48 Journal of the Mitchell Society. [March 



a hot funnel with aid of suction and washed until free from 

 acid. From each of these different sources the thorium was 

 used in the work to be described below. 



In this work the crucibles were obtained specially for the 

 purpose and were never used for anything- else. The crucible 

 in which the substance was weighed was counter-poised by a 

 crucible as near the same size and weight as possible. The 

 weig-hts were specially standardized by the Bureau of Stand- 

 ards and Weights at Washington and were never used for 

 any other work than this. The balances were adjusted to a 

 constant load and every weig-ht made at that load. The bal- 

 ances were not used for any other purpose after the beginning 

 of this work. The weigiiing-s were made by the method of 

 vibrations and were made to 0.000001 of a gramme. 



After the purity of our thorium compounds was proven by 

 spectroscopic examination, we first turned our attention to 

 the determination of the atomic weig-ht by the synthesis of 

 the sulphate from the oxide. The method of Gerhard Kruss 1 

 was used. The oxide was brought to constant weig-ht by heat- 

 ing with a blast lamp, then evaporating- with sulphuric acid 

 (1:1) several times to convert all the oxide into sulphate. 

 Then the sulphate was brought to constant weight at a tem- 

 perature of 360°C. In bringing- the sulphate to constant 

 weig-ht, a bath of platinum was used. This bath con- 

 sisted of a cylindrical tube of copper, about four inches 

 in diameter, mounted above a rose burner, and lined inside 

 with platinum and outside with asbestos. The crucible was sus- 

 pended in the center of the bath by a ring- of platinum wire. 

 The temperature was taken by inserting- a mercury thermom- 

 eter beside the crucible. The mercury was under twenty 

 atmospheres of pressure by carbon dioxide, and the thermom- 

 eter was graduated to 560°C. It was standardized at the 

 Reichs Anstalt. The results were not strictly concordant and 

 an investigation showed that the ratio between oxide and 

 sulphate varied with the temperature. 



iChern. News, Jan. 30, 1893. Pp. 32. 



