204 THE ATOMIC WEIGHTS. 



THORIUM. 



The atomic weight of thorium has been determined from analyses of 

 the sulphate, oxalate, formate, and acetate, with widely varying results. 

 The earliest figures are due to Berzelius,* who worked with the sulphate, 

 and with the double sulphate of potassium and thorium. The thoria 

 was precipitated by ammonia, and the sulphuric acid was estimated as 

 BaS0 4 . The sulphate gave the following ratios in two experiments. The 

 third column represents the weight of ThO 2 proportional to 100 parts of 

 BaSO, : 



6 754 g rm - ThO 2 1.159 grm. BaSO 4 . Ratio, 58.274 

 1.0515 " 1.832 " 57.396 



The double potassium sulphate gave .265 grm. Th0 2 , .156 grin. S0 3 , 

 and .3435 K 2 S0 4 . The S0 3 , with the Berzelian atomic weights, repre- 

 sents .4537 grm. BaS0 4 . Hence 100 BaSO 4 is equivalent to 58.408 Th0 2 . 

 This figure, combined with the two previous values for the same ratio, 

 gives a mean of 58.026, .214. 



From the ratio between the K 2 S0 4 and the Th0 2 in the double sul- 

 phate, Th0 2 = 266.895. 



In 1861 new determinations were published by Chydenius.t whose 

 memoir is accessible to me only in an abstract J which gives results with- 

 out details. Thoria is regarded as a monoxide, ThO, and the old equiv- 

 alents (O = 8) are used. The following values are assigned for the 

 molecular weight of ThO, as found from analyses of several salts : 



From Sulphate. From K. Th. Sulphate. 

 66.33 67. 2 



67.13 



67.75 

 68.03 



Mean, 67.252, d= .201 



From Acetate. From Formate. From Oxalate. 



67.31 68.06 65.87-^ Two results 



66.59 67.89 65.95 j by Berlin. 



67.27 68.94 65.75 



67.06 65.13 



68.40 Mean, 68.297, rb .219 6654 



65.85 



Mean, 67.326, .201 



Mean, 65.85, .123 



* Poggend. Annal., 16, 398. 1829. Lehrbuch, 3, 1224. 



t Keraisk undersokning af Thorjord och Thorsalter. Helsingfors, 1861. An academic disser- 

 tation. 

 I Poggeud. Annal., 119, 55. 1863. 



