484 
DR. PLAYFAIR ON THE NITROPRUSSIDES, 
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 one of the products 
evolved as a gas. This acid scarcely appears at all when the quantity of nitric acid 
used is only 1 equiv. for every 4 equivs. of potassium in the prusside. On the con- 
trary, it is a very marked product when 5 equivs. are employed. Precisely under the 
same circumstances that the carbonic acid is least in quantity, does the peculiar 
white substance, already referred to, augment, and when the carbonic acid is greatest, 
as when five equivalents of nitric acid are used, then scarcely any of the white sub- 
stance is observed. The carbonic acid is therefore obviously a product of the oxida- 
tion of the white substance. Five per cent, of the white substance were obtained 
when one equivalent of nitric acid was used to oxidize an amount of yellow prusside 
containing 4 equivs, of potassium ; to ensure this, the largest quantity obtained by 
experiment, the action of the acid on the prusside must be as subdued as possible. 
The white substance is found with the nitrate of potash, which has deposited from 
the oxidized liquid, and is separated from it by the solution of the latter in water. 
The white substance is scarcely at all soluble in cold water, and therefore may be 
collected and purified by repeated solutions in boiling water, in which it is only very 
sparingly soluble, and deposits itself, on cooling of the solution, as a white crystalline 
precipitate. It may also be sublimed without change between two watch-glasses. 
The following analyses of this white substance show its composition. Analyses I. II. 
were made upon a specimen purified by sublimation ; III. IV. upon a specimen 
purified by solution. 
I. 5’05 grs. gave 5’004 grs. carbonic acid and 2'094 grs. water. 
II. 7‘835 grs. gave 7’850 grs. carbonic acid and 3‘236 grs. water. 
III. 5‘947 grs. gave 5‘95 grs. carbonic acid and 2'46 grs. water. 
IV. 6‘992 grs. gave 6’95 grs, carbonic acid and 2'886 grs. water. 
The nitrogen analyses were made by Will and Varrentrapp’s plan, the portions 
used in analysis being in one case purified by sublimation and in the other by solution : 
4'345 grs. gave 2T835 grs. platinum salt. 
7-027 grs. gave 35’74 grs. platinum salt. 
Purified by sublimation. Purified by solution. 
Carbon 
, '27-024 
A 
27-324 
'27-255 
"I 
27 - 108 
2 
12 
Calculated. 
27-27 
Nitrogen . . . . 
31-583 
31-583 
31-961 
31-961 
1 
14 
31-81 
Hydrogen . . . 
4-607 
4-589 
4-594 
4-586 
2 
2 
4-54 
Oxygen 
36-786 
36-584 
36-190 
36-345 
2 
16 
36-38 
100-000 
100-000 
100-000 
100-000 
100-00 
The carbon is to the nitrogen as 2:1, or in the same proportion as cyanogen. In 
