FERROCYANIDE OF POTASSIUM. 257 



sent 0.5 grm. of anhydrous hydrocyanic acid, or 0.481 

 cyanogen, or 1.206 of cyanide of potassium. 



127. FERROCYANIDE OF POTASSIUM. 



2 K Cy -f-Fe Cy + 8 HO=K 2 Cfy + 3 HO. 



The water is determined by heating the finely-pow- 

 dered salt for some time to about 200. 



The cyanogen can be directly determined only by 

 an organic analysis, i. e., by a combustion. 



For the determination of the amount of iron, the 

 salt is intimately mixed with 1J parts of nitre, and as 

 much carbonate of soda, and the mixture gradually 

 heated to redness in a platinum crucible. On dissolving 

 the fused mass in water, the iron remains behind in 

 the form of sesquioxide, which is washed, ignited, and 

 weighed. Since it is liable to contain a small amount 

 of alkali, it should be dissolved in hydrochloric acid, 

 reprecipitated by ammonia, washed and ignited. 



In order to determine the potassium and iron, the 

 salt is dissolved in water, and the solution precipitated 

 by acetate of lead. The precipitate of ferrocyanide of 

 lead is filtered off* and washed. 



From the solution, which contains all the potassium 

 as acetate of potassa, the excess of lead is precipitated 

 by sulphuretted hydrogen or sulphide of ammonium, 

 the filtered solution evaporated, the residue ignited, 

 the carbonate of potassa converted, by hydrochloric 

 acid, into chloride of potassium, and weighed in that 

 form, after gentle ignition. The ferrocyanide of lead 

 is decomposed by digestion with sulphide of ammonium, 

 the solution of ferrocyanide of ammonium filtered off, 



