4203. Iodide of Potassium

4203.    Iodide of Potassium. This important medicinal compound is obtained in various ways. The United States Pharmacopoeia 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 becomes colorless, and continue the addition until tho liquid remains slightly colored from excess of iodine. (This will require about 16 troy ounces of iodine.) Evaporate the solution to dryness, stirring in 2 troy ounces finely powdered charcoal towards the close of the operation, so that it may be intimately mixed with the dried salt. Rub this to powder, and heat it to dull redness in an iron crucible, maintaining that temperature for 15 minutes. After it has cooled, dissolve out the saline matter with distilled water, filter the solution, evaporate, and set it aside to crystallize. An additional quantity of crystals may bo obtained from the mother water by further evaporation.

A solution of iodide of potassium keeps decidedly better when there is neither plain 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 tho proper shade, this is owing to the presence of iron in the alum, which is by no means a rare occurrence.

4204. Sulphuret of Potassium

4204.    Sulphuret of Potassium. Rub together 1 ounce sublimed sulphur, and 2 ounces dry carbonate of potassa; heat it gradually in a covered crucible until it ceases to swell and is completely melted. Pour the liquid on to a marble slab, and, when cold, break the mass into pieces, and keep in well-stopped bottle of green glass. ( U. S. Ph.)

4205. Sulphocyanide of Potassium

4205.    Sulphocyanide of Potassium. Take 3 parts cyanide of potassium, and 1 part sulphur; digest them for some time in 6 parts water, then add 3 parts more water; filter, evaporate, and crystallize. It forms long, Blender, colorless prisms, which are anhydrous, deliquescent, and fusible; very soluble in water and in alcohol, and not poisonous.

4206. Acetate of Soda

4206.    Acetate of Soda. This is prepared from carbonate of soda, by the same method directed for acetate of potassa (sec No. 4180), except that the resulting solution is evaporated to a pellicle, and set aside to crystallize.

4207. Sulphate of Soda

4207.    Sulphate of Soda. Also called Glauber's salt. This is usually obtained by dissolving 2 pounds of the chloride of sodium left after the distillation of muriatic acid (see No. 3883 (To Obtain Muriatic Acid)) in 1 quart of boiling water; the solution is next neutralized with carbonate of lime evaporated, and crystallized. It is soluble in cold water, its solubility decreasing as the temperature of the water is raised; insoluble in alcohol, and fuses when heated.