Descriptive Notes

The chemicals required by the amateur for use in ordinary photographic practice are not numerous. The following descriptive notes will be found useful for reference. The solutions into which they enter will be described in the various sections under which they fall.

Acid, Acetic, Glacial

A colourless liquid with a strong vinegary odour. At low temperatures it becomes solid, hence its name, "Glacial," or ice-like. It has a burning action on the skin. Used in the preparation of ferricyanide and uranium intensifying solution.

Acid, Hydrochloric

The pure variety of this acid should always be used. It is colourless, has a strong burning action on the skin and clothes. It is used in a diluted form in the platinum-printing process as a clearing solution.

Acid, Pyrogallic

A very important chemical in photographic work. The word "Pyro" is frequently used in short. It is met with in two forms, either as a very light feathery crystal or in heavier crystalline form, in which it occupies much less space. In both varieties it is white, but after being kept for some time it darkens, especially if much exposed to the air. It constitutes the reducing element in pyro-soda and pyro-ammonia developing solutions.

Alum

In large glass-like crystals. Used generally for hardening gelatine of films, plates and papers.

Ammonia, Liquid

A solution of ammonia gas in water and forms a colourless liquid with a very pungent odour. Great care should be taken when opening a bottle, especially if a stoppered one, also not to smell it. It is used sometimes as the accelerator of pyro in developing solution, also in mercury-ammonia intensification.

Ammonium Sulphocyanide

Colourless crystals, which are more or less damp and cling together. They become liquid if exposed to the air for any length of time, being deliquescent. For storing, it is probably best to keep it in a concentrated solution, representing so many grains per ounce. Used in conjunction with chloride of gold for toning P.O.P.

Borax

Large white crystals, and used in some toning solutions for P.O.P.

Gold Chloride

Bright yellow crystals and usually packed in sealed glass tubes or bulbs, containing 15 grains each. This does not represent 15 grains of pure gold chloride, but a fraction over 7 grains in combination with another chloride to bring about crystallization. The tube is best broken by first wrapping in a piece of clean white paper and then, with a mallet or something similar, giving the packet a sharp tap. The contents are then emptied into 15 drachms or 7 1/2 ounces of distilled water. These solutions will then represent 1 grain per drachm or per half-ounce respectively, which constitutes a very convenient form for storing. Used in the gold toning baths for P.O.P.

Hydroquinone (Sometimes Called Quinol)

Another of the important reducers used in developing solutions. It is a fine white crystalline powder. Its solutions are affected by low temperatures, and it will be thrown out if the solution is at all concentrated, therefore during the winter the solutions should be stored in a warm place.

Lead Acetate

White crystals or crystalline powder. It and the Nitrate - which is of similar characteristics - are soluble forms of lead, and are used in combined toning and fixing baths.

Mercury Perchloride

In dense, heavy white crystals. It is intensely poisonous and should be handled with the greatest care. Fortunately, there is some difficulty in purchasing, as its sales are regulated by law, and unless the purchaser is thoroughly well-known to the seller it cannot be obtained. Used in the mercury-ammonia intensification process.

Metol

Another of the important reducing agents in developers. Is a white powder, but darkens by oxidation when exposed to the air or when stocked for any length of time. It has a peculiarity in requiring to be dissolved before any other ingredient is added in making up solutions, otherwise it is precipitated and refuses to re-dissolve. Another characteristic is that it will attack the skin of some people, causing a soreness; those who are susceptible to its attacks should keep a vessel of clean water near at hand when using the developer and rinse the fingers in it occasionally.

Potassium Bichromate

Yellow, smooth crystals. It is somewhat corrosive and poisonous. Used chiefly as the sensitizing agent in the carbon-printing process.

Potassium Bromide

White crystals of small size. It is the most frequently used restrainer, and is a frequent ingredient in developing solutions.

Potassium Ferricyanide

(There is a distinction between this and the Ferro-cyanide, which is of no photographic utility.) It is in orange-red crystals, which, when old, become coated with powder and lose their brightness; this portion should always be washed off before making into solution. It has various uses. With sodium hyposulphite it forms a reducer - this class of reducer is entirely distinct from the reducers used in connection with the developers. With uranium nitrate, it makes an intensifier. It also forms a bleaching solution in some processes of bromide paper toning. It is a poison.

Potassium Oxalate

In white crystals, used in platinum paper development.

Potassium Phosphate

Also in white crystals, used with potassium oxalate.

Sodium Carbonate

Is in white crystals of a more or less irregular size. Care must be taken not to confound the Carbonate with the Bicarbonate, which is the article frequently sold when carbonate is asked for in the ordinary way. The bicarbonate being an acid carbonate has not the same neutralizing power as the normal carbonate, therefore make it perfectly clear when purchasing that it is for photographic purposes. Washing soda is an impure carbonate, the pure should always be used. Sodium carbonate is used as the accelerator in pyro-soda, and also frequently in hydroquinone and metol developing solutions.

Sodium Hyposulphite

Commonly called "Hypo." This is one of the most useful chemicals in photographic work, being a solvent of the silver haloids. It is used for the purpose of fixing plates, films and papers. It is in bright colourless crystals of varying size. The variety known as "Pea-crystals" is the one generally sold. It should be stored in a dry place, as it has a tendency to become damp. Its solution is frequently called simply "The Fixer."

Sodium Metabisulphite

White crystals of smaller size than those of sulphite. It is used for the same purposes. Being of an acid nature it will neutralize a portion of the alkaline carbonate in a developing solution.

Sodium Sulphide

Damp white crystals, which become liquid if exposed to the air and give off an unpleasant odour. Used in sulphide toning of bromide and gaslight papers and lantern slides.

Sodium Sulphite

In white crystals. Used in developing solutions as a preservative, also to assist in preventing stains on the negative.

Uranium Nitrate

Bright yellow crystals, and is deliquescent. It is used in the uranium and ferricyanide intensifying process, and also toning bromide papers and lantern slides.