Read Ebook: A History of Science — Volume 5 by Williams Edward Huntington Williams Henry Smith

Font size: 10 px 15 px 20 px 25 px 30 px 35 px

Background color: BlackWhiteGrayLight GrayDark GrayDim Gray

Text color: BlackWhiteGrayLight GrayDark GrayDim Gray

Apply/Save settings

Ebook has 704 lines and 75148 words, and 15 pages

"GEORGE THE THIRD, by the Grace of God King of Great Britain, France, and Ireland, Defender of the Faith, etc., to all to whom these presents shall come, greeting. Whereas several of our loving subjects are desirous of forming a Public Institution for diffusing the knowledge and facilitating the general introduction of Useful Mechanical Inventions and Improvements; and for teaching, by Courses of Philosophical Lectures and Experiments, the Application of Science to the Common Purposes of Life, we do hereby give and grant"--multifarious things which need not here be quoted. Such are the opening words of the charter with which, a little more than a century ago, the Royal Institution of Great Britain came into existence and received its legal christening. If one reads on he finds that the things thus graciously "given and granted," despite all the official verbiage, amount to nothing more than royal sanction and approval, but doubtless that meant more in the way of assuring popular approval than might at first glimpse appear. So, too, of the list of earls, baronets, and the like, who appear as officers and managers of the undertaking, and who are described in the charter as "our right trusty and right well-beloved cousins," "our right trusty and well-beloved counsellors," and so on, in the skilfully graduated language of diplomacy. The institution that had the King for patron and such notables for officers seemed assured a bright career from the very beginning. In name and in personnel it had the flavor of aristocracy, a flavor that never palls on British palate. And right well the institution has fulfilled its promise, though in a far different way from what its originator and founder anticipated.

Its originator and founder, I say, and say advisedly; for, of course, here, as always, there is one man who is the true heart and soul of the movement, one name that stands, in truth, for the whole project, and to which all the other names are mere appendages. You would never suspect which name it is, in the present case, from a study of the charter, for it appears well down the file of graded titles, after "cousins" and "counsellors" have had their day, and is noted simply as "our trusty and well-beloved Benjamin, Count of Rumford, of the Holy Roman Empire." Little as there is to signalize it in the charter, this is the name of the sole projector of the enterprise in its incipiency, of the projector of every detail, of the writer of the charter itself even. The establishment thus launched with royal title might with full propriety have been called, as indeed it sometimes is called, the Rumford Institution.

The man who thus became the founder of this remarkable institution was in many ways a most extraordinary person. He was an American by birth, and if not the most remarkable of Americans, he surely was destined to a more picturesque career than ever fell to the lot of any of his countrymen of like eminence. Born on a Massachusetts farm, he was a typical "down-east Yankee," with genius added to the usual shrewd, inquiring mind and native resourcefulness. He was self-educated and self-made in the fullest sense in which those terms can be applied. At fourteen he was an unschooled grocer-lad--Benjamin Thompson by name--in a little New England village; at forty he was a world-famous savant, as facile with French, Italian, Spanish, and German as with his native tongue; he had become vice-president and medallist of the Royal Society, member of the Berlin National Academy of Science, of the French Institute, of the American Academy of Science, and I know not what other learned bodies; he had been knighted in Great Britain after serving there as under-secretary of state and as an officer; and he had risen in Bavaria to be more than half a king in power, with the titles, among others, of privy councillor of state, and head of the war department, lieutenant-general of the Bavarian armies, holder of the Polish order of St. Stanislas and the Bavarian order of the White Eagle, ambassador to England and to France, and, finally, count of the Holy Roman Empire. Once, in a time of crisis, Rumford was actually left at the head of a council of regency, in full charge of Bavarian affairs, the elector having fled. The Yankee grocer-boy had become more than half a king.

Never, perhaps, did a man of equal scientific attainments enjoy a corresponding political power. Never was political power wielded more justly by any man.

For in the midst of all his political and military triumphs, Rumford remained at heart to the very end the scientist and humanitarian. He wielded power for the good of mankind; he was not merely a ruler but a public educator. He taught the people of Bavaria economy and Yankee thrift. He established kitchens for feeding the poor on a plan that was adopted all over Europe; but, better yet, he created also workshops for their employment and pleasure-gardens for their recreation. He actually banished beggary from the principality.

It was in the hope of doing in some measure for London what he had done for Munich that this large-brained and large-hearted man was led to the project of the Royal Institution. He first discussed his plans with a committee of the Society for Alleviating the Condition of the Poor, for it was the poor, the lower ranks of society, whom he wished chiefly to benefit. But he knew that to accomplish his object, he must work through the aristocratic channels; hence the name of the establishment and the charter with its list of notables. The word institution was selected by Rumford, after much deliberation, as, on the whole, the least objectionable title for the establishment, as having a general inclusiveness not possessed by such words as school or college. Yet in effect it was a school which Rumford intended to found--a school for the general diffusion of useful knowledge. There were to be classes for mechanics, and workshops, kitchens, and model-rooms, where the "application of science to the useful purposes of life" might be directly and practically taught; also a laboratory for more technical investigations, with a "professor" in charge, who should also deliver popular lectures on science. Finally, there was to be a scientific library.

