Gold Bath.
A solution of gold used for depositing the metal in the electroplating
process.
A great number of formulae have been devised, of which a few
representative ones are given here.
COLD BATHS. HOT BATHS.
Water, 10,000 10,000 10,000 10,000 5,000 3,000
Potassium Cyanide, 200 -- 200 10 -- 50
Gold, 100 15 100 10 10 10
Potassium Ferrocyanide, -- 200 -- -- 150 --
Potassium Carbonate, -- 150 -- -- 50 --
Ammonium Chloride, -- 30 -- -- 20 --
Aqua Ammoniae, -- -- 500 -- -- --
Sodium Phosphate, -- -- -- 600 -- --
Sodium Bisulphite, -- -- -- 100 -- --
(Roseleur.)
In the baths the gold is added in the form of neutral chloride, Auric
chloride (Au Cl6).
Gold Stripping Bath.
A bath for removing gold from plated articles without dissolving the
base in order to save the precious metal. A bath of 10 parts of
potassium cyanide and 100 parts of water may be used, the articles to be
stripped being immersed therein as the anode of an active circuit. If
the gilding is on a silver or copper basis, or on an alloy of these
metals the same solution attacks the base and dissolves it, which is
objectionable. For silver articles it is enough to heat to cherry red
and throw into dilute sulphuric acid. The gold scales off in metallic
spangles. For copper articles, a mixture of 10 volumes concentrated
sulphuric acid, 1 volume nitric acid, and 2 volumes hydrochloric acid
may be used by immersion only, or with a battery. The sulphuric acid in
such large excess is supposed to protect the copper. For copper articles
concentrated sulphuric acid alone with the battery may be used. This
does not sensibly attack the copper if it is not allowed to become
diluted. Even the dampness of the air may act to dilute it.
Graduator.
Apparatus for enabling the same line to be used for telegraph signals
and telephoning.
One type consists in coils with iron cores or simply electromagnets.
These act to retard the current in reaching its full power and also
prolong it. This gives a graduated effect to the signals, so that the
telephone diaphragm is not audibly affected by the impulses.
The telephoning current is so slight and so rapid in its characteristic
changes that it is without effect upon the ordinary telegraph.