  * Mr. Lowitz,  an eminent chemist at  Petersburg, found that charcoal
 acts on acetous acid, so as to make it resist a heat somewhat exceeding that
 of boiling water.  Therefore, by managing the distillation with great care,
 all the water  can be expelled, and what remains in the retort is the charcoal,
 combined with the acetous acid.   This state of things must be indicated by
the cessation  of drops from the neck of the retort.   The receiver must now
be changed,  and the heat raised  a few degrees. The acid will now come
over in the  most  fragrant, pure,  and concentrated state that can be
•Toduced ..EDITOR 
ACID OF TARTAR.
S7
as soon as the compound salt approaches to a  red heat, the
acid begins to. be totally destroyed.  The principles of it are
disarranged, and made to enter into new combinations with
one another,  so that we never can recover it again.  It  is
scorched, burned, and destroyed by the heat, and converted
into foetid,' watery, and oily steams,  and a black coaly matter
adheres to the alkali.
  The same change is produced by fire on all vegetable mat-
ter in general.  And as all other vegetable matter is inflamma-
ble, so is also this acid.


          SPECIES .V.....ACID OF TARTAR.

   The other species of vegetable 'acid; which is known by the
name of the acid of tartar, or the tartarous acid, is still more
gross, and farther removed from the nature of the more pure
and perfect salts. F^or although we can reduce it to a dry state,
and crystallize  it, it is neither a fusible nor a volatile sub-
stance.   I mean that, exwept a watery fusion, which the crys-
tals can undergo, it is nof capable of being melted, or convert-
ed into vapour by heat, like most other salts, so as to resume
its natural appearance and properties, when it is cooled. When
heat is applied to it, no sooner does the heat rise above that of
boiling water, than this acid begins to be scorched and burned
by the heat acting on it,  as happens to vegetable matter in gene-
ral ; and  as the heat is increased, foetid, oily, and sooty steams
 arise from it,  which may be set on fire.   A black coal remains,
 which may be burned to ashes;  and Uius the acid is totally lost
 and destroyed ;  that combination of its principles upon which
its properties depend, being  now so completely undone, that it
 never can be restored again.
    Water applied to this  acid,  dissolves it easily  and in great
 quantity.  The solution, when very strong, is  thick like a si-
 rup, and has an agreeable acid  taste,  like that of lemons.   It
 effervesces with alkalis, and unites with them as other acids do:
 but it does not affect the  v^etable tinctures so much.
    Origin.........It is extracted from the vegetable salt called tar-
 tar  which contains this acid combined with  an alkali, and
* 
8               SEDATIVE SALT.
which is found in the juices of many  of the vegetables, parti-
cularly \r that of the grape.   The nature of this compound
salt, 'vhirh was not thoroughly understood, until it was inves-
tig;.; u by Mr. Scheele of Sweden, shall be explained when we
treat of the compound salts.
  Beside  the tartar commonly known and used in medicine,
there are other kinds, a little different from it, in the juices of
other vegetables ;  as sorrel, tamarinds,  &c.  The difference
of diem from common tartar depends upon their acid, which
is a little different, though it agrees in its nature upon the whole;
all  of them being totally destructible by a burning heat, and
with the same phenomena as those that accompany the destruc-
tion of the tartarous acid of wine.
  For  a great variety of vegetable acids, mapy of  them newly
discovered, see Fonrcroy's Preliminary Discourse to the se-y
cond edition of his Elements.


          SPECIES  VI....SEDArpVE SALT.

  The sedative salt, the next in order, was so called from some
virtues in medicine,  which it was supposed to have when it
was first  discovered.   Its powers as an  acid are still  weaker
than those of the vegetable acids.   We  can hardly perceive
any acidity in it by the taste ; and it has very little effect on
the vegetable colours,   But it  effervesces  with alkalis,  and
unites  with them in the same manner as the acids  : and it can
be combined with sorce of the earths which have attraction for
acids in general.   It is obtained from a compound salt, called
borax.  And the nature of the operation by which it is ex-
tracted from the borax, is such, that the sedative salt is ob-
tained in a crystallized state ; the crystals which it  forms being
mostly fiat and thin l'-ke the scales of fish,  and feeling slip-
pery between the fingers.   When we make experiments  upon
it in this state, we find two things very  remarkable in it:
  The first is the manner in which it is affected by heat applied
to it.   When  exposed to heat in the open air,  it  generally
emits white fumes,  and seems to  melt; but this is only a
watery fusion, and it soon becomes dry and spongv.   If it be 
      SEDATIVE  SALT....ACID OF BORAX.    69

 heated in a retort,  it first undergoes the watery fusion; then
 water is distilled from it;  some of the salt sublimes;  and the
 rest remains perfectly fixed.   Were we to form a conclusion
 too hastily from this experiment, we might imagine that this
 salt is not homogeneous;  but that part is fixed, and part vola-
 tile.  But we shall be undeceived if we pursue the experiment.
 If we collect the sublimed matter, and examine it, we find it to
 be precisely the same as  the  sedative salt was at first, only
 formed into smaller, thinner, and lighter scaly crystals. When
 thes< are exposed to heat in the same manner,- they shew pre-
 cisely the same phenomena which have been mentioned above.
 On the other hand, the fixed part, which remains in the retort,
 is hard and transparent, like glass or horn.   But it dissolves
 in hot water, and crystallizes  on cooling,  and undergoes the
 same changes as that which was sublimed.
   These experiments, therefore, shew that there Is no differ-
 ence between one part of this salt and another;  but that the
 manner in which a part of it sublimes  is this: the crystals of
 it, like those of many other salts, contain a good deal of water.
 When heat is  applied to  these  crystals, watery fusion takes
 place; and  the water is gradually driven off in the form of
 vapour.  While the quantity of the water which adheres to the
 salt  is thus diminished, the remainder is retained the more
 strongly;  the greater proportion of saline matter with which
 it is combined, acting upon it with a greater power of attrac-
 tion.   And when the heat increases to such a degree as to
 force it to rise, a part of the salt rises with it.  They  cohere
 too strongly to be  completely separated by heat.  At last,
however,  so much of the water is separated,  that  none,  or
 scarcely any, remains with the  salt in the bottom of the retort.
 The saline matter then shews its natural relation to heat.  It
 is fixed in  the fire, and melts  into a transparent viscid fluid
like glass.   But this glass-like  matter can all be made to sub-
lime by repeated additions of water.
  In this manner is the sedative salt affected by heat.   The
other remarkable  particular observable in it, is the effect it
produces on spirit of wine. Sedative salt dissolves very readily
in highly rectified spirit of wine, especially if previously de- 
70       ORIGIN OF SEDATIVE  SALT.

prived of all water; and, in this state it may be taken up by
the wick of a lamp, or any bibulous substance.   The best way
of observing its effect on  the flame,  is to dip some paper into
the solution, and hold it upright while burning.  The flame is
of  short duration, but very large,  and of a beautiful green
colour, especially at the top.
   Although this salt shews strong  attraction for the water
which it contains  in its crystals, it has but little disposition to
unite with more water, or to dissolve in it.   Cold water dis-
solves very litde of it.   Hot water has much more  effect:
but when the solution cools, the greater part crystallizes.
  The origin  and natural  history of the sedative  salt  was,
until of late, very obscure.  All that we knew of it was, that it
is a part of a compound salt called Borax, imported from Bou-
tan and Thibet, in the East Indies.  But when inquiry  was
made about  the origin of the compound salt, we could obtain
no distinct accounts of it; reports only bearing that it was pro-
cured from certain mineral waters.   This, however, was not
satisfactory; because nothing like it was known in Europe or
America.
   At last, however, two or three years ago, some hot mineral
waters were discovered by Hoefer in Italy,  in the neighbour-
hood of Siena, and also in the Duke of Tuscany's dominions,
which, beside other ingredients, contain sedative salt.  (Ex*
trait des Observations sur les Lagonis au pais de Siena, et celui
de  Volterra  en  Toscan, par Paul Muscagne.   Observations de
Phys. 1780.)   The description of  the neighbourhood of the
ponds where the sedative salt is found, and the account of the
changes incessantly going on there,  in which the firmest flinty
rocks are continually mouldering away and forming new com-
pounds, is extremely curious, and will lead the philosophical
ehemist  to  very important reflections.  In these  places, the
sedative salt is sometimes found in considerable masses, gene-
rally adhering to a schist  or slate, in crystals considerably dif-
fering in form from what I have been describing.   It is also
frequently found combined with other substances, such as lime
clay, volatile alkali.  But Hoefer has not found it in that state
in which it is  rr^tin in India.....See also Experiences sur les 
           ORIGIN OF SEDATIVE SALT.        n

sels sedatifs, nitreux, marpn, et aceteux, par M. Cadet, Ac. Roy.
1780.
   It  is also found in  a  very hard stone at Luneburg in Ger-
many, and may probably be found in others*
   As I have already observed, there  are several other sub-
stances  having the chemical properties of acids.   Amber fur-
nishes one ;  ants yield another.  Several plants contain acid
juices ;  such as sorrel, rhaponticum, and the whole family of
the rumices or docks.   Most of the pulpy and fleshy fruits of
trees and shrubs  yield it in abundance.   Theseijre all  of a
very complex nature;  and are  eminently distinMished from
the mineral acids, in their being destructible by fire, in such a
way that they cannot be recovered.  You are not yet prepared
for understanding  their  distinguishing  properties.  Indeed
these are not yet  very fully investigated, having but lately at-
tracted much attention.
   Besides these, there have been discovered two  other acids,
which are not destructible by fire; namely  the acid of phos-
phorus, and the acid of fluor or spar.  These have very distinct
and very remarkable properties, and shall be duly noticed as
we proceed.
*• 
72
GENUS  III.
  OF TH^COMPOUND OR NEUTRAL SALTS.

    HAVING now given some account of  two of the most
 active classes of chemical bodies, the alkalis and the acids, and
 having  taken  some notice of their disposition to unite and
 combine with each other, I take this first opportunity of mak-
 ing you familiar with the most  important part of chemical
 science  and art,.....the composition, and decomposition of bo-
 dies.  The" relation of the alkalis and  acids affords the best
 example of this.  The  phenomena  are simple  and precise:
 and therefore are the most  proper specimens.   Besides, the
 union and separation of acids and alkalis occur in almost every
 other chemical investigation.
   I have considered three alkaline salts, and six acids.   And
 I am now to explain, how these nine salts, or saline substances,
 unite with one another to form  the  compound salts, which
 have been a long time known and in use.
   A person who knew nothing more concerning the compound
 salts which we are now to describe, but that they are formed
 by different combinations of the nine simpler salts which you
 have seen,  might naturally suppose their number to be  very
 great;  for, were the simpler salts capable of being combined
 in a great variety of ways, in respect of number and propor-
 tions of the ingredients, the different compounds producible
 from them would amount to a  very great number indeed.
• But when  you call  to mind the nature  of chemical union in
 general, and the account which I have given of  the different
 simple  salts, with respect to their power of combination that
 is, the  limited manner  in  which alone they are disposed to
                                      \ 
NEUTRAL SALTS.
73
unite, you will perceive that we can produce from them but a
very moderate number of compound salts.
  For, in the first place, it appears by mixing them variously
together, that no acid has any attraction for any other acid, nor
any  alkali for other alkalis.  Acids may be mixed intimately
with acids, and alkalis with alkalis ;  because they can be ap-
plied to one another in the form  of watery fluids:  but thus
mixed, they do not shew any chemical attraction for one ano-
ther.  The Volatility and other properties of the volatile acids
are not in the least diminished by mixture with the fixed acids,
nor  the volatility of the volatile  alkali, by the fixed alkalis.
The only manner in which we can obtain compound salts,  is
by mixing the acids with the alkalis.  These, upon all  occa-
sions, shew a chemical attraction for  one another, and are
strongly disposed to unite.   And  their  union, when we em-
ploy them in their ordinary state, is always accompanied with
that  violent effervescence which you have seen.
  But what still farther limits the  number of salts producible
in this way,  is, that almost  in every  case the  acid and  alkali
are capable of uniting firmly together, in one certain proportion
only.  What the nature of this proportion is, we cannot pre-
tend to say.   Whether it consists of an equality in the number
of the atoms of the two salts ; or whether there must be two
acid particles  or atoms to every one of the alkali,  or two  of
the  alkali to one of the acid ; or  what other proportion, dif-
ferent from either of  these, may be nec«ssary to  constitute
the compound salt, cannot be determined.   But, in order  to
explain  the  formation of these salts more distinctly, I shall
suppose that the proportion in which the acid and  alkali are
disposed to unite the most  strongly, is that of equality.   Let
us then take an acid and an  alkali dissolved separately in water,
and add a small quantity of the acid liquor to the alkaline one.
r.very atom of the acid that has been added is united with a
respective atom of the alkali, so that a certain quantity of the
alkali is changed into a compound salt, which, if there be  water
enough to dissolve it, is equally distributed through the liquor,
and blended with the  remaining alkali.   But this remaining
alkali still ictains all its properties, and is precisely the same
      m • II.                  k 
74
NEUTRAL  SALTS.
 as before.  If we go on to add more acid by degrees, v:c shall
 successively change more of the alkali into a compound salt,
 until such a number of acid atoms have been added as are suf-
 ficient to change the whole of it.   Then the mixture is com-
 plete.-" If we add more of the acid, it will suffer no change. It
 will be uniformly diffused through the liquor, but will remain
 disengaged, and retain all its properties.  Or, if a small quan-
 tity of it sometimes attaches itself to the  particles of the com-
 pound salt, its adhesion is loose and imperfect, and easily over-
 come.  This is not only  the case with regard to the same acid
 which enters into the composition of the compound salt.   But
 even although we add any other acid, it will either produce no
 effect whatever; or, if it  does unite itself to the alkali, it is sure
 to separate the first acid, so as to produce a different compound
 salt, but one of a similar nature to the former,  in so far as there
 is a limit to the proportion of acid and alkali of which it is com-
 posed.  What has now been said with respect to the mixture
 of different acids with the same alkali, must be understood also
 of different alkalis mixed with the same  acid.  As the same
 alkaline atoms  are incapable of being strongly united by at-
 traction with two or more different'species of acids at the same
time;  so  the same acid particles  are  incapable  of  being
 united at the same time with more than one species of al-
 kali.
  I have  been  thus  particular in  explaining the manner in
 which acids and alkalis unite to form compound salts, for this
 reason, that the simpler  salts,  and especially the  acids  are
among the  most active  of the  objects  of chemistry.  They dis-
 solve  a variety of earths, metals, and other bodies ;  and unite
 with these  in a manner very much similar to their manner of
 uniting with alkalis ; upon which account it was proper to ex-
 plain this once for all at full length.  On  this subject I recom-
 mend  to your serious  perusal Mr. Kirwan's  dissertation on
 the attractive forces of the mineral acids, published in the Phi-
 losophical Transactions,  and also in a separate volume.   You
 will there meet with many important enervations on the pro-
 portions of the ingredients,  and the variations to which  this
 is subject,  and many other instructive particulars.   Mr. Ber- 
COMPOUND SALTS.
75
thollet has also considered this subject with peculiar care and
great judgment.
   The compound salts, however, are not always produced by
joining together artificially the pure acid and alkali which they
contain.   Some of them are found ready  formed by nature.
Others are produced accidentally, in chemical processes, in
which their  constituent salts  are mixed together,  although
their union is not the principal object of the operation.  But
there are some which we never obtain but by mixing, on pur-
pose, the acid and the alkali necessary to their composition.
   When we produce a compound salt in  this way, and gra-
dually add the acid and alkali to  one another, in order to at-
tain  the  due proportion,  this is called saturating these salts
with one another.  And when the  due proportion is  found,
we sav they  are mutually saturated, or that we have attained
the point of  saturation.  This point is judged of commonly
by the gradual diminution and cessation of effervescence.  But
there are other marks which are  more certain and exact signs
of saturation.  If we trust to the  cessation of effervescence
alone, we may commit mistakes, especially if we do not take
care to agitate the mixture very  frequently and very briskly,
while we are adding the one salt  fo the other.
   Thus  if we add an acid to an alkali by degrees, till the ef-
fervescence ceases, we shall afterwards find that we have ad-
ded too much acid ; for the liquor will now effervesce by the
addition of alkali.  The same effect will take place,  if we be-
gin by adding alkali to  an  acid.  It was proper to take notice
of this circumstance, because  it  is  a general fact in all effer-
vescing mixtures.  Nothing will secure us against the dan-
ger of exceeding  in one of the ingredients, but frequent and
brisk agitation of  the mixture, especially  as we approach to
the term of saturation.
   But better proofs of exact saturation may be had by exami-
ning the state and qualities of the mixture:  for the compound
salts thu^produced have very  different qualities  from either
acid or alkali.  The a$d in a separate state has a strong sour
taste: the alkali has. a different one  peculiar to the alkaline
;:;dts.  The acid gives a red colour to the blue or purple tine- 
76               NEUTRAL  SALTS.
 tures of vegetable flowers:  the alkali gives a green.  But
 when they are properly united, the compound salt which they
 produce has not the taste of either acid or alkali, but one much
 milder, and of a qaite different kind.   Moreover, it occasions
 no change  of colour in the vegetable infusions.
  By these marks, therefore, we can bring  the  mixture  to
 more exact saturation, particularly by vegetable colours.  And
 the best manner of using the vegetable colours is to have some
 paper or fine linen stained with them, little bits of which being
 dipped  into the mixture, will immediately shew, by the change
 of colour,  whether there be any superfluous acid or alkali  in
 the mixture: and it is best to have different kinds of these for
 different purposes-. Thus the juice of the flowers of the March
 violet is the most sensible to alkalis.   And the infusion of the
 dying drug, known by the name of Litmus or Lacmus, is the
 most sensible to acids, though little affected by alkalis. There,
 is also a coloured infusion prepared from red cabbage,  which
 is recommended by Mr. Watt, in a paper in the Philosophical
 Transactions, as a most delicate trial of the presence of acid.
 And the purple skin of the common radish, when  scraped  off
 with a knife, gives 3 juice with which paper may be stained
 for  this purpose,  so  as to afford a very nice trial of acid or
 alkali in liquors.
  In some cases, however, it is not necessary to be extremely
nice ;  because the nature of the particular salt  produced is
 such, that though the acid or alkali be redundant,  the com-
 pound salt is easily separable from this redundant acid or  al-
 kali, by crystallization or otherwise.  Thus, when we compose
 a salt of an acid and  the volatile alkali, we choose rather to
 add a little too much  than too little of the volatile alkali; be-
 cause this  alkali is so volatile,  that  when  the water is after-
 wards evaporated, we are sure that all that is  superfluous will
 fly  away.  And we shall  see afterwards that crystallization
 likewise, in some  cases, will purify a compound salt fkorn acid
 or alkali.                                       ...■■>'*'
   The other particulars by which cor^ound  salts differ from
 acids and alkalis,  are,  1st., A weaker attraction for water;  so
 that in general they  are  easily  separable, and dried or civ.. 
NEUTRAL  SALTS.
77
      tallized ; 2d,  Much  less acrimony than either  of  them.
      Most of them do not act at all,  and the rest but weakly,
      on metallic and earthy bodies, and inflammable substances.
      From this variety  of effects, the acids and  alkalis have
>     been  considered as contrary or opposite  in their nature,
      and  as qualifying  and  counteracting  one another  in the
      compound salt.  Hence have arisen the names of neutral
      salts and sales wj^&^'Mfhough, when they are considered
      more attentively, th]ere. seems  to be but little foundation
      for this supposition of their contrariety.    The whole is
      perfectly agreeable to that general observation, given for-
      merly, with regard to mixture, that when  two bodies are
      united by a strong  attraction, their  activity or acrimony,
      and their attraction for other bodies, is very much  dimin-
      ished, or  entirely disappears.    The  epithet, neutral,  is
      applied to the compound salts with considerable propriety;
      because the compound has neither the properties of the one
      nor of the other ingredient.  Middle salts is a less  proper
      name.
         From the  view which I  have given of the  nature of
      compound salts, you must now perceive very plainly, that
      all the  varieties producible from  the nine  simpler salts
      already  described,  amount  only to eighteen:  for  each of
      the alkalis is only capable of being combined with any of
      the six  acjds; so that with three alkalis and six acids we
      can produce only eighteen compound salts.  Even of these
      eighteen, some have not been examined, or applied to any
      use;  and therefore are not  commonly prepared  or treated
      of in chemical books.
         By thus considering the  possible number, you perceive
      that they can be reduced to the form of a table, in such a
      manner that the place of each shall point  out the acid and
      alkali of which it is composed:
?■ ■"• m 
76
TABLE OF NEUTRAL  SALTS.
1	( Vitriolic 1 Acid.	Nitrous Acid.	Muriatic Acid.	Acetous Acid.	Taitarous Acid.	Sedative Salt.
Vegetable Alkali.	Vitriolated Tartar.	Nitre.	' Sal Digestivus.	Sal I'Tart. Solub. Diureticus.l and Tartar.		
Fossil Alkali.. Volatile Alkali.	Glauber's • Salt.	C ubical Nitre.	' Common Salt.	^W/foAjSal Rupellensis. -^^ Rochelle Salt.		Borax.
	Vitriolic Nitrous Ammoniac. Ammoniac.		Sal Ammoniac/	Spiritus 1 j Mindereri. 1		
    The neutral salts may be decomposed, and the simpler
 ialts of which they consist separated from one another, in
 some cases, by heat alone, but in most cases by elective
 attraction, or the addition of some third substance, which
 attracts one ingredient  of the salt  more  strongly than the
 ingredients attract one  another ; and, therefore, unites with
 that  ingredient, and separates the other, or throws it loose.
 In most cases, an addition of only one of the simpler salts
 is required : for it has been discovered by experiments, in
 mixing  neutral salts with several kinds of the  simpler
 salts, that  the  different acids have different degrees of
 attraction for the  alkalis in  general, while the alkalis, on
 the other hand, have different attractions for the acids in
 general.  If, therefore, we wish  to  have the acid  of a
 neutral salt pure, it is in our power, with  regard to most of
 the salts, to  obtain it by the addition  of  another acid and
 heat.  On the other hand, we  can likewise obtain  the
 pure  alkali  of a compound,  by the addition of another
 alkali.
   It  is very advisable for  a student of chemistry to have
 this table very familiar  to  his mind.   Much^more may be
 learned from it, than merely that such a compound salt is
 made by the mixture of such an  acid and such an alkali:
 for the table, when properly constructed, may be-jnade a
picture, as it were, of a great train^f chemical relations
 and operations, and tell us what will result  from the  mix-
ture of a compound salt, with other acids or alkalis than 
VITRIOLATED TARTAR.          79
those of which  it consists.   For it fortunately happens,
that the elective attractions of any acid for the different
alkalis proceed in the same order.   The  same thing ob-
tains in the elective attractions of  an  alkali for the diffe-
rent  acids.   Therefore the columns of the table  may be
arranged according to the  elective  attractions of an alkali
for the  different acids:  and the  horizontal rows  may be
arranged  by  the attractions of  an  acid  for the different
alkalis.  Or the columns may be arranged by the attractions
of the acids,  and the  rows  by those of the alkalis.  I have
chosen  the  first method.   The  first column and the first
row  contain the strongest,  and the last of both contain the
weakest attractions.   In the space allotted to each com-
pound salt, I have inserted the name by which  it has been
most generally mentioned by the  systematic writers, till of
late.   They  are mentioned by different authors by a great
variety of names, according to the  particular views of the
writer, whether medical, philosophical, or otherwise.   It
is proper, therefore,  to subjoin to this table  a complete
list of synonima, in the manner  of  the  natural historian.
The new systematic names, and a different arrangement of
the  compound  salts, will  be laid  before  you  after  this,
when we shall have understood  the principles which have
given rise to them.
   I  shall now describe the  compound  salts  in the order in
which 'they stand in the table.


      SPECIES I....VITRIOLATED TARTAR.

   First,  therefore,  we  consider  vitriolated tartar,  so
called because composed of vitriolic  acid and salt of tar-
tar,  which' last is now known to  be the purest form of the
vegetable alkali.  Hence  it  is named in the  Edinburgh
Pharmacopoeia,  Alkali Fixum Vegetabile Vitriolatum, a de-
nomination rather long and cumbersome.  It is now called
Sidphatff Potash.
   Its taste is a littl* pungent and bitterish ; and half an
o#nce of it purges.   Smaller doses are given as laxatives,
and  to  promote the other  secretions:  and it is sometimes 
BO            bULPHAT OF  POTASH.
 useful in scrophulous cases.   As it contains a fixed alkali,
 and the least volatile of the fossil  acids, and as these two
 sahs are  united in it by the strongest elective attraction,
 they cannot be separated from one another by heat alone;
 nor can any simple salt be employed in this case to produce
 their separation. It was, therefore, sometime ago, reckoned
 a very difficult problem to separate the vitriolic acid from
 the vegetable fixed alkali: and Dr. Stahl raised much emula-
 tion among the chemists, when he  boasted of his knowing
 a method so easy,  that he could perform it in the hollow of
 his hand.  This occasioned many attempts, and produced a
 discovery of several methods for decompounding this salt,
 which may be performed  more  or less perfectly in the
 hollow of the hand.  M<i6t of these  depend  on cases  of
 double elective  attraction,  which it will be more proper to
 explain hereafter than now.   The manner of doing it which
 Stahl seems to  have meant, depends  upon a preparatory
 opera'ion, by which the acid is converted into sulphur.  I
 have already mentioned this  preparatory experiment, when
 treating of the vitriolic acid.  Stahl's mixture of vitriolic
 acid and alkali (to  be exposed along with charcoal to a red
heat) was this  very salt.   Sulphur was produced;  and,
 therefore, some  of the alkali was left separated.   The sul-
 phur unites with  this composing  hepar  sulphuris.   The
 union is so weak, that vinegar will separate the sulphur, and
 form a compound  salt with the alkali.   Then are the two
 ingredients completely separated.   They may even be had
pure;  for we can burn the  sulphur, and thus  obtain the
acid.  And, the  compound salt being exposed to a red
 heat, the vinegar  is destroyed ;  and  thus  we obtain the
 alkali.
  This experiment has been very instructive.   Being at-
 tempted in a great variety of ways, it brought many things
 to light;  and was particularly useful, by explaining the
 frequent  appearance of sulphur in mixtures of substances
 which did not contain it.   They were  all cases of vitriolic
acid urged by red heat  in contact  with imflammafole bo-
dies.
  This compound  salt has riot a strong»attraction for wateV.
 It dissolves but slowly,  and in small  proportion, in cold 
GLAUBER'S SALT.
81
 water: and even of hot water a considerable quantity is re-
 quired to its dissolution.  It readily crystallizes: and  its
 crystals are of the decrepitating kind, and contain but lit-
 tle water in their composition.   According to Bergmann
 they contain,
            Alkali   62  J
            Acid    40  > in 100 parts by weight.
          '  Water   8  )
    The form effected by  the crystals is a hexangular prism,
 terminated by a pyramid.   But this is distinguished with
 difficulty, by reason of their grouping together.   Crossing
 at right angles is a pretty distinguishing mark of this salt*.
 But although they shew so little attraction for water, it will
 carry off a good deal of the salt with it,  if we evaporate
 too hastily.
    Origin..........It  is not  found as a fossil  production.
 There is some of it  in the ashes of vegetables mixed with
 the alkali:  and it is probably formed in their juice6 by the
 powers  of vegetation.   It is commonly prepared for the
 purposes of medicine by art.   We shall soon see an exam-
 ple of this in a  process in which the production of  it is
 not  the  principal object.   In order to   obtain it in  its
 fairest form, with the largest and most regular crystals, it
 is advisable to have the acid,  predominant in the mixture.
 Although it be considerably acid, the crystals will be  per-
 fectly neutral.   Some  chemists, however, choose  to call
 such a compound a super-sulphurated salt. '


         SPECIES II.....GLAUBER'S SALT.

   Glauber's  salt  is  called Soda  Vitriolata, in  the  Edin-
 burgh Pharmacopoeia.   Its new name is  Sulphat of Soda.
   This salt is  much more easily melted  in the fire than
 vitriolated tartar: and it  is also more soluble in water.  Its
 crystals  are in the form of long hexagonal prisms, termi-
 nated bylpyramids.   The prisms  have two broad and four

  * The crystals of vitriolated tartar form a double prismatic spectrum  by
infraction, in the same manner as several kinds of rock crystal ...editor-
VOT.. IT. 
82              GLAUBER'S SALT,

narrow faces.  They are very watery, and subject to watery
fusion, and fatiscence.   Hence for a purgative  dose of it,
an ounce is required.   100 parts of  it contain 15 of alkali,
27 of acid, and 58 of water.   It cannot be decompounded
by heat alone; but, like  vitriolated tartar, by sulphurifica-
tion  and  vegetable acid;  and  by some  other processes
which depend on double  exchanges.  We  can also decom-
pose  it, though not conveniently, by the  action  of the
vegetable alkali.   Oleum Tartari  per Deliquium, which  is
the mildest form of the vegetable alkali, must be  digested
on Glauber's  salt for a long while: and we shall then find
a vitriolated tartar, and a fixed fossil alkali in the mixture.
The attraction of the vegetable alkali for the acid  does ex-
ceed that of  the fossil alkali, as may be gathered from
many experiments ;  but it  is so little, that it was long
doubted.   Even the pr  sent decomposition of  vitriolated
tartar does not prove it; because, as we shall soon see, it
is assisted bv a double exchange.
   Origin.........This salt is no where  found, that  we know
of, as a natural production.   Many, indeed, say that it is
contained in the waters  of the sea, and in  those of purging
mineral springs.   But this is a mistake: and the substance
which we take  for it, is the bitter  purging salt, which was
long mistaken for Glauber's salt, even  by chemists  of
great  eminence.   Mr.  Model of Petersburgh relates  a
number of  experiments made by  him on a salt  found in
many waters in that neighbourhood, and  describes  the
 salt so exactly, that we  now know beyond any  doubt, that
what he calls  the Sal Miraible is nothing  but Epsom salt.
   All of it that is used in medicine  is artificially made,
 by decomposing common salt with vitriolic acid : and the
manufacture  of it  forms  a considerable  business in  the
 hands  of  trading chemist3.  Some of it is  formed from
 kelp.   The  following process for making it is published
 by the Society of  Arts:....Put a pound  of kelp  into an
 English gallon of boiling water, so as to  extract  the salts.
 Decant,' &c.  and add as much vitriolic acid as is necessary
 to saturation.  Two ounces are commonly enough.  Then
 filtrate, evaporate, and crystallize, 8cc. and you  will have
 about halt a pound of Glauber's salt.
• 
                            63


      SPECIES  III.....NITRE,  OR SALTPETRE,

     This salt is well known, and is very useful and necessary
  in many arts.   It has occasioned a total change in the art
  of war ;  for the use of it in that art was unknown to  the
  ancients.
     I have already observed, that the salt mentioned in some
  parts of  the Bible by the name of nitre, was an alkaline
  salt.   This  appears from  the  contrast or  incongruity
  remarked between it  and vinegar, and also from  its being
  employed as a  detergent  or cleanser.   In most  of the
  passages also of Pliny, where he speaks of nitre, he  plainly
  means  an alkaline salt.  It is  very clear, however, that  our
  saltpetre was known  by that name, and also by the name
  of nitre,  in the earliest ages of scientific chemistry.   It is
  frequently mentioned, and with characters which give us
  no room to doubt of its identity.                      ,
     In pursuance of  my general method of examination, I
  shall first consider the most  simple  relations  of  nitre to
  heat, and its mixture with water ; and  then proceed to
  relations of the same kind, but more complicated in their
  circumstances.  I shall employ a good deal of time in this ex-
  amination,both  because the chemical properties of nitre,and
  the phenomena  which it exhibits,  are the most remarkable
  that occurin the chemical history of nature, and also because
  these  properties  and phenomena afford, in  the easiest
  manner,  the steps of  investigation which lead us through
  almost the whole philosophy of our course.   You  will find
  the greatest part  of our important doctrines to  be little
  more than the gradual detection of the properties of nitre
:  and its ingredients.  I could begin by stating all those
  properties at once, in their full influence, and from thence
  deduce the chemical  doctrines  synthetically, as  Newton
  explains the colours of. natural bodies from the properties
  of light,  or  the motions of  the planets  by universal
  gravitation.   But, to give you  the  conviction that such
  are in  fact  the properties of  nitre, would require the
  narration of facts concerning many substances with  whose
  properties you are altogether unacquainted.   I am certain 
84   SCIENTIFIC IMPORTANCE OF NITRE.

that your conviction will be much more forcible, and your
knowledge more palpable, and, as it were, at your fingers'
ends, by  allowing those properties of nitre to open upon
you Ly degrees,  as  we come  to  consider  those other
substances, whose appearances, as affected by nitre or its
ingredients, are the very arguments by which the properties
of those ingredients are ascertained. The great doctrines
of  modern chemistry will  thus be the result  and fruits of
your own induction and analysis.   Add to this,  that you
will thus have formed the habit of philosophical investi-
gation  bv experiment ; and will perceive  its immense
superiority over all synthetical theory,  however specious
and extensive in its application.  I may add, that were I
to  treat  these subjects in  the pure synthetical  method,
which  is-thought  attainable, and which  seems, at  present,
to be most arxentable to the chemists  (especially on  the
Continent), I should  leave yrou ig lorant of the ingenious
labours  of the most eminent  chemists of  Europe,  and
unable to read and understand  their writings.
   When nitre is exposed to heat in an op n vessel, such
 as  a crucible, we  find very little water in its crystals.  It
 neither sbeWs watery fusion, efflorescence, nor decrepita-
 tion.   Its water  escapes insensibly.  If the heat be very
 hastily applied, some  nitre sublimes, very little changed.
 But a slow and gradual increase of heat melts  the nitre
 quietly,  before it be  so hot as to shine in the dark.   It
 looks  like melted white bees-wax. If the heat be increased
 a little, the fluid  begins to simmer gently, by the escape of
 very  small   bubbles  of elastic matter.  If this be  long
 continued,   the  disagreeable  smell of nitrous  acid  is
 perceived ;  and fumes are  emitted of  a deep blood-red,  v
 perfectly resembling those already described, when I was "">
 considering  t'ne nitrous acid.   By this  process,  the nitre
  gradually wastes :  and what remains frequently dissolves
  the glass or earthen  vessel in which the nitre  was  con-
  tained.   The residuum,  when examined, is  found to be
  strongly, and sometimes entirely, alkaline,  and quickly
  deliquiates  in the air.
     From this it would appear that nitre is decomposed by
  heat, th' acid beinp driven off in these red vapours.   We 
         DR. MAYHOW'S EXPERIMENTS.      85

 are naturally led, therefore, to try the effect of distillation
 in close vessels.  But we shall find it extremely difficult
 to condense the vapours ; and the quantity of acid obtained
 in this way is frequently almost nothing: in all cases, it
 is fuming and  deep coloured, and the vessels are  filled
 with blood-red vapours.  They are incoercible, and would
 burst the  vessels ; yet the acid is gone from a part of the
 nitre  at least.   Since we cannot collect  it in the receiver,
 we must conclude that it is somehow destroyed or decom-
 posed, or converted into these permanently elastic  fluids.
 Accordingly,  Dr. Hales  obtained from a cubic inch  of
 nitre  in this way, (that is, by distilling it in a gun-barrel,
 and  collecting the vapour  in a  jar standing  inverted  in
 water) 180 cubic inches of  air.   Dr. Hales  explains, by
 means of this air, the explosion of gunpowder and other
 nitrous compositions.  In the preceding century, something
 like  this  had  been done by Dr.  Mayhow of  Oxford,  in
 1674.   He collected the nitro-a; rial spirit, as he called it,
 in bladders tied on  the  spout  of  the  retort.   [See Jo.
 Mayhow  Opera Medico-physica,  published at the  Hague,
 1681  ; also his Dissertatio  de Salnitro et de  Spiritu Nitri
 Ae'reo.)   This  author wrote  in an obscure  mysterious
 manner,  as was too much  practised in those days.   But
 he  has made many  experiments, most  ingeniously con-
 trived, and has deduced from them conclusions which are
 nearly the same with  the doctrines which have been more
 clearly established of  late years.   In particular, he con-
 siders this nitro-aerial spirit  as the  cause of combus-
 tion, the  support of animal life, and the source of animal
 heat.   Since that time, and even before, there has been
 much vague speculation and discourse about a vivifying
[ nitrous spirit in the air. Muschenbroeck and others ascribe
 to ^  the  spicular form of  snow  and  hoar-frost;  but all
 this  was mere  talk,  without any distinct thoughts  on the
 subject.   (See Note 31, at the end of the  Volume.)  I shall
 very  soon give a more particular account of this elastic
 matter.
    The relation, of saltpetre  to water  offers nothing very
 remarkable.   Irdissolves  readily in six times its weight
 of cnld water.  Boiling water, however, dissolves an equal 
   86 ACTION OF NITRE ON INFLAMMABLES.

   weight.   In both cases, a considerable absorption of heat
   takes place.   It  is easily separated from water by crystal-
   lization ;  and  the absorbed heat  again emerges.  The
   crystals  are slender hexagonal prisms, of equal  sides,
   terminated by  irregular pyramids,  having one face much
  broader than the rest.   They are thus distinguished from
   Glauber's  salt, whose  prisms  have  very unequal ^ides.
   Nitrous  crystals  contain very little  water,  but so strongly
   united as not to be separable without a red heat.
     The most remarkable  properties of nitre appear when
   it is  treated in great heats in contact with  inflammable
n substances.  When charcoal,  or sulphur, or  any inflam-
   mable matter,  which is not so volatile as to rise before
  it acquires a red  heat, is put into  melted nitre, the nitre,
  which was quietly fluid, is immediately thrown into violent
  agitation, and  bursts out in explosions of elastic matter
  and  dazzling flame.  This continues,  with  a whizzing
  noise, as long  as inflammable  matter remains.   And, if
  the quantity  be  considerable,  and  intimately mixed,  the
  whole explodes  in  a moment, with almost  irresistible
  force, a bright flash, and loud noise. If a lump of charcoal
  be laid on nitre, just hot enough to act on it, the deflagra.
   tion takes place  only in  the touching parts ;  and it con-
   tinues whizzing,  and throwing  out  streams of fire, till the
   coal is expended.  Great heat is produced, and the nitre
  will all become of a bright red.  Even although the nitre
  be not so hot as to set fire to the charcoal, if only a bit of
  the coal be red hot,  it will there be acted on by the nitre,
  and -the heat produced will suffice for making the adjoining
  parts  act on each other :  and the detonation will continue
   till the  charcoal  be expended, and  the whole  nitre  be
   melted and become  red hot.
     This effect of nitre on combustible substances is  called
   Deflagration,  or Detonation.   No wonder that che-
   mists have attempted to  explain the grand operations of
   thunder  and lightning, by supposing mixtures of this salt,
   or of its nitro-aerial spirit, with inflammable substances in
  v'ne air.   Indeed it was those phenomena of nature, in all
   probability, which gave rise to the notion that such a spirit
  v as diffused through the atmosphere.   But thunder and 
  DEFLAGRATION OF NITRE EXPLAINED. 87

lightning are now well known to depend on very different
principles.
   By repeated additions of charcoal, the deflagration, and
the fusibility  of the nitre, are diminished, and the defla-
gration at last ceases entirely.   When the salt remaining
is examined,  it  is found  to be pure vegetable  alkali,  in
quantity just equal to what we know the nitre to contain.
   This fact gives an explanation of the whole phenomenon.
It is  produced  by the violent action of the nitrous acid
and inflammable matter.   This is already known to you.
The acid quits  the  alkali  to act on the combustible mat-
ter : and the action  is such, that both are converted into
elastic aerial fluids, so completely, that no part of the acid
can be recovered in its former state.  Indeed, it is decom-
pounded and destroyed.   Of this we obtain clear proof,
when the operation is performed  in  a stoppered, earthen
retort, with a receiver for condensing the volatile matters.
We find no acid in those  vapours, but, in the place of it,
a large quantity of air, of a complex  kind.  It will not sup-
port flame  nor animal life ; and it was therefore imagined
to be of that  kind that is met with in coal-mines, and is
called choak-damp, and in vessels where charcoal has burnt
till it is extinguished for want of air.   But  when we had
learned an  exact test of such air, and the method of ab-
stracting iJ^rom any mixture, it  was then found that the
air produced  by deflagrating charcoal with nitre did eon-
tain a considerable portion of it,  but that another portion
was of that kind that is  left unabsorbed by hepar sulphuris
exposed to atmospheric air,  and  is called faul  air  by
Scheele, and phhgisticated air by Priestley; and, besides
these two,  it usually contains some common air. This was
extricated  from the materials, and  it  is evident, by the
alkaline residuum, that the acid  alone  contributed  to the
production.   We shall soon understand the  change thus
produced on the acid : and I only observe at present, that
a red heat is  necessary for occasioning this  action.   The
acid, having a strong attraction for the alkali, is thus weak-
ened in its attraction for inflammables : but the union with
the fixed basis  enables it to stand the  red heat  which is
necessary.   In a separate state,  we have seen it act moat 
 88  NITRE DEFLAGRATED WITH SULPHUR.

 violently, and even excite them  to inflammation ;  but we
 are  not therefore to suppose that the heat produces this
 deflagration by first decomposing the acid, and changing it
 to elastic gas, which we  have  seen  that  it  really  does.
 Yet, no doubt, this favours the detonation : for when nitre
 is melted, and red hot,  and its acid escaping in red fumes,
 if a  bit of charcoal be held close above  it, but not touching,
 it will  presently take fire, and burn with rapidity and daz-
 zling brightness ; an  evident proof that it is the elastic
 matter of tfae nitre which causes  the charcoal to burn, and
 that the acid must be in that form, but not yet decompos-
 ed,  when it produces the effect.
   When nitre  is deflagrated with sulphur,  the  conse-
 quences  are considerably different.   The deflagration is
 equally violent  with the other,  and the flame somewhat
 more brilliant.  The acid is  destroyed in the same man-
 ner.  But the elastic matter produced is different in  some
 respects.  The most of it is the faulair of Dr. Scheele ; a
 circumstance deserving particular notice.  We have an
 evident snell of hepar sulphuris,  as we might expect, from
 the combination of the  sulphur with the alkali left behind
 in the  deflagration.   The residuum of the process is not
 alkali,  but vitriolated tartar.  Before  its chemical nature
 was  thoroughly  known, this  residuum had gotten a high
name as a medicine, useful in a  variety of-tH^prders.  It
 was, therefore, called Sal Polychrestus, Arcanum Duplicct-
 tum, Sal Prunella;, and other fanciful names.
   The rationale of this process is obvious.  There  is a
 double exchange, and the acid  of the vitriolated tartar
proceeds from the sulphur, which unites  with part of the
 air disengaged from  the nitrous acid.
   This faculty of deflagration is  a most valuable property
 of nitre to  the philosophical  chemist.   It  enables  h'm to
 discover inflammable matter where it could not otherwise
 be supposed to exist.   It is a property no  less  important
 to the  world on other accounts.   Nitre becomes the basis
 of many compositions for producing violent explosions, or
 i dazzling  light, which  may be seen at a great distance.
   Gunpowder is the most generally known of all these
 exploding compositions.  Its  many uses, besides those in 
GUNPOWDER.
89
 the art of war,  are well known.   It is formed of nitre, char-
 coal, and sulphur, so intimately mixed, that a  spark fires an
 atom or two: and this fires the rest in a moment.
   The best proportion for strong gunpowder is about  seven
 parts of pure nitre, one of charcoal, and one of sulphur, all by
 weight. Others recommend eight of nitre, two of charcoal, and
 one of sulphur.   The  usual impurity of saltpetre  is common
 salt, disengaged alkali, and  Epsom salt.  These, by attracting
 moisture, weaken the powder exceedingly,  and make it apt
 to cake in the barrels.  But saltpetre, sufficiently pure, is an
 expensive article, and  is stinted as much  as  possible  in  the
 manufacture.  Common gunpowder has a  much smaller pro-
 portion, even so little as three or four parts to the above quan-
 tity of the other ingredients.
   The charcoal and  sulphur are  ground separately in mills,
 and levigated to most impalpable fineness.   On  this depends
 much of the strength of the powder. And let me just observe,
 that gunpowder, washed from its salts and  sulphur by caustic
 alkali, affords the finest powder of charcoal for experiments.
 The nitre is dissolved in pure water, and the solution mixed
 with the ingredients in wooden troughs,  where it is carefully
 kneaded and incorporated, in  form of  a thick paste.   It is
 kneaded, for two or three days, with wooden pestles, adding
 a little water as it evaporates.  It  is granulated by forcing it
 through  sieves ; then sifted, and  the dust  returned into the
 kneading troughs.  Lastly,  it  is  superficially hardened and
 smoothed, by tossing it horizontally in shallow boxes, which
 get a brisk  reciprocating*motion  by machinery.   The  dust
 being again sifted  from  it, the powder is now fit for use.  The
 granulation makes it keep better, and also kindle more rapid-
Jy in the chambers of fire-arms, by allowing  a free passage for
 the flame among the grains.
   When gunpowder is fired, and the fluid in a state of incan-
 descence, it is as elastic as common air would be if compres-
 sed into ttj1  th part of its bulk ;  or is 1000 times more elas-
 tic than common air.  But when it has grown cold again, its
 bulk is vastly less,  not being 300 times bigger than the gun-
 powder.   (See Robins1.?  Essay on Gunnery.)
    vor. it.                  M 
90    PULVIS FULMINANS....BLUE LIGHTS.

  There is another  composition which explodes with  still
greater force than gunpowder.   It consists of three parts of
nitre,* two of fixed alkali, and one of sulphur.  When heated
slowly on a plate of metal, it first melts, and becomes black,
or of a dark liver colour;  and then explodes  with a loud
crack.  Hence it has got the name of pulvis fulminans.
  The cause of its loud and  smart explosion must undoubted-
ly be the instantaneous conversion of it into elastic vapour;
not in succession, however rapid, like gunpowder, but at once.
The effect  of this  simultaneous conversion appears even in
gunpowder.  This, if fired in a train, makes no noise.   (See
Note 32. at the end of the Volume.)
  Another service derived from this property of nitre is the
production of a brilliant light, fit*for making signals to be seen
from a great distance.   The Chinese blue lights are esteemed
much superior to any made in Europe.  A gentleman who
made very curious inquiries about their fabrication,  and saw
them made by the Chinese fireworkers, informs  me, that the
composition consists  of twenty-eight parts of nitre,  seven of
sulphur,  two of arsenic, one-half  of rice-flour,  and as much
water as will knead  them into a stiff paste.   This water and
the flour retards the inflammation.   The paste is rammed
into little earthen pots, and kept in pitched cloths.
  Nitre is very easily decomposed, so as to obtain  either the
acid or the alkali  in a pure  state.  It is from nitre only that
the nitrous acid is obtained.  You have seen that mere heat
will not give us the acid in a perfect state.  We must employ
some intermedium, which shall Ufy hold of the alkali, and al-
low the acid to rise from itbv the action of heat.   Looking at
the place of this salt in the table ofcompound salts, you see  at •"'
once that the vitriolic acid may be employed for this purpose?^'
This acid, having both a stronger attraction for the alkali, and'
less volatility than the nitrous acid has,  must be  a very fit in-
termedium.
   The  preparation of the nitrous acid is a considerable bu6|» •.,
ness, carried on by particular chemical artists.   As they pfe-.
pare it for the market, where it is not in general wanted very
strong, they usually sell it  much diluted with water, and of- 
               PROCESS FOR NITROUS ACID.       91

     ten adulterated with vitriolic acid, which is a much cheaper
     article.  Some arts, however, require it of its utmost strength,
     and very pure.  The process for accomplishing this was first
     distinctly given by Glauber: and the acid, so obtained has got
     the name of Glauber's spirit of Nitre.
       This process requires certain rules of procedure, and exhi-
     bits several very instructive  phenomena.  The nitre must be
     very pure,"*and must be prepared by melting, and keeping it
     in that state for some  time.  It is  then  broken into middle-
     sized pieces, and put into a coated glass or an earthen retort,
     already set in the  sand-pot  for  distillation.  Two-thirds, or
     three-fourths of its weight of the strongest colourless sulphu*
     ric acid must be poured on it speedily, by means of a crooked
     or retort-funnel.  The receiver is immediately joined to the
     retort, with fire lute, and then a hole pierced through the lut-
     ing with a wire.  The mixture soon grows hot; and, if the
     nitre had been in  powder, or even in very small pieces, the
     heat might chance to be so great and sudden  as to split the
     retort.  The salt gradually melts, and acquires a deep orange
     colour, and ruddy steams obscure the whole vessels.  These
     steams  are caused by small air-bubbles, which form all over
     the mixture, and come to its surface, where they break.  The
     yile smell of nitrous acid now fills  the laboratory, proceeding
     from the vapour which comes through the hole in  the luting.
     This must be allowed to continue till it abates.  The fire may
     now be kindled, and allowed to heat the retort very slowly.
     The ruddy vapours cease, and the vessels grow  clear.   Let
     the hole in the luting now be stopped.   The  distillation goes
     on; and  the  receiver soon grows too hot, and must be kept
X'jjK cold by snow,  or by a flannel covering, on which a stream of
""V^'.cold water is constantly trickling.  The fire may now be raised
   '" considerably,  and kept  up in proportion as we can promote
     the condensation in the receiver.  When the distillation is far
     advanced,  the vessels again become dim, and ruddy clouds
  /  appear.  The process is now drawing to a close.  The matter
    -'in the retort has but little fluidity, and is very apt to burst into
    ' violent ebullitions, and to drive the contents over into the re-
     ceiver.  But, by due care, the distillation may be carried on 
9-2  INFERENCES  FROM  THE PHENOMENA.

till the retort is red hot.  But, from the first appearance of thr
ruddy clouds, which  become  so  thick that we cannot see
through  them, much incoercible  vapour must be  allowed to
escaj     '\venty-four ounces of nitre will require eight hour.
forth: di.  llation, reckoned  from the time of  kindling the
fire.
   The acui thus obtained is of the most fuming  kind,  and of
a deep orange colour: but, if put into  a retort,  and a pentle
heat applied, and a little water put into  the receiver, the rud-
dy fumes and orange colour will soon cease, and the acid in
the retort become colourless, like water.  The small quantity
of vapours condensed in the receiver tinges  the  water which
condenses them with a deep blue or  green.   We get here a
diluted  acid,  and, in  the  retort,  the nitric  acid in its purest
form and greatest strength.  It is sometimes tainted with sul-
phuric acid; but it is easily freed, by distilling it from a little
pure  nitre.  A  taint of muriatic acid is more difficult to be
removed : we shall mention the most effectual method as we
proceed.
   The fuming acid has  been called the nitrous acid,  (acidum
nitrosum) and the colourless acid is called the nitric,  (acidum
nitricum).  It is intended  by this last name to denote the ori-
gin of the acid, and by the ;>ther to denote a redundancy in
the principle peculiar to nitre.  We  shall very .soon see the
principle on which this opinion of a redundancy is founded.
   It is plain that the residuum in the retort must be the com-
pound of sulphuric acid  and vegetable alkali, perhaps  mixed
with a portion of undecomposed  nitre. Before a perfect know-
ledge of the procedure of nature was acquired, it was thought
to be a.peculiar salt, and had fanciful names; Arcanum dupli- *g
catum;  Sal de duobus ;  Sal enixum, &?c.  But it is now  per-.^*3
fectly understood to be vitriolated tartar.  Indeed, this is the  *•
only way in wnich vitriolated tartar is piepared.  The manu-
facture of nitrous acid furnishes more  than  there is  any de-  x
mand for.
   Such is the process for obtaining the nitric acid  in its strong-
est state.   It is much more generally v.anted, in various  ma-
nufactures, in a far weaher  state, called Aquafortis, consist 
             PROCESS FOR NITROUS ACID.        93

   ing of  nearly  equal parts of Glauber's spirit of nitre and of
   water.  In preparing it of this strength, other methods were
   formerly practised. Intermediums, which have some, though
   perhaps not very great, affinity with the alkali, and which are
   fixed in the  fire,  are employed ; also substances containing
   vitriolic acid weakly united to some other base.   Of this kind
   are vitriol, alum, clay, &c.  These  substances enable the salt
   to stand a great  heat, in consequence of which the volatile
   ruddy fumes are very copious:  and much would be lost,  did
   we attempt  to produce a strong acid.   But, by employing
   much water  in the receiver, the steams are pretty  well con-
   densed, and a weak  acid is obtained, which can be concen-
   trated  by  another distillation *.  This difficulty arises from
   the decomposition, which I have said  that the nitrous  acid
   seems to undergo, when urged by a very great heat.
      And this leads me to take notice of some other products of
   our process for Glauber's spirit of nitre, besides the acid in the
   receiver, and the vitriolated tartar which remains behind in
   the retort: I mean the incoercible fumes which escape in the
   beginning and the end of the process.
      I  have already observed that nitre,  when urged by a  red
   heat, wastes, and is rendered alkaline; and yet,  that we ob-
   tain little or no acid by condensing the vapours.   Nitre melts,
   then simmers, and emits red vapours.  Also, in our process,
   similar vapours are produced.  There is, however, a very im-
   portant difference in the two cases ; in the one we obtain acid,
   and in  the other nothing but incoercible vapours.   This must
   evidently arise  from the intermedium, which,  by detaching
   the acid, allows it to come  off with a partial decomposition ;
   whereas, when no intermedium is used, the different narts of
t  the acid seem to come off in the order  of their volatility  and
   attraction.
      Notwithstanding the  ingenious experiments  of Mayhow,
   and his important inferences from them, and the no less in.
  . genious experiments  of Dr. Hales, nearly  to the same  pur-
      * Mr. Lavoisier says (Kefs translation of Lavoisier's Chemistry, Lon 1.
   Edit. p.  215.^  that niU-e, decomposed by clay, both yields a stronger aciu,
   ■jv<\ with lz-ss loss, than by employing1 the sulphuric  acid ,.;.editor 
94 FIRE-AIR OR SCHEELE, OR EMPYREAL AIR.

pose, no notice  was taken of the air obtained from nitre in
those experiments, till about  1772.   Dr. Scheele, whose ex-
periments with hepar sulphuris I have mentioned to you, be-
gan to take  notice of this air.  He it was who observed that
a bit of charcoal, held above  the red hot nitre,* burnt with a
dazzling flame.   Recollecting his experiments with hepar sul-
phuris, in which it appeared  that only a part of our atmos-
pheric air will support flame  and combustion ;  and now ob-
serving that this vapour from nitre supported it in an eminent
degree, it  struck his imagination that this might be the only
part of atmospheric air fit for this purpose,  and eminently fit,
because unmixed with the rest.  It immediately occurred to
him to try the effect of this air on  hepar sulphuris.  He ex-
pelled it from nitre  in  a small retort, by a strong red heat,
and collected it in a jar.   Now putting a quantity oi hepar sul-
phuris into this  air, as he had before done into common air,
he found that it was wholly absorbed, and this with great ex-
pedition.  He was now fully  convinced, that our atmosphere
consisted of two airs,  one of which supported flame, and ap-
peared to him to be a constituent part of fire itself.  He there-
fore called it Fire Air, which  his  translators have changed
into Empyreal Air.
   Much about the same time, and without any knowledge of
Dr. Scheel's labours,  Dr. Priestley made the same observa-
tions. Exposing, to a red heat, substances containing, or moist-
ened  with, nitrous acid, he obtained an air, in which bodies
burnt with dazzling flame and great rapidity.   He conceived
this to be pure air, and that the other portion, which extin-
guished  flame, has been originally the same, but that it is now
saturated with phlogiston, and cannot support'flame by receiv-
ing more.  He therefore called this depurated portion Dephlo-  ^!
gisticated Air.  Other philosophers, observing that it also
supported animal life, called it Vital Air.
   Tliese experiments have, of late years, been repeated in a   -J
 great variety of forms, with  the same results.  In particulars^
it is found that when  nitre is exposed to violent heats, adding  . •-■
a little slaked lime, which imbibes the melted nitre, and hiiu
 ders  it from corroding the vessel, and enables the acid to stand 
           DEPHLOGISTICATED AIR....VITAL  AIR.  9d

       a very great heat, the quantity of air obtainable from it is pro-
       digious.   Four ounces of pure nitre, treated in this way, fur-
       nished to Mr.  Ingenhouz 3000 cubic inches, which is about
       650 times the bulk of the nitre.  Moreover, when we compare
       its power of supporting combustion and animal life, with that
       of common air, it appears that one cubic measure of it will be
       as effectual for either of these purposes as four or five of com-
       moh*air.
         You will recollect that when considering the vitriolic acid,
       and its production from sulphur,  and the reciprocal produc-
       tion of sulphur from it, I said that it seemed  necessarily to
       result from all our experiments, that, in the inflammation of
       sulphur,  a quantity of air disappeared,  and that the acid pro-
       duced exceeded the sulphur in weight.   I also  observed, that
     ■  when sulphur \v*a% produced from substances containing vitrio-
       lic acid, by urging them with  violent heats in contact with in-
       flammable substances, there was always  a  quantity of aerial
       matter extricated: and lastly, that when hepar sulphuris was
       exposed to the air, it was decomposed, that is, the sulphur was
       separated from the alkali.  Morever, this alkali was not recov-
       ered in its pure  form, but saturated with vitriolic acid,  of
       which there was none in the mixture.   At the same time, air
       was absorbed, and  the remainder was  unfit for maintaining
       Came.   It appears, from  a combination of all these facts, that
       the air thus absorbed contributed to the formation of the vitri-
       olic acid.   Now it appears  that the ai& which is absorbed, is
       of the same nature with that which is emitted by nitre, and is
       furnished by its acid.                    ,
         From a collective view of these  facts, it wouldjseem that
;«-Y    the  same air which is contained in nitrous acid, is also contain-
j-*.'. .   ed in the  sulphuric. Farther,  as the sulphuric acid appears
 •'     to differ from sulphur in nothing but by the combination with
       this air, it seems to derive its  acidity from it: for we find that
■A*;'.,   nothing more is necessary for converting sulphur into sulphu-
       ric acid, but the absorption of vital air in inflammation, and
       that it will absorb it completely.   Analogy should lead us, in
       like manner, to suppose that the nitric acid derives its acidity
       from the same source....from vital air,....and consists of vital 
96         OXYGEN....OXYGENOUS  GAS.

air united to a certain basis, which may be considered as the
characteristical radical of nitrous acid, as sulphur is of the vi-
triolic.
  These considerations,  joined to many others of the  same
kind, have introduced Mr. Lavoisier to consider vital air as
the cause of acidity, and to call it oxygen gas.  We shall find
the proofs of this general property of vital air multiplying on
all hands as  we advance.  Ther- is «-3 acid substance from
which we cannot obtain much pure vital air, and the weight of
the  air obtained is equal to that  lost by the acid.   All com-
pounds, indeed, are not acid, or sour to  the taste, but all have
chemical properties analogus to those of the undoubted acids.
I, therefore,  admit the propriety of the  name oxygenous gas,
and  shall use it without hesitation in the rest of this course.
  You have heard how the nitre is affected 6y the  simple ex-
position  to strong heat:  and the explanation of the change,
by the escape of the oxygenous gas, is very obvious.  But the
vapours  are not nitric acid : and,  therefore, nitric acid does
not consist of oxygenous  gas alone,  but contains it, combined
with some radical: and this combination is destroyed, or de-
compounded, during the escape from the nitre.  But,  in the
process  for nitrous acid,  an  intermedium is employed, to
loosen its combination with the alkali, so that it gets off in a
more moderate heat without decomposition.  Yet the appear-
ances in the process should make us suspect that this  is not al-
together the case : for  the ruddy clouds,  at the beginning
and  end  of the process, look very like some tendency at least
to decomposition ; and the situation of things at the end of
the  process is  not very  different from that  of  nitre simply
exposed to great heat.  It is then almost dry,  and the  retort
almost,  if net altogether, red hot.   This did not escape :0
the notice of  the  sagacious Scheele.  But he found appear-   :S
ances v.hich puzzled him.  When he held a candle  to  the
>.pout of the retort during the  appearance of his last clouds, it . .$
burnt with a most vivid flame, confirming the opinion that the  'v
acid was then suffering a decomposition.  But, when ht did!  V
 lK- sr.ii-.* thing during the  appearance of the first clouds,  the
f-andK-  v.-as extinguished in an instant.  .Thislist event bap- 
     OXYGEN AN INGREDIENT OF NITRIC ACID. 9f

    pens, partly because the portion of oxygenous gas which is •:  ■r
    escaping, is very small; and chiefly because it is accompanied
    by another  substance  in the  nitric acid, which has not yet
    thrown itself in our way as  one of its constituent parts.   You
    will soon become acquainted with it.  And,  in the mean time
    I imagine that you are now convinced that  vital air is one of
    its ingredients, and that, in all probability, it is the cause  oi its
    acidity, as it unquestionably is of the acidity of the sulphuric.
    Mr. Lavoisier attributes the oxygenous eruption observed by
    Scheele to the strong attraction of oxygen for caloric in high
    temperatures,  which decomposes the nitric acid.
       I may now take notice of another resemblance in the union
    o.f the oxygenous gas, with the characteristic ingredients of the
    two acids.  The fuming Glauber's spirit of  nitre may be ren-
    dered still more  fuming, by the addition of a very minute por-
    tion of inflammable matter.  Jt is  observed, that, as this qua-
    lity is increased,  the activity as an acid is diminished.   1 he
    small quantity of acid obtained in clearing  Glauber's acid of
    its fumes, is not only weak  by dilution, but is weakened in its
    attraction for alkalis, and can be dislodged from them by Ve-
    getable acids and sedative salt, without the assistance of heat.
    It may be made so  fuming as to  be scarcely coercible, and
    scarcely acid  to the taste.   Now,  when  it  is converted into
    nitric acid,  it is plain that  its proportion of oxygenous gas is
    increased ; and when the nitric acid is made fuming,  its pro-
    portion of the radical is increased.   It is with propriety  there-
    fore called nitrous (nitrosum) as abounding in die character-
    istic ingredient.   All this has its counterpart in the sulphuric
    and sulphurous acid ; the latter containing more sulphur, or less
    oxygenous gas, has less acidity, and less attraction for alkalis.
       This process for decomposing nitre, in order  to obtain the
*    acid, has been very instructive, as I said it would, opening to
    our view a new connection of chemical substances.  It has not,
*■ > however, completely explained all the phenomena, but has
    rather rendered  the subject  more complicated, by shewing
    that the acid itself is a  compound substance, without informing
    us of its characteristic  ingredient.   I might tell  you now that
     his is nothing else than that portion of the  atmospherical air
         "OT.f II.                    I» 
 98 NITRIC ACID PRODUCED  BY CAVENDISH-

 that is not absorbed by the hepar sulphuris, or that is left be-
 hind by the inflammation of bodies, and may also be obtained
 in a variety of easy ways.   But I cannot yet dera >nstrate this
 by fairly educing it from the acid, nor confirm the doctrine,
 by recomposing the acid by their mixture.  We arrive at this
 by a very circuitous process, which requires the knowledge of
 several  things with which you are  unacquainted.  I  may,
 however, mention one fact, of which  you can see the value
 without farther acquaintance with chemical substances*   'I his
 is an experiment by the honourable Mr. Cavendish, described
 in  the  philosophical transactions  for  1785  and  1788.   He
 mixed a quantity of oxygenous gas, and Priestley's phlogisti.
 cated air, in the bend of a glass syphon, the two legs of which
 contained a solution of vegetable alkali.  When he had,  after
 many trials,  obtained the due proportion of the two airs, he
 found that, by passing a succession of electrical sparks through
 the mixture, they united, and the compound was absorbed by
 the alkaline solutions.   This, when examined by evaporation
 to dryness, or by crystallization, gave  a small portion of true
 tialtpetre.  Hence it unquestionably follows, that the union of
 these two airs composes nitric or nitrous acid.  Many ques-
 tions arise on this occasion, which I am not yet in a condition
 to answer.....And therefore, we shall quit the subject for the
present, and proceed with our decomposition of nitre.
   Margraaf first  mentions the decomposition of nitre by the
muriatic acid.  We are not yet in a condition to explain this
 completely.   I can only observe at present with propriety, that
this happens  very readily when the nitre  has  been kept for
some time in a melting  heat.   Now,,  in this case, we'know
that the acid has  a smaller portion of its oxygen,, and that in  j
this  condition it has less attraction for alkalis*  It is for the V-i
same reason, as we shall soon learn, that this anomaly in eiec«/1^
 tive attraction obtains; namely, in consequence of the muri-
 atic acid depriving the nitrous of  a portion of that  principle. :d
 (See Bergmann on Elective  Attractions, VI.)                 ^
   If we  desire to decompound the nitre to obta/in  the alkali^.-- \
alone, we must deflagrate with charcoal or some vegetable in-"' *
flammable matter.   The  common  method with  charcoal \i 
   NITRE DECOMPOSED FOR THE  ALKALI. 99

inconvenient,  by being tedious and  imperfect.  Newman's
method is to take seven parts of nitre, and one of charcoal.
These are pounded, mixed, and projected into a red hot cru-
cible.  This method is not bad, but the deflagration is too vio-
lent, and some alkali is lost. It is better to moisten this mixture
with a little water, and then to project it into a red hot cruci-
ble, and to melt it in  the end, and pour it out.   I  may take this
opportunity to remark, that when the chemists have occasion
to  throw different materials into a heated crucible or other
vessel, in order that they may act on one another, they say that
they project the subject of the operation, or perform pro-
jection.  I suspect that the words projector and project, are
derived from this chemical term.
   If a sufficient heat be applied, the alkali is in a melted state
at the end of this operation, and must be immediately poured
6ut into a warm mortar, or other vessel that is warm and dry.
The alkali thus obtained, was called nitrum flxum, or nitrum
fixatum.  When the  operation is properly performed, the quan-
tity obtained is very considerable;  generally two-thirds, some-
times three-fourths of the nitre.
   The vegetable salt tartar is also often used as a substance
to be deflagrated with nitre, in order to dissipate or consume
its acid.   The acid of the tartar being destructible by fire, and
inflammable, or containing a quantity of inflammable matter,
serves in  the place of charcoal.  And thus we obtain not only
the alkali of the nitre, but also that of the tartar itself.  Thi«
method,  therefore, of obtaining alkali for particular purposes
is often used,  because the alkali both of nitre and of tartar is
very pure.  The common method is to mix and fire them like
a  squib.   It is  not  necessary to  add water; because tartar
contains water and other volatile matters, the gradual dissipa-
tion of which keeps the mixture cool, and hinders the deflagra-
tion from going on  to©  violently.  The usual  proportion of
the substances is to  take equal parts, but in this there is too
little tartar.   I find  six parts of nitre, and seven of tartar bet-
ter for complete decomposition ; though the alkali is not then
so sharp  and acrid as in the other way, for reasons to be ex-
plained hereafter.   Exact mixture is necessary.   This pre- 
100     NATURAL  HISTORY OF  NITRE.

paration, however, must be dissolved in water, filtrated, and
evporated t   dryness, in order to free the  alkali from  the
eait:i\  ashes <:.' Jie tartar.
   Thus  we can separa.e the  two salts of which nitre is com.
pose j, ;:nd can satisfy oui selves that the analysis of it is pom.
pl/te, b\ joining them together again; by doing which pro-
peri, we can ob.ain an entire  and perfect nitre again.
   Origin..........There are considerable quantities of nitre pro*
duced  in different parts of Europe.  But the greatest quan.
tities of it are imported from  the eastern parts of Persia, from
m ;ny p<rts of China,  and also from India.  The general ac-
counts of its origin in those  parts of the world are, that it is
obtained from the vegetable mold, or superficial soil  in par-
ticular places or districts, called saltpetre grounds, which have
generally a loose, open, and marly appearance.
   These accounts appeared for a long time unsatisfactory, and
even i in probable; as  it  was  not then known that nitre  was
produced in this manner in any other part of the world.  But
since the science of natural history has been so much improv-
ed as it has been of late, saltpetre is known to be  produced in
a similar manner in many other countries, particularly in North
and South America, and in Podolia, Walachia, Spain,  and
Italy.
   In Spain and Italy, there are  districts in which the land is
very fertile, and produces very fine  wheat: but  it  happens
frequently, in dry seasons,  that the  crop  is lost  for want of
rain.   The farmers then  indemnify  themselves by extract-
ing-saltpetre from the soil which should have  afforded them   v
wheat.                                                        »
   Much the greater part,  however, of what is manufactured  M
in Europe, is got either from artificial composts, or accidental   *\
nv. -tures, in which animal and vegetable substances have been "'J
thoroughly rotted, and  exposed long to the air, with a large
pi( ortion of any spongy and loose earth, of the chalky or  .1i
ab.orbent kind, as lime, rubbish, or marie.                    **
   In a part of Poland (Podolia) where the country is an ex-     ''
tensive and rich plain, now  deserted, though formerly, very   ^
populous, nitre is extracted  from' the soil of little hillocks. 
NITRE BEDS.                 101
     which are the remains or ruins of  former habitations, and in
     which the wood of the buildings, and the dung of cattle, have
     been long thoroughly rotted, and intermixed with rubbish and
     earth.  In France, too, they extract nitre from the lime and
     rubbish of old ruinous buildings, and from the.floors of stables
     and pigeon-houses.   And sometimes  they take the richest
     part of the mold from the surface of the common soil, in
     particular places.  The same practice was common in North
     America during the last war.  The earthen floors of their to-
     bacco houses were also found to be very rich in nitre.
       These are, therefore,  examples of the extraction of nitre
     from natural or accidental mixtures, in which it is found.  To
     give you, in the next place, some  knowledge of the artificial
     composts which have been observed to afford it, I shall first
     recommend  to  your  notice an author Upon  whom  we may
     fully  depend.   Cramer advises any  person  who  desires to
     make experiments upon the production of nitre, to  choose out
     or build a little hut,  exposed to the fresh air of the country,
     and covered with thatch, to keep off the rain and sun, but not
     otherwise  close : on the contrary,  unless the air can  come in
     pretty freely through  the walls, it must have one open window
     at least upon the north side.   It must be furnished with shal-
     low boxes, about one  foot deep,  for different mixtures.  But
     the only mixture which he mentions, and he speaks of it with
     the air of one who has trieqj it, is lime-rubbish, garden mold,
     and ashes.  These are to be lighdy  moistened with  urine,
     well mixed, and placed in one of the boxes to rot and dry.  As
     soon  as  they are dry, they are to  be moistened afresh with
     urine, stirring and mixing them well up, to expose all the parts
' 4   to the air, which is found to be of great importance to the pro-
 *   duction of the  nitre.   If we thus proceed, always moistening
     and stirring  while drying,  when the mixture is dry, a consi-
     derable quantity of nitre will be produced ; so that, in a month
     or two,  each pound of the mixture will hold two  ounces ol
     nitre, or one-eighth.
   t'.,'  In whatever manner, or in whatever materials, the nitre is
     produced, the extraction of it from these materials is generally
     performed by a particular set of people, who make it their sole 
 102   NITRE NOT Jl  FOSSIL  SUBSTANCE.

 or principal business, and travel from one part of the country
 to another in search of materials in which nitre is already pro-
 duced.  After having examined materials of this  kind by a
 small essay, and having found them to  turn to account, they
 throw them into a large wooden vessel, and  intermix some
 quick-lime and vegetable  ashes.  The vessel  has a false bot-
 tom with holes, which is covered with straw; and, under the
 perforated bottom, there is another, which is water-tight.   A
 stop-cock is placed between these two bottoms.   After  the
 upper part of the vessel is full of water, it soaks  through, dis-
 solves the nitre in its passage, and filtres through  the  straw
 leaving the earth  behind.   The solution  is then drawn  off,
 and the water evaporated to such a degree that the nitre crys-
 tallizes.   In this state it is impure, of a brown  dirty colour,
 and mixed with some sea-salt, which is always found in  the
 materials affording the nitre.   It is separated by crystalli-
 zation, and by quick-lime  and  ashes.  A brown  liquor  re-
 mains,  which  does not crystallize;  and when  examined,
 is found to consist chiefly of some lime and nitrous acid.
   Thus it appears from this history of nitre, that it can hardly
 be counted with propriety among the fossil productions.   It
 is always found in the earth, it is true, but always at the sur-
 face.   There is no example of its being found at any depth, or
 the examples are rare, and the circumstances of them particu-
 lar.   Margraaf and others have  found a little in the wells of
 great cities ; the origin of which can be easily accounted for.
 Dr. Withering, in  his translation of Bergmann's Sciagraphia,
 says, some of his friends assured him they had got nitre from the
 waters of some coal-pits.  But it is highly probable that it had
 been washed down  into the coal-pits  from the  superficial soil,  "m|
 by the rain-water soaking downwards through the earth.   It ~'^m
 never occurs in mineral waters.   Some authors imagined they    i
 found it in these;  but they mistook another  salt Tor it, and
judged of its presence by the form of certain crystals which   jm
 they had obtained.  But  the form of crystals is never to be   Jsj
 trusted.   As it is  therefore found only  at the surface of the
 earth,  or not  far below it, it has long  been  a very general
 opinion that it is deposited or formed there by the air.   Some
have supposed that the air furnished at least the principal part 
CONJECTURES ABOUT  ITS  ORIGIN.   103
     of the nitre, to wit, its acid; which, finding in corrupted animal
     and vegetable substances the other necessary ingredient, the al-
     kali, united with it to form a nitre. Others have supposed that
     the air afforded, notthe nitrous acid, but vitriolic acid.  But
     these opinions have not been supported by experiments. When
     pure alkali is exposed to the air, it is not changed into nitre.
        Another idea, which occurred to some of the chemists in
     France, had a greater appearance of probability;  I mean, that
     the nitre has its origin in vegetables, being produced in them
     by the powers of vegetation, and is only extricated from their
     other principles by putrefaction, during which natural process
     all the principles of animal and vegetable substances are gradu-
     ally separated from one another.   Many plants have been long
     known to contain some nitre in their juices, separable by crys-
     tallization.  Tobacco sometimes contains so  much, that  its
     stalk burns as a squib: but they were supposed to have receiv-
     ed this from the soil in which they had been nourished.  It is
     now reported, however, that some of those plants, though
     made to grow in earth from which all saline matter has been
     completely extracted, and, though  watered with pure water
     only, will still be found to contain nitre ; which, if true, shews
     plainly enough, that the plant generates the nitre, by combi-
     ning some of the elements together in a particular manner.
        Many other opinions were formed on this subject at differ-
     ent times : but we never acquired a decisive and  satisfactory
     knowledge of the formation of nitre in soils,  and other  mix-
     tures, till the French government directed to it, in aparticular
     manner, the attention of the able chemists of that nation. This
     was done under the administration  of that patriotic  minister,
 /v.  Mr. Turgot.  Distinctions and rewards were offered to those
%£';■. who should best illustrate the origin of nfyre: and the Royal
     Academy of Sciences were appointed judges of the  merit of
     the attempts.
        A number of essays were accordingly offered, many of them
     describing ingenious investigations, and trains of experiments,
     to decide different questions relating to this subject.  The gen*
     tlemen who distinguished themselves the most are M* Thou-
     venel medicin,  and M. Thouvenel commissaire,  des poudres
     ct saltpetres de Nancy ; Mr. Lorgna ; M. Chevraud; M. Ga- 
!04      ORIGIN AND USES  OF NITRE.
 vinet.   An abstract of their discoveries has been published by
 the  academy, with  some remarks, to shew what particulars
 have been cleared up and decided,  and what still remain ob-
 scure.   It appears from the whole, that nitre  is formed by the
 action  of the atmospherical air ; and of the exhalations of rot-
 ting animal and vegetable substances, applied at the same time
 to alkaline earths,  as chalk, or lime-rubbish,  or marie ;  and
that the putrid exhalations do not produce their effect, except
 atmospheric air be allowed to mix with them in certain quan-
 tity.   It appears further, that the nitrous acid is formed most
 readily, or soonest, and the alkali afterwards.   The acid first
joins with the alkaline earth.  The alkali which is formed af-
 terwards dissolves the union, by taking the acid to itself.
   Several other particulars have been discovered, which will be
 useful  and instructive to those who have the conduct  of salt-
 petre works.  But they are only facts which point out  the me.
 thods by which saltpetre may be produced with the  greates*
 success.   They do not yet explain its production.  Other ex-
 periments since that time have thrown much light on the na-
 ture and constituent parts of the acid of nitre,  and have occa
 sioned the contrivance of new methods of producing it and
 nitre.   But of these we shall speak more fully hereafter.
   Uses........Nitre is an article of the materia medica, and is
 reckoned  the most cooling antiphlogistic of the salts ;  but it is
 often very disagreeable to the stomach.   It also promotes the
 secretion  of urine.   In the arts it is highly useful, by being
 the only subject from which we can get the nitrous acid ; and
 it is by means of  nitre that the vitriolic acid is procured  in
 quantity or perfection from sulphur.

            SPECIES IV....CUBIC  NITRE.

   The cubic nitre resembles common nitre exactly in  its most
 striking properties.   The only difference is the form of its
 crystals and the consequences of decomposing it.  The form
 which its crystals affect, is that of oblique  parallelopipeds :
 though they generally concrete together,  and adhere to  one
 another ;  so that hardly any of them have this form  perfect. 
Digest rvE salt.
105
     It melts with the same heat as common nitre, and dissolves
     in the same manner in water.  It deflagrates with inflam-
     mable substances precisely  in the same manner,  and is
     decomposed by the  same means, viz. by  vitriolic acid.
     The  only difference  is, that Glauber's  salt is produced
     instead of  the vitriolated  tartar.  It is  decomposed by
     deflagration with charcoal for the alkali, which is not the
     vegetable alkali, as in the case of common nitre, but  the
     fossil alkali.  Therefore  it is improper to  use tartar for the
     deflagration.  But we must  employ  charcoal with water,
     as the charcoal of fir (as Margraaf directs),  or we may
     take common flour, which contains a sufficient quantity of
     inflammable matter, and enough of water and other volatile
     ingredients, to keep  the  rapidity of inflammation within
     due bounds.  When  deflagrated  with  sulphur, it is plain
     that Glauber's salt must be produced.
       It  remains now only to mention the  origin of  cubic
     nitre.   It is not  produced naturally in a  quantity worth
     notice, (though I suspect it  is contained in some vegeta-
     bles ;) but is prepared artificially by chemists,  when they
     have  occasion for it in their experiments; for it  is  not
     employed in medicine or in the arts.   It may  be  obtained
     either by decomposing common salt with the nitrous acid,
     as shall be  noticed hereafter, or by joining together  the
     alkali of soda and the nitrous acid.


            SPECIES V.....DIGESTIVE  SALT.

      As digestive salt is  the produce of art only, and is pre-
--.   pared by mixing  its two ingredients, the knowledge that
• r'   we have already acquired of these will naturally suggest to
     us all its general properties, and the manner  of decom«<
   _  pounding it for either of its ingredients.
      Its external appearance so  much resembles that of com-
     mon sea-salt, that chemists of eminence have imagined it
     to be  the same. Boerhaave calls it salmarinus regeneratus.
     The London Dispensatory avoids deciding, by calling it
  '   Spiritus salis marini coagulatus: and even the author of the
     New  Dispensatory was long before he imagined it any how
vol.. ir. 
  106-              COMMON SALT.
                                                        r
  different.  It differs, however, from sea-salt, in becoming
  a much more transparent mass after fusion, but less white,
  and toughish like horn.   Even the crystals have this pro-
  perty, and are pounded with difficulty. Its most remarkable
  difference from sea-salt is, that it dissolves in much greater
 quantities in  hot than in cold water J and, by this property
 alone, these salts may be pretty well separated.  Its analysis
 is already foreseen*   It may be decomposed for its acid,
 by employing the vitriolic  acid;  and the  residuum must
 be a vitriolated tartar instead of a Glauber's salt.  I was
 perfectlyv convinced  of the difference, by decomposing it
 with the nitric acid.   The  residuum shot into hexagonal
 crystals; a sufficient proof that it consists of the muriatic
 acid and the  vegetable  alkali.  To  decompose it  for its
 alkali, we must follow the process, and deflagrate the nitre
 we have obtained  by it.
   The only other origin of digestive salt, is the decompo-
 sition of sal ammoniac by means of  potash.   This being
 the cheapest  process for obtaining it, is practised by the
 trading  chemists for supplying the druggists  and experi-
 menters with  all of it that is wanted.


         SPECIES  VI.....COMMON  SALT.

   Common salt requires a full red heat for its fusion, and»
 soon after fusion,  begins to evaporate in white fumes.   It
 has a pretty strong attraction for water, so that it deliquiates
 in moist air.   It dissolves in less  than three waters, and
 equally  in cold or hot.   Hence it  has a different  manner
 of crystallizing by evaporation.  A pellicle is formed, if
 the evaporation  be hasty ;  if slow, cubes are first formed, '*•
 then a sort of hollow pyramids, formed by steps, super-
 added on all sides to the  step last formed.   The first cube,
 formed at the  surface, being  a very little heavier than the
water, begins to  sink : and the adhesion, or viscidity of the
 water, causes  it  to drag the adjoining water down with it; *
 and thus it makes a depression on the surface, as when a
square brick is laid on a feather bed; only the saline cube
is wholly under  water, hanging by its upper surface.  "The 
COMMON  SALT.              to7
water being thus exposed to evaporation in a greater sur-
face on the sides of this pit, the next crystallization takes
place there,  preferably to  any other place.   Thus a first
step is formed,  and the solid sinks deeper, again hanging
by its upper edges.  A second step is formed in the same
manner, and so  on, till the  crystal becomes too heavy, and
it then breaks  its hold and  sinks to the  bottom.   It is
amusing to observe this operation with a magnifying glass.
Each step is formed in an instantall round,....yet it consists
of distinct  cubes;  for it will  only-break into  cubes;  or
clusters of cubes.
   The crystals  of sea-salt  are of  the decrepitating kind.
If  it  be  frequently  dissolved,  evaporated,  and  dried
thoroughly with red heat,  it is  diminished in quantity,
and a portion of earth is produced from it.   And this is
one of the chief instances  adduced to prove that salts are
composed of earth and water.  But the quantity of earth
is so small, that its origin is doubtful.
   Common salt is easily volatilized  by  fire, and by putre-
faction, along with substances  disposed  to that process.
By repeated solutions and  calcinations, it may be totally
destroyed, or converted into  earth.
   Although its acid  be very volatile,  this salt cannot be
decomposed by heat alone.   In some of the processes by
which it was attempted formerly to prepare this acid from
common salt, they trusted  principally to the force of heat.
Common  salt,  mixed with clay,  and exposed  to  a fierce
heat, is in part alkalized: but it afterwards becomes neutral
by exposure to  the air.
   The best way of decomposing it for its acid, is by another
acid, of which there are  two that will answer the purpose,
 ....the vitriolic acid, and the nitrous.   But the vitriolic is
best; and is even necessary if we desire to have the muriatic
acid  pure.   It is best, as having greater superiority of
attraction  for the alkali than the nitrous  acid has ; and
therefore  expels the muriatic acid more readily.   Indeed
 this acid is in a manner necessary for obtaining the muriatic
acid pure; because it is fixed, and does not emit any fumes;
whereas  the nitrous acid emits  them  very  copiously.
 Further,  in using the vitriolic acid, it is necessary to use 
  108     PROCESS FOR MURIATIC ACID.

  likewise a certain quantity of water.   If the strong acid
  be added to  the  dry common salt, the muriatic  acid  is
  expelled so  pure, that  it is not  accompanied with water
  sufficient for its condensation ;  so, that a great part must
  be allowed to escape ; for the fumes will fkirst the vessels
  if we attempt to confine them.   And thus we lose much
  of the acid,  and are incommoded too with  the  fumes ;
  because the water contained in the crystals of the salt, and
  in the vitriolic acid, is  too little  to repress sufficiently the
  volatility of  the muriatic acid thus detached.  We must
  therefore  dilute  the  vitriolic acid with about  an  equal
  quantity of water, before it is  added to the salt  in the
  retort.
    With all our care and skill, the separation of the muriatic
  acid is a very difficult process.   In its pure state, it 13 too
  volatile to assume the liquid form, even in our most intense
  colds.  Dr. Priestley reckons it  a species of air, calling it
  marine  acid  air.  But  it seems to differ from the other
  acids, chiefly by its smaller attraction for water, of which
  it requires a  gn ater quantity to  repress its volatility, and
  also by the very great  quantity of heat which its vapour
  holds  latent.   If we proceed wiih  a simple retcrt and
  receiver, we may use  nearly equal  weights of salt and
  vitriolic acid, and dilute the acid, before mixture,  with as
  much  water:   and we must employ a huge receiver, and
  keep it very  cool.  The tubulated  retort  containing the-
  salt, being set in the sand-pot,  and  the receiver  joined
  and luted, the diluted acid is then poured in, and the hole
  shut with  a  ground stopper.  The disengagement  of the
  marine acid commences immediately, even though  the fire
  has not been  kindled.   Some chemists think it better not
  to  dilute the vitriolic acid, but to  put the  water into the
  receiver, where it absorbs the vapour very fast, and soon
  si'ows extren  ;ly hot. .  The distillation must be conducted
  very slowly :  and it is proper to let it proceed, for  a while
  in  the beginning,  without any fire.   As  we  must use  a
  porous lute, much vapour escapes, with great loss of acid,
  and much inconvenience from the fumes,  which corrode
v >-very thing in the laboratory. It is chiefly in this process
  rhat the great value of Mr. Woulfe's  apparatus, despribed 
        PROCESS FOR MURIATIC  ACID.    109

in the Phil. Trans. 1767, appears ; and it  is so employed
by all the  trading chemists.   Mr. Woulfe found that the
condensation of about four ounces of vapour heated seven
or eight pounds of water up to  the  boiling  temperature.
Wnen  the  water has acquired an equal  weight of  acid
vapour, its bulk is increased in the proportion of  two to
three.   I recommend to your perusal the dissertation just
now mentioned, by Mr.  Woulfe, as containing many very
curious as  well  as useful observations.   I observe that
some foreign  chemists  proceed in  another way that is
pretty singular.  Two retorts  are employed, communicating
with one receiver. In one of them the distilling substances
are contained ;  and the  other has only water.   The .two
vapours thus meet in the receiver, and unite very rapidly.
I doubt not but this process will be very manageable and   .
productive.
   The salt which remains in the retort when the distilla-
tion is  finished, is Glauber's (as may be seen from  the
table.)   And this is the usual manner in which Glauber's
salt is prepared by chemical  artists, the process being per-
formed much oftener for the sake of  the Glauber's  salt
than of the muriatic acid; except in  some manufactories,
in which they employ the muriatic acid to make sal am-
moniac.
   If we desire to decompound  common salt to obtain the
fossil alkali pure, we cannot  have recourse to inflammable
substances here, as in the case of vitriolic and nitrous salts.
When the experiment is made with  common salt,  it does
not succeed ;  nor is there  any reason to expect that it
should.   The muriatic acid, in its ordinary  state,  is very
little affected by inflammable bodies, and will not quit the
alkali to act upon them.   But we can separate  the acid by
the vitriolic or nitrous acids, which,  when  joined to the
alkali in its place, will not be so difficult to remove.  The
nitrous acid  is  the  most convenient,  and  most easily
managed.
   Wljen  the  nitrous acid  is employed  to separate the
muriatic, a cubi^itre is formed : and it is  easy afterwards
to de,flagrate with charcoat'to obtain the fossil alkali, which
is the.purest alkali we  have.    But the first part of thrs 
 110  DECOMPOSITION FOR THE ALKALI.

 process requires a little attention to perform it well; and
 Mr. Macquer's directions  are very bad.   The nitric, and
 not the nitrous acid, should be employed, and in a diluted
 state,  or about the strength of aquafortis.   This must be
 poured on  the common salt, in fine powder, but retaining
 its water of crystallization.  The distillation of the muri-
 atic acid should be conducted very slowly. The first fumes
 are ruddy, and condense into a ruddy liquor, and the fumes
 of mixed acid, or aqua regia, are very perceptible in the
 laboratory.  Towards the  end the vessels grow clear, and
 the liquor is yellow, and floats on the ruddy liquor.  If the
 whole  be returned and slowly redistilled, we have less of
 the ruddy fumes and liquor.
   The acid obtained from a pound of nitre, of  whatever
 strength, will  completely decompose about eignt ounces of
 common salt.  The cubic nitre is easily separated from the
 undecomposed salt by crystallization, because it dissolves
 in much gr< ater quantity in hot than  in cold water.   The
 earthy matter  of the charcoal with which it is deflagrated
 will separate by the filtre, and  leave  the  soda  perfectly
 pure.
  Common salt  is well known to be the most universally
 useful, and the  most necessary to mankind of any.   The
 qualities by which it is so  useful are  its antiseptic power,
 attended, at the same time, with .a wholesome or innocent
 quality with regard to our  constitution; in consequence of
which  qualities, we can, in case of necessity, preserve our
 animal food in wholesome condition,  for a long time, by
means of this salt.  And  it is further much more exten-
 sively  useful  and valuable, in  consequence of  another
 quality, by  which it assists  or promotes the digestion of our
 food, and proves a most agreeable  seasoning to it.   It is
well known to be, on this account,  one of the necessaries
 of life  with regard to man  : and there is reason to think it
 necessary or useful to the greatest number of other animals
 also.   In these  islands,  [Great Britain and Ireland]  and
 in the  greatest part of Europe, which is not far from the
 sea, as well as in other similar situations, this truth is not
very obvious.   We think, on the contrary,  that we see
numbers of animals live and thrive  verv well without eve* 
         COMMON SALT IN  THE AIR.       m

 tasting salt.   But they do, however, get salt, though in an
 imperceptible  manner.   Our most inland  situations in
 these islands are at such moderate distance from the  sea,
 that some  salt is communicated to them, either by the finer
 part of the spray,  dashed  into particles perhaps  too small
 for sight,  and which must necessarily fly in the  air after-
 wards for  a  very long  time,  or  by an evaporation of the
 sea-salt in small quantity along with the water.*  In what-
 ever manner sea-salt arises into the atmosphere, and to the
 upper parts of the land, it is certainly found there.  A small
 quantity can be obtained from our purest; and freshest natu-
 ral waters.  But it does not equally reach all countries and
 all situations.  There are some far removed from the sea,
 or other large collections of common  salt,  in which the
 animals plainly  languish  for want of it, and shew very
 strong desire to have it.   In  Germany, and  some other
 parts of the great continents  of Europe and Asia, they
 give  it  to their cattle, as necessary to their health and
 thriving.  In the  inland parts of America, the wild ani-
 mals  are  observed to  flock in  incredible numbers, and
 from great distances, to places where they may have an
 opportunity of licking salt, or of drinking salt water.  Salt
 is often used there as  bait for deer, to entice them  into
 places where the hunter can reach  them :  and an  offer of
 salt is a greater temptation to horses running loose in the
 American woods, than an offer of corn.  These facts have
 occasioned some speculations concerning the manner in
 which this salt  can be so useful to animals in general; and
 a discovery  made  by the late  Sir  John Pringle has been
 thought to throw some light on this matter.  Sir John dis-
 covered, by  experiments,  that it has a power of promoting
 the putrefaction of animal and vegetable matter, when aph-
 plied in small quantities to those  substances.   And, as the
 change which the vegetable food  undergoes, in passing
 through our bodies, is supposed  to have some analogy

  * I have frcquently'observed at Glasgow,  which is a great way from the
sea-coast, that, after a strong gale from the west, the hedges, in winter, are
very salt to the  taste.* One would imagine that the twigs had been dipped
»n saltwater.  One very dry spring, I found it crystallized like hoar-frost....
 f.pitor. 
 112       ORIGIN  OF  COMMON SALT.

 with putrefaction,  it has  been thought that common salt
 had the power of promoting  this change as well as putre-
 faction.   Animals that are purely carnivorous do not agree
 with salt  added  to their  food.   In whatever  manner it
 acts, its  usefulness to animals  in  general is  sufficiently
 evident.
  Origin........As, upon these accounts, common salt seems
 the  most  important and the most extensively useful of the
 5'alts; so  it is most abundantly produced by nature.  For,
 first, it is found constituting deep and extensive masses in
  ne  bowels of the earth, from which it is  dug up by min-
 ing,  as coal or  other minerals, and is called  rock-salt.
 Many mines of this  kind are wrought in England, Mus-
 covy, Poland,   Germany, Calabria, Transylvania,  and
 Stower in the U^per  Hungary, Spain, particularly Catato-
 nia, Italv, and other parts of Europe, in the East-Indies,
 anci in America.   Salt, as thus found in mines, is a solid
 har.i substance, and is not dissolved so readily as sea-salt.
 It is generally  more or less transparent,  but tinged to a
 brown, yellowish, or  reddish colour, in consequence of the
 mixture of some earthy matter with the  salt.   Sometimes
 it is pretty bright and pure ; whence it has got the name of
 sal gem.    Many  of those mines contain amazing quantities
 of salt.   The most astonishing are some Polish and Hun-
 garian mines, of  which there is an account in the Philoso-
 phical Transactions,  No. 61. and  413.   The mine of
 Cracow in Poland, near Wieliczka  and  Bochna, is com-
 puted to hold salt enough to suffice the whole  world  for
 many thousands  of years.   The works in it are of great
 extent; and there are houses, chapels, and other buildings
 under ground,  all built of salt or salt stones.   Very large
 masses are  often  met with,  free from considerable flaws,
 and  of more pleasant colour, and more  transparency than
 ordinary,  which are cut and turned into pillars and other
ornaments of architecture,...sometimes  into toys.   And
 the whole of these mines, as illuminated artificially, have
 a most uncommon, surprising, and brilliant appearance.
   These  immense and massy collectionstof salt are found,
 in several parts of the world, to project above the level of
J.he ground, and form Kills and evgen mountains.  Of this 
           ORIGIN OF COMMON  SALT.       113

kind are two mountains in Russia, near Astracan; several
in the kingdoms of Tunis and Algiers, in Africa; several
in Asia ;  and a  great  part  of the island  Ormus,  in  the
Persian Gulf, is said to consist of salt.
   There are, likewise, in different parts of the world,  in-
numerable springs, ponds, and lakes, containing this salt,
produced by the  flowing of water through fousil salt, or
soaking through salt earths.  These waters  are of  very
different richness.   Thus, in Germany, where they have
most of their salt from springs, some are so weak, that
there are only two drachms of  salt in the pound of water.
 The spring -at Halle is  the richest,  and  contains three
ounces and  three  drachms to the pound: but in England
there are pits much richer than these.  The  springs of
Droitwich contain four ounces:  and several  pits at Nor-
wich, and at Barton in  Lancashire, contain six ounces in
the pound, which is  a saturated solution.
   Lastly, The sea,  which covers such a large proportion
of the surface of this  globe,  contains  this salt in very
considerable quantity, and renders it easily procured for  the
use of man, in almost all the inhabited parts of the world.
   These are the only, though very plentiful sources from
which salt is obtained,...the masses or strata which it forms
in the earth ;  the salt springs  or fountains,  and the sea.
And it  has therefore been often divided into these three
species,....of rock-salt, or sal gem,....fountain-salt,....and
sea-salt.  But this  division is of no  use;  because, from
whichever of these sources it is ^obtained, if it-be pure
naturally, or purified by art, it is precisely the same.   All
the differences found among the varieties of common salt,
in its native state, proceed  from impurity or admixture,
which produces great variety even in common salt of  the
same origin; it being seldom or  never perfectly pure, and
often very  foul.   Rock-salt, for example, is  commonly
attended with a large intermixture of  earthy; matter.,  and
has besides a bitterish  taste, proceeding from a  small pro-
portion of other salt intimately  blended with it.  Strit of
springs or fountains is liable also to  admixtures of  mud,
and other salts.   And in the  sea, we  find several other
salts or saline  compounds mi^ed^ with  the common salt.
  •'-.  VOL. II.                  » 
 U4       ORIGIN OF COMMON SALT.

