Tests for Impurities in Drinking Water.
In an article in The Pharmaceutical Record upon the subject of testing drinking water for impurities, Frederick J. Westling, P. H. G., says:
Sometimes the pharmacist is called upon, especially if his sign reads “chemist and druggist,” to ascertain whether a sample of water is fit for drinking and domestic purposes or unfit for that end. It isn’t a very difficult matter to apply a few tests for the simple determination of the fitness or otherwise of a sample in question. A complete examination of the character of a sample of water is a very difficult problem and should be referred to a skilled chemist. The substances to be looked for primarily are organic matter, albuminoid matter, ammonia, nitrates and nitrites.
The nitrogen compounds are usually more abundant if animal matter is present ; they of all other abnormal constituents render water the most unwholesome. Their presence and of ammonia and of albuminoid substances does not necessarily render water unfit for domestic purposes, but water containing them or either one usually becomes the breeding place of the contagious disease germs if they are around.
I. For organic matter, put a little of the sample into a beaker, add two or three drops of dilute sulphuric acid and color distinctly with a solution of permanganate of potassium. If much organic matter is present, the color of the permanganate becomes discharged almost immediately ; if less or very little, it takes longer to decolorize. If the color has not changed in twenty-five or thirty minutes it is safe to assume that organic matter was not present. This is a tolerably reliable test.
2. For nitrites, a little sulphuric acid added to the water forms nitrous acid if nitrites are present, which is easily detected by its power of liberating iodine from iodide of potassium. A little starch paste is mixed with a small quantity of a solution of potassium iodide, and the mixture added to the suspected water containing the sulphuric acid. If nitrites were present the nitrous acid formed liberates the iodine from the iodide, which turns blue with starch. This indirect method is a ready means for detecting the nitrites if present in not too small a quantity.
3. Nitrates are detected by converting into nitric acid, which turns morphia red. A portion of the water is evaporated to dryness, the residue treated with a drop of strong sulphuric acid (which makes nitric acid of the nitrate) and a portion of morphine added. If nitrate was present the morphine gives red color.
4. For ammonia, Nessler’s reagent is by far the best test. It may be made by dissolving eighteen grains of iodide of potassium in a little water, adding solution of mercuric chloride until the red iodide of mercury first formed redissolves upon agitation. To this is added a solution of fifty grains caustic potassa and distilled water to make eight ounces.
This reagent will detect 0.00375 of a grain in a pintof water by giving a yellow color. A reddish color or precipitate forms with larger quantities of ammonia.
5. Albuminoid matter requires a more elaborate proceeding for its detection. If all of the above were found it is hardly necessary to go to the trouble of looking for albuminoids ; the water would be unwholesome even if they were not present. If it is desired to test for them, nevertheless, Chapman and Wankly’s test is the simplest to employ. If the water was found to contain ammonia, the latter must first be removed, as must also any urea that may be present