148 CHEMICAL DISCOVEEY AND INVENTION 



say, half a ton of pitchblende residues from Joachimsthal. 

 These residues were delivered by the Austrian Government to 

 M. Armet de Lisle in Paris for preliminary extraction .... 



" Thorpe received from Paris 413 grams of mixed chlorides of 

 barium and radium, the radio-activity of which was 560 times 

 that of uranium. . . . 



" The method of separation of radium and barium followed 

 by Thorpe was substantially the same as that adopted by 

 Madame Curie ; 9400 recrystallisations of the chlorides were 

 carried out, towards the end in silica vessels. . . . 



" The analytical process was also identical with that em- 

 ployed by Madame Curie, namely, precipitation of silver chloride 

 from the dissolved radium chloride acidified with nitric acid, 

 subsidence, washing with distilled water six times, drying at 

 160, and weighing on an assay balance sensitive to 0-1 mgrm. . . . 



" The results of Thorpe's determinations are : 



I. 226-7 II. 225-6 III. 227-6 



" A new set of determinations has been made by Honig- 

 schmid (1911) in which quantities somewhat exceeding 1 gram 

 were used. The method of purification was again that employed 

 by Madame Curie and Thorpe, viz., repeated crystallisation of 

 the chlorides from hydrochloric acid and precipitation of the 

 aqueous solution of the salt with alcohol. The equivalent was 

 not altered after 50 such crystallisations and 13 precipitations 

 with alcohol, and that material was regarded as pure, and 

 employed in the final determinations. The method, too, was 

 the same as that described, but in two cases the chloride of 

 silver was reduced and the weight of the silver ascertained. 

 The mean result, taking Cl= 35-46 and Ag= 107-88, was 225-95. 

 The extremes in seven determinations were 225-92 and 225-97. 



" Whilst these researches show the approximate atomic 

 weight of radium it cannot be said that the results must be 

 accepted as final, for they are lacking in several of the con- 

 ditions stated at the beginning of this paper. There is the 

 possibility of contamination of the solutions with the reagents 

 used ; transference was necessary in all the experiments ; both 

 Madame Curie and Sir Edward Thorpe were troubled with 

 insoluble deposits ; and the accuracy of weighing was in the 

 former case only 1 in 8000, and in the latter only 1 in 700. These 

 disadvantages were absent from the method which we employed, 



