Haldat’s Apparatus

Haldat’s Apparatus for showing that the pressure of liquids depends upon their height and the surface of the bottom of the columns, and not upon the capacities of the vessels.
It consists of a bent tube on the bottom at one end of which is fitted a stopcock, in which can be screwed one of three available vessels, of the same height, but different in shape and capacity, the first being conical, the second nearly cylindrical and the third tilt cylindrical (which is broken). Mercury is poured into the horizontal tube until its level nearly reaches the top of the upward bend of the tube. The conical vessel is then screwed on and filled with water. The pressure of the water acting on the mercury causes it to rise in the cylindrical tube, and its height may be marked with a small collar which slides up and down the tube. The height of the water in the conical vessel is also marked. When this is done, the conical vessel is emptied by means of the stopcock [seen projecting toward the viewer], unscrewed and replaced by a vessel of a different shape. When water is now poured into this, the mercury, which had resumed its original level in the horizontal tube rises in the cylindrical tube, and when the water in the new vessel has the same height as it had before, the mercury will have risen to the height it had before. Hence the pressure on the mercury in both cases is the same. This pressure is therefore independent of the shape of the vessels, and, consequently, also of the quantity of liquid.



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