Liquefied Air, and Some of the Extravagant Claims Made for It

LIQUID AIR, AND SOME OF THE EXTRAV- AGANT CLAIMS MADE FOR IT. BY DR. JAMES E. TALMAGE, OF THE UNIVERSITY OF UTAH.

So many articles treating on the subject of liquid air, the marvelous properties of the substance, and the alleged possibilities of its application to the service of man, have appeared in the mag- azines of recent months, that additional writings of the kind call for a statement of reason or excuse for their coming forth. The present writer's excuse for appearing in print under the foregoing heading rests on the urgent and repeated requests of the Era's editors to this end; and their reasons for desiring such a contribu- tion are probably strengthened by the questionable reliability of

the great array of liquid air literature already presented to the reading public. Certainly much that has been published on this subject consists of unproved assertions and of extravagant prom- ises, the fulfillment of which is by no means assured. Prospectuses of three companies have already appeared, each specifying a cap- millions of dollars, and predicting speedy and italization of five enormous returns to those who invest their means in the utilization of this new agent of civilization and progress. The careful reader may have observed that the immoderate praise of liquid air as an agent of unprecedented efficiency, and the song of its future triumphs, have been generally voiced through the columns of semi- sensational periodicals; while scientific journals and publications of acknowledged authority in the special field of physics have been mainly silent on the subject or studiously guarded in their utter-

54 IMPROVEMENT ERA.

ances. Demonstrated facts, unsupported theories, and fanciful dreams have been so mingled in current discussions of liquid air, that the lay reader may be unable to distinguish between fact and supposition. In the first place, what is liquid air, or, more accurately stated, liquefied air? It may be profitable to preface the answer to this question by a few general considerations. We are accustomed to speak of two classes of substances with respect to physical state, viz., solids and fluids;of fluids two sub-classes are recognized, liquids and gases. The essential difference between a liquid and the same substance in a state of gas is one of condensation, the parti- cles of the gaseous substance being brought closer together in the process of liquefaction. Long ago it was demonstrated that by increasing pressure, or by lowering temperature, and more expedi- tiously by combining both of these operations, certain gases could be reduced to the liquid condition. Increased pressure was usually employed as the means of liquefaction, but experiment soon proved that pressure alone would not insure liquefaction in all cases; and that for each gas there is a certain degree of heat, commonly known as the critical point of temperature, above which the gas cannot liquefy, however great the pressure applied. It has also been proved that for every gas there exists a critical point of pressure, below which liquefaction is impossible even though the temperature be greatly reduced. which is not a single gas Air, but a mixture of gases, was one of the most obstinate substances to liquefy. Its critical temperature has been proved to be about — 140° C, and its critical pressure 39 atmospheres, or 585 pounds to the square inch. Liquefied air then is the ordinary atmospheric mixture of gases, so condensed by pressure and cold as to be brought into the state of a watery fluid. Means of producing intense cold have been eagerly sought with the hope of employing such in the liquefaction of gases. The common methods now used are based on the fact that heat is absorbed in the process of gas expansion. It is generally known that when a gas is compressed by mechanical means it becomes

warm. Conversely, when a gas so compressed is allowed to expand, heat is absorbed, and the bodies with which the expanding gas is in contact will be robbed of their sensible heat. Upon this princi-

LIQUID AIR. 55

pie the expansion of compressed ammonia in tubes is made a means of refrigeration. In 1879, Callette liquefied air in small quantities by means of pressure mechanically applied, combined with the cooling effect of expanding gases. Six years later, Solvay produced liquid air in greater quantities by employing a cumulative method of cooling, the principle of which may be stated briefly as follows: Air that has been compressed is deprived of part of its sensible heat by external cooling; it is then allowed to expand to its volume before compression, and is again compressed, cooled and allowed to expand, the process being repeated until a very low degree of temperature is reached. This method has been improved upon by Linde, of Munich, in 1895 ; and during recent months, by Mr. Charles E. Tripler of New York. The gentleman last named has been so successful in his efforts that liquid air is now produced at a very low cost, and in quantity sufficiently great to warrant the expectation that its adaptability to practical purposes may be thoroughly tested by experiment. While the means of producing the substance were so costly and difficult, practical experiments, on a large scale, were not attempted. It is interesting to note that in Mr. Tripler's ingenious and highly efficient method of apply- ing the principle of cumulative cooling, compressed air is employed as the gas which cools by expanding. Liquefied air is air in an

extreme state of compression; this substance therefore may be and has been employed as a cooling agent, which by its own evap- oration and subsequent expansion, cools, and eventually liquefies other, though smaller quantities of air. The principle underlying the process by which air is liquefied on the cumulative plan of cooling, is thus concisely described in a recent paper by Mr. E. S. Wicklin, of Chicago. It should be understood that the description

is not that of any particular machine. "Air compressed to about 2,500 pounds to the inch, and cooled by being passed in pipes through a bath of running water while thus compressed, is carried through coils of pipes to a receiver several feet away. Into this it is discharged through pinholes not large enough to reduce the pressure in the coils. As fast as set free in the receiver, the air expands to nearly its original volume, falling in temperature per- haps a hundred degrees or more. From the receiver the air flows

