Boiling-Points of Homologous Compounds, 379 



7. More extensive material is provided by the halogen 

 compounds, and since the differences between the boiling- 

 points are fairly represented by Young's law, it follows that 

 the boiling-points themselves can be represented approxi- 

 mately by the normal paraffin curve. The necessary constants 

 to be added to n are about : 



CJWiCl : a= +2-4; CJE 2 „ +1 Br : a= + 32; 

 CJWJ: a=+4'2. 



But the residuals, though fairly small, show a marl<ed 

 systematic tendency, which may otherwise be expressed by 

 an increase of the constant a with n. Hence it may be 

 opportune to illustrate the utility of another formula already 

 suggested^ namely 



T = a log (bn + c), 



which may be taken to have the numerical forms : 

 CJWC1: T=1000° log (0-155/1 + 1-6209), 

 C M H 2n+1 Br: 1000 log (0*155 n + 1*7446), 



aH 2n+1 l: 1000 log(0-155n + l-9082), 



where something of individual accuracy is sacrificed to 

 uniformity and simplicity. This is not serious, however, as 











Table IX 











C n H 



2/i+lCl 





C w H 2W 4-i 



Br. 



CnHgn+lI* 



n. 



T. 



Calc. 



O-C. 



T. 



Calc. 



O-C. 



T. 



Calc. O-C. 



1. 



249°3 



249-4 



o 



-o-i 



o 



277-5 



278°7 



o 

 -1-2 



315-8 



o o 



314-5 4-1-3 



2. 



285-5 



285-8 



-0-3 



311-4 



312-7 



-1-3 



345-5 



3460 -0-5 



3. 



319-0 



319-3 



-03 



343-8 



344-3 



-0-5 



375-5 



375-3 4-0-2 



4. 



351-0 



350-2 



+0-8 



374-0 



373-8 



+0-2 



4030 



402-8 4-0-2 



5. 



379-6 



379-5 



+ 0-1 



402-5 



401-3 



+ 1-2 



429-0 



428-7 4-0-3 



6. 



406-0 



406-7 



-0-7 



429-0 



427-3 



+ 1-7 



452-0 



453 -1-0 



7. 



433-0 



432-3 



+0-7 



452-0 



451-7 



4-0-3 







8. 



457-0 



456-5 



4-05 



474-0 



474-9 



-0-9 







s 



shown 



by th 



e comr 



)arison 



given 



inTal 



ble IX. 



The three 



constants c may be expressed in the forms : 



v^ri-tl2n^-l^l 



C n H 2w+1 Br 

 C tt H 2n+1 I : 



•=1-509+ 35-46-^318, 

 1-509+ 79-92-^339, 

 1-509 + 126-92-^318; 



and though the divisors are not quite the same this suggests 

 at least some relation between the constant and the atomic 

 weight of the halogen element entering into the compound. 



