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.
Should one desire to test prints or plates to see if all hypo has been eliminated, the following solution is recommended: Prepare a little starch paste by boiling starch in distilled water. Add to this a few drops of iodine solution. As iodine is not soluble in water, this solution must be made by dissolving the iodine in alcohol, or in a potassium iodide solution. Iodide of starch will be formed immediately upon the addition of the iodine solution to the starch paste, resulting in a deep blue color. The blue color will disappear when a drop or two of this iodide of starch is added to the wash water when hypo is present.
NaNO3. Saltpetre, or Niter.
Colorless, transparent crystals; saline, slightly bitter taste.
Soluble in 1.2 parts of water and in 50 parts of alcohol. Use.
Sometimes added to the silver bath for albumen paper; also added to developers to assist in giving a chocolate color.
White, crystalline powder. Soluble in 31 parts of cold, and in 16 parts of boiling, water. Used as a developing agent in some platinum processes.
Colorless, transparent crystals or white granular powder; cooling saline taste. Efflorescent in dry air. Crystals contain 12 parts water, while the powder is practically free from water. Soluble in six parts of water; insoluble in alcohol. Used in various toning baths.
Na2SiO3 +H2O. Water Glass. White to grayish white, hard, flat pieces. Soluble in water. Gives a strong alkaline liquid. Used in the Collotype and other printing processes.
Na2SbS4 + 9H2O. Schlippe's Salt. Large, colorless or yellow crystals; alkaline reaction. Soluble in water. Use in photography is chiefly in intensifying collodion.
Na2SO4 + 10H2O. Glauber's Salt. Colorless, efflorescent crystals. Soluble in 3 parts of cold, and in 0.4 parts of boiling water; insoluble in alcohol. Solution is neutral to litmus paper. This salt is sometimes confused with sodium sulphite, but it should not be used in developers, as it will not give the proper action.
Na2S + 9H2O - II;. IV.
Colorless to yellowish, deliquescent crystals. Easily and clearly soluble in water. Solution slightly alkaline to litmus paper. Used principally in developing solutions.
Crystals - Na2SO3 + 7H2O - I; II; IV. Colorless crystals; saline, sulphurous taste; efflorescent in air. Soluble in about 4 parts water. The crystals contain 7 parts water of crystallization. Used principally as a preservative for pyro. It is also employed in various other developing solutions. Employed as a darkening agent in mercuric intensification. It may be used in place of sodium hyposulphite as a fixing agent, but it is not as effective as the "hypo," at the same time being more expensive. Should it be necessary to use it as a fixing agent, however, 4 ounces of the chemical should be dissolved in 20 ounces of water. Sodium sulphite should be kept in well-stoppered bottles, for when exposed to air it decomposes, a white powder - sodium sulphate forming on the outside of the crystals.