A comparison of the composition of rain-water with that of springs and rivers gives some idea of the solvent work of water. From a study of the water of nineteen of the principal rivers of the world Murray has compiled the following table[38] showing the amount of mineral matter in average river water: _MATERIAL IN SOLUTION IN ONE CUBIC MILE OF AVERAGE RIVER WATER._[39] Constituents. Tons in a Cubic Mile. Calcium carbonate (CaCO₃) 326,710 Magnesium carbonate (MgCO₃) 112,870 Calcium phosphate (Ca₃P₂O₈) 2,913 Calcium sulphate (CaSO₄) 34,361 Sodium sulphate (Na₂SO₄) 31,805 Potassium sulphate (K₂SO₄) 20,358 Sodium nitrate (NaNO₃) 26,800 Sodium chloride (NaCl) 16,657 Lithium chloride (LiCl) 2,462 Ammonium chloride (NH₄Cl) 1,030 Silica (SiO₂) 74,577 Ferric oxide (Fe₂O₃) 13,006 Alumina (Al₂O₃) 14,315 Manganese oxide (Mn₂O₃) 5,703 Organic matter 79,020 ------- Total dissolved matter 762,587 Murray also estimates that the aggregate amount of water flowing into the sea annually is about 6528 cubic miles, which, on the above basis, would carry about 4,975,000,000 tons of mineral matter in solution. A large number of analyses of waters of rivers from the United States and Canada give an average of about .15,044 part in a thousand of mineral matter in solution, more than one-third being CaCO₃. The average amount of mineral matter in solution in 48 European streams cited by Bischoff[40] is .2127 part in a thousand, of which CaCO₃ is rather more than half. The average mineral matter in solution in 36 rivers cited by Roth[41] (including some of those tabulated by Bischoff) is .2033 part in a thousand, of which CaCO₃ is slightly less than one-half. An average for American and European rivers, so far as determinable from data at hand, is about .1888 part in a thousand in solution, of which CaCO₃ is slightly less than one-half. These last figures are probably not very far from an average for river water in general. The following table shows the total amount of solids carried in solution by the rivers indicated:[42] Rhine 5,816,805 tons per year. Rhone 8,290,464 „ „ „ Danube 22,521,434 „ „ „ Thames 613,930 „ „ „ Nile 16,950,000 „ „ „ Croton 66,795 „ „ „ Hudson 438,000 „ „ „ Mississippi 112,832,171 „ „ „ ECONOMIC CONSIDERATIONS.