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In this contrivance the piston, A, see fig. the lower valve B, while the smaller valve 9, has a valve which, as the rod draws up, at d is also closed by the super-incumbent is closed by the pressure of the air above water in the conduit, e, and by the attracit; but in descending it opens, and allows tion of the piston, the water rushing after it the water, which liad flowed into the lower

to prevent a vacuum. In this kind of pump part, whence the air was withdrawn, to the piston must fit extremely close; both on rusla through; as the piston is raised again, account of the intended attraction of the the weight of the water forcibly oppresses fluid from below, and to prevent its escape the valve, until it find a lateral passage at upwards when the piston is pressed down. B, whence it issues, and in this manner any wards. quantity may be raised. If the water has a The whole of those inventions which raise Jirect issue, as in the common spouts of water by alternate risings and fallings of pumps, no further apparatus is wanted; but only one piston are subject to the inconve. if it is to be retained, or pass through any nience of having the water issue in jerks, other pipes more elevated than the debou. which, in some instances,would prove highly chure, B, there must be a small angular inconvenient. To remedy this, a cistern projection, as shown by the dotted lines, to should be placed near the debouchure, or admit the valve C, also pointing upwards. spout, whence a small stream would flow In dry weather, or when the pump is not with

much less variation than from the spout much used, the leather binding of the pis. itself. But the best mode of regulating the ton, as also the valves, will become dry; issue of water is by aid of an air-vessel, as therefore it is necessary, on such occasions, in a fire-engine. See PNEUMATICS. to throw in a pail-full or two of water to To detail all the varieties of pumps that moisten them; else the air will pass down. are in use would be both beyond the limits wards as the piston rises, and prevent that of this work, and of no real utility to the exhaustion on which the ascent of the water reader; we shall therefore enter upon the depends. It is generally necessary to have description of the valves in general estimaa válve at the bottom of the pipe to keep tion, and then proceed to give a brief acin the water drawn into it, in order that count of hydraulic machinery. the labour may be decreased; and that, if The most common kind of valve consists the pumping be intermitted, there may be of a piece of stiff leather, such as is applied less trouble in bringing up the water within for soles in shoes, and is generally known by reach of the piston.

the name of pump-leather. On its upper Where the water lays near the surface, a side a piece of milled lead is rivetted firmly, lifting-pump may be used. This is nearly the and the part where it is to be fixed on the same with the former; but requires the pis- frame, or shell, of the piston, is grooved for ton should be forced down beneath the level the purpose of giving it pliancy, that it may of the water in the well. In this it is not work up and down as if on a hinge. Fig. 11, so indispensably necessary that the leather shows the plan; and fig. 12, the profile of on the piston should fit so close: though it this valve, which is cheap, simple, and easily is the better for so doing. In the lifting. repaired, though it has the defect of being pump the whole depends on actually raising liable to choke, and of not rising high the water from the well as though it were enough to allow a snfficient passage for the done by means of a bucket; this occasions many to apply that designation to the pis Fig. 13, shows a button-calve, which is ton. The same precautions are necessary merely a piece of turned metal, A, having a if the water is to be passed into any pipe, shank, B, of about eight inches or a foot in as liave been stated regarding the debou- length, according to the depth of the block, chure of the sucking-pump.

The shank passes through the bar, C, The forcing.pump has a solid piston, as at the bottom of the block, and is prevented seen at A in fig. 10, which, after the water from coming up too high by the stud, or has passed the valve at B, is pressed down, nut, 9, at its bottom. When the water and causes the fluid to pass into the con rises, it forces up the button, A, and passes ducting pipe, C, where there is also a valve, through the hollow in the block, of which d, to prevent its return. The valve at B the superior part is expanded so as to fit the closes as the piston descends, while that at button, which being the frustrum of a cone, d rises to allow its escape from the main necessarily fits close into the expanded part pipe. When the piston rises, the water fol. as the water presses it, after having passed lows, as in the two former instances, through npwards in consequence of the descent of VOL. III.

