June, 1917.] ARSENICAL RESIDUES AFTER SPRAYING. 41 



CALVES. 



In the experiments just noted it was found that the amount of 

 material dripping from trees that had been sprayed with reason- 

 able care averaged 11 per cent of the total amount applied to the 

 tree. Taking for granted that spraying is often carelessly done 

 it is assumed that we may properly allow double the percentage 

 of drip found in the experiments, namely 20 per cent of the total 

 amount applied to the trees. 



Assuming further that in the case of large trees 10 gallons of 

 spray material may be applied per tree, we may expect to find a 

 probable maximum of 2 gallons of this spray material on the 

 grass beneath such a tree. Probably this drip would be distrib- 

 uted over a rather large area, especially if any wind were blowing. 

 But as a basis for maximum concentration of the drip it is now 

 assumed that in the case of such a tree all of the 2 gallons of drip 

 would be found on an area 25 feet square beneath the tree. 



Preliminary tests were now made, applying a spray to such an 

 area of grass. These tests were carried out in an orchard in 

 which the growth of grass was of moderate thickness and 10"-14" 

 high. It was found by these tests that 2 gallons of spray material 

 applied directly to an area 25 feet square represented approxi- 

 mately what the grass would hold readily. Apparently if more 

 was applied some of it would run off onto the ground. Therefore, 

 in the experiments now to be described, the unit area selected 

 was a plot 25 feet square, including 625 square feet, and to each 

 such plot 2 gallons of spray material was applied directly on the 

 grass by means of an ordinary bucket pump. 



Three concentrations of arsenate of lead were chosen: first, 

 a mixture made up at the rate of 3 lbs. of arsenate of lead paste 

 to 50 gallons of water; second, 6 lbs. of arsenate of lead paste to 

 50 gallons of water; and third, 10 lbs. of arsenate of lead paste to 

 50 gallons of water. 



In the orchard above mentioned 3 pens were placed, each pen 

 including an area 25 feet square, or 625 square feet to each pen. 

 The pens were so arranged as to include grass of approximately 

 uniform stand. In plot I, the grass was sprayed with 2 gallons 

 of material made up of 1 oz. of dry arsenate of lead to 2 gallons 

 of water. This concentration, it will be observed, represents 

 the approximate equivalent of 3 lbs. of arsenate of lead paste to 



