All dealings with chlorine should be conducted in a well ventilated—even draughty—room, and care must be taken not to inhale the gas. It corrodes animal tissues just as eagerly as it attacks turpentine and metals. The gas is very heavy, however, and is therefore the less difficult to keep under control.
Niter Paper.—Touch-paper burns quickly, surely, and without flame. It is prepared by soaking thin tissue paper with a saturated solution of saltpeter in weak vinegar, and when dry feels rough and crisp to the touch. Moreover, it burns with a rather pleasant smell. The advertisement scheme of bygone days, wherein a lighted match was placed on a particular spot of a paper sheet, and thence the name of the advertised commodity gradually burnt itself out over the surface, was a modification of this preparation ([Fig. 5]). The name or design is simply drawn with a pointed stump of wood dipped repeatedly in the saltpeter solution, and the starting-point marked conspicuously by a cross or black spot. When dry a match is applied to this mark. If there is a tendency for other parts of the paper than the design itself to burn, a short immersion in dilute alum solution, when the saltpeter lines have dried, may be resorted to.
Fig. 5.—A niter paper experiment.
Electric Fire.—This compound is in no way of an electric nature, except that it burns rapidly with brilliant blue illumination. The constituents are flowers of sulphur, saltpeter, and antimony, four parts of the former being intermingled with ten parts of powdered saltpeter, and then one-seventh the total quantity of powdered antimony finally added. Thorough mixing by gentle stirring must be insured. A good method of firing the powder is to pack it round a twist of touch-paper in a small mustard tin, threading the fuse (A, [Fig. 6]) through a hole in the lid, so that it may be lighted easily. The mixture burns not only brightly, but with intense heat—sufficient to melt the thin iron of the inclosing tin.
Fig. 6.—Lighting electric fire.
Fig. 7.—A sodium or potassium experiment.
The Lightest Element.—Hydrogen is a gas at ordinary temperature, and has the honor of being the lightest element, for all practical purposes, known. For this reason it finds wide employment in filling balloons and airships. The most common methods of preparation consist of decomposing water or an acid in their several constituents, either by the influence of electricity or the reaction of a metal. For instance, if a pea’s bulk of sodium or potassium metal be thrown into a basin of water, A, [Fig. 7], (the experimenter should not bend directly over the vessel), a violent reaction ensues, the metal decomposes and hustles round the surface as though in feverish excitement, and in the case of potassium a purple flame springs up spontaneously. The sodium may also be ignited if it is thrown on to a floating piece of blotting-paper, or if the water be thickened with starch. This metal burns with a yellow flame, or rather colors the hydrogen flame yellow.