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To Test the Purity of Borax

4384. Το Detect Gum Arabic in Gum Tragacanth. Make the gum into a clear Its strength is best ascertained by the quantimucilage, and filter carefully; pour strong al -ty of sulphuric acid required to neutralize a cohol upon it, and if it retains its solubility given weight of borax. (See Alkalimetry.) and transparency, no gum arabic is present, The impurities in borax are common salt and but if it becomes opaque, or deposits a pow- alum, which are mixed with it to lower the der at the bottom, it contains gum arabic or value. some similar substance.

Common salt may be detected by a solution of the borax in hot water yielding with nitrate matter with equal facility-some, as starch, of silver a curdy white precipitate which is resisting its action for a long time. It must soluble in ammonia; this must be distin- be admitted, however, that it is, at present, guished from the white pulverulent precipitate the only practical test that we have, and cerof borate of silver which will be thrown down tainly shows very rapidly and clearly the from pure borax. presence of hurtful organic matter in water The presence of alum is determined by or in air. It can be applied by any one, it addition of ammonia water to a solution of being only necessary to use a weak solution; the borax giving a bulky white precipitate. the disappearance of the color indicates the