Chap. 7.]

Metallic Pumps.

221

CHAPTER VII.

Metallic pumps—Of more extended application than those of wood- Description of one—Devices toprevent water in thera from freezing—Wells being closed, no obstacle in raising water Dom them—Ap-plication of the atmospheric pump to draw water from great distances as well as depth—Singular cir-cumstance attending the trial of a Spanish pump in Seville—Excitement produced by it—Water raisedto great elevations by atmospheric pressure when mixed with air—Deceptions practised on this prin-

c jple_Device to raise water lifty feet by atmospheric pressure—Modifications of the pump innumerablc

—Pumps with two pistons—French marine pump—Curved pump—Muschenbroeck’s pump—Centrifugalpump—West’s pump—Jorge’s improvement—Original centrifugal pump—Ancientbucketsfiguredinthischapter.

That the public hydraulic machinery of the Romans was of the mostdurable materials sufificiently appears from Vitruvius . The chain of potsdescribed by him was, contrary to the practice in Asia and Egypt , whollyof metal —the chain was of iron and the buckets of brass. The pumpsof Ctesibius that were employed in raising water to supply some of thepublic fountains, he informs us, were also of brass and the pipes of cop-per or lead. Some of the oldest pumps extant in Europe are formed al-together of the latter. Leaden pumps were very common in the 16thCentury. They are mentioned by old physicians among the causes of cer-tain diseases in families that drank water out of them. The pump of thecelebrated alchymist, Dee, alluded to in the last chapter, was a leadenone; and which he expected to be able to transmute into gold, by meansof the elixir or the philosopher’s stone, which he spent his life and fortunein seeking. In the vicinity of some English lead mines such pumps havefor many centuries been in use. The Italian pump that led to the disco-very of atmospheric pressure was also a metallic one.

The introduction of metals in the construction of pumps greatly ex-tended their application and usefulness, for they were then no longer re-quired to be placed directly over the liquids they raised. Those of woodwere necessarily placed within the wells out of which they pumpedwater; but when the, working cylinder and pipes were of copper orlead, the former might be in the interior of a building, while the reservoiror well from whence it drew water, was at a distsnce outside; thepipes forming an air-tight communication between them under the surfaceof the ground.

The following figure, (No. 90) represents a common metallic suckingpump ; the cylinder of cast-iron or copper, and the pipes of lead. Itwill serve to explain the Operation of such machines in detail, and toshow the extent of their application. When this pump is first used, wateris poured into the cylinder to moisten the leather round the sucker, andthe pieces which form the clacks or valves; it also prevents air from pas-smg down between the sucker and the sides of the cylinder when theformer is raised. Now the atmosphere rests equally on both orifices ofthe pipe, the open one in the well, and the other covered by a valve atthe hottom of the cylinder: in other words, it presses equally on thewater in the cylinder and in the well which covers both ; a but when by

“Not absolutely so, or in a strict philosophical sense, but the differenee is so slight inan altitude of 25 or 28 feet, (the ordinary iimits) as to be inappreciable in a practicalpoint of view.