EE EE I ET 
Of a Suction and Forcing Air Pump. 237 
Arr. 1V.—Description of an Air Pump of a new construction, 
which acts either as an Air Pump, or a Condenser, or as both; 
enabling the operator to exhaust, to condense, to transfer a Gas 
from one cavity to another, or to pass it through a Liquid; by 
R. Hare, M.D., &c. &c. 
From the Transactions of the American Philosophical Society. 
Tus pump has one iron chamber,* one piston, and four valves. 
When in operation, it is always simultaneously exhausting and con- 
densing; and of course accomplishes as much ina given time, as 
two chambers of the usual construction, of the same calibre and 
stroke. A suction valve is placed at each end of a steel rod, which 
slides through the packing of the piston,} so as to be air tight, and 
to be pressed in opposite directions alternately. It is of such a 
length, that while it forces one valve, towards which the piston 
moves, against its seat, closing a corresponding aperture, it withdraws 
the other valve from its seat, and, consequently, opens the aperture 
with which this valve corresponds. Hence, with every reversal of 
the motion, the aperture previously opened will be shut, while that 
previously shut will be opened. Between the apertures thus alter- 
nately opened and shut, and the valve cock A, a communication is 
made by means of a forked leaden pipe, communicating with the 
valve cock at A, and with the apertures at Band C. The valve 
cock, by means of a gallows screw D, communicates, when desirable, 
with any receiver by another flexible leaden pipe P. 
Two other analogous and corresponding apertures E R, which 
communicate in like manner with a valve cock G, are furnished with 
two valves opening outwards. These, when not subjected to any 
pressure from within the chamber, are kept in their places by spiral 
springs. ‘They act as valves of efflux, and, like the valves in other 
condensers, are opened by the pressure of the air condensed by the 
piston as it approaches them, and are shut by the springs when the 
piston moves in the opposite direction. It is well known, however, 
* The diameter of the chamber in the instrument represented in the figure is 
three inches; the length is ten and a half inches, allowing a stroke of about eight 
inches, taking off the thickness of the piston. In order to render this instrument 
insusceptible of injury from mercury, it was constructed altogether of iron or cast 
steel. : 
+ This contrivance was suggested to me by an excellent pump with glass cham- 
bers, obtained many years ago from Pixii. In that pump a steel rod is made to 
open and shut one valve: in mine the same rod opens and shuts two valves. 
Vou. XX XIII.—No. 2. 31 
