It USES distilled water and alcohol to refine water soluble acid and alkali of sample and then test the extractive with PH indicator.

用蒸馏水或乙醇水溶液抽提试样中的水溶性酸或碱，然后用酸度计或指示剂对抽提物进行测定。

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In the form of a water solution or as litmus paper, it is the oldest and most-used indicator of whether a substance is an acid or a Base.

它的水溶液，或者做成石蕊纸后，是最古老和最常用的指示剂，可以指示一种物质是酸还是碱。

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A white or pale yellow crystalline powder, C20H 14o 4, used as an acid-base indicator, in making dyes, and in medicine as a laxative.

一种白色或淡黄色的晶体粉末，C20 H 14o 4，用作酸性指示剂，用于制染料，并在医学上用作一种轻泻剂。

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They found that the older soot samples contained vanillic acid, an indicator of burning conifer trees.

BBC: Human activities have left a visible mark on the Arctic