8 PARIS GREEN SPRAYING EXPERIMENTS. 



PRELIMINARY WORK AT WASHINGTON, D. C. 

 PLAN OF THE EXPERIMENT. 



Preliminary work was begun during the early summer of 1902, and 

 carried out in the following manner: A large quantity of Paris Green, 

 as pure as could be obtained, was purchased and a determination made 

 of the soluble arsenious oxid by the ten-day water-extraction method. 

 Then known quantities of perfectly pure arsenious oxid were added 

 to different quantities of the green, so that samples of a definite arseni- 

 ous oxid content were obtained. Each of these samples contained to 

 1 pound of Paris Green the following amounts of soluble arsenious 

 oxid: 



Per cent. 



No. 1 4.29 



No. 2 5. 00 



No. 3 6. 00 



No. 4 7. 00 



No. 5 8.00 



Two sets of these samples were made up and applied in the follow- 

 ing manner: 



SET I. 



Treat one-half of each of 5 samples described above with 150 gallons of water, 

 making 1 pound to 300 gallons, and spray delicate trees, such as peach trees. 



Treat the other half of each of the 5 samples with 150 gallons of water, making 1 

 pound to 300 gallons, and 1 pound of lime, and again spray delicate trees, such as 

 peach trees. 



SET II. 



Treat one-half of each of above 5 samples with 80 gallons of water, making 1 pound 

 to 160 gallons, and spray hardy trees, such as apple trees. 



Treat the other half of the 5 samples with 80 gallons of water, making 1 pound to 

 160 gallons, and 1 pound of lime, and again spray hardy trees, such as apple trees. 



The dates of spraying and taking of observations and the duration 

 of the experiment were caref u\ly noted. 



With the aid of Mr. F. C. Pratt, an assistant in the Division of 

 Entomology, the author sprayed young peach, apple, and pear trees, 

 following very closely the directions outlined above. The trees grew 

 in the Agricultural Department grounds, and, unfortunately, had been 

 used before in various experiments upon insects and sprays, so that all 

 of them were not in a perfectly healthy condition. Since they were the 

 only trees available, and the investigation was only preliminary in 

 character, to fix within wide limits the amount of soluble arsenic that 

 can be endured by the trees, it was thought they would serve the pur- 

 pose. The table on the next page, giving the weather conditions 

 during the first part of the experiment, is furnished by the United 

 States Weather Bureau. 



