LIQUEFACTION OF GASES. 312 LIQUEFACTION OF GASES. tically uiiliniiti'd aiiiouiit,s: lie was able to solidi- Professor Dewar discovered in the course of fv air as early as 1893; on May 10, 1808, he ob- his researches that the best vessel for holding tained liquid hydrogen in fairly large amounts, liquefied gases, in order to guard against access and in 1890 lie succeeded in solidifying both of heat from without, was a double-walled glass oxvgen and hydrogen. In fact, he has "succeeded bulb, the space between in liquefying all known gases with the exception of helium. whose existence on the earth DEWAR BCLB. the walls being com- pletely exhausted of air, and the glass being silvered like a mirror so as to reflect radia- tion. This vessel is called the 'Dewar bulb.' Important simplifica- tions in the apparatus of Dewar for the lique- faction of hydrogen have been made by Travers and others. As soon as it was found possible to liquefy gases with comparative ease, several machines were made in order to obtain liquefied air for commercial purposes. The most important of these are those invented by Linde in Germany, Ilanipson in England, and Tripler in America. These machines were all invented at about the same time (early in 1805), and all make u.se of the same principle — viz. the re- generative method. With these machines liquid air can be obtained in almost unlimited quantities and in a comparatively short time. Innumerable uses have been found ior liquefied gases, both in scientific in- vestigations and in indus- trial applications. The low temperatures which can thus be obtained are useful in many chemical experi- ments, and also in many where it is essential to secure pure gases. Liquid carbonic acid is used in the preparation of all kinds of aerated waters, viz. 'soda- water,' and also in the maiuifaeture of salicylic acid. Enormous quantities LINDE APPARATUS. The most important parte of the Linde machine, ae described in the specifications of the makers, are the two-cvlinder air-comproBsor and the counter-c-urrent inter- . . .- ,• changer. The former is driven b.v nipifna of a belt, from an electric or other motor, spectroscopic investigations The interchanKcr consists of a triple spiral of three copper tubes wound one inside the other. The compre8.sed air at the temperature of the coil g and at about 2UU atmospheres pressure pas!*4*8 thrnugh the inmost tube of the spiral from top to bottom, and jtasses nut at the lower end throuffh a valve a under a pressure of some 16 atmospheres. It returns Ufiward through the annular apace between the inner and middle pipc^ and is then a^ain raised to a pressure of 2llU atmospheres by the smaller cylinder tl <if the compressor, and then begins the same cycle over again. The large cylinder c of the compressor pumps a small amount of air from the atmosphere into the suction-pipe of the small cylinder, that is to sa.v at 16 atmospheres. A similar quantity of air must therefore leave the cycle at another point so that the pressure may remain constant. This escape of gas takes place at the lower end of _ _ . , the counter-current interchanger immediately after the discharge from 200 to 16 of liquid sulphurous acid, atmospheres, so that a cotitrollalile amount of air issues from Hi atmospheres to 1 ^vhich is used for nianv atmosphere through a second valve b and escapes through the outer annular space ^ '" ' ^ . • A of the triple copper tube. Part of this air, when the apparatus is cooled down to the purposes, are now preparea temperature of litiuefaction. then becomes liquefied and collects in a ' Dewar ' flask, for the market. Liquid c. which is fixed to the lower enil of the connt^T-current interchanger. By means of a " little pipe reaching to the bottom of the glass vessel the liquid may be run off through the cock //. That part of the air issuing from the second valve which is not liquefied leaves the apparatus, escaping through the space between the middle and outside pipes of the sjiiral into the atmosphere. K small quantity of water is con- tinually injected into the suction-pipe of the low-pressure c.vlinder in order to fill the clearance and to lower the final temperature of compression. This water, together with the moisture contained in the air, must be as far as possible completely separated out, so as to avoid stopping up the inside coil with ice. This is done first of all by means of a water-sej)arator, /, which holds back water carried over with the air in mechanical suspensirtn, and secondly by means of an iron i»ii»e in the form of a coil, g, which is cooled down to a few degrees below zero by a freezing-mixture of ice and chloride of calcium, and freezes out the small quantities of water-vapor con- t.ained in the highly compressed air until only traces remain. ha.s only recently been discovered. All attempts to liquefy this gas have so far failed, although temperatures as low a.s — 258° C. have been used. There is no reason to doubt, however, that this gas also can be liquefied if suitable means are used. nitrous oxide is used as an anipsthetic for minor sur- gical operations, especially in dentistry. Liquefied gases are used in the oper- ation of most ice-machine plants. Liquid oxygen can be obtained commercially and is used extensively in hospitals. It has been i liquid thought that liquid airl would be used as a motive power, but so far all] attempts to control it have failed. At temperatures as low as those of liquid airl and solid hydrogen all the ordinary properties of I matter would be expected to change, and a care- ' ful study of these changes has been made by