 The  great quantity of  water too  in  which  sea-salt and
 spring-salt are dissolved, must be considered, in a com-
 mercial view, as an extraneous matter, which it is neces-
 sary to separate from it.  The proportion of this water to
 the salt is different, however, in different springs, and  in
 different parts of the  ocean.   In general, the sea is less
 salt in cold climates, near the poles, and salter towards the
 equator.  It is a common observation of naturalists, that
 such  is  the  arrangement and  regularity of nature, that
 since this salt seems mixed with  the  sea, in  order to pre-
 vent its putrefaction,so it is mixed in the greatestquantities
 in those places  where the heat is greatest, and  where, for
 this reason, there is the greatest danger of putrefaction.
 The variety of saltness  in the ocean is produced by greater
 or less evaporation, and more or less rain.   The evapora-
 tion is much greater near the line, from  the  greater force
of the sun ; and the vapours, or the greatest part of them,
 generally move towards the poles, so as to descend in more
 frequent showers there than where  they were  elevated.
 And  though  the difference of  saltness occasioned in this
 way is hindered from going a great length, by the agitation
 to which the ocean is subject, from various causes, still, as
 these operate slowly, the difference is always considerable.
 Thus, in the northern  parts of  the Baltic, a  pound of  sea
 water scarcely  contains  two drachms  of salt.   Farther
 south, from the mouth of the Elbe to Holland, and on the
 British coasts, it contains one ounce. In the Mediterranean
 it contains two ounces ; and  in the Atlantic, near the line,'
 it contains more than three.   Mr, Boyle has observed a
 phenomenon which he ascribes to this cause.   Where the
 sea is very deep, the water is salter at the bottom than at
 the surface.   Even in moderate depths near  the land, this
 inequality of saltness obtains also.   This, in all probability,
 is owing to the freshes from the land, which float  a-top by
 their specific levity ; and it is a long  while before they are
 mixed by the agitation of the winds.   Ovid  has preceded
 Mr.  -Boyle in this observation; and describes  it most ac-
 curately in some very beautiful lines in one of his elegies.
   These are, therefore, the different stages in which com-
 mon  salt is found in nature, and Horn  which it is prepared
 and refined for use.            •              -     -<l'-.' 
        MANUFACTURE OF  BAY-SALT.      115

   Where the rock-salt  occurs  in a state of considerable
purity, it is used by many without preparation.  In Poland,
numbers of the inhabitants used their fossil salt in its natu-
ral state ; but this is uncommon.   The rock-salt is generally
so impure that it cannot be used, without being first refin-
ed.  And in general mankind almost universally use com-
mon salt that has  been  prepared or manufactured by ex-
tracting it from the waters of the sea, or of salt springs or
wells, or by refining or purifying the common salt.
   The methods which  have been  contrived,' in different
places,  for extracting  it from the v/aters of the  sea and
springs, with the least expence,  are very numerous;  and
much ingenuity has been shewn  in pursuit of this object.
But I believe  I can employ your time better than in des-
cribing all these contrivances.  You will find a  very good
account of them in Dr.  Brownrigg's book, entitled, " The
Art of making Salt."
   I shall only remark, that all the methods which have
been in use may be distinguished into two varieties, and a
mixture or combination of  these two:  1st, In the  one,
the  water is  evaporated, and  the salt made to  crystal-
lize by the heat of the  sun  and action of the air  only, in
shallow  ponds.  2d, By the other, these operations  are,
performed by the heat of fuel;  and the salt is called boiled
salt.
   The first method is practicable in the hot climates only,
where the  great heat of the sun, and dryness of the wear
ther in summer, occasion a copious and quick evaporation,
without any expence.   In those climates and  situations
where these circumstances  are  the most favourable, very
little art is required,  or scarcely: any;  for wherever the
sea-water is received at spring-tides into shallow ponds or
pools that are not overflowed at other times, the salt crys-
tallizes between one spring-tide and another.   But where
the evaporation is not so quick, more art is employed, as in
the  salt ponds on the coast of France.  The general con-
trivance is to this purpose:....On a flat beach,  the sea is
walled off, except at one  entry, which is shut by a sluice :
all within it is ttfe salt pond.   This is divided into a vast
 number,of portions, hvjhe manner of a labyrinth, all com- 
116    MANUFACTURE  OF BOILED  SALT.

municating with the main inlet;  but by so many turnings,
that any one trench, if stretched into a straight line, is very
long, and all  of  them nearly  of  the same  length.   The
different portions are made  shallower as they advance in-
land.   VVnen th<  sea is admitted at high water, the whole
is filled to a level, and the sluice  is shut.  The evaporation
reduces  the surface.   At next high water, more is admit-
ted :  this pushes before it the  water already in the pond,
which has become a little salter than what is now admitted.
Thus we see, that as the brine becomes richer in salt, it is
pushed farther in. toward the last recesses of the labyrinth;
and therefore the granulation  will begin in those places,
and the water will continue to deposit its salt chiefly there,
where it is lifted out with proper instruments.  These parts
of the salt pond are, therefore,  firmly  constructed, and
formed of stiff clav, well rammed ;  while the parts nearer
the inlet are of common earth,  or trequently of mere sand.
   The second method of preparing salt, viz. by the heat
of fu  1, is practised in these  colder and wetter climates,
which do not admit of the  first. In this country especially,
the preparation of  boiled salt is a considerable business,
because we have fuel very plenty and cheap:  and a part of
 it may be had for almost nothing, on account of its being
 unfit for household purposes.
   In some places in England, they practise both methods'
 in part; that is, they  evaporate  part of the  water, first by
 the heat of the sun, and afterwards finish with fuel.
    The salt made with the sun and air  alone, is called bay-
 salt.  Its crystals are much larger, and more solid than
 those of boiled salt, as it is commonly made, but not so
 white, by reason of light mud which remains suspended du-
 ring the whole evaporation. \ But the  bay-salt,  though  it
 has the appearance of being more impure, is  much more ef-
 fectual  for preserving provisions ; and when we  make an
 inquiry into its consvitueiv. parts by experiments, and com-
 pare it  with  boiled salt, we  discover the reason of this,
 which is, that it is  in reality purer than the common boil-
 ed salt  ; that is, it is more free  from  the admixture of
 other salts, or saline  compounds.  For, as  1 remarked al-
 ready,  sea-water contains  several salts, or saline *.com- 
         PURIFICATION  OF SEA-SALT.      117

pounds, beside common salt, and these give it the bitterish
taste. '  By  the  violent boiling,  and  hasty crystallization
commonly practised in preparing boiled salt, these extra-
neous and useless salts are but very imperfectly separated.
A great part of them remains,  and depraves the quality
of the salt for curing provisions ; whereas the bay-salt be-
ing produced by a slow  evaporation  and  crystallization,
there is  more time for the separation of the heterogene-
ous, and concretion of the homogeneous saline particles.
That this  is the  cause  of the  difference,  appears from
Sunday's salt, which  remains upon a slow fire  that is not
renewed during the whole of that day, and its crystals are
much larger,  more agreeable  to the taste, and  sell for a
higher price.   Bay-salt has a taste very sensibly sweetish,
which is not to be  found  in any boiled 'salt whatever, and
which it loses by two or three solutions and crystallizations.
It is in all probability owing  to the influence of the sun's
light, the chemical effects of  which on  other subjects are
analagous to this.
   It is, however, very much to be wished, and an object of
great consequence to trade and  the fisheries,  to prepare
common salt as free as possible from all impurities:  and
many ingenious men  have turned their attention to  this
subject.   It is the  main scope of Dr. Brownrigg's book,
though he was perhaps under a mistake in his notion of the
defect of common boiled salt.
  The Earl of Dundonald has lately published the account
of a cheap, though ingenious process, by which common
boiled salt can  be purified to a  very  considerable degree
from the extraneous salts.  The general principle of his
process is this;  the  disagreeable  salts contained in the
common boiled salt, dissolve in much greater quantities in
hot than in cold water.   In order,  therefore, to purify a
parcel of common salt, it is put into a conical vessel, or bas-
ket having an aperture at its apex,  stopped with a plug of
straw.   A saturated  solution of  common  salt in boiling
hot water,  is poured upon it,  boiling  hot.  This  trickles
down through the  salt,  and escapes through the  straw.
Being already saturated, it can carry off none of the pure
sea-«alt, but it washes it clear of the bitter brine with which 
H8          AMMONIACAL SALTS.
•it was covered ; and, being  boiling hot,  it dissolves  the
 greatest part of the crystals of the bitter purging salt which
 had tainted  the whole.  His  Lordship found, by accurate
 experiment, that a saturated solution of one  pound  of
 common salt,  poured  upon ten pounds of fait, takes away
 about four-fifths of all the bitter salts that it contains,  by
 one operation.
   My friend the late Dr. Roebuck also studied this subject,
 and practised  a process, by which he refined boiled salt to
 a very'high  degree, and made it even superior to bay-salt.
 But his process was expensive, and cannot be made subser-
 vient to the fisheries,but only to supply the luxury of the rich.
 It depends entirely on repeated and slow crystallization.
    It is much to be wished, that the preparation of common
 salt,   and the  commerce  in  it,  were  less shackled  with
 limitations,  monopolies, and  heavy duties.   It is not only
 a necessary of life to  all ranks, but of the greatest conse-
 quence to  the .fisheries: and  salt is  capable of being
 employed in  a  number of manufactures, which  are pre-
 vented from taking place  by the price of this article, and
 by the trouble to which those who use  it are subjected. >

             AMMONIACAL SALTS.

    All the compound salts which contain the volatile alkali
 combined with the different  acids, are called ammoniacal
 salts.  This general denomination is taken from the com-
 pound with the  muriatic acid,  which  is commonly used,
 and  has been long known by the name of sal ammoniac.
 The  name is derived by some from Ammonia, one of the
 Cyrenaic territories,  in  Egypt and  Lybia,  which was
 supposed to produce it.   Pliny, in treating of common
 salt,  says,  that the Cyrenaic territories were remarkable
 for producing a species of it called Hammoniac, on account
 of its being found under  the sand of the soil.   And it is
 supposed that he  meant this salt, which is very probable,
 both on account of the name, and of the description which
  he gives of it.   But it is plain that he had drily an imper-
  fect knowledge of its nature, and  had been misinformed
  concerning its origin.   Vide  Plin. Hard. torn. II. p. 559* 
              VITRIOLIC AMMONIAC.         119

    With respect to the general nature of these salts,  they*
 can always be distinguished from the compound salts,  by
 the action of a  fixed alkali  on them.  It immediately
* attaches itself to the acid, and detaches the  volatile alkali,
 which is perceptible by its pungent odour.  It is by the
 decomposition of one of these salts that we obtain a pure
 volatile  alkali, or that  which is the fittest for chemical
 experiments, or for the purposes of medicine.   If equal
 quantities of sal ammoniac and  salt of tartar be dissolved
 in an equal weight of water, we  shall immediately perceive
 the pungent  smell  of  the  volatile alkali.  If this mixed
 solution be put into a retort, and distilled to dryness, with
 a heat gradually increased, we shall find in  the  receiver a
 solution of volatile alkali,  in its least acrid form.   It is
 known by  the name of spirit of sal ammoniac or of harts-
 horn.
    Beside  this effect  of the fixed  alkali on them, which
 distinguishes the ammoniacal  salts, they are  also more
 volatile  than other  compound salts,....both  of the simple
 salts of which they are composed being very volatile. But
 their volatility is not so remarkable as we might be led to
 expect from  our knowledge of  the   volatility of  their
 ingredients in a separate state.

     SPECIES VII.....VITRIOLIC AMMONIAC.

    Th£ first  in the table is  the Vitriolic Ammoniac, likewise
 called  the Secret  Ammoniac  of  Glauber, because that
 author, who was inventor  of Glauber's salt, was  likewise
 the first who took particular notice of this, and imagined
 that it possessed some remarkable powers over metals, and
 made a sort of secret of it for some time.   But I do  not
 know of any  qualities which it possesses that deserve your
 attention.
    We may,  however, before we dismiss this salt, take the
 opportunity to explain a double elective attraction in which
 it plays a  part.   The fact, as discovered by experiment, is
 this.....'     *
    If vitriolic'ammoniac and common salt be  both dissolved
 in water,  and mixed together, and  the mixture  boiled for 
120
VITRIOLIC  AMMONIAC.
some time, there is a double exchange, or double elective
attraction.   The vitriolic  acid  leaves  the volatile alkali,
and unites with the fixed alkali of the common salt, while,
at the same time, the acid of the common salt unites with
the volatile alkali that was  in the vitriolic ammoniac ;  and
then, by  evaporating the saline mixture, we obtain  first
Glauber's salt, and afterwards common sal ammoniac*.
  The  reason of this must be, that there is  a greater dif-
ference between the attractions of the fixed alkali for the two
acids, than between the attractions of the volatile alkali for
the sametwoacids, which maybe  shortly expressed bysaying
that the fixed alkali has a greater partiality for the  vitriolic
acid than  the volatile  alkali has.   For, let us suppose
that these  differences are  the  same,  and then consider
what would be the  consequences.
  These four chemical substances, the two alkalis and two
acids, when mixed together, may be represented, in some
measure,  by four bodies placed at the  extremities of two
moveable  diameters of a circle, and  each of them attract-
ing the two that are next to it;  thus,
VOLATILE .ALKALI.   MURIATIC /ACID
VITRIOLIC 'ACID
FIXED" ALKALI
   Each of the acids is disposed to unite with either alkali,
and each of  the alkalis  consequently with  either acid.
But they cannot unite with one without leaving the other:

   * I'r is easy to perceive that the double exchange will  happen without
Hie condition required by Dr. Black, if the partiality of the  vitriolic acid for
the fixe J alkali be greater than that of the muriatic .acid|br the same alkali.
This operation must be considered in the more general.manner expressed in
note PA, p. 268.....editor.                 W*t" 
VITRIOLIC  AMMONIAC.           121
and in proportion as they are attracted by one, they are drawn
away from the other ; and while one of the acids unites with
either alkali, it repels the other  acid from it,  and in the same
manner either alkali repels the other.   Now  let us see what
will be the play of these four substances,  on different supposi-
tions  of the difference of their  attractive forces.  And first,
let us suppose that the differences  of the attracting forces  of
the two alkalis for the two acids are equal, or that each of the
alkalis attracts the vitriolic acid more strongly than the  muria-
tic, by an equal superiority of attracting force.   In this case
no exchange can happen : the. attractions are exactly balanced.
   For,  let the attraction of the  volatile alkali for the muriatic
acid  be represented by x, and  its attraction  for  the vitriolic
acid by x, and some qther quantity a, or x + a. In like man-
ner,   let the  attraction  of the fixed alkali for these two acids
be y, and y  -f- b.
  The forces which maintain things  in their present state are
x -f a and v, the sum of which is x + y -f a.
  The forces which tend to change the  state of things are x,
and y + b, the sum of which is x + y + b.
  It is plain, that if a, the difference of the attractions of the
volatile alkali for the two acids,  be equal to b,  the difference
of the attractions of the fixed alkali for them, then x +  y  + a
is equal to x + y + b, and no change can happen. -
  But if b be greater than a, it is equally plain that x -f-  y + b,
the sum of  the changing  forces, is  greater than x + y +  a,
the sum of the maintaining forces. We must, therefore, have
a change of combinations,  and  must find in the solution sal
ammoniac and Glauber's salt.
  If heat  be applied to this mixture,  the difference of attract-
ing forces will be still more increased; because this, by in-
creasing the  volatility of the volatile  alkali, and the muriatic
acid,  will weaken their connection with their primitive  and
more fixed bases.
  There are many  other ways by which the  vitriolic ammo-
niac  can be decompounded by double elective attraction, but
they will be mqrc easily understood hereafter.
   vol.  n.   "**"  ^||         Q. 
122
                    SPECIES VIII-

              NITROUS AMMONIAC.

  Nitrous Ammoniac, or Nitrum Semivolatile, or Nitrum Fhm-
mans, is fusible, volatile, and inflammable.  The volatile al-
kali contains inflammable  matter, as may be seen by  trying
all the ammoniacal salts with melted nitre.   It cannot be dis-
tinctly observed in the alkaline crystals themselves, on account
of their too great volatility, which makes a violent ebullition,
and seems to keep the nitre from coming into  contact with
them.  But in7 all cases where they can be made to mix in red
heat,  the inflammation is  even  brilliant: for  example, if the
vapour of melted nitre  be made to pass through that of vola-
tile alkali.
  This salt  dissolves readily in water;  and,  with the assis-
tance  of heat, very copiously.  This seems to proceed from
its fusibility, for it is not remarkably deliquescent.   It is de-
composed for the acid by vitriolic acid, and for tfre volatile al-
kali by either of the fixed alkalis.
  It is said to be contained in the juices of some plants, and
that it is often found in natural efflorescences ;  but when we
have occasion for it, we.always prepare it by art.  It is neces-
sary to observe  the caution of  evaporating the solution of it
with extremely gentle  heat;  for,  if we  go on with  a strong
one,  we may be deceived, and evaporate  the whole salt before
we are aware.  (See Note 33. at the end of the Volume.}


                     SPECIES IX.

                  SAL AMMONIAC.


  The last of these salts, the common sal ammoniac, ox crude
sal ammoniac, is the best known,  and the most useful; and it
is a considerable object of manufacture and commerce.' When
we examine by trial how it is affected by he#, we find it is one
of those bodies which,  under the ordinary pressure of the air 
SAL AMMONIAC.               1-23
  are more easily changed into vapour than melted ; and there-
  fore, when heated, it totally evaporates in white smoke, be-
  fore it be heated enough to make it melt.  It has nearly the
  same attraction for water as common salt.   It deliquiates in
  damp air, and dissolves in  about  three waters.  In solution
  it produces  20 degrees of cold, by Fahrenheit's scale.   It is
  easily decompounded, so as  to give either the acid or the al-
  kali pure. But we never take the trouble to separate the  acid,
. which  may be  got from  a much cheaper salt.  It is only for
  the sake of the alkali that we decompound this salt; the alkali
  which it yields being the purest volatile alkali.
    This decomposition may be effected by means of either of
  the fixed alkalis, in their ordinary mild state.  A quantity of
  pearl ashes, salt of tartar, or soda, is mixed with about twice
  its weight of sal ammoniac; and  the mixture is put  into a
  wide-necked retort, and treated in the way of distillation.
    It is usual to add water to facilitate the action of the salts,
  and the condensation of  the volatile alkali, which is difficult
  to condense  without water.   As soon as  the retort becomes
  warm, the alkali, and a part  of the  water,  begin to distil over
  together.  But the alkali comes in greatest quantity at first,
  on account of its being the most volatile; and the water, which
  comes  with  it at first, is not  sufficient for dissolving it: A
  great part of it,  therefore, condenses, in the  form of a saline
  crust, on the internal surface of the receiver.  But afterwards,
  a larger proportion of water comes over with the rest of the
  alkali; such a proportion as is sufficient  for dissolving very
  nearly the whole of it.   Thus, we have a saturated solution
  of volatile alkali in water, which, when prepared in this man-
  ner, is called spirit of sal ammoniac.
    The London chemists prepare a dry volatile alkali for smel-
  ling bottles,  which is much  more volatile  than the sal ammo
  niaci volatile, cum creta.   They decompose the salt with fixed"
  alkali, luting up the vessels  very close, with a paste of floui
  and glue,  and by taking all methods  of cooling the receiver.
  In this way, they get half the weight of the sal ammoniac.
    Origin......Tnis salt is not found native  in such quantity as
  to serve any of the uses to which it is applied.   A small ap- 
124              SAL AMMONIAC.
pearance of it is sometimes met with in the neighbourhood of
volcanoes,  and upon stones thrown out of those mountains;
also  in clefts of the ground, or of rocks in the neighbourhood
of coal-pits which had been accidentally set on fire, and have
continued to burn for a long time :  but such specimens are
extremely rare and trifling.  The great quantity of this com.
modity consumed in Europe was, for  a long time, imported
from Egypt, where it was known  and manufactured,; and
sometimes quantities of it are brought from some parts of In-
dia.   It was late, however, before any distinct accounts were
published of the manner in which it is manufactured in Egypt.
We  were only told  that soot was the principal article employ-
ed ;  until some French gentlemen, who were  in Egypt, hav-
ing given particular attention to it, communicated a detail on
thi^  su ject to the Academy of Sciences.   Their account was,
that  the fuel of the  districts in which it is manufactured is the
dung of cattle, dried in the sun ; that the soot is collected, and
without any addition, put into glass globular vessels.   These
they fix in the vault of a furnace, which has the form of a sort
of oven, built in the open air, and apply fire cautiously, &c.
   When this account was published, it was supposed that the
production of sal ammoniac depended on the particular nature
of th soot, or of the fuel from which  that soot is produced.
But  it has been discovered that soot of other kinds of fuel, and
pit-coal among the  rest, can be  made to afford it; and several
manufactories of it  are now established  in Europe, which pro-
duce it of the best quality.
   From its being observed also that the great laboratories of
sal ammoniac also prepare Glauber's salt,  employ much vitri-
olic  acid, and do not purchase the muriatic acid, it is conjec-
tured that the volatile alkali is first prepared from the soot,
then made into vitriolic ammoniac,  and this mixed with sea
salt, and the mixture sublimed.   In this process, a double ex-
change must take place :  and we must obtain sal ammoniac in
the receiver, and Glauber's salt must remain in the retort.
   This salt is used  in medicine, and in tinning iron or copper;
and  in some o'her manufactures. 
            REGENERATED TARTAR.          125

  The salts  which contain the acetous acid are regenerated
tartar and acetous ammoniac.


                      SPECIES X.

            REGENERATED TARTAR.

  Regenerated tartarwas so called, from its componentsalts,
the one being the salt of tartar, or the vegetable fixed alkali,
and the other, one of the vegetable acids.  It was supposed
that these, when joined together, should produce a salt like
tartar, in its  entire  state, or a regenerated tartar.  But we
now know perfectly well,  that the acetous acid which this salt
contains,  is quite different from  the acid of tartar; and, ac-
cordingly, the compound salt is not a regenerated tartar, be-
ing very different from tartar.  It was formerly called saldiu-
reticus, in the London Pharmacopoeia; lately they have chang-
ed this name to kali acetatum.
   This salt is always made artificially, by joining pure vege-
table alkali with the acetous acid in its purest state, or distil-
led vinegar.   A large proportion is necessary to saturate the
alkali, on account of its being an extremely weak or  diluted
acid.  A phenomenon occurs in making this mixture,  which
Dr. Boerhaave mentions, and could not  account for.   When
vinegar is first added to the alkali, it dissolves it without per-
ceptible effervescence.  But after more of the acid has been
added,  so that some part of the  alkaline salt is saturated, fur-
ther additions cause  it to effervesce violently, as in other cas-
es, when acids and alkalis are joined together.   This pheno-
menon we shall soon have an opportunity to explain.
   The process for making this salt is best conducted by put-
ting a quantity of pure fixed alkali into an evaporating bowl,
adding distilled vinegar, and evaporating the salt almost dry.
Then more vinegar is to be added, and evaporated, until fur.
ther additions of vinegar do not produce an effervescence: and
it is better to*add a little  too much than too little.   Every
time the evaporation is performed, it is only the watery parts 
 126              SAL  DIURETICUS.

 that exhale;  the acid remains combined with  the alkali.
 When full saturation is  obtained,  we may evaporate to dry.
 ness, which must be done with  a very mild heat.  Thus we
 have a salt of a dark brown colour, and very  unctuous and
 foul.  A quantity of faeculent unctuous matter is extricated
 from the vinegar, when evaporated to dryness along  with the
 alkali, though  it appeared a limpid fluid before.   This unctu-
 ous faeculency is separated from the salt by covering up the
 bowl, and gradually increasing the heat until the salt melt,
 which it does  in such a degree of heat as'is sufficient for eva.
 porating the more volatile parts of the oily matter, and scorch-
 ing or burning the rest, so as to convert it into a sort of char-
 coal.  (N. B. This heat makes polished steel yellow, and
might be measured).   By this means the  salt,  which before
was brown, becomes of an iron-grey colour; and if it be now
dissolved in water, the burnt matter is  rejected or  left un-
dissolved by the water, and forms  a sediment which may be
separated by  filtration ; and  the clear limpid solution  then
affords, by gentle evaporation, a pure and white salt.  .
  Many authors,  in describing the manner of purifying this
salt, advise to do it by dissolving in spirit of wine, which se-
parates part of its foulness from  it, and then the spirit is to be
distilled  off, and  the salt redissolved in  the same  manner
several times.   But, if our only  purpose  is to make it white
and pure, this will prove a tedious and  imperfect method.
The one I have described is much'the best.
  Dr.  Boerhaave, who  extols the virtues  of this salt very
highly, seems to think this purification of no great importance,
or rather that  the salt is a better medicine for retaining the
oil.   He had  a prejudice in favour of every  thing that con-
tained salt and oil blended together; and called all such mix-
tures saponaceous, or soapy.   But  it is certain that this salt
is greatly improved by the purification I have described. The
unctuous matter thus separated from it, has a bitter taste and
nauseous flavour, disagreeable to the stomach: and this is a
bad quality in any medicine intended for the uses to which this
salt is applied. 
TERRA FOLIATA TARTARI.
  The properties of this salt, as thus prepared, are,  that it
melts with a very moderate heat, below red, into a transparent
fluid like oil; and, upon being allowed to cool again, concretes
into a mass  composed of thin plates, or leaves, cohering to-
gether, like the plates  of the earthy or stony substances here-
after to be described  under the name of talc  or mica; for
which reason some of the elder chemists named it very im-
properly terra foliata  tartari.   When mixed  with water,  it
shews a great degree of solubility,  greatly exceeding every
other compound salt.  It is so deliquescent that it is not easy
to keep it dry\   It is also soluble in vinous spirits,, and is thus
purified from other salts.  When it  is to be separated from
water, this  is done  by evaporation to dryness with  a very
gentle- heat,  stirring often  in the end.  The salt concretes in
the form of a white  scum or skin, which, being drawn to one
side, is quickly renewed, until the whole water be thus evapo-
rated.   The salt is then a spongy mass,  as white as  snow,
 which, if the heat be increased, melts and  forms the foliated
 mass which I described.
    When we desire to decompound this salt, we may do it so
 as to have either the alkali or the acid pure.
    If we would have the alkali,  we  need only to put the salt
 into a crucible,  and heat it gradually till it becomes red hot.
 That degree of heat burns and totally destroys the  acid; dissi-
 pates great part of its principles in the form of fcetid vapours,
 which are partly watery,  partly oily, and partly  aerial;  and
 leaves only remaining with the alkali a quantity of black car-
 bonaceous and other matter, which can be  separated without
 difficulty.
    If we desire the acid, we can detach it by any of the fossil
 acids, of which the vitriolic, however, answers best, and  is
 employed sometimes for this purpose, when an acetous acid
 of  extraordinary strength is desired.  But  this  purpose  is
 better accomplished by means of the next salt in the column,
 namely, 
126
                     SPECIES  XI.

      THE  ALKALI FOSSILE  ACETATUM.

    This  consists of the acetous acid united to the fossil al-
kali.  Its properties greatly resemble those of the  salt now
described, only it melts  more readily.   It congeals in plates,
and is destructible by a great heat like the other.   It  dis-
solves copiously  in water, and  is easily separated from the
water by crystallization, forming very fair crystals ; whereas
the other is crystallized with difficulty.  This salt is  better
suited to the purpose of obtaining a strong acid by decompo-
sition, because it is easily kept in the form of a dry powder,
not being disposed to deliquiate, except in very damp air.  It
is therefore much prepared in Germany for this purpose, by
the name  of  sal  vegeto-miner ale.  It is not,  however, by the
simple mixture of its component salts that it is manufactured;
as I am informed by a person who long conducted the process;
but by double elective attractions, employing Glauber's salt,
and a salt consisting of  lead combined with the acetous acid.
When the salt thus prepared is decompounded by vitriolic acid,
the acetous acid is detached in a most concentrated and  active
form, equal in acidity to the  mineral acids,  though weaker
in its elective attractions, and possessing all its native valuable
qualities.


                     SPECIES XII.

               ACETOUS  AMMONIAC.

    Acetous ammoniac, or vegetable ammoniac, or spiritus Min-
dereri, when in a liquid form, so called from the author's name,
is a composition always produced by art.  It is very volatile,
being little inferior to water in volatility, and at the same time
of great solubility.   It  cannot be evaporated  dry.  A great
part of the water, however, can be separated  by slow distilla-
tion or evaporation: and we thus obtain a saline fluid of a 
              ACETOUS  AMMONIAC.            129 .

thickish consistence, like oil  or sirup, and of a brown colour,
which, if the heat be continued, evaporates entirely away with-
out yielding any dry part.... It is of a penetrating quality.  If
we  desire  to have a vegetable ammoniac in a dry form, we
may have it by a double elective attraction.  The sal vegeto-
minerale and common  sal ammoniac, for example, will give
it;  the muriatic acid uniting with, the fixed alkali, while  the
more volatile acetous acid unites with the volatile alkali.  For
similar reasons, we may employ a mixture of vitriolic ammo-
niac, and the salt, which I mentioned lately, consisting of lead
combined with the acetous acid.  This last will more certainly
insure the dry form of the salt obtained; but it will differ, I be-
lieve, from the salt obtained by the other process,  containing
less of the distinguishing property of the acetous acid; contain-
ing it in a state which may be called the acetic, while the other
is called the acetous.
  The different ways by which it may be decompounded are
obvious: but we never have occasion to decompound it.  The'
only point that deserves attention with regard to it, is the com-
pounding  it properly, or uniting its two  ingredients,  so as to
produce it  in perfection.  This is done by choosing good dis-
tilled vinegar,  which has been distilled  carefully,  to avoid a  •
burnt taste and flavour, and a pure volatile alkali, prepared
from  sal ammoniac.  That which is prepared  from  animal
substances  is unfit.  And further, these materials must  be
mixed so as to be exactly neutralized, the one by the qther.
Thus, it will be best fitted for  the purposes of medicine, for
which it is intended.
  Having described the salts in use which contain the acetous
acid, we proceed to those which contain  the acid of tartar.
  The compound salts, commonly known and in use, which
contain the acid of tartar, are, 1st, soluble  tartar ;  2dly, com-
mon tartar; in both of which this acid is  combined with the
vegetable  alkali  in  different  proportions;  and  3dly,  the
Rochelle salt, sal Rupellensis, or sal polychrestus Rupellensis.
in which this acid is combined in part with fossil alkali.
    vol. tt.                 k 
130
•
               SPECIES XIII.....TARTAR.
    You, no doubt, remember the appearance and properties of
 the acid of tartar.   It differs from the fossil acids,  and from
 the acteous, by being- capable of evaporation to dryness, and a
 sort of crystallization ;. which evaporation, however, must be
 perfoi  ned with a very gentle heat.  The dry acid thus obtained,
 resembles in appearance brown sugar, or sometimes is whiter.
 And, when we expose it to a burning heat, or heat of  igni-
 tion, it is burnt and destroyed in  the same manner as sugar,
 or other  vegetable substances>  It is dissolved easily, and in
 large quantity, by water, forming a solution which has the ap-
 pearance of a sirup, but is exceedingly sour.
   The  nature of this acid, and of the compounds which it forms
 with alkalis, \\y.s not explained fully and clearly until the inge-
 nious Dr. Scheele of Sweden gave a set of decisive experiments
 upon this subject.   It was he who first exhibited this acid in
 iti separate state,  and who shewed how easily it  is destroyed
 by tm ,  vithen needing to be joined to a fixed alkali, as the ace-
 tous acid doe?.   Dr. Scheele has  also  shewn,  that  it differs
 from all the other acids, by a disposition to form with each of
 the alkalis two differt nt compound salts,  in consequence of its
 being capable of  uniting with each of them firmly in two dif-
 fert nt proportions.
   When to the solution of an alkali in its ordinary  state we
 arid a certain quantity of pure acid of tartar, we have efferves-
 cer.  e;  and we form the  compound salt, named  in  the table
 "Jen-tent'; solubilis,  similar in  nature to other neutral salts,  in
 which neither acid nor alkali can be  perceived to predominate.
 But,  af,er having done this,  if we  add more of the acid, al-
though  there is  no  more effervescence,  a certain  quantity
of this  superfluous  acid joins  itself to the neutral salt  wc
had  formed  at  first,  and adheres to it strongly, constitu-
ti'ig with it another compound salt,  composed  of the same
acid and alkali, but in which  the acid predominates.  It is no
longer a neutral salt, but shews the qualities of an acid, in mix-
ture with other substances.   It is this acidulous compound of
the tartarous- acid wi;h the vegetable alkali  that is  best known i 
TARTAR.                     131
and most useful;  it is called simply tartar.   It is much used
in medicine,  and in some of the arts, and is certainly a very
valuable article of the materia medica, on account of its deob-
struent and codluig powers.  It is, therefore, worth wiiile to
attend to its hisRry and chemical qualities.
   Tartar is not an artificial substance, but is produced by na-
ture, in the juices  of some vegetables,  from  which we acquire
it.   The juices of  many vegetable fruits  contain compounds
of this kind, which resemble tartar  more or less.   But he spe-
 cies of this  saline substance that is in  common use hi medi-
cine and the arts, is obtained from the juice of the grape, Jer-
mented to a wine.  The sharper wines contain the most of it,
the  Rhenish especially ;  and, when long kept, deposit the tar-
tar,  which concretes  by crystallization  to the internal surface
of the cask, in the form of a coarse and feculent  saline crust,
called wine-stone or argal.  The wine itself is considera-
bly improved by this separation, &c. becoming more smooth
and palatable, and being therefore more valued.
   At the same time that tartar  thus crystallizes, some of  the
colouring matter of the  wine separates along with it. Hence
we  have red tartar  and white tartar.  Neither  of them is
employed in  medicine,  or much in the arts,  in  their native
impure  state.  They  are commonly  made to undergo a
refinement, by which the  colouring matter  of the wine is sepa-
rated, and the tartar is also made purer in other respects.  This
is done by solution in boiling water, clarifying the solution and
crystallizing.   Thus are produced white crystals, or crystal-
lized masses, called crystals of tartar.   I must refer vou for a
particular account of this verv considerable manufacture in the
wine countries, to Macquer*s dictionary, Rozier's. Journal de
Physique, torn, i.67; and to the  dissertation of Mr. Fizes, the
inventor  of the most approved French process,   as  practised
near Montpellier,  published in the  Mem. Acad, des Sciences,
1.725.
  This  refined or crvstallized  tartar is beaten to powder by
the  apothecaries,  and kept in that  form for  use ;  and in that
state is often called for and prescribed under the name of cream
of tartar.  The reason of this denomination is, that it was long 
132
CREMOR TARTAR!.
procured by evaporation to a pellicle, which was skimmed off
like cream, and is renewed almost as fast as it is removed.
  Let us now examine the chemical qualities of this substance.
  When exposed to a burning  heat, the acid,  as  you might
expect,  is consumed  and destroyed ;  and we find the alkali,
with which it was combined, in the coal or cinder that remains.
  We had occasion to remark formerly, that the alkali of tar-
tar is remarkably pure.  The burning  of this salt is  therefore,
an operacion frequently performed to obtain it; and  the alkali
thus obtained was  formerly called salt  of tartar.  The prepa-
ration of it is prescribed in all the pharmacopoeias.
  It is a very simple process, and may be performed either by
burning the tartar  in a crucible.or an iron pot, or by laying it
among burning coals in a moderate fire.  A strong fire would
be unfit for this purpose,  as being capable  of melting or even
evaporating the alkali.  It is usual  to take the crude tartar,
and  to wrap  it up  in wet paper before  it be put into the fire;
it then singes and  coheres like feathers or hair, and forms a
spongy  cinder or coal,  which must be left in the  fire until it
ceases to give smoke  and flame ; after which we  shall find it
easy to extract  the alkali from  the earthy and coaly  matter of
the cinder by water.
  When  we next  examine the nature  of tartar, by  mixing it
with other substances, we find, first, that it has but little solu-
bility in water, especially if the water be cold.  It then not only
dissolves slowly and with  difficulty,  but requires a very great
quantity of water.   To make the tartar dissolve more readily,
we must  apply the water boiling hot,  or boil them  together.
Even of boiling water, eighteen or twenty times its weight are
required: and when the solution becomes cold again,  the tartar
separates bv  crystallization almost entirely.
   In mixture with other things,  tartar shews the  qualities of
an acid, inconsequence of the  predominant or  superfluous
acid which it contains.  It reddens the vegetable colours,  and
it effervesces with alkalis.  The  alkali unites with the super-
fluous part of  the acid,  and changes the tartar into a perfect
neutral salt.  With the vegetable alkali it forms soluble tartar,
or tartarized tartar.  With the fossil alkali it forms  Rochelle 
 DISCOVERY OF THE PURE ACID OF TART. 133

salt, sal Rupellensis, also called sel polychreste of Seignette,
a mixed neutral, containing two alkalis.   With the volatile al-
kali it  forms another mixed neutral, which has not been ap-
plied to any use.
  All  these neutralized tartars are much more soluble in wa-
ter than tartar itself; and  hence the name of soluble  tartar
which  they had in common.   They can  be  decompounded
again,  so as to restore the tartar to its former state, by adding
any fossil acid, or even  the acetous.  The added acid joins
with the neutralizing part of the alkali, and thus restores the
tartar to  its former condition.   This has been known to hap-
pen in prescriptions, by the acid of tamarinds.  But it is re-
markable, that, after the other acids have thus separated the
neutralizing part of the alkali, they have little  power over the
rest, and act on it but slowly and imperfectly.  The abundance
of the acid  of tartar defends it from their action ; a case which
occurs not  unfrequently  in  chemical combinations.
  You now understand what  sort  of neutral compounds are
formed,  when we saturate with the different alkalis the super-
fluous  acid contained in tartar  or cremor tartari,  and in what
manner this acidulous compound salt may be decompounded.
  In the first place, if we desire the alkali, the common way, as
I observed before, is to destroy and consume  the acid by fire.
The alkali remains unchanged.
  The manner of obtaining the pure acid part of tartar is not
so obvious ; because, as I have just now observed, the acids
which may be employed for disengaging it, after having com-
bined with what may be called the neutralizing part of the al-
kali, act  but feebly on the rest,  and detach it still united with
part of the tartarous acid: and we obtain an acidulous salt
which  resembles the cream of  tartar so much,  that it Avas con-
cluded to be the .same, and chemists inquired no further about
it.  The decomposition  of the tartarine neutrals  seemed as
good as that of nitre or  common salt.
  But Dr.  Scheele was  induced,  by many reasons,  to  think
that this decomposition was very imperfect.
  When chalk, or some other  earthy substances of the same
nature, which we shall soon describe, is thrown into a hot so. 
134
TARTAROUS ACID.
  lution of tartar, it produces an effervescence,  which is renew-
  ed by* more chalk, until a certain quantity has been added, af-
  ter which no more effervescence can be produced. The liquor
  being then allowed to cool and settle, deposits a plentiful white
  sediment.
    Dr. Scheele, examining the clear fluid from which this se.
 diment had subsided, found  that it contained a tartarus solu-
 bilis, or neutralized tartar.  He therefore concluded that the
 chalk had  deprived  the  tartar of  a superfluous  acid  which  it
 contained, and had left no more combined with the alkali'than
 what was necessary to constitute a salt perfectly neutral.
    This idea induced  him to examine the sediment:  and in  it
 he actually  found a part of the acid of the tartar, combined
 with the chalk.  They form together a compound, which has
 very little,  or scarcely any solubility in water.  The moment  it
 is formed, therefore, it concretes into a quantity of small crys-
 tals or concretions, like fine  sand, much exceeding the chalk
 employed.   And as by this want  of solubility it resembles  a
 compound of chalk and vitriolic acid,  to which the chemists
 and natural historians formerly gave the name of selenites, he
 called the new compound which he had discovered,  selenites
 tartareus.
   He next discovered that  the  acid of tartar may be  extract-
 ed from  this, compound, by the  action of the vitriolic acid,
 which has a stronger attraction for the chalk than the acid of
 tartar has.
   When  I  say this,  some of you may  perhaps imagine that
 it may be extracted by an operation similar to that by which
 the  nitrous and muriatic  acid  are obtained from nitre and
 common salt;  I mean by adding the  vitriolic acid, and then
 distilling  the mixture, that the acid of tartar may rise in dis-
 tillation.  But if any person  imagines such a process could
 succeed, he has forgot the nature of the acid of tartar.  The
 acid of tartar cannot be distilled.  It cannot rise with water in
distillation, but remains behind, while the water is distilled or
evaporated from it.  And when we attempt to  convert it into'.
vapour after this, it is destroyed by the heat, in  the same man- .
rrer as wood or sugar, or the like vegetable substances. 
                   ACID OF TARTAR.              135

    But distillation in this case is not necessary. The separation
  is practicable,  in  consequence of the difference of solubility.
  The acid of tartar is exceedingly soluble in  water.   The vi-
  triolic selenite, from which it is to be separated, has very little
  solubility.  To obtain the acid  of  tartar by itself,  we  must
  therefore proceed in this manner:  First,  wash away all the
  neutral salt from the selenites tartareus;  and, secondly, add a
  proper quantity of vitriolic acid, diluted  with  four  times its
  bulk of water.   This acid immediately unites with the chalk,
  and separates from it the acid of tartar.   The  vitriolic  acid,
  in uniting with the chalk, forms with it a compound that is al-
  most insoluble in  cold water, and forms  a white sediment in
  this process.   The acid of tartar, being, in its separate state,
 exceedingly soluble, is found dissolved in the clear part of the
 fluid, after the  sediment has subsided, and can be poured off;
 or it may be filtrated ;  and  then we can  evaporate it with a
 gentle heat to dryness ; or it may be crystallized.  As first ob-
 tained,  however,  it is not perfectly pure ;  a  small portion of
 the vitriolic selenite adheres to it.   But it can be purified by
 dissolving it again in a small quantity of water, which will leave
 the selenite undissolved.
   We have now, therefore, a clear view of the nature of tar-
 tar, and of the acid which it contains ; which is truly singular
 in many respects : for, besides being capable  of uniting firmly
 with alkalis, so as to form either neutral  or  acidulous com-
 pound salts, it adheres to the alkali, with different degrees of
 force, according to the quantity of it.   The other  acids, the
 fossil for example, or the acetous, when  applied to a neutral
 or soluble tartar, very readily unite with,  and separate  from
 it part of the alkali ;  and thus reduce it to the state of-tartar
 again, or  cremor  tartari.   But, after they have done  this,
 they have much less power over the remaining alkali which it
 contains.  The abundance of acid of tartar with which it is
 combined, defends it, or adheres to it more stongly ; and pro-
 bably repels the particles of the other acid. - It does not, how-
 ever, prevent entirely the action of the fossil acids : for if these
are applied in large quantity to the  cremor  tartari,  they cer-
tainly produce a decomposition of it, by uniting with  the alkali. 
 136           VARIETY OF TARTARS.

   But the difficulty or impracticability of decompounding it,
 by moderate quantities of other acids,  concealed the nature of
 this compound salt for a long time.
   It is also remarkable, that, although the vitriolic acid  de-
 taches the acid of tartar from the alkali, the pure acid of tartar
 will partly decompose the vitriolated tartar, nitre,  and diges-
 tive salt.
   To finish this subject, I shall only further notice, that as soon
 as I learned this process of Scheele's, I discovered that the
 acid of tartar may be 'extracted more completely by a little va-
 riation of Dr.  Scheele's  process,  viz.  by using quicklime in
 place of chalk.   But of this more hereafter.
   I must also  observe, before  quitting this subject of tartar,
 that, besides this agreeable acid obtained from the fermented
juice of the grape, there is a variety  of acidulous salts obtain.
 able from other vegetables, in  their native state, which seem
 to be of the same kind, or at least very analogous to the tartar
 already described.  I am convinced,  from repeated  experi-
 ments made by myself, from the very  beginning of my che-
 mical studies, that all the native vegetable acids, whether those
 which are  unfolded during the  maturation of their fruits, or
 those contained in the native juices of the plants, as we find it
 in the whole tribes of rumices and acetosse, resemble the tartar
 of wine in this chief circumstance,  that they contain  a fixed
 alkali in their composition, super-saturated with an acid.  All
 these dry salts, and sour juices, give the same alkali by incine-
 ration* Their differences  seem  to proceed entirely irom small
 variations in the acid, consisting  either in a different propor-
 tion of the parts truly saline, or  more generally from mucilagi-
 nous or resinous matter.  These varieties are the characteris-
 tics of the different kinds,  the chief  distinctions of which are
 the degrees of solubility of the compound salts, formed by their  '
 union with the  alkali.  All of them are equally destructible by
 fire, and incapable  of being volatilized.   I  am therefore  dis-
 posed to think  that the r«*al acid is the  same  in all, and  that
 their distinctions arise from ingredients not saline.   One of.  i
 these forms is  theaartar of wine.   I would say that another
 forms the tartar of  sorrel, &c.   In short, I would call them all 
                        BORAX.                     137

tartars, were it not that it is a barbarous appellation.  I am fur-
ther of opinion that they are all ultimately resolvable into ace-
tous acid.   I think that their denominations have been mul-
tiplied without reason: Malic, citric,'oxalic, &c answer no
purpose.

                     SPECIES XIV.

                        BORAX.

    We come now to the  last compound salt in the  table,
Borax.  This salt was long known and employed in the arts,
before the nature and composition of it was understood.   The
chemists found that it possessed some alkaline  qualities, as
taste, and changing vegetable colours to green.   They were,
therefore, inclined to consider it as a particular species of al-
kali.   But this idea of it was not readily adopted, on account
of its not effervescing in the least with acids.  At last, how-
ever, its nature was thoroughly explainedjby the experiments
of some of the French academicians, which shewed it to be a
compounded salt, containing that peculiar acid, the sedative
salt, joined  with the  fossil alkali.  And hence  the  alkaline
qualities of it appear now to be a consequence of the weak-
ness of the  acid with.which the alkali is  combined in  this
salt.
  All the Borax used in Europe has hitherto come from the
East Indies, in the form of crystals, which cohere together by-
means of unctuous matter;  and the whole is called Tincal, or
Tinccl paste.  This Borax is refined in Europe by a process  -
which is still kept secret;  and  was for a long time practised
only in Holland, though surely there  can be no great mystery
in it.  The  refined borax  is sold to goldsmiths, and  other
artists, who make use of it in the form of  large crystals, some-
what resembling alum.
  The effects of heat shew that there is much water in the
composition of these crystals.   They readily undergo  the
watery fusion, and then swell up into a very spongy blistered
mass.  When the water is at last  dissipated, they become a
dear glassy salt, having all the  tough ductility of glass when
    vol.. n.                  s 
*38            ANALYSIS  OF" BORAX.

hot, and, when cold,  splitting and breaking precisely like a
piece of glass.  But it is still  a perfect salt,  dissolving
completely in a large portion of water, and crystallizing as be-
fore.
   The  compound nature of this salt is easily demonstrated,
and the two  ingredients of it separated  from one  another.
The easiest and shortest method to separate the sedative salt
is to dissolve the borax in a small quantity of hot water, and
to add a proper quantity of any of  the fossil acids, which im-
mediately  unites with the  alkali, and then allow the solution
to cool.  The sedative salt separates by crystallization.   This
is the only example of the decomposition of a salt in this par-
ticular manner.  I  may add,  that the  alkali is obtained in its
purest state, when we employ the nitrous acid for the decom-
position, and then deflagrate the cubic nitre.
   From the process, it is plain that fossil  acids have a much
stronger attraction  for the  alkali than the. sedative salt has.
There  is,  however, a fact  which,  when  I mention it,,  will at
first appear  inconsistent with this  superiority  of attraction.
The fact I mean is  this, viz. the  decomposition of nitre and
common salt by sedative salt.   It is not? however, inconsistent
with what happens in the process,  but  is an example of an
elective attraction in consequence of heat.   The volatility of
the nitric or muriatic acid,  when the compound is  urged by a
great heatr diminish its attraction for the alkali, while the at-
traction of the sedative salt  suffers little or no diminution.
The sedative salt has not, however, the power to separate the
vitriolic acid in the same manner.   If we mix some crystal-
lized sedative salt with Glauber's salt, or vitriolated  tartar,
and expose the mixture  to heat, nothing happens but the sub.
limation of a small part of the sedative salt.  Hence the pro-
cess for sedative salt by sublimation.  (Vide Experiments on
the Sedative Salt by Bourdelin,  Mem. de I'Acad. 1753 and
 1755.)
   Borax is  used in melting  gold, silver,  and sQtne  other
 metals, and  in  soldering  them,  and in  the composition of-'.;
 very fine  glasses,  or pastes  as  they are called.  It  is also  '
 exceedingly  useful in making experiments with the  blow- •
•  ipe« 
ORIGIN OF BORAX.
139
    With respect to the origin of this salt, I said already that
  hitherto all that  we have had  in Europe has been imported
  from the East Indies, under the name of tincal, or tincalpaste.
  The account given of its origin in that part of the world is, that
  it is  produced from the waters of certain  mineral springs,
  which, being  evaporated by the heat of the sun,  afford this
  salt.   (See several  partitulars relative to the production of
  borax, in a letter from Mr. Blane at ^Lucknow, Phil. Trans.
  vol.  77. Part 2d.) Nothing  like  it,  however, had been ob-
  served in any of the mineral waters  of Europe, until a few
  years past, when, in Tuscany, the Duke's apothecary having
  examined certain hot springs in a  volcanic part of his High.
  ness's dominions,  found various salts and other mineral sub-
  stances, which had been deposited by the waters; and, among
 .these saline substances,  he found considerable quantities of
 sedative salt, from which we are told borax has since  been ma-
  nufactured.  This I had occasion  to mention when speaking
  of the sedative salt.
   Borax and tartar, or cremor tartari, afford a rare example of
  two compound salts uniting together, and acting somehow on
 one another without the decomposition of either.  This appears
 when we mix sixteen ounces of cremor tartari with two ounces
 of borax.   We should expect something like  this ;  for tartar
is sensibly acid, and  borax  is sensibly alkaline.   These salts
 enter into some sort of union,  in consequence of which the
 cremor tartari becomes very soluble in water,  although it still
 retains its acidity as before.  No part of its acid appears to be
 taken  from it by  the borax,  nor  is the borax itself decom-
 pounded ;  for no part of the sedative salt separates by crystal-
 lization.  This may,  therefore, be considered as  a case  in
 which chemical attraction has sufficient power to produce one
effect, yiz. a diminution of cohesive attraction, but not enough
 of power to produce  the  full effect, which is produced in the
 most of such cases, I mean exchange or decomposition.  The
 German physicians,  I am informed, make use of this power
 of borax to increase the solubility of cremor tartari in phar.
'macy and prescription. 
140
  SYNONYMOUS  DENOMINATIONS OF  THE
                        SALTS.
                         i                  «
  Many of these  salts, which I  have described  as  resulting
from the combinations of the alkalis and the acids, were sub-
stances  never seen, or never observed before, and  therefore
were things without a name.  Yet they must be denominated.
Their names were given in consequence of some circumstance
accompanying their  formation.  Sometimes  the ingredients
from the admixture of which they resulted ;  such as vitriola.
ted tartar, tartarized tartar....sometimes expressing what was
thought to  be  their nature,  regenerated tartar....sometimes
from their medical effects, real or supposed,  digestive salts....
sometimes from their discoverer, or the place of  their first ap-
pearance} Glauber's salt, Epsom salt....sometimes from mere
whim,  sal de duobus, arcanum duplicatum, &c.
   Moreover, as what occurred to one person in  the course of
his chemical operations may as readily occur to  another, and,
particularly, as the same ultimate composition may result from
very different processes, it must have often happened,  that a
substance denominated in one way by one discoverer, received
a different denomination in  the hands  of another chemist.
And it may often be some time befofe these two names are
found  to belong to one and the  same substance; and  it may
 even require a good deal of examination to prove the identity.
   From such causes as these, it has happened  that almost every
salt that I have mentioned has been known by several different
 names.  Not only the accidental circumstances  now noticed,
 but also  the languages of different nations  and of different
 classes of people, have  augmented  this  list of synonymes.
 Novel objects imported from other countries, will retain, ina  \
 different language, the name which they had at  home.  Men
 of science will sometimes  allow a  thing to retain ftie name
 which it got among the workmen in whose daily occupations  J
  it first occurred.  Such names, having no other significancy,'
 will be considered as pure appellations, or proper names. *    >
    In reading the writings of the chemists, we shall be in a con- V
  tinual puzzle, and may often be obliged to go back through a 
   BERGMANN'S NEW NOMENCLATURE.   141

  train of discussion,  before w% are certain what substance
  it  is whose effects and properties are engaging our atten-
  tion.
     Therefore, I thought that it would be useful to collect,
  under each of the denominations that we have been  con-
  sidering,  all the  synonymous  appellations by which you
  will find them mentioned in  the  chemical  writings.   This
  will appear a disagreeable farrago at first  sight,  and many
  names will appear ridiculous or barbarous; but our future
  disquisitions will frequently  shew  some reasonable ac-
  count for theif acquiring such names.
     For  a long series of years,  while  chemistry  was only a
  collection  of processes in the  various chemical arts, these
   denominations being accidental,  and in  the language of
  persons of no general cultivation, were altogether anoma-
  lous, and  frequently  suggested  very false notions of the
   objects. ,  As chemistry'began to assume a scientific form,
   and its professors were persons of more  extensive know-
   ledge, these improprieties were observed, and great incon-
   venience was frequently7 found in employing them.   At-
   tempts were therefore made by  some  chemists to reform
   the nomenclature, by  reducing it to some rule, founded on
   a principle pervading the whole, and equally applicable to
   any new discoveries which may be made from  time to
   time.
      The first of these attempts,  of any note, was made by
   the late  Professor  Bergmann of Sweden, whose essays
   and  treatises on  different subjects in chemistry contain a
   rich fund of accurate experiments and useful facts.   His
   plan was this.....
      In the  first place, he named the alkalis and acids as they
   are named in the table before you.   And the compound
   salts were expressed  by the  name of the alkali  which they
   contained, with an adjective formed from the name of the
   acid; thus,

.. ;. Vitriolated Tartar         is
  . Glauber's Salt
  Vitriolic  Ammoniac
   Nitre
   Cubic Nitre
Alkali vegetabile vitriolatum.
Alkali fossile vitriolatum.
Alkali volatile vitriolatum.
Alkali vegetabile nitratum.
Alkali fossile nitratum. 
 142  BERGMANN'S NEW NOMENCLATURE.
• Nitrous Ammoniac        is     Alkali volatile nitratum.
 Digestive Salt                  Alkali vegetabile salitum.
 Common Salt                  Alkali fossile salitum.
 Common Sal Ammoniac          Alkali volatile salitum.
aejjrnera-ed Tartar or Sal    1    A,k u veffetabile acetatum.
  Diureticus              5
—    __    __                 Alkali fossile acetatum.
Vegetable Ammoniac            Alkali volatile acetatum.
Soluble Tartar                  Alkali vegetabile tartarisatum.
Rochelle Salt                   Alkali fossile tartarisatum.
__    __    —-                 Alkali volatile tartarisatum.
Borax                        Alkali fossile boraxatum.

   The plan of this nomenclature was suggested by Ibme
 of the old  names,  in which  something like this  was
attempted, though in a bungling and partial manner;  and
 it has the advantage of being applicable to a multitude of
other compounds,  which  contain acids  combined  with
 earthy  or metallic bodies.    It was therefore, well receiv-
ed, and many of these new names were  adopted in the last
 editions  of  the Edinburgh  Pharmacopoeia,  and  in many
 others  abroad.
   It has, however,  been objected that  these  names  are
too long; and, as it is necessary in expressing the particu-
lar state  of some of  these salts,  to add  another adjective,
the name becomes, by its length, cumbersome and disa-
greeable.
   Notwithstanding  this objection, the  advantages of  a
regular and decent nomenclature were  so sensible, that
this  method  became  very  prevalent; and would, in all
probability, have  soon obtained  the acquiescence of all the
philosophical  chemists, had  not the science itself expe-
rienced,  at this very time, a great and almost total revo-
lution.
   A number of most  important discoveries were made,.
about this time,  by  the chemists of Britain, France, and
Sweden,  relating to the constituent parts  or principles of
natural substances.   New objects were discovered, which
required  new names : and some  of the substances already. ',.
known, which had formerly been considered as simple, and) ijl
perhaps elementary,  were now found to be compounded;-^
while ethers, formerly held as compounds, were  now found "J 
 FRENCH THEORETICAL NOMENCLATURE. 143

  to be more simple than the substances of which they had
  been thought to be compounded. This being the case, it is
  plain that, while the method proposed by Burgmann is still
  advantageous,  the construction of the nomenclature must
  necessarily be changed, that it may be consistent with the
  knowledge we have acquired.
    By a most sagacious and careful consideration of those
  discoveries, Mr.  Lavoisier formed an opinion concerning
  the  composition of bodies, and the principles by which this
  composition was  effected, which comprehended the whole
  of chemistry, in such a way as to point out a series of com-
  positions in many degrees of subordination. This mustevi-
  dentlv regulate the construction of a nomenclature,  on Mr.
  Bergmann's plan.   This philosopher, therefore, associated
  several other eminent chemists in his labours, and the study
  soon acquired,  in their hands,  very  great  improvements.
  Assembled in  Paris in 1787, and, confident of the  superi-
  ority of what they called French Chemistry over all former
  doctrines  and theories, they adopted a plan by which they
  hoped to give  it universal currency and authority.   They
  hoped to effect this by means of a nomenclature, so adapted
  to their system, that the  very denominations  of the diffe-
  rent objects should imply the doctrines of their theories ;
  so that, by using this language, it should scarcely be possi-
  ble  to think on chemical subjects, in a way different from
  their  theories.   They framed the language so that the
  composition o/ the most complex substance should be ex-
  pressed by two or three words, modified by proper termi-
  nations, and so that the precise place and degree of subor-
  dination should be clearly and compendiously indicated.
    With this view Messrs. Lavoisier,  De  Morveau, Ber-
  thollet, and Fourcroy, published the Method of Chemical
  Nomenclature,  to which they annexed a corresponding sys-
  tem of chemical characters,  composed  (I  believe)  by
  Messrs.  Adet  and Hassenfratz.  This was  published at
  Paris in  1767,  and is  adopted by  Mr.  Lavoisier in hi*
  Elementsof Chemistry, as also by Fourcroy  and Chaptal
s* and, indeed, by almost all the  French chemists.
,Sf  I cannot here explain to  you the  whole  of this new
  nomenclature.  Many of the facts on which it is founded 
  144        FRENCH  NOMENCLATURE.

  nave not yet  been imlde known to you.   But when we
  shall have advanced further in this course, you will easily
  understand  it, by consulting the books I just now mention-
  ed.   In Mr. Lavoisier's Elements,  the new system and
  new language are  stated  with  the  greatest precision and
  clearness imaginable.   (Dr. Pearson of London has lately
  published a  treatise to recom#nend the new language).  At
  present we  can only give our attention to  the  names pro-
  posed for the salts in that system.   This will be fully suf.
  ficient for enabling you to see and understand the  general
  rules, by which the denominations and the whole  phrase-
  ology are offered and conducted.
    One of the  general rules which they thought it proper
 to observe in contriving  their new nomenclature was, to
 give names  ending with similar sounds, to all the things
 that are analogous in the  mode of composition, and names
 ending with  different sounds to things which differ in this
 respect:  For example,
  ,  First,  the acids, when they are in their most perfect, or
 most powerful, or most acid state, are,
   Acide sulphurique,...acidum sulphuricum,...sulphuric acid.
   Acide nhrique,...acidum  nitricum,...nitric  acid.
   Acide muriatique,...acidum muriaticum,...muriatic  acid.
   Acidum aceticum,...acide acetique,...acetic  acid.
   Acide tartarique,... acidum tar tar icum,... tartaric acid.
   Acide boracique,. ..acidum boracicum,  ..boracic acid.
   But some of these acids appear on some occasions in a
 less perfect,  or less acid, or less powerful state, by reason
 of  a redundancy of their distinguishing ingredients.   For « %
 example,-the vitriolic acid, whenSt is  in its volatile and
 suffocating form,  is so weak an acid in that state,  that
 although  it can be  joined to alkalis,  and form compound
salts,  such salts  can be decomposed by the weakest acids,
such as vinegar, or the acid of  tamarinds, or the acid of
tartar.
   The nitrous acid  is another example. In its mpt^Volatile
and deep-coloured  state,  it  has but a weak attra|fion for;<4,
alkalis and for water, and other substances.             *';'^Ms
  To  distinguish this state of the acid, the French che*'--.-*
mists, instead of the termination -ique, derived  rom the 
            FRENCH  NOMENCLATURE.        145

 Latin -icus -a -urn, which is the form of a generic epithet,
 employ  the termination  -eux,  derived  from  the  Latin
 -osus -a -um, which is the form of an epithet expressing a
 redundancy of the subject or quality.   Thus,

   Acide sulphur eux,..acidum sulphurosum,...sulnhurouiacid.
   Acide nitreux,....acidum nitrosum^...nitrous acid.
   Their names of the alkalis are,
              FOR THE VEGETABLE ALKALI,
   Potasse,... .potassa,.. ..potash.
                 tor  the fossil alkali,
   Soude,...+soda,.... soda.
               FOR THE VOLATILE ALKALI,
   Ammoniaque,....ammoniacum,.....ammoniac.
   In naming the compound  salts they use two words, the
 first suggesting the acid., and the second the alkali j  or, in
 general,  the acidiflable base.
   All the compound  salts, and other compounds that con-
 tain the sulphuric acid in its more perfect state, are  called
 Sulphats ; Sulphas in  Latin.
   All those that contain the nitric acid in its  most perfect
 or powerful state, are called  Nitrats ;  Nitras.
   All  those that  contain the  mutriatic acid are  called
 Muriats; Murias.
   All those that contain the  acetous in its most perfect or
 powerful  state,  are called' Acetats ; acetas.
   In conformity to this rule, we have the
   Sulphat of potash,....of soda,....of ammoniac.
   Nitrate of potash,....of soda,....of ammoniac.
   Muriate of potash,  &c.
   These  compounds are distinguished from those in whfeh
 the  acids are redundant in their distinguishing ingredient,
 by giving, to the latter the termination -ite, from the Latin
 -is,  or-4r£kt?,thus,
.-. - SulpMje,'..k.Sulphis,  or Sulphites, of potash, &c.
 .■•«'Nitrite,....Nitris, or Nitrites of potash, he.
   Acetite,....Acetis or  Acetites* of potash, &c.
♦ We shall see afterwards that muriates are not'properly named....edit 
146       FRENCH NOMENCLATURE.
  The acid  of  tartar is also considered as an imperfect
acid; and therefore they call the compounds formed by it
Tartrites ;   Tartris in Latin.
  The compounds that contain the sedative salt are called
Borats; Boras.
  These names have evidently been contrived to suit the
genius of the French language, in the first place, and [then
have bisen transferred into the Latin words ; or the words
which were  meant to be  used in the Latin language have
been coined from  the  French ones.    When changes are
thus made in the names of  things which are familiar to us,
I believe  most people find them disgusting at the first, on
account of the  shock and derangement which  they give to
the habits they had formed before. These latinised French
words appeared to me at first very harsh and disagreeable.
This, it must be confessed, cannot be avoided, in making
an attempt of this kind, and must therefore be overlooked.
   When  this rage,  fi^r  reformation  and innovation was
going round, it was  nVtural for every person to  think a
little on the subject, and consider of what he would propose,
were it required of him  to give  his opinion :  And, if you
will give me leave, I shall state to you what has occurred
to myself.
   When I give my plan for naming the salts, you will think
perhaps that I  have  as little mercy for languages as other
people;  but  I remarked before, that an attempt to coin new
names,  especially in our science,cannot be  made without
transgressions of this kind.
   The  following small table of the neutral salts will give
you a sufficient notion of  my plan : 

CO
O
B
<
I—I


Q
GO
u

eg
«
DR. BLACK'S TABLE OF NEUTRAL SALTS.
	Acidum Sulphuricum.	Acidum Nitric'um.	Acidum Muriaticum.	Acetum.	Acidum OEnolithicum.	Acidum Boracicum
I.ixiva.	Lixiva Sulphurica.	Lixiva Nitrata, or Nitrica sive Nitrum.	Lixiva Muriatica.	Lixiva Acetosa.	Lixiva OEnoIithica, et . OEnolithus, sive Lix. OEn, Acidula.	Lixiva Boracica.
Trona.	Trona Sulphurica.	Trona Nitrata, or Nitrica.	Trona M ariatica sive Muria.	Trona Acetosa.	Trona OEnoIithica. Trona OEn. Acidula. Oenolithus Tronatus.	Trona Boracica, sive Borax.
Ammonia.	Ammonia Sulphurica.	Ammonia Niira a, or Nitnca.	Ammonia Muriatica sive Sal Ammoniacus	Ammonia Acetosa.	Ammonia OEnoIithica Am. OEn. Acidula. OEn. Ammoniatus. "	Ammonia Boracica.
a	c	*4 3	■	i a (4	o B	a 3 e cu bO u et	o
u u 3 .b	rt	3 n u	o a	1	3 O u u		c£ p
.2"	cu		a *-> f!l	"c-	C	CO 3	a i-3 X! c. 'a
a	3 10	o E CO	'5 o a a	3 CO 8	o u 4-1 41	u	
u cs	CO »—. a ■5	73 J3	in	u 4->	CO ta-rt	u	CO a a Pi
l			3 M	a O-	eu	o B	I*. ef (4 »-a
T3 u M o	<*-	eu .2 a	a a «-> C	3 M (9	10 X. u	o *** u	
.-*	o	o	o		J3		ex
O	(0	u	♦J	R	£	D. rt	3
u	Tj	B					CO
>	C a o o.		3 a.	O	rt	'co B	73
?w*	a o u V C	<—.	3		3	u	^
n o > .c H		i/l u 3 o-3 co	e" 3 a ">	« a 3 u "2 o a	a. "a M rt '2 i	4) 0> hi O a u •s	a 3 s 3 "5
 
14*            LIST OF SYNONIMES.

   To.  express the compound salts  formed by the other
acids, I may proceed as follows:,...lixiva succinata, lixiva
formicata, fluorata, citrata, phosphorata, &c &c.  (See Note
34. at the end of the Volume.)
   The  many drl'.rent names which have been given to the
same salt by its occasional  discoverers, are a great incon-
venieuce, and cause much obscurity in reading their writ-
ings.   To remove this  in some measure, I have collected
the most usual synonymes, and arranged them  under the
leading names  which  1 have just now been explaining to
you.    With very little  trouble  you  may  arrange them,
either according  to Bergmann's or  the French  method.
You will find the  list very useful.
SALIUM ALKALINORUM  SYNONIMA.
 1. Lixiva.
 2. Alkali fixum vegetabile.
 3. Kali.  Pharm. Lond.
 4. Potassa GaJis.
 5. Sal Tartari.
 6. Sal Absynthii.
 7. Cineresciavellati. Nitrum fixatum.
 8. Oleum Tartari.
 9. Lixiv nm Tartari.
10. Aqua Kali.  Lond.

 1. Teoxa.
 .2 Al\ali hxum f s^ile.
 3 Soda.  P'arm. Edln.
 i. Natron.   Lohfi.
 5. Soda. Gallis.

 1  Ammonia.
 2  A kali volatile.  Edin.
 3. Ammonia.  Lond.
 4. Ammoniaca. Gallis.
 5. Sal volatile ammoniaci.
 6. Sal cornu cervi*
 r.,SaJUrin«c.
         Aqua dilutum.
 8. Spiritus salis ammoniaci
 9. Aqua, ammoniac. .
10. Spiritus coma cervi,
11. Spiritus Urine.
-it 
        I<IST  OF SYNONIMES.             14&


SALIUM ACIDORUM  SYNONIMA.
 1. Acidum  Sulphuricum.   Sul-
   phurosum.
 2. Acidum  vitriolicum.   Pharm.
   Lond. et Edin.
 3. Oleum vitrioli,  vel acidum, vel
   spiritus vitrioli.
 4. Acidum vel spiritus sulphuris per
   campanaro.
 5. Spiritus aluminis.
 6. Acidum chalcanthis.
 7.   ■  •   primigernum.
 8.   ■■    catholicum.
 9. ——— universale.
10.------aereum.
XI.------vagum fossile.

 1. Acidum  Nitricum.  Nitrosum.
 2. Acidum nitrosum. Pharm. Lond.
   et Edin.
 3i Spiritus nitri.
 4. Spiritus nitri Glauberi.
I. Lixiva Sulphurica.
2. Alkali vegetabile  fixum vitriola-
  tum.  Edin.
3. Kali vitriolatum.  Lond.
4. Sulphas Potassae.
5. Sal polychrestus.
6. Nitrum vitriolatum.
7. Sal enixum.
8. Sal e duobus.

1. Lixiva Nitrata.  Nitrosa.
2. Nitrum.
3. Nitras potass*.  Gallis.
4. Sal petrar.

1. Lixiva Muriatica. Muriata.
    Lixiva muriata oxygenata.
•2. Murias potassae.  Gallis.
4f. Aquafortis.

1. Acidum Murxatioum.
2. Spiritus salis marini.
3. Spiritus salis Glauberi.
—Acidum muiiaticum oxygenation

1. Acetum.
2. Acedum acetosum.
3. Acetum destillatum.
4. Spiritus aceti. ,      ♦
—-Acidum aceticum.

1. Acidum OEnolithicum.
2. Acidum tartari vel tartarosum.

1. Acidum Boracicum.   Boraci-
  num.
2. Sal sedativus.
3. Sal sedativus vel narcoticus Hont-
  borgii.
3. Sal  digestivus   vel  ftbrifugus
  Sylvii.
4. Sal marinus regeneratus.
5. Spiritus salis ruarini coagulatus.

1. Lixiva Acetata.
2. Alkali fixum vegetabile acetatum.
3. Kali acetatum.
4. Acetaspotasse....Acetis. Gallis.
5. Tartarus regeneratus.
6. Sal diureticus.
7. Terra foliata tartari.
1. Lixiva OEkolithica.
2. Alkali fixum vegetabile tartari-
  satum.
3. Kali tartarisatum.
4 Tartris potassx.  Gallis.
5. Sal vegetabile.
SALIUM COMPOSITORUM SYNONIMA. 
150            LIST OE  SYNONIMES.
6. Tartarus solubilis.
7. Tartarus tartarisatus.

I.OEnolithus.
2. Tartarus. Ed. & Lond.
3. Tartarus acidula potassae.
Gallis.
1. Trona Sulphurica.
2. Soda vitiiolata.   Ed.
3. Natrum vitriolatum.  Lond.
4. Alkali fixum fossile vitriolatum.
5. Sal Glauberi.
6. Sal mirabile Glauberi.
7. Sulphas sodae.   Gallis.

1. Tro^Nitrata.
2. Nitras' sodae.  Gallis.
3. Nitrum cubicum.
4. Nitrum quadrangulare.

1. Trona Muriata.....Muriatica-
2. Muria.  Ed.
3- Sal niarinus.  Ed.
4. Sal muriaticus.
5. Natrum muriatum.   Lond.
6. Murias sodae.   Gallis.
7. Sal communis.
8. Sal gemmae.

1. Trona Acetosa.
2. Acetissodae.  Gallis.
3. Sel vegeto-mineral.
1. OEnolithus Tronatus,
2. Soda tartarisata.  Ed.
3. Natron tartarisatum.  Lond.
4. Sal rupellensis.
5. Sal polychrestus rupellensis.

I. Trona  Boracinata.....Bora-
  cica.
2. Borax.
3. Boras sodae.  Gallis.

1. Ammonia Sulphurica.
2. Sal ammoniacus vitriolicus.
3. Sulphas ammoniacalis.  Gallis.
4. Ammoniacus secretus Glauberi.

1. Ammonia Nitrata.
2. Nitras ammoniaci.  Gallis.
3. Nitrum semivolatile.
4. Nitrum flammans.
1. Ammonia Muriata. Muriatica.
2. Sal ammoniacus.   Ed.
3. Ammonia muriata.  Lond.
4. Murias ammoniacalis.  Gallis.

 1. Ammonia Acetosa.
 2. Spiritus Mindhereri.  Edin.
 3. Aqua ammoniac acetata.  Lond.
 4. Acetis ammoniacalis.  Gallis.

 1. Ammonia OEnolithica.
 2. Tartris ammoniacalis.  Gallis.
1. Trona OEnolithica.
2. Tartris sodae.   Gallis.
  *»* Unless the chemical readerfaakes this list very familiar to his mind,
he must remain incapable of reading with intelligence the writings of all
the chemists of Europe previous to the publication of Mr. Lavoisier's system.
Yet those writings contain a vast body of solid chemical knowledge, all of
which  has a chance of being forgotten, if it have not an immediate  and
palpable dependence on the new doctrines. He will remain equally ignorant
of \Ht writings of the most eminent natural historians andmineralogistSi who
employed no other language in all their discussions.....editor. 
CHEMICAL  HISTORY.
CLASS II.
EARTHS.
   THE  nature of the  salts in general,  and that of the
 principal varieties of them, have been already explained to
 you.  It was proper to  present that class of natural sub-
 stances to your consideration  the first of all, because the
 salts are the most  active of the objects of chemistry.
 They shew an attraction, or a dissolving and active power,
 m mixture with a great multitude of other  substances. We
 cannot therefore describe conveniently  the nature of any of
 the other objects of chemistry,  without taking in the rela-
 tion of such objects to  the different salts, or to some  of the
 principal species of them.
   Next after the salts, I have found it most convenient to
 describe the earthy bodies :   and I have two reasons for
 choosing this arrangement.   The first  is, that some  of the
 earths resemble the salts so much by their chemical rela-
 tions, that the transition from the one to the other is per-
 fectly easy,  and the knowledge of the salts must therefore
 facilitate the  apprehension of  what  is to  be said of the
 earths.   The second reason  is, that we must have  some
knowledge of the earths,before we can proceed conveniently
to the study of the  other objects of chemistry which havm
not yet been considered.
  That I may prepare  you for understanding some terms
 and  expressions,  which I  shall have  occasion to »«  -
use. in 
  152    /            EARTHS.

  speaking of the different states and conditions in which we
  find the different earthy and  stony substances, I  am under
  the necessity of stating or describing a number of facts or
  appearances, which, to be clearly  apprehended, require a
  more than usual exertion  of the attention.   I trust, there.
  fore, that you  will favour me with your attention, which,
  at any rate, will be well employed, as in thus preparing you,
  I must make known to you many of the most important and
  instructive phenomena that are connected with the natural
  history  of  this globe.
    The common definition of earthy and stony substances
  is, that  they are bodies not  soluble in  water, not inflam-
  mable, and  whose  density or  specific gravity,  compared
 with that of waterjdoes not  exceed the proportion of four
 to one.   These characters are  chosen to distinguish them
 from  salts, and  from ice, by the want of solubility in water;
 from  inflammables by the want of inflammability ;   and
 from the metallic substances by inferior weight.
    This  definition,  however, as well as  that commonly
 given of the salts, is not unexceptionable.  The distinction
 taken from the  want of solubility may be  objected to, as
 not applicable to some  of the earths, which are perfectly
 and totally soluble  in water.  Such is  calcareous earth,
 and barytes, and strontian spar.  And it must be confessed,
 that some of these earths,  or  natural  substances, which
 appear to belo»g more properly to the class of earths than
 to any other, are truly of an intermediate  nature between
 salts and earths, partaking of the properties of each, in such
 a manner, that it is difficult to say which of the two classeji
 they resemble  the  most.   Mr. Fourcroy, thinking that
 they resemble the salts more than the earths, has  removed
 them from the class of earths, and described them as salts.
 But it is of little importance under what name a trikftg is
 described,  provided it be well  described, and  the nlrwre
 of it thoroughly made known.
    There is, in  every part of nature, a transition frcm one
fcet of her  productions to another;  so gradual, that we
 cannot find a precise limit between the classes or assem-
 blages of them which we choose to make. 
EARTHS.                   153
   Beside those  qualities  of "the earths  which  are  com-
monly given, to distinguish them as a class from  other
bodies, they have one which,  though not taken into the
definition, does, I believe,  always make a part of the gene-
ral idea of an earthy substance  in the mind of a chemist.
This quality is  the  great  degree of fixedness in the fire,
by which the earthy  and stony bodies, in general, excel  all
the other classes of  the objects of chemistry.
   The substances  which  belong  to this  class are well
known to exceed greatly in quantity all  the other  objects
of our science.   1 hey  compose  almost the whole of the
solid  materials of  this globe which we  inhabit.   It  is,
therefore, proper to take some  notice 1^-e of the situation
and  arrangement of the earthy  bodies m the  interior part
of the globe, so far at least as we have yet  been able to
penetrate  into it, which we must confess is only to a v^ry
small depth.  This step is necessary,  that we may have
an opportunity to explain some terms which are in general
use,  in describing  the different states and conditions  in
which the principal species of earths are found in  nature.
But  my observations on this subject have  a more impor-
tant  aim.   The  description to  be  given  of  the  natural
situation and condition of the earthy substances, and of
those which they inclose and contain, give the most evi-
dent  marks of  a gradual change, both in the situations,
forms, and  even properties, of those substances.  As,  all
these are the effects of heat and mixture, operating  by
means of chemical forces, it is plain that the changes exhi-
bit a series  of  instructive  observations, and must furnish
us with informations which nothing but the length of time,
and  the enormous pressures competent to these situations,
could procure.   This is a  valuable addition to all the mo-
mentary labours of our little laboratories and experiments.
And, on the other hand, our chemical knowledge enables
us to understand many of those  changes which must other-
wise have bedn mysterious and unaccountable.  Thus will
chemistry and  natural  history derive mutual  aid and im-
provement.
   We have acquired some knowledge of the  state of the
interior parts of  the earth, by  observing  the excavations
   wtr^r  TT                 IT   ■ 
 154 VARIETY OF SITUATIONS AND FORMS,

 formed accidentally by torrents of water, and by digging
 deep pits in many different places for the  purposes of min-
 ing, or, on some, occasions, for procuring water.
   Whenever we have  had opportunities,  in these different
 ways,  for observing  he construction of the interior parts
 of the globe, it has beei. perceived that the matter of which
 it is composed is arranged, for the most part, in extensive
 beds,  layers, or strata,  composed of different materials,
 and very various in  their thickness, but generally parallel
 to  one  another, and  in  which  we  see  many parallel
divisions, like the leaves of a book.  Where the matter of
 the earth is arranged in this manner, it is called Strati-
 fied Matter, oj: Strata.
   This arrangement, however, is perceived in few  places
 only, at the surface of theground.  The surface  is covered
 almost  every where, to different depths, with a confused
 rubbish and loose earth, composed mostly of the materials
which  lie more solid and regular below ;  a  part of these
having mouldered down into this rubbish and earth, and,
 m most cases,  having been removed by the action of water
to a considerable distance from  the  place to which thev
originally belonged.
   Before we can see the appearances of the stratified mat-
ter,  we must therefore .penetrate  through this rubbish, or
find places  where it has  been broken through,  or  swept'
away,  for a depth of some feet or fathoms, or, in many
cases, for a much greater depth ; and  then we seldom fail
to perceive them.
   The parallel position with respect  to  one another, and
the  great extent and equal thickness of these strata, have
been most distinctly seen in mining countries, where fre-
quent  pits have  been  dug, to  reach the objects  of the
miner; /also in digging of wells in populous countries.
   Derbyshire is an example of a mining country, in which
a very great number of pits have been dug, on account of,
numerous metallic veins of lead ore which it contains: and
 Mr. Whitchurst has given  an account of the general ex-
perience  and  kn9wledge  that has  been  acquired by the  '*
frequent perforations of the earth in that countrv.     '■'"•■'  '% 
         COMPETENT TO  THE EARTHS.     155

    The country  around  Newcastle is another  example,
  where, on account of the abundance and numerous strata
  of coal which are found there, the interior parts of the earth
  have been diligently examined  by numerous pits,  and by
  other  means, as boring,  &c.
    From the insight that ha3 been  got on all such occa-
  sions, it has appeared that the strata lie  in  very different
  positions with  respect to the horizon in  different  places;
  that in some districts they are level or horizontal; that in
  others, and these the greater number, they decline from
  the horizontal position, or have what is called a dip;  that
  in ethers, they  are somewhat waved, or alternately rise and
  sipk in an irregular manner:  and in others, are thrown  into
  dsorder by interruptions, sudden  bendings, and fractures,
  and  by very steep declinations from the plane of the hori-
  zon.   There are even examples  of two  sets of strata in
  different  positions,  the  one over the other; the  under-
  most  set  commonly erected,  more  or less,  and  the
  hardest;  the  uppermost less erected,  or horizontal,  and
  softer.   This is seen in the  banks of the river Jedd, near
  Jedburgh.
    Such are the different states  of  the > stratified mat-
  ter which is found in almost every place where we have
  opportunities to examine the interior parts of the earth.
    But  I  must  farther remark, that in many places,  and
  especially in those  countries in which  we find  the  strata
  the most disordered, we generally  also find large quantities
  of stony matter, in which we cannot perceive that stratified
  arrangement  of parts,  but  which constitutes  enormous
  masses, irregular in their form and size, sometimes spread
  out or interposed between the  strata,  but  never of such
  an equal thickness, or disposed  in  sucl) a  regular manner;
  and often split into  numerous pieces.
    The stony matter which  has this appearance, may be
 distinguished from stratified matter by the name of rock,
  or rocky matter.
    An example of the difference  between the rocky  and
,the stratified  matter, is to be  seen in Salisbury  Craig,
 which is an extended mass of rocky matter, with stratified
  matter below it, aud above some parts  of it-,  and Arthur's 
156             STRATA....ROCKS.

