The Optical Magic Lantern Journal (September 1897)

The Optical Magic Lantern Journal and Photographic Enlarger. 153 being properly level and the plate vertical. A metal plate with a series of holes is procurable at the dealers ; which can be attached tothe camera in place of the lens, marked with the size of plate each aperture is supposed to be suitable for. This, of course, is the most easy method, as no deviation from the usual working is necessary, of exposure. CHAPTER XVII. ALTHOUGH it may be seldom necessary for the unprofessional to collect and reduce his residues on account of their presumably small quantity, yet the knowledge of how to do it efficiently may be useful, especially if wet collodion work is practised, emulsion made, or paper prepared. There are several kinds of residues that require separate collections and treatments. There is silver nitrate from all sources, silver from the wet plate developers, intensifying solutions from the fixing solutions, waste plates, spoilt films, and emulsions and gold from spent toning baths. The most important of this salvage is the hyposulphite of soda fixing solution. Procure a large earthenware or glass pan, rather tall for its width, with a tap about half-way up the side. Into this put all the used and waste fixing baths, washings out of bottles that have contained silver, and when nearly full dissolve a little liver of sulphur or sulphuret of potassium in hot water, which will make a deep, yellow-brown, foul-smelling solution ; add some of this little by little, well stirring after each addition, until there is no further brown cloudiness produced, and the hypo waste slightly smells of the sulphuret. As long as there is any metal to be precipitated there will be no odour, but after all has combined with the sulphur, any further addition is easily recognisable by thesmell. Give it a good stir and let it stand to subside, when the supernatant | fluid, which should be nearly colourless, may be drawn off. This process can be repeated as often as the vessel gets filled. To collect, filter this mud through two thicknesses of houseflannel, let it drain, and then dry in an earthenware pan over the fire. The water from washing prints or any solution containing silver nitrate is allowed to collect in deep pans, and isthen precipitated by adding a little hydrochloric acid; some prefer salt, but as excess of salt re-dissolves the chloride, and as hydrochloric acid does not, in a dilute solution, the acid is the more economical addition. The chloride of silver will settle to the bottom, when the upper layer of fluid can be drawn off and the process repeated until there is sufficient residue to dry. As with the hypo waste, it is filtered through two thicknesses of flannel, drained and dried in readiness for reduction ; or if a quantity of scrap zinc be put into the moist chloride and left a | few days, the silver chloride will be reduced to a and the whole attention can be given to the time | metallic state, which will be known by the chloride, originally a pure white, changing to a grey throughout the mass. The zinc can now be separated from it, and the silver washed and dried ready for further treatment. Waste gold solutions, old toning baths, and any solutions containing gold are precipitated with a solution of protosulphate of iron, the solutions being made slightly acid with sulphuric acid in order to neutralise any alkali that may have been introduced into the gold, which would, in a measure, retard the precipitation. In this case the precipitate will consist of metallic gold which must be collected and washed on a paper filter, and dried previous to making it into chloride, which is, perhaps, the best way of utilising it. The films of wasted or spoilt plates are scraped together and heated with a little hydrochloric acid and water. Spoiled emulsions may be treated in the same manner. Maceration and heating with acid decomposes the gelatine ; the bromide of silver being precipitated, when it can be washed, dried and mixed with the chloride for reduction. Scraps, cuttings, and spoilt paper can be burnt in an oldiron saucepan, adding the paper by handfuls so that it all gets burnt, and left to smoulder until it is entirely reduced to a grey ash. A litile powdered nitre sprinkled on it from time to time will expedite matters. The ash is not very rich in silver, but consists chiefly of the loading and enamel of the paper, about an ounce of silver to a hundredweight of cuttings ; so, unless there is much of them, it is scarcely worth the trouble of collection. The residue from various sources can be reduced to the metallic state by fusion with suitable fluxes in a fierce fire; providing there is a stove with a good draught, small quantities may be reduced, but, first of all, the dried residue must be crushed fine, mixed with from one to two parts of flux, and passed through a sieve. The chloride of silveris mixed with bicarbonate of soda and a little borax, and the sulphide of silver with nitrate of potash for reduction separately ; the ash residue may be mixed with the sulphides and reduced together. A small fire is carefully laid, a clay crucible in a saucer