2 TJIE ATTAINMENT OF VERY LOW TEMPERATURES 



duced by a Hampson machine {loc. cit., p. 13), I have certainly over- 

 estimated the " loss due to heat absorption by liquefier." This is put 

 down as equivalent to 100 gms. of liquid per half-hour and from ex- 

 periments with a Hampson machine fitted with a vacuum vessel sur- 

 rounding the regenerator coil, so as to reduce the heat-absorption to 

 an almost negligible quantity, it appears that this amount is more than 

 twice as large as it should be. The theoretical yield of liquid air is 

 probably nearer 7.5 per cent, for the conditions investigated, or 0.045 

 per cent, per atmosphere pressure. 



The formula given on page 14 of the same paper indicates that the 

 yield of liquid should be about 0.06 per cent, per atmosphere, a result 

 which is also too high, and this is due to the fact that the value k, 

 which represents the Joule-Thomson effect in the equation, is not, in 

 all probability, independent of the pressure. 



I had intended to investigate the influence on the efficiency of the 

 apparatus of the volume of air flowing through it, and of the initial 

 pressure, temperature, etc. Since I commenced these experiments, 

 however, Messrs. Bradley and Rowe (Physical Review, XIX., pp. 330 

 and 387) have carried out an investigation on these lines with a lique- 

 fier of the Hampson type, and as their work has been carried out in 

 a most careful manner it is unnecessary for me to say more than that 

 my own results are in complete agreement with theirs. The greater 

 part of my work, however, refers to the relative behaviour of liquefiers 

 of different construction. 



HI. The Efficiency of the Regenerator Coil in Self-Intensive 



Liquefiers. 



In the various forms of my apparatus which I have described in my 

 former communication to the Smithsonian Institution, the hydrogen has 

 been cooled to the temperature of liquid air boiling in z'actio before en- 

 tering the regenerator coil. The form and dimensions of the latter were 

 determined solely from considerations based on experiments with the 

 air liquefier, and it must be considered that my success with my first 

 hydrogen liquefier was largely due to good fortune. In this machine 

 the regenerator coil was made of copper pipe, 2 mm. inside and 3.5 

 mm. outside, wound as closely as possible in flat spirals to form a cylin- 

 der 180 mm. long and 50 mms. in diameter around a brass tube, which 

 supported the expansion valve at its lower end. 



In a second liquefier, which was built for Professor Anschiitz of 

 Bonn, by Brins Oxygen Company, the regenerator coil was of the 

 same dimensions, but was constructed differently. It consisted of two 

 copper tubes, of the same diameter, wound together, so that the cylin- 

 der, so formed, consisted ultimately of two coaxial coils which were 

 connected in parallel, with the coil in the liquid air chamber above. 



