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consists of combustible substances, similar to those contained in coal gas, though in rather different proportions; but it may be extracted either from animal or vegetable oils. It yields a white and very brilliant light; and, with the exception of pure olefiant gas, perhaps no other of the inflammable gases that can be obtained by the processes of art is better adapted to afford light; and the gas itself contains nothing particularly noxious.

The apparatus, as well as the process, for the decomposition of oil, are very simple; and the heat of the retort, and the supply of the oil, are those points which principally require attention. It is also important that the oil should be exposed to a great quantity of heated surface, and therefore it is decomposed only in very small portions. When too great a degree of heat is applied to the retort, the gas is not merely deteriorated, but a quantity of lamp-black is produced, that tends to stop the pipes, and interrupts the process, besides the injury it does to the retorts. On the contrary, if the heat be too low, the oil is merely converted into vapour instead of producing gas, and thus occasions a waste of the oil.*

The size of the retorts is less than that of those

See Plate II. for the representation of the different parts of the oil-gas apparatus.

employed for making coal gas; they have usually a cylindrical form, and are laid horizontally over the fire-place. Into each retort is introduced a quantity of well-burnt coke, or hard brick, broken into pieces; and when these substances are heated to a bright-red heat, by the aid of a cock the oil is permitted to fall only by drops upon the redhot coke or brick. By this means it is rapidly converted into gas, which ascends through the upright pipe at the back of the apparatus, and enters the condensing vessel, where both the gas and the vapours that may be mixed with it are condensed.

The condensing vessel consists of an oblong square cistern, which has a smaller one placed in the inside of it, and firmly fixed to its bottom. The space between the inner and outer vessel is filled with water, in order to keep it cool. As the gas passes through the inner vessel, the coldness of its temperature occasions it to part with any vapour, and to deposit the volatile oil that may be mixed with it as it is produced. Though such very small portions of oil be operated upon at once, a considerable quantity of the oil escapes in the state of vapour; but this is made to return into the oil vessel, by means of a pipe which connects it with the inner vessel of the condenser. By this simple contrivance it is exposed a second

time to the heat of the retort, to be converted into gas.*

The oil gas, having no sulphuretted hydrogen† in its composition, is very easily rendered fit for burning. The process by which it is purified is merely by passing it through a cistern, called a wash-vessel, that contains either oil or water, and sometimes both, where it deposits any impurity that may be united with it.‡

Though it has been stated that the quality of the oil used is not material, the quantity of gas obtained has greatly varied, according to the results of experiments made by different persons; the average produce has been between 75 and 100 cubic feet from a gallon of good whale oil. The specific gravity has also varied in a similar ratio.

↑ In the course of the investigation on the London and Westminster Oil Gas-Bill in 1825, it was asserted, that sulphur had occasionally been detected in oil gas, but that contamination probably arose from using coke containing it. It was also observed that the oil-gas apparatus possessed no provision to obviate this inconvenience; but, as this must proceed from the impure state of the coke put into the retorts, it is an inconvenience which may be easily obviated.

The principal residue from the distillation of oil consists of a fluid, called volatile oil, which has a strongly offensive smell, and has generally been of little or no value. Some recent attempts have, however, been made to render it useful, by combining it with rosin, and re-distilling it so as to convert it into gas; but at present little has been made known with respect to the successful results. A patent has

In December, 1826, Mr. Edward Luscombe obtained a patent for a method of making oil or oils from vegetable substances, and also for applying them to Gas-lighting. The distinguishing feature of his process is, the formation of a mixture, consisting of one hundred weight of rosin with fourteen pounds of water, or in similar proportions, which is distilled in a vessel constructed in the shape of half a globe. This plan has been practised for some time at Bristol and Norwich.

OF THE PORTABLE GAS VESSELS, &c.

As the oil gas possesses the power of affording a greater degree of light, according to its bulk, than an equal quantity of coal gas, a less portion of it, as well as burners of smaller sizes, are required to effect its purposes. This property has given rise to the application of it to a species of moveable lights, which, in some cases, have been found very convenient. The portable gas consists of oil gas greatly compressed, and

been recently obtained for this purpose by a Mr. Daniel, and the method adopted at the Portable Gas Works.

forced into strong wrought-iron vessels, which are made of various dimensions as their intended uses may require. Some of them are spheres, but generally they are of a cylindrical form with convex ends, and to each of them two ingeniously constructed valves are connected by a screw; one of these is for admitting the gas when the vessels are filled, and the other to permit it to pass out in order to be burnt. The burner is screwed to the upper end of one of the valves, and it has a proper stop-cock to regulate the size of the flame, or to extinguish it, as either may be requisite.

By the use of a very powerful condensing apparatus, the Portable-Gas Company usually compress thirty volumes of the gas into the bulk commonly occupied by one. The object of this compression of the gas is to enable them to use vessels of comparatively small dimensions, and only of such sizes as may not be inconvenient to the consumer.* It must be evident that the strength required for the vessels must necessarily be great, and to prevent any apprehension of danger in using them, the most particular precautions are taken to have them very nicely ex

* Some of their vessels are globes, and others in the form of urns, with appropriate stands to adapt them for being placed upon a table or desk. The following is a scale of the sizes and contents of their different vessels:

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