EXPERIMENTS WITH INSECTICIDES UPON POTATOES. 1 77 



per cent of arsenious oxide, 23.08 per cent of which is free. 

 It also contains 19.31 per cent of gypsum to add weight. 

 Because of its large amount of free arsenious oxide it would be 

 apt to burn the foliage of tender plants. On such a plant as the 

 potato and in the small quantity used mixed with lime or Bor- 

 deaux mixture, the burning by this amount of free arsenic would 

 not be likely to be °reat. It was applied four time with Bor- 

 deaux mixture at the rate of one-half pound per acre to rows 65 

 to 80. The field notes follow. 



July II, potatoes just beginning to bloom, no slugs hatched 

 yet, sprayed; July 21, sprayed; July 24, very few bugs, none on 

 coated or eaten leaves; July 27, sprayed; August 1, practically 

 no bugs; August 8, practically no bugs; August 10, sprayed; 

 August 14, no bugs ; August 27,, a few leaves are browned and 

 curled on edges; no spots as in blight ; appear to be slightly 

 burned ; September 4, the "burning" has made no progress. 



The Paragrene used in this experiment was coarser than Paris 

 green and when wet up with water there was quite a little residue 

 left that would not go through a fine Vermorel nozzle. The 

 attention of the company was called to the coarseness of the 

 sample we used and in explanation they write as follows : "This 

 is no doubt due to the rent or tear in the mill in which it is 

 bolted. Sometimes this is bound to occur and a lot will go 

 through the bolter before it is discovered, but we can assure you 

 it is only an accident and instead of being coarse and gritty, the 

 goods are always as fine as it is possible to get the best grade of 

 flour." 



In this experiment Paragrene proved as effective as Paris 

 green and in the amount used did not burn the foliage so as to 

 injure it, if at all. 



ARSENOIDS. 



Under the general name arsenoids quite a number of different 

 arsenites have been placed upon the market. White arsenoid 

 was supposed to be barium arsenite, but all of its arsenious acid 

 was free so that it was no better than white arsenic diluted with 

 baryta. Pink arsenoid is arsenite (not arsenate) of lead. A 

 sample examined by the California Station* carried 40 per cent 

 of combined and 3^4 per cent of free arsenious acid. The green 



* Bulletin No. 126. 



