1899.] Centenary Commemoration, 1799-1899. 213 



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 cannot tell." The accuracy 

 of the prophecy of Lavoisier has been experimentally verified, but 

 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 Faraday was that hydrogen would ultimately be 

 obtained in the liquid and solid form. In the course of one of his 

 lectures delivered in the year 1852, he said: "There is reason to 

 believe we should derive much information as to the intimate nature 

 of these non-metallic 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 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." It must be confessed, however, that 

 later physicists and chemists were almost forced to conclude that the 

 problem was a hopeless one. The full history of the liquefaction 

 of hydrogen has been dealt with in a Friday Evening Discourse 

 delivered in January of this year, 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 one litre of liquid hydrogen. 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 way. In order to 

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

 periment 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 asbestos for the purpose of absorbing the liquid. On bring- 

 ing it quickly into the air and applying a light, it burns with the 

 characteristic appearance of the hydrogen flame (Figure C, Plate III.). 

 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 a 

 screen (Figure A, Plate III.) The liquid hydrogen appears in gentle 

 ebullition and is perfectly clear, only there is a white solid deposit in 

 the bottom of the tube, which is really solid air. This may be shown 



