ASTM D1832 Standard Test Method for Peroxide Number of Petroleum Wax
7. Procedure
7.1 Melt a representative portion of wax sample on a water bath or in an oven. Do not heat above 150°F (65.6°C) or more than 20°F (11°C) above the congealing point as excessive heating may change the peroxide content.
7.2 Weigh, to the nearest 1 mg, 1 more or less 0.2 g of the wax into a weighed iodine flask. To the flask, add 25 mL of CCl4 and quickly dissolve the sample, in an atmosphere of carbon dioxide (CO2) on a steam bath. (Precaution, a hood is advised). Do not heat above 150°F (65.5°C) unless necessary to dissolve the sample. With the flask still on the steam bath, bubble a vigorous flow of CO2 through the solution for 1 min. Reduce the flow of CO2 so that the rate is 1 bubble per second, and add 20 mL of acetic acid solution that has been warmed sufficiently to prevent precipitation of the wax. Remove the flask from the steam bath, still continuing the flow of CO2. Add 2 mL of KI solution and swirl vigorously for exactly 30 s. With the CO2 bubbling through the mixture, set the flask aside and let stand for 5 min more or less 3 s. Stop the flow of gas, add 100 mL of water, and mix thoroughly for 1 min. Titrate with 0.005 N Na2S2O3 solution to a light yellow color. Add 5 mL of starch solution and continue the titration until 1 drop of the thiosulfate solution causes the blue color to disappear and not reappear for at least 30 s.
7.3 Make a blank determination on the reagents. Proceed as directed in 7.1 and 7.2 except to omit the sample.
8. Calculation
8.1 Calculate the peroxide number as milliequivalents per 1000 g of sample, as follows:
Peroxide number = [(A - B)N x 1000]/S
where:
A = millilitres of Na2S2O3 solution required for titration of the sample,
B = millilitres of Na2S2O3 solution required for titration of the blank,
N = normality of the Na2S2O3 solution, and
S = grams of sample used.
