The Liquefaction of Cases. 27 



economy comes in. On this point Dr. Hampson states that 

 lib. liquid air at id. will expand to 800 volumes at atmospheric 

 pressure ; lib. steam to 1,700 volumes. One pound steam can 

 be made under good conditions by the combustion of i-iolb. of 

 coal, or at a cost of 1-120 of a penny, putting coal at 15s per 

 ton. Therefore the power contained in lib of liquid air at id 

 is, roughly speaking, equal to that contained in £lb. of steam at 

 i-24oths of a penny. Of course if liquid air could be produced 

 at i-240ths of its present cost, allowing for loss in carrying 

 about, it could very favourably compete with steam. 



Some years ago a Mr. Tripper, of the United States, claimed 

 that he could make it for less than nothing. We have heard 

 nothing of Mr. Tripper lately. 



Liquid air has also been proposed as a cooling agent. Much 

 tall talk was indulged in by the American Press in this 

 connection also. Hampson points out that liquid air would 

 have only i-ioth the cooling power of ice weight for weight, 

 and r as ice is usually less than id. per pound, the price of liquid 

 air, the inefficiency is so much the more evident. Liquid air 

 or oxygen as an explosive has been proposed. When mixed 

 with petroleum and infusorial earth it explodes violently. 

 Probably the difficulty of transporting it comes in the way here. 



Liquid hydrogen in sufficient quantity to be properly 

 observed and investigated seems to have been first obtained by 

 Professor Dewar in 1898. It is a clear, colourless liquid, per- 

 fectly transparent, and about i-ioth the specific gravity of 

 water. It boils at — 250 deg. C, under atmospheric pressure, 

 or within 23 deg. of absolute zero. As a cooling agent, it will 

 lower temperature to within 13 deg. to 15 deg. of absolute 

 zero. Its critical temperature is —240 deg., and critical 

 pressure 13-3 atmospheres. Professor Dewar considers the 

 step from the liquefaction of air to that of hydrogen is re- 

 latively as great in the thermo-dynamic sense as that from 

 chlorine to liquid air. Some idea of the difficulty of its 

 production may thereby appear. The solidification of the 

 gases is the next step beyond liquefaction. Atmospheric air 



