Molecule of a Substance and its Chemical Properties, 911 



of this expression will not vary much from one substance to 

 another ; and the critical pressures will therefore not vary 

 much in the case of a compound aud its substitution 

 products. 



"We have then that the values of each of the simple 



expressions ^-, ^^=p (*/^P (ST^P 



Li p 



x / — ' /-^ / — xi/4 are constant for a compound and its 



substitution products at corresponding temperatures. 



Any function of these quantities will possess the same 



properties. It is of interest to note that the form of the 



function mav be such that ?Zx/m 1 does not appear in it. 



T c 

 Further chemical properties of the quantity y / — will 



now be discussed. The chemical compounds considered will 

 be taken in groups according to their chemical properties. 



Esters. 



The values of ~ 7 — for each set of isomers of the esters 

 zv ?^i 



are practically the same, as will be seen from Tables I. and 



T c 

 II. In comparing the values of ~ / — we may therefore 



take the mean of the values of each set. These mean values 



are contained in Table III. (p. 912). 



The chemical formula for the esters may be written 



20 + a(C-l-2H)j where a denotes an integer. Now it was 



T c 

 found that the value of v / — mav be expressed by the 



equation ZV m * 



A 1 -{20-f*(C + 2H)} = (A 1 -20)-a(C-f 2H)=-^=, 



Zvwi 



where A t is a constant, and H, G, have the same value for 

 each compound. The values of (Aj — 20) and (C + 2H) were 



T c 

 determined from the values of ^ , — by the method of least 



squares, and found to be equal to 29 and 2*51 respectivelv. 

 By means of these quantities the value of the left-hand side 

 of the above equation was calculated for each ester ; the result 



