ADDITIVE RELATIONS 



33 



which, according to p. 26, is not largely the case for ethyl 

 alcohol, since liquid alcohol approximately follows the law 

 of correspondence. The data are as follows : 



D T T k P k V -~ V(calc.} 



The chief criterion of molecular doubling, so far as 

 volume relations are concerned, is therefore still the abnor- 

 mal rise of the saturated vapour volume (p. 26). Since 

 at the same time a contraction of the liquid occurs the 

 sharpest test would be the quotient of the vapour and 

 liquid volumes, as compared with the constant value deduced 

 (p. 25) from the law of correspondence. 



B. Additive and Constitutive Relations, 

 i. Volume at the Absolute Zero. 



The colligative relations, depending directly on the 

 number of molecules, thus appear at extreme dilution in 

 the form of Avogadro's law and the laws of gases, and 

 may, by means of more or less rationally based empirical 

 rules, be followed from gases to a certain extent as far as 

 the critical temperature, and thence into liquids, down even 

 to the absolute zero. 



In dealing with the additive relations of volume we shall 

 reverse this order and start from the absolute zero, 

 remembering that according to molecular mechanical con- 

 ceptions at that temperature the space between the mole- 

 cules is reduced as far as possible, and consequently the 

 volume of the whole comes closest to the sum of the 

 volumes of the parts. 



With reference, however, to the additive relations in 

 question, there is one general remark that must first be 

 made. Strictly additive behaviour is only to be expected 



c 



