4393. Test for the Presence of Blood

4393.   Test for the Presence of Blood. Gunning has discovered in acetate of zinc a reagent that precipitates the slightest traces of the coloring matter of blood from solutions, even where the liquids are so dilute as to be colorless. Blood washed from the hands in a pail of water can readily be detected in this way. The flocculent precipitate thrown down by acetate of zinc must be washed by decantation, and finally collected on a watch-glass, and allowed to dry, when the microscope will readily reveal crystals if any blood be present. (See No. 6415 (To Detect Blood-stains).)

4394. Test for the Presence of a Free Acid

4394.   Test for the Presence of a Free Acid. Dissolve chloride of silver in just sufficient ammonia to make a clear solution. If a little of the test be added to ordinary spring water, the carbonic acid present in the latter will neutralize the ammonia and precipitate the chloride. The above forms a good lecture experiment, the test being a very delicate one.

4395. Permanganate of Potassa as a Test for Organic Matter

4395.    Permanganate of Potassa as a Test for Organic Matter. As a test for organic matter in air and water, its accuracy has been called in question, on the ground that it does not attack all kinds of organic matter with equal facility - some, as starch, resisting its action for a long time. It must be admitted, however, that it is, at present, the only practical test that we have, and certainly shows very rapidly and clearly the presence of hurtful organic matter in water or in air. It can be applied by any one, it being only necessary to use a weak solution; the disappearance of the color indicates the presence of organic matter. In time of epidemics, such as cholera or dysentery, this test might be of much value in singling out the contaminated from the pure water. It is, perhaps, well also to recall the fact that this test forms the readiest means of purifying foul water.

4396. Trommer's Test for the Presence of Sugar in Urine

4396.    Trommer's Test for the Presence of Sugar in Urine. Put some of the suspected urine into a large test-tube, and add a few drops of solution of sulphate of copper, then sufficient solution of potash to render it strongly alkaline. If sugar be present, the precipitated oxide redissolves into a blue liquid, and on boiling red oxide of copper is precipitated. "White merino that has been wet with a solution of bichloride of tin is said to form a ready test for sugar in urine, etc.. A portion wet with the suspected liquor, and exposed to 260° to 300° of heat, becomes blackened if sugar is present.

4397. Quantitative Test for Sugar in

4397.    Quantitative Test for Sugar in. Urine. Dissolve 400 grains pure crystallized sulphate of copper in 1600 grains of distilled water; add this gradually to a solution of 1G00 grains neutral tartrate of potash in a little water mixed with 6000 or 7000 grains solution of caustic soda of 1.12 specific gravity. Add water to make up the whole 11,544 grain measures. 1000 grain measures are equivalent to 5 grains of grape sugar.