552 CONSIDERATION OF CARBON COMPOUNDS. 



ammonia, soluble in alkali cyanides or thiosulphates, but insoluble 

 in diluted nitric acid. 



HCN + AgNO 3 = AgCN -f HNO 3 . 



2. Hydrocyanic acid, mixed with yellow ammonium sulphide and 

 evaporated to dry ness, forms sulphocyanic acid, which, upon being 

 slightly acidulated with hydrochloric*acid, gives with ferric chloride 

 a blood-red color of ferric sulphocyanate. (Excess of ammonium 

 sulphide must be avoided.) 



3. Hydrocyanic acid, or soluble cyanides, give, when mixed with 

 ferrous and ferric salts and potassium hydroxide, a greenish precipi- 

 tate, which, upon being dissolved in hydrochloric acid, forms a pre- 

 cipitate of Prussian blue, Fe 4 (FeC 6 ]S" 6 ) 3 . This reaction depends on 

 the formation of potassium ferrocyanide by the action of the cyanogen 

 upon both the potassium of the potassium hydroxide and the iron of 

 the ferrous salt. In alkaline solutions, the blue precipitate does not 

 form, for which reason hydrochloric acid is added. 



4. Hydrocyanic acid heated with dilute solution of picric acid gives 

 a deep-red color on cooling. 



In cases of poisoning, the matter under examination is distilled (if neces- 

 sary after the addition of water) from a retort connected with a cooler. To 

 the distilled liquid the above tests are applied. If the substance under ex- 

 amination should have an alkaline or neutral reaction, the addition of some 

 sulphuric acid may be necessary in order to liberate the hydrocyanic acid. 

 The objectionable feature to this acidifying is the fact that non-poisonous 

 potassium ferrocyanide might be present, which upon the addition of sulphuric 

 acid would liberate hydrocyanic acid. In cases where the addition of an acid 

 becomes necessary, a preliminary examination should, therefore, decide 

 whether or not ferro- or ferricyanides are present. 



Antidotes. Hydrocyanic acid is a powerful poison both when inhaled or 

 swallowed in the form of the acid or of soluble cyanides. As an antidote is 

 recommended a mixture of ferrous sulphate and ferric chloride with either 

 sodium carbonate or magnesia. The action of this mixture is explained ia 

 the above reaction 3, the object being to convert the soluble cyanide into an 

 insoluble ferrocyanide of iron. In most cases of poisoning by hydrocyanic 

 acid there is, however, no time for the action of such an antidote, in conse- 

 quence of the rapidity of the action of the poison, and the treatment is chiefly 

 directed to the maintenance of respiration by artificial means. 



About ten years ago, hydrogen dioxide was proposed as an antidote, by 

 which hydrocyanic acid is converted into the harmless oxamide, CONH 2 

 CONH 2 . A solution of hydrogen dioxide is introduced into the stomach and 

 then siphoned out. It is also used subcutaneously. In case a cyanide is the 

 poison, vinegar may be mixed with the hydrogen dioxide solution given inter- 

 nally in order to liberate the hydrocyanic acid. 



Cyanogen derivatives obtained directly from nitrogen of the atmos- 



