Test for Sulphates.—To 10 cc. of water add 2 cc. of dilute HCl and 2 cc. of BaCl2. A cloudiness or the formation of a white precipitate indicates the presence of sulphates.
Test for Iron.—If a brown sediment is formed in water exposed to the air for some time, it is probably iron hydroxid. To 10 cc. of the water add a few drops of HNO3, heat, and then add ½ cc. of NH4CNS. A red color indicates the presence of iron.
Test for CaO and MgO.—To 10 cc. of H2O add 5 cc. NH4OH. If a precipitate forms, filter it off, and to the filtrate add 3 cc. NH4Cl and 5 cc. (NH4)2C2O4. The precipitate is CaC{2}O4, and the filtrate contains the magnesia. Filter and add 5 cc. Na3PO4 to precipitate MgNH4PO4.
1. How would you test a water to detect the presence of organic matter? 2. Name some mineral impurities often found in water. 3. Describe the test for chlorids; for sulphates; for iron; for lime; for magnesium. 4. Of the two classes of impurities found in water, which is the more harmful? 5. Name three ways of purifying waters known to be impure, and tell which is the most effectual.
Experiment No. 49
Testing for Nitrites in Water
To 50 cc. of water in a small beaker add with a pipette 2 cc. of naphthylamine hydrochloride and then 2 cc. of sulphanilic acid. Stir well and wait 20 minutes for color to develop. A pink color indicates nitrites.
Reagents Used
Sulphanilic Acid.—Dissolve 5 gm. in 150 cc. of dilute acetic acid; sp. gr. 1.04.
Naphthylamine Hydrochloride.—Boil 0.1 gm. of solid α-amidonaphthaline (naphthylamine) in 20 cc. of water, filter the solution through a plug of absorbent cotton, and mix the nitrate with 180 cc. of dilute acetic acid. All water used must be free from nitrites, and all vessels must be rinsed out with such water before tests are applied.