—

56 IMPROVEMENT ERA.

back through a large jacket that surrounds the incoming coils, and returns to the compressor, where it is again compressed, cooled, returned through the coils, and discharged through the pinholes. Thus it will be seen that as soon as the operation is started the coils are enveloped in an intensely cold atmosphere that greedily snatches heat from every inch that it touches. In this condition the air in the coils is every moment growing colder, and is thus discharged from the pinholes at a temperature more reduced, and filling the jacket with expanded air ever more and more eager to devour the last remaining vestige of heat in the coils. This cannot long continue. The cold becomes so intense that the expanding air gives up its latent heat, forms a cloud, and rains down a liquid shower to the bottom of the receiver. From this moment the con- denser must draw a part of its supply from the outside, as every drop of the liquid takes up seven hundred and fifty times its vol- ume of the expanded air." Of the remarkable properties possessed by liquid air much has been written, and the published descriptions, in general full and accurate, are all instructive and interesting. The boiling point of liquid air, or the temperature at which, under proper pressure, air passes into the liquid condition is about 312,° F.; that is 344 Fah- renheit degrees below the freezing point of water. Now, the tem- perature difference between water at its freezing point and water at its boiling point, (at the sea level) is only 180 Fahrenheit de- grees; yet water at its freezing point is 344 degrees hotter than The ordinary temperature of a liv- liquid air at its boiling point. ing room, say 68° F., is 380 degrees hotter than boiling liquid air. Consequently when liquid air in an open vessel is exposed to the ordinary temperature of a room, or even when poured into an ice cavity, it boils violently, and is rapidly reconverted into the gas- eous state. Alcohol, which, because of its low freezing point, —202.9° F., is used in thermometers designed to indicate very low when brought in contact with liquid air; temperatures, is solidified and mercury under similar conditions is frozen so hard that a block of the metal may be used as a hammer. Such facts as these, while interesting and curious, are of but little promise in pointing a way to the utilization of liquid air in the practical arts. The main pur- poses to which man hopes to apply the substance are those of

LIQUID AIR. 57

refrigeration and power, an^ it is along these lines that the loudly advertized schemes of immediate application are directed. Let us briefly consider each of these purposes, and the probable adapta- bility of liquid air thereto.

As a refrigerating agent liquid air has been credited with eflBciency almost beyond comprehension. And indeed there appears great promise of advantage in substituting this new liquid for ammonia and other substances which have heretofore been utilized on the principle of cooling through evaporation arid gaseous ex- pansion in large refrigerating plants. It would seem to be an easy

matter to equip ships,hospitals, and large establishments generally, with fliquid-air machines, by which ice could be readily produced, and rooms be kept cool by a system of expansion tubes. But the plan of using liquid air as a cooling agent on a small scale, by simple exposure in open vessels, is probably impracticable. Never- theless, wonderful claims have been asserted for the substance when so employed. I quote from a prospectus circulated by an eastern company now offering its stock for sale:— "A single gallon [of liquid air] will perform wonders in an ordinary city home. A tumblerful dipped out and placed in the ice chest will maintain a temperature of zero in the refrigerator for twenty-four hours. A quart of it placed in the ventilating apparatus will keep the tem- perature of the whole house at 60° during the hottest summer day. The remainder of the gallon put into the proper motor, with an electric dynamo attachment, will generate enough heat to do the cooking, run the electric lights, warm the water for the bath, and in the winter heat the entire house by electric radiators. Its application as a medicine is full of marvelous possibilities." This is perhaps a fair type of many published assertions on the subject. The prospectuses of other companies embodying statements as ex- travagant as the foregoing have reached my hand. The utter fallacy of many of these statements can be practi- cally demonstrated and mathematically proved by any capable student of physics. Not desiring to burden these pages with de- tails of calculation, which to many would be tedious, I content myself with a statement of results. One pound of liquid air is at best equal in refrigerating power to less than one pound and a half of ice; (accurately stated, 1.42 pounds of ice). Furthermore, it

