12 



BULLETIN 731, U. S. DEPARTMENT OF AGRICULTURE. 



of calcium arsenate was still more effective. This contains a much 

 higher 2)ercentage of arsenic pentoxid than any other arsenical 

 utilized and has the great advantage of being much cheaper than lead 

 arsenate. In addition, a number of tests of various mixtures of 

 these arsenicals and dilutions of them with different carriers were 

 conducted. This work is still in the experimental stage and it is 

 difficult to prophesy just what the results will be. It is obvious, 

 however, that either a dihydrogen lead arsenate containing not less 

 than 32 per cent of arsenic pentoxid or a calcium arsenate containing 

 at least 42 per cent of arsenic pentoxid will produce an effective 

 control if utilized properly. It also seems probable that it will 



Fig. 9.— Hand dust guns in operation, showing method of use; Tallulah, La., July 15, 1916. 



be possible to dilute these considerably with some cheap carrier 

 such as lime, though this has not been definitely determined as yet. 



DENSITY OF THE POISON. 



Fully as important as the actual composition of the chemical is 

 its physical condition. When the experiments were first started, 

 practically all of these chemicals were prepared only in a density of 

 about 40 cubic inches per pound. It was evident, however, that 

 a much finer powder would afford a greater distribution per pound, 

 and also that a finer powder was apparently more readily taken 

 ii]) by the dew and held in suspension for the weevils. Consequently 

 these poisons were prepared in density ranging from 80 to 160 cubic 

 inches per pound and proved much more effective in that form. 



