94 A TREATISE ON METAMORPHISM. 



It may under these conditions be a stronger acid than at the surface, 

 and if this were the case the reactions would be partly explained. 

 Bearing in this direction is the experiment of Bischof, who has shown 

 that at 100° C. silicic acid, when present in abundance, may partially 

 replace carbonic acid of carbonates." 



Ostwald's explanation of the varying strength of the bases and acids is 

 based on the varying amount of supposed dissociation. 



The velocity of a reaction is proportional to the masses of the active 

 components, and according to Ostwald these are the free ions. Therefore 

 the speed depends upon the number of free ions which are acting. But 

 the number of free ions which' are present is dependent upon the degree 

 of dissociation, and in this matter different compounds vary greatly. 

 Therefore the degree of electrolytic dissociation of the va, 'ous bases and 

 acids determines their respective strengths and is " the measure of the 

 reaction capacities of all substances." b 



From this it follows that an acid or base which is strongly dissociated 

 is stronger than, or, in other words, is able to largely replace, an acid or 

 base which is but slightly dissociated; for the number of free ions of the 

 stronger compound far exceeds that of the weaker. It therefore becomes 

 important, from Ostwald's point of view, to know the comparative strength, 

 or the relative amounts of dissociation, of the abundant bases and acids 

 which occur in the rocks. According to Ostwald the strong bases and 

 strong acids may be largely dissociated; the moderately strong bases and 

 acids under ordinary conditions are dissociated to a much less extent; the 

 weak acids, carbonic, hydrosulphuric, and boric, are usually not dissociated to 

 the extent of 1 per cent; silicic acid under ordinary conditions is scarcely 

 dissociated at all. 



STRENGTH OF THE SOLCTIOJiS. 



Saturated and strong solutions are more active than weaker solutions; 

 for the amount of the active compound increases with the concentration, 

 but not in a simple ratio. Weak solutions are relatively more active than 

 strong solutions, and by those who believe in dissociation this is attributed 

 to their nearer approach to complete dissociation; but the greater relative 

 activity of weak solutions never compensates fully for the greater dilution. 



"Bischof, Gustav, Elements of chemical and physical geology, translated by Paul and Drurmnond, 

 Harrison & Sons, London, 1854, vol. 1, p. 6. 



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

 p. 440. 



