071 the Am?nonia'Cohal( Bases. 95 



\ 



rapidly, and crystals are usually deposited in abundance long 

 before the oxydation is complete. It is best in tliis case, as in 

 the preparation of the sulphate, to employ a pure salt of cobalt 

 and pure ammonia, as the subsequent purification of the nitrate 

 of Xanthocobalt becomes much more easy. The equations rep- 

 resenting the formation of the nitrate are similar to those which 

 we have given for the sulphate. 



The nitrate of Xanthocobalt may also be easily prepared by 

 the action of NOx upon neutral, acid, or alkaline solutions of 

 the chlorids, sulphates and nitrates of Roseocobalt and Purpu- 

 reocobalt. We have alluded to the formation of the nitrate of 

 Xanthocobalt by this process already, and will here enter more 

 into detail. 



It is almost a matter of indifference which salt is selected, as 

 the nitrate is prepared with nearly equal facility from all. The 

 salt is to be uissolved in water, and to hasten the process, am- 

 monia added ; a large excess of ammonia is not necessary, but 

 the process always goes on more rapidly in an ammoniacal than 

 in an acid or neutral solution. The current of gas resulting 

 from the action of nitric acid upon starch or sawdust is then to 

 be passed into the liquid, which speedily becomes hot and grad- 

 ually changes its color from violet to orange-red, and at last to 

 orange, while orange-yellow crystals of the nitrate of Xanthoco- 

 balt are precipitated. The liquid on cooling gives more crystals ; 

 the process snould not be continued after the whole mass has 

 assumed a clear orange-yellow color. The mother-liquor from 

 which the crystals of the nitrate of Xanthocobalt have separated 

 contains only salts of ammonia, with a little nitrate in solution. 

 The whole process is very easy to execute, and yields a very 

 pure nitrate. The reactions which occur in this process are re- 

 markably beautiful, and may be expressed, in the case of the 

 a^jtion of the gas upon the chlorid and sulphate of Eoseocobalt, 

 by the equations 



5XH3.Co2Cl3+3N04+8HO=N02.5NH3,Co303, 2N05-f3HCl, 



5NH3.Coa03, 3S03^aNO4+3H0=X0a.5Xn3.Co2O3, 2N05-|- 



3H0, SO3. 



It will be seen from these equations that wben neutral solu- 

 tions of the salts of Roseocobalt or Purpureocobalt are employed, 

 chlorhydric and sulphuric acids are set free. The influence of 

 an excess of ammonia in facilitating the process is thus easil 

 understood. The nitrate of Xanthocobalt, being much less so 

 uble in cold water than the ammonia salts, is easily purified by 

 re-crystallization. In treating of the sulphate and chlorid of 

 Xanthocobalt, we have mentioned that the nitrate of Xanthoco- 

 balt is often formed while preparing these salts directly. As a 

 mode of preparation, this metiiod is not to be recommended, 

 but it possesses much theoretical interest. The equation which 



