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naturally, followed up by joint work with Pierre Curie in which they examined the gases occluded or given off by radium and in 1908 Dewar determined the rate at which it evolves helium. In partnership with Professor H. O. Jones of Cambridge James Dewar did some work on iron carbonyls and at a meeting of the Chemistry Section of The British Association for the Advancement of Science in 1907 Professor Jones gave an account of their experiments mentioning that new interesting observations were made and that a new compound of iron and carbon monoxide had been discovered. Professor R. A. Hadfield who, in connection with his father’s business, had been concerned with alloys of iron with silicon and manganese and who had prepared a material which came to be used for steel helmets in the Great War collaborated with Professor Dewar on the properties of metals at low temperatures and in problems concerning steel for armour plating and for armour piercing shells. In a lecture to The Royal Society Professor Allan Macfadyan (note 30) showed that the temperature of liquid air has no appreciable effect upon the vitality of micro-organisms even when they were exposed to a temperature of –190 degrees Celsius for a week. In a subsequent lecture he explained that by the kindness of Sir James Dewar bacteria of many kinds had been subjected to the temperature of liquid hydrogen, -252 degrees Celsius for ten hours. They were sealed in thin glass tubes and introduced directly into liquid hydrogen contained in vacuum jacketed flasks immersed in liquid air. The tubes were then opened and the contents examined microscopically and by culture. The results were completely negative so far as alteration in appearance or in vigour of growth of the micro-organisms went. So, an exposure, he added, of ten hours to a temperature of almost –252 degrees Celsius has no effect on the vitality of micro-organisms. He went on to speak of further similar experiments and Sir James Dewar appears to have conducted them, for, in a lecture on “Inter-planetary bacteria”, Professors Shattock and Dudgeon remarked that Sir James Dewar’s experiments have demonstrated that while micro-organisms are unharmed by the frozen conditions of liquid air, “the ultra violet rays will kill undried bacteria”. At a meeting of the Botany Section of The British Association for the Advancement of Science in 1901 Sir William Thistleton-Dyer described some experiments of far reaching importance by Professor Dewar on the influence of the temperature of liquid hydrogen on the germinative power of seeds (note 31). The most important one was that in which five kinds of seeds varying in size and composition were immersed for six hours in liquid hydrogen. “The temperature at which they were cooled was –435 degrees Fahrenheit below melting ice.” They were subsequently sown at Kew and germinated readily without exception. In assessing the effect of low temperatures upon metals Professor Dewar showed that lead, tin, iron and also ivory balls when refrigerated gained in elasticity and bounced higher when dropped on an iron anvil than they did before refrigeration. He also demonstrated that the breaking stress of metallic wires was considerably increased as a result of reduction in temperature. Using wires of approximately half an inch in thickness he drew up the following table:
Metal: 15C -182C
Steel (soft): 420 Pounds 700 Pounds
Iron: 320 Pounds 670 Pounds
Copper: 200 Pounds 300 Pounds
Brass: 310 Pounds 440 Pounds
German Silver: 470 Pounds 600 Pounds
Gold: 255 Pounds 340 Pounds
Silver: 330 Pounds 420 Pounds
The increase in strength is due entirely to the lower temperature for when the wires were restored to their original temperature the increase disappeared. Thus, he argued, the inhabitant of a world where the temperature approximated absolute zero would have much stronger iron and steel with which to build his bridges just as his electric cables would have more perfect conductivity.
Low temperature research brought James Dewar into collaboration once more with his earliest research colleague, with whom he had worked when he was at The Edinburgh Veterinary College,... NEXT PAGE
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