Heavy Water Content of Deep Sea Water
[Read before the Auckland Institute, August 7, 1935; received by the Editor August 22, 1935: issued separately, June, 1936.]
Through the courtesy of Dr. N. A. Mackintosh and of the Director of Research of Discovery Investigations I have had an opportunity of examining the heavy water content of samples of deep sea water collected by the Discovery in 1934. On account of ocean currents and the general mixing of the waters of the sea, it is not to be expected that any appreciable variation in the deuterium content will exist except possibly in very deep waters undisturbed by currents or circulation.
The density of heavy water is approximately 1.1, and consequently any considerable variation in the heavy water content of natural water may easily be detected by density determinations. An increase of one part of heavy water in ten thousand should increase the density by about 1 × 10-5. Since the density of water at room-temperatures changes by about 1 × 10-5 per 0.05° C., the temperature must be controlled and determined to within 0.05° in order to detect a variation of heavy water content of one part in ten thousand.
Three samples of deep-sea water, taken at depths of 4000, 4500 and 5000 metres, purified by distillation in an all-glass apparatus, were compared with similarly distilled tap-water at room-temperature by weighing in the water a glass sphere suspended by a fine platinum wire. On account of variations in room-temperature the weighings were made at several temperatures and the results plotted as curves, thus enabling comparisons to be made at definite temperatures correct to about 0.02°. From the results obtained it was found that the densities of the three samples were the same as that of distilled tap water to within 1 × 10-5 indicating that there was no difference in heavy water content exceeding one part in ten thousand. No attempt was made to determine smaller differences.
Wirth, Thompson and Utterback (Jour. Amer. Chem. Soc., 1935, p. 400) determined the densities of samples of water distilled from sea-water from different parts of the world both from the surface and from depths down to 4000 metres. The sea-water was slightly denser than distilled tap-water, the differences in density ranging from 0.21 × 10-6 to 1.67 × 10-6. A difference of 0.1 × 10-6 in the density of water at 25° corresponds to a temperature difference of 0.0004° and it is difficult to see how the temperature could be controlled and determined to the required degree of accuracy in an air bath at 25 ± 0.02°, although the authors state that through insulation the essential part of their delicate apparatus remained constant within 0.001°.
Emeléus, James, King, Pearson, Purcell and Briscoe (J.C.S., 1934, p. 1207) in a very thorough and comprehensive investigation found considerable variation in the density of water from various industrial sources. Their results and likewise those of Christiansen, Crabtree and Laby (Nat. 1935, pp. 135, 870) show that the density of water is appreciably altered by treatment on account of fractional separation, and it would consequently appear that accurate tables of the density of water at different temperatures may require revision since no account has been taken of possible variation in deuterium content.
Heavy water has been reported from the deep stratum of Lake Baikal, and it would be interesting to examine deep water from New Zealand lakes. I intend to examine waters from our thermal districts by the completely immersed float method.