WATER. 



to rife again, to pafs the furamit of a fmall hill, it will run 

 over the eminence without carrying all the air before it, as 

 it had done in other parts of the pipe, before it arrived at 

 fuch eminence. Hence feme air is left in the highefl part of 

 the bend, but the Water which pafles by the air runs forward 

 and fills the pipe again in the defcending part, and fo goes 

 on in a full bore, till it comes to the next eminence, where 

 it again runs over the higheft part of the rifing pipe, leav- 

 ing a fpace of air at top, which diminifhes the water-way. 

 Then filhng the pipe full again, it proceeds till its next 

 rifing, and there the water-way is again contrafted by the 

 air. 



To clear the pipe of this air, if the pipe is of lead, the 

 common way, as praftifed by plumbers, is thus : at every 

 rifing ground the pipe is laid bare at the higheft place, and 

 a nail is driven into the upper fide of the pipe, fo as to make 

 a hole through the metal. Whilft the nail is flicking in, the 

 lead is hammered all round the nail, with the pen of the ham- 

 mer, fo as to make a little button or fpout. When the nail 

 is withdrawn, the air viill blow out violently, till at laft the 

 water wiU fucceed the air ; and with a ftroke or two with 

 the face of the hammer the hole can be quite flopped up. 



This is done at every eminence of the pipe, until all the 

 air is difcharged, and tlie full quantity of water will be de- 

 livered at the oppofite end of the pipe. If the mouth 

 of the pipe at the fpring never receives any air, by the defcent 

 of the furface of the water, the pipe may give its full quan- 

 tity for years. 



The vi'ay to know when the whole water is delivered is to 

 meafure it, when the pipe has been fully cleared of air, as 

 above-mentioned ; and when by meafure, the quantity of 

 water appears to be deficient, the pipe muft again be cleared 

 of air or other obftruftions. 



If the fpring is much higher than the place of delivery, 

 the places where the air will accumulate in the pipe will not 

 be juft at the higheft part of the pipe, but a httle beyond 

 it ; becaufe the water running with more velocity and force, 

 drives the lodged air ftill forward down the pipe, and it 

 muft lodge in the part where the pipe begins to defcend 

 again, its own tendency to afcend to the top being counter- 

 afted by the motion of the water. In this cafe, the nail-hole 

 muft be made beyond the greateft elevation, or elfe the run 

 of the pipe muft be ftopped for fome time, fo that the 

 water may ceafe to be in motion, the air will then go back 

 gradually to the higheft part of the pipe, where it may be 

 let out. 



Suppofe that the water, inftead of coming from an ele- 

 vated fpring, be forced up its whole way from a place much 

 lower by an engine, and up the conduit, then the places 

 where the air wiU lodge will be beyond the eminences of the 

 pipes, but nearer to the upper end. In thefe cafes, it will not 

 be fufficient to prick the pipe with a nail, becaufe air will 

 be continually forced in with the water, and will refill thofe 

 places in the pipe from which the air had been ennptied. 

 The obftruftions thus happening often occafion the burft- 

 ing of the pipe, or it gives too fmall a quantity of water, 

 and does damage to the engine. 



In fuch a cafe, the following contrivance muft be ufed : 

 a fmall leaden pipe, about thirty feet in length, which i^ 

 called a rider or air-pipe, is laid at the higheft part of the 

 main-pipe, and extends along the top thereof. It commu- 

 nicates with the main at the top of the eminence, and alfo 

 at two other places, at fifteen feet on each fide of the emi- 

 nence. This air-pipe has a little branch and cock. Now if 

 the cock is opened when the engine is working, the air will 

 be pufhed forward till it is difcharged by the air-pipe and 

 cock. If the ^r goes beyond the eminence, the pipe of 



12 



communication will certainly difcharge it. When water 

 comes out at the cock it muft be ftiut, and the main-pipe 

 will then be full of water, but after fome time, the cock 

 being left fhut, air will gather again in the eminence of the 

 main-pipe and lodge ; but, if the air-cock is again opened, 

 the air will be difcharged. 



When water is forced up by an engine into an elevated 

 ciftern, from which it is to run down a main-pipe to the re- 

 fervoir where it is wanted, this air-cock will alfo be very 

 necefTary, becaufe the water in the ciftern fomctimes covers 

 the entrance-mouth of the defcending pipe, and fometimes 

 not. In that cafe, air goes down with the water. 



In leaden or iron pipes of conduit, the difcharge of air is 

 abfolutely neceflary if there are any rifes in the pipe. In 

 wooden pipes the air often paffes through the wood and 

 efcapes ; but if the pipes are tight and thoroughly foaked, 

 the air-pipes and cocks are very ufeful. When water runs 

 from a raifed ciftern through a diftance of a mile or two, 

 fome perfon (hould turn the air-cocks two or three times a 

 day. 



This trouble may in fome cafes be avoided, by carrying 

 the air-pipe perpendicularly upwards, to an equal or greater 

 height than the entrance mouth of the main-pipe. In this 

 cafe,' the water will rile up in the air-pipe to near the fame 

 level as the water at the entrance, but cannot run over. 

 Neverthelefs, if any air paffes along the main-pipe, when it 

 arrives at the air-pipe, it will rife up therein in bubbles 

 through the water contained in the perpendicular air-pipe 

 and efcape. By taking advantage of fome tall building, or 

 large tree to fnpport the perpendicular air-pipe, this ex- 

 pedient may in general be applied. 



Defaguliers contrived a valve which fhould open to let out 

 the air, and fl\ut again when the water came. It was an in- 

 verted brafs valve (hutting upwards, and falling down by its 

 own weight, with cork fixed to the under fide of it, to make 

 it rife and (hut when the water came. This fucceeded in 

 firft clearing the pipe of air, but it did not anfwer to keep 

 it clear ; becaufe, when the valve had been fhut fome time, 

 if air fhould extricate itfclf from the water, it would be 

 denfe air, whofc force would be equal to that of the water, 

 and would keep the valve fhut as well as the water did be- 

 fore, although the air at firft could not fhut the valve. The 

 only remedy for this difficulty is to make the valve very 

 fmall, and make a hoUow copper veffel for a float. This 

 will rife with confiderable force to fhut the valve, when the 

 water afts upon it ; and it will be fufHciently heavy, when 

 the water forfakes it, to pull open the valve. 



The fame author afterwards made a better contrivance. 

 It is a fmall fquare box of caft-iron, made tight on 

 all fides, except where the air-pipe communicates with the 

 bottom of it, and alfo where a fpout is fixed on the top to 

 let out the air. This fpout is provided with a cock, fitu- 

 ated withinfide of the box, and to the plug of the cock a 

 fmall arm or lever is fixed, having a hollow ball of copper 

 at the extremity of the arm or lever. This ball floats on 

 the furface of the water in the box, and when it rifes opens 

 the cock, or fhuts it when it falls. When the air in the 

 pipe accumulates, it paffes along the air-pipe and enters 

 into this box, and as the quantity increafes, the furface of the 

 water in the box fubfides, until the float at the end of the 

 lever, opens the cock and allows the air to efcape, and this it 

 will always do before any air can accumulate in the pipe. 



It is beft to place the air-box near to the main-pipe, but 

 it muft have communication by an air-pipe with the main- 

 pipe, at two or three different places, in order that it may 

 certainly receiye all the air which gathers in the great pipe. 



On the Difcharge of Wat»r by lateral Branch-Pipes from a 



Main- 



