Oxygen

Uses.

Most of the oxygen is employed in industry for the fusion welding of metals, e.g., steel, cast iron, aluminium, lead, and for the cutting of steel. Gas welding is generally accom plished by the aid of the oxyacetylene flame, the two gases being supplied to a blowpipe wherein they are thoroughly mixed before combustion. In practice a little more oxygen than acetylene is used, and the resulting flame has an inner white core with a tem perature above 4,000° C; it is quickly able to reduce these metals to the molten state locally, where two edges are to be joined. For metal cutting, a separate jet of "cutting" oxygen is provided in a similar blowpipe, either in the centre of the heating jet or behind it. As a rule, the melting point of an oxide is higher than that of the metal from which it is derived ; but the fusion point of industrial iron varies between 1,400-1,500° C, and the mix ture of iron oxides fuses at about 1,35o° C. In the cutting the oxides of iron are formed and blown away in the molten state before the unoxidized iron reaches its melting point, the necessary temperature being maintained chiefly by the heat of combustion itself, but to a less extent by an independent heating jet. When the cutting blowpipe is moved mechanically, and therefore regu larly, over the metal a remarkably smooth regular cut is obtained, even through metal 1; in. thick.

Oxygen is widely used in medical practice, inhalation being of service in cases of pneumonia, heart complaints, etc. ; also in cases of gas poisoning, especially by carbon monoxide. It is used with nitrous oxide by anaesthetists.

Liquid oxygen has considerable industrial applications. If a rod of hard gas-carbon be heated to redness at one end and then immersed in liquid oxygen, it burns in the liquid with intense evo lution of light and heat, the carbon dioxide resulting being frozen and retained as a white solid in the liquid. If the carbon is pre sented to the oxygen in a porous form, ‘e.g., wood charcoal, lamp black, soot, cork meal, sawdust, or wood pulp, the mixture forms a powerful explosive, more than twice as effective as blasting gel atine. It is so remarkably effective because the oxygen is free, and not chemically combined with other elements as in explosives like gunpowder or nitro-compounds, the explosion being an in stantaneous oxidation of carbon, hydrogen or other elements. The

materials are formed into cartridges in a paper wrapping; these may be 8in. long and I2in. in diameter. They are thoroughly soaked in liquid oxygen and placed in the bore hole, and, after tamping, fired electrically or by fuse. This explosive has the great advantage that it automatically becomes dead in a short time if not fired, owing to the evaporation of the oxygen. It is exceptionally suitable for use in iron mines and in tunnelling, as it gives rise to no harmful gases.

The highly volatile liquid is transported in double-walled spher ical vessels, made of spun copper with long, narrow necks. A good vacuum is created mechanically between the walls. When the excessively cold liquid oxygen is introduced into the vessel, ac tivated charcoal (q.v.), placed in the vacuous space and in con tact with the inner sphere, becomes cooled, and then possesses the remarkable property of absorbing the residual gas and con verting the vacuum to one of an exceedingly high order (a few millionths of a mm. of mercury). This vacuum, coupled with the highly polished metal surfaces, prevents the ingress of heat to a large extent. A 25-litre container (the usual size) loses by evaporation only 5% of its full liquid charge per day. The liquid is poured from them into smaller dipping flasks, of similar con struction, but cylindrical in shape with open top, so that the cartridges can be readily inserted and withdrawn. (For oxygen in relation to muscular contraction see MUSCLE.) N. Friend and D. F. Twiss, Text-Book of Inorganic Chemistry (vol. vii. part i., ; J. W. Mellor, A Com prehensive Treatise on Inorganic and Theoretical Chemistry (vol. i., 1922) ; "Vacuum vessels," Report of the Oxygen Research Committee (Department of Scientific and Industrial Research, 1923) ; G. Claude, Air liquide, Oxygene, Azote, Gaz rares (industrial 1926) ; K. S. Murray, "Industrial Methods of liquefaction and practical applications of low temperatures," Trans. Faraday Soc. (vol. xviii., part 2, Dec. 1922) ; R. Granjon and P. Rosemberg Autogenous Welding (Oxy Acetylene) : practical manual (1914) ; The British Acetylene and Welding Handbook (The Acetylene and Welding Journal, 1923).

(C.

R. H.)