﻿610 The Earl of Berkeley and Mr. E. G. J. Hartley on a 



mercury-cup joint very satisfactory for vapour-pressure work 

 up to 30° C, where the pressure of the mercury is still insigni- 

 ficant. There have been no signs of leak even when the joint 

 lias been under water, but in the latter case it is advisable to 

 put rubber lubricant on the ground glass that holds the cup ; 

 this lubricant is dissolved off with petrol before weighing 

 the vessel. 



The most convenient way of filling the vessel is to pass 

 the inlet tube just through a rubber plug of the right size^to 

 fit the mouth of the phosphorus-pentoxide bottle ; on in- 

 verting the bottle and gently tapping, the drying agent runs 

 freely into the vessel, thus avoiding exposure to external 

 moisture. For a large number of experiments it is better 

 Fis-. 3. Fig- 4. 



Fir-. 1. 



Fis. 2. 



to purchase stoppered bottles, each containing about one 

 charge of the pentoxide, and keep them over sulphuric acid 

 in a desiccator. 



After filling, the vessel was heated to about 240° C. in a 

 stream of dry ozonized air until ozone issued freely. By this 

 treatment Mr. Manley * has shown that the lower oxides of 

 phosphorus are completely oxidized f. _ 



The sulphuric-acid vessel is shown in figs. 3 and 4 ; it is 

 fitted with detachable mercury cups, and an inverted U tube 



* Private communication. 



+ it should be noted that of tlie various samples of phosphorus pent- 

 oxide tried, only Kahlbaum's -was treated successfully in this way. All 

 the others contained such a large proportion of impurities that even after 

 manv hours' run practically all the ozone in a rapid current was absorbed. 



