INSECTICIDES 41 



hesive, remaining on foliage for several weeks. It is made from 

 arsenate of soda and acetate of lead and may readily be prepared 

 by the user. This is not recommended on account of the vari- 

 ability in the purity of the constituent chemicals and the incon- 

 siderable saving effected by the home preparation. 



Commercial arsenate of lead may be purchased at prices 

 ranging from 10 to 30 cents per pound for the paste and from 25 

 to 50 cents for the powder. 



Powdered arsenate of lead was prepared first rather for use as 

 a dust than for spraying purposes. Perfection of the process of 

 manufacture of the dust has given a product that is as cheap and 

 in every way as satisfactory as the paste. For this reason users 

 are more and more corning to prefer the powder. It mixes more 

 readily with water, remains in suspension just as well and, being 

 of only one-half the weight of the paste, effects a considerable 

 saving in transportation. 



The powder also eliminates one source of loss to which the 

 paste is liable, that is, drying out. Paste arsenate of lead that 

 has dried is practically wasted as it is almost impossible to get it 

 thoroughly mixed with water. The dust will keep indefinitely 

 if it is stored in a dry place. Arsenate of lead in the dry form is 

 the only arsenical used to any extent in orchard dusting. 



It is well for the student to remember that spraying formulas 

 calling for arsenate of lead usually mean the arsenate in paste form 

 if the powder is not definitely specified. This is because the 

 paste was first used and formulas were established on that basis. 



Arsenate of lead is the most valuable and widely used of all 

 the insecticides used as stomach poisons, having long since dis- 

 placed Paris green which was formerly the leading arsenical. 



4. Arsenite of lead is a compound very similar to the arsenate 

 .but less effective and contains more soluble arsenic and so is more 



likely to burn foliage. It is made from sodium arsenite and a 

 lead compound but is rarely used and not to be recommended. 



5. Arsenite of lime is a home-made arsenical, very much cheaper 

 than those previously mentioned, which gives very satisfactory 

 results for certain purposes. It is not as adhesive as arsenate 

 of lead, and as it sometimes burns foliage has been largely dis- 

 carded for orchard spraying. It is, however, very satisfactory 

 for potatoes and other low-growing crops, especially when added 



