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.
Proper Color Of Plate. If the plate when fixed is too yellow, strengthen the sulphite; if there is a lack of color, the negative is a blue-gray, reduce the strength of the sulphite stock solution, but use the same quantity. The proper color of a plate is of the gray order, with the least tinge of brown.
Chemical Action. Always bear in mind that sulphite of soda regulates the color-value in the plate; carbonate of soda produces detail; and pyro being the developing agent, gives strength and contrast. If the plates are yellow you will understand that the sulphite is not strong enough. For example, we will say you are using sulphite at seventy test, and your plates are quite yellow. Strengthen it to perhaps eighty hydrometer test, all other chemicals remaining as they are. Regulate the color of the plate entirely by the strength of the sulphite of soda.
52. You will find it rarely, if ever, necessary to change the strength of the carbonate of soda. If, however, you find upon testing the water that it is strongly alkaline, you may find it necessary to change the strength of the Carbonate Stock Solution, that is, make it weaker. For if the water you are using is strongly alkaline instead of being neutral, and the regular amount or strength of alkaline solution (carbonate of soda) was used, you would have more alkali than necessary to balance the developer. If there is too much carbonate (or alkali), you will find the emulsion of the plate will be rather grainy. In such a case reduce the strength of the carbonate of soda very slightly, say five degrees, and this effect will be overcome. The pyro is used for strength. If the plate develops contrasty, use less of No. 1 (Pyro Stock Solution), but usually the formula given will need no altering whatever.
Use Of Hydrometer. A hydrometer is an instrument for determining the specific gravity of liquids. The strength of the liquid is determined by the depth to which the hydrometer sinks in the solution. It has on it a series of numbers from ten to eighty. When testing the strength of solution correction must be made for variations in temperature. If the liquid is cold it may allow the hydrometer to sink lower and the strength it would register might appear weaker than it is; if warm, it would be just the reverse. Do not prepare chemicals by weight; use the hydrometer for testing them and you will always have uniform results.
54. If chemicals in crystal form should dry to a powder by exposure to air, the weight would be altered, although the strength of the original quantity would remain the same; consequently a solution made by dissolving one ounce of the dry powder would be stronger than one ounce of crystals in the same quantity of water. Also chemicals of different brands, and even of the same brand but procured at different times, are seldom of uniform strength, and if prepared by weight instead of by hydrometer test, you will be apt to meet with frequent failures.