INSECTICIDES 43 



1. Paris green is a green crystalline powder composed of the 

 aceto-arsenite of copper. When properly made it should contain 

 at least 50 per cent arsenic oxid (As 2 Os), and there should be as 

 little water-soluble arsenic as possible, for the water-soluble arsenic 

 is the cause of the burning of foliage which often results from the 

 use of Paris green. Various State laws require that there be not 

 over 3 per cent soluble arsenic, but even this amount is often 

 injurious to tender foliage. Paris green is rather a coarse powder 

 and settles readily in water, and is readily washed off by drenching 

 rains. It costs from 25 to 35 cents per pound. It is usually used 

 at a rate of from 3 to 8 ounces to a 50-gallon barrel of water; 5 

 ounces per barrel is satisfactory for most purposes. In mixing, 

 first stir up in a small vessel with a little water into a paste, which 

 will mix more readily. Add an equal weight of quicklime, or 

 slightly more will do no harm, which will take up any soluble 

 arsenic. 



2. London purple is a waste product in the manufacture of 

 aniline dyes, and is principally arsenic and lime. It is quite 

 variable in composition and usually contains a much higher, 

 and quite variable, amount of soluble arsenic, so that it is apt to 

 scald the foliage unless thoroughly mixed with fresh stone lime. 

 For this reason it is now used only for rough work, such as poison- 

 ing grasshoppers, making poisoned bran mash, etc., and is not 

 to be recommended for general use on fruit trees and garden 

 crops. It usually costs 10 or 12 cents a pound, and is used in 

 the same proportions and in the same way as Paris green. 



3. Arsenate of lead is usually sold in the form of a white paste, 

 composed of arsenic and lead, the exact chemical composition 

 varying with the process of manufacture. To be of standard 

 grade it should contain at least 12 per cent of arsenic oxid 

 and not over f per cent water-soluble arsenic oxid (As2Os), 

 and not over 50 per cent water. Owing to the small amount 

 of soluble arsenic it may be used in much larger quantities than 

 other arsenicals and on tender foliage which others will injure. 

 From 2 to 8 pounds per 50-gallon barrel of water are used, 2 

 or 3 pounds per barrel being commonly used for most of the 



