_Anal._ This may be briefly described as follows:--
_a._ 100 gr. of the alloy is digested in nitric acid. The insoluble
portion is peroxide of tin, every 74 gr. of which, when washed and dried,
contain 58 gr. of metallic tin.
_b._ Sulphuric acid is added to the nitric solution as long as a white
precipitate falls; after a time the precipitate is collected on a filter,
washed with a mixture of water and alcohol, and ignited in a porcelain
crucible. Every 152 gr. of the residuum represents 104 gr. of metallic
lead.
_c._ The liquid filtered from the precipitate of sulphate of lead is
treated with a stream of sulphuretted hydrogen; the precipitate is
collected on a filter, washed with water mixed with a little sulphuretted
hydrogen, dried, and digested in pure nitric acid until the sulphur which
separates acquires its natural full yellow colour; the resulting solution
is next diluted with water, and reprecipitated with potassa, the whole
being boiled until the precipitated oxide of copper becomes of a deep
brown or black; it is then collected on a filter, washed, dried, ignited
in a platinum crucible, and weighed therein immediately after it becomes
cold. Every 40 gr. of oxide of copper thus obtained represents 32 gr. of
pure copper.
_d._ The liquid poured from the precipitate of sulphide of copper is
boiled for about a minute, when it is precipitated with a solution of
carbonate of sodium; the whole is then boiled for a few minutes, and the
precipitated oxide of zinc collected, washed, dried, and ignited. Every 40
gr. of this oxide contains 32 gr. of metallic zinc.
_Concluding Remarks._ In the adoption of his formula the operator should
be entirely led by the object he has in view. The larger the proportion of
copper, the deeper will be the colour, and the greater the density, and,
within certain limits, the toughness of the alloy. Zinc lessens the
specific gravity and colour. Tin gives it hardness and grain; whilst lead
toughens it, and renders it fitter for turning. These facts are known to
every experienced brass-founder. See ALLOYS, COPPER, MOSAIC GOLD, PRINCE'S
METAL, TOMBAC, &c.
=BRASS BATH= (FOR ELECTRO-PLATING). _For steel, wrought and cast iron, and
tin; using ordinary cyanide of potassium._ Dissolve together in 14 pints
of distilled or rain water:--Bisulphite of soda, 7 _oz._; cyanide of
potassium (containing 75 per cent. of real cyanide), 17 _oz._; carbonate
of soda, 34 _oz._
To this solution add the following, made up to 3-1/4 pints of
water:--Acetate of copper, 4-1/2 _oz._; neutral protochloride of zinc,
3-1/2 _oz._; the two liquors become colourless when mixed. Ammonia must
not be used for brass electro-plating baths for iron, especially for
solutions worked in the cold.
=BRASS BATH= (FOR ELECTRO-PLATING). _For zinc._ Pure or rain water, 4-1/2
gallons; bisulphite of soda, 24-1/2 _oz._; cyanide of potassium
(containing 75 per cent. of cyanide), 35 _oz._ To this add the following
solution:--Water, 9 pints; acetate of copper and protochloride of zinc,
each 12-1/2 _oz._; liquid ammonia, 14 _oz._
The filtered bath is colourless, and gives, under the action of the
battery, a brass deposit of a very fine shade, varying from red to green,
by increasing the proportion of copper or that of zinc.
=BRASS'-COLOUR.= _Syn._ BRASS-PIGMENT, B.-BRONZE. _Prep._ 1. Grind copper
filings, or the precipitated powder of copper, with a little red ochre.
Red-coloured.
2. Gold-coloured brass, or Dutch leaf, reduced to a very fine powder.
Yellow or gold coloured.
_Obs._ Before application these powders are mixed up with pale varnish, no
more being worked up at once than is wanted for immediate use. They are
also applied by dusting them over any surface previously covered with
varnish to make them adhere.
=BRASS-PASTE.= _Prep._ 1. Soft soap, 2 oz.; rotten-stone, 4 oz.; beaten to
a paste.