Packaging and storage—
Preserve in tight containers,and avoid freezing.
Identification—
A:
Place about 1g in a flask equipped with a stopper and glass tubing,the tip of which is immersed in calcium hydroxide TSin a test tube.Add 5mLof 3Nhydrochloric acid to the flask,and immediately insert the stopper:gas evolves in the flask and a precipitate is formed in the test tube.
B:
The solution remaining in the flask responds to the tests for Aluminum á191ñ.
Microbial limits á61ñ—
Its total aerobic microbial count does not exceed 100cfu per mL,and it meets the requirements of the test for the absence of
Escherichia coli.
Acid-neutralizing capacity á301ñ—
Not less than 65.0%of the expected mEq value,calculated from the results of the
Assay,is obtained.Each mg of Al(OH)
3has an expected acid-neutralizing capacity value of 0.0385mEq.
pHá791ñ:
between 5.5and 8.0,determined potentiometrically.
Chloride—
Transfer an accurately measured quantity of the Gel,equivalent to 0.6g of Al(OH)3,to a porcelain dish.Add 0.1mLof potassium chromate TSand 25mLof water.Stir,and add 0.10Nsilver nitrate until a faint,persistent pink color is obtained:not more than 8.0mLof 0.10Nsilver nitrate is required [4.7%,based on the Al(OH)3content].
Sulfate á221ñ—
Add 5.0mLof 3Nhydrochloric acid to an accurately measured quantity of the Gel,equivalent to 0.3g of Al(OH)
3,and heat to dissolve the specimen under test.Cool,dilute with water to 250mL,and filter if necessary:a 20-mLportion of the filtrate shows no more sulfate than corresponds to 0.20mLof 0.020Nsulfuric acid [0.8%,based on the Al(OH)
3content].
Arsenic,Method Iá211ñ—
Prepare a
Standard Preparationas directed in the test for
Arsenic á211ñ,except to prepare it to contain 5µg of arsenic instead of 3µg.Prepare the
Test Preparationas follows.Dissolve an accurately measured quantity of the Gel,equivalent to 0.5g of Al(OH)
3,in 20mLof 7Nsulfuric acid.The limit is 0.001%,based on the Al(OH)
3content.
Heavy metals á231ñ—
Dissolve an accurately measured quantity of the Gel,equivalent to 0.24g of Al(OH)
3,in 10mLof 3Nhydrochloric acid with the aid of heat,filter,if necessary,and dilute with water to 25mL:the limit is 0.0083%,based on the Al(OH)
3content.
Assay—
Edetate disodium titrant—
Prepare and standardize as directed in the
Assayunder
Ammonium Alum.
Procedure—
Transfer an accurately measured quantity of Gel,equivalent to about 1.5g of Al(OH)3,to a beaker,add 15mLof hydrochloric acid,and heat gently until solution is complete.Cool,transfer to a 500-mLvolumetric flask,dilute with water to volume,and mix.Pipet 20mLof this solution into a 250-mLbeaker,and add,in the order named and with continuous stirring,25.0mLof Edetate disodium titrantand 20mLof acetic acid–ammonium acetate buffer TS,then heat the solution near the boiling point for 5minutes.Cool,and add 50mLof alcohol and 2mLof dithizone TS.Titrate the solution with 0.05Mzinc sulfate VSuntil the color changes from green-violet to rose-pink.Perform a blank determination,substituting 20mLof water for the sample,and make any necessary correction.Each mLof 0.05MEdetate disodium titrantconsumed is equivalent to 3.900mg of Al(OH)3.