Seat is  a mass of rocky matter, but has stratified matter
under it.
   Th:se masses of rocky matter, in which we cannot per.
ceive any stratified arrangement, compose in some countries
vi-rv high mountains.   In  other  places,  the  ridges,  or
chains  of mountains, are formed more or less by stratified
matter that is uncommonly  hard, and the strata of which
are much declined from the horizontal position ; in con-
sequence of  which,  their edges project above the general
surface of  the globe, to form those mountainous ridges.
Frequently, however, the very high mountains are formed
by an  intermixture  of  rock with these  hard and erected
strata,  which, along with it, have sustained the injuries if
time and  of the  weather,  better  than the  softer matte*
which  surrounded them ; and therefore part of them now
remains,  and forms  those  projections, after  the softer
matter  has been demolished around, and washed away to
a great  depth.
   That the surface of the globe has everywhere undergone
great changes in  this way, by demolition, and removal of
the materials to \ ery great  distances, will be clearly seen
by any person who surveys it with a discerning eye. When
we ascend very high mountains, the rocky tops of them are
all shattered and ruinous,  and their sides are covered in
many places to a great depth with the rubbish which has
falh-n from the upper parts  of them.   In this rubbish, we
find  deep  scars and ravins, formed  in heavy  rains and
storms, by torrents  of water,  which, by their repeated
effects,  gradually  wash down that  rubbish into the lower
grounds.   During the great length of time required for
its complete descent, it undergoes  further demolition and
decay,  into  gravel, sand,  and earth ;  and, under these
forms,  is at last spread out by the brooks and  rivers, to
form the plains and  the sands  found on the  shores of the
sea.    For, as the rivers,  in consequence of the unequal
resistance of the different soils through  which they run,
have in general  a serpentine  course, and are  gradually,.*
undermining  their banks, and shifting their  channel  in/?
different places; they have the natural effect to undermil
and bring to a level,  the eminences and accumulation^ o 
      FEATURES OF ALPINE COUNTRIES.   157

  soil and rubbish which  have been formed in particular
  places.  And, for this  reason, all  great  rivers are in
  general surrounded, in their course toward the sea, with
  immensely extensive  plains,  which have been formed by
  themselves.
     Any person who wishes to be satisfied of what I have
  now said, of the demolition that is going on in the elevat-
  ed parts of the earth's surface, must visit very high, moun-
  tainous, and  Alpine  countries,, or read the accounts of
  those who have visited  them.   Common mountains and
  hills do not shew it so evidently, for although these too
  are suffering a gradual demolition and waste, it is  so slow,
  on account of  their being less exposed to the violence of
  the elements, that it is not obvious.  They become covered
  with rubbish,  and soil, and vegetables,....all which defend
  them in some  measure from the less violent impression of
  the storms ; while the tops of very high mountains are so
  much  exposed to  their  fury, that  soil  or rubbish cannot
  remain on them, but is swept away as fast as it is produced.
  There is a fine example of this in the mountains of Arran,
  in the west, which are among  the highest in these islands.
  The summits  of those mountains are all ruinous.   They
  present, in some places, lofty  precipices, which terrify the
  beholder by their awful  heights, and by the mountainous
  blocks of stone which are prominent from them, and seem
  ready to fall and crush every thing below them. They are
  accessible only to  eagles and  other birds of high  flight,
  who choose them for  their habitation.   The foot  of these
  precipices terminates in a steep slope  of  great  extent,
  forming a great part of  the side of the mountain.   This
  slope is composed entirely of blocks of stone and of rubbish,
  which, in the lapse of time, have fallen from the top of the
  precipice.
     lor more examples of similar  appearances, I refer you
  to the description of the higher parts of the Alps of Savoy,
  as  given  by Mr. Saussure of Geneva,  in his account of
  different excursions, and  journeys he  made  among them,
" ],5and  in  some of which he was exposed  to great  danger.
  His accuracy in observing, and fidelity in relating what he
  saw, may be entirely relied on : and  he presents his reader 
  158   FISSURES,...VEINS,...LODES,...DYKES.

  with a number of the most sublime objects and instructive
  facts in natural history.
    You will also find proofs of the decay and demolition of
  mountains of granite, described~-by Mr. Hassenfratz, in
  the eleventh volume of the Annales.de  Chimie.   He saw
  them on the road from St. Flour to Montpellier; and they
 are a very  striking phenomenon.
    But I  have wandered  I may  say into  a digression.
 I was led into it  by endeavouring to illustrate the remark
 I made on the nature of  many  mountains and  chains of
 mountains ;  that they are  composed  of hard stratified or
 rocky  matter, or of  a  mixture of  both, which now is
 eminent above the surface of the globe around them, in
 consequence of the gradual demolition, and removal to a
 great distance, of  the softer matter  which formerly sur-
 rounded these harder materials, which are even themselves
 liable to a more slow demolition  and waste.
   To proceed,....It is necessary further to be understood,
 that both the stratified and rocky matter are found Split or
 divided, in  innumerable  places, by fissures nearly perpen-
 dicular, or across  the strata; and that the parts, thus broken
 asunder,  are often considerably displaced  with  respect to
 one another : the  materials on the one side of the fracture
 being frequently sunk below the level of those on the other,
 or removed  to some distance from them, so as to produce
 in the stratified matter discontinuities of various wideness.
 These rents and intervals of the fractured strata, or rock,
 are in general filled with a matter different from that of the
 rock or stratum in which the rents are found.   And rents
 of a certain width, thus filled up with extraneous matter,   ' J
 are called veins, or, in Cornwall, lodes.  These veins are  'w
 subject to all the  variations of width, and irregularity of  "<iH
 direction,  which you can easily imagine in fractures and   fl
 rents of hard strata and rock; and they go down to a depth  - '■?■
 far below any to which we "can reach.   The matter which
 fills them  is generally a whitish stony matter, named spar.1  .'
 It is more  pure and more simple in its composition than'  ''"
most  other stones; but  there are several kinds of  itf*>$
and  intermixed  with  it, we  often  find  also  differeht^
metallic and mineral substances.   It is  indeed  in those ■{■■ '1
veins chiefly that the ores of metals are found.            ''*  I 
TROUBLES,...HITCHES,...MARINE BODIES.  159

   And wherever there are vacuities left in the vein, by its'
being  imperfectly filled, there we are  sure to  meet with
crystallized  matter of  the several stony and mineral sub-
stances which the vein contains.
   In a great many examples, however, the rents and dis-
continuities  I have  described, are of  greater width than
what are commonly called  veins.   The width of veins is
from an inch, or a fraction of an inch, to several feet or even
yards, in some cases.   But we have examples of rents, the
width of which is  equal to  many fathoms ;  and in this
case, rock or rubbish, or other extraneous matter, fills up
the interval.  When this occurs, the interval and materials
which it contains is not called a vein.    Our miners give it
the name of a dyke, or partition.  The  extent to which
these dykes, as well as the veins, are continued downwards
into the bowels of the earth, is hitherto unknown.   Their
depth is  plainly much greater  that what human  art and
labour can  reach.
    These  rents  and dislocations of the  strata,'with  the
 intervals thus formed, and  great quantities of rock or rub-
 bish which sometimes fill up  these   intervals, are  well
 known to our colliers, who  meet with them often in cutting
 out the coal;  and they call them in general troubles;  be-
 cause there they meet with an interruption in the coal, in
 consequence of a division and shift of the strata, which they
 call a hitch.  The coal is continued beyond this break or
 hitch,  but  upon a different level, which the  miners must
 find out, sometimes at great expence.   And often they find
 interposed,  between the edges of the  interrupted strata, a
 thick partition of rocky or  other matter, called a dyke.
   • You will see numerous examples of  small veins in Salis-
 bury rock ; and  examples of  small  dykes in the bed of
 Leith water or river; between Canon-mills  and the  mills
. above  them.
    I have  only one general fact  more to relate, which be-
 longs to this subject:  It is the discovery of sea-shells, co-
 r.als, and coraline bodies; and of the bones and skeletons of
, fish, and other  relics of  marine  productions,  which are
 found in most places intermixed with  the stratified matter.
 These have appeared  on innumerable  occasions, and in all
  p?'-"5 ^f +Ua "'"-1'1 :- — v'~u -»-—:<"   d matter, especially 
 160  GREAT  CHANGES ON THIS GLOBE.

 some kinds of it, have  been examined;....on the sides of
 the highest mountains, as well as at the greatest depths to
 which we have gone in digging the earth.  Sea-shells have
 been found at Amsterdam  100  feet deep, under the sur-
 face of the earth; at Marly-la-Ville, six leagues from Paris,
 at 75 feet deep :  sometimes in mines under a cover of 50,
 100, 200, 1000 feet:  as in the Alps and Pyrenees.  They
 have also been found in  mountainous  countries, at a very
 great height above the level of  the sea ;  as  in the  moun-
 tains of Spain, the  Pvrenees, the mountains of France and
 Of England, the marble quarries of Flanders, the mountains    ,
 of Gueldres, and in the  heights round Paris ; also in the
 Alps, particularly Mount, Cenis.*  And M.  Saussure,  in
 his instructive journevs among the Alps, describes oyster*
 shells which he  found in a part of the Alps  to the  south-
 east of Geneva, at the height of 1172 fathoms  above the
 eea ; that is, 7032 feet.   (Saussure Voyages dans les Alpes,
 p. 393.J  They have been seen also in the Appenines, and
 in most of the stone and marble'quarries of Italy.   (Vide
 Buffbn, torn. 1. p. 408.J
   We have evidence  also of their having been found in
 the highest mountains of the world, the Andes of  South
 America.  Don Antonio de Ulloa found petrified shells
 upon the Cordeliers des Andes dans le gouvernment de Wanca*
 Vellica, in 13 or  14 degrees south latitude.   These shells
 were found  at such a height,  that the barometer stood
 there  at  17 inches 1^ line French  measure ; that is, at
 22001 fathoms above the  level of the sea, or 13,202 feet.
 (Mem. de V Acad. 1771.)                                    '
   And, in all these different examples, it is in the stratified   j
 matter, only that they are fo^nd.                        ad
   We also find frequently,  in some kinds  of stratified J
 matter, impressions of the leaves and other parts of vegeta-  \\
 bles, and  pieces of wood, penetrated with  stony  matter of
 different kinds.                                            I
   From the whole of these  phenomena, it is evident,  that  M
 the  materials of this globe have been affected, in many    \
 places, with violent concussions and derangement,  and*
 have also undergone very great changes in their position
 with respect to one another; that what was once covered    \
 by the sea is now land or mountains, and what  wasoncAr jij
               •
________________________________\     > win1  g "---'   ■ i.«.-..... . -■  ■ -______4 
              ATTEMPTS TO  EXPLAIN.         161

   at the surface,  or covered only with water, is now under
   cover of  solid  matter to very  great  depths;   aid that
   these changes of situation have even been often rept?t^d;
   although the successions of the one to the other mu-t < er-
   tainly have been extremely slow, and  must havt required a
   length  of  time, the limits  of which cannot be assigned
   from the phenomena themselves.
     Such are therefore,  in general,  the  appearances  which
   present themselves, when we examine  the st?te of the
   solid  materials  of  which  this  globe  is  composed, and
   which mostly belong to the class of earths, which we are
   now  to consider.   Various conjectures and  hypotheses
   have occurred to the human imagination, to account for
   the manner in which all this has  happened.
     To give a short account of  the attempts to explain
   these  phenomena,  I shall  first  remark,  that  all  these
   attempts agree in supposing the  materials of the strata to
   have been  arranged by  water,  depositing or  arranging
   them one over the other,  in succession.   This is inferred
   not only from their  general appearance,  similar to that we
   perceive in lakes, pools,  and other small collections  of
   water; at the bottom of which, when they dry up, we find
   the sand, mud,  and other matters deposited, or  arranged
   in parallel  layers ; but  also from the appearance of shells
   and other'marine productions, which abound in  the com-
   position of a great number of strata.   These shells  are in
   many places found sd entire,  that they are perfectly well
   known. The different species of them are very numerous:
   and in some places they are collected together in  immense
   quantities;  in quantities so great, that we cannot suppose
   any other origin for them, but that the  place where they
   lie was once the bottom of the sea.   The straca are sup-
   posed  to have been originally in an horizontal, or nearly
   horizontal  position.  The slope  or declination from the
   horizon, which many of them now have, and the  apparent
   disorder in  other respects, by rents, changes of level, and
   interruption*,  have  been  imputed  to different causes by
> different theorists.   Some  have  imagined that a general .
 ^ V, VOL. II.                  35 
162  ASCRIBED TO SUBTERRANEOUS  FIRES.

convulsion  must  have shaken  the whole of  the  globe.
Others have  supposed that partial  ones have gradually
affected the different parts of its surface in succession.
   The general convulsions which have been supposed suf-
ficient to produce these great effects are,  first,  the catas-
trophe of the deluge,  described  in the scripture, and by
the poets.   And Dr. Burnet, in his Theory of the Earth,
by giving full liberty to his imagination, has shewn some
ingenuity in the contrivance, 1 may say, of a deluge equal
to these effects.
   The great Dr. Halley, whose mind was more occupied
with celestial objects than with any other, proposed a sup-
position,  that this  globe  had  perhaps  more  than  once
received a shock from a comet,  which, impinging on it
obliqueiv, gave it its diurnal rotation; and, by the sudden
communication of  such a  violent motion, shattered and
deranged all the materials of it that were near its surface.
   But the greater number of philosophers appear now in-
clined to believe that the convulsions which have deranged
the strata have been partial or local only, but with  such a
succession as gradually to affect every part, or almost every
part of the earth's surface ; and that they have been pro-
duced by subterranean fires.
   That volcanic  and subterranean fires must have  been a
very common cause of the inequalities of the earth's sur-
face, and  disorder of its materials, is plain from the natu-
ral history of this globe.  We know that in some cases
they have produced sudden and violent elevations of some
parts of it, and  as sudden sinkings and depressions of
others.   We know that  some  of the highest  mountains  *
are composed chiefly of materials thrown out of the craters   .
of volcanoes ;   and that  the most convincing  proofs are
visible, in innumerable places, of  formerly*.existing volca-  /■
noes, and  craters, the eruptions  of  which  have  ceased  j|
long since, while others have succeeded to them,  and are
at present in different states of activity.                  I   ]
   We know farther, that the action of those  subterranean  .«
fires is not  confined to the derangement of the dry landt.JH
The agitations which they produce are in many cases feltjlfl 
           CHANGES  BY VOLCANOES, &c.     163

■with great violence even at sea:  and they are so very exten-
sive, that it is plain they must act at an immense depth below
the surface ;  and therefore far below the bottom of the ocean:
a consequence of which is, that they elevate that bottom in ma-
ny places so as to make it rise above the surface of the waters,
where  it  remains  in that elevated state.  A great number of
islands  in different parts of the globe shew the most undeni-
able proofs  that they have had this  origin.   Siich are the
islands of the Archipelago in the  Mediterranean ; the Azores,
Teneriffe, and the islands  of the West Indies.  In all these
we find lavas, and other signs of the action of subterranean
fire, and  in some of them springs of hot water,  and  sulphure-
ous vapours, breaking out at the surface, shew that the internal
fires, although smothered, are not completely extinguished.
   We.find the same symptoms of internal fire in almost all the
great ridges of mountains in the world;  and many of the great-
est and most active volcanoes are found in those ridges.  Such
are the Appenihes in Italy ; the mountains  of Sicily; those
of France in Auvergne and Dauphigny ; the Pyrenean ridge
betwjfen  France  and Spain; the  immense ridge  of  South
America  named the Andes, or Cordilleras ;  the Russian pe-
ninsula of Kamtchatka;  the mountains of Iceland.   In  all
these we  find either existing volcanoes,  or indubitable proofs
of their former existence in places where their fires and va-
pours are not now seen.   Even in this country, there are some
signs of the former action of subterranean fire.  Many gentle-
men who have visited volcanic regions, and who have given
particular attention to the effects and productions of subterra-
nean fire, find so much resemblance between our whinstone
and some of the lavas of existing  volcanoes, that they are per-
suaded our whinstone has been a sort of lava.  And, even set-
ting aside that resemblance, there are many other reasons for
believing  that our whinstone has been a matter melted by sub-
terranean heat *.  This, however, does not infer actual vol-
canoes.
  • In digging the cellars and common sewers of the New Town of Edin-
burgh, freestone strata ave found to commence a few feet under the surface,
and occupy the whole ridge on which the buildings are erected.   A fissure, 
  164  BUFFON'S THEORY OF THESE CHANGES.

    Subterranean fires, therefore, and the internal convulsions,
  the eruptions and explosions which they have produced, have
  cVidemh shaken  and deranged the materials of the globe in ,
  such a verv great number of the parts of its surface, that there
  is verv-gieat reason  to think all the  derangement we find in
  other places has been produced in this way ; and this is now
  the most general  opinion.
    The author, however, who has been  the most celebrated
  for his u< .empt fo give a natural history of the globe, I mean
  the late M. Buffon, formed for himself a different system, which
  is the most fully  displayed in his Epoques de la Nature, and in
  his  Histoire Naturelle.   He admits that considerable changes
  have been  produced by subterranean fires;  but is of opinion
  that the principal phenomena are  to be'  accounted for  in
  another way.
    He undertook  by  his system to point out the  very origin of
  this  globe, as well as that of the other planets which revolve
  along with it around the sun.   In this opinion, there was a
  time  when the s*un stood alone,  without any planet,  and was
  visited only now and then by the comets.  One of these, corn-
  ing too near,  was dra vn, by the attraction of gravitation, into
  the bodv of the sun, and falling obliquely, and with immense
  velocity, against his surface,  dashed off great masses of the
  melo-d and burning matter, of which Mr- Buffon supposed the
  external parts of the sun are composed.  These masses were
  thrown off with different velocities,  and flew to different dis-
  tances, before the progressive motion was overcome by the at-
  traction of the sun.   At last,  however,  the velocities which
  these masses  had received were  so  much diminished by this
  attraction,  that it became  an equal antagonist to  them ; and   '
  th^se masses thus became  planets, and revolved in the orbits  jl
  in which they still continue to move.                         ,J

i  or rent, was found crossing all these strata, to an unknown depth, This
  fissure  is completely filled with whinstone :  and in some places, the whin-
  stone spreads out a  little above, on each  side of the fissure, in the same  \i
  manner as mortar will spread cut over the joint between two hiicks when  ; 1
  they are pressed together.  I: appears to have been in a fluid, or at leasutffl
  muddy state, and to have heen forced through from below.....editoh.    *V J 
       BUFFON'S THEORY OF  THE EARTH.   165

   The same powerful impulse by which they were driven off
 from the surface of the sun, gave each of them also a rotatory
 motion round its own centre or axis ;  and being at first liquid
 or melted  matter, the attraction of their parts for one another
 gave them«a spheroidal form, which, at the same time, became
 a little oblate, by  the greater centrifugal tendency from their
 own centre of some parts of them than of others, in consequence
 of the rotatory motion they had acquired.
   Mr.  Buffon  further supposed that,  in  flying off from  the
 sun, they carried  with them a part of his atmosphere,  which
 he imagined to  be loaded with a vast quantity of vapours, pro-
 duced from every sort of matter which can be converted  into
 vapour by intense heat, but especially a very great quantity of
 watery vapours.
   The planets continued for some time to revolve round  the
 sun, each  of them surrounded with its vaporous atmosphere;
 for  their heat at first was too great to admit of any condensa-
 tion of these vapours on their surface.  But  they cooled by
 degrees, and the  first effect of this'cooling was, that  the ex-
 ternal parts of them  became solid  or congealed.  The solid
 surface, which  was formed in this manner, he supposed to
 have had all the roughness and inequality which is commonly
 seen on the surface of earthy, stony,  and mineral substances,
 which have been  all melted together  and congealed.   There
 were eminences in some places, and depressions in others; the
 matter in  some parts of it  was cavernous and spongy,  and
 more  solid in others:  and, by the  contraction  of the cooling
 matter,  a  multitude of rents, and chasms, and vast caverns
 were formed.
   Such, he supposes, was the surface of our globe before the
 water descended from the atmosphere.  This did not happen
 until the heat was so much  abated, that the vapours,  which
 were contained  in such great quantity in the atmosphere,  be-
 gan to condense there, and to fall in rain.   His lively imagi-
 nation paints here a dreadful scene,  by  presenting the  im-
 mense quantity  and violence of those original rains which were
 destined to fill the whole bed of the ocean.  They  were  at-
' tended also with  violent explosions,  and  other effects which 
 166  BUFFON'S  THEORY OF  THE EARTH.

 the water produced when it penetrated into the crevices and
 caverns of the new earth, the heat of which was still so great
 as" to convert very quickly into vapours again the waier which
 first fell on its surface.
   This period of violence and convulsion at the surface of the
 earth, and in the  atmosphere, had  a  certain duration.   But
 the heat continuing constantly to decrease, the watery vapours
 were at last more completely condensed, and the fluid element
 gained possession  of the  surface, and lodged itself in the de-
 pressions and cavities which had been formed either originally,
 during die change of the globe from a fluid to a solid state, or
 afterwards, in consequence of the convulsions I have just now
 mentioned.  Still, however, the waters on the surface of the
 globe were for a long time excessively hot, and in some places
 even boiling.  This was  necessarily attended with great eva-
 poration,  excessive rains,  and violent commotions of the at-
 mosphere.  And  during this period, and the one which im-
 mediately preceded it, a  great part  of the solid  and hard ma-
 terials, at the surface of the earth, were penetrated by the hot
 water and vapours, and by more active substances, which had
 condensed along with the water: and thus these hard  materi-
 als were mouldered down into rubbish and  mud, which form-
 ed the first soil on which vegetables and animals were  to be
 nourished.
   Thus Mr. Buffon thought  he had accounted  for many of
 the appearances which are observable in examining this globe.
   In  order to explain  the rest, and, particularly,  the forma-
 tion of the strata, and the abundance of shells and other relics
 of marine  productions which abound  in the compositions of   *
 many of them, he supposed that the globe afterwards under-   1
 went more slow and gradual changes.                         *
   His opinion was, that the sea is making a constant, but very   i
 slow progress, over the surface of the  globe from  the east to
 the west: that this is the consequence of the  action of the'
 trade-winds, and of the  general direction of the tides in the, ij
 ocean, which is from east to west.  While the trade-winds ^j
brush the surface of the sea, they affect the water;  and in fact ;.i^
produce a current westward in the Atlantic,  which, by its in~^«j 
OBJECTIONS  TO BUFFON'S  THEORY.   167
    cessant action on the coast of America, has formt d, as  Mr.
    Buffon supposed, the great Gulf of Mexico.   The water,
    which in  consequence of this, would be accumulated thete,
    had it not found an outlet, is well known to turn back again in
    a north-easterly direWon, and to run in that direction along
    the coast of North Amauca, where it forms what is called the
    gulph stream, which nr distinguished by its  being warmer
    than the rest of the ocean W that latitude.   A current west-
    ward, similar to  that I just now described, is known to exist
    also in the Pacific Ocean,  and in a part of the  Indian Ocean,
    except where it meets with the coast and mountains of Africa,
    which reverberate it, and give it a turn the  other way.   By
    this continual impression of the sea on the eastern coasts of
    the  continents and islands,  Mr.  Buffon in^gined  that the
    shores are worn  away ;  the sea encroaches|Pthem, and by
    degrees takes possession of their place ; the materials of them
    being deposited at the bottom, either in a horizontal  position,
    or formed by the currents and tides into risings and depres-
    sions, or long submarine ridges and extensive valleys, (if they
    may be so called).   And thus he imagined the whole face of
    the globe has been modelled some time or other by the^ttifln
    of the water, and retains every where  the relics  of th«
    tions of the sea, from which it received its form.
     This splendid system has in some parts of it an air
    mity and grandeur, especially as it is  embellished by the elo-
    quence of Mr. Buffon.   But it certainly shews a degree of
    presumption  and  temerity in the author of it, which excite in
    the mind very different  emotions from those  that arise when
    the phenomena of nature are explained in a satisfactory man-
   ner, and with strict attention to  principles of reasoning that
   are  well founded and just.
     The very first supposition in this grand system is totally in-
   admissible,.... I mean the supposition that the planets received
   the  projectile motion by means of which they  revolve in their
   orbits, in consequence of their being dashed off from  the sur-
   face of the sun.   According to  this supposition,  they could
.„.  have made no more than one very eccentric revolution.   As
   ioon as bv the constant action of gravitation, they were made
ole face of
 theA&tion


lr ofsubli- 
168 THEORIES BY WHITEHURST, DE LUC, &c.

to bend their course again towards the sun, they could not do
otherwise than to complete the ellipse, the  one half of which
they had described in flying off to their greatest distance; and
incompleting this elliptic orbit,  they jnust necessarily have
fallen again into the surface of the sun.^
   Nor is the other part of his systemjgay which he endeavours
to account for the relics of sea-^ocuTctions,  which occur in
every part of the globe, at all satisfactory.   We cannot under-
stand by it how  the sea should have carried those  relics to
such a very great height above its present level, as 10,000 feet
or more.  And had the distribution of land and sea depended
on this principle, there  would have been  no land under the
line: All the land there would have been  worn away and de-
posited,      ^p^p^
   Other attern^Wiave been  made more lately to explain this
subject, such asJ\tr. Whitehurst's, in his Inquiry into the Ori-
ginal State and Formation of the  Earth.  Another by Mr. De
Luc, of Geneva, in his Letters  to the £>ueen.  But  I cannot
enter into all these systems: it would take up too much of our
time.  They are all conjectures, and liable to great objections.
 ^Baem  has lately been communicated to the public in this
: J    Roy  Dr. James Hutton,  which appears to me  much
ln^r^L^miprehensive and satisfactory than those.  But I think
I  have done enough when I have prepared you for understand-
ing and judging of such attempts, by describing the general
facts or appearances to which they refer;  while,  at the same
time, I had an opportunity of explaining some terms which I
shall have occasion to use,  in mentioning the different states
and conditions under which the  principal species of earths arc
found in nature.
   And being thus prepared for a survey of the variety that oc-
curs among  the earthy  and  stony substances,  we shall next
proceed to the examination of them.
   When we begin to do this, however, we find the variety of
them to be so immensely great,  that to give  a  full account'of  i
every particular would take up a great deal too much of your
time; and would be otherwise  improper here,  as being the^j
 province of  a separate institution,....Natur.*l  Histoky.  £v 
      ALKALINE, OR ABSORBENT  EARTHS.  169

 shall not therefore attempt a particular description of all the
 varieties of earthy bodies, but refer you to the authors who
 have published systems on this branch of knowledge.  The
 most eminent  are, Wallerius,  Cronstedt, and the  late cele-
 brated  Professor  Bergmann, who made great improvements
 in our knowledge of many earthy and stony subs ances, by his
 accurate and skilful analysis of them.   His wotk on fossils is
 translated into our language by Dr. Withering.  Mr. Kirwan
 of Dublin has also published  a mineralogy, or systematic ar-
 rangement and description of fossils, in which he takes advan-
 tage of the lights which have been thrown on this subject by
 Bergmann and others ; and has added  much from his own ex-
 periments, so as to give in his book the  most complete enume-
 ration and description of fossils that has yet appeared.
   These, authors, arid my colleague, the Professor of Natural
 History, will give you information of all the particulars.  In
 this course we have not time to follow  the subject so far, but
 must confine our attention to  the most remarkable and distin-
 guished chemical varieties which occur in nature.
   These, I think,  may be referred to five orders ;  the deno-
 minations and characters of which I shall now give you :
   The first oi these I shall call the order of the Alkaline
 Earths.  They  have  been commonly  called Absorbent
 Earths.  The state in which these are found in nature, and
 that under which they are commonly called absorbent earths^
 is not a state of purity, but of combination  with a particular
 substance with  which I shall soon make you acquainted.  But
 as there is hardly any example of their being found in a pure
 state, and as the state just now mentioned is the state of them
 to which we are most familiarised, I shall consider and describe
 them, first, as appearing in this state,  and afterwards shew how
 we render them pure, and what properties they have in their
 state.
  The characteristic of them  in their natural state is to effer-
vesce with acids. They appear under many different modes of
concretion ;  from that of loose earth to  the hardness of stone;
bitf.are never so hard as to scratch glass,  or give  fire with steel. .
  j/VOL. u.                  y 
 170  PLASTIC....HARD . .FLEXIBLE ....EARTHS.

 On the contrary, a knife can be made to scratch them, or make
 an impression on them.
   The second order I call the Plastic Earths.   They are
 commonly called the argillaceous, or clayey.
   These, when  mixed and kneaded with a moderate quantity
 of water, become a tough and ductile paste, which is easily
 modelled into any form,  and which, if it be afterwards wcj
 dried, and then  burned with a strong firc»,  contracts in its di-
 mensions, and becomes compact and hard.
   The third order I call the hard earths  or stones.  They
 are commonly called the sjliceous, or  flinty..
   They  are, in general, stony masses of a larger or smaller
 siz.-, the most eminent quality of which is hardness.  Thtir
 hardness is such that they scratch or cut glass, and give fire
 with  steel.   And when a knife or file  is applied to them, it
 does  not make the least impression.   It is also a general qua-
 lity of them  to resist the most violent heat of common fires
 and furnaces without being melted.
   The fourth order I name the Fusible.
   These are commonly stony  concretions which  have consi-
 derable hardness.  Some are  so hard as  to scratch  glass, and
 give fire  with steel;  but they are not quite so hard  as the hard
 stones.  Their most remarkable quality is fusibility, or a dis-
 position  to be melted in a strong fire.
•  Theflfth order I name the Flexible.
   They are concretions of a scaly, a plated, or a fibrous struc-
 ture,  easily divisible into parts which are flexible,  and often
 elastic.   They are so soft as to be easily scraped with a knife;
 and do not suffer-much change of their appearance and qua-
 lities when exposed to a moderately red heat.
   We shall now, therefore, proceed to describe the  earthy and
 stony bodies which come under these several divisions; and
 begin with the first,  the alkaline earths, or.  n-> they are com-
 monly called, the absorbent.
.v''.V- 
m
GENUS  I.
               ALKALINE  EARTHS.

      OF the alkaline  earths  and stones there  are  several
  kinds, which, in their natural state, are mild insipid substan-
  ces :  And it is  difficult to per»ceive in them, by experiments,
  an\ sensible degree of solubility in water.
    Their characteristic in that state is, that they effervesce wi h
  acids, and -are dissolved by those salts :  and such is their na-
  ture with regard to acids, that they produce similar effe. s in
  mixture with them to what the alkalis produ;e : Upon which
  account I call them Alkaline Earths.   Thus,  we find that
  in general they unite with acids in one certain propoi tun only.
  If there is too much of the earth, it is not all dissolved  ; if too
  little, it is united with  a.part of the acid only,  tht rest of the
  acid remaining  free.   There is, therefore, the same  matual
  saturation here as with alkaline salts.  The compound  produ-
  ced is likewise analogous to.a neutral or compound salt, and in
  most cases dissolves  easily  in water.  The  acid  is rendered
  less  volatile bv  its cohesion with the earth:  its acrimony is
  greatly  diminished, and its acid taste is not perceivable.  And
  further, these earths  attract  different acids with different de-
  grees of force,  and  this in  much the same  order as  that  in
v which they are attracted by alkalis: so that a compound earthy
  salt, which contains the nitric acid, can be decomposed by the
 .vitriolic acid ; one that contains the muriatic acid, by vitriolic
  acid o*-  nitric  acid ; and  one that contains the acetous acid,
  by any  fossil acid, &c.
   They, therefore, resemble the alkalis, both  in their attrac-
 tion for acids, and by manv' particulars in the nature or man-
 ner of this attraction.  But, on  the  whole,  its force  is less 
172           CALCAREOUS  EARTHS.
than that of the alkalis.   Most compounds of acids with the
aniline earths may be decomposed by the alkalis, and especi-
ally by the fixed alkalis.  These unite themselves to the acid
with more force, and cause the earths to separate and fall down
in the form of white powder.
   Such is the general nature of these earths.  Let  us now
attend to the different kinds of them.


                      SPECIES I.

              CALCAREOUS EARTHS.

   The principal species, which  occurs the most abundantly
in na  re, and is at the same time the most useful, is called the
Calcareous Earth.   It is distinguished from other alkaline
eai hs by the effects of a moderately strong heat, which changes
it into common Quicklime.
   It is found in a variety of forms or conditions,
   lmo, Very numerous and extensive strata are composed
entirely,  or principally,  of this kind  of earth.   Such are the
MARBt.ES,  Limestone, and Chalk, which differ from one
another only by the degree of purity in which they contain this
earth, or by  the  manner in which  it is concreted together.
Bo'h chalk  and marble  are often burnt to make lime,  and
afford it of  excellent quality.  Marbles  and  limestones are
found in all parts of the world ;  and form numerous and ex-
tensive strata,....and so does chtlk, in some countries.
   2do, This earth is  often found in  veins, or filling up rents
 and crevices in  rocky  mountains, and hard  strata.   In  this
 state, this earth is called Spar, Spathum, or, more particu-
 larly, Calcareous Spar, to distinguish it from some other
 stony substances called spars, on  account of a resemblance of
 form, and of their native situation, but which are of a different
 nature.   Its appearance in this state  is that of a whitish'stone,
 more or less transparent, and which, when broken in pieces
 bv the strokes of a hammer, is  shivered into fragments of a t
 rhomboidal figure.  In some veins it is perfectly transparent,.
  and is then  called Iceland Crystal.   This has caugHllhe^ 
     STALACTITES....PETRIFYING WATERS. 173

 attention of opticians, in consequence of its refracting light in
 a particular manner, so as to make objects appear double.   In
 veins that contain calcareous spar, wherever a vacuity remains
 not filled, the inner surface is beset with crystals of the same
 matter,  which are columnar or  pyramidal; and sometimes
 composed of two pyramids joined together, and forming one
 crystal.
   Ztio,  It  is  commonly this earth which  forms  the  stony
 masses called Stalactites.  These  are  stony  concretions,
 formed  chiefly in the roofs of subterranean caves, and cavities
 of some extent.  They are produced by waters which contain
 a small  quantity of this earth dissolved in them, and which,
 penetrating into such caves, drip from their roofs, or ooze out
 from their sides and floors, and deposit this earth.   While it
 separates slowly  from  the water,  it  concretes, and forms
 gradually large pendulous cones and columns, and a variety of
 fantastic figures;  which are found hanging from the roofs,  or
 projecting from the sides and floors of such  caverns, and some-
 what resemble the icicles more quickly  formed from dropping
 water in frosty weather.   The  famous cave at  the Peak,  in
 Derbyshire, is a well-known example of this.  There are
 similar examples near Slains Castle, north of Aberdeen, and
 in many other parts of the world.
   The waters which produce this effect are called  Petrify.
 ING Waters, on account of  their forming these stony con-
 cretions, and sometimes penetrating and encrusting vegetable
 and animal substances with the same  stony matter, so as  to
 convert them, as it were, into stone.  Such is the spring called
 the  Dropping-well, at Knaresborough  in  Yorkshire, which
 has formed a  sort of 'quarry of stone, by petrifying the  moss
 and other vegetables which its water passes over.  There is a
 similar spring in the  Duke of Hamilton's deer park, and  at
 Matlock in  Derbyshire.
   Waters of this  kind are very common in Italy,  in conse-
 quence of the  great quantities of limestones and marbles with
 which that country abounds.  There is a marsh  not far  from
Jftome, the  water of which incrusts the reeds which grow  in it. 
  174   LITHOPHYTA....ZOOPHYTA....MARLE.

  And by means of these waters they  have made very  pretty
  medallions.
    The formation of these calcareous petrifactions and sta-
  lactites, shews plainly that this earth is in some degree solu-
  ble in water: and we have many  other proofs  of this fact.
  Calcareous stalactites and incrustations,  and the petrilying
  waters which produce them, are in general found in coun ries
  which abound with limestone or marble, or other forms <\ die
  calcareous earth. Wherever any parts of the calcareous strata
  are exposed  to the rain, they shew  most evident signs of tUir
  being subject to a slow dissolution and waste.  (A calcareous
  mass at L»rd lilgin's quarry is dissolved at top, and incrusied
  at the bottom).   And when more water gains admittance into
  rents and chasms of such strata, it gradually  enlaiges the pas-
  sages through which it runs, and forms at last extensive uiv.
  erns, in which it is  common to find abundance of  stalactiUs.
  The quantity of this earth, however, which pure water can dis-
  solve,  is exceedingly small, as I have  learned by experiment.
  But water sometimes contains other things combined with it,
  whuh increase its power as a solvent of this  earth.
    4to, The stony shells of all crustaceous .inim ds, among fish
  and reptiles,  from the coarsest to  the  pearl*,  are  made  up of
  this earth, and a small quantity of  animal glue.  And of the
t  same materials are  egg-shells  formed, as also those mariie
  bodies, which, on account of their resemblance to the extein.J,
  form of plants, with the hardness of stone, were formerly call.d
  Lithophyta,  or stony  plants,....as coral, and a  v.nicy  of
  other bodies  of the coral kind, or allied to it, which Later na-
  turalists suppose to be the work of animals, or to be produced
  in the same manner as shells.   And a late author, Pallas, who
  has written particularly upon this kind of productions, repre-
  sents  them in  a still more curious light.   Hence they are
  called  Zoophyta,  or animated plants.  Whatever may be
 their nature,  and in whatever manner  they  may be formed,
 they are composed,  like the shells, principally of calcareous
 earth: and there is a very great variety of them in  respect of
 form and appeara xe.  Some are  spread like a crust upon ,
 stones  and other solid bodies, and full of microscopic pouts/'
                                                        ',  -i 
              VARIETIES OF MARLE.           175

inhabited by animals,....Millepoua.   Oihers are protuberant
masses;  others  an   assemblage of  pipes,....Madripoda.
Others are branched,.... Corals.  These are full of animals.
   Under these four forms now described, the calcareous earth
has generally  a great degree of purit} ; and in son e of them,
perhaps, is pt rfectly  pure,....that is, unmixed w ith any other
earth.  But there are also some fossil earths, which,, though
they be no  composed entirely of calcareous earth, but, on the
contrary, contain sometimes but a moderate portion of it, de-
serve, however,  to be mentii ned here,  on  account  of their
us fulness  and  importance.   These are the  earths  called
Marles,  which have been long successfully  employed as
manure to improve soil.   Every substance to which the name
of marie- is properly  applied,  and  which proves of gen ral
usefulness as a manure, contains more or less calcareous earth;
and  is  useful and valuable in proportion to the quantity it
contains.
   Maries  are commonly divided into three  kinds,....Shell
MARLh, ("lay Marle, and Stone Marle.
   1st, Shell marle is composed of the shells of shell-fish, or
other crustaceous aquatic animals, lying together in immense
quantities.  Many are entire, but in general they are decayed,
and  mostly mouldered down  to  dust, and intermixed with
more or less sand, or other  earthy substances.   When we ex-
amine this matter,  as Occurring in different places, it may be
distinguished into  two kinds,....fresh  water marle,  or bog
marle,  and sea-shell  marle.   We have an example of bog
marle in the Meadow, composed of the shells of the small
fresh water wilk  or snail, which  multiply greatly in lakes or
poncls, or brooks of fresh  water, and of other shells, which are
gradu dly deposited  in great collections by the water.  The
other kind of shell marle, the sea-shell marle, constitutes much
greater collections, which are found in many places, though at
present far removed from  the sea.   One of  the  most noted
examples has been described by Mr. Reaumur, in the Memoirs
'of the Academy*".
•  • C 1 the Falilun or marle of Tcuraine. This district, of 80 square miles
is-more than 36 leagues distant  from the sea, and is every where  filled with
">-. "■■■' 
 *™            VARIETIES OF  MARLE.

   2dly, Clay marles consist  of earths of different  colours,
 which more or less resemble, and actually contain clay.   But
 with it some calcareous earth is mixed,  in  fine powder  like
 chalk.
   3dly,  Stone marles are of very great variety in colour and
 appearance.   They are  harder  and more stony than  clay
 marles; and that is the only distinction between them.   But
 they differ  from masses properly stony in this,  that by being
 only a few  weeks or months exposed to the air, they split into
 pieces, and crumble  down into  earth, or a matter like  clay.
 Some, however, take a long time to break down in this man-
 ner : and there is all the  variety possible  in this respect be.
 tween them and the clay marles.   This disposition to moulder
 down by the weather, depends on the admixture of clay, which
 they contain.  A consequence of the  gradual,  though  very
 slow dissolution of this earth  by water, has  been observed in
 the strata of hard  marles.  It has been found by experience,
 that such strata do not contain  any calcareous  earth where
 they crop out, on  the surface of the ground,  nor even at the
 depth of a  few feet below this. Many gentlemen who were in
 possession of a stratum, which they knew, from the neighbour.
 hood, to be a rich stone marle, have, without fear, expended
 great sums of  money, and covered much of  their land with
 this crop marle. They not only lost their  money, but,  in many
 cases, spoiled their land, by filling it with a hard bakng clay*
 This effect  upon beds of  marle  is without exception: and it
 is even found that the upper plates of single strata of limestone
 are deteriorated in the same way.  This fact also explains,
 by the way, the wearing out of lime used as a manure upon
 land.

marle.  It is found about eight or nine feet from the surface, and they dig it
to the depth of 20 feet.  The marle is still deeper, but it is too expensive to
follow it.  One gentleman, f, om curiosiy, penetrated 18 feet, and did not
know how much farther it might extend.  Suppose it is of no greater depth,
it would contain above 130 millions of cubic fathoms.   It is totally composed
of shells, some qf which are entire, but they are generally decayed, or broKe» •)
into fragments, and mixed wiih other marine productions, such as coralines,  /
millepores, madrepores, &c.
6 
      CAL. EARTH  THE WORK OF ANIMALS.  177

     When we now examine with attention many of these natu-
  ral collections of this sort of earth, we are led to a  conclusion
  which may appear surprising at the first hearing of it;  but
  which is  founded on a multitude of the most authentic facts.
    The inference I mean is, that all the large collections of cal-
  careous earth have derived their origin from shells and litho-
  phyta,  or that they were once in that form.   The proofs of
  this are so numerous and striking, that they cannot be resisted.
    1. Beds of sea-shells, or other calcareous productions  of
  the  sea, are found in many parts of the world, of great extent,
  and in all the different states of decay.
    2. We find abundance of shells, or fragments of shells, and
  of zoophytes, in the greatest number of the calcareous strata of
  marbles, limestones, and  chalk ; which are the greatest collec-
  tions of calcareous earth.
    We do not find shells in calcareous spar, nor in stalactites ;
  but  it is evident that these forms of the calcareous earth have
  been completely fluid,  so that all the organic structure of the
  original matter is necessarily lost.
    There  are also  many marbles and limestones, in which we
  do not find any of the  appearances I speak of.   But this too
  can be explained, by examining their structure or aggregation,
  which shews that the matter of them has been dissolved or li-
 quefied by other operations of nature*.  Another cause of the
 non-appearance of shells and  lithophyta in some  collections of
 calcareous earth is, that the shells have been broken and worn
 down into fragments like sand,  or even reduced  to powder,
 by agitation and attrition, upon the coasts, or by other causes.
 This seems to be the case of chalk.  There is another example
 of this kind in England,  in the Bath stone and Portland stone,
 which are  calcareous: and similar stones occur in many parts
 of the world.  There are some few entire shells found in these
 stones ;  but  the greater  part of it does not exhibit any.
   The abundance and great extent of the strata of calcareous
 earth are, therefore, a proof of the great antiquity of this globe,
 and of the great changes which have happened in its surface.

  • The rapidity with which the coral rocks in the Pacific Ocean are formed,
by the little animals, is  altogether astonishing;  and it is evident to the sight.
    V*OL. II.                 7. 
i"8    UNION  OF CALCAREOUS  EARTH  '

   In some few places the bones of "land-animals have also been
found, in very considerable quantities, mixed with calcareous
matter ; as in Dalmatia, and some islands of the Adriatic ;  at
Gibraltar, in Spain,  and  in France *.
   In whatever condition  the calcareous earth is found, it  is
easily distinguished from other earthy substances, by efferves-
cing with acids ; and, when it is not very impure, by becoming
common quicklime, when exposed for some time to the  actioH
of a strong fire.
   In making.the trial with acids, however, it  is necessary that
the person who makes it should understand it well; as I have
 known  many who never had  seen  or attended to real effer.
 vescences, imposed  upon by the appearance of it. I have often
 had earths sent me by farmers,, or country gentlemen, as cal-
 careous  marles, which trfey assured  me effervesced, or fer-
 mented with vinegar, and dissolved in it too; but which, when
 I tried.them,, shewed not the smallest effervescence.   Upon
 desiring them, therefore, to shew me the fermentation and dis-
 solution they spoke of, I found that they had thrown the earth
 dry into  the vinegar ; and that what was taken for efferves.
 cence,  was the expulsion of a small  quantity of common air
 which was contained in the pores and vacuities of the dry earth,
 and which arose  slowly  in little bubbles, when the fluid was
 sucked into these pores; and.the supposed dissolution was the  Jj
 diffusion of the earth.   Remember, therefore, always to soak
  and moisten with.water,before the acid be applied.
     In describing the properties of the objects of chemistry, I
  begin commonly with the effects of heat.  But, as this earth,
  in consequence of the state in which it is found in nature, un-
  dergoes,, a,very great change  in  all its chemical relations by
  the action of a strong fire, I shall first notice its properties with
  regard to mixture,.in its ordinary or native state.

    * Memoires sur les ossemens fossils qui ont appartenus a des grands animaux:-.'
  Observations de Physique, Mai 1F81.  The author is of opinion that they are
  not the bones of elephants, but of some large aquatic animals which have in-
  habited the lakes and great rivers, or rather the sea.  His observations ren-
  derthis verv probable.  The memoir iscurious, and dec< nes a careful perifc.
  sal. 
       WITH ACIDS....GYPSUM....SELENITE.     17$

   I have already remarked that the action of acids on it is very
similar to  their action on alkaline  salts.  Let us,  therefore,
attend to the manner in which it unites with each of the dif-
ferent acids.
   The first of these, therefore, the sulphuric acid, attaches it-
self to this earth with great rapidity, and violent effervescence.
Thus, when we throw powdered chalk into diluted sulphuric
acid, violent effervescence is produced: but the chalk, how-
ever, is not dissolved.  It renders the liquor thick and muddy;
and,  if allowed to rest, falls to the bottom in the form of a se-
diment much more bulky than the chalk  alone.  The reason
of this is, that  the  compound produced  by the union of the
sulphuric acid with calcareous earth has very little solubility in
water.  It required  a  very large quantity of water to dissolve
it,  500 times its  weight  at least.   Hence, not finding water
enough in the mixture, the greatest part remains undissolved,
and is more bulky than the chalk,  because it consists of that
chalk and the salt  which it has formed  with the  sulphuric acid.
This compound was formerly called Gypsum  or Selenitbs,
or the Selenitic Salt.  The name now given to it, by the French
chemists, is Sulphat of Calcareous Earth, or  Sulphat
•of Lime.  It  is  formed naturally  in  considerable  quantities
in the bowels of  the earth,  and is valued on  account of se-
veral  useful properties which belong  to it.   These we shall
mention more fully afterwards-.
   Although this compound is difficult to dissolve, and requires
■much water to  its dissolution, it can,  however, be completely
dissolved, when enough of water is applied to it, viz. one ounce
for each grain.  And when the water is evaporated, the com-
pound concretes into numerous slender and small crystals,  as
fine as hairs, which. subside  and  form a white sediment.   A
small portion of this salt is the general  impurity of those spring
waters which are called hard waters.
   Such is the action of the sulphuric  acid upon this earth,  in
the form of powder.  But it does not operate upon it so readily
in its solid and compact form, because the surface is neutralis-
ed, and protects the interior parts  from the corrosion of the acid.
   None of the other acids, hitherto described, form insoluble
-or difficultly soluble compounds with this earth, except the tar- 
180 CALC. SALTS DECOMPOUNDED BY ALKALIS.

tarous acid,  which forms with  it the compound  called by Dr.
Scheele selenites tartareus, now named the tartrite of lime *.
    The other acids, viz. the nitric, muriatic, and acetous acids,
form with it  very soluble  compounds;  and all of these acids
too, as I before observed, are attracted by the earth in the same
order as they are  attracted by the alkali: and therefore, if the
sulphuric acid be added to the solutions  or compounds  formed
by any other acid, it immediately disengages the other acid, and
unites itself to the earth, in consequence of its stronger attrac-
tion, forming with it the sulphat of lime already described, which
therefore precipitates or falls to  the bottom.
    The calcareous earth not only has a  stronger attraction for
the  sulphuric than for  other acid, but, further, some experi-
ments shew that it has a greater partiality (so to call it)  for this
acid above others,  than  the alkalis have.   This I think appears
from what happens when we mix any compound salt containing
the sulphuric acid, with a compound or solution of the calca-
reous earth in any other acid than the sulphuric.   Thus, if we
mix a solution of Glauber's salt,  or sulphat  of soda, in  hot wa-
ter,  with some of the solution of calcareous earth in nitric acid
greatly diluted, the mixture will  become muddy, and deposit
a sediment.   There  is  therefore a double  elective attraction.
(See Bergmann.)
    There are only two  of the acids already described,  which,
as I learned by some experiments made on purpose, have not
power to act on the calcareous earth in its natural state.   These
two acids are the sedative salt or boracic  acid,  and the sulphur-
ous  acid  (acidum sulphurosum), or acid of sulphur in its vola-
tile suffocating state.   And to these we  may add sulphur itself,
which was spoken of in treating of the sulphuric acid.   These
three  chemical bodies,  the boracic acid,  the sulphurous acid,
and sulphur itself, are but weakly attracted by alkaline substances
in general.
    With regard to the  other class of simpler salts, the alkalis
shew as little disposition to act on calcareous earth as on one
another.  The only observation that belongs to this head is, that
    * It forms  insoluble compounds  also with the  phosphoriv   udic, and
some other acids....editor
P 
        ITS ACTION ON  NEUTRAL  SALTS.    181

they have a stronger attraction for acids ;  and when mixed with
solutions of the calcareous earth, immediately precipitate it,....
uniting  themselves to the acid in its place.  And the effect is
the same, whether we use a fixed or a volatile alkali in their or-
dinary state.  It should also be remarked,  that when  an alkali
is employed to dislodge calcareous earth from an acid, we have
no effervescence.
   Such is the relation of the calcareous earth to the  acids and
alkalis.
    Of the compound salts,  none are affected by it except tar-
tar,  and the ammoniacal salts.   Tartar,  when boiled  with it, is
neutralized, or,  to express it  more properly, it is deprived of
its superfluous acid.  And the ammoniacal salts can be decom-
pounded by it, but only when it is assisted by heat.
   If, for example,  we mix chalk with common sal ammoniac,
....the muriat of ammoniac; either taking this salt as  dissolved
in water, or in the form of very fine powder, we cannot perceive
any  change  or effect produced, however long they remain sim-
ply mixed together.   But if they be mixed in  the form of fine
powders, and we then apply heat to this mixture, as soon as the
heat increases to a certain degree,  the  ammoniacal salt begins
to be decompounded.  The acid of it is joined to the calcare-
ous  earth ;  and  the volatile alkali arises  into the receiver in
large quantity, and forms a very solid saline crust on its internal
surface.  The process is as easy  as the distilling of water.  The
vessels are to be  luted with chalk made into a thin paste, with
mucilage or gum-water.   The  heat may be slowly  raised  till
the sublimation begins to  dim the vessels, and then kept in that
state; and the operation stopped whenever a dimness appears
in the top or neck of the retort.   This indicates a commencing
sublimation of the  sal ammoniac, if too little chalk  has  been
employed.
   This process for decompounding sal ammoniac by the action
of chalk and a strong heat,  is often  performed in England, to
obtain a volatile alkali for the purposes of medicine.  The alkali
thus  obtained is remarkably solid and dry, and in larger quan-
tity  than that which is procured from the same quantity of sal
ammoniac, M'hcn  it is decompounded by  a fixed alkali.
■v 
182      QUICKLIME....PREPARATION  OF,

  These are the properties of the calcareous earth with regard
to mixture in its natural state.
  But it suffers a remarkable change by the action of fire on it,
which is next to be described.
  If it be exposed to the  action of a  strong red  heat for some
time, it becomes what is well known by the name of Quicklime.
For this purpose, the marble, limestone, or chalk, is broken into
pieces of small size, and piled up in a kiln built in the form of
an inverted  frustum of a cone,  mixed with a proper quantity of
fuel, taking care to have a sufficient quantity of fuel at the bot.
torn, to raise a heat in the beginning;  and also taking care that
the whole may be so piled up, with  spiracles properly conducted   ,
through it, by laying the materials open in those places, that the
heated air may have a current pretty equably distributed through
the whole mass.   This soon kindles  the interspersed fuel all
over the kiln." And it would soon  become so hot as to risk the
melting of impure limestone, were it not-checked by contracting
the apertures by which the air  enters in below,  or (if it  be a
simple clamp kiln) by covering the whole at top with .earth.   The
proper degree of heat must be learned by trials ; it  being dif-
ferent according to the nature of the limestone ;>nd also of the
fuel.   Some pit-coals have a great tendency to vitrifv even the
purest limestone.  And limestone containing iron in any  state
is very much  disposed  to vitrification.  It is only "experience  '■*
which can teach how much fuel is required for raising the due
heat, and for continuing  it  till all shall be calcined.  If it be a.
clamp kiln, the fire is allowed to burn out: and the quicklime is
taken out whenfche kiln is sufficiently cooled'. ' But limekilns are
more artificially constructed, so that the work is never stopped.
The calcined  lime is taken out at an opening properly contrived
below, by which the whole subsides:  and the limestone is con-
tinually added above, mixed with  baskets of fuel. The fuel is
entirely consumed in die lower and narrower part of the cone..
And the great heat of the glowing blocks of quicklime maintains
the current of iresh  air through the interstices, and causes it to  \
arrive at the unconsumed fuel above, in a state fit for continuing
the combustion.  The  consumption of the fuel is vastly slower
than  would happen  were it  interspersed in the  same  maunec 
         AND GENERAL  PROPERTIES.       183

among lumps of free-stone or pebbles, for reasons which you
will soon understand.
  When we want to prepare a small quantity for experiments,
we just mix. it with abundance of fuel, in any ordinary fur-
nace, and  urge it with the greatest  heat,  which will not
vitrify it when impure.   Pure limestone^ marble, or  chalk,
may  even be  calcined in  a  crucible,  without touching the
fuel: but this requires a very great heat, long continued.
   Quicklime has a number of qualities different from those
 of the natural calcareous earth.  If it have been hard before,
 it becomes more  friable  and  porous,  especially the  purest
 kinds.   It also loses  a very great part of its weight, 40 per
 cent,  in  the purest kind.   This great loss is well known,to
 those who have occasion  to bring lime from a  distance ; and
 it is the best mark of complete calcination.  Further, from
 being a mild, insipid, and inert earth, we find it now an
 active  and acrid substance, like the  alkaline, salts.   It
 shews  a very  considerable  degree of activity in mixture
 with a variety of  other bodies.  Applied to the  tongue,
 it  is extremely  acrid, giving a  taste  very  much like  an
 alkaline salt.  If left anytime upon a moist succident psrt of
 animal or vegetable substance, it either corrodes and dissolves
- it to a pulp, or weakens the cohesion of it to a great degree:-
 and it has the same effect on the most solid and firm parts, if
 it be made into  a soft paste with water before it is applied.
 This shews  that it has a  strong chemical  attraction for the
 matter of those substances.  We discover in it also a strong
 attraction for water.   This attraction is one of the most r*
 markable qualities by which it differs from calcareous earth
 in its  native  state.   Thus,  when we pour watei upon the
 lime, a quantity  of it is quickly sucked up into the pores of*
 the stone : and, after a  short time, the masses of quicklime
 which we have moistened begin to grow warm, and to smoke.
 They swell, split, and crumble down into pieces : and these
 are affected in the same  manner, until the whole,  in a  few
  minutes, is converted into a subtile white powder,  greatly
 more bulk)-, and which, if  too much water  have not been
 used, is  perfectly dry and dusty. 'While this is  going on,
  it becomes so hot,.that a part of the  water is evaporated in
 boiling hot steams: and if the quantity of lime so wetted at 
18 4
SLAKED LIME.
once is much greater than this, the heat increases to a degree
capable of inflaming combustible  bodies.   If a stick,  for
example, be thrust into a large heap of it, the extremity will
be burnt to a black coal.   Leaky ships have sometimes been
unfortunately set  on fire at sea by a cargo  of quicklime.
This is so well known, that when they venture to load with
it, they take  every precaution to prevent such a misfortune.
   As soon as the lime has been thus reduced to  a subtile
powder,  by a sufficient quantity of water, no more heat is
produced.   It  cools and  does not produce  heat again if
mixed with  water.   It is called   Slaked  Lime,...Calx
Extincta.  If we weigh  it, we find it considerably heavier
than before the water  was added to it.   This addition of
weight is from a part of the water now closely united with it;
every particle of the lime having its due proportion.   The
water thus united with the lime is retained by it with a strong
attraction ; and  cannot be separated  again without  a red
heat.   Being in  a solid form, the emersion  of  the latent
heat,  which  occasioned its fluidity, is  the  source of that
great heat which is produced during  the  slaking  of the
lime, and affords one  of  the  most remarkable instances of
this emersion.   But if such a heat be applied to the slaked
lime in a retort and receiver,  we recover the  water  in  its
former state.  The lime from which it is separated becomes   j
quicklime again, and is disposed to  produce the same effects
with water as before.   These effects,  therefore, evidently
depend on a  strong attraction which the lime and water have
for one another.   And slaked lime is  lime saturated with
water, or  combined with as much water  as can unite with it,
so as still to  form a dry compound.   The  consequences of
this union with water, however, are not such as to take away
the attraction of the lime for other substances.  It has the
same acrid taste as before, and the  same, or even a greater
corrosive and dissolving power, with respect  to a variety of
different substances.   Nor is  its attraction for water satu-
rated by  this solid  combination.  It still manifests a solu-
bility in that fluid, perfectly resembling, in this respect, the , y
relation of crystallizable salts to water.  They, after having
combined  with a certain quantity,  are dissolved in a larger   .
quantity.   This  solution is  perceived when we mix slaked 
LIME-WATER.
185
 lime with a much larger quantity of water, or dilute it largely
 in water.   If we examine this water,  we shall find that it
 has either dissolved a part of the lime, or  extracted some-
 thing from it, so as to  form a clear solution like that of the
 alkaline salts, and resembling them much in taste.
   This is the fluid called Lime-Water, the nature and best
 preparation  of  which was,  some time since,  a subject  of
 much disputation in this place.   The  general opinion was,
 that the production  of the lime-water depended on an active
 and subtile principle, extracted by the  water from the lime,
 which was imagined to contain only a small portion of it;
 and that the lime  could  therefore  make only  a moderate
 quantity  of  good lime-water, such  as 10 or 12, or at most
 20 times its weight.
   It is known now  that a much greater quantity of  good
 lime water can be made  of lime,....that  is, of a good quality;
 perhaps 300  or 400  times its weight.   And  the process for
 making good lime-water is so simple,  that  it was  thought
 unnecessary  to  insert it in the former editions of  the  Edin-
 burgh Pharmacopoeia.  But  a process was given for it in the
 last edition, viz. lmo, Slake the lime with a small quantity
 of water, about  one-fourth or one-third  of its weight, and let
 this be  done  in a vessel of earthen ware or glass, keeping it
 covered while the lime is slaking :  2do, Pour on it 30 or 40
 times its weight of more water, and after agitating to diffuse
 the lime through the water, cover up the vessel again.   The
 agitation  being repeated afterwards 10 or 12 times to pro-
 mote the  dissolution, we may then allow the  remaining lime
 to subside, and filtrate the lime-water, to have it clear.  Thus
 lime-water is made as strong as possible.   But, in its strong-
 est state  it  contains  but a small proportion of the lime, or
limy matter.    I made experiments to  ascertain this point;
 and found, that  the strongest lime-water we can make,  does
not contain a larger proportion of lime  than  one part in  500
parts  of the water.   It has, however, a pungent, acrid, dis-
agreeable taste, resembling  that of the alkaline salts ;  and
has also the power to change the vegetable colours like those
salts.   A moderate  quantity produces  first  a sea-green ;  a
little more, a grass green ; and more still, a yellow, or fille-
mot, attended with  muddiness; the  colouring matter being 
186  RELATIONS OF  LIME  TO THE  ACIDS.

corroded  and destroyed.   It is the  most transparent fluid
known.
   Such are the effects of water  mixed with lime in different
ways.
   When we next try the effects  of acids, we  find that lime
is  still more disposed to unite  with  these, than the calcare-
ous earth was when  in  its natural state.   It  unites much
more quickly with  the  vegetable acids.  Distilled vinegar,
which  dissolves  the  calcareous  earth but slowly,  dissolves
lime readily and quickly.   And when we boil  lime with a
solution of tartar in hot water,  the  lime takes to  itself the
whole  acid of the tartar,  not  the superfluous acid  alone,
which  only is separated from  the  tartar by the calcareous
earth in its natural  state.
   Further, lime can be joined wiih the boracic and sulphu-
rous acids, so as to form a borat and  a sulphite of lime ; nei-
ther of which can be produced from  the natural calcareous J
earth.   And when  we mix lime  with  the muriat of  ammonia,
it  shews such a  strong propensity to  unite with the muriatic
acid, that it decompounds  the muriat the moment they are
mixed  together, not requiring the assistance of a strong heat,
which is required by the natural calcareous earth.
   Beside the quickness and facility with which lime decom-
pounds the ammoniacal salts, the  volatile alkali,  which we  I
obtain  from the mixture by distillation, is in an uncommon
and  very remarkable state.    When heat is  applied,  this
alkali arises in vapours which are in the highest degree elas-
tic, pungent, and penetrating.   They cannot be condensed
without the aid of  some water to repress their volatility by
its attraction.   Were we  to neglect  the proper application
of water to this mixture, for the  purpose of condensation,  <
this  alkali would continue  in the staled of an  incondensible  (
elastic fluid or gas.   This is what  Dr.  Priestley called alka-
line  air,  and made the subject of many experiments.  One
of them is very pretty and amusing.  If some of this vapour
be mixed with that of the muriatic acid, we have immediately jg
a precipitation of sal ammoniac.  If this experiment be made
in the  modern pneumatic apparatus,  a disagreeable accident
sometimes happens.   The vapour of either being  suddenly
mixed  with the other, in the upper part of a jar, standing in 
   ITS ACTION ON AMMONIACAL SALTS.  18/

water or mercury, the whole collapses in an instant, and the
water er mercury dashes against the top of the jar with such
force, as to beat  it up to a considerable height, and with risk
to the operator.                   v
   When we do employ water, though in no greater quantity
than what is  absolutely necessary, no part of the alkali  is
ever condensed into  a solid form.   It  always constitutes,
with the water,  an highly pungent,  acrid, volatile,  alkaline
fluid.
   A volatile alkali is ordered to be prepared in  this state,
in both the London and Edinburgh Pharmacopoeias.  It was
formerly named Spiritus Salis Ammoniaci cum calce viva.  Now
it is named Aqua  Ammonice puras, for a reason which you will
soon understand.
   Various processes have been recommended, by different
authors, for preparing it  in the best and most  convenient
manner.   Some  have advised to put the quicklime  into the
retort unslaked,  and  then  pour  on it the  sal ammoniac dis-
solved  in  water.  But this mode  is  inconvenient,  causing
sudden and violent heat, which  makes the volatile alkali rise
so  impetuously,  and in such  incoercible vapours, that the
greater part of it is lost.   In distilling it,  a very gentle heat
is absolutely  necessary,  that time may be. allowed for  its
condensation,  by means of its union with the  water that is
to assist  in condensing it.  It requires  much caution and
patience to accomplish this •   because the  alkali rises  in
vapour more readily  than  the water, and  does not carry  off
with it a very considerable portion. And,should we attempt to
promote the condensation by putting water into the receiver,
we shall still be disappointed ; because the alkali, combined
with the water merely sufficient for its condensation, forms
a fluid considerably if|fhter than  water, which will, therefore,
float on the surface of that in the receiver, and this, being
already saturated with alkaline vapour,  will  condense  no
more.   I mention this particularly,  because similar things
frequently occur  in  distillations;  and must be carefully
attended  to,  to  avoid accidents.   Mr.  Woulfe's  method
obviates this difficulty: but is best adapted  to the distillation
of large quantities. 
 188  PROCESS  FOR  PUNG.  VOLAT.  ALKALI.

    After having tried different methods, I now practise one
 which  does not  require  this complicated  apparatus,  and
 serves  very well for preparing a small quantity of this alkali.
 Having put the sal ammoniac, in lumps, into the retort, pour
 on it a mixture of an equal quantity of Time, and thrice its
 weight of  water, stirred  till uniformly mixed, and kept till
 cold. The volatile alkali begins immediately to be separated
 in pungent  vapour : but, as there is enough of water present
 to repress and moderate  its volatility,  the vapours are not
 troublesome.  Now apply the receiver, which has first been
 well warmed,  to rarefy the air, and thus expel a  part of it;
 and immediately cloae up the joining of the two  vessels,  so
 as to make  that joining perfectly air-tight.   This  is done by
 first applying common putty,  made of chalk and lintseed oil.
 But as this paste,  though impenetrable to air,  is  in some
 degree  soft, and would be  forced open by the pressure of the
 elastic vapour from within, we may secure it  from this accident
 by  putting over it another  luting,  which will soon grow quite
 firm and  hard,  and will bind the  putty  strongly in its  place.
 This other luting is a mixture of chalk and gum-arabic,....
 nine parts of the chalk to one of the gum.  It must be made
 into a fluid-paste with water,  and spread on slips of paper,
 and these put on the  joint.   Being then brought into close
 contact with every part of it by a ligature  or bandage, it makes
 the joint so close and  strong, that the vessels would be burst
 open in any other part of them  sooner than in this.   The
joining being thus made perfectly air-tight, it is evident that
 we must be very cautious in applying the heat to perform the
 distillation.    Too  much  heat would  certainly  burst  the
 vessels, by giving too much elasticity to  the air and vapours:
and it would also bring over too much of  the water, supposing
the vessels were strong enough to withstand it. We,therefore,
apply a very gentle heat, and  apply it so long only as may be
necessary for obtaining the product in proper quantity.  Thus
the alkali, and a portion of the water, will distil over together,
slowly and imperceptibly, until we have  enough of it,' which
will be the case when the heat shall have continued 24 hours.-
(See note 35, at the end of the volume.)
  Beside this  action  of quicklime on muriat of ammoniac,
sjxd  other qualities of it  which  we  mentioned,  a  further 
       RELATION  OF LIME TO  SULPHUR.    18J9

 particular,  which  shews  that its  powers, as  an alkaline
 substance, are increased, is its effect on sulphur. It is capable
 of uniting with it in the dry way, by mixing it in powder with
 the sulphur, and applying such a heat as converts the sulphur
 into vapour, or melts it.
   But a more convenient way is to join them in the way of
 solution, or via humidd. Equal  weights of sulphur and quick-
 lime must be mixed in a flask, and a quantity of water added
 boiling hot.  The mixture  must be boiled for some time,
 and then more boiling water added, and the boiling repeated.
 After standing a proper time for subsidence, the clear liquor
 must  be decanted into a  phial, which  must be carefully
 stopped.  This gives a perfect compound  of sulphur  and
 lime.
   The compound we thus  obtain is called the sulphuret of
 lime,....sulphuratum calcis.   It is incomparably more soluble
 in water than the lime alone :  and ft has the same yellow
 colour and  disagreeable odour,  that  is  so strong in  the
 compounds  of sulphur with alkaline  salts.   The union of
 the two ingredients of this compound  is  similar to that of
 the  alkaline sulphuret.   It is  decompounded  by exposition
 to the air :  and in its place we obtain gypsum  or selenite,
 composed of  the  sulphuric  acid and   calcareous earth.
 Moreover,   this  decomposition   is accompanied by  the
 absorption of oxygenous gas,  leaving only the mephitic air
 of Scheele,  or the phlogisticated air of Priestley.   Indeed,
 it was  with  this sulphuret  that  Scheele made  his first
 experiment.  Like the alkaline  liver of  sulphur, too, it is
 decompounded  by any  acid.   The nitrous acid  does  not
 disengage from  it the hepatic or stinking gas, without some
 particular attentions,  which shall be mentioned afterwards.
   All these facts and experiments shew that lime has  a
 stronger  tendency to  unite with  other  bodies  than  the
 calcareous earth has when in its natural state.
   The most remarkable property  of lime  appears in  the
 change which it sustains by mixture with  the alkaline salts,
 and the change which it  induces on them.   This constitutes
'the chief difference between quicklime and the natural or
 crude  calcareous,  earth.  If we  mix  it  properly  with an
 alkaline  salt, the  lime  immediately loses its activity and 
 190 MUTUAL  ACTION  OF LIME AND ALKALI.

 corrosive nature,  and becomes quite  mild, insipid,  and no
 longer soluble in water.  To illustrate this,  we may notice
 the effects of an alkali upon  lime-water.  This fluid, as I
 observed before,  contains  but a small  proportion of limy
 matter dissolved in the water, about  one grain to the ounce.
 Yet, upon dropping into  it  a small quantity of  dissolved
 alkaline salt, it instantly becomes muddy, and deposits the
 lime in the form of mild insipid calcareous earth.  And the*
 effect is similar when we use,  instead of lime-water, a muddy
 mixture  of lime and water, or a quantity of water with more
 lime in it than it can dissolve into  lime-water.   Provided
 we add to such a mixture a sufficient quantity of the alkaline
 salt, both the dissolved part of the lime, and that which, for
 want of  a sufficient quantity of water, is not  dissolved, will
 be  immediately rendered  mild,  inactive, and  incapable of
 being dissolved by pure water.
   Here  is, therefore, a sudden restitution of the lime to its
 original  state of a mild, inactive, insoluble earth;  for when
 we collect and dry the mild  earth thus obtained, we find it
 has every property of the calcareous  earth, in its natural or
 ordinary state, and may again become lime by calcination.
   But, further, when this change is produced  in the lime,
 the alkali suffers  one which is as remarkable.   This is per-
 ceived when we  separate  the alkaline liquor again from the
lime, and examine this liquor, or by evaporation obtain the
 alkali again in a dry state.
   We find it incomparably more fusible than before.   It is
 melted long  before the heat of it is raised to the degree of
 ignition.
   Moreover, it becomes more susceptible of vaporisation.
 A very sensible quantity is carried off  by hasty boiling the
solution  of it in water : and if lorfg continued in a red heat,
with spongy matters to prevent its melting, it evaporates very
fast, and is lost.
   We find also that its acrimony, or activity to dissolve dif-
ferent substances, is very greatly increased.   In the treat-
 ment  just now mentioned,....the melting of  it by heat,....it
 often  happens, that  by raising it to a red heat, it dissolves
the earthen vessel in which it is melted,

                                                  '  ♦■.   • 
     PREPARATION OF  CAUSTIC ALKALI.  191

   Alkali, rendered more  active in  this manner by lime, is
much employed in some of  the arts; and, being also  used
for some purposes in  medicine, is ordered to be prepared in
both our pharmacopoeias.
   Three parts of alkaline salt, and four parts of  perfect
quicklime, are  to'be suddenly mixed in twice their weight of
water.   This will produce great heat' and ebullition.  The
vessel must be  covered, and the mixture agitated repeatedly.
It must then be poured into  a  filtrating funnel, which is set
into a phial, or other  vessel, proper for holding the lixivium.
After it has ceased running through the filtre, water  must
be  poured on above, and allowed also  to run through the
filtre, till the whole lixivium is  about thrice the weight of the
salt  and lime.   It will be without colour or smell, if these
have been pure, and must be  kept in bottles closely stopped.
The water may be expelled by heat.   When the boiling has
ceased a little while,  the purely saline part remains fluid like
sluggish oil; and  the vessel is, at this time almost red hot.
When poured out on  an  iron plate, it  quickly congeals ;
and may be divided,  while very hot, into pieces fit to go into
the  mouth of  a phial,  where  it may be kept shut  up  from
the  air.  This is the alkali causlicum acerrimum of the dis-
pensatory.   The causticum mitius is made by pouring the
melting salt on quicklime,  and mixing before  it cools.
   The advantages of this process are, 1st, The lime, being .
slacked with unusual violence,  is the more subtilely divided.
2d, The heat promotes the  action of the lime and alkali.   3d,
The small quantity of water used also promotes their action;
the lime not having room to subside.
   Here I must mention a circumstance which I am  not yet
able to explara :  namely, that this caustic ley has a singular
effect on the earthen-ware vessels in which  it is kept.   1
always used vessels of that kind of pottery called in this coun-
try stone-ware, which is a  species of  porcelain, far superior
to the soft bibulous  pottery.   I have  very often observed
that, after two  or three months keeping in such vessels, they
split all over, with a  loud crack.  The same observation has
been made by other persons of my acquaintance.   Nor  is
this confined to this particular  material.   It happens also to
glass Jbottles, though not so frequently.   The only conjecture 
 192 GREAT ACRIMONY OF  CAUST. ALKALI.
 that  I can  form on the subject is, that the alkalis, acting on
 the  inner  surface  of  a vessel not  well annealed (and it is
 scarcely possible that any can be  perfectly annealed) corrodes
 the stratum which serve to support the whole in its state of
 unequable  contraction.   Yet I  could not see any such cor-
 rosion.
   I have also observed, and my observation was confirmed
 by Dr. Irwin, that caustic ley, very long kept, loses its acri-
 mony ; and that its alkaline  properties are really impaired,
 as if the salt  had evaporated from it, or that it was neutra-
 lized by some other substance.   You will notice that  I sup-
 pose it all the while to have no communication with the air.
   Dr. Alston made an observation on caustic leys, which is
 curious, and of which I do  not  see any explanation.   The
 specific gravity of  an alkaline ley is considerably diminished
 by adding lime to it.   This  effect is very remarkable  in the
 solution of  volatile alkali.
   The activity of the allkali,  to dissolve animal and vegetable
 substances, is now increased to  a surprising degree ;  some
 of the firmest parts of animals   being soon dissolved by it
 into a pulp.  Hence it is often  used externally in surgery,
 for opening abscesses, destroying fungous flesh, or making
 issues in the skin, when the patient is afraid of the  knife.
 It acts with burning pain:  Hence it is called the Potential
 Cautery, or  the Caustic Alkali.   Notwithstanding this
 high degree of acrimony, it has been used of late internally.
 But it must be greatly  diluted and obtunded, by which means
 the fossil acids  themselves   may be taken  internally with
 safety.
   Such is  the activity of the caustic  alkali  with respect to
 animal substances.   Of the vegetable there are many which
 it will penetrate and  dissolve as readily.   But  the  dry or
 pure woody fibres of vegetables  sustain  its action for some
time.  Of this  woody or fibrous matter, cotton,  bleached
linen,  paper, and the like substances, are composed.   Even
these,  however, though they are not dissolved, are corroded,
or made tender by it, and their cohesion much diminished, as
has often happened to linen  cloth in  bleaching.   The two
fixed alkalis acquire just the same  activity from lime, and
have the  same effect upon lime.   The volatile alkali likewise 
          LIME EXPOSED  TO THE  AIR.       19^
                             r              .
produces the same  effect upon  the lime, in restoring  it to
its mild state ;  and is affected itself much in the same way
as the fixed alkalis are, if allowance be made for its different
nature.   Its volatility is prodigiously  increased, as I have-  •
already observed : and it is now  incomparably more acid and
pungent, so that it must be smelt to wjth great caution, other-
wise it  will excoriate and  destroy the nostrils.  Jdbe  the
caustic fixed alkalis, it  dissolves  animal and vegetable sub-
stances  into a pulp;  and acts on  oils and fats in the  same
manner, making them miscible with water;  in short,  ren-
dering them soaps.  It becomes precisely the same with the
spiritus salis ammoniaci cum cake viv..  As in that preparation
the vapours are incondensible without water,  so, when as little
as possible is used, they are inseparable by distillation.  Mr.
Du Hamel  imagined that the volatile alkali was  destroyed
by repeated additions of lime:  but this is a mistake, owing
to the  escape of  part of it at each addition, by the sudden
eruption of  incoercible vapours, in consequence of the  heat
produced by the addition of  the lime.
   I  have now described the more remarkable properties of
quicklime  in the  way of mixture.  I  must now observe,
that when it is  exposed to the air, it begins, after some time,
to swell, split,  and crumble down, until it is slowly reduced
to as fine a powder as when it is  slaked with water.   This
happens to it plainly in consequence of  its gradually attract-
ing humidity from the air, until  it has received enough to
saturate it, or to convert it into slaked lime.    But the lime
slaked in this manner is not so acrid and active as that which
is slaked immediately with water, and" without being much ex-
posed to the air.   The air, at the  same time that it supplies
humidity to  it,  is  also found to weaken its force by degrees,
and continues to weaken it more after it has been completely
slaked, until, in a certain length of time, it deprives it of the
qualities of  quicklime altogether,  and reduces it to the state
of insipid calcareous earth.
  The lime  does not undergo this change when it  is preserv-
ed in close vessels.   It suffers it only when  we expose iufco
the free air, or when we keep it in  vessels  that are left  open.
And we further find, that the  more wide and loosely it is
spread  out to the air, it  becomes  inert so much the sooner.
    vol.  n.                  K  h 
191                LIME-MORTAR.
 It loses its activity faster, in proportion to the more  extcn-
 sive contact or communication of the free air with it.
   But, if the lime be made into a paste with water, and this
 paste be collected  and compacted together in the  form of a
 round mass, it t;*cu retains its activity, and the other quali-
 ties of lime, mii'-h lunger than when  it  is  exposed to the
 state of a dry powder, and spread out  to the  air.   And the
 reason is plain:  when it is in the state of a paste,  the water,
 filling up the interstices between the  particles, excludes the
 air from among them  ; and only those that are at the outside
 of the wet mass can be affected by it.
   Lime-water is also liable to  a similar  cRange by exposi-
 tion.   It may be preserved  in the  same manner  for a long
 time  in close vessels,  without alteration  of  its  qualities.
 But if it be left in an open vessel,  we  may  see,  in  a few
 minutes, a thin  film produced upon its  upper surface, where
 it is  in contact with the air.  This film continues to increase
 in thickness,  until, after  a number of hours, or  perhaps a
 few days,  it will form a thin stony crust.   In proportion as
 this crust is formed on the top, ihe water  below loses its
 taste and the  other qualities of lime-water, and at last be-
 comes a mere insipid  water.   The crusty matter  itself, on
 examination,  proves a mild calcareous earth, like  the calca-
 reous earth in its natural  state.   These several particulars
 occasioned  lime-water to be considered as a surprising un-
 accountable fluid.   When  fresh drawn from the lime, it has
a pungent, acrid, alkaline taste, and several other qualities,
 as if it contained  an  alkaline  salt.   And  it  retains  these ,
qualities if  it be shut up  in close vessels.   But if exposed
to the air, it becomes quite insipid.   And yet we can observe
no cause of this change, but the separation or rejection of an
 earthv matter from it, which  is also perfectly insipid, and
 which  cannot  again be dissolved.
  There remains to be mentioned one other property only
 of lime,  and it is one of  its most useful properties; I mean
 that  of making good Mortar,  when  it is skilfully mixed
 with sand and water.   The qualities  of good mortar are, to
 adhere readily to stones  or other  solid bodies ; to cement
 them together;  and to acquire, by time, a stony  hardness.
 These qualities, in such  a mixture, have been thought the 
         PROPERTIES  OF LIME-MORTAR.     195

more surprising, for these reasons, that lime and water with-
out sand has not  all the qualities of good mortar, and that
nothing is so little disposed to cohere as sand by itself.
   After all, however, the effect of the sand, in giving cohe-
sion and hardness to the lime and water, has been exaggerat-
ed.   And  Mr. Macquer errs a little from  the  truth, when
he says that lime and water without  sand do not concrete in
the least.
   If we give to a paste of lime and water the form of a small
ball, and allow it time enough, that it may dry slowly, it will
contract its size, and become very hard,...harder, I believe,
than if sand  had  been  added.   But that is not the  way in
which lime-mortar is used.  It is  not made into balls  or
other masses that are to dry and harden without being con-
nected with other matter.  It  is employed for  cementing
stones or bricks together, and for plastering walls and other
such parts  of buildings.   And, if it were  made up so as to
be liable to contract much in drying, the consequence would
be, that  it  must necessarily separate from those  bodies to
which it is applied, and which cannot contract along with it;
or, if continued adhering to them,  it must split and divide
itself into  innumerable  small parts, and  so  become q  ite
shattered and useless.  The reason why lime  alone, when
made into  a paste with  water, contracts so much, is the great
quantity of water which  such a paste contains ; for  a good
quantity of water is required to make slaked lime  into a soft
paste.   But  this contraction  and its consequences are pre-
vented almost entirely by the addition of sand to the lime.
   Some skill, however, is required  to add the  sand in the
most proper manner.  If too much be added, the  mortar
will not be very  hard  and firm when it dries.   The sand
will give it  an openness  of  texiure, which diminishes the
cohesion of its parts, admits water too readily into its pores,
and exposes it to the. effects of frost.
   Some time ago, a French engineer, Loriot, proposed a
contrivance,  which  he  asserted to  be a great improvement
in the composition  of  lime-mortar for many purposes,  and
by  the use of  which less sand  was  necessary to prevent its
contraction.   He  made common mortar with  the  usual pro-
portion of  sand,  but with  a lit|)e moru water  than ordinary, 
196  LORIOT'S  PREPARATION OF  MORTAR.

so as to be almost fluid ;  and just before using it, he added
to it one-fourth or one-third of quick-lime, not slaked,  but
reduced to powder mechanically.    When  quicklime is thus
mixed with a good deal of cold water,  it  does not slake so
suddenlv as when no more water is used than is necessary to
.slake it.   The quicklime put in  does not swell  and slake
until the mortar is used, and put in its place.   The powder
of the quicklime, then slaking throughout the whole of the
mortar, absorbs and consolidates  a part of the water which
it contains :  and  the mortar becomes hard and dry remark-
ably soon, and witn.mt contracting.  And when the rest of
the  humidity  is evaporated, it acquires a degree of hardness
and compactness far superior to that of ordinary mortar.  It
is impenetrable by water.  Vases of it filled with water do
not  imbibe a sensible quantity.  The hardness and strength
of this mortar, is u idoubtedly owing to its density and more
perfect setting.  Mr. Loriot was of opinion that the Romans   i
made their mortar in some such manner.   Lime  mortarsets,  ]
in time, if left at rest.   This  setting is somewhat analogous
to the concretion of salt  and water in the  act of crystalliza-
tion.  Mortar  will  set again  and again,  after kneading or
beating up, but more weakly than before.   Loriot's mortar,
therefore, must set the most strongly of all, because it is not
afterwards disturbed.                                       ^
   Since Loriot, Dr.  Higgins  of  London published a little
tract on  this  subject, containing  a  description of a great
number of experiments, made to discover  the best composi-
tions for  making mortar or lime cements of different kinds.
 His  experiments 2gree  in shewing  that  the  hardness and
 strength, which mortar or  lime   cements  acquire,  depend
verymuch on the freshness and activity of the lime employed.
 And, irf his receipt for the best composition,  he insists par-
ticularly  on a method of  using  the whole lime in its most
 active possible state,  so as it may be exposed to the  air as
little as possible, after being burnt  and slaked.    And he also
found that much advantage was gained by using sands of^dif-
 fercnt sizes  mixed  together,  and  even a  small addition of
 some other ingredients  still finer than the  finest sand.   The
particulars of all this are in his pamphlet, which I think judi- 
                THEORIES  OF LIME.             197

   There is a way of making a lime-mortar or cement, the
concretion and induration of which  does not depend on its
being dried.  It is found to concrete and become hard and
very durable, even under  water, and is therefore used in
buildings or works that stand in water, or are very much ex-
posed to be washed by it;  and such mortar is named water-
mortar. Mr. Smeaton having had occasion to use this mortar
in building a most useful and  important light-house, which
stands on a low narrow rock in the  mouth of  the Channel,
where it is often exposed to the utmost  fury of the vfaves,
exerted all his ingenuity to make the building durable ; and
among many other points, made a number of experiments to
ascertain  the best composition for water-mortar. And he was
so accurate and industrious in his investigation of it, that he
is the best author to be  consulted  on  this subject.  The
detail of his experiments is given in the account he published
of the building of that light-house, which was a most arduous
work.
   I have  now  proceeded  so  far  in  the history of  the
calcareous earth, as to have related  the principal facts upon
which were founded the first  attempts to explain this subject,
and to account  for the difference between the earth in its
natural state, and in the state of quicklime.
   In general,  those  who attempted to  give an  explication
applicable to the whole,or»to the greater part of this subject,
entertained a notion,  or rather formed a supposition, that the
calcareous  earth, when burnt to quicklime, receives  some
subtile and active principle,  communicated to  it by the fire
or heat;  that from this  principle it  derives  its acrimony,
activity, and solubility  in water.   They imagined that lime-
water is produced  by dissolving such a  part of the lime as
has the largest proportion of this principle combined with itv;
and that  this principle evaporates from  the lime  or lime-
water exposed to th^e air.  Further, some supposed that this
principle is attracted fro'm the lime by alkaline salts, and that
thus are produced the caustic alkalis.   The greater number,
however, seem rather to have considered these as compounds
of  the alkali and the  quicklime in substance,  or the more
• acrid part of the quicklime.    But neither has the existence
of this active principle e;en been demonstrated ; nor is the 
198   THEORIES  OF LIME BY  STAHL, &c.

supposition of its combining with lime consistent with many
capital facts which are known to all.  Indeed it is inconsistent
with our general experience in chemistry.   When limestone
is  burnt to quicklime in  the fire, instead of receiving any
addition, it suffers, on the contrary, a  very considerable loss.
And the alkali  is also diminished in  weight  when rendered
active by the quicklime.  Moreover,  we generally find, that
the combination purely chemical,  of the most active  sub-
stances, generally diminishes their activity.   It is thus that
neutral  salts are less active  than their  ingredients.
   Other theories have been attempted, as I  said, chiefly to
explain  some parts of the  subject.    Such was Dr. St thl's
opinion.   He was  one of  those who believed salts  to be
compounds of  earth  and water.   And he supposed  slaked
lime to be a sort of salt hastily and  impenectly  formed; and
therefore liable to be easily decompounded  again into  its
constituent parts,....calv;areous earth and water.
   Mr. Macquer again, in order to  explain some particular
phenomena,  supposed that the calcareous  earth acquires a
small quantity of some acid principle in the fire, just enough
to give it  solubility in water, but  in too small quantity to
saturate it  ;  and therefore  lime is  still  alkaline.  By this
supposition he endeavours to explain the action of lime and
tartar on one another,  but  at the time when he wrote, the
nature of tartar was but imperfectly known, and ill understood.
And neither  his theorv nor  Dr. Stahl's are at all satisfactory
whtn closely examined.    You may  see  an  account  and
examination  of  those theoricb, in the second edition of the
English translation of Macquer's Dictionary,under the  article
•Causticity.
   Upon the  whole, the chemists had  been, at that time, but
little attentive to the variety of  earrhy bodies,  and had but
an indistinct  knowledge of any alkaline earth, except the
calcareous.
   They onlv knew that there were two or three earths  beside
the calcareous: and they knew some  saline*compounds which
held earths combined  with  acids.   But  they  had not turned
their attention tothern, so as to examine by expvnients how
they were  distinguished from one anotlier.  They supposed
them  to be all more or less similar  to the calcareous, or tp 
          INQUIRY  INTO ITS  NATURE.       199

have a great deal of affinity with it, if they were notthe same
thing.
   Dr. Hoffmann was the first who gave distinct  notice of an
alkaline  earth, which  he  shewed to be different from the
calcareous.   It was called  Magnesia.  When I first began
to make chemical experiments, I had  the curiosity to examine
more carefully this earth indicated  by Hoffmann.   I  made
a number of experiments to learn its properties, and how it
was distinguished from the calcareous and some other earths.
The result of these experiments suggested to me, some time
after, an explication of the nature of lime, and of its effects
on the alkaline salts, and-engaged me in an inquiry, by which
a clear light was thrown on this subject, and on many  other
important parts of the science of chemistry.
   I propose,  therefore,  to  give an account of that inquiry.
It is a long story.   But* when I began to give these lectures,
and for a long time after,  I  was in some measure under the
necessity of following this method, giving, at full length, the
investigation of the subject of quicklime, and the foundation
of the opinion and system which I formed upon that subject;
for this  reason,  that it  was  not generally understood and
approved of by the  chemists abroad.    Some chose to doubt,
or explain in a different way, the proofs which I had adduced:
and they adhered to their old opinions.   Others set up, or
supported  and  extolled another  new system, which was
directly  contrary to  mine.    So long as the opinion of a
number of reputable chemists was unfavourable to my views
of the  subject, I thought it became me to shew the grounds
of  my opinions ; and to leave those to whom  I addressed
myself at liberty to judge for themselves.  Of late, however,
most foreign chemists and philosophers agree on this subject
with me.
 'But I think  it is still worth your while to hear  a  history of
the investigation. The same facts and doctrines, when delivered
in a dogmatic or didactic manner, do not make such an  impres-
sion as when fmadjf the subjects of historical  narration.  The
mind is then hd through the most natural chain of ideas ;  it be-
ing that which took place in the mind of the person who follow-
ed out the investigation. 
200               MAGNESIA ALBA.

  I said just now, that a dissertation or essay of Dr. Hoffmann's,
on an earth called magnesia, occasioned the beginning of the
inquiry, the history of which I am going to. give you.  But I
was peculiarly excited to  it by the then recent discoveries of the
power of lime-water to give relief in cases of the stone and gra-
vel, in which it was supposed to act by dissolving those concre.
tions, and expelling them out of the body.   Dr. Whyttand Dr.
Alston, professors  in this university, were then engaged in a
dispute on this subject,   They both believed that it had efficacy.
But Dr. Whytt imagined that he had discovered that the lime.
water of oyster-shell lime had more power as a solvent, than the
lime-water of common stone-lime.  I therefore conceived hopes
that, by  trying a greater variety of the alkaline earths, some
kinds might be found still more different by their qualities from
the common kind; and perhaps yielding a lime-water still more
powerful than that of oyster-shell lime.
  I therefore began  by  examining the  alkaline  earth  which
Hoffmann had mentioned or described ;  and for the preparation
of which there was a process given in our pharmacopoeia.


              SPECIES  II.....MAGNESIA.

     We learn from Dr. Hoffmann, that it was a white earthy
powder, which had gained reputation as a secret remedy,  under
the name of the Powder  or Count Palma, or  Magnesia
Alba.   The Doctor having learned the manner of preparing it,
which he describes,  made several trials to assure himself of its
medical virtues, and to acquire some knowledge of its nature in
other respects.  And he  reports that it is an alkaline or absorb-
ent earth, which effervesces with all the acids, and,neutralizes
them ; that  it is,  therefore, proper for neutralizing acids in the
stomach, with this additional good quality/ by which it is dis-
tinguished from  the calcareous earth  coj&fmonly employed  at
that time by physicians, that the magnesljKfft purgative or lax-
alive powers, and therefore  clears the  jw/ls 9fen trie undi-
gested matter which had produced the a'cY.  AnjPtie supposed
that the purgative power was a quality of|the contjDbund of the  . 
MAGNESIA ALBA.
s201
magnesia and acid after  they  were united together in the sto-
mach.
   The subjects.from which Dr. Hoffmann prepared this earth,
were  some saline  compounds, in which it  is combined with
acids  : and these saline compounds are obtained in preparing ni-
tre and common  salt.  He first made use of that which is pro-
cured in preparing nitre, or in  extracting the nitre from nitrous
earths and composts. It is called the Mother Ley of Nitre*.
   But, afterwards, having learned, that,  in preparing common
salt from the waters that contain it, a similar liquor is obtained,
he made use of this also in some of his processes for preparing
magnesia.  This bitter saline liquor, produced in  manufacturing
cojKimon salt,  is well known to our salt boilers who prepare salt
from sea-water: And they call  it Bittern in England,....in Scot-
land commonly Oil of  Salt.
   Dr. Hoffmann described two ways of obtaining  this earth from
these saline liquors.  The first was by evaporating the saline li-
quor  to dryness,  and then exposing the dry matter to a red heat
in a crucible ; by which heat some acid vapours  were expelled,
and the  earth remained ih the crucible.   The second was  by
adding to the saline liquor a solution of an alkaline salt,  which
immediately precipitated  the earth, by uniting  with  the acid
with which this earth was combined.   And he prefers this pro-
cess to the other.
   In  this country,  (Scotland) as we cannot procure  any  of the
nitrous liquor,  we have always prepared our magnesia from the
bittern of common salt, or of sea water. Or,  which is the same,
we prepare it from  the salinercompound which is procured from
the bittern by crystallization.
   The saline  compound has been long used iii the practice of
medicine,  under the name of Sal catharticus amarus, the bitter
purging  salt.   It was  first  obtained  from the waters of some
purging  mineral  springs at Epsom,  in Surrey,  and  sold at a
high price, on actjpsMtoof the small  quantity of it which  those
    * Moder is theTplriliari^fcd for scum, mud, or dregs, which separates from
  vinegar, ale, or other liqutfjft, by careless keeping.  This term is still in use in
  the northern parts of tb&e islands,* And the liquor is said to mother.  The
  French translate it ignorjntly eaumere.....editor.
1W     vol. u.                 e c 
 202               MAGNESIA  ALBA.

 waters contained.   But afterwards, the manufacturers of coim-
 mon salt, finding thev could produce it  in plenty from the bittern
 of sea Water, and verv cheap,  prepared large quantities of it,  at
 Lymington especially, and exported it to the continent, where
 great quantities were sold.
    The appearance of it,  as commonly prepared from the binern
 is that of small prismatic or columnar crystals.  It is rather
 more purgative than Glauber's  salt, or sulphat of soda, and of
 a bitterish,  and vastly more disagreeable taste.  These crystals
 contain about one  half of their  weight of  water,  and therefore
 readily undergo the watery fusion when suddenly heated.  The
 rest of their substance is a compound  of the sulphuric acid and
 an alkaline  earth,  which  becomes  evident by the action (j>tam
 alkali on this salt.   The alkaline earth, which is the magnesia,
 is precipitated :  And, by the same experiment, we learn that the
 acid with which it was combined  is the sulphuric.   It forms,
 with the  vegetable  alkali added,  a sulphat of potash.  The
 Epsom salt is,  therefore, a sulphat of  magnesia.
   This  saline  compound, being,crystallized  with a  little more
 care than is commonly employed in manufacturing it,, concretes   I
 Into much  larger  crystals, which,  as  they resemble and even   1
 excel Glauber's salt bv their purgative quality, have  also consi-  I
 derable  resemblance to it in  their appearance.   This  became  A
 known to the manufacturers, who soon crystallized large quan. ^M
 tities of it  in this manner,, and sold it for Glauber's salt for some  M
 time.   But the fraud was detected:  and Glauber's salt has been  I
 sold so  cheap  since that time, that it  is not worth while  to  1
 attempt such a fraud, especially since the method of distinguish-   1
 ing the one of  these  salts from the other is generally  known.  1
 We need only  to dissolve a little of the salt in water, and add   1
 an alkali.  The solution of the  sulphat of soda remains trans- ' 1
 parent.   The  other-.becomes  turbid and thick by the precipita-  ■*'■
 tion of the  magnesia.                                          m
   Bv not having knowledge of this distinction, Mr. Poit,  of   I
 the  Berlin  Academy,  maintained  a dispute  wiih Mons. Du  M
 Hamel, of the Royal Academy of Sciences, about the Alkaline  ■
 basis of common salt.  Mr.  Pott  asserted that common salt  J
 contained an earth for its basis.  3Ir. Du Hamel demonstratedjfl
L v experiments, that it contains an alkaline salt.  Poit had drawn Jf^\ 
            PREPARATION OF MAGNESIA      203

 his conclusions from experiments made with the sulphat of mag-
 nesia,  which was sold at that time in Germany as Glauber's salt:
 and he did not suspect that  it was any thing else.  But,  as
 genuine  Glauber's salt is prepared from common  salt and sul-
 phuric acid,  it must necessarily have the same alkaline basis  as
 common salt. And finding that the salt, which passed for Glau-
 ber's salt in Germany, had an earth for its basis, he concluded
 that common salt must contain the same earth.
   The process I used for  preparing magnesia for my experi-
 ments, was what we have now in the Edinburgh Pharmacopoeia,
 or much the same.  I dissolved in water separately equal quan-
 tities of Epsom  salt, (sulphat of magnesia) and of potash, such
 as is commonly sold under the name of pearl-ash.  The Epsom
 salt must be dissolved  in twice its  weight of the  purest water
 and an equal  quantity of dry pearl-ashes must he  dissolved  in
 four or five times its weight of pure water. Each of these solu-
 tions must be carefully purified from ail admixture or foulness.
 The alkali  may  be purified by subsidence and decantation.   It
 is adviseable to clarify the solution of Epsom salt with tne white
 of egg, violently agitated with it when just hot enough to coagu*-
 late the egg.   This produces a  fine net-work, which  will entan-
 gle  every thing that is not chemically dissolved :  and the clear
 saline solution will then  drain slowly through a linen  cloth.
   Equal quantities of the two salts having been thus dissolved,
 the clarified  solutions must be mixed together by violent agita-
 tion, in order that the salts may act quickly on each  other,  and
 the  decomposition be as perfect as  possible.   This must be
 further promoted by making the mixture just boil  over a brisk
 fire.
   Now, add to the  mixture four times its bulk of boiling hot
 water,  and again agitate it  briskly.   Let it now stand to settle.
 The magnesia is scattered  over the  whole liquor in a most im-
 palpable powder, and will subside with extreme slowness. When
 settled, decant off the clear liquor, and again pour on it the same
 quantity of cold water, and,  when it has completely settled, again
 decant  the  clear liquor.   This  edulcoration  must be repeated
 ten or twelve times before  the  magnesia can be  cleared of the
vitriolated tartar, formed by the alkali and the sulphuric acid of 
 204       PREPARATION OF  MAGNESIA.

 the Epsom salt,  which, you know, requires  a prodigious quan-
 tity of. water for its  solution, especially  when cold ;....and  in
 these ablutions it is  found that hot water occasions  a much
 longer suspension of  the  magnesia.   But these repeated effu-
 sions will effectually clear it of all saline admixture, leaving the
 magnesia pure, and in a fit state for philosophical examination.
 Having decanted off  the tasteless water for the last time, strain
 the sediment throdgh a linen cloth, using  gentle compression  at
 last,....for very little of the powder will come through.  N.  B.
 We shail never succeed by using the finer filtering papers. For,
 although magnesia is a fine hard powder, yet, while wet, it has
 more the appearance, the feel, and even the transparency, of a
 jelly*.
    There are several  niceties in this process, which seem some-
 what capricious, but are abundantly plain  when we attend to the
 properties of the substances employed.   The. vitriolated tartar,
 being of difficult solution, impedes by its very formation the
' progress of the  decomposition ;  therefore boiling briskly is ab-
 solutely necessary.    Also,  the  magnesia  has a tendency to a
 peculiar mo.Ie of crystallization in little  round grains formed
 like  zeolyte,  of spiculse diverging from a  centre.   They are
 hard, and would be very inconvenient  for medical preparations.
  When a very minute quantity of the two salts is dissolved in a
  great deaLof water, and allowed to rest without disturbance, the
  particles have room and time to assume  this arrangement very
  regularly.   Therefore, we must prevent this by making our first
  liquors pretty .rich in- the salts, and this,  with the agitation and
  boiling, immediately destroys this regular formation of crystals,
  and causes  the  whole  to become a fine impalpable  powder.   I
  find that a quart of  water to a pound of  Epsom salt, and three
  quarts to a pound of  dry pearl-ashes, are  a very good degree of
  strength for the  first  solutions.-  The gelatinous  appearance,'

    * This  transparency is unfortunate for the  painters; for magnesia would
  otherwise give a most dazzling white, superior to any they possess, and which
  would not change its colour, as the preparations of white lead do.  But when
  ground with oil, it has hardly any colour, forming an almost transparent var-
  nish-  It will do perfectly well, however, in water colours; because it rega'
>* its'brilliancy when perfectly dry.....E»iroR.
                                                          » 
             ITS RELATION TO  ACIDS.          205

when wet, arises from a spongy adhesion of a great quantity of
the water:  and when this is evaporated to dryness, the mass is
an exceedingly light and spongy substance,....and this extreme
lightness is one of the best marks of its goodness.  Mr. Henry
of Manchester thinks that in this process too little water is used,
saying that these gritty  particles require a vast deal of water to
dissolve them.   But this is a mistake.  No quantity whatever
of pure wateu will dissolve them : and if the first liquors are not
too much diluted, and the mixture be well agitated at the  first,
these gritty particles will not be formed.
   My prescription of equal quantities of the two salts, as proper
for decompounding the Epsom  salt, is founded on an experi-
ment by which I discovered that it requires 100 grains of dry
alkali to  saturate the acid saturated  by 30 grains of calcined
magnesia.
   Having thus procured a magnesia, of the purity of which I
was  certain, I was  anxious  to examine  it as a medicine.  I
                              v
made a salt by dissolving it in vinegar, thinking  this acid the
most nearly analogous  to that which is  formed  by  vegetable
matter, imperfectly digested in weak stomachs. Two drachms
of this powder proved a good  purge  for an adult, and half an
ounce a very brisk purge : but  both operated, gently and with-
out any spasm or sensible  inconvenience.  The taste was  in a
moderate degree nauseous.
   Let us now attend to the chemical relations of this  new  sub-
stance ;  and, first, with regard  to the acids.
   1st, It effervesces with all the acids, and neutralizes them and
forms with them- compounds remarkably  different from those
formed by the-calcareous earth.  With the sulphuric acid, for
example, it forms  a compound easily soluble in water;....with
the nitric acid a compound  soluble and crystallfzable ;....with
the muriatic  acid a  deliquescent compound, but which  differs
from the calcareous  compound  with this acid, by being subject
to decomposition,  or separation of its acid, or of the  greater
part, by the action of heat alone.  Its compound with the acetous
acid has been already described.
   2dly, Magnesia, prepared in the way now described, separates
the calcareous earth from acids.  When a little uncalcined mag-
nesia is put into a solution of the  muriat of lime, and the mix- 
206      EXAMINATION OF MAGNESIA.

ture promoted by agitation, and allowed  to settle, we have a
powder lying at the bottom, which is not distinguishable at first
from the magnesia that we put in.   But when it is dried and
edulcorated, we find it to be a calcareous earth ;  for it burns to
a true quicklime, wholly soluble in  water.  If we have added
enough  of magnesia, and not too much, we shall  find that, after
having separated the powder now spoken of, if we then pour a
little sulphuric acid into this solution, we shall observe no pre-
cipitation.  Now we know that the sulphuric acid, when added
to the muriat of lime,  forms a selenite hardly soluble in water.
Again,  if,  instead of the  sulphuric acid we  put a solution of
Glauber's salt into the saline liquor we are now considering, we
shall obtain an Epsom salt and  common salt.
   3dly,  It produces a  very remarkable effect on lime or lime-
water.   In the first experiments by which  this was discovered,
I added some magnesia to a muddy  mixture of lime and water.
The lime was rendered insoluble.   In a second  experiment I
added the magnesia to lime already  dissolved; that is, to lime-
water.   After long digestion and frequent agitation, the water
was rendered perfectly tasteless, and the powder at the bottom
was a mixture of magnesia and crude  calcareous earth.
   I was induced to try these  experiments with lime and lime-
water by the  event of the  preceding experiment, which made
me imagine it was allied to the alkalis.
   4thly, When exposed to the  action of fire, it does not become
a quicklime.   Some magnesia, which had been  exposed  to a
strong  heat, was  tried with water,  to learn whether it would
slake like lime, or form a lime-water.  I also laid a little of it on
my tongue, to learn whether it had acquired any degree of acri-
mony.   But in none of these trials did it shew the qualities of
lime.  It neither slaked or shewed any attraction for water like
quicklime, nor formed  a lime-water; nor was it  sensibly acrid
when laid on the tongue.   I learned, however,  that in some of
its qualities it is considerably affected and changed by the fire;
and I called it calcined or burnt magnesia.   The changes in-
duced on it by the action of the fire, when a good red heat has
been applied to it for some hours in  a crucible, are these.:
* 
         EFFECTS OF GREAT HEATS ON IT.    207

     1st, We find that it is much diminished in bulk.
     2dly, We also find  that its weight is very considerably di-
 minished, viz.  by more than A;....or, by -^ths ; 12 parts being
 reduced to 5.
     3dly, When we try how the magnesia, in this diminished
 state, dissolves in acids,  we find it can be dissolved without the
 least effervescence.  When lime is thrown into strong and brown
 sulphuric acid, there is sometimes a violent heat produced (even
 flashes of flame) which makes the water boil.  But this happens
 only when the acid is applied too strong  ; and it is quite differ-
 rent from  the effervescence  which appears in. dissolving magne-
 sia  in its ordinary state.  And if we  dilute the acid properly
 before we  apply it to the calcined magnesia, there is no ebulli-
 tion whatever, but only a moderate degree of heat produced.
    This suggested an improvement of magnesia as a medicine
 for some cases and constitutions.  Hoffmann remarks that some
 of his patients complained of the magnesia, saying that it rais-
 ed wind in their bowels ;  and this he imputes to its effervescing
 quality.   But by thus calcining it, we deprive it  of this quality,
 although it unites with acids as effectually as before; for by dis-
 solving the calcined  magnesia  in the different acids,  I learned
 that it neutralizes the acids, and produces compounds entirelv
 similar to  those produced by the magnesia before it has  been
 calcined.   The use  of calcined magnesia m medicine  requires,
 however, some caution and attention:   For magnesia, in the
 shops, is not always perfectly pure.   Some of it contains a por.
 tion of calcareous earth ; and if such magnesia is calcined, we
 shall have  a portion of quicklime in  it; which is not safe for in-
 ternal use.   The calcareous earth which  is often found in com-
 mon magnesia, proceeds either from  a sulphat of lime, which
 is often contained, in small quantity, in the Epsom salt, or from
 a  sulphat and a muriat of  lime  contained  in the water with
 which the  m; gnesia was washed, if this  was a hard or a bad
 water.  It  very rarely happens  that any troublesome degree of
flatulence is  produced  by  common magnesia ; and  if there
should, the addition of  some aromatic will  be a sufficient anti-
dote. 
208   PERMANENTLY ELASTIC  MATTER.

