SIMPSON'S EARLY FORMULA.
to be in absolute contact. Further, frame A is provided with two pegs c fitting two holes D in frame s, and thus ensures the plate always being replaced on the exact part of the negative before printed from, and so preventing a blurred image. The advantage of such an arrangement will be chiefly felt. when a picture is required upon opal, of a tone to match a silver print, yet needing combination printing or the introduction of a sky. Every prac tical worker knows what an advantage it is to be able to examine the image from (a) Silver nitrate, oz. ; distilled water.
oz. ; warm gently till dissolved, and then add 5 oz. of alcohol : (b) calcium chloride. 160 grains ; absolute alcohol. 5 oz. ; (0 citric acid, 160 grains ; absolute alcohol. 5 oz. Take 40 oz. of plain collo dion of medium density, and add to it solution (a), a little at a time, with con siderable shaking. This may all be done
in full light, but the remainder is prefer ably carried out in a yellow light. Ordin ary gaslight may be used, and is not strong enough to cause serious damage, unless the paper is to be used for develop ment. Next add solutions (b) and (c) in the manner described for (a). If the emulsion is to be used for coating opals or glass, it may be done in the same way as varnishing a negative ; but if to be applied to paper, the paper may be folded over a sheet of glass, and a pool of emul sion poured in the centre of the paper and rolled out to the edges rapidly with a glass rod. Another method is to turn up the edges of the paper to form a wall round it. The paper is then placed on a sheet of glass and coated, as in varnish. ing a negative.