9 JOURNAL OF ‘THE 
have attributed these changes to a separation of the 
chromium sulphate from the alkaline sulphate; Berze- 
lius' and Fremy’ assigned as the cause of the changes 
the formation of a basic sulphate; Recoura and Whitney’ 
and Dougal‘ have considered the true cause to be the for- 
mation of a chrom-sulphuric acid; Schrétter? suggested 
a partial dehydration, and Etard’ also thought the 
change due to an alteration in hydration; Roscoe and 
Schorlemmer’ regarded the green solutions as containing 
mixtures of basic and acid salts; Loewel* advanced the 
theory of an isomeric change. 
It is quite manifest that any theory like that of Fis- 
cher and Jacquelain, based upon an examination of the 
alums alone, is quite inadequate. It is further evident 
that any phenomenon which has aroused so great a va- 
riety of speculations as this must be considered very care- 
fully with due weighing of every known fact. These 
facts are numerous and important. 
HOW THE CHANGE MAY BE BROUGHT ABOUT. 
Chrome-alum is soluble in six parts of water ; the vio- 
let solution suffers the alum slowly to crystallize out 
unchanged by spontaneous evaporation; but if heated to 
between 50° and 75° it turns green and, according to the 
extent of decomposition, either deposits on evaporation a 
brilliant, green, amorphous, difficultly soluble mass, or 
‘‘yields crystals of sulphate of potash, leaving green sul- 
phate of chromic oxide in solution.’” 
Schrétter says the change takes place at 65°-70°. He 
1 Ann. Phys. Chem., 61, 1. 
2 Compt. rend., 47, 883. 
3 Ztschr. phys. Chem., 1896, 20, 40. 
4J, Chem. Soc., Lond., 7896, 69, 1526. ; 
5Pogg. Ann., 53, 513. 
6 Compt. rend., 84, 1090. 
7Treatise on Chemistry, First Edition, Vol. IJ, Pt. II, 163. 
by..a, Pharm, (3),>7, Se... 
9Fischer, cited in Gmelin: Handbuch, 7850, IV, 149. 
