Relative Activities of Radio-Products of Thorium. 337 



are also present, cannot interfere ; even the latter will have 

 practically all disappeared in the half hour usually occupied 

 by the separations. 



(1) Hahn* found that Ms 2 is carried down when zirconium 

 hydroxide is precipitated by ammonia. 



(2) Marckwald t found a similar behaviour with ferric 

 iron and ammonia. 



(3) We have regularly used aluminium hydroxide in the 

 same way as a means of separating Ms 2 from solution. The 

 Ms 2 seems to be carried down quantitatively with the 

 aluminium. This reaction allows an easy and complete 

 separation of Ms 2 from barium, Ms l5 and ThX. 



(4) Mesothorium-two is not carried down with the mercuric 

 sulphide when hydrogen sulphide is passed into a slightly 

 acid solution to which a little mercuric chloride has been 

 added. This procedure will remove B and C completely if 

 repeated two or three times. 



(5) Mesothorium-two and Rt are closely alike in chemical 

 properties, but not identical. The former is not carried down 

 when a little added thorium nitrate is precipitated from a 

 neutral solution by means of hydrogen peroxide at 60° or 

 70°. All the Rt is removed by the thorium. If the thorium 

 used has been precipitated by hydrogen peroxide and changed 

 back to nitrate before being; used, it does not introduce anv 

 active impurity into the Ms 2 . This is the best method of 

 separating Rt and Ms 2 . 



(6) Barium sulphate precipitated in slightly acid Ms 2 

 solutions carries the latter down readily. Material for the 

 films used in activity measurements was prepared in this 

 way. 



RadiotJiorium. — Since Rt cannot be separated from thorium 

 by any known method J, its only practical source is a prepa- 

 ration of Msi in barium chloride, from which it can be com- 

 pletely separated by means of alumina, precipitated by pure 

 ammonia. To obtain radioactively pure Rt from this precipi- 

 tate it is not necessary to separate Ms 2 chemically, as the 

 latter will decay in the course of a few days. ThX, B, and 

 C are then easily removed, the former by precipitations of 

 the alumina by means of ammonia, the latter two by means 

 of mercuric sulphide. Three or four alternate precipitations 

 of the alumina and of mercuric sulphide in the aluminium 

 chloride solution readily give pure Rt. In addition to those 

 reactions of Rt in which it is associated with thorium §, the 



* Phys. Zeit. ix. p. 246 (1908). + Ber. xliii. p. 3420 (1910). 



% McCoy & Ross, Jour. Am. Chem. Soc. xxix. p. 1709 (1907). 

 § McCoy & lioss, he. cit. 



