284 Hartley — The Actmi of Heat on the Absorption Spectra and 



The first action of a temperature of 300° C. is then represented as follows : — 

 2CroOCl4-2H20 = Cr.Clo + CrA + 2HC1 + H^O. 



Schrotter's and Loewel's experiments lead to similar results, but are applied 

 to different compounds. 



When Kruger operated on a strong solution of chrome alum, he found that 

 from the violet solution the original salt was precipitated by alcohol. If the 

 .solution was boiled until green, and alcohol then added, the green salt was 

 precipitated as an oily liquid, and the alcohol contained a portion of the 

 sulphuric acid. The change of colour, therefore, he said, was due to the produc- 

 tion of a basic compound. On repeating this experiment, and extending it to 

 other salts, such as the chromic sulphate and chromic nitrate, similar results 

 were not obtained. I operated in the following way, taking four grams of each 

 salt and dissolving it in 40 c.c. of water. The liquid was divided into two equal 

 parts; one was precipitated by alcohol, the other was boiled, allowed to cool, and 

 alcohol in gradually increased quantity added, but the result was only a green 

 solution. The violet hydrated salts, tlierefore, are insoluble in alcohol, while the 

 green compounds are soluble. It occurred to me that Kruger had added alcohol 

 to the hot liquid, and so obtained a decomposition of the salt; I therefore took a 

 boiled solution, cooled one-half, which still remained green, and made both 

 liquids up to the same bulk with alcohol. The hot solution rendered a green oil- 

 like precipitate ; the cold one, however, did not do so. We cannot, therefore, 

 consider it proved that a basic salt existed in both these solutions. 



When the so-called chromic hydrate, CraOs-OHaO, is dissolved in nitric acid 

 and kept quite cold, it forms at first a purple solution, but after a certain amount 

 of the acid has been saturated, the solution turns green, the return to a purple 

 colour being caused by a further addition of acid. The green solution is 

 uncrystallizable ; the purple, as I have already mentioned, does crystallize. 

 Schrotter* found that, if as mucli chromic hydrate as possible is dissolved in 

 sulpliuric acid, a green liquid results which contains the salt, Cr203*2S03(A): — 



Ci'aOa, . . . 50-19 50-68 per cent. 



SO3, . . . 49-81 49-31 



100-00 99-99 



When a solution of this salt is boiled, a green precipitate separates which has 

 the composition 3Cr203-2S03 (B), with probably six molecules of water. 



If the green solution obtained by boiling the violet salt be contained in the com- 

 pound (A), it ought, on the addition of a large quantity of water and subsequent 

 ebullition, to precipitate the compound (B). But it has already been stated that 



*Pogg. Annalen, vol. liii., p. 513. 



