The exemplar shown here is a Guericke pump of the two-cylinder kind with which it is possible to arrive at minimum pressures on the order of a thousandth of a millimetre of mercury.
The greater efficiency of the two-cylinder Guericke pump compared to the one-cylinder model is due to the fact that the former is actually composed of two Guericke pumps in series, one of which creates a preparatory vacuum in the pump body above the other, thus avoiding the oil contained in it becoming impregnated with air, which, on passing into the lower pump body and then into the recipient in which the vacuum is created would greatly raise the minimum pressure that could be reached.
The two pumps, 35.5 cm in height, are supported by a heavy cast iron base (42 x 32 cm) painted black to which is attached the sturdy frame, it too cast iron, supporting the two iron levers that activate the pistons; the latter have in common the actuating arm, which is 47 cm long compared to 19 cm of the other. The overall height of the pump is 56.5 cm. ...continues