46 Variation of Surface- Tension with Temperature. 



for 7 for the esters here examined are given in Table VIII., 

 and it will be seen that as R x increases (R being constant) 

 7 steadily decreases, and that a similar result holds good for 

 increase of R (R x being constant). 



Table VIII. 



Substance. 



B. point 

 obs. 



9 C obs. 



9c 

 7 =T' 



Methyl formate 



Methyl acetate 



304-9 

 330-2 

 352-7 

 375 8 

 327-3 

 3501 

 371-8 

 3539 

 370-6 



487-0 

 506-7 

 530-4 

 554-3 

 508-3 

 523-1 

 545-9 

 537-9 

 549-2 



1597 

 1-535 

 1-504 

 1-475 

 1-553 

 1-494 

 1-469 

 1-520 

 1-467 



Methyl propionate ... 



Methyl butyrate 



Ethyl formate 



Ethyl acetate 



Ethyl propionate 



Propyl formate 



Propyl acetate 





The data are somewhat too few in number to establish 

 quantitative laws with much confidence, but it may be 

 noticed that for the series RCOO(JH 3 the relation between 

 7 and n (the number of carbon atoms in R) is very accurately 

 linear, leading to the result 



cy=d- 



n, 



where c and d are constants. In 

 c = 33"33 : the agreement between 



(xii.) 



this case d = 52*17 and 

 the calculated and ob- 



served values of 7 is shown in Table IX. From this result 



Table IX. 



n. 



7 , 

 observed. 



7 

 calculated. 



b 

 (from xiii.). 



b 

 (from iii.). 





 1 

 2 

 3 



1-597 

 1-535 

 1-504 

 1-475 



[1-565] 

 1-535 

 1-505 

 1-475 



[-004897] 

 •004276 

 •003879 

 •003555 



004695 

 •004274 

 •003891 

 •003559 



it easily follows that the temperature coefficient of surface- 

 tension — b in equation (iii.) — is connected with the absolute 

 boiling-point of the substance considered by the relation 



c 33*33 ( ... . 



b ~ (d- n )<9-273c = (52-17-700-9100 * * (Xm *' ) 



