PRUSSIC ACID 429 



vaseline or collodion. lodof ormin, a white, odourless powder, 

 insoluble in water, alcohol, ether, and chloroform, containing 

 75 per cent, of iodoform ; and iodoformal, the product of 

 the action of ethyl iodide on iodoformin, having a strong 

 odour of coumarin, are sometimes employed in place of 

 iodoform. 



PRUSSIC OR HYDROCYANIC ACID 



ACIDUM HYDROCYANICUM DILUTUM. An aqueous solution 

 containing 2 per cent, by weight of hydrogen cyanide, 

 HCN. (B.P.) 



Prussic acid was so called from being first obtained from 

 Prussian blue. Its title of hydrocyanic acid is derived from 

 its being composed of hydrogen and the compound radicle 

 cyanogen. It is one of the products of the distillation of 

 coal, and traces are found in imperfectly purified coal-gas. 

 The leaves and kernels of various stone fruits of the apple 

 and almond natural orders, when crushed and moistened, 

 undergo a species of fermentation, their albuminoid emulsin 

 decomposing the glucoside amygdalin, and producing hydro- 

 cyanic acid, benzaldehyde, and glucose. 



Prussic Benzalde- 

 Amygdalin. Water. Acid. hyde. Glucose. 



C 20 H 27 NO n + 2H 2 = HCN + C 7 H 6 + 2C 6 H 12 6 . 



Medicinal hydrocyanic acid may be prepared by the inter- 

 action of diluted sulphuric acid and potassium ferrocyanide. 



The anhydrous acid is obtained by cautiously distilling 

 the medicinal acid, and collecting the vapour in a receiver 

 kept cold by ice. It is a colourless, very volatile, inflam- 

 mable liquid, and, alike in its gaseous and liquid forms, is 

 a most active, deadly poison. 



The medicinal acid, when freshly prepared, contains two 

 per cent, of anhydrous acid, but on account of its volatility 

 it is apt to lose strength. This may be obviated by keeping 

 it in stoppered bottles, tied over with some impervious 

 covering, laid down inverted and in a dark place. It is 

 colourless, with a diffusible, peculiar odour. Specific 

 gravity, '997. It only slightly reddens litmus. Evapor- 



