238 
SELECTED ARTICLES. 
in twenty grammes of pure water. I then took two grammes 
of this solution and added them to 198 grammes of pure water. 
The whole liquid then represented 2-o,Voo ferrocyanate of 
potassa. This liquid, treated by the muriate of the peroxide 
of iron, afforded a very deep blue colour, and a little after, a 
deposit of Prussian blue which settled to the bottom of the 
vessel. This blue colouring was even very perceptible when 
the liquid contained only the ^o/oo q of the same salt of 
potassa. 
With the sulphate of copper the reddish brown tint appeared 
in a very distinct manner, in the first solution of I 
still was desirous of being convinced of the possibility of 
isolating, by the salt of silver, extremely minute proportions 
of hydrocyanic or prussic acid. For this purpose I made 
the following solutions: — gr., 1 decigramme of cyanuret 
of potassium was thrown into twenty grammes of distilled 
water, this solution formed an abundant reddish brown pre- 
cipitate with the permuriate of iron. Two grammes of this 
liquid were then added to 198 of water. There resulted a 
product of 2o,Vo^o' which the weakest solution of nitrate of 
silver formed a light flocculent deposit, capable of being 
collected after it had settled in a narrow vessel. I obtained 
in the same manner, a similar deposit with a liquid of 4-o,J-ooj 
and both the deposits, placed upon test glasses and treated in 
the way which will be mentioned directly, afforded a very 
appreciable amount of prussian blue, the presence of which 
could not be questioned. 
Upon the strength of these experiments, since they had 
been made upon the smallest scale, I endeavoured to detect 
hydrocyanic acid in complex liquids, as wine, broth, ferment- 
ed products, urine, and fluids obtained from the intestines and 
* I wished to prove at the same time the sensibility of sulphocyanuret 
of potassium by salts of the peroxide of iron. A liquid containing 
of this salt, gave me, with the muriate at a maximum^ a pretty intense red 
tint and with the ^-^^^ but with the scarcely the tint of onion peel. 
With the sulphate of copper and a deoxygenizing body with the 
there appeared a whitish cloudiness. 
20,000 ' " 
