OX A 
NEW AND SIMPLE METHOD 
FOR THE 
QUANTITATIVE ESTIMATION OF UREA. 
BY 
GEORGE B. FOWLER, M. D., 
INSTRUCTOR IN PHYSIOLOGY, COLLEGE OP PHYSICIANS AND SURGEONS, ETC., 
NEW YORK, 
[REPRIN7ED FROM THE NEWYORK MEDICAL JOURNAL, JUNE\ 1877,] 
NEWYORK: 
D. APPLETON & COMPANY, 
64 9 & 66 1 BROADWAY. 
1877. ON A 
NEW AND SIMPLE METHOD 
FOE THE 
QUANTITATIVE ESTIMATION OF UREA. 
BY 
GEOEGE b. fowlee, m. d., 
INSTRUCTOR IN PHYSIOLOGY, COLLEGE OP PHYSICIANS AND SURGEONS, ETC.. 
NEW YORK. 
[.REPRINTED FROM THE NEWYORK MEDICAL JOURNAL, JUNE\ 1871] 
NEW TOEK: 
D. APPLETON & COMPANY, 
549 & 551 BROADWAY. 
1877. ON A NEW AND SIMPLE METHOD FOR 
THE QUANTITATIVE ESTIMATION OF 
UREA.1 
Urea, being one of the most interesting and important 
constituents of the animal body, has occupied the attention of 
chemists and physiologists since its discovery in 1713, by 
Rouelle, Jr. Its properties becoming known, and its signifi- 
cance as a decomposition product appreciated, a certain stim- 
ulus has ever since attached to its study; and, as a result, 
various methods for its estimation have been devised, based, 
of course, upon its properties and chemical relations. 
Other characters of urea than those directly connected 
with the most reliable quantitative methods, do not at present 
concern us ; and a hasty survey of these, with a special view 
to judge of their simplicity, will not be out of place. 
Mitscherlich2 and Lacanu3 availed themselves of the strik- 
ing reaction manifested by urea when treated with nitric acid, 
and estimated the quantity from the very stable and copious 
precipitate of urea nitrate. But with this method consider- 
able time and chemical manipulation are necessary in order 
to insure accuracy. 
1 Prize essay of the Alumni Association, College of Physicians and 
Surgeons, Hew York, 1877. 
2 Poggendorff’s “ Annalen,” Bd. xxxi., S. 308. 
3 Jovr. de Pharm., tome xvii., p. 651. 4 
When urea is treated with strong sulphuric acid, and 
heated, it is decomposed into ammonia and carbonic acid. 
Ragsky 1 proposed to estimate the amount of urea originally 
present by the ammonia thus formed. But, in order to do so, 
a complicated and delicate process must be gone through with. 
Urea, heated with water in sealed tubes to about 100° C., is 
resolved into ammonium carbonate by the appropriation of 
two equivalents of water, thus : 
CH4N20+2H30=2(JNTI4)C02. 
This product treated with barium hydrate gives us barium 
carbonate, from which a quantitative estimation of the urea 
can be made. This is the basis of Bunsen’s2 method. 
Nitrous acid decomposes urea into water, carbonic acid, 
and nitrogen, as follows : 
0H4N2O+2KO2H=CO2+2N2+3H20. 
This reaction constitutes the basis of Millon’s method, 
whereby he estimates the quantity of urea in a given solution 
by the weight of the gases given off. A modification of 
this process has been devised by Boymond,3 in which he em- 
ploys a rather complicated flask, provided with separate di- 
visions for each of the substances used in the analysis, viz., 
one for the urine, another for the reagent, and a third for 
the sulphuric acid, through which the gases are made to 
pass to rid them of moisture. Each apartment being supplied 
with the three fluids, the urine and nitrous acid are allowed 
to come'in contact, and decomposition to continue until gas 
ceases to be evolved. Then the difference between the weight 
of the flask and its contents, before and after the reaction, 
will give the weight of nitrogen and carbonic acid lost; and 
having found that the relation of the gases to urea, by 
weight, is as 12 to 10, the subsequent calculation is very 
simple. 
Dr. H. Gr. Piffard 4 has still further modified this method, 
with a view to avoid the expensive apparatus of Boymond, 
and with exceedingly accurate results. 
