546 



Mr. W. W. J. Nicol on the 



Here the more soluble salt has its solubility increased more 

 than that of the less soluble, with the exception of NaN0 3 , 

 since E together <R separate. 



The more important part of Table V. is in the last four 

 columns, where I have compared the actual molecular volume 

 of the salt-solution with the volume calculated on the suppo- 

 sition that each salt-molecule is present in the solution with 

 the volume it possesses in its own saturated solution. In 

 the three first cases the agreement is satisfactory ; but 

 KN0 3 + NaN0 3 is exceptional, the actual volume of the 

 salts being about 10 per cent, higher than the calculated. I 

 may venture to suggest that a possible explanation of this is 

 to be found in the fact that KN0 3 is dimorphous, and in one 

 of its forms (that of rhombohedra) is isomorphous with 

 NaN0 3 . It may be that the presence of this last salt may 

 influence the form in which the KN0 3 would crystallize out; 

 and inasmuch as the isomorphous form is the unstable one 

 under usual conditions, it is probable that its molecular 

 volume in the solid state would be greater, and hence its 

 solubility and molecular volume in a saturated solution would 

 also be greater than that of the usual form. 



I have examined this point in another way: by preparing 

 a solution of one of the above salts, and then adding to it, 

 after determination of the molecular volume, a number of 

 molecules of another salt: for example, a 7NaCl 100 H 2 

 solution had 2 KCl, 3 KCl, and 4 KCl added. 



The results are given in Table VI., and compared with the 

 molecular volume calculated on the supposition that the more 



Table VI. 





M'. V. 



n. 



M.Y. 



W.Y'.Xn 



+ 1800. 



Diff. 





NaCl ... 

 NaCl ... 

 KCl ... 



NaCl ... 

 KCl ... 



NaCl ... 

 KCl ... 



KCl ... 

 KCl ... 

 KN0 3 \.. 



20 : 7 

 30-9 



209 

 30-9 



21-2 ' 

 30-9 



30 : 9 

 41-4 



7 

 7 

 2 



7 

 3 



7 

 4 



7 

 7 



2 



1941-5 

 1 2007-5 



j 2040-5 



1 2074-1 



2010-9 

 1 2098-6 



2006-7 

 2039-0 

 2072-0 



2099-1 



4- -8 

 +1-5 

 +21 



- -5 



M'. Y'.=mean molecular volume of the salt in a solution 

 as described above. 

















