A History of Science — Volume 5

by Henry Smith Williams; Edward Huntington Williams

But now suppose our portion of gas, instead of being placed under our hypothetical building, is plunged into a cold medium, which will permit its heat-vibrations to exhaust themselves without being correspondingly restored. Then, presently, the temperature is lowered below the critical point, and, presto! the mad struggle ceases, the atoms lie amicably together, and the gas has become a liquid. What a transformed thing it is now. Instead of pressing out with that enormous force, it has voluntarily contracted as the five thousand tons pressure could not make it do; and it lies there now, limpid and harmless-seeming, in the receptacle, for all the world like so much water.

And, indeed, the comparison with water is more than superficial, for in a cup of water also there are wonderful potentialities, as every steam-engine attests. But an enormous difference, not in principle but in practical applications, exists in the fact that the potentialities of the water cannot be utilized until relatively high temperatures are reached. Costly fuel must be burned and the heat applied to the water before it can avail to do its work. But suppose we were to place our portion of liquid air, limpid and water-like, in the cylinder of a locomotive, where the steam of water ordinarily enters. Then, though no fuel were burned—though the entire engine stood embedded in the snow of an arctic winter—it would be but a few moments before the liquid air would absorb even from this cold medium heat enough to bring it above its critical temperature; and, its atoms now dancing apart once more and re-exerting that enormous pressure, the piston of the engine would be driven back and then the entire cylinder burst into fragments as the gas sought exit. In a word, then, a portion of liquid air has a store of potential energy which can be made kinetic merely by drawing upon the boundless and free supply of heat which is everywhere stored in the atmosphere we breathe and in every substance about us. The difficulty is, not to find fuel with which to vaporize it, as in case of water, but to keep the fuel from finding it whether or no. Were liquid air in sufficient quantities available, the fuel problem would cease to have any significance. But of course liquid air is not indefinitely available, and exactly here comes the difficulty with the calculations of many enthusiasts who hail liquefied gas as the motive power of the near future. For of course in liquefying the air power has been applied, for the moment wasted, and unless we can get out of the liquid more energy than we have applied to it, there is no economy of power in the transaction. Now the simplest study of the conditions, with the mechanical theory of matter in mind, makes it clear that this is precisely what one can never hope to accomplish. Action and reaction are equal and in opposite directions at all stages of the manipulation, and hence, under the most ideal conditions, we must expect to waste as much work in condensing a gas (in actual practice more) as the condensed substance can do in expanding to the original volume. Those enthusiasts who have thought otherwise, and who have been on the point of perfecting an apparatus which will readily and cheaply produce liquid air after the first portion is produced, are really but following the old perpetual-motion-machine will-o'-the-wisp.

It does not at all follow from this, however, that the energies of liquefied air may not be utilized with enormous advantage. It is not always the cheapest form of power-transformer that is the best for all purposes, as the use of the electrical storage battery shows. And so it is quite within the possibilities that a multitude of uses may be found for the employment of liquid air as a motive power, in which its condensed form, its transportability or other properties will give it precedence over steam or electricity. It has been suggested, for example, that liquefied gas would seem to afford the motive power par excellence for the flying-machine, once that elusive vehicle is well in harness, since one of the greatest problems here is to reduce the weight of the motor apparatus. In a less degree the same problem enters into the calculations of ships, particularly ships of war; and with them also it may come to pass that a store of liquid air (or other gas) may come to take the place of a far heavier store of coal. It is even within the possibilities that the explosive powers of the same liquid may take the place of the great magazines of powder now carried on war-ships; for, under certain conditions, the liquefied gas will expand with explosive suddenness and violence, an "explosion" being in any case only a very sudden expansion of a confined gas. The use of the compressed air in the dynamite guns, as demonstrated in the Cuban campaign, is a step in this direction. And, indeed, the use of compressed air in many commercial fields already competing with steam and electricity is a step towards the use of air still further compressed, and cooled, meantime, to a condition of liquidity. The enormous advantages of the air actually liquefied, and so for the moment quiescent, over the air merely compressed, and hence requiring a powerful retort to hold it, are patent at a glance. But, on the other hand, the difficulty of keeping it liquid is a disadvantage that is equally patent. How the balance will be struck between these contending advantages and disadvantages it remains for the practical engineering inventors of the future—the near future, probably—to demonstrate.

Meantime there is another line of application of the ideas which the low-temperature work has brought into prominence which has a peculiar interest in the present connection because of its singularly Rumfordian cast, so to speak, I mean the idea of the insulation of cooled or heated objects in the ordinary affairs of life, as, for example, in cooking. The subject was a veritable hobby with the founder of the Royal Institution all his life. He studied the heat-transmitting and heat-reflecting properties of various substances, including such directly practical applications as rough surfaces versus smooth surfaces for stoves, the best color for clothing in summer and in winter, and the like. He promulgated his ideas far and wide, and demonstrated all over Europe the extreme wastefulness of current methods of using fuel. To a certain extent his ideas were adopted everywhere, yet on the whole the public proved singularly apathetic; and, especially in America, an astounding wastefulness in the use of fuel is the general custom now as it was a century ago. A French cook will prepare an entire dinner with a splinter of wood, a handful of charcoal, and a half-shovelful of coke, while the same fuel would barely suffice to kindle the fire in an American cook-stove. Even more wonderful is the German stove, with its great bulk of brick and mortar and its glazed tile surface, in which, by keeping the heat in the room instead of sending it up the chimney, a few bits of compressed coal do the work of a hodful.

