Heavy Waters

Every molecule of pure "heavy water" contains two atoms of deuterium, which is hydrogen of the double-weight form identified in 1931 by Columbia's Harold Clayton Urey. Deuterium is not rare in nature. It is present in ordinary water to the extent of one part in 4,500.* Thus when suitable methods for separating it were worked out, high concentrations of heavy water became common. Nowadays one or two chemical manufacturers list and sell heavy water 99.5% pure.

The case of tritium, triple-weight hydrogen, is different. Its discovery was foreshadowed by the somewhat dubious magneto-optic method which anticipated the identification of deuterium. Then, in England, Lord Rutherford bounced deutons (deuterium nuclei) together, got protons and something of mass three which he thought was either an unknown form of helium or triple-weight hydrogen. Cautious Lord Rutherford took his time ascertaining that the new particles were both helium and tritium. Meantime Dr. Merle Antony Tuve and his associates at the Carnegie Institution of Washington had identified tritium particles by measuring their mass as indicated by the curvature of their paths in a powerful magnetic field. The existence of tritium was also demonstrated at Princeton. But tritium is scarce. Physicists estimate its proportion in ordinary water at one part in ten billions.

Nonetheless at Princeton, where intensive research on the heavy forms of hydrogen was under way, Dr. Pierce Wilson Selwood took 75 tons of tap water and started reducing it by repeated electrolysis and selective evaporation. The tons shrank to hundredweights, the hundredweights to pounds, the pounds to ounces. Last week Chairman Hugh Stott Taylor of the Chemistry Department announced that Dr. Selwood's final residue is ten drops (half a gram) of heavy water containing one part of tritium in 10,000-- richest sample of triple-weight hydrogen in the world, possibly rich enough to reveal something of its properties.

* The proportion is a little higher in the Dead Sea and Great Salt Lake.

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