ELECTROTYPE MANIPULATION. 
P A R T II. 
I.-INTRODUCTORY OBSERVATIONS. 
92. Having in Part 1. given the mode of working in cop- 
per, we now pass on to other metals. First in importance 
come gold and silver. The earliest experiments in electro- 
gilding were those by Brugnatelli, who gilded silver medals 
by electricity, in 1805 ; he used a solution of nitro-muriate 
of gold mixed with a solution of ammonia. The next were 
those of De la Rive, 1841, who used a solution of chloride of 
gold. But these processes were interesting rather in a the- 
oretical than in a practical point of view; inasmuch as the 
elective chemical affinity of the elements (combined in these 
solutions with the gold) for the baser metals, which might 
be immersed in the solutions, is such, that a violent inter- 
change of elements takes place, and the gold is set free with- 
out even electric agency; and the solutions are so readily 
decomposed by the smallest adventitious aid, that it is a 
practical impossibility to. obtain a "reguline," deposit, how- 
ever much the voltaic power may be modified. 
The following are illustrations of the deposition of gold 
and silver by the mere elective affinity or ordinary chemical 
action. If an aqueous solution of chloride of gold is agitated 
with ether, the chloride leaves the water to combine with 
the ether, and the resulting compound, being lighter than 
water, floats on the surface.-If pieces of polished steel are 
dipped into this preparation, they acquire a coat of gold by 
ordinary chemical interchange.-If a design is traced with 
solution of chloride of gold upon a silk or linen fabric, and 
the fabric, while the traces are still moist, be exposed to a 
stream of hydrogen gas (which may readily be obtained by 
acting upon iron nails by diluted sulphuric acid.) the metal ELECTROTYPE MAN1PELATION. 
2 
is reduced, and a golden design is the result.-If a plaster 
cast is saturated with a solution of nitrate of silver, and 
placed under a hell-glass, and we admit to it the gas pro- 
duced by heating a few grains of phosphorus with alcohol 
and a small quantity of potash, the silver will be reduced 
upon the surface.-If the plaster-cast is made with sour 
whey instead of water, and is saturated with silver solution, 
the silver is reduced by mere exposure to sunlight, and 
forms, according to Elsren, a good conducting surface, in 
which we can deposit copper or silver according to the usual 
modes. 
The same observations apply to the ordinary salts of sil- 
ver, as, for example, the nitrate, &c. In fact, long before 
the theory of chemical deposits was understood, I made 
some experiments upon the electrolysis of this salt, and suc- 
ceeded in producing an electrotype medal with a silver sur- 
face, being I think instance of electro-plating, when 
the object of the experiment was electro-plating. But I was 
unsuccessful in my attempts to repeat the experiments; 
and simply because, in that instance, I chanced to have in 
action a power nicely balanced with the work to be per- 
formed, but in future instances ray power was not adjusted 
to the work. 
93. The first practical process for working in these noble 
metals is undoubtedly due to the patentees, Messrs. Elking- 
ton. Others have laid claim to having been the first to use 
solutions similar to theirs; but whatever may have been 
done by these others in private, it does not appear that the 
public were in possession of their processes by any authentic 
publication ; and therefore there is no alternative but to 
give the patentees the claim of originality and priority. 
94. The solutions they employ are the argento-cyanide and 
the auro-cyanide of potassium; upon which compounds it 
will be well if we make a few observations here at the out- 
set. They are what the chemists term double salts: as for 
instance, cyanide of potassium is a compound simply of po- 
tassium and cyanogen ; argento-cyanide of potassium is silver 
and cyanogen combined with potassium and cyanogen, or, 
which amounts to the same thing, cyanide of silver united 
with cyanide of potassium. INTRODUCTORY OBSERVATIONS. 
3 
When viewing (§ 13) what happened during the decompo- 
sition of sulphate of copper, we had occasion to describe that 
body as oxide of copper, dissolved in, or combined with sul- 
phuric acid: now, oxide of copper is 1 part copper 4- 1 part 
oxygen, and sulphuric acid is 1 part sulphur 4- 3 parts oxy- 
gen, and a certain quantity of water; so that, altogether, 
the arrangement is somewhat complex. This is not so 
much the case with the bodies now in question. And first, 
in respect to the simple cyanide of potassium, before it is 
united with the gold or silver. It consists simply of one 
equivalent of the metal potassium, and one equivalent of 
cyanogen; and, when it is acted upon by a voltaic current 
in the usual way, it appears to be decomposed by direct ac- 
tion, and cyanogen is liberated at the one pole, and potas- 
sium is determined to the other, but not liberated. It will 
be remembered (§ 13) that, in the solution of sulphate of 
copper, water was decomposed by the direct action, and that 
the copper was liberated by a secondary action, namely by 
the hydrogen of the water returning back into solution in 
the place of the copper. Well; the cyanide of potassium is 
decomposed by direct action, and potassium is presented to 
the negative metal; but a secondary action now occurs : so 
great is the affinity of potassium for oxygen, that it cannot 
exist in a metallic form in presence of that element; as is 
well known from the common experiment of dropping a 
piece of potassium upon water, when it combines so vio- 
lently with the oxygen as to produce heat and light; and 
the resulting products are oxide of potassium, the com- 
mon caustic potash, accompanied with a liberation of hydro- 
gen. So, also, in the present case; the potassium does not 
itself appear, but, in its place we find hydrogen and potash; 
it takes oxygen from the water and forms potash, and sets 
the hydrogen free. It is true, we are in possession of a 
means of preventing its return into solution, and this is by 
employing a mass of mercury to receive it: in which case it 
unites with the mercury and forms the amalgam of potas- 
sium; and neither hydrogen nor potash is manifested; but 
it will remain thus only under favorable circumstances; for, 
if the connections with the battery are broken, so that the 4 
ELECTROTYPE MANIPULATION. 
mercury ceases to be negatively electrified, the potassium im- 
mediately leaves it. and decomposes the water as before. 
Thus much in reference to the simple cyanide of potassium. 
Of the double cyanides, the argento may be taken as an ex- 
ample. It consists of 1 part cyanide of potassium and 1 
part cyanide of silver-the latter cyanide, like the former, 
consisting of 1 part metal -p 1 cyanogen. When a solution 
of this double cyanide is electrolyzed, silver appears at one 
pole, and cyanogen at the other. But, in order to the pro- 
duction of this result, it is absolutely essential that there 
be a considerable surplus quantity of the cyanide of potas- 
sium in solution ; indeed, it is pretty evident that the direct 
action is the decomposition of the surplus cyanide, and that 
the silver is reduced by secondary action ih the following- 
way. When the metal potassium is reduced from its cyanide, 
it returns into solution, and takes the place of the silver in 
the double salt, setting the latter metal free; so that, while 
on the one hand an equivalent of simple cyanide is consumed, 
on the other hand an equivalent is formed, and the equivalent 
previously engaged to form with the silver the double salt, 
is also free ; and thus far there is an increase in the quan- 
tity of simple cyanide of potassium. But, if the positive 
metal is silver, the cyanogen combines with it and forms 
cyanide of silver; for cyanogen is a gas, and like oxygen 
seems to combine with metals in this its nascent state; 
though, unlike oxygen, it is a compound body, consisting 
of 2 equivalents of carbon -p 1 of nitrogen, whence, it is also 
termed bicarburet of nitrogen. Well; cyanide of silver is 
insoluble in water, and hence would form an insulating 
crust on the silver plate were it not for the presence of cyanide 
of potassium in excess in solution; it readily dissolves in 
this, and so keeps up the strength of the solution; and the 
extra element of cyanide of' potassium, mentioned above, is 
thus neutralized. 
Having thus described the general character of the cyanide 
solution, it remains for us to give the processes by which the 
several elements are most favorably brought together. 
95. Cyanide of Potassium.-To obtain this, we set out 
with the ferro-cyanuret of potassium, or yellow prussiate of 
potash of commerce; and as this prussiate is readily access- INTRODUCTORY OBSERVATIONS. 
5 
ible at all chemists', it is better in general to purchase than to 
make it; the mode by which it is obtained will be found in 
any treatise on chemistry. It consists of 1 equivalent of 
cyanide of iron + 2 equivalents of cyanide of potassium. 
It is of a bright yellow color, and is converted into the color- 
less simplecyanuret in the following manner: Take 4 oz. of 
the yellow prussiate, break it in small pieces, and dry it well 
on a plate of iron ; then reduce it in a mortar to exceedingly 
fine powder. Dry and pound in like manner oz. of carbo- 
nate of potash. Incorporate the two ingredients thoroughly. 
Place a Hessian crucible in the fire ; and when it attains a red 
heat, throw into it the prepared mixture, and closely cover 
the crucible. Keep up the heat, and the contents of the 
crucible will sodn fuse, and the fluid mass will become red- 
hot. After this, immerse in it, from time to time, a hot glass 
rod; the mass that adheres to the rod in the early stages of 
the process is brown on cooling ; as the heat is continued, 
it appears yellowish, and finally colorless and transparent. 