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the piston; which may either be solid, as in the pipe, and to be carried by the revolg. a forcing-pump, or valved, as in a lifting or tions of the cylinder completely up to the a sucking pump. This valve may be ap- 'top, where it discharges into a vessel. This, plied to a piston, as well as to that part of however, raises but a small quantity, though the pipe which retains the water, that it the height may be indefinite: therefore, may be within reach of the piston's action. where such a machine is in use, it will be An improvement has been made to this found eligible to have the whole cylinder valve, by adding a ball of some weight to covered with various pipes, like the bands the bottom of the shank, B, and excavating in a rope, whereby the quantity of water the button, in order to reduce its weight in raised would be proportionably increased, proportion : this insures the regular descent with very little addition of power: the of the button to its seat,

greatest resistance would arise from the The butterfly-calve, exhibited in fig. 14, friction upon the supporting axis, especially varies from the two former, in having two

the lower one under the surface. Some of semicircular flaps appended by binges to a

these machines have been worked in strong bar passing over the centre of the excavated running brooks, by means of water-boards, piston. This valve is peculiarly eligible, the same as the great wheels in undershot because if one part should be stiff, and ad- mills. here to the piston, the other will play with The horn-drum, so called from a number an increased effect, though not equal to the of segments passing from the circumference action of both valves.

of a large flat cylinder to its centre, is an The simplest valve with which we are easy mode of raising water. The scoops, acquainted is the sphere, which is made of or mouths, by turns dip into the water, and metal, and fits into a semi-spherical cavity as they rise cause it to pass up the hom, or on the top of the piston or block. When segment, until it is discharged into a trough the piston (if it be on that) rises, the sphere placed under the end of the axis, which is falls into the socket; but when the piston is hollow, and has its pintle fastened to a cross, depressed, the rush of water from below as seen in fig. 17. Such wheels usually work forces the sphere upwards. The only in with water (or float) boards; and some of convenience attendant upon this valve, which them have projecting fins, from which rectis shown at fig. 15, is, that its diameter be- angular buckets are suspended: these dip ing nearly equal to that of the bore, leaves into the water as the wheel turns, and suc. a very narrow passage for the water. This, cessively discharge into a trough, by means however, might perhaps be obviated, by of a pin at A, which causes every bncket as making an excavation in the pipe, as shown it passes to turn to a horizontal instead of by the dotted lines, and by driving nails an erect position. The latter invention is through to obstruct the ball from rising too ascribed to the Persians. The reader will, high.

no doubt, readily perceive that a strong These are the general principles of the current, or other force, is needful to move valves in common use; though we could machines so laden as the Persian wheel, it enumerate a great variety, which have all sometimes raising near a ton of water in been strongly recommended, but in prac each revolution; and that nothing but the tice proved very deficient. We shall there. necessity for raising water could induce to fore proceed with the detail of hydraulic so great a loss of power. When treating of machines, commencing with those which Mills and of Pumps, as also of PNEUsupply the place of pumps, by raising water MATICS, with which HYDRAULICS are often to given heights. The most simple, and intimately blended, we shall enlarge more perhaps the most ancient, is the spiral pump on this subject; for the present concluding of Archimedes. It consists of a cylinder of with the ordinary mode of applying a water wood, abont a foot in diameter, and of any wheel to pumps, as may be seen at London length at pleasure: on this a leaden pipe of Bridge, and in a great variety of instances, any bore is wound from the bottom to the where immense quantities are raised by top, spirally. When the bottom of the cy- means of runuing water, referring to the linder revolves in the water, (by means of a article Steam-ENGINE for the operatious common winch handle at the top, and of dependant on that power. We have, in a pintle in the centre of its base, wbich rests speaking of Fluids, said much on their proin a box or step for that pırpose below) perties, which the reader will find both the reclined position, as shown in fig. 16, amusing and instructive: indeed we conoccasions the water to enter the bottom of sider this doctrine to be indispensable, as

a study, with those who court an intimate entire; seeds semi-orbiculate, compressed. acquaintance with hydraulics.

