396 Prof. H. E. Armstrong on Loic-Teinperature Research 



hydrogen, the reduction of the electric resistance of some metals is 

 very remarkable— copper dropping to only 1/1 05th, gold l/30th, 

 platinum l/85th to l/17th, silver l/24th of the resistance which 

 it has at 0°. The resistance of an unalloved metal diminishes 



Fig. 14. 



continually as the temperature falls and in each case appears to 

 approach to a definite asymtotic limit. Gold and silver give the best 

 measures of low temperatures. When considered in detail, the 

 observations are full of interest as throwing light on the properties 

 of individual metallic elements : obviously the last word on the 

 subject has not yet ])een said and it is important that the inquiry 

 should be extended to metals purified Avith every degree of refinement 

 which chemical skill can devise : tliis, however, will be a task of great 

 difficulty and must entail a vast amount of labour. 



One of Sir James Dewar's most beautiful applications of charcoal 

 consists in saturating it with air or hydrogen or helium and using it 

 when thus charged as a thermometric substance. An apparatus for 



" Dewar has obtained the following values for the boiling-point of hvdrogen 

 on the constant-volume hydrogen scale :- 253° -03, - 253° -37, — 252° -81, 

 — 250° '35 ; the pressure on the gas at the ice-point being 287 mm., 270 mm., 

 739 mm. and 127 mm., respectively. On the scale of a thermometer filled 

 with helium containing 7 per cent, of neon, at a pressure corresponding to 

 728 mm. of mercury at the ice-point, he found the temperature to be 252° -68 

 and 252° -84 0." 



