Surface- Tension with Temperature. 



39 



M 



So that if T-^ be denoted by y, the relation between y and 



d6 

 6 is linear. -^ was calculated over ranges of about 20° C. 



by simply taking the differences of 6 and dividing by the 



corresponding differences of T. T-^n was then plotted 



against #, and in all the unassociated liquids examined the 

 graph between these quantities was very accurately linear ; 

 the values of b and of n were read off directly from the 

 graph. 



The following table * shows the results for the fourteen 

 liquids examined. 



Table I. 

 (Showing values of b and n in the formula T = T (1— b6) n ). 



Substance. 



n. 



b. 



0c- b . 



9 c obs. 



Diff. 



Ether 



1-248 

 1-218 

 1-203 

 1-206 

 1-210 

 1-200 

 1-202 

 1-195 

 1-228 

 1-187 

 1-217 

 1-192 

 1-231 

 1-204 



•005155 

 003472 

 •002793 

 •003553 

 '004695 

 •004274 

 •003891 

 •003559 

 •003731 

 •004255 

 •0039S4 

 •003663 

 •003774 

 •003623 



194° 



288 



358 



2815 



213 



234 



257 



281 



268 



235 



251 



273 



265 



276 



193°-8 



288-5 



359-2 



283-1 



214-0 



233-7 



257-4 



281-3 



267-6 



235-3 



250-1 



272-9 



264-9 



276-2 



+0°-2 



-0-5 



-1-2 



-1-6 



-10 



+0-3 



-04 



-03 



+0-4 



-0-3 



4-0-9 



+0-1 



+ 0-1 



-0-2 



Benzene 





Carbon tetrachloride ... 

 Methyl formate 



Methyl acetate 



Methyl propionate 



Methyl butyrate 



Methyl iso-butyrate 



Ethyl formate 



Ethyl acetate 



Propyl formate 



Propyl acetate 





Mean value of w= 1*210. 



It will be seen from the above table that the critical 

 temperatures are given from the surface-tension data alone 

 with a surprising degree of accuracy. It will also be noticed 

 that n varies very little from liquid to liquid. Its mean 

 value is 1*210 and, while it is of course preferable to 

 determine n for each liquid separately, this value may be 

 used with some confidence in calculations referring to any 

 other liquid- — always provided that it is unassociated — as it 

 happens that, as a simple calculation will show, a small 



* The experimental values of T were taken from Ramsay & Shields, 

 Phil. Trans. 1893, p. 647 and Ramsay & Aston, Proc. Roy. Soc. lvi. 

 p. 162 (1894). 