All these aims were put into effect almost from the beginning. The necessary funds were supplied solely by popular subscription and by the sale of lecture tickets , and before the close of the year 1800 Rumford's dream had become an actuality--as this practical man's dreams nearly always did. The new machine did not move altogether without friction, of course, but on the whole all went well for the first few years. The institution had found a local habitation in a large building in Albemarle Street, the same building which it still occupies, and for a time Rumford lived there and gave the enterprise his undivided attention. He appointed the brilliant young Humphry Davy to the professorship of chemistry, and the even more wonderful Thomas Young to that of natural philosophy. He saw the workshops and kitchens and model-rooms in running order--the entire enterprise fully launched. Then other affairs, particularly an attachment for a French lady, the widow of the famous chemist Lavoisier , called him away from England never to return. And the first chapter in the history of the Royal Institution was finished.

METHOD AND RESULT

Rumford, the humanitarian, gone, a curious change came over the spirit of the enterprise he had founded. The aristocrats who at first were merely ballast for the enterprise now made their influence felt. With true British reserve, they announced their belief that the education of the masses involved a dangerous political tendency. Hence the mechanics' school was suspended and the workshops and kitchens abolished; in a word, the chief ends for which the institution was founded were annulled. The library and the lectures remained, to be sure, but they were for the amusement of the rich, not for the betterment of the poor. It was the West End that made a fad of the institution and a society function of the lectures of Sydney Smith and of the charming youth Davy. Thus the institution came to justify its aristocratic title and its regal patronage; and the poor seemed quite forgotten.

But indeed the institution itself was poor enough in these days, after the first flush of enthusiasm died away, and it is but fair to remember that without the support of its popular lectures its very existence would have been threatened. Nor in any event are regrets much in order over the possible might-have-beens of an institution whose laboratories were the seat of the physical investigations of Thomas Young, through which the wave theory of light first gained a footing, and of the brilliant chemical researches of Davy, which practically founded the science of electro-chemistry and gave the chemical world first knowledge of a galaxy of hitherto unknown elements. Through the labors of these men, and through the popular lecture-courses delivered at the institution by such other notables of science as Wollaston, Dalton, and Rum-ford, the enterprise had become world-famous before the close of the first decade of its existence.

From that day till this the character of the Royal Institution has not greatly changed. The enterprise shifted around during its earliest years, while it was gaining its place in the scheme of things; but once that was found, like a true British institution it held its course with an inertia that a mere century of time could not be expected to alter. Rumford was the sole founder of the enterprise, but it was Davy who gave it the final and definitive cast. He it was who established the tradition that the Royal Institution was to be essentially a laboratory for brilliant original investigations, the investigator to deliver a yearly course of lectures, but to be otherwise untrammelled. It occupied, and has continued to occupy, the anomalous position of a school to which pupils are on no account admitted, and whose professors teach nothing except by a brief course of lectures to which whoever cares to pay the admission price may freely enter.

But the marvellous results achieved at the Royal Institution have more than justified the existence of so anomalous an enterprise. Superlatives are always dangerous, but it may well be doubted whether there is another single institution in the world where so many novel original discoveries in physical science have been made as have been brought to light in the laboratories of the building on Albemarle Street during this first century of its occupancy; for practically all that is to be credited to Thomas Young, Humphry Davy, Michael Faraday, and John Tyndall, not to mention living investigators, is to be credited also to the Royal Institution, whose professorial chairs these great men have successively occupied. Davy spent here the best years of his youth and prime. Faraday, his direct successor, came to the institution in a subordinate capacity as a mere boy, and was the life of the institution for half a century. Tyndall gave it forty years of service. What wonder, then, that the Briton speaks of the institution as the "Pantheon of Science"?

If you visit the Royal Institution to-day you will find it in most exterior respects not unlike what it presumably was a century ago. Its long, stone front, dinged with age, with its somewhat Pantheon-like colonnade, has an appearance of dignity rather than of striking impressiveness. The main entrance, jutting full on the sidewalk, is at the street level, and the glass door gives hospitable glimpses of the interior. Entering, one finds himself in a main central hall, at the foot of the main central staircase. The air of eminent respectability so characteristic of the British institution is over all; likewise the pervasive hush of British reserve. But you will not miss also the atmosphere of sincere if uneffusive British courtesy.

At your right, as you mount the stairway, is a large statue of Faraday; on the wall right ahead is a bronze medallion of Tyndall, placed beneath a large portrait of Davy. At the turn of the stairs is a marble bust of Wollaston. Farther on, in hall and library, you will find other busts of Faraday, other portraits of Davy; portraits of Faraday everywhere, and various other busts of notables who have had connection with the institution. You will be shown the lecture-hall where Davy, Faraday, and Tyndall pronounced their marvellous discourses; the arrangement, the seats, the cushions even if appearances speak truly, and certainly the lecture-desk itself, unchanged within the century. You may see the crude balance, clumsy indeed to modern eyes, with which Davy performed his wonders. The names and the memories of three great men--Davy, Faraday, and Tyndall--will be incessantly before you, and the least impressionable person could not well escape a certain sense of consecration of his surroundings. The hush that is over everything seems but fitting.

