Imatges de pàgina

enters the cavity between the tubes, and issues from the circular row of apertures, where it is inflamed, and having a due supply of air within and without, burns very beautifully when a proper glass is placed over the burner. These burners, when very carefully regulated, consume about three cubical feet of gas per hour, and give light equal to that of six wax candles; but it is requisite, on account of carelessness and inismanagement, to allow four cubical feet to each burner per hour. The bat's-wing burner should not consume more than three cubic feet per hour.

At the three stations belonging to the chartered Gas-light Company, situated in Peter-street, Westminster, in Worshipstreet, and in Norton Falgate, twenty-five chaldrons of coals are carbonised daily, which actually yield 300,000 cubical feet of gas, equal to the supply of 75,000 Argand's lamps, each lamp giving the light of six wax.candles. But if the full proportion of gas were obtained, viz, 20,000 cubical feet from each chaldron of coals, then the produce should be 500,000 cubical feet, equal to the supply of 125,000 lamps of the same size, and the light afforded should equal that of 750,000 wax candles, instead of 450,000, which is the real produce.

At the City gas-works, in Dorset-street, Blackfriars-bridge, the daily consumption of coals, for distillation, amounts, at present, to three chaldrons; which afford gas for the supply of 1,500 lamps, so that the total consumption of coals daily in London, for the purpose of illumination, amounts to twentyeight chaldrons, and the number of lights supplied to 76,500.

Besides the different varieties of coal, some of which, as has been hinted, are much preferable to others, and coal-tar, an useful gas may be procured from a variety of other substances; and in the laboratory of the Royal Institution we often feed the retort with waste paper, saw-dust, pieces of wood, &c. and consume the gas for a variety of purposes, where oil was formerly employed.

The following are the results of some experiments upon these subjects, compared with the produce from coal.

1. The retort was charged with four pounds of coal. The quantity of gas amounted, after having passed the purifiers, to


twenty cubic feet. The coke remaining in the retort weighed 2 lb. 8.7 oz.

The heating power of the gas flame was compared with that of a wax candle, by ascertaining the time required by each to raise two ounces of water, in a thin copper vessel, from 550 to 212°. The flames were made as similar in dimensions as possible, and so placed that their points just touched the bottom of the vessel. The heating power of the candle being assumed as = 1. that of the coal gas flame was = 1.5.

2. Four pounds of the dried wood of the common willow yielded sixteen cubical feet of gas, and fourteen ounces of char

, coal remained in the retort. The gas burned with a very pale blue flame, and was unfit for the purpose of illumination, and contained no olefiant gas.

3. Four pounds of the wood of the mountain ash afforded fifteen and a half cubical feet of gas, and thirteen ounces and a half of charcoal. The flame was very pale and blue.

4. Four pounds of white birch wood gave fourteen cubical feet of

gas and twelve ounces of charcoal. The flame similar to 2 and 3.

5. Four pounds of hazle wood yielded thirteen cubical feet and a half of gas, and twelve and a half ounces of charcoal. Its heating power was == 1.2. It burned with a better flame than 2, 3, and 4, but the intensity was not sufficient for any useful purpose of illumination.

6. Four pounds of writing paper gave eighteen cubical feet of gas, and the remaining charcoal, which beautifully retained the form and texture of the paper, weighed eleven ounces and a half. The heating power of the gas was = 1.6. It burned with a flame nearly approaching, in illuminating power, to that of



coal gas.

These experiments, along with others which it is thought unnecessary to notice, prove that the gas from woods is not fit for the purposes of illumination, although, as evolved during the production of charcoal, it may conveniently be consumed in the laboratory as a source of heat.

Respecting the advantages of gas illumination in streets, open places, large manufactories, &c. there can be but one opinion; but its introduction into dwelling-houses involves some more important considerations. It may be urged in its favour, that the light is more equable, beautiful, and agreeable to the eye than that obtained from any other source; that superior cleanliness is attained, and the troublesome operations of filling and trimming oil lamps are superseded; that there is no danger from sparks and snuffs, as where candles are employed, and that by closing the main pipe of supply, a certain extinction of all the lights throughout the building is insured.

The following are the principal objections that have been adduced. When the gas escapes unburned, its smell is extremely disagreeable, and this may happen either from some fault in the pipes or burners, or from a stop-cock connected with a burner being accidentally left open. In the latter case the remedy is obvious, but in the former the escape of gas may prove very troublesome; but it may be guarded against by employing double pipes, by carrying them as much as possible upon the exterior of the house, and above all, by employing careful and good workmen in the construction of every part of the apparatus.

