76 PROTECTION OF PLANTS — 1922-23 



WHITE ARSENIC AS AN INSECTICIDE. 

 By G.E. Sanders, 



In discussing the above it is diflScult to say just where we shoud draw the 

 line since practically all the arsenicals on the market today are made from white 

 arsenic. In this paper I shall endeavor to confine myself to white arsenic itself 

 and the materials or compounds that may be made from it by one single farm 

 operation. 



White arsenic is not by any means a standard article. It may vary in purity 

 from 40 to 99 per cent pure. Even 99 per cent arsenic may contain enough 

 impurities, which may be antimony, bismuth, lead, sodium, etc., to affect its 

 behavior in most tantalizing ways. White arsenic as it is sublimed varies in 

 fineness from around 100 mesh to an impalpable powder. In a smelter where 

 90 per cent of the output runs 99 per cent pure with a fineness of around 150 to 

 200 meshes, the remaining 10 per cent will run from 90 to 96 per cent pure and 

 for the most part go through a 300 -mesh screen. It is this extremely fine dust 

 collector arsenic that is from 3 to 9 per cent low in purity that I have found 

 best adapted for direct use as an insecticide. 



One of the most remarkable and tantalizing things about white arsenic 

 is the remarkable effects that even small quantities of impurities have on its 

 reactions which prevent an experimenter from saying, "A certain purity of 

 white arsenic if ground to a certain fineness will do this or that". What it may 

 or may not do depends on the impurities present which may speed up the reac- 

 tion as in the case of sodium or slow it down as in the case of bismuth.This is 

 the big objection to the use of formulas that allow the farmer to utilize raw 

 white arsenic. Briefly, there are three uses to which white arsenic has been put 

 directly, vix: 



1. Dusting directlv on potato Vines. 



2. In Baits. 



3. In Bordeaux Mixture. 



1. Dusting Directly on Potato Vines. 



Experiments on this were conducted by Cooley in Montana. It was re- 

 ported that white arsenic was used directly and straight on potato vines in 

 Montana with safety. The only details that I got from Professor Cooley were 

 that a particularly pure and fine grade of whitie arsenic was used. In a dry 

 climate like Montana and where the hot, sunny summers make the potato 

 leaves very tough and where there is probably less ammonia in the air than in 

 most potato sections, we would expect this. In addition. Professor Cooley may 

 have happened to use a whit-e arsenic that was not only low in sodium and po- 

 tassium, but which contained some such impurity as bismuth. 



