August lo, 1905] 



NA TURE 



353 



of liquid oxygen compared before and after exposure to 

 the temperature of liquid hydrogen, to see whether there 

 has been any change produced. A German silver platinum 

 junction was employed, but as the result of his experience 

 the author recommends German silver gold. 



The paper on " Liquid Hydrogen and Air Calorimeters " 

 gives an account of experiments in which the specific heats 

 of .substances are determined by measuring the quantity 

 of liquid air or hydrogen which they vaporise in falling 

 through a given range of temperatures. From these ex- 

 periments it appears that, at temperatures between those 

 of these two liquids, ice has only one-third of its specific 

 heat at ordinary temperature, graphite has only one-tenth, 

 while diamond has as little as one-nineteenth of its 

 ordinary specific heat. The second part of this paper deals 

 with the latent heats of the volatile liquids, that of 

 hydrogen being given as 121 or 122 calories, of oxygen 

 51-15 calories, and of nitrogen 504 calorics. The latent 

 iieat of liquid 'air is not yet definitely determined, but when 

 there is a high percentage of oxygen it is about 54 calories. 

 The specific heat of hydrogen is found to be substantially 

 the same, whether the substance be liquid, occluded, or 

 gaseous. 



The employment, just mentioned, of liquid air to deter- 

 mine the specific heat of substances may be called a 

 practical application, though, so far, its utility is limited 

 to scientific research ; and the present time, ten years after 

 the introduction of the new and comparatively economical 

 method of producing it, is suitable for a review of its 

 applications generally, the further developments in the 

 methods of producing it, and the extent to which it has 

 been possible so far to realise the expectations founded on 

 the appearance of the new method of production. 



It will be remembered that down to the year 1895 the 

 method of liquefying air developed and employed by 

 Olszewski and Dewar was what is called the cascade 

 method, in which a gas condensed at high pressure is 

 vaporised at a much lower pressure, so as to produce a 

 much lower temperature, one low enough, perhaps, to 

 condense a more volatile gas highly compressed. Thus 

 nitrous o.xide was made to produce liquid ethylene 

 at a temperature below — go° C, and the ethylene, boiled 

 at lew pressure, similarly produced liquid oxygen, nitrogen, 

 or air at —140° C. These liquids, boiling in the open, 

 reduced their residual portions to their well known boiling 

 points, and, boiled at low pressure, produced n;uch lower 

 temperatures, but in no case low enough to act in the 

 same way as a means of liquefying compressed hydrogen, 

 which is so volatile that its critical temperature is below 

 the lowest obtainable by boiling the atmospheric gases at 

 low pressure. The nearest approach to the liquefaction 

 of hydrogen was Olszewski's imitation of Cailletet's com- 

 bination of the cascade system with sudden expansion. 

 He obtained a similar result — the brief appearance of an 

 evanescent mist, which just sufficed to show that hydrogen 

 was, under proper conditions, liquefiable. An ingenious 

 means for getting below the lowest temperatures obtain- 

 able on the cascade system by boiling oxygen or nitrogen 

 at low pressure was adopted by Olszewski and Dewar, 

 who mixed hydrogen, the former with oxygen, the latter 

 with nitrogen, in the hope of making a substitute for a 

 natural gas of intermediate properties, which, boiling at 

 low pressure, would give a temperature low enough for 

 the liquefaction of compressed hydrogen on the cascade 

 system. Both attempts were unsuccessful, though Dewar 

 thought that the nitrogen jelly behaved as if it had some 

 condensed hydrogen in solution. 



At this stage there appeared a new and more powerful 

 method for cooling and liquefying gases, the self- 

 intensive system, by which compressed gas, allowed 

 to cool itself by expanding to low pressure at a free 

 orifice, has its cooling accumulated by an interchanger, 

 and so intensified continually. Thus o.xygen, nitrogen, and 

 air starting from ordinary temperatures, and hydrogen 

 starting from a temperature below —200° C, can be made 

 to cool themselves to the liquefaction point, and gradually 

 liquefv themselves at ordinary pressure without the help 

 of any less volatile liquid to assist the fall of temperature. 



With such apparatus available, great expectations were 

 indulged in as to the future possibilities of liquid air. 

