o 



and the Surface- Tension of Solutions. 489 



point p 2 according to Quincke is 2'04, 'while at 15° C. it is 

 2*09. Thus all the data are to hand for calculating a 2 at 15" 

 C, it comes out 305 ; now (30*5/ll*6)* is 1*62, which ought 

 to be the ratio of the coefficient in (18) to that in (16). If we 

 divide '097 in (16) by 1*62 we get *06 in place of the '08 of 

 (15) or the '05 of (16), which shows that in a general way 

 the magnitudes of our quantities calculated from solutions at 

 15° C. agree with their values calculated for the pure sub- 

 stances at their high melting-points. 



We can now illustrate the determination of (M 2 2 / 2 )* for a 

 substance by a measurement of the surface-tension of a solu- 

 tion of it in the cases of AgN0 3 , Pb(N0 3 ) 2 , and MnCl 2 , for 

 which Valson's data are available ; first by (10) for AgN0 3 , 

 and by (12) forPb(N0 3 ) and MnCl 2 we calculate 



1 Ac l a 2 2 /p 2 ( 1 A l c i A 2 )% 



and then by (13) and (14) obtain (M 2 2 / 2 )* with the following 

 results : — 



Table XII. 



AgN0 3 . Pb(N0 3 ) 2 . MnCl 2 . 



p., -145 -142 ' -060 



p 1-133 1-133 1052 



a 7-575 7-546 7-551 



iK"$lpliKzKf '611 -515 -705 



M 2 /p 2 39 68 42 



(M.// 2 )£ 6-6 100 5-6 



According to the Kinetic Theory of Solids (" Further 

 Studies," p. 27) (M 2 2 Z 2 )* for AgN0 3 is 7'0 as against the 6'Q 

 just found ; with 3"6 as the value for N0 3 , 6'6 would mean a 

 value 3'0 for Ag, while from the chloride (" Further Studies," 

 p. 22) the value is 2-9, from the bromide 2*7, and from the 

 iodide 3'3. According to the principles explained in " Further 

 Studies/" the value of (M 2 2 / 2 )^ for Pb(N0 3 ) 2 must be divided 

 by 2®, giving 7*1, which is the sum of 3- 6 for N0 3 , and a 

 part due to Pb, which must therefore be 3*5 ; according to 

 the data of " Further Studies," p. 22, the part due to Pb is 3*1 

 from the chloride, 3'0 from the bromide, and 2" 7 from the 

 iodide ; on dividing the 5*6 for MnCl 2 by 2* and subtracting 

 2*1 for CI, we have the part 1*9 due to Mn. 



It has been shown that the attracting powers of the mole- 

 cules of solid bodies can be determined by measuring the 

 surface-tension and density of solutions of knov>n strength, 

 and that the values so found agree in the main with those 

 obtained by measurements of the surface-tensions of the 