  4thly, A fourth peculiarity of the calcined magnesia was, that
it did not separate the calcareous earth from acids.* And a
  5th, That it did not precipitate the lime from the lime-water.
  The result of these trials prompted me to make further expe.
riments, to learn in what manner the fire produced these changes
in  the  magnesia,  and  what was the  nature  of that matter
which was separated from it by heat in. such great quantity, and
by the loss  of  which it was so  much reduced in* its "bulk and
Weight.
  I therefore put a quantity of magnesia into a glass retort, and
joined a receiver to the retort with common lute  made of sand
and clay.   I then  placed the retort in  a sand-pot,  which was
very gradually heated until the bottom of the pot bea;an to be
ignited.   The  receiver was  kept  cool, to promote the conden-
sation of any volatile  matter that might arise from the n- ig.iesia.
But I obtained only a very small quantity of watery fluid, which
contained a small portion, scarcely perceptible, of volatile alka-
line matter.  The magnesia, which remained in the  retort, had
lost a great deal  of its  weight, (though not so much  as when
heated to a good red heat in a crucible)  ; yet the loss it had suf-
fered was equal tq more than six. or seven  times the weight of
the small portion of water condensed in  the reoeivcr.   This ap-
peared  at  first an unaccountable fact; but  it made me  recollect
some of Dr. Hales's experiments, described  in  the  essay to
which he gave the title of Analysis of the Air, and in other parts
of his works.
   Mr. Boyle had before made experiments, in which he extrac-
ted air from different substances by the use  of the air-pump, and
by  other means.   But  Dr. Hales pushed  such experiments a
great deal farther.   He expelled, by the action of heat, from a
variety of different substances, large quantities of elastic incon-
densable fluids, which he considered as different  kinds'of air,
or as air in different states, which had been concealed in these
bodies, united with their other ingredients in a^jense and solid
form.   Chemists have distinguished this class*of elastic fluids
from atmospherical air,  by the term Gas, a Grfcpufttvord used
to express the eruption from fermentations (gdfirung)' oi every
kind.   (Sec Note 36. at the end of the Volume.)
•* 
    EXPELLED FROM MAGNESIA  BY HEAT.  209

   The apparatus he used in many  of these experiments  was
very simple, consisting of a gun-barrel closed up at the breech,
and bent into a swan neck.  The substance from which the gas
is to be expelled by  fire, is put into  the barrel,  and this end is
put into the fire.  The other end is  dipped in  a tub  of water,
and ajar filled with water is inverted over the mouth of the bar-
rel.   The pressure of the atmosphere supports the water in the
jar.   The gas expelled from the gun-barrel rrseejrth*ough  this
water, displaces some of it from the jar, and occupies the  up-
per part of it #.                  \
   By such  experiments,  and by others,  Dr.  Hales  procured
great quantities of air, or permanently elastic fluids, from a great
number of vegetable, animal, and fossil substances.   And  this
explained to the chemists some facts which often occurred in their
distillations, and which they had not  been able before to under-
stand, viz. the loss of weight, and the bursting of their distil-
ling apparatus,  in spite of all attempts to promote condensation.
Obtaining a vast deal of air in the same apparatus without red
heat,  from pease, and other fermentable substances, gave some
knowledge of what happens in fermentation.
   As what had happened in the  last  experiment with magnesia
appeared to be very  similar,  I began to suspect that the loss of
weight which it suffered in the fire was occasioned, in  the same
manner,  by  the loss of a quantity of elastic aerial matter, or air,
which had escaped through the lute.   And this supposition ap-
peared the more probable,  as it was  very consistent with one of
the qualities of burnt magnesia;  I mean its uniting with acids
without effervescence.  For I began  to suspect that the efferves-
cence of the common  magnesia proceeded from air which it con-
tained, and  which was expelled by the superior attraction of the
acid ; and that the reason why burnt magnesia did not effervesce
was, that it  did not contain this air,  the air having been expel-
led from it by the action of heat.
   Another facL.which supported the same opinion, was the suc-
i ess of an exjfcrjment,  in  which I contrived to restore this air
again, ifrwgsibjle* to  the calcined magnesia.

   " The same iSpparatus was employed by Mavhow in 1674....edxto*
       vol.  ti,             r> d 
 210 DETECTION OF FIXED AIRS BY DR. HALES.

   The contrivance or plan of his experiment was suggested by
 considering  in what manner the magnesia bad obtained this air
 at the first.   It  could  not  have it while it was joined with the
 sulphuric acid in Epsom salt.   The effervescence of magnesia
 with acids, shews that it cannot be joined with an acid and this
 air at the same time.   It must therefore have received it from
 the  alkali which was employed to precipitate it from the acid.
 This  appeared  the more probable, from recollecting that Dr.
 Hales had long before  extracted much air from alkaline salts.  By
 heating some alkali of tartar in his iron retort or gun-barrel, he
 extracted from  it 224 times  its bulk of air.   In other experi.
 ments,  he procured great quantities of air, by adding different
 acids to solutions of alkalis.
   I therefore supposed that magnesia receives air from  the al«
 kali employed to precipitate it at first; that we can expel this air
 from  it by the action  of fire ; but that  it might perhaps be res-
 tored by dissolving the burnt magnesia in an acid,  and precipi-
 tating again by  the addition of an alkaline salt.
   To make trial of this,  I took 120 grains of common magnesia.
 I burnt it in a crucible with a sufficient heat, by which it lost 70
 grains of its weight.   This magnesia,  thus calcined, was dis-
 solved in a sufficient quantity of diluted  sulphuric acid, in which
 it dissolved without effervescence: and it was again precipita-
 ted by adding a clear and warm solution of a common fixed al-
 kali, which was boiled with it a little in the usual way ; and the
 precipitate was washed in the usual manner.  After being care-
 fully dried with a gentle heat, it was  found to have regained
■ the whole weight which it had lost in the fire, except  a mere
 trifle.   It also  effervesced with acids as violently as common
 magnesia.   It separated the calcareous earth from acids, and it
 made the lime separate from lime-water.  Thus it was restored
 to the state of common magnesia in every respect.  It was just
 the same as if it never had been calcined.
   The event of this experiment, therefore,  confirmed me in the
 persuasion,  that magnesia receives a quantity of air from the al-
 kali employed in preparing it;  and that the precipitation of mag-
 nesia from  Epsom salt is  not a case  of single, but of double
 elective attraction. 
           MAGNESIA  CONTAINS FIXED AIR.    2tl

      This became still more  evident, by considering attentively
   what happens in precipitating magnesia ;  for the alkali, in pre-
   cipitating it, forms with the acid a compound salt, which is pre-
   cisely the same in  quantity and quality, as if the same alkali had
   been saturated with a pure acid.  When an alkali is saturated
   with a pure acid,  we see plainly that the air of the alkali is ex-
   pelled.   The  effervescence shews this, as do Dr. Hales's expe-
   riments.  And the compound  salt produced is a compound of
   the acid with the  alkali  deprived  of its air.  But as the com-
   pound salt produced in precipitating magnesia is precisely simi-
   lar,  in quantity and quality, to a compound salt produced from
   the same quantity  of alkali and a pure acid, the alkali of it can-
   not have retained its air.  This air must have been expelled by
   the acid: and yet this expulsion of the air is not apparent by
   ^ny  effervescence.  But  as the  air is actually found in the mag-
   nesia, this accounts for the non-appearance of effervescence, and
   shews that  in the precipitation of magnesia  there is a double
   elective attraction or double exchange.  The alkali unites with
   the acid,  separating the  magnesia,  which in the same instant
   unites with  the air as it quits  the alkali.  We must therefore
   conclude, that the sum of the forces which tend to unite the al-
   kali  with the acid, and the magnesia with the  air,  is greater
   than the sum of the forces that  tend to unite the magnesia with
   the acid and  the alkali with the air.
     Thus, I found reason  to set aside the  common opinion then
   entertained of the nature  of the effervescence of acids with alka-
   lis and alkaline substances.  It was generally supposed to be a
   consequence or effect of the violent shock of the  acid  and alka-
   line particles,....but it now appeared to be a separation of a quan-
   tity of air which is present in alkalis, but which is expelled by
   the superior  attraction which the acid has for the alkali.
     When I now reflected on the great loss of weight which  mag-
   nesia suffered in being calcined,  it occurred that the quantity of
   air which it contains must be very considerable; and that it and
   the other alkaline substances, must lose a proportional part of
   their  weight during their effervescence with acids,....since we
   have reason  to conclude  that this effervescence is nothing else
t. iut a separation and discharge of this air. 
212   EFFERVESCENCE IS THE ESCAPE OFAIR.

   This idea led me  to examine what loss of weight  magnesia,
or the comirion fixed alkali, would suffer by  their effervescence
with a pure acid, for which purpose I made the following ex.
periments :
   Into a diluted acid contained \i a flask or phial, put a little
alkaline salt, or chalk, or magnesia, and immediately stop the
mouth with a cork, through which there passes a tube bent into
a swan-neck.   The  other end of the tube  is introduced (in  Dr,
Hales's manner)  into an inverted  glass jar filled with wateri
and standing  in a tub of water.   You will observe the efferves.
cence, and the elastic bubbles rising copiously through the  vva.
ter  to the  top, where  they  collect,  driving  the water out of
 the jar.
   Thus it  is manifest,  that it is not a temporary vapour,  but
 a permanently elastic fluid, which escapes in the effervescence,  >
 not condensible by cold.
    Mr. Homberg, therefore, was led into an error in the expc
 riments which he made  and published in  the  memoirs of the
 Academy, to determine  the strength of the different acids, and
 the proportion of the acid to the alkali in the compound salts.
 He saturated equal quantities  of an alkali with each,  and  con.
 eluded  that  the weight gained by  the alkali, when perfectly
 dried, was the quantity  of solid salt contained in that  part of
 the acid which had completed the saturation.   But  we now see
 that he ought to  have added the weight of all the air that is lost
 by the alkali.
    We  can also now  perceive the reason why common and
 burnt magnesia, which  differ by several properties, agree in
  forming the same salts with the different acids;  for, since the
  different qualities of the magnesia in  these two states pro-
  ceed from the presence  or absence of the  air, it must happen
  that when magnesia, in its ordinary  state, is dissolved in an
  acid, the air is expelled,....the compound  produced  must
  therefore be the same as if we had dissolved burnt magnesia,
  or magnesia previously deprived of its  air by fire.
     The only other experiments which I first published in my
  inaugural dissertation on magnesia,  were a i'ew more on the
  earth of alum, and on the ashes of animal bones,  which were, 
      NATURAL  HISTORY OF  MAGNESIA.   215

at that time employed in medicine as an alkaline earth.  I
satisfied myself that neither1 of them acquired the qualities of
quicklime in a strong fire;  and that was one principal object
of my  inquiry.   More light has been thrown upon both
these earthy substances since that time by eminent chemists
in Germany and Sweden: but of this we  shall give  further
notice soon.
   Such were the experiments  which I then made to inves-
tigate the  nature of  magnesia.   And from these you will
 perceive that this alkaline earth is very distinct from  the cal-
 careous.   I  need not add any thing further with regard to
 it at present; but  shall take some  notice of  the  different
 states in which we find it in nature.
    It is produced by nature in  great quantity.   The sulphat
 of magnesia is  contained  in  considerable' quantity in the
 waters of the sea;  and occurs  also in many spring waters, in
 which it has been often mistaken for Glauber's salt.   And
 sometimes  waters that contain it, when  they happen  to be
 exposed in  circumstances proper for evaporation,  leave this
 salt behind in a concreted or crystallized form.  Such is this
 specimen which I was told came from a coal-pit in England.
  And  I am persuaded, that the  salt called Glauber's  salt,
 which is  said  to  be found solid in Siberia in  such great
  quantities  as to supply the consumption of the  whole em-
  pire of Russia, is not in  truth a Glauber's salt, or sulphat of
  soda, but a sulphat of magnesia.  My reason for this opinion
  is, that in  Russia they do not know the  distinction between
  this saline compound and sulphat of soda.   Mr.  Model, the
  Empress's apothecary, in one of his essays, mentions, as a
  well known property of Glauber's salt, that when we dissolve
  it in water, and add a solution of the fixed alkali,  there is a
  plentiful precipitation of earth, which certainly happens with
   Epsom salt only but not with Glauber's salt.   And there
   are  other passages in his essays, which shew plainly, that
   what they called  Glaubers's  salt in Russia,  was  no other
   than this salt.
     We may further remark with respect to the natural waters
   which contain some of this salt, that they also often contain
   a small quantity of a muriat of magnesia.  There is always a
k.:  quantitv of it contained in sea water. 
 214  NATURAL HISTORY OF  MAGNE«IA.

   But these are  not the only states  in which magnesia is
found.   Mr.  Margraaf of Berlin made great additions to
the natural history of this earth, by discovering that it exists
also separate  from any acid,  and sometimes  pretty pure.
There is a set of  earthy or stony substances, concerning the
classing of which, fossilists were  a long time undecided and
disagreed.   Most ranked them among the clays, and Cron-
stedt with the rest.   They have  been known by the names
steatites, lapis surpentinus, lapis nephriticus, and lapis ollaris.
In the purest, the texture is close' and semitransparent.,   In
some species, it is somewhat plated or scaly.   In  general
they are soft like  soap  or suet; so soft as to be cut or tur-
ned.   They harden  in the fire  without melting.  Hence
some  species are turned  into vessels.    This is  the  lapis
ollaris.   Tnverary House is built of an impure species of it.
Mr.  Margraaf first  shewed  that all  these contain more or
less of  magnesia, closely combined with some  other earthy
substances, and often with much iron, by which they are tin-
ged with the green colour, more or less deep,  that appears in,
many of them.
   Mr.  Margraaf also  found that magnesia is an ingredient
in the composition of the flexible stony substances, which
we shall hereafter describe.   And  Mr. Lewis got some of
it from the ashes of vegetables, and of jthe  softer animal  sub-
stances.
   It  is  a  considerable time since Mr. Margraaf published
ihese discoveries.  I can add  further, that more recently,
JVIons. Monnet, in France, has repeated and confirmed the
experiments  of Margraaf,  and has added many new ones,
which are entirely his own, and which shew that this earth
is produced  by  nature in  much greater quantity still than
was imagined.   In making experiments' with clays,  and
marles, and  slate, he  found  that many of these contain a
quantity of magnesia, mixed  with the other earths, which
compose the  pripcipal part of,them.   There is an  extract of
his discoveries on this subject in the Observations de Physique
for June 1774, which well deserves your perusal, as a speci-
men of well conducted  investigation, and as it contains much
new information.
   There is also a lime-stone,  very abundant in the neigh-
bourhood of Doncaster, and I believe, in other parte of Eng- 
   CONJECTURES  CONCERNING  ALKALIS.  2-15

land, which,  when burnt,  and laid on land as manure, is
found greatly to injure its fertility.  TIrismas been examined
lately by an intelligent ctyemist, and£ found to contain a very
considerabe proportion of magnesia.
   When I reflected on tn^experiments already described,
 they appeared to me to lead^bo an explication of the nature of
 lime,  which  easily accoumed for the most  remarkable pro-
 perties which we find in it, and for many phenomena relating
 to it and to other  alkaline substances.        ^0^^^
   By  these experiments it was made evidd^rtnat magnesia
 and the vegetable  alkali, in their ordjfcry  state, contain a
 large  quantity of air, in an elastic, solid, or fixed state, which
 makes up a considerable part of their bulk  and weight;  and
• that their effervescence with acids is a discharge or separa-
 tion of this  air from the alkaline part of these substances,
 ....the acid acting here in the same  manner as the sulphuric
 acid  does when it expels  the less powerful acids from the
 compound salts which contain them.
   I therefore concluded, with respect to the other alkalis and
 alkaline earths, that their effervescence with acids depended
 on  the same cause; that they all contain a large quantity of
 fixed  air, which is expelled when they unite with acids;  and
 that this air adheres to them with considerable force ; since,
 notwithstanding  that it is such a volatile substance, a full red
 heat  is necessary to separate it from  magnesia ; and the same
 red heat is not sufficient to  expel it  entirely from the alkalis,
 or to  deprive them entirely of their power of effervescing  with
 acid  salts.                                * m%
    I further was induced to think that the relation of alkaline
 substances to fixed air resembled, in some  particulars, their
 relation to acids ; that, as the alkaline salts  and  earths attract
 acids strongly, and, when saturated  with  them,  become  mild
 neutral salts, theyf in the  same  manner, have  an attraction
 for their fixed air, and, in their ordinary state, are  in some
 measure  neutralized by it, appearing on this account milder,
 or  less active bodies, than when we have  an opportunity to
  examine them in a pure state. 
 216  CONJECT.  CONCERNING ALK. EARTHS.

    With respect, to the calcareous earth in particular, I ima-
 gined that, when iV is exposed to the action of a strong fire,
 and thereby converted into quicklime, the change  it suffers
 depends on the  loss of the large quantity of fixed air which
 is combined  with this earth  in  its  natural  state ;  that this
/earth is expelled by the heat ; and that the solubility in water,
                                  ich we perceive  in quick-
and  the  remarkable  acrimony^^i
lime, do not  proceed  from jrny
received in the fire, but are essential properties of this earth,
depending on an attraction for water ;  and for those  several
substances with which the lime  is disposed  to unite ;  but
that this attractive power or activity remains  imperceptible,
so long as the lfljle or  calcareous earth is in its natural state,
in which it is satur^Jd and neutralized by the air combined
with it.
   This  supposition agrees much better with our  general
experience of the consequence of combining and separating
different bodies in chemistry, than the opinion which then
prevailed concerning  the  nature  of lime.   The established
opinion was, that quicklime was a compound, formed by the
union  of the  calcareous  earth  with  a subtile  and active
principle, supposed to be communicated to it by the fire or
heat.   But subtile  and active substances, when  combined
with others, do not in general  communicate their activity
to these.  Our general experience shews us that  activity is
diminished  by combination. We have a well known example
of  this in the combination of acids with alkalis.   Both of
these salts,  in their separate state,  have great  activity  and
corrosive powers.  When united,  they form the  neutral
salts,  which, instead  of having  the  joint  activity of their
constituent parts, are  mild and inert, if compared with either
the  acid or  the alkali  of which they are composed.
   I therefore considered the calcareous earth as a peculiar,
acrid, soluble earth, appearing commonly under a mild and
insoluble form, on account of its union  with  fixed air ;  and
I considered quicklime as the same earth deprived of its air:
and therefore shewing its proper solubility an*acrimony, or
 its  natural attraction for water, and for various  other sub-
 stances  with which it  is then capable  of being combined.
< i i 
      EXPERI. OF MARGRAAF AND JAQUIN.   217

   This  idea  of the  manner  in  which the  calcareous earth
 becomes quicklime, not only  agreed with our general expe-
 rience of the  consequences of combination and separation in
 chemistry, but was  immediately supported by some  capital
 facts belonging to this subject; and which, at the same time,
 were quite inconsistent with the common opinion.  It is well
 known, that  when a  calcareous stone or mass is  burnt to
 quicklime, it  does not acquire any additional weight in the
 fire ;  but,  on the contrary, suffers a very great loss.   The
 lime, when fresh drawn from the furnace, weighs generally
 no more than 60 per cent, of the weight of the limestone.
 And when I considered  some experiments made some time
 before by  Mr.  Margraaf of Berlin, it appeared plain,  that
 the matter separated from the limestone by heat, is an elastic
 aerial matter, incapable  of being  condensed by cold into  a
 palpable  form.   These  experiments  are described  in the
 Transactions  of the  Berlin Academy for  1748, and were
made upon a particular calcareous  substance  of which he
had  undertaken  the  examination: it is  called  osteocolla.
 He put  eight ounces of osteocolla,  which is a calcareous
 earth, into an earthen retort, to which he joined a  receiver,
 and set the retort in a proper furnace, where it was gradually
 heated to a violent degree.   Nothing, however, was  con-i
 densed in the receiver, except two drachms  of water, which,
 by its smell  and properties,  shewed itself to be slightly
 alkaline.  He does not tell us the weight of the osteocolla
 remaining in the retort.  He only says that it was converted
 into quicklime ;  but this alone, and the heat he applied, are
 sufficient proofs that it  had lost about three ounces of its
 weight;  and  as  no more than the quarter  of  an ounce  of
 water was found in the receiver, it is plain that this loss was
 occasioned chiefly by the separation of an elastic aerial matter
 which could not be condensed.
   The same  thing has since been more fully ascertained by
 Professor Jaquin of Vienna.  In order to satisfy himself of
 the truth of rny theory, he put a quantity of limestone, broken
 down to small pieces,  into an earthen retort, and set it in a
 furnace,  in which  it might be heated to a violent degree.
 A receiver, with a very small bole drilled  in the bottom of
     vol. n.                 e e   * 
218 WHY SLAKING OF LIME GENERATES HEAT,

it, was luted to the retort, perfectly air-tight:  then fire was
applied, and heat raised in a slow and regular manner.
   1st, A  verv small quantity of water was condensed in the
receiver.  This all came over in the beginning of the process,
and with  a very low or moderate degree of red heat.
   2dly, After  this period of the  distillation, no more water
came, though the heat continued increasing ; but an elastic
fluid began to issue through the  little hole  of the  receiver
with a hissing noise, which continued a long time, but at last
ceased.   The limestone  being then taken out, it was found
to be excellent quicklime.
   N. B.  He repeated this proress and varied it.   When he
withdrew the fire, as soon as  all tiu- water was expelled, there  i
was no quicklime.   And when he  continued it until a part
only of the  air was expelled, a part only of the stones were
changed into lime, viz. from the  surface inwards,  and to a
greater depth in proportion  as  the heat was continued nearer
to that period at which  the eruption of the air commonly
ceased.   This supported the idea of quicklime which I  had
proposed.
   But what further tends very much  to support it, is  the
facility with which it enables us to explain the greater part,
if not the  whole of this subject.  That you may be satisfied of
this also,  I shall now state some of these facts or phenomena
which our theory explains.
   Thus,  to consider in the first  place,  the slaking  of lime,
the formation of lime-water,  and some  of the  qualities of
lime-water :  the  calcareous earth, in its quicklime state, or
deprived  of its air,, as it  has an attraction for water, will be
found to resemble the salts in several particulars in the mode  1
of this attraction.   The salts,  if We take them in their purest m
state, are disposed to combine with water in  two different W
ways.  With a certain quantity of water they unite closely,
and with  considerable  force,  to constitute  the  crystals of
salts,....in which  the water  is joined with  the particles of
salt in such a  manner as to  become solid along with them.
There are some of the s?lts which become very hot in uniting
with  this portion  of water:  such are Glauber's salt, Epsom  "
salt, fixed alkali, and several others.  This heat is supposed   1
by most authors to come out of the salts: I am rather inclined |1 
 WHY SLAKING OF LIME GENERATES HEAT. 219

 to think it comes from the water.   After this, if more water be
 added, the salt unites with it in a different manner, so as to be-
 come fluid along with it, or form a solution or liquid, in which
 the salt is dissolved in the water; and, in this  part of the pro-
 cess, cold is produced.   In the same  manner, if water be added
 to quicklime, a certain  quantity of it is attracted by the quick-
 lime, and deprived of its fluidity with violence and heat; and it
 adheres to the lime  with considerable force, constituting  with
 it a dry powder,  which is called slaked lime.   But  if this
 slaked lime  be  mixed  with a much larger quantity of water,
 a part of it is dissolved, and  composes with the water, a lime-
 water.
   The heat produced in  slaking lime, is just one of the number-
 less  examples of the emersion of latent heat.   And if any person
 should think  that the heat produced in some of these instances
 is too great  to be explained in this way,  let him  consider that
 the 140 degrees, which escape from water in congelation, refer
 only to the difference between the heats necessary for-appearing
 in the  forms of water and ice.   But we have no authority to
 say  that the  same abstraction of heat  from the same quantity of
 water, will suit  its subsequent appearance in a crystal of Glau-
 ber's salt, Epsom salt, or nitre.  A much greater emersion may
 be necessary, or a much less; therefore, till the experiment  be
 tried, we cannot say  how much heat must  emerge before  the
 water can unite with quicklime in a solid  form,   A^nd, let k
 be further remarked,  that the heat extricated in this crystalliza-
 tion, can be very little diminished by the subsequent  solution,
 because there is very  little lime dissolved  in the lime-water.
   When this fluid is exposed to the open air,  the particles  of'
lime, which are atthe surface, gradually attract fixed air, which
 is mixed with the atmosphere: but while the lime is thus satu-
rated with air,  it is  thereby restored to its original state  of
mildness  and insolubility.   And,  as the whole of  this change
must happen at the  surface of the  lime-water, the  whole  of
the lime  is successively  collected there,  in its original form  of
an insipid calcareous  earth, called the cream or crusts of lime-
water. 
^20 FIXED  AIR  IS A PARTICULAR SPECIES.

   In forming  this theory, I was necessarily led to perceive a
distinction between atmospherical air, or the greater part of it,
and that sort of  air with which the alkaline substances are dis-
posed to  unite.   It  was plain that the lime of lime-water, for
example, is not disposed to unite with the whole mass of atmos-
pherical air that happens to be confined with it, or with every
part of it equally.  If this were the case, it would be impossible
to preserve lime-water in good condition, without extraordinary
precautions  to keep  the  air from ever entering the bottles  or
other vessels in  which it is contained.   But we find, in fact, that
it is not  necessary for the preservation of the  lime-water, that
We keep the air out of these bottles,  or exhaust them of air.
They always contain as much air in the part of them that is not
filled,  as other bottles do  in which we keep other fluids; and
yet the lime-water may be preserved  good in  them for a long
time.  The only circumstances  in which lime-water loses its
qualities,  and  throws up the lime to its upper surface, are, when
we expose  it to the open  air,  or keep  it in  bottles that are
left open.   From this  it was evident that the sort of air with
which the lime  is disposed to  unite, is a particular species,
which is  mixed in small quantity only with the air of the atmos-
phere.  To this particular species I gave the  name of Fixed
A ik, the  onlv term then used to denote any air that is condensed j
and fixed in different  bodies, and is a part of their constituent
principles.
   To  return  to the explanation of the properties of quick-
lime.....
   When quicklime itself is exposed  to the open air,  it must
gradually attract the humidity and the fixed air which are con.
tained in the atmosphere.   And as our atmosphere contains  -
more of humidity than of fixed air, the change which the quick-
lime, when exposed, undergoes the most readily, is a change of
it into slaked lime.   But it attracts also some fixed air, and con-
tinues afterwards to  attract  more, until it is gradually saturated  (
with it, and thus is  restored to  its original  mild and insoluble
state.
   ^To explain  all the effects which are produced  by mixing the
  kaline salts with lime or lime-water,  we need only to suppose
* 
        CONJECTURES RESPECTING LIME.    221

that the fixed air is more strongly attracted by the lime than by
the alkali.  The lime in this case must attract the air from the
alkali to itself, and must thereby return to a mild and  insoluble
state ;  while the alkali, on the contrary, becomes more corro-
sive,....that is, shews its proper degree of activity, or  attraction
for water, and its natural action on bodies of the inflammable
kind, and those of animals and vegetables; which attraction,
and consequent action, was necessarily weaker while the alkali
was combined with its air, and in some measure neutralized by
it.  It therefore becomes what we call highly corrosive.  And,
in like  manner, the volatile alkali,  when deprived of its ah- by
quicklime, besides shewing a  stronger attraction for  water,
shews  also its proper degree of volatility, such as we see it  in
the caustic volatile alkali prepared with quicklime ; which high
degree of volatility is diminished or repressed  in the  common
volatile alkali by the air adhering to it,....in the same manner  as
it  is repressed in  various degrees, by the  union of this alkali
with the  different acids, according  to  their degrees  of fixed-
ness.
   In like manner,  the effects of magnesia, applied in its different
states to lime, or lime-water, are easily explained, by supposing
that lime  has such an attraction for  fixed air,  that it has the
power to take it from the earth of magnesia.  When the mag-
nesia is added to lime-water, the air is separated from the mag-
nesia by the stronger attraction of the  lime ;  and as  the lime,
when saturated with air, does  not become active, or percepti-
bly soluble in water, the lime-water becomes insipid,....the lime
which it contained being deposited at the bottom of the mixture
along with  the  magnesia.   But, if  we make this experiment
with magnesia which  has been deprived of its air by heat before
it  be added to the lime-water, this fluid suffers no perceptible
change.
   This  account of the  nature  of lime recommended  itself,
therefore, by thus  affording an easy explanation of many of the
facts relating  to quicklime and lime-water; and the  effects of
mixing these with  alkaline salts, and with magnesia, in different
states. 
 222     PROPOSITIONS TO  BE EXAMINED.

   But, while I was employed in  considering it  with more at-
 tention, I found it to be necessarily connected with consequences
 which were contrary to what were at that time esteemed to be
 facts, or truths, established upon experience.   And the consi-
 deration of these began to raise some doubts concerning the so-
 liditv of the whole of my system.  In every other respect, how-
 ever, ic had so much the appearance of being well founded, that
 I resolved to consider more particularly these unavoidable con-
 sequences of the theory, and not to trust  to the common opinion
 of what was fact,  but assure  myself of  what  was really so, by
 making experiments.
  I therefore found, that the consequences I speak of were re-
 ducible to these propositions:
   1.  If we only expel fixed air from the calcareous earth when   j
 we burn it" to quicklime, the quicklime  thus formed must dis-
 solve in acids without effervescence ; and, notwithstanding the
 loss pf weight  it suffered in the fire, it must saturate the same
 quantity ©f acid as the whole of the calcareous earth would have
 done  from which it was made.  And the same  qualities must
 also be found  in the alkaline  salts  when rendered caustic by
 lime.
  2.  If quicklime be only a calcareous earth deprived of its air,   (
 and whose attraction for fixed air is stronger than that of alkalis,  ;'
 it follows, that,  by adding  to  it a sufficient quantity of alkali
 saturated with air, the lime will recover the whole of its air, and
 be entirely restored to its  original  weight and condition.  And
 it also follows,  that the earth precipitated from lime-water by
 an alkali, must  be the lime which was dissolved in the water re-
 stored again to its original mild and insoluble state, by having
 attracted the fixed air from the alkali.
  3.  If it be supposed, that slaked  lime is an uniform compound
 of lime and water, and  does not contain any  parts which are
 more  fiery, active, subtile, or soluble than the rest, it follows,
 that as part of  it can be dissolved  in water, the whole must be
 capable of dissolution in that fluid.
  4.  If the excessive acrimony of  the caustic alkali depends on
its being free from air,  and not upcm a part of the lime adher-   j
ing to it, a clear caustic  ley will consequently be found free from   M 
         PROPOSITIONS  TO BE  EXAMINED.     223

 any admixture of lime, except  it should happen  bv accident,"
 when the  quantity  of lime employed in making it is much
 greater than what is  sufficient to extract the whole air of the al-
 kali :  for then we can imagine, that as  much of the superfluous
 lime may be dissolved by the ley as would be dissolved by pure
 water, or that the ley may  contain as much lime as lime-water
 does.
    5.  It was  proved by the former experiments  that alkaline
 earths lose their air when they are joined to an acid, but recover
 it if separated again from that acid by  an ordinary alkali,....the
 air passing from the  alkali to the earth  at the same time that the
 acid passes from the earth to the alkali.
    If the  caustic alkali be destitute of air, it must, therefore, pre-
 cipitate magnesia from acids in the form of a magnesia free of
 air, or which  will not effervesce with  acids.  And the  same
 caustic alkali  must precipitate the calcareous earth from  aeids
 in the form of a calcareous earth destitute of air, and saturated
 with water only, or in the form of slaked lime.
    These were the consequences of the theory which required
 the most attentive examination, as  being either quite new and
 unheard  of, or inconsistent with the  established  opinions.  I
 was encouraged, however,  to proceed in the inquiry by one or
 two  facts  which coincided  with these  propositions.  One of
 these was the nature of the caustic volatile alkali,.  Mr. Boer-
 haave having  prepared some of this with the greatest care, was
 surprised to find that it did not effervesce with acids.   He calls
 it liquor omnium acerrimus,  neque  tamen alcalinus.  Thinking
 effervescence  with acids an essential character of  alkaline sub-
 stances,  lrc thought  that he  had destroyed it.  And the  other
 was  a passage in Hoffmann, in which  he says, that  in making
 some experiments with quicklime, he once found that it was
 dissolved bjr acids without effervescence.
    I accordingly engaged in a set of experiments for provingthe
 truth or falsity of these  propositions.  And the  consequence
 was,  that they, in general,  proved true, or agreeable to the
 theorv. But it ma'v be proper to give a short  account of the ex-^
 periments, that i  may have  an  opportunity not only to explain
 this subject more fully, but alo to mention some other discove-
ries which have been the consequence of thi s set of experiments.
* 
 2*t             ANALYSIS OF  LIME.

           Experiments to try the First Proposition.

   To examine the truth of this proposition,  it was necessary,
 in the first place, to learn the quantity of acid required to dis-
 solve and  saturate the calcareous earth  in  its natural  state, in
 order to compare this quantity of acid with the quantity required
 to dissolve and saturate  it when in the state of lime.
   I therefore put 120 grains  weight of chalk into a Florentine
 flask with a small quantity of«water, and placing the flask on the
 scale of a balance, I counterpoised  it  by putting  sand in the
 other scale.  I then gradually saturated and dissolved the chalk
 with the muriatic acid diluted, as related in similar experiments
 on the fixed alkali and on magnesia:  421 grains weight of the
 diluted acid completed the dissolution of the chalk ;  and the loss
 of weight by the effervescence was 48 grains.
   Being thus  instructed by  this  previous experiment,  I took
 another bit of  chosen chalk,  of the same weight with the for-
 mer.   I exposed it to a proper heat for changing it into perfect
 quicklime, in a small quantity of distilled water  ; and then dis-
 solved it in the same manner  as I  had dissolved the  chalk in the
 last experiment, and with some of the  same  diluted  muriatic
 acid: 414 grains  of this acid were  required to complete the
 dissolution.  This was accomplished without the least efferves-
 cence or loss of weight.
   This experiment, therefore, established the truth of the first
 proposition, with respect to the  calcareous earth,  by shewing
 that quicklime, when well prepared,, and made as perfect as
 possible, can be dissolved  in  acids,  without effervescence, or
 any loss of weight.  It  is also a sufficienf« proof that qi icklime
 requires as much acid to saturate and dissolve it  as the quantity
 of calcareous  earth of  which it was made would have  done.
 For although the  quantity of  acid required for dissolving the
 68  grains  of quicklime  in  this experiment was .not quite so
 great as the quantity  required for  dissolving  the  120 grains
of  chalk, the  difference  is  sc3  small  that  it is not  worth
notice.   The  difference of  weight  between  the  chalk  and
the lime  was  52  grains  in  120.   The difference  between the
 quantity of acid required for dissolving them was only 7 in 421,
                         ■ t 
           ANALYTICAL  EXPERIMENTS, &c.      225

 and  even this difference can be accounted for.  We know by
 experience,  that in separating volatile from fixed substances by
 the power of heat, a small portion of the fixed is commonly or
 often carried away by the volatile matter.   It is therefore pro-
 bable that a little of the calcareous earth or lime is carried away
 when this last is driven off by the action of a violent fire.   This
 appears,  I think,  in Jaquin's experiment. The calcareous earth
 yielded,  in distillation, water which was slightly alkaline. This
 water would have saturated some  acid.  For  this reason the
 lime can be  dissolved by  a little less of the acid than if none of
 it had been lost.
   It was, however, the established opinion at the time when I
 first made this experiment, that quicklime or slaked lime effer-
 vesced with acids as the calcareous earth does; the experiments
 before that time having been mostly made with imperfect lime,
 in consequence of the want of knowledge of the true nature of
 lime, and of what was necessary to  make it perfect, and to pre-
 serve it in that state.
   Having thus  ascertained the truth  of the first  proposition,
 with  regard to lime, \ made some experiments with the caustic
 fixed alkali,  to learn whether these also would agree with what
 was indicated in the first proposition.
   I prepared a  caustic ley by first slaking  26 ounces of very
 good quicklime made of chalk, with nearly seven times its weight,
 or eleven pounds  of boiling water, in a glass vessel, and then
 adding  18 ounces of purified pearl ashes, dissolved in two pounds
 and a half of water.  The  mouth of the vessel was closely cov-
 ered.   kThis warm mixture was shaken frequently for two
 hours, at the end of which the action  of the lime on the alkali
 was supposed to be over,  and nothing remained to be done but
 to separate them again  from one another.   I therefore added
 12 pounds of water; stirred up the lime ; and,  after allowing it
 to subside again, I poured off as much of the clear ley as pos-
 sible, which  was immediately corked up  in bottles.
  The lime and alkali  were mixed together in this process at
 first by the medium of so much water only as reduced the mix-
ture to the consistence of thick cream ; for this reason,.that they
are thus kept in perpetual contact and equal mixture,  until they
    vol.  li.                  rf   * " 
226        ANALYTICAL EXPERIMENTS

have acted sufficiently on one another.   When more water is
used in the beginning of this operation, the lime subsides to the
bottom ; and, though often stirred up, does not act so strongly
on the alkali, which is uniformly dissolved  in every part of the
liquor.   But I added more water afterwards to dilute the mix.
ture, that the lime might subside, and the clear liquor contain-
ing the alkali might be decanted from  it.
  The  caustic ley prepared  in this manner was found, upon
trial, to mix with acids, and to neutralize them, without the least
effervescence or loss of weight.  And when some of it was add.
ed to lime-water,  it produced only a«very  small diminution of
transparency, but not a precipitate,  like that produced by an al-
kaline salt in its ordinary state.   This was a sure sign of its be.
ing  a perfect, or very  nearly perfect caustic alkali, or of its
bf ing deprived of the whole, or very nearly the whole, of its
fixed air, by  which  the  common alkalis precipitate the lime
from lime-water.
  This is the severest test of a caustic ley.  A remainder of air,
which will not make any sensible effervescence with acids, is
sufficient for saturating a minute portion of the lime contained
in lime-water,  and rendering it perceptible by a slight want of
colourless transparency.
   By evaporating a part of  the  ley, to learn  the  quantity or
weight of the caustic alkali it contained,  I also satisfied myself
that the alkali was not increased, but diminished in weight, by
being made  caustic ;  and that it required  much more  acid to
saturate it'than an equal quantity of the common fixed alkali does.
   I must  observe that many  precautions must be taken for this
 evaporation to dryness.  The caustic ajkali requires a low red
 heat for expelling all  the water; and  is so  acrid in this state as
 to  corrode common  earthen ware, and even copper and iron.
 I evaporated it therefore in a thin silver bowl.  It is not easy to
 know by the look of it when all the water is gone, for the salt
 is their fluid, and as transparent as the ley.  I knew it to be as
 much  cleared ef water as I could hope to accomplish, by ob-
 serving the bottom of the bowl beginning to  be visible  in the
 dark.   It was then removed from the fire,  and quickly congeal-
 ed  into a Hard cake.

                     •    V 
FOR A THEORY OF LIME.
227
    Thus far the experiments supported the truth of the first pro-
 position, in every part, and gave encouragement to proceed to
 the verification of the other propositions, or to try if they would
 be verified by proper experiments.

            Examination of the Second Proposition.

   If quicklime be only a calcareous  earth deprived of its air,
 and having an attraction for fixed air stronger than that of alka-
 lis, then,  by adding to it a, sufficient quantity of alkali in its or-
 dinary state, the  lime should recover the whole of its air, and
 be restored to its original weight and condition.  And it is also
 a consequence, that  the earth precipitated from lime-water by
 an alkali must be the lime which was dissolved in the water, res-
 tored again to its original mild and insoluble state, by  having
 attracted the fixed air from the alkali.
   With respect to all these points,  the following experiments
 were made:
   A piece of perfect quicklime, made from 120 grains of chalk
 and which  weighed 68  grains, was ground  to  a fine powder,
 and thrown into a clear solution of an ounce  of alkali of tartar
 in  two ounces of water.   This mixture, being digested some
 time, was then diluted with more water: and the alkaline liquor-
 was carefully washed away from the lime by repeated affusions
 of pure water,  and subsequent decantations of it from the sedi-
 ment.  The lime  or  sediment being then dried, weighed 118
 grains,  although the piece of quicklime from which it was made
 weighed only 68 grains.  It was quite mild, and similar in every
 trial to a fine powder of common chalk.  It effervesced violent.
 ly with  acids;  and was therefore saturated with air, which must
 have  been  supplied by the alkali.   The  weight of it was not
 made up completely to the weight it had before it was burnt:
 but the  deficiency is only of two grains: and  this can be ac-
 counted for upon the principle I mentioned formerly, that a very
 small portion of the lime itself is volatilized and carried away
by the air in a violent  heat.
  In order to examine the earth which is precipitated from lime-
water by alkaline  salts,  60 grains of  the alkali of lartar were 
228        ANALYTICAL  EXPERIMENTS

dissolved in 14 pounds of lime water, and the earth thereby pre-
cipitated was carefullv collected on a filtre and dried.  It weigh-
ed 51 grains.  When afterwards exposed to a sufficient heat, it
was  converted into a true quicklime-,  and had every other qua.
lity of the calcareous earth.  And this experiment being repeat.
ed with volatile alkali, and also with the fossil alkali,  the  result
was  exactly the same  as when the alkali of tartar was  used; the
precipizatecl earth being  alwas a calcareous earth.  This  was a
sufficient proof that the proposition was true.

             Examination of the Third Proposition.

   If it be supposed that slaked lime is an uniform compound of
lime and water, and does not contain any parts which are  more
fiery, active, subtile, or  soluble than  the rest; it follows, that
as part of it can be dissolved in water, the  whole of  it must be
capable of dissolution in that fluid.
   This proposition had, at that time,  less appearance of proba-
bilky than any of the former.   It was universally believed that
lime was  only partially soluble in water;  and different opinions
were entertained of the proportion of it that could be dissolved.
 Dr. Alston contended that a fourth part of it, or perhaps a little
more, might be dissolved, provided a very large quantity of
water was employed  ; such as 500 times the weight of the lime.
 But the general opinion was, that a much smaller portion of it
only was soluble and  active.   The question had never been de-
 cided by an accurate experiment.
   I therefore chose a bit of chalk, which, when heated to a suf-
 ficient degree in a crucible, afforded a little mass of perfect quick-
 lime,  weighing eight grains.        ":  \
   This little mass was thrown, while yet  warm, into a  small
 quantity of warm distilled water in a phial,  ift which it was soon
 slaked, and formed a white mixture like milk.  This  mixture
 was immediately poured into a larger glass vessel,  in which I
 had eighteen ounces  of distilled water.
   While the milky mixture was diffused through the water, the
 lime was seen to dissolve almost entirely.   Nothing remained
 undissolved but a very light faecujency, which was almost trans-
      »      *                                      • ' 
             FOR  A  THEORY OF  LIME.         229

parent,  or only like thin clouds in the liquor.  This fasculency,
when it was allowed to subside, and was collected  with  the
greatest care on a  small filtre  and  dried, weighed  only  the
third part of a grain.  In some repetitions of the experiment, it  *
weighed less, and in others a little more.   Being examined by
putting  it on a plate of glass, and adding a drop of diluted nitric
acid, it was dissolved in part,  with effervescence ; but a part of
it remained undissolved, which was ochre of iron.  It appeared,
therefore, to be  composed of a minute portion of the lime,
which had somehow recovered fixed air, and of ochre of iron,
and perhaps a little claf, which are well  known to be often pre-
sent, in small quantity,  in chalk.
  We may therefore reasonably conclude from this experiment,
that lime, when it is  quite pure and perfect, is totally soluble in
pure  water; and that the reason why it had  appeared hitherto
soluble  only in part, was, that the experiment had never been
made with perfect lime and with  pure water.  The water tasted
strongly of  the lime. It  was a true lime-water, and yielded
twelve  grains of calcareous earth, when some  alkali  of tartar
was added to it.
  The event of this experiment was even more  favourable than
I had expected.   I  expected a much  larger  quantity  of sedi-
ment produced from this lime when dissolved ;  chiefly because
I suspected that the air, which we all know to be commonly dis-
solved in water, might be attracted by the alkaline substances,
and  therefore render the lime mild and insoluble.  The result
rather surprised  me; and, raising new thoughts in my  mind
which seemed to lead to very extensive and important  conse-
quences, I was anxious, to put it to some trial.
  To learn, therefor^  whether  water saturated with lime had
given up the air wh'ien it usually holds in solution, and  whether
that air  is united with the lime,  I made a very strong lime-water,
and placed four ounces of it under the air-pump receiver, along
with  four  ounces  of common  water  in  another vessel  of
the same size.  The air was taken out of. the receiver ; and
while this was doing,* air bubbles formed and arose in both
phials, in equal quantities,  and in the same manner, as far as
I could judge;  and  the lime-water continued perfectly trans-
parent. 
 ^O       DISTINGUISHING PROPERTIES

   Hence it is evident that the air arising from the lime-water
 had been combined with the water, and not with the lime ; and
 the air which water commonly holds in solution is of a different
 nature from that which is attracted by lime and alkalis : for, had
 it been the same,  and combined  with the lime,  as  fixed air is,
 the removal of the atmospherical  pressure would not have been
 sufficient for  occasioning its separation.
   Quicklime, therefore, does not attract the air that is usually
 contained in common water, nor does it attract the whole of the
mass of atmospherical air, as I have  already observed.   It at-
tracts only a particular kind of aerial fluid which is  mixed wiih
the air of the atmosphere, in  the way of  common diffusion, in
a small quantity only.  It is mixed as spirits are in water, or
one metal with another, without any change of properties; and
alkaline substances take out this air, as aquafortis takes out the
silver which alloys a piece of gold.
   Here a new,  and perhaps boundless field seemed to open be-
 fore me.   We  know not how many different airs may be thus
 contained  in our atmosphere, nor what  may be their separate
 properties.  This particular kind has evidently very curious and
 important  ones.   Ij renders mild and salutary the most acrid
 and destructive  substances that we know.  I resolved to begin
 die study of them, by a closer examination of the species which
 I had fortunately discovered.
   I gave it the  name  of Fixed Air, for the reasons already
 mentioned, a term which was  then  common to  denote any
 elastic matter, capable of entering into the.^ com position of bo-
 dies,  and of  being condensed in them to  a jplid concrete state,
 by its chemical  attraction for some of their constituent parts.
 The name  may perhaps be thought to be not very judiciously
 chosen, to  denote this  matter in its elastic state: and accord-
 ingly it has now  bee^xhanged for gas.  But I chose   rather to
 employ a term already familiar, than invent a new^name, before
 I was well informed respecting the peculiar properties of this
substance. 
OF  FIXED  AIR.
131
    It is somewhat singular, that when a solution of mild alkali
 is rendered caustic by lime, the specific gravity is considerably
 diminished.   We  should naturally expect the contrary effect,
 from the abstraction of so rare a fluid as air.   But this shews,
 that in the solution  the fixed air is rendered considerably den-
 ser than water, being reduced to less than ^ of its aerial bulk.
    I fully intended to make this air, and some other elastic fluids
 which  frequently occur, the subject of serious study.   But my
 attention  was then  forcibly turned to other objects.    A load
 of new  official duties was  then laid oq me, which  divided my
 attention among a great variety of objects *.  In the same year,
 however,  in which my first account of these experiments was
 published, namely  1757, I had discovered that this particular
 kind of air, attracted  by alkaline  substances, is deadly to all
 animals that breath it by the mouth and nostrils together ; but
 that  if the nostrils were  kept shut, I  was  led to think that it
 might  be breathed  with safety.   I found, for example, that
 when sparrows died in it in ten  or eleven  seconds,  they would
 live in  it for three or four minutes when the nostrils were shut
 by melted suet.   And I convinced myself, that the  change pro-
 duced'  on wholesome  air  by breathing it, consisted chiefly,  if
 not solely, in the conversion of part of it into fixed  air.   For I
 found,  that by blowing through a pipe into lime-water, or a so-
 lution of caustic alkali, the lime was precipitated, and the alkali
 was rendered  mild.  I was partly led to these  experiments by
 some observations of Dr. Hales, in which he says, that  breath-
 ing through  diaphragms of cloth dipped  in alkaline scttjCn,
 made the air last longer for the purposes of life f.        15L
   In the same year I found that fixed air is the chief part of the  ,
 elastic matter which formed in liquids in the vinous fermenta-
 tion.  Van Helmoi^ had indeed said this, and  it was  to this

    * Dr. Black was at this time elected Professor of Medicine and Chem-
 istry in the  University of Glasgow....editor.
    t In the winter 1764-5, Dr. Black  rendered inconsiderable quantity of
 caustic fossil alkali mild and crystalline, by causing it to filtre slowly by
rags, in  an apparatus which was placed above one of the spiracles in the
ceiling of a church, in which  a congregation of more thau  1500 person*
ha& continued near ten hours..  editor. 
 232 F. AIR DELETERICUS EXTINGUISHES FLAME.

 that he first gave the name gas silvestre.   It could not long be
 unknown to those occupied in  brewing or making wines.   But
 it was at random that he said it was the same with that of the
 Grotto del Cane in Italy, (but he supposed the identity, because
 both are deadly) ; for he had examined neither of them chemi-
 cally, nor did he know that it was the air disengaged  in the ef-
 fervescence of alkaline substances with acids.  I convinced my-
 self of the fact by going to a brew-house with two phials, one
 filled with distilled water, and the other with lime-water.  I
 emptied the first into a  vat of wort fermenting briskly, holding
 the mouth of the phial close to the surface of the  wort.   I then
 poured some  of the lime-water into it, shut it with my finger,
 and shook it.   The lime-water became turbid immediately.
   Van Helmont says, that the dunste, or deadly vapour of burn-
 ing charcoal, is the same gas silvestre:  but this was also a ran-
 dom  conjecture.  He does not even  say that it extinguishes
 flame; yet this was known to the chemists of his day.  I had
 now the certain means of deciding'the question, since, if the same,
 it must be fixed air.  I made several indistinct experiments as
 soon  as the conjecture occurred to my thoughts; but they were
 with little contrivance or accuracy.  In the evening of the same
 day that I discovered that it was fixed  air that escaped  from fer- ■
 menting liquors, I made an experiment which satisfied  me. Un- ■
 fixing the nozzle  of a pair of chamber-bellows,  I put a bit of m
 charcoal just red hot, into the wide end of it,  and then quickly -S
 putting it  into its place again,  I plunged the  pipe to the bottom
 of a phial, and forced the air very slowly through the  charcoal,
 so as  to maintain its combustion, but not produce a heat too sud-  \
 denly for the phial to bear.   When I judged that the  air of the
 phial was  completely vitiated,  I poured linre-water into it,  and
 had the pleasure of seeing it become milky in a moment.
   I now admired Van Helmont's sagacity, or his fortunate con-
jecture ; and, for some years, I took it for granted that all those
 vapours which extinguish flame, and are destructive of animal  ;
 life, without irritating the lungs, 01 giving warning by their cor-
 rosive nature, are the gas silvestre of Van Helmont, or  fixed air.  i
   Some time after I had made, and published in my inaugural  J
 dissertation, the experiments  you have seen, the  attention of J 
      SPECULATIONS OF DR.  MACBRIDE.   233

some other persons  was excited, and keenly engaged  with
this new and  interesting subject.   The late Dr. Macbride of
Dublin began to attend to it, in consequence of some letters
which I wrote to my friend Dr. Hutcheson, then lecturer on
chemistry in  Trinity College.  In these letters I described
to him some  of my  newly contrived  experiments  and ap-
paratus, of which Dr.  Macbride made use in his  investiga-
tions.
   He made a great number of experiments to shew that the
air emitted  from fermenting vegetables is,  in all cases, an
air of this kind;  that it  is  attracted by alkaline salts and
earths,  and precipitates lime from lime-water.   He also ob-
tained some  of this  air from animal substances in a putrify-
ing state.   And he thought that when applied in quantity to
putrefying animal substances, it  stopped putrefaction, and
even restored putrid substances to a sound state.
   Concluding from what he  thought was proved  by his ex-
periments, he considered  this sort of air as an element neces-
sary* or of  great importance, in the composition of  most
kinds of matter.  He  imagined  that the  cohesion of the
parts of solid bodies depends on it; and that putrefaction,
and  the concomitant  resolution of  bodies  into  their first
principles, are entirely a consequence of the  separation or
loss of this kind  of air, which he supposed  to be the great
cementing principle of solid bodies.
   But  this system  was not well  founded, and was not only
not supported, but,  in some  measure, refuted afterwards, by
the experiments  and  discoveries of other  authors.   The
 Doctor having observed that some effervescence or ebullition
accompanies many  caSes of the  dissolution of solid bodies
by putrefaction, and isome other  natural operations, he sup-
 posed that in all these  cases, air like this was separated from
 the materials,  and   that the  separation of this air was the
 circumstance most  effectual, or  even essential to the disso-
 lution.
    But, by a little more knowledge of chemistry, he would
 soon have learned that he was wrong with respect to a great
 number of such  cases; for later experiments on  the  putre-
 faction of animal substances have shewn that the elastic fluid
 matter emitted by these is only in part this kind of air,....by 
234   EXPERIMENTS OF  MR.  CAVENDISH
much  the greater part being an inflammable  vapour, anil
other kinds.
   Next after Dr.  Macbride, the Honourable Henry Caven-
dish published, in the Philosophical Transactions 1765, some
neat and ingenious experiments on this sort of air and some
other elastic fluids.
   He, in  the first place, shewed that this air, when separated
from alkalis or earths by acids, is beyond all doubt a penna-
nent elastic fluid.   He  kept some of  it twelve months in a
vessel inverted into mercury, without any diminution of its
elasticity.
   Dr. Macbride  had before  discovered that water  could
absorb a  quantity of this air, and become thereby capable of
precipitating lime from lime-water.   Mr. Cavendish de-
monstrated this by more decisive experiments, and has de-
termined  the full quantity which the water can absorb.  When
of a middle temperature of heat, or about 55°,  it will absorb
rather more than an equal bulk.
   From Mr.  Cavendish's experiments, it appears that when
the water is warm., it does  not  absorb the air so readily, nor
so much of it.   and after cold water is saturated with it, if
we make  it hot  to a  certain degree,  the air  is separated,
forming itself into bubbles which arise  out of the water.  It
also escapes  slowly and imperceptibly, if the  water be left
in an  open vessel, atmospherical air  having rather more at-
traction for this sort of air than water has.
   Mr.  Cavendish also  discovered that other  fluids beside
water can absorb some of this  air; as spirit of wine, which
absorbs more  than twice its bulk;  and  some of the oils ab-
sorb as much as water  does.   In these experiments  with
water  and other fluids, he thought there was reason to infer
that this air is not homogeneous, but that some  parts of it
are more  absorbable than the rest, and  that a certain part of
it could not be absorbed.  I suspect, however,, that this was
a deception, proceeding from  the common air  which water
contains,  and which arises  with the fixed an during the ex-
trication of this last from the alkaline subwances.
   From some of his experiments, Mr. Cavendish calculated ^
with great exactness the quantities of  this air contained in
marble, in pearl-ashes or common^xed  alkali,  in volatile'ai- ...
i 
     ON FIXED AIR AND ITS COMBINATIONS. 235

  kali,  and in magnesia, when these alkaline substances are in
  their ordinary state. And ne thereby explained some pheno-
  mena  which occur in  mixing  the alkalis with solutions of
  marble, or of magnesia by  acids.
     Thus he found that marble contained -f-^ of fixed air.
            Mild volatile alkali     -    TWo
            Pearl ashes     -     -     7VsV
            Crystals of soda   -   -   ^2/o
            Magnesia     -     -     - jjfo
     And that a certain quantity of acid  saturated—
        Of marble     -                1000 grains.
            Mild volatile alkali     -   1661
            Pearl ashes     -     -     1558
            Crystals of soda   -    -  2035
     Crystals of soda effervesce with a solution of chalk in an
  acid.   They do not precipitate  magnesia without heat;  and
  a considerable effervescence  attends the precipitation.  Mild
  volatile alkali effervesces  also with a solution of magnesia
  in an acid ; and  frequently does not precipitate it, but yet
  detaches it from the acid, and redissolves it by the fixed air
  which is extricated.
     He also ascertained the precise density of this air, which
^ he has shewn to be greater then that of common air, in the
  proportion of 157 to 100;  and has shewn that the air of mar-
  ble and of fermenting vegetables agree in this as  well as in
  other respects.   In consequence of this, it lies at the bottom
  bf a vessel, and may be poured out like water.  When thus
  poured out on a candle,  it extinguishes it as water would do.
  It affords an amusing spectacle by letting a large  soap-bubble
  fall on it in  a vessel.   The  bubble rebounds from it like a
  football, and seems to rest on nothing.     A burning candle
  may be held in  it, having the top of  the wick about half an
  inch ur.der the  surface,  in which case the flame will continue
  for a few  seconds, but altogether detached from the candle.
  The wick  remains hot enough to cause the tallow still to eva-
  porate; and thet4vapour kindles at the surface of  the fixed
  air.   The floor of the  Grotto del Cane,  in  Italy,  is lower
  than the door ;  and this  hollow is always filled with fixed air,
  which  can rise  no higher than the  cill, or threshold of the
 ••door,   but flows out like"' water.  If a dog go in, he is im- 
236  OBSERVATIONS OF DR. BROWNRIGGS, &c.
mersed in the fixed air, and dies immediately.   But a man
goes in with safety, because his mouth is far above the sur-
face of this deleterious air.
  He  also mixed this air  with common air,  in different
proportions to discover what effect these mixtures had upon
flame or burning bodies.   All his experiments are ingeni-
ously contrived, and executed with accuracy.
  Immediatelv  after Mr.  Cavendish had published his ex-
periments, some of them, particularly those which shew that
wrter is capable of absorbing such a large quantity of this
air, recalled the  attention of  Dr. Brownrigg to an opinion
he  had long entertained* and had communicated, with his
reasons for it, to the Royal Society so early as the year 1741.
The Doctor had been at  Spa, where the appearance of the
waters had drawn his attention    They are among the most
remarkable  of those  waters  called acidula.   They  have a
pleasant light acidity  and briskness, and sparkle in the  glass
like a  fermented liquor.   They appear as if «omething very
elastic  and volatile were  contained in them.   He also ob-
served, that  not far  from their  fountain, there are caverns
which  contain the choke-damp, and that something like the
choke-damp  hovers  upon  the  water,  by which  ducks are
killed.
   He  therefore  supposed that the waters  derived  these
qualities from a quantity of this choke-damp  combined with
the water, the nature of which choke-damp, however, was at
that time unknown, excepting its  power to kill animals im-
mersed in it, and to  extinguish flame.
   When  Dr. Brownrigg saw Mr. Cavendish's  experiments,
he  became still more inclined to this opinion of  the nature
oLthe waters at Spa ; and very soon .after going back to that
place, he gave a full demonstration or proof of it, in a number
of  experiments made with the waters on  the  spot;  which
shewed that they do in reality contain a considerable quantity
of  a' sort of air, which,  when  separated from the water by
heat,  kills  animals.    And it  furthefc anaeared, by the
experiments  ci others, that common wafer^^hen combined
with this sort of air, extracted by art from alkaline substances,
acquires all the remarkable qualities of the acidulous mineral
waters.   From hence has  aristn tile art of imitating  those 
FIXED AIR DISSOLVES ALKALINE EARTHS. 237
waters exactly, by an  artificial  compound of this  air with
water, by small additions of some of the salts, or alkaline
earths, or iron, which,  by accurate analysis, have been found
variously mixed in the  composition of mineral waters. When
this air is combined  with pure water,  the water acquires the
briskness  and light  sourish pungent taste  of the acidulous
mineral waters ;  and,  like  them, has the power to  change
the infusion of litmus  to a red colour.
   Thus, Dr. Brownrigg explained some of  the  qualities of
the most remarkable mineral waters, which had never before
been  well understood.   But our knowledge of some varieties
of natural waters was made still more perfect by the further
discoveries of Mr. Cavendish and Mr. Lane.  Many waters
are well known to have  a petrifying quality.   They deposit
a calcareous earth in the pores or on the surface  of different
substances which are exposed to them : or at  least they cover
the insides of tea-kettles  with  a calcareous  incrustation.
There  are other waters which  contain a small quantity of
iron  dissolved in them, but which are sure to  deposit the
whole of  it in  the form  of ochre, if they are exposed to the
air, or are corked up  in bottles not sufficiently close.  Mr.
Cavendish, while  employed in  examining a   water  near
London, at Rathbone Place, discovered that calcareous earth
can be dissolved  by aerated  water; that it is  deposited when
such  water is  deprived of its air ; and  that the  water of
Rathbone Place actually contained calcareous earth  dissolved
in this manner.
   This discovery explains the  nature of most  petrifying
waters.   They contain a small quantity of calcareous earth,
dissolved in this manner, and some perhaps of the earth of
magnesia : for this  earth also  can be dissolved  by water
charged with fixed air, and even more easily, and in  greater
quantity,  than the calcareous earth.   When such waters are
boiled often in tea-kettles, ihe air is driven away .by the heat;
and the earth separates  from the water, forming the earthy
incrustation thjit  is found on the inside of them.   The earth
is also deposited more slowly when  such waters are long
exposed to the air,  or run along the  surface of the ground, *4
and suffer evaporation. The fixed air, in this case, evaporates,   ■* 
 238. THEORY OF  PETRIFYING  WATERS.

 and the  earth often forms incrustations, and stalactites, and
 petrifactions.
   It may appear to you surprising that the same substances
 which, added to lime-water, precipitate the lime, by making
 it insoluble, should also  be the cause of  its  redissolution
 when added  in larger quantity.  But the fact is certain, and
 it is not  singular.   There are .many  other facts in chemistry
 which are similar to it: for example, most of the compound
 salts can be' made  more soluble in  water than  they aYe in
 their perfect or n'eutral state, by adding to them a superfluous
 quantity of acid.  A certain quantity of this superfluous acid
joins itself to the compound salt with a weak attraction, and
 forms an acidulous  compound salt, which is more soluble in
 water than  the  perfect neutral.   There is no exception to
 this but  in the compounds with acid of tartar, which, in this
 acidulous state, are less soluble than in their neutral state ;
 and differ also  in this, that the superfluous acid is strongly
 united.  All the other compound salts become more soluble
 in water by  being acidulated  with some superfluous  acid ;
 which however adheres to  them with an  attraction that is
 very weak.   The phenomenon you have now seen appears
 to be analogous to this. The first  effect of the aerated water
 on  the lime-water is to precipitate the lime, by supplying it
 with that quantity of fixed air which changes the  lime into
 chalk, which,  though not perfectly insoluble, is  very nearly
 •>o.   But after this, if we add more  of the aerated  water, a
 superfluous  quantity of fixed  air joins itself to  this chalk,
 riiul forms what may be called acidulous chalk, which is more
 soluble than  chalk.   But this  superfluous  quantity  of fixed
 air adheres to the chalk with a weak  attraction, and is sepa-
 rated and driven off from it by the  heat of boiling water, and
 also  by  the  attfaction of atmospherical air.    We cannot
therefore reduce this  acidulous chalk to a dry state.   It is
sure to lose  its  superfluous quantity of fixed  air when we
attempt to evaporate the water from it ; and then  it becomes
common chalk.   The solution  of a saline1' crystal is  also
analogous to this phenomenon.
   From  all  this, you will easily understand the necessity of
one step  of the process, which I recommended, for preparing
magnesia from Epsom salt.   The stepp,'!  mean is  the boiling 
    MEDICINAL  VIRTUES OF  FIXED  AIR.   239
                                          i
over the fire,  for a little while, the mixture which contains
the solution of  Epsom salt and the solution of potash,  by
which the magnesia is precipitated.
   The reason of the necessity for  boiling this mixture  is,
that a great quantity of  fixed alkali is necessary for the
complete precipitation of  the magnesia : and this proceeds
from  the great  quantity  of  acid  which  is united  to  the
magnesia in Epsom salt.  I found  that one pound of pearl
ashes,   or little less,  is necessary for  precipitating  the
magnesia completely from a pound  of Epsom salt, although
that salt contains one half of its weight of water in its crystals.
   When the pound of alkali therefore unites with the acid,
although there is no visible effervescence, so great a quantity
of air is extricated from it, that this air is sufficient, not only
for saturating the magnesia, but for acidulating both it and the
cold water with which the mixture is made; and consequent-
ly, a great part of the acidulated magnesia is dissolved in the
acidulous water. But the mixture being boiled, the superfluous
air evaporates from the water and  from the magnesia ;  and
thus the magnesia is  completely precipitated.   This proce-
dure, which explains a very  extensive and curious natural
phenomenon, was discovered by Mr. Cavendish.  The nature
of the volatile chalybeate waters, which, when fresh from the
spring,  he'd some iron in solution,  and sparkle  in  the glass,
but lose their briskness and inky taste by  careless keeping,
and gradually  deposit the  iron in form of a red,  or brown,
or  yellow ochre, were  explained in the  same manner  by
Mr. Lane.  The  iron had been dissolved by the  acidulous
water containing fixed air.
   It will perhaps appear to some of you surprising that any
physician should have been so bold as to think of giving this,
substance internally,  when it is known to extinguish life so
suddenly when applied to the  lungs  and organs of smell (for
this seems  a necessary condition).   But  the truth is, that
these dangerous and fatal effects of it happen only if applied
in that particulaf manner.  It has no  such effect when applied
to the nervepbf the stomach, or other parts.  On the contrary,
we have daily experience  that it is  grateful to the stomach,
and has a most agreeable, refreshing, and cooling effect when
applied  there.  This  appears, both  from the agreeable effect 
240   MEDICINAL  VIRTUES OF  FIXED  AIR.'

of acidulous waters on the stomach, and from that of very
brisk fermented liquors, such as champagne, beer, &c. which
are highly grateful in hot climates.   Even to the lungs, fixed
air  may be applied,  not only with  safety,  but even with
advantage, as  we are informed by practitioners, who have
tried it in consumption and ulcerated lungs.   But it must be
employed with four or five times its bulk of  atmospherical
air, or even in a  greater proportion.  Were it to be breathed
in considerable quantity in its pure state, I have no doubt but
that  it would extinguish life in a short time.
   Those who ventured to apply fixed air to the lungs, were
induced to this  by observing its effects  on  some very bad
external ulcers, to which it proved an useful stimulant, and
a powerful corrector of the putrid and acrid humours which
bad  ulcers  often emit.
   The first physician who formed an opinion of the salutary
qualities of fixed air,  was, I  think,  the late  Dr. Macbride
of Dublin.  His opinion was formed  very "much  on the
theoretical views which I mentioned lately.   TJr. Percival,
of Manchester,  esteems  fixed air highly  medicinal  in pul-
monic  consumptions, and in maglinant fevers.   The hap-*
piest effects have been experienced from the use of  it, both
external and internal.   And he  says  that he does not know
a more powerful  remedy  for foul ulcers, as it mitigates pain,
promotes  a  good digestion of the sore, and  corrects the .
putrid disposition of  the  fluids.   He thought that he  had
reason to infer from several experiments that water with fixed
air is a solvent of the urinary calculus; and that the urine of a
person who drinks plentifully of such water becomes strongly
impregnated with the  fixed air,  and dissolves the dalculus.
Some  calculi are best dissolved by alkalis ; others by acids.
but  fixed air acts on them all.
   The late Dr.  Dobson of Liverpool, afterwards of Bath,
has  published a  number of cases in which he found it very
useful  and salutary;  particularly, in putrid  fevers, in the
cure of ill-conditioned ulcers,  and in certain relaxed and
debilitated states of the stomach, occasioning want of appetite
and indigestion.   But .he.-duSflpot  find it effectual in relieving
symptoms of the stone and "gravel ;  though  it proved often
useful in ulceration of the organs. 
        FIXED AIR  IS A COMPOUND, &c.     241

   The aqua acalina a'erata is  certainly an excellent medicine
in calculous cases,....not as a solvent, but as a most effectual
palliative,  ascertained by experience.   I know no solvent
to be relied on.   Caustic alkali  is very powerful:  but,  that
it may not act on the bladder itself, it must be so employed,
that its action on the calculus is very slow; and the patient
is fatigued and tires.   The aerated alkaline water  continues
agreeable.
   I have  now considered, at as great length as was proper^
the properties of fixed air, considered as an object of  che-
mistry, and have taken notice of its natural history,  or the
forms  in  which we meet with  it, and  also of  the" many
sources from  which it may be obtained by art.   But there
remain some observations on it, from which we are  led to
assign it  a more remote origin, shewing it to be itself a
compound substance. Soon after its properties and  particular
nature were fully made known by the gentlemen who occupied
themselves so seriously with  this discovery of mine, various
opinions were formed as to its real origin.  All these opinions
were  connected  with the belief of the existence of  a phlogis-
ton ; and,  in one way or another, I believe all of them  con-
sidered fixed air as an emanation from inflammable bodies,
or as a compound of air with their inflammable principle, or
something containing it.  This was almost an unavoidable
inference  from our observing, that all fuel, and inflammable
substances commonly employed for producing a burning heat,
when burned in air,  produce a  great quantity  of  fixed air,
and diminish the quantity of air in which they burn :  and
as all fixed air appeared to be of the same nature, phlogisti-
cation appeared the  only way of producing it from Such a
variety of bodies.
   But it was afterwards found that some bodies, not familiar
indeed as  fuel, or ever employed as  such, yet which  burn
with great vivacity, spoil the air, making it lethal, and  unfit
for maintaining flame, yet void of the acid quality of fixed
air, without  attraction for alkalis  or  calcareous earth, and
causing no precipitation of  lime from lime-water.  This i*
the  case  with  sulphur, with  phosphorus, with  zinc,  and
 some other metals, which we know burn like a bit of char-
 coal, or even with flame,
    VOL.   II.                 H h 
242      FIXED AIR  IS A COMPOUND,  &c.

  This was, I think, the  first observation that made any change
m the opinions formed on this subject, and caused the chemists
to seek for the circumstance of resemblance  among all the
fuels whose combustion produced fixed .air.  I cannot say who
was the first who observed that all such  fuels will be changed,
in one way or another, by great heats in close vessels, into what
we call charcoal.*   This is the case with all animal and vege-
table  substances  in  their natural state.   Careful  observation,
and a well conducted chemical analysis, shew this to be equally
true with respect to all the substances which art can any how   |
extract from them,  or form by mixing  them.  Even spirit of
wine and jether, when properly treated,  afford charcoal.  One
simple mode of treatment  will have this effect on all.  This is   ,
to mix them with vitriolic acid, so as to force them to stand a
strong red heat along with it.  Sulphurous acid  is always pro-
duced, and sometimes real sulphur ;  but, at the same time, there
 is a black residuum in the retort, which is found a perfect char-  (
 coaL  I  believe  it was  among the French chemists who were
 associated with Mr.  Lavoisier in his ingenious investigations, i
 that the  universality of this fact was first observed.
   All such fuels produce fixed air by their combustion.   Vege-
 table and animal substances  alone are subject to the vinous and
 putrescent fermentations which emit fixed air.  Charcoal seems i
 the only common principle among  them, distinguishing them  f
 from  other combustible bodies.  It was, therefore, a natural
 inference that charcoal is the primitive source of fixed air.  Ac-
 cordingly Mr. Lavoisier  assumes charcoal for the radical or
 characteristic ingredient of this  acid  gas.  But  as  common
 charcoal, from, whatever  substance we  obtain it,  contains an
 earthy uninflammable part, Mr. Lavoisier desires it to be un-
 derstood, that it is the pure inflammable part only that he con-  '
 siders as the radical of fixed air; and, to distinguish this from   i
 any  compound, he uses  the word  Carbone.  He considers
 fixed air, therefore, as a compound of oxygen  and carbone,
 in the same manner as the vitriolic aqd is considered by him   '
 as compounded of  oxygen  and sulphur.   And,  as he calls
 this the sulphuric acid,  he calls fixed air the Carbonic  Acid«   \
   * Dr. Hooke says this in many parts of his Cutlerian Lectures.,...ebitoi.   j 
FORMATION OF CARBONIC ACID.    243
    Mr. Lavoisier has made some very ingenious experiments,
 which seem to demonstrate this composition.  He burned small
 quantities of charcoal in pure oxygen gas, in close vessels, and
 he found that a part of this gas  was converted into fixed air.
 He separated this from the rest of the oxygen by means of caustic
 alkali, and weighed  the alkali after  it had attracted the fixed
 air.   He also expelled the air again by an acid, and examined
 its bulk.  Thus he  learned the weight of the air, and what
 measure of it had been produced. •  Then, comparing this weight
 with  that lost by  the charcoal which had been consumed, he
 found it to exceed greatly the weight of the charcoal, and was
 exactly  equal to the  weight of the charcoal and of that portion
 of the oxygen gas which had been ehanged into fixed air.  He
 found that 100 grains of carbonic acid contained  72 grains of
 oxygen  gas  and  28 grains of  carbone.  This composition-and
 this proportion of the ingredients, have been confirmed by many
 other  direct  experiments of the same kind; and they agree sur-
 prisingly with the results of more complicated  experiments, in
 which this proportion is taken for granted in the explanation of
 other phenomena.  I therefore readily  adopt his denomination
 of carbonic acid as extremely proper, indicating the nature of
 the substance.
   It appears then, from some experiments which have  been
 mentioned occasionally, that this  carbonaceous matter is sepa-
 rated and thrown off from  the blood in  the lungs in  the act of
 respiration:  for air that has been  breathed always contains car-
 bonic acid.   In proportion to the quantity of this acid which
 air contains,  it is  deficient in its due proportion of free oxygen
 gas, a part of it  having been changed into carbonic acid, by
 meeting  with carbone in  the  lungs.    This has  been ascer-
tained  by the experiments of Scheele, Lavoisier, Dr. Good-
win, and Dr. Menzies ; which two last gentlemen have publish.
ed good  experiments on this subject in their inaugural disserta-
 tions.
  You will,  therefore, easily  understand  what happens when
atmospherical air passes through burning fuel.   The oxygenous
part of that  air, and the carbone of some of the charcoal, unite
 and form a quantity of carbonic acid ; and, when  the air arise 
 244     FORMATION OF  CARBONIC  ACID.

 from  burning fuel, instead of being a mixture of foul air and
 oxygen gas, as«*t was  before, it is now a mixture of this foul air,
 carbonic acid, anxl the remainder of oxygen gas, which has not
 yet been saturated with carbone, but would become saturated by
 a somewhat longer and more effectual application of the one to
 the otlu-r.   The  heat, which  is produced in great quantity on
 this occasion, is supposed to have come chiefly from the oxygen
 gas, which, becoming more dense, and  having its capacity for
 heat diminished by this condensation  must throw out a consi-
 derable portion of heat which it previously contained, and along
 with the heat a quantity of light, which is perhaps the same mat-
 ter, acting or modified in a  different manner.*                   I
   Other names have  been  given  to  this  fluid by the  many
 chemists who were occupied on these subjects.  I called it fixed
 air, because it was found by me fixed in a number of substances.
 Mr. Cavendish changed this name to  fixable  air.   Many pre.
 ferred the name gas, and called it acidulous gas.   Mr. Henry
 of Manchester, and  Professor Bergmann, called it the  aerial
 acid.   Mr.  Fourcroy  called it acide er ay eux,....acid of chalk;
 but all seem now agreed in giving it the scientific name carbonic
 acid.
   In conformity wjth the general plan of  their reformed chemi-
 cal language, the French chemists have named the compounds i
 which contain this acid carbonats.   Thus, chalk or limestone is
 the carbonat of lime;  mild  vegetable alkali  is  the carbonat  of
potaeh;  mild fossil alkali is the carbonat of soda; :rude mag- ■>•
 nesia the carbonat  of magnesia ; and mild volatile alkali the car-   1
 bonat of ammonia, &c.                                            J
   Thus,  gentlemen,  have I thrown together "the  chief disco.   J
 veries which have  been made concerning the nature and chemi-  1

  * This I.avoisieriah theory of  the combustion of charcoal is precisely the   I
 same with that published by Dr. Hooke in his Micrographia,  in 1664-5, (page   I
 103), as a general theory of combustion.  All combustion is, according to him
 the solution of what we call the combustible body in the pure nitro-aerial spirit   j
 which makes part of the atmosphere.  In the case of certain  bodies, there is
 not only no incombustible or recrementitious matter, but the compound itself is
 volatile, and is dispersed in the air.  The  great heat proceeds entirely from   J
 the nitro-aerial spirit;  and the light is the the vibratory pulse produced in tb«  M
 gethcr, whose \induHtions produce  in us the sensation of light.....editor. 
        RISE OF PNEUMATIC CHEMISTRY.     245

 cal properties of the elastic fluid which I discovered in 1756.
 These discoveries have been made at very different times, and
 by many different authors.  For the public attention continued
 for a long while  to be very much turned to this substance, which
 comes so often in  our way in chemical processes, and also in
 the great operations of nature. The curiosity of philosophers be-
 ing thus turned to a very novel kind of object, an elastic fluid, this
 gave rise to a new kind of manipulation, and a new apparatus,
 and a  manner of management equally  novel,....all which made
 it give much entertainment.  And in this new path a number of
 other objects of  the  same  uncommon  kind came in their way,
 and increased the interest taken in the study.   Curious chemists
 even tried  to produce new airs, as they were called, by every
 possible  means,  in expectation of singular results and  disco-
 veries  ; and thus has arisen a  quite new species of chemistry,
 which  maybe called  Pneumatic Chemistry, because occupied
 in the  study of fluids permanently elastic, like air.  In the pro-
 secution of these investigations, chemical apparatus was greatly
 improved ; and  we can now manage those slippery substances
 as easily as we formerly managed the solids and liquids in our
 ordinary vessels.    The  boundaries of  chemistry have been
 wonderfully enlarged, and discoveries have  been made of  the  ,
 most unexpected  nature.  Common water,  which, from  the
 dawn of natural  science, has been considered as an unchangeable
 element, is now  found to be a compound of  two kinds of air.
 Diamond,  seemingly the  purest  and  most  unchangeable of
 things, is now found to be coal.  And all our  former notions of
 chemical relations are now changed.
   Among these  new chemists, Dr. Priestley is certainly one of
 the most eminent.   He was one of the  first in respect of time ;
 and he has surpassed them all in the number and variety of his
 experiments, and I may add, in his discoveries.  Dr. Priestley
 firsf narrated a number of experiments on fixed air and some
 other elastic fluids, in several succeeding volumes of the Philo-
 sophical Transactions in 1772, &c. and  then published them in
 several separate volumes.  The elastic fluids which engaged  his
 attention were,  1st,  Fixed Aair.  2d,  Atmospheric Air, in its
ordinary state, and as changed or vitiated for the purposes of 
 246  SURPRISING DISCOVERIES OF PRIESTLEY.

 life by various means.   3d,  What he called Marine Acid Air,
 which is nothing else than  the incoercible vapours of pure mu-
 riatic acid without water to condense it.  4th, The incoercible
 vapours of the suffocating sulphurous acid, named by him Vitri-
 olic Acid Air.   5th, The incoercible vapours of pure volatile al-
 kali,  which he calls Alkaline Air.  6thy The highly inflammable
 elastic fluid which we have long known  by the name of Inflam.
 mable Air.  7th,  The incoercible vapours which escape from a
 solution of metals in  nitrous acid, which he calls Nitrous Air.
 Sth, That surprising sort of air in which inflammable substances
 burn with extraordinary rapidity and brightness, and which sup-
 ports animal life  and flame four or five times  better than com-
 mon  air.  This he called Dephhgisticated Air.   In giving the
 name air to some of these elastic fluids, he followed the practice
 of others.  But he was the first  who applied this term to them
 all.   He has  not  been followed in this  practice  by many che-
 mists.   The  most general  practice has been, to denominate all
 permanently -elastic fluids,  except air, gas,.... a name first given
 by Van  Helmont to the vapour which is emitted by fluids in the
 vinous fermentation. *
   Dr. Priestley's writings contain  the description of various
 and  very curious  experiments, by applying water and  many
 other substances to these airs; by exposing in  them living ani-

  * This is probably a latinisation of gxscbt, a vulgar word for leaven, whence
 v/e have our word yeast; it is likely derived from gahren, to ferment  Van
 Helmont calls the vapour emitted by fermenting liquors, gas silvestre,  an epi-
 thet borrowed from Paracelsus, who calls it spiritus sihestris. Van Helmont
 considers this as of the same kind with that of the Grotto del Cane in Italy,
 because both kill breathing  animals and extinguish flame.  He mentions, how-
 ever,  several such vapours which he" considers as of a different nature,....£<M
 tientosum,....fiainvieum,....pingue,  Isfc.; and he says, that these gases do not
 exist in their elastic form in  the bodies from which they proceed,....nor in-
 deed exist at all in  them, but arise from new cx.ibinations of the ingredi-
 ents, which cannot exist in a solid or liquid form, but which require parti-
 cular circumstances  to change their former combinations, and enable the
 ingredients to form these  new ones.  His notions on this  subject are won-
derfully sagacious,  and even precise, considering the time in which he wrote,
 when vague and indistinct  conceptions seemed to be more generally accepta-
 ble.  (See his Complexionum atqus Mixtionum ckmenthriuin Figmentum.)
                                                   EDITOR
                  * 
         DISCOVERIES BY  DR. PRIESTLEY.     247

 mals and vegetables,  or animal and vegetable substances under
 the vinous, acetous,  or putrescent  fermentation; by  burning
 bodies, or by calcining or reducing metals in them ; or by mix-
 ing  the different airs together, and  treating the mixtures with
 great heats, or the electrical spark, See.  He notices many pro-
 perties of the air which we have been so minutely considering;
 but  I suspect that he  has not good authority  for some of his
 notions on this subject.  He has made many surprising disco-
 veries.  But his experiments are so  numerous,  and the  succes-
 sion  in which they were made and published  is such, that no
 general account can be given of them.   It will be better for you
 to read his own  accounts of them,  when you  are  farther ad-
 vanced in this course : for you must be acquainted with a great
 many more chemical substances and general facts, before you
 can peruse Dr. Priestley's writings so  as to understand them.
 I shall have occasion, in the rest of this course, to notice the
 greatest part of his leading experiments and discoveries.
   Soon after Dr. Priestley, or much about the  same time, the
 late Mr. Lavoisier in France,  a gentleman distinguished for his
 love of science, and particularly of chemistry, eminent also for
 a penetrating genius, sound judgment,  and logical  accuracy;
 and having an ample fortune, which enabled him to execute the
"most extensive and cosdy experiments,....this gentleman, I say,
 made and published experiments on this very  subject.   He
 began, by repeating with scrupulous exactness, and on a large
 scale, and with fine instruments, the experiments already made
 by others.  But he afterwards pushed on his investigations much
 farther,  and made some decisive experiments, which led him to
 great  discoveries,  and enabled  him to  explain many  general
 phenomena of nature, and to compose a new system or  theory
 exceedingly ingenious and ably supported by numerous and con-
 vincing experiments.   This theory has changed the whole face
 of chemistry.   I shall have an opportunity very soon to  take
 further notice of the outlines at least of this new chemical philo-
 sophy.
   While Dr. Priestley in England, and others elsewhere, were
 attending to these objects, Dr. Scheele of Sweden, whom I for-
 merly had occasion to mention,  engaged in an inquiry into the 
248       DISCOVERIES BY  SCHEELE, &c.

nature of fire and light and heat;  and, without any knowledge
of what was done and doing by others, carried on a most inge.
nious investigation,  in which he was led, by  the train  oi his
researches, to make  many of the experiments and discoveries al-
ready made by these gentlemen.   He added mam  of his own.
His work has been translated, but very badiy indeed, by J. Rhein.
hold Foster, and is entitled, " Scheele on Fire."
   Among the remarkable discoveries which these experiments
on gases have produced, perhaps the chief is that of Vital Air,
by Dr. Priestley.    It is this, in combination with Lavoisiei's
theory of combustion, that has totally changed our notions of
the chemical relations of most substances, and  made a revolu-
tion in all  the leading doctrines of chemistry.   I have  already
taken notice of its  remarkable property, when we were con-
sidering the decomposition of nitre, in order to obtain its acid.
We shall meet with  it again, almost  at every step ;  and its vari-
ous chemical relations will be discovered as we proceed.
   Scarcely inferior  to vital air in chemical importance is the
faul air of Dr. Scheele,  which I mentioned on the same occa-
sion, as that noxious portion of atmospherical air which remains
when the vital air has been absorbed by the hepar sulphuris.  I
must here observe,  that this portion of our atmosphere was
first observed in  1772 by  my colleague Dr.  Rutin rford, and
published by  him in his inaugural dissertation.   He had then
discovered that we were mistaken in supposing that all noxious
air was the fixed  air which I had discovered.   He says, that
after this  has been  removed by caustic  alkali or  lime, a very
large proportion of the air remains,  which extinguishes life and
flame in an instant.
   Soon  after this,  Dr.  Priestley met with this noxious air,
which was produced  in a  variety of experiments,  in which
bodies were burned,  or putrified, or thickened in certain cases,
or metals calcined,  or  minerals effloresced, Sec. &c.    In all
these cases,  he thought that he had reason to believe that phlo-
 giston had quitted  the  substances  under consideration,....had
 combined  with the air,....and had thus vitiated it.  Now satu-
rated with phlogiston, the air could take no more, and therefore
 extinguished flame.   He called all these processts'phhgisticat-
 ing processes,  and the air thus tamtcdphlogisticated air. 
    DISCOVER. BY CAVENDISH,....NITROGEN.  249

