In a note on “the hydrolysis of thallic sulphate” which I communicated to the Society some time ago, I commented on theconflicting nature of the statements, made by various investigators, as to the exact composition and nature of thallic sulphate. As the subject appeared of some interest, I subsequently commenced an investigation of the salt and of the double salts derived from it. The results so far obtained are in some respects rather striking, but the investigation is not yet completed, and my reason for now publishing a general statement of these results is, that apparently others besides myself are working in the same field. A paper has just been published by James Locke, in which the author describes a caesium thallic sulphate which he obtained while endeavouring to prepare cæsium thallic alum. No alum could be obtained, the most hydrated salt corresponding to the formula CsTl(SO4)2, 3H2O.