It is generally prepared from the ammoniacal liquor obtained as a by-product on distilling coal.
The liquid products of the destructive distillation of coal are tar and ammoniacal liquor.
The ammoniacal liquor must be treated with hydrosulphuret of ammonia as long as it is clouded, then thrown upon a filter.
It should be provided with an overflow pipe for the tar and ammoniacal liquor.
By adding sulphuric acid to the ammoniacal liquor distilled over from the coal, &c., the salt is crystallized out.