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the refiners (aqua secunda forti feparatoria , eau forteseconde) by which I suppose he means, not aquafortisitself, but the solution of copper in aquafortis remainingafter the silver has been precipitated. Washing withaquafortis was found to prevent the production of anyblack colour on the application of vitriol and astringents,as indeed was expected, this acid liquor destroying thecolour of ink already made : a saturated solution of copperin aquafortis appeared to be of no immediate injury, butit appeared also to be of no advantage.

II. Ivory, bone, horn, &c.

Ivory, bone, horn, and other solid parts of animals, maybe stained black in the same manner as wood. Theylikewise receive a deep black stain from solution of silver,which should be diluted with water to such a degree, asnot sensibly to corrode the subject, and applied two orthree times, if necessary, at considerable intervals, thematter being exposed as much as possible to the fun, tohasten the appearance and deepening of the colour: feepage 350. Hair also, made perfectly clean, and moistenedwith the same solution, is changed from a red, grey, orother disagreeable colours, to a brown or deep black: theliquids commonly fold under the name of hair-waters areat bottom no more than solutions of silver, diluted largelywith water, with the addition perhaps of other ingredients,which contribute nothing to their efficacy. The solutionshould be fully saturated with the silver, that there maybe no more acid in it than is necessary for holding themetal dissolved; and besides dilution with water, it will beproper to add a little rectified spirit of wine for the furtherdulcification of the acid. It must be observed, that fordiluting the solution, distilled water or pure rain watermust always be used; the common spring waters turning

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