468 
NOTES AND ABSTRACTS IN CHEMISTRY AND PHARMACY. 
Nitroprussides, their Composition and IMEanufacture. 
Some doubt has always been attached to the composition of the jo-^^m 
prussides since their discovery by Playfair. Some recent researches, however, 
by E. A. Hadow, which are remarkable for the skill and ability they display, 
have removed all uncertainty in the matter, and have given us a clear insight 
into the formula for this interesting class of salts. Mr. Hadow started from 
the assumption that the nitroprussides are formed from the ferridcyanides, by 
the displacement of an atom of alkaline cyanide by one of the oxides of nitrogen. 
Thus 
Fe2 Cyg M3 — M Cy + N 0 a; = F e^ Cyg N O x Mg. 
/' -^ ;—s. ^ \ 
Fcrridcyanide, Nitro-prussid®. 
The question to be solved was, WTiat oxide of nitrogen replaces the M Cy ? In 
the first instance, pure binoxide of nitrogen was passed through a warm solu¬ 
tion of ferridcyanide of potassium, which was acidulated with sulphuric acid, so 
that the NOg might have the easier work of replacing H Cy, if it could. The 
liquid became blue and muddy, but no trace of nitro-prusside was formed. The 
next experiment was to pass the red nitrous vapours from starch and nitric acid 
through the warm acid solution of ferridcyanide. The difference was wonder¬ 
ful ; no Prussian blue appeared, the colour changed rapidly to the red of nitro- 
prusside, and much hydrocyanic acid came off. The conversion to nitro- 
prusside was almost perfect. It thus became clear that the replacing oxide of 
nitrogen is either NO 3 or NO 4 . That such is the case is further shown by a 
very simple experiment, the reverse of the last. On adding to a solution of 
pure nitroprusside a solution of potash and some prussic acid, and warming, 
the red of the nitro-prusside changes for an instant to deep yellow, and then to 
pale yellow. The solution is found to contain ferridcyanide, with plenty of 
nitrite, but no trace of nitroprusside. Hence NO 3 or NO 4 has been replaced 
by K Cy, and ferridcyanide reproduced. 
To determine between NO 3 and NO 4 the author sought to replace the KCy 
by pure NO 3 , obtained by the action of acetic acid on an alkaline nitrite, 
whereby NO 4 is absolutely excluded. Ferridcyanide of potassium solution was 
mixed with a solution of corrosive sublimate and acetic acid, and a nitrite added, 
and the whole was left for some hours, when, on examining the mixture, nitro¬ 
prusside was found in abundance. 
The reaction was as follows:— 
Fe^ Cy, K 3 + Hg Cl + NO 3 = Fe^ Cy, NO, K, + Hg Cy -b K Cl. 
And the true formula of the sodium salt is— 
Fog Cy5N03-|-Na2-}-4H0= 306. 
Curiously enough, this formula agrees more closely with Playfair’s analysis than 
any yet proposed. 
The success of this reaction on the small scale suggested it as a means of 
manufacturing nitroprusside on the large scale. The following is the process 
Mr. Hadow gives:— 
A strong solution of caustic soda is prepared, and thoroughly saturated with 
the nitrous acid vapours from starch and nitric acid (old battery acid does well). 
The amount of true nitrite of soda, NaONO,, in this solution is determined by 
permanganate, by taking a small measured quantity, diluting largely with 
water, acidifying with sulphuric acid, and observing the amount of standard 
