_Reagents._—1. Standard iron solution. Dissolve 0.7 gram of crystallized
ferrous ammonium sulfate in 50 cc. of distilled water to which 20 cc. of
dilute sulfuric acid has been added. Warm the solution slightly and add
potassium permanganate until the iron is completely oxidized. Dilute the
solution to 1 liter. One cc. of the standard solution equals 0.1 mg. Fe.
2. Potassium sulfocyanide solution. Dissolve 20 grams of the salt in 1
liter of distilled water.
3. Dilute hydrochloric acid. One volume of acid (Sp. gr. 1.2) and one
volume of distilled water. This shall be free from nitric acid.
4. N/5 potassium permanganate. Dissolve 6.30 grams of the salt in
distilled water and dilute to 1 liter.