;J02 Agricultural Chemistry. 



Paige found, in connection with reported poisonings associated 

 with combating the gypsy moth, that the amount of lead arsenate 

 consumed hy herbivora with the grass from beneath sprayed 

 trees might lead to serious results. These findings emphasize the 

 need of care in the use of poisonous spraying mixtures. 



Hellebore, from the root of the pokeroot plant, and Pyrethrum 

 or insect powder, from the flower heads of certain plants, have 

 poisonous insecticidal properties attributed to alkaloids. Both 

 deteriorate with age. 



Purity and efficiency of insecticides can only be insured by 

 purchasing them under guarantee or under recommendations 

 from reliable authorities, such as the state experiment stations, 

 or by the purchase of simple constituents to be combined by the 

 purchaser. 



Contact poisons may act by their caustic properties and by 

 absorption from the surface of the insect, or by closing the tra- 

 eheae or breathing tubes. These will now receive our consid- 

 eration. 



Lime-sulphur wash is typical of the former class of insecti- 

 cides. It was used in California as a sheep dip, where it was 

 Mist applied also to the San Jose scale in 1886. The wash was 

 prepared by boiling sulphur and slaked lime in equal parts, 

 which produced first a simple sulphide of lime (CaS) of a white 

 eolor. Prolonged boiling causes the color of the wash to pass 

 through shades of yellow to a deep orange color with the forma- 

 tion of poly-sulphides of lime carrying increasing proportions of 

 sulphur. The chemistry of lime-sulphur wash has been inves- 

 tigated at the New York Experiment Station. The chief com- 

 pounds were found to be calcium penta-sulphide (CaS 5 ), calcium 

 tetra-sulphide (CaS 4 ) and calcium thiosulphate (CaS 2 O 3 ). Boil- 

 ing converts the last-named compound into calcium sulphite and 

 free sulphur, and the calcium sulphite then oxidizes by exposure 

 to the air into calcium sulphate. 



The specific gravity of the wash and the amount of calcium 

 and sulphur in solution increased with tli<> amount of lime used. 



