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If you put a tea-spoonful of a liquor composed of copper infused in

acid of vitriol, into a glass, and add two or three table-spoonfuls of

water to it, there will be no sensible colour produced; but if you add

a little volatile alkali to it, and stir it, you will perceive a very

beautiful blue colour. Add a little acid of vitriol, the colour will

instantly disappear upon stirring it; and by adding a little fixed

alkali dissolved, it will return again.