214 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 Ber- 

 zelius,* who worked with the sulphate, and with the double 

 sulphate of potassium and thorium. The thoria was pre- 

 cipitated by ammonia, and the sulphuric acid was estimated 

 as BaSOi- The sulphate gave the following ratios in two 

 experiments. The third column represents the weight of 

 ThO, proportional to 100 parts of BaSO^ : 



.6754 grm. ThO, = i-i59 gini. BaSO^. Ratio, 58.274 



1.0515 " 1.832 " " 57.396 



The double potassium sulphate gave .265 grm. ThO 2, .156 

 grm. SO 3, and .3435 K^SO^. The SO 3, with the Berzelian 

 atomic weights, represents .4537 grm. BaSO^. Hence 100 

 BaS04 is equivalent to 58.408 ThO,. This figure, combined 

 with the two previous values for the same ratio, give a mean 

 of 58.026, ± .214. Hence ThO, = 269.940, ± .997. 



From the ratio between the K2SO4 and the ThO, in the 

 double sulphate, ThO, = 268.284. 



In 1861 new determinations were i^blished by Ch3^de- 

 nius,t whose memoir is accessible to me only in an abstract ;|: 

 which gives results without details. Thoria is regarded as 

 a monoxide, ThO, and the old equivalents (0 = 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 , 67.02 



67-13 

 67.75 

 68.03 



Mean, 67.252, dz .201 



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



f Kemisk undersokning af Thorjord och Thorsalter. Helsingfors, 1861. An 

 academic dissertation. 



t Poggend. Annal., 119, 55. 1S63. 



