Transfer about 5 gm of sample in a dry clean cylinder and observe. It should be white to pale yellow liquid.
Transfer about 1 gm of sample in a dry clean beaker and add about 30 ml of water with continue stirring. It should be soluble. Repeat the test with alcohol and acetone.
Dissolve about I0.0 g of the substance, accurately weighed, in 50 ml of a mixture of equal volumes of alcohol and ether (which has been neutralize d to phenolphthalein with 0.1 N potassium hydroxide) contained in a flask. If the test specimen does not dissolve in the cold solvent, connect the flask with a suitable condenser and warm slowl y, with frequent shaking, until the specimen dissolves. Add 1 ml of phenolphthalein TS, and titrate with 0.1 N potassium hydroxide VS until the solution remains faintly pink after shaking for 30 seconds. Calculate the Acid Value by the formula:
56.11 VX N / W
56.11 is the molecular weight of potassium hydroxide;
V is the volume, in ml;
N is the normality of the potassium hydroxjde solution;
W is the weight, in g, of the sample taken.
In case the substance is a liquid at room temperature, carry out the determination using a bath temperature about 15° below the expected congealing point. When the test specimen has cooled to about 5° above its expected congealing point, adju st the bath to a temperature 7° to 8° below the expected congealing point. Stir the specimen continuously during the remainder of the test by moving the loop up and down between the top and bottom of the specimen, at a regular rate of 20 complete cycles per minute. Congelation frequently may be induced by rubbing the inner walls of the test tube with the Thermometer, or by introducing a small fragment of the previously congealed substance. Pronounced super cooling may cause deviation from the normal pattern of temperature changes. lf the latter occurs, repeat the test, introducing small particles of the material under test in solid form atl O intervals as the temperature approaches the expected congealing point. Record the reading of the test tube thermometer every 30 seconds. Continue stirring only so long as the temperature is gradually falling, stopping when the temperature becomes constant or starts to rise slightly. Continue recording the temperature in the test tube every 30 seconds for at least 3 minutes after the temperature again begins to fall afte r remaining constant. The average of not less than four consecutive readings that lie within a range of 0.2° constitutes the congealing temperature. These readings lie about a point of inflection or a maximum, in the Temperature-time curve, that occurs after the temperature
becomes constant or start to rise and before it again begin to fall. The average to the nearest 0.1° is the congealing temperature.
Weigh accurately about 1.0 gm Test sample. Let its weight be WI. Transfer carefully the test sample into the titration vessel having methanol and close the vessel with cover and press the “start” push button carry out the titration. Record the burette reading (V). Determine the KF factor using water as a reference.
Fx lOOxV /WI
F = water equivalency factor of the Reagent, in mg per ml
V = volume of the KF reagent consumed for the sample in ml. Wl = weight of the sample in mg.
- Residue on ignition:
Ign ite a suitable crucible (for example, silica, plati num, quartz, or porcelain) at 600 ± 50° for 30 minutes, cool the crucible in a desiccator (silica gel or other suitable desiccant), and weigh it accurately. Weigh accurate ly I to 2 g of the substance, or the amount specified in the ind ividual monograph, in the crucible. Moisten the sam ple with a small a mount (usually I ml) of s ul furic acid, then heat gently at a temperature as low as practicable until the sample is thoroughly charred. Cool; then moisten the residue with a small amount (usually 1 ml) of sulfuric acid; heat gently until white fumes are no longer evolved; and ignite at 600 ± 50°, until the residue is completely incine rated. Ensure that flames are not produced at any time during the procedure. Cool the crucible in a desiccator (silica gel or other suitable desiccant), weigh accurately, and calculate the percentage of residue.
Note: Unless otherwise speci fied, if the amount of the residue so obtained
exceeds the limit specified in the individual monograph, repeat the moistening with sulfuric acid, heating and igniting as before, using a 30-minute ignition period, until two consecutive weighings of the residue do not differ by more than
0.5 mg or until the percentage of residue complies with the limit in the individual monograph.
Weight of empty crucible———————— gm
Weight of crucible + sample : — ·——- gm
Weight of only sample :———— gm
After ignition weight of crucible—————– gm
Weight of residue——————————— gm
Weight of residue x 100
Calculation = ————–
Weight of sample
Lead Nitrate Stock Solution: Dissolve 159.8 mg of lead nitrate in 100 ml of water to which has been added 1ml of nitric acid, then dilute with water to 1000ml. Prepare & store this solution in glass containers free from soluble lead salts.
Standard lead Solution: On the day of use, dilute 10.0 ml of lead nitrate stock
solution with water to 100.0ml. Each ml of standa rd lead solution contains the
equivalent of 10µg of lead. A Comparison solution prepared on the basis of 100µl
of standard lead solution per g of substance being tested contains the equivalent of 1
part of lead per million parts of substance being tested.
pH 3.5 acetate buffer: Dissolve 25.0 g of ammonium acetate in 25 ml of water, and add 38 ml of 6N hydrochloric acid. Adjust, if necessary with 6n ammonium hydroxide or 6N hydrochloric acid to a pH of 3.5, dilute with water to 100 ml, and mix.
Standard preparation: into a 50 ml color comparison tube pipette 2 ml of standard lead solution (20 µg of Pb) and dHute with water to 25 ml. Using a pH meter or short range pH indicato r paper as external indicator, adjust with lN acetic acid or 6N ammonium hydroxide to a pH between 3.0 and 4.0, dilute with water to 40 ml, and mix.
Test Preparation: Transfer the weighed quantity about 2 gm of the substance to a suitable crucible, add sufficient sulfuric acid to wet the substance, and carefully ignite at a low temperature until thoroughly charred. (The crucible may be loosely covered with a suitable lid during the charring.) Add to the carbonized mass 2 ml of nitr ic acid and 5 drops of sulfuric acid, and heat cautiously until white fumes no longer are evolved. Ignite, preferably in a muffle furnace, at 500°C to 600°C, until the carbon is completely burned off. Cool, add 4 ml of 6N hydrochloric acid, cover, digest on a steam bath for 15 minutes, uncover, and slo wly evaporate on a steam bath to dryness. Moisten the residue with 1 drop of hydrochloric acid, add IO ml of hot water, and digest for 2 minutes. Add 6N ammonium hydroxide drop wise until the solution is just alkaline to litmus paper, dilute with water to 25 ml, and adjust with lN acetic acid to a pH between 3.0 and 4.0, using short-range pH indicator paper as an external indicator. Filter if necessary, rinse the crucible and the filter with l0 ml of water, combine the filtrate and rinsing in a 50 ml color comparison tube, dilute with water to 40 ml, and mix.
Procedure: To each of the tubes containing the Standard Preparation and the Test Preparation, add 2 ml of pH 3.5 Acetate Buffer, then add 1.2 ml of Thioacetamide glycerin base TS, dilute with water to 50 ml, mix, allow to stand for 2 minutes, and view downward over a white surface
* The color of the solution from the Test Preparation is not darker than that of the solution from the Standard Preparation.