322 INORGA.NIC AGENTS 



Class 7. — Miscellaneous Carbon Compounds. 



AciDUM Hydrocyanicum Dilutum. 

 Diluted Hydrocyanic Acid. HON. (U. S. & B. P.) 



Synonym, — Prussic acid, acidum hydrocyanatum, s. 

 borussicum, E.;* acide cyanhydrique, s. hydrocyanique, Fr.; 

 cyanwasserstoffsaure, blausaure, G. 



Derivation. — A liquid composed of 2 per cent., by 

 weight, of absolute hydrocyanic acid, and 98 per cent, of 

 water. Obtained by distillation of ])otassium ferrocyanide, 

 20 ; sulphuric acid, 8 ; and water, 65 ; into distilled water. 

 The following reaction first occurs : K^ Fe Cg Ng + 2 Hg S 

 O4 = 2 K2 S 0^ + H^ Fe Cg N^ ; then on the application of 

 heat, the hydroferrocyanic acid resulting in the first reaction ' 

 reacts with the remaining potassium ferrocyanide and sul- 

 phuric acid, as follows : H, Fe C, Ng + K, Fe C, N^ + H^ S 

 O, = 6 H C N + K, S O, + K, Fe (Fe C, X). 



Diluted hydrocyanic acid can also be made by mixing 

 hydrochloric acid, 5 ; with distilled water, 55 ; silver cyanide, 

 6. Shake together in a glass- stoppered bottle. Ag C N + 

 H CI = H C N + Ag 01. When the precipitate of silver 

 chloride falls, pour off the clear, supernatant fluid. 



Properties. — A clear, colorless liijuid, of a characteristic 

 taste and odor, resembling those of bitter almond. It is 

 very unstable and is apt to be inert as obtained from ordi- 

 nary drug stores. It should be kept in inverted glass-stop- 

 pered dark bottles. 



Incompatibles. — Salts of iron, copper and silver ; sulphides 

 and red mercuric oxide. 



I)o8e.—K. & 0, 1l\xx.^xl. (1.3-2.6); Sh., y([x.-xY. (.6-1.); 

 Sw., 11lii.-v. (.12.3); D , nii.-iii. (.06-.2). 



Action External. — Prussic acid is absorbed to some 

 extent through the unbroken skin ; paralyzes the peripheral 

 sensory nerves, and acts as a local anaesthetic. If the finger 



* Scheele's prussic acid contains 4 to 5 per cent, of the pure hydro- 

 cyanic acid. 



