122 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1934 



atoms had a mass of 2 instead of 1. Since the mass of the molecule 

 H2O would be 2X2 + 16=20, whereas ordinary water would be 

 2X1 + 16=18, it is evident that, granting equal volumes of the two 

 molecules, the new water might have a density of 20/18=1.11. The 

 experiments were followed by the changing density of the product, 

 and it is now known that heavy water with hydrogen of mass 2 has 

 a density of 1.1079 at 25° C. referred to ordinary water at the same 

 temperature. 



Shortly after the isolation was accomplished, Urey, Brickwedde, 

 and Murj^hy christened the isotopes; hitherto this had not been 

 necessary with isotopes, since there had been no chemistry of separate 

 isotopes to be considered. The discoverers of heavy hydrogen sug- 

 gested, for hydrogen of mass 1, the name protium, since this would 

 conform with current usage of the name proton for the nucleus of 

 the hydrogen atom. For the isotope of mass 2 they proposed tlie 

 name deuterium, which, for the nucleus of this atom, suggests deu- 

 teron or, more briefly, deuton, the nucleus of mass 2 and unit positive 

 charge. They also suggested that, if the isotope of mass 3 were 

 discovered, the name tritium might be considered. These names 

 have found general acceptance, except in England, where, following 

 a suggestion from Lord Rutherford's laboratory, the name " dip- 

 logen " has been employed. The best excuse for this latter is that it 

 gives " diplon " instead of deuton, which latter does not find favor 

 with the English scientists who, with colds in their heads in winter 

 time, may confuse deuton with the " neutron ", the particle of 

 mass 1 and zero charge. Considerable discussion has arisen as to 

 the symbols to be employed. Previous custom has sanctioned H^, 

 H^, and H^ for the symbolic representation. There is, however, an 

 increasing use of H for Hi, of D for Hs and of T for H3. For- 

 tunately, D and T have not hitherto been used as symbols for any 

 elements; also, D stands, equally well in England and elsewhere, 

 for both deuterium and diplogen. 



For the technique of preparation of pure heavy water or deuterium 

 oxide, the Princeton procedure may be cited, since, in this manner, 

 about 13 tons of commercial electrolyte corresponding to upwards 

 of 50 tons of ordinary Avater have already been treated to yield 

 approximately one pound of the purest heavy water. About 15 

 gallons of commercial liquor are electrolyzed daily to one-fifth vol- 

 ume in a battery of 960 cells using nickel anodes and iron cathodes. 

 The residue is distilled to remove excess electrolyte, and the distillate 

 after addition of alkali is passed to the second stage, a unit of 160 

 cells shown in plate 1, where it is again electrolyzed to one-fifth 

 volume. These two stages concentrate the deuterium from 1 part 

 in 1,600 to 0.25 percent, and 1 percent, respectively. From the third 

 stage onward a modified form of electrolysis is employed in which 



