PROGRESS IN PHYSICAL CHEMISTRY. 227 



at ordinary temperatures — (CH 3 OH ),.,,, (C 2 H 5 OH) r65 , 

 (H.O),*,, (CH,COOH)„ 3 , Br 2 , P 4 , (H s S0 4 ) 3 „ 

 (HN0 3 ) 2 . 



Deferring for the present the discussion of the mode 

 of estimating the degree of complexity, it may safely be 

 said that several other physical properties give definite 

 evidence of the presence of molecular aggregates in 

 hydroxy liquids. From the large effect which temperature 

 exerted on the viscosity of the acids and alcohols, and from 

 their general behaviour as regards this property, Thorpe 

 and Rodger (15) concluded that they consisted of mole- 

 cular aggregates which decomposed as the temperature 

 rose. Young's results have shown that hydroxy compounds 

 do not accord with van der Waals' generalisation of corre- 

 sponding states. Thorpe and Rodger (15) have also pointed 

 out that Thorpe and Riicker's formula for calculating the 

 critical temperature of a liquid from its thermal expansion 

 does not apply to hydroxy compounds ; this formula is based 

 on van der Waals' theory. Guye (16) has shown that the 

 constant in van der Waals' vapour-pressure formula has for 

 most liquids the value 3*06, for hydroxy liquids it is larger. 

 Now van der W f aals' equation is deduced on the supposition 

 that no molecular aggregation occurs in the liquid state, 

 hence the large deviations of hydroxy compounds may 

 reasonably be assigned to this cause. 



Another important indication of the same thing, which, 

 so far as I know, has not been pointed out, lies in the fact 

 that the boiling-point of a hydroxy compound is higher than 

 that of the corresponding sulphur compound, although the 

 theoretical molecular weight of the sulphur compound is the 

 greater. Alcohol, for example, has a higher boiling-point 

 than mercaptan. On the other hand, if hydroxy compounds 

 be excluded, the sulphur compound has the higher boiling- 

 point ; ethyl sulphide, for example, boils at a higher 

 temperature than ethyl oxide. If we regard the boiling- 

 point of corresponding compounds as depending mainly 

 on the weight of the liquid molecule, the above facts 

 indicate that, due to molecular aggregation, the molecular 

 weight of the liquid hydroxy compound is greater than that 



