4-58 



Messrs. Plavfair and Joule on 



water and dilute solutions expand according to the square of 

 the temperature from that of greatest density. From Des- 

 pretz's table of the expansion of water, it appears that the 

 law is not true as far as 212^. As far however as it does hold 

 good, it is evident, from the properties of the parabola, that 

 the volume occupied by a salt in solution will increase in arith- 

 metical progression with the temperature at which the experi- 

 ment is made. 



For instance, let a a in the following diagram be a parabola 

 representing the expansion of water, and let Z> 6 be a similar 

 parabola representing the expansion of a solution. Let the 

 latter parabola have its vertex or point of greatest density 

 opposite 30°, while the former parabola has its vertex at 40°; 

 then xx^ x' x', x" x", &c., quantities which increase in arith- 

 metical progression, will represent the volumes occupied by 

 the salt in solution at the temperature of 10°, 20°, 30°, &c. 



In a similar manner it may be shown that the volume occu- 

 pied by each equivalent of a salt in solution at any given tem- 

 perature will increase with the density of the solution. In 

 order to ascertain the amount of influence exercised by a 

 change in the position of the point of maximum density, we 

 have made a series of experiments on the expansion of water 

 and of solutions by heat, which we propose to lay before the 

 Society in a succeeding memoir. In order, however, to render 

 evident the augmentation of volume caused by increased den- 

 sity, we have constructed the following table of the volumes 



