When all has been mixed and thoroughly stirred, cover the top of the dish and allow the temperature to be at 140 degrees for eight hours, occasionally stirring the emulsion during that time, which should be done in the dark.

At the end of that time there should be weighed out, of Nelson's soft gelatine 250 grains, and of French hard gelatine 150 grains.

This 400 grains of gelatine must now be added to the emulsion, and occasionally stirred until all of it is thoroughly dissolved and incorporated with the emulsion, which will take about a quarter of an hour; it is then poured out in a clean 12x10 deep porcelain dish to set, and should be allowed to set for forty-eight hours, when it may be wrung through a piece of coarse canvas and allowed to fall into a solution of

Common salt..... .................. ½ lb.

Water.............................1 gallon

Let it remain in this for five minutes, then strain through a horse hair sieve and wash it well for an hour and a half. Allow the shreddy emulsion to drain well in the sieve for about a quarter of an hour; at the end of that time place it in a clean stone-ware jar to melt, with the addition of four drachms of saturated solution of nitrate of potash upon melting, which may be done by setting the jar into a dish of water at a temperature of about 120 degrees F.

It will be found on measurement to be nearly 25 ounces of emulsion; as soon as it is ready for filtering four ounces of methylated spirit may be mixed with it, to which have been added four drachms of an alcoholic solution of tannic acid, made by mixing ten grains of tannic acid with one ounce of alcohol; this is to prevent frilling.

The rapidity of the plates will be about eight times that of a wet collodion plate, which for all ordinary purposes will be as rapid as could be desired.

Dr. Eder, the distinguished German scientist (who is a great authority on gelatine emulsions, and has published a book on this subject), gives the two following formulae:

Gelatine Emulsion. C

GELATINE EMULSION. C.

EDER,

Bromide potassium.

4

grams,

equal to

61

grains.

Gelatine.....

7½ to 8

grams,

"

115

"

Water............

50

c. c.

"

1

ounce.

Nitrate of silver....

5

grams,

"

77

grains.

Water............

50

c. c.

"

1

ounce.

Dissolve the silver in water and precipitate it with ammonia. Continue the addition a few drops at a time, until the brown oxide of silver re-dissolves and the liquid looks as bright as pure water; the strength of the ammonia is immaterial.

The nitrate of silver may be warmed to 93 degrees F., and poured into the bromized gelatine a little at a time, continually stirring with a glass rod. Rinse the silver bottle with 10 c. c. about 1½ drachms of water and add it to the emulsion, place the bottle containing the emulsion in a basin or saucepan of water heated to 90 degrees F., leave it therein from 15 to 30 minutes without further heat; after 30 minutes the emulsion is ready to be congealed previous to washing.

This emulsion never fogs, but it is imperative that in no part of the progress the temperature should exceed 100 degrees F., and it is a safe rule not to go beyond 90 degrees F. It is recommended to use French gelatine.

Gelatine Emulsion. D

GELATINE EMULSION. D.

EDER.

Bromide of potassium .......................

61 grains.

Gelatine ...........................................

115 "

Water...............................................

1 oz. (plus)

The bromide of potassium must be pure and not alkaline, ditto the gelatine.

The bromized gelatine must be melted at 140 to 160 degrees, and then add 77 grains of silver nitrate in one ounce (plus) of water. The silver may be warmed to the same temperature as the gelatine, but this is immaterial. Rinse the silver bottle with three drachms of water and add it to the emulsion. The bottle with the emulsion is now put in a saucepan partly filled with hot water, covered to exclude all light, and the water in the saucepan set boiling, which should be continued for 25 to 30 minutes, then both water and emulsion cooled down to 90 degrees F., then add 340 minims of ammonia, stirring it thoroughly through the emulsion, which should be left for from 30 to 40 minutes at a heat of 90 degrees F., then it is ready to set and wash.

Dr. Eder says this last is quicker and better for portraits.