538 



Mr. W. W. J. Nicol on the 



of the specific gravity of a salt-solution is less than the rate at 

 which it increases in concentration; consequently the mole- 

 cular volume of each successive molecule of a salt added to a 

 solution is a constantly increasing quantity. Tables I. and II. 

 contain the results of experiments with NaCl. 



Table I. gives the density (S) and the molecular volume 

 (M. V.) of solutions containing n molecules of NaCl in 100 

 molecules of water, at t° = 20°. The column headed A gives 

 the difference in molecular volume produced by each, succes- 

 sive molecule of salt added. 



Table I. 





n '. 



tfaCl-|-100H 2 O. 





t°. 



n. 



B. 



M.Y. 



A. 



o 



20 



-5 



1-01145 



1808-54 



17-08 



>> 



1-0 



1-02255 



1817-52 



1796 



>> 



20 



1-04393 



1836-29 



18-77 



>) 



30 



106437 



1856-03 



19-74 



5) 



4*0 



1-08408 



1876-23 



20-20 



.'J 



5-0 



1-10276 



1897-42 



21-19 



J) 



60 



1-12099 



191884 



21-42 



5J 



70 



1-13838 



194092 



22*08 



5) 



8-0 



1-15503 



1963-59 



22-67? 



)> 



90 



1-17140 



1986-09 



22-50 



}J 



100 



1-18707 



2009-15 



2306 



;> 



1099 



1-20191 



2032-76 



2361 



The molecular volume therefore increases from 17*08 up to 

 23-61 for the last -99 molecule added. In Table II. the data 

 are treated differently. The molecular volume of the water 

 is assumed constant = 1800, and is subtracted from the mole- 

 cular volume of the solution; the remainder (M. V.~ 1800) = r 

 is what Thomsen has called the " Rest" — it is the volume of 



the salt in the solution ; and — is the mean molecular volume 



n 



of a molecule of the salt in a solution of strength n : this in 

 the case of NaCl increases from 17*08 to 21*16 in the satu- 

 rated solution. The molecular volume of the salt in the solid 



state — ^ — is given by Schroder =27*1. 



