FOSSIL SHELLS OF THE JOHN DAY REGION

ROBT. E. C. STEARNS
1902 Science  
SCIENCE. siphon tube, both legs of which are 10 cm. or 15 cm. longer than the barometric column. The bore of the tube should be small (about 2, sq. mm.) to work well. Let one of the legs, BC, dip down into a larger tube CD, partly filled to D with mercury. Fill ARC with mercury, and start the siphon drawing mercury from C over to A in the usual way. In order to start the siphon the vertical height of B above the surface D of the mercury should be less than the length of a mercury barometer
more » ... cury barometer column, but as the flow continues, the mercury surface descends and keeps on descending until its vertical distance below C is considerably greater than this length. To make this experiment work sufficiently well for demonstration purposes, excessive care in purifying the mercury and cleaning the glass is not necessary. Boiling the mercury in the actual tubes used, for instance, is superfluous. With ordinary redistilled commercial mercury and tubes cleaned with alcohol the writer has made the siphon work to a height of 70 cm. AS the altitude of the University laboratory, where the experiment was performed, is a little over one mile, and the barometer pressure, tharefore, only about 61 em., this means that the siphon worked 9 am. above the barometric height. The most plausible errplanation of the above fact is that the atmospheric pressure is not the only force pushing the mercury up the shorter leg. It is drawn up partly by the cohesive attraction of parts of the lnercury for each other, and the column is kept from dwindling by the adhesive force exerted by the sides of the tube on the mercury. I t follows from the above that if a mercury siphon is placed under the receiver of an air pump, it can be made to work over a height of several centimeters, even though the air pressure is reduced to only a few millimeters. This experinlent also has been shown to the writer's students. The apparatus was similar to that described above, except that the tubes were much shorter.
doi:10.1126/science.15.369.153 pmid:17781014 fatcat:oklnnit435dqfew2w3rjli367a