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用两支同样大小的试管,分别取约占试管体积1/5的浓硝酸,把铜导线(或用塑料线栓一小铜片),同时放入两试管的浓硝酸中,(试管后衬
Use two tubes of the same size, take about 1/5 of the volume of concentrated nitric acid, and place the copper wire (or a small piece of copper with a plastic wire) into the two tubes of concentrated nitric acid.