Liquid air

“ Now, though we are accustomed to see water-atoms thus stirred into an activity which gives us the giant steam as servant, it has probably fallen to the lot of but few of us to encounter certain gaseous substances so utterly deprived of their self-assertiveness [Pg 214] as to collapse into a liquid mass, in which shape they are quite strangers to us. What gaseous body do we know better than the air we breathe? and what should we less expect to be reducible to the consistency of water? Yet science has lately brought prominently into notice that strange child of pressure and cold, Liquid Air ”

“ They buy liquid air.
“Big mills that manufacture locomotives use liquid air. They freeze up whole engine wheels with liquid air, then put on the tires, which are not frozen. When the wheel thaws out it expands and there you have your tire on tight as a drum. Funny business isn’t it?
[149]
“But mostly,” he slid another jug into position, “liquid air is split up before it’s used.”
“Split up?” Johnny stared.
“Sure,” Donald grinned. “Air contains six gases. The principal ones are oxygen and nitrogen. Oxygen is used a great deal, nitrogen very little, except in time of war. ”

“ But a use to which liquid air machines have already been put to a large extent is for obtaining oxygen from the atmosphere. Although when air is liquefied the oxygen and nitrogen are condensed simultaneously, yet owing to its greater volatility the latter boils off the more quickly of the two, so that the remaining liquid becomes gradually richer and richer in oxygen. ”

“ If air, under high pressure, be cooled first to the temperature of boiling ethylene, and then to -150° C., it liquefies, and, on reducing the pressure slowly, liquid air is obtained boiling under atmospheric pressure. During the process a considerable quantity of the liquid air evaporates, and the proportion of nitrogen to oxygen in the remaining liquid is less than in air liquefied under high pressure. ”

“ The curious effects of liquid air, only a few of which can be mentioned here, are not irrelevant to the subject of atmospheric resources, since they aid in various ways in carrying out important scientific researches. Almost all liquids are solidified and almost all solids are hardened and stiffened by immersion in liquid air. ”

“ Now that liquid air is available in many laboratories, it forms an advantageous starting-point in the preparation of argon. Being less volatile than nitrogen, argon accumulates relatively as liquid air evaporates. That the proportion of oxygen increases at the same time is little or no drawback. The following analyses (Rayleigh, Phil. Mag., June 1903) of the vapour arising from liquid air at various stages of the evaporation will give an idea of the course of events:—
(R.) ”

“ Moreover the steam which is thus formed has the same composition as the water. The boiling point of liquid air, on the other hand, gradually rises as the liquid boils, the nitrogen escaping first followed by the oxygen. If the two were combined, they would pass off together in the ratio in which they are found in the air.
Why the air has a constant composition. If air is a mixture and changes are constantly taking place which tend to modify its composition, how, then, do we account for the constancy of composition which the analyses reveal? ”

“ Some of the methods of exploring these depths of cold are treated in the chapter on liquid air already referred to. Our interest here centres in the other extreme of temperature, where the heat vibrations are inconceivably rapid; where nearly all substances known to man become liquids and gases; where, in short, if the experimenter could go high enough, he could reach the awful degree of heat of the burning sun itself, estimated at over 10,000 degrees. ”

“ Now carefully fix in the mind that a liquid does not need to be raised to its boiling point before vaporization begins, for it operates at all temperatures, even after the liquid is frozen, but much more rapidly from the liquid. ”

“ The cold of liquid air is far greater than that of ice or even a freezing mixture of salt and ice. Liquid air is simply air that is so cold that it becomes a liquid just as steam when cooled forms water. Steam has only to be cooled to the temperature of boiling water, while air must be cooled to 314 degrees below zero on the Fahrenheit scale. ”

“ Atmospheric air, for instance, frozen at the temperature of liquid hydrogen, is a hard solid, the strength of which gives no hint that with a further cooling of some 20 degrees it would crumble into powder. On the contrary, the lower the scale of temperature is descended, the more powerful become the forces which hold together the particles of matter. ”

