« ForrigeFortsett »
inch of the sides should be made very thin, for bulwarks, and a ledge should be left just below for the deck to rest upon. This is made of a thin piece of pine, cut to the proper shape. Some boats require a false keel to make them float properly. This is of lead, shaped in a mold made of three laths nailed together to form a narrow channel, which with the dimensions given above must be an inch and a half in depth and three-eighths of an inch thick. The channel is stopped at the ends with wood, so as to be exactly the length of the boat's keel. Six or eight nails are driven into the bottom of the mold, so that they will project from the lead keel when molded, and enable it to be fastened to the boat. The bottom of the mold should therefore be thin, so that it can easily be pulled away
from the nails. The mold is now filled with melted lead, which is taken out when it has hardened, and may then be shaped with a plane, as if it were of wood. The lower end of the false keel, at the bow, should be rounded.
Before nailing down the deck, holes must be bored in it for the mast and rudder. The hole for the mast in a boat of the size described should be half an inch in diameter, and eight inches from the bow. A similar hole must be bored part way through the bottom of the hull to fix the lower end. The mast should be half an inch in diameter, and is best made of pine. It is made in two parts, the lower of which must measure, between the deck and the topmast, just three times the greatest width of the vessel, in this case fifteen inches. Adding four inches for the part below the deck, and two and a half for the mast-head, the total length becomes twenty-one and a half inches. The mast must be rounded with a plane, or by whittling, and the mast-head (the upper two and a half inches) must be whittled down to half its diameter, to join it to the topmast. A quarter of an inch at the top must be made still smaller. The topmast is fastened to
luff of the mainsail is sewed to the rings on the mast, and its upper edge is fastened to the gaff by cords. The lower edge is fastened to the boom only at the corners.
BOAT RACING. See Rowing.
BOBECHON, a game played by any number of persons with the toy shown in the illustration, which is made as follows: ' Make a tight roll of flannel or cloth, about three inches high and half an inch in diameter, and secure it by winding thread around it. Sew this to the center of a circular piece of fur or very thick cloth, an inch and a half in diameter, so that it will stand upright on this circle as a base. This toy is called the Bobechon. It
is placed upright in the center of an ordinary dinner plate, and a small coin is laid on the top of the flannel roll. The object is to remove both BoWchon and coin from the plate with a flexible rod or cane, like the end of a fishing rod. The coin need not keep its place on the flannel roll, so long as both it and the Bobechon fall clear of the plate. The players take turns, and he who succeeds most times, in a number previously agreed upon, is the winner.
The task seems an easy one, but it is really very difficult, as will be seen on trial. If the rod be applied near the base, the Bobechon with its coin may be slid along till it reaches the sloping edge of the plate, and if it
is then given a push, the coin will fall off into the plate. If, on the other hand, the rod be now applied to the upper part of the toy, it will tip over, throwing the coin outside, but itself falling on the plate. The proper way is to press the end of the rod on the farther edge of the plate so that it curves downwards, as shown in the second figure, the lower part of the curve touching the flannel roll just where it is sewed to the circle. The Bobechon is then pushed slowly along till it reaches the sloping edge, when by a peculiar twist of the rod, learned only by practice, both it and the coin can be thrown without the plate. The toy is shown in the upper part of the cut; the way of removing it in the lower.
Bobechon is a French game, and is said to be much used by sharpers in that country, who, being practiced, can always succeed, while their victims, who think the task very easy, always fail.
BOILING, Experiments in. 1. The boiling of water is described in C. C. T. in the article Steam. It is best observed by filling a test-tube (see Chemical Experiments) a quarter full of cold water, and holding the lower end in the flame of an alcohol lamp or Bunsen burner. Little bubbles will first form and stick to the sides of the tube. By and by these will disappear, and other little bubbles, like white specks, will form in the lower part of the liquid, and rise toward the top, but will disappear before they get there. These rapidly increase in numbers and size and go higher and higher, till finally they burst from the top, when it is seen that they consist of steam. When they vanish before reaching the top a simmering or "singing" noise is heard. Afterward the noise is the bubbling sound of boiling. The first formed bubbles, which stick to the sides, are composed of air, which was dissolved in the water. The others are composed of steam, but as fast as they
get further away from the heat of the flame they condense back to water, making the sound of simmering. By and by the water gets so hot all the way through that they can rise out of the top.
2. Buy a small chemical thermometer, which is simply a thermometer without any tin case, so that it can be put into liquids to get their temperature. The scale is marked directly on the glass tube. One can be made by taking an ordinary thermometer, scratching the divisions of the scale on the tube with a diamond, or a sharp file, and then removing the bulb and tube from the case. Put the thermometer into water before it begins to boil, being careful that it does not touch the bottom or sides of the vessel. As the water gets hotter, the mercury will rise until it boils, when the thermometer will stand at about 212°, if it has a Fahrenheit scale, or at ioo° if it is Centigrade (See Thermometer, in C. C. T.). Chemical thermometers usually have the Centigrade scale, but if the one used has been made from an ordinary thermometer it will probably be Fahrenheit. This temperature is called the boiling point. If you now try to make the thermometer rise higher by continuing to hold it in the boiling water, you will find it-impossible. No matter how much the heat is increased, the mercury will not rise any more, but the water will simply boil away faster. The reason is, that as soon as the water begins to boil all the heat is used in turning it to steam and not in raising its temperature.
3. Boil some water for ten or fifteen minutes; let it cool and then heat it again with the thermometer in it. By keeping it very still, you will probably find that it can be raised several degrees above the boiling point, without causing it to boil. If some scraps or filings of metal he now cast into it the water will at once begin to boil, and the mercury will fall to the boiling point. The
reason is that water with air dissolved in it boils sooner than pure water, and by boiling it once the air is driven out, so that at the second heating it rises higher than 212°. But when scraps of metal are dropped in they carry air with them, and boiling begins.
4. Find the boiling point of water with various substances—for instance salt or sugar—dissolved in it. In all cases it is higher than the boiling point of pure water. The reason is that it takes some heat to separate the water from the salt or sugar when it is turning to steam.
5. Boil water in a glass flask, and while it is boiling cork the flask tightly, and remove it at once from the name. When it stops boiling pour cold water over the flask, and it will begin to boil again. This may be done several times. The same result will follow if the flask be plunged into cold water. The reason is that when a flask of boiling water is corked the space above the water is filled with steam, when this steam is turned to water by being cooled some of the pressure is removed from the surface of the water, which, accordingly, begins to boil again, since it is easier for the bubbles of steam to get out of the water,
6. Some time when you go up on a high mountain, take with you a chemical thermometer and an alcohol lamp, and find the boiling point of water there. It will be lower than 2120. This is because not so much air is pressing on the water on the summit as in the valley below. Sometimes the height of mountains is measured by finding the boiling point of water on their summits. On a mountain 6000 feet high, water boils at about 2000 Fahrenheit, in stead of 212".
7. Find the boiling points of other fluids than water. It will be found that some are higher and some are lower, and that it is impossible to boil some of them at all—oils for instance.