3924. Dilute Phosphoric Acid

3924.    Dilute Phosphoric Acid. Mix

5 troy ounces nitric acid with 1/2 pint distilled water in a porcelain capsule of the capacity of 2 pints; add 6 drachms phosphorus and invert over it a glass funnel of such dimensions that its rim may rest on the inside of the capsule, near the surface of the liquid. Place the capsule on a sand-bath, and apply a moderate heat until the phosphorus is dissolved, and red vapors cease to rise. If the reaction becomes too violent, add a little distilled water; and if the red vapors cease to be evolved before the phosphorus is all dissolved, gradually add nitric acid (diluted as before) until the solution is effected. Remove the funnel, continue the heat until the excess of nitric acid is driven off, and a syrupy liquid, free from odor and weighing 2 troy ounces, remains. Mix this, when cold, with sufficient distilled water to measure 20 fluid ounces, and filter through paper.

Or: Dissolve 1 troy ounce glacial phosphoric acid in 3 fluid ounces distilled water; add 40 grains nitric acid, boil to a syrupy liquid, free from tho odor of nitric acid, add distilled water to make up to 121/2 fluid ounces, and filter.

3925. Tests for the Purity of Phosphoric Acid

3925.    Tests for the Purity of Phosphoric Acid. The U. S. Pharmacopoeia directs that an aqueous solution of the acid should yield no precipitate with sulphuretted hydrogen, showing the absence of metals; it should cause a white precipitate with chloride of barium, soluble in excess of acid; and, with an excess of ammonia, should cause only a slight turbidness, proving the almost total absence of earthy salts. If the presence of arsenic is denoted by the tests for that metal, it may be separated by boiling with muriatic acid, so as to convert tho arsenic into a volatile chloride, which would escape with vapors of the muriatic acid.

3926. Test for the Presence of Phosphoric Acid

3926.    Test for the Presence of Phosphoric Acid. Hydrochloric acid is added to the solution to acid reaction, and afterwards 1 or 2 drops of a concentrated solution of ses-quichloride of iron; a solution of acetate of potassa is next added in excess, when a floc-culent white precipitate (sesqui-phosphate of iron) will bo found if phosphoric acid was present in any form or combination in the original liquor. Arsenious acid, if present, should be removed by sulphuretted hydrogen before applying the test. (Cooley.)

3927. Phosphorous Acid

3927.   Phosphorous Acid. This is prepared by burning phosphorus under a bell-glass with a very limited supply of air. White and pulverulent. It is a powerful deoxidizing agent. With the bases it unites to form phosphites.

3928. Hypophosphoric Acid

3928. Hypophosphoric Acid. A name erroneously given by M. Dulong to a mixture of phosphoric and phosphorous acids. (Cooley.)