PUMP PUMPKIN. 



755 



is at the bottom. In the piston there is a valve 

 which opens upwards, and at the bottom of the 

 cylinder there is another valve C also rising up- 

 wards, and whicli covers the orifice of a tube fixed 

 to the bottom of the cylinder, and reaching to the 

 well from whence the water is to be drawn. This 

 tube is commonly called the suction tube, and the 

 cylinder, the body of the pump. When the piston 

 is at the bottom of the cylinder, there can be. no 

 air, or at least very little between it and the valve 

 C, for as the piston was pushed down, the valve in 

 it would allow the air to escape, instead of being 

 condensed, and when it is drawn up, the pressure 

 of the air would shut the valve, and there would 

 be a vacuum produced in the body of the cylinder 

 when the piston arrived at the top. But the air in 

 the cylinder being very much rarefied, the pressure 

 of the valve C on the water at the bottom will be 

 greatly less than that of the external atmosphere 

 on the surface of the water in the well ; therefore, 

 the water will be pressed up the pump to a height 

 not exceeding 3:1 or 33 feet. As the valves shut 

 downwards, the water is prevented from returning, 

 and the same operation being repeated, the water 

 may be raised to any height, not exceeding the 

 above limit, in any quantity. The quantity of 

 water discharged in a given time, is determined by 

 considering that at each stroke of the piston a 

 quantity is discharged equal to a cylinder whose 

 base is the area of a cross section of the body of 

 the pump, and height the play of the piston. The 

 piston, throughout its ascent, has to overcome a 

 resistance equal to the weight of a column of water, 

 having the same base as the area of the piston, 

 and a height equal to the height of the water in 

 the body of the pump above the water in the well. 



The lifting piimp. This pump, like the suction 

 pump, has two valves and a piston, both opening 

 upwards ; but the valve in the cylinder instead of 

 being placed at the bottom of the cylinder is placed 

 in the body of it, and at the height where the water 

 is intended to be delivered. The bottom of the 

 pump is thrust into the well a considerable way, 

 and if the piston be supposed to be at the bottom, 

 it is plain, that as its valve opens upwards, there 

 will be no obstruction to the water rising in the 

 cylinder to the height which it is in the well ; for 

 by the principles of Hydrostatics, water will always 

 endeavour to come to a level. Now when the 

 piston is drawn up, the valve in it will shut, and 

 the water in the cylinder will be lifted up ; the 

 valve in the barrel will be opened, and the water 

 will pass through it, and cannot return as the valve 

 opens upwards ; another stroke of the piston 

 repeats the same process, and in this way the water 

 is raised from the well : but the height to which it 

 may be raised is not in this as in the suction pump 

 limited to 32 or 33 feet. To ascertain the force 

 necessary to work this pump, we are to consider 

 that the piston lifts a column of water whose base 

 is the area of the piston, and height the distance 

 between the level of the water in the well and the 

 spout, at which the water is delivered. 



In the forcing pump the piston 

 has no valve, but there is a 

 valve at the bottom of the 

 cylinder as seen at A. In the 

 side of the cylinder, and imme- 

 diately above the valve B, there 

 is another valve A opening out- 

 wards into a tube, which is 

 bent upwards to the height H, 

 at which the water is to be de- 

 livered. When the piston is 

 raised, the valve in the bottom 

 of tie pump opens, and a 



u 



vacuum being produced, the water is pressed up 

 into the pump on the principle of the sucking pump. 

 But when the piston is pressed down, the valve A 

 at the bottom shuts, and the valve B at the side 

 which leads into the ejection pipe opens, and the 

 water is forced up the tube. When the piston is 

 raised again the valve B shuts, and the valve A 

 opens. The same process is repeated, and the 

 water is thrown out at every descent of the piston, 

 the discharge therefore is not constant. 



It is frequently required that 

 the discharge from the pump 

 should be continuous, and 

 this is effected by fixing to 

 the top of the eduction pipe 

 an air vessel. This air vessel 

 consists of a box AB, in the 

 bottom of which there is a 

 valve C opening upwards 

 into the box. This valve 

 covers the top of the eduction 

 pipe D. A tube, E, is fas- 

 tened into the top of the box, which reaches nearly 

 to the bottom of the box, it rises out of the. box, 

 and is furnished with a stop cock. If the stop cock 

 be shut, and the water be sent by the action of the 

 pump into the air vessel, it cannot return in conse- 

 quence of the shutting of the valve C ; and because 

 of the space occupied by the water, the air in the 

 box is condensed, and will therefore exert a pres- 

 sure on the water in the air vessel. If the water 

 fill three-fourths of the box, then the air will be 

 compressed so as to exert four times the pressure 

 that it did while the box or air vessel remained 

 empty of water, and will, therefore, according to 

 the law of Marriote, force the water up the tube E , 

 and the result will be that a continuous jet will 

 issue from the upper orifice of that tube. Large 

 air vessels are now employed in Blowing Engines, 

 instead of the apparatus on the hydro-pneumatic 

 principle described in the article Blowing Engine. 

 The fire-engine (q. v.) consists of two forcing 

 pumps, working into one common air-vessel, placed 

 between them, and from which the spouting pipe 

 for directing the water proceeds. The chain pump 

 used in the navy is an upright barrel, through which 

 leathers strung on a chain are drawn by means of 

 wheels or drums in constant succession, carrying 

 the water in a continual stream before them. They 

 are employed only when a large quantity of water 

 is to be raised, and must be worked rapidly to pro- 

 duce any effect. 



PUMPERNICKEL; a coarse, heavy, brown 

 bread, made, in Westphalia, of unbolted rye. It 

 is baked in large loaves, sometimes weighing sixty 

 pounds. The following account of the derivation 

 of the word is given : A French traveller in West- 

 phalia, on asking for bread, was presented with 

 some of this kind, on which he observed that such 

 stuff was bon pour nickel (good for Nickel, i. e. 

 either his horse or his servant) whence it came to 

 be called pompernicker, or pumpernickel. The 

 story is obviously made to fit the case. In fact, it 

 is called by the inhabitants grobes brot, the former 

 name being only used by foreigners. 



PUMPKIN, or POMION (cucurbita pepo); a 

 species of gourd, or squash, distinguished from 

 most varieties of the latter by the rounded form of 

 the fruit, which sometimes grows to an enormous 

 size. It has hispid, branching, and prostrate stems, 

 which, in good soil, will cover an eighth part of an 

 acre. The fruit is esteemed inferior to most 

 varieties of the squash, but, notwithstanding, is 

 very commonly cultivated, both in Europe and 

 America. 



