No. 4.] SHADE-TREE INSECT PROBLEM. 99 



These ingredients should be carefully weighed, placed in 

 separate packages, and, when wanted for use, dissolved in 

 separate wooden or fibre pails. When the solutions are 

 completely formed, pour the contents of each pail into a 

 spraying tank partly filled with water. Arsenate of lead 

 will then appear as a fine white precipitate. 



The above formulae are based on nitrate of lead containing 

 66.5 lead oxide, arsenate of soda of 9(3 per cent purity (con- 

 taining 59.8 per cent arsenic oxide), the arsenate of lead 

 required being the actual dry product. It will be noted that 

 the ingredients give a little more than one-half their weight 



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in actual arsenate of lead. The same holds true with the 

 arsenate of lead pastes previously mentioned. The cost of 

 ingredients is a variable quantity. Arsenate of soda 9(3 per 

 cent pure retails at about 15 cents per pound, and nitrate of 

 lead at about 10 cents per pound ; therefore the cost of one 

 pound actual arsenate of lead would be about as follows : — 



Nitrate of lead, 1.2 pounds, at 10 cents, . . . $0 12 

 Arsenate of soda, .5 pound, at 15 cents,. . . 075 



Bags, twine, etc., 01 



$0 205 



To these figures should be added the cost of the labor of 

 weighing and packing the ingredients, and that consumed 

 in dissolving and mixing them. Even with these factors 



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included, the cost of one pound of arsenate of lead is 

 somewhat less than that purchased in paste form. The 

 manufacturers of the pastes, on the other hand, urge- the 

 superior merit of uniform composition and availability for 

 immediate use, and the saving of time and skilled labor. 



In small spraying operations, where only a few hundred 

 pounds of the insecticide are needed, probably it would be 

 more advantageous to purchase the prepared paste. In 

 larger operations, where a ton or more of the insecticide is 



