a Neiio Class of Salts. ' 275 



The discussion as to the constitution of the acid is also deferred 

 to that place. 



Nitroprusside of Ammonium. 



20. When ammonia is added to an excess of nitroprusside 

 of iron the latter is decomposed, oxide of iron being precipi- 

 tated, but during the action nitrogen gas is evolved. If the 

 red-coloured solution caused by fiUration be evaporated in 

 the air-pump, a difficultly crystallizable salt is obtained, which 

 very readily decomposes, turning blue in the water-bath, and 

 even when dried over sulphuric acid in vacuo. This salt is 

 probably the true nitroprusside of ammonium, but it has not 

 been obtained pure for analysis. If a solution of this salt be 

 heated, prussian blue is deposited, and the filtered dark-red 

 liquid, being evaporated by a gentle heat, now crystallizes in 

 a warm place very readily, and in fine large red crystals, 

 which are so dark as to be almost of a black colour. These 

 have been measured by Prof. Miller ; they are prismatic, but 

 the angles given are only approximative, the faces of the 

 crystal examined being imperfect. 



Symbols : — c 001 , »z 11 0, m 01 1 . 



Angles between normals to the faces : — 



vS 



They are twin crystals, the twin faces being m. 



This salt is very soluble in water, from which it is not pre- 

 cipitated by alcohol. It is very slightly deliquescent. The 

 salt dried in air loses water in the water-bath. 



18*648 grs. lost at 212° 2-928 grs., or 15*701 per cent. 

 10-915 grs. lost at 212° 1*800 gr., or 16*491 per cent. 

 11*502 grs. lost at 212° 1*948 gr., or 16*936 per cent. 

 45*400 grs. lost at 212° 6*850 grs., or 15*088 per cent. 



16*054 



The iron was determined by calcination. 



I. 10*905 grs. gave 3*455 grs. peroxide of iron. 

 II. 12*954 grs. gave 4*070 grs. peroxide of iron. 



The combustions made with chromate of lead gave the fol- 

 lowing results: — 



I. 9*822 grs. gave 2*903 grs. HO and 8*251 grs. CO*. 



II. 12*765 grs. gave 3*682 grs. HO and 10*494 grs. CO^. 



III. 7*215 grs. gave 2*010 grs. HO and 6*020 grs. CO^. 



