170 u00b0 c u2192 140 u00b0 c 160 u00b0 c the 2nd section 170 u00b0 c u2192 200 u00b0 c u2192 170 u00b0 190 u00b0 c the 3rd section 200 u00b0 c u2192 230 u00b0 c u2192 200 u00b0 220 u00b0 c the 4th section 230 u00b0 c u2192 260 u00b0 c u2192 230 u00b0 250 u00b0 c the 5th section 260 u00b0 c u2192 290 u00b0 c u2192 260 u00b0 280 u00b0 c the 6th section 290 u00b0 c u2192 320 u00b0 c u2192 290 u00b0 310 u00b0 c ______________________________________ in the case of example 1 30 minutes was required for raising the temperature from minimum temperature to maximum temperature and 5 minutes was required for cooling from the maximum temperature to the minimum temperature in respective sections in comparative example 1 temperature was controlled to a constant temperature in each respective section when infusibilization was performed under the above conditions infusibilization was able to be completed without problems in example 1 after infusibilization bulk of the pitch fibers was reduced to 6 cm in height when infusibilization was performed according to the method of comparative example 1 uncontrollable exothermic reaction took place when the first container moved to the 4th section resulting in ignition and so infusibilization was discontinued coal tar pitch as a raw material was hydrogenated in tetralin in an amount of twice that of the pitch in an autoclave then subjected to filtration and distillation to remove insoluble matters and the solvent and further to heat treatment to obtain an optically anisotropic spinning pitch this pitch contained 97 of optically anisotropic part 91 of benzene insolubles and 32 of quinoline insolubles and had a softening point of 275 u00b0.