— 
19 BULLETIN 131, U. S. DEPARTMENT OF AGRICULTURE. 
of calcium arsenate was still more effective. This contains a much 
higher percentage 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 
Fic. 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 
up 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. 
