Laws of Molecular Fi 



orce. 



279 



we might imagine that the effective value of W in a solution 

 experiences a small change proportional to the concentration ; 

 but the equations as they stand will prove to be sufficient for 

 our purpose if, in comparing solutions of different substances, 

 we calculate cA _1 for the same value of n throughout. 



In all subsequent calculations n— 18/1000. The experi- 

 mental data for surface-tensions of solutions are abundant, the 

 chief that I know of and have used being those of Valson 

 (Compt. Rend, lxx., lxxiv.), Volkmann (Wied. Ann. xvii.), 

 Rontgen and Schneider (Wied. Ann. xxix.), and Traube 

 ( Jour n. fur Chem. cxxxix.). 



The following Table contains the values of cA _1 for a certain 

 number of compounds, the surface-tension being measured in 

 grammes weight per linear metre and the half molecules of the 

 salts of the bibasic acids being regarded as molecules. 



Table XXXI.— Values of ckr\ 



Li .. 



Na .. 

 K .. 



I. 



Br. 



CI. 



N0 3 . 



OH. 



*S0 4 . 



*0O,. 



4-15 



2-46 



•83 



1 61 



•83 



1-61 





399 



221 



•70 



1-54 





1-45 





4-74 



3-06 



1-45 



2-30 



1-37 



2-30 



1-95 



4-99 



331 



1-78 



2-55 



1-71 



2-72 



221 



The study of this table brings out the fact that the differences 

 of the numbers in any two rows or in any two columns are 

 constant: thus the differences for the iodide and chloride of 

 the four bases are in order 3*32, 3*29, 3'29, and 3*21, while 

 the differences of cA _1 for the Xa and Li salts of the mono- 

 basic acids are in order '59, *60, *62, '69, and *54. Accordingly 

 each atom contributes a certain definite part to the value of 

 cA _1 for the molecule in which it occurs, and that part is 

 independent of the other atoms in the molecule. I shall call 

 this part the parameter-reciprocal modulus of the atom ; we 

 have not at present sufficient data to get its absolute value in 

 any case, but if we make Li our standard positive radical, and 

 CI the standard negative, we can calculate the average values 

 of the difference between the parameter-reciprocal modulus of 

 a radical and its standard, — thus in the case of iodine this 

 difference is 3'28, and in the case of Xa '61, and so on. 



Before tabulating these mean values I will give the values 

 calculated for the salts of some other metals with the values 

 for the same salts of Li subtracted. 





