Let the water run through the tube to bottom of pitcher and off at faucet below. To tell when the emulsion is sufficiently washed, take some of the waste water running from the faucet into a 2oz. bottle and add a few drops of silver solution; there will be a precipitate of silver bromide. In an hour take some more of the waste water, and add a few drops of silver solution, and if there is no precipitate of silver bromide, the emulsion is washed enough. If there is still a precipitate of silver bromide, continue to wash until, upon trial, there is no precipitate formed. Stirring the emulsion several times will hasten the washing. Never take off the cover to the washing box, except in red light after you add the brine.
The emulsion is now ready to be preserved for future use, or to be used at once.
To use at once, tie a piece of coarse canvas over a large bowl, pour the emulsion on to canvas and let it drain free of excess of water; put back into pitcher and place into hot water in apparatus described hereafter. Melt at a temperature of 140°-150° F. Add 2 oz. alcohol and 2 oz. pure albumen. (To prepare the albumen, beat the white of eggs to a stiff froth and set aside to go back to liquid.) Add 2 drops of a saturated solution of chrome alum in water to each ounce of emulsion: this is to keep the gelatine from frilling. There should be 35 oz. of emulsion when finished; if not, make up with water. Make smaller quantities in proportion.