硝酸钍容量法测氟的指示剂前人已进行过大量的试验研究,被试验过的指示剂有数百个之多,一般认为茜素红S最好,但终点仍不够灵敏,后有的改用茜素红S与次甲基蓝混和指示剂,但终点不易观察。我们在测定氟硅酸制酸工序下脚料中的氟化钙时,采用茜素红S与孔雀绿混和指示剂,终点由暗灰色至紫红色,非常灵敏,极易观察。准确称取分析样0.5克,在高氯酸介质中于130—140℃用蒸馏法将氟蒸出.以2％氢氧化钠溶液吸收。吸收液移入500毫升容量瓶中,稀释至刻度,分取50毫升于100毫升烧杯中,滴加 Nitric acid thorium volumetric method of measuring fluorine indicator has been carried out before a large number of experimental studies have been tested hundreds of indicators, generally believed that the best alizarin red S, but the end is still not sensitive enough, after some Use alizarin red S and methylene blue mixed indicator, but the end is not easy to observe. When we measured calcium fluoride in the flotation process of fluorosilicic acid, we used alizarin red S mixed with malachite green indicator, the end point from dark gray to purple, very sensitive, easy to observe. Accurately weighed 0.5 grams of analytical samples, in the perchloric acid medium at 130-140 ° C by distillation of the fluorine is distilled off with 2% sodium hydroxide solution absorption. Absorbed liquid into 500 ml volumetric flask, diluted to the mark, dispensed 50 ml in 100 ml beaker, dropping