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原理硫氰酸锌在含有甲基紫(methylviolet)的溶液中沉淀的时候,假若用透过光或强烈侧面照亮观察,可以看邮颜色由绿变紫。甲基紫的酸性溶液与镉盐,汞盐,铜盐,银盐,金盐,四价锡盐,钼盐,钨盐,三价铁盐,镍盐,钴盐,铑盐,钯盐,铱盐和铂盐亦发生颜色反应。但金,铱,钼和钨在盐酸溶液中,没有硫氰酸盐存在,能发生颜色;有硫氰盐存在,则不能发生颜色。其他元素,除三价铁以外,如有酒石酸存在,亦不发生颜色。贵金属和铜可使沉淀而分出,同时亦可使三价铁还原而成二价铁,二价铁对于锌的颜色反应,并无妨碍。所以试样溶液中,假若加入盐酸和酒石酸,并使三价铁还原而成二价铁,就可利用硫氰酸盐和甲基紫来检定锌。
Principle When zinc thiocyanate is precipitated in a solution containing methyl violet, it can be seen that the color of the message changes from green to purple if it is observed with transmitted light or intense side illumination. Methyl violet acid solution with cadmium salts, mercury salts, copper salts, silver salts, gold salts, tetravalent tin salts, molybdenum salts, tungsten salts, ferric salts, nickel salts, cobalt salts, rhodium salts, Iridium salts and platinum salts also occur color reaction. However, gold, iridium, molybdenum and tungsten in hydrochloric acid solution, there is no thiocyanate, can occur color; with thiocyanate, the color can not occur. Other elements, in addition to ferric iron, the presence of tartaric acid does not occur color. Precious metals and copper can be precipitated and separated, but also allows the reduction of ferric iron and ferrous iron, ferrous iron for zinc color reaction, without prejudice. Therefore, the sample solution, if the addition of hydrochloric acid and tartaric acid, and ferric iron reduced from divalent iron, you can use thiocyanate and methyl violet to test zinc.