June, 1917.] ARSENICAL RESIDUES AFTER SPRAYING. 23 



sis. No rain had fallen. The cabbages from the remaining 

 two plots were removed August 9, after a very light rain the night 

 of August 3 and a moderately heavy rain the afternoon and night 

 of August 8. 



Four plots of lettuce were sprayed, each plot including 10 

 heads. The spray was applied August 2. The heads from plots 

 1 and 2 were removed August 3, before any rain had fallen. 

 Those from plots 3 and 4 were removed August 8, having received 

 a Hght shower the night of August 3 and a heavy rain the after- 

 noon and evening of August 8. 



The results of analyses are given in Table No. 6. 



It was expected that the cabbage might show relatively large 

 amounts of residues because of the spray material collecting in 

 the base of the leaves. In lesser degree this was anticipated in 

 the case of lettuce. The results bore out the expectations. As 

 will be noted, the cabbages showed 43.5 to 51.4 milligrams 

 AS2O3 per head; the lettuce 1.6 to 10.6 milligrams AS2O3 per head. 

 There is no indication of reduced amount because of rain. This 

 is not surprising, if we assume that most of the poison had col- 

 lected in the base of the leaves. Rain would not be likely to 

 remove it from such a position. 



If the outer leaves had been broken off and discarded before 

 making the analysis, the result would, no doubt, have been 

 quite different. Probably in ordinary commercial practice the 

 outer leaves would have been removed. However, the idea in 

 these experiments was to determine the maximum that could be 

 found. The writers would assume that in the ordinary course 

 of events, even if cabbages or lettuce had been directly sprayed 

 as thoroly as was done in this experiment, the amount of arsenic 

 that would eventually find its way to the table would be only a 

 small fraction of the amount indicated in the analytical result, 

 allowing for the intervening operations of removing the outer 

 leaves, washing and preparing for human consumption. 



In experiments at the Kentucky Station, described by Garman 

 (6), one lot of cabbage was sprayed four times with arsenate of 

 lead at the rate of 2 lbs. to 100 gallons of water. Later, one of 

 these heads, with the outer leaves removed, was submitted for 

 analysis. The amount of arsenious oxid found was 5.2 milli- 

 grams. Another head, from a row sprayed twice, gave 7.8 milli- 

 grams AS2O3. 



