Mercuruü Pump.

275

Chap. 4.]

was to avoid the friction and consequent loss of power in common pumps,he therefore “ contrived a new waj of raising water without any frictionof solids; making use of quicksilver instead of leather, to keep the air orwater from slipping by the sides of the pistons.” Various modificationsof it were soon devised by the inventor, by Dr. Desaguliers , and by Mr.William Vreem, the assistant of the latter, “ who was an excellent mecha-nic.” One form of it is represented by the figure. A is the suction pipe,the lower end of which is inserted in the water to be raised. Its upperend terminates in the chamber C, and is covered by a valve. The forcingpipe B, with a valve at its lower end, is also connected to the chamber.

Between these valves a pipe, open at both ends,is inserted and bent down, as in the figure. Thestraight part attached to it is the working cylinderof the pump and should be made of iron. Anotheriron pipe, a little larger in the bore than the last,and of the same length, is made to slide easilyover it. This pipe is closed at the bottom andsuspended by chains or cords, by which it ismoved up and down. Suppose this pipe in theposition represented, and filled with mercury—ifit were then lowered, the air in the cylinder andbetween the valves would become rarified, andthe atmosphere pressing on the surface of thewater in which the end of A is placed, would forcethe liquid up A tili the density of the containedair was the same as before; then by raising thepipe containing the mercury, the air, unable to es-cape through the lower valve, would be f’orcedthrough the upper one; and by repeating the Ope-ration, water would at last rise and be expelledin the same way; provided the elevation to whichit is to be raised does not exceed thirteen timesthe depth of the mercurial column around the cy-linder; the specific gravity of quicksilver beingso many times greater than that of water. Whenthe depth of the former is 30' inches, the lattermay be raised as many feet in the suction pipe and forced up an equaldistance through the forcing one, making together an elevation of sixtyfeet; but if water be required higher, the depth of the mercurial columnin the moveable pipe must be proportinably ilicreased. To make a smallquantity of mercury answer the purpose, a solid piece of wood or ironthat is a little less than the cylinder, is secured to the bottom of the move-able vessel as shown in the centre: this answers the same object as anequal bulk of mercury.

These pumps have their disadvantages: they äre expensive; and how-ever well made, the quantity of quicksilver required is considerable—theagitation consequent on the necessary movement soon converts it into anoxide and renders it useless—great care is also required in working thesemachines; if the movements are not slow and regulär, the mercury is veryapt to be thrown out; to prevent which the upper end of the vessel contaming it is dished or enlarged. For experimental researches modifica-tions of such pumps may be useful, but for the reasons above stated, theyhave never been extensively employed in the arts. A simple form of oneis described in a late volume of the London Mechanics’ Magazine, andalso in the 22d vol. of the Journal of the Franklin Institute, p. 327. See

No. 125. Mercurial Pump.

WM