October 10, 1902.] 



SCIENCE. 



573 



range, only the Linde method gives us a 

 miach wdder range of temperature within 

 which liquefaction can be effected. This 

 is not the case if, instead of depending on 

 getting cooling by the internal work done 

 by the attraction of the gas molecules, we 

 force the compressed gas to do external 

 work as in the well-known air machines of 

 Kirk and Coleman. Both these inventors 

 have pointed out that there is no limit of 

 temperature, short of liquefaction of the 

 gas in use in the ciz'cuit, that such machines 

 are not capable of giving. While it is 

 theoretically clear that such machines 

 ought to be capable of maintaining the 

 lowest temperatures, and that with the 

 least expenditure of power, it is a very 

 different matter to overcome the practical 

 difficulties of working such machines un- 

 der the conditions. Coleman kept a ma- 

 chine delivering air at minus 83 degrees for 

 hours, but he did not carry his experiments 

 any further. Recently Monsieur Claude, 

 of Paris, has, however, succeeded in work- 

 ing a machine of this type so efficiently 

 that he has managed to produce one liter 

 of liquid air per horse power expended per 

 hour in the running of the engine. This 

 output is twice as good as that given by the 

 Linde machine, and there is no reason to 

 doubt that the yield will be still further 

 improved. It is clear, therefore, that in 

 the inunediate future the production of 

 liquid air and hydrogen will be effected 

 most economically by the use of machines 

 prodiicing cold by the expenditure of me- 

 chanical work. 



IJQUID HYDROGEN AND HELIUM. 



To the physicist the copious production 

 of liquid air by the methods described was 

 of peculiar interest and value as affording 

 the means of attacking the far more diffi- 

 cult problem of the liquefaction of hydro- 

 gen, and even as encouraging the hope that 

 liquid hydrogen might in time be employed 



for the liquefaction of yet more volatile 

 elements, apart from the importance which 

 its liquefaction must hold in the process 

 of the steady advance towards the absolute 

 zero. Hydrogen is an element of especial 

 interest, because the study of its properties 

 and chemical relations led great chemists 

 like Faraday, Dumas, Daniell, Graham and 

 Andrews to entertain the view that if it 

 could ever be brought into the state of 

 liquid or solid it would reveal metallic 

 characters. Looking to the special chem- 

 ical relations of the combined hydrogen in 

 water, alkaline oxides, acids, and salts, to- 

 gether with the behavior of these substances 

 on electrolysis, we are forced to conclude 

 that hydrogen behaves as the analogue of 

 a metal. After the beautiful discovery of 

 Graham that palladium can absorb some 

 hundreds of times its own volume of hy- 

 drogen, and still retain its luster and gen- 

 eral metallic character, the impression that 

 hydrogen was probably a member of the 

 metallic group became very general. The 

 only chemist who adopted another view 

 was my distingu,ished predecessor. Pro- 

 fessor Odling. In his 'Manual of Chem- 

 istry,' published in 1861, he pointed out 

 that hydrogen has chlorous as well as basic 

 relations, and that they are as decided, 

 important, and frequent as its other rela- 

 tions. From such considerations he arrived 

 at the conclusion that hydrogen is essen- 

 tially a neutral or intermediate body, and 

 therefore we should not expect to find liquid 

 or solid hydrogen possess the appearance 

 of a metal. This extraordinary prevision, 

 so characteristic of Odling, was proved to 

 be correct some thirty-seven years after it 

 was made. Another curious anticipation 

 was made by Dumas in a letter addressed 

 to Pictet, in which he says that the metal 

 most analogous to hydrogen is magnesium, 

 and that probably both elements have the 

 same atomic volume, so that the density of 

 hydrogen, for this reason, would be about 



