July 80, 1870.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
93 
other one seen in the large broad crystals being very 
small, as shown in the margin. The end faces 
\ of large, long prisms are generally very im¬ 
perfect, but the outline of the broad sides is 
most like that in the small prisms. Masses of 
minute crystals, such as are at first obtained 
by method (5), form, when successfully dried, 
soft, lustrous flakes. When proof spirit is added to a 
concentrated solution of the carbonate, strong in ammo¬ 
nia, so as to avoid immediate precipitation, minute crystals 
form, and soon render the fluid semi-solid ; shortly after¬ 
wards, larger prisms often shoot across the semi-fluid 
mass. A phenomenon like the last also generally occurs 
when the semi-solid mass obtained by method ( b) is 
cooled in ice, nitre-like prisms shooting across it. When 
only a very little spirit is used, short, broad prisms 
sometimes form at the base of the clear solution. A so¬ 
lution not too strong in ammonia, mixed with a suitable 
quantity of spirit, and left to stand in a covered vessel, 
becomes filled with interlacing, apparently four-sided 
prisms. 
Chemical Composition. 
C 0 2 (0 H 2 ) 2 (N H 3 ) 2 . 
Carb.anhyd. 
Amm. 
Eound 38T5 
27-85 
33 
37-43 
28-59 
33 
38-44 
— 
33 
39-84 
28-21 
33 
39-15 
26-50 
33 
— 
26-23 
33 
38-33 
28-98 
33 
39-42 
— 
33 
— 
27-85 
3 ) 
— 
27-82 
33 
— 
29-00 
Calc. 
. 38-60 
29-82 
Wafer. 
31-58 
Behaviour on Exposure. —Ammonium carbonate gets 
very damp when exposed to the air. A similar change 
takes place in the half-acid ammonium carbonate, and 
has been specially pointed out by Deville. Before crys¬ 
tals of the ammonium carbonate can be dried, they lose 
their lustre, and become semi-opaque and moist, but re¬ 
tain their general shape; when pressed, they break down 
to a mass of wet acid carbonate. This change is not the 
result of absorption of moisture from the air, but of the 
instability of the salt in an atmosphere not charged with 
the products of its own decomposition; for the action 
goes on in a stoppered bottle until the air in the bottle is 
thus affected, and the salt is wet. The change may be 
thus represented:— 
C 0 2 (0 H 2 ) 2 (N h 3 ) 2 = c o 2 9 h 2 n h, + o h 2 + n h 3 . 
It is because -of this evolution of moist gas that a feel¬ 
ing of dampness in the paper used to dry the salt must 
not be regarded as proof that some adhering moisture 
has not been removed from it. 
Behaviour when heated. —At about 58° ammonium car¬ 
bonate is converted into water, carbonic anhydride, and 
ammonia, when surrounded by an atmosphere formed of 
products of its own decomposition. When first heated 
by a water-bath in a retort connected with a tube dip¬ 
ping under mercury, signs of decomposition are appa¬ 
rent by the formation in the retort-neck of drops of fluid 
and the fibrous crystals already described when the ther¬ 
mometer in the bath registers about 49° or 50°, but the 
progress of the change is soon arrested unless the tem¬ 
perature is raised, and no marked and continuous change 
is effected until the water-bath is at a temperature of 
about 59° or 60°. By maintaining the temperature of 
the bath at 60° no gas escapes from the apparatus, a 
moist, solid distillate is formed in the neck of the retort, 
and the contents of the retort gradually liquefy. Both 
the residual liquid and the solid distillate contain the 
ammonia in normal proportion to the carbonic anhy¬ 
dride, but the solid is too deficient in water, that moisten¬ 
ing included, to allow of its being represented as an 
ammonium carbonate, while the fluid in the retort is a 
solution of the normal carbonate, and, provided the 
operation is not carried too far, crystallizes out on cool¬ 
ing. The crystals have not been analysed, but they 
were evidently the normal carbonate. The product of 
the distillation was analysed. 
If the heat be carried some degrees beyond 60°, am¬ 
monia escapes during the distillation, and more water 
rises in vapour with the other constituents. In this case 
the condensed salt is very moist, but still has not suffi¬ 
cient water to constitute it an ammonium salt of carbonic 
acid, and, besides, is wanting in ammonia. I shall have 
again to refer to these products of distillation, and will 
then give the numerical data of my analyses. The de¬ 
composition of the salt by heat is thus represented:— 
C 0 2 (O H 2 ) 2 (N H 3 ) 2 = C 0 2 + 2 0 H 2 + 2 N H s , 
and is therefore quite distinct from that it undergoes by 
free exposure to the air. 
Behaviour with Water. —Ammonium carbonate is so¬ 
luble in its own weight of water, or slightly more, at 15°. 
By cooling the solution contained in a closed vessel, some 
of the salt crystallizes out again, but mixed with other 
carbonates. 
The saturated solution is of somewhat oily consistence. 
It smells very strongly of ammonia. Exposed freely to 
the air it loses ammonia. Heated, it begins to effervesce 
between 70° and 75°, and boils freely between 75° and 
80°, yielding vapours which condense into a moist solid. 
After boiling for awhile, and then cooling the solution, 
it is found to be unchanged in properties, except that it 
is weaker. 
A warm saturated solution of ammonium carbonate 
exhibits the phenomenon of supersaturation and sudden 
crystallization in a well-marked manner when it is 
allowed to cool in a closed flask. If the solution does 
not crystallize while left at rest, it will do so suddenly on 
stirring it with a glass rod or pouring it out into another 
vessel. 
Behaviour with Alcohol .—Ammonium carbonate is in¬ 
soluble in alcohol. Crystals of it, treated with rectified 
spirit, are converted into acid carbonate and free am¬ 
monia. An aqueous solution of it is precipitated by al¬ 
cohol, the precipitate being acid carbonate, or interme¬ 
diate in composition to this and normal carbonate. 
Behaviour with Ammonia- Water. —Ammonium carbo¬ 
nate dissolves in ammonia-water only very sparingly at 
a low temperature, but, by digestion at ordinary tem¬ 
peratures, the quantity dissolved becomes greater. 
Strong ammonia-water, added to a concentrated solution 
of the carbonate, precipitates it unchanged. Ammonia 
gas, passed into a moderately strong solution, has the- 
same effect. In cases -tfhere no precipitate is produced, 
the mixture will generally deposit some of the salt when 
cooled in ice. The small solubility of ammonium car¬ 
bonate in ammonia-water is a fact which is most ser¬ 
viceable in preparing it. Thus, nearly all the methods- 
already given, including, perhaps, that in which the salt, 
is precipitated by spirit from a weak ammoniacal solution, 
depend upon this influence of ammonia. 
Conversion of the Carbonate into Carbamate. —But am¬ 
monia has a much more remarkable effect upon ammo¬ 
nium carbonate than that described in the last para¬ 
graph. By digesting crystals of the salt with water 
saturated at a low temperature with ammonia, gas for 
two or more days at a temperature of 20° to 25°, they 
dissolve in apparently unlimited quantity, and are- 
changed into ammonium carbamate. The mode of pro¬ 
ceeding is similar to that adopted in method (5) for¬ 
getting ammonium carbonate in minute crystals. Some 
of the strongest ammonia-water of commerce is placed in 
a wide-mouthed bottle, surrounded by ice, and treated 
with a rapid stream of ammonia gas ;* a third of its 
* During the passage of the gas the bottle is loosely closed 
by a cork, perforated to admit the gas delivery-tube, so as to 
diminish loss by diffusion. 
