314 Scientific Intelligence. . 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Melting Points and Thermoelectric Behavior of Lead 

 Isotopes. — The several kinds of lead produced by the spontan- 

 eous transformation of radioactive elements appear to be abso- 

 lutely identical in their chemical reactions, and hence, like sev- 

 eral other similar cases of isotopes, they cannot be separated by 

 chemical means. The isotopes of lead vary, however, in their 

 physical properties, such as atomic weight and specific gravity, 

 and it has been shown by Richards and Wadsworth, several 

 years ago, that the atomic volumes of these isotopes — the ratios 

 of their specific gravities and atomic weights — are practically 

 identical. 



Further knowledge in regard to the physical properties of 

 samples of isotopic lead is a matter of much interest, and Theo- 

 dore W. Richards and Norris F. Hall have recently made an 

 important contribution to this subject. Using a sample of Aus- 

 tralian radioactive lead derived chiefly from the transformation 

 of uranium, they first compared its melting point with that of 

 ordinary lead after carefully purifying both samples to such an 

 extent that the maximum impurity probably did not amount to 

 more than 5 parts in 100,000. The heating and cooling curves 

 during melting and solidification were carefully compared by 

 the use of thermoelectric measurements. It Avas thus found 

 that the difference in melting points of the two specimens of 

 lead differing to the extent of 0.8 in atomic weight is, if apprecia- 

 ble, not over 0.05° C, and it is concluded that it is fairly safe to 

 assume that the kinds of lead not only have very nearly the same 

 melting point, but also (since the sample consisting chiefly of 

 the lighter isotope doubtless contained ordinary lead) they mix, 

 or rather mutually dissolve without affecting the melting point. 



The authors found also that there is no thermoelectric effect 

 produced by wires of ordinary lead and the radioactive Austra- 

 lian lead, and it has been found by Bridgman, using the same 

 samples of lead, that there is no difference, beyond the range of 

 experimental error, in the electrical conductivity of the two 

 kinds of lead, nor in the effect of pressure or temperature upon 

 their conductivity. — Jour. Amer. Chem. Soc, 42, 1550. 



H. L. W. 



2. Inter molecxdar Transpositions of Atoms of the Same Kind. 

 Von Hevesy and Zechmeister have studied the question of the 

 exchange of identical atoms between different molecules in a 

 novel way. They prepared compounds of ordinary lead and of a 

 radioactive isotype of lead, put two different ones of two kinds 

 into solution together, separated the compounds, and by testing 

 their radioactivity determined whether or not an exchange of 

 atoms had taken place. 



There was found, as was undoubtedly to be expected from what 