All that is as it should be. But there are other memories connected with these surroundings which are not so tangibly presented to the senses. For where, amid all these busts and portraits, is the image of that other great man, the founder of the institution, the sole originator of the enterprise which has made possible the aggregation of all these names and these memories? Where are the remembrances of that extraordinary man whom the original charter describes as "our well-beloved Benjamin, Count of Rumford?" Well, you will find a portrait of him, it is true, if you search far enough, hung high above a doorway in a room with other portraits. But one finds it hard to escape the feeling that there has been just a trifling miscarriage of justice in the disposal. Doubtless there was no such intention, but the truth seems to be that the glamour of the newer fame of Faraday has dazzled a little the eyes of the rulers of the institution of the present generation. But that, after all, is a small matter about which to quibble. There is glory enough for all in the Royal Institution, and the disposal of busts and portraits is unworthy to be mentioned in connection with the lasting fame of the great men who are here in question. It would matter little if there were no portrait at all of Rumford here, for all the world knows that the Royal Institution itself is in effect his monument. His name will always be linked in scientific annals with the names of Young, Davy, Faraday, and Tyndall. And it is worthy such association, for neither in native genius nor in realized accomplishments was Rumford inferior to these successors.

FROM LIQUID CHLORINE TO LIQUID HYDROGEN

This same web of association extends just as clearly to the most important work which has been done at the Royal Institution in the present generation, and which is still being prosecuted there--the work, namely, of Professor James Dewar on the properties of matter at excessively low temperatures. Indeed, this work is in the clearest sense a direct continuation of researches which Davy and Faraday inaugurated in 1823 and which Faraday continued in 1844. In the former year Faraday, acting on a suggestion of Davy's, performed an experiment which resulted in the production of a "clear yellow oil" which was presently proved to be liquid chlorine. Now chlorine, in its pure state, had previously been known only as a gas. Its transmutation into liquid form was therefore regarded as a very startling phenomenon. But the clew thus gained, other gases were subjected to similar conditions by Davy, and particularly by Faraday, with the result that several of them, including sulphurous, carbonic, and hydrochloric acids were liquefied. The method employed, stated in familiar terms, was the application of cold and of pressure. The results went far towards justifying an extraordinary prediction made by that extraordinary man, John Dalton, as long ago as 1801, to the effect that by sufficient cooling and compressing all gases might be transformed into liquids--a conclusion to which Dalton had vaulted, with the sureness of supreme genius, from his famous studies of the properties of aqueous vapor.

Between Dalton's theoretical conclusion, however, and experimental demonstration there was a tremendous gap, which the means at the disposal of the scientific world in 1823 did not enable Davy and Faraday more than partially to bridge. A long list of gases, including the familiar oxygen, hydrogen, and nitrogen, resisted all their efforts utterly--notwithstanding the facility with which hydrogen and oxygen are liquefied when combined in the form of water-vapor, and the relative ease with which nitrogen and hydrogen, combined to form ammonia, could also be liquefied. Davy and Faraday were well satisfied of the truth of Dalton's proposition, but they saw the futility of further efforts to put it into effect until new means of producing, on the one hand, greater pressures, and, on the other, more extreme degrees of cold, should be practically available. So the experiments of 1823 were abandoned.

But in 1844 Faraday returned to them, armed now with new weapons, in the way of better air-pumps and colder freezing mixtures, which the labors of other workers, chiefly Thilorier, Mitchell, and Natterer, had made available. With these new means, and without the application of any principle other than the use of cold and pressure as before, Faraday now succeeded in reducing to the liquid form all the gases then known with the exception of six; while a large number of these substances were still further reduced, by the application of the extreme degrees of cold now attained, to the condition of solids. The six gases which still proved intractable, and which hence came to be spoken of as "permanent gases," were nitrous oxide, marsh gas, carbonic oxide, oxygen, nitrogen, and hydrogen.

These six refractory gases now became a target for the experiments of a host of workers in all parts of the world. The resources of mechanical ingenuity of the time were exhausted in the effort to produce low temperatures on the one hand and high pressures on the other. Thus Andrews, in England, using the bath of solid carbonic acid and ether which Thilorier had discovered, and which produces a degree of cold of--80? Centigrade, applied a pressure of five hundred atmospheres, or nearly four tons to the square inch, without producing any change of state. Natterer increased this pressure to two thousand seven hundred atmospheres, or twenty-one tons to the square inch, with the same negative results. The result of Andrews' experiments in particular was the final proof of what Cagniard de la Tour had early suspected and Faraday had firmly believed, that pressure alone, regardless of temperature, is not sufficient to reduce a gas to the liquid state. In other words, the fact of a so-called "critical temperature," varying for different substances, above which a given substance is always a gas, regardless of pressure, was definitively discovered. It became clear, then, that before the resistant gases would be liquefied means of reaching extremely low temperatures must be discovered. And for this, what was needed was not so much new principles as elaborate and costly machinery for the application of a principle long familiar--the principle, namely, that an evaporating liquid reduces the temperature of its immediate surroundings, including its own substance.

