20 ADVEXTURES IS RADIOISOTOPE RESEARCH 



tician, suggested he should now mail the "letter", Niels Bohr was shocked 

 by this suggestion, since, he said, this was the first trial of the first con- 

 cept of the "letter." In this spirit all his papers were written. 



How fabulously far-sighted Bohr was, is seen from a letter which the 

 present writer addressed to Rutherford after the Birmingham meeting 

 of the British Association for Advancement of Science from Budapest 

 the 14th October 1914. 



"The meetings on Monday and Tuesday have been very interesting. 

 It is a most remarkable fact that Aston succeeded to separate the two 

 Neons by diffusion and gave a definite proof that elements of different 

 atomic weights can have the same chemical properties. Thomson came 

 in his paper on Xg to the conclusion that the latter is a polymerized 

 hydrogen, a kind of H3 (like O3). In the following discussion Bohr— in his 

 usual modest way — suggested the possibility that X3 being an H atom 

 with one central charge, but having a three-times heavier nucleus than 

 hydrogen. He suggested to let a mixture of H and X3 diffuse through 

 palladium and try if it is possible to separate them, as the heavier X3 

 atom has to diffuse much slower. 



"Bohr had not been understood properly and Thomson gave a rathei 

 quick answer, saying — after a brief consultation with Ramsey — 

 that Bohr's suggestion is useless, for not molecules, but the atoms 

 of H diffuse through Palladium. Certainly, but this was just Bohr's 

 point. 



"The general appearance was, that he told something highly ingenious 

 and Bohr something very stupid. Just the contrary was the case. So I 

 felt bound to stick up for Bohr and explained the meaning of Bohr's, 

 suggestion in more concrete terms, saying that Bohr's suggestion is that 

 X3 is possibly a chemically non-separable element from Hydrogen . . . 

 Of course not very probable, but still a very interesting suggestion; 

 which should not be quickly dismissed" ... 26 years later Tritium was 

 discovered. 



Simultaneously with the isotope separation studies, I carried out 

 among other things some tracer- work on the interchange between the 

 atoms of lead compounds and lead, all in molten state. 



In 1921 Bohr's institute was opened. Those working at the institute 

 at its start were, besides its director, H. Kramers, H. M. Hansen, I. C. 

 Jacobsen, James Franck, who was invited for a short visit, and myself. 

 In my first study at the institute I measured the conductivity first 

 of a single crystal of sodium nitrate and then after it was molten and 

 resolidified into a polycrystalline mass. This crystalline conglomerate 

 was found to have a specific conductivity, fifty times higher than the 

 single crystal. From this result it was concluded that deviations from the 

 ideal crystalline state promote electrolytic conductivity. While increase 

 of temperature produces a reversible loosening of the lattice, we are 



