1909-10.] Solutions of Tetra-propyl-ammonium Chloride. 517 
concentration. A 5 per cent, solution has a density of 1*058, while the 
density of a 25 per cent, solution is 1*0730. In the case of tetrethyl- 
ammonium chloride * the increase of density with concentration is even 
smaller, 4*14 per cent, and 16*30 per cent, solutions having densities of 
*9971 and *9994 respectively, while in the present case of tetra-propyl- 
ammonium chloride under certain conditions the density actually decreases 
as the concentration increases. 
The curves in fig. 2 show the connection between density and 
temperature for solutions whose concentrations are constant. 
Since the density of a dilute solution is less than that of water, it is 
evident that there must be expansion on solution. In order to find out 
whether the volume of a solution was greater than the combined volumes 
of solid and water, it was necessary to determine the density of the solid. 
To do this the method of floating was employed, the density being 
* Taylor and Moore, loc. cit. 
