18 BULLETIN 
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 col orime trie 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 and 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, 
which 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 
four 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 
