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grains, chloride, silver and calcium

COLLODIO-CHLORIDE EMULSION.—In this a chloride is substituted for the bromide usually used in the manufacture of collodion emulsions. It must be pointed out that there are two kinds of collodio-chloride emulsions used for different purposes—the one in which the image is developed, and the other in which it is printed out in the same manner as albumenised paper. The latter is called a collodio-chloride printing-out process and is described under that heading.

The formula for making a collodio-chloride emulsion is thus given by Abney: Pyroxyline 15 grains Calcium chloride 20 grains Silver nitrate. 5o grains The calcium chloride is first dissolved in half an ounce of alcohol .8os by warming it in a test tube. Five grains of the pyroxyline Imre then placed in a two-ounce bottle, and the alcohol containing the calcium poured on to it. After a few minutes the addition of half an ounce of ether should be made, when the cotton will soon dissolve.

In another test tube dissolve fifty grains of nitrate of silver with the smallest quantity of water capable of dissolving it. Then add one ounce of alcohol heated to boiling point, and mix. While the silver was dissolving in the test tube the remaining ten grains of the pyroxyline should have been put into a four-ounce bottle. and the alcohol and silver solution poured on to it. Now add one ounce of ether, gradually shaking the solution the while. We have now two collodions the one containing the calcium chloride, and the other the nitrate of silver. The two are taken

to the dark room, and the calcium chloride collodion is very gradually added to the other, stirring the whole of the time. We have now a silver chloride emulsion with an excess of haloid. A trial plate should be coated, half of it exposed to the light, and the whole placed in a ferrous citrate developer. Only that part which has been exposed to the light should blacken with the action of the developer. If, however, the unexposed portion shows, signs of fog, three or four drops of a twenty-grain solution of cupric copper in alcohol should be added to the emulsion. (Abney.) The emulsion can be washed before coating the plates; but this is not really necessary.

Glass plates are cleaned, polished, coated with a substratum, then with the emulsion, and afterwards flooded over with the preservative : Beer 6 ounces.

Sugar z drachm. Pyrogallic acid 6 grains.

After exposure, the plates are rinsed in water and developed with the ferrous-citro-oxalate developer, and if a warmer tint is required they can be afterwards toned in Uranium nitrate to grains.

Potassium ferricyanide zo grains.

Water . 22 ounces.

Upon immersion in this toning bath the tint will gradually become warmer, and if kept in long enough will assume a very agreeable cholocate tint.

This process is admirably suited for transparencies and used for collodion transfers. Many other develepers may be used.