LIQUID AIR

Dominion, Volume 31, Issue 242, 9 July 1938, Page 3 (Supplement)

LIQUID AIR

Some Facts About It

Did you ever wonder what is meant bv the term “Liquid Air”? asks -W. p. Keakbey in the “Christian Science Monitor.” , t , We are all familiar with liquid water. We probably also know that when sufficient heat is added, as when a kettle is put on a hot stove, the water will “boil away”; that is, it will change to a vapour. Further, if the water is cooled sufficiently, it will change to a solid, known as Ice. Most substances change their form if enough heat is added or taken away. Even iron, wheu made extremely hot, will liquify, and when made still hotter it will turn to heavy vaporous fumes. It is by cooling that air is made to change to a liquid. In the manufacture of liquid air three compressors are used. In the first, a pressure of 90 pounds to the square inch is obtained: the second increases the pressure to 500 pounds; and tho third to 2200 pounds. Both the compressors and the air are water-cooled. The air under a pressure of 2200 pounds is allowed to pass through a small jet into expansion chambers. The cold of expansion is so intense that the air liquifies, and may be drawn off as clear, bluish liquid. -.The main commercial use for liquid air is in the manufacture of nitrogen (for fertilisers, ammonia, etc.) and oxygen. The temperature of liquid air is 312 degrees Fahrenheit below zero. It can be poured like water, and a kettle of liquid air will boll vigorously on a cake of ice. Liquid air is so intensely cold that it must be handled and transported In special glass containers. These containers have double walls, between which the air has been exhausted (as jn vacuum bottles), and this airless space keeps out the heat, which would otherwise promptly change liquid air back to its normal gaseous state. Thermometers, w'hether of mercurv or alcohol, would freeze soli'd if immersed in liquid air. Its temperature, consequently, must be measured by a device which Indicates the degree of cold by the shrinkage of metal. It is interesting to note that while air is a liquid at —312 degrees Fahrenheit, it is not wet, any more than quicksilver or molten iron are wet,