266 Hartitey—The Action of Heat on the Absorption Spectra and 
permanganates, solid and in solution, cobalt glass, cobalt hydrate, cobalt chloride, 
blue, solid, the same red, solid. Cobalt chloride in water, hot and cold, cobalt 
chloride in alcohol, in strong and dilute solution. Uranium nitrate solid, and 
dissolved in alcohol and in water. 
The change in the spectrum of cobalt chloride, he mentions as one of the most 
remarkable examples which had come under his observation. He examined also 
various chromium compounds. Vogel does not appear to have sought the cause of 
the change in the spectra of these substances. Von Babo* tried the influence of 
dehydrating substances and of heat on cobalt chloride solutions. A few drops of 
a concentrated solution of cobalt chloride, when added to a solution of calcium or 
magnesium chloride boiling at 114°, became blue at ordinary temperatures ; a more 
dilute solution boiling at 108° gave a red liquid under the usual conditions, but 
became blue on boiling. 
A solution of common salt mixed with the cobalt compound is red until heated. 
With zine chloride the same alteration did not take place, a fact explained by 
von Babo by the probable formation of a double salt being supposed. If we 
regard the matter from the point of view that dissociation takes place in these 
solutions, then the addition of a dehydrating substance facilitates this change in the 
solution, and the action of calcium and magnesium chlorides is easily understood. 
In the case of zine chloride, if we presume, as von Babo suggested, that a double 
salt is formed, we can just as readily understand that cobalt-zine chloride does not 
undergo dissociation, or that the zinc chloride of the compound does not favour it, 
but on the contrary prevents it, for its very action, as a dehydrating substance 
attracts water to the molecule and retains it, so that the hydrated zinc-cobalt 
chloride molecule is not dissociated, or, in other words, the metallic haloid 
compound is not separated from its combined water at or about 100° C., when 
in solution in water. 
* Jahresbericht, 1857, p. 72. 
