94 Mr. Patien’s Air Pump, Gazometer, &c. 
bea quantity of air left in the globe, and should there be 
expansion, the mercury would be thrown out at t 
aperture; but a great objection to it is, that any meth- 
od that could be proposed to open or shut the cock except 
y hands, would be either pielhie a or complicated, 
and after all the “i improvement,” seems to be an awkward 
eration of the very cock that is now ieee the pump; for 
let that cock be as represented in fig. 2nd, (Pl. 2, Vol. 
VIII, No. 1 ) if now the plug be ect “half round, ” (see 
the Profs, description,) so that the back of the plug i is 
against the hole a in the bulb, then there is only a com- 
munication between the receiver R and the globe K; 
—now let an exhausition be made, then turn the plug 
‘one quarter round,” with its hole a downwards, the air 
now from the globe can escape only into the atmosphere 
through the hole a@ drilled in the bulb where it should 
be, and not through a useless and crooked one that inter- 
feres with the screw that holds the plug tight—it is therefore 
apparent that as yet the only way of closing the ee is 
by valves, and if — with the least accuracy, 
no mo or secure way of doing it, nie 
their weight i in this Cie’ is a matter of perfect indifference 
as iti is impossible from the manner of opening and shut- 
, that they should interfere with the exhaustion. 
If f have not already intruded too far upon your patience, 
I transmit for insertion, a modification of the other pump, 
or rather an adaption of the principle to the ones of the 
usual construction; it was cotemporaneous with the first 
but I did not send it at that time, as I considered the other 
the most perfect; the only objection however to this is 
that it has an air tight collar, and the vapor of the oil is not 
removed ; but it has its advantages—there is no glass that 
can be broken—it takes but an ounce or two of mercury— 
d there are no caps to be cemented 3 the glass, a diffi- 
ty that you feared might be experienced. ABCD rep- 
ts an iron barrel with a solid piston E, the piston rod 
hrough an airtight collar at F ; at G is a valve open- 
ng inward at H and I valves opening out; K is the plate 
of the pump connected with the top and bottom of the bar- 
rel by the tube aaaa—the top of the barrel is made with a 
rim round it for the purpose of holding an ounce or two of 
mercuty—through the piston rod a small diagonal hole is 
etc 
