1915] Problems of Hydrogen and the Rare Gases r)4a 



WEEKLY EVENING MEETING, 



Friday, January 22, 1915. 



Sir James Crichton-Browne, J.P. M.D. LL.D. D.Sc. F.R.S., 

 Treasurer and Vice-President, in the Chair. 



Professor Sir James Dewar, LL.D. D.Sc. F.R.S. JI.R.L, 

 Fallerian Professor of Chemistry, R.I. 



Problems of Hydrogen and the Rare Gases. 



Ix the course of the Friday Evening Discourse of last year on " The 

 Coming of Age of the Vacuum Fiask " attention was drawn to some 

 low temperature determinations of the amount and distribution of 

 hydrogen, helium and neon in gases from various sources. This work 

 has now been extended by the use of improved apparatus and methods 

 of manipulation. To measure with accuracy the presence of a few 

 parts per million of one or other gases, either by volume or weight, 

 diluted to such a large proportion in another, is not an easy problem. 

 What a millionth part represents is shown in the model on the table. 

 The framework encloses a cubicle space one metre in the side, in the 

 centre of which a cube of one centimetre in the side is suspended. 

 The relative volumes of these cubes are as 1 to 1,000,000. When it 

 is stated that the air contains less than one part in a million of 

 hydrogen, this means less than one cubic centimetre per cubic metre. 

 The values given last year were derived from measurements of the 

 partial pressure observ^ed in a McLeod gauge, after the gases had 

 been cooled to 20° Abs. by the use of liquid hydrogen from an initial 

 pressure of 760 mm., or one atmosphere. The unit of pressure 

 adopted to express the recorded results was 10~* do wo) ^^' 

 mercury pressure, and that mode of expressing the experimental 

 results will be continued in this lecture. 



Comparative Condensability of Gases by Charcoal at 

 Liquid Air and Liquid Hydrogen Temperatures. 



The relative condensability by charcoal of the gases, air, hydrogen, 

 and helium, can be shown by filling three similar sets of double 

 tubes with samples of these gases. The two tubes of each set are 

 filled with the particular gas at atmospheric pressure and the 

 ordinary temperature, and dip into a little bottle of mercury. The 

 tubes are bent twice at right angles and sealed up. Thus the closed 

 end of either tube of each set can be cooled by immersion in a 



2 N 2 



