ASTM D156 for Saybolt color of petroleum products (Saybolt Chromometer method)
6. Apparatus
6.1 The Saybolt chromometer consisting of sample and standard tubes, optical system, light source, and color standards, is described in detail in Annex A1 and illustrated in Fig. A1.1.
7. Standardization of Apparatus
7.1 Remove the glass disk from the bottom of the oil tube. Clean the disk, oil tube, and plain tube. When deposits are not removable by wiping or solvent rinsing, wash with soap and water. After cleaning, rinse with distilled or deionized water and with acetone or some other suitable solvent, and dry. Assemble the oil tube, and position the tubes in the instrument.
7.2 Using the specified light source and illumination, observe the comparative light intensity of the two halves of the optical field, with both tubes empty, and with the 12-mm diaphragm removed from under the plain tube. The intensity of light observed in each half of the optical field must be the same. Adjustment in the position of the light source may be necessary to achieve this match.
NOTE 3 - On some instruments, removal of the 12–mm diaphragm can prevent the assembly from seating against the base (about a 1/4 in. gap), which can let a lot of stray light in that may affect the light intensity when trying to compare the two halves of the optical field in 7.2. If this occurs, follow the procedure in 7.3 (where the 12–mm diaphragm has been reattached) as the basis to ensure the light source has been properly set to provide the same light intensity in both halves of the optical field.
7.3 Replace the 12-mm diaphragm under the plain tube, and fill the oil tube to the 20 in. (508-mm) mark with distilled or deionized water. The intensity of the light observed in each half of the optical field must be the same, for the instrument to be judged satisfactory for use. The optical properties of glass, from different batches, can vary significantly and it is recommended that only matched tubes, such as described in the Appendix, be used in this test. When a tube is broken, replace both tubes with a matched pair of tubes.
8. Sampling
8.1 Samples shall be taken in accordance with the instructions in Practice D4057.
9. Preparation of Test Specimen
9.1 When the sample is turbid, filter through a sufficient number of qualitative filter papers until it is clear.
9.2 When preparing petroleum wax for testing do not heat excessively, because oxidation can occur, with consequent discoloration of the test specimen.
