. Principles of agricultural chemistry [microform] . licate and aluminiumsilicate. In the presence of carbon dioxide, potassium carbonateis produced and hydrated silica set free, the quantity dependingupon the amount of carbon dioxide present. A lime felspar isdecomposed in the same way, and the calcium carbonate dissolvedby aid of the carbon dioxide the water contains. Silicates of ironare decomposed with the production of hydrated oxides of ironand silicic acid. If the silicate is a ferrous silicate, the iron isoxidized by the oxygen in the 58 PRINCIPLES OF AGRICULTURAIv CHEMISTRY Ca
. Principles of agricultural chemistry [microform] . licate and aluminiumsilicate. In the presence of carbon dioxide, potassium carbonateis produced and hydrated silica set free, the quantity dependingupon the amount of carbon dioxide present. A lime felspar isdecomposed in the same way, and the calcium carbonate dissolvedby aid of the carbon dioxide the water contains. Silicates of ironare decomposed with the production of hydrated oxides of ironand silicic acid. If the silicate is a ferrous silicate, the iron isoxidized by the oxygen in the 58 PRINCIPLES OF AGRICULTURAIv CHEMISTRY Carbonic acid increases the solvent power of water. Rain watercontains from 5 to 10 parts (by volume) of carbon dioxide. Riverand spring waters contain more, but most of it is in combinationwith lime. The capillary water of soils containing much organicmatter, holds more carbonic acid in solution than river or springwater. Water containing carbon dioxide is especially active in dissolv-ing carbonate of lime or limestone, and removing it from the soil. Fig. 12.—Limestone cavern. or rock. Carbonate of lime is slightly soluble in water (20 partsper million), but much more soluble in water containing carbondioxide, owing to the formation of calcium bicarbonate:CaCO, + H,0 = CaCHCOg),. Water saturated with carbon dioxide dissolves about 880 partsper million. This solvent action has resulted in the formationof large caverns in limestone regions. Oxygen is also dissolved in most natural waters, and acts uponthe ferrous or manganous compounds which occur in a greatnumber of minerals. When oxidized, these occupy a larger spacethan before, and thus hasten the disintegration of the mineralscontaining them. Some ferrous silicates are oxidized rapidly onexposure to moist air, falling into a brown powder in a few weeks. ORIGIN OF SOIIvS 59 As a rule, silicates containing much iron are easily changed byweathering agencies. Action of Animal and Vegetable Life.—Animal and vegetablelife act on
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