The London, Edinburgh and Dublin philosophical magazine and journal of science . ratures above700° C. the Th D is completely separated from the Th C, andby heating the active deposit to a suitably high temperatureit is possible to remove practically the whole of the Th B also,thus leaving Th C almost pure/ The method of volatili-zation has proved a simple and efficient means of obtainingTh C free from Th D. Methods used by other experimentersthave depended on the difference of electrochemical behaviour * Loc. cit. t Von Lerch, Wien. Ber. cxiv. ii. a (1905); von Hevesv, Phil. 628, April
The London, Edinburgh and Dublin philosophical magazine and journal of science . ratures above700° C. the Th D is completely separated from the Th C, andby heating the active deposit to a suitably high temperatureit is possible to remove practically the whole of the Th B also,thus leaving Th C almost pure/ The method of volatili-zation has proved a simple and efficient means of obtainingTh C free from Th D. Methods used by other experimentersthave depended on the difference of electrochemical behaviour * Loc. cit. t Von Lerch, Wien. Ber. cxiv. ii. a (1905); von Hevesv, Phil. 628, April 1912. 816 Mr. A. on the of these two substances. Such methods are rendered unsatis-factory by impurities in the metal employed for the separationrand it is only by taking special precautions that the Th C isdeposited free from Th D. It is interesting to note thatHahn and Meitner * employed the method of volatilizationfor the separation of Act C and ActD. V. Lerch andv. Wartburg f also found that Th D was readily separatedfrom the active deposit by heat. Fiff. 3. 100 X. 20 50 40 SO 60 70 T/M£ /A/ M//VS. {AFTER ffEAtOML FF?OA1 FVtfK/lCfJ Fig. 3 A shows the result of an experiment in which thewhole of the Th D has been volatilized. It will be noticedthat there is a pronounced initial rise due to growth of Th Drthe curve then decaying with a period a little greater than * Hahn & Meitner, Phys. Zeit. ix. p. 649 (1908). t V. Lerch & v. Wartburg, Wien. Ber. cxviii. p. 1575 (1909). Volatility of Thorium T). 817 that of Th C. The presence of a small percentage of Th Bwith the Th C in no way affects the point to be discussed, asthe soft /3 rays from Th B are completely absorbed by thebottom of the electroscope. Fig. 3 B represents the logcurve for the exponential portion of curve A, whence wecan at once obtain the whole curve of /3 activity in the casewhere no Th D has been volatilized; this is represented by thedotted portion (6) of curve A fig. 3. It is obvious that thediffere
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