1 “ Ann. der Chem. nnd Pbarm.,” Bd. Ivi., S. 29. 
2 Ibid., Bd. Ixv., S. 29. 3“ De I’Uree,” Paris, 1872. 
4 New Yoke Medical Joxtbxal, December, 1874. 5 
It will be seen that the foregoing methods involve the 
skillful use of delicate and expensive scales, and most of them 
necessitate a degree of technical skill and a supply of appa- 
ratus not generally possessed by physicians. 
Liebig having discovered that mercuric nitrate added to a 
solution of urea would precipitate a white compound com- 
posed of one equivalent of urea with four of mercuric oxide, 
U+IHgO, thereon based bis well-known method for the volu- 
metric analysis of urea, simply by the use of a graduated 
solution of the reagent. 
This perhaps is the most reliable and popular procedure 
ever proposed, but, like all of those thus far mentioned, offers 
difficulties in chemical manipulation not readily overcome by 
a novice. 
Urea is resolved into hydrochloric acid, water, carbonic 
acid, and nitrogen, by hypochlorous acid, formulated thus: 
CH4N30+2ClH0=2HCl+2HaO+C0a+^a. 
As far back as 1853 Wohler determined the ammonia in 
guano by the hypochlorites; and in 1854 Dr. Davy 1 pub- 
lished his celebrated process for estimating urea by measuring 
the volume of nitrogen set free from it by solutions of the hy- 
pochlorites. 
Davy’s familiar process has been variously modified, first 
by Knop,2 who, instead of using hypochlorous, employed hy- 
pdbromous acid, which he found would effect the same result, 
his apparatus consisting of flasks with a complicated series of 
glass stopcocks. 
Hiifner3 then proposed an improvement on Knop’s meth- 
od, consisting chiefly in the employment of moderate heat 
to hasten reaction. But by this procedure oxygen is evolved 
from the hypobromite solution, which has to be subsequently 
estimated. 
Bussell and West4 next came forward with a very much 
1 Philosophical Magazine (4), vii., p. 385. 
2 Fresenius’s Zeitschr. fur analyt. Chem., ix., 2, S. 226. 
3 Journal of Chemical Society, New Series, ix., p. 162. 
4 Practitioner, February, 875, p. 86, and Journal of Chemical Society, 
1874, p. 749. 6 
less complicated apparatus, adapted to the use of sodium hy- 
pobromite, and the collection and measuring of the nitrogen 
disengaged by it from urea. This method has deservedly be- 
come very popular. 
Last of all, Blackley1 has invented still another form of 
apparatus for the hypobromite method; but in my hands it 
has proved very inconvenient and difficult to manage. 
As a general objection to the use of a standard solution 
of hypobromite, it may be said that it is very unstable, and 
therefore the preparation of a fresh supply becomes necessary 
at very short intervals. And, on account of the disgusting 
odor and injurious fumes of the bromine employed, this pro- 
cedure itself is not one of the most agreeable. 
Having experienced the difficulties in the way of technical 
details which most of these methods involve, it seemed to me 
that a simple and sufficiently accurate process for clinical pur- 
poses for the quantitative analysis of urea had not yet been 
published. I therefore submit the details of the following: 
Every one who has been in the habit of making volu- 
metric analyses of sugar in urine must have had his patience 
tried by the frequently sudden and unexpected behavior of 
the test, which necessitated a complete washing out and new 
beginning; and I know he must have been delighted when 
Dr, Roberts published the description of his simple plan, 
which consists in determining the amount of sugar in a solu- 
tion, merely by the difference in specific gravity before and 
after fermentation. It occurred to me that the difference in 
specific gravity before and after decomposition by the hypo- 
chlorites oi’ hypobromites should bear a definite relation to the 
quantity of urea originally present in the solution. I there- 
fore instituted a series of experiments, of which the following 
is an account, and which proved my theory to be correct. 
How, between stable and fermenting saccharine solutions, 
there is obviously a wide margin as regards specific gravity ; 
for, by the action of yeast, not only is there a loss of matter, 
C02, but a generation of a liquid lighter than water, alcohol. 
