Packaging and storage—
Preserve in tight containers.
Identification—
It responds to the
Identification test under
Bentonite.
Viscosity—
After determining the
Loss on drying, weigh a quantity of Purified Bentonite test specimen equivalent to 25.0 g on the dried basis. Over a period of a few seconds, transfer the undried test specimen to a suitable 1-L blender jar containing an amount of water, maintained at a temperature of 25 ± 2
, that is sufficient to produce a mixture weighing 500 g. Blend for 3 minutes, accurately timed, at 14,000 to 15,000 rpm (high speed).
[NOTE—Heat generated during blending causes a temperature rise to above 30
.
] Transfer the contents of the blender to a 600-mL beaker, allow to stand for 5 minutes, and adjust, if necessary, to a temperature of 33 ± 3
. Using a suitable rotational viscosimeter equipped with a spindle having a cylinder 1.87 cm in diameter and 0.69 cm high attached to a shaft 0.32 cm in diameter, the distance from the top of the cylinder to the lower tip of the shaft being 2.54 cm, and the immersion depth being 5.00 cm (No. 2 spindle), operate the viscosimeter at 60 rpm for 6 minutes, accurately timed, and record the scale reading: the viscosity is between 40 centipoises and 200 centipoises.
Microbial limits 
61
—
Its total aerobic microbial count does not exceed 1000 cfu per g, and it meets the requirements of the test for absence of
Escherichia coli.
pH 791:
between 9.0 and 10.0, in a suspension (5 in 100) in water.
Acid demand—
After determining the Loss on drying, weigh a quantity of Purified Bentonite equivalent to 5.00 g, and disperse in 500 mL of water with the aid of a suitable blender fitted with a 1-L jar. Using a stopwatch, designate zero time. With constant mixing, add 3.0-mL portions of 0.100 N hydrochloric acid at 5, 65, 125, 185, 245, 305, 365, 425, 485, 545, 605, 665, and 725 seconds, and add a 1.0-mL portion at 785 seconds. Determine the pH potentiometrically at 840 seconds: the pH is not more than 4.0.
Loss on drying 731—
Dry it at 110
to constant weight: it loses not more than 8.0% of its weight.
Arsenic, Method I 211—
Prepare the
Test Preparation as follows. Transfer 13.3 g to a 250-mL beaker containing 100 mL of dilute hydrochloric acid (1 in 25), mix, cover with a watch glass, and boil gently, with occasional stirring, for 15 minutes without allowing excessive foaming. Allow the insoluble material to settle, and decant the hot supernatant through a rapid-flow filter paper into a 200-mL volumetric flask, retaining as much sediment as possible in the beaker. Add 25 mL of hot dilute hydrochloric acid (1 in 25) to the residue in the beaker, stir, heat to boiling, allow the insoluble material to settle, and decant the supernatant through the filter into the 200-mL volumetric flask. Repeat the extraction with four additional 25-mL portions of hot dilute hydrochloric acid (1 in 25), decanting each hot supernatant through the filter into the volumetric flask. At the last extraction, transfer as much of the insoluble material as possible onto the filter. Cool the combined filtrates to room temperature, add dilute hydrochloric acid (1 in 25) to volume, and mix.
Procedure—
Use a 25-mL aliquot of Test Preparation for the Procedure. The absorbance due to any red color from the Test Preparation does not exceed that produced by 5.0 mL of Standard Preparation (5 µg of As) when treated with the same quantities of the same reagents and in the same manner. The limit is 3 ppm.
Lead—
[NOTE—The
Standard preparation and the
Test preparation may be modified, if necessary, to obtain solutions of suitable concentrations, adaptable to the linear or working range of the instrument.
]
Standard preparation—
On the day of use, dilute 3.0 mL of
Lead Nitrate Stock Solution (see
Heavy Metals 231) with water to 100 mL. Each mL of the
Standard preparation contains the equivalent of 3 µg of lead.
Test preparation—
Transfer 10.0 g of Purified Bentonite to a 250-mL beaker containing 100 mL of dilute hydrochloric acid (1 in 25), stir, cover with a watch glass, and boil for 15 minutes. Cool to room temperature, and allow the insoluble matter to settle. Decant the supernatant through a rapid-flow filter paper into a 400-mL beaker. Add 25 mL of hot water to the insoluble matter in the 250-mL beaker, stir, allow the insoluble matter to settle, and decant the supernatant through the filter into the 400-mL beaker. Repeat the extraction with two additional 25-mL portions of water, decanting each supernatant portion through the filter into the 400-mL beaker. Wash the filter with 25 mL of hot water, collecting this filtrate in the 400-mL beaker. Concentrate the combined extracts by gentle boiling to approximately 20 mL. If a precipitate appears, add 2 to 3 drops of nitric acid, heat to boiling, and cool to room temperature. Filter the concentrated extracts through a rapid-flow filter paper into a 50-mL volumetric flask. Transfer the remaining contents of the 400-mL beaker through the filter paper and into the flask with water. Dilute with water to volume, and mix.
