u\-i'nV:i^a New Class of Salts. 205 



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 

 4f'66; of this quantity ri9 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 re- 

 maining 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 nitro- 

 prusside has now to be examined. The 4'7'51 grs. copper 

 nitroprusside contain 9*93 grs. of carbon, that in the nitro- 

 prusside 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 yel- 

 low prusside, of which about 1| equiv. has been converted 

 into nitroprusside; 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 approximation, 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 + 2K)+19(HO, N05) = 16(KO, N05)+ (Fe^Cy^^ 

 3NO + 5H) + FeCy + Fe^03 + 2HCy+9Cy + 12HO. 



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 con- 

 stitution of nitroprussic acid, 12 equivs. of water being formed 

 by the oxidation. Of the cyanogen, 12 equivs. remain in the 

 nitroprussic acid, 2 equivs. escape as hydrocyanic acid, 9 

 equivs, 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 in this state ; but when we consider 

 the small quantity present and the variable nature of prussian 

 blues, such a discordance is not fatal to the correctness of an 

 explanation, which is only given as an approximation. 



8. It has already been mentioned that carbonic acid was 



• 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. id 



