The fire-tube being heated to a moderate red heat, oil is admitted by means of the cock, e, and in its passage through the heated tube is decomposed, or partially so, and makes its escape by the pipe, f, back again into the oil-cistern in a gaseous, or va porous state, where such particles of the oil, as have merely been volatilized, are again condensed, and the permanent gas passes forward through the pipe, g, to a gasometer, or otherwise as required.
To render this apparatus more complete and con venient, the ingenious patentee has arranged it, for general use, nearly in the manner and form represent ed in figs. 10, 11, 12, which are different views of the same thing; the fire-tube here is bent in the shape of the letter U, as shown at a a a a• ' 6, the grate ; the oil is admitted at one extremity by the pipe, e e (having a regulating cock upon it), from the oil cis tern, c, and the gas taken off from the other by the pipe, h; as in fig. 9, above described.
The vessel, c, has a funnel, d, attached to it for the purpose of supplying oil when required. The pipe, f, which conveys away the gas (and any va pour which may be formed from the admission of a greater quantity of oil than can be decomposed in its passage through the fire.tube), is connected to a close vessel, h, which is surrounded with water con tained in a cistern, i i; and this cistern also contains a spiral-tube, or worm, k k, the lower end of it con necting with the vessel, h, and its upper end with a descending pipe, 1. The vessel, 6, and worm, k, be. ing immersed in cold water, serve for the purpose of condensing any oil that may arise in a mere ly volatilized state ; and this oil being collected in the bottom of the vessel, is allowed to descend again into the cistern, c, by a tube connected there. with.
The gas, though now separated from the vapour in a great degree, is, in order to render it more per. fectly pure, conveyed by the pipe, 1, above mention ed, into an air-tight chest, m m, in which water is contained up to the level represented ; n is an in clined partition fixed across the chest, having diago. nal ribs attached to its under side, so that when gas is forced in beneath it through the pipe, 1, it circu lates underneath the partition in a zigzag direction, gradually ascending till it escapes at the upper end, and rising through the water, is taken off at g, to a gasometer (such as has been already described) for use.
In order to increase the effect of the fire-tubes, they are loosely filled with different substances, the better to cause the decomposition of the oil. Pieces of brick, Cr coke, answer this purpose ; and as these require to be taken out and renewed from time to time, there are, at q q, two openings, with air-tight covers, for allowing this to be effected, and by means of which the tubes can also be cleaned by scraping out such carbonaceous matter as adheres i to their inner parts : p p p are stoppers, also for the purpose of allowing the pipes, e and f, to be cleaned in the like manner. Such an apparatus as is here re presented (to a scale of one-third of an inch to the foot) will yield 100 to 120 cubic feet of gas per hour.
Illuminating Powers of Coal and Oil-Gases.
To compare the expence of oil-gas with that ob tained from coal, a knowledge of the comparative illuminating powers of equal bulks is necessary. It is stated (Quarterly Journal of Science, &c. No. XIV.), that one cubic foot of oil-gas will yield as much light as four of coal-gas; but, in another part of the same article, that the proportion is only five to nine. Mr Brande (Annals of Philosophy, December 1819) gives one to two as the proportional value of the two gases : our own experiments give seven to thirteen. Much discrepancy may arise from the way in which such experiments are conducted : an argand burner, which will, when burning coal-gas, give, with the greatest advantage, a light equal to any number of candles, should, when used with oil-gas, be adjusted to emit a considerably greater quantity of light, in order to burn that gas in the most economical man ner. There is always a portion of blue or dark co loured flame adjoining the burner ; and to make the comparison fair, this ought to bear an equal propor tion to the white flame in both cases ; and though some attention was paid to this circumstance in mak ing our experiments, we have little difficulty in be lieving that the result would have been somewhat more favourable to the oil-gas, had the proportions of white and blue flame been more accurately ad hered to ; and we therefore incline to consider Mr Brande's numbers of one to two as the most cor rect.