Prep. One ounce of chloride of calcium is dissolved in eight fluid ounces of distilled water, and sufficient water is added to make the bulk of the solution ten fluid ounces.

Use. This solution is used as a means of recognizing citric acid in citrate of potash. Citric acid forms with lime the citrate of lime, a salt which has the peculiarity of being soluble in cold water, but insoluble in hot, so that when the solution of calcium is added to the solution of citrate of potash, no precipitate occurs until the solution is boiled, when a white precipitate separates, which is readily soluble in acetic acid. The production, with chloride of calcium, of a white precipitate of arseniate of lime (2 Ca O, HO; As O5) soluble in nitric acid, is also given as one of the characteristic reactions of a solution of arseniate of soda.