and the Surface- Tension of Solutions. 479 



the rest of this paper surface-tensions are given in mgrms. 

 weight per millim. 



Table II. 



NaCl solutions at 20° C. 



p 2 -255 -214 -144 -101 052 00 



p 1-1932 1-1596 11074 1-0720 10360 1-000 



aexper 841 820 7"89 7*74 7'61 7'44 



acalcul 842 8'22 793 7'73 7'57 



For CaCl 2 the values are a + b — 2c = 8'7, and 2(a — c)=9'48, 

 whence the comparison : — 



CaCl 2 solutions at 19° C. 



p 2 -360 -294 -200 -1135 -065 -024 00 



p 1-3511 1-2773 1-1789 1-0971 1-0540 10179 100 



aexper. ...931 8-84 822 7'81 7'61 7*51 7'45 



acalcul. ... 9-41 8'83 8-21 7'81 7'63 7'48 



These comparisons show that the form (8) is competent to 

 represent the experimental facts, for the differences between 

 the two sets of values of a lie within the limits of experimental 

 error ; the difference between 9*31 and 9*41 for the most 

 concentrated of the CaCl 2 solutions seems large, but the 

 experimental difficulties of measurement increase as the satu- 

 ration point is approached. 



With the values just given for the coefficients in (8) we 

 get for NaCl :— 



a^/p^TU, b=* 2 /p 2 *=647, o= ( -^ y| (^)i = 3'61, 



so that 1 A 2 /( 1 A 12 A 2 )*=:-52 ; 



similarly for CaCl 2 it is . . . '38. 



Thus it appears that for water and such substances as NaCl 

 and CaCl 2 the relation 1 A 2 2 = 1 A 12 A 2 does not hold good ; but 

 we must remember that as the peculiarities of water are largely 

 due to its molecules being paired, it is possible that the 

 addition of a dissolved substance may cause the breaking up 

 of some of the pairs and so cause the solution to be really a 

 mixture of three substances, and yet the form of our equation 

 (8) might meet the circumstances of such a case although the 

 meaning of the coefficients might be altered ; thus we cannot 

 at present be sure that b as derived from experiments is really 



« 2 /jo 2 2 , and c really -r-^ — t~ti( \ % f • Under these circum- 



stances it seems best to study first all the values of b and c 

 obtainable from Volkmann's data. 



2 L 2 