   In these processes the air was not only spoiled, but also di-
 minished  in bulk.  This  had been  observed long  before  by
 Boyle and Hales.   They ascribed this to a diminution of its
 elasticity.   Dr. Priestley ascribed it to the precipitation of fixed
 air.  Mr. Cavendish ascribed it to the combination of some Of
 its ingredients in such a manner as to form water.   His cele-
 brated experiment,  by which he demonstrated the composition
 of water,  will be mentioned particularly in another place.
   Dr. Scheele chanced to take a very different view of the whole
 of this subject,....led to his singular notion of it by some precon-
 ceived  and very strange theory of  fi*-e and heat.   But Scheele
 found that this diminution of bulk  was owing to  a real abstrac-
 tion of all  the vital air which the atmospheric  air contained.
 For when any of these phlogisticating processes of Dr. Priestley
 were performed in  vital air,  it was totally absorbed.   The re-
 mainder therefore, when the experiment was made in common
 air, was considered by him as a  primitive air,  unchanged in
 its properties.   He  called it faul air, which  may mean either
 rotten air, because it is produced in vast abundance by putrefy-
 ing bodies, or  simply foul air,  i. e.  tainted occasionally,  when
 the phlogiston  is more than will saturate the vital  air.  When he
 burned  phosphorus in atmospheric air, he found  the  remaining
 noxious air free from all admixture.
   Mr.  Berthollet obtained this faul air,  not  only from animal
 and vegetable  substances in the putrefactive fermentation,  but
 also in great abundance,  by pouring nitric acid on  the fresh mus-
 cular fibre.  Fourcroy found that it was contained almost pure
 in  the swimming bladders of carp, bream, and other fisnes.
 Other chemists have found it in volatile alkali, as will be parti-
 cularly noticed afterwards.
   In all these methods of procuring it, it  must be cleared from
 fixed air by means of lime or caustic ley.
   This air, having been procured in so many different ways, ap-
 peared in differeat lights to the discoverers,  as you have seen,
 and got different names,....phlogisticated,....foul,....mephitic,....
 choke-damp (in German)", &c.  Mr.  Chaptal, and other chemists
 of the first rank, gave it still another,  and perhaps more proper
name, calling it nitrogen.   This took its rise f^gm a celebrated
   , VOL. n.                 l l 
250  AZOTE,....AZOTIC  GAS OF  LAVOISIER.

discovery  of Mr. Cavendish, reco;  t *•  in the  Philosophical  ■
Transactions of 1783.  A train of experiments,  begun several
years before, ended in his combining seven parts  of oxygen and
three of this air,  by  means of repeated discharges of electricity.
The mixture was wholly absorbed by a solution of  potash, and
formed perfect nitre.   Therefore, he  concluded  that this pro-   j
portion of these  two airs composes that  remarkable substance,
nitrous acid.  Hence these gentlemen called this gas nitrogen,
with as much propriety as inflammable air was called hydrogen.
But Mr. Lavoisier, after having repeated the experiment of Ca-
 vendish  with complete success, and  after being  convinced, by
 the comparison of numberless facts,  and particularly, after re-
fleeting on all the processes for producing saltpetre, all of which
 employ animal and vegetable substances in a state  of putrescence,
 in the free air,....after this full conviction that this was really the
 composition of nitrous acid, rejected the appellation of nitrogen,
 and  called it Azotic Q.as, from its  deleterious  quality.  This
 denomination has taken place of all others ;  and I shall abide by
 it in the rest of the course,  although I think that a better name
 might have been found  than this,  which  really is no distinc-
 tion,  because all the  gases are azotic, that is, deadly to breath-
 ing animals, except those which contain  a very great proportion  '
 of oxygen  gas,  or vital air.   (See Note 37. at  the  end  of the  1
 Volume.)
    In the meantime,  this discovery by Mr. Cavendish is one of
 the most important in the whole  science of chemistry.  I mean, j
 the discovery that  Azote is the  radical  or characteristic ingre-1
 dient of the nitrous acid.   I have given you only that simple ;
 fact, by which the truth of this doctrine  was established by that
 gentleman.  Numberless proofs, both by composition and de-
 composition, will come before us, as we proceed in the exami-
 nation of other bodies.  I only remark at present,  that the pro-
 portion of ingredients, in the experiment of Mr. Cavendish, cor-
. responds to the most fuming state of the acid that can be prepa-
 red.  It is even redundant in azote, which the nature of the ex-
  periment did not permit Mr. Cavendish to observe.  The acids
  are susceptible of different proportions  of Oxygen, as we shall
  afterwards see^ckarly;  and, in  these different  states, they arc's
■I 
            PROPERTIES OF AZOTIC GAS.         25i

permanent, and have very distinct properties and modes of ac-
tion.   None of them is so remarkable in this respect as the nitric
acid.  And the knowledge of its distinctions will lead  us through
the most  intricate paths of the investigation yet before us,....so
that it is with great justice  that  I have said that this discovery
by Mr. Cavendish is one of the most important in the science.
  In nitric acid,  which is  its most perfect state as an acid, the
proportion of oxygen to azote is  nearly that of 80 to 20. Nitrous
acid,  or spiritus nitri fumans Glauberi, has that of 75 to 25.
Nitrous .gas, which escapes  from nitrous acid when inflammable
substances are mixed with it, has the proportion 68 to 32 nearly.
But this  is scarcely,  if at  all acid.   You  will learn all this by
degrees, when you previously know the nature of the substances
mixed with the perfect acid.
  With respect to the other properties of azote,  I  cannot say
much at present, because you know as yet  but few of the sub-
stances to which those properties relate.
  It is rarer than common air, about ^di*   The specific gravi-
ties of atmospheric air, oxygenous gas, and  azotic  gas, are
1,0000,  1,0625, and 0,9444 *.
  Azotic gas does not mix with water.
  It has no acidity.  It does not affect the ordinary test colours,
nor contract any union with alkaline substances: therefore it
does not precipitate lime from lime-water.
  Although it combines with oxygen, by means of the electric
spark, and composes nitrous  acid,  and although there is always
this mixture in the ajr, we do not find nitrous acid  there.  These
gases are susceptible of simple commixtion, as water  mixes with
spirits, or one metal with another, yet they retain their proper-
lies unchanged, like the mixtures now mentioned.   It is not
simp]|r a high temperature that will cause them  to combine :

    • A thousand cubic inches, or a box, wjiose length, breadth, and  depth
is 10 inches, contains, in the ordinary  pressure of the atmosphere, and tem-
peraWe 55o of Fahrenheit, very nearly the following quantities:
    Common air   -    -   315 grains Troy.    One inch ss  0,315
    jOxygenous gas    •     335    -    -       -        0,335
    Azotic gas            297               -   -    0,297
                                                 EDITOR. 
252        ANALYTICAL EXPERIMENTS

for they do not combine when forced through a red hot tube of
glass.   (See Note 38.  at the end of the Volume.)
   I have been led into this long digression by the experiments
adduced in support of the third proposition of my theory of lime.
These  gave  me an opportunity of explaining to you, by means
of the  acquaintance which  you have already acquired with se.
veral chemical substances, the properties of the three remarks.
ble gases,....fixed air,  vital air,  and  foul air; or, as  I shall now
call them, carbonic  acid  gas, oxygenous gas, and  azotic gas.
The knowledge of their leading properties will greatly expedite
our progress tnrough the rest of this course.  I now return to
the theory of quicklime.
  The experiments made to try the fourth and fifth propositions
were found to agree equally well with the theory. Several of them
concurred, in the first place,  to shew that the caustic alkalis do
not contain any lime or limy  matter combined with them. I sa-
tisfied myself of this by three  trials: li?,  Evaporation to dry-
ness,  and examination of the dry caustic alkali.  2d, Saturation
with sulphuric acid.   This,  if there be any lime, should pro-  •
duce a selenite almost insoluble in water.  I found none.  I ob-  ^
serve some experiments of others in which a precipitate was ob-
served ;  but, by the very account given, it  appears to have been  <*
vitriolated tartar,  which  a large quantity of hot  water would
have  dissolved.   3d, Exposition to  the Atmosphere, to learn ^
whetht.r crusts of calcareous earth wouloVbe formed on its sur-
face,  like those on lime-water.  But no1  such  thing appeared.
Aii these trials verified  the fourth  propositiop, shewing that
caustic alkalis contain no lime.
  And in my experiments relative  to the  fifth proposition, I
succeeded perfectly in changing the calcareous  earth into lime,
without exposing it to the action of heat.  The precipitate from  \
a muriate of lime by a truly caustic alkali proved a perfect quick-
lime dissolving completely in water, and making lime-water.
  It now it  appears that by whatever way we contrive to sepa-
rate jhe carbonic acid from calcareous earth,  even without mak". 
         FOR A THEORY OF  CHJICKLIMS.      253

kig use of fire, the earth is thereby rendered active, and appears
in the state  of  acrid and soluble  lime.   We have, therefore,
abundance of reason to conclude, that the state of solubility and
activity of this earth depend on its  being simply  reduced to a
state of purity,  or freed from the carbonic acid with which it is
combined in its natural state.   The same conclusion  must also
be admitted with respect to the volatile alkali, when we consi-
der the  processes by which it is made to appear in its caustic
or most active  form.  The particular nature of this alkali en-
ables us to deprive it of its carbonic  acid, or make it free of it,
by a greater variety of methods than  can be followed with either
of  the fixed alkalis, or with quicklime.  And,  whatever  way
we take to free it from this acid, we are sure to find it caustic,
or  in its  liquid,  or  its highly acrid and volatile form.   The
common way of obtaining it is by decomposing sal ammoniac
by quicklime.  In the ammoniacal salt it has no carbonic acidv
It is plain that  it must also be obtained  in  the  same state, for
the same reason,  if the sal ammoniac be decomposed  by the ac-
tion of a caustic fixed alkali.  Accordingly, in this way also
are we sure to  have the  volatile alkali in a  caustic state.   But
what may appear the most satisfactory, is a way discovered by
Mr. Margraaf  for obtaining a volatile  alkali from an ammonia-
cal salt by heat alone,....namely, from the essential salt of urine,
or  microcosmic  salt.  Thissalt is an ammoniacal salt, at least
in part,  or contains the volatile alkali,  which may be  sepa-
rated,  asTrom  other ammoniacal salts, by either fixed alkali or
by quicklime.  And, in these cases, we obtain  the volatile al-
kali in the same  state  as we would  obtain it by the same pro-
cesses from other ammoniacal salts.  But Mr.'Margraaf disco-
vered that the sal microcosmi will yield its volatile alkali by the
action of heat alone, because the acid is of the most fixed kind.
He puc some of this salt into a retort, and fitted to it a receiver
having a small  perforation.  First of all  escaped  some incon-
densable matters  with which we are' now pretty well acquainted.
These  were followed by the  volatile  alkali in  a most pun-
gent state.   Some of it condensed with water in the receiv-
er : and  he was surprised  to find that it  did not  effervesce
with acids.
 4
f 
  254     ANALYTICAL EXPERIMENTS

    There is, therefore, no doubt, that if we could separate,
  the fixed alkali from an acid by an operation as simple, we
  should have it also in a caustic form.   But I am not acquain-
 ted with anv instance of such separation in chemistry.  There
 are twp which might at first sight appear of this kind.  The
 first is the separation  of the  fixed alkali from nitric acid by
 deflagration with charcoal;  and the second, its separation
 from the vegetable acid merely by heat.  But in neither of
 these  cases is the  alkali  obtained free  from carbonic acid.
 On the contrary, it contains a good quantity of it, and is
 disposed to effervesce  strongly with acids.   And the reason
 is, that  in the first  case the nitric acid and the charcoal, in
 acting  upon one another,  produce a great quantity of car-
 bonic  acid, of which  a part, it seems, is  attracted by the
 alkali.   It  is easy  to understand how this  carbonic acid is
 produced.   It is produced from the charcoal,  and the vital
 air which the nitre affords in very great quantity when expo-
 sed to the action of  red heat.   And in the second case, the
 acetous  acid is not simply separated.   It is destroyed by
 the  fire, and converted into water, oil, charcoal, and a  large
 quantity of carbonic acid, which, together with the charcoal,
 is found  adhering to the fixed alkali*.
   In every case, therefore,  in  which we contrive  to  have
 lime or the alkaline salts in a pure state or free from carbo-
 nic acid, we find them in their state of greatest activity, ort
 causticity, as it was formerly termed.   And if we examine
 the c i verse of these experiments, and consider the different
 ways ?y  which quicklime or the caustic alkalis may be ren-
 dered mild, we shall find  that their return  to  a mild  state
 is al1  ys attended with the recovery of their carbonic  acid,
 and is evidently a consequence of it.                     «*.
   One example of  this is the restoration of the caustic vola-
 tile alkali to its milder state, by an experiment which I made
 in the  year 1757 or 1758, and  communicated, with  some
 others, to my  friend Dr.  Hutcheson,  of Trinity College,
 Dublin, and which has  been published by Dr.  Macbride in
his Essays, page  50.  A small quantity of caustic alkali is
put into  a phial.   In another phial an  effervescing mixture

      * Nitre deflagrated with zinc gives caustic alkali....editor: 
ESTABLISHING A THEORY OF  QUICKLIME. 255

is put: and  the fixed air expelled  from it is  made to pass
through a siphon tube fixed  into its mouth, and having the
other leg  inserted  mto the caustic alkali.  By this simple,
apparatus, the fixed air is made to  rise through the alkali,
which rapidly absorbs part of it, and soon acquires so much
as to effervesce  briskly with acids.   If a bladder, fitted up
like a common medical injection bladder, with a pipe and a
cork, be distended with fixed air, and the pipe (having put in
the cork) be now inserted into the phial containing the caus-
tic alkali, and if the pipe fit the mouth of this phial so as not
to allow air to get  past it, then, on pulling out the cork, the
compressed  fixed  air will be  forced  in  among the alkali,
and will be  gradually absorbed by it, and we  shall see the
bladder collapse by degrees, till perhaps all  be absorbed.
The alkali will  now effervesce with acids.   The pure  fixed
alkalis are also easily restored to a mild effervescent state by
the same  process.   They absorb the carbonic acid gas  very
quickly, even more quickly than milk of lime ; not because
they have a stronger attraction for it than lime has, (for the
contrary  is the  fact)  but because we can employ a much
stronger solution of these alkalis than  the solution we  have
of lime in lime-water.
 •  It is scarcely necessary to remark that the  caustic fixed
alkalis become mild also by  communication with the atmos-
phere  for a sufficient length of time ;  and that when  they
become mild in this way,  it is by attracting carbonic acid.
This happens  more quickly than ordinary, when  solutions
of them are  boiled over an open fire :  the reason of which
you will easily perceive to be the quantity of  carbonic acid
which is  incessantly forming  by the  consumption of  the
fuel.
   They are rendered mild also by adding to them a proper
quantity of magnesia, that has not been calcined, (now named
carbonat  of  magnesia) or a proper quantity   of  common
mild  volatile alkali (the carbonat of ammonia) ; the fixed
alkalis having a stronger attraction for the carbonic acid than
eitjler of  these two alkaline  substances; of which I assured
mySelf by direct and conclusive experiments.
   From the knowledge we now have of the effervescence of
alkaline salts with  acids,  it is easy to  explain  the  very 
 256      THEORETICAL EXPLANATION

 remarkable  manner  in  which  the  vegetable alkali,  in  its
 ordinary state,  effervesces  with some of the weaker  acids,
 of which you saw an example, when the acetite of potash
 was described, and the process for-preparing it.
   The same  phenomenon occurred to me also when I tried
 to make a borat of potash by saturating the  common alkalis
 with sedative salt.
   Borax has  sometimes been referred to the class of alkalis,
 on account of some resemblance its bears to  those salts. But
 it has  been demonstrated  by accurate experiments,  that we
 should rather consider it as a  neutral salt%  that it is com-
 posed  of an alkali, and of a particular saline substance,  called
 the sedative  salt,  which adheres to  the  alkali in th<  same
 manner as an acid, but  can be separated by the  addition of
 any acid whatever, the added acid joining itself to the alkali
 in place of the sedative  salt.   As this conjunction of an acid
 with the  alkali of borax happens  without  the  least  effer-,
 vescence, our principles  lay us under a necessity of allowing
 that alkali  to  be perfectly free of  air, which must proceed
 from its being incapable of  union with  fixed air, and with
 the sedative salt, at the  same time :  whence it follows, that
 were we to mix the  sedative  salt with an alkali saturated
 with air, the air would immediately be expelled,  or  the two
 salts,  in joining, would produce an  effervescence.   This I
 found  to be really the case, upon making the trial, by mixing
 a small quantity of the  sedative salt with an equal quantity
 of each of the three  alkalis, rubbing  the mixtures well in a
 mortar, and adding a little water.   It is, however, proper  in
 this place to observe,  that if the  experiments be made in a
 different manner, they are attended with a singular circum-
 stance.  If a small quantity of the  sedative salt be  thrown jj
 into a large proportion of a dissolved fixed alkali, the sedative if
 salt gradually disappears, and is united to the alkali  without
 any effervescence.  But, if the  addition be repeated several ■
 times,  jt will at last be  accompanied with a brisk efferves-
 cence,  which  will become more and'more remarkable,  until
the alkali be entirely saturated with the sedative salt.
   This phtnomenon may be explained by considering", the
 fixed alkalis as not perfectly saturated  with air : and the sup-
 position will appear very reasonable, when we recollect that 
           OF SINGULAR  PHENOMENA.        257

those salts are never produced without a considerable degree
of heat,  which may easily be imagined  to dissipate a small
portion of so volatile a body as air.  Now, if a small quan-
tity  of the sedative salt be thrown into  an alkaline liquor,
as it is very slowly dissolved by water, its particles  are very
gradually mixed with the atoms of the alkali.  They are most
strongly attracted by such of those atoms as are destitute of
air, and therefore join with them without producing an effer-
vescence ; or, if they expel a small quantity of air from some
of the salt, this air is at the same  time absorbed by such of
the contiguous particles of it as are destitute of it; and no
"effervescence  appears,  until that part  of the alkali which
was in a caustic form, or destitute of air, be nearly saturated
with the  sedative salt.  But if,  on the other hand, a large
proportion  of the sedative salt  be perfectly and  suddenly
mixed with the alkali, the whole, or a large part of the air,
is as suddenly expelled.
   In the  same manner, we may also explain a similar phe-
nomenon,  which often presents itself in saturating an alkali
with the different acids.   The effervescenceis less consider-
able in the first additions  of acid, and becomes more violent
as the  mixture approaches the  point of saturation.  This
appears  most evidently in making the sal  diureticus, or
regenerated tartar. The particles of the vegetable acid here
employed, being always diffused through a large quantity of
water, are more gradually applied to those of the alkali ; and,
during the first additions, are  chiefly united to those that are
freest of air.
   But still this explication rested on a supposition, and there
was no necessity for letting it rest there.  It was easy to
try1 whether this supposition  was  agreeable  to truth by an
experiment.
   I exposed a small  quantity of a pure vegetable fixed alkali
to the  air, in a broad  and shallow vessel, for the space of two
months ;  after which I found  a number of  solid  crystals,
which  resembled a neutral  salt so much, as  to retain their
form pretty well in the air, and to produce  a considerable
degree of cold when  dissolved in water.   Their taste  was
much milder  than that of ordinary salt of  tartar:  and yet
they seemed to* be composed  only of  the alkali, and of  a
      vol. n.            k k 
258  ALKALIS SELDOM  PERFECT  CARBONATS.

larger quantity of air than is  usually contained in that  salt, and
which had been attracted from the atmosphere: for  they still
joined very readily with  any acid, but with  a more violent ef.
fervescence than  ordinary :  and they could not be mixed with
the smallest portion of vinegar, or of the sedative s? t, without
emitting a sensible quantity of air.
   Thus, therefore, I learned that the fixed alkali, in the ordinary
state of it, is never completely saturated with carbonic acid, or
combined with the largest  quantity of it which it is capable of
receiving.  And  further experiments on this and the other al-
kalis shewed that they contained more or less of it according to
the process by which they have been prepared, or the treatment
they have undergone in preparing them ; but that they may be   i
all completely saturated by different mediods, especially by ex.   4
posing them to the gas of fermenting liquors, or to the gas ex-
pelled from chalk by the sulphuric acid.  As they  are usually
prepared, I believe the mildest or most nearly saturated with
fixed air, is that called black flux, which is tartar no farther burnt
than to destroy the acid, and  intimately  mixed with charry mat-
ter,  from which  it may be obtained pure by  lixiviation. The   j
chemists of last century, or  rather the pharmacists, mention a   1
general class of alkaline salts  by the name of salts of Tachenius,  J
which were remarkably mild (in a medical sense).   By the ac-  1
count given of their  preparation, they  must have been mild in   1
the sense which  I have  affixed to the term.   They were pre- *j[
pared from vegetables  by a smothering heat, which did little   \
more than char the  plant,  and must therefore have retained a  /
great portion of carbonic acid. Pearl-ashes comes next to blacktdj
flux in saturation with carbonic acid.  White  flux comes next W
to pearl-ashes, and should be followed by potash, which is of|» r
pretty acrid by long continuance in the melting heat.  Of the  ■■}
volatile alkalis, the mildest is surely the volatile ammoniac pre-
pared with chalk.  Next to  this  is salt of  hartshorn, tainted
with much burnt oil ;....spiritus cornu cervi  is more acrid,...«so  .
 is spiritus salis ammoniaci, as prepared with fixed alkali. ." *~     "
   The result of all this investigation is, that the  alkaline" sub-
 stances,  in their mild state,  are to be considered as compound  t;
salts, consisting of the pure alkaline substances united to the carVj
bonic acid.*-                                 • 
       AFFINITIES OF  CARBONIC ACID.        259

   As this is to be considered as a new acid, and must be added
to our list of  simple  salts, we have a new column to be added
to the six already placed in your table of compound salts.  We
must, therefore, see what is  to be the arrangement of this  co-
lumn, having carbonic acid or fixed air at the head.
   1st, then, It is evident from the whole tenor of the investi-
gation,  that  pure quicklime  must be placed first in the  co-
lumn of  alkaline substances.   The process for caus#c fixed al-
kali, and the precipitation of lime from lime-water by a mild al-
kali in a  mild state,  prove  it  in  respect of the fossil alkalis.
That the attraction of lime for carbonic acid is greater than that
of the volatile alkali,  is also evident by the process for caustic
volatile alkali without heat, and  by the  precipitation  of lime
from lime-water in a mild state by mild volatile alkali.    *
   Lime must also come before the pure earth of magnesia:  be-
cause crude magnesia precipitates lime in a mild state from lime-
water.
   2d,  The  fixed alkalis come next in  order:  for they will
rentier  a solution of volatile alkali caustic.   Moreover,  a
caustic ley becomes mild, or will effervesce with  acids, if we
put into  it crude magnesia,  and digest the mixture for a little
 while.
   3dly, Magnesia comes before the volatile alkali: for caustic
volatile alkali  makes  no change on crude magnesia ;....but  cal-
cined magnesia will effervesce  with acids after being  digested
with mild volatile alkali.
   The column must therefore stand thus :

                      Carbonic  Acid.
. '£■«                  Quicklime.
                      Fixed alkali.
                      Magnesia.
                     Volatile alkali.

   If remains  to determine  the  proportion of the attractions
of quicklime, and magnesia, and the alkalis for the other acids.
   1st, Fixed alkali has a stronger attraction for the other acids
\nan. quicklime has.   This  appears from  the  process by which 
 260  AFFINITIES  OF ALKALINE SUBSTANCES.

 we make quicklime, by precipitating it from a solution in any
 acid by  means of a caustic  fixed alkali.  We have  also seen,
 that fixed alkali, in its pure or caustic state, precipitates mag-
 nesia from the acids in a non-effervescent state ;....and we know
 that it disengages the  volatile alkali without heat.
   2dly, Quicklime must have the next place :  for we  have seen
 that the precipitate by  means of lime from a solution of magnesia
 was not a quicklime, but a pure  non-effervescing  magnesia.
 Also we found that quicklime, whether ground with sal ammo.
 niac in a dry powdeiy state, or put into a solution of it in water,
 instantly detached the volatile alkali.  It is true  that a mild vo-
 latile alkali will precipitate calcareous earth from an acid.  But
 the precipitate is a carbonat of lime: and the  change has been
 effected by a double elective attraction, proving that the partiality
 of the volatile alkali for any other acid is greater than  that of
 the quicklime.  The precipitation of calcareous  earth, in a mild
 state, by carbonat of magnesia,  is explained in the same way.
 The precipitate is a carbonat.
  I cannot decide,  by any experiment that has occurred to me,
 whether magnesia or volatile alkali has the strongest attraction.
 I am therefore obliged to class these two substances in the same
line of the column.  And it stands thus:                        ;

                           Acids.
                        Fixed Alkali.
                        Quicklime.
                 Magnesia....Volatile Alkali.

  This undetermined situation of magnesia and  the volatile ah/   4
kalis relates only  to their mixture and action on  each other iff.!1 '1
the ordinary low temperatures.   For it is plain that if we em?.   :
ploy great heats,  the volatility of the ammonia  disposes  it to
qi': t the more fixed base to which it is joined.  Magnesia, treated   \
along with this compound, tends, by  its attraction for  the acid,   ,'
to repress  the volatility of the acid.  This will  evidendyfttitl
further  promote the separation of the volatile alkali:  and 'thus
magnesia will certainly  decompose the ammoniacal salts with  r 
    BEST METHOD  FOR VALUING MARLES. 261

the assistance of heat, and disengage the alkali, either caustic or
mild.
   I  cannot better conclude this inquiry, than by mentioning
some important consequences which have  resulted from the
discovery of the carbonic acid.  Besides the improvements in
chemical science to which it has led us, it has also given rise to
some useful inventions, and has enabled us to decide questions
which occur in some of the most interesting of the arts.  We
know now, that the alkalis are compound salts, of immense de-
mand in the arts of bleaching, dyeing, soap-boiling, glass-mak-
ing, &c.  In their ordinary state, we have learned that they con-
tain a  very considerable proportion of a substance which is of
no value in those arts, that we  know of as yet, and which there-
fore diminishes the value of the commodity.  The artists who
employ them can now ascertain with a certain precision, in what
degree any parcel  offered to them is of use, and can choose or
reject, or correct them as they see occasion.
   Thus, in agriculture, a question is now decided  which has
been often put  to me,....whether fresh or acrid lime is better or
worse than such as has been long exposed to the air,   The ef-
fect of  marles  and of limestone gravel, which are known to be
the  most excellent of  natural manures,  decides this question.
The only useful purposes of burning limestone seems to be the
reduction of its weight, and the easy method of reducing it to
powder, and thus fitting it for being uniformly spread on the
ground.
   The value of marles is also  easily  ascertained by these doc-
trines.   Maries are valuable only in proportion to the calcareous
matter  they contain.   ScHne do not hold ^,th of their  weight;
3hd it is a very rich marle that holds Ith.  Suppose a marle to
(Jontain -fVth, a farmer will consult his interest if he pay ten times
the  price for a cart of lime that he must pay for marle at the
same distance ; for he*will bring home the same quantity of the
useful material with yVh of the labour and carriage.
   Now of all the modes of trial of  the quantity of calcareous
matter in marle, the one  best suited to the unlearned farmer is,
to observe how much fixed air it contains.   And this  he will
learn certainly, within  ^th of  the truth, by dissolving a little of 
262        CALCAREOUS  COMPOUNDS.

the marle in an acid, the muriatic, for example, and observ-
ing what portion of its weight it loses.   Thus,  if any lit-
tie quantity, suppose half an ounce, loses 40 grains he may
conclude that it contained 100 grains of crude  calcareous
earth, or 60 grains of lime.   Or he may reckon 2\  grains of
lime-stone,  or l\ grains of lime, for every grain that his
marle loses by this operation.   But  he must  take care to
make the trial in a  deep glass,  that sparks of water may not
be lost, and computed for limestone.   For the same reason,
the acid must be weak, that the effervescence  may be very
gentle.   Vinegar, however is too weak, and will not detach
all the air.   It becomes clammy also in the operation, which
makes the  froth remain on  the surface for days:  and this
entangles much  air that has been really disengaged.   Let
the acid be such muriatic acid as is sold in the shops.  Dilute
it with twice or thrice  as much water, and keep it for use.
Weigh  the marle  exactly, and  also  the  quantity of acid
which is to be poured on it, taking care that  it  be more than
enough for dissolving all the calcareous matter.  When the
solution  is over, after repeated agitation without more effer-
vescence, weigh the whole.   The weight lost is  two-fifths
of the weight of the calcareous  matter.
   Should  we attempt to measure this  by solution  and pre-
cipitation, we are led into a number of examinations which
will puzzle even an experienced chemist.
   And having now finished the chemical history of the cal-
careous earth and mgnesia, I must take notice  of some com*
pounds produced by nature, in which the calcareous earth
is  combined with acids, and which are  worthy of your at-
tention.

           Calcareous earths combined with acids.         :*  $
                                                     *  r* •
   These compounds are, 1st, Gypsum^ or the sulphat of
lime.  2dly, Fluor, or the fluat of lime, which is formed by
a very peculiar acid not yet described.  3pi/, Phosphatof
lime, which contains another peculiar acid not yet described/1
Athly, Borat of  lime, but lately discovered, which contains
the sedative salt; or boracic acid, combined with  lime and
with magnesia. 
GYPSUM.
263
                          1.... Gypsum.

      Gypsum, the most abundant  of these calcareous' com-
    pounds, was formerly considered  as  a peculiar species of
    earth.   But now we are better acquainted with its nature ;
    and are well assured that it is a compound of the calcareous
    earth with the sulphuric acid;  or is, in the new language, a
    Sulphat  op Lime.
      This compound is found in nature under several forms, or
    in several  states.   The greatest part is found  in the form of
    stony masses, which, however, are remarkably soft, so as to
    be easily scraped with a knife, or even with the nail.   They
    are distinguished from  alkaline  earths and  stones  by not
    effervescing with acids, and from all other stony bodies, by
    making sulphat of potash with the mild vegetable fixed alkali,
    if boiled in water with this salt, or melted with it. When this
    vitriolated tartar is separated  by repeated washing with hot
    water, the remaining powder is found to be a mild calcareous
    earth.  The same materials also, with the addition of char-
    coal dust, form, by  fusion, a hepar sulphuris, or sulphurat of
    potash.   Thus, the  ingredients of  gypsum are made suffici-
    ently evident. (See Note 38.  at the end of the Volume.)
       Gypsum is found  in some places in great abundance.   In
    the neighbourhood of Paris there are hills chiefly composed
    of it.   In most places where it occurs,' it is intermixed with
    a marly clay, forming separate masses  interspersed through
    the  stratum :  and  it  is  also sometimes found in veins.
tt>t ^nen Pure» i* is  white and semi-transparent in the larger
   ^masses, and perfectly transparent in its small particles.  The
    structure  or aggregation of these masses has some variety.
    X)ften small crystalline  grains are compacted together  like
    ^Sugar.  This is called gypsum, and sometimes alabaster.  A
    second  kind 'is the flbraria,  or  fibrous gypsum, having a
    somewhat fibrous structure,  or being composed of  oblong
    crystallized congestions, plosely compacted together, which
    are  mostly parallel  among themselves,, but  lie across  the
    mass, from the upper to the under surface.  This  sort  has
    varieties accordjngto the size *and regularity of the concretions
    of which it is composed. In some  kinds, the concretions are 
264                    GYPSUM.
larger,  and more irregular in'disposition ;  in others, more
slender and regular.   A third species is that which is com-
posed of clear transparent plates, like the finest glass, lying
parallel to  one  another,  and in close  cohesion through their
whole extent, but easily  separable by  splitting them asunder
with a knife.   These plates are excessively thin, or can be
subdivided, by splitting into very  thin  ones, and have an
apparent flexibility, but no elasticity.   This species is called
Glacies Mar ice, and sometimes, but improperly, Muscovy glass,
or Muscovy talc.   A fourth appearance of this substance is
in the state aof separate crystals, in the forms of which there
is some variety.   They are found,  I believe, in those strata
of clay which contain gypsum in some  of the  other states
already described ; and these separate  crystals were especially
named selenites, by naturalists.   Fifthly and lastly, it is very
often met  with in waters, in a dissolved state ; for it is evi-
dently capable  of dissolution  in water, though only in very
small quantity, like  the artificial gypsum, requiring not less
than 500 times its weight of hot  water to dissolve it.  But
it can be dissolved more plentifully, if it be acidulated with
some superfluous sulphuric acid.   It  occurs dissolved in the
waters of  many  springs and wells,  and is  the  most general
taint of what are called  hard waters ;  but most copiously in
sea water.   When water containing gypsum is slowly evapo-
rated, the gypsum separates, or is deposited in a white sedi-
ment, which, by  the microscope, is seen to consist of minute
crystals, like hairs.
   The  composition  of gypsum was  first clearly  explained by
Margraaf,  in the  Berlin Transactions.   He first shewed it to
be a compound of calcareous earth with vitriolic acid.  Andfi
by thus knowing that  it is a saline  compound,  we can moreji
easily understand some of its properties.                 1/
   When gypsum is  exposed to a moderate heat,  it loses nF-
transparency and glittering appearance, and bejSomes a wniti
opaque  mass like chalk,  in which the  former appftarance^of^.V,
its  structure is  destroyed.  It also  becomes vefy f^a4>le,"v
rather more so than  chalk, whatever may have been its forr
mer firmness.    During this  change, we hear*a continual
crackling.   This must be considered as a sort of decrepita-\
tion.   If powdered first, and  then  heated, it swells;  seems ^ '$ 
GYPSUM.
265
as if set afloat; and is agitated like a boiling fluid.  This is oc-
casioned by the water being extricated from its crystals, which
are thus destroyed.   But after some time, it subsides into a
dry powder.   In close vessels it emits water, and some kinds
of it a little sulphurous acid.  After being heated in this man-
ner, until the bottom of the Vessel begins to grow red, if it be
then cooled,  it is disposed to  concrete with water in a very re-
markable  manner.   When  mixed hastily with  water, to the
consistence of very thick cream, it remains in that state with-
out any perceptible subsidence.   After a little while  it grows
sensibly warm ; and, in a minute or two after, it is solid, and
a little enlarged in bulk.   This concretion seems to be a hasty
and confused crystallization,  or return of the gypsum to a cry-
stallized state, or state of combination with water, which is the
natural state of it.   In this state it is extremely porous and light,
when thoroughly dried; because the water employed in diluting it
is of more bulk than the gypsum.  It is used for casting figures
and impressions of every kind, and it gives them with wonderful
sharpness.  If one of these casts, of a medal, for example, be
laid on the surface of melted white wax with the impression up-
permost, it fills itself completely with the wax, and has the appear-
ance of a piece of fine sculpture in marble, or of a porcelain  cast.
   If  gypsum be exposed to  a very violent heat,  it  is at last
brought into  fusion, without the separation of any considerable
part  of the  acid,  provided,  however,  it  be heated  without
touching the fuel.   If it be allowed to come into contact  with
the fuel, a very different effect is produced.   The inflammable
matter of the fuel acts on the acid, and volatilizes the greater
figrt  of it, in suffocating vapours of sulphurous acid and va-
tk>urs of hepar  sulphuris.   Another  part remains  adherent  to
thjfearth, in  the form of imperfect sulphur, or sulphurous acid,
ancl fajrms withjt a  particular species of phosphorus, of which
hereafter.  The 'other qualities of gypsum will be easily per-
ceivedTrom  the nature of its two constituent parts.  And it
is 'heedless to takemotice  of the  action of alkalis and acids
      1
upon it.
   The uses to which it  is applied, are,  the casting of figures
   vol. n.                          l 1 
266
GYPSUM.
 in what is called plaster, or plaster of Paris, and for making
 the moulds in which they are cast; also for ornaments in stucco.
 And at Paris  it is much used in the building  of houses.  In
 Minorca,  they have a coarse and strong kind in plenty, which
 is employed in building.  They form  arches and floors of it,
 without needing timber to support their work.  It also has great
 effect as a fertilizer of land.   Its effect is greatest upon the le-
 gumina and  leguminous grains.  Grain, however,  is  not so
 much improved by it as by lime. Its effects last two years, and
 are greatest upon strong and rich land.  One of the  best ways
 of using it is to scatter  it upon  wheat-stubble, to promote the
 growth of  clover sown in the  spring, and harrowed  in  among
 the wheat.  The gypsum must be thrown on the stubbles in au-
 tumn,  or the  following  spring.  If done  sooner, it  would fill
 the wheat with weeds.  The quantity need not  exceed that of
 the grain sown. It is used in  Switzerland, even at a very great
 expence, both in a raw and  calcined state ; chiefly on the grass
 lands,  as a top dressing.  I do not find, however, that the tri-
 als  made  of  it in this  country  have been successful.   Yet it
 seems unwarrantable to  doubt  the numerous and circumstantial   j
 accounts given by the Economical Society of Berne, composed  «
 of perhaps the most intelligent practical farmers in Europe.


               2.—Fluor,  or Fluat of Lime.


  Since the compounded nature of gypsum was discovered by ^9
 Mr. Margraaf, another  kind of  stony  matter, which was  for-jijB
merly known by the name of fluor, and fluor mineralis, andccffljnH
sidered as a particular species of earth, has been  found to be an'- ™
other compound of the calcareous earth with an acid.  We ovije
this discovery to Dr. Scheele of Sweden, whom I have^bften   ?
had occasion to mention with praise : and in consequence of the
light he has thrown upon the compound I speak  of* it deserves
now to be considered as  one of'the most remarkable oDjeqts of
philosophical chemistry.
  The stone or stony substance I speak of, is called by. the Ger-  * 
FLUOR.
267
  mans flus, or flus spat; in the books of natural history, fluor
  and fluor spathosus.   It had these names from its effect in pro-
  moting the melting of ores and minerals  in metallurgical opera-
  tions.
    Its appearance and more obvious qualities are these: It is a
  stony substance,  which, so far as I know, never composes stra-
  ta, but is  always found either in veins, or in small masses.  It
  has a close glassy texture, and receives a fine polish, and gene-
  rally is transparent, though often tinged  of  a green  colour, or
  purple, or yellow, or deep blue.   There is much of it in  Der-
  byshire ; and on  account of these colours, it is called in Eng-
  land,  blue John ; and  formerly in apothecaries  shops, false
  emerald, false amethyst, &c.
    It is often found crystallized in the cavities of veins: and
  the most regular form of its crystals is cubical.
    In point of hardness, it holds a middle place between the cal-
  careous stones and the stones of the hard class ; being too hard
  to be easily affected by the edge of a knife,  but not too hard to
  be cut or scraped with hard steel, and capable of being wrought
  by the turner with proper instruments, and formed  into very"
  thin and delicate  vessels.
    It has a quality which is found also sometimes in the crystals
  of calcareous spar; but this stone has it more generally: I mean
  a power to emit  light,  or a subtile luminous  volatile matter,
  when the stone is heated.   After it is once  red hot,  it shines
  no more.  I said " emits a luminous  matter,"—for  the phos-
.  phorescence of fluor  is accompanied by a pretty strong unplea-
 x saint  smell.   And there is a kind of it mentioned by  Mr.
 * Wedge wood, junior,  in his observations on phosphorescent bo-
  dies, which is  fcetid when rubbed,  and this kind is much more
  Heinous than the others.  The light is first green, then verges
  to a  pfcrple or hlac.   (Phil. Trans. 1791.)
   When we-apply a violent heat to this substance,  it melts most
  perfectly ; a»d is very powerful in promoting the fusion of other
  earthy-substances,—especially if calcareous spar and it be mix-
  ed together ; then flowing almost as thin as water.  Whence it
  is much valued for the smelting* of ores.  If we melt  any con- 
268                 FLUORIC ACID.
siderable quantity of it in a crucible by itself, or  without ad-
ding any thing to it, such is its power to dissolve other earthy
substances in the fire, or to promote their fusion, that it will
melt the bottom of the crucible and run out.
  The most surprising part of this substance is the acid which
it contains, and which can be  expelled from it by  the sulphuric
acid.   To effect this separation of  the acid,  the  fluor must be
reduced to a very fine powder, and an equal,  double,  or  even
triple,  weight of the strongest sulphui ic  acid must be poured
on it in the retort.  As soon as the materials are  mixed,  they
begin to act slowly on each  other.   We must apply heat to
quicken their  action,  and join a receiver, previously  warmed
(to expel some of its  air) having  water in  it to  promote the
condensation of the acid.  While  the water attracts and  con-
denses the vapours, a white and very  tender  spongy  earth is
usually deposited on its surface, and hinders the further condensa-
tion.   We must agitate the vessels to break this crust, and then
the condensation is renewed.  And thus, by frequent agita-
tions, we condense the whole acid.  Such a quantity of earth
is precipitated as to make the water quite thick.   The glasses
are found much corroded by this process.  For a more particu-
lar account of it I refer you to Scheele's Essays,—Essay 1.
   Dr. Scheele called this acid the acid of spar, or acid of fluor.
It is now called Fluoric Acid :  and its compounds are called
Fluats.   It is very volatile, like  the  muriatic acid, and  will
not condense without water.  But it differs from  the muriatic
acid by many properties; as,  1st,  By forming with calcareous
earth a compound perfectly insoluble in water.   2dly, It has
the power to dissolve, and even volatilize,  the silicious earth,
which is perfectly insoluble by other acids.   And 3dly, It has
a greater attraction for lime than for alkalis :  and it fprms pecu-v
liar compounds with  the alkalis,  alkaline earths,  and  metallic
substances.
   Dr. Scheele learned by a number of experiments, that this
fine earth, which is mixed with the acid in the receiver, has all
the qualities which belong to the silicious when in  fine  powder.
And a further investigation by Dr. Scheele,  and by other che- 
                    FLUORIC ACID.                 269

mists, has proved that this silicious earth is generally a part of
the materials of the glass vessels dissolved  and volatilized by
the acid, but  deposited  again in part,  when the  acid  vapours
unite with water.   This was proved by distilling the spar in  a
retort of lead, and condensing the vapours in a receiver of lead,
or of glass defended with wax.   Thus we  obtain a pure acid,
not tainted with silicious earth.   There are, however, some
varieties of this spar unfit for this experiment, on account of
their containing some silicious earth in their composition, which
is dissolved and volatilized by the  acid during the distillation.
I could find no difference between  this  curious compound,  and
the purest silicious earth that I could obtain from liquor silicum
by precipitating it by the sulphuric acid.   I subjected these
compounds to a great variety of trials.   But whether the acid
be tainted with  silicious earth in this nfanner, or in consequence
of its being  distilled  in glass vessels, there  is a method by
which the silicious earth can be separated and the acid obtained
pure, viz. by saturating  the acid with volatile alkali, which pre-
cipitates the  whole silicious earth from it, and forms with it an
ammoniacal  salt, purely saline.  If a  quantity of this  ammo-
niacal salt, be prepared,  and then decompounded with sulphuric
acid  in leaden vessels, a pure sparse acid is thus  obtained ;
sometimes, indeed, not quite pure, but tainted with a little mu-
riatic acid.  But Dr. Scheele has  taught a method,  by means
of silver precipitated from nitrous  acid, for separating this also.
The  fixed alkali cannot be employed to precipitate the  silicious
earth and  to form a pure saline compound.   It has an attraction
itself for the silicious earth, and forms a triple compound, from
which it is impossible to obtain by crystallization a  pure neu-
tral salt.
-% Dr. Scheele discovered many other  qualities of the acid of
'fluor which it'shews in  mixture with  metals,  &c. for which  I
refer you to  his essay.     ^
   Some oP the  French chemists committed great mistakes and
errors in their first experiments and reasonings concerning fluor
and its acid.  You will  see Dr. Scheele's remarks*on them in
his essays.  And Dr.  Scheele himself  was at first in a  mistakeV 
270
FLUOR, AND ITS ACID.
 with respect to the origin of this silicious earth, which this acid
 deposits in uniting with water.
   Fluor is dissolved bv nitric acid or muriatic acid.  Sal tartari
 precipitates calcareous earth from this solution.  But caustic al-
 kalis, or aerated volatile alkali,  precipitate fluor in fine powder.
 Sulphuric  acid precipitates gypsum.   A gypsum is also formed
 by adding to the solution Epsom salt, or vitriolated tartar, or vi-
 triolic ammoniac,  which also acts by  sublimation,  in  decom-
 pounding fluor by double elective attraction.
   Phosphoric acid decompounds fluor by distillation, and the re-
 siduum is  a substance perfectly the same with bone ashes.
   Distilled vinegar and acid of  tartar have no effect on fluor.
   Caustic  fixed  alkali melted with fluor, does not  decompound
 it, but may be afterwards separated by water, and it leaves the
 fluor unchanged.   Mild fixed alkali,  four parts,  melted with
 powdered  fluor, one part, decompounds it.   The fixed alkali
joins with  the fluoric acid, and  forms a salt not  deliquescent.
 The rest is mild calcareous earth.   A solution of mild fixed al-
 kali  decompounds by digestion fluor  made of lime-water, and
 fluoric acid.
   The acid  of  fluor may be obtained without employing any
 fossil acids.   Melt the fluor with mild fixed alkali, and extract
 the compound salts from the mixed matter by means of water.
 To  the solution add acetated lead.   We obtain a precipitate,
 which, when exposed to a strong heat in a retort with charcoal
 •Just, gives reduced lead and the spatose acid-
   Fluor mineralis, if pure from quartz, can be dissolved com-
 pletely by aqua regia.  The fluor must  be in fine  powder,  and
 must be digested with a  sufficient quantity of .the aqua regia.'
 Bergmann (on Elective Attractions, p. 123.) proposes this as a.
 trial, to learn whether the fluor had contained any  quartz.
   The most remarkable property of the acid of fluor is its at-r
 tion  on silicious  earth, which is susceptible of no  union with any
other acid, so far as has  yet been  discovered*   Bergmann has
given a curious example df this.  He put into a phial some fine-
ly powdered quartz, and having filled  it with diluted acid-of
fluor, he closed  it up.   After two years, he found intermixed 
FLUORIC  ACID.
271
with the flinty powder thirteen crystals  as big as small pease.
They were of various forms. Some were hexahedral pyramids :
others  were similar pyramids on the end of hexahedral columns:
most of them, however, were cubes, having the angles cut off.
They  had all the chemical  qualities, and wanted little of the
hardness of perfect quartz.   Hence he was induced to believe
that this acid had great influence in forming the hard-figured
fossils.
  This action on silicious earth has been applied to a very curi-
ous purpose, namely, engraving,  or more properly speaking,
etching on glass.  A German nobleman, and Mr. de Puymarin
of Thoulouse, without knowing of each others labours, reflect-
ing on Scheele's experiments, applied the acid to this use.  The
plate was covered with engravers varnish, and traced with points
in the usual manner.  A  border of wax being also made as usual
round  the plate, it must be covered with a mixture of equal parts
of pounded fluor and vitriolic acid, and left there two or three
days.*
\at of Lime. '
   The next singular and remarkable compound of the  calcare-
 ous earth with an acid, is the Phosphat of Lime.   This was
 first discovered and analysed by Dr. Scheele, in compan)'  with
 another Swedish chemist, Mr.  Gahn.
   This compound consists of lime, or  calcareous  earth, com-

 . * This action on glass has been known long before.  In 1670, an artist at
Jqjrfenburgh,  named Schankhard, practised it.  Also in 1725, one Paidi in
Dr/sden, employed it for etching on glass. (See Beckmatfs History of Inven.
tiatu, t. \\\. p. 547.  Also Breslavi Collection, xxxi. 1725. p. 107.) Little seema
taliave been done with it; and it was forgotten till Scheele's experiments
revived the art on principle.      ,
  The etching done mthiS way is far from being neat.  As soon as the acid
gets at ti||e glass, it eats away sideways below \he varnish. Also the lines are
extremely shallow, and when  viewed through a microscope, shew us that
the acid acts unequally on the different ingredients of the glass.  The glass
seems to exfoliate.—Editor. 
 272              PHOSPHORIC ACID.

 bined with a particular acid which was discovered first,  or first
 described with precision, by that excellent chemist, Margraaf of
 Berlin.  It is now called the phosphoric acid.  He found it in
 the salt which first crystallizes from urine, when it is evaporated
 to about jS.   This is called sal microcosmi, sal microsmicum.
 He also discovered that the phosphorus of urine,  of which we
 shall speak when we describe the inflammable substances, is con-
 verted into this acid by inflammation.  It. was therefore called
 Phosphoric Acid.
   The phosphoric acid resembles the boracic, by  enduring, in
 its pure state, very strong red heats,  without  being changed
 into vapour.  It only melts very easily into  a transparent sub-
 stance like glass.  This glassy-like matter dissolves, however,
 easily in water,  but cannot be crystallized.   It forms with the
 water a liquid acid, from  which  the water  can  be evaporated
 again.  But, near the end of the evaporation, the remainder of
 the water is strongly retained; and when forced off by heat, car-
 ries away a part of the acid, as you know happens with  the bo-
 racic.               ^s^^^^^^^^^_^_
   Mr.  Margraaf disc^WMjl           properties  of this
 phosphoric acid, which are detailediri^rWI Bin  memoirs. But
 he did not know that it existed in any other natural productions
 excepting urine, and  the seeds of some plants in which  he dis-
 covered it.
   More lately, however,  since the study of the productions of
nature has so much engaged the attention of philosophers, the
phosphoric acidhas been found  in other states  or conditions.
The first example of this was discovered by  Dr.  Scheele, and
Mr. Gahn of Sweden, who were making a set of experiments *
in company.   They made some on the earthy part of bones and
herns, commonly called bone-ashes, that is,  the white  matter
which remains from bones and.horns,  when all the inflammable
matter has been completely burnt opt of them. This white mat-
ter was  formerly kept in our apothecaries shops, under the name
of cornu cervi calcinatu'm: and it was supposed to be an alkaline
earth.  I gave a few experiments on it in the essay on magnesia,
which shewed that it had very little of an alkaline quality.  But 
PHOSPHAT OF LIME.
273
 the Swedish chemists, having examined it with different views,
 and in a quite different way, found it to be compounded of cal-
 careous earth and phosphoric acid.   Their first process for de-
 compounding it has been reduced to  greater simplicity by other
 chemists.   This simpler process is given very distinctly in the
 last edition of the  Edinburgh Pharmacopoeia, as  a step in the
 process for preparing the soda phosphorata, which is a phosphat
 of soda, recommended lately by Dr. Pearson of London, as  a
 pleasant and effectual laxative and purgative.
   Since Scheele and Gahn published their process for analysing
 bone ashes, a similar compound, or phosphat of lime,  has been
 found in vast abundance among the fossil productions of nature.
 The first example of this was communicated by a letter from
 Mr. Proust, an able chemist, in the service of the King of Spain,
 to Mr. Darcet of the late  French Academy of Sciences, and
 published in the Journal de Physique June 1788, informing him
 that in Eetremadura it constituted extensive rocky strata.  Mr.
 Proust found it in a stone so abundant in  the province of Estre-
 madura, that it is quarried and employed in building.   In ap-
 pearance,  it resembles a stone composed of felt spar.   But  it
 consists of the calcareous earth saturated with phosphoric acid,
 or at least containing it in the  same proportion with the earth of
 bones, that is, nearly  one-fifth.  It is highly  phosphorescent'
 when heated.  It is also found in Saxony and in Bohemia.  Mr.
 Werner discovered it similar to the Spanish in Saxony.  At
 Schlackenwaldt, in Bohemia, it is found crystallized; generally
 in six-sided prisms, and also in the forms of tables and plates.
 It is seldom solitary,  but generally mixed with fluor, spar, li-
"'tho-marga, steatites, and several of the metals.   It is rarely ac-
 companied with quartz, as it is  in Spain.  The Germans say
 that it contains 4.5 parts of phosphoric acid per cent.:  and they
 call the compjpund apatit. I suspect that there is something like
 it in the north of  Ireland, noar the  Giant's  Causeway.   And,
 perhaps the foetid marbles,  and lapis suillus,  are of this nature.
   The phosphat df  lime is  used  in making vessels for the re-
 finement of silver and gold, to be described hereafter.  From
 it too the phosphoric acid is now obtained.   And lately, it has
   vol.  xi.                             m  m 
274        BORAT OF LIME.—BARYTES,

been recommended by a  French practitioner as a remedy for
the rickets.  We shall have a better opportunity for treating of
its decomposition, when we consider it as the  matrix of phos-
phorus.  This interesting process has  occasioned this com-
pound to be tortured in every way that chemistry can discover.


                    4.—Borat of Lime.


   There now remains to be mentioned but one more compound,
formed by.nature,  of the calcareous earth with an acid: And
it has been but lately discovered, (in 1791.)  It is a compound
of this earth, and partly too of magnesia, with the boracic acid.
It is found crystallized.  From its hardness, it was mistaken
at first for silicious matter.   The above crystals are found near
Lunenburgh, in the Dutchy of Brunswick, in a vein of a moun-
tain which abounds with gypsum.  It is called  cubical  quartz.
For an account of  it see the  Annales de Chymie, tome ii.J>. 101,
by Mr. Westrumb,  and p.  132, by Mr. Heyer.  It contains
about two-thirds of its weight of sedative salt, about one-eighth
of magnesia,  one-tenth of lime, and some other earths.


               SPECIES  III.—-BARYTES.


   Thus far we have been employed in considering the common
calcareous earth, or lime, and some  remarkable compounds
which it forms in nature with different acids.
   I am next  to make known to  you two other  kinds of earthy
or stony bodies,  which bear a great resemblance to the calcare^
ous by some of their properties, though they are quite different
from it by others :. and the differences are of great importance.
   One of the earths I now mean had first the name of  Terra
Ponderosa, on account of its bewig remarkably heavy.  Now
that name is  chang&'cj  to Barvpes, derived from the Grtfek,
and alluding to the same property.        •
   When reduced to-its purest state, it has the acrimohy and ac-
* 
OR  TERRA PONDEROSA.
275
    tivity T)f lime, which it  shews by its acrid taste and corrosive
    quality, like those of common lime.  It likewise dissolves in
    water, so as to form a  lime-water, which, however, contains
    less of the earth dissolved in it than common lime-water does,
    viz. only ^th ; that is,  very litde more than half a grain to
    the ounce.
      In this  pure and active state, it also decompounds the ammo-
    niacal salts readily, and dissolves sulphur, by boiling in water,
    as common lime does.
      It has a strong attraction for fixed air, or carbonic acid; and,
    when joined  with it by art, forms a species of chalk, quite  in-
    sipid, and which efferyesces with acids.   The attraction of this
    earth for fixed air is so strong, when it is pure,  that it readily
    takes it from the alkaline salts, and renders them caustic: and
    the air is with difficulty separated from  it by fire.  It contains,
    however,  much less fixed air than crude calcareous  earth, and
    vastly more water, almost one-third of  its weight.
      When combined with fixed air, or in the state of a chalk, it
   can be dissolved in small quantity by aerated water.   When cal-
  i cined, it dissolves sulphur.
      In all these particulars, therefore, it agrees with the common
   calcareous earth.—It differs from the same earth,
      1. By its weight, or the weight of the  compounds which it
   forms with acids.  They are-all much heavier than  the  corres*
   ponding compounds formed by the calcareous earth.
'y     2. It differs  from  the  calcareous earth by having a stronger
I  attraction  for acids in general,  and especially for the vitriolic
   acid. It has the power to separate most of the acids, but es-
   pecially the vitriolic acid, from the fixed alkalis, as well as from
  ?hme. This constitutes a  very remarkable, and often a puzzling
   distinction.
     3. The compound which it forms  with the vitriolic acid is
   much more dense and heavy than common gypsum:  and it is
   perfectly insoluble, in water. .\
     4. With nitric or with muriatic acid it forms saline compounds,
   soluble in  water, bdt not deliquescent like the compounds of the
   same acid with lime.  On,the contrary, the nitrat and muriat

        * 
276                    BARYTES.

of barytes.are easily crvstallizable.  The crystals of the nitrat
are of various flattish forms, as if they  were slices of a very
low pyramid.  The crvstals of the muriat are also slices of a very
low pyramid:  but their base is alwa}"s an oblong rectangle, but
generally havirg the four angles truncated,  so as to  make it an
octagon, having very unequal sides.
  With  the acetous acid barytes forms a  deliquescent saline
compound, not crystallizable; the reverse in this respect of the
compound formed by lime.
  After the vitriolic acid, the acid of sugar has the strongest
attraction for barytes, and, next to it, the acid of sorrel.   These
are very remarkable distinctions.
  The state in which barytes is most commonly or abundantly
found in nature, is combined with the sulphuric acid, or under
the form of a sulphat of  barytes.   In this state  it occurs most
frequently in the veins of the mountains in which ores of me-
tals are found:  for which reason it  is called by some  authors
Marmor Metallicum.   But in some rare veins it has  also
been  found combined with the carbonic acid, or in the  state  of
carbonat of barytes.  It is found in this state in the mine cal-
led Anglesark, near Chorly, in Lancashire.   (Vide  Manchester
Memoirs.)
  This earth has lately become  an  interesting object,  since it
has been found to have very uncommon  and valuable powers in
medicine.   This appears from Dr. Crawford's trials of it,  in a
number of cases published  in the  second  volume  of  Medical •
Communications of a Society at London. He gave  it in cases
of scrophula, or bad sores, and obstructed glands.   Its  sensible
effects  were gently to increase appetite, and the discharge, bf,
urine and perspiration.   These effects were in some cases ino£
peded at first by plethora, or an inflammatory  diathesis, which
was removed by  a vegetable diet.   He has published all the
cases in which he has tried it, which is a very candid way of
communicating the knowledge of any new medicine.  And it
evidently has eminent  healing  powers.   Much  caution, how-
ever, is required in the use  of  it, as too  large doses  of it might
prove a poison.  He, therefore, warns practitioners to diminish 
                                                          f
                                                         %
                      STRONTITES.                  277

the dose, when it produces nausea or giddiness.  Mr. Watt
poisoned dogs with half a drachm of it.   Professor  Blumen-
bach, of Gottingen,  found that the warm-blooded animals only
are with certainty poisoned by it; while both the warm and cold-
blooded animals may take with  safety  the similar compounds of
an earth which has been confounded  with  it,  and will be de-
scribed in the next place.
               SPECIES IV.—STRONTITES.


    The other alkaline earth,  which I said resembles the calca-
  reous, by several properties,  has been known for some time  in
  this country as occurring in som« of our mines, and was sup-
  posed to be  the barytes,  or  a mixture of it with calcareous
  earth ; until lately that Dr. Hope of Glasgow employed himself
  in examining it, by a number of experiments, which he commu-
  nicated to our Royal Society.   His experiments were very ju-
  diciously planned : and the conclusions he drew from them are
  perfectly well supported.   I  shall now give a  general abstract
  of them.
    He finds reason to conclude that it is a peculiar species of al-
  kaline earth,  different from any described  before.  The mine
  in which  it is found intermixed with other spars is in the  west
  of Scotland, near a village called Strontian :  He therefore gives
.  it the name of Strontites.
    1.  The carbonat  of strontites of Dr. Hope  is of a specific
  gravity from 3.650 to 3.726.   The natural carbonat of barytes
^■fis, 4.338.   The carbonat of lime is about 2.700.
'  •* *2.  Its external characters are,—considerable hardness, fibrous
  or crystallized texture, muddy transparency, and colour inclin-
  ing to yellow  or green.
    3.  It is insipid, but has a  little solubility in water.  Four
  ounces of distilled water being boiled with  10 grains of it in
  fine powder, dissolved 2£,t=t*t.
    4.  The gas extricated  during its effervescence with acids i*
  carbonic acid  gas:  and it loses 30.2 per 100  during efferves-
  cence. 
0
278                  STRONTITES.   ,

   5. The greatest heat of a common open fire is not sufficient
to expel its air;  but only makes it decrepitate a little, and be-
come opaque by the loss of some water.
   A violent heat in a smith's forge, of 45 minutes, applied to a
small mass of strontites inclosed in a Sturbridge clay crucible,
and which softened the  crucible, melted the outside of the mass
into a green glass ; while, within  this vitrified,crust, the rest
was white, opaque, and caustic. When it is thus rendered cau-
stic, it loses 38.79 per 100 of its weight.  With water it now
unites in the same manner as quicklime, but more violently, and
is slaked by the  air in the same manner.  The vitrified part be-
ing dropped into muriatic acid, is slowly acted on.  At length
a jelly is formed, which becomes perfectly fluid by the addition
of water;  a minute portion of powdery matter, which proba*
bly comes from  the crucible, remains undissolved.
   Dr. Hope was not able to vitrify strontites with the flame  of
the blow-pipe.  This makes it emit a brilliant light. (Fourcroi.)
   The constituent parts of natural carbonat of strontites, are by
the above experiments, in 100 parts,
      Earthy  basis,     .    ..     .~     .    .     61.21
      Carbonic acid,   .....     30.20
      Water,......8.59
                                               100.00
  6. Hot water dissolves a much larger  quantity of pure or
caustic strontites than cold water; and in cooling deposites the
superfluous quantity in crystals.  It is very remarkable  by the
great quantity of heat which is extricated from it in slaking. A
few small bits thrown into a flask of hot water, make it boil vio-
lently : and the ebullition may be kept up for a great length of
time by fresh additions.  Nine ounces and a half of water yield-
ed bv refrigeration rather more than an  ounce of transparent
crystals.   A hundred grains of these crystals contain 68 of wa-
ter, one part of which is easily expelled from them by heat, at
first  without fusion: but  at last a part of the water adh&ng
more stronglv, makes "them undergo  a watery fusion,  which
ceases  when the water is totally  evaporated.  These crystals
must be kept in phials very closely stopped; otherwise they at-
                                                     ft
              It                                     ~* 
                         STRONTITES.                  279

    tract carbonic acid, and fall down in powder.  The great quan-
    tity of water rendered solid  in these crystals, and so- strongly
    united, accounts for the great heat produced by mixing calcined
    strontites with water.
      One ounce of water at 60° Fahrenheit, dissolves slowly 8.5
    grains of these crystals.  One ounce of water kept boiling dis-
    solved no less than 218 grains.  These solutions have  all the
    alkaline qualities of lime-water.
      (N. B. Dr. Hope discovered that barytes can also be crystal-
    lized  in the same manner.)
      7. Sulphuric acid forms with strontites a compound more dif-
    ficultly soluble than gypsum.   Four ounces of  distilled  water,
    boiling, dissolved only one-half grain.   The solution  was ren-
    dered turbid by carbonat  of  potash, by  barytic water, and by
    muriat of barytes.
      Sulphuric acid dissolves the sulphat, and dilution makes it se-
    parate again.
      8. Nitric acid diluted dissolves it totally, but  does not  act on
    it when not diluted.  It rather precipitates a nitrat previously
    formed.  The solution easily yields crystals, which are octohe-
    dral, or formed of two four-sided pyramids joined by their basis.
   .One ounce  of water, at 60°, dissolves one ounce of these crys-
    tals; and at 212°, one ounce seven drachms fourteen grains. In
    dry air, a part of their water is evaporated from them.   In very
    moist air they deliquesce.   They deflagrate with combustibles,
    and  give a bright  red flame or light.  Or if they be  exposed
    to heat alone, they lose the acid, and the pure or caustic earth
    remains.
  »    9. Muriatic acid must also be diluted to dissolve strontites.
^    And the solution  gives  long  slender six-sided  crystals,  often
   disposed in a radiated form.  (N. B.  By this mode of crystal-
   lizing, this  earth is distinguishable from others.   By putting a
   little of the muriat on  a  plate of glass, it will evaporate and
   crystallize.  The muriat of barytes crystallizes into plates which
   are much less soluble in water.)  These crystals are not pulve-
   rised by the air; but in extremely damp^air shew a tendency to
   deliquesce.   One  ounce of distilled water, at 60°,  dissolves
   one ounce four drachms one scruple  of  them.   One ounce of
n* 
280                   STRONTITES.
water Kept boiling, dissolves four ounces, or more.  They con-
tain 42 per cent,  of water, and  undergo the  watery  fusion.
But the acid is not easily separated by heat.  The muriatic acid
may, however, be expelled from the strontites, by the heat of
a blow-pipe applied to it in a platina spoon.
   10.  Acetous acid dissolves strontites  slowly.   The solution
tinges  vegetable colours green ; and by spontaneous evaporation,
gives minute undiscernable  crystals.   One ounce of water dis-
solves, in a boiling heat, 196 grains of them, which remain dis-
solved when the water cools.
   11.  The oxalic, tartarous,  and fluoric acids, form very inso-
luble compounds.
   12.  Phosphoric acid,  applied in large quantity, dissolves it
slowly; but if we attempt saturation,  the whole compound pre-
cipitates.  Four ounces of boiling water dissolved only one grain
from 10 of this precipitate.
   13.  With succinic acid it forms crystals which are durable in
the air.
   14.  Acid of arsenic forms a solution which cannot be evapor
rated by heat,  without undergoing a change in which the earth
is more closely combined with the acid,  and also with a smaller
quantity of it than before : and this new state of combination
renders the compound insoluble.   One ounce of boiling water
was able to dissolve  little more than one  grain.
   15.  With boracic  acid, it is sensibly alkaline, and water dis-
solves  yjo.
   16.  With carbonic acid it presents the same  phenomena  as
those which are exhibited by lime.
   17.  Strontites, and  all its compounds, give a red colour  to
flame.  The muriat does it most; and is  best used for this puf-
pose by putting a crystal of  it on the wick of a  candle.   Mu-
riat of lime also produces this effect in some degree.  But mu-
riat of barytes gives a greenish celcmr to flame.  A certain
portion of humidity is necessary to enable these  compounds  of
strontites to tinge the flame.   Without it they have no <ff ct.
   18.  Aerated alkalis  jfrecipitate strontites from  its solutions;
at first in form of a gelatinous matter. But by adding more- al-
kali, and agitation, an opaque white curdled precipitate is formed, 
STRONTITES.
281
 which Dr. Hope calls artificial carbonat.   It loses its air more
 easily in the fire, and dissolves more quickly.in acids than natu-
 ral carbonat, but is in every other respect the same.
   19. The prussiat of potash or of lime do not in the least pre-
 cipitate strontites from its solutions in acids; in which property
 it differs remarkably from barytes.
   20. With sulphur it forms a hepar, either in  the dry or humid
 way in the same manner as lime.
   21.  Crystals  of caustic strontites  were dissolved,  but very
 sparingly, by alcohol,  which afterwards burned with a reddish
 flame.
   The following is the  order of attractions of the acids  for
strontites:  Sulphuric  acid,  oxalic, tartarous,  fluoric,  nitric
muriatic, succinic, phosphoric, acetous, arsenical, boracic, car-
bonic.
vol. ii.                             a n 
282                   STRONTITES:
  Strontites, compared with  other alkaline substances, in its

force of attraction for the different acids.
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2. S 
(  283  )
GENUS II.
PLASTIC EARTHS.
    W E  shall now  proceed to study the second order  of the
   earths,—the Plastic, which are commonly called in our lan-
   guage Clays, or Clayey Earths.
      The  natural earths which are assembled under this division,
   all contain more or less of a particular  kind  of earth in their
   composition, which gives them their plastic qualities ; or gives
   them, in different degrees, the qualities which belong especially
   to itself.
      The  earth I now mean is at present considered by the che-
   mists as another of the  pure elementary earths, and is called
   the argillaceous.   It is distinguished  from  the  earths hitherto
   described by these properties :
      lmo,  It does not effervesce with acids when they are simply
   mixed with it.
      2do,  It is composed of exceedingly fine impalpable particles.
   It therefore feels fat or smooth between the fingers, like mar-
   row ; and is not in the least gritty between the teeth.
•  *■'.'« 3tio,  When a dry mass of it is applied to the tongue, it im-
   bibes the superficial humidity of that  organ so  strongly that it
  - adheres to it: and  it gives a peculiar odour on  all these occa-
   sions when humidity is applied to it.
      4to,li it be mixed and well kneaded, and worked with a pro-
   per quantity of water, it forms a soft and plastic mass, not easily
   diffusible or dilutible in more water;  and which, if dried well,
   and afterwards burned with a strong heat, becomes very com-
   pact and hard, and  impenetrable by water. 
 284           PLASTIC EARTHS—CLAY.

   5to, It has some  notable qualities which it shews in mixture
 with acids;  the  most remarkable of which qualities  shall be
 mentioned presently.
   The plastic earths, therefore, all contain more or less of this
 simple earth: and they constitute every where numerous strata.
 They also make  a part of every strong and rich soil.
   That property  of plastic earths,  by which  they become so
 tough a paste, and so difficultly dfffusible or penetrable by wa-
 ter, when wrought  and compressed with a proper quantity of
 that fluid, occasions their being employed  for confining water
 in canals,  and ponds,  and reservoirs, and other works  in which
 large  quantities   of water are to be  confined,  or preserved
 from  being  wasted by  soaking through  the soil.    It  also
 explains  the bad effects of  what  is called  poaching clayey
 grounds ; that is, allowing cattle to tread On them much when
 they are wet or soft; as they are thus reduced to that plastic
 state in which they do not transmit water  easily, but  occasion
 it to stagnate on  their surface, and to rot or sicken the plants  ;
 and at the same time they are so dense and viscid, that the roots
 of plants cannot  penetrate them without  the greatest difficulty.
 The remedy for  this is,  to plough them when they are mode-
 rately dry,  and when dry weather or frost is expected.  If the
 clods  once become dry,  the first rain will make them  moulder
 down, and alternations of dry weather and showers will com-
. pletely divide them.
   Mr. Bergmann says that a  fine  clay does very well for wash-
 ing and cleansing linens.   Though it does not  chemically com-
 bine with greasy filth, it adheres to it, and  carries  much off
 with it bv rubbing.  Smectis,  or fuller's earth, is  a marly clay,
 and is much employed in this way.                         ''
   There is great variety of the earths which come under  this
 division,  and under the common denomination of clay. They
 are  various  by their colour ; by  the fineness  and smoothness
 of their particles ;  by their degree of  cohesion  when we at-
 tempt to diffuse them in water, and the degree of toughness, or
 plastic quality, which they  assume when wrought or kneaded
 with a proper quantity of that fluid ;  and also by their qualities
 with respect to heat, or the changes they undergo from the  dif- 
CLAYS—GENERAL CHARACTERS.
285
  ferent degrees of its action on  them.  But all this variety is
  produced by the various admixture of siliceous earth, or mag-
  nesia, or calcareous earth, or iron, or inflammable  and other
  matters, in various proportion with the  argillaceous  earth.  It
  is so liable to admixtures of this kind, that a pure argillaceous
  earth is one of the rarest productions  of nature :  and  in the
  very few examples that have occurred, it was in small quantity.
    The  clays which contain it in the' greatest quantity, or in a
  state less impure than ordinary, are either naturally white ; or,
  if they have a dark or dull colour,  it proceeds from a small
  quantity of inflammable matter: and they become white when
  burnt in an open fire.  Those that  become  red  in the fire  con-
  tain iron.
    Clay, by being kept very long in a wet state, becomes evi-
  dently sour to the taste and smell.   I was  assured of this fact
 by Mr.  Wedgewood,. who is,  perhaps, the most perfectly? ac-
 quainted with all the qualities of the plastic earths of any  per-
 son in Europe, and the most interested to know them in their
 state of greatest purity.   The fact  is curious, and perhaps im-
 portant  to the chemical philosopher.  Perhaps it receives some
 explanation from another fact which he also told me, viz.  That
 by long  exposure to the air, the surface appears  powdery:  and
 when this dust is carefully  swept together,  it is found tainted
 with a calx of iron.  It is not unlikely that this  arises from  a
 minute portion of pyrites,  which is known  to decompound by
 humidity, and to yield its acid.  May  not this also account
 for  the  hardening of clays by  the fire, even in their purest
 state ?
 .  The most useful qualities of clays in the  arts are,—their dis-
 position  to constitute, with a proper  quantity of water, that duc-
 tile plastic mass, which is easily formed  on the potter's wheel,
 or otherwise, and which can be baked afterwards by fire to a sto-
 ny hardness.   In consequence  of which, they are employed for
 the manufacture  of numerous  vessels, tiles, bricks, and many
 other useful productions of art. The best kinds of it acquire dif-
ferent degrees of  compactness  and hardness in the fire, accord-
ing to their dryness in the  first kneading, and the violence of
the heat. 
  286    CHEMICAL PROPERTIES OF CLAYS.

    When clay has been made very soft, by kneading it with much
  water, in order to make it work easily on the potter's wheel,  it
  must be very porous when burnt to a tile :  for whatever quanti-
  ty of water is employed, the piece does not contract much by
  drying; and by no means in proportion to the water in it. Such
  ware, therefore, must be very open and  spongy, and  may be
  used for filtres.*
    In a moderate red heat they become hard, but porous ; and
  are formed into tobacco-pipes, &c.  In a much stronger one they
  are rendered compact and hard like- flint.  But pure clays never
 melt in ordinary furnaces or fires.  The more coarse and impure
  clays have these qualities in inferior degrees. They do not grow
  so hard in moderate heat. And many of them cannot Withstand
  a strong fire without melting, on account of the mixture of dif-
 ferent earthy substances and other  matters which they contain,
 and which give .them this disposition.
    Experiments made with clays,  in the way of mixture with
 other substances, have shewn that the argillaceous earth, although
 it does not effervesce with acids, can be  combined with them;
 and that, when combined with the sulphuric acid, it constitutes
 Alum.
   This, however, is a late discovery; for although alum has long
 been in use, and well known to contain the sulphuric acid com-
 bined with an earth, the nature of this earth was not distinctly  .»
 understood, until two of the  academicians of Berlin, Pott and
 Margraaf, published their experiments on this subject, in which
 they made perfect alum by dissolving the argillaceous earth of
 clays in the sulphuric acid.  Mr. Pott made the first step in this
 discovery : and Mr. Margraaf afterwards brought it to  perfec-
 tion.

  * Accordingly, vessels* of this porous ware are used in the hot  climates
for cooling liquors ;  which service they perform,by the copious evaporation
from the surface. Vessels are also made in this country as porous as possible,
and have their external surface turned into deep notches, "or furrows, on the
potter's wheel.  They are filled with water ; and small seeds, such as those
of cresses and mustard, are sprinkled into those furrows, where they receive
enougli of moisture to make them grow, and cover the outside with foliage.
A sallad is thus easily raised at sea, and in winter in a warm room.—Editor.
3- 
              ALUM,—EARTH OF  ALUM.        \87

   It was ascertained by  Mr. Margraaf's experiments that the
 argillaceous earth can be  combined with  the vitriolic acid in two
 different proportions, or so as to form two compounds conside-
 rably different. One of them contains a  large proportion of the
 acid, and is very soluble  in water, and deliquescent, and cannot
 be crystallized.   This is called alum  liquor.   The other, viz.
 alum, contains a small  proportion of acid to the  earth ;  is but
 moderately  soluble in water ;  easily crystallizes, and is not at
 all deliquescent, but rather calcines spontaneously.
   The first of these'two  compounds  is almost always formed
 when we attempt to make alum  by combining its two ingredi-
 ents, which may be done by boiling the best kinds of clay in
 strong sulphuric acid until the mixture is dry, and then adding
 water to dissolve the alum or aluminous compound which has
 been formed.  We thus procure an alum liquor, or acidulous
 liquid alum, from which it is necessary to abstract a part of the
 acid, by adding a  small quantity of an alkaline salt, or by a pro-
 per degree of heat,  before we can have alum that can be crys-
 tallized.
   Mr. Beaume of Paris has made an addition to these discove-
 ries of Margraaf.   He discovered that a third compound can
 be formed of the sulphuric acid and aluminous earth;__a com-
 pound in which there is still less of the acid than in perfect alum ;
 and which is therefore not soluble in water.  This compound is*
 formed by boiling a solution of alunyn water with some of the
 pure argillaceous earth ; the consequence  of which is, to change
 the whole of the alum into this third compound, which subsides
 to the bottom, and forms a sediment which cannot be dissolved.
   All these particulars have been discovered by the experiments
 made to combine the sulphuric acid in different ways with the
 argillaceous earth.
   It is not,  however, in this way that alum is  manufactured for
the purposes of different arts.  It is obtained from materials
which afford it much cheaper, by a process which was long prac-
 tised before it was well understood.  You will see a fuli account
 of the processes by v. hich alum is manufactured, and of the ma-
terials employed in making it,' in  Fourcroy's Elements,  under
the article alum ; and in Chaptal's, where he describes a new 
 288        MANUFACTURE  OF ALUM.

 process of his own.   Bergmann  also has given  an  instructive
 essay on  the manufacture of alum.
   Alum  is generally manufactured  from a soft laminated stony
 matter found in strata, (and which bears some resemblance to
 slate, but is softer,  and commonly dark grey or  black), called
 alum ore; aluminous schtstus,—Schale.  It is composed of  clay
 combined with sulphur, and very often some bituminous matter.
 It hardly ever produces alum until after it has been burned with
 a very slow heat for a considerable  time,  which  consumes the
 bituminous matter, and changes the  sulphur into sulphuric acid.
 It is accordingly burned by setting fire to very large heaps of it,
 which are covered up in such a manner as to occasion a slow and
 long?continued inflammation and  very gentle heat.   There  are
 some of these ores, however, which, when formed into heaps,
 take fire of themselves,  and burn slowly, without needing to be
 set on fire by means of fuel.  And  in some volcanic countries,
 they find materials which  are  already  prepared for affording
 alum, in  consequence of their having been affected  by the vol-
 canic heat.   In some few cases also, the action of the atmos-
 phere alone, continued for a length of time upon such materials,
 prepares  them for affording  alum,  although they never have
 been set on fire.   They are observed to be covered with a whi-
 tish dust, which, when examined, is crystallized alum.  When
 this is washed  off, more  forms in a day or two.  Such matrices
 properly built up, so that the rain may wash it off into gutters
 which lead to  a cistern, afford a lixivium  ready for  boiling.
 There is at Hurlet, in the neighbourhood of Glasgow, a stratum
 of shale which has been left in the old workings of coal mines,
 which,  by the singularity of its  situation, exhibits a wonderful-
 ly rich appearance.  It is about ten inches thick ; and, if cut
 out from a newly opened pit, does not yield an atom of alum. •
 But lying in the open waste  for more than a century,  it has de-;
 composed, and effloresced.  Moreover, there is above it a vast
thickness of shale, which is too poor for working;  but in the
process of time, has afforded, by filtration, enough  to  enrich
the stratum below, which effloresces, and thus renews  its waste.
The result of this has been,  that each lamina of the schistus has
not only separated from the next, but the interstice is filled with 
MANUFACTURE OF ALUM*
 crystals continually increasing; so that in some places the stra-
 tum of ten inches has swelled so as completely to fill the space
 from which the coal has been taken.  I  thought this singular
 fact not unworthy your notice.
    In all these cases, whether the alum ore has actually been set
 on fire and burned, or whether it be prepared by the long-con-
 tinued action of the air alone, the change produced is a combi-
 nation of the sulphur with vital air,  and consequently a change
 of \t into sulphuric acid, which acts on the clayey matter;  after
 which, being steeped in water,  it affords an aluminous liquor,
 which requires the addition of some alkali, fixed or volatile, to
 prepare it for affording good  crystals of alum by evaporation.
 The use of  the alkali is partly to precipitate some calx of iron,
 which is commonly dissolved in this liquor with the alum,  and
 partly, as is supposed, to saturate a portion of superfluous sul-
 phuric acid.  The crystals are first obtained of a moderate size;
 but are afterwards united into  large masses by roaching.
    Mr. Chaptal's process is very refined and artificial.  He ob-
 served that a gentle roasting of clay disposes it to a more ready
 union with  the acid, especially when  this is  in the form of
 steam.   He therefore makes up the clay into small balls,  and
 roasts them in  an oven or kiln.  One effect of this must be the
 driving out the water, and leaving the whole mass very porous
 and accessible to  the steam of the sulphurous acid.    The balls
 are now spread out on the floor and shelves  of a great room,
 whose walls and ceiling are covered with a fat  luting impene-
 trable by the fumes.  There is a furnace constructed  in a cor-
 ner of the room,  wherein sulphur is made to bum in  a manner
 which disperses it through the room in  steams  of the suffoca-
 ting acid.  The balls are  penetrated, and the clay unites  with
$&:; When judged to be superficially saturated with it,  and alum
 formed in them, which requires some days, the room is opened,
 and the balls taken out and exposed to the  air under cover.
 The volatile acid becomes sulphuric by extracting oxygen from
 the air, and dissolves the clay : and the balls are then lixiviated.
 This manufacture is said to be very profitable.  (Ann. de Chem.
 vol.  3.)
    VOL. II.                             O O 
290         MANUFACTURE OF  ALUM.

   The most instructive  dissertation  that I  have  seen on  this
manufacture is, Disquisitio Chemica de Confectione Aluminis,
Auctore Gustavo Sued'ilio, Upsal,  1767.
   The appearance and more obvious qualities of alum are more
or less known to you.  It is exposed to  sale in large crystalline
masses containing much water.   By the application of heat it
melts, swells, boils, and  dries ;  and is then called burnt alum,—.
alumen ustum, which has often a good effect on foul ulcers.   In a
greater heat, it does  not undergo real fusion,  but part of the
acid is dissipated.  It dissolves in cold water,  but slowly,  and
in small quantity.   Hot water  dissolves it much  better.*   Its
taste is sweetish,  sour,  and astringent.   It tinges some vege-
table blues red.  These last qualities it  derives from  the acid,
 which is so little neutralized by the earth,  or is present in the
alum in such quantity, that it  is  less  changed in its  properties
than in other  cases.   It is also united with the earth by a weak
attraction.   This appears from the facility with which alum is
decomposed by other substances ; for net only the fixed alkalis,
but calcareous earth, the volatile  alkali and magnesia, if added ''■ :
to a warm  solution of alum,  cause effervescence and  precipita-
tion.  The effervescence  shews  that  the  argillaceous earth is    i
not disposed to unite with the  air, or with very little of it, if
the solution be warm.   This  earth, when  properly  separated    '-\
from the acid and neutral salt,  is  purer argillaceous earth  than
any clay ; and if it be precipitated from a cool solution, so that
the earth may unite with  a portion of the air of the alkali, it    \
has the plastic qualities in the highest degree of perfection.       i
                                                                   I
   * It therefore readily crystallizes by cooling.  In repeating Mr. Lowitz's    1
experiment with a mixture of alum and nitre, I observed the whole alum cry-     1
stallized in one form (oct: c Iral) which I hud never seen before, it being com-
monly a mixture of both kinds. The observation of Mr. Lowitz naturally
made me think it probable, that not only the alum alone was made to crystal-
lize by touching the mixed solution with a crystal of alum, but also that  the
form of the crystal presented would dispose the whole to the same aggrega-    <
tion.  The notions which I had of crystallization lead almost necessarily to
this.  I tried it, by presenting to the  same aluminous solution a cubical crys-
tal : and the  effect was  as I expected.   All rvere cubes or composites of
cubes.  I have found the same tiling to happen in some other salts, which of.
ten appear in truncated crystals.—Editor. 
MANUFACTURE OF ALUM.
    The French chemists have given a new name to  this pure
 earth ; alumine  in French, and alumina in Latin.  I confess I
 do not like this alumina.  If a name is to be contrived, I would
 make it argilla.
    Great quantities of alum are employed in the arts of dyeing,
 and in printing or painting of linens and cottons.
    To complete the natural history of the argillaceous  earth; we
 may remark, that it is found in manv other natural productions
 beside the plastic earths or clays;  in the alum ore, for example,
 which is indurated-clay with sulphur; in what  is called black
 halk, in which there is some inflammable matter which gives
 the blackness; in  slate, which  appears to have been formed
 from clay, indurated naturally by length of time and subter-
 ranean heat.  There  is a very  great variety of strata of this
 kind,  which have different  degrees of hardness and cohesion,
 and are more or less laminated like slate; all of which contain
 some of the argillaceous earth mixed with others.  And they
 appear evidently  to have been clays, which have been indurated
 more or less by some operations of nature, until many of them
 have  acquired great degrees of hardness and durability.  The -
 general denomination for them all is Schistus.   The hard-
 est of them arc so closely concreted,  that the strata they form,
 called Gneiss, are among the most  durable.   The less hard
 constitute different kinds of Slate,'and the softer ones Shale.
 In  the neighbourhood of Geneva, and I suppose in  France,
some  are called Pierre de Corne.
  The argillaceous earth is also a principal article in the compo-
sition of some of the  hard stones, as we shall notice hereafter. 
( 292 )
GENUS III,
HARD STONY BODIES.
X N this section I comprehend most of the stony substances
called Siliceous, or Flinty, by natural historians.
   They are eminently hard, and they are unfusible by the most
violent  heats of common  furnaces or fires.   Their hardness is
such, that they are not affected by the hardest steel, but on the
contrary scratch it, and strike fire with it. And they also scratch
or cut glass.
   The  greater number of the stony substances which belong
to  this  division  have also been  called  crystalline  and vitres-
cent,—crystalline, on account of their being oftener found in the
form of regular and transparent crystals than other kinds,—and
vitrescent, as being the principal ingredients in glass, and  more
disposed than any other earthy or stony matter to produce good
glass with proper additions.
   All the stony bodies of this division contain a particular kind
of earth, which I have had occasion several times  to mention,
but not  yet to describe in this course. It predominates or bears
a principal part in the composition of this order;  and is at pre-
sent considered as one more of the simple elementary earths.  It
has  been commonly called the  siliceous earth.  The  French
chemists lately contrived the names for  it, of Silice in French,
*■—and a barbarous term,  Silica, in Latin;
  We can  easily extract it  by a chemical  process from the
stones of this division.  And the nature of the process is such,
» 
SILICEOUS EARTH.
293
 that the earth is obtained in the form of a precipitate, which is
 an exceedingly tender, light, and spongy earth.
   The properties of it are these:
   lmo,  It  is not dissolved or otherwise affected by any acid,
 except the fluoric, which, when applied warm to it, and especial-
 ly in the form  of vapour,  not only dissolves this earth, but vo-
 latilizes it.
   2do, It is not fusible in our most violent fires.
   3tio,  When mixed in powder with half its weight of potash
 or soda, or the carbonats  of those  alkalis, the mixture can be
 melted easily in a strong heat; and forms a perfect glass.   It is
 even in some measure dissolved or combined with potash,  by
 boiling in a strong watery  solution  of that salt.   This experi-
 ment  will not succeed  with any siliceous substance reduced
 mechanically to a powder, however subtile.  The utmost effects
 of mechanical division and  trituration fall infinitely short of the
 subtile division and attenuation which we obtain on many occa-
 sions by chemical solution and precipitation. And this earth, in
 order to make  it combine with an alkali that is dissolved in wa-
 ter, must either be  in this state of the most subtile and tender
 powder, or  it must be previously combined with a smal propor-
 tion of alkali in the dry way, or by fusion.
  This experiment and others enabled me to understand the na-
 ture of an earth which occurs in some parts of Scotland, in the
 form of a sediment or mud, at the bottom of lakes of fresh wa-
 ter.   There is  a lake in Galloway in which  it is found.   Sam-
 ples of it were  brought to me a long time  since, to know if it
 was a marle.   I quickly perceived that it was  not a marle : but
 the properties of it were such, that for a considerable time I was
 at a loss to give it a name.   At last I found that the qualities of
 it were those of the silex, or siliceous  earth, and  that it was
 principally composed of this earth.   It may therefore be named
 limus siliceus, or silex limosa.   It is undoubtedly deposited  in
 those lakes, in consequence of the  demolition and decomposi-
 tion of stones and rocks, which contain it in the higher parts of
the country, from which those lakes are supplied with water.
  This completes the list of the earths that are at present con-
sidered as the most remarkable and most abundant elementaru 
294      VARIOUS  STATES AND FORMS

earths.   They are six in number, distinctly known,  namely, the
calcareous earth or lime, magnesia, barytes, strontites, alumina or
the argillaceous earth, silica or the siliceous earth.
   We have been lately informed of a very few more lately dis-
covered, which appear to be simple earths, and yet are different
from any of these.  But they are produced by nature in very
small quantitv,  and have only been found in the composition of
some particular and rare stony concretions of a small size ; nor
have they yet been sufficiently examined.   I do not, therefore,
think it proper at present to take up  your attention with them.
You will see mention  made of them  in the new systems of mi-
neralogy which I lately recommended to  your notice.
   To return to the consideration of  the  hard stony bodies.—
They appear to have their hardness more or less from the silice-
ous earth, or silica, in their composition.  But they contain it,
however, in  different proportions, or in different states of purity.
I shall first enumerate those which contain it in largest quantity,
or in a state which approaches the nearest to purity. These are,
   1. Crystal, or rock  crystal, which is transparent.
   2. Chalcedony, which has an imperfect transparency resem-
bling that of whey.
   3. Quartz, which  has a whiteness like that of  milk and wa-
ter, and shattered appearance, and breaks with an uneven surface,
not a plated  structure like spar.  It  is abundantly produced by
nature.
   4. Agate, in which the stony matter is diversified with
streaks and spots, whitish, or of other colours.
   5. Flint, silex, which has an uniform dark colour like dark
coloured horn, but becomes, white in  the fire.
   6.  An exceeding fine  loose earth found at the bottom of some
of our lakes in the mountainous parts of  this country.  It may
be called limus siliceus, or silica limosa.
   These varieties of hard stones contain the silica the most
abundantly, or most approaching to a  pure state.
   But in many of the other stones of this order it is very impure,
or mixed with a large proportion of other matter.
   When iron is mixed with it in such quantity as to colour it
strongly, and render  it opaque,  it forms Jaspers  of various 
OF SILICEOUS  EARTH.
295
colours.   These are distinguishable from flint by breaking with-
out the smallest lustre, like dry clay, and void of all transparen-
cy.  Or if the quantity of the iron is less, and the stone is semi-
transparent, and of a red colour, it is named Carnelian, from
the resemblance of its colour to that of raw flesh.
   These are the principal appearances of the hard stony matter.
   But it may  also be proper to give a general view of the vari-
ous situations "and collections of the hard stones in nature.
   lmo, They are found constituting numerous and extensive
strata: and those which are the most abundant, are the strata
of common sand and gravel, and sand-stone, and gravel-stone,
which  are very numerous  and common, and of great extent.
The origin of sand and gravel was formerly explained.
   Some sands are white, or free from any colour, and are totally
composed of small grains of crystal or quartz, such as the sand
from Lynn in Norfolk.  It is the fittest  of all for fine glass.
   The greatest number of sands, however, are variously colour-
ed, by the admixture of other  matter with the siliceous in the
composition of many of the grains.   And some are  perfectly
opaque, and dark  coloured, and even black, from the large pro-
portion of iron.
   2do, Gravel is in many places of the  same  nature as com-
mon sand; and is found in the composition of strata, either by
itself,  or more commonly mixed with sand or clay in different
proportions.   It consists principally of the same kind of matter
as the  sands, only in larger grains or masses, more"irregular in
their form and size, and more coarse and  opaque  by the more
plentiful admixture of other earthy  matter with the  siliceous
earth.  Gravel is, however, of  very different kinds in different
places: and it must be so, as being formed of the hardest frag-
ments of the stones of the country in which it is  found.
   3tio, Sand-Stone is the third  kind of stratified matter, which
I said is found in great abundance ;  and  which, in most  places,
is composed of hard stony materials.  It has evidently been pro-
duced from common sand concreted together.
   When the sand of which it is composed does not cohere too
strcngly, this stone is employed in buildings which are erected
with hewn stone,  and it is then called Free-stone.   All the 
296       SAND  STONE—PUDDING-STONE.

free-stone of this country is composed of siliceous sand, and
is therefore remarkably  durable:  and  we have plenty of it.
The sand of which it is composed was first collected and wash-
ed clean byr water in the long lapse of time, and was afterwards
cemented together by  some operation of nature.   The  proofs
of this are, an undulated appearance which often occurs in the
surfaces of its strata,  and which is exactly similar to the undu-
lated surface formed on the  sands of the sea-shore, or of lakes,
by  the  action of the  waves.  And  we often find also  in the
strata of sand-stone the  relics of  sea productions.  There is,
in particular, a very remarkable  object found in many free-stone
quarries in this country.   The stone itself is observed  to take
the form of a plaited (not twisted) rope, of considerable thick-
ness, and generally flattish,  the  greatest  diameter being hori-
zontal.   In the different plaits of  it there is a  small  indenta-
tion : and the plaits are most regularly disposed.   When broken
across,  it has a sort of core, black and  soft:  and fibres are ob-
served to go out from  this to the indentations on the surface.
This object is sometimes of great extent, traceable through the
stratum in a horizontal direction many  yards, varying in dia-
meter from half an inch  to five  or  six  inches,  and  sometimes
sending off branches.  An example of  it was seen  lately in a
quarry on the sea-shore near Musselburgh,  which resembled
the trunk of a vast tree sending  out branches in  all directions.
   Sand-stone is of very various  hardness. In  some the sand
has but a weak degree of cohesion.   In others the grains are so
closely and strongly coherent, that the stone has  the  appearance
of solid flint, and cannot be wrought as a free-stone.
   4to, The strata of what I called gravel-stone have been formed
in the same manner as sand-stone,  only that gravel is intermix-
ed with the sand  in the  composition of the  stone.  From  its
appearance this stone is named by the English pudding-stone ;
and the name has been adopted by foreigners.    -
   Such are  the strata, principally or totally composed of the
hard stony bodies.  There are also some kinds of rock in which
more or less of them  is contained,  as granite, ^ be soon de-
scribed; and the more  compounded kind of rock  which abounds
in this country, named Whin-stone, some kinds of which are 
                    FLINT—CHERT,  &c.              297

  a more coarse and compound granite.  The whin-stone often
  contains  nodules and pebbles of  all different  sizes, some of
  which are hard stones.
    The  schistuses also, or indurated argillaceous strata, <tften
  contain a large  proportion of quartz irregularly  intermixed
  through them.
    The hard stones constitute therefore a great part of the ma-
  terials of many strata and rocks.  They are also found often in
 veins, or otherwise interspersed through rocky or stratified mat-
 ter.   The species most frequently found in this  state is quartz;
 but we also find occasionally, crystal, chalcedony, agate, jasper,
 and flint.
    There are great quantities of flint in England, interspersed
 in a very irregular manner through the  calcareous strata of
 chalk and limestone,  traversing  and running through  them in
 different directions.   As  found  in  chalk, it is more especially
 named flint; as occurring in limestone, it is named chert by
 the English.
    From the appearance of this matter, as  found.in  this state,
 there is reason to be convinced that it has been introduced in a
 very fluid state, or that it has been produced in  these strata by
 the action of some  very fluid  matter which has penetrated
 them.  The proof of this  is,  our  finding shells, lithophyta,
 and other  marine  productions, originally calcareous, but which
 are now completely  penetrated by this sort of matter, and
 seemingly converted into flint or agate, without losing their ex-
 ternal form.  The same fact is further established by the quan-
 tities of fossil wood penetrated and  petrified with this  matter,
 found in many parts of the  world.   It  is found in all  states,
 from that of  stony wood,  still combustible, to that of pure
 flint.
   It also deserves notice, that  the nodules  of  flint  found in
chalk and lime,  often in very strange forms, are  not simply ly-
ing there, but seem forming, or else decaying, in  that situation,
being always surrounded  by a crust, which  changes gradually
from a calcareous to a  siliceous nature.        •
   Another curious fact relating to this stony substance is, that
masses of it are .sometimes found which include water perfectly
   vol. II.                           p p 
 298 SILICEOUS PETRIFACTIONS AND CRYSTALS.

 inclosed in the hard stone.  This has been  observed in crystal,
 in common  flint, and in agate.
   In whichsoever of these states  the  hard stones are found,
 when masses of them occur that are not solid, but have vacui-
 ties within thtm, in  these we find their matter crystallized, and
 very  often  into remarkably  regular and transparent crystals.
 Such are often found  in hollows of  veins, and of pebbles.
 They are generally columns of six sides, terminated by a  six-
 sided pyramid: or sometimes  they are  pyramids alone.   All
 these crystals are chiefly found in cavities or veins  of  hard
 stones.
   I have yet to mention one other state or condition in which
 the  silica has been found, and that  is, dissolved in water.
 There is one very remarkable example of this in Iceland, parti-
 cularly at the celebrated Geyser, where some hot springs contain
 so much as  to form  siliceous petrifactions.
   These are the different forms and states in which we find the
 hard stony bodies.  We are now to take notice of their chemical
 properties.
   The purest kinds, or those which contain the most of the si-
 lica, when they are exposed to a strong heat, generally become
 opaque,  white, and brittle.  But they sustain the most violent
 heat without melting, or being  softened by  it.   We can  melt
 thtm,  however, easily  and perfectly, with  fixed alkaline salts,
 with which they unite in the fire to form a perfect and workable
 glass.   By workable glass,  I mean a glass, which, while  it is
 allowed to cool from its melted  state, continues soft and ductile
 a considerable time, and passes through all the degrees of soft-
 ness before it becomes hard and rigid.   During these states of
 softness it has great ductility, and can be wrought or moulded to
 any form.   Glass  that is workable in this manner is one of the
 most valuable  productions of chemistry.
   All good  glass contains siliceous matter and a fixed alkali as
 is  only  or principal ingredients.  And sand, when it is  com-
 posed of pure, or nearl) pure, siliceous matter,  is preferred to
 the other forms of  the hard earths, on  account of its being
 easily mixed with the alkali and other materials, without re-
quiring the expensive operations that w ould be necessary for re- 
COMPOSITIONS FOR GLASS.
 during to powder, or to small grains, the hard masses of other
 siliceous matter.
    In the composition of some kinds of glass, other  materials
 are added to the sand and alkali.   But the effect of these other
 materials is chiefly to increase transparency, or to affect the co-
 lour, or to diminish expence.
    The siliceous matter and alkali must bear certain proportions
 to one  another, to make good glass.  If the alkali be deficient
 in the due quantity or goodness, the siliceous matter is not com-
 pletely dissolved, and the glass not sufficiently transparent.   If
 the alkali be redundant, the- glass is liable to be corroded, or to
 have its surface tarnished by clamp air.   By increasing  the al-
 kali to twice the weight of the siliceous  matter, we make a sort
 of glass  which dissolves completely in water.  Thus  is  pro-
 duced what is called the liquor silicum,  which coagulates into a
 jelly by exposition, or by the admixture of acid, or by volatile
 alkali (according to Neumann).   This is the chemical process
 by which we obtain the pure siliceous earth.
   Although glass turns out very faulty when it thus contains an
 over proportion of  alkali, it is however found necessarv,  in
 making  good  glass,  to  use  rather more alkali than what  is
 barely sufficient to melt the sand; and then, by a  continuance
 of the fire, to evaporate the superfluous quantity.  Thus we
 are more certain of perfect solution or fusion  of the  siliceous
 matter.
   It is also common to use a quantity of nitre in place of part
 of the fixed alkali,  in making the  finer kinds of glass, to con-
 sume the inflammable matter:  and borax likewise is frequently
 added,in  small experiments.   A mixture of these salts with  a
 very pure or chosen sand, or other siliceous matter, produces
 glass of uncommon brightness  and transparency, which  can be
 coloured  by the addition of  metallic substances; and gives
 those imitations of the gems  which in this country are  called
pastes.
   The author who has given the best account of the art of ma-
king glass of different kinds, especially the fine and coloured
glasses which are made in imitation of the gems, is Kunkel, in
an edition he gave of Ner'Cs art of making Glass. 
300          REAUMUR'S PORCELAIN.

