CHEMICAL ACTION OF WATER 171 



on casual inspection, owing to the fact that the material is 

 carried away in solution, leaving only the insoluble impurities 

 behind. In such cases it is possible to estimate the amount of 

 corrosion through a comparison of the proportional amounts of 

 various constituents in this residue with those in the fresh rock 

 (see p. 217 et seq,), and the time limit of corrosion through 

 determining the percentage amounts of the constituents in the 

 water which annually drains from any given area.^ By such 

 methods it has been estimated^ that some 275 tons of calcium 

 carbonate are annually removed from each square mile of Cal- 

 ciferous limestone exposed in the Appalachian region alone; 

 while a well-known English authority^ has calculated that with 

 an annual rainfall of 32 inches, percolating only to a depth of 

 18.3 inches, there are annually removed by solution from the 

 superficial portions of England and Wales an average of all 

 constituents amounting to 143.5 tons per square mile of area. 

 He further calculates that the average amount of carbonate of 

 lime annually removed from each square mile of the entire 

 globe amounts to 50 tons.* It is to this corrosive action of 



^The following calculations by Sir Jolin Murray show the amount and 

 kind of material in solution in one cubic mile of average river water: 



Constituents Tons \n one cubic mile 



Calcium Carbonate (CaCOa) 327,710 



Magnesium Carbonate (MgCOa) 112,870 



Calcium Phosphate (CasPaOg) 2,913 



Calcium Sulphate (CaS04) 34,361 



Sodium Sulphate (NaS04) 31,805 



Potassium Sulphate (K0SO4) 20,358 



Sodium Nitrate (NaNOa) 26,800 



Sodium Chloride (NaCl) 16,657 



Lithium Chloride (LiCl) 2,462 



Ammonium Chloride (N* H4CI) 1,030 



Silica (SiOo) 74,577 



Perric Oxide (PeaOg) 13,006 



Alumina (AI.O3) 14,315 



Manganese Oxide (MuaOs) 5,703 



Organic Matter 79,020 



^A. L. Ewing, Am. Jour, of Science, 1885, p. 29, 



^ T. Mellard Eeade, Chemical Denudation in Eelation to Geological Time. 



* The total dissolved constituents thus removed are divided up as follows : 

 Carbonates of lime, 50 tons; sulphate of lime, 20 tons; silica, 7 tons; car- 

 bonate of magnesia, 4 tons; peroxide of iron, 1 ton; chloride of sodium, 

 8 tons; alkaline carbonates and sulphates, 6 tons. 



