OF ASCERTAINING THE PRESENCE OF DIFFERENT METALS. 
157 
its solution, and to add a drop of muriatic acid to it, when the mercury will be 
immediately reduced, and the copper whitened. Similar effects also take place 
when a number of other compounds of mercury are similarly treated, as the 
oxides, cyanuret, the yellow precipitate from corrosive sublimate by the fixed 
alkalies, the white precipitate by ammonia, &c. Acetate of mercury does not 
yield to such treatment, unless heat be applied, when the copper is readily 
whitened ; but with diluted aquafortis, the acetate is easily reduced on copper. 
Calomel is slowly decomposed in a platina crucible, when mixed with di- 
luted muriatic acid, and the zinc applied ; the reduced mercury is deposited 
on the platina and combined with the zinc, or in case gold is present, it is 
whitened. 
The following is a much readier and better mode of treating calomel. Mix 
a little of this compound, with a few drops of diluted aquafortis, and boil for 
an instant or two in a small platina crucible, add a little water, and apply 
the zinc; the mercury will be readily reduced. Break the contact of the zinc 
with the platina, and the bright mercurial surface of the latter will at once be- 
come tarnished. Restore the contact, and the lustre of the surface will re- 
appear ; and these changes will occur as often as the contact is broken and 
renewed. Add some pure water whilst the zinc is in contact, and the surface 
will remain bright. The mercury may be collected by sublimation, as in the 
case of corrosive sublimate. Operating in this manner, the mercury from a 
very small quantity of calomel may be obtained. Calomel may also be readily 
detected, by placing it on a clean surface of copper, mixing a little muriatic 
or diluted muriatic acid with it, and applying a gentle heat ; when the mer- 
cury will be instantly reduced, and the copper whitened. 
Compounds of lead . — The soluble compounds of lead, in general, like those 
of mercury, are readily reduced to the metallic state when placed on a surface 
of platina, and the zinc applied ; as the nitrate, acetate, &c. The insoluble 
compounds, as the oxides, patent yellow, the carbonate, sulphate, tartrate, &c. 
require previous mixture with diluted aquafortis or muriatic acid. The lead 
thus reduced is usually of a dark grey colour, and exhibits little lustre, unless 
pressed, as by the blade of a knife, when its metallic lustre becomes quite ap- 
parent. It feels quite soft as the zinc is drawn over it. Its cohesion to the 
platina is generally so feeble that most of it may be easily removed by a cloth 
