16 BULLETIN 1027, U. S. DEPARTMENT OF AGRICULTURE. 
effect upon the copper content of the tomatoes. It appeared that 
the copper found in the tomatoes came from the soil, whence the 
plants assimilated it in different proportions, according to the nature 
of the soil or under the influence of other factors. 
In 1917 Carles (19) stated that copper occurs in small amounts in 
agricultural products and in larger amounts in calf liver and heef 
liver. O'Kane. Hadley. and Osgood (102) reported the following 
amounts of arsenic (calculated as As 2 3 ) on fruits and vegetables 
that had been sprayed with dry lead arsenate equivalent to 3 pounds 
of lead arsenate paste to 50 gallons of water: Apples picked at 
intervals ranging from 3 to 91 days after spraying, 0.08 to 0.77 
milligram per apple when picked carefully. 0.02 to 0.50 milligram 
when picked in the ordinary way, 0.10 to 0.21 milligram when picked 
with cotton gloves, and 0.08 to 0.18 milligram when picked with 
cotton gloves and wiped; strawberries picked 2 and 6 days after 
spraying, from S.6 to 34.2 milligrams per quart; currants picked 3, 
6, and 8 days after spraying, from 6.8 to 10.2 milligrams per quart; 
blackberries picked on the day they were sprayed, from 3.8 to 11.2 
milligrams per quart: cabbage gathered 2 and 8 days after spraying, 
from 43.5 to 51.4 milligrams per head; and lettuce gathered 1 and 6 
days after spraying, from 1.6 to 10.6 milligrams per head. The 
maximum amount of lead arsenate spray that would adhere to an 
apple, when sprayed directly, was found to be an amount equivalent 
to 4 milligrams of arsenious oxid. Such fruit gave evidence of spray 
material on its surface. 
EXPERIMENTAL WORK. 
The investigation conducted by the United States Department of 
Agriculture included experiments on peaches, cherries, plums, 
apples, pears, grapes, cranberries, tomatoes, celery, and cucumbers. 
The spraying schedules are shown in Tables 5 to 14. 
METHODS OF ANALYSIS. 
The following methods of analysis were employed : 
Of the whole fruit and pulp, dry 200 to 300 grams of sample on the steam 1 ath in 
glass dishes, and report loss as "'loss on drying.'' (For the determinations on the 
skins, use parings from 4 apples: for the calyx and stem end determinations, use 12 
apples and corresponding amounts in the case of other fruits. I Transfer the dried 
residues to casseroles and add 100 to 200 cc. nitric acid. Heat the mixture, if neces- 
sary, to start action, and when violent action is over cautiously acid 20 cc. sulphuric 
acid. Heat on hot plate, removing at intervals to add small amounts (3 to 5 ce. of 
nitric add (do not allow the solution to become 1 lack), and when the oxidation is 
complete evaporate until sulphuric acid fumes are given off. Cool, dilute with waic r. 
and again evaporate to sulphuric acid fumes. Cool, dilute with al out 100 cc. of 50 
per cent alcohol, and let stand over night. Filter and wash with 80 per cent alcohol. 
Save sulphate precipitate for lead determination. The copper and arsenic are deter- 
mined in the nitrate. Evaporate the nitrate to small volume on steam 1 ath to remove 
alcohol. Make to volume. 
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