Abstract
A special calcium arsenate containing only about 20% arsenic calculated as As2O5 was found to be equally as effective a boll weevil control as commercial calcium arsenate in extended cage and field tests. The material caused no plant injury. This special calcium arsenate was prepared by heating precipitated chalk and white arsenic (As2O3) in the presence of excess air at a temperature of 650oC. for about one hour. In this manner it was possible to prepare a calcium arsenate containing any dcsired percentage of arsenic as As2O5 up to 57.6%, the theoretical for normal calcium arsenate, Ca3(AsO4)2. The conversion from the trivalent to the pentavalent state is practically complete, and there is scarcely any free lime formed under these conditions. Any arsenic lost in this process is recoverable on a commercial scale. The particles of the special calcium arsenate containing only 20% arsenic as As2O5 consisted of an inert core of calcium carbonate covered with a coating of substantially 100% normal calcium arsenate. This direct oxidation method of preparation is adaptable for arsenates other than calcium.
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