A NEW CLASS OF SALTS. 
501 
A silver salt made from the well-crystallized acid showed that the iron was in 
excess, and that the carbon was in the usual proportion (see p. 506). The analyses 
of these silver salts are given further on, in order to avoid repetition. The discus- 
sion 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 de- 
composed, oxide of iron being precipitated, but during the action nitrogen gas is 
evolved. If the red-coloured solution caused by filtration 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 m 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 exa- 
mined being imperfect. 
Symbols : — c 00 1 , w 1 1 0, w 01 1 . 
Angles between normals to the faces : — 
me 90 0 
mm! 88 4 
uc 55 3 
uu' 110 6 
They are twin crystals, the twin faces being m. 
This salt is very soluble in water, from which it is not precipitated 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° T800gr., 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 following results : — 
I. 9*822 grs. gave 2*903 grs. water and 8*251 grs. carbonic acid. 
II. 12*765 grs. gave 3*682 grs. water and 10*494 grs. carbonic acid. 
III. 7*215 grs. gave 2*0 10 grs. water and 6*020 grs. carbonic acid. 
The nitrogen was determined by Dumas’ quantitative method. 
MDCCCXLIX. 3 T 
