A Practical Treatise on Gas-light / Exhibiting a Summary Description of the Apparatus and Machinery Best Calculated for Illuminating Streets, Houses, and Manufactories, with Carburetted Hydrogen, or Coal-Gas, with Remarks on the Utility, Safety, and General Nature of this new Branch of Civil Economy.

by Friedrich Christian Accum

When the operation commences, the gasometer is sunk down nearly to a level with the surface of the water in the outer cistern, and is consequently filled with water; but as the gas enters, it rises up to receive it. It is to be noted, that the balance-weights q q, should not be quite so heavy as the gasometer, in order that some pressure may be exerted, to force the gas out of the burners with a proper jet. The gas which issues from the retort enters the purifier as stated already, and ascends the pipe o, into the vessel, p, from which it displaces the water, and passes out at the small holes, as before described, rising through the water into the gasometer, and raising it up: the gas then passes away to the burners, u u. In this manner the process proceeds until the whole of the volatile products of the coal in the retort is evaporated. The use of the gasometer is, to equalize the emission of the gas which comes from the retort more quickly at some time than others. When this happens, the interior vessel rises up to receive it, and when the stream from the retort diminishes, the weight of the gasometer expels its contents. When the process is finished, the retort is suffered to cool, and its ground stopper is then removed to replenish it with coal. The residue found in the retort is coke. v v are cocks to let off any liquid that may collect in the pipe o or t; for if the smallest portion of liquid were to obstruct the free passage of the gas to the burners, the consequence would be, that the lights would not burn steadily—they would, as it is called, dance, or become extinguished. x is the main stop-cock which communicates with the burners—these, of course, may be placed as convenience may require. z z are two projecting parts in the top of the gasometer; they are intended to receive the hood p, and the upper extremity of the pipe t, so as to allow the gasometer to be wholly immersed into the cistern. The wheels or pullies of the gasometer have a groove to allow the links of the chain to pass freely.

In this apparatus there is no provision made for the unequal pressure which the gas suffers, accordingly as the gasometer is more or less immersed in water. It will be observed that, in this apparatus, the weight of the interior vessel is constantly increasing, in proportion as it fills with gas, and rises out of the water, and consequently, if a constant, uniform, counterpoising weight, equal only to that of the gasometer in the first moment of its rise, be employed, the gas becomes gradually more and more compressed by that part of the weight of the gasometer which is not counterpoised, and if its pressure or quantity be then estimated by the bulk which it occupies, without making allowance for the increasing pressure, a material error must arise, and this, in the large way, would give rise to insurmountable difficulties with regard to the regulation of the size of the flames; which could not be rendered uniform.

Suppose the cistern or exterior vessel full of water, and the gasometer partly filled with gas and partly with water, it is evident that the balance-weight may be so adjusted, as to occasion an exact equilibrium, so that the external air shall not tend to enter into the gasometer nor the gas to escape from it; and in this case the water will stand exactly at the same level both within the gasometer and within the outer cistern. On the contrary, if the balance-weights be diminished, the gasometer will then press downwards from its own gravity, and the water will stand lower in the gasometer than it does in the cistern; in this case, the included air or gas will suffer a degree of compression above that experienced by the external air, exactly proportioned to the weight of a column of water, equal to the difference of the external and internal surfaces of the water.

To compensate for this increasing weight of the gasometer, and render a scale of equal graduations accurate, some have ingeniously adopted the plan of a spiral pulley to the chain, which has the effect of gradually avoiding the evil, but the best way of accomplishing it will be stated hereafter.

With regard to the philosophy or the production of coal-gas, it proves that pit-coal contains solid hidrogen, carbon, and oxigen. When the intensity of the heat has reached a certain degree, a part of the carbon unites with part of the oxigen and produces carbonic acid, which by means of caloric is melted into the gazeous state and forms carbonic acid gas; at the same time, part of the hidrogen of the coal combines with another portion of carbon and caloric, and forms the carburetted hidrogen gas, which varies considerably in its constitution, according to the circumstances under which it is produced; a portion of olifiant gas, carbonic oxid, hidrogen, and sulphuretted hidrogen, is also produced during the process. The quantities of these products vary according to the nature of the coal employed in the process.

Pit-coal is not the only substance which affords carburetted hydrogen; this gazeous fluid may be obtained in a great variety of ways, and with very considerable differences in specific gravity and proportion of ingredients.

It is found plentifully native or ready formed on the surface of stagnant waters, marshes, wet ditches, &c. through which, if examined closely, large bubbles will be seen to rise in hot weather, and may be increased at pleasure by stirring the bottom or mud with a stick.

In close still evenings if a lighted candle is held over the surface, flashes of blue lambent flame may sometimes be perceived spreading to a considerable distance. All that is not fabulous concerning the ignis fatuus is probably derived from this source. This species of gas is termed for distinction the carburetted hydrogen of marshes. In the purest form in which it can be collected it is mixed with about 20 per cent. of azot or nitrogen.

To procure the gas for the purpose of philosophical amusement, fill a wide-mouthed bottle with the water of the ditch, and keep it inverted therein with a large funnel in its neck, then with a stick stir the mud at the bottom just under the funnel, so as to cause the bubbles of air which rise from the mud to enter into the bottle; when by thus stirring the mud in various places, the air may be catched in the bottle.

Carburetted hidrogen gas is also given out very abundantly by all kinds of vegetable matter when subjected to a scorching heat sufficient to decompose them. When heated in close vessels much more gas is obtained than when burnt in the open air. If moistened charcoal be put into an earthen retort and heat be applied till the retort becomes ignited; gas will be evolved, consisting partly of carbonic acid, and partly of carburetted hidrogen. A gas of similar properties is obtained by causing steam to pass through a tube filled with red-hot charcoal; by passing spirit of wine, or camphor, through red-hot tubes; by distilling oils, wood, bones, wax and tallow, or any animal or vegetable body whatever.