IJ4 MAINE AGRICULTURAL EXPERIMENT STATION. I9OO. 



a sufficiently powerful pump to use double nozzles, and on this 

 account are not well adapted to practical spraying in a potato 

 growing district. 



RESULTS WITH INSECTICIDES. 



While experiments at this time included only Paris green, 

 arsenate of lead, Paragrene and the arsenoids, notes are here 

 given on other insecticides which are used to a greater or less 

 extent in the State. 



PARIS GREEN. 



Since the advent of the Colorado potato beetle, Paris green 

 has been the favorite and indeed practically the only insecticide 

 used. According to the L. S. Dispensatory, Paris green is the 

 aceto-arsenite of copper and "is made by mixing 5 parts of verdi- 

 gris with sufficient water to form a thin paste, and adding to this 

 a boiling solution of 4 parts of arsenious acid in 50 parts of water, 

 keeping the mixture at the boiling temperature and adding a little 

 acetic acid to cause it to retain a brilliant color/' The pure 

 aceto-arsenite of copper should carry 58.65 per cent of arsenious 

 oxide. There is also another compound sometimes sold under the 

 name of Paris green which is practically the arsenite of copper 

 and theoreticallv carries 52.94 per cent of arsenious oxide. ( See 

 arsenoids beyond.) 



Formerly Paris green was used only as a pigment and the first 

 aim of the manufacturer was to produce a good bright green. 

 Since its use as an insecticide the consumption has greatly 

 increased and different manufacturers have modified the process 

 of manufacture so that in many instances they differ quite widely 

 from that outlined above. In at least one plant the green is made 

 from copper oxide, arsenious acid, and a soluble acetate. The 

 ingredients used will always contain varying amounts of impuri- 

 ties and on this account very little, if any. Paris green is strictly 

 pure aceto-arsenite of copper. As the arsenious acid is the 

 cheapest single constituent, the claim made by one manufacturer 

 that '*as long as the green is pure, the manufacturer will endeavor 

 to get as much arsenic into it as possible, consistent with making 

 a good bright green," is probably true. So-called "pure"' Paris 

 greens which do not bear evidence of adulteration have been 

 found to carry as little as 47 per cent of arsenious acid and others 



