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If there is any hæmorrhage, bathe with very cold water in which alum has been dissolved, and apply a styptic, as tannic acid or perchloride of iron.

For the latter reason I do not use the subsulphate and perchloride of iron; for the former, the permanganate of potassium.

A red sympathetic ink may be made in the following manner: Write with a very dilute solution of perchloride of iron—so dilute, indeed, that the writing will be invisible when dry.

The action of the etching mordant—perchloride of iron—being in exact proportion to the light and shade of the developed print.

A strong solution of perchloride of iron penetrates only the thinner parts of the film, whereas a weaker acts also through the thicker parts.