220 Dr. Playfair on the Nitroprussides, 



The formula of the copper salt is therefore Fe^Cy^^SNO, 

 CuHHO. 



Nitroprusside of Iron. 



16. This salt is obtained by adding sulphate of the prot- 

 oxide of iron to a soluble nitroprusside. When the solutions 

 are dilute the precipitate does not at first appear; as however 

 it is very sparingly soluble, it may be purified by washing 

 either with hot or cold water. 



This salt is a salmon-coloured precipitate, nearly though 

 not absolutely insoluble in water; it is more soluble in water 

 rendered acid by nitric acid. It is decomposed by caustic 

 alkalies, with the precipitation of oxide of iron and the forma- 

 tion of a soluble nitroprusside. Before, however, being com- 

 pletely decomposed, a dark-coloured basic nitroprusside of 

 iron is produced. 



A salt dried in the hot chamber, at a temperature about 

 90° Fahr., still lost water when exposed in the water bath : — 



14-162 grs. lost at 212° 2*890 grs., or 20-406 per cent. 

 10-893 grs. lost at 212° 2-320 grs., or 21-298 per cent. 

 17-500 grs. lost at 212° 3-545 grs., or 20-257 per cent. 

 In the two first analyses given below, the iron was deter- 

 mined by decomposing the salt by sulphuric acid, oxidizing 

 with nitric acid and precipitation by ammonia. The third 

 estimation was by calcination, a little nitrate of ammonia being 

 used to effect complete oxidation. 



I. I8-O75 grs. gave 9-917 grs. peroxide of iron. 

 II. 30-935 grs. gave 16-900 grs. peroxide of iron. 

 III. 9-220 grs. gave 4-995 grs. peroxide of iron. 

 The combustions were performed with chromate of lead. 

 I. 7-218grs. gave 0-717 gi*- water and 5-255 carbonic acid. 

 II. 7-347grs. gave 0-810gr. water and 5*360 carbonic acid. 

 III. 6-360grs. gave 0*693 gr. water and 4*695 carbonic acid. 

 The nitrogen was determined by Dumas' quantitative method. 

 5*427 grs. gave 86 CC. nitrogen gas, the thermometer being 

 48°' 7 Fahr. (9*4 Cent.) and the barometer 29*285 inches. 



