Fig. 5 is another variety of gasometer, which ap pears lately to have got into use, though it is very imperfect, or rather totally deficient in the essential property of giving an uniform pressure to the gas contained within. Having no counterpoise, it re quires to be elevated by the forcing in of gas under a considerable and varying pressure, and the addi tion of a regulator or governor (described hereafter) is necessary to equalize that pressure where the gas is emitted for the purposes of combustion. The parts, a a, 66, ff, are similar to those of fig. 1, but instead of the pulleys and counterpoise, the gas.. ometer moves vertically upon the slides, c c. A spe cies of counterpoise is sometimes applied to this gas. ometer, consisting of a vessel, z, open at the bottom, and attached by its top to that of the gasometer ; as the gasometer sinks, the air in this vessel becomes compressed more and more, and exerts itself so as to act as a counterweight in some degree.
Fig. 7 is a revolving, or partially revolving, gaso meter, described by Mr Clegg, with whom the con trivance originated : a a a, a cistern nearly filled with water, as shown ; 6, an axle, hollow at each end, and working on friction sectors ; d d d, a vessel sup ported by arms radiating from the axle, and formed of parts of two concentric cylinders, closed at their ends, and also closed at g, except where the entrance and exit gas pipes, passing from g to the hollow axis, are connected (one of these is only shown in the figure, the other being directly behind it); the end, h, is open, and when the gasometer is filled with gas, it is just immersed in the water ; i, a pulley, to which is attached a chain and weight, k, disposed as represented. The whole apparatus is construct. ed so as to be in equilibrium in any position, the framing being made heavy at that part of the circle to which the gas-holder does not extend, so as to counterbalance the matter opposed to it. The gas enters at one of the hollow ends of the axis, and passes through one of the tubes g, into the gas ometer ; and it is discharged, under any required pressure (obtained by means of the weight k), through the other tube behind g, into the farther extremity of the axis. This form of gasometer is somewhat expensive ; but, from the circumstance of its requir ing a shallow water cistern, may be resorted to in some cases with propriety.
The vertical section of another of Mr Clegg's de vices, and which he calls a Collapsing Gasometer, is shown in fig. 8. The sides close together like the two boards of a book, and the formation and action of the ends cannot be better described than by a reference to the opening and closing of the folding divisions or pockets of a pocket-book. The
difficulty of making such a length of joint gas tight will be found no small objection to the use of this gasometer ; and the single' advantage it appears to possess is the shallowness, and conse quent cheapness of the cistern a a, in which it is placed. The balance ,weights b, b, act upon the bent levers c, d ; c, d ; which cross each other, and are at tached to the sides of the vessel, and with the pres sure of the gas cause the same to expand or collapse as required; imitating (in effect) the rising and fall ing of the common gasometer. This construction scarcely admits of an uniform pressure being given to the gas when expelled, and that must, therefore, be accomplished by means of a regulator attached to it.
Gasometers are usually made of sheet iron of from two to three lbs. to the square foot, with internal frame of wood, cast or bar iron. When constructed to rise and fall vertically, as in figs. 1, 2, 5, a cylin drical form is to be preferred, as the water pits, or cisterns over which they are suss:tied, are more easily constructed of that shape, of square, ob long, &c.
Various methods of suspending gasometers have been adopted, the principal end in view being, as above stated, to equalize the pressure as much as possible ; and, in the furtherance of this object, it is desirable to make the working parts of the machin ery on a construction the least liable to the effects of friction. The pivots, or axes of the suspending pulleys, are usually placed on friction rollers or sec tors, such as are represented in figs. 8, 4, 7 ; the first of Which we consider as the most perfect, having seen it applied to gasometers of great magnitude with all desirable success; there being no other friction than that occasioned by the steel edges a a, which carry the whole, and work upon bolsters of the same substance: 6 6 are two sectors, having the curved parts on which the pivots of the pulley c roll, con centric to the edges a a. The application of two sets of these to a gasometer is shown in Plate LXXXIV., where the counterweight is represented as working within a central tube, thereby making the arrange ment very compact. In this plate are also shown weights to preserve the sectors in equilibrium, and counteract the effect Which would otherwise be pro duced when they are moved from a vertical posi tion.