This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Dried - Na2SO3.
A white powder containing from 85 to 90 percent of sodium sulphite. The best form of sodium sulphite to use, as it works better and its purity is more certain than the crystalline form.
(See Sodium Hyposulphite.)
Na2WO4 + 2H2O.
The opposite to contrast. Harsh, contrasty results are seldom desired in the photographic print, and it is for this reason that the photographer usually aims towards securing soft effects. One should not go to the extreme, however, as flatness and a picture lacking life would result. It is necessary to have high-lights and shadows, but the intervening tones should all be well represented, for it is the half-tones that give contrast to the picture. The individuality of the photographer and his own likes and dislikes will have much to do with his individual idea of what is meant by soft effects.
(See Camera, Solar.)
The changing of a substance from a solid or gaseous state to the liquid state. In photography, however, the term solution is used when a substance is dissolved in water.
A liquid in which is dissolved a large amount of a substance. The object of such a solution is usually to decrease the amount of solvents, having as much of the dissolved substance as possible.
A solution is said to be saturated when it will hold no more of a solid. To obtain a saturated solution of any solid, it is advisable to dissolve the chemical in warm water until some of the solid remains at the bottom. Upon cooling some of the chemical which was in solution will be thrown down precipitated. The solution will now be a saturated one. As a rule, warm water will dissolve and hold in suspension a greater quantity of a solid than cold water. Saturated solutions for use should have a temperature of 6o° Fahr., or 15o Cent.