The chemical illumination of some writers, by using oil of vitriol, iron filings, and water, and inflaming the vapour as it proceeds from a bottle, is nothing else than the inflammation of hydrogen gas. The "white vapours," which they describe, is the gas in question.

Having noticed the use of candles and lamps for illumination, we purpose, in concluding this article, to give the result of some experiments on the relative intensities of light, and duration of different candles, made by Dr. Ure, which we extract from his Dictionary of Chemistry.

Number in a pound.Duration of a candle.Weight in grains.Consump. per hour: grains.Proportion of light.Economy of light.Candles equal one argand.
10 mould5 h.9 m.68213212¼685.7
10 dipped4366721501365½5.25
8 mould63185613210½59½6.6
6 do.72½116016314⅔665.0
4 do.936178718620¼803.5
Argand
Oil Flame51269.4100

The doctor remarks, that 1/8th of a gallon of good seal-oil, weighs 6010 gr. or 13 and 1/10th oz. avoirdupois, and lasts, in a bright argand lamp, 11 hours 44 minutes. The weight of oil it consumes per hour, is equal to four times the weight of tallow in candles, 8 to the pound, and three and one-seventh times the weight of tallow in candles, 6 to the pound. But its light being equal to that of 5 of the latter candles, it appears, from the above table, that 2 lbs. weight of oil, in an argand, are equivalent, in illuminating power, to three pounds of tallow candles. The larger the flames in the above candles the greater the economy of light.[28]

Sec. XXIX. Of Imitative Fire-Works.

Imitative fire-works are nearly of the same character as the transparencies and illuminations mentioned in the last section; but, as this subject may be interesting to some of our readers, we thought proper for that reason to appropriate a section to its consideration.

Imitative fire-works are formed in the following manner: Take a paper that is blacked on both sides, or instead of black, let it be coloured on each side with a deep blue, which will be still better for such as are to be seen through transparent papers. It must be of a proper size for the figure intended to be exhibited. In this paper, cut with a pen-knife several spaces, and with a piercer make a great number of holes, rather long than round, and at no regular distance from each other.

To represent revolving pyramids and globes, the paper must be cut through with a pen-knife, and the space cut out between each spiral should be three or four times as wide as the spirals themselves. They must be so cut, that the pyramid or globe may appear to turn on its axis. The columns that are represented in pieces of architecture, or in jets of fire, must be cut in the same manner as if they are to be represented as turning on their axis.

In like manner may be exhibited a great variety of ornaments, cyphers, and medallions, which, when properly coloured, cannot fail of producing a most pleasing effect. There should not be a very great diversity of colours, as that would not produce the most agreeable appearance.

When these pieces are drawn upon a large scale, the architecture or ornaments may be shaded; and to represent different shades, pieces of coloured paper must be pasted over each other, which will produce an effect that would not be expected from transparent paintings. Five or six pieces of paper, pasted over each other, will be sufficient to represent the strongest shades. To give these pieces the different motions they require, we must first consider the nature of each piece: if, for example, we have cut out the figure of the sun, or of a star, we must construct a wire wheel of the same diameter with those pieces. Over this wheel a very thin paper is to be pasted, on which is drawn with black ink the spiral figure. The wheel thus prepared, is to be placed behind the sun or star, in such a manner that its axis may be exactly opposite the centre of either of those figures. This wheel may be turned by any contrivance.