Blue Compounds of Cyanogen and Iron. 167 



from common prussian blue by its darker colour. It was 

 washed in the usual manner and dried at a temperature of 

 from 30° to 40°. 



I. 1*400 grm. burnt in an open porcelain basin gave 

 0*6487 peroxide of iron, corresponding to 32*1 per cent. iron. 



II. 1*0365 grm. gave 0-481 peroxide of iron, correspond- 

 ing to 32-0 per cent. iron.. 



III. 1-0035 grm. gave 0-463 peroxide of iron, correspond- 

 ing to 31-8 per cent. iron. 



Burned with chromate of lead, — 



I. 0-6934 grm. gave 0*4405 carbonic acid and 0-1919 

 water, corresponding to 17*3 per cent, carbon and 27*9 per 

 cent, water. 



II. 0-415 grm. gave 0-269 carbonic acid and 0*127 water, 

 corresponding to 17*7 per cent, carbon and 28*6 water. 



III. 0*304 grm. gave 0*233 carbonic acid and 0*119 water, 

 corresponding to 17'4 per cent, carbon and 20 - water. 



Nitrogen determination according to Will's method : — 



I. 0*4065 grm. gave 0*3077 chloride of platinum and am- 

 monium, corresponding to 20*2 per cent, nitrogen and 0*574 

 platinum. 



II. 0*543 grm. gave 1*780 chloride of platinum and am- 

 monium, corresponding to 20*6 per cent, nitrogen and 0*780 

 platinum. 



The following table shows the degree of approximation to 

 the formula Fe 7 Cy 9 : — 



In each combustion fresh-prepared substance was taken. 

 The slight excess of iron and loss of carbon and nitrogen are 

 doubtless to be attributed, in spite of the precautions taken to 

 prevent it, to a decomposition having taken place during the 

 drying, by which hydrocyanic acid was set free, as indeed 

 might be recognised by the smell, and peroxide of iron formed. 

 The oxygen combined with iron is in the table calculated as 

 water, hence the deficiency of water. This decomposition, 

 which takes place very easily, explains the formation of the 

 so-called basic prussian blue, a substance considered as a 

 compound of prussian blue and peroxide of iron, but of which 

 little is known. 



3Cfy 4Fe + 3aq-3CyH = 2Cfy 3Fe + Fe 2 3 . 



By the action of light a process of reduction takes place, 



