434 



AN ECONOMIC ENTOMOLOGY. 



addition. As a rule, it is safer to purchase only materials of 

 known composition from a reputable firm and prepare as needed. 



White arsenic is the cheapest, simplest, and most active ma- 

 terial of this class, and is effective at the rate of one pound in 

 from two hundred and fifty to three hundred gallons of water. 

 The objection to it is that so much of the arsenious acid is soluble 

 in water that it burns foliage seriously, and at any strength at 

 which it is fatal to insects becomes fatal to the plants as well. 

 To neutralize this, three pounds of lime should be added for each 

 pound of arsenic, as follows : to three pounds of good stone lime 

 add water enough to slake completely ; mi.x the arsenic with 

 water enough to make a thin paste and add to the slaked lime ; 

 add water as needed and stir thoroughly until the lime is com- 

 pletely reduced and forms a thin milk of lime ; strain to get rid of 

 coarse particles and reduce with water to spraying strength. The 

 lime forms a combination with the white arsenic, unites with the 

 soluble arsenious acid, and forms an insoluble arsenite of lime 

 which may be applied with reasonable safety at about half the 

 strength at which Paris green is used. 



A somewhat more effective way of combining the arsenic and 

 lime is to boil one pound of the former and two pounds of the 

 latter in two gallons of water, and then dilute as required. This 

 combination is especially useful as an addition to the Bordeaux 

 mixture where a combined insecticide and fungicide is desired, 

 and it also is used in half the amount of Paris green. 



Yet another combination is made as follows : In an iron pot boil 

 one pound of white arsenic with four pounds of sal soda in one gal- 

 lon of soft water until the arsenic dissolves, leaving only a small 

 muddy sediment. The product is an arsenite of soda which may 

 be kept in a closely stoppered jug until needed, though not 

 longer than the season for which it is made. To prepare for use, 

 take two pounds of lime, slake, and dilute with two gallons of 

 water and add one pint of the arsenite of soda solution. When 

 this is thoroughly combined, add water to make forty gallons. 

 This equals Paris green at the rate of one pound in one hundred 

 and sixty gallons of water, and remains in suspension about three 

 times as long ; in fact, all the arsenic and lime preparations have 

 the advantage over Paris green in this respect. The arsenate 

 of soda is very destructive to foliage in any dilution, and should 

 never be used alone, , 



