A text-book on chemistry : for the use of schools and colleges . itforms white fumes. SILICON. Si = 22-18. This element may be prepared by igniting the silico-fluoride of potassium with potassium, Fig. 256. acting upon the resulting substancewith water, which removes the fluor-ide of potassium, and leaves the sili-con as a nut-brown powder. It exhibits two allotropic as first described, it takesfire and burns when heated in atmos-pheric air ; but if previously ignitedin close vessels, it shrinks in volume,and, passing into its other state, becomes incombustible inoxygen gas. SI
A text-book on chemistry : for the use of schools and colleges . itforms white fumes. SILICON. Si = 22-18. This element may be prepared by igniting the silico-fluoride of potassium with potassium, Fig. 256. acting upon the resulting substancewith water, which removes the fluor-ide of potassium, and leaves the sili-con as a nut-brown powder. It exhibits two allotropic as first described, it takesfire and burns when heated in atmos-pheric air ; but if previously ignitedin close vessels, it shrinks in volume,and, passing into its other state, becomes incombustible inoxygen gas. SILICIC ACID. Si03 = 46-219. Silicic acid is one of the most abundant bodies in na-ture, existing under the innumerable forms of the quartzminerals, sands, and sandstones. Rock crystal and flintare pure silicic acid. It may be obtained in a more convenient form by fusing What is the color it communicates to flame ? How may silicon be pre-pared? In what respect does it differ after ignition? What is the con-stitution of silicic acid, and how may it be prepared ?. 248 FLUORIDE OF SILICON. white sand with four parts of carbonate of potash, dissolv-ing the resulting silicate in water, and decomposing thesolution with hydrochloric acid. The silicic acid sepa-rates as a gelatinous hydrate, slightly soluble in water,which, when washed and dried, yields a white powderabsolutely insoluble in water. There is reason to be-lieve that the silicon exists in its different allotropic statesin these two forms of silicic acid. Silica is a gritty substance, sufficiently hard to scratchglass. Its specific gravity is 2-GG. It combines with thealkalies in excess to form glass. It requires a high tem-perature for fusion. Hydrofluoric acid is the only acidwhich dissolves it. Fig. 257 FLUORIDE OF SILICON, SiF3 = 78-22,may be obtained, as just stated, by dissolving silica in hy-drofluoric acid, or by heatinga mixture of fluor spar andsand with sulphuric acid. Itis colorless ; fumes in theair ; its specifi
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