478 Mr. W. Sutherland on Molecular Force 



and the second is 2, and &s p x = l— p 2 , only p 2 is given. The 

 surface-tensions are expressed in dynes per centim. : — 



Table I. 

 Toluene and Piperidine at 15°'2 C. 



p v a v p 2 . a 2 . p 2 . p. a. A/(A A)'* 



•8682 28-18 -8670 2967 -156 -8677 28-55 1-02 



•822 -8674 29-43 100 



Benzene and Carbon Tetrachloride at 11 0, 8 C. 

 •8865 29-13 1-6063 27"03 -6633 1-267 28-29 1-00 



•77 1-3533 2783 101 



Chlorobenzene and Ethylene Dibromide at 10°. 

 1-1176 33-65 2-192 39-22 -6253 16064 3538 -97 



Chloroform and Carbon Disulphide at 10°. 

 1-5077 27-62 1-277 32-73 -3892 1-4009 29-09 -98 



It may be taken as proved that in the normal case 



]A 2 = ( l A l2 A 2 ) 2 . 



If we apply the formula (6) just as it stands to aqueous solu- 

 tions of substances which are solid at 15° C, the usual 

 temperature of experiment; on solutions, we have to deal 

 with the surface-tension a 2 of solids, which up to the present 

 has not been measured ; but we need not concern ourselves 

 with this fact for a 2 stands for k 2 A 2 p 2 2 (ni^/p 2 )^, where k is the 

 same for all bodies at all temperatures if p 2 is the density in 

 the surface-layer whose tension is measured, but if p 2 is the 

 density in the body of the substance, then k becomes a function 

 of temperature. 



As water has many peculiarities we cannot assume that for 

 water and any substance dissolved in it, 1 A 2 =(iA 12 A 2 )*, but if 

 water is 1 and the dissolved substance 2, then in (6) a^p 2 is 

 a constant, a say, and for different solutions of the same sub- 

 stance «i/p 2 2 is also a constant, say b, and in the last term the 

 coefficient of pip 2 is a constant 2c say, then 

 a/p 2 = api* + bp 2 2 + 2cpip 8 , 



a/p 2 -*Jp 1 2 = 2{c-a)p 2 + (a + b-2c)p 2 2 . . . (8) 



We can show by Volkmann's data (Wied. Ann. xvii.) that 

 this is a suitable form to express the relation between the 

 surface-tension of a solution and its concentration : thus in 

 the case of NaCl we get the values a + b — 2c = 6*7, 

 2(a— c)=7*67, and as a=7*44, b and c are determined. The 

 values of the surface-tension given by these constants in (8) 

 are compared with the experimental in the following. In 



