The invention of glass bottles necessarily brought with it the introduction of a new kind of plug, and a material for such a plug was found in the bark of the cork-tree, a species of oak. This bark possesses the capability of compression to a very great extent, and, being highly elastic, it expands as soon as the pressure is removed.
Thus, in bottling wine, the corks are always made much too large to go into the mouths of the bottles. They are first dipped in a cup containing the same wine, and are then compressed violently by a machine worked by a handle, and which, being practically a powerful pair of nut-crackers with a rounded gripe, must suit the shape of the cork. It is then taken out of the machine, and, before it has had time to expand, is rapidly fitted to the neck of the bottle, and driven home with a wooden mallet. Expansion then takes place, and the bottle is rendered air-tight, so that no damage is done to the wine.
If the whole of the wine were to be drunk when the cork was removed, this plan would be amply sufficient. But there are many cases where the bottle is opened, and only part of the wine consumed. To re-cork the bottle would be too troublesome, and to leave it uncorked would spoil the wine. So the Conical Stopper was invented, which fits the neck of any ordinary wine-bottle, according to the depth to which it is introduced, and, by a slight screwing movement, sufficient compression is obtained to render the bottle air-tight. One of these Conical Stoppers is shown in the illustration on [page 352]. Sometimes they are made of cork, and sometimes of india-rubber; but the principle is the same in either case.
Perhaps some of my readers may have seen the Self-fitting Candles, which require no paper to make them fit the candlestick. These are enlarged at the base, which is made in a conical form, and slightly grooved. The “Candle-fixers” that are so much in use at the present day are made exactly on the same principle, being hollow cones of paper, which take the place of the solid cone.
The Vent-peg of casks is another instance of the cone used as a stopper.
Another example is to be found in the Blow-guns and Arrows of tropical America. In some districts the base of the arrow is fitted with a conical appendage of light cotton, rather larger than the tube, but capable of compression, so that it exactly fits the tube when pressed into it. In other districts the cone is hollow, and made of some thin and elastic bark.
Some years ago one of our most eminent gun-makers hit upon the same idea while making improved missiles for the game of “Puff and Dart,” and very much surprised he was when I showed him the South American arrow, not only with the same hollow cone at the base, but having also spiral wings along the shaft, so as to give it a rotatory motion as it passed through the air. The hollow cones of his darts were made of india-rubber, but the shape of the two was identical.
If the reader will refer to the left-hand figure of the illustration, he will see a beautiful example of the Conical Stopper as existing in Nature.
This is the “Stopper,” as it is popularly called, and, scientifically, the “infundibuliform operculum.” I prefer the former term myself, as being less liable to misapprehension.
The Serpula lives in a shelly tube of its own construction, and has the power of protruding itself when it desires to obtain food, and of withdrawing itself within the tube when alarmed. This movement is performed so rapidly, that the eye can scarcely follow it, and the mechanism by which it is done has already been described when treating of War and Hunting.