596 Proceedings of Royal Society of Edinburgh. [sess. 
The Hydrolysis of Thallic Sulphate. 
By Hugh Marshall, D.Sc. 
(Read June 5, 18S9.) 
The alteration of the amount of hydrolysis by change of 
temperature has been directly observed in connection with various 
salt solutions. In the case of ferric salts, quantitative deter- 
minations have been carried out by Wiedemann, employing 
magnetic methods. He showed that, in the case of the sulphate, 
the amount of hydrolysis is considerably increased by rise of 
temperature. A similar effect is observed in the case of gallic 
sulphate, and here the change is directly evident; a solution of 
the salt when heated deposits white basic salt, which re-dissolves 
on cooling. A somewhat analogous case which has recently come 
under my notice, and which, so far as I am aware, has not been 
noted previously, is provided by thallic sulphate solution. The 
thallic salts generally are decomposed more or less easily by 
water, with formation of a brown precipitate, but dissolve in 
dilute acids, giving colourless solutions (Crooke, Lamy, Willm, 
Strecker). An acid solution of thallic sulphate, provided it does 
not contain too great an excess of sulphuric acid, may be used to 
illustrate several points connected with the hydrolysis of salts. 
Dilution with water produces a brown precipitate. A similar 
precipitate is formed in considerable quantity when the solution 
is warmed; when the mixture cools, the precipitate slowly re- 
dissolves, and a clear colourless solution is again obtained. It is 
therefore evident that the formation of the precipitate is not due 
simply to a colloidal substance being rendered insoluble, but to 
a greatly increased hydrolytic action. A further interesting point 
observed with some of solutions examined, though not with all, 
was the effect of other sulphates upon the action. Certain 
solutions which gave deposits on heating, and cleared again on 
cooling, were found to give no precipitate after a considerable 
quantity of solid ammonium sulphate had been dissolved in the 
solution, indicating that at higher temperatures there is less 
hydrolysis in presence of the other sulphate. Other solutions 
gave a precipitate even after the addition of ammonium sulphate, 