There are fifteen species. Fig. 18, shows the section of three forcing HYDRODYNAMICS treat of the pow. pumps, o p q, with their pistons, as acted

ers, forces, and velocities, of Auids in moupon by three cranks, a b c, each equally tion. Having entered fálly into the deradiated from the branch d e, and moved tail of all relating thereto while treating of by a water wheel, of which f is the axis: it FLUID, HYDRAULICS, HYDROSTATICS, is plain that the several cranks stand at an Mills, and WATER wheels, we forbear angle of 120 degrees respectively. By this from that repetition which would trespass means there is a counterbalance among on the space allotted to other articles, rethem mutually, and each gives one stroke ferring the reader to those heads for what or plunge during each revolution of the appertaius thereto. wheel. If the wheel is large, it will of HYDROGEN. It had been long known course move slowly; and, unless the pumps to the chemists, that a vapour or air is disbe very large, but little water will be raised: engaged in some processes, which kindled therefore it is usual to accelerate the motion

on the approach of an ignited body. Van of the branch bearing the cranks, by means Helmont gave this the name of gas igneum, of a spur, or of a trundle, turned by the and it seems to have attracted the attention water-wheel, and bearing such proportion of Boyle, Mayow, and Hales. The che. thereto as the required increase of velocity mists knew, that such a vapour or air was may demand. For the manner of applying commonly disengaged during the solution such a spur, &c. see the article Mill- of certain metals, in muriatic or dilute sulWORK.

phuric acid, that it burnt at the montb of HYDRAULICON, water organ, in mu the phial, and if mixed with atmospheric sic, an instrument acted upon by water, air, exploded when kindled by a match. the invention of which is said to be of higher Mr. Cavendish, however, first examined antiquity than that of the wind organ. its properties fully, shewed that it is per

HYDROCELE, in surgery, denotes any manently elastic, not absorbed by water, hernia arising from water, but is particu- and that it is much lighter than atmosphelarly used for such a one of the scrotum, ric air. (Philos. Trans. vol. Ivi. p. 141). which sometimes grows to the size of one's This substance forming water when comhead, without pain, but exceeding trouble- 'bined with oxygen, and being therefore the some to the patient. See SURGERY. radical of that compound, the name hydro

HYDROCEPHALUS, in surgery, a pre- gen was given to it, at the formation of the ternatural distention of the head to an un new nomenclature. common size, by a stagnation and extrava

It is always obtained from the decomposation of the lymph, which, when collected sition of water, as it cannot, from other sub. within side of the bones of the cranium, the stances in which it exists, be easily disenhydrocephalus is then termed internal; as gaged in perfect purity. Some substance it is external, when retained between the is made to act on water, which exerts an common integnments and the cranium. See attraction to the oxygen, without combinMEDICINE.

ing with the hydrogen, when, of course, the HYDROCHARIS, in botany, a genus of hydrogen is disengaged, and passes into the the Dioecia Enneandria class and order. elastic form. Natural order of Palmæ. Hydrocharides, At the common temperature of the globe, Jussieu. Essential character: male, spathe this decomposition cannot be effected with two-leaved; calyx, trifid; corolla, three- rapidity by any single affinity. Iron, moistpetalled; filaments the three iuner style ened with water, decomposes it very slowly, bearing: female, calyx trifid; corolla and evolves hydrogen; but at the temperathree petalled; styles six; capsule six-cel- ture of ignition, the decomposition is more led, many seeded, inferior. There is but rapid. If a coil of iron wire, or a quantity one species, with many varieties, viz. H. of iron filings be put into an iron or coated morsns ranæ, frog bit.

glass, or earthern tube, which is placed HYDROCOTYLE, in botany, marsh across a small furnace, and surrounded with pennywort, a genus of the Pentandria Digy. burning fuel, so as to be brought to a red nia class and order. Natural order of Um- heat, on distilling water from a retort conbellatæ. Essential character: umbel sim- nected with it, the vapour, in passing over ple, with a four-leaved involucre; petals the surface of the ignited iron, is decom.

water.

