40 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



at least 50 per cent arsenic oxid (As 2 O 5 ), 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 1 per cent soluble arsenic, but even this amount is often 

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

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

 rains. It costs from 35 to 50 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. Ar senate of lead is sold in the form of a white paste con- 

 taining about 50 per cent water and also as a dry white powder. 

 Standards of purity for this material require that the paste con- 

 tain not more than 50 per cent water and not more than f per 

 cent water-soluble arsenic oxide, while there must be not less 

 than 12J per cent total arsenic oxide. The dry powder will lack 

 the water and contain a correspondingly larger percentage of 

 other ingredients. Since this material contains a relatively small 

 amount of soluble arsenic it may be used at a greater strength than 

 the other arsenicals without injuring foliage of plants which are 

 susceptible to injury from the other arsenicals. From one to eight 

 pounds, paste form, are used to the 50 gallon barrel of water, 2 or 

 3 pounds being most commonly recommended for the majority of 

 the pests of orchard and garden. Arsenate of lead remains in 

 suspension well, much better than Paris green, and is very ad- 



