The invisible, and not the visible, rays of the sun have the greatest heating power, and do the principal work in the melting of the mountain snows, and in vaporising the waters of the seas and rivers. Water absorbs or filters away the dark rays from the light ones; so that, if you pass the rays from an electric lamp through a narrow glass trough filled with water, and then bring them to an intensely sharp and brilliant focus, although the rays thus filtered contain sufficient heat to set fire to brown paper, hoar-frost is not touched by them, because, being transparent to these rays, it lets them pass through without absorption. Proof:—You can and do set fire to paper in the focus, and then place a flask, covered outside with hoar-frost, in the same focus, yet the snow remains unmelted. Then you can stop all the visible rays by the interposition of a glass trough filled with solution of iodine in bisulphide of carbon—which is, however, transparent to the invisible rays—and on removing the trough of water, this allows invisible rays to pass on to the focus, whilst the visible rays are cut off by the solution of iodine. When the flask coated with hoar-frost is placed in the dark focus, the heat at once melts it from the surface, wherever the glass is brought into the centre of action.
COMMON GAS.
Bituminous coal contains chemical compounds, nearly all of which can, by distillation, be converted into an illuminating gas, and with this gas cities are lighted. Fill with coal dust (or walnut or butternut meats) the bowl of a tobacco-pipe; then cement the top over with some clay, place the bowl in the fire, and soon smoke will issue from the end of the stem. When that has ceased coming, apply a light, and it will burn brilliantly for several minutes; after it has ceased, take the pipe from the fire, and, when cool, remove the clay, and a piece of coke will be found inside. Toy balloons can be filled by this means. They are made of goldbeater’s skin, sheet gutta percha, &c., and are miniatures of the aëronautic machines seen on gala occasions.
THE FAIRY IRIS.
Fig. 120.
Well mix in two ounces of spirits of wine half a drachm each of nitrate of baryta, nitrate of copper, chloride of copper, and nitrate of strontian. Put this liquid in a strong metal globe, holding a quarter of a pint, by an aperture into which screws tightly a small fountain-jet with a tap. Boil over a spirit-lamp. When the spirit boils, shut off steam for five minutes. On turning the tap the whole of the spirit will blow out and spread like a cloud, to which a light being applied, the whole will become a fiery spray, tinted blue, green, red, yellow, &c.
Perform only in an empty room, where no harm can be done by an explosion.
THE COLD LIQUID BECOMING SOLID UNDER HEAT.
Put equal parts of fixed alkali and of powdered quicklime, and boil them in sufficient water rapidly; filter, and put in a well-stoppered bottle. Again boil this liquor, either in the bottle or another container, until it becomes pasty, or like thick glue. Let it cool, and it will become a transparent liquid again. Repeat at pleasure.