ON THE HALOGEN HYDEIDES AS CONDUCTING SOLVENTS. 



103 



Ilie Vapour-pressure, Curves, 



In order to measure the vapour-pressure, a tube containing the liquid was immersed 

 in the bath and simultaneous observations of the temperature and corresponding 

 vapour-pressure were taken. 



This simple arrangement could not be used with hydrogen bromide and iodide on 

 account of the action of these gases on the mercury of the manometer. The errors 

 due to this action were avoided by the use of a special 

 form of apparatus which is shown in fig. 2. 



To use this apparatus, the tube in was attached to 

 the pump, and the bulb a placed in the low-tempe- 

 rature bath, after which the whole apparatus was 

 exhausted to a pi*essure of about 60 millims. and the 

 stop-cock h closed. 



The outer portion of the apparatus was completely 

 exhausted and the stop-cock cj closed. A vessel 

 containing the liquefied gas was then attached to n by 

 rubber tubing, the point I broken within the tube, and 

 as soon as a sufficient quantity of liquid had distilled 

 into the bulb a the apparatus was sealed off at k. 



Before making any measurements the stop-cock g 

 was opened for a few moments, and all traces of air 

 were displaced from the tube by allowing a small 

 quantity of liquid to evaporate into the pump. 



The bath was cooled to the lowest temperature at 

 which observations were to be taken, and the stop- 

 cock h opened. As the vapour-pressure of hydrogen 

 bromide and of hydrogen iodide, even at the lowest 

 temperatures employed, was greater than 60 millims., 

 a flow of gas from c into c' followed, and continued until the pressure in the 

 manometer became equal to the vapour-pressure of the liquid. As soon as the 

 pressure ceased to rise, the temperature and pressure were read and the stop-cock h 

 was immediately closed. The temperature was then raised to the next point of 

 observation, and the stop-cock h again opened, until the pressure in the manometer 

 became constant, when readings were again taken and the stop-cock closed. 



In this way a succession of readings was obtained without the hydrogen generated 

 by the action of the gas on the mercury of the manometer finding its way into the 

 bulb a. As a precaution against diffusion, the bulbs c, c and the capillary tube e 

 were introduced, the stop-cock g being opened after each observation and the 

 contents of the bulbs c and c withdrawn through the pump. 



Fig. 2. 



