260 LIQUID HYDEOGEN. 



that basis and the matter of heat. What appearance and properties that 

 basis would have, were it deprived of its latent heat and elastic form, 

 and quite separated from all other matter, we can not tell." The accu- 

 rac}' of the prophecy of Lavoisier has been experimentally verified, l)ut 

 until recently we had no distinctive answer to the riddle of Black. The 

 object of this lecture will be an attempt to advance the solution of the 

 problem suggested by Black a century ago. It is interesting to note 

 how" confident Farada}^ was that hydrogen would ultimately be o))tained 

 in the liquid and solid form. In the couree of one of his lectures deliv- 

 ered m the year 1852 he said: "There is reason to ])elieve we should 

 derive much information as to the intimate nature of these nonmetallic 

 elements if we could succeed in obtaining hydrogen and nitrogen in the 

 liquid or solid form. Many gases have been liquefied; one, carbonic- 

 acid gas, has been solidified; but hydrogen and nitrogen have resisted 

 all our efforts of this kind. Hydrogen, in many of its relations, acts 

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

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

 has 3'et 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." It must 

 be confessed, however, that later phvsicists and chemists were ahiiost 

 forced to conclude that the problem was a hopeless one. The full 

 history of the liquefaction of hydrogen has been dealt with in a Frida}^ 

 evening discourse^ delivered in January of this yqiiy, so that all questions 

 dealing with the work of other investigators may for the present be 

 omitted in order to save time for the experimental illustrations. 



This large spherical double-walled and silvered vacuum vessel 

 contains 1 liter of liquid hj^drogen. You observe it is lifted out 

 of a large cylindrical vessel full of liquid air. In order to diminish 

 the rate of evaporation it is necessary to surround the vessel in which 

 the hydrogen is collected with liquid air. Under such conditions 

 the rapidity of evaporation is about the same as that of liquid air 

 when kept in a similar vessel in the ordinary wa}'. In order to 

 prove that hydrogen is present in the liquid form, the simplest 

 experiment is to remove the cotton-wool plug, which takes the place 

 of a cork, and insert a metallic wire, to the end of which is attached 

 a ball of asbestus for the purpose of absorbing the liquid. On bring- 

 ing it qviickly into the air and applying a light it burns with the 

 characteristic appearance of the hydrogen flame (Fig. C, PL II). 

 The liquid can readily be poured from one variety of vacuum vessel 

 into another, so that by means of this unsilvered cylindrical form the 

 appearance of the liquid and other experiments may be projected on 



* Reprinted in Smithsonian Report, 1899, pages 131-142. 



