A compendium of the course of chemical instruction in the Medical Department of the University of Pennsylvania / by Robert Hare.

  • Hare, Robert, 1781-1858.
Date:
1834
Catalogue details

Licence: Public Domain Mark

Credit: A compendium of the course of chemical instruction in the Medical Department of the University of Pennsylvania / by Robert Hare. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    latter is then the proper point for the upper zero. As the strip of wood to which the scale is attached, slides upon the iron rod, R, the scale may be fixed at a pro- per height by a set screw.* _ As the air pump will not produce a perfect vacuum, in order to wash out ot tne receiver all traces of atmospheric air, successive portions of the gas to be substi- tuted, may be introduced and removed by exhaustion.t The rise of the mercury in the tube will cause the surface of it in the receptacle, D, to be lower; but the breadth of this vessel is so great, and the descent of the mercurial surface in it, is so inconsiderable, that no error worthy of attention is thus produced. I ought to mention, that the cavity of the tube ought to be so small in proportion to that of the receiver, as to create no error worthy of attention. 30. APPARATUS FOR ILLUSTRATING THE DIFFERENCE BETWEEN THE LIFTING AND FORCING PUMPS. JS, SHE—*- j TTHIIIIHliiii'iiiNiiiii I>•.»••••, ™ iiV The process by which the water is drawn into the chamber, is the same in the case of the forcing, as in that of the lifting pump. In the lifting pump, L the water which has entered the chamber, during the ascent of the piston, passes through the piston, during its descent, and is lifted by it, when the motion is reversed. In the forcing pump, F, the piston, being imperforate, in descending, forces the water into the adjoining air vessel, A, whence its regress is prevented by a valve v. The stroke being repeated, the water accumulates in the air vessel, compressing the contained air, until it reacts upon the water sufficiently to cause an emission of this liquid, (through the jet pipe, J J,) commensurate with the supply. * Both the gage tube and the rod, R, should be longer than they are represented in the figure. t One gas may be employed to wash another out of a cavity, in a mode analo- gous to that in which water may wash out alcohol, or alcohol, water.