this way is a tangent to the inner surface of all the strips, and presents in section a circumference inscribed within a polygon. In the second method, No. 2, thin strips of cork, glued to cloth, by a kind of India-rubber cement, are wrapped spirally round the pipe. The third method consists in employing two hollowed half-cylinders (No. 3) exactly fitting the surface of the pipe. These cylinders, which can be
Fig. 9.—Pipes Covered with Non-conducting Cork. No. 1, bands laid side by side, No. 2, band of cork pasted on cloth and rolled in spiral shape. No. 3, artificial cork.
made of any length, are composed of cork-powder mixed with starch, and are covered with strips of cotton cloth rolled spirally over them, which can be painted with coal-tar or any other suitable paint. Either of the methods will effect a great economy of fuel.
Cork, being also a very poor conductor of sound, is employed successfully in finishing the interior of telephone-cells. It may be put over the doors of consulting-offices; floors made of it are very acceptable in cure-houses and sick-chambers; and it has been adopted in some stringed musical instruments to prevent waste of sound.
Cork has superior buoyant qualities, which are sufficient not only to keep it on the surface, but also to enable it to support tolerably heavy bodies. It is thus employed as a float for night-lamps, for bath-thermometers, and for fish-lines. It is excellently adapted to use in swimming-jackets and life-saving apparatus, in the construction of which inventors have exercised their genius industriously. Many ships carry cork mattresses, which have proved of great service in cases of shipwreck. Life-saving buoys are composed of pieces of cork, are usually in the form of rings, and are furnished with knotted pieces of rope, permitting them to be easily taken hold of. They are also usually covered with painted sail-cloth, to insure their preservation.
