A system of instruction in qualitative chemical analysis / by Dr. C. Remigius Fresenius .. ; edited by J. Lloyd Bullock, F.C.S.
- Carl Remigius Fresenius
- Date:
- 1855
Licence: Public Domain Mark
Credit: A system of instruction in qualitative chemical analysis / by Dr. C. Remigius Fresenius .. ; edited by J. Lloyd Bullock, F.C.S. Source: Wellcome Collection.
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![engagement of fluosilicic gas, which commences even in the cold, hy exposing the flask to a gentle heat in the sand-bath. Every gas bubble ascending through the mercury produces in the water a precipitate of hydrated silicic acid. The rationale of this process is, that of every three equivalents of fluoride of silicon (Si Fl2) one equivalent decomposes with two equivalents of water into silicic acid (Si 02), which separates, and hydrofluoric acid, which combines with the two undecomposed equivalents of fluoride of silicon, forming hydrofluosilicic acid. [3 Si Fl2 + 2 H 0=2 (Si Fl2, H FI) + Si 02]. The precipitated hydrate of silicic acid renders the liquid gelatinous, and it is for this reason that the aperture of the exit tube must be placed under [mercury, since it would speedily be choked if this precaution were neg- lected. It sometimes happens in the course, and especially towards the end, of the operation, that the gas forms complete channels of silica in :the gelatinous liquid, through which it gains the surface without under- going decomposition, if they are not occasionally broken by stirring the liquid. When the evolution of gas has completely ceased, throw the gelatinous paste upon a linen cloth, squeeze the fluid through, and filter it afterwards. Keep the filtrate for use. Tests.—Hydrofluosilicic acid, mixed with two parts of water, must produce no precipitate in solutions of salts of strontia. Uses.—Bases decompose with hydrofluosilicic acid, forming water and metallic silicofluorides. Many of these are soluble, whilst others are insoluble '; the latter may therefore by means of this reagent be distin- guished from the former. In the course of analysis, hydrofluosilicic acid is applied simply for the detection of baryta. § 46. 10. Oxalate of ammonia (N H40, O). Preparation.—Dissolve commercial oxalic acid in twenty parts of water, add caustic or carbonate of ammonia until the fluid begins to manifest a feebly alkaline reaction ; let it stand at rest for twelve hours, filter, and evaporate to crystallization. Dissolve one part of the salt in twenty-four parts of water for use. Tests.—The solution of oxalate of ammonia must not be precipitated nor rendered turbid by hydrosulphuric acid, nor by sulphide of ammonium. Lses. Oxalic acid forms with lime, strontia, baryta, oxide of lead, and other metallic oxides, insoluble or very difficultly soluble compounds ; oxalate of ammonia produces therefore in the aqueous solutions of the salts of these bases precipitates of the corresponding oxalates. In ana- lysis it serves principally for the detection and separation of lime.](https://iiif.wellcomecollection.org/image/b28080361_0069.jp2/full/800%2C/0/default.jpg)
