CABLE 



56$ 



The two slanting-cut ends are made to approach each other; heated up to a high tem- 

 perature, the expert workman, by a peculiar blow, detaches the scales of oxide, and 



320 



instantly presses both surfaces together ; two men then by repeated blows effect the 

 welding junction, and thus the link is formed. 



The shape of the link, after due consideration of the advantages of particular 

 patterns, seems to resolve itself into the decided preference for a link of parallel sides, 

 unchanged in form from the round of the iron employed, while the ends may be 

 reduced, somewhat flattened, and increased in breadth. The links thus in contact 

 have the pressure sustained by a greater breadth of surface, and compression can 

 scarcely alter the form. 



The length of a good link may be of round iron 6 diameters in length of link A A 

 (fig, 323), and from B to B 37 to 4 diameters of the iron rod employed, and 17 to 2 

 diameters inside. 



The stub, staple, or cross-bit is of cast iron, and is placed across ; its use is to pre- 

 vent the sides from collapsing by extension of the chain ; in fact, to keep up a suc- 

 cession of joints, and prevent the chain from becoming a rigid bar of metal. 



The stud or cross-piece shown at c is of cast iron, with dates and marks upon the 

 surface. It is cast with a hollow bearing, having a curve to receive the round iron of 

 the link ; its shoulders, or feathering, enables the workman to insert it readily, and a 

 few blows upon the yielding iron give the requisite grip; and all proper service only 

 tends more firmly to keep it in position, very different indeed from the form Jig. 312 

 which would positively injure the link. 



In all cases this cross-piece has been of cast iron. Wrought iron was tried, but found 

 to be too expensive. Malleable iron has been patented, but it is a question whether 

 it can supersede common foundry iron, from the cheapness and facility of the latter. 



The cables are proved and tested by regulated strains brought to bear continuously 

 up to the proof strain, and then even up to the ultimate destruction of some of the 

 links, if the final strength or opposition to resistance is required to be known. The 

 proof of cable should be 600 Ibs. for each circle of iron |th of an inch in diameter. 



The chain is attached at one end horizontally to a hydraulic press, the other end to 

 the enormous heat of a bent iron lever, whose power is multiplied by second and third 

 iron levers, all working upon knife-edges, and to the last lever a scale pan is attached ; 

 1 Ib. being here placed is equivalent to a strain of 2,240 Ibs. upon the bar or chain 

 that is being tested. This machine of Brown, Lenox, and Co., Millwall, is more 

 powerful than that used in the Koyal dockyard. The proving machine, invented by 



Captain Brown in 1813, was a great step towards the production of confidence. 



In practice, length after length is tried up to the proof required ; when the tension 

 is to be exerted to the uttermost, a few links are taken : in such experiments it is usual 

 for one link alone to give way, and the strength of the cable itself is uninjured by 

 . .testing to find its ultimate strength. 



