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(e. g. it can act in a weak way, both as a base and an acid), which make it extremely useful as a base for the preparation of other compounds, salts, etc., more freely soluble and more powerful as developers. As a base paramidophenol readily Paramidocombines with strong acids, such as phenolhydrochloride hydrochloric and sulphuric acids. With -QH the first it forms paramidophenolhydrochloride, C,H.OHNH.HCl. This is the salt most generally obtainable commercially, and that usually intended in formulas where "paramidophenol" is '-./ -NH2HC] mentioned without further specification. It comes in fine, prism-like crystals, more or less white, according to the purity of the product. A good sample should contain 75 per cent or more of paramidophenol. The hydrochloride salt is said to possess 20 per cent more developing power than the sulphate, and is sold under its own name, aa well as under various trade names, as Kodelon, etc. Generally speaking, the purity and Teat for quality of a sample of paramidophenolPurity hydrochloride is assured, if purchased from a responsible maker or dealer. The following test, for which I am indebted to Mr. L. H. Wallace, is simple and efficient for its purpose. Add 10 grains paramidophenol-hydrQchloride to I ounce distilled water in a clean glass vessel. If the sample is pure, it will dissolve readily and give a clear, colorless solution which will remain clear for several hours. If when first prepared the solution shows a purplish, yellowish, or greenish color, this denotes the presence of dyestuff; if particles of insoluble matter remain in suspension in the solution, this indicates the presence of organic impurities; both are detrimental to the keeping and developing power of the sample, in proportion to the showing on test. Paramidophenol-hydrochloride is SolubWty- readily soluble in water (I :Io) but keeps Keeping better in faidy strong so1ut10ns 路 路 Qualities t han m diluted solutions. Dissolved in 5 or 10 per cent sodium sulphite solution it will keep clear and


Modern Photographic Developers  

A Practical Handbook to the New Developers Telling What They Are and How to Use Them with Reliable Formulae by The Photo Miniature, January...