FORM OF SILICA IN SOLUTIONS. 67 



underground solutions are very dilute, at least where somewhat free circu- 

 lation is the rule, if the theory of dissociation be true we may suppose 

 that the salts held in solution are largely separated into their ions. While 

 the theory of dissociation and the explanation of chemical reactions by 

 interchange of free ions (see pp. 84-85) have a strong foothold in theoretical 

 chemistry, they have never gained universal support; and recently the 

 theory has been strongly attacked by Kahlenberg, who not only holds 

 that the theory is unnecessary to explain chemical reaction, but brings 

 together many facts which appear to controvert it." He has shown, more- 

 over, that instantaneous chemical changes take place in solutions that are 

 the best of insulators.'' 



Until recently it has not been known how the most important of the 

 geological compounds, the silicates, behave when dissolved. However, 

 Kahlenberg and Lincoln c have shown that when dilute solutions of sili- 

 cates are made the silica exists in such solutions in the form of colloidal 

 silicic acid. To illustrate: If a sufficiently dilute solution of sodium 

 silicate be made, but much more concentrated than ordinarily occurs in 

 underground waters, the compound breaks up into NaOH and colloidal 

 silicic acid. From this fact it would not be supposed that the silicic acid is 

 a chemically active compound, and it is not active near the surface of the 

 earth at ordinary temperatures and pressures; but on subsequent pages it 

 will be seen that at considerable depth, where the pressure and temperature 

 are much above the normal, silicic acid is a most active compound. 



Before the . ionic theory of solutions gained recognition it was cus- 

 tomary in the published analyses of underground waters to suppose that 

 the bases and acids of the dissolved materials are united in a definite way. 

 For instance, chlorine was ordinarily considered as united with the potas- 

 sium, sodium, or calcium. The sulphuric oxide radical S0 4 was supposed 

 to be united with the oxides of potassium, magnesium, calcium, and sodium. 

 The carbon dioxide radical C0 3 was supposed to be united with the oxides 

 of iron, magnesium, sodium, and calcium. The aluminum and silica were 



a Kahlenberg, L., The theory of electrolytic dissociation as viewed in the light of facts recently 

 ascertained: Bull. Univ. of Wisconsin No. 47, 1901, pp. 299-351; also Jour. Phys. Chem., vol. 5, 1901, 

 pp. 339-392. 



6 Kahlenberg, L., Instantaneous chemical reactions and the theory of electrolytic dissociation: 

 Jour. Phys. Chem., vol. 6, 1902, p. 1. 



c Kahlenberg, L., and Lincoln, A. T., Solutions of silicates of the alkalies: Jour. Phys. Chem., 

 vol. 2, 1898, pp. 88-90. 



