The base which it occupies is no larger than what would be required for a gas holder of equal capacity, built on the plan of the gas holders of which descriptions have been just given.
It regulates its own specific gravity. And though more expensive in the construction, yet as it does not require a deep cistern, like the machines already described, it can be erected at the same cost. The revolving gas holder is exhibited, fig. 8, [plate VI.] Its capacity is 15,000 cubic feet; it weighs 12 tons. [Plate I.], (on the title page,) exhibits a perpendicular section of the gas holder.
On inspecting fig. 8, [plate VI.], it will be seen that this machine is the segment of a hollow cylinder, or broad wheel, formed by two concentric cylindric surfaces of 250° each, revolving upon an horizontal axis, and supported upon a wooden frame or truss, in a brick cistern, I, K, L.
The extremity C, D, fig. 8, [plate VI.], or C, [plate I.], of the segment of the cylinder, is open, and the other extremity A, is closed. E, is a balance pipe, which connects the closed with the open extremity of the machine.
This pipe is made of such a weight as to counterpoise the interval between the open and closed end of the gas holder, so that the machine may move in a segment of a circle equally, in whatever position it may happen to be placed, and hence the gas will be discharged from the gas holder with an uniform velocity.
The balance pipe E, is closed at the part where the letter E is placed; H, is a straight pipe, which forms the communication between the balance pipe E, and the horizontal axis upon which the machine moves. This axis is hollow: it is supported by stays and braces, as shown in the design on the title page. The cistern in which the gas holder moves is 71⁄2 feet deep. It must be evident that the gas being conveyed into the open end of the hollow axis, it will pass through the pipe H, into the balance pipe E, and this being stopped up near E, the gas will proceed into the closed end of the gas holder. The operation will therefore be as follows:
Let us suppose the closed extremity of the machine to be at the surface of the water in the cistern, and the gas flowing through the axis as described, the extremity of the machine will begin to fill, and consequently to ascend; the gas holder will therefore continue to move upon its axis until the open end C, D, fig. 8, [plate VI.], or C, [plate I.], comes nearly to the surface of the water, and when the gas is required to be discharged, it will return through the same channel by which it entered. A sufficient pressure is given to this gas holder for discharging the gas at the velocity required, by means of a weight suspended to one extremity of a chain, passing over a pulley, whilst the other end is fastened into the groove of a small circle attached to the stays of the machine, as shown in the designs. The circle is graduated to express the capacity of the machine. Thus any degree of pressure may be given to the gas, and the gas holder will retrograde in an arc describing 270° of a circle, as the gas becomes discharged, until the end A, again arrives at the surface of the water.
The small curved pipe T, [plate I.], serves to let the common air escape out of the angular extremity of the machine, whilst filling with gas, when the margin of this part of the machine becomes immersed in the water, and to let the common air enter again, when the gas holder is discharging its contents.
S, [plate I.], is a friction sector, upon which the axis of the machine revolves. The advantage of this contrivance is, that the friction is very much diminished. The length of the friction sector is eight feet, the diameter of the gudgeon or axis four inches; therefore the space described by its outer circumference and its centre is in the proportion of 96 to 4.