262 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 
and requiring no dead points in their operation they would be desirable 
especially in large horse power machines, yet I think the general results 
of past experience with them for other purposes shows that they are 
less durable than the common reciprocating pi stoned pumps. 
HYDRAULIC BELLOWS. 
The hydraulic bellows are closely related to oscillating pumps, but do 
not require the packings which are necessary to the latter, and there is 
less friction in their working. These are very simple instruments for 
ejecting liquids. They are really simpler than most purops. Yet, here- 
tofore, they have generally not proved preferable, chiefly from weak- 
ness or imperfection of construction, or from lack of durability of the 
materials in their composition. The faults of constiuction are over- 
come by the methods of bellows construction%hich I have designed 
and tested as set forth in another part of this work. The materials can 
be protectively treated, and hence the use of a small hydraulic bellows 
immersed in a tank or barrel, or other vessel, is a very simple and prac- 
tical device for distributing liquids. 
OSCILLATING FORCE-PUMPS. 
The oscillating force-pump proper has for its chamber a radial seg- 
ment of a cylinder. In it a radial septum or one of its radial sides is 
made to oscillate, or the chamber itself may oscillate when the other 
part is fixed. The motion is solely oue of reverting partial rotation of 
either the piston or its chamber with reference to tbe other. The 
oscillating relation is between the piston and its encasement. Thus de- 
finition precludes many falsely so-called " oscillating pumps," in which 
the oscillation is not between the piston and its chamber. It precludes 
all true, straight cylinder pumps. I have tested only one pump of this 
group suitable for use in ejecting poison. It is patented by A. G. Brust 
and W. H. Douglas, of Washington, D. C. The latter gentleman is its 
manufacturer. 
RECIPROCATING FORCE-PUMPS. 
These are most conveniently considered under four headings: a, LTy- 
dtonettes ami Fountain pumps ; />, Bucket pumps and Knapsack pumps j 
c, Aquupults, &c; Barrel and Tank pumps. 
IlYDRONETTES AND FOUNTAIN PUMPS (Plates XXXVIII, XXXIX, 
XL, XLI, and XLI.V). — Certain hand-pumps known to the trade under 
the above names are capable of very general application to purposes 
for which other special forms of pumps and syringes are used. Tliev 
deserve the following notice respecting their use in the tillage of cot- 
ton, &c. : 
The double-acting, hand force-pumps that discharge through a piston - 
fcabe or hollow piston-rod) which has an outside capacity equal to one- 
