the Unit-Stere Theory, 



335 



their critical temperatures gradually increase with the com- 

 plexity of the compounds. For this reason, no doubt, the 



M.P. 

 ratios w~p- gradually diminish as the complexity of the 



compounds increases; and thus it is probable that the melting- 

 points are all similarly related to the critical points of the 

 paraffins under consideration. 



The Volume Relations of Carbon and Hydrogen at the 

 Boiling and Critical Points. 



It was Kopp's fundamental statement, that the differences 

 in volume for the addition of the homologous increment CH 2 

 are invariably constant when examination is made of the 

 volumes of homologous compounds at the boiling-point. 

 Schiff and Grartenmeister have, however, shown that this is 

 not quite true ; for the difference in question as a rule rises 

 as the complexity and of course the molecular weight of the 

 compounds increase. This is in part due to the fact that 

 the boiling-point is not a strictly corresponding temperature. 

 It is thus necessary to find out if Kopp-'s dictum is true under 

 precisely corresponding conditions. Young has given the 

 following table (Brit. Assoc. Address, Cambridge, 1904). 



It is found that the molecular volumes and the differences A 

 for an addition of CH 2 are given under the following con- 

 ditions : — 



A. At 0° C. 



B. At the respective boiling-points under 1 atm. 



pressure. 

 0. At equal reduced temperatures (0'G396). 



D. At the respective boiling-points under equal reduced 



pressures (O022I1). 



E. At the respective critical points. 



Table IX. 



Paraffin. 



A. 



B. 



D. E. 



1 



M.Vol. 



A. 



1 

 M.Vol. 



1 



A. 1 M.Vol. 



A. 



M.Vol. 



A. M.Vol. 



A. 



n Butane*... 







96-00 



21-80 











251 



58-3 



n Pentane ... 



111-33 





I 117-80 





116-13 





116-13 





) 309-3 









15-44 





2213 



2009 





2106 





56-8 



n Hesane ... 



126-77 





139-93 



136-22 





137-19 





366-1 









15-69 





22-63 



20-18 





21-49 





602 



n Heptane... 



142-46 





162-56 



156-40 





158-68 





426-3 









15-88 





23-70 



20-54 





21-83 



62-6 



n Octane . . . 



158-34 





186-26 



176-94 





180-51 



; 488-9 



i 





* The numbers for butane were not given in Young's table. 



2 A 2 



