UNITED STATES DEPARTMENT OF AGRICULTURE 



BULLETIN No. 1115 fMI 



jrwV 



Washington, D. C. 



November 28, 1922 



CHEMICAL CHANGES IN CALCIUM ARSENATE 

 DURING STORAGE. 



By C. C. McDonnell, Chief, and G. M. Smith, Assistant Chemist, Insecticide and 

 Fungicide Laboratory, Miscellaneous Division, Bureau of Chernistry, and B. R. 

 CoAD, Entomologist in Charge, Delta Laboratory, Bureau of Entomology} 



CONTENTS. 



Purpose of investigation 1 



Results of previous investigations 2 



Results of present investigation 3 



Discussion 23 



Summary 27 



PURPOSE OF INVESTIGATION. 



Soon after calcium arsenate had been introduced into the Cotton 

 Belt for use in the control of the cotton boll weevil, the United States 

 Department of Agriculture began to receive complaints of injury to 

 cotton plants resulting from the application of this material. Chemi- 

 cal analyses showed that much of the calcium arsenate being used 

 in the cotton-growing region at that time contained from 1 to 5 per 

 cent of ''water-soluble" arsenic oxid,^ which explained to some extent 

 the injury that was being done to the plants. 



In an endeavor to place the responsibility for this unsatisfactory 

 condition, it was suggested that perhaps commercial calcium ar- 

 senates deteriorated somewhat when stored for a period of several 

 weeks or months and that this deterioration was more rapid under 

 the climatic conditions existing in the cotton-growing States. This 

 problem was a very serious one, not only from the standpoint of the 

 consumer but from that of the manufacturer as well, for on its 

 solution depended the answer to the question whether or not it was 



1 L. N. Markovitz and A. Shaver, junior chemists, of the Bureau of Chemistry, assisted in the analytical 

 work, and T. P. Cassidy and M. T. Young, of the Bureau of Entomology, cared for and sampled aU the 

 material stored at TaUulah, La. 



2 As determined by the official method of the Association of Official Agricultural Chemists, J. Assn. 

 Offlc. Agr. Chemists, 5 (1921): 37. 



3835°— 22 1 



