DISTRIBUTION OF GAS THROUGH MAINS. 171 



To obtain the velocities of the same gas from any other opening, say, 



As the square of given opening, 



Is to the given quantity discharged, 



So is the required opening 



To the required quantity discharged. 



It therefore follows, from the preceding corollaries in general, that the dis- 

 charges of the same gas during the same time, from different openings and 

 under different pressures, are to one another nearly, in the compound ratio, 

 of the squares of the diameters of the openings, and the square roots of the 

 pressures. 



By the preceding rules the initial velocity of a gas through any opening 

 and under any pressure may be calculated, and it remains to show what effect 

 the length of a pipe will produce on the discharge. The quantity of gas of 

 the specific gravity '420 discharged in one hour through a circular orifice (on 

 the top of a gasometer) six inches diameter, with a pressure equal to five- 

 tenths of an inch head of water, is 46,150 cubic feet. 



In order to determine the diminution of velocity sustained by the same gas 

 in passing through similar pipes of different lengths, the following experi- 

 ments were made by Mr. Clegg and myself. To the outlet-main of a 

 gasometer (which main was sixteen inches diameter) a cast-iron pipe six 

 inches in diameter, and exactly 3'46 yards long, was jointed in a horizontal 

 position, the gas discharged from the open end being allowed to escape. At 

 the end of an hour 44,280 cubic feet was found to have been discharged. 

 For the second experiment an additional piece was jointed on to the first pipe 

 by a thimble, making the length equal to 4*50 yards ; at the end of the hour 

 38,838 cubic feet was discharged. The length was again increased to 7*50 

 yards, and at the end of an hour the quantity discharged was exactly 30,000 

 cubic feet. The variation in this last, from the quantity given by calculation, 

 although small, was greater than that in the preceding experiments ; we were 

 therefore induced to carry them out considerably further. Three lengths of 

 six-inch pipe were jointed on to the existing length, making altogether 16'50 

 yards ; and the quantity found to be discharged at the end of an hour was 

 20,270 cubic feet. Three pipes were again added, making an entire length 

 of twenty-five yards ; and the quantity of gas discharged at the end of the 

 hour was 16,460 cubic feet. Lastly, three additional pipes were jointed on, 

 making the total length equal to 34-20 yards ; and the discharge was 14,080 



z2 



