DISTRIBUTION OF GAS THROUGH MAINS. 1 73 



gas having the specific gravity '420 in one hour. And to find how much a 

 sixteen-inch main will deliver, same specific gravity and pressure, say, as 36, 

 the square of the diameter of the six-inch pipe, is to 1963, the quantity of 

 gas delivered, so is 256, the square of the diameter of the sixteen-inch pipe, 

 to 13959, the required quantity delivered by a sixteen-inch one mile long. 

 For the difference of specific gravity, say, 



As \/'390 = '197, the specific gravity of the lighter gas, 

 Is to 13,959, the quantity delivered of the specific gravity '420, 

 So is \/'420 = '204, the specific gravity of the heavy gas, 

 To 14,455 = the quantity delivered of the specific gravity '390. 

 And for the difference of pressure, say, 

 As ^/'50 = '707, the first pressure, 

 Is to 1 4,455, the quantity discharged through a sixteen-inch pipe by that 



pressure, 



So is ^'60 = '774, the required pressure, 



To 15,824, the required quantity, of specific gravity '390 discharged from 

 a sixteen-inch pipe, with a pressure equal to six-tenths of an inch 

 head of water. 



The actual quantity discharged is about 16,500 cubic feet*. 

 An accurate experiment was made by Mr. Clegg in the spring of 1831, at 

 the Pancras Station of the Imperial Gas Company, on the quantity of gas 

 discharged through a four-inch main, six miles in length, with a pressure of 

 three inches perpendicular head of water. The specific gravity of the gas 

 was not taken until some hours after the experiment, when it was found to 

 be -398. 



As this experiment exactly bears out the previous rules, I will describe the 

 manner in which it was conducted. A new four-inch main had to be laid for 

 the purpose of supplying parts of the parish of St. Marylebone with gas ; 

 after completing a circle of nearly six miles in circumference, it terminated 

 within the distance of a short street from the point at which it left the works. 

 By completing this distance, the two ends of the pipe were brought together 



* This difference of 676 cubic feet from the quantity given by calculation is owing to the de- 

 crease of friction in the sixteen-inch pipe, the rubbing surface bearing a smaller proportion to the 

 area than in a six-inch pipe. The exact amount of this difference has never been satisfactorily 

 determined ; I have therefore omitted the consideration of it in my calculations. At present, prac- 

 tice must give the amount. 



