328 SCHOOL ENTOMOLOGY 



bugs, which suck the juices from beneath the surface. 

 Poisons may not always, however, be the most effective 

 means of combating biting insects, for some caterpillars are 

 sometimes effectually checked by use of contact insecti- 

 cides. 



Pans green is a green crystalline powder composed of 

 the aceto-arsenite of copper. When properly made it 

 should contain at least 50 per cent arsenic oxid (As2Os), and 

 there should be as little soluble arsenic as possible. Various 

 State laws require that there be not over 3i per cent soluble 

 arsenic, but even that amount often injures tender foliage. 

 Paris green is rather a coarse powder, settles readily in 

 water, and is washed off by drenching rains when used alone. 

 It is usually applied at the rate of from 3 to 8 ounces to a 50- 

 gallon barrel of water, 5 ounces to the barrel being satis- 

 factory for most purposes. If stirred up into a paste with a 

 little water it will mix more readily and uniformly. Add an 

 equal weight of quick lime, slightly more will do no harm, 

 which will help neutralize any soluble arsenic. 



Ar senate of lead is sold both as a white paste and as a pow- 

 der. To be of standard grade the paste should contain at 

 least 12 J- per cent of arsenic oxid and not over f per cent 

 water-soluble arsenic oxid, and not over 50 per cent water. 

 Owing to the small amount of soluble arsenic it may be used 

 in much larger quantities than other arsenicals and on tender 

 foliage which others would injure. From 2 to 8 pounds of 

 the paste per 50-gallon barrel of water are used, 2 to 3 pounds 

 per barrel being sufficient for most of the pests of the orchard 

 and garden. Only about half as much of the powdered form 

 is required. Arsenate of lead remains in suspension in 

 water better than Paris green and is much more adhesive. 

 It has, therefore, very largely displaced Paris green and is 

 superior to it for most purposes. 



