CLEANSING. The clea,nsing of bottles, papers, stirrers, and ap paratus in general, is a matter of essential importance in many photographical operations ; and the great rule must be to dean immediately after use, when purity is obtained with much more cer tainty and much less labour. All dirty glasses, Acc., should be im mediately put in a particular place and attended to at the first leisure moment. The following directions will be found useful :— (a) To clam Albumen from Glass Plates. Use a solution of caustic potash, or ammonia, for albumen is soluble in alkaline solutions ; then wash with water ; and lastly, with dilute nitric acid and plenty of water.
(b) Collodion Bottles. Leave the stopper out until the ether and alcohol have evaporated, and the film is hard and horny, when it will be easily removed without any adhering to the glass by means of cold water and a bottle brush. Drain and rinse out with a little alcohol.
(c) Developing Measures and Trays. Wash well with tow or a rag and common water, then with a little strong nitric acid if the black precipitate has dried in the vessel. The acid should remain some time in contact with the blackened parts, even after they appear clean : lastly, plenty of water and a clean dry cloth.
(d) Gallic Acid and Gallo-Nitrate. Bottles in which gallic acid has been allowed to become discoloured or mouldy require the use of nitric acid, which decomposes most organic matters, before they are fit to rec.eive solutions of other compounds.
(e) Glass Plates and Vessels. These should be washed and rinsed, if possible, as soon as they are done with, and before they have got dry : even common water if allowed to dry on them will leave matters which often require considerable force to remove. If plain water will not clean them a little tow and the ashes from the fire will generally remove every thing. Sand or gravel should not be used with white glass vessels, since it always scratches the soft flint glass of which English vessels are made. They must after washing be rinsed, drained, and wiped with a clean coarse cloth. New window glass or crown glass requires particular care in clean ing, and especially, in hot weather. Glass plates which have re ceived pictures before are, contrary to the general opinion, better than new, if carefully cleaned after each experiment. Nitric acid with or without tripoli is the best detergent for new glass : better without tripoli, if possible. If a plate be cold and then take the the breath in an even film, it is clean. If a collodion picture has been developed with pyrogenic acid, it requires only water, but, if, with an iron salt, nitric acid will be necessary.
(f) Grease. Greasy glasses should not be washed but, in the first place, wiped with tow to remove as much as possible of the grease, and then a dry cloth .should be used until the surface appears clean. It should afterwards be washed with nitric acid or caustic
potassa and tow which removes the thin film of grease remaining, and it may then be rinsed, drained, and wiped as before. A special duster should be appropriated to remove grease.
(g) Lenses. Do not use silk, for it is apt to scratch : a soft wash leather, free from the powders used in cleaning it, is best ; if the lens be greasy, soft tissue paper will clean it quickly, especially if moistened with a little alkali. Rub off the alkali with fresh paper, and finish with the wash leather kept for this purpose.
(h) Nitrate of Silver Stains. Nothing is so good as nitric acid for porcelain, or glass. For linen, or the hands, mix together alcohol 10 ounces, iodine ounce, nitric and hydrochloric acid each I of an ounce. Apply a little to the stain, and when it has become yellow dissolve it out with cyanide of potassium, and wash well.
(i) Papers containing Metallic Spots. Make two solutions, one of one ounce of tartaric acid in 10 of water, and the other of one fl. ounce of liquor ammonire in 20 ounces of water. Let the papers soak in the first for a quarter of an hour one over the other, then place them for a few minutes in the second. Rinse in plain water and hang up to dry. The metal is removed as ammonio-tartrate.
(7) Resinous, Bituminous, and Tarry Varnishes. As much as pos sible should be scraped off with a knife ; then use tow with a little strong caustic potash or sulphuric acid ; rub the glass well, and after a few minutes the resin 8r,c., will wash off with water, and the glass may be cleaned in the ordinary way. Wood. spirit is a clean solvent of these substances.
(k) Spots qf over-development in Photographs. The solution given above for nitrate of silver stains has been found to answer, but it requires care in using.
(l) SuWate of Iron Stains, and Iron Afould,s, and Ink Stains% To remove these from linen make use of a solution of oxalic azid, and from glass ve,ssels hydrochloric.
(m) SuWuret of Silver Films in Hypo-bottles. Remove all that can be rubbed off with tow and water and then use nitric acid which will form nitrate of silver : finish with plenty of water.
(n) Turpentine. Strong alkali and tow will soon soften it so that it will be moveable by water, or perhaps better, sulphuric acid, which will decompose it.
(o) Varnishes and Varnished Collodion Pictures. These are all easily removed by wood sphit even if asphalt or brimswick black has been applied : or, if time be not pressing, let them soak for some days in water, when the varnish will peel off.
(p) Yellow Lighla in Photographs. A very weak solution of bi chloride of mercury will speedily remove the yellow appearance after -the hyposulphite of soda is entirely gone, but the prints must be removed immediately on the effuct taking place or the picture will be attacked.