December s, 1870.] THE PHAEMACEUTICAL JOURNAL AND TRANSACTIONS. 
445 
crystalline particles of the normal carbonate, they are 
perfectly transparent. The incrustation consists of 
prisms arranged perpendicularly to the surface of forma¬ 
tion. The translucency of the mass attains a high de¬ 
gree of perfection in those parts formed nearest to the 
source of heat. Fragments from this part of the incrus¬ 
tation appear almost perfectly transparent when thrown 
into water. In appearance this form of the carbamate 
differs little, if at all, from a similarly formed deposit of 
acid-carbonate—with one exception. This is in the parts 
formed near the source of heat, which acquire an in¬ 
creased translucency by the continued action of the heat 
employed in carrying on the process, and also undergo 
marked contraction, so as to exhibit gaping fissures, and 
become partly separated from the walls of the retort on 
which they rest. This phenomenon is always observed 
in the carbamate, whether formed by the action of potas¬ 
sium carbonate or calcium chloride, and never with hy¬ 
drated incrustations, according to my experience. The 
prisms which sometimes project from the free surface of 
the incrustation are thick and generally very short, but 
sometimes they pass right across to the opposite wall of 
the retort-neck or condensing-tube. 
Chemical Composition. —It is unnecessary for me to ad¬ 
duce evidence to prove that ammonium carbamate is 
composed, according to the formula— 
C0 2 (N HA-,, 
of 
Carbonic anhydride . . 56•41 
Ammonia.43'59 
100-00 
Behaviour on Exposure .—It evolves an odour of am¬ 
monia which, when a solid lump of it, or a crystal, is 
exposed freely to the air, rapidly diminishes in intensity; 
at the same time the carbamate gradually deliquesces ; 
by continuing the exposure it is nearly dissipated. The 
residue left is acid carbonate, generally in the form of a 
porous cast or superficial skeleton of the original frag¬ 
ment. 
The deliquescence of the carbamate is an interesting- 
fact, not only as affording further evidence that the car¬ 
bamate has only a slowly-manifested chemical affinity 
for water, but also as distinguishing between the mere 
physical attraction of a body for water, and its chemical 
transformation with water into a new substance. 
Behaviour when Heated .—Ammonium carbamate, un¬ 
like the true carbonates, does not fuse when heated. Ac¬ 
cording to John Davy it is converted into gas at 60° C. 
My own experiments very nearly confirm this statement. 
I was not able to fix the point very closely, but found it 
to be about 59°. 
It has been for many years familiar to chemists that 
the carbamate obtained from two volumes of ammonia 
and one volume of carbonic anhydride yields three 
volumes of vapour. A fact like this is now held by most 
chemists to be proof that a substance thus behaving is 
decomposed at the moment when it assumes the gaseous 
state. Bineau took the density of the vapour of the 
carbamate at ordinary temperatures,* and foimd it also to 
accord with the sum of the volumes of the ammonia and 
carbonic anhydride which form it. Another proof that 
it is decomposed when dissipated at ordinary tempera¬ 
tures, is to be found in the powerful odour of ammonia 
which is then perceived; for it is inconsistent with what 
we know for certain of the change in properties produced 
by chemical combination, to suppose that a compound of 
ammonia should smell like ammonia itself. 
Bineau has also furnished us with special evidence that 
the vapour, obtained by distilling carbamate, is nothing 
but a mixture of the two above-named gases. He ob¬ 
* “ Recherches sur les Densities dc Vapeur.” Ann. de Chimie, 
vol. lxviii. p. 416. 
served* that the gaseous product obtained by exposing 
the. salt to heat retains its gaseous state at a temperature 
which is lower than that at which it is formed. I am 
myself able to confirm this statement. 
Behaviour with Water. —One part of ammonium car¬ 
bamate dissolves in about one and a half parts of water, 
sensible cold being produced by the solution. It dis¬ 
solves unchanged, as is shown by the reactions of the 
solution immediately after it is prepared. But the car¬ 
bamate in solution soon combines with water and be¬ 
comes carbonate, according to this equation,— 
C0 2 (NH 3 ) 2 + 20H 2 =C0 4 (NH 4 ) 2 H 2 . 
Behaviour with Alcohol. —Ammonium carbamate is 
soluble in spirit of sp. gr. -829, according to John Davy. 
In absolute alcohol, when heated with it in a sealed 
tube, it dissolves, and crystallizes out when the solution 
is allowed to cool (Kolbe and Basaroff). I have made 
no experiments on this subject myself. 
Behaviour with Ammonia-water. —It dissolves freely in 
the strong ammonia-water of commerce, with production 
of cold. At 15° one part dissolves in a little more than 
two parts of the ammonia-water. The solution, left to 
itself for some time, yields crystals of the noimal carbo¬ 
nate. But when cooled down to about 0° soon after it is 
made, it yields the carbamate again in relatively large 
crystals. Ammonia, therefore, has the power, well 
marked, of impeding the hydration of the carbamate. 
To this fact is probably due the success in obtaining the 
carbamate from the carbonate by heating its solution in 
presence of ammonia. 
Iteactions which serve to distinguish the Carbamate from 
the Carbonates generally. —Rose has pointed out the fol¬ 
lowing : —The carbamate is not perceptibly affected by 
dry hydrochloric acid in the cold, and warmed in the 
acid is decomposed without liberation of water. In dry 
chlorine gas it is not at first affected, but is slowly de¬ 
composed without formation of water. It assumes in 
the cold a pale yellowish colour when placed in sulphu¬ 
rous anhydride. Heated in sulphuretted hydrogen gas, 
no water is produced. It yields carbonic anhydride 
ivithout effervescence when the vapours of sulphuric anhy¬ 
dride are passed over it. 
Besides these, it has a special reaction in solution with 
calcium chloride; when mixed with anhydrous calcium 
chloride it can be expelled by a gentle heat, leaving the 
chloride unchanged; it does not melt or become moist 
when heated, and it dissolves freely in strong- ammonia- 
water. Its becoming moist on exposure is not charac¬ 
teristic, as both the half-acid and the normal carbonates 
become moist also, though from a different cause. 
Chemical Constitution of the Carbamate. —Analogy has 
caused this salt to be regarded by Gerhardt, and most 
chemists after him, to be like the salts formed by the 
union of other anhydrides with ammonia; conclusive 
evidence on this point i3 still wanting. There are no 
metallic carbamates known. With calcium chloride and 
with barium chloride it does not, however, behave like 
ammonium carbonate; and this is probably due to the 
formation of a not very insoluble calcium carbamate. 
In connection with this point I may state that by adding 
to the solution obtained from the commercial carbonate 
by water—method if) —a concentrated solution of cal¬ 
cium chloride, I have obtained a crystalline precipitate 
not only somewhat soluble in its mother-liquor, but 
which, after being filtered off and pressed between bibu¬ 
lous paper, has sometimes proved almost perfectly so¬ 
luble in water, though in a few minutes its solution 
deposited calcium carbonate ; it did not smell of ammo¬ 
nia. I am not sure that this precipitate, however, was 
really calcium carbamate ; but I made analyses of it in 
its impuro and damp state, not venturing to wash it, and 
* “ Sur quelques Combinaisons ammoniacales et sur le role 
que joue l’Ammoniaque dans les reactions chimiques. ’ Ann. 
de Chimie, vol. lxvii. p. 249. 
