½-in. plates, to stand a working pressure of 150 lbs. to the square inch. The reservoirs are provided with gun-metal inlets and outlets, and also with a low-level outlet, to admit of drawing off the hydro-carbon which is thrown down owing to the compression of the gas. A combined engine and pump is employed to pump the gas from the reservoir to the receiver, whence it is conveyed by pipes to the cylinders attached to each carriage, at a pressure of 150 lbs. to the square inch, each cylinder, as well as the main, being supplied with a pressure gauge, so as to show at a glance when they are full.
The gas is conveyed from the works where it is made, to the station or shed where the carriages are charged, through an underground main of iron pipe, having an outside diameter of 1¼ in., and an inside diameter off ¾ in., connecting hydrants are then attached to the main, to which gas-hose is attached at distances of about 120 ft. for filling the cylinders in the carriages. The hose is of india-rubber and canvas knit together, and is capable of withstanding a pressure of 150 lbs. to the square inch; it has attaching unions and stopcocks at each end, so that it can be taken off the main without waste of gas, the main and the carriage cylinders having stop valves, so that all can be closed before detaching the hose. The gas in the main can also be drawn off into the gas-holder when it is desired, for any reason, to empty the carriage cylinders. Each carriage has one or two cylinders, which are filled to a pressure of 110 lbs. to the square inch, and are made of lined steel, with the seams welded, and two of these, 16 feet in length, with a diameter of 13 in., will carry a sufficient supply of gas to keep twenty lights, burning on a journey from London
