ASTM D168 Standard Test Method for Coke Residue of Creosote
5. Apparatus
5.1 Crucible and Cover - Platinum crucible and cover with dimensions as shown in Fig. 1. The cover shall be tightly fitting, shall have a depth of between 10.0 and 10.2 mm, and shall have a hole 2.0 mm in diameter at its center. The crucible without cover shall have a capacity of 25 to 30 mL. It shall have an outside diameter at the top of 34 to 35 mm, and outside diameter at the bottom of 19 to 21 mm, and a height of 40 to 45 mm. The weight of crucible with cover shall be 25 to 35 g.
5.2 Crucible Holder - The crucible holder shall be made from No. 20 Nichrome wire and a brass ring as shown in Fig. 2. The holder serves as a support for the platinum crucible during the coking operation.
5.3 Furnace - A vertical electric tube furnace having a heating chamber 1 1/2 in. (38 mm) in diameter, by 6 in. (150 mm) in depth. The power input shall be 300 to 400 W at 115 V. The furnace shall be equipped with a suitable rheostat or variable transformer and pyrometer, for control at 950 more or less 20°C. A thermocouple shall be installed through a central hole in the bottom of the furnace, and sealed in place so that its junction is located 2 to 5 mm below the eventual position of the bottom of the platinum crucible.
5.4 Gas Burner - A gas burner of the bunsen or Meker type.
NOTE 1 - In case of dispute, the tube furnace method shall be considered the standard method.
6. Precautions
6.1 Conduct the test in a part of the laboratory free of drafts.
6.2 It is important that the tip of the inner cone of a bunsen burner flame shall be below the bottom of the crucible. The burner should, therefore, be adjusted so that the inner cone is 60 to 70 mm in height. The bottom of the crucible shall be 5 to 10 mm above the tip of the inner cone.
