Chain
A chain consists of a series of iron links welded one within the other. The very critical and particular uses made of chains in a foundry and elsewhere should suggest the propriety of devoting more attention to their careful preservation. The fewer their number the greater probability of a right selection and legitimate use. The tensile strength of good chain iron is about 41,000 lbs., but in order to maintain that high state of efficiency chains must not be subjected to the barbarous system of hammering one sees sometimes in order to release a few kinks. Another vile method is to take heavy lifts when one or more of the chains have been purposely shortened by twisting. A few fractured chains, and mayhap a life lost, would be of infinitely greater cost than a handy set of swivel-chains, by which means an even lift can be obtained as precisely as may be desired. Instead of being thrown down on the damp floor, chains should always be hung up and carefully protected from rust. An occasional heating to a dull red in a charcoal fire, followed by a long protracted cooling while shielded from the atmosphere, is of great service, and tends to restore the quality of ductility. Hard knocks, overstraining, lifting with twists, moisture, sudden changes of temperature are all favorable to crystallization, and hence fatal to the well-being of chains (see SWIVEL-CHAIN). For strength of chains and ropes, see ROPES.