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5Vermilion is occasionally adulterated with lime. The following is a method by which its goodness may be proved. Let the vermilion be placed on an iron plate over the fire, and remain till the plate is red hot: when the heat has changed the colour, and it appears black, let the plate be removed from the fire. If, when cooled, it returns to its original colour, it may be considered pure. but if it remain of a black colour, it is quite clear that it has been adulterated.
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