PRUSSIC ACID IN MEDICINAL PRUSSIC ACID, ETC. 
253 
ed in small boxes filled with poppy-leaves, and sent to the ba- 
zaars, where they are sold by okkas and dramms. — Archiv der 
Pharmucie, September, 1850, p. 293. 
PROCESS FOR DETERMINING THE AMOUNT OF PRUSSIC ACID 
IN THE MEDICINAL PRUSSIC ACID, BITTER ALMOND AND 
CHERRY-LAUREL WATERS. 
By Prof. J. Liebig. 
When a solution of caustic potash is added to a liquid contain- 
ing prussic acid until it has a strong alkaline reaction, and a di- 
lute solution of nitrate of silver is then slowly poured into it, a 
precipitate is formed, which on agitation immediately disappears 
again to a certain limit. When the prussic acid is mixed with a 
solution of caustic potash and a few drops of chloride of sodium, 
and then the solution of silver added, a certain proportion of 
the latter may be added as in the previous case before a perma- 
nent precipitate forms, which in this case is white chloride of 
silver. 
The liquid containing prussic acid, when mixed with potash, 
contains cyanide of potassium, in which the oxide or chloride of 
silver are soluble, until the well-known double compound, consist- 
ing of equal equivalents of cyanide of potassium and cyanide of sil- 
ver, is formed, and which is not decomposed by excess of potash. 
When, therefore, the amount of silver in the solution is known, 
and at the same time how much of it in volume or weight has been 
added to the alkaline liquid containing the prussic acid, until the 
formation of a precipitate, we can thence determine the amount of 
cyanogen or prussic acid in the liquid, for 1 equiv. of con- 
sumed silver exactly corresponds to 2 equivs. of prussic acid. 
The following experiments by Dr. Fleitmann will show the ac- 
curacy of the method. In the first place, the amount of prussic 
acid in a very dilute solution was determined directly by precipi- 
tation with nitrate of silver ; 100 cub. centim. of this prussic acid 
furnished 0*332 grm. cyanide of silver, corresponding to 067 per 
