Page:The American Cyclopædia (1879) Volume III.djvu/533

 CABLE 527 gether to make the cable. The twist is re- versed at each successive operation ; that is, the yarn is formed by twisting the fibres from right to left, the yarns are twisted together from left to right, &c. It is customary to des- ignate the size of a hempen cable by the length of its circumference, and that of a chain cable by the diameter of the rod of which the links are made. The largest usual size of cable is 24 inches circumference ; it weighs 1 cwt. per fathom, is made of 3,000 threads, is equal in strength to a chain 2^ inches in diameter, and is tested to carry safely 80 tons. Hemp in its nat- ural state is stronger than when wet or tarred ; nevertheless, it is advantageous to tar the cord- age which is to be used at sea, as tar protects it against water, which would weaken and ul- timately rot it. It is obvious that the process of tarring after the cable is made is imperfect, and simply better than nothing, as the tar does not reach the core ; the true way is to tar the yarns of which the ropes are made. As early as 1634 a patent was obtained by Philip White, an English blacksmith, for mooring ships with chains. In 1804 John Slater, a sur- geon in the English navy, patented a chain ca- ble, but want of capital prevented him from demonstrating by experiments the value of his invention. In the year 1811 Oapt. Brown, of the Penelope, 400 tons burden, made a voyage of four months to the West Indies, using a chain cable with twisted links. During the following years several vessels were saved by their iron cables, and thenceforward the change from hemp to iron proceeded uninterruptedly, till at the present time it would be difficult to find a ship without a chain cable on board. The form of links adopted by Oapt. Brown was most imperfect ; several other shapes were suc- cessively tried, till the best form was found and patented in England by Brunton. The general shape of Brunton's link is that of an ellipse (see fig. 1). The inside curve, at each extremity of its long axis, is of the same curva- ture as the rods used to make the chain. In this manner there is just room enough for the next link, and no more. Across the link in the direction of the small axis is a cast-iron stay enlarged at its extremity, having a groove in each end to embrace a portion of the link. At certain intervals along the chain are placed swivels, which together with the studs pre- vent the cable from getting into kinks and be- coming unmanageable. If an obstacle is op- posed to the side of the chain, the link or links acted upon may assume two different positions : the link may rest against the obstacle by its side, the axis of the stay being perpendicular to the face of the obstacle, in which position the link is strongest, as all its parts brace each other to prevent the bending of any; or the link may rest flat against the obstacle, in which position it is very weak ; but this cannot hap- 137 VOL. m. 34 pen if the obstacle is large, as in such case the next links would rest first against it by their sides, and if the obstacle is small, it is pressed between the sides or the back bone of the two next links, which close upon it and crush it to pieces. The links wear out much faster by their friction against each other than by any other cause. Experience has taught that the ends where the friction is greatest should be of rod iron of a larger diameter than that of the sides ; the rods are therefore manufactured with swellings at the places which are to form the ends. Several simple machines are used to manufacture chain cables. The successive operations are as follows: 1, heating the round bars of iron red-hot ; 2, cutting them of the re- quired length, but with opposite bevels (a, fig. 2) ; 3, bending the rods around an elliptic man- drel. One end is placed against the side of a vertical mandrel, and held there by a vice at- tached to the last, and a lever provided with a projecting pin extending outside the rod is made to describe an ellipse, carrying the hot rod around the mandrel ; this lever does not turn around a pin in the centre of the mandrel, but is attached to two slides, which are forced to move in grooves occupying the position of the two axes of the mandrel ; thus the pin of the lever describes an ellipse parallel to the pe- riphery of the mandrel. 4. The new link (J, fig. 2) is hooked to the last preceding link of the chain in process of making, and welded at a small forge. 5. While it is still hot, the cast- iron stay is introduced, and the link placed in a press, which compresses the two sides close upon the stay, at the same time that it makes these sides straighter ; during this last opera- tion an auxiliary straight rod is placed inside the end of the link, where the next link is to come, to prevent its closing. There are some- times circumstances in which it is necessary to sever or slip (as it is called) a cable, or to shorten or lengthen it ; this is done by means of a bolt and shackle substituted for a link every 15 fathoms, the portion of the cable be- tween the shackles being called a length or "shot." The shackle is represented in fig. 3, in which a is the bolt, secured in its place by the pin 5, which is again held in its place by having its head in a conical chamber filled with lead. One of the links FIG. 3.