Approach to Absolute

The nadir of cold called Absolute Zero exists not as a reality of nature but as a textbook definition, as a goal which haunts the minds of low-temperature researchers and which they do not expect to attain. Cold is the absence of heat. Heat is molecular activity. Thus Absolute Zero is the point at which the molecules that compose matter would lie like heaps of corpses in rigid juxtaposition. Physicists locate Absolute Zero at --273.13DEG Centigrade.

Much has already been learned about the properties of matter at temperatures close to the utmost cold. Lead, for example, shows superconductivity, which means that an electric current passing through it keeps on flowing after the circuit is broken. It is unlikely that another fraction of a degree will bring any startling revelation. But the remote chance that it might keeps the low- temperature men pressing indefatigably closer & closer to the inaccessible bottom of the pit.

The technique of approach is a complicated cycle of cooling, compression, magnetization, demagnetization. Liquid air cools compressed hydrogen until it liquefies, the liquid hydrogen cools com- pressed helium until it too liquefies. The last stage depends on the fact that magnetization heats matter, demagnetization chills it. The substance is powerfully magnetized and the heat generated drawn off; then a step farther down the scale of cold is obtained by demagnetization, and the cycle is repeated. The temperature is read by a system, of delicate balances, using the principle (discovered in the Curie laboratories of Paris) that the magnetic force of a magnetized body is proportional to its temperature.

Lately the struggle toward Absolute Zero has been led by Holland's University of Leyden and the University of California, both of which have tremendous magnets. For the final push they used highly magnetic salts--gadolinium sulphate octahydrate in California, cerium fluoride in Leyden. In 1933 Leyden was within .27DEG C. of Absolute Zero. Then California got it down to .16DEG. Then Leyden reached .03DEG.

Then in Leyden, Professor W. J. de Haas turned to another magnetic com- pound, containing potassium, chromium, alum. Last week he revealed that he had taken a huge bite from the tiny distance remaining. His compound was .0002DEG C. above Absolute Zero.

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