January 3, 1919] 



SCIENCE 



HYPOTHESIS CONCERNING THE DISINTEGRATION OF 

 CRANIUM 

 Uranium 



i ^3 Helium ' 

 Radium 



i ^ 1 Helium !• 8 Helium 

 Emanation 



■J' ^4 Helium 

 Lead (Isotopic) 



Thus each atom of uranium is supposed 

 to be converted into radium by losing three 

 atoms of helium, and each atom of radium is 

 supposed to be converted into a kind of lead 

 by losing five more, as already stated. 



If uranium can thus disintegrate, should we 

 call it an element ? and should we call its 

 smallest particles atoms? The answers de- 

 pend upon our definition of these two words. 

 If the word " element " is supposed to des- 

 ignate a substance incapable of disintegration, 

 apparently it should not be applied to ura- 

 nium ; neither should the word " atom '' be 

 applied to the smallest conceivable particles of 

 this substance. But no one would now main- 

 tain that any element is really incapable of 

 disintegration. A method of still retaining 

 the terms in this and analogous cases is to 

 define an element as " a substance which has 

 not yet been decomposed artificially,'' that is 

 to say, by the hand of man — and an atom as 

 " the smallest particle of such a substance, 

 inferred from physicochemical behavior." The 

 atom, then, is not to be considered as wholly 

 indivisible, but only as indivisible (or at least, 

 as not yet divided) by artificial means. For, 

 as in the case of radium, the disintegration of 

 uranium can not be hastened or retarded by 

 any Icnown earthly agency. So long as it 

 stays intact, the atom of uranium behaves 

 quantitatively in the same fashion as any 

 other atom: Dalton's laws of definite and 

 multiple combining proportions apply without 

 exception to its compounds. In this connec- 

 tion one should remember that the atomic 

 theory, as a whole, including Dalton's and 

 Avogadro's generalizations, is not in the least 

 invalidated by the new discoveries of radio- 

 activity. On the contrary, the atomic theory 



is entrenched to-day more firmly than ever 

 before in its historj-. 



Interesting speculations by Drs. Russell, 

 Fleck, Soddy and Fajans and others have in- 

 terpreted in extremely ingenious and plausible 

 fashion the several transitory steps of the 

 changes, and indicate the reasons why the end- 

 products of the decomix)sition both of uranium 

 and thorium should be very similar to lead, if 

 not identical with it. Therefore a careful 

 study of the properties of lead of indubitably 

 radioactive origin became a matter of great 

 interest, as a step toward confirming these 

 speculations, especially in comparison with the 

 properties of ordinary' lead. Such investiga- 

 tions should throw light on the nature of 

 radium and uranimn and the extraordinary 

 changes which those metals suffer. Moreover, 

 by analogy, the resulting conclusions might 

 be more or less ajiplicable to the relations of 

 other elements to each other; and the com- 

 parison of this new kind of lead with ordinary 

 lead might afford important information as to 

 the essential attributes of elementary sub- 

 stances in general, in case any differences be- 

 tween the two kinds should be found. 



Before the subject had been taken up at 

 Harvard University, chemists had already 

 recognized the fact that the so-called uranium- 

 lead is indeed qualitatively very like ordinary 

 lead. It yields a black sulphide, a yellow 

 chromate, and a white sulphate, all very spar- 

 ingly soluble in water, just as ordinary lead 

 does. Continued fractional crystallization or 

 precipitation had been shown by Professor 

 Soddy and others to separate no foreign sub- 

 stance. Hence great similarity was proved; 

 but this does not signify identitj'. Identity 

 is to be established only by quantitative re- 

 searches. Plato recognized, long ago, in an 

 often-quoted epigram, that when weights and 

 measures are left out, little remains of any 

 art. Modem science echoes this dictum in its 

 insistence on quantitative data; science be- 

 comes more scientific as it becomes more ex- 

 actly quantitative. 



One of the most striking and significant of 

 the quantitative proi^erties of an element is 

 its atomic weight — a number computed from 



