ELISHA MITCHELL SCIENTIFIC SOCIETY. 11 
He has also prepared a chromo-disulphuric acid; ete); 
by evaporating solutions of chromium sulphate with 
two. three, etc., molecules of sulphuric acid, and then 
heating to 110°-120°. Calvert and Ewart’ have shown that, 
on diluting these, they all leave a colloidal Cr,(SO,);.H,- 
SO, upon the septum, the liquid passing through free of 
chromium. ‘The behavior of these solutions makes it ap- 
pear probable that the chromo sulphuric acids de not exist 
‘1 them as such, but are hydrolyzed, forming the colloidal 
substance, Cr,(SO,),.H,SO,, and free sulphuric acid. Our 
repeated experiments have failed to show the presence of 
this colloidal body in the ordinary green solutions of the 
alum or sulphate. A boiled solution of either, even 
though very concentrated, will pass entirely through an 
unglazed porcelain suction filter, such as Calvert and Ew- 
art made use of. There seems to be no colloidal body 
present. 
We cannot regard the experiments of Recoura as ad- 
vancing the subject in any degree. Asan explanation of 
the changes it is by no means satisfactory. Dougal’s 
formula for the reaction causing the change, is even more 
remarkable and baseless : 
2[Cr,(SO,),. K.SO,J+ 0,0 ra [Cr,O(SO,),JSO, + 2K,S0,-+- 
| H,SO,. 
This is not based upon Dougal’s own experimonts but is 
offered as an explanation deduced from the work of Re- 
coura, Whitney, Favre, and Valson. 
THE ACTION OF ALCOHOL. 
There have been several investigations of the action of 
alcohol, both upon the sulphate and the alum, with the 
hope of throwing some light upon the changes under con- 
sideration. ‘[raube? states that the solid salt is unatf- 
fected by boiling alcohol. Schrétter has observed’ that 
1 Chem. News. 74, 121. 
2 Hun. Chem. (Liebig), 66, 168. 
3 Pogg. Ann., 53, 413. 
