_Amalgamated Zincs._ Local action might be prevented by the use of
chemically pure zinc, but this, on account of its expense, cannot be
employed commercially. Local action, however, may be overcome to a
great extent by amalgamating the zinc, _i.e._, coating it with
mercury. The iron particles or other impurities do not dissolve in the
mercury, as does the zinc, but they float to the surface, whence the
hydrogen bubbles which may form speedily carry them off, and, in other
cases, the impurities fall to the bottom of the cell. As the zinc in
the pasty amalgam dissolves in the acid, the film of mercury unites
with fresh zinc, and so always presents a clear, bright, homogeneous
surface to the action of the electrolyte.

The process of amalgamating the zinc may be performed by dipping it in
a solution composed of

Nitric Acid 1 lb.
Muriatic Acid 2 lbs.
Mercury 8 oz.

The acids should be first mixed and then the mercury slowly added
until dissolved. Clean the zinc with lye and then dip it in the
solution for a second or two. Rinse in clean water and rub with a
brush.

Another method of amalgamating zincs is to clean them by dipping them
in dilute sulphuric acid and then in mercury, allowing the surplus to
drain off.

Commercial zincs, for use in voltaic cells as now manufactured,
usually have about 4 per cent of mercury added to the molten zinc