236 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 
may be made as usual. This on tbe excurrent orifice may be through 
either head of the bellows, the latter preferably toward the poison res- 
ervoir. Across either head may be added a cleat, which also can be 
hollow, with a discharge or suction passage, and may extend beyond the 
bellows as a spout or handle. A reacting spring to expand or open the 
bellows can be placed inside, or else outside between the projecting ends 
of the cleats, spouts, or handles. Some varieties of these bellows, 
methods of operating them, and ways in which they are susceptible of 
being combined with nozzles, reservoirs, &c, will be particularly noticed 
in the special apparatuses to be described. 
Oscillating Blowers of Powder.— Instead of the various hop- 
pers, which generally allow the poison to escape beneath the cover, or 
permit moisture to enter there when the plants are wet or in case of 
rain, it is better to employ a water-tight can, closed by a large can-screw 
cap or plug. The can may be of any convenient size or shape, and 
any other ordinary reservoir, as a tight keg or barrel with a large bung, 
can be used in its stead. 
The device to supply the blast with powder must be certain to feed 
continuously and adjustable to apply as much or little as may be 
desired, yet not capable of clogging. To produce such an effectual 
arrangement for feeding minimum quantities of poison mixed with 
materials which pack and clog easily, like flour, for example, was diffi- 
cult, and for a long time threatened to be an impossibility ; but the prin- 
ciples already noticed above apply here, and their employment in these 
devices is described below ; but it must be remembered that the blast of 
the rotary blower is large and weak, while that of the oscillating blower 
is small and intense, so some adaptive modification is advisable. 
A blast with an independent passage for itself is made to feed itself 
by the attrition of its lateral parts or by a side blast. Thus tbe blast 
force is ut ilized to cat out and carry the powder from the mass where it is 
exposed for an area extended by a slot or a group of openings through 
the segmental or interrupted wall between the blast passage proper and 
the reservoir which adjoins or surrounds it. Thus a reliable positive 
feeding force is directed and controlled without depending solely on 
gravitation or on ordinary mechanical feeding devices, which will not 
feed regularly in minimum quantities. This kind of apparatus works 
freely and the direct unimpeded blast throws the powder a good dis- 
tance. The blast thus acts to open the narrow feeding entrances. At 
the same time a passage to deliver a part of the blast or another blast 
simultaneously above the poison to produce a pressure downward upon 
it assists gravitation, but is not necessarily employed, for, especially 
where the bulk of the poisou is small, the air will alternately and in- 
termittingly force up through the poison, opposing gravity, and then 
react downward, assisting it. For flour mixtures the feeding is done 
pretty well by passing the blast tube through the base of the powder- 
can, therein providing the tube with numerous holes having one-eighth 
