20 BULLETIN 866, U. S. DEPARTMENT OF AGRICULTURE. 
Lot 1. — The copper of the Pickering sprays adhered to the leaves 
in proportionally greater amounts than that of the Bordeaux spray. 
Per unit of copper sulphate in the spray more copper was deposited 
on the leaves sprayed with the three Pickering sprays which contained 
the highest percentages of copper sulphate than on those sprayed 
with Bordeaux, but less on the leaves treated with the other Pick- 
ering sprays. The results for copper on the leaves sprayed with 
barium water were low. Of the leaves treated with the 3-3-50 and 
3-1^-50 sprays those receiving the 3-1^-50 spray showed the largest 
deposits. 
Lot 2. — As a rule, more copper adhered to the leaves sprayed with 
Bordeaux than to those to which any of the other sprays were applied. 
In several instances, however, the results for the Pickering-sprayed 
leaves were equal to those for the Bordeaux-sprayed leaves per unit 
of copper sulphate in the spray. The addition of lead arsenate or 
rosin-fish-oil soap to the Pickering sprays did not increase the amount 
of copper which adhered to the leaves. More copper adhered to the 
leaves sprayed with standard Bordeaux than to those sprayed with 
barium water or Burgundy mixture. 
Average results. — More of the copper of the Pickering (A) than of 
the Pickering (C) sprays adhered to the leaves. In three of the eight 
Pickering sprays tested, the copper adhered to the leaves in a higher 
proportion per copper sulphate content of the spray than the copper 
of the standard Bordeaux, 5-5-50. The Bordeaux, 3-1^—50, spray 
gave higher results than either the Burgundy mixture or barium water. 
In proportion to the amount of copper sulphate present in the spray, 
the Burgundy mixture gave the lowest results of all. 
IN 191S. 
During the season of 1918, the adherence of copper to potato leaves 
was determined for Pickering (A) spray, containing 0.7 per cent 
of copper sulphate, for barium-water spray, with the same copper 
sulphate content, and for Bordeaux, 4-4-50, 4-2-50, and 4-1-50, 
sprays, each containing 1 per cent of copper sulphate. The results 
(Table 5) are very uniform except those for the Bordeaux, 4-1-50, 
spray, used on plat 5, which gave lower figures than the sprays used 
on plats 1, 2, 3, 4, and 6. The highest average figure for copper per 
unit of copper sulphate in the spray was obtained in the case of the 
Pickering (A) spray with a copper sulphate content of 0.7 per cent, 
applied to plat 1. In the tests on plats A, C, D, E, and F, in which 
sprays containing 0.6 per cent of copper sulphate were employed, the 
amount of copper adhering on the leaves treated with Pickering (C) 
spray was the same as the amount adhering to those sprayed with 
Bordeaux. The leaves sprayed with Pickering (A) spray gave 
slightly lower results and those treated with the barium-water spray, 
