Photography

In all English photographic formula; the solid and fluid measures of apothecaries' weight are used; but in buying or selling chemical articles, the avoirdupois weight is employed.

Positive Collodion

Pyroxilin and iodide of cadmium or ammonium 15 grs. of each; ether 3 1/2 oz., alcohol 1 1/2 oz. Place the first in a dry bottle, then pour on the alcohol, shake the mixture well, then add the ether, shake again, and let it stand for 12 hours. Decant the clear portion into a wide-mouthed bottle, keep well stoppered and in the dark. Avoid shaking the bottle when about to use the collodion, and never use quite all the bottle contains, as the sediment, which will accumulate at the bottom, would spoil the picture.

Nitrate of Silver Bath (for positives)

Recrystallized nitrate of silver 5 drms., dissolved in 10 oz. of distilled water. Filter the solution until it is quite clear, then add 3 drops of nitric acid and 10 drops of collodion. Shake well together and filter. Blue litmus paper should slightly redden in this bath; should it turn very red, add a little ammonia, or oxide of silver; should it not redden at all, add a little acid carefully drop by drop. It is preferable to have a slight excess of acid.

Developing Solution (for positives)

Protosulphate of iron 2 drms. dissolved in 8 oz. of distilled water, add 2 1/2 drs. of glacial acetic acid, 2 1/2 drs. of alcohol, and 5 minims of nitric acid. Filter, and pour into a well-stoppered bottle; do not expose to the air.

Fixing Solution (for positives)

50 grs. of cyanide of potassium dissolved in 5 oz. of distilled water; that is to say, for every fluid ounce of solution required, mix 10 grs. of cyanide of potassium in 1 oz. of distilled water. Filter and keep in a well-stoppered bottle, and label " Poison."

Positive Paper

Plain paper requires preparing or salting before it is ready for use, or it may be purchased already salted. Procure some sheets of plain Saxe paper, and immerse them for five minutes (removing air-bubbles) in the following solution. Hang the sheets up to dry. For portraits and most other uses the paper is albuminized on one side. When photographs are printed to be afterwards coloured, unalbumi-nized paper is used.

Plain Paper

Albuminized paper may be used as plain paper, if, instead of sensitizing the glazed side, the plain side is placed in the sensitizing solution.

Plain Collodion

Mix in a bottle gun-cotton 450 grs., ether 25 oz. spirits of wine 7 oz. Shake these well together, and leave to settle for several days. If well corked, the mixture will keep for a long time.