Chemical lecture experiments . ride. Hydrofluoric acid gas is generated in the presence of boricanhydride by heating a mixture of 24 g. of powderedcalcium fluoride, 10 powdered boric anhy-dride, and 20 g. of con-centrated sulphuric acidin a 100 cc. Jena glassErlenmeyer flask. A one-holed cork, carrying aglass elbow, is insertedin the neck of the flaskand two dry cylinders are arranged as in Fig. 113. Provision is made for con-ducting the escaping gas into a flue. The flask is thengently heated, and the boron trifluoride evolved soon expelsthe air from the flask and the two cylinders, and
Chemical lecture experiments . ride. Hydrofluoric acid gas is generated in the presence of boricanhydride by heating a mixture of 24 g. of powderedcalcium fluoride, 10 powdered boric anhy-dride, and 20 g. of con-centrated sulphuric acidin a 100 cc. Jena glassErlenmeyer flask. A one-holed cork, carrying aglass elbow, is insertedin the neck of the flaskand two dry cylinders are arranged as in Fig. 113. Provision is made for con-ducting the escaping gas into a flue. The flask is thengently heated, and the boron trifluoride evolved soon expelsthe air from the flask and the two cylinders, and fumesstrongly in the air as it escapes into the flue. The corksare then withdrawn from the cylinders, which are quicklycovered with glass plates. H3BO3 + 3 HF =BF3 + 3 H20. Apparatus (Fig. 113) ; 100 cc. Jena glass Erlenmeyer flask; two200 cc. cylinders ; CaF2 powdered ; B203 powdered. 4. Properties of boron trifluoride.—A cylinder of thegas, when opened to the air, gives off dense white fumes,which are acid to litmus Fig. 113 280 CHEMICAL LECTURE EXPERIMENTS A cylinder of the gas is opened with its month underwater. The gas is absorbed, water rising in the cylinderwith almost explosive violence. 5. Preparation of boric acid from borax. — Hydrochloricacid decomposes sodium diborate (borax), setting free boricacid, which, owing to its insolubility in cold water, may beeasily crystallized therefrom. Sixty grams of borax are dissolved in 240 cc. of boilingwater, and concentrated hydrochloric acid is added to thealkaline solution until the reaction is decidedly acid tolitmus. The beaker is then immersed in a large vessel ofcold water, and the boric acid on cooling, separates out inlarge crystals. Na2B407 + 2 HC1 + 5 H20 = 2 NaCl + 4 H3BOs. Large vessel of cold water ; Na2B407 ; litmus paper (blue). 6. Dehydration of boric acid by heat. — Boric acid, whenstrongly heated in a crucible, loses water and fuses to acolorless anhydride which resembles melted glass. A platinu
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