The relation of thallium to the alkali metals: a study of thallium-zinc sulphate and selenate

Abstract

In a communication made to the Royal Society in May, 1907, the results of the study of the normal sulphate and selenate of thallium were presented, and certain interesting conclusions concerning the position of the thallium salts in the rhombic series R 2 S Se O 4 discussed. It became particularly important that a similar study should be made of the monoclinic double salts of the series R 2 M ( S Se O 4 ) 2 .6H 2 O containing thallium as the R-metal, not only for the sake of confirming or otherwise the conclusions arrived at from the study of the simple salts, but also because it is desirable that the investigation of the monoclinic series of double salts should be completed as far as possible by the inclusion of the thallium salts of the series. For this reason, a begining has been made with the two salts containing zine as the M-metal, preliminary attempts at preparing a number of thallium salts of the series having shown that while all these salts, in general, were very difficult to prepare in good and transparent crystals of thallium-zinc sulphate were least difficult to obtain. The greatest difficulty of all is to procure them free from opacity, and while eventually excellent crystals of thallium-zinc sulphate were obtained of adequate transparency to permit of a complete optical investigation, thallium-zinc selenate has invariably proved white and opaque, and resisted all efforts at optical examination. Both salts, however, have been thoroughly investigated goniometrically, and thallium-zinc sulphate not only optically but also as regards its volume. The magnesium salts, which it was hoped to have included in this memoir, results at all comparable with the author's previous work. The crystals of the sulphate and selenate of thallium and zinc were both measured by Werther as regards a few of the principal angles, and later the crystals of the double sulphate were measured by Des Cloizeaux, who also examined some of the optical characters of the salt. The density of this salt and also its refractive indices were subsequently determined by Perrot.