on the Ammonia-cohalt Bases. 87 





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f 



The salts of Xantliocobalt have a dark sherry-wine or brown- 

 yellow color. They are rather more soluble, both in liot and 

 cold waterj than the salts of Roseocobalt, Purpureocobaltj or 

 Luteocobaltj the solutions when dilute have a yellow color ; 

 when concentrated they are dark-brown yellow. Solutions of 

 these salts are decomposed by boiling, though sometimes with 

 difficulty; in some cases, however, a temperature much below 

 the boiling point produces an incipient decomposition after a 

 short time, so that great care must be taken in evaporating for 

 the purpose of crystallization. During the decomposition by 

 boiling, ammonia is given off, while a heavy black or dark-brown 

 i powder is thrown down. The addition of a mineral acid pre- 



^ vents the decomposition, but produces, even when in very small 



quantity, a chemical change of a different kind, deutoxyd of ni- 

 trogen being given off, while a salt of Purpureocobalt is formed, 

 which remains mixed with the undecomposed salt of Xantho- 

 ^ cobaltj and which it is difficult to separate. A few drops of 



acetic acid, however, added to a solution of a salt of Xantlioco- 

 balt, so as to produce a slightly acid reaction, will usually suffice 

 to prevent decomposition, if the solution be evaporated at a 

 gentle heat. The dry salts of Xanthocobalt heated in a porce- 

 lain crucible are easily decomposed, with copious evolution of 

 red vapors, and afterwards of ammonia, while a black powder 

 remains. We have not been able to detect any new ammonia- 

 cobalt bases among the products of the decomposition of solu- 

 tions of these salts, by simple boiling or heating in the dry way. 



Xanthocobalt differs from the other ammonia-cobalt bases by 

 containing deutoxyd of nitrogen as a couplet in addition to am- 

 monia. Considering it as a primary radical, we attribute to it 

 the formula NO2 .5NPI3.C02, and it is evident that it differs 

 from Eoseocobalt and Purpureocobalt only by one equivalent of 

 deutoxyd of nitrogen. The passage of the salts of these tAvo 



I^A ' form of mixed sulphates of cobalt and potash. According to Stromeyer, Fischer's 



salt has the formula 



Coi03.2XOc+3KO, NO:-f 2H0. 



"When this is heated with sulphuric acid till the excess of acid is expelled, there re- 

 mains a mixture of sulphates having the formula 



2C0O, SO34-3KO, S03. 



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w 



We, therefore, dry the salt carefully, biim the filter upon the coyer of a deep pla- 

 tinum crucible, and bring the ashes and salt into the crucible itself A few drops of 

 fi sulphuric acid are then added, so as to cover the mass, and the whole is then treated 



precisely as we described on page 237, though in this case a higher heat is to be 

 used. From the weight of the mixed sulphates the quantity of cobalt is easily cal- 

 culated. This method gives very accurate results, because the cobalt forms only 

 about 14 per cent of th'j substance weighed. In an experiment made to test the 

 accuracy of Stromeyer's formula 



0*6671 grs. gave 0-6437 grs. mixed sulphates of cobalt and potash = 13'66 per 



cent cobalt. 



fc 



cent cobalt. 

 The formula requires 13'63 per cent. 



