ON THE HALOGEN HYDKIDES AS CONDUCTING SOLVENTS. 101 



The hydrogen bromide was prepared by the action of bromine on red phosphorus 

 suspended in water. Traces of bromine were removed by passing the gas through a 

 thin paste of amorphous phosphorus and a saturated solution of hydrogen bromide. 

 The gas was then dried by passing it over about 40 centims. of phosphoric anhydride, 

 and, in order to remove impurities other than water- vapour, it was passed through 

 two U-tubes surrounded by solid carbon dioxide, in each of which a small quantity of 

 liquefied gas soon collected. The gas bubbled through this liquid, which was thus 

 submitted to a process of fractional distillation. It was finally condensed in a vessel 

 surrounded by a mixture of carbon dioxide and ether. 



The hydrogen iodide was made by the action of iodine and water on amorphous 

 phosphorus, in a similar manner to that employed for the preparation of hydrogen 

 bromide, and similar means were used to purify it. The liquid was invariably 

 coloured, and it could not be obtained quite colourless even by repeated distillation. 



The hydrogen sulphide was prepared by the action of dilute sulphuric acid on 

 ferrous sulphide. The gas was washed by passing it through water, dried by passage 

 over phosphoric anhydride, and condensed by means of carbon dioxide and ether. It 

 was purified by distillation. 



Phosphuretted hydrogen was prepared by the action of a solution ot potassium 

 hydroxide on phosphonium iodide. It was dried by means of phosphoric anhydride 

 and condensed in a receiver which was immersed in liquid air. 



The Constant-temperature Bath. 



The constant-temperature bath consisted of ether which was contained in a vacuum 

 vessel and cooled by liquid air. The temperature was measured by a constant-volume 

 hydrogen thermometer, similar to that described by TRAVERS, SENTER, and JAQUEROD 

 ('Phil. Trans.,' 1902, A, 200, pp. 105-180). The arrangement of the apparatus is 

 shown in fig. 1 , in which C represents the hydrogen thermometer, A the large vacuum 

 vessel containing the ether, and B a large vacuum flask containing liquid air. The 

 bulb, a, of the thermometer was connected to the dead space of the manometer by a 

 fine capillary tube. A mercury reservoir was attached to the stop-cock k by rubber 

 tubing, and by raising or lowering this reservoir the mercury in the dead space could 

 be adjusted to the level of the glass point c. 



The volume of the thermometer bulb and dead space was carefully determined by 

 calibration with mercury. The constants were volume of 



(1) Bulb and portion of stem within the liquid = 17 '480 cub. centims. at ; 



(2) Stem from s to surface of ether = 0'1358 cub. centim. ; 



(3) Dead space and stem to mark s = 0'5719 cub. centim. 



It has been assumed, in making our calculations, that the average temperature of 

 the section (2) was midway between that of the bath and that of the atmosphere ; an 

 error of a few degrees in the temperature of this section is without influence on the 

 bath temperatures, which are given only to the nearest tenth of a degree. 



