408 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1939 



An algicide acts directly by killing the algae. Chloramine (am- 

 monia and chlorine) and copper sulfate, used separately or together, 

 and potassium permanganate are the algicides usually used. Very 

 minute quantities of them are effective, and remaining traces of them 

 are usually removed in the course of the subsequent sand-filtration. 

 A few bacteria may remain after slow sand-filtration. Small quan- 

 tities of chloramine are generally used to destroy these survivors. 

 The chloramine treatment is preferable to chlorination (the use of 

 chlorine alone) because the chloramine has greater power of destroy- 

 ing bacteria and does not leave the bad taste of chlorine in the water. 



The following table, published by Hale and based on his experience 

 and on data published by Moore and Kellerman, Whipple, and 

 others, indicates the amount of copper sulfate and clilorine necessary 

 to destroy some of the most frequently occurring plankton forms. 



CHEMICALS REQUIRED FOR TREATMENT OF DIFFERENT GENERA 



OF PLANKTON 