The operation is then complete; the crucible must be remo- 
ved ; and after its contents have been allowed to settle, the 
fused mass may be poured oft': the greater portion of which 
consists of the simple cyanuret of potassium* The impuri- 
ties contained in this product are not detrimental to its use, 
in a general way, for the purposes in view; however, in cases 
where it is required pure, it must be boiled in strong alcohol; 
and when the alcohol cools, the pure cyanide will be deposited 
in the form of small white crystals. This salt is very deli- 
quescent, and must therefore be retained in close bottles; it 
will readily be recognized by its powerful odor-similar to 
that produced by peach blossoms. The mere mention of 
prussic acid almost entering into its composition will be 
sufficient to induce my readers to exercise common caution 
in handling it. A solvent solution is prepared by adding- 
two ounces of this salt to a pint of rain or distilled water; 
when the salt is well dissolved, the liquid is ready for use. 
96. Silver Solution.-Silver may be presented to the above 
solution in various forms ; as the oxide, the chloride, the 
corbonate, the nitrate, &c.; solution will in either case occur ; 
♦This method was first described by Messrs. Rodgers, in the Philosc,pineal Magazine for 
Feb. 1834; and since by Prof. Liebig. 6 
ELECTROTYPE MANIPULATION. 
and the double cyanide of silver and potassium will be pro- 
duced. But since the silver, as we hinted before, must become 
a cyanide of silver before it can thus unite with the cyanide 
of potassium, it is obvious that one portion of the solution 
must give up its cyanogen to the silver, and take to itself 
the bodies previously in combination with that metal. So 
that, from the oxide of silver, potash would occur in the 
solution; from chloride, chloride of potassa; from corbonate, 
carbonate of potassa; and from nitrate, saltpetre. Of these 
the least likely to interfere with this general action is the 
potash; and hence oxide of silver has been frequently used. 
It is thus prepared :- 
97. Oxide of Silver.-Place pieces of silver in a glass 
vessel, and pour on them about equal parts of water and 
strong nitric acid; the metal will soon dissolve, giving off 
fumes of nitric oxide. Should the solution have a green 
hue, which is invariably the case unless the metal has been 
obtained fine from the refiners, it indicates the presence of 
copper; in which case immerse some pieces of copper in the 
solution, and the nitric acid, by elective affinity, will com- 
bine with the copper ; and a precipitate of pure silver in the 
form of a grayish powder, will take place. Throw away 
the liquid, and wash the silver precipitate several times in 
sulphuric acid and water, and afterwards in water alone. 
Then redissolve it, as before, in nitric acid and water: and 
a of pure nitrate of silver will be obtained. Place 
this in an evaporating dish, or a saucer, and apply the heat 
of a spirit-lamp, or place the saucer by the fireside, till some 
portion of the liquid is driven off in vapor. Allow the res- 
idue to cool, and it will shoot out into long, colorless, trans- 
parent crystals which are nitrate of silver. They must be 
handled with care, as they possess the property of staining 
animal and vegetable substances with an almost indelible 
black; fused nitrate of silver being the lunar caustic of sur- 
gery, and the main ingredient also of marking ink.-Next 
prepare some lime-ivater, by stirring lime into water, and 
filtering the solution. As lime is very sparingly soluble in 
water, requiring at 60° Fahrenheit 750 times its weight, it 
is necessary to make an abundant supply. Place the lime- SOLUTIONS. 
7 
water in a glass or other vessel, and drop in it a few crystals 
of nitrate of silver : the colorless solution will instantly 
assume an unsightly brown hue ; and, after remaining qui- 
escent for a time, the oxide of silver will subside in the form 
of a dark brown precipitate. The liquid is then poured off, 
and the precipitate is washed with water. Before throwing 
away the liquid, fresh lime-water should be added to it; and 
if the dark hue recurs, the precipitate must be allowed to 
subside again: if no change takes place, it may be inferred 
that the silver is all extracted. The oxide of silver should 
not be dried, but be kept in bottles with water. A quarter 
of an ounce of oxide of silver, added to a pint of the solvent 
solution, forms a very useful plating solution. 
98. Cyanide of Silver.-But, as the above solution is im- 
pure, in that it contains as much potash as is equivalent to the 
oxide of silver added, it may not be applicable to accurate 
experiments ; and as the potash is produced, in the formation 
of cyanide of silver, at the expense of a certain portion of 
the cyanide of potassium, it is a wise plan, for it is no more 
costly, to form the cyanide of silver in a separate vessel, and 
to wash away the impurities before adding it to the solvent. 
Take then a neutral solution of nitrate of silver; add care- 
fully a solution of cyanide of potassium, when a white pre- 
cipitate of cyanide of silver will fall; continue adding until 
precipitation ceases. The liquid, which is a solution of 
nitrate of potash or saltpetre, is to be poured off, and the 
precipitate well washed. It will be pure cyanide of silver, 
if the materials employed were pure; and it is now fit to be 
added to the solvent liquid, to form a plating solution free 
from impurities. 
99. Preparation of the Gold Solution.-Warm a pint of 
pure rain or distilled water, and dissolve in it two ounces 
of cyanide of potassium as before; then add a quarter of an 
ounce of oxide of gold. The solution will at first be yel- 
lowish, but will soon subside to colorless transparency. 
Those not versed in chemical manipulation will be wiser to 
purchase than to prepare oxide of gold; but, for general 
information, I give the process. Dissolve pure gold in two 
measures of muriatic with one of nitric acid; evaporate to 8 
ELECTROTYPE MANIPULATION. 
dryness ; dissolve the residuum in twelve times its weight of 
water; add to this a solution of pure carbonate of potash, 
dissolved in twice its weight of water ; apply a moderate 
heat, about 170°, and a reddish-yellow precipitate occurs. 
This is the hydrated peroxide of gold. Wash it well; and, 
to render it anhydrous, boil it in water. It then assumes a 
brownish-black color, which is the oxide required. 
100. I by no means give these as standard proportions of 
the several ingredients required. They are the proportions 
which I employed with success in gilding and plating the 
series of Metals (submitted to the Electrical Society at their 
meeting, Sept. 21, 1841,) by the battery process to be here- 
after described. When the same object is effected by the em- 
ployment of a single cell, it will be requisite to alter the 
degree of saturation according to circumstances ; to which, 
however, I shall have further to allude in the sequel. 
101. Single Cell for Plating and Gilding.-The necessity 
of economizing solutions of such value as these has led to 
certain modifications in the apparatus contributing to that 
end. The porous cell (§ 17,) which in other arrangements 
contains the zinc and acid, and is surrounded by the copper 
or other negative element, in the present process contains 
the cyanide solution, and the negative element or object to 
receive the deposit, and is surrounded by the zinc, &c. 
102. This arrangement will be readily 
understood by a glance at the annexed wood 
cut, which represents a porcelain cell con- 
taining a cylinder of zinc, and an inner po- 
rous tube filled with the solution of silver 
or gold. Connection is made between the 
zinc and medal or mould by a binding 
screw; or by a mere contact, as in the fig- 
ure. 
103. 1 must again dwell upon the phil- 
osophy of the action of this arrangement, 
and return to first principles, in order to 
impress them more firmly on the minds of those who read 
these pages with the intent to repeat the experiments. Em- 
it is a matter of some importance, in employing the costly 
Fig. 11. SOLUTIONS ANI» APPARATUS. 
9 
salts of' the noble metals, to have the principles of the 
experiment traced out as distinctly as possible. 
104. In the arrangement just described, the nature of 
the deposit will depend upon the principles elsewhere (§ 78) 
set forth ; and d fortiori, from the facility with which the 
salts of silver or gold are decomposed, there will be a much 
greater chance of releasing hydrogen, and spoiling the ex- 
periment; to prevent which, therefore, ample provision must 
be made. For instance, if the silver solution is weak in pro- 
portion to the energy of action between the zinc and acid 
water, the electricity developed will be more than sufficient to 
release pure metal, and hydrogen will be evolved, the result 
being a deposition of oxide. Or, if the balance between 
the strength of the solutions be duly adjusted, the relation 
between the size of the zinc and of the medal or mould may 
be such as to determine the same result. It is therefore 
requisite that the water which excites the zinc should con- 
tain very little acid-a few drops, more or less in proportion 
as the cyanide solution contains more or less of the oxide; 
and that the strength of the latter should be maintained by 
a fresh supply of oxide from time to time. 
105. Another, and in some cases more convenient form for 
the single cell apparatus is given in the annexed wood cut;'in 
Kig. 12. 
principle it differs nothing from the former ; the porous cell 
to contain the cyanide solution being Hat, affords the means 
of immersing a larger medal, without an extravagent suppl y 10 
ELECTROTYPE MANIPULATION. 
of liquid. The zinc which envelops the porous cell is also 
flat. The connections are made as before. 
106 Plating by means of a single Cell.-Having charged 
cither of these arrangements with the weak acid water and 
the solution of silver, let it remain for a few minutes, in 
order that the porous cell may be moistened through, and 
that action may commence as soon as the circuit is com- 
pleted. 
