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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![Uses.—Chlorine has a greater affinity than eitlier iodine or bromine for metals and for hydrogen. Chlorine water is therefore a useful reagent for expelling iodine or bromine from their compounds. Chlorine serves moreover to effect the solution of certain metals (gold, platinum), to de- compose metallic sulphides, to convert sulphurous acid into sulphuric acid, ferrous oxide into ferric oxide, &c.; and also to destroy organic substances, as in presence of these it withdraws hydrogen from the water, whilst the liberated oxygen combines with the vegetable matters and decomposes them. For the latter purpose, it is better to produce the chlorine in the liquid which contains the organic substance; this may be done by adding hydrochloric acid to the solution, heating the mix- ture, and then adding chlorate of potassa. This gives rise to the for- mation of chloride of potassium, water, free chlorine, and hypochlorous acid which acts like chlorine. §30. 3. Nitro-Hydrochloric Acid. Aqua regia. Preparation.—1 part of pure nitric acid is mixed with from 3 to 4 parts of pure hydrochloric acid. Uses.—Nitric acid and hydrochloric acid decompose each other, form- ing free chlorine water and nitrosyl chloride (chloronitrous acid, oxy- chloride of nitrogen); HO,NO. + 3HC1 = 2C1 + NO.Cl + 4H0 [HN03 + 3HCI = Cl2 + NOCI + 2HjO]. This decomposition ceases as soon as the liquid is saturated with the gas; but it recommences the instant this state of saturation is disturbed by the application of heat or by decomposition of the acid. The presence of the free chlorine, and also, but in a very subordinate degree, that of the nitrosyl chloride, makes aqua regia the most powerful solvent for metals (with the exception of those which form insoluble compounds with chlorine). Nitro-hydrochloric acid is principally used to dissolve gold and platinum, which are insoluble both in hydrochloric and in nitric acid, and also to decompose various metallic sulphides, such as cinnabar, pyrites, &c. § 31. 4. Hydrofluosilicic Acid, HF,SiF, [H.SiFj. Preparation.—An intimate mixture is made of 1 part of perfectly dry fluor spar in powder * with 1 \ part of powdered glass, or 1 part of powdered ignited flint, or 1 part of quartz sand which has been care- fully freed from dust by washing and then ignited; 6 parts of concen- trated sulphuric acid free from arsenic are poured on to the mixture in a retort, and carefully mixed by shaking the vessel. As the mixture froths up when it gets warm, the retort should not be more than one-tliird filled. The neck of the retort must be connected aii'-tight ■ndth a small tubulated receiver, and the tubulus of the latter again, by means of india-rubber, with a wide glass tube twice bent at a right angle. To the descending limb of the glass tube a funnel is attached by means of * If the fluor spai- contains organic matter or metallic sulphides, it must be ignited with free access of air before use.](https://iiif.wellcomecollection.org/image/b21966953_0068.jp2/full/800%2C/0/default.jpg)
