238 ESSENTIALS OF BOTANY 



The occurrence of blue-green and green algae in city 

 water-supplies is often a matter of serious importance, as 

 it may give rise to very disagreeable tastes and smells. 

 Some of the odors have been described as the moldy, the 

 fishy, the " pig-pen " odor, and so on. Various means have 

 been adopted for getting rid of the organisms, and most 

 of them (including some animalcules) may readily be de- 

 stroyed by adding a small proportion of copper sulphate 

 to the water in the reservoir.^ A bag of the copper salt 

 trailed behind a boat rowed about over the surface will 

 readily supply the needed amount of sulphate. Some of 

 the most objectionable organisms are killed by as small a 

 proportion of copper sulphate as one pound to five or ten 

 million pounds of water, and in such a dilute solution as 

 this the salt is not capable of exerting any poisonous 

 action upon the drinkers of the water. 



1 See Bergen and Davis' Principles of Botany, pp. 170, 171. See also 

 Whipple's Microscopy of Drinking Water, Chapter IX, John Wiley & Sons, 

 New York. 



