S50 Dr. Playfair on the Niiroprussides, 



that it might, when quite free from nitroprusside, contain an 

 additional equivalent of potash. 



It has been stated that a solution of this salt is decomposed 

 on boiling. Oxide of iron falls down, nitrogen escapes, and 

 the solution is now found to contain ferrocyanide of potassium, 

 nitrite of potash and traces of oxalate of potash. 



26. The products of transformation were determined (I) 

 by precipitating the ferrocyanide by alcohol ; (2) by adding 

 nitrate of lime to precipitate the oxalate*, which was always 

 accompanied by a minute quantity of a pink compound con- 

 taining cyanogen 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 70*12 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 nitroprusside, and as 

 the products of decomposition varied with the period of ebul- 

 lition, 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 nitroprusside 

 with an excess of alkali. Without therefore giving the details 

 of the experiments 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 ac- 

 cording to the conditions of the experiment, principally ac- 

 cording 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 097 to 1*5 per cent. 



The transformation was now examined in the following 



* To prove that this was an oxalate, a portion was precipitated by ni- 

 trate of lead from the solution after precipitation by alcohol. The preci- 

 pitate was of a pink colour, and was now decomposed by sulphuretted 

 hydrogen, neutralized by pure carbonate of soda, and again precipitated as 

 a lead salt, which was now quite white. Calcined with nitrate of ammonia, 

 1*660 gr. gave 1-250 gr. oxide of lead, or 753 per cent. Oxalate of lead 

 contains 75*5 per cent. 



