Abstract
In the determination of phosphorous in ferromolybdenum, a modified molybdenum blue method which used molybdenum in the sample as the reagent was tried. For this purpose, analytical conditions of the molybdenum blue method were experimented, and then the determination method was established.
The procedure which used 4∼5 mL of hydrazine sulfate (0.15%) as the reducing agent and digested in boiling water for 20 min was fitted for the reducing condition of phosphomolybdic acid. The relation between sulfuric acid (N) and molybdenum (mg) was as follows:
H2SO4(N)=K ×Mo (mg)^K’, K=a ∼b.
K and K′ are constants which depend the reducing condition. The range (a∼b) of K shows the range of molybdenum in which a constant absorption takes place at a constant acid concentration. In the reducing condition of this experiment, K was 0.0234∼0.0395 and K′ was 0.78. For example, if 7 mL of 10N sulfuric acid and 90 mL of the total solution, the absorption was constant between 50 mg and 85 mg molybdenum: 50∼85% ferromolybdenum can be determined when 0.1 g of the sample is taken. The amounts of the solution at the digested time scarecely effected. After the sample was dissolved, the acid concentration was adjusted by adding a small amount of sulfuric acid and evaporated to dryness. Then ferric ion was reduced with sodium bisulfide at the acid concentration higher than that of the color developed time in order to prevent the reduction of molybdenum itself. Even in case ferric ion and phosphomolydic acid were reduced at the same time with hydrazine sulfate, satisfactory results were obtained.
