4. Note on Sprengel's Mercurial Air-Pump.

Extract

The ordinary Sprengel, requiring careful manipulation, and being apt to get out of order, has not yet become an essential piece of lecture apparatus as it ought to be. The author exhibited to the Society two modifications adapted to lecture illustration. In both instruments the mercury receptacle is made of iron, and instead of the india-rubber joint of the original, a well-ground iron stopcock is substituted, the portion of iron tube before the stopcock terminating in a Y-shaped piece bored out of the solid. In the one form the drop-tube is of glass, attached by means of marine glue; in the other, of carefully made india-rubber tube four or five millimetres in thickness, of a very small uniform bore, made expressly for the purpose by the Edinburgh Rubber Company.