AMMONIA-COBALT BASES. 41 



Roseocobalt in ammonia. The reaction which takes place in this case may be 

 represented by the equation 



5NH 3 .C 2 3 ,3S0 3 + NH 3 = 6NH 3 .Co 2 3 ,3S0 3 , 



the sulphate of Eoseocobalt simply absorbing one equivalent of ammonia. The 

 quantity of sulphate of Roseocobalt dissolved in the ammonia is very variable, 

 being sometimes extremely small. In other cases, however, no sulphate of Luteo- 

 cobalt is formed, but only a solution of sulphate of Roseocobalt in ammonia, from 

 which, by evaporation, the sulphate crystallizes unchanged in large dark-red 

 crystals, frequently of the form represented in Fig. 3. We are unable to assign a 

 satisfactory reason for the capaciousness of the behavior of the red sulphate 

 towards ammonia. 



Fremy asserts that sulphuric acid, continuously added to a completely oxidized 

 ammoniacal solution of sulphate of cobalt, throws down an acid sulphate of Roseo- 

 cobalt to which he assigns the formula 5NH 3 .Co 2 3 ,5S0 3 +5HO. When this acid 

 sulphate is boiled for a few minutes with ammonia, a yellow precipitate of sulphate 

 of Luteocobalt is thrown down. The author does not attempt to explain the reac- 

 tion which takes place in this case, but states that the red mother liquor from 

 which the sulphate of Luteocobalt has- separated, yields on evaporation crystals of 

 the neutral sulphate of Roseocobalt. We have never succeeded in preparing an 

 acid sulphate of Roseocobalt by the process above mentioned, nor by any other. 

 On the contrary, we have uniformly found that sulphuric acid precipitates from 

 the oxidized solution only the neutral sulphate of Roseocobalt in small bright-red 

 crystals, easily recognized by their form. Fremy's salt must have contained free 

 sulphuric acid, in consequence of imperfect washing. 



When a pure solution of the sulphate of Roseocobalt is boiled, ammonia is 

 evolved, while sulphate of ammonia and sulphate of Luteocobalt remain in solu- 

 tion, and a dark-colored oxide of cobalt is precipitated. From the solution the 

 sulphate of Luteocobalt may be obtained by evaporation and crystallization. This 

 method yields but little, and is not to be recommended. 



Sulphate of Luteocobalt is also sometimes obtained, with other products, by 

 digesting sulphate of Roseocobalt with sulphuric acid, before the period of complete 

 decomposition sets in. 



A very simple and easy method of preparing the sulphate of Luteocobalt consists 

 in decomposing the dry sulphate of Roseocobalt by heat. When the latter salt is 

 gently heated in a porcelain crucible over a spirit lamp, or better still, in a glass 

 flask in a bath of rosin oil to about the temperature of melting lead, ammonia is 

 given off in abundance, and the mass, which should be constantly stirred, assumes 

 a fine purple-lilac hue. The heat, when the lamp alone is used, must never rise 

 to low redness, and no vapors of sulphate of ammonia should be given off. The 

 resulting mass is then to be dissolved in hot water, which gives a fine purple red 

 solution, and chlorhydric acid added in excess. An orange precipitate of sulphato- 

 chloride of Luteocobalt is immediately thrown down, which is easily purified, 

 as above, by sulphate of silver and recrystallization. The acid mother liquor 

 sometimes deposits more sulphate on cooling. The supernatant liquid contains 

 6 



