The Molecular Volume of Solids. 



459 



of the tables which follow, the author thought it right to state the 

 physical conceptions by which he was guided in his work. It must, 

 however, be premised, as will appear more fully in the sequel, that 

 these conceptions are provisional only, and should they hereafter prove 

 erroneous, their invalidity would not affect the truth of the main 

 result arrived at, which it is now proper to formulate in the shape of 

 a general proposition as follows : — 



(3.) Every element is capable of assuming different volumes in its 

 various compounds, but these diverse volumes always bear to each 

 other a simple numerical proportion, such as 1 : 2, 1 : 3, 2 : 3, &c, &c. 



Attention must now be directed to the tables which follow, and 

 which contain the evidence for the principles put forward in this paper. 



Table I contains a list of the molecular or atomic volumes. The 

 expression "molecular or atomic" is used as implying that the two 

 values are identical, as indeed they must be by virtue of the principle 

 enunciated in proposition (1). It will be observed that by virtue of the 

 same principle equal molecular volumes are attributed to each of the 

 allotropic forms of an element, the allotropism being supposed to consist 

 in the different number of atoms contained in their respective mole- 

 cules. With regard to the third column of the same table, it should 

 be pointed out that, since chemists are possessed of no means of 

 determining the number of atoms in the molecule of an element in 

 the solid state, the molecular weights here assigned to the elements 

 have been chiefly derived from a consideration of the volumes which 

 the element is found to assume in the various substances of which it 

 is a constituent. The atomic volumes of the elements whose specific 

 gravities in the solid form are known, have been deduced from the 

 specific gravities of such elements and their compounds conjointly, but 

 the atomic volumes of such elements as hydrogen, oxygen, and ni- 

 trogen, whose specific gravities in the solid form are unknown, have 

 been deduced from the specific gravities of their compounds alone, 

 without the assistance to be derived from the specific gravity of the 

 element itself. These last-mentioned compounds, however, are so 

 numerous that their atomic volumes may be considered to be deter- 

 mined with greater accuracy than those of any of the other elements, 

 with the exception of carbon. 



It would be impossible to present the evidence in favour of the pre- 

 ceding propositions without an adequate notation, and, therefore, it is 

 necessary to explain the system of notation that has been adopted. 

 The atomic volume of each element is represented in the tables by the 

 ordinary symbol used to denote that element, accented ; whilst the 

 submultiple of its atomic volume which the element assumes in a 

 particular molecule is indicated by a suffix. Thus the atomic volume 

 of potassium (90) is represented by K' ; whilst K' 3 in an expression 

 for the molecular volume of any substance containing potassium 



2 l 2 



