18 BULLETIN 866, U. S. DEPARTMENT OF AGRICULTURE. 



the leaves. The area of one side of the leaves only was used in mak- 

 ing the calculations. The leaves' were dried and used for analysis 

 for copper. The results were expressed as milligrams of copper per 

 square millimeter of leaf surface. By weighing the leaves when dry 

 it was then possible to express the results both as parts of copper per 

 million on the dried leaves and as milligrams of copper per square 

 meter of leaf surface. 



Method of determining copper on leaves. — The leaves were placed 

 in 4^-inch porcelain dishes and ashed in the muffle at dull red heat. 

 The ash was covered with 30 cc. of 1-3 nitric acid and allowed to 

 stand over night. It was then filtered and washed, the filtrate made 

 faintly ammoniacal, and brought to a boil. Next it was cooled, 

 made to suitable volume, and filtered. An adequate aliquot was 

 taken for the colorimetric estimation of the copper. This aliquot, as 

 well as solutions of standard copper sulphate, containing added am- 

 monia and nitric acid, were evaporated to dryness in clean, white, 

 3-inch porcelain dishes. To the residues 5 cc. of distilled water anq\,3 

 drops of acetic acid were added, and finally 3 drops of 10 per cent 

 potassium ferrocyanid, the dishes being rotated to mix the solutions, 

 winch were immediately compared with the standards. The results 

 are expressed as parts of copper per million. This method has been 

 checked against the electrolytic copper method and found to give 

 good results. The standard copper sulphate solution was made to 

 contain 0.0001 gram of copper per cc. 



IN 1916. 



On August 12, two days after the third spray had been applied, a 

 set of leaves (lot 1) was taken from the vines on the sprayed plats. 

 On August 24, seven days after the leaves had been sprayed, addi- 

 tional samples of leaves (lot 2) were taken. The results of the analy- 

 ses, which were made in duplicate, are given in Table 5. Average 

 results for four sets of leaves, or 200 leaves, from each plat show that 

 •the barium-water and three of the seven Pickering sprays employed 

 left a higher percentage of copper on the leaves to 0.1 per cent of cop- 

 per sulphate present in the spray than Bordeaux, 5-5-50. The other 

 I on v Pickering sprays did not show as high a ratio of copper on the leaves 

 as did the Bordeaux, 5-5-50. It must be remembered, of course, 

 that the Pickering sprays were applied four times, while the Bordeaux 

 spray was applied five times. Although the Bordeaux-sprayed leaves 

 always showed the presence of more copper than any of the others, it 

 is apparent that, considering the amount of copper sulphate used, the 

 copper of the Pickering sprays adhered equally as well. The leaves 

 from the vines treated with Pickering (A) spray and rosin-fish-oil 

 soap showed the presence of more copper than did those from the 

 vines sprayed with plain Pickering (A) spray containing 0.38 per cent 

 of copper sulphate. The amounts of copper on the leaves of the vines 



