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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![4S, 49.1 MTEITE OF POTASSA. magnesia; also to separate sulphide of arsenic, which is soluble in it, from sulphide of antimony, which is insoluble, § 48. 7. Bisulphite of Soda, NaO,HO,2SO, [NaHSO,]. Preparation.—6 parts of copper clippings and 20 parts of concen- trated sulphuric acid are heated together in a flask, and the sulphurous Acid gas evolved is passed first through a wash-bottle containing some water, then into a flask containing 4 parts of purified bicarbonate of soda (§ 46), or 7 parts of pure crystallized carbonate of soda, and from 20 to 30 parts of water: it should not be much more than half full. The current of gas is passed until carbonic acid no longer escapes from the solution with efiervescence. The solution, which smells strongly of sulphurous acid, should be kept in a well-stoppered bottle. J'ests.—Sulphite of soda, when evaporated to dryness with pure sul- phuric acid, should leave a residue,* the aqueous solution of which is not altered by sulphuretted hydrogen, and does not yield a yellow pre- <3ipitate when heated with a solution of molybdate of ammonia mixed with nitric acid. Uses.—Sulphurous acid has a great tendency to absorb oxygen and pass to the state of sulphuric acid; it is therefore a very powerful reducing agent. Sulphite of soda, which has the advantage of being less readily decomposed than sulphurous acid, acts in an analogous manner on adding an acid to it. It is used principally to reduce arsenic .ncid to arsenious acid, chromic acid to sesquioxide of chromium, and ■sesquioxide of iron to protoxide. §49. 8. Nitrite of Potassa, KO,m [KNOJ. Preparation.—1 part of nitre is fused in an iron pan, 2 parts of lead are added, and the mixture is kept stirred with an iron rod. Even ;at a low red heat the lead becomes for the most part oxidized and con- verted into a yellow powder. To oxidize the remainder, the heat is increased to visible redness and maintained at that for half an hour. When cold, the product is treated with cold water, filtered, and carbonic 4icid passed through the filtrate; this precipitates almost the whole of the lead in solution, and the remainder may be removed with a little sulphuretted hydrogen. The clear solution is evaporated to dryness, finally with stirring, and then fused in order to destroy any hypo- sulphite of potassa which may have been formed (A. Strom'eyer). When required, 1 part is dissolved in 2 parts of water, neutralized cautiously with acetic acid, and filtered.t Tests.—On adding dilute sulphuric acid to nitrite of potassa, it should •copiously evolve nitric oxide gas. Uses.—Nitrite of potassa is an excellent reagent for detecting and separating cobalt, in the solutions of which metal it produces a pre- cipitate of the nitrite of potassa and cobalt oxide. It sei-ves also in presence of free acid to liberate iodine from its compounds. * 8ulpljiirous acid is copiously evolved during the evaporation. t For most purposes nitrite of soda may be employed instead of the potassa salt. The commercial article, which is now made in immense quantities for the manufacture of coal-tar dyes, is almost chemically pure.—[Editok.]](https://iiif.wellcomecollection.org/image/b21966953_0085.jp2/full/800%2C/0/default.jpg)
