516 Proceedings of the Royal Society of Edinburgh. [Sess. 
From the above table it is seen that at all temperatures the density of 
a dilute solution is less than the density of water at the same temperature. 
As the concentration increases the density gradually diminishes up to a 
certain point, depending on the temperature, and then begins to increase. 
By drawing four isothermals to represent the connection between the con- 
centration and density of the solutions (fig. 1), it will be noticed that in each 
case the curve has a minimum, and that the minimum point moves away 
from the origin as the temperature increases. For example, the concentra- 
tion of the solution of minimum density at 0° C. is about 7 per cent., at 
25° C. it is 16'5 per cent., at 35° C. 19 per cent., while at 56° C. it is 
approximately 22*5 per cent. It will be noticed that it is possible to obtain 
two solutions of different concentrations which have the same density. 
Thus at 25° C. a solution whose concentration is 3T2 per cent, has the same 
density as a 27*7 per cent, solution at that temperature. If now these two 
solutions are mixed, the resulting solution would have a smaller density. 
Similar results are obtained at the other temperatures. 
Generally the density of a solution of a solid increases considerably as 
the concentration increases. It has been found, however, that the density 
of a solution of ammonium chloride * increases very slowly with the 
* Landolt and Bornstein’s Tables. 