It is one merit of the low-temperature work, I repeat, to have called attention to the possibilities of heat insulation in application to "the useful purposes of life." If Professor Dewar's vacuum vessel can reduce the heat-transmitting capacity of a vessel by almost ninety-seven per cent., why should not the same principle, in modified form, be applied to various household appliances—to ice-boxes, for example, and to cooking utensils, even to ovens and cook-stoves? Even in the construction of the walls of houses the principles of heat insulation might advantageously be given far more attention than is usual at present; and no doubt will be so soon as the European sense of economy shall be brought home to the people of the land of progress and inventions. The principles to be applied are already clearly to hand, thanks largely to the technical workers with low temperatures. It remains now for the practical inventors to make the "application to the useful purposes of life." The technical scientists, ignoring the example which Rumford and a few others have set, have usually no concern with such uninteresting concerns.

For the technical scientists themselves, however, the low-temperature field is still full of inviting possibilities of a strictly technical kind. The last gas has indeed been liquefied, but that by no means implies the last stage of discovery. With the successive conquest of this gas and of that, lower and lower levels of temperature have been reached, but the final goal still lies well beyond. This is the north pole of the physicist's world, the absolute zero of temperature—the point at which the heat-vibrations of matter are supposed to be absolutely stilled. Theoretically this point lies 2720 below the Centigrade zero. With the liquefaction of hydrogen, a temperature of about -253 deg or -254 deg Centigrade has been reached. So the gap seems not so very great. But like the gap that separated Nansen from the geographical pole, it is a very hard road to travel. How to compass it will be the study of all the low-temperature explorers in the immediate future. Who will first reach it, and when, and how, are questions for the future to decide.

And when the goal is reached, what will be revealed? That is a question as full of fascination for the physicist as the north-pole mystery has ever been for the generality of mankind. In the one case as in the other, any attempt to answer it to-day must partake largely of the nature of a guess, yet certain forecasts may be made with reasonable probability. Thus it can hardly be doubted that at the absolute zero all matter will have the form which we term solid; and, moreover, a degree of solidity, of tenacity and compactness greater than ever otherwise attained. All chemical activity will presumably have ceased, and any existing compound will retain unaltered its chemical composition so long as absolute zero pertains; though in many, if not in all cases, the tangible properties of the substance—its color, for example, and perhaps its crystalline texture—will be so altered as to be no longer recognizable by ordinary standards, any more than one would ordinarily recognize a mass of snowlike crystals as air.

It has, indeed, been suggested that at absolute zero all matter may take the form of an impalpable powder, the forces of cohesion being destroyed with the vibrations of heat. But experiment seems to give no warrant to this forecast, since cohesion seems to increase exactly in proportion to the decrease of the heat-vibrations. The solidity of the meteorites which come to the earth out of the depths of space, where something approaching the zero temperature is supposed to prevail, also contradicts this assumption. Still less warrant is there for a visionary forecast at one time entertained that at absolute zero matter will utterly disappear. This idea was suggested by the observation, which first gave a clew to the existence of the absolute zero, that a gas at ordinary temperatures and at uniform pressure contracts by 1-27 2d of its own bulk with each successive degree of lowered temperature. If this law held true for all temperatures, the gas would apparently contract to nothingness when the last degree of temperature was reached, or at least to a bulk so insignificant that it would be inappreciable by standards of sense. But it was soon found by the low-temperature experimenters that the law does not hold exactly at extreme temperatures, nor does it apply at all to the rate of contraction which the substance shows after it assumes the liquid and solid conditions. So the conception of the disappearance of matter at zero falls quite to the ground.

But one cannot answer with so much confidence the suggestion that at zero matter may take on properties hitherto quite unknown, and making it, perhaps, differ as much from the conventional solid as the solid differs from the liquid, or this from the gas. The form of vibration which produces the phenomena of temperature has, clearly, a determining share in the disposal of molecular relations which records itself to our senses as a condition of gaseousness, liquidity, or solidity; hence it would be rash to predict just what inter-molecular relations may not become possible when the heat-vibration is altogether in abeyance. That certain other forms of activity may be able to assert themselves in unwonted measure seems clearly forecast in the phenomena of increased magnetism, and of phosphorescence at low temperatures above outlined. Whether still more novel phenomena may put in an appearance at the absolute zero, and if so, what may be their nature, are questions that must await the verdict of experiment. But the possibility that this may occur, together with the utter novelty of the entire subject, gives the low-temperature work precedence over almost every other subject now before the world for investigation (possible exceptions being radio-activity and bacteriology). The quest of the geographical pole is but a child's pursuit compared with the quest of the absolute zero. In vital interest the one falls as far short of the other as the cold of frozen water falls short of the cold of frozen air.

Where, when, and by whom the absolute zero will be first reached are questions that may be answered from the most unexpected quarter. But it is interesting to know that great preparations are being made today in the laboratories of the Royal Institution for a further attack upon the problem. Already the research equipment there is the best in the world in this field, and recently this has been completely overhauled and still further perfected. It would not be strange, then, in view of past triumphs, if the final goal of the low-temperature workers should be first reached in the same laboratory where the outer territories of the unknown land were first penetrated three-quarters of a century ago. There would seem to be a poetic fitness in the trend of events should it so transpire. But of course poetic fitness does not always rule in the land of science.