510 
DR. PLAYFAIR ON THE NITROPRUSSIDES, 
26. The products of transformation were determined (1) by precipitating the ferro- 
cyanide by alcohol; (2) by adding nitrate of lime to precipitate the oxalate*, which 
was always accompanied by a minute quantity of a pink compound containing cya- 
nogen and iron ; (3) by examining the liquid which remained, and was found to evolve 
nitric oxide on the addition of an acid. It gave a precipitate with nitrate of silver, 
which, though sparingly soluble in cold water, dissolved in hot water and crystallized 
on cooling; 13’25 grs. of the crystalline salt thus obtained, treated with hydrochloric 
acid, gave 12‘33 grs. chloride of silver, or 70'03 per cent. Nitrite of silver (AgO, NO^) 
contains 70T2 per cent. 
In examining the relative quantities of these products of transformation, recourse 
was first had to the yellow salt itself. But as this generally contained a little nitro- 
prusside, and as the products of decomposition varied with the period of ebullition, 
on account of the slower action from the insufficient quantity of alkali, it was found 
more accurate to examine the transformations by acting upon a solution of nitro- 
prusside with an excess of alkali. Without therefore giving the details of the expe- 
riments on the yellow salt itself, some of the general results may be stated ; from 
these it will be seen that the quantities of oxide of iron and of prusside produced vary 
according to the conditions of the experiment, principally according to the longer or 
shorter period of ebullition. 100 parts of the yellow salt gave, on boiling its aqueous 
solution, — 
I. II. III. IV. V. 
Peroxide of iron .... 3‘0 3*58 3’0 3’56 2‘71 
Ferrocyanide of potassium . 60‘86 60‘59 59*48 68*83 64*50 
In all these cases there was more or less nitroprusside of potassium undecomposed. 
The amount of oxalate of potash found in solution varied from 0*97 to 1*5 per cent. 
The transformation was now examined in the following manner. A weighed quan- 
tity of a nitroprusside was dissolved in water and boiled, caustic potash or caustic 
soda (according as the nitroprusside was a salt of potassium or sodium) being added 
to the boiling solution, until a drop taken out gave, after being neutralized, no purple 
colour with a sulphide. The precipitated oxide of iron was now collected and 
weighed. The filtrate was precipitated by alcohol, and the prusside collected and 
determined on a weighed filter. The filtrate was now neutralized with acetic acid, 
and chloride of ealcium added, but the oxalate of lime was generally not in sufficient 
quantity to collect and weigh, mere traces being obtained. It was now attempted to 
estimate the amount of nitrate by the process described by Nesbit for analysing 
nitrates'!'', that is, by converting its nitrogen into ammonia by zine and muriatic 
acid, the hydrogen being slowly evolved. The ammonia thus formed was separated 
* To prove that this was an oxalate, a portion was precipitated hy nitrate of lead from the solution after 
precipitation hy alcohol. The precipitate was of a pink colour, and was now decomjjosed hy sulphuretted 
hydrogen, neutralized hy pure carbonate of soda, and again precipitated as a lead salt, which was now quite 
white. Calcined with nitrate of ammonia, T660 gr. gave T250 gr. oxide of lead, or 75'3 per cent. Oxalate 
of lead contains 75 '5 per cent. 
f Memoirs of Chemical Society. 
