354 Improved Air Pump Receiver. 
«The accompanying drawing represents a metallic cylinder A, 
which is to be connected with P, the plate of 
a common air pump by means of a screw, and 
the vacuum is to be made in the receiver D. 
B, is a piston well packed, and fitted to move 
up and down in the cylinder; C, a stuffing 
box through which the piston rod passes air 
tight; E and F, metallic tubes of small bore 
communicating with the air pump plate P, the 
cylinder A, and the receiver D. 
“Having screwed the apparatus upon the 
plate P, open the stop cocks 1, 2,3, and ex- 
haust the air within the receivers, in the 
usual way until the elasticity of the air with- 
in, is no longer capable of raising the valves. 
Then closing the stop cock 1, force the pis- 
ton B, nearly to the bottom of the cylinder, 
by which the air before occupying the whole 
of the cylinder is so much condensed that its 
elasticity will raise the valves of the air pump 
and is by itremoved. ‘The air which before 
depressing the piston B, filled only the receiv- 
er D, is now expanded so as to fill also the 
cylinder A, while the piston B remains at the 
bottom of the cylinder, close the stop cocks 3 and 2, and then open 
1 and elevate the piston by the hand to near the top of the cylin- 
der. The air which before elevating the piston occupied the whole 
spaces of the cylinder is now compressed into that, occupied by the 
bore of the tube E, G, F anda small portion of the upper part of 
the cylinder and has now acquired sufficient elasticity to raise the 
valves, and by working the pump, as before, isremoved. ‘Thus by 
elevating the piston B, and exhausting, and then depressing it and 
exhausting, provided the apparatus be well made it is believed that 
the most perfect vacuum can be formed, equal for all practical pur- 
poses to the torricellian. ‘The size of the cylinder A, may be in- 
creased to any dimensions, and the rapidity of the exhaustion will 
be in the same proportion.” . 
The above apparatus it must be remembered is intended only for 
such pumps as have their valves raised by the elasticity of the air 