It was therefore a question at the outset whether we would 
have sufficient margin, with urine and the proposed reagents, 
1 Journal of Chemical Society, 1876, p. 466. upon which to base a calculation, and whether small differ- 
ences in the amount of urea would be indicated with sufficient 
accuracy. Theoretically it seemed that there should be a loss 
in gravity, after the mutual decomposition between urea and 
a hypochlorite or hypobromite, as shown in the preceding for- 
mula, where, besides the loss of nitrogen, there is a production 
of water. According to Dr. Davy, the carbonic acid does 
not escape from the solution, but is reabsorbed by the excess 
of caustic alkali of the reagent. My own observations sup- 
port this statement, and therefore this product does not add to 
our margin. 
Again, urea consists of by weight of nitrogen. There- 
fore almost one-half of the urea in the solution will disappear ; 
and this loss, together with the water introduced, should cause 
a perceptible difference in gravity. 
The reagent which I have found to be the most convenient 
for this analysis is sodium hypochlorite (the liquor sodce chlo- 
rinatce of the pharmacopoeias), on account of its cleanliness, 
and because it is easily procured. But, unfortunately, the 
preparations of this article vary exceedingly as regards compo- 
sition and specific gravity, some giving an insoluble precipi- 
tate of lime carbonate with urine, and having a gravity of 
from 1050 to 1100. Of course, we must not have a precipi- 
tate, and such a density would require an hydrometer of very 
long stem and large bulb, and would necessitate the use of a 
larger volume of fluid than would be desirable. 
In the standard solution prepared by Dr. E. R. Squibb, of 
Brooklyn, however, these objections are overcome, as there is 
not the slightest opacity following its addition to urine; and 
he informs me that the density, when it is bottled, is about 
1048. By exposure to air and light it is reduced. 
The next important step is to procure a suitable hydrom- 
eter. The requirements are a stem which will indicate the 
gravity of the hypochlorite, and also that of the urine, that 
is, an index ranging from 1000 to 1050, and that each gradua- 
tion should indicate one degree, and be about two millimetres 
(one-twelfth of an inch) apart, in order to allow of accuracy 
in the reading. To be able to work with smaller quantities 
of fluids, the instrument should be divided into two of equal size, one reading from 1000 to 1025, the other from 1.025 to 
1050.1 
Dr. Davy found that about six parts of the hypochlorite 
were required to one of the urine, to decompose the urea ordi- 
narily contained. 
This accords with my experience, but, in order to insure 
complete decomposition, and to provide for an excess of urea, 
I employ seven parts of the reagent. 
My preliminary experiments were performed with solu- 
tions of pure urea of known strength, and it was found that 
after decomposition every degree of density lost indicates 7.791 
milligrammes of urea per cubic centimetre of the solution 
(3.55 grains per ounce). Or every degree lost corresponds to 
.77 per cent. 
I then took different specimens of urine and analyzed 
1 Such hydrometers will be made on application to John Tagliabne, 69 
Fulton Street, New York. 9 
them by this method, taking these figures as a basis of calcu- 
lation, and compared the results with those obtained with the 
same specimens bj Liebig’s process. 
Table showing comparative results obtained by Liebig’s method 
and that described in this paper (calculated as milli- 
grammes per cubic centimetre): 
Liebig’s. New. 
1 26.155 26.203 
2 32.461 32.500 
3 34.983 34.983 
4 31.192 31.220 
It will be seen that, with one exception, where there is an 
absolute agreement, the results by the new process are in 
excess of those by Liebig’s by a few thousandths of a milli- 
gramme, which is probably due to the decomposition of ni- 
trogenous ingredients other than urea, of which we will pres- 
ently speak. 
In order to use this method, proceed as follows : Procure 
two glass cylinder jars, one about nine inches in height by 
one and a half in diameter, the other about seven inches by 
one inch. Into the smaller pour a quantity of the urine, and 
ascertain its specific gravity. Take about fifteen cubic centi- 
metres (one-half ounce) of it and pour it into the large jar. 
