Description of the Process of Manufacturing Coal Gas, for the Lighting of Streets Houses, and Public Buildings / With Elevations, Sections, and Plans of the Most Improved Sorts of Apparatus Now Employed at the Gas Works in London and the Principal Provincial Towns of Great Britain; Accompanied With Comparative Estimates, Exhibiting the Most Economical Mode of Procuring This Species of Light

by Friedrich Christian Accum

It will be obvious, that when a gas holder of this construction becomes immersed in the water, it loses as much of its weight as is equal to the bulk of water which it displaces, and hence to render its descent uniform, and to preserve the gas within, of an invariable density, at any degree of immersion, a greater counterpoise is required as the gas holder rises out of the water.

Among various methods which have been adopted to attain this object, the ends of the chains by which the gas holder is suspended, have been fastened in separate grooves, in the edge of a large wheel or pulley, of such a diameter, that the gas holder rises to its full height, before the wheel makes one revolution.

In another groove in the edge of the same wheel, was fixed the end of another chain, to which a balance weight was suspended. This weight was made nearly equal to the weight of the gas holder. To equalize the density of the gas within the gas holder, at any degree of immersion of the vessel, the weight chain was made to pass over a wheel, furnished with a spiral groove, so as to make the radii of the wheel, change reciprocally with the relative weight of the gas holder, and consequently to render the pressure of the gas holder constant and uniform.

Another and more elegant method of obtaining an uniform elasticity of the gas within the gas holder, and which has been more generally adopted, consists in passing the chain or chains by which the gas holder is suspended over a pully or wheels, and making the weight of that portion of the chain, which is equal to the depth of the gas holder, or that part of it which becomes immersed into the water, equal to one half of the weight of the specific gravity of the gas holder.

It is obvious that before the purified gas can be admitted into the gas holder, the vessel must be allowed to descend to the bottom of the exterior cistern, in order to get rid of the common air which it contains. This may be effected rapidly by opening the man hole at the top of the gas holder, to cause the vessel to descend completely into the outer cistern filled with water. The man hole is then screwed up again air-tight, and the machine is ready to receive the gas. It is obvious that the operation of opening the man hole for letting out the common air, requires only to be done once prior to the commencing of the working of the apparatus.

Gas Holder with Governor, or Regulating Gauge, lately brought into use.

It must be obvious that the gas holder, of which a description has been given in the preceding page, requires a machinery at once ponderous and very delicate, qualities not easily reconciled in the construction of such a machine. It is necessary that the specific gravity apparatus, or regulating chain, wheel work and balance weight, should be constructed so correctly as never to suffer the gas within the vessel, to alter its elasticity. The machinery requires an expensive framing for its support, and independently of this, the gas holder must be inclosed in a building, in order to protect it from the impulse of the wind, the action of which would render the lights supplied from the apparatus unsteady, as already stated. The expensive and cumbersome specific gravity apparatus has been wholly superseded by an ingenious contrivance called the regulator or governor. The action of this machine, for which we are indebted to Mr. Clegg, is, that it regulates the density of the gas prior to its entering into the mains, to any required degree, whatever its density may be in the gas holder.

To accomplish this object, the apparatus through which the gas passes into the mains, is provided with an aperture which is capable of being enlarged or diminished by a very slight force. To effect this object the gas is made to enter a small vessel, and then to pass through a regulating aperture, the capacity of which becomes enlarged or diminished by the velocity of the gas to a certain standard. If the pressure of the gas in the gas holder becomes increased, the regulating aperture through which the gas passes into the mains, becomes diminished, in such a proportion, that the velocity with which the gas issues into the mains, remains constant and uniform. And on the other hand, if the pressure of the gas in the gas holder becomes diminished, the regulating aperture of the governor becomes enlarged to effect the intended regulation.

The following is a concise description of the manner in which this instrument is constructed.

A, B, C, D, fig. 9, [pl. III.] is a hollow cylindrical vessel, or the outer case of the machine. It is made of sheet iron or copper, japanned within and without, closed at the top and bottom. It is placed between the gas holder and the mains, into which the gas is to be conveyed. a, x, is a pipe which proceeds from the outer vessel and branches upwards in the centre of the base of the outer vessel A, B, C, D. It brings the purified gas into the governor. b, T, is the outlet pipe which conveys the gas from the governor into the mains. It is placed above the inlet pipe and communicates with the interior vessel. G, H, a short projecting hollow cylinder, which proceeds downwards from the centre of the base of the outer case of the machine A, B, C, D. u, x, y, z, is the regulator, properly so called; it consists of a small conical vessel, also made of sheet iron or copper, closed at the top and open at bottom, japanned within and without. This vessel rises and falls vertically in the outer cylindrical case. A, B, C, D, of the machine, when the latter is filled with water. It is kept steady in its motion by two slender guide rods, as shewn in the sketch.