76 JOURNAL OF ECONOMIC ENTOMOLOGY * [Vol. 15 



All mixtures were made at the laboratories. The clay referred to is 

 in all cases Milltown Ball Clay No. 9, dried and g^round to a mesVi 

 mostly exceeding 200. This is a more or less colloidal clay mined 

 locally and so far as the writers know not reliably analyzed. The 

 calcium oxide referred to is in all cases the best grade of Palmer selected 

 stone lime around to about 200 mesh. The grinding machines employed 

 were the common ball mills used in ceramics. The nicotine in all cases 

 is derived from "Black-leaf 40." The calcium hydroxide referred to is 

 in all cases a good grade of commercial hydra ted lime. The Sanders' 

 dust was secured from Riches, Piver & Co., and consisted, according to 

 the manufacturers, of dehydrated copper sulphate, calcium arsenate 

 and inert ingredients. The nicotine was introduced into the partic- 

 ular dust mixture concerned and gi'ound in in the ball mills above 

 referred to. 



Two sets of investigations form the subject of this paper. They are 

 concerned with the determination of the following points : — 



(1) The relative effectiveness of nicotine delivered as a dust and as a 

 liquid spray; 



(2) The disadvantages of nicotine delivered as a dust as compared 

 with nicotine delivered as a spray; 



(3) The advantages of nicotine delivered as a dust over nicotine 

 delivered as a spray 



(4) The lelative value of different dusts as carriers for nicotine. 

 The field work was devoted entirely to the pink and green aphis of 



the potato and tomato, while the laboratory work was concerned with 

 the rate and the amount of nicotine delivered from the different dust 

 earners. 



Table I will serve to set forth the data relative to the killing power of 

 nicotine delivered as a dust and as a spray and will serve to show some 

 of the disadvantages of dust as compared with spray. 



Table I. — Table Showing the Relative Effectiveness of Nicotine delivered as a Dust 

 AND AS A Spray and the Length of Period over which the Kill Extends when Nicotine is 

 USED as a Dust. Tests were made on M. solanifolii on American Giant Potatoes. 