The idea of explosions, in rooms lighted by gas, has frequently occurred; but when the probability of such an event is calmly considered, much of the alarm that it has excited must vanish. For the formation of an explosive atmosphere, a large quantity of gas must escape into an apartment which must be nearly air-tight; and in a room with an open chimney, and two or three doors and windows, it would scarcely be possible to obtain a dangerous mixture, though it might occur in a cellar or any other very small and close apartment. In a dwelling room the gas would announce itself by its smell, very long before any dangerous mixture could ensue, and the quantity of gas required would be very great. A room twelve feet square, or containing 1728 cubical feet of atmospheric air, would require an addition of 247 cubical feet of coal gas to render its atmosphere explosive. If we suppose a large Argand's burner accidentally left open in this apartment, whence gas is flowing at the rate of 4 cubical feet per hour, it would require 62 hours for the above quantity of gas to flow into the room, which also must be nearly air-tight; these circumstances can scarcely be supposed ever to occur; a very little attention to ventilation, Vol. VI.

2 N

No. 23.



which whenever gas is used should be strenuously insisted on, would remove all possibility of danger. But the best proof of the safety of gas illumination is, that notwithstanding the many thousand lamps nightly burning in London, six* accidents only are known to have occurred, and those of a very trifling and almost unimportant nature, though the pipes and lamps are generally badly and very carelessly managed. In matters of this kind, facts, and not arguments, must be looked to for evidence.

It was my intention to have concluded this paper with some observations on the construction of burners, and with an account of several important improvements lately made in the general apparatus by Mr. Clegg: the hope of rendering my account of these subjects more correct and perfect than is at present in my power, induces me to defer it till the appearance of the next number of this Journal.

Observations on the Nature and Properties of Caoutchoue, and on the Construction of Elastic Beds, Pillows, Hammocks, &c.

[From the London Monthly Magazine, for March, 1816.] THE term Caoutchouc may be considered as the generic name for a concrete vegetable substance which possesses the properties of elasticity and extensibility, and is soluble in the essential oils, &c.; and its not being acted on by those fluids which are solvents for

gums and resins, renders the term elastic gum, or elastic resin, improper for it. The specific name may be that of the vegetable producing it: as, caoutchouc of Urceola elastica, caoutchouc of Ficus indica, caoutchouc of Artocarpus integrifolia, &c.

This production is common to the East-Indies, and to all tropical climates, from whence it is imported in various artificial forms; chiefly in that of bottles and solid blocks; sometimes in the shape of balls, or in the rude figures of birds, horses,

• Two of these arose from holes having been mischievously bored in the pipes of supply.

and part Qui -ana; quat at ne tropi the S

respo Engl lected lation

Cat modei but li mode geous herein facts from, tion to fore su physici lowing Linnæu


M. Bomare describe fuid state, capable of
The memoires de lsite shape, impervious
description of it by destructible excepting
the manner of softeniric ether, essential oil
Herissant, 1763; alsoality of oils, will not
on the caochouch dture.
publication for 1769 melting or by solu-
Turgot on the elastisorm, and most of its
trees, vines, and planen nitric ether is em.

and of vat the common tempenumerous,

The vegetable svlution be afterwards produced from the tc. and exposed to the imported in its origi caoutchouc unaltered fermentation which sparent, of an amber useless. It is techni, rises to the surface, from its being an lue great elasticity and purpose of erasing ruc: but, as the ether rent property for with longer time than the indurated juice purposes is not eligicisions made in that for it, with the

apbranches. The fluide caoutchouc bottles and of a glutinous eces are examined a by exposure to th solvent, they will be changes to a dark leir size by absorbing less deep beneath tnt, that all the differ. ness. It is pliable, he bottles, and other gree; being capabl-ucted, may easily be afterwards of regas: this solution may the extending forcatedly straining it by renders it stiff ands of paper or of silk ginal elasticity, relinseed oil and dried, pability of extensvards exposed to the producing at the sa oil-case completely creased beyond thia remarkable degree with a bright flam two or more such torches.

ed together to expel All its qualities great firmness; and, and its original vear to have been held of Chinese or Inf the elastic gum on

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