   In the finer kinds of glass, therefore, the siliceous earth is
combined chiefly with a pure fixed alkali, and brought into a vi-
trified state by means of that salt; for when nitre is used, it is
changed into pure fixed alkali.  The calces of lead, as they were
named formerly, such as white-lead, and red-lead, are employed
in the manufacture of the English flint glass,  so remarkable
for its pure transparency, which fits it for being cut into  facets,
and other ornamental forms, and gives it remarkable brilliancy.
In mak*ing the coarser and cheaper kinds, as bottle glass, window
glass, and the like, they do not use a pure  alkali, but take the
ashes either of land vegetables, or kelp, or barilla, which are the
ashes of marine plants, with the salts they contain.   And these
ashes are mixed with sand, or other siliceous matter, to make
such kinds of glass.  In this case, the earthy part of the ashes,
which in part consists of alkaline earths, assists the  fixed alkali
in bringing the siliceous matter into fusion, and enters into the
composition of the glass. It is not nearly so powerful a solvent,
however, as the pure fixed alkali: and therefore we must employ,
in the composition of such glass, a smaller proportion of silice-
ous matter than when the glass is made with pure alkali.  And
it is also necessary to frit the materials before they are melted in
the pots in which the glass  is formed.   This is exposing the ma-
terials  in a furnace, generally adjoining to the working furnace,
and deriving its heat from  it.   This is a reverberatory,  where
the materials are spread out on its hearth, and kept roasting for
many hours, or even days, with a red heat.   This is necessary,
for two reasons : 1st, and chiefly, to consume completely all re-
mains of the inflammable matter of the ashes.  2dly, To expel
from the fixed alkali and ashes some part of their fixed air.
   The earthy part of the ashes of vegetables always contains
some iron, which gives a green colour to such glass.  I  must
observe, that the coarsest kind of glass, on account of the large
quantity of earthy matter which it contains ;  and the penury  of
salt, is fitted for giving  what is  called Reaumur's porcelain  of
glass.   This is a curious change produced on those hard glasses,
by long exposition to a red heat in contact with sand, gypsum,
and other substances.  The glass  gradually aiquires  a^rystal-
line structure, formed in fibres  which are  perpendicWJF  to ihf
 
     CRYSTALLIZATION OF  COARSE  GLASS.   301

external surface.   The  longer the piece is continued in that si-
tuation, this singular arrangement  penetrates deeper, till the
growdi from each surface meets in the middle of the thickness.
After this,  if much longer continued, the fibrous structure be-
comes somewhat granular, and the grains  in the middle become
large and  detached,  and sometimes the piece separates in the
middle of its thickness.  When this change is completed, and
no more than completed, the glass  has greatly changed its na-
ture with  regard to the effects of heat.   It is now infusible by
the heat of a glass-house furnace,  and will bear to be plunged
into water when  red hot.  It is also extremely hard, and can-
not be scratched by the hardest file.   Mr. Reaumur discovered
this by accident; and recommends this preparation for retorts,
mortars, and other chemical vessels, where these qualities are of
importance.
   It is a curious circumstance in  glass,  especially the coarser
kinds, that  when allowed to cool very slowly in great masses,
it takes a crystalline opaque form.   When broken, it would be
taken for a natural fossil. The structure is fibrous : and tl^Ebres
all converge to centres ; but are commonly interrupted f^^thers
converging  to  other centres.  The whole  is extremely like,
and may be mistaken, even by a fossilist, for a zeolite.  Some-
times we find,  in large  lumps of green glass,  little round balls
like pin heads, or pease, of the same dirty white colour. These,
when examined by a microscope, are found to be crystallizations
of the same kind,—the fibres all standing inwards, perpendicu-
lar to the spherical surface. Now, looking at the confused crys-
tallization of the great masses just now mentioned, we see that
they affect the same arrangement: and we can  trace the circum-
ference of each sphere, of which  these radiated crystals are a
portion. .  By the way, this appearance puts  an end to the doc-
trine of those who ascribe all crystallization to watery solution.
Here wre see it produced altogether by heat.   Indeed we know
that many metals, and sulphur, always crystallize in cooling, and
will congeal in no other way.
   After this digression on die nature and manufacture of glass,
which its importance will sufficiently justify, it is proper to con-
sider a little more the union  of the alkali  and  siliceous earths. 
302        PECULIARITIES OF QUARTZ.
I observed that they not only united by melting, but even by
boiling the earth in a watery solution.  When the liquor silicum
is mixed with an acid, the earth is precipitated  in an impalpable
powder,  which will be completely redissolved  by adding more
acid, and again precipitated by adding more  alkali ; and th's
may be repeated as often as we  please.  But th' re are differ-
ences in this  respect which are remarkable.  The  Ch«.valier
Dolomieu observed, that when quartz was precipitated in this
way, it would not be redissolved by acid, if kept in the state
of a precipitate even for a few hours.  This,  with some other
peculiarities  of the quartz, attracted  his  attention.   Quartz
emits a very peculiar smell when  rubbed or  struck by another
bit of quartz, and emits much light.   If the dust struck off be
examined* with a microscope, particles of it are found scorified,
and  spungy.   Quartz froths when  melted on charcoal.  He
therefore  suspected that it contained elastic  and  imflammable
matter.
  Hgjnixed 10 drachms of quartz  with a solution of caustic
alkali^^i retort, joined to a pneumatic apparatus.  By gradu-
ally  raising the heat to the greatest  intensity that his retort
would bear, he expelled from it,  1st, 22 inches of azotic gas ;
2d,  12 inches of hydrogenous gas ; 3d, 22  inches of airs, of
which 16 were carbonic acid, and the rest  a  mixture of azotic
and hydrogenous gas.   The residuum was, in some cases, a
spongy glass,  and  in others solid and green coloured.
  He thinks that quartz, when dissolved in acids, has  quitted
the azote and hydrogen ; and when precipitated  by alkali, h?s
regained it  by decomposing the  water.   When deprived of
these airs, it has an attraction for acids; but  loses it v. hen re-
united to the azote and hydrogen and carbone; as lime has its at-
tractions diminished by its  union with fixed air.
  Dolomieu  subjoins to these experiments  several ingenious
observations on the siliceous earths,  and substances which con-
tain them, particularly the gems.   Although  he advances  some
opinions which seem to me  very unwarranted  %>y  experiment,
his  observations are  curious and interesting.   You will  find
an abstract  of his dissertation in the Journal  de Physique,
Mav 1772. 
(  303  )
GENUS V.
FUSIBLE STONES.
  1 HE ingenuity and industry of the modern chemists and na-
 tural historians,  particularly of Margraaf,  Woulfe, Bergmann,
 Scheele,  Kirwan, and others,  have discovered that the natural
 earthy or stony substances which I comprehend under the titles
 of Fusible and Flexible, do not contain any simple elemen-
 tary earth that is different from those six we have already  de-
 scribed.  •
   The fusible and flexible stones are all compounded of two or
 more of these six earths, intimately united  and incorporated to-
 gether.
   You will find in Bergmann's Opuscula, and in Mr. Kirwan's
 Mineralogy, an account of  the processes by which earths  and
 stones may be analysed, and the simple  earths of which they
 are composed,  separated exactly from one another.   We can-
 not describe these processes here.   They are too complicated
 and tedious to be a  fit  subject for a lecture.  A person who
 would make himself master of them must study them at home,
 and at leisure.
   Professor Bergmann, in his  Outlines of Mineralogy, and Mr.
 Kirwan, in his valuable work on the same subject, have formed
 their arrangement of the earthy and stony substances, and their
 distinctions  of |hem, from the  prevalence of the simple earths
most abundant in the composition of each.   And for this rea-
son they have no divisions or classes which correspond to these
two last of mine. 
304      VARIETIES OF FUSIBLE STONES.

  Their method, however, assembles together things  so very
unlike to one another in every other respect, that I have not
chosen to follow it.  The greater part of the gems, for exam-
ple, the ruby,  emerald, topaz,  and others, are put  into the
same class with the clays, on account of their having  more of
the argillaceous than of any other simple earth in their compo-
sition.
  But a person.who wishes  to  have some knowledge of the
riches and variety of nature  in this  part of her wouks,  ought
surely not to confine his attention too  much to that point. There
are many other differential qualities  of her productions, which
are more easily perceived, and more striking ; and therefore
more proper to be attended to in distinguishing  and arranging
them, and in giving general views of. them.  And this is the
reason that has induced me to prefer the method I follow in giv-
ing a general account of the earthy and  stony bodies.  And I
must premise that there is scarcely any method for these stones
that is not very imperfect.  This results from their compound
nature.   Accordingly,  it is extremely difficult to class a speci-
men that comes in our  way by means of the descriptions  given
by the fossiiists.  Nor are they agreed in  their denominations.
What one calls a granite, another calls a porphyry :  and a third
calls it a trap.
  The natural stones which I think it is  proper to assemble un-
der the  title oi fusible,  are of six kinds :
  1. Feldt spat, or felt spar.
  2. Porphyry.
  3. The garnat.
  4. The stony matter  called schoerl or scherle by the Germans
and natural historians,  and cockle, by the English miners.
  5. The zeolite.
  6. The lavas, basaltes, pumice, and  other, fusible matters,
which have evidently been thrown out of the bowels of the earth
by volcanic fires and  explosions ; or which appear to have been
formed and  accumulated by them under the  surface.
  The first of the fusible stones, therefore, is ^frc Feldt Spar,
the appearance and qualities  of which are these : 
                       FELDT SPAR.                  305

   It is a stone generally less transparent than quartz: some kinds
 are as white or free from colour.   More commonly, however, it
 has a reddish tint or flesh colour. In hardness, it is nearly equal
 to the hard stones, and therefore strikes fire with steel.  When
 it is broken we can always perceive by the reflection of the light
 from its surface, that it has a plated structure, and it has a dis-
 position to be broken into rhombic  fragments.  These two qua-
 lities are never found in quartz.
   Feldt Spars are,
   lmo, The most common,.of a reddish colour.
   2do, The white.
   3tio, The crystallized.
   4to, Crystallized and transparent,—adularia.
   When feldt spar is exposed  to the action of heat, it first be-
 comes more brittle and pulverable.  And afterwards, if the heat be
 increased to a violent degree, it melts into a viscid glass, which
 is white and semi-transparent; on account of which projxrtv, and
 some others,  it is excellently fitted to be  an ingredient in the
 composition  of porcelain.
   It  has been analysed by Mr. Woulfe,  Professor Bergmann
 and others: and the definition given of it by Bergmann, in con-
 sequence of this analysis, is,
   " Siliceous earth  united with argillaceous earth, and a small
 quantity  of magnesia and sometimes barytes." The proportions
 have  been found  very different in different feldt spars, or in the
 different  analyses that have been made  of them, of which you
 will find  a comparison in Mr. Kirwan's Miner dogy.  From the
 whole  he concludes,  that any compound of silica and  alumina,
 in which the silica predominates, and'to which a smaller pro-
 portion of lime and magnesia, or of lime, magnesia, and barytes
accedes, so as  form a compound, fusible in a strong  heat, may
constitute a feldt spar.  The magnesia and alumina may be ex-
actly separated from one another by dissolv ing them in the mu-
riatic  acid, and precipitating by carbonat  of  ammonia.   The
whole of the aluiaina is precipitated, and the magnesia remains
dissolved in the ilbrm of an acidulous carbonat.
VOL. II.
<*■<! 
306           FELDT SPAR—PORPHYRY.

  Feldt  spar abounds in the composition of the rock or stone
called granite, and is the  distinguishing ingredient in that stone.
Granite has its name from being composed of angular grains of
various sizes, in the different varieties of this stone ; the greatest
number of which grains are feldt spar ; the rest quartz and mica,
which we shall soon describe.
  The granites form some  of the  highest and most extensive
chains of mountains  in many parts of the globe, being in general •
very durable stones, though some of them are not so remarkable
for durability.   And, as we never find any relics of marine pro-
ductions in them, they are considered by many as original or pri-
meval  stones, and their  formation  as long prior to that of any
stratified matter.  But  my friend Dr.  Hutton, having  visited
some parts of this country where granite is found, and examined
with attention those places where the granite was bounded by
the stratified matter,  or  came in contact with it,  he found the    <
stratified matter, which was of the hardest  and most  durable   i
kind, split and broke in  those places in  a remarkable manner,   ■
and the  granite constituting or forming veins in  it; that is to
say, that tffe granite  had penetrated into the fissures and rents of  M
the stratified matter, and had filled them up  completely:  shew-  ■
ing therefore that the stratified matter had, in this case, existed  ■
first, and that the granite was applied to it with violence and in
a fluid state.  Some  of  the hardest granites  that are known are
rendered extremely  friable  by a very moderate heat, even that
of a small bundle of straw burning in contact with  them.
   Feldt spar, besides entering thus largely into the composition
of granite, occurs also sometimes by itself in veins.
   The second species of fusible stone is Porphyry.   It is of
various colours, of which a  dirty brownish  green is the most
common.   It is#also of a deep red, black, and rusty brown, and
sometimes  of a dark grey.  All of them have spots; and the
ground is compact,  and breaks with somewhat less lustre than
marble, but mor-e than flint.  The spots in it are feldt spar. Its
hardness is greater than that of marbles, but inferior to that of
hard stones: and it is easily fusible.
   It forms large masses and rocks in the places in which it is   ' 
GARNAT—SCHOERL.
307
found; and some kinds of it have beauty, by their colour and
capability of polish:  but  these are rare.   The Upper Egypt
alone supplied Rome  with fine porphyries.
   The third kind of fusible stony matter, the Garnat, is very
commonly crystallized  into roundish polyhedral masses  of a
small size; and is generally of a deep red colour, and transpa-
rent.   In some of these stones,  the deep  red colour is accom-
panied by great transparency and brightness: though in the
greatest number it is obscured, by innumerable flaws and cracks,
or the admixture of other  earthy matter.   By chemical analysis
a considerable quantity of iron can be extracted from the deep?
coloured garnats: and to this metal the colour is imputed.  But
some specimens of this stone contain little or no iron; and  such
have very little of the  red colour.
   It is found, and appears to have, been formed, in stones that
abound with mica or with  feldt spar.  It has its name, granatus,
from its resemblance to the pulpy seeds of the granate apple, or
granate fruit.
   The fourth of the fusible stony substances is named Schoerl ;
and is found  in many  compounded or mixed stones which
never are of the stratified  kind, but are  some of the species of
what I call rock.
   The schoerl  appears on these stones in the form of separate
grains or masses, always  crystallized into extended  columnar
forms, or into  fibrous or plated  masses.   Sometimes it forms
groups of straight fibrous crystals, like the brisdes of a brush, or
even more slender than fine haii«; and in some cases is found in
this form traversing transparent crystals.   Another singular form
is the cross stone,  consisting of two of these crystals crossing
each other, not  as adhering, but crossing through the centre,
some perpendicularly, and others in an angle of 60 degrees.  A
fine specimen was seen -in  this country in  crystals, which were
hexagonal prisms, some of them almost an inch in diameter, and
some inches long.  They were deeply indented  transversely, as
if  made up of plates not all of one size.  Examining some fine
hair-like  crystals in my possession with a microscope, I found 
308             SCHOERL—ZEOLITE.

them of the same structure.   It is often black and opaque:  and
some of these varieties are named hornblend.
  Many kinds of it, however, are transparent,  and have even
the brightness of gems, with a green colour more or less deep.
The  colour and opacity in this stone  always proceed from more
or less of iron. The most remarkable of the schoerls is the tour-
malin,—remarkable for its primitive and permanent electrici-
ty and electric polarity, perfectly analogous to magnetism.
  All schoerls melt without difficulty in a strong fire, and form
a black or dark-coloured vitrified mass.
  The fifth kind of fusible stone-in the enumeration I gave, was
the Zeolite.   It was first distinguished and characterised by
Cronstedt.   It occurs in general in the form of small masses
involved in rocky stones, or forming  veins in such stones. That
part of the rock of Arthur's Seat, which shews a  tendency to
the form of six-sided columns, or prisms, contains small veins of
zeolite harder than common.
   The zeolite is always crystallized, or shews some regular ex-
ternal form or internal arrangement of its matter. Some of these
forms are the most wonderful and beautiful of all that have been
observed in the  mineral kingdom.   Some are hollow, and are
formed within into transparent or whitish crystals; sometimes
slender and long, like fine bristles, in diverging bunches.  And
sometimes even these bristly crystals  of the zeolite pervade chal-
cedony : and sometimes small siliceous crystals like grains of
corn are involved in them.
   The chemical qualities of the zeolite are,  to melt in the fire,
or by the heat of the blow-pipe, with remarkable facility.  And
most kinds of it swell at  first  into a  spongy mass like froth, or
sometimes as borax does in its watery fusion.  It  is from  this
circumstance that it acquires its name.  Indeed, they contain a
considerable  quantity  of water  in their composition;  but that
cannot be the cause of this fusion. But after this, by increasing
the heat, the zeolite contracts again, and melts more perfectly,
either into a  clear and bright glass;  or some kinds of it, which
are more difficultly melted, form only a white opaque glass, or
white enamel.
  When diluted nitric acid is applied to the zeolite, this stone 
            ZEOLITE—LAVA—PUMICE.         309

is dissolved into a clear liquor, which after some time becomes
a jelly.
  These chemical properties of it were discovered by Mr. Cron-
stedt.   But my friend Dr. Hutton proceeded farther in this ex-
periment ;  and by examining the solution, and the gelatinous
matter formed in it,  he discovered that the zeolite is a com-
pounded substance,  and  contains  a fixed alkali combined with
siliceous and with argillaceous  earth.   The proportion  of the
alkali to these earths is different in the several varieties of this
stone :  and this is the reason of the different degrees of  fusibi-
lity which  we find in them.  They all contain a great quantity of
water.
  The last kind of fusible earthy and stony substances are those
which are thrown out, or formed,  by volcanic fires.  Of these
there is a considerable variety.   We find among them what are
called Lavas and Pumice, and what are called Ashes.
  The lavas are very various.   Some  parts of them  are black
and perfectly vitrified, resembling the darkest and coarsest kind
of glass.   Generally, however, they are a mixture of earthy sub-
stances, which have not been brought to a state- of perfect fluidi-
ty.    Some of the materials only, were fluid when they came out
of the volcano ; and the whole had the consistence of thin mor-
tar,  or  sometimes has been more fluid.  When it  cools, it has
not an uniform or glassy texture, but is composed of particles
and fragments of many different  kinds, cemented together by
the matter which was melted.
   The  fluidity of lava appears  to me  to depend on latent heat,
combined  with the materials by the long-continued action of sub-
terranean  fire.  While they are still flowing, their heat is not
very intense.  (Dolomieu Journ. de Phys. 1793).  Yet they re-
tain part of this heat a long time,  with some degree of fluidity
or softness.   A lava, erupted in 1614, continued to move for ten
years, and in that time slipped downwards about two miles.  It
was probably soft below : and as it lay  on a slope, the indurated
 mass above could slide a little way.*

  * The spongy texture of the indurated matter must greatly retard  the
emersion of  the latent heat, and consequently the congelation below.
                                                    Editor. 
 310   BASALTES—TRAP—WHINSTONE, &c.

  Most natural historians are now of opinion that the rocky
stone,  of-which there are many varieties in this country*under
the name of Whinstone, but in other places called Toadstone,
Ragstone, or Rowley-rag, and also Trap and Basaltes,
and by other  names, is of tbe same nature with lava,  and be-
longs to this  division of volcanic matter,—a matter which has
been melted by subterranean fire.  Dr. Hutton, however, makes
a distinction between many, or most of these stones or lavas.
He considers the term lava to bte properly applicable to that melt-
ed matter only which has been thrown  out  by volcanoes, so as
to flow down their sides, or along the, surface of the earth.  But
there cannot  be a doubt, that the same fires must produce, at a
great depth,  large quantities  of  melted matter, which  is never
thrown out, but continues melted a long time, and is driven by
the immense force of the explosive matter in  lateral directions,
forcing its  way between the strata which are around, or penetrat-
ing into the rents and fissures of these; and thus forming what
we call dykes,  or in other cases, flat  and extended masses of
unequal thickness, such as Salisbury Rock, and many others that
are around it, and the toadstone  of Derbyshire*.
  Whinstone is called basaltes, when it is split into columns or
prisms, most of them six sided, and standing in close contact
together, generally upright,  though sometimes inclined to  the
horizon, and even bent.
  There are  famous examples of this in the Giants' Causeway
in Ireland,  and in the island of Staffa, and other islands and rocks
on the west coast of Scotland. And there is a tendency to it on
the south-east side of Arthur's Seat here, beside many exam-
ples on the continent.
  This columnar appearance  seems to arise from a  kind of
shrinking,  as the heat which gave it  the imperfect fluidity gra-
dually abates.  I was informed by a gentleman who visited Ice-
land not long after the late eruption of  Hecla, that the inhabi-
tants shewed him extensive masses of lava of former eruptions,
which  were not thus shivered, when  they had cooled so much

  * A dyke of this kind pervades the coal strata in Newcastle Moor: and it
has charred the coal on each side of h to the distance of several yards.
                                                  Editor. 
            WHINSTONE—BASALTES, &c.         31!

that they could be approached, but that year after year, the re-
gular columnar  divisions appeared, more evident,  and at the
time the gentleman saw them, they were very distinct basaltes.
We observe an appearance very similar to this in common starch,
which always separates by shrinking into pentagonal and hexa-
gonal columns.
  The opinion that this  stone, and whinstone in general, has
been formed from melted subterraneous matter, is founded  on
the similarity of its appearance to that of many lavas : and there
is a similarity too  in  their constituent  ingredients.  And fur-
ther, the lavas of some well known and now-existing volcanoes,
have been  found in some parts  of  them formed into these pilj
lars; as the Chevalier Dolomieu observed in the lavas of ./Etna.
   In basaltes and whinstone we  commonly perceive many par-
ticles which have a plated structure or extended prismatic figure,
more or less  resembling schoerl.   The colour of  the stone is
commonly grey or black, or dark red;  but sometimes, though
rarely,  light grey,  or whitish.
   There is a considerable variety of the stones or rocks which
belong  to  this species, or may be included in it; and  most of
them are not  formed into columns, but  are in general split into
oblong  angular masses, which are often upright, as in Salisbury
Rock;  but in some cases  inclined to the horizon.   Some ap-
proach  very nearly in nature to granite;  others as nearly to por-
phyry.   The rock of the Calton Hill is a stone of this  kind,
which has the nature of porphyry in some parts of it. The rock
of the Bass approaches to granite.
   They often contain nodules, or small masses of stony matter,
different from that of the rock itself.   These small masses are
either siliceous, or calcareous;  or  barytic, or zeolite, or a col-
lection of some of these stony bodies in the same mass.  The
greater number of agates, and especially the small ones, called
Scotch pebbles, are small siliceous masses, which have  been
formed in rocks of this kind; and are  found in the gravel and
rubbish produced  from the decay of these rocks.
   The toadstone, of Derbyshire, is a whinstone containing no-
dules of calcareous matter.
   It is always in these whinstone rocks too, and particularly the
basaltic kind, that  zeolite is found, either in nodules or in veins. 
312      PUMICE—TUFA—PUZZOLANA.

  Anciently, whinstone and other  fusible stones appear to have
been employed, in this country, to construct walls or ramparts
round little camps, or strong posts, into which the inhabitants re-
tired when invaded by an enemy.  And they appear to have been
cemented by fire,—rthe external parts, on both sides of the wall
being melted into an imperfect slag.  There are  ruins of such
works in different parts of Scotland ;  the construction of  which
must have been long prior to any tradition that now remains, or
to the use of lime.   A description of some of them has been
given in the Transactions of the Royal Society here, by my  col-
league, the  Professor of Civil History.
  Pumice is the next volcanic matter.  It has the appearance of
having undergone very perfect fusion.  The most  remarkable
quality of it is its sponginess.   It has nearly the contexture  and
appearance  which glass  would have, were it wrought up into a
froth while  it is cooling.  The Chevalier Dolomieu, in his ac-
count of the Lies Cyclopes, a cluster  of islands near Sicily, has
given the natural history of pumice.  And I have observed some
facts and phenomena, occurring in some of the arts, which may
suggest conjectures of the way  in which it is formed, viz. what
appears in slags of lead, and also slags of iron hastily cooled.
  The last volcanic matter, called Ashes, is a sort of gravel and
sandy dust, composed of vitrified  and  spongy particles of all
sizes ; and is undoubtedly a sort of rubbish, into which different
materials are changed, when softened by the heat and exposed
to the violent concussions and explosions which  happen  in the
bowels of the mountains, or during eruptions.   It is sometimes
thrown up to a very great height in the air; and is then carried
away by the winds, so as to fall, on  some occasions, at a great
distance from the volcano.
   When this matter is amassed in great quantity, and compress-
ed by incumbent weight, it concretes into  a spongy soft stone,
called tufa  by the Italians.  And other parts of it, which remain
in the state of a sort of gravel, are excellently adapted for form-
ing strong mortar with lime.   They  are brought from Italy for
that purpose, and are called puzzolana.  They are used for wa«
ter buildings. 
( 513  )
GENUS V.
FLEXIBLE  STONES.
  JL HE last section of the earthy bodies only now remains to be
described,—that of the Flexible  Stony Bodies.  They are
distinguished by being flexible, or easily divisible into parts
which have great flexibility.
   These  are  concretions which are in general so  soft as to be
easily scraped or cut with a knife ; and do not suffer any change
of their hardness or structure from the heat of a moderate fire :
but in a strong one many  of them are easily melted.
   Two of the  classes formed by Cronstedt,  his Micacea and
Asbestina, are comprehended in this section of flexible earths.
And  'it may  with propriety be  distinguished into three sub-
sections,  the  plated,  the  fibrous, and the membranous or cel-
lular  kinds.
   The first of these subdivisions, therefore,—the plated flexible
stony bodies,  contains  the micaceae of Cronstedt, or the taleky
fossils of  the  English naturalists; so called from  the principal
species long known by the name of mica or talc.
   It is  a  stone  which feels unctuous and slippery between the
fingers, and splits easily  with a knife, like  the foliaceous gyp-
sum,  into innumerable and  excessively  thin  leaves, not only
very flexible, but elastic;—employed for confining the objects
in microscopical observations.   It is easily distinguished from
the foliaceous gypsum  by its  elasticity, and by the effects of
heat.
      VOL. II.                         R r 
tU         TALC—MICA-^AMIANTHUS.

  This  stone  is generally  transparent in the thin plates, and
often colourless.   It is more commonly tinged,  and some-
times quite opaque.   The colour  is very  various,—dusky,
greenish, silvery, golden, and many other glittering appearances,
which often deceive those who are unacquainted with it. These
appearances do not proceed from metal, but from the disposi-
tion  of the  plates.
  Mica is  found very plentifully in the composition of some
kinds of rock, especially some of those which contain a large pro-
portion of the fusible earths;—in  granite especially, and in the
schistuses which contain garnets or granates.  -
  But it is mixed besides with some of the strata  which have
been formed from  the materials of demolished rocks,  as  sand,
and sand-stone, and gravel, and some clays.
  The largest specimens of transparent mica come from Russia,
where they have it in such plenty and perfection, that  in  some
parts of the country it is used for windows and lanterns.
  The flexibility of this fossil explains the flexibility of a stone
which was  exhibited here in 1791, and is now in the cabinet of
Lord Gardenstone.  It is  about half an inch thick, and more
than a  foot square.  It is  flexible to a moderate degree, but
without elasticity.   It is composed of small thin plates of mica,
all parallel  to one another,  and intermixed with thin disconti-
nuous plates of quartz.  The great number and smallness of the
plates, and  the presence of the quartz, prevent this stone  from
being elastic.
  The second division of the flexible  earths,—the fibrous,—
comprehends fossils which have  the same chemical qualities
with mica,  and differ from it chiefly in their structure, which is
fibrous instead of being plated.  There are many varieties of
these, diversified by the fineness and flexibility of the fibres, and
by the closeness or looseness of their connection.   Those reck-
oned the most curious and perfect, called amianthus,*may be
teased into a  matter  like cotton,  which, being  milted  with a
small quantity of flax, may be spun  into yarn^nd wove into a
cloth, which does not suffer  from  ordinary fire.  Trie only use
that has been  made  of this fibrous stone, is one for which mo-
dern customs do not find room.  The ancients made a sort of 
        ASBESTOS—SUBER MONTANUM, &c.   31*

cloth of it, on which they laid dead bodies on the funeral pile,
to preserve the ashes of the body by themselves, and unmixed
with those of the fuel.  Some have attempted to form it into
paper; but it makes very bad paper.
  The other  fossils which belong to this subdivision, are formed
into membranes like leather, or elastic spongy masses like flesh
or cork.  These  are named mountain-leather,  mountain-fleshy
and mountain-cork, by the miners.
  All these fibrous or  membranous flexible stones are found in
veins, or cavities of veins: and all contain the  silica in largest
quantity, but  intimately combined with magnesia, alumina, lime,
and a small  portion of iron.   You  will find the  proportions
stated in  Mr.  Kirwan's  Mineralogy, and in Professor  Berg-
mann's Essays.
  Magnesia  is always a constituent part of the flexible stones,
and is generally their most abundant ingredient after the silica. 
C  316  )
APPENDIX.
PRECIOUS  STONES.
XTL ND now, gentlemen, I have taken some notice of the dif-
ferent kinds of earthy and stony bodies that appear to be most
remarkably distinguished from one another*  Among all these,
however, I have  as yet made no  mention of  the Precious
Stones, which may perhaps be thought a material omission.
  The reason is, that this  title does  not assemble together a
set of stones  that are similar to one another by their nature or
chemical qualities.  It is a general name given to all stones re-
markable for more or less  transparency and brightness, or for
some colour, or mixture of colours, or smoothness of surface,
which has pleased the  taste of mankind.   And the stones, in
which these qualities are found, happen to be very different with
respect to their nature  and to the materials of which they are
composed.   I shall here give a short enumeration of them.
  I shall begin by making a division of them into Stones and
Gems.   Under the first title I comprehend those produced by
nature in large masses, or in considerable quantity.  Under the
second,  those which occur of small sizes only, and much more
rarely, on which account they are far more cosltly than the others.
  To the first division belong,              •
  1. Marbles.
  2. Serpentines. 
MARBLES.
.317
    S. Alabasters.
    4. Some Porphyries.
    5. Some Granites.
    6. The English Pudding-stone.
    7. Some Spars.
    8. Some Jaspers.
    9. Some of the siliceous petrifactions of wood.
   10. Some kinds of the Lapis Nephriticus.


                       1.  Of Marbles.


   The marbles are all limestones,  or are  composed of calca-
reous matter; and are different from the mere common lime-
stone only by agreeable colours,  or  mixtures of colours, and a
more perfect compactness and greater hardness, which fits them
for being more highly polished.
   Many marbles appear to have been formed from small frag-
ments of shells, ground  down by  agitation and attrition into
sand, which has afterwards been cemented by some natural ope-
ration.  In many others we see distinctly  the  relics  of the
shells or lithophyta entire,  or in large fragments.   Marbles, in
which shells are seen in this manner, are named by the Italians
Limacelli.
   When marbles are  clouded or spotted with different colours,
this is produced^ either,
   lmo,  By these relics of  shells and corals appearing in them ;
or more generally,
   2do, By an unequal and irregular  intermixture of iron, or in-
flammable matter through the stone, so as to form streaks and
spots which please the eye, by the contrast of their colours, and
the variety of their shades  and distribution ; or,
   3tio, The variety of colour* in some marbles have been form-
ed by an operation they have undergone.  We can plainly per-
ceive that the sjone has been fractured into a number of pieces,
which have been set afloat in a liquid marble paste of a different
colour, and are now cemented together by it.
   Such marbles are named Breccia by the Italians. 
318 SERPENTINES—ALABASTERS—PORPHYRIES.

  All  these have more  or less beauty.   But  we may reckon
among the most valued marbles, the pure white  statuary,  and
the perfect black.  Such must naturally be rare.  It cannot of-
ten happen that a block, of size sufficient for a statue or a groupe,
is entirely free from spots or clouds,  or streaks  of a different
colour or tint.
                     2. Of Serpentines.


  The most obvious distinction of serpentines from marbles is
by their colour, in which a deep and dusky green prevails:  and
this is a colour, but very rare in marbles.   As to the nature of
serpentines, some are partly calcareous; but all contain mag-
nesia and  iron.  A species  of porphyry is improperly called
serpentine.


                    3. Of the Alabasters.


  This name is applied by the lapidaries to white  stones  that
are softer than marbles, but capable  of being  well  polished.
They are generally composed of the natural sulphat of lime.
But often calcareous stalactites and spars are also named alabas-
ters by the stone-cutters.


                   4. Of the Porphyries.


  Of the porphyries there are only a few species, reckoned pre-
cious or beautiful. One is dark green,  with light green or white
spots.   Another  is dark- red or (purplish, with  whitish spots.
And  there are some,  the ground of which is almost black.
They are harder than the marbles, but softer than the hard stones.
I rank the porphyries  among the fusible stones,  to  which divi-
sion they certainly belong by their properties and constituent in-
gredients.   And many;of our whinstones, and  many lavas in
the volcanic countries, are coarse porphyries. 
GRANITES—PUDDING-STONES—SPARS.  31#
                       5. Of Granites.


   Som« of the granites are also considered as stones of value.
 The nature of this stone was formerly described.   The  only
 certain species of k reckoned  valuable are the Egyptian, the
 Russian, and the Scotch.


                    6. Of Pudding-Stone.


   Many pieces of the pudding-stone or gravel-stone found in
•England are also reckoned beautiful and precious.


                        7. Of Spars.


   The spars reckoned precious or beautiful are some few cal-
 careous spars, but chiefly fluors and lapis  Lazuli.  Fluors, ad-
 mired  for their beauty, are found plentifully in Derbyshire.
 Labrador-stone is a feldt spar, or is nearly allied to it by its consti-
 tuent parts.   It derives its beauty from a  certain disposition of
 its transparent elements, which, like those of pearl and mother
 of pearl, exhibit different lights as they are viewed in different
 directions.   It frequently appears as  if the surface was undu-
 lated, although it be perfectly flat.  The opal has its  beauty
 from the same, cause.   We see appearances of the  same  kind
 in some woods, such as mahogany,  satin-wood, &c. and in these
 the microscope discovers the circumstance on which it depends.
 We even see a little of it in some slates.  .When examined in
 their natural plates, they are really undulated: but wheh the sur-
 face is made flat and polished, the undulated appearance' is not
 entirely removed. 
320 JASPERS—PETRIFIED WOOD—LAP. NEPHRIT.


                      8.  Of Jaspers.

  The name of jasper is sometimes applied to some marbles,
but improperly.  When used with propriety, it means hard
stones, opaque and agreeably coloured by  admixture of other
matter with the siliceous, especially iron.   The most noted jas-
pers that are beautiful are Sicilian, yellow, red, and white; green
jasper spotted red; Heliotropium.


            9. Of Siliceous Petrifactions of Wood.


  Some of the siliceous petrifactions of wood, when  they hap-
pen to have the density of agate or Jasper, and  are  agreeably
coloured, are also wrought by the lapidaries, as precious stones;
and snuff boxes or other toys are made of them.


                10. Of the Lapis Nephriticus.


  Lastly, some kinds of the lapis nephriticus are in request,
on account of their agreeable colour, and the  polish or smooth
surface that can be given to them.   The  Turks,  in particular,
are  fond of this stone to make the handles of their scimitars.
  Having now said enough of  the  first section  of precious
stones, those,  to wit,  produced.by nature in large masses, we
proceed to the second; in which I include the gems, or  those
produced in smaller masses, and  more rarely.
  The title of Gem was applied not long ago to a much greater
number of stones than it is by late authors.  I shall follow the
old method, according to which  the stones called  Gems  were
divided into Semi-Pellucid and Pellucid Gems. 
       AGATE—CARNELIAN—CHALCEDONY.  321


                    1.  Semi-Pellucid Gems.


   The greater number of these belong to the order of hard sto-
 ny substances, and are  chiefly composed of the siliceous earth.
   They are, in general, formed into small masses in some kinds
 of rock,  or fill up small veins in it: or they are found among
 the gravel and earth into which such rocks are resolved,  by the
 influence of time and the weather.
   The siliceous matter, of which they are principally composed,
 has generally some degree ofi transparency.  But this transpa-
 rency is diminished, and in some cases a great degree of opaci-
 ty induced, by the admixture of other matter. Often this diver-
 sity of materials is so disposed as to produce clouds, or spots, or
 streaks of different colour and appearance,  which add  to the
 beauty of these stones.
   Among  the most  notable kinds  of these stones, we may
 reckon,
   1 mo, Agates.—Great numbers  of them are  found in some
 parts of this country, [Scotland]  of a  small size, but some of
 them very pretty when polished,—called Scotch Pebbles.  I have
 already pointed out the origin of them.  The internal arrange-
 ment of their matter is remarkable, and will be explained by Dr.
 Hutton, in a  work he  is now publishing on the formation of
 stones.
   2do, Chalcedony, of the colour of the whey of milk.   It is
 much esteemed by seal-cutters, for a kind of toughnesjs, as they
 term it,  which makes it work without tearing up by their pow-
 ders.  This must arise from its having no grain or symmetrical
 arrangement of  parts.
   3tio, Carnelian, also valued hy seal-cutters, as being very ea-
 sily worked.  The natural formation of carnelian is one of the
 most curious objects that mineralogy presents to our eye. It has
 certainly been fluid as chalcedony; and the fluidity has been im-
 perfect or clammy, and has been a very slow exudation from the
rock or matrix to which it adheres.  It is found hanging in tears
from the sides of the cavities : and these appear to have harden-
 vol. n.                              s s 
322     ONYX^-MOCOE—OPAL—TURCOISE.

ed superficially as it sweated out;  so that  the long string is all
mcrusted with little excrescences,  which have been,  in succes-
sion, the end of the drop.   These  icicles often dip into a mass
of chalcedony, whose  surface is perfectly smooth and flat, as if
it had been fluid in a dish, and the  icicles can be traced through
it, (it being in a  small degree transparent) to the  bottom,  with-
out mixing with this mass.  The curious, and not inelegant form
of the  exudation, may be precisely imitated, by putting a lump
of hard pitch on a shelf,  in warm  weather.  It will soften and
drop down from the shelf in  strings, which  are figured  in the
very ssame manner.
   4to,  Onyx, fit  for cameos, by reason of its  strongly contracted
coats.  Sardonyx is either a mixture of chalcedony and carnelian,
or is a chalcedony spotted with small red points.
  5to,  Mocoe, finely  diversified by tree-like figures,  elegantly
ramified.  .
   6to,  Opal, of  varying colours like mother of pearl.
   7mo, Turcoise.


                      2. Pellucid Gems.


  Most of these  also belong to the  order of the hard stony sub-
stances : and some of them are the hardest substances produced
by nature.  A iew belong to the fusible class. They are always
found in very small masses, crystallized  into regular figures,
more or less peculiar to each kind ;  and when they are reckoned
gems,  have extraordinary transparency and  brightness.  They
appear to be originally formed by nature in some kinds of rock,
or in the veins of rock, and some  are actually cut out of such
veins.   But most of them are picked up from among gravel or
earth formed by  the decay of suqh rocks which contain them.
  The more common kinds of them, which bear but  a mode-
rate price, are siliceous crystals, composed of the siliceous earth,
with very litde admixture-of  any other.
  But  those which have  the  greatest hardness and brilliancy,
and which are named by the jewellers true or oriental gems,
have been found less simple in their composition.  A number of 
PELLUCID  GEMS.
323
 -accurate analyses of them, by Achard of Berlin, Professor Berg-
 mann, Mr. Kirwan, and others, have shewii that they contain the
 argillaceous earth in greatest quantity, intimately combined with
 a smaller proportion of the siliceous, and a still smaller of the
 calcareous, and of iron, to  which metal they owe their beautiful
 colours.  And it is only these transparent stones, which contain
 more of the argillaceous than of any other earth, which are  dis-
 tinguished by the title of gems by Professor Bergmann.  I see
 no reason however for restricting the title so much.
   We may here remark, that those gems which contain a larger
 proportion of the argillaceous than of the siliceous earth, have
 not the same chemical qualities as the other hard stones in which
 the siliceous earth prevails ahove all others.  They not only re-
 sist the most violent heat without melting, when exposed to it
 without addition, buttit is extremely difficult to melt them by
 means of alkaline salts, which easily dissolve the siliceous crys-
 tals  into a glass.   You may see, in  Bergmann's Opuscula, the
 Other particulars by which they differ from the siliceous crystals.
 Some of the siliceous crystals are tinged, as well  as those rec-
 koned true  gems,  with blue, or purple,  or yellow,  or other co-
 lours.   But these are much rarer than the colourless crystal;
 and, when they have brightness they pass for gems : though, on
 account of their inferior hardness^they are not so highly valued,
 nor indeed have they so much brilliancy.
  There are also siliceous crystals which have a dusky or brown
 colour, and yet have  great transparency and brightness.  Such
 are those found in.the mountains of  Arran,  and some other
 mountains of this country.   And some of these brown crystals,
 by being heated equally and cautiously, to a degree that is short
of ignition, lose the  brown colour,  and retain  a  yellow one,
 which  may be lost also if the stone be heated too much. I knew
 a person who made profit by collecting these brown  crystals, and
converting them  into  yellow ones.  These convertible brown
crystals are found in some mountains to the north-west of Aber-
 deen.                          "    N
  The pellucid gems may therefore be thus enumerated:
  Imo, Siliceous Crystals, colourless or coloured. 
324
PELLUCID  GEMS.
  2do, The Emerald, of a bright green colour, of which there
are many varieties.   It is much allied to schoerl: and some of
the pale emeralds, named aqua marines, are true schoerls.
  3tio, The Tourmalin, though it  be  not a beautiful stone,
being of a very dusky green, is however at present reckoned a
gem.  Its remarkable property is to be electrified by gentle heat
alone, without being rubbed.  It is also a schoerl.
  4?o,-Garnats, that have transparency and  brightness, are
used as gems.  They have all of them  a rich red colour, but
differ very much in the deepness of this colour: when it is  v: ry
deep, the stone has less brightness. The very bright garnats, in
which the colour is  less intense are named scarlats.
   5to, The Amethyst, of a bright and beautiful purple.
   6to, The Sapphir, of a perfect and rich blue.
   7mo, The Topaz, of a beautiful and brilliant yellow.
   8vo, The Ruby, which has a red colour  of great richness and
brightness.                             ,
   9no, The Diamond the most valuable of all.  It is sometimes
slightly coloured, and even dusky and opaque: but the most co-
lourless and brilliant are the most highly valued.  The diamond
is remarkable for four particulars:
   1. It'is one of the rarest productions of nature.  We are not
certain that it is to  be found any where except in the peninsula
of India, and in the Brazils.  In both places it is always found
in detached solitary crystals, which are octaedral, or often  pris-
matic, terminated by a pyramid.  These have sometimes smal-
ler crystals as it were growing out of them. But we have never
met with the diamond in groups adhering to a shapeless base, as
is the case in all other crystals.  They have never been met with
in  the cavities of other stones: nor do we  know any kind of
rock or vein which may be said to be the-matrix of diamond.
All that have been hitherto seen, are found  in  loose gravelly
earth, at no very great depth.   This is  washed and picked for
the diamonds it  may chance to contain.  There are to  be met
with, in the cabinets of the curious, a very small number of dia-
monds terminated at bodvends with  pyramids. This is, indeed,
a very rare crystal of any kind.  From the circumstance of one 
I
         DIAMOND.
325
 end wanting a pyramid, we are entitled to suppose, that, like
 other crystals,  they have originally adhered to some matrix.
 But, as has been said, they have never  been met with, except
 among what may be called the rubbish of some former condition
 of things.  Several specimens have been found wholly or partly
 incrusted with an opaque whitish matter of great hardness, but
 yet  so soft as to have all its asperities rounded by the attrition
 which the pebble had received.   The jewellers callthis mother
 of diamond, and, I think, with some propriety: for in some that
 I have seen, the transition from diamond to this substance is not
 abrupt, but gradual, as in the case of the onyx.  It was in the
 course of this century that diamonds were discovered in Brazil:
 and their price is now greatly fallen.
   2.  Diamond is no less eminently distinguished by its extraor-
 dinary brilliancy and great  refractive and dispersive power,__
 far exceeding all other natural crystals.   Mr. Zeiher, a German
 artist, has approached very near to the brilliancy, and to the re-
 fractive and  dispersive power of the diamond, in some of his
 compositions for imitating precious stones.   But these fall  infi-
 nitely short of the diamond in its next remarkable property, viz.
   3.  Its superior hardness.    In  this it exceeds all  substances
 that are known.  It is therefore employed for sawing and boring
 the hardest stones,  and for  engraving seals.   For this purpose '
 it is reduced to powder.
   This powder is used in the same manner as sand, emery, or
 other cutting powders, are employed by the lapidaries, viz. by
 moistening it with empyreumatic oil, and applying  it to their
 wheel or drill; or  the metal point  used by the seal engravers,
 like a crayon.   The metal  employed for  this purpose is  the
 purest and softest  iron.  This takes  fast hold of the diamond
 powder,—it being  pressed  into  it by the force exerted in  the
 operation: and the little particle never  quits its place  to  roll
 about, but is carried along by the  tool, acting like the tooth of a
 file, and tearing up whatever it  touches.  There is  something
 curious in the way in which diamond acts in cutting common
glass.  The glazier's diamond is by no means sharp pointed.  I
have seen them as blunt, and round, and  smooth as the head of 
326                    DIAMOND.
a  large pin.  Yet this, with a moderate pressure,  causes the
plate to shiver under it wherever it is drawn.  This is by no
means a crack: but the glass  being made somewhat  weaker
there, splits immediately, when gently patted on the other side
with a hard body.
   4. The diamond  is still more distinguished from  the rest of
the gems by ks chemical properties, or the effects produced on
it  by heat and mixture with other bodies.  The utmost violence
of heat, even that of a burning mirror, does not induce the least
appearance of fusion.   Its asperities are not perceptibly round-
ed, as  has been observed in the ruby.  The only effect of simple
heat is, to dissipate certain foulnesses which sometimes  taint its
purity, or water,  as it is called by the jewellers.  But it makes
no change in its texture, if the diamond has been free from pre-
vious cracks or flaws.
   Nor doe's the  utmost violence of simple heat volatilize the
diamond.   If it be protected from the action of the  air, it suf-
fers no diminution  of its weight by the longest continuance in
the fire.   But if it be subjected to intense heat, and to a  current
of free air, it will be entirely dissipated, and this dissipation is
accompanied by the emission of a dazzling white light.  This
was long thought to be a phosphorescence, as in the case of ma-
ny other crystals  and spars:  and the dissipation was thought to
be an exfoliation  and dispersion, like the decrepitation of salts.
But if this v/ere the case,  the  dispersed dust might be found.
As this has never happened, chemists began to conclude  that the
emission of light was an inflammation, and that the diamond was
wasted by combustion like a piece of charcoal.   The great rari-
ty of diamonds, and the inability of most speculative chemist6
to afford the expence of the necessary trials, has retarded the de-
cision of this question.   But it is now past a doubt, that the dia-
mond is a pure inflammable substance. I shall therefore defer the
consideration of its combustion and its chemical relations, till I
come to the consideration of that class of inflammables in which
it  must be, placed. 
CORUNDUM.
327
               Of the Conine, or Corundum.

  After this notice of the gems, it may be proper to mention a
singular fossil, which, though not a gem, (for it is totally desti-
tute of beauty) is yet allied to some of the gems by its constitu-
ent parts, and by some of. its properties.  This is  the Corun-
dum, or, as it is  called by the British lapidaries, the adamantine
spar.  The first specimens of it came from China to Britain: and
it was afterwards found, that it was  to be had in India, not far
from Bombay ;  and our naturalists have  now found it in several
granites of France and Spain.  It is of a grey colour, like emery.
The entire pieces are opaque: but very thin  plates of it have
considerable transparency.  What comes from  China has very
evident hexagonal crystals: but all other specimens that I have
seen,  are  of an indeterminate granulated  structure.   What
comes from Bombay is more unlike to emery, and considerably
whiter than all others: and it is this which  is called corundum
by the natives.
  The remarkable quality of corundum, and for which it is
chiefly valued, is its extreme hardness.   It scratches every sub-
stance but diamond; and is therefore of great value to the lapi-
daries and seal engravers of this country, who employ it by the
name of adamantine spar. It is but a little harder than the ruby, the
sapphir, or the oriental topaz. It is far superior to emery,particu-
larly for grinding on the wheel, to which  it adheres like diamond
dust.   One  part of it does as much work as four of emery, and
does it in half the time.
  The corundum unites with caustic soda, but with great diffi-
culty.  When the liquor siiicum formed with it is decomposed
by acids, it is found to consist of one-third of a peculiar earth,
and two-thirds of clay.
  Many of the precious stones are imitated by art; the marbles,
and porphyries, and'jaspers, by means of pastes  composed of
lime and gypsum,  with other materials added to  increase the 
 328         FACTITIOUS GEMS—PASTES.

 hardness and smoothness, or to give the colours. The art of mak-
 ing these imitations has been carried to a great  degree of per-
 fection.   Large columns, pilasters, pannels, tables, mouldings,
 festoons, and other embellishments of  the inside of buildings,
 have been executed very like to the more beautiful and cosdy
 kinds of marble and porphyry.  And these imitations have  the
 advantage of being procured at very little expence compared
 with the originals.  But they are only fit for the inside of houses.
 The materials do not withstand the weather.
   The pellucid  gems  are imitated with glass, made  with great
 care and in small quantities for this purpose alone; the very
 purest materials being employed,  and  certain additions being
 made to improve the transparency and brightness of it, such as
 borax, and some of the metallic substances; some of which also
 give to the glass the different colours of the gems.   The most
 celebrated authors who have written on  this art, are Neri, Mer-
 ret, and Kunkel, whose works appeared  first in the German lan-
 guage,  but  have been collected together and  translated  into
 French,  with the title oi Art  de la Verrerie,^— the art of glass-
 making.
   These artificial gems, or pastes, as they are called, by our jew-
 ellers, are very  good imitations in some respects;  and repre-
 sent the  beauty  and brightness of the natural  productions very
 nearly:  but they cannot be compared with them in hardness and
 durability.
   Setting aside, however, the attempt to imitate  the  natural
 gems, we may venture to say that art has in some respects far
 excelled nature in the productions it  has  obtained  by working
 on the earthy substances.  We have. examples of  this in  the
 manufacture of the  common kinds of glass, and in that of porce-
 lain, and of the other beautiful and useful kinds of pottery.
   The common  kinds of glass must no doubt  be allowed to be
 far inferior in brightness, as well as in hardness and durability,
 to some of the transparent stony bodies produced by nature. But
the inferior hardness  of glass  is a great advantage in  some
respects, by rendering  it more easily cut, engraved, and polish-
ed, and  thereby making it  a fitter subject  for  manufactures. 
MANUFACTURE OF  PORCELAIN.
And the facility with which we can procure large masses and
quantities of it,  and the softness and ductility which it receives
from heat, in consequence of which it is  so easily formed into
any shapes we desire, render it a most useful production; and
raise  its intrinsic  value far above that of the gems, which are
produced by nature in such very small quantities, and are with
so much difficulty wrought into any form, that they are rarely
applied to any other purpose  than the gratification of weak*
minded vanity.

                       Of Porcelain.

   Porcelain is another production of art which has been invent-
ed upon  principle, by making chemical experiments upon the
earthy and stony substances, and which deserves to be admired
for the elegance  and usefulness  of its productions.
   The art of making porcelain was long confined to the eastern
parts  of Asia.   It is now understood and practised in several
parts of Europe, especially Dresden, Paris and some other pla-
ces in France, and in several towns in England.   It is a branch
of the art of pottery, brought to an extraordinary degree of per-
fection, so as to  produce vessels and other pieces of work, not
only very elegant, and capable of high decoration, but which
have the qualities the most desirable in vessels of earthen ware
intended for the purposes of common life.  The qualities I
mean are, 1st, Great compactness of texture, by which it is both
stronger, and made impenetrable and untainted by any thing put
into  it:  whereas all the  soft pottery is comparatively much
weaker;  and is  moreover bibulous, and indelibly impregnated
with almost every thing that we put into it; 2dly, A smooth-
ness of surface which gives the  vessels beauty, and makes them
easily cleaned; 3dly, A texture which allows considerable alte-
rations of heat and cold suddenly applied without cracking, as
glass does.
  We cannot tell by what steps this art arose to perfection so
early in China and Japan, from whence the art  was imported
into Europe about fifty years ago. Du Halde has given a faith-
ful account of the Chinese manner, as far as he  understood it
But unluckily Du Halde was but a sorry chemist.
   irnt . IT.                            T t 
  530     MANUFACTURE OF PORCELAIN.

     Perhaps the circumstance which gave origin  to  it in those
  countries was the abundance of proper materials, which are but
  rarely found in Europe. The materials of which the  best kinds
  of porcelain are composed, are two.  The first is a clay of the
  best and whitest kind, called by the Chinese kaolin.   The other
  is a stone,  which they are under a  necessity of reducing to a
  fine powder,  to prepare it for mixing with the clay in different
  proportions.   This they call petuntse.  This stone is no other
  than either pure feldt spar, or, in want of it, a species of gra-
  nite abounding with feldt spar, and quite free from any admix-
  ture of  iron,  or other dark coloured matter, which might  spoil
  the whiteness of the porcelain.  The effect of this stone, when
  added in moderate quantity to the clay, is to make it assume a
  greater  degree of compactness in a moderate  fire, and to give it
  semitransparency, without communicating too great a degree of
  fusibility.   The Chinese-call it the flesh, and the clay the bones.
  A granite, quite free from iron or other colouring matter, is rare
  in Europe.   But there are places where such are  found, parti-
  cularly in Cornwall, where there is a great Variety of granite, cal-
  led moor-stone.  And a company  some time ago obtained a pa-
  tent for the  establishment of a  porcelain manufactory* of the
  best quality, in England, with intention to use that Qornish moor-
  stone.
    Though  these two ingredients are in general the  constituent.
  parts of the best porcelain, it has not been always necessary to
  mix them artificially together.   It  has happened both in China
% and in England that nature has in some places  performed this
  part of  the work,  or furnished materials which do not need ad-
  mixture.  In  some parts  of Cornwall, where  the granite  or
  moor-stone abounds, they  find a white clay mixed with the san-
  dy rubbish of the moor-stone in such  proportions, that, without
  any other trouble .than separating it by water from the coarser
  particles, it makes excellent porcelain*.
    A considerable mass of  Chinese  porcelain clay was  brought
  to this country some time  ag6,*and worked up by our  best,ar-
  tists.  .It makes perfect porcelain, but of that kind called stone
  china, viz. less transparent than common.  To give it the degree
  of semitransparency expected in common porcelain, it is neces- 
MANUFACTURE OF  PORCELAIN.
sary to add some pf the petuntse.  But it may also be used alone,
and then forms stone china, or Nankeen cfrina.  This kind of  ,
clay is manifestly produced by the gradual decay of the granite
into rubbish and powder, during which decay it appears to lose
some degree of its fusibility.   We have proof of its origin by
microscopic examination, by which we find in it the  mica and
quartz,  and other  materials of  the granite.   Magnesia, or the
earthy bodies which contain it, are also excellent ingredients in
the composition of porcelain.   There is some of it contained in
feldt spar and the granite, &c.   Some of the porcelain manufac-
tories in England  employ the  soap-stone, or  steatites, in their
compositions with good effect. The good qualities of this earth,
are, 1st, To  increase or improve the whiteness of the porce-
lain ; 2dly, To preserve it from softening too much, or melting
by heat.
  The clay being worked into the intended form, is dried in the
air, and then put into the kiln, and baked with a moderate heat,
and for  a short time.   This brings it into  the state of our soft
potteries.   It is then glazed and painted.  The glazing is made
by dipping it into a cream of powdered flint, with the addition
of a little borax or barilla and other colourlessi materials, to make
it take a thin fusion.  Before dipping the piece, the blue colours
have commonly been put on, because this  colour is too apt to
diffuse or run.   The other colours are penciled on after it has
been dipped.  Many of the more*ordinary European porcelains
are covered with an opaque white varnish or enamel..  But this
is to cover ill-coloured clay, and may be known by its thickness
and softness.  The fine porcelain glaze is perfectly transparent,
and as thin as a film of water.  The piece is now baked again
with a much greater heat, and for a much  longer time,; the
partkles now take a new cohesion and  arrangement; and the
piece becomes hard and compact, breaking with a dull lustre and
somewhat of a granulous texture.   But in the very finest por-
celain no grain can be perceived,  even with a microscope: and
the fracture  has scarcely any lustre, and resembles the fracture
of white wax.                     4
  These are, therefore, the materials of the best kind of por-
celain.  But that we may not leave any part of this subject un- 
 332     MANUFACTURE OF  PORCELAIN.

 touched, it is necessary to mention, that very near imitations of
 this kind of pottery may be made with materials different from
 these.  And many of  the manufactories which have been estab-
 lished in Europe make use of those other materials, and produce
 only imitations of porcelain.  They must all employ a fine and
 white clay for one ingredient in the composition.  In this they
 necessarily agree.   But they have  gone different ways in search
 of their fusible ingredient, which gives to the clay the proper
 degree  of compactness and semitransparency.  As a granite or
 feldt spar sufficiently free from irony particles occurs only in ve-
 ry few places of Europe, they have endeavoured to supply its
 place by other substances.  Some have employed different kinds
 of gypsum, which, being fusible in a violent heat,  answers in
 some measure the purpose of feldt spar.   Others employ some
 of the  alkaline earths, which, though not fusible themselves,
 produce fusible mixtures with clay and flinty earth.  But great-
 er numbers have had recourse to the ingredients of glass made
 into what is called frit, ground to a fine powder.   The quantity
 of alkali in this composition is not sufficient to make it melt in-
 to a transparent and fluid glass, but makes it approach a little to
 that state, or makes it semitransparent.  But these imitations
 are not  porcelains.  They are glasses or enamels not completely
 vitrified:  and a greater heat will melt them.   Even  in inferior
 heats they go out of  shape in the  kiln by their own  weight.
 Such ware cracks by any sudden change of heat.   It is also soft
 externally, and soon scratched and sullied, because the ware will
 not stand the heat necessary for fusing a hard varnish.  Mr. ,
 Reaumur,  of  the  French Academy, who first  examined the J^
 Chinese materials, was also the first who suggested this substi-
 tute of  frit in place of petuntse, where the latter  could not be
 procured. And upon the same principle he attempted to change
 common glass into porcelain.  He was led into this project also
 by accidental experience, as has been already mentioned.
  Another author, in pursuitof the same object,  sometime ago
 was  induced to make a ver^great number of  experiments,
which have proved a considerable addition to our  knowledge on
the subject of earths.   The author I now mean is the late Mr. 
IMITATION OF  PORCELAIN.        333
 Pott of Berlin, who published these experiments  in two small
 volumes, with the title of Lithogeognosia.  But the nature of
 many of the earths and stones was not so well understood at that
 time as it is.now;  and he considered many compounded  sub-
 stances as simple earths.  His experiments, however, excited
 a curiosity in o,her chemists to examine some of the purer 11
 thy bodies in this manner.   And there have since appeared, in
 the Memoirs of Berlin, papers, containing experiments of this
 kind, by Mr.  Margra.if, and by Mr. Achard:  and a multitude
 of experiments have been made in France, by  Mons. d'Arcet,
 and by several others.  Such experiments are interesting, as
 having a tendency to improve  or illustrate the arts of pottery,
 glass-making, and metallurgy.           %
    But no person has made,  perhapte, so  many experiments on
 the mixture of different earths for the  composition  of earthen
 ware and porcelain as  Mr. Wedgewood.   His  object was to
 discover pastes, or compositions, which  should have, not only
 the density and hardness of porcelain, but different colours.  And
 he has succeeded in finding some of very agreeable colours,—
 such as what he calls his artificial jaspers, with  which  he  exe-
 cutes beautiful pieces of workmanship, with figures in basso re-
 lievo,  of the finest white porcelain, on a coloured ground.  In
 this wav he  has imitated a famous  vase, which is  reckoned one
 of the most extraordinary examples of the excellence of ancient
 workmanship,—the Barbarini vase, now in the possession of the
 Duke of Portland.  Mr. Wedgewood viewed this piece of an-
 tique pottery with the highest  admiration, declaring that the ar-
 tist deserved a thousand guineas for his work.  The work in re-
. lievo is executed with the most perfect sharpness and precision,
 and. is an enamel altogether opaque ; so that where it is not so
 thick as the finest post paper, the colour of the ground does not
 appear through it,—an excellence which  all his  labours had not
 yet attained.
    The true porcelains are now made in several  parts of Europe
 in great perfection,—equalling t% Asiatic in the  beauty of the
 material, and even exceeding it in the most valuable  qualities,
 of strength and ability to withstand great and sudden heats with- 
334        IMITATION OF PORCELAIN.
out splitting or softening,  and going out of shape.   Saxony
produced the first of superior quality: but it is now excelled by
the porcelain of Seve in France.  The manufacture is daily ex-
tending, by the discovery of more copious materials.   But still,
the Oriental is far cheaper than any European porcelain of equal 
(  3SS  )
APPENDIX.
    OBSERVATIONS BY DOLOMIEU ON QUARTZ AND
                      PRECIOUS STONES.


                 (Obierv. de Phys.  May 1792 J


     1. xxUARTZ,  or crystal, phosphoresces when  heated or
     struck.
       2. It also, when struck, emits a peculiar odour.  These phe-
     nomena indicate inflammable matter.
       3. It decrepitates when suddenly heated: and the more phos-
     phorescent it is, the more it decrepitates.
       4. It boils and bubbles very much when melted with the heat
     of vital air acting on charcoal; and is formed into globules,
     white or opaque, with air bubbles.
       5. When melted with fixed alkalis, there  is a great efferves-
<<■   cence or boiling, although the alkali  be caustic.  (The  author
"kK; has  also observed a flame come from this mixture: and  so has
  ^  also Mr. Pelletier.)
       6. If there be enough of the fixed alkali, the compound dis-
     solves injwater, and  forms the liquor silicum,  which contains
     the siliceous earth, certainly different from what it was before.
     For, if we precipitate it with an acid, and instantly add super-
     fluous acid, it is redissolved by that acid.
       7. The author had'long suspected that quartz contained some
     condensed gas, or elastic aereal matter:  and he at  last made
     some experiments along with Mr. PeMetier.  They put into an
     earthen retort of twelve cubic inches capacity,  ten drachms of 
OBSERVATIONS ON QUARTZ.
 le vi gated quartz, and two ounces of caustic potash, fresh made and
 quite dry: and set the retort in a reverberatory furnace, with a re-
 ceiver and apparatus for elastic fluids, which were confined in this
 process by water.  1 st, There came some air, which he expected to
 be atmospherical air,  from the cavity of  the  retort: but after
 two or three cubical inches were come, all the  rest extinguished
 flame, and appeared to be azote, to the quantity of 22 cubic in-
 ches.  2d, A little cessation happened in the emission  of elas-
 tic matter: and a tendency appeared to the absorption or intro-
 pulsion of the water.   The fire was  therefore increased; and
 soon after, that is, when the bottom of the retort began to be
 red, an elastic fluid was again emitted, along with a good quan-
 tity of white watery vapours, and a white smoke,  which, while
 it rose in bubbles through the water, was pot totally dissolved or
 combined  with it.  This  white smoke disappears after it has
 risen out of the water into  the bell.   During  this second pro-
 duction  of  elastic matter,  12  cubic  inches  of it  are obtained:
 and there is a limit here too, marked by a cessation, attended
 with still greater danger of intropulsion of the water than in  the
 first instance. It must be avoided, either by letting in some air,
 or by increasing the intensity of the fire with  bellows..  The na-
 ture of this second product is different from that of the  former.
 It is all inflammable air, which explodes with atmospherical air,
 excepting a small portion of it, which is mixed  with air and gas
 azote. 3d, The third product, which requires a very strong heat
 to make it come, amounts to 20 or 22 cubic inches.  About 16
 of these are fixed air, which is gradually absorbed by the water,__
 the remaining five or six are a mixture-of inflammable and azo-
 tic gas, in which the last prevails.  After this, whatever heat
 be applied, no more elastic matter can be obtained.   (The au-
 thor observed signs as if some of this matter were  attracted''and
 absorbed by the water.)  They repeated this experiment with
levigated crystal of Madagascar, and caustic fixed  alkali, which
was prepared by Mr. Pelletier, with all precautiorfsno have it pure
and untainted with inflammabfi^matt^r.  And the  process was
twice performed with this crystal.  The first time,  the heat was
not raised so high as to bring over the  third product of  gases."
But the second was completed.  The residuum in the retorts. 
EXPERIMENTS BY DOLOMIEU.
 after the first and last experiment, was a white, vitrified, opaque,
 blown-up matter.   That of the second experiment was perfect-
 ly vitrified, and proved a  greenish  glass.   But  all  these  three
 were very dissolvable, and even deliquescent;  and were dis-
 solved by water into a liquor silicum, which by rest deposited
 a fuliginous-like  matter.
   8. The author is of  opinion that the inflammable and azotic
 gas come from the quartz, for these reasons ;.lst, The alkali is
 not decompounded or  destroyed ; but can be separated again
 entire from the silica by acids.   But the quartz  is certainly ve-
 ry much changed,  for it is become soluble in all  the acids, even
 the acetous, provided these are added in  a  sufficient quantity,
 as soon as it is precipitated from the liquor silicum.   The sul-
 phuric acid sometimes redissolves k so quickly that the precipi-
 tation or separation of  it from the alkali is not perceptible ; and
 the same thing happens with  any other acid, if the  solution of
 the liquor silicum be largely diluted.  That there is a real  solu-
 tion here by the acid, becomes evident when we add enough of
 alkali to saturate  the acid; for then  the siliceous earth is preci-
 pitated again, especially when the alkali we use is a mild alkali,
 and  most certainly if the volatile alkali.   For if we  use a caus-
 tic alkali, it is necessary to take care  that  no more be added
 than just enough.   A little superfluity of it redissolves the silica
 very quickly again : and thus it can be redissolved by acid or al-
 kali  as often as we  please.
   The author believes that the inflammable  and phlogisticated
 airs  come from the quartz ; and that the boiling and blowing of
 it up into a spongy glass, when it is melted by the heat of  vital
 air,  is occasioned by the extrication of those airs from it; that
 the fire odilight, and the smell of burnt air,  produced by strik-
 ing pieces jjf quartz against one another, are to be imputed to
 the bases of  those- airs in its composition; and that the differ-
 ence between qxifertz in its natural state, and quartz fresh preci-
 pitated from lfquor silicum, is somewhat analogous to that of
quicklime and calcareous earth; the fresh  precipitated silica, in
consequence of its  purity and  simplhuty, having an  attraction
 for acids, which quartz has not.   And as the  quicklime recovers
 "vol. ii.                             u u 
338       EXPERIMENTS BY  DOLOMIEU.
its fixed air, if left exposed, the author is of opinion, that the
precipitated silica can recover from  water the principles which
it lost when it was melted with the alkali; for the precipitated
silica continues soluble in acids for a very short time only after
tt is precipitated.   If we  observe it while we are precipitating
it, we can  see intermixed with it, and forming around the par-
ticles of it, numerous little bubbles of aereal matter, wnich rise
afterwards to the top of the water.   And heat promotes and in-'
creases this appearance, which is soon over: and then the silica
is  insoluble in acids, as much as  quartz in its  natural state.
And if we now wash and dry it,  and melt  it again with an al-
kali, it gives the same effervescence that it gave at the first.  It
must be acknowledged that  inflammable air is not absorbed by
newly precipitated silica: but the author supposes that it is on-
ly the  basis of it which is  present  in quartz; and that basis,
when once combined with caloric, is not very easily separated
from it.
   If these airs are supposed to come from the alkali, how can
we account for the effervescence or intumescence of pure quartz
and crystal when melted with the heat of vital air; or for the
light and the smell of burnt matter, which are produced by strik-
ing pieces of quartz against  one another?  The Chevalier de
Lemanon, performing  this  experiment over white paper, and
examining afterwards with a microscope the minute dust or par-
ticles which had been rubbed off from the quartz, found among
them,  particles which had been scorified, and which when rub-
bed or bruised on the paper, marked it like charcoal.  (Journ* X-
de Phys. July 1785.)                                      ??
   The matter we find thus  combined  with the silica in quartz
is probably the matter,  whijbh, when combined witlffevater-at a
great depth below the surface of the earth, enables i(|to dissolve
quartz, and to transport it and to crystallize it,  which matter
cannot probably remain combined with water when it comes to
the surface and is exposed  toTight.   Bergmann was deceived
when he imagined fixed air  combined with water to be a solvent
of  quartz.  The experiments of other chemists have not sup-
ported this opinion.  I have not been able to make it dissolve 
            ON QUARTZ AND CRYSTAL.         339

silica, even when fresh precipitated from liquor silicum.  Sili-
ceous crystals are often formed in nature on the surface of cal-
careous ones,  without the smallest appearance of dissolution or
corrosion in these last, which would certainly happen, were the
solvent of the siliceous matter carbonic acid water.   Mr. Mor*
veau  also mistakes this water.   (Encyclopedic Methodique).
For, in an experiment in which siliceous crystals were formed
by shutting up in a vessel aerated water  and siliceous earth,
there  was iron also,  which became corroded and rusted:  and
the crystals.were found smong  the rust of the iron.   He  had
four glasses, containing aerated water and silex.  Into one was
put silex ; into another limestone ; into a third, argilla; and h>
to the fourth, iron.   After nine months, no change  appeared,
except in the last,  in  which both the pieces of quartz and the
iron were evidently corroded, and small crystals found among
the rust  of the iroft.   Dolomieu  therefore concludes that the
hydrogen, separated by the action of the dissolving iron on a
small part of the water, produced, in conjunction with the rest
of the water, a solvent which acted on the quartz.   He learned,
however, by experiments, that iron has no effect on the liquor
silicum,  or the liquor on the iron.  A bit of polished iron pre-
serves its brightness unimpaired in this fluid.  That the solvent
of silica in nature  is an inflammable substance,  is  also render-
ed probable by the dusky  colour of some crystals and of flint,
which dark or dusky  appearance is dissipated by fire.   He adds
one more argument to support his opinion of the compounded
nature of quartz and crystal.  This is drawn from its inactivity,
or want of attraction  for most other substances.
   He then enters on the consideration of the gems, which have
stilLmore inactivity,  and are  insoluble  even by alkali, though
they are Anetrable by it to a certain degree.   He  appears in-
clined to suppose  that these are still more completely saturated
than quartz, with the matter which he has discovered in its com-
position.   And some of the properties of the  diamond may give
room for supposing that it is theffnost completely saturated of
them all, and therefore the most difficultly penetrable  and dis-
solvable by the most  active solvents.*" 
34Q     DOLOMIEU'S OBSERVATIONS, &c.

   He considers the argil, which is the most abundant ingredient
in many of the gems, as dissolvable by the same solvent which
is necessary to quartz.  The argillaceous earth shews, by its
odour when moistened,  and by many other particulars, that it
has a disposition to unite with inflammable matter.
   He afterwards considers the different gems, as differing not
only by the number and proportion of earths they contain, but
also by the close coalition of those  earths, which has been pro-
duced by the action of their common solvent; and supposes that
the hardest :and brightest of them retain a larger proportion of
the remainder of this common solvent,  or are more completely
saturated with it,  than the rest are.
   But I refer you to the conclusion of his paper, which, I con-
fess, is not so clear and distinct as the preceding parts. 
C  341  )
CLASS III.
INFLAMMABLE SUBSTANCES.
  1 HE third  class of the  objects of chemistry,  in the plan
 which I have adopted, is that  of the Inflammable or Com-
 bustible Substances.
   By the inflammation of a body, is meant a rapid  destruction
 and change, which it suffers  when exposed to the action of heat
 and air at the same time; which change is  attended with the
 emission of a great quantity of heat and light, and ends in a to-
 tal loss or privation of the quality of inflammability.
   When the general effects of heat were formerly explained to
 you,  some notice was taken of the phenomena of inflammation,
 and of the general nature of this class of bodies.  And  the
 opinions which formerly prevailed, as well as those  which now
 prevail concerning the nature of it, were briefly stated, and have
 since been more fully explained to you occasionally.
   Tjhe opinion that is now the most generally approved, had its
 rise from the numerous investigations and experiments that have
 been  made during  the last twenty or thirty years, on the na-
 ture and properties of the different elastic fluids which are found
 in nature, or may be produced-by art.
   After I had discovered the particular nature of the carbonic
 acid,  and had shewn that some of it isjgroduced by the action of
air and burning fuel on one another, and also by the breathing 
342    VARIOUS OPINIONS OF CHEMISTS.

of animals, I supposed that it was formed by the union of com-
mon air, with a  quantity of the phlogiston of the  chemists,
the existence of which was not doubted at that time.  And I
supposed, that atmospherical air had a strong tendency to unite
with this principle, and to separate it on many occasions from
other bodies.
  This opinion, of a tendency in the atmospherical air to unite
itself with the supposed phlogiston, was afterwards adopted by
Dr. Priestley and others.  But the Doctor  did not admit the
carbonic acid or fixed air to be produced in  the manner I had
supposed.  He examined with  more care than I had done the
change  which the  air undergoes in contributing to the  inflam-
mation of burning bodies and the breathing of animals; and thus
discovered the distinction between carbonic acid gas and azotic
gas.  This distinction had been  in fact clearly pointed out be-
fore, by my colleague Dr. Rutherford, in his  inaugural disserta-
tion, printed in June 1772.
  When atmospheric air is completely  vitiated by the  breath-
ing of animals, or the burning of fuel,  we find in such vitiated
air a much greater quantity of the azotic gas than of the carbo-
nic. Dr. Priestley was of opinion that the azotic gas was formed
by the combination of the atmospherical air with the phlogiston.
He therefore named the azotic gas phhgisticated air.  The car-
bonic acid gas, he supposed, had existed before,  but was con-
cealed in the atmospherical air, or was intimately combined with
it until phlogiston was added, which, uniting  with the air, made
it separate from the carbonic acid gas.  Or,  as he expressed it,
the carbonic gas,  or  fixed air, was precipitated,  or extricated,
in  consequence of the phlogistication of the  atmospherical air.
   So far had Dr.  Priestley proceeded, when  the late Dr. Craw-
ford of London employed his attention upon this subject. By
availing himself of the discoveries of others, and  making use
too of  experiments made by himself, be formed a new theory
of inflammation,  which he published in his  work  on Apaimal
Heat.
   He made a number of experiments to learn what capacity for
heat different substances have when compared with one another.
These  experiments were made in the manner which  I  pointed 
DR. CRAWFORD'S THEORY or INFLAMMATION. 343

 out, by  applying different bodies one to another, unequally
 heated.   A  part of the heat of one  is communicated to the
 other,, until they come to an equilibrium or equal temperature
 of heat.   While this happens, the alteration of temperature  in
 the one body is very different from that of the other, although
 the heat which the one receives be precisely the same quantity
 which the other loses.
    This  shews, therefore, that  different kinds of matter have
 different capacities for heat; that some are more heated by the
  same quantity of heat than others; or that a  smaller quantity
  of the matter of heat is sufficient for raising their temperature
  or thermometrical heat by the same number of degrees, (for this
  is the mark  and the only measure of capacity).
     Dr. Crawford, making a great number of experiments in this
  way, with different materials, thought that he discovered that
  those which he supposed to contain the phlogiston in their com-
  position, had less capacity for heat than others, or required less
  of the matter of heat to raise their temperature ; and that in pro-
  portion as they contained the more of the imaginary phlogiston,
  they had the less capacity for heat.
     He therefore began to think  that atmospherical air, while it
  received this phlogiston  from burning fuel, must have its capa-
  city for heat diminished, and must throw some of its heat  in-
  to the contiguous bodies ; and that  the increase of heat which
.  appears  during inflammation,  might be this very heat extri-
  cated  and  expelled from  the  air, and not  from the burning
  body.
     This led him to examine, by actual experiments, the capacity
  for heat of the air in its different states.   And he thought that
  he discovered such a very great difference between the capacity
  of atmospherical or respirable air, and that of the azotic and
  carbonic gases,  that he was able  to  shew by calculations, that
   this is sufficient to account for all the heat that appears during
  the inflammation of fuel.
     These are the general outlines of  his theory of inflammation,
  which he has applied also to explain the heat  maintained in the  *
  bodies  of animals.   For  particulars'! must refer you  to  the
  first and second editions of his treatise on this subject, which 
   344    DR. SCHEELE'S SINGULAR THEORY.

   contains experiments made with amazing labour and much inge-
   nuity.
     While Dr. Crawford was thus  employed, another person in
   a distant part of the world, had already formed for himself a
   very different theory of inflammation.   This person was  the
   late Dr. Scheele of Sweden, whom I have had frequent occa-
   sion to mention already in this course,  as  an  eminent chemist
   and philosopher.
     He engaged himself in  an inquiry which had for its object
   the nature of inflammation, and how heat and light are produced
   by it.   And he thought that he had  discovered how  they  are
   produced.  He thought he had reason to conclude that heat and
   light are compounded substances; that he could actually pro-
   duce them, by combining together their constituent ingredients;
   and that he could decompound them, by separating these ingre-
   dients from one another.
     Assiduously occupied in this research, he was one of the first
   discoverers of vital air, or oxygen gas.  Dr. Priestley also dis-
   covered it about the same time, having ohtained it from nitric
   acid, and from other things, in some of his numerous experi-
   ments.  Mr. Lavoisier also discovered it soon after, while
   he was employed in investigating the action of air on the me-
   tals.
     But Scheele was the first person,  who, from a number of in-
   geniously contrived experiments, concluded by very fair reason-
   ing, that atmospherical air is a mixed fluid, composed of about
   two parts of azotic gas, and one part of vital air or oxygen gas,
   along with a very small admixture of carbonic acid.  The great-
   er part of the carbonic acid gas, found in the  air which has
   contributed to  the  burning of fuel, he supposed to be extri-
   cated from the fuel, most kinds of which he supposed contain-
   ed this acid, or the basis of it.  But he observed that there are
   some inflammable substances, which do not contain any of this
   basis, and therefore do not communicate carbonic acid to  the air
   which  contributes to  their inflammation.  Such are  sulphur,
»   phosphorus, and some of the metallic substances.
     Scheele, after making  many experiments with atmospherical 
OF FIRE, HEAT, AND LIGHT.
air, repeated them also with the oxygen gas, by burning some of
the most  inflammable substances  in  limited quantities of it,
which he had confined in close vessels.  And he found that in
some of these experiments the whole of it was expended, or *
disappeared during the bright  and violent inflammation which
it occasioned.  TKis  he learned by opening the phials under
water, after the experiment.   The water was pushed in by the
pressure of the atmosphere,  and filled them quite full.   He
therefore concluded that the oxygen gas had penetrated through
the glass of the phial, and had escaped in the forms of heat
and light,  into which forms it had been changed by uniting with
the phlogiston  of the inflammable matter.   The heat, he sup-
posed, was produced by a lesser, and the light by a greater pro-
portion of the phlogiston combined with it.
  We must not form  a light opinion of Scheele's acuteness and
judgment from the extravagance, and  I may almost call it  ab-
surdity, of such  a theory,  as  it  appears  to  us  at  present,
Scheele was one  of the most judicious, as well as ingenious
chemists that ever lived.  But in the active time of his life,  the'
existence  of phlogiston was  universally believed.   It was so
firmly established in  the imagination of every chemist, that
it presented itself to their mmds on every  occasion.   It must
be confessed, however, that he maj/ be blamed for a gross over-
sight or neglect, in omitting to weigh  the phial and its contents
before and after the inflammation.  Had he weighed  it accu-
rately, he  would  have  learned that  the oxygen gas. had not
flown away through the sides of the phial, but was still there,
having only lost its elastic* aereal form.  Had he examined'the
weight of the acid into which the inflammable body was changed,
he would have  found  that this acid matter contained the oxygen
in a  condensed  state ;  the weight of it being equal to that of the
inflammable body and of the oxygen gas taken together.
  When he performed the same experiment with atmospherical
air,  no more than one-third or one-fourth  of it was expended,
or had disappeared.   The remainder was become  totally unfit
to contribute to the. inflammation of burning bodies, or to sup-  •
 vol. n.                              x x 
346           DR. SCHEELE'S  THEORY.

port the life of animals by respiration.  And when he examined
it further, he found it to be either pure mephitic gas, in some
cases, or a mixture of this  gas with carbonic acid gas in others.
He then, by the use of lime and water, separated the carbonic
acid ga6 when it was present:  and he added to the mephitic gas
as-much pure  oxgyen  as  made  up the whole  to the original
quantity of  the atmospherical air with  which he  had begun the
experiment.   He  found this mixture to be exactly similar,
in its powers and properties,  to  good atmospherical  air.  He
exhausted it of its oxygen, by burning bodies in  the same man-
ner as before.   And he again renewed  its powers in the same
way several times over: and, as the quantity of the azotic gas
always continued the same,  he concluded that atmospherical air
is effectual in promoting inflammation and supporting the life of
animals, only in consequence of its containing near a third part
of its bulk of oxygen gas in its composition'; and that it is only
this part of the atmospherical air that is capable  of uniting with
the phlogiston, and of being converted along  with it into heat
and light.
  The most surprising and ingenious  part of his treatise was
the apparent facility with which he thought he could explain the
various processes by which oxygen  gas could be  obtained in its
separate state.  They  are  all  processes  in which substances,
which were supposed by the chemists to have a strong attraction
for the phlogiston, were exposed to the action of heat.  And he
supposed that they decompounded  the heat applied to them;
thajt they attracted the phlogiston, and disengaged the oxygen
from  it.   And no person discovered so many ways to obtain the
oxygen gas in a separate state, or to extract it from so many dif-
ferent substances, as Scheele did.
  You must perceive that all the  attempts to explain combuf
tion that have been mentioned,  agree in supposing or assumir
the existence of a  common or general principle of inflammab
lity contained in all inflammable substances.  It  is further su]
posed, that this is  a most subtile kind of matter; -and that it
separated from such bodies with great rapidity during their  i 
OF COMBUSTION.
347
  fiammation, appearing then in its separated  state, according to
  the first opinion of the chemists, in the form of heat and light;
  or, according to the opinion which I had formed, and to that of
  Priestley, Cavendish, Crawford, Kirwan, and others, uniting, at
  least in part, with common air, and forming carbonic acid and
  azotic gas ; or, thirdly, according to Scheele, uniting itself with
  the vital air of the atmosphere, and forming with it the heat and
  the light.
    I must now make you acquainted  with some  other opinions
  which have been more lately imagined, and which are of a quite
  opposite and contrary nature to all those I have  yet explained.
  The principal author of the first of these new opinions is Mr.
  Lavoisier, whom I have frequently had occasion to name as the
  author of many excellent experiments upon elastic fluids, as the
  subjects of chemical investigation.
    Mr. Lavoisier was induced to form this opinion chiefly by a
 number of facts observed in the inflammation of bodies.  Some
 of these have been already  touched on occasionally, but must
 now be more particularly insisted on.
   You will find the detail of these facts  in a series of  disserta-
 tions, published in the Memoirs of the Academy of Sciences, par-
 ticularly in the volumes 1781,1782,1785;—in his Opuscles Chy*
 miques, published in 1777 ;  and in his Elements of Chemistry,
   He remarks,  that although it has been hitherto supposed by
 the chemists that a subtile kind of matter flies off from bodies
 or is separated from them, during their inflammation, no person
 Hs been able, either to exhibit this common substance by itself
    o shew that the body, which was  supposed to sustain  this
     of  matter, suffered any diminution of its weight.   Just the
    :rse appears, in the greatest number of experiments,  when
    inflammable body is of such a nature, that we can collect
   curately together all the inflammable matter that is left after
 he inflammation is over.  In such cases, we always find that
this matter exceeds in weight thej&flammable body from which
it was produced.   This fact alone had long occasioned many to
doubt of the existence of a principle of inflammability.
   But  further, among  the numerous  experiments which have
been made of late upon different kinds of aereal fluids,  several 
348  DECISIVE EXPERIMENTS ON COMBUSTION.

 have been made by Mr.  Lavoisier, in which  the  inflammable
 bodies were exposed to the action of measured quantities of air,
 in close vessels.  They were burnt, in part: and  nothing was
 lost or gained by the whole apparatus.  This was weighed with
 most  scrupulous accuracy before and after the inflammation.
 But the inflammable body was found to have gained a quantity
 of* weight  proportioned to the quantity  that had been  burnt.
 Moreover, the air was found to be diminished both in bulk and
 in weight.   That a quantity had been absorbed by the burning
 body, or had somehow disappeared, was evinced by opening the
 vessels  under water.   The water rushed in,  and occupied the
 room of the absorbed air.. The specific gravity of the remain-
 der being examined, andcompared with the diminution of room,
 it appeared "that the air remaining also weighed less than the air
 before the  inflammation ;  and, lastly, it was found that the los9
 of weight in the air was  exactly equal to the augmentation of
 weight in the remains of the inflammable body.
   The most simple, elegant, and unexceptionable experiment to
 this purpose, is that of F. Beccaria, of Turin. Two small glass
 matrasses were joined hermetically by the necks.   One of them
 contained a small quantity of  an inflammable body which emit-
 ted no vapour in burning.  The rest of the space in both ves-
 sels was filled with vital air: and the vessels were then sealed up
 and carefully weighed.  This  apparatus was  accurately poised
 on an axis, so as to vibrate like a common balance which is in
 equilibrio.   A burning-glass was now employed  to kindle the
 bodyr, and  to keep up the combustion as long as  possible.'  It
 was observed, that as soon as the combustion had proceeded a
 very little way, that end of the balance which contained the burn-.
 ing body, began to preponderate.  When the burning could be
 maintained no longer by the action of the burning-glass, the ba-
 lance remained in a very oblique position, shewing a great addi-
 tion of weight on the side of the burning body. But, as the heat
 may be supposed to have exp^ded that arm of the balance, the
 whole was allowed to grow as cold as at the first.   It required
 about 13 grains  to be laid cm the Other end to restore the equi-
 librium.
   Here, therefore, is an evident transference of matter from one 
             MR.  LAVOISIER'S THEORY.         349

end of the apparatus to the other.  For, when the apparatus was
again weighed, it was found of the same weight as at first.  The
vessels were now opened, and air rushed in.  It was  again
weighed, and had gained five grains.  The ashes or remains of
the body were now carefully collected and weighed.  They were
found seven grains heavier than before.
   Nothing can be conceived more convincing and unexception-
able than this experiment, as a proof, that, in the inflammation
of this body, it had united to itself part of the air contained in
the two vessels.   In other experiments made by Mr. Lavoisier
and his copartners, contrived for ascertaining the precise quan-
tities of air consumed or combined, and the  weight gained, it
was found that the one was precisely equal to the other.
   It was chiefly on these facts that  Mr. Lavoisier founded his
new theory of inflammation and combustion.   He was of opi-
nion that there was no such thing  as a principle of  inflammabi-
lity, the phlogiston, assumed by the chemists,  nor  any separa-
tion of a subtile  principle from bodies, in the  act of their in-
flammation.  The very reverse of this happens, says he.   The
inflammable body sustains no loss, but receives a considerable
addition  of matter, which  is  now strongly combined with it;
and,  during its combination, produces a total  change in its na-
ture  and qualities, making it appear a substance of a quite dif-
ferent kind from what it was before.
   The matter thus combined with the inflammable body is sup-
posed by Mr. Lavoisier to be  the basis,  or ponderable part of
vital air.  He considers this air as a compound of  this matter,
and  of the matter of heat, or cahrique,  which calorique is so
combined with the other matter as to give it the form of an elas-
tic fluid, not condensable by cold, like the vapour of water, but
requiring the application of  some proper substance, for which
it has a stronger attraction than for calorique.   An'inflammable
body is a proper substance.   But a certain high temperature is
necessary for enabling them toilet on each other. The basis of
vital .air then combines with the inflammable body; and the ca-
lorique is allowed to escape, in the same manner that fixed air is
allowed to escape, when a mild alkali  combines with an acid.
The heat thus let go is sufficient to enable the adjoining parti- 
350         MR.  LAVOISIER'S THEORY

cles of the inflammable body to act upon, and decompose more
vital air, and besides, to heat all surrounding bodies.
  This opinion of inflammation, and of the  change which in-
flammable bodies undergo, was held by Mr. Lavoisier as prov-
ed by the most convincing experiments.  For 1st, It is proved
that vital air is absorbed during its action on  inflammable sub-
stances ; 2dly, Many of those substances which have been burnt,
or have been exposed to the action of air and heat, so as to suf-
fer  a change similar to inflammation, can afterwards be made to
afford, by means of heat,  very considerable quantities  of vital
air.   For the  proof of this,. Mr. Lavoisier refers to those very
experiments in which Dr. Scheele supposed that such bodies de-
composed the heat applied to them.  Lavoisier could not con-
ceive that heat could be decomposed in any of our experiments;
and maintains that it acts  simply by expelling the vital air from
such bodies in which it is contained, by furnishing what is to be
its latent heat when it is in its  elastic gaseous form.
  Mr. Lavoisier further says, that it has long been remarked,
with respect to inflammable  substances,  that  the  incombustible
matter into which they are changed during inflammation, is, in
the greatest number of cases, either an evident acid,  or has the
qualities  and appearances of a matter which contains a quantity
of acid combined with it, and which it  had an opportunity of
getting during the combustion.  This is eminently the  case in
the combustion of sulphur, of phosphorus,  of charcoal,—from
which we obtain the sulphuric, the phosphoric, and the carbonic
acids.  An acid is obtainable from the ashes or calxes of some
metals destroyed by fire and air; and all these calxes are simi-
lar  to what  the metals are changed into  by  actually combining
them with a due portion  of  acknowledged acids.
  Mr. Lavoisier, therefore, induced by these general facts, sup-
posed that vital air is the general principle of acidity.  Although
it has not the properties of an acid itself, it forms acids of dif-
ferent kinds, by combination with inflammable bodies.   Com-
bined with  sulphur, it forms the vitriolic acid,—with charco
it forms the carbonic acid, &c. &c.  He therefore gave  it f
name of the oxygenous or acidifying principle.   (See Note 4?
at the end of the Volume.) 
         OF COMBUSTION  AND  ACIDITY.      351

  As to the heat and light which are emitted from these bodies
in such quantity during their inflammation, or as Mr.  Lavoi-
sier views it, during their combination with  the  basis of vital
air, he supposes that it is extricated chiefly, or rather solely, I
think, from this air; which in its aereal state, contains it in great
quantity, in consequence both of what is necessary,  as latent
heat,  for its aereal form, and also because in that form it has a
very great  capacity for heat, requiring much of it to elevate its
temperature any number of degrees.
  This theory of Lavoisier is bold and ingenious.  And,  as-
suredly,  it applies with great facility to explain  very many of
the facts which belong to this subject.   We must certainly ad-
mit, as a thing proved by his experiments, that when bodies  are
inflamed, a great quantity of vital air is combined with them, and
increases their weight.  But there are many chemists, and che-
mical philosophers, who, although they admit this as a fact suf-
ficiently proved, are not yet satisfied that nothing else happens
in inflammation.  They still, suspect, or suppose,  that the burn-
ing body sustains the loss of  some subtile and active principle,
(suppose it heat and light)  ; and that it is the loss of this prin-
ciple  which disposes them  to  attract the air, and unite with it
so strongly as they are known to do.   For my own part, I was
much disposed to this opinion, on the general tenor of  chemi-
cal  combinations.   The uninflammable matter  produced  by
combustion is generally a much more  active substance,  or has
an attraction for a greater  number of bodies, than the  inflam-
mable substance had, from which it came.   This is manifest in
sulphur and sulphuric  acid, and  many other instances.   This
disposed me to consider these substances as in a state of great-
er simplicity, when they were so much more active on other
substances.  But, when I considered that inflammation cannot
now be viewed as  a  decomposition  alone, it  being now  proved
that the inflammable body  is,  in  fact,  combined  with a great
quantity  of vital air, wre cannot say that it is reduced to a state
of greater simplicity than before inflammation: For, admit that
 t has lost one principle, it must  be acknowledged that  it has
 -ained another,  and therefore the observed increase of activity 
 352          EDITOR'S OBSERVATIONS.

 does not entitle us to say that it is rendered more  simple.   It
 is a new subject, and has new relations: and we really do not
 know whether these are or are not more numerous and close
 than before*.
    The difficulties, therefore, and objections against this theory,
 are now become so few and of so little weight, and the experi-
 ments which support it are so numerous, direct, and conclusive,
 that it is gaining the ascendency over all the others, and becom-
 ing the most general opinion among the chemists.


