CABLE 



563 



Btay ; two operations performed at one heating. Whenever the welding is finished, 

 while the iron is still red hot, the link is placed upright upon the stake, i. e., the 

 shorter axis vertical and the longer axis of the link horizontal ; then a workman 

 introduces the stay with a pair of tongs or pincers ; while another workman strikes 

 down upon it. This mechanical compression first of all joins perfectly the sides of 

 the link against the concave ends of the stay, and afterwards the retraction of the iron 

 on cooling increases still more this compression. If each link be made with the same 

 care, the cable must be sound throughout. It is not delivered for use, however, till it 

 be proved by the hydraulic press, at a draw-bench made on purpose, and examined 

 link by link, on the side of the machine, or on a bench erected for the purpose, to 

 detect any flaw the strain may have caused. 



The following Table of compared materials and strains is given as a matter of historical 

 eference. It is believed the dates of the experiments are 1815 and 1816 ; since then, 

 alterations in the make of iron, and the introduction of new fibres, as well as hemp, 

 render this Table of value, as the materials here employed were, no doubt, good 

 examples, and subjected to critical attention : 



Table of Iron Cables as substituted for Hemp, with ike Strains applied at that Date. 



It would be imprudent to put hemp cables to severer strains than those indicated in 

 the Lloyd's Table, drawn up from experiments ; but the iron cables of the above sizes 

 will support a double strain without breaking. They ought never, in common cases, 

 however, to be exposed to a greater stress. A cable destined for ships of a certain 

 tonnage should not be employed in those of greater burden. Thus treated, it may be 

 always trusted to do ite duty, and will last longer than the ship to which it belongs. 

 It has often been stated, that chain cables possess double the strength of the iron of 

 which they are made, owing to the forms of the links employed : this, however, is an 

 absurd error ; for, suppose the two sides of a link to be of inch-iron, yet a part of the 

 strength must be lost in the bending of the ends, for the straining force is at right 

 angles, at the ends, to what it is at the side, or would be exerted upon portions of straight 

 rods ; next, to make a link, the two ends have to be joined by welding, and wherever 

 this join is made, there is every chance for less union, and no possible means of getting 

 the fibre to be stronger than if they had never been separated ; strength really must 

 be lost by heating the iron and shaping the link. 



Mr. Lenox has found in practice, that an inch bolt will bear 21^ tons, while the 

 inch cable will break at 34 tons, and not at the double strength, or 43 tons, of two 

 lengths of straight iron. 



One of the most valuable qualities of iron cables is their resisting lateral as well as 

 longitudinal strains, as explained under figs. 311 and 313. 



Vessels furnished with chain cables have been saved by them from the most immi- 

 nent peril. The ' Henry,' sent out with army stores during the Peninsular war, was 

 caught on the northern coast of Spain in a furious storm. She ran for shelter into 

 the Bay of Biscay among the rocks, where she was exposed for three days to the hur- 

 ricane. She possessed fortunately 70-fathoms chain cables, which held good all the 

 time, but it was found afterwards to have had the links of its lower portion polished 

 bright by attrition against the rocky bottom. A hemp cable would have been speedily 

 worn to pieces in such a predicament. 



In the contracts for the Admiralty of chain cables for the British Navy, it is stipu- 

 lated that ' the iron shall have been manufactured in the best manner from pig iron 

 smelted from ironstone only, and selected of the best quality for the purpose, and shall 

 not have received in any process whatever, subsequent to the smelting, the admixture 

 of either cinders or oxides produced in the manufacture of iron, and shall also have 



o o2 



