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 determinations 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.