METHOD OF APPLYING THE COPPER SULPHATE. 25 



of their food and depriving them of protection from fish and other 

 enemies. This is probably the explanation of the reported decrease 

 in the number of mosquito larva? after spraying a lily pond with 

 Bordeaux mixture, although it is possible that the strength of the 

 solution r^d may have been partly responsible for their death. It 

 is belie vi that it will not be impracticable to use the amounts of 

 copper si ;hate necessary to actually destroy such larva?. Certainly 

 this method if effective offers considerable advantages over any now in 

 use, and it should be thoroughly tested. Cooperative experiments 

 are now under way with the Bureau of Entomology to determine the 

 strength of solution necessary to kill larvae of different species and ages 

 under various conditions. 



METHOD OF APPLYING THE COPPER SULPHATE. 



The method of introducing the copper sulphate into a water supply is 

 extremely simple. Though aiw plan will suffice which distributes the 

 copper thoroughly, the one recommended and used b} T the Department 

 of Agriculture is as follows: Place the required number of pounds of 

 copper sulphate in a coarse bag gunny-sack or some equally loose 

 mesh and, attaching this to the stern of a rowboat near the surface 

 of the water, row slowly back and forth over the reservoir, on each 

 trip keeping the boat within 10 to 20 feet of the previous path. In 

 this manner about 100 pounds of copper sulphate can be distrib- 

 uted in one hour. By increasing the number of boats, and, in the 

 case of very deep reservoirs, hanging two or three bags to each 

 boat, the treatment of even a large reservoir may^ be accomplished in 

 from four to six hours. It is necessary, of course, to reduce as much 

 as possible the time required for applying the copper, so that for 

 immense supplies with a capacity of several billion gallons it would 

 probabl} T be desirable to use a launch, carrying long projecting spars 

 to which could be attached bags each containing several hundred 

 pounds of copper sulphate. 



In waters that have a comparatively high percentage of organic 

 acid it is sometimes advisable to add a sufficient amount of lime or 

 some alkali hydrate to precipitate the copper. The necessity for this 

 will never occur in a limestone region, as in this case there will always 

 be enough calcium hydrate or carbonate to cause the desired precipita- 

 tion. The precipitation of copper does not mean the destruction of 

 its toxicity, for experiments conducted in this laboratory have con- 

 firmed Rumm's * results that the insoluble salts of copper, such as the 

 hydrate, carbonate, and phosphate, are toxic only if they are in con- 

 tact with the cell, but are highly toxic in that case. In this connection 

 it should be mentioned that Hedrick has described a method for con- 



Hedrick, Gardening, 11: 295. & Rumm, 1. c. 