          OBSERVATIONS BY THE EDITOR.


    There were, however, some points that presented great diffi-
 culties,  and almost put a bar in the way to the confident adop-
 tion of the theory, in the extent in which it was proposed. For
 it  must be remarked, that Mr. favoisier's  theory goes much
 farther than the mere explanation of the phenomenon  of com-
 bustion.   He  states the basis of vital .air as the principle of aci-
 dity : therefore the combination of this principle with an inflam-
 mable body is equivalent,  chemically speaking,  with the burn-
 ing of that body.  The theory, therefore, embraces almost.the
 whole of chemistry.   And combustion,  the  most remarkable
 phenomenon of material nature,  and almost characteristic of
 chemistry, is now but a subordinate fact,—a particular mode of
 oxydation.  But there were several effects of the yitriolic and'
 muriatic acids which could not be explained  by  the theory in-,
 this its simple  form.   Most fortunately,.some experiments were
 made by Mr.  Cavendish at the very timel.whife this theory was

  * Dr. Black used to remark in some of his  courses, that Mr. Lavoisier's
system did not explain the remarkable effect of light on bodies; and that Dr.
Lubbock had given some useful hints on this subject, in his dissertation de pri*'*
cipio sorbili,  which also professes to be a theory of .combustion' and acidifica-
tion.  But I do not see that Lavoisier is any how bound to  explain this phe-
nomenon.   Berthollet and others affect io assign its mode of action, which is*
always^ accompanied with separation of oxygen.  And tSfey very frequently.
explain phenomena by shewing that they are really instances orHhis expul-
sion by means of light.—Editor.                    ;' 
HISTORICAL OBSERVATIONS.
   in its cradle,  which opened a way out of all the difficulties that
   then embarrassed it.   The discovery of the composition of wa-
   ter by Mr. Cavendish in 1781,  and fully demonstrated by him
   in June 1783, was carried to Paris by Mr. Blagden, secretary
   of the  Royal  Society ; and by him  communicated to Mr. La-
   voisier, who  immediately repeated the experiments, and with
   great address and ingenuity, applied the discovery to his theo-
   ry ; and not  only surmounted the difficulties now mentioned,
   but by  inverting the experiment, and resolving the  water into
   its constituent parts, he gave his principles an influence almost
   unbounded, explaining almost all the phenomena  of active na-
   ture.   It is here,  much more than in the first conception of the
   theory  of  combustion, that the  penetration,  the  inventive ge^
   nius, and the sound judgment of Mr. Lavoisier are most conspi-
   cuous.   The  precise logic, to which he endeavoured always to
   adhere, would have preserved Lavoisier from many errors, in-
   to which his followers, in all parts of Europe, have frequently
   fallen,—misled by precipitant and overweening notions of their
   own knowledge.   The composition and decomposition of water
   affords  a mode  of explanation  susceptible of so  many  forms,
'  according to the fancy and the wishes of the employer, that there
   is scarcely a phenomenon of  which a specious explanation may
   not be given in more ways than  one.
     Dr. Black says most justly, therefore, that  science has cause
   greatly to deplore  the death  of that eminent philosopher.  He
   always expressed a high opinion  of Mr, Lavoisier's genius and
   sound sense;  but was  much displeased with  the  authoritative
   manner in which the junto of chemists at Paris announced eve-
   ry thing, treating all doiibt or hesitation about the justness of
   their opinions, as  marks of the w.ant of common sense.
     But,  perhaps,: Dr.  Black was not a competent judge of the
   matter.   In the .'course of his own discoveries, he  was satisfied
   with the justness of his view of the subject.   And he  found
   himself able to communicate  his knowledge to his students  by
   nae'ans of very plain arguments, and the most familiar and sim-
   ple experiments^  He despised the parade of multiplying expe-
   ments ancrargujment.  But he employed, with becoming  ac-
   knowledgment ctf his obligation, the experiments furnished him
     vol.  ii.                             y y 
354     CORRESPONDENCE OF  DR. BLACK
by Mr. Watt and other friends, in further confirmation of his
doctrines.  Having sufficiently instructed his students, he had
no farther care ;  and was contented with that reputation which
he enjoyed without struggle, and which he was conscious of
deserving.
  But Mr. Lavoisier was in a very different situation.   He saw
that he was about to operate a complete revolution through the
whole extent of  chemical science.  He could not but foresee
doubt and opposition on  all hands.  Confident of victory (after
his happy employment  of Mr.  Cavendish's discoveries), the
prospect was very flattering.   I  may perhaps add to  this the
genius and character of his nation.  This is scarcely left in my
choice,—for, almost at the first, the doctrines of Lavoisier were
preached by the associated chemists as the system of French
chemistry.  Mr. Fourcroy,  Monge, De Morveau, and others,
repeatedly give it this name, with some exultation. It was pro-
pagated as a public concern ;  and even propagated in the way in
which that nation always chooses to act,—by address,  and with
authority.   Every thing pertaining to the system was treated u
council,  and all  the leading  experiments were documented b
committees of the academy  of sciences.  To accomplish  this
purpose  more effectually, they published the Annales de Chymte
in concert :  and they formed a new language, with the pretext
indeed of improving science, but, in reality, that every thing
might be forgotten which did not originate in France.  A Swiaf
gentleman, affectionately attached to Dr. Black,  was in Paris at
die time, viz. 1787, and wrote to him in these words :  " Vobjet
qui occupe les chymistes surtout h present, c'est la nouvelle Nomen-
clature.   II paroit qu'on veut par la donner le coup de grace au
pauvre phlogistique; quant  a Pair fixe, ilfaut qu'elle devienne
Vacide carbonique,"  &c.   The writer had surely caught the pa-
triotic flame; otherwise  he would have recollected that it could/
not amuse his friend to learn that his discovery,  which had led
the way, must vanish  with  the rest.   The  plan was  the same
with that of Fabre d'Eglantine with his new calendar; and the 
AND MR. LAVOISIER.
255
     principle was that of Rabaud,—;" ilfaut tout detruire,—out,__
     tout detruire,—parce qtfilfdut tout recreer*."
       Dr. Black disliked this way of proceeding, so unlike science
     and philosophy.   He disliked the avowed principle of the no-
     menclature, thinking it more likely to corrupt science than to
     promote it: and he began to write some observations on it, but
     he soon desisted.
       Some time after this, he had more reason to be displeased, and
     even to be offended. Mr.  Lavoisier  saw that his theory of com-
     bustion depended on the doctrine of latent heat; and was ex-
     tremely anxious to obtain Dr.  Black's  acquiescence.   In the
     course of 1789, Dr. Black received  two letters from the Mar-
     quis de Condorcet, full of respect for his " illustre confrere"
     (Dr. Black having not long before been elected associe etranger
   .  de l'Academie des Sciences).  In October 1789,  Mr. Lavoisier
     wrote to him in these words:  " C'est un des plus zeles admira-    i
     teurs de la profondeur de votre genie, et des importantes  revo-  €
     lutions que vos decouvertes ont occasionne dans la chymie, qui
 .^jjprofite de l'occasion du voyage de Mr. B. a Edinbourg," &c
 "   Learning, by the return  of this gentleman, that Dr. Black
     thought well of his theory, and had  introduced it into his leo-
     tures, he wrote to him again in July  14th, 1790, as follows:
       " J' apprends avec une joie inexprimable, que vous  voulez
     bien attacher quelque merite aux idees que j'ai professe le pre-
    mier contre la doctrine do phlogistique.   Plus confiant dans vos
     Idees que dans les miennes propres, accoutume a vous regarder
     comme mon maitre, j'etois en defiance contre  moi meme (cre-
     dat Judceus Apelld) tant que je me suis ecarte,  sans votre aveu,
      * It is not undeserving of remark, that not only does this principle or aim of
>u    the new nomenclature greatly resemble that of the new calendar, and the new
'*.    pleasures of France, but that also several of this chemical convention were al-
y.. • iflrassistants, officially, to Fabre d'Eglantine in his project. La Place was in a
   '■ nigh department of public business.  Monge was a minister of state, and ere
    this, had signed the death-warrant of his sovereign. Meunier was a general
     Officer.  Morveau was a commissary of the convention; and persecuted with
    the most cruel virulence the noblesse of his province, •who had twice paid his
    debts, and given him 24,000 livres to enable him to prosecute his chemical in-
    quiries,  rle was the chief agent in framing the nomenclature.  Hassenfratz,
    the publisher of the nomenclature, and of the symbols which he had contriv-
    ed, was also high in office, and most active in all the projects of Robespierre.
    It is not, therefore, on light grounds that I have assigned  the same motive to 
356           STATEMENT OF  FACTS.
de la route que vous avez si glorieusement suivie.   Votre ap-
probation,  Monsieur, dissipe mes inquietudes,  et me dcmne un'
nouveau courage,   je ne serai content jusqu a ce que les cir-
constances me pertnettent de vous aller porter moi meme le te-
moignage de mon admiration, et de me ranger au nombre des
vos disciples.   La revolution qui s'opere en France  dcvant na-
turellement rendre inutile une partie de ceux attaches a l'ancien
administration, il est possible que je jouisse du plaisir de la li-
berte:  et le premier usage que j'en  ferai, sera de voyager, et
surtout en  Angleterre, et a Edinbourg, pour vous y voir;  pour
vous entendre, et profiter de vos lecons, et de vos conseils."
  Dr.  Black wrote him a very plain, candid, and unadorned let-
ter  in answer, expressing his acquiescence in his system.   Mr.
Lavoisier answers this by praising, in the highest terms, the ele-
gance of the style,  the profoundness of the philosophy, &c. &c.
and begs leave to insert the letter in the Annales de Chymte. Dr.
Black, who had been in very low spirits when he wrote that let-
ter, and was much dissatisfied with  its feebleness, was disgust- .
ed with what he now conceived to be artful flattery ; and refus-
ed to grant the request.  Yet his letter appeared in that work *fc
before his  refusal could reach Paris.
  This wheedling, in order to extort from Dr.  Black an acqui-
escence, on which he put a high value, for the influence which
it .would have on the minds of others, was surely unworthy of
Lavoisier.   Dr. Black was not only disgusted with the flattery,
but seriously offended with its insincerity ;  and with a sort of
insult on his common sense, by the supposition that he could be
so wheedled, by a man whose publications never expressed the
smallest deference  for his opinions.   For, by this  time,  Dr.
Black had read Mr. Lavoisier's Elements of Chemistry, and the »v
various dissertations by him and Mr. De la Place, published in_ i
the Memoirs of the Academy.  His name is not once mentioned,^:'
even in the dissertations on the measures of heat, where his doc-
trine of latent heat is delivered and employed as the resu^ of
Mr. Lavoisier's own meditations.   Nor is he named in^^fiose
passages of the earlier dissertations, where the characters  and  '
properties  of fixed air, and of the mild and caustic alkalis, are
treated of.  All appears to be the train of Mr.  Lavoisier's own
thoughts, for which he was indebted to no  man.  Such incon- 
             REFLEXIONS SUGGESTED BY  THEM.   357

      sistency with the deference expressed in the above cited letters,
      provoked Dr. Black to such a degree, that he resumed his cri-
      tique on the nomenclature, and began to express his dissatisfac-
      tion with some parts of the theory, and his utter disapprobation
      of the  unscientific and  bullying manner  in which the  French
      chemists were trying to force their system on the world.  But,
      by this time, his health had become  so delicate, that the least
      intensity of study not only fatigued him, but made him serious-
      ly ill, and forced him to give it up.  I saw him but seldom  at
.      this time, being then in very bad  health myself;  but had this
^     information from Dr. Hutton, who shared all his thoughts.   It
      was at  this  time that he gave up his intention of making a consi-
      derable change in the arrangement of his lectures, and that he
      expressed himself, as I have related, at the end of the introduc-
      tion to  the particular doctrines of chemistry.  But still, notwith-
      standing the contempt which he expressed for the folly of a man
      who had tried, by  fulsome and insincere flattery, to obtain what
    .  he had given him  unasked,  by teaching all his doctrines, Dr.
      Black considered the death of Lavoisier  as a  great loss to the
  ^"  science*.   He expected much from his penetration and sound
      sense:   and he considered him  as the  only person who could
      keep his followers right, by checking  their precipitant manner of
      proceeding.
        Professor Lichtenberg, of Gottingen, a man of extensive and
      accurate knowledge in every department of natural science, gives
      9x1 entertaining and instructive account of the introduction  of
      these doctrines into Germany.  It is to be found in his preface
      to the edition 1794, of Erxleben!s Introduction to Natural Phi-
      losophy ; as also in the Literary Magazine oi Gotha.   Great
,«■'*'hesitation,  doubt,  and objections,  were to be expected in Ger-
: §  ... many,  the  native soil of chemistry,  and the resort of all who
 • •  ■'« wished to perfect themselves in mineralogy.  The new doctrines
      were even received with aversion and disgust.   This, he says,

        1
        * Jiliis ornament of France fell a sacrifice to the ambition of the very men
      whonihe had associated with him in his labours and honours.  They were all
      persons in office, or national representatives, and, in that character, gave their
      consent (to say the least of it) to his sentence of death. But he was rich, and
      loyal,—they were---and--- 
358       REFLECTIONS SUGGESTED, &c.
was chiefly owing to the character of the nation  from whence
they came.  The Germans, who had been accustomed to con-
sider themselves as the chemical teachers of Europe, could not
bear to hear the opinions  of their master, Stahl, treated with
contempt; to be told by Frenchmen, living among them for in-
struction,  that  the principles of Stahl were  such as no man
could embrace who had a spark of common  sense ; to be told,
in letters from  France,  that the principle of Stahl  was a  mera
qualitas; a mera contemplatio, a fancy of the brain, which dis-
graced any man who entt rtained it for a minute ; and to h-ive it
added, with  saucy  politeness,  dulci requiescat in pace!  But
what most provoked them, was  the pitiful  triumphs of victory
in which the French chemists indulged themselves.  He says,
that when the association had finished their experiments on the
composition and decomposition  of water, which filled up all the
gaps of the system, they  had  a solemn meeting in Paris, in
which Madame Lavoisier, in the habit of a priestess, burned
on an altar Stahl's Chernia dogmata a et Experimentalis Funda-
menta, solemn music playing a requiem.  And he remarks, that
if Newton had  been  capable of such a childish triumph  over  .
the vortices of Des Cartes, he could  never be supposed the man
who wrote the Principia.  I  might add, that if  Newton or
Black had so exulted over Des  Cartes and Meyer,  their coun-
trymen would have concluded that they were out of their senses.
But at Paris every thing becomes a mode, and must be fete.
Dr. Black's nice sense of propriety made the intriguing conduct
and arrogant  assumption of all  merit by the French chemists
extremely offensive to him ; and probably made him so minute-
ly careful to place in full view all the labours and discoveries of
the British and  Swedish chemists, particularly those of Caven-  '
dish and Scheele, which supplied the great facts on which the
ingenious doctrine of Lavoisier is established.—I flatter myself '  '
that this statement of facts, and these reflections, will not be
thought improper or unimportant. 
.^
VARIETIES OF INFLAMMABLE SUBSTANCES. 359
  We shall now proceed to take a nearer view of the different
kinds of the inflammable substances.
  The most remarkable inflammable substances may be arranged
under seven titles,  which are these :
  1. Inflammble air.
  2. Phosphorus.
  3. Sulphur.
  4. Charcoal.
  5. Spirit of wine.
  6. Oils.
  7. Bitumens.
  Of these, the first four may he called Simple  Inflamma-
bles ; because we have not been able to resolve them into sub-
stances more simple.  Ardent spirits,  oils, and bitumens, are
very easily resolvable, and are vastly complex.


               I__INFLAMMABLE AIR.


  The first  in this  order, the gas pingue of Van Helmont, the
substance which has been long known by the name of Inflam-
mable  Air, is certainly the most subtile and most  highly in-
flammable of all the bodies that belong to this class.   The pe-
culiar phenomena and consequences of its inflammation, as well
as what was observed in combining it with other bodies, caused
,it to be considered by some  authors, of the first  rank  among
chemists, as the true phlogiston of the chemists, or as totally
Tnade up of their principle of inflammability.   This opinion of
it was formed by  Mr.  Cavendish, and by Mr. Kirwan, who
published his thoughts  on this subject in the Philosophical
Transactions for the  year 1782; and, after that time,  in a se-
parate volume.   And Dr. Priestley had nearly the  same opi-
nion of it.  But, since  that time, Mr. Kirwan has abandon- 
  360           %  INFLAMMABLE AIR.      /      f

  ed  the supposition  of a phlogiston in the inflammable sub-
  stances.
    This inflammable  substance has been  known a long  time.
  Indeed,  it must have been known  as early as any  considerable
  progress was made in the knowledge of nature and chemistry.
  Van Helmont calls it gas pingue.  It is not always  precisely the
  same. There are great varieties of it, occasioned by impurities or
  admixture : and some of these are found  in almost all that is
  obtained already formed by  nature.   But it may be  also pro-
  duced, or extricated from different substances artificially, by a   #  i
  variety of chemical operations.                                  J
     It is frequently met with in mines, especially in those of coal;   ■
  and renders the working of them  extremely dangerous.  It is    «1
  called by the miners*the fire-damp, or wild-fire.   It is also ex-
  tricated or produced from  animal and  vegetable substances,
  when these are decompounded and destroyed by fire or putre-
  faction.   And hence it  is that there  is a small quantity of it
  mixed with the black mud of putrid  ditches and marshes in
  summer, which mud is composed  of the putrid remains of ve-%> (  ;
  getables and animals.   If a stick be thrust down to the bottom '  •
  of such ditches, and the mud be stirred, a number of air-bubbles
  rise to the surface of the water, and a candle being held near it  '  \
  at the same time, the air will take fire, and give a momentary
  flash.   Or it may be collected in inverted  glasses filled with the   '/[
  water, and may be afterwards fired.  This was first discovered
  by the celebrated Dr.  Franklin*.   The knowledge of that kind
  of it which occurs in coal mines, must have been as early as the
  art .of mining coal.
     In  those coal mines which are infested with it, it is  observed  ^
  to issue  from crevices of the  strata in the subterranean cham* V/ffl
 ' bers of the mine, in form  of a vapour or aereal fluid, whicfilV.  3
  mixing with the  air of the mine, is said to produce some de-    "•
                                                                  i
    * Van Helmont mentions this, and acids, " Stercoraceus flatus, per flam.
  " mam candelte transmissus, transvolando accenditur; ac flammam diversico-
'  " lorem, instar iridis exprimit."  (De Flatibus, § 49.)
    It is even produced by some living plants. The Dictamnus Fraixnella emits
  it from its flowers in such abundance in a calm evening, that it may be set on
  fire by a candle, nay, take fire of itself. 
INFLAMMABLE AIR IN MINES.
     gree of misty appearance in it.  And, when it is not very abun-
     dant, it does  not communicate any unwholesome  quality to
     that air.
       The greatest danger attending it proceeds from its high de-
     gree of inflammability; the smallest flame, as that of a candle,
     being sufficient for firing the largest quantities of it, with a vio
     lent explosion.  And, unfortunately, in those places, no work
     can be done without  artificial light.   In some mines they are
     obliged to work by the dull  light produced by a piece of flint
l    rubbing against the circumference of a steel wheel, which is
m   jagged like a file.  When it happens unfortunately that consi-
f   derable quantities take fire, the  inflammation of it is as rapid
     and violent as  that of  gunpowder.   And it produces an explo-
     sion almost like thunder, and which is attended with most dread-
     ful effects.  In some cases, the whole  works of the mine are
     demolished,  and numbers of  miners killed, and sometimes
     blown up,  with heavy  machinery, to a considerable height in
     the atmosphere.  These  shocking effects are produced by the
     great expansion which the flame occasions in the air and vapour
     that is mixed with it. . The inflammable air itself does not ex-
     pand in the act of inflammation, but, on the contrary, collapses
     into very small bulk.   But it is then mixed with the vapour of
     water, and with azotic  gas, both of which it expands, and forces
     them along the long and narrow chambers of the mine ; and
     sweeps every thing along^with it, just as the firing of gunpow-
     der accelerates  a bullet along the barrel of a musket.
       In some mines, in which the sources  of this vapour are  but
     scanty, and in which it requires a long time before a considera-
     ble quantity is collected, they preserve themselves from danger
■:£*' bjf firing it frequently, and therefore, by small  quantity  at a
V-.   tlmje.   They observe the places in which it collects, which are
     always over their heads,  or in the hollows of the roof of their
     subterraneous workings,  it being the rarest or  lightest of all
    fluids that we know.  When pure, it is but one-fifteenth of the
    weight of an equal bulk of common air.   At stated times they
    set fire to it with a candle fastened to the end of a long stick,
    or tied to the middle of a long string, the two ends of which
    are held and drawn by two men at a distance from the spot.
      Vol.  ii.                              z 2 
362     INFLAMMABLE AIR IN MINES, &c.

   But there are some coal mines in which the sources of it are
too abundant to be easily  managed in  this manner.  In these
they have recourse to another method, by which it is constantly
carried off  and destroyed, namely, by having wooden trunks
or pipes conducted  along the  roof of the  workings,  (so the
chambers of a mine are named) with branches carefully leading
to all the places where this air most  copiously gathers.   All
these trunks meet at the bottom of a shaft;  and from thence a
great trunk is carried up, to the surface, in a corner of the shaft,     1
where it enters into a small chamber having a tall chimney.  A    J
fire is kept in this chamber, and air is supplied to it only from   M
this trunk.  The warmth of the chamber and chimney produces   ■
a current:  and thus the air is  collected  from  all  parts of the    1
mine.  When the inflammable air is very copious,  it is said to    j
burn at the top of the trunk,  and produce heat enough, with-    ■
out any more fuel,  for maintaining a continual flame and cur-   fm
rent.                                                         v j
   There are  several places on the Continent, particularly in
Italy, where a vapour  of this kind breaks  out at the suriace of  t)
the earth,  and is liable to take  fire, producing a lambent flame.
In England there is an example or two, recorded in the Philo-    j
sophical Transactions.  In Persia, there is a small district,   1
where the  inhabitants collect it into one place by means of co-    1
vered gutters, and there  setting fire to it, use it for dressing   jjl
their victuals, and even for lighting their huts.  I doubt much   J
that these are exaggerated accounts; for this extremely rare fluid
gives so little heat, that its flame scarcely will scorch the hand;
and the light is proportionably feeble.  When  it rises  through   I
the water  of  wells in bubbles, they burst at the surface: and   I
when they are very copious, so that while one is burning another , '■., 1
rises close by it,  then  a candle being applied,  flame catches at   -j
the surface, and continues with a crackling noise.   In the burn-^f. %
ing well at Chittagong, in India, it takes fire of itself after hav-   I
ing been extinguished by  dashing pailt'uls of  water in it.
   Besides these  examples, where it is formed by nature, I said    *
that it is also very frequently produced from different substances
artificially, by a variety of chemical operations.
   The examples of  this are too  many to admit of  my enume- 
INFLAMMABLE AIR,
363
     rating them all here*.  I shall for the present mention only one
     simple process  by which this gas is produced in a high degree
     of purity.   We need only to mix some of the strong sulphuric
     acid with about eight times its weight of water, and throw into
     the mixture some very clean iron filings, equal in weight to half
     of the  sulphuric acid.   The  iron is dissolved  with ebullition
     and heat: and a great quantity of this a^eal inflammable sub-
     stance arises from the solution, and  may be collected in vessels
     filled with water, and inverted into  a vessel of  water.
       This has been long known to the  chemists  : and it? was usual
i    with them,  when they had occasion to dissolve iron  in the sul-
r    phuric acid, to amuse themselves by firing this vapour, to make
     it give  explosions,  or burn in different ways.
       But no other experiments were made to  investigate its na-
     ture in other respects, until after  I had made the experiments
     on quicklime, and on fixed air, which I have already described
     to you.
       I had then the curiosity to try whether this gas was attracted
     by alkaline substances,  in  the  same  manner as fixed air  is at-
     tracted by them ; and I satisfied myself that it was not.  I was
     also accustomed to exhibit to my pupils the different manner in
     which it  burns when pure  or when mixed with  air.   When it
     issues pure, in a  continued stream, from a  pipe, a candle ap-
     plied to the jet will kindle it: and it will continue to burn qui-
     etly as fast as it issues;—but not  till it is out of the pipe, be-
     cause it burns only where it is in contact with vital air.  But,
     if the vessel from which it issues contain vital  or atmospheric
     air also,  mixed all over with the inflammable  air, then a candle

 .;'i5  .s-.» yye must, however, carefully distinguish the inflammable  air of which
    Dr. Black is now speaking, from a vast multitude of inflammable vapours
i; itfwhich nature and art produce.   Oils, vinous spirits, and many other inflam-
 ' : 'mable substances, can be changed into vapour by heat; and the vapours are
\   inflammable, of course.  But we are now speaking of a peculiar substance,
    which we have never been able to decompound, and therefore  assume as a
    simple substance.  This, when pure, is always the same,  in whatever way
    we procure it.  The other inflammable and incondensible airs are not simple,
    but yield, by burning, carbonic acid g*s.—Editoh. 
 364     INFLAMMABLE AIR—ITS LEVITY.

 applied to the mouth will fire the whole in an instant, with an
 explosion that will burst the vessel, if not very strong.
   The Honourable  Mr. Cavendish, some time  after, (anno
 1766) published in the Philosophical Transactions, experiments
 on this and other kinds of air ; by some of which he ascertain-
 ed, with great ingenuity and exactness, the density of different
 airs or gases, compared with that of common air.   He found
 that the gas we are now speaking of, has a surprising  degree of
 rarity.   It weighs less than the one-tenth  part of the weight of    J
 an equal bulk of common air.  Therefore, if you would keep    J
 it in  an open vessel for any immediate experiment, you must   r,
 keep the mouth of the vessel down, and the bottom uppermost.   w
 If you fire it in this  situation in a tall glass, and  immediately   I
 turn it  up,  the inflammable air rises  in a beautiful burning co-
 lumn.                                         *
   As soon as this discovery  of its great levity was published,
 it pointed out an obvious consequence, which immediately oc-
 curred to me,—that if a quantity of  gas could be confined in a
 vessel,  or other containing matter that wras exceedingly thin and    j
 light, the gas and vessel together might form a mass lighter than    (
 an equal bulk of common air, and which would rise in the atmos-
 phere, as cork does in water.  I therefore thought of providing   i
 a vessel or envelope for this purpose ;  and that which first oc-
 curred  to me was either the allantois or the  amnion of a calf,  'M
 which I procured.  But not getting it ready soon enough to shew    |
 the experiment at the time I intended it, I did not exhibit it; but
 mentioned it in  my lectures  as a thing which might be  found
 practicable, though I  did not see that it could be  applied to any
 use.  I did not  imagine that the same idea would have  been
 improved to such a degree as it was afterwards in France.  All. * •„'.
 the world has been amused with their air-balloons,  which  they <. £
 soon made of such a monstrous size as to lift very heavy weight* -
 to a great height in the air*.  Of these balloons two kinds have
 been made use of in their experiments.                           j

  * It is worthy of notice, that Dr. Mayhow, in his dissertation de spiritu ni-
tro-aereoy describes experiments which have certainly been made with oxygen
gas. He also gives very plain hints of balloons filled with a substance much
lighter than air, which he says was known to him.—Editor. 
             VAIN PROJECTS WITH  BALLOONS.     365

        Mr. Mongolfier, a paper-maker  at  Lyons, first thought of
     making a balloon so light as to float in the air, merely by burn-.
     ing shreds of paper or straw under the mouth of a great globe
     Qf paper or thin linen.  Having succeeded,  he  made another
     so large as even to carry up a considerable weight; and, in or-
     der to keep it afloat, he hung under it a choffer,  in which the
     fuel was renewed by the persons who were  carried up by it.
     He made others of 40 feet diameter, and 70 feet high, which
     carried six or seven persons.
       When accounts of this contrivance reached Paris, the inhabi-
     tants of which  are keen for amusement, Mr.  Charles, an intel-
     ligent chemist, immediately recollected the immense superiority
     of inflammable gas for a project of this kind;  and readily found
     men of fortune and pleasure to contribute to  die great expense
     of such entertainment, which in several cases amounted to more
     than 500/.  His balloons were made of a thin but strong  silk,
     made air-tight  by varnish: and they were filled with gas  pro-
     duced from  iron dissolved in vitriolic acid,—but so far from
     pure, that it was not more  than seven times lighter than com-
     mon air.  Indeed, this is as much as should be  reckoned  on;
     because the iron employed  is generally rubbish, rusty, and even
     cast iron,  which produce much fixed air.  His balloons were
     much smaller than Mongolfier's, but rose to a very great height,
     sometimes almost three miles.
       Since,  in order merely to float, the weight of the balloon  and
     air must not exceed that of common air, there is a minimum of
     size, depending on the weight of a square foot of the covering.
     The smallest balloon of thin post paper, that will merely float,
     is seven inches  in diameter. Strong post paper must not be  less
    , than thirteen inches.  Oiled silk  will float, if two feet ten in-
.•>   ';ches,—and oiled linen, if four feet six inches.   An oiled linen
    •balloon, of nineteen feet diameter, will lift  a weight of 250
     pounds a mile high. And other sizes will lift nearly in the pro-
     portion of the cubes of the  diameters, when they are large.
       These experiments gave rise to a number of projects for per-
     forming voyages with such  machines; though  it must have  ap-
    peared evident to any person who understood their nature, and 
366
INFLAMMABLE AIR.
considered it well, that they were totally unfit to be applied to
any such purpose.
  That air balloons cannot be applicable to the purpose of making
voyages, or of traversing the air in any direction that we please,
is evident, by these reasons :
  1st, We cannot find a power that will be sufficient for mov-
ing such bulky masses through the air, and that  can be lifted up
by them.   The force of one man, or of any number of men
which the balloon can lift, is  very far  from  sufficient for mov-
ing it with the requisite velocity  for performing voyages, even
in a perfectly calm air.  And if there be the least of a contra-
ry wind, they could not move it an inch in  the  proposed direc-
tion.   All this is true, even supposing that the  whole  force of
those men could be  employed or  exerted in  order to move it.
But how are we to employ  or exert this  whole force, when the
balloon is  suspended in mid air ?  Had the men some fixed im-
moveable body, towards which they could draw the balloon with
ropes, or from which they could push  it with poles, their whole
force  might be exerted. But they have nothing to push it'from,
except the empty air,  (as it is styled  by the poets) a fluid so
rare, that it gives very little resistance.  And the force of the
men would be mostly expended in moving their own limbs and
the instruments, whether oars or  wings, with which they should
attempt to beat or to push that air.   When  a boat is impelled
through the waters by men  and oars, the oars are applied to a
medium, which, though fluid and yielding,  yet gives incompa-
rably  more resistance  and power  to the stroke of the oar, than
air.   It is more than 800 times as dense as  air.   And  besides,
the boat is formed for moving through the water with the least
resistance possible.  The two machines cannot be compared to-  *
gether.
  Some again have  thought of the  example of ships, which can
be made to go in different directions  with  the  same wind,  by
setting their sails obliquely to the  wind in  different positions.
And they thought that some sort of sails might be applicable to
a balloon.  But here again  the case is  totally different.   A ship
has a hold of the water by her bottom  and hull while she is im-
pelled by the wind.   And the form of the vessel disposes it to 
         VAIN PROJECTS WITH BALLOONS.    367

  glide easily through the water with the prow foremost, but  to
  be difficultly moved with  the broad side.  In consequence  of
  this, it is made to sail in many different directions with the same
  wind.  The balloon has no hold of any thing whatever, but the
  air or the wind itself.  It is, therefore,  carried  along by that
  air, as a feather would be ;  and has as little power to resist the
  action of the air on it as a feather has.
    2dly, Beside all these,  there is still another and an insupera-
  ble reason against the possibility of using balloons to make voy-
  ages,  and to command their motion and direction.  They must
  necessarily be made of very thin  materials, and  of the most
  flimsy construction, that they may be sufficiently light.   Now,
  supposing we could apply a power to them that could move them
  with sufficient velocity, they could not support the impulse and
  resistance of the air against them while they moved through  it.
  They would immediately be torn in pieces.
    In the common manner  of  using them, when no attempt is
  made to direct or  modify their motion,  they  are  secure from
  this accident, being then carried along by the wind as a feather
  would  be;  so  that although they are moved  sometimes  with
  great velocity, they are not exposed to any violent impulse of
  the air on any one side of them more than another. They move
  as fast as the air itself, and the persons who are  in them feel as
  if they were becalmed.
    3dly, They cannot remain suspended in the atmosphere for
  any considerable time.
    4thly, Another inconvenience, and  even danger to which bal-
  loons  are exposed, is a whirlwind, which they sometimes raise,
  and by which some of them have been agitated, with great dan-
»  ger to the aeronauts.       '
    Thej only use to which they have been found applicable,  is
  one which occurred to me, and which I have occasionally men-
  tioned ever since they were  contrived, viz. for  reconnoitering
  the position and strength of an enemy's encampment, and posts,
  in the art of war.   It has been common to ascend steeples and
  rising grounds for this purpose.   But in calm weather, a bal-
  loon, secured with a rope, can  easily  be made to rise  to many
  times the height of a steeple. 
 368             INFLAMMABLE AIR.

   Let us now return to the examination of inflammable air.
   Another remarkable property of inflammable air, is its high
 degree of inflammability*.
   The flame of this gas, in its unconfined state in common air,
 is extremely weak, as is reasonable to expect from a fluid so ve-
 ry rare, that a cubic foot weighs only 37 grains.  The best way
 of observing it in this situation, is to blow up a soap bubble with
 it, and fire it with a candle.   A  more showy way is to fill with
 it a tall glass, having a movable bottom.   It must be held with
 the bottom uppermost, otherwise  the gas will soon disperse by
 its great levity.  Holding the glass upright, and a candle a lit-
 tle way above it, (about twice the height of the glass) remove
 the bottom suddenly ; and the gas, pushed up by the air below,
 Will rise and meet with the candle, and form a beautiful column
 of lambent flame not  hot enough to singe the finest down.   It
 burns with a brighter flame at the mouth of a pipe ;  because it
 is denser there, especially if  strongly pressed out, by squeezing
 the bladder which contains it.
   It burns with more vivacity in vital air:  but the difference is
 not so remarkable as one should expect.  Yet, on reflection, we
 must be  sensible that  so small a quantity of inflammable matter
 must be completely and instantaneously inflamed, even in com-
 mon air, with which it readily mixes.
   The examination of the phenomena which accompany the in-

  * It catches fire by the smallest spark.  The most trifling electric spark is
 sufficient.  But  it  seems as if the  mere  elevation of its temperature  is not
 enough ; for it is very difficult to fire it by passing it through a red hot tube,
 or by blowing it against a lump of ignited, but uninflumed matter.  Even in
 the cases where we succeed, I am doubtful whether it is not by a spark of in-
 flammable  matter in the act of composition, that it is kindled.  For I observe,
 that when the purest that I  could obtain, by dissolving a metal in muriatic acid,
 is kindled at the end of a tube, from which it issues in a stream, the dullflanie
 with which it Ixirns has in  the very middle a continual train oi" brighter ruddy-
 sparks, which not only rush straight forward,  but frequently split and dart
 sideways, with a momentary brilliancy, like the sparks ^brandishing iron.
I suspect that these are scarifications and  explosions.  These may be effected
by the contact of a red hot tube, and will fire the gas. We know, without be-
ing able to  explain it, that the action of the electrical spark is of the same
kind.  It seems to be only  a comparative security wlueh the light from flint
and steel gives to the miners. Yet I confess that I have not been able to fire
it in this way.—Editor. 
               EXPLODED WITH VITAL AIR.       36S

    flammation of it in vital air has been productive of such exten-
    sive consequences, and has so enlarged  our knowledge of the
    chemical operations of nature, that I think it necessary to give
    you an historical account of it,  and of the contributions which
    different authors have made by its means to the general stock of
    knowledge.
      Dr. Priestley's examination of  the gaseous fluids had  exhi-
    bited a great number of concrete substances brought into an aere-
    al form, contrary to all our former conceptions of things.   But
    this particular gas occasioned a discovery still more unlooked
    for.  A substance  which had been  considered as an element,
    not only in the very dawn of  natural philosophy, but whichhad
    maintained the character undisputed by the most acute and pe-
    netrating chemists of this most inquisitive age, is now found to
    be a compounded substance, and its ingredients fairly put into
    our hands.
      Dr. Priestley was occupied with the examination  of inflam-
    mable air, and tried the effect of  almost every substance on it.
    He also tried  the effect of the electrical shock and  spark.   As
    he expected, he found that it was expanded by it; but could not
    be inflamed by it in close  vessels,  unless  mixed with common
    air.  In this state it  fired with a violent explosion.  He was
    particularly surprised at the great  diminution of bulk,—finding
    that a mixture of one part of  inflammable air, and two of  com-
    mon air,  might be made to contract into  half the bulk, and that
    it was now phlogisticated air.   Having already discovered the
    vital air,  he fired a mixture of .these, and found that when two
    parts of inflammable air and one of vital air were exploded to-
    gether, it collapsed  into almost nothing, or nearly the whole dis-
  appeared.   Mr. Warltire, who assisted  in these experiments
• *  observed that  the inside of the vessel in which the deflagration
   had been made, .was always moistened with dew.  Dr. Priest-
    ley naturally a^^ribed this to moisture, which probably adhered
    to the ai'rs employed ;  as they  were always produced in proces-
    ses in which water in some form or other was  present.   These
    experiments were.made abgut  the year 4 782.
      My friend Mr. Watt had taken  great interest in these expe-
   riments of Dr. Priestley's : and communicated his opinion  con-
      vol. n.                           3  a 
370
INFLAMMABLE AIR.
cerning them to Mr. De Luc, in a letter dated April 1783. This
letter is, in part, a transcript of one written some months before
to Dr. Priestley, with a desire that it should be communicated
to the Royal Society.   In this he declares his opinion,  that the
water observed in these experiments arose from the combination
of the two airs; and says, that water is the compound of de-
phlogisticated or vital air, and inflammable air, deprived of their
latent heats ; and that  dephlogisticated air is water deprived of
its phlogiston (i. e. of the inflammable air)  in an  aereal form,
that is, saturated with  the matter of light and heat.  Dr. Priest-
ley did not communicate  this to the Society, because (he says)
some experiments which he had made since he saw  Mr. Watt,
were directly contrary  to this opinion.
   Dr. Priestley's experiments excited the attention of  the Ho-
nourable Mr.  H. Cavendish ; and recalled to his mind his own
observation of the moisture in the vessels in which he  had ex-
ploded these two airs.   These experiments had been begun in
the summer 1781 ; and were continued from time to time, along
with those by which he had discovered the composition of the
nitrous acid.  He immediately set about repeating the explosion
of dephlogisticated and inflammable airs by the electrical spark.
And in May 1783, he found that when six  parts by weight of
pure dephlogisticated air were  exploded with one of inflamma-
ble air, they disappeared entirely; and that  the result was a
quantity of pure water, equal in weight to the airs employed.
The  utmost care had  been taken to free the airs made use of,
by making them pass through the dry muriat of lime.  The ves-
sel burst in several of his experiments ; because, in the instant
of explosion,  the vapour of the produced water was expanded
by the heat extricated  from the airs.   Much of this heat, to be
sure, was expended in giving these the vaporous form, or sup-
plying it with latent heat.   But the vessel was instantaneously
heated, shewing that the heat contained in  the  two airs more
than sufficed for this purpose.  These experiments were publish-
ed in the Philosophical Transactions for 1784.
   Such curious experiments, and so interesting a result, could
not remain a  secret, had such a thing been intended. But there
was no such intention.   Mr. Blagden, secretary of the  Royal 
COMPOSITION OF WATER.
 Society, went to Paris in June 1783; and  communicated these
 experiments of Mr. Cavendish to Mr. Lavoisier, and his asso-
 ciates, De la Place, Meunier, Monge, &c. knowing that they
 were much interested in their result, which was so intimately
 connected with the new theory which Mr.  Lavoisier was then
 establishing.
   Accordingly, Mr. Lavoisier, who saw the immense conse-
 quence of this discovery to his theory,  immediately set about
 repeating the experiment of composing water by the combina-
 tion of the two airs; and in September 1783, with the assistance
 of Mr. Meunier, effected the composition in a way that admit-
 ted no doubt.  Instead of effecting it by the explosion of a few
 grains of gas, which is all that a manageable vessel of glass can
 contain, he did it by admitting two  fine streams,  one  of each
 gas, into a balloon, through two tubes leading from large maga-
 zines of gas, and having their points so near to each other that
 the streams mixed immediately.   The gases were  supplied in
 the due proportion by regulated pressures of water on the gases
 in the magazines.  While the  pipes were  thus delivering the
 due proportion of gas, it was fired by an electric spark, and the
 flame continued as long as the gases  continued to be supplied.
 In this manner, very great quantities of  gas were inflamed,  so
 that the unavoidable errors in the ultimate measurement bore a
 very small proportion to the whole. At the end of the operation,
 there was commonly a remainder of  carbonic acid and of azote,
 from which it is almost impossible to free the gases completely.
   The result of this capital experiment was perfectly conforma-
 ble to that of Mr. Cavendish.  When the exact proportion  of
 gases  was attained,  the result was  water  slightly  acidulated.
 This  proportion was fourteen  parts by weight of inflammable
 air, and eighty-six of vital air.
   Mr. Monge made a similar experiment at Mezieres, in June
 1783,  with the same result, and (he* says) without having heard
 of the experiments of Mr. Cavendish,  or  those of Lavoisier
 and Meunier. The vital air employed weighed five ounces five
 drachms twelve grains :  and it left thirty-five grains of water  in
the muriat of  lime through which it passed.  The inflammable
air weighed six drachms thirty grains, and left forty-four grains
of water.   Therefore the quantities which really burned were__■ 
S72     INFLAMMABLE AND  VITAL  AIRS

                                          oz.  dr. gr.
     Vital air    .     .     .     .     .     5  4  49
     Inflammable air    .    .    .    .      5  58
                                            6  2  35
      Mixture remaining unburnt      .          6  24

      Quantity of gases compounded    .     5  4  11
      Water produced    ...    .     5  4  41
   This excess of thirty grains must be ascribed to errors in the
estimation and weighing of the different articles.  The water
was not perfectly pure, but contained five grains of nitrous acid
in each ounce.
   Some time after, in 1798, Mr. Seguin again repeated this
experiment, expending 25582 cubic inches, or nearly two hogs-
heads  of  inflammable air, and  12457 of vital  air.  The first
weighed  1039i grains,  and  the  second 6210, amounting  to
7249\ grains. And the water obtained amounted to 7245 grains,
which is nearly 5944 grains English troyr, about three-fourths of
an English wine pint.  No greater loss than four grains, in an
experiment of this kind, is an exactness of which one  has no
idea.   I doubt not,  however, as this relation is a formal report
from the Academy  of Sciences, but that the experiment was
very accurately performed, and the result extremely satisfactory.
   Another experiment still was  made by Le Fevre de Geneau,
in which 35085 inches of oxygenous gas, and 74967 of inflam-
mable gas were burned, weighing two pounds three ounces and
sixty-four grains, (French poids de marc): and two pounds three
ounces and thirty-three grains of water were obtained, contain-
ing twenty-seven grains of nitrous acid.   Still more trials were
made by Von Hauch, employing  3000  and  5000 inches, also
with 1600 and 3000.  The aim of so many laborious and expen-
sive trials was, to hit the proportion of gases So exactly that the
water should be pure ;—but it was always contaminated with ni-
trous  acid.  This valuable information, however, was obtained
from it,—that it was indifferent what acids  had  been employed
for obtaining either of the gases.  Nitrous acid only was found
in the water. 
COMPOSE  WATER.
373
   A very candid and intelligent account is given of all the dis-
 coveries relating  to  the  inflammation  of these two gases in
 the  translator's preface  to the second edition of Fourcroy's
 Chemistry.
   Mr.  Cavendish, the original author of these  experiments,
 and of  the doctrine deduced from them,  concluded that water
 is a compounded substance, and that its constituent parts  are
 vital air and phlogiston, viz. inflammable air.  For at that time
 Mr. Cavendish was of opinion that inflammable air is the true
 phlogiston of  the chemists.
   But,  although Mr.  Cavendish is the undoubted author of this
 decisive experiment,  and, with Mr. Watt, is also the author
 of the  important  doctrine of  the composition of water,  Mr.
 Lavoisier has the  still greater  merit of seeing this proposition
 in all its importance.   This incited him to undertake these la-
 borious  and expensive experiments, which confirmed those of'
 Mr. Cavendish beyond a doubt.   And he had also the sagacity
 to-perceive immediately,  that by means  of this proposition, he
 should extricate his great system from difficulties and objections
 which I think would otherwise have been unsurmountable;  and
 even to convert them into strong arguments in its favour,  and
 make them the means of extending it  to chemical facts,  and
 to the great operations of nature, which seem otherwise inex-
 plicable.
   Thus excited, Mr.  Lavoisier was not contested with having
 demonstrated that the explosion of vital and inflammable airs
 produce pure  water:  but, in September 1783, with the assist-
 ance of Mr. de la Place, he confirmed this demonstration of the
 composition of water  by decomposing it,  and producing its in-
 gredients in a separate state.  I shall therefore relate to you Mr.
 Lavoisier's experiments on this subject, and the manner in which
 he reasoned from  them.
   His first experiment consisted in simply putting some clean
• filings of the purest iron into distilled water,  which filled a jar
 standing in the same water.  After standing some  days, a
 quantity of pure inflammable air is found collected in  the  top
 of the  jar, and the  iron is found  corroded and black; and
 when carefully dried, weighs  more than before, and if  ex- 
374  MR. LAVOISIER DECOMPOSES WATER.

posed to heat in a retort,  affords vital air.   The iron, says he,
attracts the oxygen of the water, and the inflammable air is set
at liberty.
  The second experiment is more remarkable.  A small glass
retort, having a very long neck, and holding an ounce or two
of water, is so placed that this neck passes through a choffer of
live coal, by which it is maintained red hot, while the water in
the  retort is made to boil gently.  The vapour is collected and
condensed  in  a proper pneumatic apparatus.   It  is found to
be  pure water, and precisely  equal  in weight to the  water
boiled off.
  But, having put into the neck of the retort 28 grains of pure
charcoal, and  repeated the distillation,  he found that the  char-
coal had vanished;  and that the water collected in the receivet
was 86-j^ grains less than the water which had quitted the retort,
which was 113^ grains.   But he found in the pneumatic vessel
connected with the retort and receiver,  100 grains of carbonic
acid,  and  12 of inflammable air.   Here, therefore,  it appears
that the carbone had attracted the oxygen of the water, and thus
decomposed it.  The quantity of the carbonic acid  was  deter-
mined by passing the whole elastic matter obtained through milk
of lime, which absorbed it.  Now 100 grains of carbonic acid
had been long before proved, by his experiments, to contain 72
grains of oxygen.  This quantity of oxygen, combined with
13-^ grains of iriflammable air, would  compose 85^ grains of
water.  There appeared,  therefore, a deficiency of  1T7„  grains
of inflammable air.
  In  a third experiment, he placed, instead of the charcoal,
274 grains  of  fine soft iron wire, loosely coiled.  At the end
of the operation, he found the iron changed into  black  iron
scales, such as are found to fly from iron  in forging, and 85
grains heavier than before.  In the receiver he found 15  grains
of pure inflammable air;  and there was'a loss of 100 grains of
water.  Now 85 grains of vital air, when united by inflamma-
tion with 15 grains of inflammable air, should compose very
nearly 100 grains of water.
  The conclusion from these experiments is so evident,  that it
is needless to go through it minutely.   I have not used the pre- 
    INFLAMMABLE AIR, OR HYDROGENOUS GAS. 375

    cise numbers which occurred in Mr. Lavoisier's experiments,
    but such numbers in the very same proportions, as enable you to
    make the calculations without any trouble.  Mr. Lavoisier and
    his associates give the name Hydrogen to the ponderable basis
    of inflammable air, (which they call Hydrogenous Gas) ; be-
    cause, when combined with oxygen it composes water.
      Notwithstanding this body of evidence, some chemists, unable
    to relinquish their habits of explaining  every thing by phlogis-
    ton,  have made many observations upon and objections to these
    experiments.   And when they could not gainsay the facts, they
    endeavoured to explain them  by  different suppositions.   But I
    confess that I think their explanations infinitely embarrassed and
    hypothetical.   There has since appeared, long after the date of
    these experiments, a proof of a very different kind.
       Messrs. Van Troostwyck  and Dieman, of Haerlem, pro-
    duced electric sparks under water by the discharge of a square
    foot of coated glass between two balls of gold.   At every spark,
    a small bubble of air was formed between the balls, which as-
    cended through the water, and occupied the upper part of the
    tube that contained it.  The air thus collecting, caused the sur-
    face  of the water gradually to subside.   At last, it sunk so as
    to be below the uppermost of the two gold balls.   The next
*»  spark, therefore, was not under water, but in the air.   The
    very first spark that was made in these  circumstances, exploded
    the whole air which had  been collected.   When this did not
    burst the tube, (which it sometimes did), the water immediately
    filled it to  the very top,  the whole air having vanished.  Here
    is a  decomposition, and  subsequent recomposition of  water,
    which I see no way of gainsaying*.

      * If further proof be still wanted, the wonderful effects of galvanism sup-
    ply them in abundance.  Mr. Woolaston also has greatly improved the method
    of the Dutch Philosophers, by availing himself of the well known property of
    fine points, by which  they promote the transference of electricity; (a pro-
    perty happily explained by Mr. Cavendish, in the 61st volume  of the Philo-
    sophical Transactions).  By employing  a very small shred of fine gold-leaf,
    all coated with sealing-wax, except the very extremity formed by breaking it
    across, he so constipated the stream by which the electric fluid is supposed
    to flow in or out, that a very middling machine, without coated glass, pre-
   . duces a continual decomposition.—Editor. 
 376              INFLAMMABLE AIR.

   By the help of this discovery of the composition of water,
 Mr. Lavoisier easily explains the production of inflammable air
 during the solution of iron in diluted sulphuric acid, which, you
 may remember, I told you was the best process for obtaining it
 pure.   While the sulphuric acid dissolves the iron, and divides
 it into parts inconceivably minute, it puts it into a condition for
 more powerfully attracting the oxygenous principle of the water.
 It attracts  some  of it, and thus leaves disengaged  hydrogen,
 which  assumes the form of inflammable  air*.  Lavoisier re-
 marks that we do not obtain inflammable air, but sulphur, or •
 sulphurous acid,  when the sulphuric acid is concentrated.   It
 must be largely diluted.  Here the dissolving iron, having plenty
 of water to act upon, attracts oxygen  more easily  from it than
 from the acid.   It is certain that it unites with oxygen on this
 occasion ; for if we separate it from the acid, we find it in fact
 combined with oxygen, and can obtain this from it again.
   Thus,  you will now understand the opinion which at present
 prevails concerning the nature of  water, and of this highly in-
 flammable substance, and the consequences of inflaming it.
   We  may now further remark with regard to inflammable air,
 that it is at present considered as one  of the simple or elemen-
 tary bodies in nature.   I mean, however, the basis of it, called
 hydrogen by the French  chemists ; for the inflammable air it-
 self, namely, hydrogen gas, is considered as a compound of that
 basis, and the matter of heat.   What appearance  and proper-
 ties that basis would have, were it deprived  of its latent heat
 and elastic form, and quite separated from all other matter,  we
 cannot tell.   But it is supposed to be an elementary principle in
 the composition of a great number of natural bodies;  particu-

  * I do not see how its attraction for oxygen is increased.  The iron is cer-
 tainly, by this doctrine, combined with oxygen derived from the sulphuric
 acid,—a compound of oxygen and sulphur. How can this increase its attrac-
 tion for oxygen already combined with hydrogen ? Tlie first action of the iron
is generally supposed by the French chemists to be eferted on the water.  And
they suppose that the sulphuric acid acts only on the compound already form-
ed of iron and oxygen. This may perhaps assist, by removing the iron alrea-
dy saturated with the oxygen taken from the water: but there is still a diffi-
 culty,—to be noticed afterwards.—Editor. 
EXTEN. INFLUENCE OF THE NEW DOCTRINES. 377

 larly, it is an ingredient in all animal and vegetable substances.
 The attention of chemists was much directed to this object by
 some most ingenious experiments and reasonings of Mr.  La-
 voisier and Mr. Berthollet:  and it is now pretty generally re-
 ceived as a position fully demonstrated, " that  nothing is to be
 found in the bodies of plants and animals, except the four kinds
 of gas which we have discovered, namely, hydrogenous, carbo-
 nic, oxygenous, and azotic ;  and a small quantity of earthy and
 saline matter."   And these substances, hydrogen, carbon, oxy-
 gen, and azote, are supposed to exist in the plant or animal in
 various states of  composition,  forming  solids and fluids, in
 which these simple substances do not exhibit their peculiar pro-
 perties,  by reason of their composition.   The chemists of the
 new school further hold, that the union by which these substances
 exist as ingredients in the distinctive solids and fluids of orga-
 nised bodies, is but slight; so that it readily gives way to chan-
 ges of temperature, and to the vital  functions  of the plant or
 animal; and that this is the  cause of those fermentations and
 corruptions which we observe in them all.  By these mutual ac-
 tions of the sensible ingredients,  these ultimate simples change
 their partners, (so  to speak), and become ingredients of new
 compounds, uniting  by pairs or  triplets,  in consequence  of a
 change produced in their former attractions,—-a change occasion-
 ed by a change of temperature, or by the  living powers  of the
 plant or animal.
   When we maturely reflect  on the subject, we see that the opi-
 nion has a great degree of probability, and that an inconceivable
 variety of appearances may fairly result from this seemingly ve-
 ry simple constitution of things.  The theory here aimed at is
 most magnificent and comprehensive, embracing almost all the
 chemical phenomena of nature.  And it  even  promises  some
 introduction to the  knowledge of those mysterious functions of
 vegetable and animal life, by which plants and  animals assimi-
 late, or convert into tneir own  peculiar substances, the various
 materials which serve them for food  and nourishment; so that
 even air, and light, and heat,  become part of their composition.
 But it is at the same time.very  evident, that the most scrupu-
 lous caution is necessary in all our disquisitions  on this subject,
   trnT . T-T.                            3 B 
  37*             INFLAMMABLE AIR,

  and the utmost moderation in our theories.  The combinations
  of pairs and triplets, in a collection of five ingredients, are so
  numerous, that it is in our power to bring out any ultimate com-
  pound we please, by properly selecting the  order of succes-
  sion of their mutual actions.
    I shall give you one example of this manner of proceeding,
  which seems to  meet with general  approbation; and will give
  you a pretty clear notion of the kind of reasoning employed in
  the French school.  This is the explanation given of the com-
  position and formation of the volatile alkali. (See Note 41, at the
  end of the Volume.*)
    All the volatile alkali that we know is produced from animal
  and vegetable substances, or substances derived from these, by
  the action of heat, or by putrefaction.  Yet we cannot discover it
  to be present in the substances from which it is thus obtained
  (ex. gr. in silk, animal jelly, &c) before the action of great heat,
  or before putrefaction.
    We have long had reason to believe that volatile alkali is a
' compound substance, and  contains inflammable matter.  The
  deflagration of nitrous ammoniac, and of all the ammoniacal salts
  with nitre, put this past doubt.   Putrid steams, when copiously
 produced, are generally alkaline.  They are always inflamma-
 ble : and it is not till the putrefaction, accompanied by such
 steams, has proceeded a certain length, that the alkaline  smell is
 perceived.  It becomes gradually more sensible and less foetid.
   Mr. Berthollet observed that the muscular fibre, when fresh,
 gave out a great quantity of azotic gas, if digested with nitric
 acid;  but if so treated when in a putrid state,  it gave none,  but
 gave inflammable air and volatile alkali.  He was induced by
 this to think that the ammonia, which appears in this process of
 putrefaction, arises from a combination of the azotic gas  and the
 inflammable air, in the instant of their extrication from the com-
 pounds from which they were disengaged.  He supposed that
 ammonia is composed of inflammable air and azotic gas, or of
 the hydrogenous and azotic gases.
   This opinion appeared to Mr.  Berthollet  almost demonstrat-
ed, by the effect produced on volatile alkali by the muriatic acid
 sorcharged with  oxygen.   Although the liquid alkali was per- 
      COMPOSITION OF VOLATILE  ALKALI.  379

fectly caustic, the mixture produced a considerable/effervescence.
But the gas which escaped was not carbonic acid, but pure azo-
tic gas : this,>being a simple substance, must have existed in the
materials.  The acid contains none ; it therefore made a part of
the alkali.  In the mean time, the acid became ordinary muriatic
acid,—its redundant oxygen had disappeared,—it had combin-
ed with the hydrogen of the alkali, and formed water.
  This opinion  explains, and is confirmed by, many observa-
tions  of different chemists before this conjecture of Berthollet;
and, in the first place, some very remarkable experiments by Dr.
Priestley, in which he shewed that inflammable air had the pro-
perties of other inflammable bodies, but with circumstances that
were characteristic.   Thus,  we know that minium, or red lead,
is converted into lead by making it red hot, in contact with oils
and other inflammable liquids and solids.   In like manner, it is
converted  into lead, if heated by a burning-glass, when exposed
in a vessel filled with inflammable air.  In this experiment, the
inside of the vessel is covered with dew, which trickles down
the sides, and proves to be pure water.  The inflammable air
 is almost completely absorbed.
    But it is also converted into lead, if treated in the same man-
 ner,  in a vessel filled with pure caustic volatile alkali.   But in
 this experiment, there is a great remainder of unabsorbed gas.
 Dr. Priestley expected to  find this  nearly pure vital air,—the
 lead having (according to his theory) absorbed all the phlogis-
 ton of the alkali.  He was astonished to find it,  on the contra-'
 ry, highly phlogisticated;  that is, nearly pure azotic gas.
    Mr. Berthollet explains  these two experiments in a very satis-
 factory manner. Minium contains (as we shall learn in due time)
 a quantity of oxygen.  This, uniting with the hydrogen in  the
 first experiment, produces the water which Dr.  Priesdey  ob-
 served ; and the hydrogen disappeared.  But, in the second ex-
 periment, the azote, which is a simple substance, and must have
 existed in some of the ingredients, but cannot be  demonstrated
 in minium carefully prepared, must have come from the ammo-
 nia, and must have been one of its ingredients.   The other is,
 in all probability, hydrogen; for it is a simple substance, and it
  is yielded by putrid muscle when  digested  with nitric acid; 
380
INFLAMMABLE  AIR,
which putrid muscle also yields volatile  alkali.  It yields vola-
tile alkali only when it ceases to yield disengaged azote, the pu-
trefactive process having combined it with the hydrogen.
   This  is the general theory, founded on a very  few experi-
ments indeed, but these abundantly simple.  They are not, per-
haps, decisive.  But this theory gathers strength by attending
to a number of more complex facts, and taking along with us
the two discoveries of  Mr. Cavendish,—the composition of
water, and that of the nitrous acid, as propositions fully der
monstrated.
   1. Our newspapers inform us that  the  French chemists pro-
cured saltpetre for the army, by blowing alkaline gas, and even
putrid steams,  through red hot substances which readily yield
oxygen.   We know that such steams  yield both  inflammable
air and azotic gas.  The last of these seizes part of the oxygen
presented to it, and forms nitrous acid; while another part com-
bines with the inflammable air, and composes  water, which di-
lutes  the acid.   It seems to be for such reasons that putrescent
substances are useful in nitre beds,  and that the nitre first ob-
tained is frequently nitrous ammoniac.
   We often find the older chemists expressing their surprise af
the strong smell of volatile alkali  from  the  mixture of sub-
stances which contain none. Thus, iron or copper filfcgs, when
dissolved  in strong nitrous acid, often emit the smell of volatile
alkali, instead of the offensive smell generally emitted from this
mixture.  The metal may be supposed to decompose the water:
and the hydrogen, uniting with the azote (now redundant in the
nitrous gas in consequence of the dissolution of some metal by
the acid) will form ammonia.
   Dr. Austin, who had early formed the same opinion of vola-
tile alkali, narrates, in the Philosophical Transactions for 1788,
several facts of the same kind.  The following is one of the
most simple, and  is very constant:—Put a small quantity of
iron filings,  very pure and clean, into a phial containing azotic,
gas, having previously wetted the filings with pure water.  The
gas will be quickly absorbed, and signs of ammonia will appear.
The smell becomes very  distinct,—test-paper becomes green,—
paper dipped in the solution of copper in muriatic acid, will be- 
        ITS VARIETIES AND  RELATIONS.      381

come blue ;—these are all  marks of ammonia.  All this  will
happen, but more slowly, in common air, which contains azote
in abundance.   The process is  obvious.  We know  that the
iron decomposes the water which wets it,—the disengaged hy-
drogen combines with  the  azote.  For the  same reasons, we
smell volatile alkali in a mixture of iron filings, sulphur, and wa-
ter.   It would seem, however, that in all these experiments one
or both of the gases must be catched by the other in its nascent
state,  in the very act of its extrication.   Dr. Austin could not
combine them when already in the form of  a  gas.  (See Note
42. at the end of the Volume.)
   On the other hand, facts have frequently occurred which are
best explained by the decomposition of volatile alkali.   Mr.
Milner, by blowing alkaline gas through red hot manganese,
which yields oxygen in great abundance, produced nitrous acid,
as the French did.   Also,  the muriatic acid, taken in a state  in
which, it is overcharged with oxygen, being blown through,  or
made to mix with alkaline  gas, (ammonia) produces water and
azotic gas.   The oxygen seizes the hydrogen of the alkali, and
forms water: and the azote is disengaged.   In general, when
.ammonia is forced to bear a red heat, in contact with substances
which readily yield oxygen, we obtain azote and water.  If they"
strongly^fttract azote,  we obtain inflammable air.
   Such are  the facts which seem to  establish  Mr. Berthollet's
opinion of the composition of volatile alkali.  He imagines  it
to consist of one part of hydrogen,  and four parts (by weight)
of azotic gas nearly.
   The union of inflammable with vital air came in our way  in
considering the effect of heat on  inflammable air.   Its import-
ance has occasioned me to take up a good deal of time with  it.
I now proceed to consider how inflammable air is  affected by
mixture with other substances.
   It has little disposition to mix with pure water.  It does, how-
ever,  mix in a small proportion ;  and gives  it a  very nauseous
smell.  It is this that offends so much when water is thrown on
red hot coals.   In its pure gaseous state, it is by no means of-
fensive, although rather unpleasant.   I upeak of the pure hy-
drogen gas,  obtained from iron or zinc, dissolving in the mine- 
282             INFLAMMABLE AIR.

ral acid.  This is distinguishable, by its great levity, from that
obtained  from vegetable and  animal substances.   When  its
weight is more than one-thirteenth of that of common air, it is
impure, and has various  smells (all bad), according to the
sources from which it was obtained, or the mixture it  holds in
solution.   All of them are considerably  heavier than the one
now under consideration.  They generally emit a brighter flame.
The inflammable air from  marshes is usually called the heavy
inflammable air.  Another produced from charcoal has  some re-
markable  properties, particularly its operation on living animals
who respire it.  It is called hydrocarbonat,  and will be noticed
very soon.  It is reasonable to doubt whether these inflammable
gases have any thing in common with hydrogen besides their in-
flammability.   Yet all cjjmpose water by deflagration with oxy-
gen.  Therefore they contain some common substance.
   Hydrogenous gas loses much of its inflammability by frequent
agitation with water ; and  gives it a bad smell.
   It has Tittle action on the alkaline salts.  Mr. Lavoisier was
once disposed to consider it as the alkaline principle :  and I ob-
serve that Chaptal, and others, have still a leaning to this opi-
nion.   This gas combined with quicklime is supposed to form
potash, and soda when mixed with magnesia*.   But I see ve-
ry little to support  this notion.
   Its action on the acid salts is much more distinct.   If a little
strong sulphuric acid be heated in the bottom of a very narrow
and tall glass,  which swells out  at the other end like a pear,—
and if,  in this state, inflammable air be blown through it by a
long pipe from a bladder, they unite very readily.  The hydro-
gen from the gas unites with the oxygen of the acid,—and thet
form water.  The acid, deprived of its due proportion of oxy-
gen,  becomes redundant in sulphur,  which is manifest by its
suffocating fumes : and even sulphur in powder will sometimes
collect  in the wide part of the  glass.  When the acid is concen-
trated as much as possible, and made to boil before the inflam-
mable air pass through it,  it acts in  another way.  Instead of

   * See a letter from Van Tlons in the Annales de Chymie, of which an e>.
tract is given m Nicholson's.Philosophical "Journal, IV. 334.—Editor. 
ACTION ON  NITRIC  ACID.
 abstracting the oxygen, and combining with it, it combines with
 some of the sulphur; and comes off in form of an abominably
 foetid gas, which will be considered afterwards by the name of
 hepatic gas, or hydrosulphuret,  only noticing at present that it
 preserves in some measure  the chemical relations of an acid.
 When passed through an alkaline solution, it forms a sort of neu-
 tral salt, having a disgusting fcetor and taste.  But,
   Nitric acid also absorbs this gas very readily.  We can  see
 at once what must be the effect of an acid which yields oxygen
 so readily,~it becomes ruddy and fuming; because water is
 formed of part of its oxygen, and the nitrogen or azote is now
 predominant.
   This mixture  gives me the  first opportunity of confirming the
 discovery of the composition of nitrous acid by Mr. Cavendish,
 which I mentioned  when  giving you* an account of the gases
 discovered by different chemists, after  the publication of  my
 dissertation on fixed air and quicklime.   I  considered it as
 abundandy proved by that experiment of Mr.  Cavendish.   But
 it has been proved  since that time by  many experiments, in
 which the two ingredients, oxygen and azote, are* separated.
 None exhibit this more clearly than the mixture of nitrous acid,
 or nitrous salts, with* inflammable substances.   Inflammable
 air is#the -first and most simple of them, at least in its chemical
 relations.
   When a long continued stream of inflammable air is made to
 pass though nitric acid, we obtain  (in a pneumatic  apparatus)
 the gas which Priestley calls nitrous air, which  is colourless at
 last, though ruddy in  the beginning, and has no acidity, nor
 changes the colour of test  paper, and is scarcely absorbed by
 water.  This gas, when mixed with vital air,  (oxygenous gas),
 collapses with it into nitrous acid.   Here then is  a  proof that
vital air is one of its component parts.   The inflammable  air
had united with a part of the oxygen that is more easily detach-
ed from the perfect acid, and the  gas which  came  from it is
therefore deficient in it;  so deficient as  not to  be acid.  But
when oxygen is  presented to  it,  it is  combined,  and we have
again nitrous acid. In the mean time, the nitric or perfect acid 
384
PHOSPHORUS.
is become fuming, and also weaker, or diluted, by the water that
is formed by the inflammable and vital air.
  It is to be particularly remarked in this experiment, that al-
though the gas produced is clear, and nearly colourless, and vi-
tal air is  the same, yet these two, on mixing, form, for a few
seconds,  a thick ruddy cloud :  and a very sensible heat is pro-
duced by their condensation into nitrous acid*.
  If the experiment be made with common air, in the place of
oxygenous gas, we still produce nitrous acid, and have the rud-
dy cloud: however, the two airs do not vanish, but leave a con-
siderable residuum of azotic gas.   The reason of this is now
obvious.  The nitrous air combines only with the oxygen of the
atmospheric air, and  leaves the  azote.  It was no part of the
nitric acid employed in the experiment.  We now also se£..th«
cause or  origin of those red fumes which appear in most expe-
riments with the  nitrous acid.  They  are  formed during the
combination of nitrous air with the vital portion of common
air.
  This experiment is therefore instructive.   But it is extremely
tedious,  because the quantity of matter in a reasonable bulk of
inflammable air is so very minute.  We shall have much better
examples as we proceed.              %
  Its relations to the other acids, to the  compound salts, andf^
the  earths, have been but little examined as yet.  We aj-cjflivv
to be occupied with the other inflammable substances; arkt shall
consider  the relation of it to each.  Some are very remarkable.
                  II.—PHOSPHORUS.  >


  The next ^ort of inflammable substances we proposed to de-
scribe are those named Phosphori.   The principal species of
these is commonly named the Phosphorus of Urine, on ac-
count of  its having been prepared  formerly from urine.

  * These ruddy fumes are most evidently  vesicular, and some of the vesi
des very larsr—Eihtor. 
      EXAMPLES of its GREAT INFLAMMABILITY. 385

        When pure and newly prepared, it is semitransparent; and by
      its degree of cohesion bears  some resemblance to white bees
      wax.  It makes nearly the same resistance to a knife in cutting
      it: and it melts with a heat even inferior to that of melting wax,
      coinciding rather  with the heat of the human body.
        It may be melted with this heat safely,  if immersed in water,
      and  covered by it from the contact of air; or even without wa-
      ter, provided the glass vessel containing it be of a small size,
      and  closed up, to prevent the renewal of the  air in it.
        In a small retort, with a suitable receiver closely luted to  it,
      this  phosphorus can both be  melted, and by  an increase of  the
      heat to the lowest degree of ignition, can be  converted into va-
      pour, and thus made to pass over into the receiver, which being
              , the phosphorus quickly congeals in it,  and  is in  the
              te as before.   It is sometimes subjected to this sort of
      distillation in order to purify it.
        But, in all such operations with  it, we must  be very careful
     that  no fresh air be admitted into the vessels until they be per*-
     fectly cold again:  and, even then, the moment the receiver is
      separated from the retort, it ought to be filled with cold water.
        This precaution is necessary, on account of the extraordinary
     propensity of this  substance to be inflamed by the action of fresh
      air,  especially if it be in the least  warm,  or  exposed to the air,
     with an^xtensive surface of communication with it.  And, when
      it taK§6 |ire, it burns with amazing rapidity and violence.  It is
     therefore proper to be cautious in handling it; as the warmth of
      the fingers may set it on fire.
        The low degree of heat at which it takes fire shews the extra-
(fjfl^/ ordinary inflammability of this substance ; and is the founda-
fr •   tion  of many of its remarkable properties, and of some of the
     tricks that are played with it,  such as setting paper on fire by
     rubbing the paper*.   We may kindle tow, which conceals a lit-
       * This is done by previously drawing a strong line with a piece of phosphorus
 " •   on a piece of stiff and rough paper, such as cartridge paper, laid upon some
     very cold briny during  the friction.  The warmth of the fingers being sufficient
     to set  phosphorus on fire while it is  so hard rubbed, it must be wrapped two
     or three times round in a piece of wet paper.  In order to shew the trick, the
     paper is folded upon the stroke, and  briskly rubbed very hard one part upon
     the other.  The phosphorus that was left upon it is generally sufficient to set
     it on fire.
                                              3 C
kept cool
sjfljt^sta1 
386
PHOSPHORUS.
tie bit of it, and is loosely wrapped round a phial, by pouring
hot water into the phial, or by mixing in it two cold liquors
which grow hot by mixing.  Another trick is to light a candle
by touching a glass of cold water.  The glass has a minute bit
of phosphorus stuck on its edge.  The showman pours cold wa-
ter into it, blows out the candle, and while the wick is still hot,
he touches  the phosphorus with it, which instantly takes  fire.
With this phosphorus also are made what are called phosphoric
matches.   These philosophical toys are slender wax tapers, hav-
ing an atom of phosphorus at the end : and each must be kept in
a glass tube hermetically sealed.   It  is warmed by putting that
end into the mouth,—then broken, and the taper suddenly drawn
out.  It generally takes fire.   They are costly,  offensive by
their vile smell, and very childish.
   During the  rapid inflammation of the phosphorus, it is quick-
ly changed into a Valine substance,  which is no longer inflamma-
ble in the same degree, and which is thrown out of the flame or
burning vapour in the form of a thick white smoke.  A part of
this smok e is dispersed in the  air, and unavoidably lost.  But a
considerable part of it is immediately condensed on the surface
of the vessel,  in the form of a saline crust,  which has a strong
attraction for the humidity of the air, and is very soon liquefied
By it, forming with it an acid  liquor.
   Although this acid matter, when first produced,  fe^po fonger
inflammable in the same degree as the phosphorus, it still retains
a small degree of inflammability.   This we learn when we ex-
pose it to a stronger heat, such as that of  red hot iron.  Then,
after glowing a little, it becomes, at last, a white or transparent
saline substance, which has lost all  remainder of inflammability,
and is a perfect acid.
   The properties of this acid were first investigated by Mr.
Margraaf  of  Berlin,  and published in the Transactions ©f the
Royal Academy there, and  since,  in his  Opuscula,  which have
been translated from  the German into the French language.
The compounds which it forms with  different substances are al-
so described by M. Fourcroy.
   Mr. Margraaf made it return to the state of phosphorus, by
rriixirig it well with charcoal powder, and exposing this mixture 
       FORMATION  OF PHOSPHORIC  ACID.    387

in earthen retorts to a violent heat in the way of distillation, with
the proper precautions for preventing the phosphorus from tak-
ing fire in the receivers.
   His opinion of the  conversion of the phosphorus into an acid
by inflammation was the same  with that of other chemists at
that time; namely, that it happened in consequence.of abstract-
ing the phlogiston.  And yet he particularly remarks, that the
quantity of the acid which he collected by burning it gradually,
or by small bits in succession,  greatly exceeded the  quantity of
the phosphorus.
   This  fact has been more exactly ascertained since that time
by the experiments of Mr. Lavoisier, and others.   And many
instructive discoveries have been made by means of the inflam-
mation of phosphorus, and its conversion into  an acid.  It is
peculiarly fitted for  being useful  in investigations  relating to
combustion.  Sulphur and inflammable air are equally  simple
and effective.   But the compounds which they make by inflam-
mation are so volatile, or offensive, or troublesome, that they are
almost unmanageable. Here it is quite otherwise.  This pointed
it out to Scheele and Lavoisier  as  the  fittest  substance for as-
certaining the change produced on air by combustion.  No vo-
latile matter from the phosphorus will in any way taint it.  It is
now well known, that when it is burned in a limited  quantity of
atmospherical air, the vital part of the air, or the oxygen  gas, is
expended and  disappears, without any formation of carbonic
acid.   And when burned in pure oxygen gas, it burns with
amazing brightness and violence, and the whole of the gas is ab-
sorbed and disappears.
   The burning of phosphorus in oxygen gas was first tried  by
Dr. Scheele.   But the same experiment was afterwards repeat-
ed by Mr. Lavoisier, with larger quantities of the phosphorus,
and with the most careful attention to every circumstance which
could affect the conclusion to be drawn from it.
   Scheele put his bit of phosphorus into a phial filled with oxy-
gen gas; closed the mouth of the phial with  a cork ; and then
warming the phial, he thus kindled the phosphorus.  When the
inflammation was finished, and the  phial was  cool again, he
plunged it into water, and drew out the cork under water.   The 
388
PHOSPHORUS,
 water was suddenly pressed into it by the atmosphere, and filled
 the phial perfecdy full, or very near it.  He therefore concluded
 that the oxygen gas had united with the phlogiston of the phos-
 phorus, so as to form with it heat and light, which had  passed
 through the  glass.
    But  Mr. Lavoisier, performing a similar experiment, took
 the precaution to weigh the glass with what it contained  imme-
 diately before the inflammation of the phosphorus.   Weighing
 it again, after the inflammation, and  before  it was opened, he
 found it was precisely of the same weight.   Afterwards,  exam-
 ining as exactly as possible the weight of the acid into which the
 phosphorus  was changed,  he found that it exceeded the weight
 of the phosphorus consumed, by a quantity exactly equal to the
 weight  of the  gas  which  had  disappeared.   It was therefore
 evident that the gas was now changed, by  the loss of its latent
 heat, into a dense matter, which made up the greater part of the
 weight of  the  acid.  One part of phosphorus  absorbs  in this
 way a litte more than 1 *- parts, by weight, of the  oxygen gas.
 The acid is made up of the phosphorus and oxygen, in the pro-
 portion of 100  to 154*.
   The  change  of phosphorus into an  acid  is, therefore,  fre-
 quently named  the  Oxydation of phosphorus.   And other si-
 milar changes of other  inflammable  substances are also  called
 OxypATiONsf.

