Page:Radio-activity.djvu/437

 It would be of scientific value to separate radium D from pitchblende and obtain it in the pure state, for, a month after removal, the β ray activity from it would be about 300 times as great as from an equal weight of radium. By placing a bismuth plate in a solution of this substance, radium F (polonium) should be separated, and, provided a sufficient interval is allowed to elapse, a fresh supply of radium F can at any time be obtained.

The rate of transformation of radium D (half transformed in 40 years) is sufficiently slow not to interfere seriously with its utility in most experiments.

The results of the comparison of the products of radium with those contained in polonium, radio-tellurium and radio-lead are summarized below.

{ Radium D = product in new radio-lead, no rays. Half transformed {  [v]        in 40 years. Products in old { Radium E gives out β rays, separated with bismuth, iridium Radio-lead  {   [v]        and platinum. Half transformed in 6 days. { Radium F = product in polonium and radio-tellurium. Gives {             out only α rays. Half transformed in 143 days.

242. Temporary activity of inactive matter separated from radio-active substances. We have seen in the last section that the platinum metals and bismuth acquire temporary activity by their admixture with a solution of radio-lead, and that these effects are very satisfactorily explained on the view that some of the products of change of radio-lead are removed with the inactive substances. Very similar effects have been observed by Pegram and von Lerch (section 186), when inactive substances were added to solutions of thorium and of the active deposit of thorium. These results, too, are almost certainly due to the removal of one or more of the products of thorium with the inactive matter. Examples of this character may readily be multiplied, and some of the more interesting and important of these will be briefly discussed later.

There have been two general points of view regarding the character of this activity which is temporarily acquired by inactive matter. Some people have supposed that the inactive molecules of the substance, mixed with the solution, acquire by "radio-active induction" temporary activity, the underlying idea being that the close admixture of an inactive and an active substance has communicated