180 EXPERIMENT STATION. [Jan. 



which Scheele's greeu ^ in 1875, London purple ^ in 1877, lime 

 arsenite '^ in 1891 and lead arsenate "* in 1893 are the most im- 

 portant. Paris green and lead arsenate are to-day the most 

 extensively employed food poisons for leaf-eating insects. Lime 

 arsenite is more particularly a farm preparation. Scheele's 

 green and London purple have been largely superseded by the 

 other compounds. 



The Investigation. 



The object of the investigation, planned by Dr. H. T. Fernald 

 of the entomological department, was " to ascertain why and 

 under what conditions insecticides burn foliage." The princi- 

 pal arsenicals were to be applied " under differing known con- 

 ditions of light, temperature and humidity," and where injury 

 resulted, its character and extent carefully determined. Work 

 of this type would naturally extend over a considerable number 

 of growing seasons to furnish sufficient data to warrant positive 

 deductions. The chemical department of the experiment station 

 was required to co-operate so far as to provide the necessary 

 amount of chemicals of known composition, suitable for the 

 purpose intended, together with any information relative to 

 solubility, hydrolysis and power of suspension, that would be 

 of service in their application. 



At the outset the laboratory phase of the project appeared an 

 easy matter, — simple analytical work on a relatively small 

 number of samples of similar nature. In February, 1908, let- 

 ters were sent to several large manufacturers of high-grade 

 chemicals stating the object of the investigation and asking if 

 they could supply Paris green, copper arsenite, lime arsenite 

 and lead arsenate of the necessary purity and, if not, the best 

 method of securing such salts. The replies were rather unsat- 

 isfactory, though the order was finally placed with a firm mak- 

 ing a specialty of guaranteed reagents. The dry salts were 

 received, but on examination proved unfit for the purpose in- 

 tended. Work on methods of analysis and study of arsenical 

 reactions were continued, so far as other duties would permit, 

 during the next two years. 



1 C. V. Riley, Potato Pests, p. 67. 



>E. G. Lodeman, Spraying of Plants, p. 65. 



' N. Car. Exp. Sta., Bui. No. 77b. pp. 7-8, (1891). 



<Mass. Bd. Agr. Ilept., 41. p. 282 (1894). 



