To compare my synthesis of nitrate of ammoniac with analysis, I
endeavoured to separate the ammoniac and nitric acid from each other,
without decomposition. But in going through the analytical process, I
soon discovered that it was impossible to make it accurate, without
many collateral laborious experiments on the quantities of ammoniac
soluble in water at different temperatures.
At a temperature above 212°, I decomposed, by caustic slacked lime, 50
grains of compact nitrate of ammoniac in a retort communicating with
the mercurial airholder, the moisture in which had been previously
saturated with ammoniac. 22 cubic inches of gas were collected at 38°,
and from the loss of weight of the retort, it appeared that 13 grains
of solution of ammoniac in water, had been deposited by the gas.
Now evidently, this solution must have contained much more alkali in
proportion to its water than that of 55°, otherwise the quantity of
ammoniac in 50 grains of salt would hardly equal 8 grains.[77]
[77] The accounts given by different chemists of the composition of
nitrate of ammoniac, are extremely discordant; they have been chiefly
deduced from decompositions of carbonate of ammoniac (the varieties of
which have been heretofore unknown) by nitrous acids of unknown degrees
of nitration. Hence they are particularly erroneous with regard to the
alkaline part. Wenzel supposes it to be 32 per cent, and Kirwan 24.
_Addit. Observ._ pag. 120.
IX. _Of the loss of Solutions of Nitrate of Ammoniac during
evaporation._
The most concentrated solution of nitrate of ammoniac capable of
existing at 60°, is of specific gravity 1,304, and contains 33 water,
and 67 fibrous salt, per cent. When this solution is evaporated at
temperatures between 60° and 100, the salt is increased in weight by
the addition of water of crystalisation, and no portion of it is lost.
During the evaporation of solutions of specific gravity 1,146 and 1,15,
at temperatures below 120°, I have never detected any loss of salt.
When the temperature of evaporation is 212°, the loss is generally from
3 to 4 grains per cent; and when from 230° to the standard of their
ebullition, from 4 to 6 grains.
In proportion as solutions are more diluted, their loss in evaporation
at equal temperatures is greater.