LIQUID AIR.

Dominion, Volume 7, Issue 1866, 27 September 1913, Page 18

LIQUID AIR.

MADE FOR COMMERCIAL PUR. POSES IN NAPIER, A WONDERFUL INDUSTRY, ■ it is characteristic of Hawkc's Bay enterprise that Napier should bo one of t'he fow places in the Southern Hemisphere where liquid air i 3 manufactured for commercial purposes. Most people by this time have read magazine articles about liquid air, hut few liavo any idea that its manufacture is part of the ordinary daily routine work of a stuff of men in Napier. The liquid air, it should bo explained, is not manufactured for its own sake, and it is not put up in bottles for summer drinks. It is made for the solo purpose of immediately being separated into its two component gases—oxygen and nitrogen —and of these two tho oxygen is bottled and stored ready for dispatch all over New Zealand. The liquefying of the air Is wonderful enough, but the method of separating the oxygen from t'he nitrogen is equally ingenious. It is based on the fact that liquid nitrogen boils at a lower temperature than liquid oxygen', and that if yoa bring liquid air down to and hold it at this temperature the nitrogen will'immediately boil away and only oxygen be left. ■ Liquid air can only be produced by a cold so intense that the interior of an ordinary freezing chamber would be like tho tropics alongside it. As a mat-tor of fact- the air is given a preliminary run through a Linde freezing machine before the sorious work of cooling it begins.' The point then arises—how is tho air to be brought down to the temperature of -196 decrees centigrade at which it becomes liquid? The visitor, already sufficiently bewildered, is calmly told at this stage that that little difficulty is easily overcome—'the air is made to freeze itself! It has been scientifically established that .a gas in expanding cools itself, and that therefore you cau bring a gas down to any temperature you please by alternately 'compressing it and allowing it to expand. Tho explanation begins to bristlo with technicalities' about this point, and there are a lot of qualifica- | tions that ought to go in, but this is tho gist of it. Of course it is all quite simple, the only thing necessary to get further ahead is tiie brains to make a niachino in whidh you can compress air to 2500 lb. to the square inch and let it do its expanding and contracting at exactly tho right moments and so on. Tho plant for producing tho liquid l air stands in a roomy concrete building, and the principal part of it to catch tho eye is four cylinders standing in a row in tho middle of the floor, and linked together by a number of pipes. There are various other cylinders and machines scattered about, and the whole arrangement is hitched on to a f?as engino. You start tho engine going -nt one end and bottle the oxygen at the other. The nitrogen which tho plant makes, in addition to tho oxygen, lias no great commercial value, and is used incidentally to cool the compressed air coming into the separator, and thus render it more dense, so that it is easily liquefied. The present writer does not intend to give A technical description of tho plant and disclose his lamentable ignorance to tho few readers who ' do know something of the subject while bewildering those who don't. He was, however, informed by Mr. Edmondson, the managing director of the Acetone Illuniinating and Welding Company, Ltd. —whose works it is that have been described — that the liquid air machine is capablo of producing oxygen with a

purity of 98.2 per cent, in quite a rapid manner sufficient to supply New Zealand's requirements. In a stack near by some 5000 cubic feet of oxygon is stored in long iron cylinders, while a gasometer at the rear of tho building holds an additional 1000 feet. If tho manufacture of the oxygen is remarkable, tho uses to which it is put are still more marvellous. In tho Acetone Company's workshops the .stray scientific facts which have been lying about unused in text-books for years are gathored up and put into harness. Every schoolboy has been told at some timo or other that in an atmosphere of oxygon iron would burn like coal. The Acetone Company has supplied the atmosphere of oxygen and now one lias only to turn on the tap and light up a tiny jet that in a few moments will pierce right through a piece of solid boiler plate. It is at this end of the proposition that the Acetone comes in. Acetone, which is n form of alcohol akin to methylated spirits, is used for tho production of an exceptionally intense acotyleue gas. This "gas is now used extensively for lighting marine beacons which can only be tended at long intervals. Lights, it may be noted, can bo provided which will burn untouched for three years. The Government is installing an Acetono light at Torawhiti, the Gisborno Harbour Board has one in its lighthouso at Tuahine Point, and tho system has been adopted by the Auckland Harbour Board, the Wliangarei Board, and also by the Marino Department. Acetono motor lights aro in use and aro unusually powerful. The Acetone is used in conjunction with oxjgen for tho purpose of cutting and welding iron and steel. The apparatus needed, for instance, for cutting one of tho battleship New Zealand's turrets up would be only a cylinder of oxygon, another of Acetone, and a length or two of tubing and a blowpipe. Tllis blow-pipe, to which tiie tubes are attached, has two separate jets, a central one for the oxygen, and an annular olio surrounding it for the Acetone. Tho Acetono flame is used to heat tho metal whore it is to be cut to a bright red. A fine jet of oxygen is then admitted, and tho result is wonderful. The - flame immediately pierces straight through the metal like so much paper, and armour plate up to. 24 inches in thickness can bo cut to any shape desired. Boiler plate, threequarters of an inch thick, can be cut at the rate of 60 feet an hour with one jet. By means of a different jet tho two gases can be used similarly for welding. The temperature of the flame resulting from the combustion of tho two gases in combination is 6300 Fahrenheit, and is one of tho hottest known to science. Another branch of the Acctono Company's business deals with the manufacture of nitrous oxido. the well-known' anaesthetic used by dentists. "Until the company began operations recently, all this gas had" to bo imported. The plant now in operation is sufficient to manufacture all' tho gas required in New Zealand.