RELATION OF SOLUTION AND TEMPERATURE. 79 



the totals of the salts in solution are in general increased by pressure, 

 and the volumes of the solution are less than those of the salts and solvents 

 separately. 



RELATIONS OF SOLUTION AND TEMPERATURE. 



The relations of solution and temperature have three phases; first, the 

 speed of solution; second, the quantity of material which may be held in 

 solution; third, the relations of solution to absorption and liberation of heat. 



speed of solution. — The speed of solution is commonly increased greatly by 

 rise of temperature." A slight increase in temperature may increase the rate 

 of solution out of all proportion to the absolute change in temperature. At 

 temperatures above 100° C, and especially above 185° C, the activity of 

 water may increase to an amazing degree. The rapid solution of glass, by 

 Barus, 6 at temperatures about 185° C. illustrates this. At any temperature 

 solution will continue until the point of saturation is reached, but this state 

 will be attained at high temperatures in but a small fraction of the time 

 required at low temperatures. For instance, to saturate an underground 

 solution with the refractory silicates or sulphides at ordinary temperatures 

 might require months, or even years, while to saturate them at temperatures 

 above 185° C. might require only an equal number of minutes, or at most, 

 hours. The capacity of water for action at high temperatures combined 

 with pressure, considered above, is adequate to explain the complete 

 recrystallization of great volumes of rock. (See pp. 749-751.) 



Quantity of material which may be held in solution. The effect of temperature Upon 



the quantity of material which may be held in solution does not admit of a 

 simple general statement." For most substances moderate increase of 

 temperature gives greater capacity for solution; but for many substances 

 there exists a temperature at which there is the maximum capacity for 

 solution, and the amount of material which may be held in solution at 

 higher and lower temperatures is less than this maximum. The quanti- 

 tative relations of solution and temperature at ordinary pressure between 



aJSfemst, W., Theoretical chemistry, translated by C. S. Palmer, Macmillan & Co., London, 1895, 

 p. 568. 



& Barus, C, Hot water and soft glass in their thermodynamic relations: Am. Jour. Sci., 4th ser., 

 vol. 6, 1898, p. 270, and vol. 9, 1900, pp. 167-168. 



"Ostwald, W., Solutions, translated by M. M. Pattison Muir; Longmans, Green & Co., New 

 York, 1891, pp. 55-77. 



