278 Hartley — The Action of Henf on the AI)Sorpt.ion Hpectra and 



The experiments of Tichboriie,* made chiefly on the cobalt and copper chlor- 

 ides, are similar to those of von Babof and of Schiff.J With dilute solutions 

 in sealed tubes at high temperatures, he obtained apparentl}^ the same changes of 

 colour as those I have sliown 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 whicli 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. If 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 CrCls would not have 

 been formed. 



*• Chem. News, vol. xxv., p. 133, 1872. f Jahresbericht, 1857, p. 72. 



t .\nn. Chem. Phar., ex., p. 203. § Wiener Akad. Beriohte, Ivi. (2), p. 724. 



II Aunalcn der Chemie, vol. 13, 148, 253. 



