He then took a globe of copper fitted with pump and stopcock, and discovered that he could pump out air as well as water.
The "Regency portable fountain," patented in 1825 by Charles Plinth, was the prototype of the modern siphon, from which it differed in having a stopcock in place of a spring valve.
One tube, called the "measuring tube," is provided with a capillary stopcock at the top and graduated downwards; the other tube, called the "level tube," is plain and open.
To use the apparatus, the measuring tube is completely filled with water by pouring water into both tubes, raising the level tube until water overflows at the stopcock, which is then turned.
The test gas is brought to the stopcock, by means of a fine tube which has been previously filled with water or in which the air has been displaced by running the gas through.