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LECTURES TO SCIENCE TEACHERS. 



exhausting apparatus for pumping out the gases. This 

 exhausting apparatus is composed of a large fixed glass 

 bulb (a) connected by a piece of india-rubber tubing (d) 

 with a second bulb (6), which can be raised or lowered at 

 pleasure by means of a winch and chain. At the upper 

 end of a is a three-way stopcock (#), by which a can be 

 entirely shut or be made to communicate at pleasure with 



FIG. 4. Mercurial pump for extracting the gases from the blood. 



a tube (A) dipping into a pneumatic trough, or with the 

 apparatus use. The bulb b, which instead of being some- 

 what smaller than a, as represented on the diagram, ought 

 to be larger, is lowered to the position b' and filled with 

 mercury. The stopcock g being then opened, the bulb b 

 is raised by the winch to a higher level than a, so that the 

 M.ercury flows from b into a until it is quite full, the air 



