Hydrostatic Balance
The Encyclopedia of Founding (1892)
A specific-gravity balance. See SPECIFIC GRAVITY; SPECIFIC-GRAVITY BALANCE. Hydrostatic Bellows is an apparatus which serves to explain that peculiar property of liquids, including molten iron, in virtue of which they transmit pressure in every direction. The hydrostatic bellows consists of two boards held together by a band of rubber, which allows a bellows motion to take place when force is applied inside. These form an absolutely tight chamber, to which a small tube is attached by inserting it in the top side. The water is poured down the tube, and as the chamber fills the upper board rises with the pressure. If the surface of the board is fifty times as large as the end of the tube, one pound of water will balance fifty pounds of weight on the board. Because the surface of the cover is fifty times larger than the orifice of the tube, there are fifty times as many particles of water in contact with the board as there are at the end of the tube, and as each particle throughout the whole surface is made to exert the same pressure, one pound of water in the tube should balance fifty pounds on the board. If the moulder who may be unacquainted with these subjects will carefully examine this apparent paradox, and in his mind substitute for the tube a down-runner leading to a mould below, in which molten metal instead of water is to be poured, he will at once discover that the only difference betwixt the two is the difference in weight of the water and the metal. This will enable him to realize why so small a runner will lift such a great weight. See WEIGHTING COPES; PRESSURE OF MOLTEN METAL. Igneous Rocks include granitic, trappean, and volcanic series, all of which rocks have been produced by fusion, on the surface, or in the interior, of the earth's crust. See ROCK.
What Has Changed in the Last Century
The physics in this 1892 foundry entry is still exactly right: a body weighed in air and again suspended in water gives its specific gravity, and Pascal's principle means a narrow down-runner of molten iron really can lift a heavy cope. What has changed is the hardware. The hydrostatic balance with its beam and rider now survives as a clip-on "density determination kit" for an electronic analytical balance, which reads a value to four decimals in seconds, while foundries hold copes down with mechanical flask clamps rather than stacked weights, and much metal is now delivered by die casting or low-pressure machines instead of a gravity runner. The moulder the entry addresses would still recognise the lesson; he would not recognise the shop.
Written for this edition, 2026.