74 A TREATISE ON METAMORPHISM. 



The conclusions of van't Hoff, Ostwald, and others in reference to 

 osmotic pressure being due to gaseous pressure of the dissolved substances 

 have never been accepted by Mendeleeff, and have recently been strongly 

 opposed by Kahlenberg. Certainly there are many discrepancies between 

 the observations made as to the amount of osmotic pressure and the amount 

 which the pressure should be under the gas law. But, so far as the 

 observations of geology show, I see nothing that controverts or confirms 

 van't Hoff's theory. In studying the work of underground solutions I 

 have been unable to discover any criteria which will separate the work of 

 gases in water solutions from the work of solids in water solutions. So 

 far as geology is concerned, solutions of gases in water and solutions of 

 solids in water can' not be discriminated. It has been held by some that 

 the presence of fluorite and other minerals is evidence of gaseous action, 

 but, as yet, I have not been able to find valid evidence offered by any 

 author for this conjecture. It may be that gases dissolved in water and 

 solids dissolved in water are held in solution in consequence of chemical 

 affinity, as held by Mendeleeff, or they may be in solution as gases, as 

 held by van't Hoff, but in either case the manner of action of the two is 

 the same, and therefore there is no warrant for attributing the development 

 of fluorite, tourmaline, etc., to the presence of " mineralizers " in the sense 

 that these compounds are the products of the action of gases as opposed to 

 water solutions. 



When a soluble solid is placed in a liquid solvent it at once begins to 

 dissolve. The temperature and pressure remaining constant, if an excess 

 of the solid be present after a sufficient time there is no further decrease 

 in the amount of the solid present, nor is there any increase. When this 

 state is reached the solution is saturated. 



When a solid is in a saturated solution, and therefore constant in 

 amount, even if temperature and pressure remain constant it does not follow 

 that no interchange takes place between the dissolved and solid salt. The 

 kinetic theory of solutions leads to the conclusion that many molecules are 

 released from the solid to the solution, and pass from the solution into the 

 solid, but these amounts balance. This is well illustrated by sug-ar solu- 

 tions. If finely pulverized sugar be placed in the bottom of a saturated 

 sugar solution and sugar-covered threads be suspended in the solution, 

 sticks of rock candy will be formed. The crystals of the candy grow at 



