46. Sulphite Of Soda

Sulphite Of Soda. Transparent crystals, also granular and dried ( anhydrous) very soluble in water, two parts of crystal are equivalent to one part dried (anhydrous or granular). Chemical action, neutral or slightly alkaline. Do not confuse sulphite with sulphate of soda.

Carbonate of Soda, - Commonly called washing soda. Transparent crystals, also granular and dried (anhydrous). Very soluble in water, two parts of crystals are equivalent to one part dried (anhydrous or granular). Chemical action, strongly alkaline.

Pyrogallic Acid. - Developing agent. A white crystal-ine substance, poisonous, although termed an acid its action is neutral.

Sulphuric Acid, C. P .- Chemically pure. A colorless, oily liquid. Commercial sulphuric acid is yellow or brown and should never be used. Caution: - Never pour water into sulphuric acid, as this would be most liable to cause an explosion. Always pour the acid into the water. Coming in contact with flesh it will burn. Do not confuse sulphuric acid with sulphurous acid.

Bromide of Potassium. - Colorless crystals, dissolves readily in water.

Hypo-Sulphite of Soda. - Commonly called Hypo. (Thiosulphate of Sodium.) Put up in crystals and granular form, colorless.

Nitric Acid, C. P. - (Chemically pure.) A colorless liquid of a pungent, suffocating odor, is a powerful dissolvent of all metallic bodies, and if coming in contact with the flesh will burn.

47. Pyro Formula. - Stock Solution, No. I

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

24 ounces

Pyro....................................

1 ounce

Sulphuric Acid, C.P ..................................

10 drops

Stock Solution, No. 2

Sulphite Soda, Hydrometer Test 70, or, if by weight,

Sulphite Soda (crystals) .................

2 ounces

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

7 ounces

Stock Solution, No. 3

Carbonate Soda, Hydrometer Test 40, or, if by weight,

Carbonate Soda (Crystals) .............

2 ounces

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

10 ounces

When making up solutions by weight and anhydrous carbonate or sulphite of soda is used one-half the amount is required.

The Stock Solutions of Sulphite and Carbonate of Soda can be made up in any quantity, and they should be kept in a corked bottle.

48. Anhydrous sodas have no water in their composition; therefore, they are twice as strong as the crystal, which has water in its composition. It is advisable to use anhydrous, or if the crystal is used be sure and get pure crystals. Sodas should be purchased in sealed packages or bottles; never in loose quantities.

49. To Develop, take one ounce of No.1, one ounce of No. 2, one ounce of No. 3, and add six ounces of pure water in cold, and eight ounces in warm season. The action of the developing agent (pyro) is more rapid in warm than in cold weather. In warm weather the emulsion softens more readily, and the action of the pyro is more rapid; therefore, if the same strength developer was used in warm as in cold weather the negatives would thicken up too rapidly, resulting in harsh, strong negatives. This is overcome by adding more water to the developer. In cold weather the emulsion remains firmer, and the pyro does not affect it so readily; therefore, it is necessary to use a stronger developer - consequently less water is used than in warm weather.

Developer should never be used but once, whether one plate or a batch of plates are developed in a tray. After a plate or a tray full of plates have been developed, that developer should be discarded, or poured into the second tray to be used as a restraining bath. All normally exposed plates should be started developing in a fresh bath.

In preparing a pyro stock solution, first place the water in the graduate, then add the sulphuric acid, and last add the pyro. If the water used is strongly alkali, and the chemicals were not mixed in the order given, this stock solution would discolor very rapidly.