June, '17] LOVETT AND ROBINSON: ARSENIC AS AN INSECTICIDE 345 



ARSENIC AS AN INSECTICIDE 



By A. L. LovETT, Entomologist, and R. H. Robinson, Assistant Chemist, Oregon 

 Agricultural Experiment Station 



From the standpoint of physical chemistry, it is generally known 

 that many solid materials have the power of adsorbing certain ions 

 from solutions. By the use of the term "adsorption" we mean the 

 existence of a difference in the concentration of a film surrounding a 

 solid and the concentration of the liquid which bathes this solid. In 

 other words, the solid has a high retaining power for the material in 

 solution. Since, therefore, it is the arsenic of the arsenical sprays 

 that is the active element, if some inert material could be easily ob- 

 tained in considerable quantities at a reasonable cost, which would 

 adsorb sufficient arsenic to make the substance efficient as a spray, 

 it would be worthy of consideration as an insecticide. 



Acting on this hypothesis, a series of experiments were outlined, 

 using lamp black and fuller's earth as adsorbants of arsenic from a 

 water solution of arsenic acid. No determination of the amount of 

 arsenic adsorbed by the lamp black and fuller's earth was made, but 

 water solutions of arsenic acid were prepared from the chemically 

 pure arsenic oxide and to various solutions of different concentrations 

 of arsenic, the carbon black and fuller's earth were added as indicated 

 in the tables. The materials were tested first as to their toxicity for 

 insects, second for burn on apple fohage in the field. 



Experiment A 



April 9, 1916. Uniform samples of clean, unsprayed apple foliage 

 were used. These were placed in large vials of water in the laboratory 

 and thoroughly and uniformly covered with the spray solution. The 

 fohage was allowed to dry for a period of six hours, after applying the 

 spray, and approximately 500 small tent caterpillars (M. pluvialis) 

 were introduced on each. 



The materials were prepared according to the following proportions: 



No. 1. AS2O5 at the rate of 5 grams to 1000 c.c. H2O, plus lamp black at the rate 



of 5 grams to 300 c.c. H2O. 

 No. 2. AsoOs at the rate of 5 grams to 1000 c.c. H2O, plus fuller's earth at the rate 



of 5 grams to 300 c.c H2O. 



The foliage of No. 1 was absolutely covered with a thick, heavy 

 coat of black. The caterpillars were restless and dissatisfied, and 

 piled up and suspended themselves from the foliage by webs. Event- 

 ually they covered over most of the foliage closely with a fine web. 

 The worms on No. 2 seemed more contented. 



