During the course of the researches on the hexahydrated double sulphates and selenates it was only found possible to obtain in adequately perfect crystals two of the salts containing thallium, namely, thallium zinc sulphate and selenate. Attempts have from time to time been renewed, however, and success has lately attended the efforts with two more of these salts, the two mentioned in the title of this communication. A complete study of them has, therefore, been made, with the results which are now given. The nickel salt was investigated in the year 1864 by Werther, and a few of the crystal angles were measured by him, just sufficient to determine the crystal elements. No optical or density observations whatever appear to have been made. Thallium cobalt sulphate has not, apparently, been investigated at all.