122 EXPKIUMEXT STATION. [Jan. 



THE DETERMINATION OF ARSENIC IN 

 INSECTICIDES. 



BY E. B. HOLLAND, 



During the past three years the writer ^ has given considerable 

 time to the study of arsenical insecticides, with special reference 

 to their manufacture, composition and use, — the main object 

 of which was to provide the entomological department of this 

 station with chemicals of known composition, suitable for an 

 extended investigation to determine their effect in practical ap- 

 plication under varying climatic and atmospheric conditions. 



Eor more than a decade the analysis of arsenicals has received 

 marked attention because of the high value of a number of these 

 salts as insecticides. The sale of inferior, adulterated or imita- 

 tion products lacking in efficiency, or causing severe injury to 

 foliage, has rendered necessary a certain amount of supervision 

 by the agricultural experiment stations of the country. In sev- 

 eral States special laws have been enacted to regulate the sale 

 and to provide for an inspection of such materials. Arsenic as 

 trioxide or pentoxide is the active constituent of these com- 

 pounds, and various methods of several distinct types and nu- 

 merous modifications have been proposed for its determination. 

 Some of the methods are applicable to arsenous acid and others 

 to arsenic acid. 



Methods.- 



As the work ]ilanned liv the entomological department would 

 require many analyses, it was desirable that the methods adopted 

 should be reasonably short and simple, though accuracy would 

 be the controlling factor. The literature on the determination 

 of arsenic was reviewed at some length. The results, while 

 somewhat overwhelming, can be roughly summarized under 

 gravimetric methods, volumetric methods and processes for the 

 elimination of substances liable to affect the determination. A 



> Assisted by Dr. R. D. MacLaurin, Prof. S. F. Howard, C. D. Kennedy and J. C. Reed. 



