UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 1115 ¥& 
Washington, D. C. Vv November 28, 1922 
CHEMICAL CHANGES IN CALCIUM ARSENATE 
DURING STORAGE. 
By C. C. McDonnett, Chief, and C. M. Smiru, Assistant Chemist, Insecticide and 
Fungicide Laboratory, Miscellaneous Division, Bureau of Chemistry, and B. R. 
Coap, Entomologist in Charge, Delta Laboratory, Bureau of Entomology.) 
CONTENTS. 
Page Page 
furpose of investigation......................- Pa DISCUSSIONS £2 AG.e oars os ett te ina ce eee 23 
Results of previous investigations... .. ase ey SM eSTEETPOIRDY.. «222 oA PSS) we ee 27 
Results of present investigation................ 3 | 
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 
1L. 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 all the 
material stored at Tallulah, La. 
2 As determined by the official method of the Association of Official Agricultural Chemists, J. Assn. 
Offic. Agr. Chemists, 5 (1921): 37. 
3835°—22—_1 
