40 « 



EXPERIMENT STATION 



[Jan. 



arsenic was slowly added during the slaking and thoroughly 

 mixed in. After the slaking had been com])leted, water suf- 

 ficient to make 5 gallons was added, and the whole thoroughly 

 stirred. A sack containing 5 pounds of copper sulfate was 

 then suspended in the mixture and shaken frequently until 

 the copper sulfate had entirely dissolved. About a day later, 

 when ready to spray, 5 pounds of lime were slaked in a few 

 gallons of water, and diluted to make 25 gallons. The other 

 mixture, prepared the day before, was also then diluted with 

 water to make 25 gallons, and the two lots were poured to- 

 gether, stirred and sprayed. 



It is evident that as a result of this work the material sprayed 

 is no longer arsenic itself. It is probable that it, at least in 

 part, combines with the copper, forming copper arsenite, 

 which alone is often very injurious to foliage, but in this case 

 is rendered non-injurious by the lime present. The Bordeaux 

 mixture made in this way was green in color. Its suspension 

 did not quite equal that of ordinary Bordeaux-arsenate of 

 lead, but it adhered to the leaves fully as well. No leaf 

 injury was observed in any case where this material was used, 

 and good protection from potato insects was secured. No 

 blight appeared on the potatoes. 



The amounts of lead arsenate, both in dry form and as 

 paste, required to furnish the same amount of poison (expressed 

 in terms of metallic arsenic) as was supplied by one-half pound 

 of white arsenic, together with the relative costs of the three 

 materials, are as follows: — 



1 In 50-pound lots 



Evidently the white arsenic is by far the cheaper material 

 to use. There is a little extra labor in preparing the Bordeaux 

 mixture with arsenic as compared with the use of the other 



