INSECTICIDES IN GENERAL: STOMACH POISONS 45 



the poison must not dissolve, or burning of the foliage will result. The 

 poison, instead, must be suspended in the water, which acts merely as a 

 carrier from the pump to the plant over which it distributes the poison. 

 This distribution should be as uniform as possible in order that all parts of 

 the plant may be equally well protected and covered. If the poison be 

 heavy, settling quickly to the bottom of the pump, uneven distribution 

 will result, some parts of the plant receiving too much of the poison while 

 others will get but little. The best stomach poison from this standpoint 

 therefore, is one which is so light that after mixing it with water it will 

 take a long time to settle to the bottom. 



The chief stomach poisons now in use in the United States are Paris 

 green, Arsenate of lead, Arsenate of lime, Hellebore, and Sodium fluorid, 

 the last two having only a limited application. Standard formulas for 

 these are given below. Variations from them will be found in connection 

 with the special cases where change from the standard is desirable. 



Paris Green. This was probably the first stomach poison used against 

 insects, having been first employed about 1868 for the treatment of the 

 Colorado potato beetle. Chemically, it is a combination of copper, 

 arsenic and acetic acid, containing when pure, nearly 60 per cent of arsenic, 

 which is high as compared with the other arsenicals in use, and this gives 

 the substance its chief value. 



Paris green has three serious disadvantages. One of these is that 

 some of the arsenic will dissolve in the water it is mixed with, causing 

 injury to the foliage. This can in part be avoided by the addition of lime, 

 which combines with any of the arsenic that separates from its combina- 

 tion with the copper and acetic acid and would cause burning, converting 

 it into arsenite of lime which is only slightly soluble under such circum- 

 stances. Sometimes though, a slight burning takes place, even under 

 these conditions. By Federal law, not over 3 per cent should be soluble. 



A second disadvantage is that Paris green is a heavy substance, 

 settling quickly through the water to the bottom of the pump, which 

 results in an uneven distribution over the plant. 



The third disadvantage is that it does not adhere well to foliage, being 

 easily washed off by rains. This means that more frequent sprayings are 

 necessary for the protection of the plants than would otherwise be the 

 case, involving greater cost for material and labor. 



A standard formula for Paris green is: 



PER BARREL PER GALLON 



Paris green , Y% Ib. } teaspoonful (level) 



Quick lime 1 Ib. 1 teaspoonful (level) 



Water 50 gal. 1 gal. 



Use fresh stone lime, slaking this in some of the water: work up the Paris 

 green to a paste in a little of the water: add the lime slaked, to the rest of 

 the water, then stir in the Paris green paste. It is not advisable to mix 



