Abstract
THE liquefaction of air, and the rest of the so-called permanent gases, is an achievement which belongs to quite recent times. Faraday cooled and compressed gases by such means as were at his disposal, with results which are well known; but it was the experiments of Andrews, published in 1869, which taught physicists the fact that until the cooling has been effectual no amount of pressure will liquefy the gas; in fact, that every gas has a critical point below which its temperature must be reduced before pressure can bring about liquefaction. The critical points of oxygen and the components of air are very low. Hence it was not till 1877 that these gases were liquefied by Pictet and by Cailletet. The former reached the, necessary temperature by two stages, using first liquid sulphur dioxide, then liquid carbon dioxide, both boiling under reduced pressure. Cailletet used the principle of cooling by sudden release from higher to lower pressure. The introduction of liquid ethylene as a cooling agent enabled experimenters to make another step forward; for, with the help of liquid ethylene, Wroblewski and Olszewski first obtained liquid oxygen in quantity far larger than would be possible in any form of Cailletet's apparatus, and without the complicated machinery of Pictet. Liquid oxygen itself thus became available as a refrigerating agent, and afforded the means of cooling a tube containing any other gas to a temperature lower than ever; namely, about 211° below zero Centigrade. With this cooling agent, and with the further cooling produced by expansion of the confined gas from a pressure of 150 atmospheres to 20 atmospheres, hydrogen has been liquefied by Olszewski. Suggestions have from time to time been made as to the possibility of applying the reduction of temperature, consequent upon the expansion of a gas when released from a high pressure, to the further cooling of the compressed gas; but no practical steps had been taken in this direction till the publication, in October last, of Herr Linde's successful liquefaction of air by the application of this principle. It now appears, however, that Linde has not only been anticipated in the application of the principle, but that a more effective apparatus than his has been devised. On Saturday, March 21, a demonstration was given, at Brin's Oxygen Works, of the construction and use of a new apparatus, the subject of an English patent, dated May 23, 1895, standing in the name of Dr. William Hampson. The apparatus consists of three coils of narrow copper tubing, arranged concentrically in a metal case, and connected successively together, as shown in the accompanying diagram (Fig. 1), which displays a vertical section of the apparatus. The gas, say oxygen, enters the outer coil under a pressure of 120 atmospheres, passing from this into the second, and from this into the central coil, which is surrounded by a cylindrical glass vacuum-jacketed vessel as devised by Prof. Dewar. The two outer coils are separated from each other by vertical divisions of the case, and the spiral of the central coil is followed by a flat spiral of sheet copper. When the gas reaches the extremity of the central coil, it escapes through a fine orifice of peculiar construction, formed by bringing two knife-edges closely together (shown in Fig. 2). The size of the orifice can be regulated by means of an ebonite rod, which passes up the axis of the apparatus, and terminates in a handle at the top. After its escape the whole of the gas cooled by expansion passes through the spaces surrounding the pipe through which the compressed gas is passing to the point of expansion, and so makes this gas, still under pressure, cooler than it was itself while under compression. The compressed gas consequently becomes at the point of expansion cooler than that which preceded it, and in its turn follows backwards the course of the still compressed gas, and so makes the latter cooler than before expansion, and therefore also cooler than ever after expansion. This intensification of cooling (always assuming sufficient protection against access of heat from the outside) is only limited by the liquefaction of the gas, the temperature of liquefaction being in the case of oxygen – 180°C. The apparatus exhibited measures 28 inches deep by 7 inches in diameter, and when once cooled down, that is, in about half an hour, it yields liquid oxygen at the rate of about seven cubic centimetres in four minutes. No carbonic acid, nitrous oxide, or other artificial cooling agent is employed either inside or outside the apparatus. With the liquid oxygen obtained, a series of interesting experiments were shown, which, however, were not in themselves new, such as the freezing of ether and alcohol, and the pulverisation of india-rubber after cooling. The expanded gas, after leaving the apparatus by the wide tube shown in the diagram, was led back to the suction pipe from which the pump was drawing. The impulse of the pump thus caused rhythmical variation in the pressure of the expanded gas over the surface of the liquid which had collected, and this in its turn produced a rhythmical variation in the small amount of ebullition visible in the liquid. Dr. Hampson's experiments, performed in the presence of a considerable number of representative men, constitute the first complete demonstration in England of the efficiency of the process of self-intensification of cold produced by expansion alone without the aid of extraneous artificial refrigeration.
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The New Process for the Liquefaction of Air and other Gases. Nature 53, 515–516 (1896). https://doi.org/10.1038/053515a0
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DOI: https://doi.org/10.1038/053515a0