12 JOURNAL OF THE 
solutions covered with a layer of alcohol become gradu- 
ally green and the concentrated green solution is not dis- 
solved by alcohol. Of course the first observation does 
not necessarily connect the alcohol with the change. Al- 
cohol in large amounts precipitates from violet solutions 
ef the sulphate a pale violet colored, crystalline pow- 
der, and decolorizes the liquid.’ This can be used as 
a mode of purifying the alum.? S:ewert® states that, 
when the violet sulphate is dissolved in a small amount of 
water and boiled with alcohol until the crystals formed 
are again taken up and then precipitated with ether, a 
green syrup is gotten which consists of 5Cr,O,12SO,.7H,O 
and the mother-liquor contains suiphuric acid in a condi- 
tion in which it is net precipitated by barium chloride. 
Kriiger’ states that alcohol precipitates from a green so- 
lution of the alum a green oil which solidifies and which 
contains only two-thirds of the sulphuric acid. Siewert 
confirms this and says that this substance has approxi- 
mately the composition 6K,0.5€r,O,.18SO,.H,O. Kri- 
ever mentioned the acidity of the alcohol used in precipi- 
tating the green oily liquid and evidently regarded it as 
withdrawing sulphuric acid from the original salt. He 
also mentioned the formation of a basic salt, by heating 
the green solution until it becomes rose-red, which con- 
tains half as much acid as the neutral salt and is insolu- 
ble in water. 
After a careful consideration of the results obtained by 
others by means of alcohol, it seemed to us quite possible 
that these might afford a clue to the explanation we were 
in search of. It was necessary to examine with care the 
action upon both the violet and the green solutions. Our 
experiments are therefore given in detail, and it will be 
1 Gmelin’s Handuch, IV, 127. 
2 Baugigny and Pechard :Loc. cit. 
3 Ann. Chem. (Liebig), 125, 97. 
4 Ann. Phys. Chem., 61, 318. 
