End-Products of Thorium

Abstract

IN a letter to NATURE of May 24, 1917, Prof. Soddy states that 65 per cent, of thorium-C expels first a β- and then an α-ray, transforming into an isotope of lead, and suggests that (on the analogy of radium-D) this isotope of lead may be further disintegrated. He says that he has detected the presence of thallium in thorite in amounts that sufficed for chemical as well as for spectroscopic identification, and suggests that the lead isotope referred to may be transformed into thallium owing to an α- and β-change. If thallium were an end-product of thorium, we should expect that it would be found in all thorium minerals, unless, of course, these have been sufficiently altered to account for the removal of the products. I have lately been engaged in the examination of thorianite for Prof. Joly, the chief object of the investigation being the determination of the proportion of thallium, if any, and its relation to thorium. I have not been able to detect any thallium in the mineral, and I am confident that it does not contain even 0.005 Per cent.