Blue Compounds of Cyanogen and Iron. 159 



advantage. This liquid, in which the white salt, prepared as 

 above described, is suspended, is heated in an open basin, 

 during which the liquid is frequently stirred. At a low tem- 

 perature no apparent action ensues ; but when the liquid has 

 nearly reached the boiling-point, an evolution of nitric oxide 

 commences, which gradually increases in briskness, and is 

 accompanied by a speedy change of the white colour to dark 

 blue. As soon as this action has commenced, the basin must 

 be removed from the fire to prevent too violent an action, 

 which would cause the admixture of another substance. If 

 the correct proportion of white salt to acid has been used, the 

 action continues without further heating until the transforma- 

 tion into the blue compound is complete. If, however, the 

 colour should indicate that some of the white salt remains, a 

 small quantity more acid must be added, and the mixture, if 

 necessary, again heated. In order to proceed with certainty, 

 a small portion of the blue substance should be decomposed 

 with potash ; should the peroxide of iron which is thus set free 

 contain protoxide, the treatment with nitric acid must be con- 

 tinued ; the presence of ferridcyanide of potassium in the so- 

 lution indicates, on the contrary, that the action has gone too 

 far, in which case the operation must be recommenced w T ith 

 a fresh portion. In this manner a body of a beautiful violet 

 blue colour is formed, containing less potassium than the pre- 

 ceding one. The liquid contains nitrate of potash, but no 

 trace of iron. The substance prepared in this way was thrown 

 on a filter and washed out until the washings left no residue 

 on polished platinum. The compound was not in the least 

 degree affected by this treatment. It retained its original 

 colour, and contained no peroxide of iron soluble in muriatic 

 acid. After being carefully dried at 100° C, it was analysed 

 in the manner which I shall now proceed to describe. 



The cyanogen was completely oxidated by a gradually in- 

 creasing heat applied to it in an open flat-bottomed porcelain 

 crucible. It was thus converted into a mixture of peroxide 

 of iron and carbonate of potash, from which the alkali was 

 extracted by repeatedly boiling with water, and determined 

 as chloride. The residue was determined as peroxide of iron. 

 The cyanogen was determined indirectly by suspending a 

 weighed quantity of the compound in water and decomposing 

 it with potash. The peroxide of iron thus separated neces- 

 sarily corresponded to the quantity of percyanide, as all proto- 

 cyanide remained in solution in the form of yellow prussiate. 



I. 3*41.7 grms. gave 0*694 chloride of potassium and 1*630 

 peroxide of iron, corresponding to 10*6 per cent, potassium 

 and 32*4 per cent. iron. 



II. 4*225 grms. gave 0*871 chloride of potassium and 1*986 



