ARE THE ELEMENTS ELEMENTARY ? 467 



ing by themselves they would signify comparatively little ; but con- 

 sidered with other analogous evidence they help to found an almost 

 overwhelming argument. The concurrent testimony supplied by the 

 specific or atomic volumes of the elements is particularly strong. 



The specific volume of any substance is the quotient obtained upon 

 dividing its atomic weight by its specific gravity. This value may be 

 supposed to represent the volume of an atom of the substance plus the 

 sphere of unoccupied space immediately surrounding and belonging to 

 it. Leaving theoretical definitions out of account, however, we shall 

 find, upon comparing the specific volumes of solid and liquid sub- 

 stances, many extraordinary relations. Often, all the members of an 

 elementary group have equal values. This is the case with the closely- 

 related metals platinum, iridium, osmium, palladium, rhodium, and 

 ruthenium. They have difi'erent atomic weights and difierent specific 

 gravities ; yet the quotient obtained upon dividing the former by the 

 latter is the same in every instance. The same thing holds good of 

 the group formed by iron, cobalt, nickel, chromium, manganese, cop- 

 per, and perhaps also uranium. Here the regularity extends even 

 beyond the elements themselves, for their corresponding compounds 

 have, Vv'ith few exceptions, equal specific volumes also. An altogether 

 different, but on tlie whole more remarkable, relation is furnished by 

 the alkaline metals lithium, sodium, potassium, and rubidium; whose 

 sj)ecific volumes are respectively 11.9, 23. 7, 45.1, and 56.2. These 

 values are almost exactly multiples of the first, standing to it in the 

 ratio of 1 : 2 : 4 : 5. The slight variations from accuracy in this case 

 are very far within the limits of experimental error. Almost as re- 

 markable multiple relations are found in several other series, and 

 apply not only to the specific volumes of the solid elements, but to 

 their values in liquid compounds also. Closely connected with this 

 subject is that of crystallyie form. As a general, though not invari- 

 able rule, elements having equal specific volumes are isomorphous ; 

 that is, crystallize alike ; a fact which may be extended to a very large 

 number of compound sei'ies as well. 



It would be easy to go on to almost an indefinite extent multiply- 

 ing examples of relationship between the elements. There is hardly 

 any set of physical properties which may not be made to emphasize 

 the idea that these substances are internally related. Take, for exam- 

 ple, their specific heats, which, multiplied by their atomic weights, 

 give a constant quantity in the neighborhood of 6.3. That is, accord- 

 ing to the law of Dulong and Petit, all elementary atoms have equal 

 capacities for heat. But space is limited, so that we must omit the 

 consideration of many important facts, and pass to the theoretical dis- 

 cussion of those already cited. All this evidence suggests quite em- 

 phatically that the elements are not totally distinct and independent 

 bodies. Are they, then, compounds formed from a few simple sub- 

 stances, or are they modifications of but one primal matter ? Strong 



