ASTM D848 Test Method for Acid Wash Color of Industrial Aromatic Hydrocarbons
12. Procedure
12.1 Fill a clean, dry test container to the 7-mL mark with the acid of the strength specified in Table 1 for the type of sample to be tested (Note 3). Add sufficient sample to bring the total volume to the 28-mL mark (Note 4). Insert the stopper, hold a finger over the stopper, and give vigorous shakes with a stroke of 13 to 25 cm (5 to 10 in.), shaking for a total of 150 cycles over a period of 40 to 50 s, that is at a rate of 3 to 3.75 cycles/s. (Use of an automatic shaker is allowed given it can be shown to produce comparable results to the manual technique.)
NOTE 3 - Warning: Concentrated sulfuric acid will cause severe burns on contact with the skin. As a precaution the test container should be wrapped in a towel or enclosed in a plastic bag during the shaking period. The test should be performed using appropriate personal protective equipment.
NOTE 4 - If the room temperature is above 85°F, maintain the acid, sample, and reference color standards at a temperature between 77 and 85°F (25 and 29°C) through the test, and insulate the test container in some convenient way, such as wrapping with a cloth, during the shaking period.
12.2 Allow the container to stand, protected from direct sunlight, for the period of time shown in Table 1. Without further delay, invert the container gently once or twice to obtain a uniform color in the acid layer, and compare the color of the acid layer with that of the standards (11.3). Make the comparison against a white background or against daylight, using transmitted light (Note 5). When testing samples in Group 1 (Table 1), observe the color of the oil layer as well as that of the acid layer. Standards used shall include standards one number above and one number below the sample, except for the samples reading 0 or 14.
NOTE 5 - Agreement of results may be improved by using a color comparator of a suitable type for observing the color of the acid layer in comparison with the reference standard color solution.
12.3 Designate the color of the acid layer by the number of the nearest matching standard, following the number with a plus or minus sign if the sample is darker or lighter, respectively, than the standard. Disregard any difference in hue and determine only whether the color of the acid layer is darker or lighter than the color of the reference standard to which the sample most nearly corresponds. If the hue of the acid color is different from the hue of the reference color standard, record the color number followed by (X). Thus "No. 4 - (X)" means that the acid wash test color is slightly lighter than No. 4 color standard and that the hue of the No. 4 color standard is not the same as the hue of the acid layer.
NOTE 6 - Dispose of the acid and hydrocarbon properly before cleaning the container. Clean the test container by flushing thoroughly with water (tap grade or better) until traces of acid have been removed. The test container must be completely dry before being placed back into use. Suitable solvents, that will not impact the results, may be used after the water rinse step to assist in drying the container.