posed, the iron attracts its oxygen, and by. can be ascertained by weighing. Its spedrogen gas issues from the extremity of the cific gravity varies considerably, according tube,

to its state with regard to humidity. When This process is a troublesome one, and it has been transmitted through water, or by the agency of an acid, water is decom. has remained for some time exposed to it, posed as rapidly by iron or zinc, at a natu it is about ten times lighter than atmospheral temperature, Zinc affords the hydro- ric air ; when it has been received over gen in the greatest purity. One part of it, quicksilver, and exposed to any substance in small pieces, is put into a retort, or a which attracts water strongly, as quicklime, bottle with a bent tube adapted to it; it is nearly 13 times lighter, or atmosphetwo parts of sulphuric acid, previously ric air being 1,000, hydrogen is 84. Its diluted with five times its weight of specific gravity in this state, water being water, are poured upon it, an effervescence 1,000, is stated by Lavoisier at 0.0946. is immediately excited, hydrogen gas es. 100 cubic inches weigh 2.613 grains. It is capes, and is to be collected in jars filled from this levity, that it was applied with with water, and placed on the shelf of the success to the construction of balloons; a pneumatic trough. Its disengagement con varnished silk or linen bag, filled with it, tinues until the zinc is dissolved. Iron may having a specific gravity so much less than be employed in place of zinc, but contain- atmospheric air, as not only to rise in the ing generally a little carbon, which is dise atmosphere, but also to elevate an addisolved by the hydrogen, it affords a gas less

tional weight. pure. Muriatic acid serves the same pur The chemical property by which hydropose as sulpburic acid, but inust be diluted

gen gas is most eminently distinguished, is with only twice or three times its weight of its great inflammability. When an ignited

body is approached to it, in contact with In the experiment, the hydrogen gas is the atmosphere, it is immediately kindled, derived entirely from the decomposition of and continues to burn while the air is ad. the water, the oxygen of which is attracted mitted ; if previously mixed with atmospheby the metal. That the acid suffers no de• ric air, and a burning body approached to composition, is proved by the liquor at the the mixture, or an electric spark sent end of the experiment, being capable of sa through it, it instantly inflames with detoturating as much of an alkali as the quantity nation; and when it has been mixed with of acid employed would have done in a

oxygen gas, the detonation is more violent, pore state. The agency of the acid was When burning at the extremity of a capilformerly explained, on the absurd doctrine lary tube, on bringing a wide tube over the of disposing affinity,—that it had no attrac- flame, a singular phenomenon, accidentally tion to the pure metal, but to the oxide of observed by Dr. Higgins, is produced, that the metal; that to satisfy this affinity, it of sounds of various tones, which vary in caused the oxidation of the metal at the ex

acuteness and strength, according to the pence of the water, and then combined width, the length of the tube, and the kind with the oxide thus formed. In conformity of substance of which it is formed, owing, apto Berthollet's speculations, it may be re parently, as Picket and De la Rive bare ferred to the affinities of the acid to iron, explained it, to the vibrations excited in and to oxygen, conspiring with the affinity the matter of the tube by the rapid expanof iron to oxygen: these, co-operating, pro- sion and condensation of the watery vapour duce a ternary combination, while the hy. Dear and around the fame, and which, redrogen gas is disengaged.

gulated and equalized by regular reflections Hydrogen gas is permanently elastic. from the sides of the tube, constitute a moWhen collected over water, it is observed sical sound. (Nicholson's Journal, 8vo. to have a peculiar smell, slightly fetid, vol. i. p. 129; ibid, vol. iv. p. 23). which is not so perceptible when it is col Though hydrogen gas be inflammable, it lected over quicksilver, and which is lost is incapable of supporting the combustion when the gas is exposed to substances which of other inflammables. If a burning body powerfully attract humidity. It is not the be quickly immersed in it, it is immediately only substance in which water appears re- extinguished. quisite to develope odour.

This gas is incapable of supporting aniThis is the lightest of the gases, and in mal life by respiration; an animal immersed deed the lightest substance whose gravity in it is soon killed. At the same time, it

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