PRACTICAL TESTS OF THE METHOD. 27 



injuring 1 the latter if the solution is used by anyone capable of observ- 

 ing ordinary care. The question of how long a treatment is effective 

 must, of course, depend upon conditions, but it is believed that the 

 application of the proper amount of copper once or twice a year will 

 in most cases be sufficient to keep down any algal pest. The manager 

 of the Virginia Cress Company writes, under date of April 12, 1904: 



The "moss" has given me no trouble at all this winter. In fact I have for six 

 months only had to resort to the copper sulphate once. * * * All the conditions 

 were favorable last fall and early winter for a riot of "moss," but it did not appear 

 at all until just a few days ago, and then yielded to treatment much more readily 

 than it did when I first began to use the copper. 



WATER RESERVOIRS. 



The successful elimination of algae from the cress beds of the South, 

 under conditions which were particularly favorable to the growth of 

 these pests, made it desirable that experiments be inaugurated calcu- 

 lated to demonstrate the possibility of ridding water reservoirs of the 

 disagreeable odors and tastes caused by similar organisms. While it 

 was realized that the popular prejudice against any chemical treat- 

 ment of drinking water was strong, it was believed that the very weak 

 solution, together with the very rapid disappearance of the salt added, 

 would not render it a prohibitive method when applied under the 

 direction of the proper authorities. It was also found that consumers 

 of a water which possessed a disgusting odor and taste were not so 

 prejudiced against the use of even a chemical method of extermina- 

 tion, provided it could be proved that no bodily harm would result. 



In the spring of 1903 there was brought to the notice of the Depart- 

 ment the supply of a water company in Kentucky, which promised to 

 furnish a most satisfactory test. Ever since the construction of their 

 reservoir it had given off an unpleasant odor. For the first two sea- 

 sons this was supposed to be due to decaying vegetation, but later 

 years demonstrated the well-known "pigpen" odor due to algae, and 

 this increased from year to year until it was almost unbearable. 



In July, 1903, when the trial was begun, the microscopical examina- 

 tion demonstrated an average of 



Anabsena per cc. . 7, 400 



Clathrocystis do 1,100 



Eudorina % do 200 



There were about 25,000,000 gallons of water in the reservoir at the 

 time of the experiment, and on account of the great number of blue- 

 green algae present it was decided to apply the copper at a strength of 

 1 to 4,000,000. About 50 pounds of copper sulphate was accordingly 

 placed in a coarse sack and this, attached to a boat, was dragged over 

 the surface of the reservoir, giving especial attention to the region 

 which seemed to contain the greatest number of Andbsena filaments. 



