LEAD ARSENATE. 



INTRODUCTION. 



It is only in more recent years that lead arsenate has been used as 

 an insecticide for spraying purposes. Its use was first suggested by 

 Mr. F. C. Moulton in 1892, while acting as chemist for the gypsy 

 moth commission of Massachusetts, after having made a study of 

 numerous materials to be used as insecticides for the extermination 

 of the gypsy moth. It was found that Paris green could not be 

 used successfully for this purpose, principally because it could not be 

 applied in sufficient quantity to kill the caterpillars without seriously 

 injuring the foliage. While lead arsenate was not found entirely 

 satisfactory in destroying this pest, it possessed several advantages 

 over Paris green, and this has resulted in its replacing the latter 

 material for spraying purposes to -a very large extent, in fact, almost 

 entirely in some of the Rocky Mountain and Pacific Coast States. 

 Some of these advantages are: (1) It is not so injurious to foliage 

 when applied thereto, on account of its being less soluble in water. 

 (2) When sprayed upon leaves it forms a thin film, which is quite 

 adhesive and is not so easily washed off by rains. (3) It remains in 

 suspension much better, thereby requiring less' effort to keep the mix- 

 ture agitated, and thus insuring a more uniform application. (4) 

 Being white, it forms a visible coating and is easily distinguished 

 when it has been applied. 



The initial cost of this material is slightly greater than that of Paris 

 green, owing to the fact that it contains a smaller percentage of arsenic 

 than the latter, and therefore more of it must be used to produce the 

 same effect, Because of its greater adhesive qualities, however, it 

 remains on the foliage better, requiring less frequent application, and 

 thus in the end lead arsenate is no more expensive than Paris green ; 

 in fact, it may be even cheaper, as the greatest expense in spraying 

 is the cost of applying the material to the trees. 



The use of lead arsenate has increased very rapidly during the last 

 few years, as is shown by the fact that less than ten years ago no one 

 was manufacturing it to any large extent, while at the present time 

 there are at least eighteen manufacturing chemists in the United 

 States making it in greater or less quantities, and a number of other 

 firms are preparing to do so. An attempt was made to determine the 

 total amount sold in the United States for the years 1907 and 1908 by 

 writing to the various manufacturers for figures showing their sales. 



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