206 Dr. Playfair on the Niiroprussides, 



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 contrary, 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 sub- 

 stance, 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 substance is observed. 

 The carbonic acid is therefore obviously a product of the 

 oxidation 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 sub- 

 limation ; 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*85 grs. CO^ and 3*236 grs. HO. 



III. 5*947 grs. gave 5*95 grs. CO^ and 2*46 grs. HO. 



IV. 6*992 grs. gave 6*95 grs. CO^ and 2-886 grs. HO. 



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 21*835 grs. platinum salt. 

 7*027 grs. gave 35*74 grs. platinum salt. 



Purified by sublimation. Purified by solution. Calcu- 



t "" ^ ( ^ ^ lated. 



C 27*024 27*324 27*255 27*108 2 12 27*27 



N 31*583 31*583 31*961 31*961 1 14 31*81 



H 4*607 4*589 4*594 4*586 2 2 4*54 



O 36*786 36*584 36*190 36*345 2 16 36*38 



100*000 100*000 100*000 100*000 100*00 



