286 Harritny— The Action of Heat on the Absorption Spectra and 
would be expected of it if the green colour be caused by simple loss of water. 
These facts, taken together, suggest that the green solutions of chromium differ 
from the violet in the following manner :— 
Salts of Chromium, Cr., Violet. Salts of Chromyl,* Cr20, Green. 
Olnllomge, 5 o o  CreGll ese. Cinkorls, 5 5 »o CrOOhELO, 
Sulphate, . . . Cr.3S0,15H,0. Sulphate, . . . Cr,0-2S0,:7H,0. 
Nitrates 9s. 4 Cr GINO SEO: INEM, 4 9 o (CrRORINTO-lsL(0), 
The relation of the green to the violet compounds is similar to that existing 
between the salts of uranium and uranyl: as, for instance, the chloride— 
Chloride of Uranium. Chloride of Uranyl. 
Ur(Cl,. UrOCl. 
If one-third the sulphuric acid in chromic sulphate is neutralised by sodium 
carbonate, experiment has shown that, though boiling does not precipitate a 
moderately strong solution, yet ebullition, with about 3000 times its bulk of water, 
causes a precipitate. This is caused by the formation, first, of chromyl sulphate, 
which is afterwards decomposed by water at 100°C. to produce the insoluble basic 
salt. 
The view I have advanced of the constitution of the chromium salts was first 
published in the Proceedings of the Royal Institution of Great Britain for 1875, 
being contained in a report of a Friday evening lecture ‘‘ On the Action of 
Heat on Coloured Liquids.”+ ‘The experimental evidence was not communicated, 
but only an outline of the conclusions. 
It has been confirmed of late years by the thermo-chemical researches of 
Recoura.t He found that the sulphate Cr,O;°3S0; was split into two molecules 
represented by 2Cr,035SO, and H,SO, When the sulphate was decomposed 
by alkali, a new hydroxide was formed which combines with only 2H,S0O,; 
therefore Cr,O3'SO3, a green sulphate, was obtained, Cr.O;°3SO,°11H,O in the 
solid state, which is easily converted by water into the violet modification. It was 
also shown that, if the compound Cr,O;°3SO; is mixed with a sulphate, such as 
CuSO,, the two instantly combine to form a chromo-sulphate with the formula 
(Cr.480,)Cu; and that chrome alum, when partially dehydrated, becomes 
potassium chromosulphate (Cr.4S0,)Ky'4H,0. 
Cross and Higgin§ also have shown the existence of chromo-sulphates. 
* This was the name originally proposed in the paper from which this is an extract, but the compound 
CrO,Cl, is now called chromyl chloride. 
+ See also Proc. Roy. Soc., vol. 33, p. 872, 1875. Abstract, and also Chemical News, vol. 65, p. 15, 
1892. 
+ Comptes Rendus, vol. 100, p. 1227; vol. 101, p. 485; vol. 102, p. 515, also pp. 548, 865, and 921; 
vol. 110, pp. 1029, 1198; vol. 112, p. 1489; vol. 113, pp. 857, 1037; vol. 114, p. 477. 
§ Jour. Chem. Soc. Trans., vol. 41, p. 118, 1882. 
