Abstract: To efficiently produce a fine powder of silicon carbide or silicon nitride useful as engineering ceramics material, a granulated or pelleted mixture of silica powder and carbon powder is put into a plurality of containers each of which has ventilating means such as vent holes, and the containers are introduced into an upper section of a vertically extending heating zone in turn. In the heating zone a nonoxidizing gas atmosphere, which is a nitriding gas atmosphere when producing silicon nitride, is maintained at a temperature of 1400.degree.-2100.degree. C. The granulated or pelleted mixture in the containers undergoes reaction while each container is downwardly moved in the heating zone, either continuously or stepwise, so as to stay in the heating zone for a predetermined length of time.

Abstract: The compound thiohumic acid resulting from replacing at least a part of the carboxyl groups in humic acid by thiocarboxyl groups, i.e., ##EQU1## as well as a heavy metal adsorbent containing thiohumic acid as its active ingredient. This new compound is obtained by treating humic acid with a halogenating agent to form humic acid halide and treating such halide with a thiolating agent.