COATING THE PLATE.
Before the emulsion is applied to the plate, it must be rendered colour sensi tive, or, as it is sometimes called, pan chromatic ; this is clone by the addition of certain dyes. The following formula, recommended by Dr. R. Ncuhauss, of Berlin, is very suitable:— Alcoholic solution of cyanine, 1 in 500 50 minims.
Alcoholic solution of erythrosine.
1 in 500_ 33 minims.
Alcoholic solution of glycin red, saturated ... 170 mimes.
These qnantities are to be added to every 3i oz. of emulsion. The latter is then filtered through fine flannel or silk, and, the plates being first thoroughly cleaned, the coating is immediately proceeded with. The plates are now allowed to set on a levelling slab, at as low a tempera ture as possible, ice being used for the purpose if necessary. When perfectly set, they are washed for half-an-hour, drained, and allowed to dry. Plate glass is best for coating, and the gelatine may be either Nelson's No. 1, Drescher's, or Lautenschlager's. The latter, obtainable
alcoholic solution of aceto-nitrate of silver over the plate, immediately before ex posure. Lumiere employs the same agent, but with water instead of alcohol as the solvent. Mr. Edgar Senior has obtained good results by adding 3 grs. of silver eoside (a chemical compound of silver and cosine) to each 3/ oz. of emulsion. Edward Valenta prefers, however, to add sodium sulphite to the emulsion, which it is claimed enables the latter to be heated to a higher temperature subse quently, without affecting the fineness of the grain. The temperature in this case may be raised to 102° Fahr. As may be readily imagined, except in the hands of an expert, it is far easier to secure good results with the original emulsion, for any attempts at increase of speed simply add to the likelihood of failure, by introducing many possibilities of complication.