[ I0 4 ]

which they supposed to be endowed with extraordinarymedicinal powers; not aware, that the gold constantlyseparated in the process, and that the colour of the pre-paration was no other than that which concentrated acidsproduce with essential oils however pale or colourless.

Liquors containing a grosser inflammable matter, aswine, vinegar, solution of tartar, are likewise found toextricate gold from aqua regia in its metallic form ; withthis difference from the preceding, that the gold, insteadof floating on the surface, falls here generally to thebottom.

VII. Precipitation of gold by alkaline salts.

On adding to solution of gold a solution of any fixtalkaline salt or a volatile alkaline spirit, in sufficient quan-tity to satiate the acid ; the mixture becomes turbid, andon standing for some hours, the gold falls to the bottom,in form of a brownish yellow muddy substance, retainingsome of the saline matter, great part of which may beseparated by repeated washing with hot water. Thatthe gold may precipitate the more freely, the solutionshould be diluted with three or four times its quantity ofwater, or more. The alkaline liquor should be addedby degrees, in little quantities at a time, till the mixture,after the gold has settled, appears colourless, and a freshaddition of the alkali occasions no further precipitationor turbidness.

When gold has been thus totally precipitated by volatilealkaline spirits, as spirit of sal ammoniac, the additionof more of the spirit renders the liquor again yellow,occasioning a part of the gold to be redissolved : by addinga large quantity of the alkaline spirit, almost all the pre-cipitate is taken up; and even when the precipitated goldhas been washed from as much of the adhering saline

matter