Procedure—
Determine the absorbances of the Test preparation and the Standard preparation at 284 nm in a suitable atomic absorption spectrophotometer equipped with a lead hollow-cathode lamp, deuterium arc background correction, and a single-slot burner, using an oxidizing flame of air and acetylene. The absorbance of the Test preparation is not greater than that of the Standard preparation (0.0015%).
Change to read:
Assay for aluminum and magnesium content—
[NOTE—The
Standard preparations and
Assay preparations may be diluted quantitatively with water, if necessary, to obtain solutions of suitable concentrations, adaptable to the linear or working range of the instrument.
]
Lanthanum solution—
Stir 88.30 g of lanthanum chloride (LaCl3) with 500 mL of 6 N hydrochloric acid until solution is complete, transfer with the aid of water to a 1000-mL volumetric flask, and dilute with water to volume.
Test preparation—
Transfer 0.200 g of Purified Bentonite to a 25-mL platinum crucible containing 1.0 g of lithium metaborate, and mix. Using a muffle furnace or a suitable burner, heat slowly at first, and ignite at 1000
to 1200
for 15 minutes. Cool, place the crucible in a 100-mL beaker containing 25 mL of dilute nitric acid (1 in 20), and add 50 mL of dilute nitric acid, filling and submerging the upright crucible. Place a polyfluorocarbon-coated magnetic stirring bar into the crucible, and stir gently with a magnetic stirrer until dissolved. Pour the contents into a 250-mL beaker, and remove the crucible. Warm the solution, and transfer through a rapid-flow filter paper with the aid of water into a 200-mL volumetric flask, dilute with water to volume, and mix.
Aluminum standard stock preparation—
Dissolve 1.000 g of aluminum in a mixture of 10 mL of hydrochloric acid and 10 mL of water by gentle heating. Transfer the solution to a 1000-mL volumetric flask, dilute with water to volume, and mix. This solution contains the equivalent of 1 mg of aluminum per mL.
Aluminum standard preparations—
Transfer 2-, 5-, and 10-mL aliquots of the Aluminum standard stock preparation to separate 100-mL volumetric flasks containing 200 mg of sodium chloride, dilute each with water to volume, and mix.
Aluminum assay preparation—
Pipet 20 mL of the Test preparation into a 100-mL volumetric flask. Add 20 mL of a solution of sodium chloride (1 in 100), dilute with water to volume, and mix.
Procedure for aluminum—
In a suitable atomic absorption spectrophotometer equipped with an aluminum hollow-cathode lamp and a single-slot burner, using an oxidizing air–acetylene–nitrous oxide flame, determine the absorbances of the Aluminum assay preparation and each of the Aluminum standard preparations at 309 nm. From a linear regression equation calculated from the absorbances and concentrations of the Aluminum standard preparations, determine the aluminum content of the Purified Bentonite.
Magnesium standard stock preparation—
Place 1.000 g of magnesium in a 250-mL beaker containing 20 mL of water, and carefully add 20 mL of hydrochloric acid, warming, if necessary, to complete the reaction. Transfer the solution to a 1000-mL volumetric flask, dilute with water to volume, and mix. This solution contains the equivalent of 1 mg of magnesium per mL.
Transfer 10.0 mL of this solution to a 1000-mL volumetric flask, dilute with water to volume, and mix.
NF24
Magnesium standard preparations—
Transfer 5-, 10-, 15-, and 20-mL aliquots of the Magnesium standard stock preparation to separate 100-mL volumetric flasks. To each flask add 20.0 mL of Lanthanum solution, dilute with water to volume, and mix.
Magnesium assay preparation—
Transfer a 25-mL aliquot of the Test preparation to a 50-mL volumetric flask, dilute with water to volume, and mix. Transfer a 5.0-mL aliquot of this dilution to a 100-mL volumetric flask, add 20.0 mL of Lanthanum solution, dilute with water to volume, and mix.
Procedure for magnesium—
In a suitable atomic absorption spectrophotometer equipped with a magnesium hollow-cathode lamp and a single-slot burner, using a reducing acetylene–air flame, determine the absorbances of the Magnesium assay preparation and each of the Magnesium standard preparations at 285 nm. From a linear regression equation calculated from the absorbances and concentrations of the Magnesium standard preparations, determine the magnesium content of the Purified Bentonite: the ratio of the aluminum content to the magnesium content is between 3.5 and 5.5.
