550 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1923 



absolute zero, that unpluinbed depth where molecular movement is 

 no more. Helium alone remained unsubjugated by Dewar, and 

 that he would unquestionably have liquefied had not Onnes, of 

 Leyden, working on his lines, accomplished the feat while he was 

 preparing for it. 



Now that liquid air is an article of commerce, Dewar's liquid- 

 air work has become popular knowledge, but only an expert who 

 has essayed such an enterprise can conceive the patience, the indus- 

 try, the ingenuity, the constructive genius required in it. Dewar 

 devoted to it years of unremitting toil and pursued it not without 

 risk to life and limb, and sometimes embarrassed by the question 

 of ways and means to carry on so costly a campaign. To obtain a 

 degree of cold sufficient to liquefy hydrogen by means of internal 

 work done by the molecules while a gas was being forced through 

 a porous plug, involved the building up of a machine capable of 

 sustaining pressure in many tons to the square inch, even at a tem- 

 perature of —260° C, and fitted together with a nicety and pre- 

 cision of which even first-class engineering knows little. To pro- 

 tect the liquid gases when produced against the influx of heat, 

 special measures were necessary, and the search for these led to the 

 invention of the vacuum bulb, the parent of the thermo flask which 

 Dewar's nimble brain devised, which must have brought him a 

 huge fortune had he chosen to patent it, and which, if properly 

 designated, should keep his name alive for ever, even amongst the 

 masses of mankind. But the vacuum bulb, even when silvered, was 

 not enough. In order to examine the liquefied gases in a static 

 condition, and unevaporated for long periods, specially high vacua 

 were needed, and these were procured by Dewar's utilization of the 

 absorptive power of carbon. " The discovery of the marvelous power 

 of charcoal to absorb gases at low temperature," says Professor 

 Armstrong, " will render the period 1900 to 1907 ever memorable." 

 Dewar's liquefied gases, thus obtained, became themselves instru- 

 ments of research, and enabled him to conduct novel and illumina- 

 tive investigations on electrical conductivity, thermo-electric powers, 

 magnetic properties, and electric constants of metals and other sub- 

 stances at low temperatures and on the effects of extreme cold on 

 chemical and photographic action. Having established that chemi- 

 cal changes are almost quite inhibited at temperatures about 300° F. 

 below zero, Dewar, with the assistance of Professor Macfadyen, 

 determined to test how far vital processes were affected by the same 

 conditions. A typical series of bacteria was employed for the pur- 

 pose, possessing varying degrees of resistance to external agents. 

 The bacteria were first simultaneously exposed to the temperature 

 of liquid air for 24 hours. In no instance could any impairment of 

 their vitality be detected in either growth or functional activity. 



