ASTM D453 Standard Test Method for Tar Acids in Creosote-Coal Tar Solutions
7. Preparation of Sample
7.1 Warm the sample, if necessary, to dissolve crystalline material before taking portion for analysis. Determine water content of the sample by Test Method D95.
8. Procedure
8.1 Distill 100 g of the sample, weighed to the nearest 0.1 g, to 355°C by the procedure described in Test Method D246, and collect the distillate in a Squibb-type separatory funnel. Add 50 mL of C6H6 to the freshly distilled fraction and extract the resulting solution with three successive 30-mL portions of 20 % NaOH solution. After each portion of caustic solution is placed in the funnel, shake vigorously, allow to settle completely, then draw off the lower layer into the second Squibb separatory funnel before placing the next 30-mL portion in the funnel containing the sample.
8.2 Wash the combined caustic layers in the second separatory funnel with 50 mL of C6•H6. Draw off the washed caustic layer into a 250-mL beaker and heat on a hot plate under an efficient hood until the odor of benzene is no longer detectable. Cool the NaOH solution in a water and ice bath. Then acidify with 40 % H2SO4 solution until the sodium sulfate solution is definitely acid to litmus, taking care to keep the mixture cool at all times.
8.3 Place 65 to 66 mL of C6H4(CH3)2 in the Type II separatory funnel. Submerge the lower portion of the funnel in a water bath at room temperature. After 30 min record the temperature of the bath to the nearest 0.1°C and read the volume of solvent to the nearest 0.1 mL. Pour the sulfate solution with the liberated tar acids through the solvent layer. Draw off the sulfate solution at the bottom of the separatory funnel into the original beaker, washing down the sides of the beaker, and pour it back into the funnel. Repeat this operation until all visible oil is transferred to the separatory funnel. Finally, with all sulfate solution in the funnel, shake well and allow to stand until the layers have separated and no drops of solvent are dispersed in the sulfate solution. Then draw off the sulfate layer slowly and completely, immerse the lower part of the funnel in the water bath, and adjust the temperature to within 0.5°C of the recorded temperature. After 30 min read the volume of the solvent layer. The increase in volume of the solvent is the tar acid content of the sample taken for distillation.
