把管内的氢氧化钠残液倒入水中，你就会发现：溶液会使红色石蕊试纸变蓝。
Turn the remnant of sodium hydroxide in the tube into water, and you'll find the solution turns red litmus blue.
这种变化虽然不同于碱滴定酸时石蕊由红到蓝的突然转变，但也相差不远了。
It was not quite the sudden shift from litmus red to blue of an acid being neutralised by an alkali, but it was not far off.
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