24 RESEARCHES ON THE 



blue talcose scales, while the solution and the crystals obtained from this have 

 a very fine violet-red tint. 



The chloride of Purpureocobalt may be prepared by other methods. One of 

 the most interesting of these is, by the action of strong chlorhydric acid upon a 

 salt of Xanthocobalt. It is almost a matter of indifference which salt of Xantho- 

 cobalt is employed. As, however, the nitrate is, perhaps, most easily obtained in 

 a pure state, it is usually most advantageous to employ this. The nitrate has the 

 formula 



N0 2 .5NH 3 .Co 2 3 ,2N0 5 + HO. 



On boiling with chlorhydric acid, the salt is slowly converted from a brown-yellow 

 to a lilac-purple powder, which is insoluble in the supernatant acid liquid. After 

 boiling strongly for an hour or two, almost all the original salt is decomposed, N0 2 

 is given off in abundance during the boiling, while a lilac colored uncrystallized 

 mass remains at the bottom of the flask. The supernatant liquid is to be poured off, 

 and boiling water added to the insoluble portion." A brown-yellow or dark sherry 

 wine colored solution is usually formed, which is again to be poured off, and the 

 washing repeated till the liquid has a clear purple color. The red mass is then to 

 be dissolved in boiling water, to which a little chlorhydric acid has been added, 

 and filtered. On cooling, the chloride of Purpureocobalt crystallizes in small bril- 

 liant crystals, which must be repeatedly recrystallized to separate all traces of impu- 

 rity. The washings, on boiling with chlorhydric acid, yield a fresh portion of the 

 chloride. The reaction which takes place under these circumstances may be 

 expressed by the equation 



N0 2 .5NH 3 .Co 2 03,2N0 5 +3HCl=N0 2 +2N0 5 ,HO+5NHs.Co 2 Cl 3 +HO. 



As already remarked, the chloride or sulphate of Xanthocobalt may be employed 

 in a precisely similar manner, and also yield the chloride of Purpureocobalt. When 

 the sulphate is used, however, the resulting chloride is apt to retain sulphuric acid 

 with much obstinacy, and can with difficulty be freed from it. 



Another method of preparing the chloride of Purpureocobalt, consists in boiling 

 the chloride or nitrate of Roseocobalt with chlorhydric acid. This method is very 

 convenient, and yields a very pure chloride. 



The chloride of Purpureocobalt may also be prepared by boiling the acid sul- 

 phate of this base with chlorhydric acid. In this case, however, as in all others in 

 which sulphuric acid is present in the solution, the chloride should be boiled with 

 a little chloride of barium, and repeatedly recrystallized, to separate traces of the 

 isomorphous sulphate of Roseocobalt formed at the same time. 



The chloride of Purpureocobalt has a beautiful violet-red or purple color, and is 

 dichrous, the ordinary ray being colorless, while the extraordinary ray has a rich 

 violet-red tint. Its solution is violet-red. The salt is nearly insoluble in cold 

 water, but is soluble without decomposition in boiling water, to which a few drops 

 of chlorhydric acid have been added. From this solution it separates, on cooling, 

 in very brilliant small crystals, which are simpler in form, the purer the solution 

 from which they have crystallized. The crystals belong to the square prismatic or 

 dimetric system, according to Prof. Dana, and not to the regular system, as stated 



