7. Procedure
7.1 Heat and adjust the temperature of the uncovered, empty furnace to 950 more or less 20°C. Clean the platinum crucible and cover, place them in the crucible holder, and suspend them in the temperature-adjusted furnace for at least 5 min. Remove the holder with contents from the furnace and cool the crucible and cover to about 150°C, being careful not to contaminate the bottom of the crucible. Then place the crucible with cover in a desiccator until they have cooled to room temperature and weigh (P). Record all weighings to the nearest 1 mg.
7.2 If the coke residue determination is made shortly after completion of the distillation test (AWPA Standard A1, Section 2) transfer a 1 more or less 0.1-g portion of the well-stirred distillation residue at 355°C directly from the distillation flask to the tared platinum crucible. Since the tare weight (P) includes the weight of the platinum cover, the cover must also be on the balance pan during this operation.
7.3 If the residue is in a storage container, carefully heat the container and contents in a water bath or on a steam bath until sufficiently liquid for pouring. Then transfer a 1 more or less 0.1-g portion to the platinum crucible as directed in the preceding paragraph. After the desired amount of distillation residue has been transferred to the platinum crucible, insert its cover firmly and weigh (Q). Weight of sample of distillation residue taken for coking: Q - P = W.
7.4 Place the covered crucible with sample in the crucible holder and suspend in the furnace at 950 more or less 20°C for exactly 7 min. At the end of this period immediately remove the crucible holder from the furnace, cool the crucible and contents to about 150°C as before, and transfer to a desiccator. When at room temperature, weigh ( R). Weight of coke in sample of distillation residue: R - P = A.
7.5 If a gas burner of the bunsen or Meker type is used (Note 1), it shall have a free flame 200 mm in height. The crucible shall sit in a Nichrome triangle with approximately two thirds of its height below the triangle and with the bottom of the crucible 60 to 80 mm above the top of the burner. Assurance of the desired temperature of test may be indicated by the fusion of crystals of potassium chromate in the crucible when exposed in the specified position for the test. Expose the crucible and contents to the full flame of the burner for exactly 7 min (see 6). Then transfer to a desiccator, cool, and weigh the crucible to the nearest 1 mg.
8. Calculation
8.1 Calculate the percentage of coke residue on the basis of original oil (creosote-coal tar solution) as follows:
where:
W = weight of sample of distillation residue taken for coking,
A = weight of coke in sample of distillation residue, and
B = percentage of distillation residue at 355°C of original oil (creosote-coal tar solution).
Example: W = 1.100 g; A = 0.308 g; B = 29.0 %
