190 



THE EARL OF BERKELEY ON SOME 



Temperatures, 



-The temperatures at which the densities, solubilities and osmotic pressures were 

 determined are given with those quantities respectively. 



Part III. will be devoted to the application of the results to theory. 



The selection of the particular salts whose solutions were examined was governed 

 by the following considerations : 



(1.) Fairly soluble salts should be used, so that differences between the ordinary 

 phenomena of dilute and those appertaining to concentrated solutions 

 may be the more marked ; 



(2.) They should have as wide a range of molecular weights as possible, so as to 

 bring into prominence any effect the interacting masses may have on the 

 space occupied by the molecules ; 



(3.) For the purpose of comparing members of the same family of elements the 

 salts should be isomorphous, the presumption being that isomorphous 

 salts give similarly constructed molecules in solution. 



i. (A). 



Determination of the Constants. 



The densities were obtained by the following method : An approximately saturated 

 solution was kept in contact with crystals of the salt at a definite temperature by 

 means of a thermostat, and continuously stirred. When a sufficient length of time 



had elapsed, a pyknometer, whose capacity was known, 

 was immersed in the solution and filled to a mark, then 

 washed and dried by means of pure alcohol, and weighed 

 against a counterpoise which had been similarly washed 

 and dried. The solubilities were determined by washing 

 the contents of the pyknometers into platinum crucibles 

 and weighing them after evaporating to dryness. It 

 was found in the course of the work that, in the case of 

 very soluble salts, this method was not satisfactory, 

 because a crust of salt formed on top of the solution in 

 the platinum crucible, and the accumulation of steam 

 under it, on finding its way out, carried particles of 

 solution with it. Glass bulbs, represented in fig. 1 and 

 made of Jena glass, were therefore substituted for the 

 platinum crucibles and the solution evaporated to dry- 

 ness in them. This was effected by passing a current of dry air through the tubes 

 while they were being heated to 110-170 in an air oven, the air current and the 



nat. size. 









