514 
DR. PLAYFAIR ON THE NITROPRUSSIDES, 
0*820 gr. water. Hence this changed purple compound, before complete transform- 
ation, contained in 100 parts, — 
Iron . . 
Sodium . 
Sulphnr. 
Carbon . 
Hydrogen 
Nitrogen ") 
Oxygen J 
100*00 
11*31 grs. were now boiled in water, and 0*94 gr. of the brown precipitate was 
obtained by filtration, and 5*90 grs. of prusside of sodium were precipitated by 
alcohol. Hence of the total quantity of 1*58 gr. of iron present 1*08 gr. was found in 
the ferrocyanide, the remainder being in the brown precipitate. As the ferrocyanide 
of sodium is of constant composition, which the brown mixture is not, the iron in the 
latter is here estimated by loss and would amount to 0*50 gr. The proportion in 
equivalents is nearly, though not exactly, as 7 : 3, which would have made the iron in 
the brown precipitate 0*46 gr. instead of 0*50 gr.. 
Taking these proportions as leading to a general view of the transformation, it 
may be expressed by the following equation : — 
2 (Fe 5 Cyi 2 3 NO-l- 8 Na-}- 3 S)-l- 2 HO= 7 (Na 2 Fe Cy 3 )-)-(Na, Cy S 2 )H-(Na O, NO 3 ) 
+Fe 3 04 - 1 - 84 -l- 2 HCy -|- 2 N. 
The only point in which this transformation does not agree with experiment, is in 
the supposed production of ferrous-ferric oxide, whereas, when the brown precipitate 
is washed with acid, only peroxide of iron unaccompanied by protoxide of iron passes 
through. It is therefore probable that the oxidation of this oxide may give rise to 
the small quantity of ammonia observed, the oxygen from decomposed water uniting 
with it, and the nascent hydrogen with nitrogen to form ammonia. Allowing this to 
be the explanation of the disagreement with experiment, the following scheme may 
render the above equation more immediately intelligible. Two equivalents of the 
blue compound with 2 equivs. of water, by boiling, are resolved into — 
7 equivs. ferrocyanide of sodium. 
1 equiv. sulphocyanide of sodium. 
1 equiv. nitrite of soda. 
1 equiv. oxide of iron (Fe 0 - 1 -Fe 203 ). 
4 equivs. sulphur. 
2 equivs. hydrocyanic acid. 
2 equivs. nitrogen. 
18*33 
6*59 
14*98 
1*51 
44*54 
