Young — Boiling -Points, Sfe., of Homologous Compounds. 97 



Table II. 

 Boiling -■points of Isoparaffins. 



The agreement is not so satisfactory as with the normal paraffins, and it 

 may be noted that whereas in most homologous series the calculated values 

 of A are higher than the observed in the case of the lowest members of the 

 series, they are lower in this series. 



On the Relation between the Critical Temperatures and Boiling -points 

 of Homologous Compounds. 



It was first suggested by Pawlewski [Berichte, xv., 460 and 2460 (1882) ; 

 xvi., 2633 (1883)] that the difference between the critical temperature and the 

 boiling-point was the same for all substances; but the compounds examined 

 by him were of too similar character, and the rule is not really even roughly 

 applicable to all substances. For example, the difference for hydrogen is 15°, 

 and for benzene 208 - 3 c . 



In 1890 Guldberg (Zeitschr. phys. Chem., v., 374) pointed out that the 

 absolute critical temperatures are roughly proportional to the absolute 

 boiling-points; thus for hydrogen and benzene the ratios are 1"75 and 163. 



I have shown (Stoichiometry, p. 183) that — 



T c 



(1) In any homologous series the ratios -~ diminish, though usually at a 



decreasing rate, with rise of molecular weight. 



(2) The ratios are generally nearly the same for the members of closely 



related (not homologous) substances. 



(3) In the case of isomeric substances the ratios for iso-compounds are 



higher than for normal, and for di-iso-compounds they are still 



higher. 

 It is now possible to add normal and iso-butane to the list of paraffins 

 available for comparison, and as regards rules (1) and (3) we have the data 

 given in Table III. 