Then attach a thin/', pliable wire to the medal or mould, 
and place its other end in contact with the wire attached to 
the zinc: complete the circuit by immersing the metal in 
the silver solution, and a deposition will instantly take place. 
It will present a dead whitish appearance. At the meeting 
of the British Association in Birmingham, in 1849, Mr. 
Elkington stated, "that a few drops of the sulphuret of 
carbon, added to the cyanide of silver in the decomposing 
cell, had the property of precipitating the silver perfectly 
bright, instead of being granulated so dead as it is when 
thrown down from the solutions ordinarily employed." 
107. Should the silver deposit present a whitish surface, 
streaked with perpendicular black lines, it may be regarded 
as an indication that the action is attended with a develop- 
ment of hydrogen : this must be prevented by some of the 
means so often mentioned (§ 78, &c.) By careful attention 
at the commencement of the process the right degree of 
action is readily obtained: and if the process is continued 
(with occasional watching) for about half an hour, the 
medal will be beautifully coated with dead silver. In that 
condition it may remain, after being washed, and dried in 
blotting paper. Or, if a burnish is desired, the leather and 
plate brush must be used; or it may be thrown down bright 
as above (§ 106.) 
Mr. Bain has patented an instrument which he styles a 
"Voltaic Governor." The plates of the voltaic arrangement 
are immersed to a depth sufficient to produce the electricity 
required. They are suspended in the liquid as weights to a 
clock-work arrangement. When the action diminishes, a 
keeper from an electro-magnet, through which the current 
* This principle, so often alluded to, of retarding or restraining the energy of the action, 
is regarded in the employment of iiiin wire ; it is a very valuable adjunct to the other means 
78) of obtaining the same end ; and may often be adopted with advantage. SOLUTIONS AND APPARATUS. 
11 
passes, is moved, and the plates are said to sink until enough 
of electricity is generated to cause the electro-magnet again 
to attract the keeper.* 
If, instead of plating medals, the object is to deposit silver 
in a mould, as mentioned elsewhere, the same preparations 
are to be made; but the mould should be allowed to remain 
lor some minutes (more or less according to the thickness 
required) subject to the action of the current. It may then 
be removed, after being washed with water, and afterwards 
with water containing a few drops of nitric acid, may be 
placed with proper connections in a copper solution (§ 57,) to 
remain there till it is sufficiently backed up with this metal. 
108. Gilding hj means of a single Cell.-The operation of 
gilding is conducted much in the same manner as that of 
plating-gilding, however, requiring a little longer time, 
and occasionally hot solutions. 
109. The operations of gilding and plating seem at first 
to have been very generally effected by means of the single 
cell, in a manner more or less in accordance with the direc- 
tions I have just given, as the nature of the case permitted. 
In fact, plating by this process had been adopted on a scale 
of some magnitude in the great manufacturing town of 
England: the strength of the solution being maintained 
by fresh supplies of the oxide of either gold or silver. And 
if attention be paid to the instructions given, there is little 
fear of failing. 
110. Before describing a method which appears far supe- 
rior to this, I would direct attention to the source whence 
the silver and gold in the single cell process are obtained, 
viz. from the oxides, for instance. For every ounce of these 
metals deposited, a quantity of the oxide must be furnished 
which shall contain in it an ounce of pure metal; and 
hence for every ounce of metal, much more than an ounce of 
oxide is consumed. The time and trouble required to effect 
the combination between these metals and oxygen are bv 
no means inconsiderable; and hence the expense of first 
producing the oxide of gold or silver, and then releasing 
either from the after-combination with cyanogen, far exceeds 
T7</e Meeh. Mag. 5th Aug. 1S43. 12 
ELECTROTYPE MANIPULATION. 
the actual cost of the metal employed: how far depends 
upon circumstances. The object, however, may be accom- 
plished with far more certainty, and at considerably less 
expense by means of an additional cell (§ 56,) and a plate or 
wire, &c. of gold or silver, to keep up the strength of the 
solution, as in the case of sulphate of copper. This method 
is now adopted generally by several patentees; for experi- 
ments with solutions of silver and gold in union with cya- 
nogen, have shown that cyanogen nascent at the positive plate 
in a decomposition cell will combine with silver and also with 
gold. This furnishes a means of gilding and plating, by 
the use of a generating cell to furnish the electricity, and 
a decomposition cell to contain the cyanide solution; the 
nature of the changes produced has already (§ 95) been 
described. 
111. Battery Process for Plating and Gilding.-The gen- 
erating cell for acting upon solutions of silver need not be 
large. A pint Daniell, similar to that in the wood-cut, or 
a series of two, is sufficient for larger medals than can be 
placed in the decomposition cell attached. The latter is of 
porcelain or glass. Of course, the size varies according to 
the extent of the experiment. The zinc may be used una- 
malgaraated, and excited with salt and water; the copper 
cell of the Daniell's battery contains, as usual, a solution of 
the sulphate (§ 57.) Gilding may be better accomplished 
by using three cells of Daniell's battery. 
112. Voltaic Condenser.-Prof. De la Rive has introduced 
an instrument, which he has named the Voltaic Condenser* 
and which may probably be of some service in electro-gild- 
ing and plating. Its property is to give to one cell of a bat- 
tery the intensity of two or three, being the power required 
for these processes; and it does this at the expense of only 
one equivalent of zinc. It is well known to electricians that 
at the moment contact is made with the battery, so as to 
send a voltaic current along a wire in one direction, a secon- 
dary current, vAnch endures but for an instant, is induced 
in the wire in the reverse direction ; and when contact is 
broken, so that the original current ceases, the secondary 
*Vide JrcA <U- IKlect. No. 8, p. 373, and Klect. Man. p. 38. SOLUTIONS AND APPARATUS. 
13 
current is induced to move in the direction contrary to its 
original motion: and therefore in the some direction as that 
Fig. 13- 
pursued by the primary current, when contact was first 
made. The intensity of this current greatly depends on 
the quantity, the character, and the form of the wire em- 
ployed ; and if the wire is coated with silk and wound 
round a bobbin, the intensity is greatly increased. M. De 
la Rive uses 100 convolutions of three stout copper wires, 
and places within the coil a bar of soft iron, the use of 
which will soon become evident. The object of the arrange- 
ment is to convey the battery current, and with it the secon- 
dary current through the solution to be decomposed. 
113. For example, we will select the gold solution to 
illustrate the use of the condenser. Metallic connections are 
applied between the ends of the coil and the two termina- 
tions of a Daniell's or Sinee's battery. The connections are 
continued to a vessel containing the gold solution, the ar- 
rangement being somewhat like the figure co, where the 
generating cell is to the right, the coil in the centre, and 
the decomposition cell to the left. The current, on leaving 
the battery, has thus the choice of two paths, the one being 
through the coil, the other through the solution; but from 
the great comparative resistance of liquids, compared with 
metals, far the larger portion would pass through the coil. 14 
ELECTROTYPE MANIPULATION. 
while a comparatively small share would traverse the solu- 
tion of gold. In passing through the coil, however, it con- 
verts the soft iron core into a magnet; this magnet instantly 
attracts a piece of iron, which is so arranged that, on being 
raised, it removes a wire and thus breaks off communication 
between the coil and the generating cell, except by means 
of the cell containing the solution. The current, therefore, 
now passes through the gold solution. But when the coil 
ceased to be alone in the circuit, a secondary current was in- 
duced in the same direction as the original battery current: 
this, therefore, joins with the said generating current, and 
both pass together through the gold solution; by which 
means the actual power of the battery is very greatly exalted. 
Now, the iron core looses most of its magnetism, as soon as 
the liquid is included in the circuit; and hence the piece of 
iron, the raising of which broke contact, falls again, and 
the coil is again included, when the same phenomena recur : 
and thus, by a continual succession of breaking and making 
contact, the current of a moment, namely, the secondary cur- 
rent, is created, and employed with very great advantages. 
My readers must be content with this general description: 
and I must trust to their own ingenuity for making arrange- 
ments agreeable to these directions. 
114. Application of Heat.-Considerable advantage accrues 
in all cases of the deposition of metals where adhesion is 
desired, by the use of heat. It expands the baser metal, 
and so far opens its pores that the subsequent contraction, 
consequent on the effect of common temperatures, is likely 
to operate favorably in binding the metals together. It 
has other advantages, especially in gilding. The mode of 
heating the solutions will depend entirely on the circum- 
stances under which the experiments are conducted. If a 
hot stove, or a sand-bath be at hand, the object is soon 
accomplished; but, in most cases, a simple plan is to use a 
lamp and a glass or other retort, and convey steam by a 
glass tube into the metallic solution, either of the single 
cell apparatus, or that contained in the decomposition cell. 
115. With regard to the time requisite for plating and 
gilding, it is entirely dependent on the nature and uses of SOLUTIONS AND APPARATUS. 
