309 



GAS, MANUFACTURE OF. 



GAS, MANUFACTURE OF. 



310 



The gas holder is a large wrought-iron vessel, either of one or more 

 lifts, according to the nature of the locality (but wherever it is 

 possible, of only one), which should be made large enough to hold one 

 day's normal consumption (at the period of the shortest days) of gas. 

 The holder is, in fact, an inverted cup, working in water, and in a close 

 brick or iron tank, and rising by the elasticity of the gas entering 

 through the inlet pipes ; the discharge taking place through the exit 

 pipes to the gmernor, by the mere weight of the holder. The pressure 



required to raise a holder is ascertained by the formula p = 



in which p = the pressure in inches (of a column of water) ; w = the 

 weight of the holder in pounds; aud a = the area of the water 



surface in feet ; the constant 5'2 is the weight in pounds of a super 

 ficial foot of water one inch thick. The effluent pressure is found by 



the formula p = w , in which p and w represent as before the 



pressure and weight, and d = the diameter of the holder in feet ; the 

 constant 547 representing the weight of a column of water in inches, 

 of the area of the holder. Strictly speaking it would be necessary to 

 allow for the levity of the gas, and for loss of weight in the sides 

 of the holder as it may descend; but these considerations are so 

 habitually neglected in practice as to justify the reference of the 

 practical student to Clegg's ' Practical Treatise on the Manufacture of 

 Coal Gas,' for further details. 



The Gmernor if a machine for the purpose of regulating the pressure 

 upon the outlet pipe, according to the hours of the day, and the 

 draught upon the mains ; and one of these machines must be placed at 

 least upon each leading main of a town distribution, large or. small. 

 There are numberless patents for the construction of governors ; but 

 practically the system described by Clegg is the best, and therefore 

 a sketch of it is appended. Its action and principles are described in 

 detail in the work above mentioned. 



Attached to the outlet-pipe of the governor there should be placed a 



'tittering pretture gaui/e, in order to control the operations of the 



men charged with the regularisation of the pressure ; and one or more 



ordinary pressure gauges should be placed upon the leading main, 



<asional observations The Belf-regiatering gauge invented by 



the late Alexander Wright is one of the beat, if not actually the best, 



instrument of this description. 



4. The distribution of gas is effected by means of cast-iron mains, 

 in all cases where their diameter exceed* 2 inches ; and indeed in all 

 cases where the pipes would be exposed to the action of moisture it 

 is preferable to employ cast, rather than wrought, iron for street 

 mains, even at the risk of employing larger ones than would theoreti- 

 cally be required. The service pipes, or those through which the gas 

 ia led into the consumer's meters, are, however, almost always of 

 wrought iron when the diameter exceeds half an inch; below that 

 dimension they are either made of tin or of composition, on account 

 of the greater facility with which they can be bent to the abrupt 

 curves frequently required in house fittings. The joints of the cast- 

 iron pipes are usually of the description known as tocket-juinls ; those 

 of the wrought-iron pipes are of the description known as tcreui- 

 couplinfji ; whilst those of the smaller pipes are made by soldering in 

 the ordinary way. The wrought-iron services are tapped and screwed 

 into the cast-iron mains, and the composition pipes are joined to 

 the wrought-iron ones by means of a brass screwed end, which is 

 run upon the composition and fits into a female screw on the service 

 pipe. 



Before describing the laws which are now admitted with respect to 

 the flow of gas in pipes, it may perhaps be advisable to make some 

 remarks upon the quality, and the mode of manufacture, of gas mains ; 

 because the economical results of any operation of this description 

 must, after all, greatly depend upon the manner in which those mains 

 discharge their functions. It has been stated above, that the " unac- 

 counted for gas" frequently amounts to as much as 20 per cent, of the 

 total quantity made ; and as very probably one-half or one-third of 

 this loss is to be attributed to the permeation of the gas through the 

 mains, it becomes a matter of serious importance to prevent such a 

 loss. The principal difficulty lies in this case, as in so many other 

 practical ones, in the prices of the various goods considered ; and gas 

 companies are too often tempted to use cheap porous pipes, obtained 

 from first runnings, rather than incur the expense of sound second 

 runnings. This is a very mistaken economy ; and it may be laid down 

 as a rule in these matters, that no gas mains should be allowed to be 

 made in any works where a blast furnace exists ; all mains should, in 

 fact, be made from second runnings, and under the immediate inspec- 

 tion of the engineer of the gas-works ; and they should all be cast 

 vertically, with a requisite length of feeder to ensure the solidity of 

 the metal. The very conditions of manufacture of wrought iron pipeg 

 render them lens likely to be porous than cast-iron ones frequently are; 

 but the cheap composition pipes are so fearfully defective, that the 

 greatest precautions should be taken in their application, and none but 



