In coating, pour the emulsion out of the bottle into a glass measure (I have several sixes), using a drachm to every ten square inches of surface; thus, a ten by eight will take eight drachms or one ounce. I consider it very important to measure the quantity on each plate. Spread with a light bent glass rod, and when all the plates are coated put the lid over, and you can admit white light until they are set, which will probably be in two or three hours. Do not disturb them till thoroughly set, then transfer them to the drying-box, light the Bun-sen burner, and in about twenty hours the plates will be dry.
In storing the plates when dry, place them face to face, without anything between them; wipe the backs from any emulsion that may be upon them, and so place them in pairs 1 usually make them up in parcels of eight plates, the box, etc., being adapted for making sixteen plates at one heat I wrap up in yellow paper two thicknesses and brown paper ditto-- J. A. Forrest.
The drying-box is illustrated in Figs. 84 and 85. A is an oblong box 71/2 X 11 inches, and 80 inches high, inside measurement. B is a tin tube 4 inches in diameter, and a little longer than the height of the box. a is another tin tube, 2 inches in diameter, reaching from the diaphragm, g, in the large tube, up through its top. The tubes d and e, each 11/4 inches in diameter and 4 inches long, connect the large tin tube with the box, the tube e entering the box 1 inch below its top, and the tube d 1 inch above its bottom. The shelves, 2, 2, are each fastened tightly in the box, but are each only 10 inches wide, thus leaving a space at their ends 1 inch wide between the doors of the box, c. The large tin tube, B, is perforated with a row of half-inch holes just above the diaphragm, g, to admit air. The lamp, c, is placed in the bottom of the large tin tube. The sides of the box, a, between the shelves, 2, 2, are full of grooves, 1 1/4 inch deep, 1 1/4 inch wide, and 1 1/4 inch apart, as shown in the sectional figure, 85. I use only 5x8 and 8x 10 plates; and when I begin putting plates in the box, I slide the first plate into the first upper pair of grooves, leaving it so that the door of the box will touch it when it is closed. If the plates are 5 x 8, I put two plates into each pair of grooves, and if 8 x 10, only one. The second plate I put in the second pair of grooves, but slide it back against the back of the box. The third I lean against the door, and the fourth against the back, and so on until the box is full or the batch is all in. The figures 1,1,1,1,1 show the position of the plates in the box. When the plates are all in, I close the door, c, which fits tightly, and light the lamp in the bottom of the tin tube. I use a small night-lamp, burning kerosene oil. The air for the lamp has to come through the tube, d, and out of the box, A. The heat of the lamp warms the tube, a, also warming the air in the space between the two tubes, which rises and passes into the box, a, through the tube, e, its place being supplied with cold air through the holes in the large tube just above the diaphragm, g. A current of warm air (as shown by the arrows in Fig. 84) is thus kept up over the plates, and they will dry very quickly. The upper ones will dry first, and, as they dry, it is well to shove them in against the back of the box, thus giving the warm air a better chance at the plates below. A batch of plates, from four ounces of emulsion, put in in the evening will be nice and dry in the morning. - Jay Densmore.
It often happens, in very damp weather, that a gelatin negative refuses to dry for hours,
and even when flooded with spirit takes a considerable time. To those who do not possess a good drying cupboard, the following is offered as a thoroughly efficient substitute, which any one can make for himself with a little help from the blacksmith. The annexed wood-cut will almost explain itself. The box may be of any form most convenient, but the more shallow the better; the one in actual use stands on an ordinary work - bench, and the gas - burner and iron cone, etc., on the floor, enclosed with a few bricks piled up to keep in the heat and protect any woodwork. The box measures thirty inches high, thirty inches wide, and ten inches deep from back to front; the front is closed up at the lower part about six inches, and a sliding door, running in grooves, closes the upper part all but about half an inch at the top, a balance weight over a pulley supporting it in any position required. This is found a much better way than having doors opening on hinges, for various reasons. The current of warm air is conveyed in at the bottom, through a three-inch circular opening, the iron stove - pipe arrangement being screwed on underneath. Above the opening, at a little distance, is supported a thin shelf of wood about an inch smaller all round than the inside of the box, which acts as a diffuser, and stops the current of hot air from rushing up in one spot; above this, at any convenient height, two bars are fixed to carry the feet of the drying-rack containing the plates. It will be found that plates will dry without running, at a very considerably higher temperature than that at which gelatin melts, if the heated air is kept in continual motion. - Alexander Cowan.
I use the following substratum: Take the white of one egg to twenty ounces of water, to which add an ounce of methylated spirit and about twenty drops of carbolic acid. It is better to add the carbolic acid to the spirit and stir, and then add the whole to the albumen; agitate well, allow to stand until next day, and filter clean. This will keep for months. I find this a " perfect cure " for frilling; the substratum adheres thoroughly to the glass, and the gelatin adheres thoroughly to the substratum. No alum water is necessary while developing, nor any tampering with the emulsion. I have never lost a single plate from frilling since I adopted this method, but dozens before. - J. A. Forrest.
Defects in plates. Spots may generally be discovered by passing the finger softly over the surface. Local intensification may be given by applying a saturated solution of bichloride or mercury with a brush to the parts requiring it, and local reduction may be obtained in the same way, substituting potassium cyanide for mercury salt. White points or round spots with a sharp outline, which, after fixing, have a glassy appearance, are caused by air-bubbles adhering the plate, and preventing the developer from penetrating. These bub-18