204; Dr. Playfair on the Nitroprussides, 



the preparation. The two following experiments may be 

 taken as giving mean results : — 



o^. 1. 105*5 grs. yellow prusside gave 8*275 green precipitate, 

 yielding on incineration 7*95 grs. peroxide of iron; the filtrate 

 gave 48*90 grs. nitroprusside of copper. 



II. 105*5 grs. yellow prusside gave 8*32 grs. green precipi- 

 tate, yielding by calculation 6*30 grs. peroxide of iron ; the 

 filtrate gave 46*12 grs. nitroprusside of copper. 



Taking the mean of the two experiments, 105*5 grs., or 

 one-fourth of the double equivalent of yellow prusside, yield 

 8-297 grs. green precipitate containing 4*984 grs. iron ; the 

 filtrate yields 47*51 grs. nitroprusside of copper. But befoi'e 

 drawing deductions, it is necessary to know the composition 

 of the green precipitate. It consists of a mixture of prussian 

 blue, nitroprusside and peroxide of iron, this mixture not 

 being constant. However, to take a special case as an 

 example, — 



22*26 grs., calcined and treated with nitrate of ammonia, 

 gave 13*62 grs. peroxide of iron, or 42*83 per cent, of metallic 

 iron. 



9*49 grs. burned with oxide of copper gave 4*13 grs. car- 

 bonic acid and 0*96 gr. water; the carbon is therefore 11*87 

 per cent., the water 10*11. 



35*02 grs. treated by caustic potash, gave, when neutralized 

 by acetic acid, a red filtrate, from which the ferrocyanide of 

 potassium was precipitated by alcohol ; the filtrate from this 

 had all the properties of nitroprusside of potassium, and gave 

 by precipitation with sulphate of copper 13*98 grs. nitroprus- 

 side of copper, equal to 13*24 grs. nitroprusside of iron, or 

 37*80 per cent. 



The reactions in the preparation of the nitroprusside may 

 now be approximatively explained. 



By reference to the ascertained composition of the nitro- 

 prussides, it will be seen that the 47*51 grs. of the copper 

 nitroprusside obtained from the 105*5 grs. of yellow prusside, 

 are equal to 35*69 grs. anhydrous nitroprussic acid: this 

 quantity contains 9*66 grs. of iron. Now 14 grs. iron were 

 present in the yellow prusside used, so that about two-thirds 



acid gives a slaty precipitate, which consists mainly of oxide of iron mixed 

 with prussian blue. Under somewhat similar conditions, I believe, though 

 on this subject I am not certain, the precipitate on boiling, instead of being 

 green, is brown, like oxide of iron. On washing and exposure to the air 

 it becomes green. 



In an experiment where this precipitate came, 105'5 gi"s. yellow prusside 

 gave 6-83 grs. of a brow n precipitate, and 50"66 grs, of nitroprusside of 

 copper. In another experiment with a like quantity, 4*755 grs. of the 

 brown precipitate were obtained. 



