November, 1920 BETTER FRUIT 



Late Developments in Arsenical Insecticides 



By R. A. Cooley, Bozeman, Montana 



THE old classification of insect pests There are certain qualities of arsen- 



into those with biting and with icals which we need to consider in 



sucking mouth parts and the corre- making a selection. They are: (1) 



sponding division of insecticides into killing power, (2) solubility in water, 



stomach poisons and contact poisons (3) quality of sticking on the foliage, 



are familiar to horticulturists. It is (4) settling in water, (a) cost, 



rather generally realized, I believe, The killing power of an arsenical 



thai practically all of the stomach insecticide is roughly parallel to the 



poisons used are different forms or percentage content of actual oxide of 



compounds of arsenic. Probably nearly arsenic as determined by chemical 



all of us remember back to the time analysis. By referring to the table 



when Paris green made its appearance you may see the relative strength of 



in connection with the control of the the various old and recently discov- 



Colorado potato beetle, and many will ered poisons, expressed as oxides of 



recall an earlier day when we used arsenic. The comparison of amounts 



London purple on potatoes. Since of oxides in the insecticides is to be 



those early days much progress has looked upon as only an approximate 



been made in our knowledge of arsen- indication of the relative killing pow- 



icals and a number of new poisons ers . T n this connection it should be 



have been brought to our attention. I stated that the figures for arsenate of 



have thought that it would be profit- ] eac i are f or a dry preparation and not 



able to discuss and compare the vari- a paste. Arsenate of lead paste, which 



ous arsenical insecticides and to men- wa s commonly in use a few years ago, 



tion the underlying principles which was composed of 50 per cent of water, 



should govern the selection of a poison in the wet paste, therefore, the per- 



for any particular use, so as to get centage of arsenious oxide would be 



the best results and at the same time only 12 Y2 and the number of pounds 



not use one that is more expensive to be added to 100 gallons of water 



than necessary. , for a given purpose would be double 



I have made a table of the more as much with the paste as with the 



important arsenical insecticides which dry preparation. It follows, of course, 



compares them and gives much infor- that in order to correctly judge of the 



mation in a condensed form. relative value of these insecticides it 



Arsenic Cost' Soluble Slicking Settling 



Oxides per lb. Arsenic Quality Quality Texture 



Paris green 50% fiOe 3.5% Poor Rapid Coarse 



Arsenate of Lead 25% 34c 1.50% Excellent Slow Fine 



Arsenile of Zinc Ill'; 26c .67% Good Slow Fine 



Arsenate of Calcium 42.5% 30c 1% Good Slow Fine 



Refined White Arsenic 97% 15c Poor Rapid Coarse 



Crude White Arsenic 80% 12c Fair Medium Medium 



•Wholesale prices in 100-pound lots f.o.b. factory. 



Page 9 



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