Relative Activities of Radio-Products of Thorium. 339 



(6) ThX is partially carried down with ferric hydroxide, 

 from ferric chloride and pure carbon-dioxide-free ammonia, 

 the fraction carried down varying with the amount of iron. 

 If ordinary ammonia, containing carbonate, is used, all the 

 ThX is found in the precipitate. 



(7) ThX is not carried down to an appreciable extent 

 when the following are precipitated by pure ammonia : — 

 Aluminium, zirconium, cerium, lanthanum, yttrium, and 

 didymium hydroxides. 



(8) ThX is not carried down when the following are 

 precipitated by hydrogen sulphide : — Lead, mercury, tin, 

 zinc, and iron. 



llwrium B and C. — (1) B and C are not separated from 

 thorium when the latter is precipitated by most reagents ; 

 but precipitation by pyridine * or by metanitrobenzoic acid f 

 leaves B in the filtrate. 



(2) B and C are removed very completely from a thorium 

 solution when mercury, lead, or zinc are precipitated in it as 

 sulphides by means of hydrogen sulphide. 



As is well known, B and C are most easily obtained in 

 free form by exposure of a negatively charged plate to the 

 emanation. We have used very active Rt, contained in a 

 few milligrams of ferric carbonate, as a very satisfactory 

 source of the emanation. We found that a small amount of 

 ThX, thrown out by recoil J, also accompanies the B and C 

 in the active deposit. To exclude the ThX, the Bt was 

 covered with a piece o£ tissue paper, which did not prevent 

 the diffusion of most of the emanation. The deposit obtained 

 in the course of a day or two was very active. It was dis- 

 solved from the platinum plate by hot dilute hydrochloric or 

 nitric acid, and used in studying the reactions of B and C. 

 Since B is inactive, with a period o£ 10*6 hours, and C gives 

 alpha rays, with a period of 60'8 minutes, it is very easy to 

 recognize the presence of either or both by observations of 

 the change o£ activity with time. B and C behave similarly 

 in the following reactions carried out with solutions of the 

 active deposit : — 



(3) B and C are carried down with aluminium or cerium 

 when these are precipitated by ammonia. 



(4) They are also carried down with lead, mercury, or 

 zinc, when these elements are precipitated as sulphides by 

 hydrogen sulphide in slightly acid solutions. 



* Moore & Sclilundt, Trans. Am. Electrocheni. Soc. viii. p. 269 (1905). 



t Ashman, Amer. Jour. Sci. [4] xxvii. p. 65 (1909). 



X Halm & Meitner, Verh. d. Phys. Ges. xi. p. 55 (1909). 



