80 ORCHARD CATERPILLARS. 



see no advantage, but rather disadvantage, therefore, in the use of the 

 mixture." — A. J. V. 



The above clear observations of Dr. Voelcker's require no comment ; 

 and I felt myself much favoured in being thus aided to place the exact 

 state of the case regarding admixture of Paris-green and soft-soap 

 before those to whom a certain knowledge of what they are dealing 

 with is of great importance. With regard to the mixture itself, I can 

 quite endorse Dr. Voelcker's views as to its being a tenacious sticky 

 mass most difficult to deal with, and also involving great uncertainty 

 as to proportion of Paris-green therein contained. Consequently there 

 may be more or there may be less than the quantity needed, and great 

 difficialty or loss ensue. In these observations the matter under con- 

 sideration was solely mixture of Paris-green with soft-soap. 



About the same time, being then in correspondence with Mr. James 

 Fletcher, the Entomologist of the Dominion of Canada, who assisted 

 us greatly in the first trials of use of Paris-green in England, I men- 

 tioned the subject, and he subsequently favoured me with the following 

 notes of experiments carried out by Mr. Frank Shute, the Chemist of 

 the Experimental Farms of the Dominion of Canada. These (which, 

 it will be seen, especially regard whether the poisonous action of the 

 Paris-green is changed by mixture with solution) deal with chemical 

 changes, or changes in condition, which are caused to Paris-green by 

 various combinations specified ; also give notes of results of experi- 

 ment of mixtures of Paris-green with various kinds of soaps, alkaline, 

 or not alkaline to test paper ; and notes of the inferences to be drawn 

 from the experiments. I beg here also to express my best thanks for 

 the favour of being permitted to offer such useful information for 

 general service ; and I give the report as follows : — 



" Laboratory, Central Exp. Farm, Ottawa, Canada, 

 "June 9th, 1891. 



" The application of Paris-f/reen inmff^sonp sohition as an insecticide. 

 — The question has arisen whether the toxic action of Paris-green as 

 an insecticide is to any extent weakened or destroyed when the poison 

 is applied with soap solution. For the purpose of answering this 

 question I have carried out a number of laboratory experiments, the 

 results of which form the basis of the present report. 



" Paris-green (aceto-arsenite of copper) is an emerald-green salt, 

 which is practically insoluble in water. Experiment 1 consisted in 

 shaking up Paris-green with water constantly for more than a week. 

 The Paris-green was then filtered off. Not a trace of arsenic could be 

 detected in the filtrate, though the most delicate chemical process was 

 employed. 



" Strong ammonia readily and completely dissolves Paris-green, 



