On the Absorption Spectra of Cobalt Salts. 269 



to prepare a blue liquid which gives an absorption spectrum identical 

 with that produced by a piece of blue glass. 



Winkler showed some years ago that when finely divided metallic 

 cobalt, oxide of cobalt, or a salt of cobalt was boiled with caustic 

 potash, a blue solution was formed, which he attempted to show con- 

 tained cobaltate of potash. To the acid forming oxide he at first gave 

 the formula Co0 5 , and afterwards that of Co0 3 . Schultze, however, 

 immediately repeated Winkler's experiments and came to the conclu- 

 sion that instead of its being a solution of cobaltate of potash, it was 

 merely an alkaline solution of cobaltic hydrate. The absorption 

 spectrum seems clearly to show that the blue liquid is not a new 

 cobaltic salt, bat that it contains essentially oxide of cobalt in solution 

 and the same potash or soda compound as exists both in the glass and 

 in the precipitated oxide. Again, it may further be deduced from the 

 similarity of these spectra that the blue precipitate is not a hydrate, 

 for it gives the same spectrum as exists in the glass, or at all events 

 the water can only be so feebly combined with the oxide as not to alter 

 the individuality of the compound. Again, if oxide, or, in fact, any 

 ordinary salt of cobalt, be dissolved by fusion in borax, a glass which 

 gives the same spectrum as ordinary blue glass is obtained. The posi- 

 tions of the bands, however, are apparently intermediate in position 

 between those in the glass and those in the precipitated oxide ; these 

 differences are, however, very small. 



The blue oxide of cobalt can be made to undergo another change 

 which is of much interest. If a solution of cobalt chloride be pre- 

 cipitated by caustic alkali, taking care to keep the cobalt chloride in 

 excess, thus on well agitating the precipitate and solution together, or 

 even on slightly boiling them, the precipitate will be found to be of a 

 green colour, and to contain, as an integral part, cobalt chloride. 

 Evidently an oxychloride has been formed. Fig. 12 gives the 

 spectrum produced in this way ; it is a mixed spectrum of oxychloride 

 and of oxide. The same body may also be obtained if the blue oxide 

 be first prepared, drained rapidly and washed and then shaken up in 

 a solution of the chloride. The stronger the solution used the more 

 chloride attaches itself to the oxide, and apparently one or more 

 oxy chlorides are formed. If any other salt than the chloride or 

 bromide and probably the iodide of cobalt, be used and precipitated 

 by a small amount of caustic alkali, no salt corresponding to this oxy- 

 chloride is formed, but the oxide is at once thrown down. This green 

 substance is but very slightly decomposed by cold water and not at all 

 by alcohol. A sample of washed blue oxide was divided into three 

 portions : one was shaken up with a very dilute solution of cobalt 

 chloride, another with a solution made by adding 3 cub. centims. of a 

 saturated solution of chloride to 50 cub. centims. of water, and the 

 third portion with a saturated solution of the chloride ; the green com- 



