1913] J- E. Greaves 523 



to which equivalent quantities of various so-called insoluble arsen- 

 ical Compounds had been added, showed great dissimilarities in 

 water-soluble arsenic content. The portion to which Paris green 

 was added contained four times as much water-soluble arsenic as 

 did a portion of the same soil to which an equivalent quantity of lead 

 arsenate had been applied. Arsenic trisulfide, when first applied to 

 soil, is less soluble than lead arsenate, but as time progresses, at least 

 in some soils, the arsenic trisulfide becomes more soluble. For this 

 reason lead arsenate is probably safer than any of the other arsen- 

 ical insecticides. 