  * This experiment must be considered as one of the most convincing proofs
 of the doctrine  of the French chemists. Whatever notion we have of the
 phosphoric acid, it  is plain that the phosphorus itself enters into its composi-
 tion ;  for the phosphorus disappears, and we have the  acid in  its stead.  It
 Gan never be said,  therefore,  that phosphorus consists of the phosphoric acid
 and phlogiston; for phosphoric acid consists of phosphorus, and something be-
 sides: These are irreconcilable.—Editor.
  f It is rather  an unlucky term, chosen in the heat of discovery, and before
 Mr. Cavendish had discovered the composition of water.  Had this been
 known, it is not likely that a person of Mr. Lavoisier's general knowledge and
 good sense would have included the formation of water in the list of acidifica-
 tions.  Most of his  followers were less sensible of the violence done to com-
 mon language.  Perhaps they even liked a diction which will cause the unin-
 itiated  to stare. We see this very plainly  in the phraseology of some of
them, who are fond of using the term combustion in cases where a plain man
 can see nothing like it.  What he would call combustion, they cull  oxyda- 
 ITS OXYDATION, OR CONVERSION INTO ACID. 389

    Since these discoveries were made,  Mr. Pelletier, another
 French chemist, who has distinguished himself by many in-
 structive experiments relating to phosphorus and the process for
 preparing it, contrived a process  for oxydating  phosphorus,
 which appears to be very effectual,  and very well fitted for pre-
 venting the loss of any part of the acid.
    He melts the phosphorus under water, in a cylindrical glass
 vessel, and then throws into it oxygen gas, by very small quan-
 tities at a time, through a glass tube, connected with a bladder,
 containing  the gas.  Every little  addition of the oxygen  gas
 kindles that part of the phosphorus with which it comes in con-
 tact, and is absorbed by it.  That part of the phosphorus is thus
 changed into acid, and dissolved by the water:  and thus  the
 whole of it can be thus oxydated, or changed into acid, which
 is dissolved by the water.
    Another process or experiment, founded on the same disco-
 veries, may also be mentioned here.  It is  an  experiment by
 which we learn the proportion of oxygen gas contained in atmos-
 pherical  air.  The  eudiometer  of phosphorus, or  method  for
 learning  exactly, by the  use of phosphorus,  the proportion
 of oxygen gas contained in atmospherical air, contrived by Se-
 guin and Lavoisier.  Annales de Chymie, torn. ix. p. 301.
   Get a glass tube about one inch in diameter, closed above and
 widened. beloW, and about seven or eight inches long.  Fill it
 with quicksilver; and invert it into a cistern of the same fluid.
 Throw up or introduce into it  a little bit of phosphorus, and ap-
 proach a burning coal to the upper  end  of the tube, to warm
 and melt  the phosphorus by blowing on the coal.   Then, having
 measured a proper quantity of the air to be tried,  throw it up
 by small portions at once, each of which will cause the phospho-
 rus to burn, and will thus  consume or saturate some of it, and
 in so doing will be saturated,  and changed into acid,  in as far
 as  it consists of oxygenous gas.  When it  is all  thrown up,

tion: and what he would call oxydation they call combustion.  The forma-
tion of water is an oxydation of hydrogen: but the formation of nitrous acid is
the combustion of azote. There is little science in this, but abundance of Ta-
nity.—Editor. 
290                  PHOSPHORUS
warm the tube again,  to be sure that  the  oxygen gas shall be
completely expended or saturated.   Lastly, let it cool; and
transfer the air into another tube which is graduated for measur-
ing exactly the bulk of the remaining  air.   This will shew the
quantity of the oxygen gas which it  originally contained.  A
glass funnel, having  the  extremity of its  tube closed up, may
serve very well in place of the above  apparatus.
  These are the most remarkable particulars of  the properties
of phosphorus with respect to heat, and the manner in which it
is inflamed and changed into phosphoric acid.
  It has also a quality, upon which have been founded many of
the curious experiments  and  surprising tricks that  have been
performed with it.  This quality of it appears when  it is ex-
posed to the air in an extended surface, but in degrees of heat
inferior to that necessary for its bright inflammation.  It then
emits a pale  light, visible in the dark only.  We do this very
effectually by drawing lines with phosphorus on strong  white
paper.
  When we view the paper in day light, the light of the phos-
phorus is not perceived, in consequence of its weakness :  but a
white smoke  is seen to arise from it.  A small solid mass of
phosphorus continues to  emit this pale light and smoke a sur-
prisingly long time.   Mr. Boyle relates that a bit of phosphorus,
weighing  only three grains, continued to emit this  weak light
fifteen days and nights before it was exhausted.
  From the consequences observed, when a bit of the phospho-
rus is thus exposed on a plate of glass a little inclined, we find
reason to be  satisfied, that this luminous state  of  it is only .a
state of very slow inflammation.   It is gradually  converted into
an acid, which attracting humidity from the air,  forms an acid  '
liquor,  much the same with that formed by the bright and vio-
lent inflammation of the  phosphorus ; only that it is not  quite
so perfect an acid.  It is still somewhat deficient of the proper
quantity of oxygen.   This trickles down  along  the glass, and
may be thus collected.
  One of the processes for converting phosphorus into an acid
is founded on. this property.   The phosphorus, formed into
small cylindrical pieces, is put into a.glass funnel, the throat of 
WITH SULPHURIC  ACID.
391
       which is slightly stopped with a pebble or a bit of glass, to pre-
       vent the descent of the phosphorus into the pipe.   A phial is
       then placed under the funnel, and the whole apparatus set in a
       moderately cool place.  Thus the acid of the phosphorus, in
       proportion as it is formed, drops into the phial.   But we must
       take care that the place in which the apparatus stands,  be suffi-
       ciently cool.   A small increase of the heat of the air has great
       effect in accelerating the process: and if it be much accelerated,
       the phosphorus becomes warm by the very oxydation, and there'
       is danger of its taking fire, and burning with violence.  Scheele
       discovered that even the weakest lumination of the phosphorus
       is attended with the production of some perceptible heat, disco-
       verable by a thermometer.  But when the process I speak of is
       rightly conducted, this heat being weak and slowly  produced
       it is carried off by the surrounding air, so that it never is accu-
       mulated in such quantity as to dispose the phosphorus to be ra-
       pidly inflamed.
         We come now to consider phosphorus in mixture with other
       bodies.  Being a substance of recent  discovery, its chemical
       relations have not yet been thoroughly examined.  Many of those
       we know are very remarkable.  Mr.  Margraaf, to whom  we
       are indebted for the knowledge of the  chemical nature of this
       substance, has made  these cgmbinations with his  usual judg-
       ment and accuracy.
         A drachm of phosphorus was distilled by him with an ounce
       and  a half of sulphuric acid, giving at last a violent  heat.  A
       few grains of phosphorus remained, mixed with a spongy white
      mass, which deliquesced in the air.  The liquor which distilled
      was  thickish, and a little milky.   Both liquors contained a mix-
|L *v ture  of sulphuric and phosphoric acids*
        A drachm of phosphorus was distilled with an ounce of strong
      nitric acid.   As soon as it was dropped into the acid,  blood red
      fumes were disengaged, which made him fit  on the receiver in
      a hurry.  The solution went on with great vehemence and heat:
      and in a short time the greatest part of the nitrous acid came
      over, without applying any fire to the retort.  At last the phos-
      phorus yet remaining, took fire, and burst the retort with great
aoise. 
392
PHOSPHORUS
   The union of the oxygen and azote in the nitric acid is so
 weak, that scarcely any body which attracts oxygen can be pre-
 sented to the acid which will not overcome their union and  de-
 compose the acid.  The azote,  or rather nitrous gas, escapes
 and produces those red fumes, by uniting with the atmospheric
 air.  The latent heat of the oxygen, as it is contained in the ni-
 tric acid, greatly exceeding what  is necessary  for the acid of
 phosphorus, emerges and produces heat enough to inflame  the
 remaining phosphorus.
   But, by  another way of conducting the process,  it is very-
 manageable.  Put strong nitric acid into a tubulated retort fitted
 with a receiver.   Have ready a quantity of phosphorus cut into
 very small pieces ~ drop in one, and immediately stop the hole.
 The phosphorus will dissolve very quickly,  and will produce
 heat.   When all is cool, drop in another bit;  and continue this
 till the last bit dissolves and seems to saturate the acid.   Now
 apply heat:  apd the nitric acid will distil over in fiery  fumes,
 and leave nearly pure phosphoric acid in the retort.
   This mixture also gives us a pretty phenomenon.   Put about
 half an ounce of strong nitric acid into a small  and  thin flask
 with a narrow mouth.   Drop in a bit of phosphorus like a large
 pea.   There is an effervescence, or rather an explosion, during
 «vhich a slender column of flame is darted out of the glass along
 with the vapours and drops of acid.   Care must be taken so to
 regulate the quantity, to the size  of the  orifice,  that the vessel
 do not burst; and to have it of such a shape,  that few drops of
 acid may come out.
   This is the next opportunity given us for examining the com-
 position of nitrous acid :  and it is  incomparably better than the  ^
 last with inflammable air.   Accordingly, all the phenomena are&
 the same  in kind,  but much more remarkable.  The produc-
 tion of the phosphoric acid, in the same quantity precisely asr-if
 it had  been  produced by inflaming the phosphorus, she*pfevi-
 dently that  oxygen constitutes a great portion of nitric acid.
The gas which escapes is the same as when inflammable air  is
 employed, provided  that the combination be slowly effected.
 If rapidlv, much phosphorus is volatilized, and taints the gas,
 sometimes even making it inflammable.  The fumes are blood 
TREATED WITH NITROUS  ACID.      393
red^ while they mix with common air or with oxygen: and ni-
trous acid is produced by the union.   If all access of air be pre-
vented, the gas is colourless, and without acidity.   By compa-
ring the gain to the phosphorus, with the oxygen necessary for
forming nitric acid with the gas, Lavoisier found that the pro-
portion of oxygen and azote in the gas, is that of 68 to 32 near-
ly.  It requires about 24 parts (in bulk) of common air to satu-
rate 11 parts of this gas, and form with it nitrous acid.  In this
mixture,  the whole nitrous gas disappears, and a fourth part of
'the common air; so that 35 cubic inches, after mixture, will
only occupy 18 inches.  This is azotic gas.
   That the red vapours are true nitrous acid, appears from an
experiment of Dr. Priestley.   Hang in the glass a piece of
sal ammoniac.   When the red fumes are over, a snowy pow-
der settles all over the vessel, which is  imperfect  nitrous am-
moniac.
   The nitrous  gas may be decomposed, and the composition of
nitrous acid completely demonstrated, by  filling a jar with ni-
trous  gas, and  putting into  it a quantity  of hepar sulphuris.
This will immediately attract the oxygen remaining in the gas,
and leave the other ingredient alone.  This is found, by this ex-
periment,  to be pure azotic gas.
   We may surely now assume the  composition of the nitrous
acid as a thing as firmly established as any doctrine in chemistry.
You will recollect, that, in order to answer an immediate pur-
pose,  I mentioned the precious experiment of Mr.  Cavendish,
in which he found, that  when seven parts of  vital air were de-
flagrated  with  three of phlogisticated  air, or azotic gas,  the
whole collapsed into pure nitrous acid.  But I did not at that
"time assume this constitution of the acid as a fixed point;  be-
cause  I was not  then in a condition to  shew you how the acid
might  be separated or  resolved into those its constituent parts.
I was Enable to do this, because you were unacquainted with
the substances whose  properties and manner of action were to
operate this decomposition.'  Enough of these have now occur-
red : and I have given you most distinct examples of the fact.
More  will yet occur as we proceed; and some of them perhaps
still more perspicuous.   But we have enough:  and it will be
   ..-.  T.              ■&'            3  D 
te*                   PHOSPHORUS

agreeable now to meet with the others, as phenomena which arc
explained by this principle now in our possession.
  The muriatic acid did not appear to Mr. Margraaf to act at
all on the phosphorus, which did not dissolve.  At the end, in-
deed, of the distillation, the phosphorus  also  came over, but
without any remarkable change.
  The pure or caustic fixed alkalis may be combined with phos-
phorus, or can be made to dissolve it,  as they dissolve sulphur,
and indeed all the inflammable substances  in the  humid  way.
In consequence of this  combination,  an inflammable gas, ex-
tremely foetid, smelling like rotten fish, is produced, which takes
fire the moment it comes in contact with atmospherical air; and
which therefore exposes the vessels to the risk of being burst
by its explosions.
  This gas  is undoubtedly produced  from  a small portion of
the water decompounded  by the  dissolved  phosphorus.   It is,
the hydrogen in its form of gas; and  as fast as it is produced,
it dissolves  and volatilizes a small portion of the phosphorus it-
self, and from this receives the quality of spontaneous  inflam-
mability*.   This small portion of the phosphorus, however,
is very slightly united with the hydrogen ; for it is deposited or
separated, if the gas be kept for some time confined with wa-
ter.   It  gradually deposits the phosphorus on the sides of the
vessel; loses its spontaneous inflammability;  and  is changed
into common inflammable air or  hydrogen.  The same gas
is produced  by quicklime.  (See Note 43. at the end of the
 Volume.)
   By these experiments,  you will perceive  that phosphorus is
one of the most easily inflammable bodies that we know ;  that

  * Is the series of operations  here stated very satisfactorily established ? I
cannot help considering this experiment, and those which are analogous to
it in the treatment of sulphur with alkaline substances,  as examples of that
"•ratuitous employment of the decomposition of water, which the followers
of Lavoisier indulge in with so little circumspection or n.oderation. All de."
uends on the order in which the different actions succeed each other.  I think
Uiat phosphorus and sulphur, and perhaps, charcoal, afford a probable op-
portunity of settling the point, by means of a previous determination of their
simple affinities.  This is not in our power,  perhaps, in the  more compli-
cated substances of animals and vegetables.-—Editor. 
DECOMPOSES  CARBONIC  ACID.
 it has a strong propensity to take fire, and to be inflamed ; or,
 in other words, that it has a strong attraction for oxygen.   A
 very ingenious  and instructive experiment has lately been
 founded on this strong attraction, or has been contrived in con-
 sequence of it.  It has been a great  desideratum  among  the
 chemists to decompound the carbonic acid; that is, to contrive
 some way by which the carbone or coal may be separated from
 the oxygenous gas or vital air, which is now held to be its other
 ingredient.  This has been attempted with very flattering ap-
 pearances of success by Mr. Snaithson Tenant.   You have  an
 account of it in the  Philosophical Transactions, vol. 81. part ii.
 I shall give you a brief account of  it.
   Mr. Tenant put a small bit of phosphorus into a glass tube
 that was shut at one end ;  and then put over it marble reduced
 to a fine powder.  He shut the other end, but loosely, that the
 common air expanded by heat, might escape ;  and yet so that
 the free circulation of air, which might kindle the phosphorus,
 should not take place.  He  heated this apparatus red hot for a
 few minutes.  When all was cold, he broke the tube, and found
 therein a black powder, which consisted of coal,  phosphorated
 lime, and phosphorus  mixed with quicklime.  When the phos-
 phorated lime was separated by solution in  an acid, and filtra-
tion, and the phosphorus by sublimation, the coaly matter that
 remained did not appear to differ from vegetable coal in any re-
 spect.   Mr. Tenant explains the experiment by saying that the
 coal  is separated from the oxygen,  although it has a stronger
 attraction for it than the phosphorus has, in consequence of the
 sum  of the attractions of the phosphorus for oxygen, and the
 phosphoric acid for  quick-lime.
   Dr. Pearson observing that the compounds of phosphoric acid
 and the  fixed alkalis could not be made to yield phosphorus  by
, treating them in contact with charcoal in a red heat, while the
 calcareous phosphat yields it with great readiness, thought that
 the fossil alkali would be a better intermedium than calcareous
 earth, for operating  the decomposition effected by Mr. Tenant.
 He therefore employed, with perfect success, a mixture of two
 parts of phosphorus, and eight of carbonat of soda, cleared of
 its water of crystallization.   The process was similar to Mr. 
396
PHOSPHORUS.
 Tenant's, and very easy.   The rationale of these processes  is
 by no means obvious.  But the production of carbone, and this
 in due quantity, completes the theory of carbonic acid.  A let
 ter of Dr. Pearson  to  Hassenfratz, and some observations by
 Fourcroy, which accompany it in the 18th volume of the Anna-
 tes de Chymie,  deserve perusal.
   Phosphorus will also combine, though loosely, with the caus-
 tic volatile alkali; and produces a gas with an abominable smell.
 This gas also takes  fire in  the air; and, which is remarkable,
 deposits the greatest part of the phosphorus in the flash.   In-
 deed, in all these gases, containing phosphorus volatilized by hy-
 drogen, the union seems exceedingly slight.  They all decom-
 pose by long keeping, even in corked phials.   Westrumb says
 that they deposit the phosphorus, even in  phials hermetically
 sealed.  That the phosphorus is not inflamed in these experi-
 ments, but  deposited, appears singular at first view, seeing that
 it is so very inflammable.   But when we  consider the extreme
 rarity of the gas, and reflect that the inflammation even of this
 rare gas, which takes place by the mere contact of air, is pro-
 bably the  low  inflammation, in which phosphorus itself only
 shines without ordinary  combustion, we  shall be sensible that
 the complete inflammation  of  the phosphorus is not to be ex-
 pected.
   These are some of the most remarkable qualities and relations
 of this inflammable substance.  It is also capable of being com-
 bined with some of  the other inflammables*, and with the me-
 tals;  and forms singular compounds, which  shall be noticed
 hereafter.
   The acid which it affords is  also now become one of the  im-
 portant objects of chemistry.   It is fixed and verifiable. With
 the fossil alkali it forms a salt, now used in medicine, and recom-
 mended by Dr. Pearson by the name of Soda Phosphorata.

  • Indeed all the inflammable substances are susceptible of a perfect admix-
:ure : and this has, in many cases, some appearance of a chemical combina-
tion,__the compounds having certain  general properties which do not belong
to the ingredients,  at least in the same degree.  They are, in general, more
fusible, volatile, and inflammable, than should be expected from the ingredi-
ents : and they are more disposed to anion with another inflammable substance
                                                   Editor. 
SODA  PHOSPHORATA.
397
      A. process for preparing this neutral salt is given in a new edi-
      tion of the Edinburgh Pharmacopoeia*.

             * Process for Soda Phosphorata, communicated by Dr. Pearson.

        Take bone ashes : Those to be had at the hartshorn manufactures are com-
      monly used, and ground to a coarse powder,  in the state they are in for ma-
      nure, and as sold for about a shilling a bushel—ten pounds.
        Pour on them, in an earthen, or iron pan, oil of vitriol,  of specific gravity
      about 1800—six pounds.
        Stir the mixture well, and add to  it gradually rain or river water—nine
      pounds.
        Stir the whole well together, and set the mixture to digest in a sand  heat
      of about 130°, for two or three days.   Then add to this mixture nine pound*
      more of very hot water, and pour it on a filtre of coarse linen cloth, upon
      which pour boiling water till it passes through with little acid taste.  Let the
      filtrated liquors,  all mixed together, stand for the  sediment to  fall.  Decant
      the clear liquor,  and evaporate to about nine pints.  Filtrate, to separate tne
      selenite precipitated in boiling, and evaporate again to seven pints.  Cool the
      liquor, and separate more  selenite. Heat the liquor in  an earthen yessel, and
      add pure crystallized fossil alkali, dissolved in 1 *  its weight of water,  until
      the effervescence ceases.  Filtre the saline liquor hot, into a shallow vessel,
      and let it crystallize three  or four days.  Decant the remaining liquor  from
      the crystals : and if it be acid, neutralize it again with the solution of fossil
      alkali, and  evaporate agajn and crystallize; repeating these operations,  until
      a liquor remain which will not give any more crystals,  either by evaporation
      or addition  of more alkali.

                 Shorter Process, but with more waste of phosphoric acid.
        Add as much water to a mixture of sulphuric acid and bone ashes, as will
      reduce it to a thin paste, which must be put into a coarse thick hempen bag,
      tied up close at the mouth.  Then press and moisten it with water repeated-
      ly, until the whole, or greatest  part of the  acid  liquor is extracted.   The
      turbid acid liquor must be purified from the selenrte, by decantation and fil-
      tration.  And  if the quantity of this liquor be more than  six pints, reduce it
      to that quantity by evaporation :  and saturate, as before described, with  a so •
      lution of fossil alkali.
        The quantity  of phosphorated soda should be at least equal  to the weight
      of the alkali,  and about five-sixths of that of the bone  ashes;  so that the
      above quantities should yield above &i pounds of the salt.
        This salt is liable to be contaminated with Glauber's salt, or superabundant
      alkali, which are distinguishable in it by the taste.  Pure soda phosphorata
^    has a slight taste of marine salt.  The bone ashes sometimes contain more,
      sometimes less acid, and the fossil alkali is often impure.
        The surest way to succeed,  is to be careful that the sulphuric acid be ra-
      ther too little for decompounding the whole of the bone ashes, than that there
      should be too much of it.  In the above process this is attended to. 
398
PHOSHHORUS.
  When the acid is completely freed from phosphorus, and may
therefore have the distinctive name, Phosphoric Acid, it forms
with the alkalis, salts, which crystallize with great  difficulty.
But, when it retains some phosphorescence and volatility, in
which  state we may call it Phosphorous Acid, these com-
pounds'crystallize very well.
  With calcareous earth it forms a substance insoluble in water,
resembling, in all respects,  the earth of  bones.


           Origin and Preparation of Phosphorus.


  The first process, by which phosphorus was obtained in its
pure state, appears to have been an accidental discovery in 1669,
(Leibnitz de Invent. Phosph. Miscell. Berol. 1.) by Brandt, a
merchant in Hamburg, who was employed in experiments on
urine,  in  the hopes  of making gold; and it remained in his
hands, or in the hands of a few others, who acquired the'know-
ledge of it, but concealed it from the public for a long time after.
It was brought to England by a Dr. Kraft*  At last, some hints
relating to it were published in the Philosophical Transactions,
No. 196, by Mr. Boyle, who had practised Kraft's  process
with some degree of success.   Meantime,  Kunkle, a chemist
in Dresden, by dint of labour,  discovered an  effectual pro-
cess, which he published, and claimed  the invention.  A full
description  of  a better process  appeared afterwards in the
Memoirs of the Royal Academy of Sciences at Paris, for the
year 1737, in consequence of the purchase of the secret from
a chemist who  was possessed of it.  All this is detailed very
distinctly by Mr.  Macquer, in his  Dictionary of Chemistry.
The urine was  evaporated  to a dry  extract or  coalv  matter.
Then some of the salts were separated from this extract by wa-
ter : and the remaining matter was distilled with a violent heat
in earthen retorts.
  Although some phosphorus may be produced by this process,
it is far from being a good one.  Some parts of  it are actually,
very detrimental, or diminish the quantity of phosphorus whit l 
IMPROVED  PREPARATION OF IT.
might be obtained from the materials:  and the process is ex-
ceedingly troublesome and hazardous.   The best management
of the process, and the manner in which the phosphorus is ac-
tually produced by it, were never understood until Mr. Margraaf
applied  himself to the study of it, and  published his experi-
ments in the Berlin Transactions.  By them it appears that the
production of  phosphorus from urine depends upon a salt  con-
tained in the urine, and which had been observed in  it before,
but not  sufficiently examined.   Dr. Boerhaave takes notice of
it, and  calls it the essential salt  of urine.  Mr. Margraaf col-
lected a quantity of this salt, and examined it.   He found it
ammoniacal,  or containing a volatile  alkali in  its  composition.
It is a mixed neutral, composed of a peculiar acid,  combined
partly with each of the fixed alkalis,  and partly with ammonia.
With charcoal dust this salt gave a larger yield of phosphorus
than ever had been obtained from any other materials.  And
the remains of the urine from which this salt had  been extract-
ed,  gave hardly any sensible quantity of phosphorus.   Mr.
Margraaf  also shewed,  by a train  of  experiments, that the
phosphorus is changed by inflammation into an acid, now named
the phosphoric acid; which acid can again be changed into phos-
phorus.  This cleared up the whole matter, and  gave reason
to be assured, that the  salt just now mentioned  contains  this
very acid.
   In consequence of these discoveries, Mr. Margraaf contrived
some improvements of the process  for  preparing phosphorus
from urine; by which improvements the operation was facili-
tated, and the quantity of  phosphorus much increased.
   This process of Margraaf's  continued to be the best, until
Mr. Scheele  of Sweden, in company with Mr. Gahn, another
eminent chemist, taught us one  still  better.  The two gende-
men just mentioned have saved us the  trouble of evaporating
urine, by discovering that  the acid of phosphorus is contained
in th« bones of animals; and when combined with the calcare-
ous earth,  forms their basis, or their most solid and fixed mat-
ter—that  is,  the white earthy-like  matter which remains of
them after all  their inflammable matter  is consumed; in short.
what is usually calkd the  earth of honey   The procrss these 
400                  PHOSPHORUS.
gentlemen  propose  for extracting the acid from this matter,
was a little complicated.  A more simple one  has been disco-
vered since that time.  We need only to mix with the bone
ashes some sulphuric acid and water, &c.—(Vide first part
of the process for sodo phosphorata,  in the Pharmacopoeia Edi-
nensis).
  But the phosphoric acid may be extracted by  other processes,
as lmo, By applying the mild volatile  alkali, or carbonat of
ammonia, to the bone ash reduced to fine powder.   (N.  B.
The double  exchange will probably happen  best  in a cold
place).
  2do, By applying sulphat of ammonia, dissolved in water, to
the bone ashes.
  Since these discoveries have  been made,  the  production of
this inflammable substance is a much easier operation than it
was formerly.  Mr. Pelletier, at Paris, has sometimes  made
60 ounces  of it a\ once ; and in one year he made inijvards of
300 pounds  of it.   (Journ.  de  Phys. 1785.. Juh^'Tn'e only
nicety is in the choice of the vessels, and management of the
condensation, which must be so contrived as to -allow a very
great quantity of gases produced during the opexotioja to escape. .
These gases seem to arise from the  water of.th^iacidy and its
action on the charcoal and the phosphorus nearly formed.   It
acts on these substances in the form  of vapour,  therefore  in the
most extensive surface possible, and furnished  with grea*t stort
of heat.   With the  charcoal  it forms inflammable akr^tof the
heavy kind, as we shall  learn afterwards : and with the phofr-
phorus it forms a gas which takes fire when it comes in contact
with the external air. This immediately kindles the inflamma-
ble air,  which issues along  with it: and the whole produces a>'
bright flame.  The gases are not formed in an  equ^le manner,
but  bv  sudden paroxysms, or explosions,  whicrorrequently
burst the vessels.   Mr.  Hellot found it necessary to have a
hole in the receiver, lightly stopped  with a wooden peg,  which
was blown out  when the vapours became too  elastic.   Other
chemists had a tube, which communicated with the receiver, and
had its mouth immersed.  A small quantity of generated phos-
phorus was saved in this way.            .. 
     PHOSPHORUS—ITS  NATURAL  SOURCES. 401
                               •
  Having thus learned how phosphorus may be obtained pure,
we  are curious to learn how its acid comes into the composi-
tion of animal bodies ; for phosphorus must surely be added to
the list of simples which the French chemists allot to the forma-
tion of animal and vegetable substances.   There  is  reason to
think that  it -is introduced into them from the  vegetable sub-
stances by which animals are ultimately nourished.   Margraaf
obtained phosphorus from the  charcoal of wheat, iye, and other
nutritive vegetable  substances.  Whence these  receive it,  is a
question not so easily answered.  It may be produced in them
by the powers of vegetation.  For we know that there is  in ve-
getables a power to combine their elements together in different
ways, so as to generate productions which would not otherwise
be formed.   Oil,  sugar, &c. are manifestly formed in the ves-
sels,  or organs of plants,  of materials which  before were of a
quite different nature*.
  But a;quantity  of this acid  has also been found in some fos-
sil substances ; for example, in the green  ore of lead.   There
is also a* bed of stone in Spain, in the province  of Estramadu-
ra,  and district of  Truxillo,  near Lagrosana, which contains
this acid united to calcareous earth, as copiously as the earth of
bones does.   This was discovered by Mr. Bowie, and commu-
nicated to the" French Academy by Mr.  Proust.  It forms very
extensive strata, resting on quartz; is of  a  white colour,  and
fibrous texture,  not so hard as to strike fire with steel, but hard
enough for building.  It is so employed for houses and inclo-
sures.  Thrown  into  the fire, it  burns faintly,  with a pretty,
green light, which it keeps for some time after being taken out

  •  We must, as yet, suppose that the phosphorus exists in the soil, and is
taken up by the vegetative functions of the plant; for we have no authority
to say that it-is.a substance composed of  more simple  ingredients.  But fur-
ther, as tbo^fl^ts  now mentioned will grow  and thrive in pounded glass
moistened with distilled water, enjoying at the same  time the benefit of air
and light,  we must,  if  they yield this salt when so raised, look for phospho-
rus in these sources.  This leads to very nice speculations.  I found it, in
very great quantity, in a piece of fine coral rock  from Port Royal, in Jamai-
ca ;  and am  inclined to  think that  all corallines contain it; and that, by a
proper treatment, they  may be rendered true phosphori, like the Bononian
stone, without the sulphur employed in that preparation.—Editor.
   VOL. II.                              3 K  v 
402
SULPHUR.
of the fire.  A fossil of the same kind was discovered by Wer-
ner at Lunenberg in Saxony,  and at Slackenwald in Bohemia,
crystallized in hexahedral prisms,  and in plates, generally mix-
ed with fluor, spar, lithomarga, and steatites, but rarely with
quartz.   The pure specimens  are called Apatit by the  Ger-
man fossilists ; and they say that it  contains 29ffths of phospho-
ric acid.
   1 think that a stone, forming thin white strata, near the Gi-
ant's Causeway in  Ireland, is of  this nature:  and perhaps the
lapis suillus,  and other foetid marbles are so*.


                     Ill__SULPHUR.


   This is the next inflammable body in the order in which I
 proposed to consider them.  Its common appearance istoofami-
liar to need any description.   When held in the warm hand, we
feel it crackle, and even hear it.   This is  a real  splitting* and
the same thing is observed in the large crystals of saltpetre, and
some other salts.   It smells when rubbed,  and becomes highly
electric.
   Several of its properties have already been occasionally noticed.
It has long been an object of  great attention by  the .chemists ;
and has acted the chief part in all their explanations' of pheno-
nomena.   It  was considered as the first principle of metalliza-
tion, and of every species of  combustion.   It  has nowitunV to
the condition of a simple ordinary chemical substance, of vast
extent indeed, existing in an endless variety of bodies, but de-
prived of all  its former pre-eminence.
   Sulphur melts and evaporates without change, in very mode-

  * It may be advisable to observe with some care the vegetation of the Spa-
nish district now mentioned.  If this stratum of phosphat crops out on the
surface, it is not improbable that its rubbish will affect the vegetation.  Ex-
periments should be tried with plants raised on powder of this stone, espe-
cially of such plants as are superficial.   It is most probable that plants so
raised will take up some phosphoric acid, or phosphorus.  If they do not, the
origin of it in plants and animals is not a little mysterious : aud speculations oft
this subject seem to open a door to much research, which may greatly affect
our current theories.—Ediior. 
SULPHUR.
403
rate heats ; but with some peculiarities that are worth mention-
ing.   When  heated to 170°  of Fahrenheit's thermometer,  it
begins to evaporate : and we feel a very disagreeable suffocating
smell.   This, long continued in open air, produces a considera-
ble change in it, which we shall not consider at "present.   In
close vessels, there is no such change: but at 185° or 190°  it
begins to melt; and before 220° it is fluid.  If the heat be
quickly increased, it loses its fluidity, and becomes firm, and of
a deeper colour.   It regains its fluidity,  if we reduce the tem-
perature : and this may be repeated  at pleasure in close vessels,
if the  changes of heat be not too slow : otherwise it  begins to
evaporate so copiously, that we cannot apply heat in sufficient
plenty suddenly to raise its temperature.  These  peculiarities
were first observed by the eminent naturalist, Fontana.
   If, after being quite melted, we let it cool, it congeals in a
crystalline form, but so confusedly, that we cannot easily define
the shape of  the crystals, further than that they are slender in-
terlaced fibres.  If a great mass be  kept fluid below, while it
fixes at the surface,  the crystallization there  is much  more dis-
tinct.   If melted sulphur be poured into  water, the  congealed
mass has  a considerable pliancy : but this does not last.
   When heated in open air above 300°,  it takes fire,  and burns
with a very weak blue flame.  By this inflammation it is totally
changed; and from  being a solid, mild, tasteless substance, now
bejcomes a fluid immensely corrosive, and in  the highest degree
aci4,.%ing now what you are well acquainted with by the name
of vitriolic or sulphuric acid..
   When  this acid is treated in a red heat, and in  contact with
an inflammable body, it is changed into sulphur: and any inflam-
mable body, whatever will answer, if it Can be made to bear the
heat.   Even inflammable air will do.
   Hence it was inferred by Dr. Stahl, that there was a princi-
ple common  to all inflammables, and the cause of  their inflam-
mability,—the Phlogiston.   Hence it was inferred that sul-
phur consisted of the peculiar acid now spOken of, and phlogis-
ton ; and that this  phlogiston was expelled during inflammation,
but restored to the acid by any inflammable body, in consequence
of a greater attraction for the acid. 
 404  SULPHUR—ITS  RELATIONS TO  HEAT.

   But no person ever saw this phlogiston in a separate state, or
 could prove that there was such a thing in  sulphur.  Mr. La-
 voisier first obliged the chemists to attend to a thing which they
 had either overlooked,  or accounted for  in  an unwarrantable
 manner,—namely, that the weight of the  acid is vastly greater
 than that of the brimstone from which it is produced.  From
 eight grains of sulphur we can produce twenty-six of vitriolic
 acid: part of  this indeed is water, collected from the atmos-
 phere, but by no means the whole.  Moreover, he found that
 in burning, the sulphur absorbed and attached to itself a great
 quantity of the pure part of the air.   And at last, he found, by
 careful measurement, that it absorbed a quantity exactly equal
 to the augmentation of its weight by inflammation :  and he gave
 good reasons,—reasons which have at last  been  acquiesced in,
 that this air is the cause  of the  acidity of vitriolic acid,—he
 therefore called it oxygen.
   Sulphur, therefore, is now considered as a simple substance :.
 and sulphuric  acid is a compound of sulphur and oxygen: and
 in this light I  shall continue to consider it.
   At the temperature of 140°, or 150°, sulphur begins to at-
 tract oxygen sensibly :  and if the heat be increased to 180°, or
 190°, the combination becomes pretty rapid, accompanied by a
 faint light: and if this be long continued,  the sulphur will be
 converted into acid, in the form of suffocating steams.  But the
 heat is insensible ; at least, it is so weak, that the inflammabili-
 ty of the sulphur  in gunpowder  will be completely destroyed
 without setting fire to the charcoal, and the  powder is now quite
 useless.  This is  similar to what happens in phosphorus and
 many other inflammable substances.   It is  an imperfect, or ra-
 ther a slow inflammation, which shall be noticed more particu-
 larly in the sequel.
   When sulphur is evaporated in close vessels, it sublimes into a
 fine dust or powder,  called flowers of*sulphur.   They are fine
 crystals, generally  a little acid, by reason of the  air which filled
the vessels. This acidity may be removed by washing the flow*
ers> in water.
   I come now to consider  the properties of sulphur discovera-
 ble by' mixing it with other bodies. 
    SULPHUR—WITH ALKALI—SULPHURET. 405

   Sulphur unites readily with the fixed alkalis,  as you have al-
ready seen, especially when they are caustic :  and this combina-
tion is effected both in the dry and the humid way.  It combines
also with all the alkaline earths, and the compounds are  called
Sulphurets.  It can alsO be combined witii volatile alkali.  It
then forms a volatile hepar, called also  volatile tincture of sul-
phur.   This combination of sulphur with volatile alkali is pro-
duced by mixing together two parts of the muriat of  ammonia,
two parts of lime, and one part of sulphur, and distilling the
mixture briskly.  The sulphuret does not begin to form till to-
wards the end of the operation; the lime immediately detach-
ing the ammonia in  its pure state.  This volatile hepar is mix-
ed, but not compounded with the pur% volatile  alkali.  It may
be separated, and will even crystallize.
   The propensity which sulphur has, when thus cdmbined with
alkaline substances,  and dissolved in water,  to absorb oxygen
more quickly and easily than when it is pure, was formerly no-
ticed.   In its pure or separate state, or even  when combined
with alkaline substances, via sicca, it does not attract oxygen,
except when it is heated to such a degree as to make it melt and
begin to evaporate.   Then indeed its union with oxygen begins
to take place, or it enters into a state of imperfect inflammation.
But, when united with alkaline salts or earths,  and at the same
time dissolved in water, it gradually attracts oxygen from the air
to which it is exposed;  and is thus changed into sulphuric acid,
wfthoutneeding the assistance of  heat.  You  doubtless  recol-
lect examples of this  when  I  was considering the different
kinds of gas, and the experiments by which Scheele and Lavoi-
sier demonstrated the composition of atmospheric air.
   There cannot be a doubt but that this increase of its disposi-
tion to attract oxygen proceeds from the change induced upon
its cohesive attraction by the alkali.
   Many of the foreign chemists explain this  in another way.
Sulphur, say tney, attracts oxygenous gas so weakly in low heats,
that it cannot take it from the air in that form.  But being mix-
ed with alkali, this  prevents the first approach  to saturation.of
the  sulphur with oxygen, by its attraction for the naseent sul-
phuric acid,  with which it instantly unites and  forms a sulphat. 
 406        SULPHURETS—HEPATIC  GAS.

 This is carried off by the water, and leaves the rest of the sul-
 phur equally ready for combination.
   The attraction of sulphur for alkaline substances is not  very
 strong.   It may be separated by any acid, even the carbonic;
 and in the moment of  this separation, the mixture emits a gas
 or elastic fluid.  If the acid be poured on a dry hepar sulphuris
 in powder, the copious escape of this  hepatic  gas occasions a
 brisk effervescence, although the hepar has been prepared with
 a caustic alkali.
  This hepatic gas has very singular properties.
   lmo, It has an intolerably offensive smell, which is common-
 ly said to resemble the smell of rotten eggs.   Indeed, the va-
 pour coming from an egg when boiled, whether fresh or rotten,
 contains this gas, and blackens  silver, &c. like  it.   If a Bit of
 hepar sulphuris, a boiled egg,  or a piece of newly manufac-
 tured horn, be. shut up in a cupboard, all the silver in it will be
 stained almost black in a few days.  A few hours will stain it
 brown.
  2do, It can be condensed  into a sort of oily-like matter by
 intense cold, as appears from experiments of  Mr. Monge, nar-
 rated by Fourcroy in his Preliminary Discourse, page xxxi.—
 Kerr's edition, 1788.
  3tio, In its elastic or vaporous state, it is highly inflammable;
 and burns something like hydrogen gas, but not so ranidly: and
 while-it burns, a small  quantity of sulphur is separated from it.
 The sulphur  also undergoes a slight degree of inflammation, and
 is in part changed into  sulphurous acid.  This gas is much hea-
 vier than the hydrogenous.  It unites with alkalis,  in  the same
 manner as the hepar from which it was produced ;  and is sepa-
 rated without decomposition by an acid, provided that acid "do
 not too readily part with some oxygen.                       4
  The nature of it was not understood,  until  the late improve-
 ments were made in our science by the study of gases or elas-
 tic  fluids.   It is now considered as an hydrogen gas,, holding a
small quantity of sulphur  combined with it.   (See Note 44,  at
the  end of the Volume).
  The inferior degree of rarity, or of elasticity and  volatility,
which it has,  when compared with pure hydrogen gas, proceeds 
HYDRO-SULPHURET.
407
from the sulphur which it contains.  The sulphur, by its attrac-
tion for the hydrogen gas, diminishes its volatility; and there-
fore renders it a denser or heavier fluid, and disposes it also to
be condensed by a great degree  of cold : and, probably from
the same cause, it derives an aptitude to be  condensed  or ab-
sorbed by water, to which it communicates its own  detestable
odour.   Hence the smell of sulphurous mineral waters, and the
deposition of  sulphur observed at many such springs.
   If such water, however, be exposed to the air, or put into
bottles, without using every  possible precaution to prevent the
escape of the  elastic matter,  a part of  the gas evaporates,  or is
lost.   And it leaves behind in the water a part of the  sulphur
which was united with it.  This renders the water milky, and
is deposited by it.  Hence the sulphur  deposited by some fa-
mous mineral springs.   This happens  in consequence  of the
great volatility of the hydrogen gas, which makes it  evaporate,
carrying away with it a part  only of the less volatile  sulphur*.
   Such water is also  made to deposit the sulphur immediately,
by adding to  it  a small quantity of very  strong  nitrous  acid.
And the sulphurous acid produces the same effect.  But  neither
the sulphuric  acid,  nor the muriatic in its ordinary state,  have
any power to  precipitate the  sulphur : and even the  nitric has
but little of this power.
   If is supposed that the strong nitrous acid and the sulphurous
acid act by a loose and separable oxygen, which unites with the
hydrogen, and changes it into water.  The sulphur, when alone,
not being soluble in water, must therefore make its appearance
in  an  undissolved state.  But I cannot  understand why the
sulphuric and the nitric do not produce the  same  effect.   (See
Note 45. at the end of the Volume.)
   Several of  these experiments  were first made  by Professor
Bergmann, and also by Scheele.  Bergmann was the first who
explained by them the nature of many of the  mineral waters,
called sulphurous waters.

  * Is it not more probable that this decomposition of the gas, and precipita-
tion of the sulphur, is effected by the oxygen in the air ? This was Scheele's eu-
diometer; and is perhaps superior  to any other.—Editor. 
408                     SULPHUR,
   They have the odour, and the other properties, more or less,
 of an artificial compound of water with this gas.   This will be
 exhibited again hereafter, when we describe the mineral waters.
   The authors who have thrown the most light on the forma-
 tion of this gas, are a little society of chemical philosophers in
 Holland, Messrs. Von Deiman, Troostwyck, and others, who
 have published a volume or two of their experiments on differ-
 ent subjects.   Their doctrine on this subject may also be seen
 in the 14th volume of the Annales de Chymie, page 294.
   According to these gentlemen,  a  small  portion of the dis-
 solved sulphur acts on a small portion of the water, so as to
 take its oxygen from it.  The separated hydrogen of that small
 portion of the water does not immediately assume the form of
 a gas ; but is joined to the remaining unchanged sulphuret, at-
 taching itself to it by an attraction  for both the sulphur and the
 fixed alkali.   But when we add an acid to saturate .the alkali,
 the separated hydrogen has nothing left with it but the sulphur,
 the attraction of which is not sufficient for entirely repressing its
 volatility.   It therefore assumes the form of gas,, aided in this
 by the heat produced or extricated by the action of the acid and
 alkali on one another.   And while it assumes the form of gas,
 it volatilizes a part of the sulphur, which is combined with the
 gas thus produced*.
   This hydrogenous sulphuret has  already  come  before us,
 while we were considering sulphur  in its connection with the al-
 kaline substances.
   We come next in order to consider its relation to the acids.
 Its relation to the sulphuric acid is already known.
   We may foresee what will be the  effect of mixing sulphur
 with the nitric acid.  It must be very similar to that of a mix-

  * This explanation seems both gratuitous and embarrassed.  We assume,
without warrant, that water is decomposed, and is afterwards recompounded.  'y
in the Ann. dt Chymie, vol. 14. /?. 311- the  hepar, sulphuris is supposed to de- .  „••;
compound the water, not of itself, but by help of an acid, whose calorie-forms  ".
a hepatic gus with the hydrogen and part  of the sulphur.  Eut here the.de-»  Jg
composition of the oxygen becomes still more  mysterious: and we cannot see
why the hydrogen, which at first detached the caloric from an acid, should af-
terwaids let it go, and again unite with the acid, and compose water.—
Editor. 
      SULPHUR—ITS NATURAL HISTORY.     409

ture of phosphorus with it.   Accordingly, if we pour on a quan-
tity of sulphur twenty times its weight of nitric acid, and distil it,
we shall obtain sulphuric acid double the weight of the sulphur.
This arises from the very loose and separable state of the oxy-
gen  in nitric  acid.  For the same reason,  this change  may be
produced by the oxygenated marine acid.
   You all know that melted nitre forms the sulphuric acid with
rapidity and vehemence, by deflagrating it with sulphur:  for
we have in the crucible a sal polychrest, or sulphat of potash.
   Phosphorus ci.n be combined with  sulphur in the way of fu*
sion and sublimation, in a retort and receiver.  Margraaf form-
ed a compound of this kind, in which the attraction  of both
these inflammable substances for oxygen appears to have been
more powerful  than when in their separate state.  The com-
pound took fire, and burned with violence, whenever it was ex-
posed to ihe  air*.  The chemical  combination of these highly
inflammable substances produced this  effect probably  by a di-
minution of their cohesive attraction.


                 Natural History of Sulphur.


   Sulphur is to be found in all the kingdoms,  as they are call-
 ed,  of nature;  It is formed by the decomposition both of ani-
 mals and vegetables.   The  fcetor of animal excrements is found
 to arise from hepatic gas.   A  Considerable quantity of  sulphur
 was collected in cleaning an old common sewer at Paris.  (See
 Chaptal, torn. i. p.  91.;  The  same  gas is found  in all putrid
 collections of decaying  vegetables.  The pit in which flax is
 steeped, year after year, impregnates the clay around it to such

  * I rather think that Margraaf's account of it indicates less inflammabili-
ty.   It inflamed with  some difficulty, he  says, by friction, giving a yellow
light.  A dry heat, equal to  that of boiling water, caused it to  burn with
Violence, giving a strong smell of hepar sulphuris.   It swelled in water, im-
bibing much of it, and rendered the water acid and sulphurous. The water,
into  which it dropped in the distillation, effervesced violently with alkalis.
  This is a very curious and somewhat puzzling experiment. Whence did
the acid come, and what was it ?  Did the compound decompose the water,
and become oxydated ?—Editor.
                                         3 F 
410
SULPHUR.
a degree, that it burns with a blue suffocating smoke.  Nay, sul-
phur is found in the juices of  some plants, particularly the ru-
mices or docks.
   But it is most abundant in the mineral kingdom.   And there
it is generally in a state of combination, chiefly with metals.  The
ores of most metals contain it.  But the ore or mineral sub-
stance, most remarkable for the quantity of sulphur which it
contains, is the Pyrites, in which the sulphur is combined with
iron or copper,—chiefly, however, and oftenest, with iron.  This
 compound is of metallic opacity and lustre,  and a pale brassy
 colour.   It is found in entire veins,  or sometimes in separate
 masses.  It generally is so found among coal.  Relics of ani-
 mal and vegetable substances  are frequently  found completely
 penetrated with it, and, as it were,  changed  into pyrites.   In
 the island of Sheppey, and other parts of Kent, such  specimens
 are very abundant; particularly vast quantities of the cornu am-
 monis, some of them of  enormous size.   What is curious, the
 shell onlv is penetrated with pyrites: and its hollows are  filled
 with sand-stone or other common matters.  Pyrites is also found
 very frequently crystallized.  The cubical brass-like  crystals in
 common slate are the purest  specimens of iron  pyrites that I
 know.  But there is a vast variety of other forms, many of them
 very beautiful,  adhering to almost all ores and spars in metallic
 countries. These crystals are commonly the most showy parU^f
 a fossilist's cabinet.
    It is only from the richest pyrites that sulphur is now extract-
 ed.  Such as give less than  one-fifth of their weight, are not
 worth the labour and expence; but are long roasted in open
 heaps, to drive away the sulphur, and reduce the pyrites into a
 state fit for smelting for its metal.   In some of these heaps, ca-
 vities are left in proper places,  into  which the sulphur,  which
 evaporates or melts from the rest of the heap, is directed, and
 there collected.
    Very rich pyrites are treated for their sulphur by a rude kind
 of distillation.  The. retorts are nothing but conical earthen
 pipes, about four feet long, ten inches wide at one end, and two
 at the other, and open at both ends.   The furnace is an oblong
• space between two walls three feet asunder, having several holes 
MANUFACTURE OF  SULPHUR.      411
    in the roof for the smoke, and also a row of holes in the floor, to
    admit air to maintain the fire.  The conical pipes lie across this
    gallery, the wall on one side having holes ten inches wide, and
    the  opposite wall having as many two inches wide.  Thus the
    pipe fits both  holes,- and is made tight with  lute.   It lies with
    a small descent towards the narrow end, which projects  three
    or four inches ; and a rude receiver is there joined to it.  The
    lumps of pyrites are put in at the wide end : and when the pipe
    is full, that end is shut up by a round tile luted into it.  The
    narrow end of the  pipe is also  plugged with a bit of tile shaped
    like a star.   This allows the melted or vaporized sulphur to get
    out, but keeps in the lumps of pyrites.  The  space  round the
    pipes being filled with fuel, the fire is kindled, and kept at a
    moderate heat, by opening or shutting the holes in the roof.
    The sulphur melts  and evaporates, and runs into the  vessels un-
    der the small end of the  pipes : and when no more runs, the tile
    is taken out of the wide end,  and the effete pyrites are raked
   "out, and fresh put in immediately; so that the work is not in-
    terrupted.  The pyrites taken  out still retain sulphur.   This is
    driven away by roasting them  in a heap :  and then the remain-
    der is smelted for its metal.
      But the greatest part  of the sulphur  used in  Europe is ob-
    tained much more  easily.   It is found in vast abundance, ready
   4»«ned, in the volcanic countries, particularly at Solfatara in Ita-
    ly.  It is undoubtedly produced in those countries in the  same
    way that we produce it by art.   The subterranean fires are oc-
    casioned chiefly by the  decomposition of the matrices of sul-
    phur ; and they act on them in the same way as the fires in our
    laboratories,  causing the sulphur to fly  off in vapours through
   "every fissure'andcavity.   It sublimes into  those  cavities, and
    collects in vast quantities,  so as even to break down  by its own
    weight.   The vapours even penetrate  upwards to the very sur-
    face, impregnating  even  the soil, so that the very earth taken up
    with the spade will yield sulphur.  In the cavities, and adhering
    to the stones and rubbish, it is often found pure and crystalliz-
•'   ed,—sometimes transparent. This is called sulphur vivum. But
   it is  generally foul,  like what is obtained from the  pyrites. 
412                    SULPHUR.

  Crude sulphur is contaminated by earthy matters diffused in
it, and also by metals whkh are in some  measure united to it.
It is purified by melting, and  keeping for some time  fluid ;  by
Which  means  the impurities  subside, and the pure sulphur is
raked off, and poured into moulds, which form it into the little
rolls in which we commonly see it.
  It is also puniivd more completely by sublimation.   For this
purpose, a furnace, holding a pot, in which the sulphur is melted,
is built at one end of a room,  which is shut on all sides, and has
the walls, ceiling, and floor, covered with lead or a proper ce-
ment.   The sulphur rises  from the pot in steams, which are
condensed on the walls, ceiling, and  floor, in  the form of fine
dust, called Flowers of Brimstone.  These are sometimes a
little acid, owing to the air which originally filled the  room, the
oxygen of which decomposes  some of the sulphur.  They must
be cleared from it by washing before the sulphur can be used for
all purposes of medicine.
  The medicinal preparations of sulphur are  not many.  It is
combined with quicklime, in the moist way, forming  a calcare-
ous  hepar, which we have paid sufficient attention to already.
But this is only a previous step for the preparation of Lac Sul-
phuris, by precipitating the sulphur with any  acid.  The muri-
atic  is  the one prescribed in the London Pharmacopoeia for this
purpose.
  Sulphur is  also combined with some oils, to compose Bal-
sams of Sulphur,—nauseous medicines, having  a mos. of-
fensive fcetor, occasioned  by the  emanation  of an inflamma-
ble gas.
  The chief  preparation from sulphur, and it is a very import-
ant one, is its acid.  This  can be obtained only by  inflamma-
tion ;  for we need not speak of the process of distilling a great
quantity of iiin'rl acid from sulphur.   This, indeed,  gives  the
acid, but in a way vastly too expensive.   In  the ordinary way
of burning sulphur, the acid  is obtained in a volatile suffocating
form.   It is  an acid vapour, holding, but very slightly, a consi-
derable portion of sulphur in solution, and a  great quantity of
water, collected from the.atmosphere.  It is what we named
sulphuroui acid.   That this  is its nature and composition, is 
           MANUFACTURE OF ITS ACID.       413

proved by distilling vitriolic  acid, into which a bit of sulphur,
or almost any inflammable substance, has been put.   If we ex-
pose some of  this volatile acid to vital air, under a glass, it will
absorb it *m a  minute,  gain weight, and lose entirely its volati-
lity and  suffocating  fumes, becoming sulphuric acid.  This is
not altogether by saturating the redundant sulphur, for some of
it is precipitated.
   Sulphurous acid is scarcely acid to the taste; also its chemi-
cal relations,  as an acid, are exceedingly weak, so that almost
any acid will  detach it  from an alkali.   It has distinguishing
properties ; particulary that of quickly discharging vegetable co-
lours.  The suffocating  vapour of burning brimstone will make
a red rose white in a few minutes.  It is employed for whiten-
ing woollen, and silk, and linen goods.  This volatile acid could
  ot be obtained in a tangible form, were it not for the moisture
diffused through the air;  and it is  this alone  which makes it
liquid in the  old  process.  This process was  to  burn  sulphur
with  a small flame,  under a large glass bell, kept cool by a wet
cloth.  The acid formed on its  inside ;  and thence it dropped
into a funnel.  This produced the spiritus sulphuris per ca?npa-
nam, now called sulphurous acid, to denote its redundancy in
sulphur.
   To obtain  sulphuric acid  free from these suffocating fumes,
we need only expose the sulphurous acid to the air.  The re-
 dundant sulphur partly attaches  to itself more oxygen, and part-
 ly is lost, perhaps by  precipitation in the air.
   The manufacture of sulphuric acid, in the state  in which it is
 required in chemistry and the arts, is a  very  difficult process ;
 and a* very lucrative manufacture to those who are possessed of
 the secret.   It is,  as yet, in very  few hands.  This much is
 known of it, that the sulphur is kept burning in a pot,  set on a
 small furnace, built at one end of a  chamber which is closed on
 all sides,  and lined and  floored with  lead.  Water  is  kept on
 the floor, to  aid the condensation of the acid vapours.   Nitre
 is employed, mixed  with  the  sulphur,  before inflammation.
 This maintains the combustion, which otherwise  would soon
 cease, because the sulphur quickly absorbs the oxygen of the air
 that  fills the  chamber in which  it is burned, and  its  vapours 
 414 SULPHUR—MANUFACTURE OF ITS ACID.

 condensed.  The remaining azote, and the acid vapours already
 produced, soon put an end  to  the  inflammation.  The nitre
 maintains it by supplying oxygen.   But nitre  is a  very, costly
 article:  and no more can be  afforded than  what just keeps up
 the inflammation.  Even with this help, a great many nice con-
 trivances are practised in the great manufactures of Great Bri-
 tain, (which country7 alone, as yet, possesses the secret) to keep
 up the inflammation: and, after  all, the acid is loaded with
 much redundant sulphur, and is very weak, because much wa-
 ter was employed for condensing the vapours.   It must there-
 fore be concentrated.  This would be a simple operation with
 sulphuric acid, which is much  more fixed than water.  We
 needed only to evaporate the superfluous water.  But here it is
 difficult, partly because the volatile steams contain sulphur, which
 would be lost, and partly because,  in a very diluted acid, the
 water will carry off much acid.   It is concentrated by a distilla-
 tion in great retorts,  several  times repeated, in a  way which
 would be tedious  to describe, but which a little reflection on the
 properties  of the substances will  suggest to you.  Attempts
 have been made to supply oxygen in this part of the process by
 means of manganese, a mineral of low price, which  contains
 much of it very loosely combined.   The acid must be dephleg-
mated till it acquire a specific gravity almost twice as great as
that of water.   It must be at least 1,6 or  1,7 before  it is fit iox'
 dissolving indigo for the dyers.
 When fully saturated with oxygen, it seems to contain seven-
 tenths of sulphur, and three-tenths of oxygen. 
%
NOTES  AND  OBSERVATIONS-
BY  THE EDITOR.
                      [Note 26. p. 8.] .

  THERE are among Dr. Black's papers several sketches of
an arrangement of the chemical substances, with a view to make
the consideration of them  more synthetical and systematic.
One of.them,  in which he has made many changes and correc-
tions, begins with water, and goes on in this manner:
  41 Water....Margraaf's experiments....silex, foreign to it....
44 Dr.  Austin,  with iron  filings....inflammable  air....ignifying
44 air....Cavendish....water....nitrous acid....nitrous air, or choke-
f* damp....acids."
  J. think that I perceive the connections by which £ his  may be
made a skeleton of chemical philosophy.  There is another paper,
in which the properties of nitric acid  are  gradually developed
and applied^ so as to terminate in the establishment of the anti-
phlogistic system, in a very familiar and easy manner.
   I recollect a  conversation which I had with Dr. Black, and
Dr. James Hutton, soon after the appearance of Mr. Lavoisier's
sketch of a scientific arrangement of chemical objects.   I was
telling him how highly I was pleased with that arrangement, on
account of the happy train of synthetic deduction which it enabled
Mr. Lavoisier to carry through the whole  of the chemical
history of bodies.....    *
   44 This," said Dr. Black,  " is the very thing I dislike it for.
44 Chemistry is not yet a science.  We are very far  from  the
44 knowledge of first principles.  We should avoid every thing 
4J6       NOTES AND  OBSERVATIONS.
 44 that has the pretensions of a full system. The whole of chemical
 44 science should, as yd, be analytical,  like Newton's Optics:
 44 and we should obtain  the connecting principle, in the form
 44 of a  general law,  at  the very end  of ou. induction,  as  the
 44 reward of our labour.  You blamed, and, in m\ opinion, justly,
 44 De La Grange's Mechaniqae Analytique, for being the very
 14 opposite  to  a  real analytical process ;....for  adopting  as  the
 44 fundamental proposition, as  a first principle, a theorem which
 44 in  fact is nothing more  than a sagacious observation of an
 44 universal fact, discoverable  indeed  in  every  mechanical phe.
 44 nomenon ;  but still not a principle,  but the mathematical and
 44 not the physical result of all our inductions.  This is not a
 44 fundamental theorem, fit for instructing a novice in the science,
 44 but for adepts alone.    The case is the same in chemistry.
   44 But this  is not the greatest fault in the arrangement which
 *4 sets out from the  constitution of  the atmosphere..:" In order
 " to get the proofs on which the validity of this first principle
 *4 must  entirely rest, we must fall  to work with a  number of
 44 complex, very complex substances, of which we know nothing,
 44 and whose  modes of action  are among the most mysterious
 44 things in  chemistrv: and the  conclusions  which  we must
 41 draw, require a steadiness and  contention of thought which
 44 very few possess,....which a beginner in philosophical in^esti-
 44 gation cannot possibly  possess.   It  is by no meant  fair to
 44 appeal to a Lavoisier,  a Cavendish,  or  a Berthollet, or other
 44 great  chemist, for  the  clearness of  the evidence.  They are
 44 not the proper judges.   Lay it before a sensible metallurgist,
 44 ignorant of chemistry.   Ask this man whether he sees  the
 44 incontrovertible force of the  proof.  When I take the matter
 44 in this light, I affirm that, even to a philosopher,  the proofs
 44 of the fundamental propositions wbich have been acquiesced
 44 in by  the authors of this arrangement,  are very scanty, very
 44 slight, and very refined.   This is a fault in a system published
 44 for the instruction of the ignorant;  and,  in the  present day,
 44 it is a very great fault.   There is just now a rage for system,*
44 ....for complete systems.   We have  got such a high conceit of

  * Much of what follows is taken from an introductory lecture with whic*i
Dr. Black was accustomed to begin his course. 
NOTES  AND OBSERVATIONS.       417
    14 our knowledge, that we cannot be pleased with a system which
    44 acknowledges any imperfection : it must not leave one open
    44 link :  it must not leave any thing unexplained.  And I see it
    44 always happens that if  the  application of a system to the
    44 explanation  of phtnomena be very comprehensive, leaving
    44 no blanks, and if the explanation have some feasibility, this
    44 catches the fancy,....it dazzles the understanding.   Nay, we
    44 think  it impossible that a principle that is  false  can tally with
    44 so many phenomena. This seeming coincidence is considered
    44 as a proof of its validity: and  we are no  longer  solicitous
    44 about the direct proofs adduced in the beginning. I have often
    44 heard such arguments for what I knew to be great nonsense.
    44 This kind of authority accruing to a theory from its specious
    44 and extensive application to phenomena, is always bad: and,
    44 with mere beginners  in philosophy, it is doing  them an irre-
    44 parable hurt.  It nourishes that itch for theory ; and it makes
    44 them uUsolicitous about the first foundations of it.   Thus  it
    44 forms in their minds the worst of all philosophical habits.
      44 I am resolved to go on in a  very different way.  I subscribe
    44 to almost all Mr. Lavoisier's doctrines : and I will teach them
    44 all.   And I  affirm that I shall teach them  with  an impression
    44 of their truth which his method can never make. My students
  i  "jsh^ll get all these doctrines piece-meal;....every one of  them
    44hy steps which shall be quite easy and confident, because they
    44 shall be acquainted with every substance before I  employ its
    44 phenomena  as  proofs.   Each of  Mr. Lavoisier's  doctrines
    44 shall arise in course,  as a small and obvious addition to the
    44 properties of some substance already known.   Then I  shall
    44 carri/the student back, and shew him that the influence of our
—   *4 new discovery extends  also  to  those  substances  which we
    44 had been considering before.   Thus, all the doctrines will be
    44 had easilv, familiarly, and with confidence  in their truth.
      44 I even think that this method  will be more pleasant,....the
    44 novelties, or reformations,' being, by this method, distributed
    44 over the whole course.   And it  will have  yet another advan-
    44 tage.  It w'ill make the student acquainted with  the chemistry
    14 of former year*,, which  is  far from being  unworthy of the
    44 attention of a philosopher.. Newton, Stahl,  Margraaf, Cramer,
    tt C/.V,ool»  Rpyrrmonn  '<""•" r«.r..i \ c«»S fJOt belOW  tlie COIIimOIl
w 
418        NOTES AND OBSERVATIONS.

44 level.^ But the person who  learns chemistry by Lavoisier's
44 scheme may remain ignorant of all that was done by former
44 chemists, and unable to read thei* excellent writings.
  44 I do not find that my old arrangement needs much change ;
44 some I will  make,....chiefly in the order in which I treat the
44 inflammable substances and the metals."
  Such was very nearly the manner in which my excellent pre-
ceptor expressed his sentiments  and intentions on the occasion
that I mentioned  above, and at several  other times.  I cannot
but think that he had much reason for what he said.  The proofs
which were acquiesced  in at that time were verv scanty indeed,
and very refined, unless they were deduced from known pro-
perties of substances, which can be  familiar only to  an adept in
chemistry.  And the dashing boldness with  which the chemists
applied  them to the  most complicated phenomena, and the
authority with which  our acquiescence was demanded, were
disgusting; particularly to a man  of Dr. Black's scrupulous
caution, which scarcely ever allowed him to hazard a conjecture.
The public has great reason to regret that this sagacious philo-
sopher, and faithful  follower of Newton's steps,  did not live to     ♦
put the  finishing hand to  the arrangement of facts on which
chemical science should be rested.
  Dr. Black's feeble constitution, and  low  state of health for    J
several years before his decease, put this out of his power.  The   . M
close thinking which such a task required,  not only fatigued  ". .1*
him, but greatly deranged his health : and he  was always obliged
to give it over.  He employed himself,  however, from time to    <
time, in making small changes in the arrangement of the articles
of his course.  In the last conversation  I had with  him on che-
mical subjects, he told me that he was about to make a general   . j.,
revision of his treatment of the metallic substances, in order to   , "
put into a  more regular and connected form the way of consid-
ering each metal in different stages of oxydation.   It does not
appear that he had proceeded far in this revision.
   I regret also that no distinct notes are to be found respecting
the  difficulties which, Dr. Black found in the antiphlogistic     ,
system of chemistry.   He  remarked,  in some of his  annual
courses of lectures, that Mr. Lavoisier's system did not explain
the light which is  so  characteristic of combustion ; and said 
NOTES  AND OBSERVATIONS.        419
 that some very judicious observations on this subject we&e to be
 found in Lubbock's inaugural dissertation, de Principio Sorbili,
 which also professes to give*a theory of combustion  and acid-
 ification.
                       [Note 27. p. 13.)

   There are innumerable facts which shew that common air is
 contained in fluids, chemically, but slightly combined.   When
 water is gradually heated in a glass vessel, or is put under an air-
 pump receiver, and the pressure of the atmosphere on its surface
 is removed, innumerable bubbles are formed all over it, and rise
 to the top.   If,  on the other hand, the water be put into a con-
 densing apparatus, and be agitated for along while with air vio-
 lently compressed, we shall observe,  that as soon as we  open
 the cock, and let out the condensed air, air-bubbles will form in
 the water in the  same manner, and rise up and escape.  If the
 water,  and the air which  come out in the first experiment, oc-
 cupy the whole phial, the air being now collected in one mass at
 the top, the water will reabsorb it all after some time.
   This evident mixture of air and water is perfectly transparent:
 and it appears by Mr.  Canton's experiments, that it is no  more
 compressible than  water purged of all air.  The air, therefore,
 is not in its elastic state.   It is chemically combined.
*  In those experiments, the air bubbles form  most copiously on
. the sides of  the vessel, or on any body immersed in the water.
 Part of this probably was adhering to those solids.    This,  how-
 ever, is not certain from this appearance alone, because the su-
 perior attraction of the water and the glass should detach the air
 dissolved in the  water contiguous to the glass sooner than in any
 other place.   But it is  in part owing  to air adhering to the
 glass:  For when we drive out the air from the mercury in the
 upper end of a  barometer by boiling, and  then brifi§ the  same
 mercury in contact with apart of the tube farther down, we shall
 obtain more  air  from it.   This must  have adhered to the tube.
 I have also found that I could obtain a much greater quantity of
 air  by  boiling,  or the air-pump, from water into which  I had
 thrown a quantity of powdered glass.  It is very probable, there-
 fore, that a very considerable portion of the air which escapes
 r___! a cnlntinn of salt  in water, proceeds from the salt, and had 
420       NOTES  AND  OBSERVATIONS.
                       [Note 28. p. 15.]

     The general  appearance of a#clouded atmosphere is ex-
   tremely agreeable  to  this theory.  It generally consists of
   extensive  strata of clouds, of no great  thickness,  separated
   by strata of clear air, of much greater thickness.   The under
   surfaces of the clouds are pretty even.  This  is  precisely
   what should happen.   One great stratum of air, coming  from
   one  quarter of the heavens, glides over another, coming per-
   haps from another quarter. These, having a relative motion,
   rub  as it were on each other, and mix a little way  into each
   other, producing a precipitation, that is, a fleecy cloud.   But
   the  interior  parts  of  the  strata of air  which do  not  mix,
   remain clear.   This constitution agrees also finely with the
   electrical phenomena of the atmosphere, giving an extensive
   conducting coating to the strata of air which are  in opposite
   states of electricity.   A thunder clap is soon succeeded by
   another, in the same place, because it only restores the  elec-
   tric  equilibrium in a certain,  perhaps small, thickness in the
   clear strata of air : and the opposite electricities still remain-
   ing  in the  rest of the  stratum, soon enable the coatings to
   give another  discharge.   It is like the residuum shock  from
   glass that is coated only in spots.   When an irregular  wind
   tosses the  strata, and  jumbles them  together, then we see
   great roundish clouds  of a vast thickness vertically.   These
   clouds are probably clear within, and only superficially opaque,
   viz. in the touching boundaries of the masses of air so  fum-
   bled, &c.

                         [Note 29.  p. 27.j

     It is n%S> very clear in what  case  we have a  proof of a
   greater, and in what of a lesser attraction in the crystallization
   of a salt.   It is true,  the salt is  let fall by the  water ; and
v  one  attraction,  or principle  of  union,  has  prevailed  over
   another.   But,  since a saline  crystal  is a compound of salt
   and  water, the formation  of a crystal is rather the evidence
   of a prevailing attraction between the salt and water.   Why
   it takes place at a particular proportion of the ingredients,
   seems owing to the same cause  as the  regular forms which 
NOTES  AND  OBSERVATIONS.      421
the crystals assume.   It was observed on a former occasion,
that the  form of solidity required the attracting forces to be
different in different directfbns,  and perhaps in the different
parts of the particle;  so that two particles of a  crystal may
tend to unite  in one way rather than in another.  Suppose a
particle of a saline crystal to consist of one particle of salt,
and one  of  water,  and suppose that they unite  because the
particles of water attract those of salt more strongly than the
particles of salt attract one another ; the consequence of this
must be, that two such particles, floating in the  water, can-
not  unite  indifferently.    They will approach each other so
that the saline ingredient of the  one will apply itself, in pre-
ference, to the watery ingredient of the other.   For similar
reasons, even the two  ingredients of a particle will unite in a
particular manner.   In short,  their manner of coming toge-
ther will resemble the manner in which magnets floating on
quicksilver Will  come together.   Polarity  seems  to  be as
good a term as any for expressing this affectation of a parti-
cular position or attitude.    We  have no authority for saying
that the figure of a crystal must resemble that of the primitive
atom, although it undoubtedly depends much on that figure;
because  that must greatly influence the inequality of the cor-
puscular attraction in  different directions and different points
of the particle.  It is plain, and we see it in magnets, that
this inequality must increase as we come nearer to the parti-
cle.   This seems to be the  effect of abstracting  the water of
the solution.   When  this is done to  a certain degree, the
polarity begins to operate ; and then the attracting points of
the particles bring them briskly together.   It is not, there-
fore, a superior strength, but a certain modification of the
corpuscular force which produces the crystallization.

                      [Note  30. p. 31.]

   Mr. Lowitz, of the Imperial Academy of Sciences in Pe-
tersburgh, has made some considerable improvement in the
crystallization of salts.  He makes the solution very warm :
and when  it is almost ready to shoot*into crystals, he puts
into it a small crystal.  The crystallization  instantly begins,
          _- _.. .u~ k..:„.  „™ie i-.«-oducing beautiful crystals. 
422       NOTES AND OBSERVATIONS.

As the brine becomes weaker, it begins to act on the crystal
put in, and dissolves it.   He puts in another, which renews
the crystallization,...and repeats  jhis till all that will separate
is crystallized.   The crystallization  is more  beautiful the
more slowly we allow the brine  to cool.   It should there-
fore be set in a tub of hot water.   He  obtained fine crystals
in this way, even from the most deliquescent salts ;  and suc-
ceeded with  some that never had been crystallized before.
   Mr. Lowitz, in the practice of this  method, made an ob-
servation that is extremely curious, and peculiarly serviceable
in this method of separating salts  of different kinds.  Re-
flectingon Mr. Beaume's having obtained pure crystals from
a muddy solution, he thought it not improbable that a salt, in
crystallizing, rejected  any thing which did not correspond
with its  own manner of going together ; and  therefore that
a crystal of saltpetre would not affect a solution of Glauber's
salt. He found it so upon trial.  He then concluded that in a
mixture  of different salts, a crystal of one  of them would in-
duce the  crystallization only upon its own kind.  He dissolved
two ounces  of saltpetre,  and three ounces  of Glauber's salt,
in five ounces of water almost boiling hot.   He divided the
brine into three phials: and into one he put a crystal of nitre,
into  another  a crystal of Glauber's salt.   His expectations
were  completely answered. Nitre alone crystallized in the
first; and Glauber salt in the second ; and a mixture in the
third.   Taking out  these  crystals, he then put into  the re-
maining  solutions  a bit of the salt  which  had not crys-
tallized.   This immediately induced the crystallizatirfi.
   This observation  is equally important to the artist and to
the philosopher.   It greatly aids the practical chemist in this
troublesome  process : and it is most instructive to  the philo-
sophical  chemist.   It is not explained by the  simple  notion
of things of one kind going together,   of nitre uniting  with
nitre, and borax with borax ;  for this  is  not the operation.
It is that nitre induces water to unite in the way of  crystalli-
zation only with  nitre: and  borax disposes it to unite only
with borax.    I th'u.k it one of the  strongest confirmations of
the operation  of  those  peculiar modifications or  composi-
tions of  corpuscular attraction, which I have called polarity. 
          NOTES  AND  OBSERVATIONS.       423

                    [Note 31. p. 85.]

  Dr. Robert Hooke had published his theory of combustion
in his  Micrographia, in 1664, (page 103),  in which  he ex-
pressly says  that combustion is nothing but the  solution of
the combustible body in this nitrous spirit, which constitu-
ted the greatest part of our air. And in his Lampas, published
in 1676, he again gives his theory at length; and observes
that it had been very well received eleven years before  by
the learned at Oxford, and adopted by them in their writings,
evidently  alluding to Mayhow's work.   It does not appear,
however,  that  Hooke had  evinced, by  direct experiments,
the presence of this air  in nitre ;  but that  he had mferred
it from  the  fact that air was  necessary for the burning of
all  inflammables ;  and that nitre enabled any inflammable to
burn  without  air,  and must therefore have  supplied  it in
the very  act of combustion.   We  must  acknowledge the
justness of  his inference, and  admit him as the real original
author of this  theory of combustion.  Mayhow is not more
explicit;  and certainly had never made any chemical experi-
ments  with  the air obtained from  nitre, which  he seems to
call the nitro-acreal spirit.   Had he tried it as the supporter
of  flame, the phenomena are so remarkable, that they would
have  been minutely described.   Even in his explanation
of  combustion by this spirit, he is extremely obscure : and
it is impossible to  decide whether his explanation  is  upon
chemical principles, or by motion  and mechanism.   Dr.
liookfc, on the contrary, is most simple and perspicuous in
his theory,  which  is purely chemical.    And when he ex-
plains the phenomena of flame, he does it  with as much pre-
cision and philosophical propriety as can be conceived. In-
deed, there is no where to be met with  so  accurate a de-
scription and  explanation of the flame  of oil or spirits, as
is to be seen in Hooke's Lampas, page 5, &c.  His numerous
writings on  many parts of natural philosophy  give him many
occasions of applying this theory;  and it  is therefore  most
strange that  it  should have been so  entirely forgotten. As he
promised to bring his theory into better form, and undoubt-
edly  made many notes on  the subject, I am persuaded that
<mme  of them will vet  be found in that chest of papers 
424       NOTES  AND OBSERVATIONS.

which  was delivered by his friend Mr. Waller to the Royal
Society.

                    [Note 32. p. 90.]

   A groove eight lines wide, four deep, and 386 feet  long,
was filled with good powder.    It employed thirty-three se-
conds in burning from one end to the other.   It was  filled
again,  and then  covered with deal boards,  simply laid on
it.   Ten feet of the  covering weighed one  pound.   1 he
train now burnt from end to end in seven and a half seconds ;
so much was it expedited by this  slight pressure,  which
obliged»the  flame to blow through  among the 'grains.   It
made no sensible noise.  I was within a quarter of a mile of
a  magazine of 350 barrels of gu..powder, in a l^rge  tent.
It caught fire and blew 14     The  explosion did not last
above  a second,  and was prodigiously loud.   The  barrels
were  the  only confinement  in this  case,  yet sufficient for
making the explosion almost instantaneous.
   The composition  just  now described by Dr. Black does
not fire till all is fluid,....therefore  all in the  same state,....
and therefore all fires at once.    The first  expansion of this
composition appears to be immensely -greater than  that of
gunpowder.   Half an ounce  fired  on an  ordinary  parlour
fire-shovel  will generally beat the place where it lay into a
hollow.  Half an ounce of gunpowder fired on  a card, or
even a bit of stiff  paper, will not tear it.   Yet pulv.is  fulmi-
nans, when  inclosed  in  the chamber of a* musket, and
exploded with a ball lying above it will impel it with very
little force. This shews that the expansive force of the elastic
matter produced in the explosion diminishes much more by
an increase of bulk than in the case  of gunpowder.

                    [Note 33. p. 122.]

   In a bundle, marked " old notes,  excerpts, &c."   I find
some experiments on this salt, which deserve some notice.
Dr.  Black seems  to aim  at  the best process for preparing it
for medical purposes by sublimation. He was aiming at the
same thing with  the  salt called acetous  ammoniac; and is 
NOTES  AND OBSERVATIONS.       425
surprised that he can prepare the latter very easily, but that
the nitrous ammoniac could not be condensed,  although  its
ingredients are  not nearly so volatile as those of the other.
   In one experiment with a dry nitrous ammoniac, which he
had prepared himself by mixing colourless nitrous acid with
the  purest volatile alkali, the vapours were  incoercible  in
part:  and what did condense was almost pure water, greatly
exceeding in quantity what could be supposed necessary for
the crystals of  the salt.    He was obliged to  give a passage
to the incondensible vapours.  He tried whether they  were
inflammable, by presenting  a bit of lighted paper  to the
hole in the luting.   It did  not  take fire,  but it made the
paper burn with prodigious  violence.   He  thought,  from
this circumstance,  that it was the nitrous acid.  But, put-
ting alkalin^B^ into the receiver,  he did not  find  it  con-
dense more^^lily,  nor produce a nitre.   Putting lime-
water into the receiver, he found no precipitation, when he
used  the p,ure salt prepared by himself: but employed  some
gotten in the. the  shop of Mr.  Hill, (which I mention, be-
cause it shews-the date of the experiment to  be previous to
1766) he had precipitate.  He attributes this to impure alkali,
containing inflammable matter.   He says, that  although the
incoercible fumes  filled  the laboratory,  the  effect on his
breathing and sensations was very far from being unpleasant.
He suspects that the  acid suffers some decomposition;, and
again  wonders at the quantity of water obtained.   With
some particular  view, he had mixed with the salt thrice  its
weight of" finely pounded glass.   In three succeeding trials,
the mixture detonated,  and burst the vessels, although the
heat was not much above  that of  boiling water.
   These experiments tally, in many  particulars, with those
in the judicious analysis of  this salt by Mr. Davy of the
Royal Institution.    Dr Black has had some  experience  of
the wonderful effects  of the gaseous oxyd of azote, or nitrous
oxyd, which have given so much amusement of late, and from
which  such mighty  medical consequences are expected by
some  physicians.   This subject will come before us some
time hence.
    vor. it.                  3 H 
426       NOTES  AND OBSERVATIONS.

                     [Note 34. p. 148.]

  Dr.  Black»highly  approved of a systematic nomenclature;
and thought the French one extremely ingenious ; and that its
many barbarisms and philosophical incongruities should be over-
looked, as  something unavoidable, or that they should be cor-
rected.   Accordingly he occupied himself a good deal on  this
subject; but his notes are so  imperfect,  and, I may' say, unde*
tided, that I could not make  any use of them.  He disapproved,
however, exceedingly of the  entire  substitution of this for all
other denominations  of  chemical substances ; and affirmed  that
proper names, where they can be had, should on all occasions
be preferred.   The  emplo< ment of  the  scientific names only
gives an appearance of knowledge without the realty of science.
It is merely an abbreviation of language.  aJ^B is the same
necessity of learning that the muriat of soda H^mmon seasalt
as that sea salt is the muriat of soda.  Without the Ja$t, indeed,
you are not a chemist;  but without the first, your chemistry is
of no use.   He was, therefore, for retaining all thft old names
that  were,   strictly speaking,  proper names ;  such  are',  kali,
muria, soda, natrum, nitrum.  He thought air as good a name
as gas, and combustion  as chemical a phenomenon as oxygena-
tion.
  A determination to be the founder of a systefh and a sect of
philosophers seems to have seduced Mr. Lavafshtr,  and made
him acquiesce in measures which may be called violent and un.*
becoming.   As for the imitatores, servum pecu4>, they hesitated
at no incongruity with common language  and  sentiment;  and
rather had  a pride in it, as a mark of their authority over the
opinions of other men.  What can be more absurd than to give*1
the name oxygenation  to  the formation of tasteless  water or*
charcoal, or  of combustion to phenomena where neither heat
nor light are observed?  No knowledge, whatever is acquired by
the exclusive use of this nomenclature :  and it  hasrintroducjd
into chemistry the same licentious dialectic that the Aristotelian
metaphysics introduced into the schools of philosophy, and will
produce, the same bigotry and the same  ignorance.   It gives
the appearance of research to mere  technical  language :  and
many  pages of modern systems of chemistry 44 are but the
naming of their tools."....Hudibras. 
NOTES AND OBSERVATIONS.       427
        Not only no  acquisition is made of knowledge, but if the
     theory be erroneous  in any circumstance, (and what philoso-
     pher will say that this is impossible ?) the error must inseparably
     adhere to every name,  and every phrase, and every opinion.
        But all this is only the licence of literary ambition and vanity.
    . The same principles, and the  very same men, formed this no-
     menclature and  the  new kalendar and  metrical system of the
     French.   But these  inconveniences are  not essential to a good
     systematic nomenclature.   Had all the proper  names been re-
     tained, and had a becoming  deference  been paid  to ordinary
    •language  and  sentiment,  the  nomenclature would  have been
     much more intelligible,....would be free from paradox,....and
     Mr. Lavoisier's well deserved honours would have  been. fully
     secured to hirjfc  Newton still stands at the head  of philoso-
     phers,. althoug^hey still speak of  the  sun's path round  the
     heavens,  and retain the old astronomical  languag .   But New-
     ton had n6 such ambition ; nor did the Royal  Society furnish
     such  a legion of honour as Mr. Lavoisier found  among  his
     countrymen.

                         [Note 35. p. 188.]

       I must mention here that it was discovered by Mr.  Milner in
     1787, that if this alkali be made to pass through a red hot tube,
    along with vital air, (oxygenous gas) we obtain nitrous  acid.
    The experiment was this: He  put a quantity  of a  substance
    called manganesfc (much employed in glazing the coarser black
    earthen wares) into a gun barrel, and making this red hot,  he
    sent this alkaline gas through it.   It is well known that the man.
. + ganese yields only oxygen gas by this treatment.   I am inform.
|p  «d that the French, availing themselves of this discovery, pro-
Wf cured saltpetre for their military operations, by passing common
    air (which contains oxygenous gas) through vapours which con.,
    tain this alkaline  gas.  It  appears, however, in this, and  in
;   many other instances of such mixtures of gases,  that the com-
    bination cannot be effected,  unless one or other of the gases be
    mixed in the very act of its forrrfation.  The gases themselves,
    in many instances, will not mix, even when red hot, when com-
    pletely formed.  This alkali also combines with sulphur, form-
    intr a iras of a most abominable smell.
I 
428 '       NOTES AND OBSERVATIONS.

                     [Note 36. p. 208.]

   The word was first employed by Van Helmont,  and particu-
larly to express the vapour which escaped from liquors in the
vinous fermentation.   He  ascribes to this gas the effects of the
Grotto del Cane, in Italy,  so named from the number of dogs
killed  in that cavern by breathing it.   With a skill and justness
that is surprising, he explains many changes which happen in
animal substances  by the  extrication of  gases.   He  says that
those gases, into which many bodies are completely resolved, do
not exist in them in an elastic, but  in a liquid,  or even a con-
crete and solid form.   He gives them  the general name  gas;
but distinguishes several kinds, such as gas silvestre, (an epi-
thet borrowed from Paracelsus,) flammeum, ventosum, pingue,
&c.  By gas, then, we are to  understand a r^BectJy invisible
elastic fluid, that can be contained in a vessel^vhic.h; expands
by heat and contracts by cold, but is not condensed by cold into
a liquid or solid, as the vapours of water or of camphor.  It
is proper to add the first character, to  distinguish gases from
fire, light, and the supposed elastic atmosphere of magnetic and
electric  bodies.  Some chemists would  except respirable-air
from the gases,  and consider them as all distinct from air.  But
it is not improper to employ gas as the object of chemical exami-
nation, and to call  them airs, when we examine them mechani-
 cally,                                                   i* ■
                                               «.
                      [Note  37. p.  250.]

   It is indeed a very improper denomination, on the principle
 by which  it is pretended that the French  nomenclature is regu-
 lated.  It neither follows  the rule adopted for the simgle  sub-  k  .
 stances, nor that for those of a second order.  It is not dis. ''vt
 tinctive.   For almost every aereal fluid, except the tftygenous
 gas, is azotic,  i. e. extinguishes the life of the warm blooded
 animals.   Moreover,  knowing the wonderful augmentation
 which the respiration of the nitrous oxyd makesin the vivacity
 and energv of animals, ft seems extremely incongruous to call
 its  chief  ingredient azote.  Lavoisier intended another  name
 for it.  Some experiments of  Berthollet had made him hope to 
NOTES  AND OBSERVATIONS.        429
establish it as the alkaline principle, as vital air was assumed by
him as the acid principle,  and thus to embrace, in one  propo-
sition, the whole round  of chemistry.  But Mr.  Cavendish's
experiments put an end to this, seeing that itmust be adopted as
the distinctive ingredient of the nitrous acid.   Yet he would not
call it nitrogen, because  it  was discovered to be also one of the
two ingredients of volatile alkali.   He  gave this  reason, and
             this little history, to Mr. De Luc, in conversa-
                De Luc could not extract  more  out of  him,
              [uirers are more pertinacious.   Perhaps Lavoi-
           ^>f making it the alkaline  principle were not yet ex-

                      [Note 38. p. 252.]
            »•
   It is not infcrobable that electricity has something to do  here.
The light ol^he electrical spark, visible in a great extent of
air between the discharging balls,  is,  I think, the indication of
some chemical action going on in the whole of that extent; in-
deed, on the principles of  the new chemistry,  it cannot be any
thing else.  There is no such thing as the transference of some-
thing luminous from the one body to the other.  There  is a de-
composition of oxygenous  gas taking place wherever we see the
light.   It seems  to be simultaneous  : but it is successive and
amazingly rapid. There is a smell accompanying all electrical
experiments.   This  smell  is also a  strong indication of  some
chemicaljStction.   But this is  very distinct, or peculiar,  and has
no resemblance to the smell in any process with the nitrous acid.
I suspect, therefore,  that electricity acts otherwise than merely
by exciting a  great  heat.   Great heat will produce  a combi-
nation  of Oxygenous  and   azotic gases,  if either of them be
taken in its nascent state, /. e. in the  very act of its extrication;
but not when they are completely formed.  This may arise from
the constituent parts of the completely formed gas.   When ni.
trous acid is decomposed by detonation, much light and heat are
disengaged.  It may happen, that, in the formation  of  these gas-
es, the mutual  attraction between them may  be very great,
while both or either of them are unprovided  with the heat or
light required for their gaseous form, but may be much weaker
when they are furnished with it. This will even be analogous ta 
430       NOTES AND  OBSERVATIONS.
the greatest part of  chemical combinations.  The effect of
electricity may be  to discharge part of this heat and light
from the air in which it is seen.   But, on the whole, there
are several phenomena in the relations  of azotic gas which
are not easily reconciled with our present notions, and even
affect considerably the whole  system of  Lavoisier.*
   I may here mention another peculiarity  of this gas.   It
communicates the  green  fsecula  to plants  grja||^in  the
dark, which would  otherwise be white.   This    Kfrom
a series  of experiments "by  Sennebier.

                     [Note 39. p. 263.]

   The order of composition expressed by this  termination
et, (etum,  in Latin), has  not been  yet explained by Dr.
Black.   It  means,  in the French nomenclatur^Phe combina-
tion of a radical, such as sulphur, carbon, phosphorus,  &c.
with any substance  except oxygen, without an intermedium.
Thus, we have the sulphuret of potash, the carburet of iron,
the hydrogenous phosphoret, &c.   But when the same radi-
cal substance is  combined  with  potash  by the intervention
of oxygen, the compound is then  a sulphat of potash, or a
sulphite  of  the same, according as  the proportion of  oxygen
is great  or small.
   The sulphat of potash  is  not, however,  considered as a
compound  of these   ingredients,  but  as  a  compound.,  of
potash   united  with  sulphuric acid  which is pcjrasionally
considered as a substance sili generis, having affinities  and
properties truly distinctive,  in which the properties of  its
ingredients, sulphur  and   oxygen,  are in  some -measure
dormant.   This was  undoubtedly  the way in  which  Mr.
Lavoisier considered these things.    I  apprehend that this
«s the only accurate idea that can be hWd of  a  true chemical
combination.; and that there  is no such  thing as a compound
of three iigredients,  in  which the  primary properties of

 * M;mv chemists of eminence imagine thaft its radical part is the same with
that of oxygenous gas ;  and that^jjhe difference in its chemical qualities pro-
ceeds from a difference in the proportion of caloric combined \vi# it.  Others
imagine that it has not calor'rt combined with it, but the matjcr of light.  But
thes" are all conjectures.    -     . 
NOTES  AND OBSERVATIONS.        431
 each are immediately efficient.   Such compounds, however,
 are frequently spoken of by the new chemists, especially
 in their attempts to point out the procedure ofonature in the
 fermentations.....vinous, acetous,  and putrefactive.  But I
 know no substance in which the ingredients exert the  same
 combining energies as if they were all separate.   They take
 this method, because it gives them a vastly greater latitude
 in  their explanations.   But  once this liberty  is taken,  you
 will scaAely see two chemists explain the phenomenon in the
 same yflafy   Had the political ambition of those whom La-
 voisierfresociated with himself in  his labours  and honour,
 suffered him to remain at their head, he  would have saved
 his followers from many embarrassments in which they have
 involved themselves hy this manner of proceeding.

            %     [Note 40. p. 350.]

   I cannot omit mentioning in  this place, that my colleague,
 Dr.  Daniel Rutherford, read,  in the  year 1775, to the  Phi-
 losophical Society of Edinburg,  a dissertation on nitre and
 nitrous acid, in which this doctrine is more than hinted at
 or surmised.    By a series of  judiciously  contrived experi-
 ments, he obtained a great quantity of vital air from nitric
 acid ;  about one-third of that  quantity from  the sulphuric
 acid, as contained  in alum ;  and a small  quantity (and this
 very variable and uncertain) from  the muriatic  acid.    The
 manner iA which it cafne off from the compounds, in various
 circumstances, led  him to  think that  the different quantities
 obtained did not arise from thedifferentproportions in whichit
 was contained in those acids, but merely in the different forces
 with which it was retained. He  therefore concluded that vital
 air was contained in all acids; and thought it likely that it was
 a necessary ingredient of an acid ; and, seeing that it was the
 only substance found, as yet, in them all,  he thought it not
 unlikely that it w#s by this that  they were acid: and he points
„ out a  course of experiments which  seems adapted to the
 decision of this question.  I was appointed to make a report
 on this dissertation ; and I recoiled stating as an objection to
 Dr. RutheVford's opinion,'44 that it would lay him under the
 44  necessity of supposing that vitriolic acid was a compound
 of sulphur and vital air J " which I could not but  think  an 
432        NOTES AND  OBSERVATIONS.
absurdity.   So near were we at that time to the knowledge
of the nature of the acids 1

                    [Note 41. p. 379.]

   Dr. Black's notes, from which he was accustomed to lec-
ture on this subject, for the last four years of his teaching,
are extremely imperfect;  and consist of nothing more than
references  to  experiments by Priestley, Austin, ; Milner,
Berthollet, and an intimation that the French che'nAts prac-
tised a certain process to procure saltpetre for thearony, and
here and there a slight thread of reasoning from the experi-
ments.   I think that I have found out all the experiments to
which he refers,  and I have put them down in  the order in
which they stand in the notes :  but I confess that unless  I
greatly exceed any  authority  derived from the^aaanuscript, I
cannot give that clearness that will satisfy a cautious mind.
Nor can I  adhere to the rule laid down in the  beginning of
this  chemical  history, namely,  to employ in argument no
substance of which the properties have not been previously
discussed.   I have availed myself of the notes taken by  a
young gentleman who attended the two last  courses of Dr.
Black's lectures, so that T  presume that what I have inserted
in this place does not differ much from what he delivered.

                    [Note 42. p. 381.]     ;' ■''.'•'" ;'*•

   It must  be confessed, that the evidence for tlfis composi-
tion  of  ammonia is in a  great measure hypothetical^ even
when the  composition of  water and  of  nitrous  acid  is
fully acquiesced in : and the  followers of  Lavoisier  differ
much among themselves in the ways in which they  explain
the phenomena which are  adduced as arguments.  Having a
number of substances before us, which exert mutual actions,
it is  plain that we  can match or pair them in  a Variety  of
ways, and may select that double exchange which suits our
purpose.  We do not, in many cases, see clearly why either
azotic or hydrogenous gas is not always produced. •   Mr.
Berthollet  obtained azotic gas, and Dr.  Priestley obtained
hydrogenous gas fr,om ammonia by the electric spark.   Ni- 
NOTES  AND OBSERVATIONS.       433
   trous ammoniac does.not always yield azotic gas and water,
   but  another  gas considerably  different.  We ask what be-
   comes of the hydrogenous gas in  Mr. Berthollet's  experi-
   ment?  It is said that the mercury is  always covered by a
   film of mercury combined with oxygen; and that this is de-
   tached by the hydrogenous gas  and water formed.   It is also
   said that nitrous acid was formed in Dr. Priestley's  experi-
   ment : but there  is no proof of this  offered.  It  is an as-
   sumption on the authority  of  a previous theory;  and this,
   without having  ascertained  the elective attraction which that
   theory necessarily  supposes.   The same gratuitous proce-
   dure is observable in many explanations given by the followers
   of  Mr. Lavoisier, in all cases where they employ the decom-
   position of water.   They  have not ascertained, by  experi-
   ments instituted on purpose, the double exchanges that are
   possible  among*the substances employed.   I can point out
   instances  which cannot both be possible : and yet I see both
   employed.

                      [Note 43. p. 394.]

     Two ounces of slaked lime, and one drachm of  phospho-
   rus  cut  into very small  bits,  are made into a soft, paste,
  which must be hastily put into a small earthen retort, having
  a swan neck  tube luted into its neck.  This  is  introduced
  into the ordinary  pneumatic apparatus, as  it is called, and
  heat is cautiously applied, on account of the explosions which
  frequently happen. The gas soon comes over, and continues
  to distilfor a great while.   This quantity of materials will
  yield three English quarts of gas.
     If a quantity of it.be let up through v/ater into the air, it
,-sgives a bright flash, and a fine ring of white smoke rises from
'  i£pvThis^combination was made by  Dr. Raymond.....Ann.
  de Chym. x.
     Dr. Pearson at London lately made an experiment, which
  shews still more distinctly the nature and hydrogenous origin
 • of this gas.  He combined phosphorus with quicklime, and
  put the  compound into  water.   While it slowly penetrates,
  and partly dissolves it, a small part of the water is gradually
  decompounded ;  the  dissolved  phosphorus  attracting its 
Si
434       NOTES  AND OBSERVATIONS.

oxygen,  and allowing the hydrogen to escape : and this is
collected in the  upper part of the  apparatus in its ordinary
form,  containing (but not always, nor in equal quantitx) a
small portion of phosphorus.   The  gas,  accordingly,  will
not always  kindle  by simple contact with atmospheric air.
It rarely fails to kindle in pure  vital  air: and in all cases it
kindles by any spark.   The inference is plain.              S
   This combination of phosphorus and alkaline substances, a
is in many  respects similar to  the combination of sulphur
with these salts, and like it, produces a hepatic gas, having nj
similar properties.   This experiment of Dr. Pearson illus- d<
trates  all these hepatic phenomena.                         dt
                                                          en
                     [Note 44.  p. 406.]                   d

   The proofs of this not being adduced in Di# Black's manu-
script,  and  its  properties  being remarkable,  and chiefly ,
because the mode of its formation  is  one of the corap'"  ,
Cated  applications of the new  theories, it seems  necessa ^
to mention some of  the more direct and simple arguments
   Dr.  Higgins, by passing the steam of water over melt
ing  sulphur,  produced sulphurous  acid  and  hydrogenous

gaS*      .             .                  „              rft
   Mr. Gingembre,  bringing  the focus of the  sun's  ray*
through a  large lense on a piece of sulphur inclosed ^^
mercury in  inflammable air, produced this gas an perfection "X
   Dr.  Priestley,  by passing a stream of inflammable a
through strong vitriolic acid boiling  hot, produced this he .
patic gas.                                           ..   ^
   Dry hepar sulphuris,  made  with  caustic alkali or lime,r
when treated in a retort with great heat, does not afford this
gas, but sulphur :  but if  it be moistened, or have  bee^  pr'
pared  in the humid way,  it yields hepatic'gas in grea^b*^*
dance.  Dr. Austin precipitated sulphur from it byfthe'elet  -*
spark.   The remainder was inflammable air, of jthe ligl§j|
kind,                                                  ;t0
                    [Note 45. p. 407.]*                 v^

   This observation  of Dr.  Black's  is very just: and, the n
language of the French chemists in  explaining these  phe- :-
I 
            NOTES AND OBSERVATIONS.       435

  them8ubi[cta PFl°f ^^ ^^ ^"^ W'Uh°Ut distinct notion* <>f
  " Phure,,, ^  F°Urcr°y> for  sample, says,  «« L'acide sul-
  " rant k^T™*0*' * gaz hydrogene  sulphui ",  en sepa-
  "cetarhll       Parceclue  ^xygene, en partie lib*e dans
  " L'a -H    ^ P°rte facilement sur IVdrogene de ce gaz.
  Supp   rifi5  xhUnqUC  "e  Pr°duit  paS le   meme  effet-"
  acid ha    «       '  SUrely in their theory»  the  sulphurous
  s0u/F,  S n°   0X^ene en Part™ libre"....on the contrarv it has
f  *ou£e en partie libre.   I may say the  same  thing  of the
>   itrou. or fuming acid.   He says in the  same page, that the
  dephlogisticated marine acid (acide  muriatique oxvgenee)
  decomposes this hepatic gas.   Here  I grant the 44 oxygene
  en  partie  libre.''   Surely in as far  as  the  decomposition
   spends on oxygen,  the, operation of the  sulphurous and
  mtrous acids^hould be the reverse of that of  the oxygenated
  muriatic acid.    In truth, this decomposition embarrasses
  those chemists :  and they differ exceedingly in the way  in
  which they conceive it  to be effected.    Fourcroy,  and the
  Uutch  chemists,  of whom  Dr.  Black speaks in the next
 paragraph,  do it  in one way : and in the  Annales de Chymie,
 vol. 14. page 313, we have quite a different  account  of the
, procedure.  Gren, a German chemist of great reputation,  is
, of  opinion,  that the theory is imperfect without another sub-
stance which he calls frematter: and with the  help of this
■fe^solyp all the  phenomena very easily and elegantly.  But
 there is no  end to substitutions founded  on  such fancies as
this.  It is like the aethers and  other invisible fluids,  which
the mechanicians  have introduced, because their explanations
11 '  impulsion cannot go on without them.   Before we can
  oceed with safety in those explanations  which employ the
  ^composition of water, a series of experiments should be
  "*e for ascertaining the elective attractions of the. radicals
       ^ses, with a precision equal to what we have attained
      —em  familiar substances.  Till this be  done, we may
    orm  in ,ous conjectures concerning the  hidden operations
  of narr' m bodies of a complicated nature:  but  we gain
  no con/ent knowledge.   The followers of Lavoisier, grasp*
  ing-nt<fer>r ln,ng> nn(1 no difficulty^of  giving what  may be"
  "callediiarr'!'!0n of tn's internal procedure, taking the com- 
436       NOTES AND OBSERVATIONS.

binations  and decompositions in such order as suits their
purpose :  and this is contrived  so as to terminate in  the
ultimate combination  which we all observe.   This  is not  a
very difficult task, even  when we limit our combinations to
two substances, and produce them  by simple affinities.   If
we take compounds of three ingredients, as in the present
case, and employ double affinities, our means of accomplish-
ing the desired end are increased prodigiously ;  and there is
nothing that  can escape us.  1 he new phraseology is so
significant, that every epithet indicates an operation ; so  that
our explanation has great appearance of a real knowledge of
the facts.   But that  all this is little better than conjecture,
and very  precipitated and unwarranted conclusions, appears
from this,....that two  eminent chemists, explaining the same
ostensible phenomenon, and employing the same agents, give
quite a  different story, merely by taking a different order of
succession in the  steps of  the internal procedure.    They
therefore  employ quite different combinations and decompo-
sitions.   This cannot be, if the  affinities of the substances,
when in the  same situations, be  constant.   Lavoisier  has
rarely, taken much libtrty this way.   But his more zealous
followers set  no bounds to their theories.




             END OF THE  NOTES TO VOL.  II
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