CONDITIONS OF SOLIDS IN SOLUTION. 73 



one another that molecular attraction produces an effect, and in this case 

 the osmotic pressure does not vary directly as the concentration. But, 

 Cameron says, in so far as the molecules in solution are sufficiently sepa- 

 rated so that the}* may act as a gas, "the volume, pressure, and temper- 

 ature relations are dependent only upon the number of molecules involved."" 



Since all of these relations are the same as the laws controlling- the 

 behavior of gases, it is held by many physical chemists that when a solid 

 passes into solution it is transformed to a gas. Under this explanation the 

 osmotic pressure is a gaseous pressure. "The kinetic energy of the 

 molecules of the dissolved substance is equal to that of the gas at the same 

 temperature ; and, moreover, as the kinetic energies of the molecules of the 

 dissolved subtance and of the solvent must agree, because these molecules 

 are in immediate contact, it follows also that the kinetic energy of the 

 molecules of the liquid must, on the whole, be the same as that of gaseous 

 molecules at the same temperature." 6 



If the above theory be correct, it follows that the solution of solids in 

 liquids is similar to that of gases in liquids; for in both cases the compound 

 when dissolved is in the form of a gas; and the geological work of under- 

 ground water, whether the solutions be produced by a mingling of gases 

 and water, solids and water, or the three combined, could be considered as 

 a unit. (See pp. 63-64.) 



In case, a salt dissolved in water be an electrolyte, under the dissocia- 

 tion theory it is separated into ions to some extent. If this be so, the 

 number of dissolved particles is represented by the number of ions plus the 

 number of undissociated molecules. Therefore in very dilute solutions, 

 where the dissociation is held to be complete, the number of dissolved 

 particles and consequently the osmotic pressure is doubled in the case of 

 a salt of a monad acid with a monad base. Thus the law of equal gaseous 

 pressure for equal number of molecules is believed by many to still hold 

 good. For instance, if NaCl dissociates into the ions Na and CI, or KOH 

 into the ions K and OH, thus giving twice as many molecules as in the 

 case of a compound which does not ionize, under the law the osmotic 

 pressure is twice as great as that of the compound which does not dissociate. 



"Cameron, F. K., Application of theory of solutions to the study of soils: Report No. 64, Field 

 Operations of Division of Soils, 1899, U. S. Dept. of Agric, 1900, p. 144. 

 »Gstwald, op. cit, p. 148. 