15 
the article. The thickness of the deposit, of course, depends 
on the duration of the action. For medals, and such things 
as are not exposed to wear, a few minutes' immersion may 
be enough; for spoons, forks, plated goods, &c., subject to 
much wear, six or eight, or even more hours ; always taking 
care to watch the process at times, in order to prevent the 
occurrence of the black lines : whenever they appear, the 
action must be retarded. Large objects, or those which are 
subject to a long action, should be occasionally withdrawn, 
and their position should be altered : so that a uniformity of 
deposit may occur. Motion of the articles during the pro- 
cess has been recommended, and with some show of reason. 
The readiest method of producing it is to suspend the article 
in the solution from a common bottle jack, and connect the 
latter with the battery. Or, on the large scale, when it would 
not be convenient to have a roasting-jack for each group of 
articles, it might be convenient to have a constant flow of 
the solution. The surface obtained in the deposition of 
silver by electrolysis is technically termed "dead." Medals 
thus coated, if care be exercised during the operation, are 
very beautiful, and should be prepared for the cabinet by 
simply washing in water. If a bright surface is desired, 
they are polished with a leather and plate powder (§ 107.) 
Ordinary plated goods are finished off by polishing and 
burnishing. A steel or agate burnisher is used. In articles 
of jewelry some parts are left dead, and others are made 
bright. 
116. Preparing Surfaces to unite with Gold and Silver.- 
But we are going on too fast: I must return to certain things 
preliminary to plating and gilding, which I had passed over, 
in order not to interrupt the progressive illustrations of the 
nature and preparation of the solutions. I allude to the 
preparation of the surfaces, previous to applying the metals: 
which is a point of such paramount importance that, unless 
duly regarded,- all subsequent operations will be futile; and 
it would be vain to hope for perfect adhesion between the 
metallic base and the deposit: the latter will rise up in 
blisters where the surface is not properly prepared, and can 
easily be rubbed off. 16 
ELECTROTYPE MANIPULATION. 
117. There are two methods of preparing metals for the 
reception of other metals-the wet way and the dry way. 
The experiments of M. Becquerel and others are decidedly 
in favor of the latter; but, as it cannot be adopted, except 
in certain cases where the work of the article is plain, and 
the article itself is not delicate, it will be necessary to de- 
scribe both modes. The main intent of cleansing is that 
the contact between the two metals may be perfect; and it 
effects this by removing grease and all extraneous matter, 
especially the oxides, which are ever found on the surface of 
the less noble metals. 
118. Cleansing by the Dry Method.--The advantage of the 
dry process over any in which moisture has been employed, 
is that, in the latter case, several seconds, at least, must 
always pass between the act of removing the article from its 
last liquid bath, and placing it in the solution of the metal 
to be deposited ; and during this short interval, the article, 
or some portion of it, very frequently undergoes an altera- 
tion, trivial, indeed, but still an alteration, by the action of 
the air, which produces a film of oxide, infinitely thin, it is 
true, yet quite enough to militate against the success of the 
experiment, as regards permanent adhesion. Therefore, 
wherever the dry process can be adopted, it is decidedly the 
better: although, from the very nature of the articles sub- 
jected to the process, the number of cases in which it is avail- 
able is very limited. The dry process is merely the opera- 
ration of scouring with sand, or glass, or emery-paper, as 
the case may be, or with very fine powder of pumice-stone : 
using clean brushes, utterly free from grease. Sometimes 
tine files may be used ; indeed, all depends on the value and 
character of the article operated upon. It must be remem- 
bered throughout that grease and oxide arc the great ene- 
mies to be expelled: and therefore, especial care must be 
taken to avoid contact with the moisture of the hand, which 
is of a nature to produce either. 
119. Cleansing by the Wet Method.-The solutions em- 
ployed may be divided generally into two classes, the acid 
and the alkaline; the action of the former is directed more 
towards the removal of oxides, A'c.: that of the latter to the CLEANSING PROCESSES. 
17 
removal of grease. As a rule, 1 would always follow the 
use of an acid hath by an alkaline, having first washed 
away the acid in several waters; and this may be done, 
whether the operation commence with an alkaline bath or 
not. The following arc some of the modes in use; they are 
all effectual according to the circumstances which give pre- 
ference to one over the other : The method recommended by 
M. Boettiger, in his account of gilding, given in the Annalen 
der Chimie und der Pharmacie* may be adopted. He says: 
"It is very necessary to rub the metal according to circum- 
stances, t with extremely fine sand, moistened with hydro- 
chloric acid mixed with a little chalk, so that there shall 
remain no trace of oxide of copper." Another effectual 
methodis immersing the article in a mixture technically 
termed "pickle." This may be made of 
Sulphuric acid. ..... 64 parts. 
Water, . . . . » . . 64 " 
Nitric acid, . . . . . . 32 " 
Muriatic, ...... I part. 
The "pickle" is used by tying a wire round the article and 
immersing it for a second or two; the action is very ener- 
getic, and, of course, is not suited to the preparation of 
medals: for medals, the mixture should be very much 
diluted, and they should remain in it for a short time. A 
mere bath of dilute nitric acid is often used. Nitric acid 
mixed with sea-salt and soot, is often rubbed on the article. 
Concentrated sulphuric acid and sea-salt is another mode. 
Of the alkaline solutions are caustic soda, or solution of 
soda and ammonia, or caustic soda and sal ammoniac; or 
the articles may be boiled in a solution of common soda or 
potash, which is a very good method of cleansing them. 
120. Whatever solution is used, whether acid or alkaline, 
or the detergent paste of soot, or chalk and acid, fresh water 
must not be spared for rinsing off all remaining traces; 
and the article must be dried for immediate use by pouring 
over it boiling distilled or rain water; or, if the process of 
deposition is not to be commenced immediately after „the 
*Vol. xxxv. p. 350. 
tZ. e. when it can be done without injury to the object of experiment; and tins, too, must 
be the guide in the application of the other modes. 18 
ELECTROTYPE MANIPULATIONS. 
rinsing, it may be buried in hot or cold boxwood sawdust, 
until required; it may often be dried for immediate use in 
hot saw dust. In addition to the detergent methods already 
given, an ancillary means, which has been found effectual, 
depends upon the fact that metallic and other surfaces, after 
exposure to the air for some hours, become coated with a 
film of air so intimately as to retain it, even (as in electro- 
type cases) between themselves and any metal deposited 
upon them. In fact, we have been advised, in copying large 
subjects by electrotype, to take advantage of this, and to 
allow the film to arrange itself, before the plate is submitted 
to the action of the battery. For it is found that the pres- 
ence of this natural film very materially operates in prevent- 
ing adhesion between the plates and the deposit: whereas, 
in the absence of the film, unless its place has been supplied 
by something else, other things being in order, the two will 
effectually become one. We are advised, too, after soldering 
a wire to a copper plate, to allow the latter to remain an 
entire day, to regain the film of air which had been driven 
off by the heat. Carrying out this principle, the boiling 
alkaline solution and the boiling water answer a double end; 
and hence are very effectual means of promoting perfect 
union between the metals. Heat operates still more favor- 
ably in causing the expansion of the metal, as I mentioned 
when recommending its adoption in the process itself of 
electric deposition. Iron may be prepared and cleaned by 
electrolytic action, as described elsewhere (§ 166.) In pre- 
paring steel for gilding it must be polished without oil, as 
the oily particles adhere so closely that it is scarcely attacked 
by strong muriatic acid. The last cleansing method I have 
seen, and it is a capital one, is to scour the surface with 
Calais sand, moistened by the silver or gold solution, and 
rubbed in with a scratch-brush. 
121. Amalgamation to promote Adhesion.- Another method 
in this' preparatory stage of the proceedings, to which I 
shall allude, is that recommended by M. Becquerel;* and 
which promises to be of great avail in insuring a successful 
termination to the experiment. After the articles are thor- 
* Vide Les Comptes Rendus, July 3, 1843. CLEANSING PROCESSES. 
19 
oughly cleaned, according to the instructions now laid 
down, they arc dipped into a solution of proto-nitrate of 
mercury; when taken out they are washed in abundance of 
water: and are then rubbed with leather, in order to pro- 
mote the equal spread of the mercury. These operations 
are repeated until the whole surface is well coated with 
mercury. The ultimate character of the metallic deposit 
depends on the surface given to the mercury ; if the employ- 
ment of the leather is only such as is needed to etfect the 
more equal diffusion of the mercury, the surface is dull or 
dead, and so is the deposit; whereas, if brisk friction is ap- 
plied, and the mercury receives a good polish, such will be 
the character of the metal thrown down. And thus may 
burnished gold or dead gold be produced at pleasure. By 
adopting this method of giving a mercurial coat as the 
foundation for the plating or gilding (and it is especially 
valuable for the latter.) a double advantage accrues; the 
close adherence between the metals is insured-and a coat- 
ing of gold of any thickness may be thrown down. The 
mercury is subsequently driven off by heat ; either heat 
applied for the purpose, or the heat employed in some of 
the operations by which the work is finished. 
122. German silver is prepared by allowing it to remain 
for three or four hours in a cold solution of carbonate of 
potash. It is then washed in cold water, and dipped into 
dilute nitric acid. After again washing and drying it, it is 
rubbed with leather; and immediately before placing it in 
the silver solution it is dipped into a solution of common 
salt, containing a little gum. 
