Section 207. It Will Be Shown That the Active Deposit of Thorium

contains two distinct substances which have different rates of transformation.

=187. Effect of temperature.= The activity of a platinum wire which has been exposed in the presence of the thorium emanation is almost completely lost by heating the wire to a white heat. Miss F. Gates found that the activity was not destroyed by the intense heat, but manifested itself on neighbouring bodies. When the active wire was heated electrically in a closed cylinder, the activity was transferred from the wire to the interior surface of the cylinder in unaltered amount. The rate of decay of the activity was not altered by the process. By blowing a current of air through the cylinder during the heating, a part of the active matter was removed from the cylinder. Similar results were found for the excited activity due to radium.

F. von Lerch (loc. cit.) determined the amount of activity removed at different temperatures. The results are shown in the following table for a platinum wire excited by the thorium emanation.

Temperature Percentage of activity removed

Heated 2 minutes 800° C. 0

then „ ½ minute 1020° C. 16 more

„ „ ½ „ 1260° C. 52 „

„ „ ½ „ 1460° C. 99 „

The effect of heat on the volatilization of the active deposit of radium has been examined in detail by Curie and Danne. The interesting and important results obtained by them will be discussed in chapter XI,