278 HartLeyv—The Action of Heat on the Absorption Spectra and 
The experiments of ‘Tichborne,* made chiefly on the cobalt and copper chlor- 
ides, are similar to those of von Babo} and of Schiff.t With dilute solutions 
in sealed tubes at high temperatures, he obtained apparently the same changes of 
colour as those I have shown are produced in saturated solutions when heated 
to 100° C. 
All cobalt salts are stated by Bersch§ to be turned blue by heat. The nitrate 
does so just at the temperature when decomposition of the salt commences; but 
this cannot in any way be said of the sulphate which may be heated to redness 
without change. In the case of cobalt nitrate, it is not improbably due to the 
formation of an oxynitrate; for a blue oxynitrate may be produced by precipi- 
tation with alkali, and an intermediate product of the decomposition of cobalt 
nitrate by heat would probably be an oxynitrate or basic salt. 
The view formerly held, that the haloid salts of cobalt and copper when 
dissolved, and the solution diluted, were decomposed into hydrochlorides of 
cobaltous or cupric hydroxides, has been recently revived in a modified form 
by supposing that these and other salts are hydrolysed. 
On the authority of Winkelblech,|| it has been stated that the blue precipitate 
formed by caustic alkali in cobalt chloride solutions is a basic salt, which, by the 
action of water, is converted into a pink hydroxide. I have completely confirmed 
this observation, and distinctly shown that the salts are not hydrolysed, the 
evidence being of the following character :— 
When cobalt chloride, bromide, or iodide is mixed with a solution of barium 
hydrate or of potassium or sodium hydroxides, the liquid being contained in a 
Torricellian vacuum, and the metallic chloride being in excess in the solution, the 
salt precipitated is blue, and its composition is that of an oxychloride. It passes 
into the pink hydroxide by the continued action of water, and when exposed to the 
air, it undergoes simultaneously more or less oxidation. Jf washed with water 
continuously for three weeks, it is found that the salt is losing chlorine, but is still 
not freed from that substance, notwithstanding it has been in contact with from 
1200 to 2500 times its volume of water. If the salt had been hydrolysed, it could 
not have survived the action of caustic alkali followed by a copious washing with 
water, and no oxychloride would have been formed, nor would its decomposition 
in presence of water have been so exceedingly sluggish. Another instance occurs 
in the case of the hydrated chromium chloride, which, when heated strongly, yields 
partly anhydrous chromium chloride, and partly chromium oxide. This salt could 
not have been hydrolysed in its solution or the insoluble CrCl; would not have 
been formed. 
* Chem. News, vol. xxv., p. 138, 1872. + Jahresbericht, 1857, p. 72. 
+ Ann. Chem. Phar., cx., p. 203. § Wiener Akad. Berichte, lvi. (2), p. 724. 
|| Annalen der Chemie, vol. 13, 148, 253. 
