or Sesquisilicates. Silicate of lime silicate of magnesia) + 2110. lime) Neutral copper) ± HO.
Dibasic silicates. - Olivine 2(Mg.Fe)0,Si02.Iron forge cinder • Bisillcates. The composition of many of the erd Mary varieties of glass may be approximately represented by mixtures of different silicates which have this formula.
In the above formula3 MO stands for 1 equivalent of any metallic protoxide, such as lime, magnesia, or protoxide of iron.
The following are the general characters of the silicates: Most of them are fusible, the basic silicates fusing more readily than those which are either neutral or,contain an excess of acid. Excepting the silicates of the alkalies no silicatq, are soluble in water, The anhydrous, neutral, and acid silicates of the earths resisethe action of all acids except the hydrofluoric.
In conclusion we may remark that silica derives its name from silex,• flint, of which it is the essential constituent, and that it is largely employed in the manufacture of glass, china, and porcelain. For these purposes it is obtained in a finely comminuted state by heating flints or portions of colorless quartz to redness, and plunging them in cold water. The silica splits up into a friable mass, which may be easily ground to a fine powder. The use of silica in giving firmness and rigidity to various parts of the animal organs is exemplified in its free occurrence in the quill-part of the feather of birds, in the shields of certain infusoria, and in the spicula occurring in sponges; while its similar use iu the vegetable kingdom is seen in its more or less abundant presence in the stalks of the grasses, noire particularly in the cereals and in the bamboo (where it is especially depos ited about the joints, and is known as tabasbeer), in tire equisetw, etc.
Silicon may be made to combine with several other elements besides oxygen, but, with the exception of silicofluoric acid, these compounds are of no practical value Thus silicon and hydrogen form a hydride of silicon, a colorLss and spontaneously inflammable gas. INTitride of silicon is a bluish fibrous body, while sulphide of silicon is a white earthy powder. Silicon unites with chlorine, bromine, and probably iodine and fluorine, in two proportions corresponding to its oxygen compounds. Fluoride of silicon is a colorless pungent gas, liquefiable under strong pressure, and solidifying at —220°, intlainmable, and a non-supporter of combustion. It is obtained by heating powdered glass with 12 times its weight of oil of vitriol, and when a stream of this gas is transmitted through water a reaction takes place; two atoms of water and three atoms of the fluoride of silicon yielding silicolluoric acid (IIF,SiF,), which remains in solution, and silicon, which is deposited. A saturated solution of this acid forms a very sour fuming liquid, which does not directly attack glass, but if allowed to evaporate on it, causes erosion from the fluoride of silicon becoming evaporized, and free hydrofluoric acid being left. A dilute solution is frequently employed in the laboratory as a precipi tant of potash, which it throws down in a transparent gelatinous form. With salts of haryta it giveg a white crystalline precipitate. It combines with bases to form salts,, none of which arc of any special importance.