254 
PRUSSIC ACID IN MEDICINAL PRUSSIC ACID, ETC. 
cent, of acid. The same solution required for the complete pre- 
cipitation of a normal liquid containing in 100 cub. centim. \ a 
grm. of metallic silver, 53*5 cub. centim. 100 cub. centim. of the 
same prussic acid, mixed with potash, and then constantly shaken 
with the same solution of silver until the appearance of a milki- 
ness, required 27 cub. centim. 150 cub. centim. of the same prussic 
acid required 40 cub. centim. of the silver solution ; according to 
these experiments the liquid contained — 
By a measured quantity of 
normal liquid in 
alkaline solution. 
By Direct , A . acid 
determination. I. II. solution. 
Prussic acid 0-067 p. c. 0-068 0-067 0-067. 
Similar results w T ere obtained by M. Fabre. 
It follows from these experiments, that the method of determin- 
ing the amount of prussic acid in an alkaline liquid by means of 
a normal solution of silver is as trustworthy and accurate as any 
of the best methods hitherto employed ; whilst in several other re- 
spects, for instance the ease and quickness with which the experi- 
ment is made, it far surpasses them. 
The presence of formic acid or hydrochloric acid in the prussic 
acid, which would render the determination of its amount by a 
normal solution of silver inaccurate, has not the slightest influence 
on its estimation in the alkaline liquid ; and it has moreover the 
advantage, that as soon as the reaction becomes perceptible the 
operation is terminated, in which it is preferable to similar me- 
thods the completion of which depends on the cessation of the re- 
action. In the estimation in the alkaline liquid, both liquids that 
are mixed remain clear ; as soon as the slightest permanent milk- 
iness is perceptible, the analysis is finished, and to arrive at this 
point one or two minutes suffice. In ascertaining the quantity di- 
rectly by nitrate of silver, a precipitate is formed, which renders 
the liquid turbid ; towards the end of the operation it is necessary 
to wait until this has subsided and the liquid again become clear, 
in order to determine when no further precipitations occurs. Now 
with the dilute liquid the last traces of cyanide of silver settle with 
much greater difficulty than in the estimation of chlorine ; and it 
