CYANIDES. 375 



the agency of heat. This metal retains cyanogen as 

 it does oxygen, but feebly. A method more commonly 

 employed is to produce and decompose the cyanide of 

 mercury at the same moment. This is effected by 

 mixing chloride of mercury, to furnish the metal, with 

 the double cyanide of iron and potassium, which fur- 

 nishes the cyanogen. The other elements unite to 

 form chlorides of iron and potassium, while the cyanide 

 of mercury is decomposed as fast as it is formed. The 

 double cyanide of iron and potassium, above referred to, 

 is the commercial yellow prussiate of potash. Two parts 

 of this salt are to be heated with one of bi-chloride of 

 mercury, in the above process. The prussiate cannot 

 be used alone for the production of cyanogen, on ac- 

 count of the firm retention of this radical by the 

 highly electro-positive metals which enter into the com- 

 position of the salt. 



How isc a- ^^* CYANIDE OF POTASSIUM. Cyanide 



nide of potas- of potassium is a white substance, resem- 



siumprepar- , .. ... , 



ed? Mention bling porcelain m appearance, and quite 

 soluble in water arid Alcohol. It is largely 

 employed in preparing solutions of the precious metals, 

 for galvanic gilding and silvering. It is produced on a 

 large scale, by fusing together carbonate of potash and 

 refuse animal matter. The latter furnishes the carbon 

 and nitrogen required for the production of cyangen, 

 while the carbonic acid and oxygen of the salt, are 

 principally evolved as oxide of carbon. The cyanide 

 of potassium is best extracted from this residue by alco- 

 hol, which leaves the other material undissolved. 



