26 FIRST ANNUAL KEPORT OF THE STATE EISTTOMOLOGIST. 



gathering having proved insufficient) which could be employed for the 

 destruction of the hordes of the Colorado potato-beetle, which were in- 

 vading and threatening the entire ruin of every potato field throughout 

 Northern and i>Iiddle United States east of the Rocky Mountains and 

 southward into North Carolina and Northern Texas.* It was found 

 that by no other means could this be accomplished so quickly, eco- 

 nomically and effectually, and it has, therefore, notwithstanding the 

 popular prejudice against so free an use of a virulent poison, been very 

 extensively resorted to, for several years past, in the cultivation of the 

 potato. It has also been successfully employed in protection from 

 other insect ravages. 



Paris green is a combination of arsenic and copper, known in sci- 

 ence, as arseniate of copper. In its pure state it contains fifty-eight 

 per cent of arsenic (arsenious acid). The enormous demand for it — 

 druggists in some of the great agricultural centers of the West have 

 ordered it by the ton — and the prevalent disposition to economize in 

 its use by purchasing it at the lowest price, have led to its great adul- 

 teration. As frequently sold, it contains less than one-half its proper 

 proportion of arsenic. In rising it as an insecticide, it is important 

 that it be obtained pure, for otherwise the directions for its use are 

 not applicable to its altered condition. 



It may be used either in its dry form as a powder, or mixed with 

 water or other liquid. 



Diluents. — In its dry application, it is mixed with some other mate- 

 rial to reduce it to a degree that will admit of its use without injury 

 to the plants upon which it is cast, and of its convenient distribution. 

 The materials usually employed are flour, plaster, finely sifted wood 

 ashes, air-slacked lime and road dust. Care is necessary that it be 

 thoroughly mixed, by long-continued stirring, unless some special con- 

 trivance is arranged for the purpose. f 



The Dry Mixture. — The best results have been obtained when flour 

 is used, as the compound seems to adhere better to the leaves of plants 

 and to be more readily eaten than are the mineral and other sub- 

 stances. The proportion of flour required will vary with the crop to 

 be protected. Potato leaves will safely bear a pound of Paris green to 



*See map of iuvaded territory, iu Ninth Missouri Report, p. 36,>nd estimates of area ua 

 p. 38. 



+ A simple contrivance for the purpose is thus constructed : " It consists of a barrel 

 which has a longitudinal wooden axle projecting somewhat at each end. Five or six staves 

 run through tlie barrel longitudinally but do not project at either end, and on one side is 

 an aperture large enough to admit the ingredients. When they are in, the aperture is 

 closed and the barrel is placed over a large open box, or fixed in any way so that it can be 

 revolved by means of a handle attached to the projecting axle. {Bulletin, No. S, of the U. 

 8. Eld. Comiais. — The Cotton. Worm, 1880, p. 74.) 



