174 ON THE MANUFACTURE OF PRUSSIATE OP POTASH. 
The mother liquor from the crude prussiate is concentrat- 
ed by evaporation 10 degrees of Baume's hydrometer and 
again allowed to stand two or three days. A copious deposit 
of white crystals now forms out of this liquor, which is called 
the salt.'^ From this " salt" by solution in hot water to 30° 
Baume, and crystallizing, from 10 to 15 per cent, of its weight 
of prussiate is obtained. The residue consists of various salts, 
chloride of potassium, carbonate of soda, and sulphate of 
potassa, from the impure potash used, phosphates of soda 
&c., from the animal material, various salts of ammonia 
and lime, traces of cyanides, ferrocyanides, sulphocyanides, 
&c. The largest portion being chloride of potassium, which 
forms a large per centage of impurity in commercial potash, 
the amount of this impurity, (at all times existing,) being 
sometimes increased by the fraudulent addition of common 
salt to the wood-ash ley, which by double decomposition 
forms chloride of potassium and carbonate of soda. 
The mother liquor from which the "salt" has crystallized 
consists chiefly of a solution of carbonate of potassa, which 
is recovered by evaporation to dryness, to be used again in 
the furnace. In this way about half the potash originally 
employed is recovered. 
As horn contains about fifteen per cent, of nitrogen, and 
crystallized prussiate of potash only about twenty per cent., 
it is obvious that theory would indicate a much larger pro- 
duct of prussiate than is obtained in practice. The great 
loss of nitrogen probably occurs chiefly in mixing the stuff 
with the potash; that portion which is decomposed before 
it is thoroughly incorporated with the fused potash being 
lost, the nitrogen passing away in the form of ammonia. 
There is also loss of nitrogen by generation of ammonia 
ill the solution of the cake, this gas being sensibly evolved 
from almost all the kettles in the prussiate factories ; from 
the liquor which is boiled down for the recovery of the pot- 
ash after the separation of the prussiate and "salt," a large 
quantity of ammonia is uniformly disengaged. This forma- 
