Carbonic acid, magnesium salt, basic; or, Carbonic acid, magnesium salt (1:1), hydrate
Magnesium carbonate, basic; or, Magnesium carbonate (1:1) hydrate
Packaging and storage
Preserve in well-closed containers.
When treated with 3 N hydrochloric acid, it dissolves with effervescence, and the resulting solution responds to the tests for Magnesium 191
Mix 2.0 g with 100 mL of a mixture of equal volumes of n
-propyl alcohol and water. Heat the mixture to the boiling point with constant stirring, cool to room temperature, dilute with water to 100 mL, and filter. Evaporate 50 mL of the filtrate on a steam bath to dryness, and dry at 105
for 1 hour: the weight of the residue does not exceed 10 mg (1.0%).
Mix 5.0 g with 75 mL of water, add hydrochloric acid in small portions, with agitation, until no more of the magnesium carbonate dissolves, and boil for 5 minutes. If an insoluble residue remains, filter, wash well with water until the last washing is free from chloride, and ignite: the weight of the ignited residue does not exceed 2.5 mg (0.05%).
Arsenic, Method I 211
Prepare the Test Preparation
by dissolving 750 mg in 25 mL of 3 N hydrochloric acid. The limit is 4 ppm.
Limit of calcium
Dilute hydrochloric acid
Dilute 100 mL of hydrochloric acid with water to 1000 mL.
To 58.65 g of lanthanum oxide add 400 mL of water, and add, gradually with stirring, 250 mL of hydrochloric acid. Stir until dissolved, dilute with water to 1000 mL, and mix.
Transfer 249.7 mg of calcium carbonate, previously dried at 300
for 3 hours and cooled in a desiccator for 2 hours, to a 100-mL volumetric flask, dissolve in a minimum amount of hydrochloric acid, dilute with water to volume, and mix. Transfer 5.0, 10.0, and 15.0 mL of this stock solution to separate 1000-mL volumetric flasks, each containing 20 mL of Lanthanum solution
and 40 mL of Dilute hydrochloric acid
, add water to volume, and mix. These Standard preparations
contain 5.0, 10.0, and 15.0 µg of calcium in each mL, respectively.
Transfer 4 mL of Lanthanum solution
and 10 mL of Dilute hydrochloric acid
to a 200-mL volumetric flask, dilute with water to volume, and mix.
Transfer 250 mg of Magnesium Carbonate to a beaker, add 30 mL of Dilute hydrochloric acid
, and stir until dissolved, heating if necessary. Transfer the solution so obtained to a 200-mL volumetric flask containing 4 mL of Lanthanum solution
, dilute with water to volume, and mix.
Concomitantly determine the absorbances of the Standard preparations
and the Test preparation
at the calcium emission line at 422.7 nm with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering 851
) equipped with a calcium hollow-cathode lamp and an airacetylene flame, using the Blank solution
as the blank. Plot the absorbances of the Standard preparations
versus their concentrations of calcium, in µg per mL, and draw a straight line through the three points. From the line so obtained and the absorbance of the Test preparation,
determine the concentration, in µg per mL, of calcium in the Test preparation
. Calculate the percentage of calcium in the specimen by multiplying this value by 0.08: the limit is 0.45%.
Heavy metals, Method I 231
Dissolve 0.67 g in 10 mL of 3 N hydrochloric acid in a suitable crucible, and evaporate the solution on a steam bath to dryness. Ignite at 550 ± 25
until all carbonaceous material is consumed. Dissolve the residue in 15 mL of water and 5 mL of hydrochloric acid, and evaporate to dryness. Toward the end of the evaporation, stir frequently to disintegrate the residue so that finally a dry powder is obtained. Dissolve the residue in 20 mL of water, and evaporate in the same manner as before to dryness. Redissolve the residue in 20 mL of water, filter, if necessary, and add to the filtrate 2 mL of 1 N acetic acid and water to make 25 mL: the limit is 0.003%.
Boil 50 mg with 5 mL of 2 N nitric acid for 1 minute. Cool, dilute with water to 45 mL, add 2 mL of hydrochloric acid, and mix: the limit is 0.02%.
Dissolve about 1 g of Magnesium Carbonate, accurately weighed, in 30.0 mL of 1 N sulfuric acid VS, add methyl orange TS
, and titrate the excess acid with 1 N sodium hydroxide VS. From the volume of 1 N sulfuric acid consumed, deduct the volume of 1 N sulfuric acid corresponding to the content of calcium in the weight of Magnesium Carbonate taken for the assay. The difference is the volume of 1 N sulfuric acid equivalent to the magnesium oxide present. Each mL of 1 N sulfuric acid is equivalent to 20.15 mg of MgO and to 20.04 mg of Ca.