IMPORTANCE OF SOLUTION. 485 



acid have been accounted for by processes in the belt of weathering'. But 

 the source of the hydrochloric acid, producing the chlorides, has not 

 been explained. This subject is considered on pages 789-790. 



The amounts of the compounds which are taken into solution by 

 ground waters depend very largely upon the number and amounts of 

 the above active chemical agents or solvents. Also the amounts of the 

 compounds which are taken into solution depend upon the relative propor- 

 tions of the elements present, and the manner in which they are com- 

 pounded. If all the important bases occurring in the rock-making minerals 

 were equally abundant the stronger bases would be taken into solution to 

 a larger extent than the weaker bases. Therefore there would be dissolved 

 more sodium and potassium than calcium and magnesium, more calcium or 

 magnesium than iron, more iron than aluminum. And as a matter of fact, 

 the percentages of the compounds dissolved are in this order. But the 

 amount of alkalies in the rocks is much less than that of the alkaline earths, 

 iron, or aluminum, and consequently the total amount of the former 

 elements dissolved may be less than the latter — indeed, is commonly much 

 less than the amount of the dissolved alkaline earths. Further, the greater 

 the proportion of bases present as compared with the acids — i. e., the more 

 basic the compounds — the more readily the minerals are decomposed and 

 the greater the amount of bases which are dissolved. If the acids were 

 present in equal quantity there would be dissolved a greater amount of the 

 salts of the stronger acids than of the weaker acids. Thus there would be 

 a greater quantity of sulphates, nitrates, and chlorides than of the car- 

 bonates. Since, however, in the solutions carbonic acid is so much more 

 plentiful than any other active acid, carbonates greatly predominate. The 

 only acid in solution which can be compared with carbonic acid in 

 abundance is silicic acid, produced by the decomposition of the silicates. 

 However, the liberated silicic acid, as explained on pages 115, 176, sep- 

 arates in a colloidal state, and in that form is exceedingly inactive and, 

 notwithstanding its great quantity, does comparatively little work. The 

 great power of the weak acid, carbonic, in the solutions shows that the law 

 of mass action is of great consequence in the relative amounts of the 

 compounds formed and taken into solution. 



The above general statements are very well illustrated by T. Mellard 

 Reade's estimate of the amount of salts which are abstracted from each 



