igof\ Davis — Atomic Wkigiit of Thorium. 53 



ratio between the chloride and the oxide of thorium by direct 

 evaporation of the chloride solution and the subsequent igni- 

 tion of the residue to the oxide. But noting - that the hard 

 glass tube, in which the chloride was formed, seemed to be 

 attacked by the chlorine at the temperature required for the 

 formation of the chloride, it seemed possible that the disa- 

 greement of our values might be due to the formation of other 

 chlorides from the glass. A series of experiments confirmed 

 this view that the glass was causing a contamination of our 

 thorium compound. Hence we set about to eliminate this 

 trouble. 



Quartz tubes were imported especially for the work. These 

 were about 2 cm. in diameter and 25 cm. long. In one end of 

 one of these was placed the carbon boat with the mixture of 

 carbon and thorium oxide, and the whole inserted in a porce- 

 lain tube and placed in the furnace. The porcelain tube was 

 heated while a stream of dry chlorine was passed through. 

 The "Weisser-dampf" settled on the walls of the porcelain 

 tube, near the end, and the crystals of tetrachloride formed 

 in the quartz tube. 



For weighing the chloride, special weighing bottles, 39 cm. 

 long, were obtained. Into one of these the quartz tube was 

 quickly inserted on withdrawing it from the porcelain tube, 

 and after removing the carbon boat. A second weighing bot- 

 tle was used as counter-poise. The solution of the chloride 

 was evaporated and the final ignition to constant weight was 

 the same as when the glass tubes were used. The water used 

 for the solution of the chloride was purified by redistillation 

 in a platinum still. 



The quartz tubes also showed sigms of attack by the chlo- 

 rine. at the high temperature used, and so the oxide, after 

 becoming constant in weight, was treated with hydrofluoric 

 acid and the loss in weigdit, usually very small, applied as a 

 correction to the weights of both the chloride and oxide. 



Using every precaution in the work we still failed of con- 

 stant values, most of them falling between 221 and 230; yet 



