160 Dr. Williamson on the 



peroxide of iron, corresponding to 10*87 per cent, potassium 

 and 32*5 per cent. iron. 



Determination of Cyanogen. 



I. 3*744 grms. gave 0*940 peroxide of iron, corresponding 

 to 17'4 per cent, iron as cyanide. 



II. 6*125 grms. gave 1*585 peroxide of iron, corresponding 

 to 17*9 per cent, iron as cyanide. 



The formula Fe 4 Cy 6 K + 4Aq requires — 



Fe 4 108*8 = 32*0 



K 39*2 = 11*5 

 precipitated by potash — 



Fe 2 54*4 = 16*28 17'4 17'9. 

 The deficiency of potassium and corresponding excess of 

 iron are sufficiently accounted for by the imperfect separation 

 by water. The excess of peroxide of iron, corresponding to 

 the cyanide, was caused by its containing some of the potash 

 employed in its separation. In order, however, to remove all 

 doubt of the correctness of the formulas deduced from these 

 numbers, several combustions with chromate of lead were 

 performed with the greatest accuracy. These are as follows : — 



I. 0*427 grm. gave 0*331 C0 2 and 0*046 water, corre- 

 sponding to 21*14 per cent, carbon and 10*78 water. 



II. 0*320 grm. gave 0*247 C0 2 and 0*036 water, corre- 

 sponding to 21*05 per cent, carbon and 11*15 water. 



III. 0*721 grm. gave 0*559 C0 2 and 0*081 water, corre- 

 sponding to 21*14 per cent, carbon and 11*3 water. 



Calculated. I. II. III. 



C 12 . . 72 21*17 21*14 21*05 21*14 

 4Aq . 36 10*59 10*78 11*15 11*3 



The approximation here is sufficient. 



This compound is particularly remarkable for its brilliant 

 violet-blue colour. In a finely divided state, as is obtained 

 by suspension in a large quantity of water, it is transparent 

 with a gree* colour. It does not possess when dry the cop- 

 pery lustre so characteristic of prussian blue. It may be 

 viewed as ferridcyanide of potassium, in which 2 atoms of 

 potassium are replaced by iron, and it bears the same re- 



fFe 

 lation to the above-described white compound, Cfy< t^ , as 



Gmelin's salt to the yellow prussiate. The manner of its 

 formation is also the same, for 2 atoms ferrocyanide of iron 

 and potassium unite, giving up 1 atom of potassium, just as 

 in the case of yellow prussiate. 



2 (Cfy{| e ) + CI = 2Cfy{f ,e + KC1. 



