_Of approximations to the quantities of AMMONIAC,
such as exists in the aëriform state, saturated with
water at 52°, in AQUEOUS AMMONIACAL SOLUTIONS of
different specific gravities._
+----------+-----+----------+--------+
| 100 | | Ammoniac.| Water. |
| Specific | | | |
| Gravity. | | | |
+----------+ +----------+--------+
| 9054 | | 25,37 | 74,63 |
| 9166 | | 22,07 | 77,93 |
| 9255 | | 19,54 | 80,46 |
| 9326 | c | 17,52 | 82,48 |
| 9385 | o | 15,88 | 84,12 |
| 9435 | n | 14,53 | 85,47 |
| 9476 | t | 13,46 | 86,54 |
| 9513 | a | 12,40 | 87,60 |
| 9545 | i | 11,56 | 88,44 |
| 9573 | n | 10,82 | 89,18 |
| 9597 | | 10,17 | 89,83 |
| 9619 | | 9,60 | 90,40 |
| 9684 | | 9,50 | 90,50 |
| 9639 | | 9,09 | 90,91 |
| 9713 | | 7,17 | 92,83 |
+----------+-----+----------+--------+
As yet no mode has been discovered for obtaining
gases in a state of absolute dryness; consequently
we are ignorant of the different quantities
of water they hold in solution at different
temperatures. As far as we are acquainted with
the combinations of ammoniac, there is no state
in which it exists so free from moisture, as when
aëriform, at low temperatures.
That no considerable source of error existed in the two experiments,
is evident from the trifling difference between the estimations of the
quantities of real ammoniac, in the solution of,9684, as found in the
first experiment, and as given by calculation from the last.
The quantity of ammoniac in a solution of specific gravity not in the
table, may be thus determined—find the difference between the two
specific gravities nearest to it in the table; _d_, and the difference
between their quantities of alkali, _b_; likewise the difference
between the given specific gravity and that nearest to it, _c_.
then _d_ : _b_ :: _c_ : _x_
_bc_
and _x_ = —————
_d_
Which, added to the quantity of the lower specific gravity, is the
alkali sought.
The differences in specific gravity of the solutions of ammoniac at
temperatures between 4O° and 65°[70] are so trifling as to be hardly
ascertainable, by our imperfect instruments, and consequently are
unworthy of notice.
[70] The expansion from increase of temperature is probably great in
proportion to the quantity of ammoniac in the solution.
It is possible at very low temperatures to obtain ammoniacal solutions
of less specific gravity than,9, but they are incapable of being kept
for any length of time under the common pressure of the atmosphere.
IV. _Combinations of Ammoniac with Nitric Acid, Composition of Nitrate
of Ammoniac, &c._
200 grains of ammoniacal solution, of specific gravity,9056, were
saturated by 385,5 grains of nitric acid, of specific gravity 1,306.
The combination was effected in a long phial, the nitrous acid added
very slowly, and the phial closed after every addition, to prevent any
evaporation in consequence of the great increase of temperature.[71]
The specific gravity of the solution, when reduced to the common
temperature, was 1,15. Evaporated at a heat of 212°,[72] it gave 254
grains of salt of fibrous crystalization. This salt was dissolved in
331 grains of water; the specific gravity of the solution was 1,148
nearly.
[71] From the combination.
[72] I had before proved that at this temperature the salt neither
decomposed nor sublimed.
Hence it was evident that some of the salt had been lost during the
evaporation.
To find the quantity lost, fibrous nitrate of ammoniac was dissolved
in small quantities in the solution, the specific gravity of which was
examined after every addition of 3 grains. When 16 grains had been
added to it, it became of 1,15.
Consequently, the solution composed of 200 grains of ammoniacal, and
of 385,5 of nitric acid solution, contained 262 grains of salt of
fibrous crystalization, and of this salt 8 grains were lost during the
evaporation.
But the alkali in 200 grains of ammoniacal solution of,9056 = 50,5
grains. And the true nitric acid in 385,5 grains of solution of 1,306 =
190 grains.
Then 262-240,5 = 21,5, the quantity of water.
And 262 grains of fibrous crystalized nitrate of ammoniac, contain 190
grains true acid, 50,5 ammoniac, and 21,5 water. And 100 parts contain
72,5 acid. 19,3 ammoniac, and 8,2 water.
In proportion as the temperature employed for the evaporation of
nitro-ammoniacal solutions, is above or below 212°, so in proportion
does the salt produced contain more or less water than the fibrous
nitrate. But whatever may have been the temperature of evaporation, the
acid and alkali appear always to be in the same proportions to each
other.
Of the salts containing different quantities of water, two varieties
must be particularly noticed. The prismatic nitrate of ammoniac,
produced at the common temperatures of the atmosphere, and containing
its full quantity of water of crystalisation; and the compact nitrate
of ammoniac, either amorphous, or composed of delicately needled
crystals, formed at 300°, and containing but little more water than
exists in nitric acid and ammoniac.
To discover the composition of the prismatic nitrate of ammoniac, 200
grains of fibrous salt were dissolved in the smallest possible quantity
of water, and evaporated in a temperature not exceeding 70°. The
greater part of the salt was composed of perfectly formed tetrahædral
prisms, terminated by tetrahædral pyramids. It had gained in weight
about 8,5 grains.
Consequently 100 grains of prismatic nitrate of ammoniac may be
supposed to contain 69,5 acid, 18,4 ammoniac, and 12,1 water.
To ascertain the composition of the compact nitrate of ammoniac, I
exposed in a deep porcelain cup, 400 grains of the fibrous salt, in a
temperature below 300°. It quickly became fluid, and slowly gave out
its water without any ebullition, or liberation of gas. When it was
become perfectly dry, it had lost 33 grains. I suspected, that in this
experiment some of the salt had been carried off with the water; to
determine this, I introduced into a small glass retort, 460 grains of
fibrous salt; it was kept at a heat below 320°, in communication with a
mercurial apparatus, in a regulated air-furnace, till it was perfectly
dry: it had lost 23 grains. No gas, except the common air of the retort
came over, and the fluid collected had but a faint taste of nitrate of
ammoniac.
Though in this experiment I had removed all the fluid retained in the
neck of the retort, still a few drops remained in the head, and on
the sides, which I could not obtain. It was of importance to me to be
accurately acquainted with the composition of the compact salt, and for
that reason I compared these analytical experiments with a synthetical
one.
I saturated 200 grains of solution of ammoniac, of,9056 with acid,
ascertained the specific gravity of the solution, evaporated it at
212°, and fused and dried it at about 300°-260°. It gave 246 grains
of salt, and a solution made of the same specific gravity as that
evaporated, indicated a loss of 9 grains. Consequently, 255 grains of
this salt contain 50,5 grains alkali, 100 grains acid, and 14,5 grains
water.
We may then conclude, that 100 parts of compact nitrate of ammoniac
contain 74,5 acid, 19,8 alkali, and 5,7 water.