TECHNICAL AND SANITARY PROBLEMS 1077 



been found sufficient to destroy the algae. The amount required 

 depends upon the kind of organisms present, and the amount and 

 character of the other organic matter. Copper sulphate is applied 

 to a reservoir by putting crystals of the salt in a gunnysack, or coarse 

 bag, and dragging it around the reservoir after a boat, letting it 

 dissolve in the water as it will. Preferably this should be done 

 while the wind is blowing, and when the water is in a state of some 

 agitation, so as to obtain a rapid dissemination of the solution 

 through the water of the reservoir. Unless care is exercised in this 

 regard there is danger that fish may be killed, and in any case there 

 is always danger that some fish may be killed. The method, there- 

 fore, is one that should not be used by one whose experience and 

 judgment is insufficient. 



The copper sulphate treatment is not always entirely successful. 

 Sometimes after one kind of an organism has been destroyed by 

 its use some other organism will appear and be more troublesome 

 than the first. A single treatment of a reservoir with copper sul- 

 phate therefore does not always suffice, and when a second dose is 

 required it is usually necessary to use larger quantities than the 

 first time. 



Purification of Water Containing Algae. Water that contains algae 

 may be purified by filtration, though the ordinary processes may 

 require some modification, depending upon the number and char- 

 acter of the organisms present. One of the essential elements of 

 successful filtration is that the water shall always contain a sufficient 

 quantity of oxygen throughout the process. Aeration, therefore, 

 may be necessary before or after filtration or both. It may be 

 accomplished by spraying the water into the air so that it falls in 

 drops, or by exposing it in thin films as it passes over a weir with a 

 considerable fall through the air. Generally speaking an exposure 

 from one to two seconds is necessary and sufficient. 



As an illustration of successful purification of a water heavily 

 laden with algae may be mentioned the old Ludlow supply of Spring- 

 field, Massachusetts, which during the summer contained very 

 heavy growths of Anabaena. The method employed was inter- 

 mittent sand filtration, similar to that commonly used for the treat- 

 ment of sewage. The water was first aerated and allowed to spread 



