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not found that either moderate fire or aquafortis willdestroy it. Pieces of different stones, marbles, pebbles,flint, &c. were washed over with a saturated solution ofcopper made in aquafortis : when dry they were put intoa crucible, and kept for a little time in a fire just suf-ficient to make the vessel almost red hot. All of themwere stained, in the parts which had been moistened withthe solution, of a black colour, durable and pretty deep,though it had penetrated only a very little way into thesubstance of the stones.

When the smooth surface of an agate, or other stonesnot diffolvible in aquafortis, is moistened with the coppersolution j if a small iron nail be set upright on its headin the middle, the iron absorbs the acid from the copper,and the copper, now separating from the fluid, shoots intofine ramifications like the branches of trees or shrubs,generally of a very elegant appearance. If the nail bethen removed, and the corroded iron carefully washedoff by dipping the stone in water, the vegetations may bechanged by heat to the same black colour as the simplesolution of copper in the foregoing experiments, so asgreatly to resemble the figures naturally found in certainstones, as that called the Mocho stone. The colour isnot indeed fixed on the stone, like that resulting from thesolution of copper alone; but a plate of crystal laid overit in the manner os a doublet, conceals this imperfection..The only difficulty in this operation consists in the wash-ing, in which great dexterity is requisite, to separate thecorroded iron, which would give a rusty stain, withoutwashing off or disordering the fine vegetations of thecopper.

SECT.