332 Report of the Department of Entomology of the 

 STATION EXPERIMENTS WITH ZINC ARSENITE. 



CONDITIONS OF THE EXPERIMENTS. 



Tests to determine the effects of weather on zinc arsenite and its 

 safeness for use on foliage were conducted in the field while most of 

 the feeding tests were performed in the laboratory under conditions 

 that made it possible to observe closely the behavior of the poison 

 upon the insects. The feeding tests were made by supplying sprayed 

 foliage to a definite number of insects enclosed in cages. The 

 leaves and twigs used in most of these experiments were sprayed in 

 the laboratory with an aspirator. To determine the lasting properties 

 of the mixtures when exposed to weather, trees were sprayed in the 

 field from which at intervals foliage was removed and fed to insects. 

 If there was only a small consumption of foliage the amount of 

 feeding of the insects was estimated in square centimeters, but if 

 the amount consumed was large it was approximated and designated 

 by such terms as moderate, extensive, etc. 



In addition to these laboratory studies, field tests were made in 

 the Station nursery and orchard by spraying trees upon which the 

 insects were already established, to compare the action of the poisons 

 on host and parasite under out-of-doors conditions. To each fifty 

 gallons of the diluted spray mixture one of the poisons was added as 

 follows : zinc arsenite one pound, lead arsenate (paste) three pounds, 

 or lead arsenate (dry) one and one-half pounds. The zinc arsenite 

 contained 40.28 per ct. arsenious oxide, and the arsenate of lead 

 paste 17.75 per ct. arsenic oxide. 1 



Determinations were made of the solubility of zinc arsenite in 

 tap water, distilled water and dilute carbonated water. One series 

 of analyses was conducted according to the official method employed 

 to determine the water-soluble arsenic of paris green, which is done by 

 shaking one gram of the sample in one thousand cubic centimeters 

 of water eight times a day for ten days. The second series of 

 analyses was similar to the above except that the shaking continued 

 for a shorter time. The results are shown in the following table: 



1 The arsenious and arsenic oxides are not entirely comparable as they are different 

 compounds and probably do not have the same toxic values. It would appear from 

 the experiments described later that as an insect poison .40 lb. arsenious oxide was 

 roughly equivalent to .53 lb. arsenic oxide. There are two other facts about arsenites 

 in general that should be taken into consideration in view of the variable results in 

 the use of zinc arsenite secured by different workers: (1) Arsenites in general are 

 not so stable as the arsenates; and (2) all arsenites usually retain some arsenious 

 oxide so that it is difficult to obtain definite compounds. 



Through the courtesy of Dr. L. L. Van Slyke and Mr. E. L. Baker, the moisture 

 determinations of the poisons were made by Mr. Otto McCreary and the analyses 

 by Mr. A. W. Clark. 



