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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![Special Eeactions of the more common Oxides of the first group. § 89. a. Potassa, KO [K,0]. 1. Potassa and its hydrate and salts are not volatile at a low red-heat. Potassa and its hydrate dehquesce in the air; the oily liquids thereby formed absorb carbonic acid rapidly from the ah-, but without soHdifying. 2. Nearly all the salts of potassa are soluble m water. Those with colourless acids are colourless. The neutral salts of potassa with strong acids do not alter vegetable colours. Carbonate of potassa crystallizes (in combination with water of crystaUization) with difficulty, and deli- quesces in the air. Sulphate of potassa is anhydrous and suffers no alteration in the air. 3. CMoride of platinum produces in the neutral and acid solu- tions of potassa a yellow, crystalline, heavy precipitate of chloride of platinum and chloride of potassium (platinochloride of potas- sium), KCljPtCl., [K,PtCI„]. In concentrated solutions, this precipitate separates immediately on adding the reagent: in dilute solutions it is formed only after some time, often after a considerable time. Very dilute sohitions are not precipitated by the reagent. The precipitate consists of octahedrons discernible under the microscope. Alkaline solutions must be acidified with hydrochloric acid before the chloride of platinum is added. The precipitate is very sparingly soluble in water; the presence of free acids does not greatly increase its solubility; j it is insoluble in alcohol. Chloride of platinum is therefore a par- ] ticularly delicate test for salts of potassa dissolved in spirit of wine. I The best method of applying this reagent is to evaporate the aqueous solution of the potassa salt with chloride of platinum nearly to dryness on the water-bath, and to pour a little water over the residue (or, i better still, some spirit of wine, provided no substances insoluble in that menstruum be present), when the platinochloride of potassium will be left undissolved. Care must be taken not to confound this double salt with platinochloride of ammonium, which greatly resembles it (see § 91, 4). 4. Tartaric acid produces in neutral or alkaline* solutions—a 1 white, quickly su.bsiding, f/mwM^fM'crystalline precipitate of acid tar- trate of potassa, K0,H0,C3Hp^^ [KHC^H.OJ. In concentrated solutions, this precipitate separates immediately; in dilute solutions often only after the lapse of a considerable time. Vigorous shaking or stirring of the liquid greatly promotes its formation. Very dilute solutions are not precipitated by this reagent, Pree alkalies and free mineral acids dissolve the precipitate; it is sparingly soluble in cold, •but pretty readily soluble in hot water. In acid solutions, the free Acid must, if practicable, first be expelled by evaporation and ignition, or the solution must be neutralized with soda or carbonate of soda. : * If the solution is alkaline, tlie reagent must be added until the liquid shows A strongly acid reaction.](https://iiif.wellcomecollection.org/image/b21966953_0109.jp2/full/800%2C/0/default.jpg)
