PROTIUM — DEUTERIUM TRITIUM — TAYLOR 121 



The net success was vanishingly small. One or other method gave 

 separations of one or two parts per thousand at such a prodigious 

 expenditure of effort that the recovery of the pure components of 

 an isotopic mixture seemed to be an unattainable objective. The 

 hydrogen isotopes, of masses 1 and 2, represent the most favorable 

 case, since the mass difference is 100 percent. Even in this case the 

 problem seemed to be discouragingly difficult when it was shown 

 that the fractional evaporation of 40 liters of liquid hydrogen until 

 only two liters of gas remained raised the concentration of the 

 heavier gas only to 1.5 percent. Hertz in Germany has separated 

 the two isotopes by fractional diffusion through special porous ma- 

 terial to yield the separate constituents spectroscopically pure. His 

 method, however, only yields a few cubic millimeters of gaseous 

 product. 



The development which revolutionized the whole subject of isotope 

 chemistry is due to the late Dr. E. W. Washburn of the United 

 States Bureau of Standards. Washburn determined, late in 1931, 

 to test the efficiency of electrolysis of water solutions as a method 

 of concentrating the hydrogen isotopes. While his own experiments 

 were in progress, he secured samples of water from commercial cells 

 which had been used for several years in the electrolytic production 

 of hydrogen and oxygen. Urey analyzed this water for him by the 

 spectroscopic method and found an enrichment of the mass 2 isotope. 

 Washburn himself found that the density of the water was greater 

 than that of ordinary water by 50 parts per million, a further evi- 

 dence of enrichment. As Washburn and Urey wrote in their joint 

 communication " the above results are of great importance, for we 

 now know that there are large quantities of water in these electro- 

 lytic cells containing heavy hydrogen in relatively high concentra- 

 tions and, also, there is available now a method for concentrating this 

 isotope in large quantities." Washburn's determination of the ab- 

 normal density of water from electrolytic cells will take rank with 

 those classical determinations by Lord Rayleigh of the densities of 

 chemical and atmospheric nitrogen, from which, with the work of 

 Sir William Ramsay, there resulted the discovery of the rare gases 

 of the atmosphere, helium, neon, argon, krypton, and xenon. 



The isolation of the mass 2 isotope in approximate purity was not 

 achieved by Washburn, The race was to the swift and to those richer 

 in available resources of apparatus and men. In rapid succession, 

 from the University of California, Princeton, Cambridge, England, 

 Columbia University, Frankfort, and Vienna came records of the 

 success of Washburn's method in producing water in which, with 

 continued electrolysis, 80, 60, 92, 99.9 percent of all the hydrogen 



