POISON INSECTICIDES 15 



jury caused.-' Distilled water with salt added 

 causes decided injury to foliage; distilled water 

 with sodium carbonate added causes decided in- 

 jury; distilled water alone almost no injury; dis- 

 tilled water with lime added almost no injury. 

 Clear sunny weather following application seems 

 favorable to injury; dew followed by sunshine 

 seems favorable to injury. 



Soap is sometimes used as a sticker for arsenate 

 of lead and as an agent to hold it in suspension.-^ 



Drying and freezing of the paste and effect on 

 its powers of suspension and adherence to foliage. 



The powdered form -'—It is a fine, white, 

 amorphous powder, the commercial brands of 

 which seem to be largely composed of the biplumbic 

 form. It was first used in fighting the Mexican 

 cotton-boll weevil. The commercial brands are 

 high in arsenic oxid containing generally about 

 30%. Experiments have shown that it is equal in 

 effectiveness to the paste form when combined with 

 a suitable carrier. Experiments have also shown 

 that when tested on glass slips some brands do not 

 adhere quite as well as the paste form. It can be 

 used in combination with liquid lime-sulphur or with 

 Bordeaux mixture or alone in water or it can be 

 used as a dust alone or combined with dry sulphur. 



Arsenate of calcium 



Arsenate of calcium ^^ is cheaper than the lead 

 form of arsenates and is apparently effective in 

 poisoning power, although perhaps not quite equal 

 to the hydrogen lead arsenate. In general the two 

 forms (i) calcium hydrogen arsenate CaHAs04 



25 Haywood and McDonnell— U. S. Bii. Chem., Bull. 131. 



26 Cooley— Montana Expt. Stat., Bull. 86. 



27 Hinds— Jr. Ec. Ent., Vol. 6, p. 477. 



28 Lovett and Robinson— U. S. Dept. Agr., Jr. Agr. Res., Vol. X, 

 p. 199. 



