A text-book on chemistryFor the use of schools and colleges . alline forms. Alumin-um appears to determine the crystalline form of siliconand boron. In decomposing the vapor of chloride ofsilicon by aluminum in a vessel of hydrogen, silicon maybe obtained in hexahedral prisms that can even cutglass. The amorphous form burns when heated in air, but ifpreviously ignited in close vessels it shrinks in volume,increases in density so as to sink in sulphuric acid, and,passing into another allotropic state, becomes incom-bustible in oxygen. Silicon can deoxidize carbonic acid,and unites with chlorine
A text-book on chemistryFor the use of schools and colleges . alline forms. Alumin-um appears to determine the crystalline form of siliconand boron. In decomposing the vapor of chloride ofsilicon by aluminum in a vessel of hydrogen, silicon maybe obtained in hexahedral prisms that can even cutglass. The amorphous form burns when heated in air, but ifpreviously ignited in close vessels it shrinks in volume,increases in density so as to sink in sulphuric acid, and,passing into another allotropic state, becomes incom-bustible in oxygen. Silicon can deoxidize carbonic acid,and unites with chlorine, bromine, and fluorine. Silicic Acid, a&03 —46,is one of the most abundant bodies in nature, existingunder the innumerable forms of the quartz minerals,sands, and sandstones. It is found in every soil, in allwaters, is a constituent of many plants, and forms the What are the properties of fluoboric acid ? How may silicon beprepared? What allotropic states does it present? What changesoccur in it by heating ? What is the constitution of silicic acid ?. 304 SILICIC AXD FLUOSILICIC ACIDS. skeleton of tribes of the lower animals. RoGk crystaland flint are pure silicic acid. It may be obtained for chemical uses as follows : Hea^rock crystal to redness and quench it in water. Fuseone part of this with three parts of a mixture of carbon-ate of soda and carbonate of potassa, dissolve the result-ing silicate in water, and decompose with hydrochloricacid. The silicic acid separates as a gelatinous hydrate,slightly soluble in water, which, when washed and dried,yields a white insoluble powder. Silica is a gritty substance, sufficiently hard to scratchglass. Its specific gravity is It combines withthe alkalies in excess to form glass. It requires a hightemperature for fusion, and is insoluble in any acid ex-cept hydrofluoric. At ordinary temperatures the sili-cates are decomposed by carbonic acid, and it .is to thisagency that the disintegration of many rocks is glass
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