16 BULLETIN 1027, U. S. DEPARTMENT OF AGEICULTURE. 



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 beef 

 liver. O'Kane, Hadle}^, and Osgood (102) reported the following 

 amounts of arsenic (calculated as AS2O3) 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 8.6 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 lath 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, I'se 12 

 apples and corresponding amounts in the case of other fruits.) 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 add 20 cc. sulphuric 

 acid. Heat on hot plate, removing at intervals to add small amounls (3 to 5 cc.) of 

 nitric acid (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 water, 

 and again evaporate to sulphuric acid fumes. Cool, dilute with alout 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 filtrate. Evaporate the filtrate to small Aolume on steam 1 ath to remove 

 alcohol. Make to volume. 



