February, '22] sanders: cheaper arsenicals 73 



dehydrated copper sulphate and five pounds of arsenate of lime. Some 

 seven hundred tons of this dust was used on the apple in the Annapolis 

 Valley last season and there is no doubt but that there will be an enor- 

 mous increase in its use in 1922. A few tons of copper arsenic dust 

 containing, twenty pounds of dehydrated copper sulphate, eight pounds 

 of arsenate of lime and seventy-two pounds of hydrated lime, were used 

 on potatoes during the past year. We have found arsenate of lime 

 absolutely safe, efficient and satisfactory in every way in this type of, 

 what we term mixed copper arsenic dusts. 



In addition to the above mentioned uses, arsenate of lime is the best 

 of all arsenicals for straight dusting on such crops as potatoes, cotton 

 etc. 



White Arsenic 



The base from which practically all arsenicals are manufactured, is 

 of course infinitely lower in cost than any of its products. 



We entomologists in the past have for the most part regarded white 

 arsenic simply as white arsenic and have not paid sufficient attention to 

 fineness, the effect of impurities, texture and source of our material. 

 In working out the formulas that I will describe later, we found it 

 almost impossible to get samples of white arsenic from different sources 

 that gave exactly the same reactions. 



The experiments of Davis and Tumer\ and Ford and Larrimer^ 

 show that the metallic arsenic in the white arsenic used by them was a 

 less efficient insecticide than the arsenic in Paris green. We have been 

 using generally a super-fine dust white arsenic, that is caught in a 

 special baghouse, by the Deloro Smelting and Refining Co. In grass- 

 hopper baits, this material we have found, is superior to Paris green on 

 an arsenic basis. 



In our opinion the efficiency of white arsenic as an insecticide in 

 baits is primarily a matter of fineness; purity being a minor considera- 

 tion. It must be said here that freedom from, impurities will almost 

 as readily decrease as increase the toxic value of white arsenic. 



During the past three years, a considerable number of farmers in the 

 Maritime Provinces have been using white arsenic as a poison in Bor- 

 deaux mixture. In 1919 and 1920, this was confined to the potato, 

 but in 1921, it was used with entire success on the apple in the 3-10- 

 40 Bordeaux that is generally used on the apple there. 



Briefly, the formula for using it is, mix one pound of quickly reacting 

 super-fine white arsenic with one pound of hydrated lime and mix 



'Experiments with cutworm baits by John J. Davis and C. F. Turner. Canadian 

 Entomologist Vol. L, No. 6, pp. 127—192. 



^Some factors influencing the efficiency of grasshopper baits. A. L. Ford and 

 W. H. Larrimer. Journal of Economic Entomology Vol.14, No. 3. pp. 292 — 299 



