本文于1964年写成,“煤炭学报”拟意刊用,后因学报停刊,文稿失散。该文虽已10余年,其试验方法尚有一定参考价值,现本刊重新发表。 This article was written in 1964. The “Coal Journal” was intended to be published. After the journal was discontinued, the manuscript was separated. Although the article has been for more than 10 years, its test method still has certain reference value. The current publication is now republished.