Ingenious means of applying this principle, in connection with the means previously employed, were developed independently by Pictet in Geneva and Cailletet in Paris, and a little later by the Cracow professors Wroblewski and Olzewski, also working independently. Pictet, working on a commercial scale, employed a series of liquefied gases to gain lower and lower temperatures by successive stages. Evaporating sulphurous acid liquefied carbonic acid, and this in evaporating brought oxygen under pressure to near its liquefaction point; and, the pressure being suddenly released , the rapid expansion of the compressed oxygen liquefies a portion of its substance. This result was obtained in 1877 by Pictet and Cailletet almost simultaneously. Cailletet had also liquefied the newly discovered acetylene gas. Five years later Wroblewski liquefied marsh gas, and the following year nitrogen; while carbonic oxide and nitrous oxide yielded to Olzewski in 1884. Thus forty years of effort had been required to conquer five of Faraday's refractory gases, and the sixth, hydrogen, still remains resistant. Hydrogen had, indeed, been seen to assume the form of visible vapor, but it had not been reduced to the so-called static state--that is, the droplets had not been collected in an appreciable quantity, as water is collected in a cup. Until this should be done, the final problem of the liquefaction of hydrogen could not be regarded as satisfactorily solved.

It must be noted, however, that this final stage in the liquefaction struggle was not effected through the use of the principle of evaporating liquids which has just been referred to, but by the application of a quite different principle and its elaboration into a perfectly novel method. This principle is the one established long ago by Joule and Thomson , that compressed gases when allowed to expand freely are lowered in temperature. In this well-known principle the means was at hand greatly to simplify and improve the method of liquefaction of gases, only for a long time no one recognized the fact. Finally, however, the idea had occurred to two men almost simultaneously and quite independently. One of these was Professor Linde, the well-known German experimenter with refrigeration processes; the other, Dr. William Hampson, a young English physician. Each of these men conceived the idea--and ultimately elaborated it in practice--of accumulating the cooling effect of an expanding gas by allowing the expansion to take place through a small orifice into a chamber in which the coil containing the compressed gas was held. In Dr. Hampson's words:

"The method consists in directing all the gas immediately after its expansion over the coils which contain the compressed gas that is on its way to the expansion-point. The cold developed by expansion in the first expanded gas is thus communicated to the oncoming compressed gas, which consequently expands from, and therefore to, a lower temperature than the preceding portion. It communicates in the same way its own intensified cold to the succeeding portion of compressed gas, which, in its turn, is made colder, both before and after expansion, than any that had gone before. This intensification of cooling goes on until the expansion-temperature is far lower than it was at starting; and if the apparatus be well arranged the effect is so powerful that even the smaller amount of cooling due to the free expansion of gas through a throttle-valve, though pronounced by Siemens and Coleman incapable of being utilized, may be made to liquefy air without using other refrigerants."

So well is this principle carried out in Dr. Hamp-son's apparatus for liquefying air that compressed air passing into the coil at ordinary temperature without other means of refrigeration begins to liquefy in about six minutes--a result that seems almost miraculous when it is understood that the essential mechanism by which this is brought about is contained in a cylinder only eighteen inches long and seven inches in diameter.

As has been said, it was by adopting this principle of self-intensive refrigeration that Professor Dewar was able to liquefy hydrogen. More recently the same result has been attained through use of the same principle by Professor Ramsay and Dr. Travers at University College, London, who are to be credited also with first publishing a detailed account of the various stages of the process. It appears that the use of the self-intensification principle alone is not sufficient with hydrogen as it is with the less volatile gases, including air, for the reason that at all ordinary temperatures hydrogen does not cool in expanding, but actually becomes warmer. It is only after the compressed hydrogen has been cooled by immersion in refrigerating media of very low temperature that this gas becomes amenable to the law of cooling on expansion. In the apparatus used at University College the coil of compressed hydrogen is passed successively through a jar containing alcohol and solid carbonic acid at a temperature of--80? Centigrade; a chamber containing liquid air at atmospheric pressure, and liquid air boiling in a vacuum bringing the temperature to perhaps 2050 Centigrade before entering the Hampson coil, in which expansion and the self-intensive refrigeration lead to actual liquefaction. With this apparatus Dr. Travers succeeded in producing an abundant quantity of liquid hydrogen for use in the experiments on the new gases that were first discovered in the same laboratory through the experiments on liquid air--gases about which I shall have something more to say in another chapter.

