Instead of sending the residues to the refiners they can be all mixed together with nitrate of potash and charcoal, and fused in a crucible.
The silver bromide from old waste emulsion can be recovered by first melting and then adding a small quantity of hydrochloric acid, and boiling for a few minutes. The gelatine is thus destroyed, and is poured off, the precipitated silver bromide is then collected, and can be placed among the other residues.
The following processes* of recovering silvering waste may also be found useful : I. rappers' Waste Add solution of caustic potash or lime, as long as there is a brown precipitate; allow it to settle; pour off the liquid and collect silver oxide for reduc tion. See III.
(2) For i pound of silver add i ounce of sulphuric acid and one half pound zinc and allow it to stand two days. Precipitate as a chloride, wash eight or ten times by decantation, and dissolve gradually in nitric acid. Test the complete washing by hydrochloric acid. Wash with water till the zinc nitrate is removed. If zinc clings to silver, wash with hydrochloric acid.
(3) Suspend a sheet of copper in bath for two or three days.
(4) Acidify with nitric acid, precipitate as silver chloride by sodium chloride or hydro chloric acid, and reduce as III.
(5) Immerse in bath two strips of copper attached to a Daniell's battery. Silver deposited on the copper as in No. 3.
(6) Add sodium carbonate or hydrate. Reduce as in III. below, or, if pure enough, dis solve the precipitate at once in nitric acid.
(7) Concentrate bath made alkaline by sodium carbonate and add aqueous solution of oxalic acid neutralized with sodium carbonate. Filter, dry, and fuse with equal weight of sodium carbonate.
(8) Deposit either with or without a battery on iron. Fuse with potassium nitrate and sodium carbonate.
II. Hyposulphite Precipitate as silver sulphide by potassium sulphide. Reduce as III., or dissolve in nitric acid.
(2) Precipitate with hydrosulphuric acid and reduce as III.
(3) Decompose the hyposulphite by waste nitrosulphuric acid from manufacture of gun cotton for collodion. Have silver sulphide and sulphur with sodium nitrate and sulphate in solution. Suspend zinc in the solution, then boil two or three hours; wash and filter, dry, fuse
with borax and sodium carbonate.
(4) Suspend sheet copper in the solution (5) Add hydrochloric acid, which sets free sulphur and precipitates silver chloride. Oxi dize the silver by aqua regia and reduce silver chloride as in III.
(6) Add sodium hypochlorite to the alkaline solution. Wash precipitate, and fuse with mixed carbonates. This gives no fumes of sulphur. Sodium bisulphite and chlorides are by-' products.
III. Reduction of Silver Chloride, Oxide or Mix with its weight of colophony. Heat moderately in a crucible till greenish-blue flame ceases, then suddenly increase the heat, when a button of the metal is obtained.
(2) Melt with alkaline carbonates enough to cover surface from air; then mix with 75 per cent, chalk and 4 per cent. charcoal and heat.
(3) Ignite with nitre on red-hot plate, carefully, and in small quantities to avoid explosions, run down to a bead with sodium carbonate and borax.
(4) If a chloride, reduce to an oxide by boiling with strong potash, then reduce by glucose, or boil the chloride with glucose and sodium carbonate.
(5) Add silver chloride dissolved in ammonia to a boiling solution of i part glucose and 3 parts sodium carbonate in 4o per cent. of water, keeping up the boiling all the time.
(6) Add to silver chloride sodium hydrate in solution and grape sugar, and expose to sun light in an open dish with occasional stirring. Reduce to dark-brown oxide of silver soluble in nitric acid.
(7) Mix with five times its weight of sodium carbonate. Fill a Hessian crucible half full and sprinkle sodium chloride over the top. Heat slowly in anthracite fire. After half an hour increase the heat until the crucible is white hot. When complete fusion has taken place, allow to cool and break out the button of silver.
(8) Fuse with 2 parts carbonate sodium and potassium mixed.
(9) Add pure zinc and dilute sulphuric acid and let it stand two days. Wash silver off with water acidulated with sulphuric acid and remove all zinc ; finally fuse to a button.