Now wash out the smaller jar thoroughly, and in it take the 
specific gravity of the hypochlorite solution. Then add to 
the urine in the large cylinder exactly seven times as much 
hypochlorite as there was urine taken.1 
When the two fluids mingle there will be a brisk efferves- 
1 It is not absolutely necessary to employ a special hydrometer except 
where great accuracy is desired. The instrument ordinarily possessed by 
physicians, if it is marked up to 1050, does very well for clinical work, a 
little care and patience enabling one to read the exact specific gravity after 
a few trials. With this short stem we have a small bulb, and gain the ad- 
vantage of economy in the nse of the fluids. The first tiling to do is to 
procure a couple of jars (or large test-tubes with feet) whose calibre will 
freely accommodate the hydrometer, and then ascertain, by using water, 
what will be the smallest quantity of liquid which, in a particular jar, will 
float the hydrometer. One-eighth of this quantity will be the measure of 
urine to employ. 10 
cence, and care must be taken that none of the mixture be 
lost. After several minutes the disengagement of gas is less 
rapid ; and now, by vigorously shaking the jar at short inter- 
vals, I have found the process to be hastened, so that at the 
expiration of an hour the decomposition is complete. It then 
only remains to take the gravity of the quiescent solution, de- 
duct from what it was before decomposition, and estimate 
the amount of urea on the basis already given ; after this 
manner : 
Suppose the specific gravity of the urine to be 1020, and 
that of the hypochlorite 1015. But it is impracticable to take 
the specific gravity of the mixture of these two on account of 
their immediate reaction ; we therefore resort to the law of 
proportion, and estimate it as follows : 
1 part at 1020 = 1020 
7 parts at 1045 = 7315 
8 )8335 
1041J sp. gr. of mixture. 
From the gravity of the eight parts we subtract that which 
is obtained after decomposition, which, we will say, is 1038-|. 
There is then a loss of 3°. Every degree of loss equals 1,791 
milligrammes per cubic centimetre of urine used. Therefore, 
the urine contained 23.373 milligrammes of urea per cubic 
centimetre, or 2.3 per cent. 
It is, of course, highly important that the temperature of 
the fluicfs should all agree when their specific gravity is taken. 
This may be regulated by the use of a plain thermometer, or 
by the combination hydrometer and thermometer now so gen- 
erally employed. But the simplest method is to mix the urine 
and reagent, and set the mixture aside with the pure urine 
and hypochlorite in the same locality, when the specific grav- 
ity of the three can be taken at a uniform temperature. 
The presence of neither albumen nor sugar interferes with 
the accuracy of this method. 
But it may be urged as an objection that other nitrogenous 
ingredients of the urine, such as uric acid and creatinine, suf- 
fer the same decomposition as urea, and therefore constitute 
elements of error. Yet, when we take into consideration the 11 
facts regarding these substances, namely, that, of the nitrogen 
contained in uric acid, thirty-five per cent., in hippuric acid, 
eighty-two and a half per cent., and in creatinine twenty-five 
per cent., is not disengaged by solutions of the hypochlorites, 
and when we remember how insignificant are the quantities of 
these substances in the urine compared to urea—the excretion 
per day being respectively about 0.7, 0.35, and one gramme, a 
total of 2.05 grammes—it is obvious that their presence does 
not establish a serious fallacy. Ammonia, however, would 
interfere, and give an erroneous result. 
When the urine contains a great excess of urea, more than 
would be decomposed by seven parts of hypochlorite, it is 
simply necessary to dilute it with an equal volume of water, 
use one part of the dilution to seven of the reagent, and mul- 
tiply the result obtained by two. 
It is evident that with this method we must be able to fix 
the point at which the hydrometer floats in the several liquids 
with nicety. When these liquids are perfectly transparent 
there is no difficulty, the proper way being to read from the 
under surface of the fluid, bringing the eye on a level with 
that surface. But, when the urine from any cause is opaque, 
this process is not practicable, and, under these circumstances, 
I resort to the following simple device : 
Take a piece of soft pine, and shape it into a circular disk 
somewhat smaller than the calibre of the smallest jar to be 
used. Make it exceedingly thin and uniform, and perforate it 
in the centre with a round hole which will freely accommo- 
date the stem of the hydrometer. Having put the stem of 
the instrument through this opening and immersed it in the 
fluid, the bit of wood will float on the surface, and the specific 
gravity can be readily taken by noting the point at which the 
float comes in contact with the stem. The weight of the wood 
will cause a slight increase in density, but, when used, in every 
case the error will be the same, and therefore corrects itself.