PRINCIPLES AND EXPERIMENTS

At first blush it seems a very marvellous thing, this liquefaction of substances that under all ordinary conditions are gaseous. It is certainly a little startling to have a cup of clear, water-like liquid offered one, with the assurance that it is nothing but air; still more so to have the same air presented in the form of a white "avalanche snow." In a certain sense it is marvellous, because the mechanical difficulties that have been overcome in reducing the air to these unusual conditions are great. Yet, in another and broader view, there is nothing more wonderful about liquid air than about liquid water, or liquid mercury, or liquid iron. Long before air was actually liquefied, it was perfectly understood by men of science that under certain conditions it could be liquefied just as surely as water, mercury, iron, and every other substance could be brought to a similar state. This being known, and the principles involved understood, had there been nothing more involved than the bare effort to realize these conditions all the recent low-temperature work would have been mere scientific child's-play, and liquid air would be but a toy of science. But in point of fact there are many other things than this involved; new principles were being searched for and found in the course of the application of the old ones; new light was being thrown into many dark corners; new fields of research, some of them as yet barely entered, were being thrown open to the investigator; new applications of energy, of vast importance not merely in pure science but in commercial life as well, were being made available. That is why the low-temperature work must be regarded as one of the most important scientific accomplishments of our century.

At the very outset it was this work in large measure which gave the final answer to the long-mooted question as to the nature of heat, demonstrating the correctness of Count Rumford's view that heat is only a condition not itself a substance. Since about the middle of the century this view, known as the mechanical theory of heat, has been the constant guide of the physicists in all their experiments, and any one who would understand the low-temperature phenomena must keep this conception of the nature of heat clearly and constantly in mind. To understand the theory, one must think of all matter as composed of minute isolated particles or molecules, which are always in motion--vibrating, if you will. He must mentally magnify and visualize these particles till he sees them quivering before him, like tuning-forks held in the hand. Remember, then, that, like the tuning-fork, each molecule would, if left to itself, quiver less and less violently, until it ran down altogether, but that the motion thus lessening is not really lost. It is sent out in the form of ether waves, which can set up like motion in any other particles which they reach, be they near or remote; or it is transmitted as a direct push--a kick, if you will--to any other particle with which the molecule comes in physical contact.

But note now, further, that our molecule, while incessantly giving out its energy of motion in ether waves and in direct pushes, is at the same time just as ceaslessly receiving motion from the ether waves made by other atoms, and by the return push of the molecules against which it pushes. In a word, then, every molecule of matter is at once a centre for the distribution of motion , and, from the other point of view, also a centre for the reception of motion from every direction and from every other particle of matter in the universe. Whether any given molecule will on the whole gain motion or lose it depends clearly on the simple mechanical principles of give and take.

From equally familiar mechanical principles, it is clear that our vibrating molecule, in virtue of its vibrations, is elastic, tending to be thrown back from every other molecule with which it comes in contact, just as a vibrating tuning-fork kicks itself away from anything it touches. And of course the vigor of the recoil will depend upon the vigor of the vibration and the previous movements. But since these movements constitute temperature, this is another way of saying that the higher the temperature of a body the more its molecules will tend to spring asunder, such separation in the aggregate constituting expansion of the mass as a whole. Thus the familiar fact of expansion of a body under increased temperature is explained.

But now, since all molecules are vibrating, and so tending to separate, it is clear that no unconfined mass of molecules would long remain in contiguity unless some counter influence tended to draw them together. Such a counter influence in fact exists, and is termed the "force" of cohesion. This force is a veritable gravitation influence, drawing every molecule towards every other molecule. Possibly it is identical with gravitation. It seems subject to some law of decreasing in power with the square of the distance; or, at any rate, it clearly becomes less potent as the distance through which it operates increases.

Now, between this force of cohesion which tends to draw the molecules together, and the heat vibrations which tend to throw the molecules farther asunder, there seems to be an incessant battle. If cohesion prevails, the molecules are held for the time into ? relatively fixed system, which we term the solid state. If the two forces about balance each other, the molecules move among themselves more freely but maintain an average distance, and we term the condition the liquid state. But if the heat impulse preponderates, the molecules fly farther and farther asunder, moving so actively that when they collide the recoil is too great to be checked by cohesion, and this condition we term the gaseous state.

Now after this statement, it is clear that what the low-temperature worker does when he would liquefy a gas is to become the champion of the force of cohesion. He cannot directly aid it, for so far as is known it is an unalterable quantity, like gravitation. But he can accomplish the same thing indirectly by weakening the power of the rival force. Thus, if he encloses a portion of gas in a cylinder and drives a piston down against it, he is virtually aiding cohesion by forcing the molecules closer together, so that the hold of cohesion, acting through a less distance, is stronger. What he accomplishes here is not all gain, however, for the bounding molecules, thus jammed together, come in collision with one another more and more frequently, and thus their average activity of vibration is increased and not diminished; in other words, the temperature of the gas has risen in virtue of the compression. Compression alone, then, will not avail to enable cohesion to win the battle.

But the physicist has another resource. He may place the cylinder of gas in a cold medium, so that the heat vibrations sent into it will be less vigorous than those it sends out. That is a blow the molecule cannot withstand. It is quite impotent to cease sending out the impulses however little comes in return; hence the aggregate motion becomes less and less active, until finally the molecule is moving so sluggishly that when it collides with its fellow cohesion is able to hold it there. Cohesion, then, has won the battle, and the gas has become a liquid.

