166 Prof. W. Ramsay and Miss E. Aston. [June 14, 



Katio. 



Methyl formate 295-6/280' 1 = 1-055 



Ethyl formate 3ir4/310'9 = 1-002 



Methyl acetate 31375/317-5 = 0'9879 



Propyl formate 332-5/348' 2 = 0-9545 



Ethyl acetate 327'7/342'l = 0'9625 



Methyl propionate 331-1/346-3 = 0'9559 



Propyl acetate 34675/369-2 = 0-9393 



Ethyl propionate 344-6/367-0 = 0'9391 



Methyl butyrate 348-3/375-0 = 0'9290 



Methyl isobntyrate 338'75/362'0 = 0'9356 



These numbers may be roughly arranged into four groups : methyl 

 formate, the isomerides of the formula C 3 H 6 2 , those of the formula 

 CiHgC^, and those of the formula C 5 Hi 2 . They suffice to show that 

 the molecular surface-energies are not comparable for non-isomeric 

 bodies at corresponding pressures. 



It must, therefore, be concluded that, although a certain rough 

 analogy exists between the corresponding temperatures and pressures 

 of the esters and their molecular surface-energy, yet the causes 

 which determine deviation from the deductions from the equations 

 of condition for fluids, are still more operative in causing deviations 

 when surface forces are under consideration. 



These experiments add eight more compounds to the list of six 

 given in the ' Phil. Trans.,' 1893, A, p. 662, showing that within wide 

 limits of temperature the molecular surf ace- energy of non-associating 

 compounds is a linear function of the temperature ; and as the law 

 has been found to hold between more restricted limits of temperature 

 for other thirty (' Trans. Chem. Soc.', vol. 63, p. 1191), it may be 

 taken as placed on a firm basis. 



A certain number of substances, among which are to be found the 

 alcohols and the acids, show deviation from this law. Reserving to 

 another occasion the grounds for inferring that this deviation points to 

 molecular complexity, it is advisable to inquire here whether it is legi- 

 timate to assume for compounds which follow the law that their mole- 

 cular weight in the state of liquid is the same as that of their gases. 



Strictly speaking, the conclusion does not follow. The similar 

 form of the surface-energy equation to that expressing volume-energy 

 is a mere analogy ; there is no physical connexion as yet manifest 

 between the two.* There is no positive evidence to show that the 

 molecules of such liquids as follow the law do not associate in twos, 

 or threes, on assuming the liquid state. But one thing is certain, if 

 they do, all associate to an equal extent, and the degree of associa- 

 tion is not altered by rise of temperature. 



* This conclusion must be modified in view of the recent memoir by ran der 

 Waals (seep. 181). 



