AIR-PUMP

An instrument designed for the removal of air from closed ve els. The simplest form of air-pump is the exhausting syringe, which consists of a cylinder fitted with a stop-cock, and having a valve at the bottom opening inwards. Another valve opening outwards is attached to a piston working inside the cylinder, and by screwing the instrument on to a ve el, and alternately elevating and depre ing the piston, all except a very small quantity of residual and comparatively inelastic air is pumped out of the ve el (Figs. a and b ). The accompanying figures show relative positions of the valve during ( a ) the elevation, and ( b ) the depre ion of the piston. In the usual and more convenient form of air-pump, a bra tube pa es from the bottom of the syringe and terminates in the centre of a disk of bra or gla ground accurately; the ve el from which the air is to be exhausted has its edge very accurately ground, and is mounted upon the plate as shown in the subjoined figure. IMG:596405606043057898_i065-2.png: