A NEW CLASS OF SALTS. 
483 
filtrate, from which the ferrocyanide of potassium was precipitated by alcohol ; the 
filtrate from this had all the properties of nitroprusside of potassium, and gave by 
precipitation with sulphate of copper 13'98 grs. nitroprusside of copper, equal to 
13'24 grs. nitroprusside of iron, or 37’80 per cent. 
The reactions in the preparation of the nitroprusside may now be approximatively 
explained. 
By reference to the ascertained composition of the nitroprussides, it will be seen 
that the 47*51 grs. of the copper nitroprusside obtained from the 105*5 grs. of yellow 
prusside, are equal to 35*69 grs. anhydrous nitropriissic acid : this quantity contains 
9*66 grs. of iron. Now 14 grs. iron were present in the yellow prusside used, so that 
about two-thirds of the iron have been converted into nitroprussic acid. The other 
third is in the green precipitate, which was found to contain 4*98 iron ; if it had 
been one-third it should have been 4*66; of this quantity 1*19 is as nitroprusside of 
iron, and therefore 0*59 as nitroprussic acid. Hence we have out of the 14 grs. iron 
present in the ferrocyanide 10*25 grs. converted into nitroprussic acid, or very 
nearly three-fourths ; the remaining one-fourth is partly as prussian blue and oxide of 
iron, and partly as the basic iron in the nitroprusside of iron. 
The quantity of carbon or of cyanogen converted into nitroprusside has now to be 
examined. The 47*5 1 grs. copper nitroprusside contain 9*93 grs. of carbon, that in the 
nitroprusside of iron of the green precipitate would amount to 0*60, hence the carbon 
converted into nitroprussic acid is 10*53. There were 3 equivs. or 18 grs. of carbon 
in the yellow prusside, of which about If equiv. has been converted into nitroprus- 
side ; of the remaining 7 ^ grs. carbon or 16*2 grs. cyanogen, about 0*38 gr. carbon 
or 0*823 gr. cyanogen remain in the green precipitate as a cyanide, the remainder 
escaping as a gas. It is true that the results here given only form a rude approxima- 
tion, but they denote sufficiently the final, though not all the intermediate changes 
which occur ; the ultimate action may be expressed by the following equation : — 
8(FeCy3-l-2K)-|-19(HO, N 05 ) = 16(K0,N05)-f-(Fe5 Cyi 2 3NO+5H) 
-|-Fe Cy-f-Fcg O 3 -I- 2 H Cy-}-9Cy-|- 12 HO. 
Thus 8 equivs. ferrocyanide of potassium lose their potash by 16 equivs. of nitric 
acid, and the hydroferrocyanic acid formed is oxidized at the expense of 3 equivs. 
nitric acid, the 3 equivs. of nitrous oxide thus formed entering into the constitution 
of nitroprussic acid, 12 equivs. of water being formed by the oxidation. Of the cva- 
nogen, 12 equivs. remain in the nitroprussic acid, 2 equivs. escape as hydrocyanic 
acid, 9 e(ijuivs. as cyanogen, and 1 equiv. remains united with iron as a cyanide. This 
scheme would require 10*04 grs. of the iron experimented on to be converted into 
nitroprussic acid, and direct experiment gave 10*2 grs. We should indeed find 
1*8 gr. cyanogen in the cyanide of iron*, whereas only 0 823 gr. cyanogen was found 
* The empirical formula Fe Cy represents the actual proportion of iron and cyanogen in certain prussian blues, 
although the elements are not arranged according to this simple expression. 
