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Iodide of Potassium

This important medicinal compound is obtained in various ways. The United States Pharmacopœia gives the following formula for its preparation: To 6 troy ounces potassa, dissolved in 3 pints boiling distilled water, add gradually finely powdered iodine, stirring after each addition until the solution bemade from the sulphate is much purer, and, when the process is well managed, merely contains a trace of sulphuric acid. The sulphate of soda is mixed with an equal weight, of chalk and about half its weight of coal, each being previously ground to powder, and the mixture is exposed to a great heat in a reverberatory furnace, and during the calcination is frequently stirred with a long iron rod. comes colorless, and continue the addition The dark grey product usually contains about until the liquid remains slightly colored from 22 or 23 per cent. of carbonate of soda. This excess of iodine. (This will require about 16 is now lixiviated with tepid water, and the troy ounces of iodine.) Evaporate the solu- solution, after defecation, evaporated to drytion to dryness, stirring in 2 troy ounces fine- ness, mixed with a little sawdust, and roasted ly powdered charcoal towards the close of the in a reverberatory furnace at a heat not exoperation, so that it may be intimately mixed ceeding 700° Fahr., until all the sulphur is with the dried salt. Rub this to powder, and expelled. The product now receives the heat it to dull redness in an iron crucible, name of soda-ash, or soda-salt, and contains maintaining that temperature for 15 minutes. about 50% of alkali. It may bo purified by After it has cooled, dissolve out the saline solution in water, defecation, evaporation, matter with distilled water, filter the solution, and crystallization; it then becomes commerevaporate, and set it aside to crystallize. An cial crystallized carbonate of soda, consisting additional quantity of crystals may be ob- of large transparent crystals, which effloresce tained from the mother water by further eva- by exposure to the air, crumbling into a poration. white dry powder. The carbonate used in crystallization.

A solution of iodide of potassium keeps medicine is prepared from the commercial decidedly better when there is neither plain crystals by dissolving, filtering, and careful nor aromatic syrup or sugar in it. When gargles of honey of roses, with alum and water, have a black color, though that of honey be of the proper shade, this is owing to the presence of iron in the alum, which is by no means a rare occurrence.