SUMMARY. 



31 



Amounts of soluble arsenious oxid allowable in Paris Green. 

 [Samples analyzed by ten-day water-extraction method.] 



A study of the weather charts for the various stations shows that 

 the following periods elapsed between the dates of spraying- and the 

 first rainfall: Washington, D. C., about 10 days; College Park, Md., 

 about 12 days; Ithaca, N. Y., about 3 days before a very light rain 

 and then 13 days before the next rainfall; Kingston, R. I., about 5 

 days and then 1 more before another rain; Clemson College, S. C., 

 10 days, followed by a very light rainfall and a long dry term. It is 

 thus seen that in nearly all cases the weather conditions were almost 

 ideal, if the word may so be used, for producing the maximum damage 

 from the sprays. During the rather long diy period after spraying, 

 when only light rains fell, if any, the dew and carbon dioxid of the air 

 acted upon the Paris Greens, causing them to decompose and set free 

 the arsenious oxid, so that when rain finally came a large amount of sol- 

 uble arsenious oxid was present, which the leaves absorbed and thus 

 caused burning. These conditions were especially striking at Clemson 

 College, where no rain fell for 10 days, after which just about enough 

 rain fell for 3 days to dissolve the soluble arsenious oxid and yet riot 

 wash it off. Another dry period followed, terminated by rains, which 

 caused the soluble arsenious oxid to burn the foliage. 



Taking the weather conditions into consideration, and judging the 

 results in a very conservative manner, it would appear from the 

 figures given in the table that the following conclusions may be drawn: 



(1) For apple trees sprayed without the use of lime the amount of 

 soluble arsenious oxid a allowable lies between 4: and 8+ per cent, a 

 fair average being 6 per cent. 



(2) For apple trees sprayed with the use of lime the amount of solu- 

 ble arsenious oxid allowable is between 6 and 8+ per cent, a fair 

 average being 7 per cent. 



(3) For pear trees sprayed without the use of lime the amount of 



a By soluble arsenious oxid is meant the amount extracted from 1 part of Paris 

 Green by 1,000 parts of carbon dioxid-free water during the course of 10 days* 



