24 METHOD OF DESTROYING ALGiE IN WATER SUPPLIES. 



gent purposes is one-fourth orain, or O.oiO i^i'auj; as an emetie, a close 

 of live grains, or 0.33 gram. Thus it is seen that even if the maximum 

 concentration of copper sulphate necessar}^ to dastroy algte in reser- 

 voirs were maintained indefinitel\% the total absorption from daily use 

 would be very far below an amount that could produce the least 

 unpleasant effect. Taking a dilution of one to one million, which in 

 all cases would be sufficient to prevent the growth of a polluting algal 

 form, it would be necessary to drink something over twenty quarts of 

 water a da}' before an amount which is universally recognized as 

 harmless would be introduced into the system, while more than fffty 

 quarts would have to be consumed before there would be danger of 

 producing an unpleasant or imdesirable effect. As will be seen from 

 the preceding tables the use of copper sulphate at this maximum 

 strength of one to one million would need to be resorted to only in 

 extreme cases, and for a ver}' short length of time, for, the reservoir 

 once entirely free from the organisms, a very much weaker solution 

 would be sufficient should any further application be necessar3\ 



Perhaps the strongest argument in favor of using a chemical treat- 

 ment of this kind is that even though enough copper should be added 

 to a reservoir to make a one-millionth solution, nothing like this 

 amount would appear in the water distributed. A verj^ large percent- 

 age of the copper is combined with the algaj and precipitated in other 

 ways, so that practically none would remain in solution after the first 

 few hours." Samples of water taken from a reservoir treated with 

 sufficient copper sulphate to make a solution of one to one million, 

 failed to show any reaction for copper after twenty-four hours, 

 although all the algje were killed. It is believed that the process used 

 of evaporating down the original quantity and testing by the delicate 

 potassium ferro-cyanide method would certainly have detected copper 

 had it been present in the proportion of one to fifty million. Other 

 tests were made by different chemists, but always with negative results. 



In addition to the use of copper sulphate in reservoirs containing 

 water to be used for domestic purposes, there are possibilities of its 

 application in treating irrigation reservoirs, small pleasure lakes, fish 

 ponds, oyster beds, etc. Here it may often be desirable to exceed the 

 strength of solution that would represent the maxinunu required in a 

 municipal water supply. This would be done not only to kill all the 

 alg{», but to destro}' or drive away reptiles and other pests, leaving 

 the water perfectly clear and clean. The use of some such method 

 for the destruction of mosquito larviB also seems worth}' of attention. 

 The mere removal of the great mass of algal growths in stagnant pools 

 undoubtedly reduces the number of larva^ ])y destroying this source 



« Adsorption, according to True and Ogilvie (Science, N. S., 19: 421), would materi- 

 ally reduce the quantity of co])per in solution. See also Bull. No. 9, Yeg. Phys. and 

 Path., U. S. Dept. Agric. 



