10 



SCIENTIFIC AGRICULTURE 



September, 1921 



from trees on the area sprayed with Bor- 

 deaux mixture. 



Thissse leaves were picked at random iii 

 each case from about a dozen or fifteen 

 trees, and from all positions on each in- 

 dividual tree. Each bunch of five hun- 

 dred leaves wa.s then washed for three 

 or four minutes in one thousand ce. of 

 water contaiiiino: four cc. of concentrated 

 nitric acid. This solution was then fil- 

 tered from the leaves, and thie. copper in 

 the solution was quantitatively determined 

 by the colorimetric method of Winston 

 aiad Fulton (The Fi-eld Testing of Cop- 

 per-Sprav Coatings, Professional Paper, 

 Bui. No. "785, U. S. Dept. of Agric.) The 

 arsenic in the solution was qiiantitatively 

 determined by the Gutzeit method as 

 modified by Sangar and Black. 



The following tables show the result 

 of these determination leixpressed in mili- 

 grams per one thousand leaves, together 

 M"ith the amounts of metallic copper and 

 metallic arsenic applied to the trees, ex- 

 pressed as pounds per acre. Tlie 

 poisoned Bordeaux mixture used was 

 of the 2-10-40 formula with one pound 

 of calcium arsenate, and there were aj^plied 

 one hundred and thirty three gallons per 

 acre for each of the first two applications 

 and one hundred and fifty gallons per 

 acre for each of thOi last two applications. 

 The dust was of the 3-1 formula, and there 

 were applied fifty pounds per acre for each 

 of the first two applications, and fifty-five 

 pounds per acre for each of th?' last two 

 applications. 



Poisoned Bordeaux Mixture. 



Dates of Ap- 

 plication 

 Mav 13th 

 Mav 24tli 



June 9th 



June 21st 



May nth 

 May 24th 



Jun;a lOtli 



June 20th 



Amt. of Cu. Amt. of As. 



applied in lbs applied in lbs 



per acre per acre. 



Miligrams of Milligrams of 



1,66 

 1.66 



1.88 



1.88 



1.5 

 1.5 



1.65 



1.65 



.83 

 .83 



.94 



.94 



.5 



Dust. 



.55 



In exiilanatioii of the above table it 

 may be stat)?d that the successive increase 

 in the amount of copper and arsenic pre- 

 sent upon a thousand leaves immediately 

 after each application, is of cour.se due 

 to the incrleiase in size of the leaves. There 



10 

 8 



23 

 12 

 10 



30 



28 

 4 



is evidently some error in the determina- 

 tions of June 10th and June 17th in the 

 case of the Bordeaux spray, as the latter 

 shows a higher amount of copper and 

 arsenic present than the former although 

 there was no intermediatte application. 



