METHOD OF APPLYINO THE COPPER RI^LPHATE. 25 



of llit'ir food iiiul (lrpri\ iuj;- tlu-m of i)roteetioii from lisli and otiior 

 onoinios. This is probably the exphiimtion of the reported" decrease 

 in the luiniber of mosquito hirviB after sprayino- a lily pond with 

 Bordeaux mixture, although it is possible that the strcno'th of the 

 solution used inay have been partly responsi))le for their death. It 

 is believed that it will not be imi)racticable to use the amounts of 

 copper sulphate necessary to actually d(>str(n' such larva\ Certainly 

 this method if ett'ective otters considerable^ advantaj'es over any now in 

 use, and it should be thoroughly tested. Cooperative experiments 

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

 strength of solution necessary to kill larvtu of diti'ercnt 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 any plan will suffice which distributes the 

 copper thoroughly, the one recounnended and used by the Department 

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

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

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

 of the water, I'ow slowly back and forth over the reservoir, on each 

 trip keeping the boat within 1(> 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 

 probably 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 alwa3^s 

 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 Eumm'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 cou- 



rt Hedrick, Gardening, 11: 295. «< Rumm, 1. c. 



