Manual of qualitative analysis / by Robert Galloway.

  • Galloway, Robert.
Date:
1861
Catalogue details

Licence: Public Domain Mark

Credit: Manual of qualitative analysis / by Robert Galloway. Source: Wellcome Collection.

    66/272 (page 48)
    If the solution is acid, the free acid must be expelled, if practicable, by evaporation or ignition; or if not expelled, it must be neutralized with soda or carbonate of soda before testing for potash either with bitartrate of soda or tartaric acid. Bitartrate of soda cannot, of course, replace tartaric acid as a test for potash when the solution to be tested contains a free alkali, because bitartrate of potash is soluble in free alkalies; but if the other bases are sought for, the solution cannot be alkaline when we arrive at the examination for potash, and it is not often that we have to deal with an alkaline solution, even when the alkalies are the only bases that are examined for. 111. Bichloride of platinum produces, in neutral and acid solutions of potash, a yellow, crystalline precipitate,* a double salt of CHLORIDE OF POTASSIUM and CHLORIDE OF PLATINUM (KCl, PtCl,). The presence of free hydro- chloric acid promotes the formation of this precipitate. It is shightly soluble in water, but wholly insoluble in alcohol. This is a very delicate test for potash or any of its com- pounds: the best method of applying it is to mix the solution under examination for potash with bichloride of platinum, evaporate to dryness upon a water bath, and treat the residue with alcohol, the excess of bichloride of platinum dissolves in the alcohol, colouring the solution yellow; the double salt of bichloride of platinum and chloride of potassium is left undissolved as a yellow, crys- * Bichloride of platinum gives with iodine a dark-red colour ; and as this colour prevents the yellow precipitate of bichloride of platinum and chloride of potassium from being distinctly seen, iodine should be expelled, if present, before testing for potash by this reagent. To expel it, evaporate to dryness with concentrated nitric acid; dissolve the residue in water, add hydrochloric acid and bichloride of platinum, and then proceed in the usual way.