Take a bladder of any size, (let us suppose for the sake of illustration, the bladder to hold 30,000 grains of water,) and having furnished it with a stop-cock and small jet pipe, fill it with the combustible gas the heating power of which is to be tried. Take also a tinned iron vessel with a concave bottom of the same capacity, pour into it as much water as will make the vessel and water together equal to the bulk of the water in the bladder, viz. 30,000 grains. Then set fire to the gas at the orifice of the pipe, bring the point of the flame under the bottom of the tinned vessel, and suffer it to burn there, by squeezing the bladder till the whole of the gas is consumed. The increase of temperature of the water in the tinned vessel before and after the experiment, expresses very accurately the heating power of the given bulk of the inflammable gas. It was thus proved that—
| Olifiant gas raises an equal volume of water | 14 | deg. |
| Carburetted hydrogen, or coal gas | 10 | |
| Carbonic oxid gas | 4 | |
| Hydrogen gas | 5 | |
| Spermaceti oil, 10 grains burnt in a lamp raised 30,000 grains of water | 5 | |
| Tallow | 5 | |
| Wax | 5,75 | |
| Oil of turpentine | 3 | |
| Spirit of wine | 2 | |
The best method for this purpose is to make an aperture of about two or three inches in diameter into the chimney near the ceiling, and inserting into it a tube bending upwards into the interior of the chimney. A complete ventilation of the room will thus be established, by producing an extra vent which will be amply sufficient for carrying off the heated air. The aperture can easily be masked with some ornamental open work, corresponding with the style of the room.
If there happens to be no chimney in the apartment, the ventilator may be made in the ceiling, and the tube may be carried between the ceiling and the floor above, into the open air. The mode of ventilation now suggested, has been uniformly found most efficient, and has, under existing circumstances, a decided superiority over another method, which we see in some instances adopted. This method consists in enclosing the gas burner in a bell-shaped glass, from the upper part of which a large copper tube proceeds, and leads out into the open air. It is certain that by this means not only the heated air is carried off, and the possibility of any waste gas escaping into the apartment is also completely prevented. But at the same time, by taking away all occasion for a prudent limitation in the use of the gas, it exposes it to a degree of improvident waste, in the hands of dishonest and careless individuals, which must prove ruinous to the manufacturer. The mode of regulating the light of the flames by means of the governor, of which a description has been given, [page 232], indeed provides a check against such waste, and there can be no doubt that in proportion as this instrument gets into general use, the objection on this score must of course fall to the ground; but under any circumstances the inelegance of the contrivance of such an object in a chamber, as the large branching tube, must always induce a preference, for the more simple, and for all necessary purposes, equally efficient method, of the ventilator before described.
PART XV.
Gas from Coal Tar.
Although the tar which forms one of the products obtained from the decomposition of pit coal, in the manufacture of coal gas, has become an article of commerce, being found applicable to most of those purposes to which vegetable tar has hitherto been used, it appears from experiments made on a large scale, that instead of thus disposing of the coal tar, it is more profitable, under certain circumstances, to submit this substance to a destructive distillation, for the purpose of obtaining from it carburetted hydrogen gas, which it is capable of affording, not only in abundance, but of a superior quality.
The chief circumstances which must determine the manufacturer of coal gas in this respect, is the price at which he can sell the coke produced in his establishment. If the price of this article is high, if he finds a ready market for coke, there is every reason to believe, that the manufacturer will find it more to his advantage to dispose of the tar, and to manufacture gas from coal alone, in order to increase his store of coke. But if coke happens to be at a low price, and not disposable with advantage, the manufacturer will do well to make the coal go as far as possible in the production of gas, and under such circumstances he will keep and convert the tar into gas, thus consuming less coal and having less of the burdensome article, coke, to dispose of.