SOILS, CHARACTER OF. 475 SOILS, CHARACTER OF. 



the metal aluminium with oxygen, or in 

 other words, oxide of aluminium. It 

 occurs very abundantly in the mineral 

 kingdom, both free and in combination 

 with acids. In its crystallised state it 

 forms the hard mineral known as cor- 

 undum, and, in combination with oxide 

 of chromium, the sapphire and the ruby ; 

 and emery is a dark-coloured granular 

 variety of it. In an uncrystallised state 

 it is a white, tasteless, powdery substance, 

 obtained by adding a solution of carbonate 

 of soda to alum. It constitutes a large 

 proportion of shale and slate rocks, and is 

 a principal ingredient, in combination with 

 silica, in pipe, porcelain, and agricultural 

 clays, to which it gives tenacity and stiff- 

 ness. It is rarely found in the ashes of 

 plants, and therefore not considered as 

 directly contributing to their nourishment, 

 although useful as a mechanical agent in 

 absorbing ammonia from the atmosphere, 

 and in detaining the volatile as well as the 

 alkaline salts of manures, which would 

 otherwise be dissolved by the first heavy 

 shower, and carried into the subsoil beyond 

 the reach of the roots of the plant. 



IRON. This metal, both in the black 

 or protoxide, and the red or peroxide 

 state, abounds in all soils, the red being 

 most abundant, and easily observable from 

 the red colour it communicates. Even 

 soils in which the protoxide obtains, which 

 arc of a bluish-grey colour when brought 

 to the surface, are changed to the red 

 colour by the atmosphere, oxygen uniting 

 with and acting on it. Oxide of iron is 

 found in the ashes of all plants and in the 

 blood of animals. The presence of iron is 

 easily detected in soils by the ochry de- 

 posits in the beds of springs and ditches, 

 where the oxide dissolved in carbonic acid 

 produces the metallic-coloured deposit in 

 question. Sulphate of iron also occurs in 

 some soils, produced from iron pyrites: 

 such soils are unproductive ; for it is a 



compound of sulphuric acid with protoxide 

 of iron, better known under the name of 

 green vitriol. Lime added to such soil? 

 combines with the sulphuric acid, forming 

 gypsum ; and sweetens them and removes 

 the injurious properties. 



MANGANESE. This metal, in combina- 

 tion with oxygen, associated with oxide of 

 iron, occurs naturally in many soils. In 

 the ashes of plants traces of it are also 

 found ; but iron usually predominates. 

 The ash of the horse chestnut and oak 

 bark is rich in manganese, with no trace 

 of iron. 



SILICA, OR SILEX. This mineral occurs 

 abundantly in nature, either in a free state 

 or in the form of sand, sandstones, flint, 

 chalcedony, rock-crystal, or quartz, and in 

 combination with lime, magnesia, iron, 

 potash, soda, and other minerals. Silica 

 is insoluble in hot or cold water, and 

 resists the action of some strong acids ; 

 but hydrofluoric acid dissolves it, when 

 mixed with soda or potash, and exposed 

 to the heat of a glass furnace. Silica is 

 dissolved, or rather enters into combination 

 with the alkali, and forms glass; or when 

 the alkali is in excess, it dissolves into 

 water. On the addition of muriatic acid s 

 or sulphuric acid, to a solution of this 

 silicate of potash, the silica separates into 

 a gelatinous mass, in which form it is 

 soluble in water, and thus becomes the 

 food of plants. 



SULPHUR. This compound, in the 

 form of sulphuric acid, enters into the 

 composition of all cultivated soils, chiefly 

 in combination with limestone, magnesia, 

 potash, and other bases. With hydrogen 

 it forms sulphuretted hydrogen, a remark- 

 ably disagreeable smelling gas, the product 

 of the decomposition of organic matter 

 contained in the soil and impregnating 

 many medicinal waters, as at Harrogate. 



PHOSPHORUS. This ingredient is a 

 soft, waxlike, highly inflammable sub- 



