THE FIXING SOLUTION.
There are several reagents which have the property of dissolving out the silver salts that remain unreduced by the de veloper, the two principal of which are cyanide of potassium and thiosulphate, or as it is commonly called, hyposulphite of soda. The latter is now generally used for the purpose, and has the merit of being harmless, while the former is a deadly poison. Fixing is accomplished by simply immersing the negative in a solution of hyposulphite of soda for twice as long as the negative takes to become completely transnarent and clear, generally about ten or fifteen minutes. The hyposulphite of soda costs very little, and may be bought in 1 lb. packets or barrels of 1 cwt. A quantity of solution should be made up at one time in a large bottle or stoneware jar with a tap. and labelled " Hyťo. Stock Solution." The proportion is 1 lb. of hypo. to 4 pints of water. No special apparatus is required for fixing. A porce lain dish to hold the solution is all that is necessary. A large vulcanite dish, if it can be obtained, will prove still better, in front of it. Next, 1 oz. of No. 1 de veloping solution is poured into the 2 oz. measure, and then 1 oz. of No. 2. The slide is now opened, and the first plate, supposing only one has been exposed, taken out ; the slide can be refilled later, but at present should be closed and placed out of the way of splashes. The exposed
plate is laid film side up in the developing dish, arid the developer poured quickly over it, moving the dish so that the solu tion flows evenly all over the plate. The dish must be regularly rocked, so that airbubbles may not settle on the film and to prevent uneven patches being formed. After a few seconds the image will slowly appear, and gradually become stronger. When the picture is apparently dark enough, it. should be held up in front of the lamp and examined. A holder for films or plates, as shown, is very conveni ent, as it avoids the necessity of wetting or staining the fingers. Fig. 19 shows a holder for films but those for plates are similar. A perfect reversal of the original should be presented in which the lights are indicated by opaque patches and the shadows by unaltered or slightly altered white emulsion. The plate must be re placed in the developer, and the rocking continued till a slight veil forms over the white portions or shadows, and the rest of the negative looks quite dark and obscure, with the image distinctly showing. The negative is then rinsed for a few minutes under the tap, or in a pail of water.