123. Cleaning Electro-plate.-Electro-plating, especially 
of dead silver, is very liable to turn yellow, after a few days' 
exposure to the light. M. Mourey found* that this was due 
to the decomposition of a cyanuret or a sub-cyanuret remain- 
ing on the silver surface on its emersion from the solution. 
He removes it in the following manner. The articles are 
covered with a thick layer of dissolved borax, and, being 
placed in a muffle, are submitted to a heat somewhat below 
cherry red, which is sufficient to calcine the borax. They 
*Viie Conipt ;s llsndus, Ap.'il 3,1843, p. 660. 20 
ELECTROTYPE MANIPULATION. 
are then thrown into water acidulated with sulphuric acid, 
and allowed to remain. After being withdrawn from this, 
they are washed in water and dried, first in hot sawdust 
and then on a stove or otherwise. The result is the pro- 
duction of that white color so essentially requisite to dead 
silver, especially in articles of jewelry. I may add to this 
a process for cleaning tarnished silver in general, which, 
though not much known here, is practiced constantly by the 
natives in India. A few tamarinds are placed in water 
contained in an earthen vessel, and the silver articles arc 
boiled in it for a time, and they emerge clean and very 
white. 
124. Gilding-Wax.-The proper color is given to the sur- 
face of electro-gilding by covering it with gilding-wax, and 
heating it till the mass begins to smoke. Gilding-wax con- 
sists of the powders of saltpetre, sal-ammoniac, sulphate of 
iron, and verdigris, mixed with melted wax. This opera- 
tion removes the brassy appearance, which the surface often 
presents, and gives the rich gold color, on which the beauty 
of the work depends. GOLD. 
21 
G OLD. 
Preparation.- 1. From gold ore, which has been tolerably 
well freed by mechanical means from matrix or river-sand, 
the gold may be obtained by simple fusion with borax, or 
other substances adapted to bring the adhering earthy 
matters into the liquid state. 2. Poorer gold ores are either 
fused with lead, in a similar manner to silver ores, or directly 
treated with mercury, after which the lead or mercury is 
separated in the manner already described in the case ot 
silver. 
If by these various modes of preparation, fin alloy of gold 
and silver is obtained, the separation of these metals may be 
effected in the following ways: 1. Fusion with Sulphur. 
The granulated alloy is fused with 0.3 pt. sulphur, which 
combines with the silver, and forms a liquid sulphide, while 
the finely divided gold remains suspended in it; a small 
quantity of litharge is then added, which gives rise to the 
formation of sulphurous acid and sulphide of lead, and again 
separates a portion of the silver, which then combines with 
the gold, forming an alloy, richer in the latter metal. This 
alloy sinks to the bottom of the crucible, and, after cooling, 
is separated by the hammer from the superposed sulphide 
of silver and lead (the PlachmaV) This substance, when 
fused with the addition of a small quantity of litharge, 
yields silver, which, for the most part, still contains a little 
gold. When the Plachmal has thus been completely ex- 
hausted of gold, it is generally cupelled with lead to obtain 
the silver. This mode of separation is adopted with alloys 
which contain but very little gold. The resulting alloy is 
often treated repeatedly with sulphur in th© same manner, 
till the proportion of gold is raised to one-fourth, after 
which the treatment with nitric acid is usually adopted. 
2. Fusion with Sulphide of Antimony. The alloy is mixed 
with twice its weight of sulphide of antimony, and fused, 
with constant stirring, in a crucible previously glazed with 
borax ; if the amount of silver in the alloy exceeds one-third, 
a proportional quantity of sulphur is added to the mixture. 22 
GOLD. 
Sulphide of .silver is then formed, and the gold combines 
with the antimony, forming a lower stratum of alloy, which 
is afterwards freed from antimony by ignition in the air, or 
by fusion with nitre. As the sulphide of silver thus formed 
still contains gold, it is again twice fused with sulphide of 
antimony, whereby an additional quantity of antimonide of 
gold is obtained. The whole amount of antimonide of cold 
thus produced is again fused with twice its weight of sul- 
phide of antimony, then freed from antimony, cither by 
fusing it alone, while air is blown upon it, or by fusion with 
three times its weight of nitre, and sometimes finally melted 
into a mass by heating it with % pt. borax, nitre, and | 
glass. 3. Separation by Cementation. The granulated alloy 
is arranged in alternate layers, with a mixture of 2 parts of 
brick-dust and 1 part of common salt, in porous crucibles, 
which are exposed for a period varying from 24 to 36 hours, 
to a low red heat. Under these circumstances, the aqueous 
vapor from the wood fire penetrates the crucibles, and acts 
upon the mixture in such a manner as to separate hydro- 
chloric acid, which then forms chloride of silver, with evolu- 
tion of hydrogen; and the chloride of silver, together with 
the common salt, sinks into the brick-dust. The gold obtain- 
ed by this process is, after washing, from 21 to 22 carats fine : 
from the remaining mass, the silver is obtained by amalga- 
mation. This processus employed in America. (Boussin- 
gault.) A mixture of 4 pts. brick-dust, 1 pt. common salt, 
and 1 pt. calcined green vitriol, may also be used as a cement. 
4. Separation by Sulphruric .Acid. The granulated alloy, 
in which the gold should not amount to quite one-half, but 
the silver may be in considerable excess, is heated in a pla- 
tinum or cast-iron vessel, with oil of vitriol, 1he quantity of 
which amounts to 3 parts for every 4 parts of silver to be 
dissolved, the heat being continued as long as sulphurous 
acid is evolved; and the resulting silver-sulphate is separated 
from the gold-powder by boiling water. To free the gold 
still further from silver, it is again heated for three hours in 
the platinum vessel, with a small quantity of oil of vitriol. 
After this treatment, the gold retains only !f per cent, of 
silver. The silver solution is warmed in leaden vessels, with GOLT). 
23 
metallic copper immersed in it, whereby the silver is sepa- 
rated, and blue vitriol obtained, (Sobolewsky, Ann. Pharin. 
24, 94 ; J. C. Jordan, J. pr. Chein. 9, 49.)-This process 
lias Lately been made the subject of an elaborate investiga- 
tion by Pettenkofer (Dingl. pol. J. 104, 118; abstr. Jaliresber. 
Ij. <(• A. 1, 1027 ; further, Dingl. pol. -1. Ill, 357; Jaliresber. 
2,635,) of which the following arc the principal results. The 
gold obtained by the first operation contains small quantities 
of lead-sulphate, basic ferric sulphate, and traces of sulphide 
of copper, which may be removed by digestion with carbon- 
ate of soda, washing, and subsequent treatment with nitric 
acid. The residue contains, on the average, 97 per cent, of 
gold, 2-8 of silver, and 0-2 of platinum. The silver is con- 
tained in it in the state of regulus, and cannot be dissolved 
out, cither by boiling sulphuric or by boiling nitric acid. 
After digesting in solution of sesquichloride of iron, not a 
trace of chloride of silver is dissolved out by ammonia. The 
gold thus purified may also be heated several times in con- 
tact with sulphur, till all the sulphur is volatilized, without 
giving rise to the formation of sulphide of silver. When 
it is treated with boiling sulphuric acid, to which pounded 
bichromate of potash is added, chromic oxide is formed, the 
gold is rapidly dissolved, while the silver and platinum 
remain unaltered. The only reagents capable of dissolving- 
out the residual portion of silver from-the refined gold, are 
the alkaline bisulphates, the soda-salt being the most eligible 
on account of its cheapness. The best mode of proceeding 
is to mix the gold with one-fourth of its weight of Glauber's 
salt in an iron vessel, pour in another equivalent of oil of 
vitriol (0.7 of the weight of the neutral sulphate,) and heat 
the mixture till the salt becomes liquid. Sulphate of silver- 
oxide is then formed, with evolution of sulphurous acid (and 
of hydrochloric acid, from the common salt contained in the 
Glaubers salt,) and the excess of sulphuric acid likewise 
escapes; the mass has a great tendency to cake together, 
which must be prevented by stirring. The greater part of 
the sulphate becomes reduced to the neutral state, and to 
dissolve out the rest of the silver, it is merely necessary to 
repeat the process once, heating the mixture, however, only 24 
GOLT). 
till about half the sulphate has become neutral. To separate 
the gold from the resulting mass, it must be boiled with sul- 
phuric acid in the ordinary way, whereby the sulphates of 
soda and silver-oxide are dissolved; the residue is then 
washed, dried, and fused with nitre. The first fusion yields 
refined gold, containing 994 parts of pure gold in 1000 ; and 
the second, from 998 to 999 parts, or not more than 0'1 or 
0'2 per cent, of silver. The facility and success of the oper- 
ation depends greatly upon the proportion of Glauber salt 
and upon the temperature, which should be kept a little 
below redness. The presence of platinum in refined gold 
explains the well known fact that this metal never exhibits 
a proper degree of fineness and softness, until it has been 
fused with nitre, platinum being easily oxidized by fusion 
with that substance. A portion of gold likewise passes into 
the slag together with the platinum ; for although gold is 
not oxidized, or but very slightly, when fused alone with 
nitre, it is nevertheless acted on with great facility when 
platinum is likewise present. A small portion of platinum, 
amounting to 1 or 2 parts in a thousand, escapes oxidation, 
and remains in the refined gold. The slag which remains 
after the fusion leaves, when treated with water, a soft grey 
powder, containing alumina, silica, and lime (from the 
crucibles)-potash-certain insoluble metallic compounds 
formed during the treatment with sulphuric acid, viz. lead- 
sulphate, basic ferric sulphate, and sulphide of copper-the 
oxides of gold, platinum, palladium, and osmium, formed 
by the action of the nitre-and finally a small quantity of 
metallic gold. Formerly this powder was merely levigated 
with water to separate the metallic gold, and the remainder 
was thrown away. But Pettenkofer has shown that this 
rejected matter contains 19 or 20 per cent, of gold, from 
2-5 to 35 per cent, of platinum, and a small quantity of 
silver. The lightness of the residue had caused the pre- 
sence of these metals to be overlooked, and prevented their 
separation by the amalgamation process. Pettenkofer, 
however, has devised a method by which the gold and pla- 
tinum may be profitably separated. The slags collected 
from several operations are soaked in water, and left to stand GOLD. 
