mixing two volumes of strong commercial nitric acid with one of strong
sulphuric acid in a cell measuring, say, 12 X 10 X 15 inches.

Copper or brass articles are dipped in this bath for a few seconds,
then rinsed with water, then dipped again for a second or two, or
until they appear equally white all over, and then withdrawn as
rapidly as possible and plunged into a large quantity of clean water.
Care must be taken to transfer the articles from the bath to the water
as quickly as possible, for if time be allowed for gas to be evolved,
the surfaces become mat instead of bright.

In order to save acid it is advisable to make up a third bath, using
those odds and ends of acids which gradually accumulate in the
laboratory. Sulphuric acid from the balance cases, for instance,
mixed with its own volume of commercial nitric acid, does very well.

The objects to be dipped receive a preliminary cleansing by a dip in
this bath, the strong bath being reserved for the final dip. Sheet
brass and drawn tube, as it comes from the makers, possesses a really
fine surface, though this is generally obscured by grease and oxide.
Work executed in these materials, cleaned in alkali, and dipped in
really strong acid, will be found to present a much better appearance
than work which has been filed, unless the latter be afterwards
elaborately polished.

On no account must paraffin be allowed to get into any of the baths.
When the final bath gets weak it must be relegated to a subordinate
position and a new bath set up. A weak acid bath leaves an ugly
mottled surface on brass work.

Sec. 129. A metallic surface which it is intended to electroplate must,
as has been mentioned, be scrupulously clean. If the metal is not too
valuable or delicate, cleaning by dipping is easy and effectual. The
following notes will be found to apply to special cases which often
occur.

(1) Silver Surfaces intended to be gilt. These are first washed
clean with soap and hot water, and polished with whitening. They are
then dipped for a moment in a boiling solution of potassium cyanide.
A 20 per cent solution of common commercial cyanide does well, but the
exact strength is quite immaterial. The cyanide is washed away in a
large volume of soft water, and the articles are kept under water till
they are scratch-brushed.

Mat surfaces are readily produced on standard silver by dipping in hot
strong sulphuric acid. The appearance of new silver coins, whi