300 AGRICULTURE. 



The following year the development of the 

 Hessian fly in this field may be prevented by 

 putting in a crop upon which it does not feed — 

 as, corn or clover. 



VIII. Insecticides. 



In general, insecticides also are divided into 

 two groups. 



Group I. — Poisonous Insecticides, or those 

 that kill by being taken into the stomach of the 

 insect. The principal poison in this group of 

 insecticides is arsenic in some form. 



Paris green is the most common, and if una- 

 dulterated is a very effective arsenical insecti- 

 cide. It is prepared as follows: 



Paris green i pound 



Quicklime i pound 



Water 100-300 gallons 



Mix thoroughly, and strain' the mixture 

 through a gunny-sack or sieve. The purpose 

 of the lime is to render any free arsenic in the 

 Paris green insoluble, since soluble arsenic 

 would poison the tissue of the plant. It must 

 be remembered that the particles of arsenic are 

 held in suspension and not in solution ; hence, 

 the mixture must be kept well stirred while 

 being applied. In spraying plants with tender 

 foliage — as, the peach and plum — the Paris green 

 mixture should be diluted. 



Scheele's green differs from Paris green in 