25 
for 8 or 12 days, till they are reduced to a fine soft paste, 
which is then mixed with 2 parts of litharge, 1 part of 
tartar, 4 of dry carbonate of soda, and 2 of pounded glass, 
these proportions being calculated for 8 parts of the dry slag. 
The mixture is thoroughly dried in a copper or iron vessel; 
then thrown, by small portions at a time, in a red-hot cru- 
cible; and exposed to a gradually increasing heat, till it is 
brought to a state of tranquil fusion. If the process has 
been allowed time enough, a sharply separated regulus of 
lead is found, after cooling, at the bottom of the greyish 
slag. This lead is then cupelled, and the resulting bottom 
of metal is granulated and dissolved in aqua-regia in a 
retort, to which a receiver is adapted, because the vapors 
carry small portions of gold and platinum along with them. 
The heat is continued till all the nitric acid is driven off, 
the remaining solution filtered from the insoluble residue 
(AgCl and PbCl,) put into a porcelain dish, and precipitated 
while still warm with green vitriol. The gold which falls 
down in lumps, is separated by decantation, washed and 
fused with of its weight of nitre, to remove a trace of 
palladium : the product is fine gold. The solution poured 
off from the gold is precipitated with metallic iron, the pre- 
cipitate (chiefly consisting of platinum) boiled with nitric 
acid, then dissolved in aqua-regia, and precipitated as chlo- 
roplatinate of ammonium. An attempt to disintegrate the 
slags with sulphuric acid, led to difficulties insuperable in 
5. Separation by Nitric acid; Separation by Quartation.- 
The granulated alloy, which must contain at least 3 pts. of 
silver to 1 of gold, is first treated with cold weak nitric acid, 
and afterwards with strong acid at a boiling heat; the gold- 
powder is then separated from the silver-nitrate by washing 
with hot water, and afterwards fused with borax and nitre. 
The gold, after this treatment, retains but a mere trace of 
silver.1[ According to Pettenkofer (Jahresber. 1, 1030) the 
proportion of 3 parts of silver to 1 gold is not absolutely 
necessary in this process, the separation taking place quite 
sharply when the quantity of silver added does not exceed 
1'75 pt. Moreover, gold refined by quartation retains a 26 
GOLD. 
larger quantity of silver, the more the proportion of the 
Latter metal is increased beyond the limit above 
6. Separation by Acqua-regia.-The granulated alloy, 
very rich in gold, is resolved by repeated treatment with 
nitric acid, into chloride of gold which dissolves, and chlo- 
ride of silver which remains undissolved, and must be 
washed. The gold solution is freed by evaporation from 
the nitric acid still present, then diluted with water, and 
mixed with green vitriol, whereby the gold is precipitated 
in the form of a brown powder, which must be fused with a 
small quantity of borax and nitre. Pure gold is also obtained 
on the small scale by solution in aqua-regia, precipitation 
with green vitriol digestion of the precipitate with hydro- 
chloric acid, washing, and fusion with borax. 
The Kremnitz ducats contain in 24 carats, 23 carats 9 
grains of gold, and, therefore, only 3 grains of foreign metal; 
the Dutch ducats contain 23 carats 7 grains of gold. (1 carat 
=12 grains.) 
Gold is obtained in the pulverulent state by precipitating 
aqueous chloride of gold with green vitriol and other redu- 
cing agents ; and according to the nature of the precipitant, 
and the mode of conducting the process, the powder exhibits 
various degrees of fineness, and is consequently more or less 
adapted for gilding on porcelain, &c. The powder formed 
by pouring the gold-solution into the green vitriol is softer 
than when the contrary method is adopted, in which case it 
is more laminar and shining. (Otto, Ann. Pharm. 26, 86.) A 
peculiarly fine gold powder is obtained by pouring the gold- 
solution, at 100°, into a solution of mercurous nitrate; also 
by precipitating the gold-solution with hydrochlorate of 
terchloride of antimony. to C. T. Jackson {Sill 
J. [2,] 6,187,) gold is obtained in the form of a soft, yellow, 
spongy mass, by adding to a concentrated gold-solution, a 
small quantity of oxalic acid, then a sufficient quantity of 
carbonate of potash to dissolve nearly all the gold in the 
form ofaurate of potash, then a large quantity of crystallized 
oxalic acid, and finally heating the liquid rapidly to the 
boiling point. * PURPLE OF CASSIUS. 
27 
B. Stannate of Aurous Oxide.-Gold-purple, Purple of 
Cassius, Purpura mineralis Cassii. 
Formation. 1. By mixing a solution of chloride of gold 
with the solution of a stannous salt.-Pure protochloride 
of tin forms with chloride of gold, when tolerably concen- 
trated, a brown precipitate, consisting of an alloy of the 
two metals; it is only in case of very great dilution that 
the purple is produced. (Berzelius.)-A very dilute solution 
of protochloride of tin likewise forms with gold-solution, 
not the purple, but a black-brown opaque mixture, probably 
containing an alloy of tin and gold, but this mixture when 
kept in an open vessel, turns red from above downwards, 
and slowly deposites a very fine purple, which, however, is 
not always soluble in ammonia. (Fuchs.)-The brown 
powder is formed only with an excess c-f tin-solution ; when 
the gold solution is in excess, pure gold is precipitated. 
(Oberkampf.)-When both liquids are as neutral as pos- 
sible, or when the chloride of tin is in excess, metallic gold 
is precipitated, exhibiting a brown, blue, or green color; 
and on heating this precipitate with excess of gold-solution, 
it is slowly converted into purple of Cassius; if, however, 
nitric acid be present, the purple may be produced by its 
oxidizing action. (Buisson.) The color of the purple is 
bright red when a small quantity of tin-solution is used, 
and violet when the quantity of the latter is larger. 
(Oberkampf.) It is violet when an excess of bichloride 
of tin is present. (Bisson.) If the tin solution contains 
more protoxide than bioxide of tin, or if it is not suffi- 
ciently diluted, a dark-colored, nearly black precipitate is 
produced, which also dissolves in ammonia while yet moist, 
but forms a perfectly brown solution; after drying, it is 
black, gives off water when ignited, and leaves a brick-red 
mixture of gold and stannic oxide. (Berzelius.) ' If the 
solution of protochloride of tin contains a very large excess 
of acid, metallic gold is precipitated instead of the purple. 
Stannous sulphate likewise forms the purple with gold- 
solution (Proust,) but only after a considerable time.- 
(Sarzeau.) Stannous nitrate yields, under all circum- 28 
GOLD. 
stances, even with concentrated solutions, a beautiful 
purple. (Fischer, Schiv. 56, 363.) Metallic tin, tin-foil, for 
example, likewise throws down purple of Cassius from an 
acid solution of chloride of gold. Bichloride of tin gives 
no precipitate with gold-solution. (Proust.) Potash added 
to the mixture, forms a brown precipitate, which retains 
its color when dry; when heated under the liquid, it is 
converted into a brick-red mixture of gold, tin, and stannic 
oxide, which exhibits a conchoidal fracture when dry.- 
(Berzelius.) The purple of Cassius is not formed by pouring 
a solution of bichloride of tin on protochloride of gold. 
(Schweigger-Seidel, Schw. 62, 265.) 
2. By pouring a solution of chloride of gold on hydrated 
sesquioxide of tin. If the action be too long continued, the 
purple decomposes again, especially if the gold-solution is 
not dilute, part of the gold being reduced to the metallic 
state, and the rest dissolving in the form of auric oxide, 
together with stannic oxide, in the hydrochloric acid. 
(Fuchs, Kastn. Arch. 23, 368.) 
3. By boiling protoxide of gold witli aqueous stannate 
of potash. (Figuier.) 