“ In pouring out ale or other liquid, the falling stream becomes mingled with a portion of the atmospheric air which surrounds us; and it also buries, as it were, the air contained in the apparently empty glass: the result is, a mixture of ale and air, instead of ale only. Under ordinary circumstances, liquids contain as much air as they are capable of absorbing; the additional quantity is expelled. But how? It cannot rise in a body to the surface, but divides into minute spherical portions or air-bubbles, which ascend to the top of the liquid on account of their levity or comparative lightness. ”

“ Air is a vapor in our ordinary temperature, but has been transformed into "liquid air" under tremendous pressure, which produced a very low degree of temperature, and, theoretically, it may be transformed into a [Pg 64] solid under a sufficiently low degree of temperature, although so far, Science has not been able to produce a degree of cold sufficient to "freeze" the liquid air. ”

“ Water, exposed to the air, is constantly undergoing this change. It is changed from the liquid form, and becomes a vapor in the air. Water in the form of vapor occupies nearly 2000 times the space that it filled as a liquid. As the vapor at the time of its formation is of the same temperature with the water, and, from its highly expanded condition, requires a great amount of heat to maintain it as vapor, it follows that a given quantity of water contains, in the vapory form, many times as much heat as in the liquid form. ”

“ If currents of air are continually removing the saturated atmosphere from above the surface of a liquid, evaporation takes place most rapidly, since new portions of air, capable of absorbing moisture, are presented to it. ”

“ That liquid air is a real and wonderful discovery, and that for a certain small range of purposes it will prove highly useful, cannot be doubted by those who have seen and handled it and are familiar with its properties, but that it will ever be successfully used as an economical source of mechanical power is, to say the least, very improbable. ”

“ When we consider that in converting a given volume—say, one cubic metre—of water into vapour, enough heat is consumed to lower about 1,650,000 cubic metres of air by 1° C. in temperature, and that the same amount of heat is liberated when the vapour so produced returns to the liquid state, we perceive how powerfully the ordinary processes of evaporation and condensation must affect the temperature of the air. ”

“ An uncorked bottle of cologne scents an entire room, the odor of a rose or violet permeates the atmosphere near and far. These simple everyday occurrences seem to show that the molecules of a gas must be in a state of continual and rapid motion. In the case of the cologne, some molecules must have escaped from the liquid by the process of evaporation and traveled through the air to the nose. We know that the molecules of a liquid are in motion and are continually passing into the air because in time the vessel becomes empty. ”

“ Aer, L. (from αηρ Gr.) ; Luft, Ger.; Atmospheric Air; The Atmosphere. This name was formerly given to any aëriform body; thus, by the old chemists ammoniacal gas was called alkaline air; oxygen,—dephlogisticated, vital, or empyreal air; carbonic anhydride (carbonic acid) , fixed air; hydrogen, inflammable air; heavy carbonetted hydrogen, olefiant gas, heavy inflammable air; nitrogen,—mephitic, phlogisticated, or nitrous air. At the present time the term air is usually restricted to the gaseous envelope surrounding the solid and liquid parts of our globe. ”

“ Attention has been called to the fact that both oxygen and nitrogen can be obtained in the liquid state by strongly cooling the gases and applying great pressure to them. Since air is largely a mixture of these two gases, it can be liquefied by the same methods.
The methods for liquefying air have been simplified greatly in that the low temperature required is obtained by allowing a portion of the compressed air to expand. The expansion of a gas is always attended by the absorption of heat. ”

“ No, my dear; vapour is, indeed, an elastic fluid, and bears a strong resemblance to a gas; there are, however, several points in which they essentially differ, and by which you may always distinguish them. Steam, or vapour, owes its elasticity merely to a high temperature, which is equal to that of boiling water. And it differs from boiling water only by being united with more caloric, which, as we before explained, is in a latent state. When 183 steam is cooled, it instantly returns to the form of water; but air, or gas, has never yet been rendered liquid or solid by any degree of cold. ”

