THE ATOMIC WEIGHT OF THORIUM.* 



BY R. Q. : B. DAVIS. 



The atomic weight of thorium has been determined with 

 varying- results. The values are dependent upon the analyses 

 of the oxalates, sulphates, formate, acetate and acetonyl-ace- 

 tonate. The first value is due to Berzelius 1 and was obtained 

 from the sulphate and double sulphate of thorium and potas- 

 sium. The thorium was estimated by precipitation with 

 ammonia and the sulphuric acid as BaS04. The value obtained 

 was 234.8. 



In 1861 Chydenius 2 published new determinations from 

 analyses of sulphates, acetate, formate and oxalate. The 

 mean of his determinations gave thorium, 233.1. Two years 

 later in 1863 Marc Delafontaine published some researches on 

 thorium 3 . His studies were particularly on the sulphates. 

 The thorium he estimated in two ways: (1) by precipitation as 

 oxalate and subsequent ignition, (2) by direct calcination. 

 From his work a value of 230.3 for thorium was obtained. 



The next determinations were those of Cleve 4 . His work 

 was with the sulphates and oxalates. Next came the work of 

 Nilson 5 on the sulphates. Then in 1887 Kruss and Nilson 6 

 published determinations. Of the most trustworthy values 

 given by Clarke 7 the value for thorium varies from 223.06 to 

 236.93, a mean giving the value 232.6. 



*[ Dissertation presented to the faculty of the University of North 

 Carolina for the degree of Doctor of Philosophy. 

 l Poggend Annal., 16, 398. 1829. 

 2 Poggend Annal, 199, 55. 1863. 

 sArch. Sci. Phys. et Nat. (2) 18, 343, 

 4 Jour, fur Prakt. Chem., 93, 114. 

 5 Ber. Deutsch. Chem. Gesell., 15, 2519. 1882. 

 6Ber. Deutsch. Chem. Gesell. 20, 1665, 1887. 

 7 Constants of Nature, Part V. 



1905] 46 



