June, 1917.] ARSENICAL RESIDUES AFTER SPRAYING. 39 



drip continued to fall from a sprayed tree. Squares of heavy 

 muslin, measuring 25 feet each way, were now laid out on the 

 ground and to these squares spray was applied directly. The 

 square was weighed before being sprayed. The weight of spray 

 material applied to it was recorded. At the end of 5 minutes 

 the square was again weighed. Five such squares were so tested 

 lying in the sun, and five squares tying in the shade. The 

 results of the tests, together with the average of each lot and the 



final average, are shown in Table No. 10. 



It will be observed that in the case of squares of cloth lying 

 in the sun the percentage of loss due to evaporation varied from 

 17.8 per cent to 55.3 per cent, with an average of 35.1 per cent. 

 In the case of the squares of cloth lying in the shade the evapora- 

 tion ranged from 17.3 per cent to 43.6 per cent, with an average 

 of 32.7 per cent. Since the cloths to be used beneath the trees 

 would lie partly in sun and partly in shade, it was deemed fair 

 to take an average of the above two lots, which is 33.9 per cent, 

 as representing the allowance that should be made for evapora- 

 tion in computing the drip from sprayed trees. 



Similar squares were now placed beneath trees of various size. 

 These trees were sprayed and a record was kept of the weight of 

 material applied. The cloth was weighed just before spraying, 

 and at the end of 5 minutes the cloth was again weighed. The 

 results are shown in Table No. 11. 



In setting down in Table No, 11 the difference in weights of 

 the cloths allowance was made for evaporation in accordance 

 with the data described above in Table No. 10. In other words, 

 to the difference in weight in each case was added one half to 

 account for evaporation. 



It will be noted that the results show, in the first column of 

 the chart, actual total amounts of spray applied to the tree 

 ranging from 236.3 oz. to 264.9 oz. The amounts recovered on 

 the cloth, allowing for evaporation, range from 7.5 oz. to 49.5 oz. 

 Reducing these amounts to percentages, we find that the drip 

 from these sprayed trees ranged from 3.2 per cent to 19.1 per 

 cent. 



The average of 12 trees was 11.2 per cent. This amount is 

 assumed to represent a fair percentage of drip from a sprayed 

 tree where the material is applied with reasonable care. 



