AMMONIA-COBALT BASES. 19 



or monoclinic system, much resembling some of the simpler forms of augite. The 

 salt is very insoluble in cold water ; hot water readily decomposes it. It forms an 

 extremely characteristic test for the salts of Boseocobalt in general, as well as for 

 the chloride of Purpureocobalt, but, as already remarked, it is precipitated from 

 the sulphate of Eoseocobalt only after some hours. The crystals are usually 

 remarkably large when compared with the mass of liquid from which they are 

 thrown down. They are more distinct in form the more slowly the precipitation 

 takes place. The salt has the formula 



5NH 3 .Co 2 Cy 3 + Co 2 Cy 3 + 3HO 



as the following analyses show : 



0.1924 grs. (from chloride of Purpureocobalt) gave 0.1540 grs. sulphate of cobalt = 30.46 per 



cent, cobalt. 

 0.7150 grs. (from chloride of Roseocobalt) gave 0.5755 grs. sulphate of cobalt = 30.63 per 



cent, cobalt. 

 0.8111 grs. (from chloride of Roseocobalt) gave 272 c. c. of nitrogen at 10° C. and 761°"°.99 



(at 10° C.) = 259.48 c. c. at 0° and 760 mm = 40.18 per cent. 



The formula requires 



Eqs. Calculated. Found. 



Cobalt ... 4 30.57 30.63 30.46 



Nitrogen . .11 39.89 40.18 



The analyses of the ferridcyanide of Roseocobalt give additional evidence of the 

 correctness of the formula adopted for this salt. 



FERBID CYANIDE OF ROSEOCOBALT. 



The ferridcyanide is formed like the cobaltidcyanide by adding a solution of fer- 

 ridcyanide of potassium to one of chloride or nitrate of Eoseocobalt or chloride of 

 Purpureocobalt. A very beautiful orange-red precipitate is thrown down in dis- 

 tinct and usually extremely well-defined crystals, which under the microscope, 

 exactly resemble those of the corresponding cobalt salt. The crystals exhibit a 

 remarkable dichroism, the ordinary image being of a fine purple rose color, while 

 the extraordinary image is bright orange red. The crystals are insoluble in cold 

 water ; hot water easily decomposes them, ammonia being evolved, while a dark- 

 brown precipitate is thrown down. Heat decomposes the dry salt very gradually 

 and uniformly, and leaves a black residue which contains much carbon. We 

 availed ourselves of this fact to determine accurately the sum of the cobalt and 

 iron in the salt, by first decomposing it by heat, then burning off the carbon in a 

 gentle current of oxygen, and finally reducing the mixed oxides of cobalt and iron 

 in a current of hydrogen. The formula of this salt is 



5NH 3 .Co 2 Cy 3 +Fe 2 Cy 3 +3HO 

 "as the following analyses show: 



0.3613 grs. gave 0.1086 grs. metallic iron and cobalt = 30.05 per cent. 



1.5028 grs , burnt with oxide of copper and oxygen, gave 1.0302 grs. carbonic acid = 18.69 per 

 cent, carbon. 



