1899.] on Liquid Hydrogen. 13 



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 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 gaseous state and in 

 hydrogenised palladium is 3*4, but may very probably be 6*4 in 

 the liquid substance. Such a liquid would be unique in its pro- 

 perties ; 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 Maxwell had doubts as to the possibility of ever liquefy- 

 ing 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 repulsive force. In 

 hydrogen the repulsive force seems to prevail even at ordinary 

 pressures. This gas has never been liquefied, and it is probable 

 that it never will be liquefied, as the attractive force is so weak." In 

 concluding his lectures on the non-metallic elements delivered at the 

 Royal Institution in 1852, and published the following year, Faraday 

 said f : " There is reason to believe we should derive much informa- 

 tion as to the intimate nature of these non-metallic elements, if we 

 could succeed in obtaining hydrogen and nitrogen in the liquid and 

 solid form. Many gases have been liquefied : the carbonic acid gas 

 has been solidified, but hydrogen and nitrogen have resisted all our 

 efforts of the kind. Hydrogen in many of its relations acts as 

 though it were a metal : could it be obtained in a liquid or a solid 

 condition, the doubt might be settled. This great problem, however, 

 has yet to be solved, nor should we look with hopelessness on this 

 solution when we reflect with wonder — and as I do almost with fear 

 and trembling — on the powers of investigating the hidden qualities 

 of these elements — of questioning them, making them disclose their 

 secrets and tell their tales — given by the Almighty to man." 



* See Scientific Papers, 2, 412. 



t See Faraday's Lectures on the Non-Metallic Elements, pp. 292-3. 