Such, stated in terms of the mechanical theory of heat, is what is brought to pass when a gas is liquefied in the laboratory of the physicist. It remains only to note that different chemical substances show the widest diversity as to the exact point of temperature at which this balance of the expansive and cohesive tendencies is affected, but that the point, under uniform conditions of pressure, is always the same for the same substance. This diversity has to do pretty clearly with the size of the individual molecules involved; but its exact explanation is not yet forthcoming, and, except in a general way, the physicist would not be able to predict the "critical temperature" of any new gas presented to him. But once this has been determined by experiment, he always knows just what to expect of any given substance. He knows, for example, that in a mixture of gases hydrogen would still remain gaseous after all the others had assumed the liquid state, and most of them the solid state as well.

These mechanical conceptions well in mind, it is clear that what the would-be liquefier of gases has all along sought to attain is merely the insulation of the portion of matter with which he worked against the access of heat-impulse from its environment. It is clear that were any texture known which would permit a heat-impulse to pass through it in one direction only, nothing more would be necessary than to place a portion of gas in such a receptacle of this substance, so faced as to permit egress but not entrance of the heat, and the gas thus enclosed, were it hydrogen itself, would very soon become liquid and solid, through spontaneous giving off of its energy, without any manipulation whatever. Contrariwise, were the faces of the receptacle reversed, a piece of iron placed within it would be made red-hot and melted though the receptacle were kept packed in salt and ice and no heat applied except such as came from this freezing mixture. One could cook a beefsteak with a cake of ice had he but such a material as this with which to make his stove. Not even Rumford or our modern Edward Atkinson ever dreamed of such economy of fuel as that.

But, unfortunately, no such substance as this is known, nor, indeed, any substance that will fully prevent the passage of heat-impulses in either direction. Hence one of the greatest tasks of the experimenters has been to find a receptacle that would insulate a cooled substance even partially from the incessant bombardment of heat-impulses from without. It is obvious that unless such an insulating receptacle could be provided none of the more resistent gases, such as oxygen, could be long kept liquid, even when once brought to that condition, since an environment of requisite frigidity could not practicably be provided.

But now another phase of the problem presents itself to the experimenter. Oxygen has assumed the quiescent liquid state, to be sure, but in so doing it has fallen below the temperature of its cooling medium; hence it is now receiving from that medium more energy of vibration than it gives, and unless this is prevented very soon its particles will again have power to kick themselves apart and resume the gaseous state. Something, then, must be done to insulate the liquefied gas, else it will retain the liquid state for too short a time to be much experimented with. How might such insulation be accomplished?

The most successful attack upon this important problem has been made by Professor Dewar. He invented a receptacle for holding liquefied gases which, while not fulfilling the ideal conditions referred to above, yet accomplishes a very remarkable degree of heat insulation. In consists of a glass vessel with double walls, the space between which is rendered a vacuum of the highest practicable degree. This vacuum, containing practically no particles of matter, cannot, of course, convey heat-impulses to or from the matter in the receptacle with any degree of rapidity. Thus one of the two possible means of heat transfer is shut off and a degree of insulation afforded the liquefied substance. But of course the other channel, ether radiation, remains. Even this may be blocked to a large extent, however, by leaving a trace of mercury vapor in the vacuum space, which will be deposited as a fine mirror on the inner surface of the chamber. This mirror serves as an admirable reflector of the heat-rays that traverse the vacuum, sending more than half of them back again. So, by the combined action of vacuum and mirror, the amount of heat that can penetrate to the interior of the receptacle is reduced to about one-thirtieth of what would enter an ordinary vessel. In other words, a quantity of liquefied gas which would evaporate in one minute from an ordinary vessel will last half an hour in one of Professor Dewar's best vacuum vessels. Thus in one of these vessels a quantity of liquefied air, for example, can be kept for a considerable time in an atmosphere at ordinary temperature, and will only volatilize at the surface, like water under the same conditions, though of course more rapidly; whereas the same liquid in an ordinary vessel would boil briskly away, like water over a fire. Only, be it remembered, the air in "boiling" is at a temperature of about one hundred and eighty degrees below zero, so that it would instantly freeze almost any substance placed into it. A portion of alcohol poured on its surface will be changed quickly into a globule of ice, which will rattle about the sides of the vessel like a marble. That is not what one ordinarily thinks of as a "boiling" temperature.

If the vacuum vessel containing a liquefied gas be kept in a cold medium, and particularly if two vacuum tubes be placed together, so that no exposed surface of liquid remains, a portion of liquefied air, for example, may be kept almost indefinitely. Thus it becomes possible to utilize the liquefied gas for experimental investigation of the properties of matter at low temperatures that otherwise would be quite impracticable. Great numbers of such experiments have been performed in the past decade or so by all the workers with low temperatures already mentioned, and by various others, including, fittingly enough, the holder of the Rumford professorship of experimental physics at Harvard, Professor Trowbridge. The work of Professor Dewar has perhaps been the most comprehensive and varied, but the researches of Pictet, Wroblewski, and Olzewski have also been important, and it is not always possible to apportion credit for the various discoveries accurately, since the authorities themselves are in unfortunate disagreement in several questions of priority. But in any event, such questions of exact priority have no great interest for any one but the persons directly involved. We may quite disregard them here, confining attention to the results themselves, which are full of interest.

