107 



with sulfur or gypsum, and this mixing is difficult without 

 special machinery. Dust mixtures are now on sale, however, 

 the more usual proportions of the materials being 85 per cent 

 of sulfur or gypsum and 15 per cent of arsenate of lead. The 

 sulfur is of some insecticidal value and is therefore probably 

 the better mixture to use. 

 As a spray the usual formula is — 



Arsenate of lead, paste (pounds), 3 



Water (gallons), . 50 



If the powder is used instead of the paste, take 1^ pounds 

 instead of 3 pounds. Its price is higher, but there is about 

 twice as much poison in a pound of powder as in the paste. 



In preparing the paste, stir it up thoroughly in a little of 

 the water, to get a uniform mixture before adding the rest of 

 the water. 



The paste will be of little value after it has once been al- 

 lowed to dry, and it is also injured by freezing. 



Arsenate of Lime. — This is a rather recent spray material, 

 which like arsenate of lead can be obtained either as a paste 

 or a powder. There is more arsenic in the latter, but as the 

 price is correspondingly higher there is little difference between 

 the two forms from this standpoint. 



This material cannot be used with safety on leaves unless 

 an excess of lime is present. Accordingly, the usual formula 

 is — 



Arsenate of lime, paste (pounds), . 2 



Quicklime (pounds), 2 to 3 



Water (gallons), • ■ 50 



For the powder take — ■ 



Arsenate of lime, powder (pound), i 



Quicklime (pound), 1 



Water (gallons), . ■ .50 



In either case slake the quicklime in some of the water; 

 strain it into the rest of the water and then mix in the arsenate 

 of lime. 



