1894,] The Molecular Surface-energy of the Esters, fyc. 167 



These two assertions are probably not true ; it is unlikely that 

 mere liquefaction should produce in all cases equal association ; and 

 it is unlikely that a rise of temperature should not cause the dissocia- 

 tion of an associated body. Change from the gaseous to the liquid 

 state may be regarded as essentially equivalent to increase of pres- 

 sure, since each produces approach between the molecules, diminish- 

 ing intermolecular distance, and bringing so-called chemical forces 

 into play. Now it is well known that equal rise of pressure does not 

 always produce equal increment of association ; hence it is unlikely 

 that association to an equal extent should be caused by the reduction 

 of the volumes of compounds until they are approximately equal. 



This kind of proof is not unknown to chemists ; it is employed, 

 tacitly perhaps, in the fundamental statement that the molecular 

 formulae of hydrogen, oxygen, nitrogen, &c., are H 2 , 2 , and N 2 . On 

 this basis rests the usually accepted molecular formulae of all com- 

 pounds, and they are accepted because they are the simplest expres- 

 sions which admit of equations of chemical interchange being 

 written. It is true that subsequently to the adoption of such a 

 standard its justice was confirmed by Kundt and Warburg's deter- 

 mination of the ratio between the specific heats of mercury gas at 

 constant pressure and at constant volume, thereby rendering it ex- 

 tremely probable that the molecular formula of mercury is Hg!, and 

 consequently that of hydrogen H 2 ; and by the discovery by Victor 

 Meyer that the molecular formula of iodine at high temperatures cor- 

 responds with Ii. But such confirmations merely supported the 

 generally received assumption (for assumption it was then) that the 

 molecular formulae of most gases are directly comparable with that of 

 hydrogen as H 2 . 



Even at this present date the doctrine of the uniform expansion of 

 gases at high temperatures rests on a similar basis. It has been 

 shown by Victor Meyer that at the highest temperature attainable in 

 a gas-furnace some 1700 hydrogen, oxygen, and nitrogen main- 

 tain the same ratio of expansion towards each other. One of two 

 conclusions follows : either that the expansion of all three gases is 

 uniform with increase of temperature, or that all three gases dis- 

 sociate equally with equal rise of temperature. Needless to say that 

 the first alternative is universally adopted. 



We have thought it well to state in full the reasons for adopting 

 the assumption that the molecular weights of such liquids as the 

 esters are not changed on their assuming the liquid state. It is now 

 evident that such a statement is an assumption, a hypothesis ; but it 

 is one for which there is a great deal of probability, probability of 

 the same kind as that which led to the adoption of the usually 

 received molecular formulae for gases. 



