a New Class of Salts. 357 



this alcoholic solution. Sulphur, prussian blue, and ferrocy- 

 anide of sodium, are very gradually precipitated; the action, 

 however, is very slow, and must be long continued. The alco- 

 holic solution is now of a reddish olive-brown colour. When 

 the sulphuretted hydrogen has ceased to act, this supernatant 

 brownish liquid gives no coloration when mixed with an alka- 

 line sulphide. If allowed to stand for a few hours, it deposits 

 a little of the precipitates which it held in solution. After 

 this the brown solution is found to contain neither ferrocy- 

 anide nor nitroprusside of sodium ; a persalt of iron is slightly 

 deepened in colour when mixed with it, showing the presence 

 of a mere trace of a sulphocyanide. When this reddish-brown 

 solution is evaporated in the water-bath, it deposits oxide of 

 iron and sulphur, and becomes decomposed. Evaporated in 

 vacuo over sulphuric acid, it deposits, when nearly dry, black 

 crystalline needles, but these seem to be a product of decom- 

 position, and are mixed with oxide of iron and other sub- 

 stances ; attempts were therefore made to ascertain the com- 

 position of the original substance by precipitating its solution 

 by metallic salts. Bichloride of mercury produces a brown 

 precipitate, sulphate of copper a pinkish-brown, and nitrate of 

 silver a black precipitate. But these were obviously products 

 of decomposition, for during the precipitation nitric oxide is 

 abundantly evolved. This is especially the case in the preci- 

 pitate with silver. If that precipitate, after being washed, be 

 now mixed with a small quantity of hydrochloric acid to take 

 up the silver, sulphuretted hydrogen is evolved, protochloride 

 of iron and abundance of sulphocyanic acid are now found in 

 solution ; the first is recognized by the prussian blue formed 

 on adding red prusside of potassium, the second by the blood- 

 red colour which it strikes with perchloride of iron. When 

 nitrate of silver is added to the red-brown solution, the black 

 precipitate already alluded to falls down, but at the same time 

 the supernatant liquor had a reddish-brown colour ; on ex- 

 amining this it was found to contain a persalt and protosalt of 

 iron, the dark coloration being due to the escaping nitric 

 oxide. The amount of sulphur precipitated during the pass- 

 age of sulphuretted hydrogen through the nitroprusside is 

 about 17 per cent. ; the amount of ferrocyanide of sodium and 

 of prussian blue has been found to vary much. 



From the difficulty of obtaining the products of transfor- 

 mation in a pure state, I have not yet been able to make direct 

 quantitative examinations of the various substances formed ; 

 it is therefore impossible to express the transformation in the 

 form of an equation. From some experiments now in pro- 

 gress, I trust, however, to overcome those difficulties which 



