650 



SCIENCE. 



[N. S. Vol. XI. No. 278. 



similar conditions. It follows that its re- 

 sistance curve, in all probability, deviates 

 less from a straight line than is the case 

 with platinum. Either cause vpould ex- 

 plain the differences observed, but the lower 

 boiling point (—246° or 27° absolute) 

 seemed to be the more probable as it agreed 

 very fairly with the value for the boiling 

 point calculated by the author from Wrob- 

 lewski's results. As the use of other pure 

 metals or alloys was not likely to lead to 

 more satisfactory results, the problem had 

 to be attacked in a different way, namely, 

 by means of an ' air ' thermometer contain- 

 ing hydrogen under diminished pressure. 



A first attempt has been made at deter, 

 mining the boiling-point by a constant- vol- 

 ume hydrogen thermometer, working under 

 diminished pressure. This thermometer, 

 which gave the boiling point of oxygen as 

 90.5° absolute or — 182.5°, gave for hydro- 

 gen 21° absolute or —252°. The three de- 

 terminations that have been made are then 

 as follows: (1) pure platinum resistance 

 thermometer, 35° absolute ; (2) rhodium- 

 platinum resistance thermometer 27° abso- 

 lute ; (3) hydrogen thermometer, 21° abso- 

 lute. From this it appears that the boiling 

 point of hydrogen is really lower than was 

 anticipated, and must range between 20° 

 and 22° absolute. Further experiments 

 will be made with thermometers filled with 

 hydrogen prepared from different sources. 

 A hydrogen thermometer filled with the gas 

 obtained from the evaporation of the liquid 

 hydi-ogen itself must be employed. 



The approximate density of liquid hydro- 

 gen at its boiling point was found by measur- 

 ing the volume of the gas obtained by evapo- 

 rating 10 cc. of the liquid, and is slightly 

 less than 0.07, or about one-sixth that of 

 liquid marsh-gas, which is the lightest liq- 

 uid known. It is remarkable that, with so 

 low a density, liquid hydrogen is so easily 

 seen, has so well defined a meniscus, and 

 can be so readily collected and manipulated 



in vacuum vessels. As hydrogen o<'claded 

 in palladium has a density of 0.62, it fol- 

 lows that it must be associated with the 

 metal in some other state than that of lique- 

 faction. 



The atomic volume of liquid hydrogen 

 at its boiling point is about 14.3, the atomic 

 volumes of liquid oxygen and nitrogen 

 being 13.7 and 16.6 respectively at their 

 boiling points. The weight of a litre of 

 hydrogen gas at the boiling point of the 

 liquid is about the same as that of air, at 

 the ordinary temperature. The ratio of the 

 density of the hydrogen gas at the boiling 

 point to that of the liquid is approximately 

 1:60, as compared with a ratio of 1:255 in 

 the case of oxygen under similar conditions. 



The specific heat of hydrogen in the gas- 

 eous state and in hydrogenized palladium 

 is 3.4, but may very probably be 6.4 in the 

 liquid substance. Such a liquid would be 

 unique in its properties ; but as the volume 

 of one gramme of liquid hydrogen is about 

 14-15 cc, the specific heat per unit volume 

 must be nearly 0.5, which is about that of 

 liquid air. It is highly probable, therefore, 

 that the remarkable properties of liquid 

 hydrogen predicted by theory will prove to 

 be less astonishing when they are compared 

 with those of liquid air, volume for volume^ 

 at corresponding temperatures. 



With hydrogen as a cooling agent we 

 shall get to from 13° to 15° of the zero of 

 absolute temperature, and its use will open 

 up an entirely new field of scientific inquiry. 

 Even so great a man as James Clerk Max- 

 well had doubts as to the possibility of ever 

 liquefying hydrogen.* He says: "Similar 

 phenomena occur in all the liquefiable 

 gases. In other gases we are able to trace 

 the existence of attractive force at ordinary 

 pressures, though the compression has not 

 yet been carried so far as to show any re- 

 pulsive force. In hydrogen the repulsive 

 force seems to prevail even at ordinary 



* See Scientific Papers, 2, 412. 



