METHOD OF SIZING AND SALTING.
The operations of sizing and salting the paper may be conveniently carried out together. and for this purpose the follow ing bath is employed :—Crystallised am monium chloride, 130 grains : recryst a llised sodium carbonate, 200 grains ; citric acid, GO grains : arrow root, 180 grains ; water, 1 pint. This formula gives the normal amount of chloride to be used, and it is doubtful if the worker will ever have occasion to alter it. Modifications of this, however, may sometimes be made with advantage. For example, the chlo ride may be reduced to one half the amount, when printing from hard nega tives. or increased to double in the case of weak, flat negatives. Mix the arrow root to a thin paste, and pour it into 15 oz. of water. Place this on a stove, and heat gently almost. 'to boiling point ; the solution should not be allowed to boil, as this is apt to fill it with bubbles. When the solution is quite clear, it may be removed from the stove and placed aside to cool. In the meantime, place together in a small vessel the three quantities of crystals, and pour over them what re mains of the water. Cold water should be used, and they should be allowed to dis solve without agitation. The combination of the sodium carbonate and citric acid makes an effervescing mixture, which if stirred would overflow and probably be come unmanageable. When the solution
of arrowroot is cool, pour into it the dis solved crystals. The whole of the solu tion may then be poured into a clean flat dish, when it will be ready for use. Hold the paper up to the light so that the watermark reads correctly, that side nearest to the eye being the one to be sensitised. Lay the paper 'face downwards and make a pencil mark from corner to corner, so that the right side may be easily recognised. The paper should be kept scrupulously clean. Be careful to lay it upon a clean sheet of blotting paper, not upon a bench which may have been used for other operations. Cut the paper according to the size of dish being used, and float it upon the solution for five minutes ; then draw slowly off over the side of the dish and dry evenly. The paper while in this condition is ready for sensitising, and will keep indefinitely, so that it is usual to prepare a sufficient quantity up to this point, as the salting and sizing solution will not keep. After a time, the gela tinous part of the solution slowly sinks to the bottom, it being thus rendered useless.