Packaging and storage—
Preserve in well-closed containers.
Identification—
A:
Dissolve about 200 mg in 10 mL of 2 N nitric acid, and add, dropwise, ammonium molybdate TS: a greenish yellow precipitate of ammonium phosphomolybdate is formed and it is soluble in 6 N ammonium hydroxide.
B:
Dissolve 0.1 g in 0.7 mL of 1 N acetic acid and 20 mL of water. Add 1 mL of
ferric chloride TS, allow to stand for 5 minutes, and filter: 5 mL of the filtrate responds to the test for
Magnesium 
191
.
Loss on ignition 733—
Ignite it at 425
to constant weight: it loses between 20.0% and 27.0% of its weight.
Acid-insoluble substances—
If an insoluble residue remains in the test for Carbonate, filter the solution, wash well with hot water until the last washing is free from chloride, and ignite the residue: the weight of the residue does not exceed 4 mg (0.2%).
Soluble substances—
Digest 2.0 g with 100 mL of water on a steam bath for 30 minutes, cool, add sufficient water to restore the original volume, mix, and filter. Evaporate 50 mL of the filtrate to dryness, and ignite gently to constant weight: the weight of the residue does not exceed 15 mg (1.5%).
Carbonate—
Mix 2.0 g with 20 mL of water, and add hydrochloric acid, dropwise, to effect solution: no effervescence occurs when the acid is added.
Chloride 221—
Dissolve 0.50 g in 50 mL of 2 N nitric acid, and add 1 mL of
silver nitrate TS: the turbidity does not exceed that produced by 1.0 mL of 0.020 N hydrochloric acid (0.14%).
Limit of nitrate—
Mix 0.20 g with 5 mL of water, and add just sufficient hydrochloric acid to effect solution. Dilute with water to 10 mL, add 0.1 mL of indigo carmine TS, then add, with stirring, 10 mL of sulfuric acid: the blue color persists for not less than 5 minutes.
Sulfate 221—
Dissolve 0.50 g in the smallest possible amount of 3 N hydrochloric acid, dilute with water to 48 mL, and add 2 mL of
barium chloride TS: the turbidity does not exceed that produced by 3.0 mL of 0.020 N sulfuric acid (0.6%).
Arsenic, Method I 211—
Prepare a
Test Preparation by dissolving 1.0 g in just sufficient 3 N hydrochloric acid (about 9 mL) to dissolve the specimen. The limit is 3 ppm.
Barium—
Mix 2.0 g with 40 mL of water, heat, add hydrochloric acid, dropwise, to effect solution, and then add 1 mL of acid in excess. Cool, dilute with water to 50 mL, and filter. To 5 mL of the filtrate add 1 mL of
potassium sulfate TS: no turbidity is produced within 15 minutes.
Calcium—
Mix 0.50 g with 15 mL of water, heat, and add sufficient hydrochloric acid, in small portions, to effect solution. Cool, add 6 N ammonium hydroxide, in small portions, to produce a slight permanent precipitate, then add 2 mL of 6 N acetic acid. Dilute with water to 25 mL, and filter. To 10 mL of the filtrate add 2 mL of
ammonium oxalate TS: not more than a slight turbidity is produced within 5 minutes.
Dibasic salt and magnesium oxide—
Ignite about 2.5 g to constant weight. Weigh accurately about 2 g of ignited salt, and dissolve it by warming with 50.0 mL of 1 N hydrochloric acid VS. Cool, add 1 or 2 drops of
methyl orange TS, and slowly titrate the excess 1 N hydrochloric acid VS with 1 N sodium hydroxide VS to a yellow color, vigorously shaking the mixture during the titration. Between 14.8 and 15.4 mL of 1 N hydrochloric acid is consumed for each g of the ignited salt.
Lead 251—
Prepare a
Test Preparation by dissolving 1.0 g in 20 mL of 3 N hydrochloric acid, evaporating on a steam bath to about 10 mL, diluting with water to about 20 mL, and cooling. Use 5 mL of
Diluted Standard Lead Solution (5 µg of Pb) for the test: the limit is 5 ppm.
Heavy metals, Method I 231—
Dissolve 0.67 g in 4.5 mL of 3 N hydrochloric acid, and dilute with water to 25 mL: the limit is 0.003%.
Assay—
Weigh accurately about 200 mg of Magnesium Phosphate, previously ignited at 425
to constant weight, and dissolve in a mixture of 25 mL of water and 10 mL of 2 N nitric acid. Filter, if necessary, wash any precipitate, add sufficient 6 N ammonium hydroxide to the filtrate to produce a slight precipitate, and then dissolve the precipitate by the addition of 1 mL of 2 N nitric acid. Adjust the temperature to about 50
, add 75 mL of
ammonium molybdate TS, and maintain the temperature at about 50
for 30 minutes, stirring occasionally. Wash the precipitate once or twice with water by decantation, using from 30 to 40 mL each time and passing the washings through a filter. Transfer the precipitate to the filter, and wash with potassium nitrate solution (1 in 100) until the last washing is not acid to litmus. Transfer the precipitate and filter to the precipitation vessel, add 50 mL of water and 40.0 mL of 1 N sodium hydroxide VS, agitate until the precipitate is dissolved, add
phenolphthalein TS, and then titrate the excess alkali with 1 N sulfuric acid VS. Each mL of 1 N sodium hydroxide is equivalent to 5.716 mg of Mg
3(PO
4)
2.
