﻿Critical Temperatures of Homologous Compounds. 605 



which is the most convenient form for computation, we 

 have 



log C = -2650 + 1-929 (log M)' 4134 - -120 log n, (xvi.) 



as the empirical equation which gives the relation between 

 the critical temperature and molecular weight of the normal 

 paraffins. 



It now remains to compare the values calculated from 

 formulae (x.), (xi.), (xiii.), and (xvi.) with the observed 

 values of C . Unfortunately the data for critical tempera- 

 tures, like those for boiling-points, are of very different 

 value, and one has either to adopt certain more or less arbi- 

 trary canons of selection or rejection, or to take the average 

 value of the various figures given for any one substance by 

 different experimenters — a process about as likely to result 

 in the true critical temperature as the averaging of half-a- 

 dozen slightly erratic public clocks is to result in Greenwich 

 mean time. 



In comparing, therefore, the calculated and observed values 

 of C , I have restricted myself to the accurately-determined 

 values for pentane, hexane, heptane, and octane given in 

 Young's Royal Dublin Society paper*. The comparison is 

 shown in Table III. below. 



Table III. 





Be. 



obs. 



Calc. 





Calc. 





Calc. 





Calc. 



i 



Paraffin. 



from 



Diff. 



from 



Diff. 



from 



Diff. 



from 



Diff. 





(x.). 





(xi.). 





(xiii.). 





(xvi.). 



o 





o 





o 



o 







o 



o 



o 



C 5 H 12 ... 



470-2 



[481-21 + 



473-7 



4-3-5 







470-7 



4-0-5 



oh£... 



507-8 



[514-6] 



+6-8 



5106 



4-2-8 



508-3 



4-0-5 



5076 



-0-2 



C 7 H IC ... 



539 9 



544-8 



+4-9 



542-6 



4-2-7 



541-2 



4-1-3 



540-3 



+0-4 



PA«- 



5692 



5725 



+3-3 



5714 



+2-2 



569-7 



4-0-5 



569-6 



+0-4 



C 9 H 20 ... 





597-8 





597-3 





5960 





596-5 





C 10 H 22 . 





622-2 





6219 









621-2 





The first two values in the third column are bracketed, 

 since Walker's boiling-point formula only has reference to 

 the paraffins between C 7 H ]6 and C 16 H 34 . It will be seen that 

 the values given by formula (xiii.) deduced from Young's 

 boiling-point equation are in close agreement with the ex- 

 perimental numbers, and that the values calculated from 

 equation (xvi.), which is deduced from the boiling-point 



* Proc. R. D. S. xii. 31. p. 374 (1910). 