The questions investigated have to do with the physical properties, such as electrical conductivity, magnetic condition, light-absorption, cohesion, and chemical affinities of matter at excessively low temperatures. It is found that in all these regards most substances are profoundly modified when excessively cooled. Thus if a piece of any pure metal is placed in an electric circuit and plunged into liquid air, its resistance to the passage of the electricity steadily decreases as the metal cools, until at the temperature of the liquid it is very trifling indeed. The conclusion seems to be justified that if the metal could be still further cooled until it reached the theoretical "absolute zero," or absolutely heatless condition, the electrical resistance would also be nil. So it appears that the heat vibrations of the molecules of a pure metal interfere with the electrical current. The thought suggests itself that this may be because the ether waves set up by the vibrating molecules conflict with the ether strain which is regarded by some theorists as constituting the electrical "current." But this simple explanation falters before further experiments which show, paradoxically enough, that the electrical resistance of carbon exactly reverses what has just been said of pure metals, becoming greater and greater as the carbon is cooled. If an hypothesis were invented to cover this case there would still remain a puzzle in the fact that alloys of metals do not act at all like the pure metals themselves, the electrical resistance of such alloys being, for the most part, unaffected by changed temperature. On the whole, then, the facts of electrical conduction at low temperatures are quite beyond the reach of present explanation. They must await a fuller knowledge of molecular conditions in general than is at present available--a knowledge to which the low-temperature work itself seems one of the surest channels.

Even further beyond the reach of present explanation are the facts as to magnetic conditions at low temperatures. Even as to the facts themselves different experimenters have differed somewhat, but the final conclusion of Professor Dewar is that, after a period of fluctuation, the power of a magnet repeatedly subjected to a liquid-air bath becomes permanently increased. Various substances not markedly magnetic at ordinary temperatures become so when cooled. Among these, as Professor Dewar discovered, is liquid oxygen itself. Thus if a portion of liquid air be further cooled until it assumes a semi-solid condition, the oxygen may be drawn from the mass by a magnet, leaving a pure nitrogen jelly. These facts are curious enough, and full of suggestion, but like all other questions having to do with magnetism, they hold for the present generation the double fascination of insoluble mystery. To be sure, one may readily enough suggest that if magnetism be really a whirl in the ether, this whirl is apparently interfered with by the waves of radiant heat; or, again, that magnetism is presumably due to molecular motions which are apparently interfered with by another kind of molecular motions which we call heat vibrations; but there is a vagueness about the terms of such guesses that leaves them clearly within the category of explanations that do not explain.

When it comes to the phenomena of light, we can, as is fitting, see our way a little more clearly, since, thanks to Thomas Young and his successors, we know pretty definitely what light really is. So when we learn that many substances change their color utterly at low temperatures--red things becoming yellow and yellow things white, for example--we can step easily and surely to at least a partial explanation. We know that the color of any object depends simply upon the particular ether waves of the spectrum which that particular substance absorbs; and it does not seem anomalous that molecules packed close together at--180? of temperature should treat the ether waves differently than when relatively wide apart at an ordinary temperature. Yet, after all, that may not be the clew to the explanation. The packing of the molecules may have nothing to do with it. The real explanation may lie in the change of the ether waves sent out by the vibrating molecule; indeed, the fact that the waves of radiant heat and those of light differ only in amplitude lends color to this latter supposition. So the explanation of the changed color of the cooled substance is at best a dubious one.

Another interesting light phenomenon is found in the observed fact that very many substances become markedly phosphorescent at low temperatures. Thus, according to Professor Dewar, "gelatine, celluloid, paraffine, ivory, horn, and india-rubber become distinctly luminous, with a bluish or greenish phosphorescence, after cooling to--180? and being stimulated by the electric light." The same thing is true, in varying degrees, of alcohol, nitric acid, glycerine, and of paper, leather, linen, tortoise-shell, and sponge. Pure water is but slightly luminous, whereas impure water glows brightly. On the other hand, alcohol loses its phosphorescence when a trace of iodine is added to it. In general, colored things are but little phosphorescent. Thus the white of egg is very brilliant but the yolk much less so. Milk is much brighter than water, and such objects as a white flower, a feather, and egg-shell glow brilliantly. The most remarkable substances of all, says Professor Dewar, whom I am all along quoting, are "the platinocyanides among inorganic compounds and the ketonic compounds among organic. Ammonium platinocyanide, cooled while stimulated by arc light, glows fully at--180?; but on warming it glows like a lamp. It seems clear," Professor Dewar adds, "that the substance at this low temperature must have acquired increased power of absorption, and it may be that at the same time the factor of molecular friction or damping may have diminished." The cautious terms in which this partial explanation is couched suggest how far we still are from a full understanding of the interesting phenomena of phosphorescence. That a molecule should be able to vibrate in such a way as to produce the short waves of light, dissevered from the usual linking with the vibrations represented by high temperature, is one of the standing puzzles of physics. And the demonstrated increase of this capacity at very low temperatures only adds to the mystery.

