VOL. 4. NO. 3 HISTORY o s THE! CXORMH INDUSTRY 319

The productive capacity of the chlorine industry both in the United States of America and elsewhere had overtaken the demand before the World War. The war needs added to the capacity and since 1918 in England, France, Germany, Italy, and the United States of America the available capacity has far outstripped consumption. This has led to renewed searches for more uses. The noxious character of chlorine gas, its corrosive action in the presence of moisture, its readiness to attack nearly all known sub- stances, and to unite with nearly all gases but the rarer ones, render its manufacture, handling, and use a very technical matter. Nevertheless, its manufacture, handling, and use in the industrial arts have been re- markably free from serious accidents.

Chlorine is indispensable today, and the measure of its use is an index of the comparative civilization of a country.

BIBLIOGRAPHY

"The Early History of Chlorine," Alembic Club Reprint No. 13, Edinburgh, 1902. Mellor, "A Comprehensive Treatise on Inorganic and Theoretical Chemistry,"

Longmans, Green and Co., New York, 1922. Ludwig Mond, "History of the Manufacture of Chlorine," 3. Sac. Chem. Ind.,

15, 713-719 (1896). Thomas Northmore, "Experiments on Condensed Gases," Nicolson's Journal

( J o u ~ l of Natural Philosophy, Chemistry and the Arts), 13, 234-235 (1806). D. A. Pritchard, "Economics of Chlorine," Trans. Am. Electrochem. Soc., 1926.

Metal Shrinks When Magnetized. Changes in monel metal, a widely used alloy of nickel, capper, iron, and other metals, as i t is magnetized, are just in the opposite direction from similar changes in iron, Prof. S. R. Williams, of Amherst College, told members of the American Physical Society a t their recent meeting.

"If a rod or bar of magnetic material such as iron or steel is magnetized in its long direction," said Prof. Williams, "it will change its length as the magnetizing farce is increased from zero upward. This is known as the Joule magnetostrictive effect." Iron, he explained, first increases in length as it is magnetized until a certain degree of magnetism has been attained, and then shortens. Nickel shortens for all degrees of magnetization, while manganese lengthens for all.

However, the speaker continued, the change in monel metal is just the opposite of that in iron. First, a bar of the material shortens as it is magnetized, and then i t lengthens. It also changes in length while a constant magnetic force is applied. This is done by means of a solenoid, or coil of wire, around the metal rod, through which an electric current is passed. The shortening has only been studied, however, over a period of application of the magnetizing force for about two minutes, for by that time the solenoid begins to get heated by the current flowing through it. This in turn heats the rod, and causes i t to expand.

"It is an interesting effect," said Dr. Williams, "to watch this contest between the shortening due to the magnetic field and the lengthening due to the heat effect. The spot of light which records the changes in length of the metal bar swings up and down like the breathing of some living organism."-Science Service