EXPERIMENTS WITH INSECTICIDES UPON POTATOES. 1/9 



more readily kept in suspension than Paris green. The field 

 notes show the arsenoids to have been about as effective as Paris 

 green but not so effective as the arsenate of lead. While they 

 may contain more free (uncombined) arsenious acid than the 

 best made Paris greens, they probably contain no more than the 

 average Paris green. There is little reason for using them 

 instead of Paris green unless they can be had at a considerable 

 lower price. 



ARSENATE OP LEAD. 



The Massachusetts Gypsy Moth Commission have during the 

 past ten years made exhaustive comparative studies of different 

 arsenical compounds as insecticides. In 1893 Mr. F. C. Moulton, 

 a graduate of the Chemical Course of the University of Maine, 

 was employed by the commission and suggested the use of arsen- 

 ate of lead as an insecticide. It was found to be "the most effec- 

 tive poison yet used" and for the last year or two of the commis- 

 sion it was employed almost exclusively. The findings of the 

 commission are summarized as follows :* 



"Although nearly all poisons known to us which can be used 

 as insecticides have been experimented with during the past five 

 years in the hope that something would be found which would 

 prove fatal to the gypsy moth, only one which is more effective 

 than Paris green has been discovered. This is arsenate of lead, 

 a poison slower in its action than the other, but which has three 

 distinct advantages : ( 1 ) It can be used at any desired strength 

 without serious injury to the foliage; (2) It is visible wherever 

 used, as it forms a whitish coating on the leaves; (3) It has 

 adhesive qualities, given it, probably, by the acetate of lead, and 

 therefore remains on the leaves for a much longer period than 

 Paris green. When sufficient glucose was added to a strong 

 mixture of arsenate of lead, it withstood rainstorms and remained 

 on the foliage during an entire season." 



The arsenate of lead used by the commission was prepared, for 

 the most part, by using 30 parts of arsenate of soda and 70 parts 

 of acetate of lead. Prof. C. H. Fernald directs that arsenate of 

 lead can be prepared in the proportions of 1 1 ounces of acetate 

 of lead, and four ounces of arsenate of soda. The materials are 



*The Gypsy Moth, Forbush and Fernald published by the Massachusetts Board 

 of Agriculture, pages 141 and 142. 



