PUMP 



215 



Pump. 



in pump 

 work. 



Clack 

 Valve. 



water continues to rush through F, expelling the air 

 from F through (i at I), which air a^am expel-, the 

 w.itcr from 1) through H up to C, until F and G are 

 filled with \\ater, .md O with air, when the machine 

 has returned to the same state as at the commence- 

 ment of the operation, F and G being filled up to the 



level of H. 



If it H dcdired to supply a house with water at the 

 level of the middle story, the vessel F may be placed 

 in the kite lien, and C in the bed-room, and every gal- 

 lon of water under the kitchen will give nearly a gal- 

 lon in the bed-room. The pipe F may be supplied 

 with impure or even dirty water; and in that case, 

 the whole of the spring water of B will be doubled to 

 C, instead of half of it being wasted at L ; so that the 

 whole of any spring may be raised by forming a dam 

 as in mills, and obtaining a fall for a part of the wa- 

 ter equal to the height to which it is required to pump 

 up the spring. The effect will be the same, whether 

 R is on a level with B or not. The water will always 

 rise as nigh above D, as R is from S. The superiority of 

 this pump arises from its acting with very little friction, 

 and, as a proof of this, it may be mentioned, that Mr. 

 Hunter had a small one which wrought, without being 

 touched, for three months, raising eight hogsheads of 

 water every day. 



24. Description of Different Valves used in Pump 

 Wort, 



In considering the best forms which can be given 

 to valves, we must attend to the different purposes 

 which they serve. The first and most obvious requi- 

 site of a valve is, that it be tight ; the second, that it 

 have sufficient strength to resist the forces to which it 

 is exposed ; the third, that it allows the water to rise 

 through it freely ; and the fourth, that it does not al- 

 low much of the water to flow back while it is in the 

 act of shutting. 



1. Clack Valve. This valve, which is the simplest, 

 is represented in Fig. 2. and 3. of Plate CCCCLXX. 

 and has already been described in page 205. In cases 

 where it is difficult to get at the valve to repair it, the 

 valve is often fixed in a box like a piston, having its 

 outer surface a little conical, so as to fit a conical seat 

 made for it in the tube. In this case it has an iron 

 ring, or an iron handle, like that of a basket, which can 

 be seized by a long grappling hook when it is required 

 to be drawn up. When the clack valve is opened, it 



obviously allows a good deal of water to go back dur- Pump. 

 in;,' its shutting. Desaguliers considers the lots as equal " -<^~ ' 

 to one-half of a cylinder of water, whose height if 

 equal to the diameter of the valve. l)r. Kobison, how. 

 ever, considers it as less than this quantity. Clack 

 valves are represented in most of the figures in Flat* 

 CCCCLXX. 



2. Mutter fly Valve This valve, which derives its Butterfly 

 name from its resemblance to the two wings of a but- Valve, 

 terfly, may consist of either two, three, four, or more 

 valves joined together, so as to form a sort of pyramid, 



and resembling the compound valves which nature 

 has formed in the hearts of minerals. The hinges of 

 each of the clacks of the pyramidal valves are in the 

 circumference of the tube, and the points of the clacks 

 meet in the apex of the pyramid, being supported by 

 four ribs, which rise up from the scales and unite in 

 the middle. When this kind of valve is used for a 

 piston, the rod of the piston is branched out on four 

 sides, when the clacks are four in number, and the 

 branches pass through the piston box, and are fastened 

 below with screws. The four clacks are supported by 

 these four branches. 



3. Button or Tail Valves. This kind of valve is re- Button or 

 presented in Plate CCCCLXXI. Fig. 13. It consists of ! lv. 

 a piece of metal turned conical, so as to fit exactly the PLATB 

 conical cavity of its box. A tail projecting from its " !CCI * XI ' 

 lower end passes through a cross bar in the bottom of Pi ' !o 

 the box, and there is a little knob to prevent the valve 



from rising too high. This valve is extremely strong, 

 and may be made perfectly tight by grinding it into 

 its seat with emery. It has the disadvantage of a small 

 water way. Dr. Robison suggested that the lower 

 surface, instead of being flat, should taper below like a 

 boy's top, to diminish its resistance" to the water. 



4. Spherical Valve. This valve is represented in Spherical 

 Plate CCCCLXXI. Fig. 14. and consists of a sphere of valve- 

 metal, which falls into a spherical cavity. It is pre- Fl S* ** 

 vented from rising too high by the inverted box shown 



in the figure. It is obvious, from the mere inspection 

 of the figure, that this valve must obstruct the water 

 way too much. Dr. Robison remarks, that the sphe- 

 rical valve must not be too light, otherwise it will be 

 hurried up with the water, much of which may flow 

 back while the sphere is returning to its place. 



For a popular account of pumps of different kinds, 

 and for tables to calculate their effects, see Ferguson's 

 Lectures on Mechanics, &c. vol. i. edit. 1823. See also 

 the other works quoted in this article. 



Purace 



Pur beck. 



PUR 



PURACE, a village of New Granada, situated in 

 an elevated plain of the Andes, about 10,000 feet above 

 the sea. It is inhabited by Indians, and is celebrated for 

 the fine cataracts of the river Pusambia, or Rio Vina- 

 gre, the waters of which are loaded with oxide of 

 iron and muriatic and sulphuric acids. M. Humboldt 

 visited this plain in 1801, and has described the scene- 

 ry, &c. which it presents. 



PURBACH, GEORGE. See ASTRONOMY, Vol. II. 

 p. 594, col. 2. 



PURBECK, ISLE OF. See DORSETSHIRE, Vol. VIII. 

 p. 52, &c. ; and p. 54, col. 2 ; and p. 55, col. 2. 



PUR 



PURCELL, HENRY. See Music, Vol XV. p. 48. 



PURPUR1C ACID, is the name of a new acid, re- 

 cently discovered by that able chemist Dr. Prout. It 

 has long been known to chemists that .1 fine purple 

 liquid is produced by the action of heat and nitric 

 acid upon lithic acid. * When the excess of nitric acid 

 is neutralised by ammonia, and the whole concentrated 

 by slow evaporation, granular crystals of a dark red 

 colour, and sometimes of a greenish hue, are formed. 

 These crystals are the purpurate of ammonia. In 

 order to obtain the purpuric acid, digest these crystals 

 in a solution of caustic potash till the red colour dis- 



Puree" 

 ^urpii 



The excrement! of the boa coiutrictor consist of pure lithic acid. 



