of Homologous Compounds, 9 



It will be seen that, while for the lower members the mean 

 of all the differences between the calculated and observed 

 values of A is +3°*50, that for the higher members, — 0°'05, 

 is very small indeed. 



It is. however, improbable that all the individual differences 

 in the case of the higher members of each series can be due 

 to experimental error ; the composition and constitution of 

 the compounds must, no doubt, have some influence : thus, 

 the differences for the alkyl halid.es are uniformly negative. 

 Taking the results as a whole, however, it would seem that 

 the values of A for the higher members may be calculated 

 with a fair degree of accuracy from the formula derived from 

 the boiling-points of the normal paraffins. 



The Esters. 



According to Ramsay and Shields* the esters should be 

 classed among the non-associating compounds, but the be- 

 haviour of the lower members of the series is slightly abnormal 

 in many respects ; thus the ratios of the actual to the theo- 

 retical density at the critical point are highf, but do not 

 show the usual slight rise with increase of molecular weight, 

 and this would seem to indicate that the lower members are 

 associated to some extent, but that the association diminishes, 

 as in other cases, as the series is ascended. Again, the values 



of — . ™ at the boiling-points under normal pressure J are 



somewhat small for the lower members, and do not show the 

 usual diminution as the series is ascended § ; and these facts 

 point to the same conclusion. 



A- the question of molecular association may be regarded 

 as an open one, and the number of esters examined is very 

 large, 1 have taken them separately in Table V. 



* Zeit. physik. Chem. xii. p. 4:J:i (189: J). 



t Phil. Mag. 1. p. -303 (1900). 



X Trans. Chem. Soc. lxxxi. p. 780 (1902). 



§ It may he noticed that the abnormality in physical properties is 

 most marked in the case of those esters in which both alkyl groups are 

 of normal structure ; the physical properties appear to be less abnormal 

 when one or both alkyl radicals contain an iso-group, thus the values of 



-,— . ™are higher and the fall with increase of molecular weight is quite 



marked. 