4. By the action of oxidizing agents on metallic alloys 
containing gold and tin. When an alloy of 500 pts. silver, 
1 gold, and 25 tin is dissolved in nitric acid, 32-5 pts. of a 
pale red gold-purple are formed, in consequence of the excess 
of stannic oxide. Formation of purple likewise takes place 
when auriferous silver is dissolved in gently heated nitric 
acid, and metallic tin is added during the solution : stannic 
oxide has no action. Alloys of gold with tin, or with tin 
and zinc together, yield the purple when dissolved in nitric 
acid, the color being particularly line in the case of the alloy 
of tin and zinc; on dissolving these alloys in hydrochloric 
acid, on the contary, metallic gold separates out. (Merca- 
dieu, Ann. Chim. Phys. 34, 147 ; also A7". Tr. 15, 2, 30.) An 
alloy of 1500 pts. silver, 200 gold, and 350'5 tin (fused 
together under borax to prevent all oxidation of the tin) 
yields, by solution in nitric acid, a quantity of gold-purple, 
which weighs 701 parts when dried at 100°, and at a red 
heat gives off 53 parts of water, with a trace of hyponitric PURPLE OF CASSIUS. 
29 
acid. Hence the composition calculated further on. The 
gold-purple thus obtained from alloys by nitric acid appears 
homogeneous, but is denser than the ordinary variety, its 
density being greater, the smaller the quantity of silver that 
was present in the alloy; it is likewise insoluble in ammonia. 
(Gay-Lussac, Ann. Chim. Phys. 34, 396.) 100 parts of tilings 
of an alloy to 1 part of gold and 99 of copper, intimately 
mixed with 3 5 parts of tin, yields no purple with nitric 
acid, and a very dingy product with boiling oil of vitriol. 
An intimate mixture of tin, gold, and a large quantity of 
silver, or of 2 pts. gold, 7 tin, and 900 sugar or phosphate 
of lime, yields no purple when treated with nitric acid. 
Neither is the purple produced by heating auriferous copper 
with a solution of tin in boiling oil of vitriol, whereby the 
copper is dissolved, and the gold separated in the metallic 
state. (Sarzeau.) Some very much corroded coins of the 
Roman empire dug out of the ground in France, yield cupric 
oxide to aqueous ammonia when triturated with that liquid; 
the undissolved portion consists of two powders of different 
densities, which may be separated by levigation. The lighter 
powder, which has a dingy red color, is a mixture of silver 
spangles and purple of Cassius (containing metallic gold 
and tin,) which assumes a purple-red color after the silver 
has been dissolved out by nitric acid; but the color is often 
dingy from admixture of sulphide of silver. When the 
filings of the better preserved coins are repeatedly moistened 
with acetic acid and exposed to the air, and the resulting- 
cupric acetate dissolved out of water, there likewise remains 
a mixture of silver-spangles and gold-purple, which, when 
freed by nitric acid from silver, and by hydrochloric acid 
from the iron of the file, exhibits a fine color. (Sarzeau, N. 
J. Pharm. 3, 373.) 
Preparation.-1. By mixing aqueous susquichloride of 
iron with aqueous protochloride of tin till the yellow color 
is converted into pale green, and precipitating the gold-so- 
lution with the mixture thus formed. (Fuchs, J. pr. Chem. 
5,318.) This process yields the finest purple; the proto- 
chloride of iron contained in the liquid does not affect the 
product. (Fuchs.) One part of the Liquor ferri muriatici 30 
GOLD. 
of the Phannac Bor. is mixed with 3 parts of water, and a 
solution of 1 pt. tin-salt in 6 pts. water added, till the mix- 
ture acquires a greenish tint, after which 6 pts. more of 
water are added. (If the water were added at first, the 
change of the brownish into the greenish tint could not be 
so well observed.) On the other hand, gold is dissolved in 
boiling hydrochloric acid, with gradual addition of nitric 
acid-care being taken, however, to avoid as much as pos- 
sible an excess of acid, especially of the nitric acid: the 
solution is diluted so far that 360 parts of the liquid contain 
1 part of gold: and the tin-solution is then added, with con- 
stant stirring, as long as a precipitate is produced. By this 
process, 100 parts of gold yield 360 parts of dried purple, 
soluble in ammonia, and capable of imparting a strong color 
to glass. If the gold-solution contains only one part of gold 
in 450, instead of 360 parts of the liquid, a good purple is 
likewise obtained at temperatures between 30° and 35°; but 
at ordinary temperature, it is not deposited: and on heating 
the liquid to the boiling point, it falls down in red-brown 
Hakes, which are not soluble in ammonia, and impart but a 
slight color to glass. (Capaun J. pr. Chem. 22, 152.-2. 
Ten parts of pink-salt (V, 94) are heated with 1-07 tin-foil 
and 40 water, till the tin is dissolved, after which 140 parts 
of water are added : 
3(NH4C1, SnCl2)+Sn-3NH4Cl+2Sn2Cl3. 
On the other hand, 1'34 pt. gold is dissolved in aqua-regia, 
the acid not being in excess, and a quantity of water is added, 
sufficient to bring the mixture up to 480 parts. Finally, 
the former solution is added to the latter slightly warmed, 
as long as a precipitate is produced. The purple, which is 
quickly deposited, weighs 4'92 parts after washing and dry- 
ing at 100°; the filtrate has a very pale red color. (Bolley, 
yffin. Pharm. 39, 244.)-3. a. A neutral solution is prepared 
of part of tin in hydrochloric acid ; b. a solution of 2 pts. tin 
in cold nitro-hydrochloric acid (1 pt. hydrochloric acid to 3 
nitric,) the liquid being merely heated, if necessary, towards 
the end of the process, so that the solution may not contain 
any protoxide of tin, and therefore may not precipitate the 
gold-solution; c. 7 parts of gold are dissolved in nitro-hy- PtTRPLE OF CASSIUS. 
31 
drochloric acid (6 hydrochloric to 1 nitric,) and the solution, 
which is tolerably neutral, diluted with 3500 parts of water. 
To this solution c the solution b is first added, and then the 
solution a, drop by drop, till the right color is produced. 
If the quantity of a be too small, the precipitate is violet; 
if too large it is brown. It must be washed quickly, so that 
the liquid may not act too long upon it. If the precip- 
itate will not settle down, the mixture must be slowly 
poured into a glass of water, so that it may sink to the 
bottom, and the two liquids may mix but slowly. (Buisson, 
«/. Pharm. 16, 629.) The purple thus obtained weighs only 
6'2 pts.; it dissolves in ammonia while fresh, but imparts a 
scarcely perceptible color to glass-fluxes; the filtrate is red; 
but deposits no more purple on the further addition of pro- 
tochloride of tin. (Capaun.) Lentin (/ScAer. J. 3, 30) drops 
fuming nitric acid into aqueous protochloride of tin, till a 
sample of the mixture forms a fine purple with the gold- 
solution, and then mixes the liquids. 4. To obtain a blue 
precipitate, a solution (a) as neutral as possible, of 3 grammes 
of tin in hydrochloric acid, is prepared out of contact of air, 
and (6) a solution as neutral as possible of 3 grammes of 
gold in aqua-regia; each of these solutions is diluted with 
a litre of water; 10 measures of solution a are heated 
to between 50° and 60° with 3 measures of nitric acid; 1 
measure of b is then added, and immediately afterwards 
water, with agitation. The indigo-blue precipitate (or 
violet, if sufficient water has not been added,) must be 
quickly washed by decantation, as, jf left for any length of 
time under the liquid in an open vessel, it changes color 
first to violet and then to purple. (Golfier Besseyre, Ann. 
Chim. Phys. 54, 40; also J. pr. Chem. 20, 65. 
Properties.-In the moist state, dark, purple-red (dark 
brown according to Berzelius.) Brown after drying.- 
(Capaun, Bolley.) 
Proust. 
Berzelius. 
Buisson. 
Gay-Lussac. 
Oberkampf. 
violet. 
purple. 
Au 
. . 24 . 
28*2 
. 28'5 . 
. 28'53 . . 
39-82 . 
. 79-42 
SnO2 . . . 
. . 76 . 
. 64 0 . 
. C5-9 . 
. 63-56 . . 
60-18 . 
. 20-58 
HO .... 
. . 7*6 
7-56 
01 
5*2 
. NO5 trace. 
100 
. . 99'8 . 
. 99'6 . 
. 99-65 . . 
100-00 . 
. 100-00 32 
GOLD. 
The purple examined by Proust was obtained with gold- 
solution and aqueous protochloride of tin, and well dried ; 
that examined by Berzelius was obtained with very weak 
solutions of terchloride of gold and protochloride of tin. 
Buisson's purple was prepared by (3;) if the tin-solution 
contains too much nitric acid, basic nitrate of stannic oxide 
is precipitated, instead of the stannic oxychloride. Buisson 
does not appear to have looked for water, and his amount 
of chlorine is doubtful, since, according to Berzelius, the 
purple neither gives off hydrochloric acid nor chloride of 
tin when ignited. Gay-Lussac's purple is the product 
obtained from the alloy of gold and tin by the action of 
nitric acid, and dried at 100°. Oberkampf's violet purple 
was obtained by precipitating the gold-solution with excess 
of tin-solution; in the preparation of his purple product, 
the gold-solution was in excess. The analyses are partly 
incorrect, for this reason, that if an excess of stannic salt is 
present, an excess of stannic oxide is precipitated; and if 
the stannous salt is in excess, the brown alloy of gold and 
tin mixes with the precipitate. 
