Many of us, no doubt, have often tried to picture to ourselves a volcano in eruption, but most will confess that unless we have seen some very good pictures of an actual eruption, we are not at all certain that our self-made picture is correct.
Now to detail an experiment which gives a vivid idea of a volcano in action.
At the bottom of a large glass bowl put a flask containing red wine, or spirits of wine, in which has been dissolved a little aniline (B, [Fig. 8]). This flask should be closed by a cork pierced with a very narrow hole. By the aid of plaster, or, simpler still, of earth or clay, fashion a mountain around the flask, leaving at the top a hole through which the cork can just be seen. This will form the crater.
Having made your volcano, fill the bowl with water (A, [Fig. 8]), and you will now witness the eruption.
We know that, owing to the difference in the density of the two liquids, the water will penetrate into the flask, thus displacing the wine, which escapes in a thin red column. As this column nears the surface, it will spread out, thus resembling a cloud of fiery smoke as seen issuing from a volcano.
Care must be taken to shake the water, in order that the streak of color may represent in as realistic a manner as possible the reddish smoke of a volcano disturbed by the wind.
Fig. 8.—The eruption of Vesuvius.
Fig. 9.—Vesuvius in eruption.