To A. L. Henderson is due the credit of proposing the addition of 1/3 acetate to 1/3 each of the citrate and chloride salts. From some experiments he exhibited, I at once thought he had found a process suitable for the production of lantern slides. After a few experiments, I decided to do away with the citrate because of the cold tones it gave, and because I could not obtain the same? brilliancy and range of tones as when I used acetate and chloride of silver only.

So far, I have obtained the most satisfactory results by producing a fine sepia tone with the following formula. There is hardly anything, perhaps, in which the taste of different persons varies so much as in the tone of a lantern slide For myself, I much prefer a warm sepia tone to the cold black or purple tones. But almost any color can be got from red through the brown shades to purple. The sodium -chloride converts about 11} of the 28 gr. of silver nitrate into silver chloride. By using a larger proportion of chloride there is far less brilliancy, and I did not want to use a larger amount of acetate than possible on account of it being a more unstable salt, and a large proportion might affect the keeping qualities.

I have not yet experimented in the direction of having an excess of silver nitrate in the film. It is quite possible that we might increase the speed of printing by so doing, and by adding a little citric acid make the plates keep well, the same as with albumenised paper. But we must remember that we have a quantity of nitrate of soda in the films, which probably acts the same as the free silver, because it was formerly used with silver nitrate to sensitise albumenised paper.

To prepare the emulsion, put in a small jam pot:

Gelatine... 40 gr.

Acetate of soda . 8 „ Water ... 2 oz.

The gelatine is allowed to swell, and is then dissolved by standing the jampot in hot water.

In a test-tube or small bottle is dissolved:

Silver nitrate . 28 gr. Distilled water . 1 oz.

This is stood in the same hot water, so as to be about the same temperature.

When the gelatine is thoroughly dissolved, the nitrate of silver solution is poured into the jam-pot in a gentle stream, quickly stirring with a glass rod all the time.

Into another test tube put:

Chloride of sodium .. 4 gr. Acetate of scdium . 6 „ Water ... 1 oz.

When dissolved, this is added to the above, the stirring being continued.

Meanwhile 2-3 oz. waterris poured on to 160 gr. gelatine. In about 1/4 hour the surplus water is poured off, and the gelatine is added to the emulsion; the contents of the jam-pot are to be kept at about 100° F. until the whole of the gelatine is dissolved. It is then put aside in the dark for 24 hours to set.

The details of filtering, coating the plates, printing, and toning, I will go into soon, and will now only refer to one or two points about the preparation of the emulsion. I generally use a Swiss gelatine, but Hen rick's or any good gelatine will do as well; indeed, this process does capitally for using up samples of gelatine which are not quite up to the mark for dry-plate work. As to the light, I prepare the emulsion and coat the plates by the light of a small paraffin lamp in perfect safety.

I will now describe the mode of preparing the plates, printing, etc. The jam-pot containing the emulsion is stood in hot water until the latter has thoroughly dissolved; 1/2 oz. alcohol and sufficient water is added to make the quantity up to 6 oz.

It is then filtered. For filtering, use a small paraffin lamp glass with the bottom edge turned up (they can be bought at an oil shop for about 2d. each). A piece of wash leather or 4 or 5 thicknesses of fine muslin is tied on the bottom of the lamp glass. The dissolved emulsion is poured in, and by blowing in at the top of the glass the emulsion runs rapidly through, and is then ready fur coating tbe plates.

To clean the plates, scrub them with a nail-brush and water in which a little washing soda has been dissolved; they are then well rinsed in cold water, and stood up to dry in the racks. After they are dry, they are just dusted with a piece of clean washleather and stacked in a heap.

For coating such small plates, the best way is with a small silver teaspoon. A spoonful of the emulsion is poured on the centre of the plate, and can be guided to the edges with the spoon if necessary.

For amateurs or those not accustomed to plate coating, this is an important point, besides a measured quantity being put on each plate. When the emulsion is poured from a small teapot or similar article, it has to be put down and a glass rod taken up. While looking after these things the emulsion is meanwhile cooling, and perhaps running off the edges of the plate, but with the spoon the eyes need not be taken from the pool of emulsion on the plate.

For levelling the plates after coating do not use a large glass or slate slab, but have some strips of plate glass about 2 ft. long and 2 1/2 in. wide; these are stood in rows on a level table or board. Suitable strips of glass can be got very cheap at a glass-cutter's, because any odd sizes from his scrap heap will do. When a large flat slab is used, if any emulsion gets on the back of the plates, they stick to the slab, and in the dull light of the dark room, when coating rapid bromide plates, this sticking is a great nuisance. With the strips of glass, the plates can be laid down on them without the emulsion running off the plates, and can be easily detached from them even if stuck with some emulsion on the backs.

The plates are put away to dry in the usual way. I never find it necessary to use heat when drying plates on a small scale. My drying-box is in a room at the top of the house; the fireplace of which is closed up. The outlet of the drying-box goes into the chimney, and gets a capital draught, keeping the window in the room closed when drying plates.