WATER. 



focond film pafTcs beyond the tirft orinnermoft, and becomes 

 the outermoft, and rubs along the tube. The third does 

 the fame in its turn, and thus the central filaments will at 

 lail come to the outfide, and fuftain their greateft poflible 

 obftrudion. When this is accompliflied, the pipe is in 

 train. 



This requires a certain length of pipe which we cannot 

 determine by theory ; but it is evident that pipes of greater 

 diameter muft require a greater length, and this is probably 

 in proportion to the number of filaments, or as the fquare of 

 their diameter. 



Du Buat found this fuppofition agree with his experi- 

 ments. A pipe of one inch in diameter fuftained no change 

 of velocity by gradually fhortening it, until it was reduced to 

 fix feet, and then it difcharged a little more water. But a 

 pipe of two inches in diameter gave a fenfible augmentation 

 of velocity, when fhortened to twenty-five feet ; he there- 

 fore fays, that the fquares of the diameter in inches, mul- 

 tiplied by 72, will exprefs the length in inches neceflary for 

 putting the water in any pipe in train. 



When pipes are of any confiderable length, the waters of 

 a larger pipe will run with a greater velocity than thofe of a 

 fmaller pipe having the fame Dope. A pipe of two inches 

 diameter will give much more water than four pipes of one 

 inch diameter ; it will give as much as five and a half of fuch 

 pipes, or more, becaufe the fquares of the difcliarges are 

 very nearly as the fifth powers of the diameters. 



On the requijtte Strength for IVater-Pipes. — We have (hewn 

 that, in certain cafes, the water running through a pipe will 

 exert little or no ftrain to buril the pipes. This may be 

 the cafe in great portions of the length, or even in the 

 Iwhole length ; neverthelefs we may obferve, that at all parts 

 'fo fituated, an open canal would anfwer all purpofes as well 

 las a clofe pipe. It is not neceflary to employ a clofe pipe 

 in any cafe, except where it is fiibjedled to a ilrain. We 

 may alfo obferve, that it is prudent in all cafes to make the 

 pipe fufficiently ftrong to refift the full prefTure of the im- 

 ,pelling colunui, when the motion of the water is flopped ; 

 ibecaufe this may happen accidentally, and then the pipe 

 will burft. 



I In order to adjuft the ftrength t)f a pipe to the ftrain, we 

 may conceive it as coiififting of two half cylinders joined by 

 'earns, parallel to the axis or length of the pipe ; the 

 Arength of fuch feams to refift the feparation of the two half 

 :ylinders will be equal to the ordinary ftrength of the ma- 

 iierials of which the pipe is made. The infide prefTure tends 

 •uO burft the pipe by tearing open thefe feams, and the force 

 'which adts upon any given length of the pipe (as an inch or 

 ■1 foot), is the weight of a column of water whofe bafe is 

 i:he diameter of the pipe, by the given length (as an inch or 

 n foot ), and whofe height reaches up to the furface of the 

 j.vater in the refervoir. This follows from the common prin- 

 ;iples of hydroftatics, and may be calculated by the rules 

 "or columns of water already given. 



J Suppofe the pipe to be of lead, one foot in diameter, 

 What will be the force to burft open one inch in length, at 

 ihe depth of 100 feet under the furface of the refervoir? 

 iWater weighs 625 pounds per cubic foot, the bafe of the 

 rolumn is I foot by i inch, or -,Vth of a fquare fo A, and the 

 endency to burft open an inch long of the pipe is 100 x 



- T 6250 . , 



>2A X t'-- = --=— = ;2I pounds nearly. 

 12 



'therefore, an inch long of each ffeam is ftrained by 2605 

 Js. A rod of catt lead, one inch fquare, is pulled 

 Icr by 860 pounds. (Sec Strekgth of Materials.) 



Therefore, if the thicknefs of the feam is = -— inches, or 



860 



one-third of an inch, it will juft withftand this ftrain. But 

 we make it much thicker than this, efpccially if the pipe 

 leads from an engine which fends the water along it by 

 flarts. 



M. Montgolfier ftates, that a pipe one inch in diameter, 

 and one line in thicknefs, will bear a column of 50 feet, 

 French meafur6> from which if we defire to know the 

 proper thicknefs for any other diameter, with the fame pref- 

 fure, we ftiall find it by fimple proportion. Thus, if the 

 diameter be 4 inches, the thicknefs muft be four lines ; or 

 if the prefl"ure is augmented we proceed in the fame man- 

 ner, by direft proportion, fo that for 100 feet it muft be 

 two lines thick for one inch diameter, and 8 fines thick for 

 4 inches diameter. 



To make full ufe of this mode of reckoning, he gives the 

 following table of the preflure which pipes of different fab- 

 ftances will fuftain. 



Feet 

 high. 

 Copper pipe, i inch bore, and i line thick, will 7 



fupport a column of water . . - j 4°° 



Brafs pipe of good quality, and the former dimenfions 300 

 Lead pipe, made of flieet lead . - . ^o 



Caft-iron pipe, 2 inches bore, and 4 lines thick, willl 



fuftain Ttleaft - 1 . . ' | 5°° 



Elm wood li inch diameter, and 2 inches thick, 30 or 40 



That is, they may fafely be made of that fize, but 

 will bear fometimes 1 10 feet prefl"ure. 



Lead Pipes. — The plumbers ufe caft pipes of lead, and 

 alfo make pipes of tough fheet lead turned up, and burned 

 or melted together in the longitudinal joints ; the different 

 lengths of lead pipe are fometimes burned together with 

 lead at the joints, when they are laid in the field, inftead of 

 foldering, becaufe this is much cheaper. Leaden pipes may 

 be turned up of any fize, but are not ufually caft of more 

 than four inches bore. Unlefs the caft pipes are very 

 found, they are not fo good as turned-up pipes ; hence it is 

 not advifable to ufe caft pipes of more than 25 inches bore. 

 There muft be great care taken in making the turned-up 

 pipes, that they may be perfeftly cylindrical. 



Small lead pipes are made by cafting and drawing them 

 through a plate, like wire. See our article Pipes. 



The proper thicknefs for lead pipes, according to Defa- 

 guliers, is as follows : a pipe, 7 inches diameter, fituated 

 from 140 to 80 feet below the refervoir, mud be |^ of an 

 inch thick ; that part which is from 80 to 60 feet beneath 

 the refervoir, muft be half an inch and an eighth thick ; from 

 60 to 30 feet I an inch ; and the remainder from 30 feet up 

 to the refervoir g of an inch. 



For pipes of four inches diameter, half an inch will do 

 from a depth of 200 feet to 100 feet ; from 100 to 40 feet 

 depth I of an inch thick ; and from 40 feet deep up to the 

 refervoir ^ of an inch in thicknefs. 



Dcfaguliers defcribes a method of proving the ftrength 

 of pipes experimentally, by a fmall forcing-pump, to injeft 

 water into a piece of the pipe at one cud, whilft a valve is 

 applied to the other, which valve is loaded with fuch a 

 weight as will equal the weight of the intended column of 

 water ; therefore, if the pipe bears this preffure, it will bear 

 the column of water. 



Lead pipes are very improper for water-works, where the 

 water is forced by an engine ; for at every ftroke or pufh 

 from the engine, the water raifes the ftop-valve of the pump, 



and 



