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 31⁄4 pints of water:—Acetate of copper, 41⁄2 oz.; neutral protochloride of zinc, 31⁄2 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, 41⁄2 gallons; bisulphite of soda, 241⁄2 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 121⁄2 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.