The following are the principal theories which have been 
put forward regarding the composition of gold-purple:- 
I. It contains metallic gold rvith hydrated stannic oxide, (or, 
according to Buisson, with stannic oxychloride.)-1. The 
two substances are mechanically mixed ; the very finely 
divided gold is the coloring principle, and the stannic oxide 
assists by its interposition the development of the color, in 
the same manner as alum in the colors called lakes. 
(Buisson, Sarzeau.) | In that case, an excess of stannic 
oxide would merely weaken the purple color, but could not 
change it into violet; moreover, in lakes, the alum is chem- 
ically combined with the coloring principle. | 2. The gold 
is chemically combined with the stannic oxide. (Proust.) 
Gay-Lussac likewise supposes a combination by affinity, or 
at least by intimate adhesion.-II. The purple of Cassius 
contains oxidized gold. This view is the more probable of the 
two.-2. It contains protoxide of gold. Purple of Cassius, 
freed by potash from excess of stannic oxide, lias the com- 
position: AuO,3SnO24~5Aq. (see Calculation a.) This is PURPLE OF CASSIUS. 
33 
exactly the composition of the gold-purple obtained by 
boiling protoxide of gold with stannate of potash, or by 
immersing tin-foil in the solution of chloride of gold ; and 
the gold-purple analyzed by Berzelius contains exactly 
the double quantity of stannic acid = AuO,6SnO2-|-7Aq. 
(Figuier.) | 6Aq. is nearer; vide Calculation b ; but Figuier's 
view is in opposition to the observation made by Berzelius, 
that the purple gives off no oxygen when ignited.] Schweig- 
ger-Seidel (Seine. 65, 265) regards the purple of Cassius as 
stannate of aurous oxide and stannous oxide = SnO,3Sn()2 
4-AuO, 2SnO2-|-6Ax.-2. The purple of Cassius contains a 
purple oxide of gold=AuO2, intermediate between the 
protoxide and teroxide. (Berzelius, Fuchs, Desmarest.) Tt 
is composed of Au02,2Sn303 (perhaps also with 4 At. water? 
see Calculation c.] This formula agrees with Oberkampf's 
analyses of the violet gold-purple. (Berzelius.) [But this 
is not the true gold-purple.] Its formula is : 2(SnO,Sn 
O2-j-AuO2,2SnO24-6Aq. (Calculation dd) Fuchs (Poggd) 
27, 634.) The formation of gold-purple from a mixture of 
hydrochlorate of auric oxide and hydrochlorate of sesqui- 
oxide of tin would accordingly take place as follows : 
AuO3,3HCl+3(Sn2O3,3HCl=r2(SnO,Sno2)-|-AuO2,'2SnO2]4-1*2HCl 
Calculations according to the preceding hypotheses. 
At. Figuier, a. 
A t. 
Figuier, b. At. Berzelius, c. 
At. 
Eucli 
is, d. 
Au 
1...199. 
42-51.. 
.. 1...199 
27-99...1 ...199... 
. 37-20.. 
. 1.. 
.199... 
28-31 
Sn 
3...177. 
37-82.. 
. 6...354. 
49-79...4...236... 
44-11.. 
. 6.. 
.354... 
50-35 
0.. 
7... 56. 
11-97.. 
.13...104. 
14-62...8... 64... 
11-96.. 
.12.. 
. 96... 
13-66 
no 
4... 36. 
7-70.. 
. 6... 54 
7-60...4.. 36... 
. 6-73.. 
. 6.. 
. 54... 
7'68 
468. 
100-00.. 
. ...711. 
100-00 535.. 
.100-00.. 
.703... 
100-00 
Decomposition.-Purple of Cassius retains its water when 
heated above 100Q, but gives it up at a red heat, without at 
the same time emitting any permanent gas, and acquires a 
brick-red color. (Berzelius.) Aqua-regia dissolves out the 
gold from the ignited residue, leaving white stannic oxide. 
(Proust, Berzelius.) Hydrochloric acid has no action upon 
it. (Berzelius.) Berzelius regards ignited gold-purple as a 
mixture of gold and stannic oxide, inasmuch as, at a red 
heat, the red oxide of gold gives up its oxygen to the ses- 
quioxide of tin, and forms bioxide of tin: for an intimate 34 
GOLD. 
mixture of oxide of gold with a large quantity of sulphate 
of potash likewise forms, when ignited, a red powder, from 
which water extracts the salt, and leaves metallic gold. 
According to Fuchs, the ignited purple is only to he 
regarded as de-hydratcd, for mercury does not dissolve gold 
from it; the affinity of the stannic acid for the red oxide of 
gold prevents the decomposition. Gold-purple fused with 
nitre yields stannate of potash and a white globule of an 
alloy of gold and tin. (Berzelius.) It is but slightly altered 
by red-hot fusion with bisulphate of potash. It likewise 
remains unaltered when fused with carbonate of potash, 
and does not expel carbonic acid from that salt. (Berzelius.) 
[This fact is in favor of Fuchs's theory, that ignited gold 
purple still contains stannic acid in the combined state.) 
Gold-purple is blackened by protochloride of tin and other 
deoxidizing liquids. (Desmarest, J. Pharm. 17, 219.) Aqua- 
regia extracts from the unignited purple all the gold, 
together with a small quantity of tin. leaving the greater 
part of the stannic oxide undissolved. (Proust.) This liquid 
dissolves the purple easily, at first with a violet color. 
(Buisson.) Hydrochloric acid acts upon it slowly, dissolv- 
ing up all the tin, after long boiling, in the form of bioxide, 
free from protoxide, and leaving all the gold in the metallic 
state. (Proust, Fuchs.) [This action favors the views of 
Fuchs and Berzelius, and is against that of Figuier.] Boil- 
ing nitric acid brightens the color of recently prepared gold- 
purple, and dissolves out some of the stannic oxide, together 
with a small quantity of auric oxide. (Proust.) Boiling 
dilute sulphuric acid likewise heightens the color, and ex- 
tracts a small quantity of stannic oxide. (Proust.) The 
purple while moist is not decomposed by long boiling with 
water, merely falling more quickly to the bottom. (Robi- 
quet.) Boiling potash has likewise no action on the moist 
purple. (Berzelius.) It dissolves out the excess of stannic 
oxide. (Figuier.) Mercury docs not extract gold from re- 
cently prepared gold-purple (Proust;) not even with the aid 
of heat or sunshine; neither does it dissolve gold out of the 
ignited purple. (Fuchs.) At temperatures between 100° 
and 150°, it dissolves out all the gold from the dried and PURPLE OF CASSIUS. 
35 
pulverized purple, and leaves stannic oxide. (Buisson.) 
At this temperature, the mercury may exert a reducing 
action on the red oxide of gold. (Berzelius.) Gold-purple 
fused with 4 parts of lead-oxide and 1 part of borax, yields 
a violet glass on the addition of a large quantity of boracic 
acid, and a red glass on the addition of a large quantity 
of hydrate of potash. 
Gold-purple, while yet moist, dissolves in aqueous am- 
monia, forming a deep purple-red liquid, from which the 
purple separates both on evaporation and on the addition of 
acids, but not on dilution with water, unless the quantity 
dissolved is excessive. (Proust.) After drying, the purple 
is no longer soluble. (Berzelius.) The solubility of the 
moist purple is also destroyed by allowing it to freeze. 
(Fuchs.) The purple obtained by treating the hydrated 
sesquioxide of tin with solution of chloride of gold (Fuchs,) 
and that produced on dissolving an alloy of gold, silver, and 
tin in nitric acid (Gay-Lussac,) are not soluble in ammonia, 
even while moist, the insolubility probably arising from 
their greater density. The solution when not completely 
saturated, is quite clear: but a perfectly saturated solution, 
though it appears dear by transmitted light, nevertheless 
exhibits some degree of turbidity when viewed by reflected 
light. The solution, when left in the dark for some weeks, 
becomes decolorized from above downwards, while gelatinous 
gold-purple, mixed with metallic gold falls to the bottom; 
on agitation, a red liquid is again obtained-which, how- 
ever, quickly deposits the purple again-and after a while, 
metallic gold is precipitated, the quantity continually 
increasing. When the ammoniacal solution is kept in a stop- 
pered bottle at temperatures between 60° and 80°, the pur- 
ple is more quickly deposited, and is not re-dissolved on 
agitation. On evaporating the solution at a gentle heat, 
the purple separates in the form of a jelly, no longer soluble 
in ammonia, but otherwise unaltered. (Berzelius, Lehrbuch.') 
The ammoniacal solution of gold-purple turns violet when 
exposed to light, and gradually deposits the whole of the gold 
in the metallic state, the transparent and colorless liquid 
containing ammonia free from stannous oxide. (Fuchs.)