UNITED STATES DEPARTMENT OF AGRICULTURE 
DEPARTMENT BULLETIN No. 750 
-„ t\ p w Issued, October 5, 1918. 
OD, V. <L. V Revised, September, 1923. 
* 
A METHOD FOR PREPARING A COMMERCIAL 
GRADE OF CALCIUM ARSENATE. 
By J. K. Haywood, Chief, Miscellaneous Division, and Chairman, Insecticide and 
Fungicide Board, and C. M. Smith, Assistant Chemist, Bureau of Chemistry. 
CONTENTS. 
Page. 
Calcium arsenate as a substitute for lead 
arsenate 1 
Preparation of calcium arsenate 1 
Slaking the lime 4 
Proportions of arsenic oxid and lime 4 
Page. 
Effect of dilution and temperature upon the 
compound 6 
Experiments with limestone 8 
Summary 8 
Labeling the product 9 
CALCIUM ARSENATE AS A SUBSTITUTE FOR LEAD ARSENATE. 
Attention has been directed to the use of calcium arsenate as a 
substitute for lead arsenate, principally because of the cheapness of 
lime as compared with the cost of lead oxid. While no one recom- 
mends the use of calcium arsenate alone on tender foliage, experi- 
ments by investigators in the United States Department of Agri- 
culture x and in the Canadian Department of Agriculture 2 and others 
have shown that it gives excellent results on some of the more resist- 
ant plants, as well as very promising results when combined with 
other sprays, especially sulphids, which cause to some extent the 
breaking up of lead arsenate. The greatest development in its use, 
however, has been for the control of the cotton boll weevil, many 
million pounds being used each year for this purpose. 
PREPARATION OF CALCIUM ARSENATE. 
The Bureau of Entomology of this department has conducted 
experiments with " homemade " calcium arsenate prepared by slaking 
burned lime with a solution of sodium arsenate. Others 3 have 
i XJ. S. Dept. Agr. Bui. 278; Farmers' Bui. 908. 
2 Crop Protection Leaflet 10. 
3 Oregon Agr. Exp. Sta. Bui. 131. 
59904°— 23— Bull. 750 
