i 9 8 SCIENCE PROGRESS 



possess Kopp's value of 7*8. It is, of course, easy to construct 

 structural formula for P 4 6 (which is known to possess this 

 molecular formula) complying with these assumptions, and 

 consistent with its reactions. 



Fairly accurate values for molecular volume have now 

 been obtained for the greater number of the non-metallic 

 elements, including the metalloids, and for the relatively few 

 metals which furnish suitable liquid compounds. It is un- 

 necessary to set out these values here or to show in greater 

 detail how they vary with constitutive influences. But one 

 or two considerations arise in connection with them. It was 

 pointed out by the present writer many years ago that a 

 periodic relation may be traced between them. This fact is 

 referred to by Mr. Le Bas and has been confirmed and ex- 

 tended by him. In his work he gives a suggestive diagram 

 which serves to illustrate it very clearly. From it he draws 

 the following conclusions : 



(1) That there is a periodic relation between the atomic 

 volumes of the elements. 



(2) There is a tendency for the atomic volumes to diminish 

 in each series as the atoms increase in weight. The smallest 

 occur at Group 7. 



(3) There is a general increase in the atomic volumes of 

 the members of each Group from Series 1 onwards, that is, 

 in the direction of increasing atomic weight. This increase is 

 usually 3*6 or some multiple thereof. 



Mr. Le Bas concludes his work, of which the present article 

 is a very imperfect digest, with a thoughtful summary of the 

 present state of the theory of molecular volumes in which 

 from limitations of space we are reluctantly unable to follow 

 him. The resume is, however, most suggestive and cannot 

 but serve to quicken renewed interest in the subject. What 

 is needed is fresh investigation directed in the light of modern 

 conceptions of molecular physics and of constitutional 

 chemistry. Any earnest worker in physical chemistry who 

 may be in search of a fruitful field of inquiry will find in this 

 subject abundant opportunity for the exercise of his powers, 

 and he can have no more profitable preparation for his task 

 than a careful study of the monograph with which Mr. Le 

 Bas has enriched the literature of science. 



