at the Royal Institution, 1908-1916 749 



in Picfcet's experiments, from the tube in which liquefaction was 

 supposed to have taken place, was material " primed over " from the 

 vessel in which the hydrog'en was produced by heating sodium 

 formate with caustic soda. I was informed in Geneva, a good many 

 years ago, that when the apparatus was taken to pieces this tube was 

 found to be choked with solid. 



Prof. Dewar himself was the first to produce liquid and solid 

 hydrogen. 



The new field of work was first taken up by two Polish chemists, 

 Wroblewski and Olzewski, who made notable progress. 



But under the influence of the genius loci, fired by prophetic vision 

 of the rich harvest in store. Prof. Dewar was early in the field. 

 His singular ability as a manipulator and his engineering genius, 

 combined with great imaginative power, have enabled him, in the 

 cramped quarters of the Institution and with very inadequate re- 

 sources, to overrun the field of inquiry to an extraordinary extent. 

 The wide u<e that he has made of liquefied gases, for the purpose of 

 studying the changes in the properties of matter brought about by 

 lowering the temperature to the neighbourhood of the absolute zero, 

 is the remarkable feature of his work, distinguishing it from that of 

 all other inquirers. 



His first original communication on the subject to an Institution 

 audience was on June 1:3, 1884, when he gave an account of his own 

 researches on liquefied gases and exhibited an apparatus more 

 suitable for demonstration than the Cailletet apparatus. With this 

 apparatus, all the phenomena brought to light by the Polish chemists 

 above named were reproduced and the series of demonstrations 

 inaugurated for which the Institution has since been famous. The 

 apparatus is figured in the abstract. 



Oxygen was liquefied in an inner tube surrounded by an outer tube 

 filled with liquid ethylene ; on reducing the pressure above the 

 liquid to 25 mm., the temperature was reduced to about - 140° and 

 the oxygen then liquefied at a pressure between 20 and 30 

 atmospheres. 



The liquefaction of oxygen in this apparatus was also effected 

 by using either solid carbon dioxide or liquid nitrous oxide as coohng 

 agent. These gave the temperatures - 115° and —125°, both below 

 the critical point of oxygen, then said to be - 113° ; it was necessary, 

 however, to raise the pressure of the oxygen above the critical 

 pressure of the gas (50 atmospheres) and liquefaction took place 

 easily only at pressure of from 80 to 100 atmospheres. 



The density of the liquefied gas was easily determined with the 

 aid of the apparatus by noting the volume of the liquefied gas, then 

 evaporating the liquid and measuring the volume of gas produced. A 

 determination near the critical temperature of oxygen gave d = ■ 65. 



