The quality of the steel depends upon the presence and the relative
proportions of these ingredients, and a variation of a tenth of 1 per
cent. in certain of them will make a different metal out of it. For
instance, the steel becomes stronger and tougher as the proportion of
nicked is increased up to about 15 per cent. Raising the percentage to
25 we get an alloy that does not rust or corrode and is non-magnetic,
although both its component metals, iron and nickel, are by themselves
attracted by the magnet. With 36 per cent. nickel and 5 per cent.
manganese we get the alloy known as "invar," because it expands and
contracts very little with changes of temperature. A bar of the best
form of invar will expand less than one-millionth part of its length for
a rise of one degree Centigrade at ordinary atmospheric temperature. For
this reason it is used in watches and measuring instruments. The alloy
of iron with 46 per cent. nickel is called "platinite" because its rate
of expansion and contraction is the same as platinum and glass, and so
it can be used to replace the platinum wire passing through the glass of
an electric light bulb.
Pages:
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421