“ When its vapour is inhaled in sufficient proportion mixed with air, it soon produces a complete insensibility to pain. In the case of a full-grown man who inhales air containing 45 per cent. of the 736vapour, about 2 drams per minute of the liquid are consumed. The air is allowed to stream over the surface of the liquid in a proper apparatus, where it takes up the vapour, and the two pass through a flexible tube to a piece fitting over the mouth and nostrils of the patient. ”

“ Pressure facilitates evaporation, and on more closely examining this reaction we arrive at the conclusion that vapour can never spontaneously condense itself when liquid drops already formed are not present, unless forces of another nature intervene to diminish the effect of the capillary forces. In the most frequent cases, these forces come from the dust which is always in suspension in the air, or which exists in any recipient. ”

“ Conditions for Saturation.—If a liquid is evaporating into a vacuum, the molecules on leaving find no opposition until they reach the limits of the vessel containing the vacuum. Evaporation under these conditions goes on with great rapidity and the space becomes saturated almost instantly. If, however, air be present at ordinary pressure, many of the ordinary water vapor molecules on leaving are struck and returned to the water by the air molecules directly above. Those escaping gradually work their way upward through the air. ”

“ By still more recent experiments made by Professor Dewar, it has even become possible to liquefy the air we breathe, with the result that at a temperature of about 270 degrees below freezing-point and at an increased pressure, the otherwise invisible and gaseous air may be changed into a liquid, and poured out from one vessel into another in the same way that water can be poured out. ”

“ Eight hundred gallons of common air are compressed into one gallon of the liquid. The liquid is unattractive and very common-looking. You would not suspect its great powers by merely looking at it in a dish. But when it expands into common air it has tremendous energy. A few drops confined in a closed iron pipe will explode and blow the metal to atoms. ”

“ CHANGING ATMOSPHERE.—If the air is full of moisture, as it may be at some places, while comparatively dry at other points, the reflection throughout the moist area is much greater than in the dry places, hence evaporation will take place and whenever a liquid vaporizes it means heat. ”

“ A. The current of hot air up the chimney, striking against the oblique vanes of the smoke-jack, drives them round and round; in the same way as the sails of a wind-mill are driven round by the wind.
Q. Why are some things solid, others liquid, and others gaseous?
A. As heat enters any substance, it drives its particles further asunder; and a solid (like ice) becomes a liquid; and a liquid (like water) becomes a gas.
Q. Why does water simmer before it boils?
A. The particles of water near the bottom of the kettle (being formed into steam sooner than the rest) shoot upwards ”

“ In his first public contribution to science, 'Experiments on Factitious Airs,' sent to the Royal Society in 1766, he defines 'factitious air' as air which is driven off when compounds are heated or treated with acids, and the questions of the permanent elasticity of 'factitious airs,' their solubility in different liquids, their power to support combustion, their specific gravity, and likewise their combining equivalents, were all carefully considered. ”

“ I saw four manner of dryings: the first was bloodlessness; the second was pain following after; the third, hanging up in the air, as men hang a cloth to dry; the fourth, that the bodily Kind asked liquid and there was no manner of comfort ministered to Him in all His woe and distress. Ah! hard and grievous was his pain, but much more hard and grievous it was when the moisture failed and began to dry thus, shrivelling.
These were the pains that shewed in the blessed head: the first wrought to the dying, while it had moisture; and that other, slow, with shrinking drying, [and] ”

“ When the heavier penetrates to a sufficient depth, the interior being still warm, it is converted into gas and driven back to the surface, only to be recondensed on reaching the upper air. Thus it may happen that two rains composed of separate liquids may fall together. There being but little of any other atmosphere, much of it consists of what you might call the vapour of hydrogen, and many of the well-known gases and liquids on earth exist only as liquids and solids ”