Hydraulic Architecture, Volume One, Part Two

HYDRAULIC ARCHITECTURE, BOOK III.

...though the column of air corresponding to branch C is a little higher than that which acts on branch B; but as the difference between these two columns is too small an object to create a noticeable inequality in their weight—the branch B having 12 inches, for example, and the other branch C having 13—the difference between the two columns of water will be one-twelfth of their heights. Thus, one sees that the water in branch B, relative to its weight, will be pushed upward by the air with more force than the water in branch C will be relative to its own weight. Thus, the water of the latter will descend, and the water of the former, finding its way into the pipe, will be forced to pass through it as long as there is any in the upper vessel to be delivered into the lower one. This will occur with every kind of siphon, of whatever size one makes them, provided that the shortest branch is less than 30 or 31 feet The author refers to the maximum height a vacuum can pull water before gravity overcomes atmospheric pressure, roughly 10 meters..

798. Here is another small experiment to prove the weight of the air, or if one prefers, the force of its spring original: "ressort"; here meaning the elastic force or pressure of the air, which everyone is in a position to perform: fill a glass with liquid until it rises above the rim, and having covered it with a piece of wet paper which one presses with the hand to apply it exactly against the edges, invert it in this state with the base upward. Then, one sees the paper support the liquid contained in the glass without a drop being spilled, because the air presses the paper from the bottom upward with more force than the liquid has to descend.

799. The vacuum machine, which is called the Pneumatic machine Now commonly known as an air pump., is too useful in physical experiments not to provide a description of it, as I do not wish to leave anything for those who have not seen this machine to guess. It is composed of a copper plate ABC, which may be 10 to 12 inches in diameter, supported horizontally by three iron branches E, which lead to a circle FG that surrounds the body of a syringe FGHI. This syringe passes through a wooden platform KL, to which it is well attached, the whole supported by three feet M, held together by iron branches that meet at a circle N for greater stability.

The piston of the syringe is sometimes made of wood surrounded by tow original: "filasse"; coarse hemp or flax fibers used for caulking or packing, or of several leather washers mixed with felt, pressed together like the heel of a shoe. The piston is attached to an iron rod OP, at the end of which is a stirrup S, used to place the foot during the time of aspiration The operator used their foot to pull the piston down, creating a vacuum in the chamber above..

At the head of the syringe is attached a copper stopcock original: "robinet"; a valve or faucet V, closed...