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.
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![^ 32.] SULPHURETTED HYDROGEN. 45- indica-rubber; this funnel is lowered into a beaker containing 4 parts of water. The disengagement of the gaseous fluoride of silicon, which commences even in the cold, is assisted by moderately heating the retort; towards the end of the process, a pretty strong heat should be applied. Every gas bubble produces in the Avater a precipitate of hvdrated sihcic acid, with simultaneous formation of hydrofluosilicic acid, 3Sir.. + 2H0 = 2(HF,SiF,) +Si0,[SiF,+ 2H,O = 2H,SiF„+SiO,]. The precipitated hydrate of silicic acid renders the liquid gelatinous, and it is for this reason that the aperture of the descending limb of the tube cannot be allowed to dip directly into the water, as in that case it would soon be choked. It sometimes happens in the course of the operation, especially towards the end, that complete channels of silica are formed in the gelatinous liquid, through which the gas passes to the sm-face without undergoing decomposition if the liquid is not occasionally stirred. When the evolution of gas has entirely ceased, the gelatinous paste is thrown on to a linen cloth, the liquid squeezed out, and subse- quently filtered. The filtrate is kept for use. Tests.—Hydrofluosilicic acid should not produce any precipitate in solutions of salts of strontia (sulphate of strontia). jjses.—^With hydrofluosilicic acid, bases yield water and metallic silicofluorides. Many of these are insoluble, whilst others are soluble the latter, therefore, may be distinguished from the former by means of this reagent. In the course of analysis, hydrofluosilicic acid is applied simply for the detection and separation of baryta. c. SuLPHUK Acids. § 32. 1. Sulphuretted Hydrogen {Hydrosuliolmric Add), HS [H„S]. Preparation.—Sulphuretted hydrogen gas isevolved best from sulphide of iron, which is broken into small lumps and then treated with dilute sulphuric or hydrochloric acid.* Fused sulphide of iron may be procured so cheaply in commerce that it is hardly worth while to take the trouble of preparing it. However, if you wish to prepare it yourself, this may be done by heating iron turnings, or 1 to 1-J inch iron nails, in a covered Hessian crucible to a white heat, and then adding small lumps of roll-sulphur until the entire contents of the crucible are in fusion. As soon as this takes place, the fused mass is poured on to sand, or into an old Hessian crucible. Or a hole may be made in the bottom of the crucible in which the mass is fused, when the sulphide of iron will run through this hole as fast as it is formed, and may be received in a coal- shovel placed in the ash-pit. Or an intimate mixture of 30 parts of iron filings with 21 parts of flowers of sulphur may be pro- jected in small portions into a red-hot crucible, awaiting always the incandescence of the portion last introdiiced before a fresh one is added. When the whole of the mixture has been thus introduced into the crucible, the latter is closely covered, and exposed to a more intense heat, suflB.cient to cause the sulphide of iron to fuse more or less. The gas is evolved in the apparatus illustrated by fig. 31. W^ater is poured on to the sulphide of iron in a, concentrated sulphuric acid introduced through the thistle funnel h, and the mixture shaken; the- * In respect of the preparation of sulpliuretted hydrogen for medico-lesral pur- poses, see § 225.](https://iiif.wellcomecollection.org/image/b21966953_0069.jp2/full/800%2C/0/default.jpg)
