. The silver sunbeam : a practical and theoretical text-book on sun drawing and photographic printing. is in the uranium will fall to the bottom of thebottle, leaving a top layer of ether containing pure uranium,and it is this top layer which is used for the emulsion. It isdesirable that the nitrate of uranium should be acid ; andshould it not after solution in ether test acid, it will be ad-visable to add a minim or two of acid per ounce—nitricacid in preference. The quality of an emulsion depends very greatly on thecotton used in making the collodion—a short, powdery cottonbeing best. After
. The silver sunbeam : a practical and theoretical text-book on sun drawing and photographic printing. is in the uranium will fall to the bottom of thebottle, leaving a top layer of ether containing pure uranium,and it is this top layer which is used for the emulsion. It isdesirable that the nitrate of uranium should be acid ; andshould it not after solution in ether test acid, it will be ad-visable to add a minim or two of acid per ounce—nitricacid in preference. The quality of an emulsion depends very greatly on thecotton used in making the collodion—a short, powdery cottonbeing best. After the plate has received its coating of collodion, it isplaced in a dish of distilled water, and left until all greasi-ness disappears. It is then taken out and drained, and placedfor three minutes in the preservative. Mr, H. Cooper makeshis preservative as follows : 534 COLLODIONS. Distilled water, . 4 ounces. White sugar, 20 grains. Gum Arabic, 60 Gallic acid, 12 The plates are then dried carefully in the dark. These plates are said to be as sensitive as the wet, beingdeveloped by the Fig. Alkaline Development. Mr. M. C. Lea recommends the following three solutions, viz. : 1. Progallic acid in alcohol, sixty grains to the oumce. 2. Carbonate of ammonia in water, eighty grains to theounce. To be kept well corked. 3. Bromide of potassium in water, sixty grains to the ready to develop, mix together in a small vial half an ounce of the bromide solution and three quarters of anounce of the carbonate of ammonia solution, and mix them well. Then put into a dish of proper size four ounces of water, towhich add half a dram of the pyrogallic acid solution, andimmerse the plate so as to avoid uneven wetting. Then take out the plate and add fifteen or twenty drops ofthe mixture of bromide and carbonate, and put the plate backagain in the mixture. If the plate has been properly exposed,it develops rapidly. When the details are well worked out, COLLODIONS. 535
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