June, 1917.] ARSENICAL RESIDUES AFTER SPRAYING. 9 



that would throw light on the toxic properties of lead arsenate, 

 both by means of experimental feeding of guinea pigs and by 

 deteiminations of the solubility of lead arsenate in normal human 

 gastric juice. Other inquiries were begun, to determine the 

 facts about the danger to live stock. Finally, the study was 

 made to include determinations of the residues found on small 

 fruits and vegetables. The work was brot to a close at the end 

 of the summer of 1916. 



ACKNOWLEDGEMENT. 



The authors are indebted to Mr. B. E. Curry, head of the de- 

 partment of chemistry of this station, for analyses of residues on 

 apples and forage. 



Acknowledgement is offered also for assistance rendered by 

 Mr. C. R. Cleveland and Mr. C. A. Weigel. 



MATERIAL USED. 



The arsenate of lead used in all of the experiments that follow 

 was from one lot of ''electro" dry lead arsenate. A sample was 

 submitted to analysis November 12, 1912, and was found by the 

 station chemist to contain moisture 0.18 per cent, arsenic oxid, 

 AS205, 33.4 per cent. 



RESIDUES ON FRUITS AND VEGETABLES. 



APPLES. 



In July 1912, 10 trees were selected on or near the station 

 farm, representing 6 varieties of apples. These trees were of 

 varying size. All weie in fruit. 



Arsenate of lead was prepared at the equivalent of 3 lbs. of 

 arsenate of lead paste to 50 gallons of water. This spray was 

 appHed to one tree, a Porter, No. 8, July 29, this tree being of 

 medium size. Twelve quarts of spray material was used. The 

 spraying was done thoroly. 



Nine other trees were sprayed four days later, August 2, with 

 arsenate of lead at the equivalent of 3 lbs. of the paste to 50 gal- 

 lons of water. Two of these trees were dolman Sweets, two 

 Early Harvest, two Astrachans, one Benoni, one Porter and one 

 Fameuse. The amount of spray material applied per tree varied 

 from 3 to 12 quarts. A record of the amount will be found in 

 Table No. 1. 



