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SCIENCE 



[N. S. Vol. XXXIV. No. 871 



it 239.4; but the general mean, calculated 

 by Clarke, is 239.0. Subtracting 12 from 

 these numbers, we have the values 227.0, 

 and 227.4 for the atomic weight of radium. 

 It is as yet impossible to draw any certain 

 conclusion. 



The importance of the work which will 

 enable a definite and sure conclusion to be 

 drawn is this: For the first time, we have 

 accurate knowledge as to the descent of 

 some of. the elements. Supposing the 

 atomic weight of uranium to be certainly 

 239, it may be taken as proved that in los- 

 ing three atoms of helium, radium is pro- 

 duced, and, if the change consists solely in 

 the loss of the three atoms of helium, the 

 atomic weight of radium must necessarily 

 be 227. But it is known that ;8-rays, or 

 electrons, are also parted with during this 

 change; and electrons have weight. How 

 many electrons are lost is unknown ; there- 

 fore, although the weight of an electron 

 is approximately known, it is impossible 

 to say how much to allow for in estimat- 

 ing the atomic weight of radium. But it 

 is possible to solve this question indirectly, 

 by determining exactly the atomic weights 

 of radium and of uranium; the difference 

 between the atomic weight of radium -plus 

 12, i. e., plus the weight of three atoms of 

 helium, and that of uranium, will give the 

 weight of the number of electrons which 

 escape. Taking the most probable num- 

 bers available, viz., 239.4 for uranium and 

 226.8 for radium, and adding 12 to the 

 latter, the weight of the escaping electrons 

 would be 0.6. 



The correct solution of this problem 

 would in great measure clear up the mys- 

 tery of the irregularities in the periodic 

 table, and would account for the devia- 

 tions from Front's law, that the atomic 

 weights are multiples of some common 

 factor or factors. I also venture to suggest 

 that it would throw light on allotropy, 



which in some cases at least may very well 

 be due to the loss or gain of electrons, ac- 

 companied by a positive or negative heat- 

 change. Incidentally, this suggestion would 

 afford places in the periodic table for the 

 somewhat overwhelming number of pseudo- 

 elements the existence of which is made 

 practically certain by the disintegration 

 hypothesis. Of the twenty-six elements de- 

 rived from uranium, thorium, and ac- 

 tinium, ten, which are formed by the emis- 

 sion of electrons alone, may be regarded as 

 allotropes or pseudo-elements; this leaves 

 sixteen, for which sixteen or seventeen gaps 

 would appear to be available in the peri- 

 odic table, provided the reasonable supposi- 

 tion be made that a second change in the 

 length of the periods has taken place. It 

 is above all things certain that it would be 

 a fatal mistake to regard the existence of 

 such elements as irreconcilable with the 

 periodic arrangement, which has rendered 

 to systematic chemistry such signal service 

 in the past. 



Attention has repeatedly been drawn to 

 the enormous quantity of energy stored up 

 in radium and its descendants. That in its 

 emanation niton is such that if what it 

 parts with as heat during its disintegra- 

 tion were available, it would be equal to 

 three and a half million times the energy 

 available by the explosion of an equal 

 volume of detonating gas — a mixture of 

 one volume of oxygen with two volumes of 

 hydrogen. The major part of this energy 

 comes, apparently, from the expulsion of 

 particles (that is, of atoms of helium) with 

 enormous velocity. It is easy to convey an 

 idea of this magnitude in a form more rea- 

 lizable, by giving it a somewhat mechanical 

 turn. Suppose that the energy in a ton 

 of radium could be utilized in thirty years, 

 instead of being evolved at its invariable 

 slow rate of 1,760 years for half-disinte- 

 gration, it would suffice to propel a ship 



