Licence: Public Domain Mark
Credit: Qualitative chemical analysis / by C. Remigius Fresenius. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
102/526 page 78
![FLUORIDE OF CALCIUM. [§§ 77, 78, 70'. § 77. 2. Hydrate of Baryta, BaO,HO [BaH,Oj]. Preparation.—The crystals of baryta jirepared in the manner directed in § 3G are heated gently in a silver or platinum dish, until the water of crystallization is completely expelled. The residuary white mass is- pulverized, and kept for use in a well-closed bottle. Uses.—Hydrate of baryta fuses at a gentle red heat without losing its water. When silicates which resist decomposition by acids are fused with about 4 times their weight of hydrate of baryta, basic silicates are formed which acids will decompose. If, therefore, the fused mass is- treated with water and hydrochloric acid, the solution evaporated to dryness, and the residue digested with dilute hydrochloric acid, the- silicic acid is left behind, and the oxides are obtained in solution in the form of chlorides. Hydrate of baryta is used as a flux when we wish to test silicates for alkalies. This reagent is preferable as a flux to car- bonate or nitrate of baryta, as it neither requires a very high tem- perature for its fusion, as is the case with the carbonate, nor does it cause any spirting in the fusing mass, arising from disengagement of gas, as is the case with the nitrate. The fusion with hydrate of baryta is done in silver or platinum crucibles. § 78. 3. Fluoride of Calcium, CaF [CaF^]. Fluor-spar as pure as can be procured and, more particularly, free- from alkalies, is reduced to fine powder, and kept for use. Uses.—Fluoride of calcium in conjunction with sulphuric acid is used to decompose silicates insoluble in acids, and more especially ta detect the alkalies which they contain. If pure aqueous hydrofluoric acid (which must volatilize completely when heated in a platinum dish) or pure fluoride of ammonium is to be had, they are preferable to fluoride of calcium for decomposing silicates. Compare Section III, SiliciG acid, § 150. § 79. 4. Nitrate of Soda, NaO,NO, [NaNOg]. Preparation.—Pure nitric acid is exactly neutralized with pure car- bonate of soda, and evaporated to crystallization. The crystals are dried thoroughly, powdered, and kept for use. Tests.—A solution of nitrate of soda should not give any turbidity with solution of nitrate of silver or nitrate of baryta, nor be precijaitated by carbonate of soda. Uses.—Nitrate of soda is a very powerful oxidizing agent, jdelding oxygen to combustible substances when heated with them. This reagent is used chiefly to convert various metallic sulphides, more particularly the sulphides of tin, antimony, and arsenic, into oxides or acids; also to efiect the rapid and complete combustion of organic substances. For the latter purpose, however, nitrate of ammonia is sometimes preferable; it is prepared by saturating nitric acid with carbonate of ammonia.](https://iiif.wellcomecollection.org/image/b21966953_0102.jp2/full/800%2C/0/default.jpg)
