THE LIQUEFACTION OF GASES 55 



the effects of conduction and convection to such 

 an extent that liquid air, placed within, evaporated 

 at only one-fifth of the normal rate. An addi- 

 tional device enabled the effects of radiation to 

 be diminished also. A polished metallic surface 

 is the worst radiator and the worst absorber of 

 radiation known, and, by coating the opposite 

 walls of the vacuum space with a film of bright 

 silver or mercury, the rate of evaporation of liquid 

 air was again reduced to the sixth part. By the 

 combined results of the vacuum and the silvering, 

 the rate of loss of liquid was thus reduced to the 

 thirtieth part of its value in an ordinary open 

 vessel. Without the use of these vessels, liquid 

 air could not be kept for any length of time, and 

 liquid hydrogen, at any rate, could never have 

 been collected at all. 



With the liquefaction of hydrogen the old class 

 of so-called permanent gases disappeared. In 

 place of them, however, a number of gases, pre- 

 viously unknown to science, have been discovered. 

 Argon, shown by the late Lord Rayleigh and 

 Sir William Ramsay to exist in the atmosphere, 

 was the first of these gases to be detected. Its 

 name attempts to describe its general chemical 

 inertness ; and since this discovery several other 

 new gases of somewhat similar chemical properties 

 have been detected. 



The story of the discovery and isolation of 

 argon Is an excellent example of the Importance 

 in science of the infinitely little, and shows how 

 striking discoveries may be made as a conse- 

 quence of experiments which seem at first sight 

 simply adapted to Investigate, with the greatest 



