26 METHOD OF DERTROYINO ALG^ IN WATER SUPPLIES. 



trolling' the t^iowth of al^al .scum in lily [)onds hy the u.se of Bordeaux 

 mixture which .seems to have been temporarily effective. However, 

 the impracticability of using such a mixture is apparent for the 

 destruction of microscopic alga? distributed through a reservoir or a 

 lake containing millions of gallon.s. 



PRACTICAL TESTS OF THE METHOD. 

 WATER-CRESS BEDS. 



The first practical test of the treatment of water for the purpose of 

 killing out extensive growths of algae was made in the fall of 1901 near 

 Ben, Va. , in connection with the cultivation of water cress for market. 

 Water cress is grown there, as well as in other parts of the country, 

 in large quantities during the winter, it being a valuable crop at that 

 season of the j^ear. The cress is confined in beds made by construct- 

 ing dams across a small stream, which maintains a water level not too 

 high for the growth of the plants and yet permits flooding when there 

 is danger of a freeze. In the locality where the experiments were 

 carried on the water was obtained from a thermal spring with a tem- 

 perature the year around of about 70^ F. Such a temperature was 

 particular!}' favorable to the development of Sjjirogi/ra and similar fila- 

 mentous alga3, so that when the cress was freshly cut they frequentl}' 

 increased to such an extent as to completel}' smother out a large part 

 of the young and tender plants. The only known remedy under such 

 conditions was to rake out the water cress and alga? and reset the entire 

 bed. This was an expensive method, however, besides being success- 

 ful only about half the time. Consequently, it was very desirable to 

 devise some means of preventing the growth of the algae without 

 injuring the water cre.ss, and the treatment b}' means of copper sug- 

 gested itself. At first a strong solution of copper sulphate was used, 

 spraying it on the algal covered surface of the l)eds, but this only 

 destroyed the few filaments with which the copper came in contact, 

 the large mass of algae being practical!}' unaffected. The method of 

 applying the copper by means of dissolving it directly in the beds was 

 next tried, and the success of the treatment was almost immediately 

 evident. In this case the amount of copper added was about equal to 

 a strength of 1 to 50,000,000 parts of water, but it is probable that by 

 the time it reached most of the Sjjirogyra it was considerably 

 weakened, as it was impossible to prevent a slight current of fresh 

 water from pa.ssing through the beds at all times. 



The success of the copper treatment for eradicating alga? from cress 

 beds has been thoroughly demonstrated, and there is no reason why 

 growers should have trouble from this cause in the future. The strength 

 of the .solution nsed for killing the alga^ is so very much weaker than 

 that which might affect the cre.ss that there is no possible danger of 



