that metal) continuing a very strong heat till all the mercury has
evaporated, stirring the amalgam all the while with a glass rod;
when the mercury has entirely left the gold, grind the remainder in
a Wedgewood's mortar, with a little water, and when dried it will be
fit for use. The subliming the mercury is, however, a process
injurious to the health.


171. COLOUR HEIGHTENING COMPOSITIONS

For yellow gold, dissolve in water 6 ozs. of saltpetre, 2 ozs. of
copperas, 1 oz. of white vitriol, and 1 oz. of alum. If wanted
redder, add a small portion of blue vitriol.


172. FOR GREEN GOLD

Dissolve in water a mixture consisting of 1-1/2 oz. of saltpetre;
vitriol and sal-ammoniac, 1-1/4 oz. of each, and 1 oz. verdigris.


173. FOR RED GOLD

Take 1-1/2 oz. of red ochre in fine powder, the same quantity of
calcined verdigris, 1/2 oz. of calcined borax, and 4 oz. of melted
yellow wax; the verdigris must be calcined, or else, by the heat
applied in melting the wax, the vinegar becomes so concentrated as
to corrode the surface, and make it appear speckled. These last
three are colours for heightening compositions.