204 SHADE-TREES IN TOWNS AND CITIES 



When sprayed in midsummer, leaves retain some of the 

 arsenate of lead when they fall in autumn. 

 Arsenate of lead may be prepared as follows : 



Acetate of lead 12 oz. 



Arsenate of soda 4 oz. 



Water 15 to 20 gallons. 



Pour the acetate of lead into two quarts of water and the 

 arsenate of soda into another two quarts; then pour these 

 two solutions into a tank containing fifteen or twenty gal- 

 lons of water. This gives a white precipitate of arsenate of 

 lead. Good chemicals should be used. 



It very seldom pays in actual spraying operations to pre- 

 pare the arsenate of lead. It is best to buy it in paste form 

 ready made. The manufacture of insecticides has become 

 more general during the last few years, and with the 

 passage of the National Insecticide Law their adulteration 

 will be prevented. This law is known as "The Insecticide 

 Act of 1910," and came into effect January 1, 1911. It is 

 "an act for preventing the manufacture, sale, or transpor- 

 tation of adulterated or misbranded Paris greens, lead ar- 

 senates, and other insecticides, and also fungicides, and for 

 regulating traffic therein, and for other purposes." The 

 standards of strength and purity of insecticides and fungi- 

 cides are prescribed in section 7 of the act, which is as 

 follows : 



"Sec. 7. That for the purpose of this Act an article shall 

 be deemed to be adulterated — 



"In the case of Paris green: First, if it does not contain 

 at least fifty per centum of arsenious oxid; second, if it 

 contains arsenic in water-soluble forms equivalent to more 

 than three and one-half per centum of arsenious oxid; 



