ASTM D2416 Test Method for Coking Value of Tar and Pitch (Modified Conradson)
6. Bulk Sampling
6.1 Samples from shipments shall be taken in accordance with Practice D140, and shall be free of foreign substances. Thoroughly mix the sample immediately before removing a representative portion for the determination or for dehydration.
7. Dehydration of Sample
7.1 Hard Pitch - If the solid bulk sample contains free water, air-dry a representative portion.
7.2 Soft Pitch - If the presence of water is indicated by surface foam on heating, maintain a representative portion of the bulk sample at a temperature between 125 and 150°C in an open container until the surface is free from foam. Take care not to overheat, and remove heat source immediately when foam subsides.
7.3 Tar - Dehydrate a representative portion of the bulk sample in accordance with Test Method D370, but stop the distillation when the temperature reaches 170°C. Separate any oil from the water that has distilled over (if crystals are present, warm sufficiently to ensure their solution), and thoroughly mix the oil with the residual tar in the still after the latter has cooled to a moderate temperature.
8. Preparation of Working Sample
8.1 Hard Pitch - If the pitch can be crushed at room temperature, prepare a 20-g working sample by suitable crushing, mixing, and quartering of a representative portion of the dry sample. The crushing can be done with a small jaw crusher and a mortar and pestle. No particle in the representative sample should be larger than 5 mm in any dimension. Crush this sample so that all of it will pass the No. 30 (600-µm) sieve but have a minimum of fine particles.
8.2 Soft Pitch - If the pitch is too soft to grind and to sticky to mix, heat a representative portion of the dry sample to the lowest temperature that will permit passage through the No. 30 (600-µm) sieve, taking care to avoid excessive loss of volatile matter. Do not exceed 10 min for this melting period. Pass the heated sample through the No. 30 (600-µm) sieve to remove foreign matter.
8.3 Tar - Heat a representative portion of the dry tar rapidly to the lowest temperature that will permit passage through the No. 30 (600-µm) sieve, then filter through this sieve to remove foreign matter.
8.4 Preservation of Samples - Store samples as large lumps or as solidified melts in closed containers. Do not save crushed samples for future analyses since changes in composition sometimes occur in pulverized pitch.