If this increased strength and hardness of a contracted metal are what one would expect on molecular principles, the decreased chemical activity at low temperatures is no less natural-seeming, when one reflects how generally chemical phenomena are facilitated by the application of heat. In point of fact, it has been found that at the temperature of liquid hydrogen practically all chemical activity is abolished, the unruly fluorine making the only exception. The explanation hinges on the fact that every atom, of any kind, has power to unite with only a limited number of other atoms. When the "affinities" of an atom are satisfied, no more atoms can enter into the union unless some atoms already there be displaced. Such displacement takes place constantly, under ordinary conditions of temperature, because the vibrating atoms tend to throw themselves apart, and other atoms may spring in to take the places just vacated--such interchange, in fact, constituting the essence of chemical activity. But when the temperature is reduced the heat-vibration becomes insufficient to throw the atoms apart, hence any unions they chance to have made are permanent, so long as the low temperature is maintained. Thus it is that substances which attack one another eagerly at ordinary temperatures will lie side by side, utterly inert, at the temperature of liquid air.

Under certain conditions, however, most interesting chemical experiments have been made in which the liquefied gases, particularly oxygen, are utilized. Thus Olzewski found that a bit of wood lighted and thrust into liquid oxygen burns as it would in gaseous oxygen, and a red-hot iron wire thrust into the liquid burns and spreads sparks of iron. But more novel still was Dewar's experiment of inserting a small jet of ignited hydrogen into the vessel of liquid oxygen; for the jet continued to burn, forming water, of course, which was carried away as snow. The idea of a gas-jet burning within a liquid, and having snow for smoke, is not the least anomalous of the many strange conceptions that the low-temperature work has made familiar.

PRACTICAL RESULTS AND ANTICIPATIONS

Such are some of the strictly scientific results of the low-temperature work. But there are other results of a more directly practical kind--neither more important nor more interesting on that account, to be sure, but more directly appealing to the generality of the non-scientific public. Of these applications, the most patent and the first to be made available was the one forecast by Davy from the very first--namely, the use of liquefied gases in the refrigeration of foods. Long before the more resistant gases had been liquefied, the more manageable ones, such as ammonia and sulphurous acid, had been utilized on a commercial scale for refrigerating purposes. To-day every brewery and every large cold-storage warehouse is supplied with such a refrigerator plant, the temperature being thus regulated as is not otherwise practicable. Many large halls are cooled in a similar manner, and thus made comfortable in the summer. Ships carrying perishables have the safety of their cargoes insured by a refrigerator plant. In all large cities there are ice manufactories using the same method, and of late even relatively small establishments, hotels, and apartment houses have their ice-machine. It seems probable that before long all such buildings and many private dwellings will be provided with a cooling apparatus as regularly as they are now equipped with a heating apparatus.

The exact details of the various refrigerator machines of course vary, but all of them utilize the principles that the laboratory workers first established. Indeed, the entire refrigerator industry, now assuming significant proportions, may be said to be a direct outgrowth of that technical work which Davy and Faraday inaugurated and prosecuted at the Royal Institution--a result which would have been most gratifying to the founder of the institution could he have forecast it. The usual means of distributing the cooling fluids in the commercial plants is by the familiar iron pipes, not dissimilar in appearance to the familiar gas, water, and steam pipes. When operating, however, the pipes themselves are soon hidden from view by the thick coating of frost which forms over them. In a moist beer-cellar this coating is often several inches in thickness, giving a very characteristic and unmistakable appearance.

Another commercial use to which refrigerator machines are now put is in the manufacture of various drugs, where absolute purity is desirable. As different substances congeal at different temperatures, but the same substances at uniform pressure always at the same temperature, a means is afforded of freeing a drug from impurities by freezing, where sometimes the same result cannot be accomplished with like thoroughness by any other practicable means. Indeed, by this means impurities have been detected where not previously suspected. And Professor Ramsay has detected some new elementary substances even, as constituents of the air, which had previously not been dissociated from the nitrogen with which they are usually mixed.

Such applications of the refrigerator principles as these, however, though of vast commercial importance, are held by many enthusiasts to be but a bagatelle compared with other uses to which liquefied gases may some time be put. Their expectations are based upon the enormous potentialities that are demonstrably stored in even a tiny portion of, say, liquefied air. These are, indeed, truly appalling. Consider, for example, a portion of air at a temperature above its critical point, to which, as in Thilorier's experiments, a pressure of thirty-one tons to the square inch of the encompassing wall is being applied. Recall that action and reaction are equal, and it is apparent that the gas itself is pushing back--struggling against being compressed, if you will--with an equal power. Suppose the bulk of the gas is such that at this pressure it occupies a cubical space six inches on a side--something like the bulk of a child's toy balloon, let us say. Then the total outward pressure which that tiny bulk of gas exerts, in its desperate molecular struggle, is little less than five thousand tons. It would support an enormous building without budging a hair's-breadth. If the building weighed less than five thousand tons it would be lifted by the gas; if much less it would be thrown high into the air as the gas expanded. It gives one a new sense of the power of numbers to feel that infinitesimal atoms, merely by vibrating in unison, could accomplish such a result.

Share on: WhatsApp @Hash Facebook Tweet