630 EVERYDAY SCIENCE 



PROJECT LI. How to Test the Home Water-supply for 

 Organic Impurities, page 447 



(a) In a clean porcelain dish boil one quart of the water to be 

 tested. Continue to boil it until it evaporates. 



If what remains in the bottom of the vessel immediately after the 

 water is evaporated is white and powdery, there are probably only 

 harmless mineral substances in solution in the water-supply. 



If what remains immediately after the water is evaporated is 

 partly white and partly yellowish or greenish, with gum-like stains 

 around the edge of the residue, the water contains organic impurities 

 of either vegetable or animal origin. 



Continue to heat the residue. If the yellowish or greenish or 

 gum-like portions turn black, sputter, and burn away, giving out 

 an offensive smell like burning feathers, the organic matter is pretty 

 certainly of animal origin and is unwholesome if not positively 

 poisonous. 



(6) Unless you live directly on the seacoast or in a region of 

 salt-bearing rocks, neither the surface nor the underground water- 

 supply should contain more than a minute trace of common salt. 

 Anything more than a trace of common salt probably has its origin 

 in vegetable or animal refuse. 



To Test for Salt. To a tumblerful of the water to be tested, add 

 20 drops of nitric acid, and a small crystal of nitrate of silver or 

 5 drops of a solution of nitrate of silver. Stir with a clean strip of 

 glass. The normal amount of salt will be indicated by a faint 

 bluish-white cloudiness. If the water shows marked cloudiness 

 or a solid curdy substance, too much common salt is present. 



The presence of both organic matter and considerable salt in- 

 dicates that the water is probably contaminated by sewage or 

 stable drainage. The source of pollution should be discovered and 

 removed without delay. In the meantime, none of the water 

 should be used for drinking or cooking without purifying it since 

 such water may contain bacteria dangerous to the health. If 

 there is the slightest doubt about the fitness of water for drinking 

 purposes, it should be treated as directed in Project LII. 



