SS* Dr. Playfair on the Nitroprussides, 



low colour due to a prusside being seen in the solution. If 

 the sulphide originally employed contained sulphuretted hy- 

 drogen, a soluble prussian blue is also found in the liquid. 

 During these changes, ammonia, hydrocyanic acid, and a gas 

 possessing the properties of nitrogen are given off. In fact, 

 on mixing the solutions of sulphide and nitroprusside, it is 

 difficult, even by keeping the solutions quite cold, to prevent 

 the formation of a little ammonia and escape of nitrogen. 

 The solution of the purple compound in water decomposes 

 even under the air-pump, depositing the brown precipitate, 

 and it does so immediately when it is boiled. 



When the solution is filtered from the brown precipitate^ 

 the addition of alcohol separates ferroey an ide of sodium. The 

 alcoholic filtrate strikes a blood-red colour with a persalt of 

 iron, and with sulphuric acid evolves nitric oxide, which is 

 immediately rendered sensible by a protosalt of iron, a nitrite 

 being thus shown to be in solution. Ammonia cannot be 

 detected in the solution, neither does it appear to any great 

 extent when the transformation takes place in the cold, though 

 it always does so when ebullition is used to hasten the trans- 

 formation. It therefore appears to be the product of an after 

 action. 



The brown precipitate is first to be examined. It is found 

 to consist of peroxide of iron and sulphur, the latter remaining 

 when the former is dissolved out by an acid. It was analysed 

 by oxidation with nitromuriatic acid. 7'21 grs. gave 16"90 

 grs. sulphate of barytes, equal to 2*33 grs. of sulphur, and 

 4*22 grs. peroxide of iron, the rest being water. Hence the 

 proportion of sulphur to iron in equivalents is nearly as 4 : 3; 

 the proportion for 2*33 sulphur would yield 3*0 iron, while 

 2*95 was found by the experiment. 



It was now desirable to ascertain what proportion of iron 

 was thrown down as ferrocyanide and how much remained in 

 the brown precipitate. For this purpose a portion of a pre- 

 paration, which had become green by standing in the air- 

 pump, was first analysed in order to ascertain the relative 

 proportion of its constituents, and it was then dissolved in 

 water and boiled. 



14-41 grs. gave 693 grs. sulphate of barytes, 17*68 grs. 

 gave S'55 grs. peroxide of iron and 10*00 grs. sulphate of 

 soda. 6*025 grs. gave 3*31 grs. carbonic acid and 0*820 gr. 

 water. Hence this changed purple compound, before com- 

 plete transformation, contained in 100 parts, — 



