THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. [December 3, is:o. 
411 
tills way decomposed, giving insoluble black oxide of 
copper:— 
2 (Cu 2 N 0 3 ) = 2 Cu 0 + 2 N 2 0 2 + 3 0 2 , 
whilst the nitrate of silver remains unchanged. On 
treating with distilled water the latter alone dis¬ 
solves. 
[§ 10 grains dissolved in distilled water give with 
hydrochloric acid a precipitate, which, when washed 
and dried, weighs 8'44 grains. The filtrate when 
evaporated by a water bath leaves no residue.] 
Adulteration of the fused stick with nitrate of potash 
would in tills way be detected. 
{To be continued.) 
ON THE COMBINATIONS OF CARBONIC 
ANHYDRIDE WITH AMMONIA AND WATER. 
BY EDWARD DIVERS, M.D.* 
{Continued from page 385.) 
Ammonium Carbamate. 
History. —"Who discovered that ammonia and carbonic 
anhydride unite to form a solid I do not know. Gay- 
Lussac first determined the proportion in which these 
gases combine. 
Preparation. —(«.) By the direct union of dry ammonia 
and carbonic anhydride gases, when it is deposited partly 
as an incrustation on the walls of the vessel in which it 
is formed, and partly as flocculi. This is the earliest 
method known. 
(i b .) (Rose’s method.)—By distilling together ammo¬ 
nium sulphamate and anhydrous sodium carbonate, when 
it is also obtained as an incrustation on the walls of the 
condensing vessel.f 
{c.) (Kolbe and Basaroff’s method.)—By passing car¬ 
bonic anhydride and ammonia gases, both perfectly dry, 
into cold absolute alcohol, separating the copious crys¬ 
talline precipitate by filtration from the greater part of 
the liquid, and heating it with absolute alcohol in a her¬ 
metically-sealed tube to 100° or above, when the liquid 
on cooling deposits the carbamate in large crystalline 
laminae.f I have not repeated any of these processes. 
I am able to add to them several others made out by 
myself. 
{el). By passing carbonic anhydride and ammonia gases 
into concentrated aqueous solution of ammonia, when the 
carbamate separates in crystals, which, when dried as well 
as possible by pressure between folds of bibulous paper, 
contain only a little carbonate. 
{e.) By digesting in a closed vessel an aqueous solution 
of ammonia, saturated -with the gas at a low temperature, 
with either the commercial carbonate, or any other car¬ 
bonate of ammonium, at a temperature of 20°-25° for 
thirty-six or forty hours, when the carbamate either 
crystallizes out at once on cooling, or will do so after 
cooling the solution, passing more ammonia gas into it, 
adding more carbonate, repeating the digestion as before, 
and then again cooling. This process has been already 
described in the account of the reactions of the normal 
and acid carbonates. The best carbonate to employ is 
the commercial carbonate, because it yields more of the 
carbamate, as might be anticipated from its composition. 
.(/•) By heating the commercial carbonate of ammonia 
mixed with a sufficient quantity of anhydrous potassium 
carbonate in a retort, immersed in a water-bath at a tem¬ 
perature carried slowly from about 50° to about 80°, and 
connecting the neck of the retort with a wide tube dip- 
ping under mercury, when the neck of the retort becomes 
incrusted with the carbamate in a translucent crystalline 
* Abstracted by the author from his paper in the Journal 
of the Chemical Society. 
t Poggendorff’s c Annalen,’ vol. xlvi. p. 373. Also Taylor’s 
‘ Scientific Memoirs,’ vol. ii. p. 98. 
X Direct conversion of ammonia carbamate into urea. 
Journal of the Chemical Society (2), vol. vi. p. 194. 
condition. The water-bath- is to be maintained at a tem¬ 
perature not much exceeding 60° C. until ammonia gas, 
which is at first generated in large quantities, has nearly 
ceased to escape through the mercury. The temperature 
of the bath is then to be raised, but not so rapidly as to 
cause any material escape of gas through the mercury. 
{g.) By distilling, as in the last process, a mixture of 
the commercial carbonate of ammonia and anhydrous 
calcium chloride, when an incrustation forms, similar in 
every respect to that obtained in the last case, which is 
the carbamate. At a temperature of the water-bath of 
about 48° a considerable quantity of carbonic anhydride 
escapes through the mercury, and at about 52° the in¬ 
crustation begins to form, and continues to do so with 
very little further escape of gas, while the temperature 
is allowed to rise very slowly to 65°, a temperature which 
is sufficient to carry the process to its completion. 
(A.) By distilling the commercial carbonate extremely 
slowly, when the more remote part of the earlier formed 
incrustation will be found to be impure carbamate. I 
have obtained samples from an incrustation thus pre¬ 
pared, in which six-sevenths and five-sixths respectively 
of the contained ammonia were in the state of carbamate. 
There are no sensible qualities by which the composition 
of the product can be inferred, so that it is quite pos¬ 
sible, indeed, more probable than not, that parts of the 
incrustation were more nearly pure carbamate than the 
samples selected for analysis proved to be. This process 
is, of course, only of interest from a theoretical point of 
view. The product obtained by Rose by a similar pro¬ 
cess is not the same as that obtained by me, a fact which 
admits of a ready explanation, as will be presently seen. 
{i.) By distilling the normal carbonate at a heat not 
exceeding 60°, when a solid condenses containing even 
less water than the product of method (A). 
(j.) By repeatedly dissolving commercial carbonate at 
a gentle heat in the same quantity of water, cooling after 
each addition, and separating the crystals, as already de¬ 
scribed, until crystals of normal ammonium carbonate 
are deposited; then once more warming the solution, 
dissolving a fresh quantity of commercial salt in it, allow¬ 
ing it to cool and crystallize for a day, separating the 
crystals, passing ammonia gas, straining off or not (as may 
be necessary) the precipitate of normal carbonate pro¬ 
duced, renewing or continuing the stream of ammonia till 
the solution (kept cool) is about saturated, and straining 
off the precipitate of normal carbonate, when the solution 
will prove by its reactions to be apparently a solution 
of carbamate with a little carbonate dissolved in it. I 
think it not unlikely that by carrying this process fur¬ 
ther, with some modification, crystals of carbamate might 
be obtained; but I have made no experiments in this 
direction. 
(A.) By distilling the commercial carbonate with 
strong spirit, or, probably better still, with absolute alco¬ 
hol. The carbamate is wet—mixed with water and 
spirit—but contains very little carbonate. 
Sensible Qualities .—Ammonium carbamate has a strong 
smell of ammonia, but not at all equal to that of the 
normal, or even half-acid, carbonate. As regards its 
taste also, it is strongly ammoniacal, but without the 
causticity of the normal carbonate. 
Form .—It occurs in the form of flocculi; of an incrus¬ 
tation more or less crystalline; of prisms found some¬ 
times projecting from this incrustation; of crystalline 
laminae (Kolbe and Basaroff); and of crystals neither 
tabular nor decidedly elongated or columnar. 
Of the system of the last-named crystals, I am unable 
to speak with any degree of assurance, but they seem to 
belong to either the right or the oblique rhombic pris¬ 
matic system. They frequently occur massed together, 
like crystals of alum, one crystal capping the other, as it 
were. When solitary they are not only of no groat size, 
but also are rapidly deprived of their angles and edges 
by the changes they undergo. When their growth is 
not interfered with by contact with each other and with 
