30 



Mr. Marlatt read the following paper: 



COMPARATIVE TESTS WITH NEW AND OLD ARSENICALS ON 

 FOLIAGE AND WITH LARV^l. 



By C. L. Marlatt, Washington, D. C. 



In the last volume of Insect Life, in an article on Paris green, atten- 

 tion was called to the very large amount of this substance now being 

 used annually as an insecticide, amounting to 2,000 tons or more. The 

 same matter was also briefly discussed before this association at its last 

 meeting, at which time attention was called again to the possibility of 

 the use of a simple arsenite of copper rather than the much more 

 expensive aceto-arsenite hitherto employed under the name of "Paris 

 green. 7 ' The tests made with the simple arsenite of copper, or Scheele's 

 green, last season were very favorable to this new insecticide, but 

 were not carried out with sufficient fullness to justify its being unre- 

 servedly recommended. The present summer has been taken advan- 

 tage of to give this insecticide a much more thorough test, making the 

 trials in conjunction with the ordinary Paris green and a sample of the 

 same which had been somewhat finely pulverized, and also parallel 

 tests with London purple, arsenite of lead, 1 and a mixture submitted 

 to us for experiment which consisted of a combination of arsenite of 

 lead and simple arsenite of copper in equal proportions. With these 

 six substances many tests were made on foliage, and by feeding larvae 

 on leaves poisoned at different strengths. Through the cooperation of 

 the Division of Chemistry, also, chemical and physical examinations 

 were also made of the several arsenicals. The results of this work are 

 here summarized: 



Foliage tests. — All of the first series of experiments to test the effect 

 of these arsenicals on foliage were made on young and vigorous pear 

 trees, and with freshly mixed poisons, both with and without lime. 

 An entire tree was devoted to each experiment, the application being 

 made most thoroughly. When lime was added the amount was equal 

 in weight to the poison employed. The washes were applied at the 

 following strengths : 



Paris green, ord.-j 



Paris green, pul. ^at the rate of 1 pound to 160 gallons ; 1 to 100 ; 1 to 80 ; and 1 to 53^. 



Scheele's green. J 



London purple, arsenite of lead,^i 



and the mixture of Scheele's lat the rate of 1 pound to 160 gallons, and 1 to 100. 



green and arsenite of lead. J 



ISTo injury or scalding resulted in any case, even with the very strong 

 mixtures of Paris green and Scheele's green. The weather conditions 

 were such as to give the applications a very fair trial. 



Subsequently foliage tests were also made on peach, apple, cherry, 



Colored by the addition of a fraction of 1 per cent of aniline dye and styled 

 ''pink arsenite." 