58 IMPROVEMENT ERA.

is certain that the loss through evaporation, etc., will be much greater in the case of liquid air than in that of ice, and therefore this theoretical efficiency will not be realized. Therefore, liquid

air and ice may be considered as about equal in practical refriger- ating value, weight for weight. A tumblerful of liquid air weigh- ing about half a pound, is therefore equal as a refrigerating agent to about half a pound of ice. The second statement quoted in regard to the great cooling effect of a small quantity of liquid air, viz., that "a quart of it placed in the ventilating apparatus will keep the temperature of the whole house at 60° during the hottest summer day," is likewise untrue. As a matter of fact the refrigerating effect of a quart of liquid air so used would be equivalent to that of about two pounds of ice. The assertion that the unused portion of the gal- lon of liquid air (five and a half pints) would furnish motive power sufficient torun a dynamo, warming and lighting the house and furnishing heat for the cook-room and the bath, is a gross exag- geration. In considering it we are brought to the second proba- ble means of liquid air utilization, viz., as a source of power. That the great expansive power of liquid air can be used as a convenient means of mechanical energy, there can be little doubt. The value of this source of energy can be practically determined. The full theoretical efficiency of a gallon of the liquid is equivo- lent to a force of one-horse power operating forty-five minutes; and the five and a half pints referred to above would furnish one- horse power during thirty-one minutes only. Practically this efficiency would be greatly lessened through the inevitable losses in working. It is, however, probable, almost certain indeed, that liquid air will be very widely employed as a motive power; the ease and con-

venience attending its use being among its strong recommendations to this service. But no one can reasonably hope to gain from the expansive power of liquid air greater force than was employed in producing the liquid; indeed, as shown, the practical yield will be necessarily less. It may suit our convenience, and therefore be of advantage to us, to employ the power of steam to drive a dynamo, thereby transforming the energy into electricity; we may then use the electric current in operating a motor, which in turn may drive

LIQUID AIR. 59

a mill, a printing press or a street car; yet who would expect to realize in the motor as great a manifestation of energy as was yielded by the steam engine in the first place? Every transforma- tion has cost much in loss of available power. Compressed air has been found serviceable, because convenient, in driving small en- gines; but the power resulting is always less than that employed to compress the air; and with appliances theoretically perfect could never be greater than the initial energy developed. Uses at once varied and great already appear in the prospect for liquid air; there is little excuse for the unfounded claims that have been asserted as among its assured applications. The sub- stance will probably find a place among the cauterizing agents used in surgery. Its employment in the manufacture of explo- sives and as a means of securing more thorough combustion of fuel appears reasonably certain. Its adaptability to the purposes last named may be thus explained. As before stated, the atmos- phere is a mixture of gases, the principal ingredients being oxygen and nitrogen. When reduced to the liquid state and allowed to boil, the nitrogen disappears first, its boiling point (— 320° F.),being about twenty degrees below that of oxygen, (— 300° F.) the oxygen ;

therefore is soon in excess. Now, oxygen is the common supporter of combustion; and if liquid oxygen, thus readily obtainable, can be safely and successfully fed to carbon undergoing combustion, the present woeful waste of fuel may be largely obviated. In a similar way the addition of liquid oxygen to explosive materials may greatly add to their efiiciency. But of all the wonders, real or imaginary thus far declared of liquid air, the most astounding is the following: It is asserted that a given amount of liquid air, when employed to drive a liquid air engine, actually produces a quantity of the substance greater than that used in the machine. Mr. Tripler is quoted as saying: "I

have actually made about ten gallons of liquid air in my liquefier by the use of about three gallons in my engine. There is therefore a surplusage of seven gallons that has cost me nothing, and which I can use elsewhere as power." This surprising statement is the cause of the almost unparalleled excitement incident to the an- nouncement of the successful manufacture of liquid air in quantity. Certainly to any one who can accept the declaration as made above

60 IMPROVEMENT ERA.

it is sufficiently astonishing. To the physicist it is simply a mis- statement. Eitherwe have not understood Mr. Tripler or he has failed to fully comprehend his own operations. Fanciful pictures have been drawn of the boundless possibilities of a power that costs less than nothing, and of energy that perpetuates itself in an ever increasing proportion. Such a solution of such a problem be- littles the impossibilities of perpetual motion. However, the state- ment is not yet fortified by the proof which physicists demand. It

may be noted that the article in which Mr. Tripler is quoted as having used the words given above, closes as follows: — "Much has yet to be done before liquid air becomes the revolutionizing power which Mr. Tripler prophecies. * * * Mr. Tripler has yet to perfect his machinery for producing liquid air without expense." The assurance which to some may seem presumption, in reject- ing the positive statement concerning the increasing production of liquid air through itself alone, is justified by the fact that laws of

nature are opposed to the declaration. It is not given to man to create either matter or energy. His drafts on the bank of nature will be honored to the extent of his deposit honestly made therein, and no further. He may utilize matter and the forces about him, by exchange and transformation, but he cannot get something for nothing.