(4) _Ammonia._—The strong ammonia used should have a specific gravity of about 0.90 and the dilute of 0.96 at 15.5°. (5) _Molybdic Solution._—Dissolve 100 grams of molybdic anhydrid in 400 cubic centimeters of ammonia of 0.96 specific gravity and pour the solution slowly, with constant stirring, into one liter of nitric acid of about 1.20 specific gravity. Heat the mixture to 45° and add one cubic centimeter of a ten per cent solution of sodium phosphate, stir vigorously, and allow to stand in a warm place for eighteen hours. Filter before using. (6) _Add Ammonium Sulfate._—To half a liter of water add 27.5 cubic centimeters of 0.96 ammonia and twenty-four cubic centimeters of strong sulfuric acid, and make the volume one liter with water. (7) _Potassium Permanganate for Titration._—Dissolve four grams of potassium permanganate in two liters of water, heat nearly to boiling for an hour, allow to stand for eighteen hours, and filter on asbestos felt. The solution must not come in contact with rubber or other organic matter. The solution may be standardized with thoroughly air-dried ammonium oxalate in solution with a little dilute sulfuric acid and with ammonium ferrous sulfate partly crystallized in small crystals from a slightly acid solution. The crystals should be well washed and quickly air-dried in a thin layer. The factors 1/1 1/4 2/2 and 1/7 should be used respectively to calculate the iron equivalent. The phosphorus equivalent is obtained by multiplying the iron equivalent by 31 ÷ (36 × 56) = 0.01538. [Illustration: FIGURE 7. JONES’ REDUCTION TUBE.]