This test is used to detect the presence of unsaturated (olefinic) contaminants in aromatic hydrocarbons, typically BTX, following reaction with concentrated sulphuric acid.

Any colour that develops in the acid layer provides an indication of impurities, which if sulphonated, might result in the discolouration of the aromatic hydrocarbon.

PROCEDURE

A clean and dry glass container (as specified in ASTM D 848) should be rinsed and then filled to the 7-ml mark with sulphuric acid of the strength specified in Table 1 for the type of sample to be tested. Thereafter the test sample material (e.g. wall wash sample) will be added to the container to bring the total volume to the 28 ml mark.

Stopper the container and WITH CAUTION, vigorously shake the mixture for about 40-50 seconds.

Allow the container to stand, protected from direct sunlight, for the period of time shown in table below.

Without further delay compare the colour of the acid layer with the respective colour standards (as specified in ASTM D 848). For testing of chemicals in Group 1 in Table 1, the colour of the acid layer as well as the colour of the oil layer should be observed and recorded.

RESULTS

Group 1 samples pass the test only when the oil layer shows no change in colour and when the acid layer is not darker than the specified colour standard. A cloudiness or haze in the oil layer will not be interpreted as a change in colour.

Group 2 and 3 samples will pass the test when the acid layer is not darker than the specified colour standard. The colour of the oil layer can be disregarded.

Table Acid Strengths and Standing Times

Groups	Sample	Sulfuric Acid Strength	Standing Time
Group 1	Benzene Toluene Xylene (nitration grade) Xylene, 5°  Xylene 10°  Any other more highly refined products.	96	15
Group 2	Xylene (industrial grade) Refined Solvent Naphtha	96	5
Group 3	Hi-flash solvent Heavy solvent Naphtha	78	5