Fig. 7.—CAR.
It may be made out of cardboard, or, if you like, of wire. You need not be particular about any sort of elegance. Fire-balloons are designed to be sent on their travels at night, when any sort of ornament or elegance lavished on the car would not be seen.
The usual flame for heating the air in a paper balloon is spirits of wine. Methylated spirit does very well, and is much cheaper than pure spirits of wine. I do not recommend this source of flame when the balloon comes to be actually let off, as you will by-and-by see; but for our present experiment I do recommend it. You must make a note of the weight of spirits of wine presently to be used, and, if you do not happen to have scales and weights handy, you may take it for granted that a sherry wineglass full weighs about an ounce.
Ascertain, too, how much the car weighs. Probably, when the time comes for letting off the balloon, you will not require the car, so you should have ascertained its weight, that you may supply a weight equivalent, in the shape of fireworks, for example.
Fig. 8.—CHAMBER TRIAL OF THE BALLOON.
Two boys will be wanted for performance of the chamber experiment; one to stand upon a chair or stool, so as to be able to lift the crown of the balloon, the other to manage the flame department—to do what engineers would call the stoking ([Fig. 8]).
The spirit, you will remember, is not to be burned loosely, but absorbed by something or other. Sponge is the absorptive medium usually employed, though some operators use cotton wick. On the present occasion of chamber experiment I recommend you to employ sponge. The very coarsest sponge will do as well as the finest and most expensive. Such a piece as most oilmen sell under the name of ‘slate sponge,’ and generally for a penny, will do quite well for the chamber experiment.
Let me now give you boys a piece of advice, and do not consider it of small value. It is of enormous value, being the value of the difference between success and failure. I do not only mean success or failure in the experiment you are about to perform, but any experiment. The advice is this:—Attend well to detail. Before you set about performing any experiment take care that you have provided, and arranged well to hand, everything necessary to the performance of the experiment. Do not say to yourself, this, that, or the other is a trifle, and as a trifle neglect it. In all experimental work, having once determined in your own mind the various things and arrangements necessary, nothing amongst them can be a trifle. Well, to the point. Provide yourself, by loan if your pocket-money does not run so far, with some handfuls of farthings. This little coin will be about the most convenient thing you can use for seeing how much weight your balloon will take up. You are ready. Well, No. 1, as I will call you, lay hold of the crown of the balloon, then jump on a stool or chair, lifting the entire balloon up in such way that the mouth of it may be conveniently disposed for what has to be done by No. 2.