Space occupied by Atoms. 345 



The determination o£ the true atomic volumes of an element 

 in its elementary state and in its various combinations is also 

 of considerable importance in other directions. Thus the 

 determination of the space occupied by, for example, an 

 oxygen or a nitrogen atom is helpful in arriving at the 

 constitution. Ring compounds — such as the benzene ring — 

 are characterized by so great a reduction in the volume of the 

 carbon atom, that by means of the molecular volume it becomes 

 possible to determine the number and even the nature and 

 tension of the rings. The small space occupied by the carbon 

 atom in its elementary state as compared with the large space 

 which it occupies in compounds, is characteristic throughout 

 of the behaviour of carbon in its elementary and combined 

 states — and what holds for carbon is equally applicable to 

 other elements. 



Already in my first memoir * on chemical volumes I drew 

 attention to the intimate connexions which primarily exist 

 between the molecular volume and that her mo-chemical constants > 

 especially the heat of formation. Now although Richards 

 was not the first to point out the close relation between atomic 

 volume contraction and heat of formation, he nevertheless first 

 showed, in a large number of cases, that a far-reaching paral- 

 lellism exists between heat of formation and atomic contrac- 

 tion, and that the heat of reaction is, as a first approximation, 

 equivalent to the work represented by the contraction of the 

 atoms. 



Now when we consider that the electrical energy which a 

 galvanic cell is capable of generating may, as a first; approxi- 

 mation, be equated to the heat which under ordinary circum- 

 stances the reactions taking place in the cell are capable of 

 developing, it necessarily follows from the relation of this 

 heat development to the dynamical contraction-energy, that 

 the electric energy of a cell is to be attributed to the mechanical 

 icork accompanying atomic contraction^. 



In this respect my views are in complete agreement with 



impurities, I beg to refer him to my own experiments, Zeitschr. anorg. Chem. 

 Bd. xxxviii. p. 399, especially p. 402. When in using Teichner's method 

 it is found that after the equalization of the densities during cooling these 

 differences of density again appear above the critical temperature, then 

 surely this cannot be due to admixtures ! It will be necessary to get 

 accustomed to the supposition that Andrews' theory is in need of a very 

 essential modification • that the temperature at ivhich the meniscus vanishes 

 is not the critical temperature • that this latter has, unfortunately, not been 

 determined accurately in any case, but that in all cases it lies considerably 

 higher than has hitherto been supposed. 



* Zeitschr. anorg. Chem. Bd. hi. p. 23 (1892). 



t J. Trauhe, Zeitschr. anorg. Chem. Bd. xl. p. 382 (1904). 



