In some recent experiments, Hofmann, Gonder and Wölfl11 have made a close chemical examination of the radio-active lead, and have shown the presence of two radio-active constituents, which are probably identical with the products radium E and F. The radio-active measurements were unfortunately not very precise, and the periods of change of the separated products have not been examined very closely.
Experiments were made on the effect of adding substances to a solution of radio-lead, and then removing them by precipitation. Small quantities of iridium, rhodium, palladium, and platinum, in the form of chlorides, were left in the solution for three weeks, and then precipitated by formalin or hydroxylamine. All of these substances were found to give out both α and β rays, the activity being greatest for rhodium and least for platinum. A large proportion of the β ray activity disappeared in the course of six weeks, and of the α ray activity in one year. It is probable that the two products radium E and F were in part removed with the metals from the radio-lead. We have seen that radium E gives out β rays and loses half of its activity in about six days, while radium F gives out only α rays and its activity falls to half value in 143 days. This conclusion is further confirmed by experiments on the effect of heat on the activity of these substances. By heating to a full red heat, the α ray activity was lost in a few seconds. This is in agreement with the results (section 232) where we have seen that radium F is volatilized at about 1000° C. and radium E is left behind.
Salts of gold, silver and mercury added to the radio-lead were found to show only α ray activity on removal. This is in accordance with the view that radium F alone is removed with these substances. Bismuth salts on the other hand showed initially α and β ray activity, but the latter rapidly died away. The presence of β rays in freshly prepared polonium was early observed by Mme Curie. The α and β ray activity of the radio-lead is much reduced by the precipitation of bismuth added to the solution. The α and β ray activity of the radio-lead, however, recovers itself again. This result is exactly what is to be expected if radio-lead contains radium D, E and F. Radium E and F are removed with the bismuth, but the parent substance, radium D, is left behind, and, in consequence, a fresh supply of radium E and F is produced.
While further experiments are required to settle definitely whether the products separated from radio-lead are identical with radium E and F, there