 As with electricity, the enthusiast and the impostor were 



soon at work, making unlimited promises to attract the 

 interest of the public, and company schemes to attract 

 their money. Licjuid air as a source of power was going 

 to eclipse and replace steam and electricity. As an 

 artificial refrigerant'it was to banish ice, ammonia, sulphur 

 dio.xide, and carbonic acid. In surgery it was soon to be 

 the only anaesthetic, antiseptic, and caustic employed ; in 

 medicine it was to cure consumption and many other 

 diseases. Our prominent scientific men cannot claim much 

 credit for doing their duty to the public in this matter. 

 In a few reported interviews some of them mildly recom- 

 mended caution. In this country only one prominent 

 worker with liquid air plainly warned the public at the 

 beginning of this boom that such promises were either 

 foolish or fraudulent, and declared that on the score of 

 expense liquid air, as made by the new method, could 

 never compete with steam as a source of power or with 

 ice as a source of refrigeration. The last ten years have 

 too fuUv justified the warning ; but in the meantime large 

 sums of money were extracted from the public in America 

 bv fraudulent liquid air companies, one of which attempted 

 to continue operations in this country ; and many business 

 men in England held over orders for new refrigerating 

 plants for some years, for fear lest, as soon as they had 

 put one down, they might find it superseded by a liquid- 

 air contrivance. Apart from scientific research, the nearest 

 approach to a commercial application of liquid air began 

 last autumn, when experiments were given at music-halls 

 under the name of the " Magic Kettle." The performance 

 was anything but a popularising of scientific knowledge, 

 of which the performers themselves in most cases had 

 none ; besides which they purposely deepened the mystery 

 of the matter by adding a little juggling, and making 

 misleading statements. 



Air liquefiers of the best make are now such perfect 

 machines that they seem to offer no scope for improve- 

 ment within the existing system. The chief attempt to 

 improve the system consi.sts in substituting an engine to 

 do work for the free-expansion valve, in order to obtain 

 mere cooling for a given amount of compression. This 

 device, in the form of a turbine, was discussed as 

 earlv as 1895, but rejected on the ground of compli- 

 cation. In 1896 Lord Rayleigh suggested it in a 

 letter to N.^ture, and others have proposed or attempted 

 it since. Thermodynamically it would be a great 

 gain ; but in apparatus of this kind a thermodynamic 

 gain often actually involves a greater practical loss, 

 owing to the importance of simplicity. In Comptes rcitdus, 

 vol. cxxxiv. pp. 156S-1571, is an account of such an 

 apparatus made by M. G. Claude, which is declared 

 to have been entirely successful. As this is purely _ a 

 question of economy and convenience, which are domin- 

 ating factors commercially, the fact that this apparatus 

 is not yet displacing others makes it likely that the com- 

 plications involved are found to be a serious stumbling- 

 block. They have hitherto prevented the adoption of a 

 similar device in commercial refrigerating machines worli- 

 ing with ammonia and carbonic acid, %hich are now made 

 on such a very large scale that in them, if anywhere, the 

 thermodynamic gain would outweigh the complications. 



One of the most promising practical appl'cations pro- 

 posed for liquid air has been the manufacture of oxygen 

 from air by liquefying it and letting thi nitrogen boil 

 awav before the oxygen, separating them by distillation. 

 Theoretically the power, that is, the cost, required should 

 be small. The latent heat taken up by the two gases 

 separately in volatilising should balance that given out by 

 the air in condensing. One of the prominent names 

 associated with attempts of this kind is that of Pictet, 

 who was long believed to have liquefied oxygen and 

 hydrogen at the time when Cailletet undoubtedly produced 

 a mist of oxygen. In New York Pictet was associated 

 with others in an attempt of this kind under a patent 

 (U.S. A.I in which he commits the fallacy of expecting 

 the gases to separate at a low temperature, but while both 

 are still in the gaseous condition, the greater density of 

 the o.xygen taking it to the bottom of the container ! The 

 oxygen did not drop, but the scheme, the patent, the 

 fallacv, and the investors' money did. Pictet next 

 appeared with a French patent, in which the U.S. patent 

 fallacy was replaced by another. He arranged to make 



NO. 1867, VOL. 72] 



