ctions from the cables at Fairmount Park, Philadelphia, and at Niagara
Falls show that long use has not materially changed the structure. The
_Journal_ says: "It is a serious question, and one which time only can
completely answer, whether steel structures will prove as uniformly and
permanently reliable as wrought iron has proved itself to be. In other
words, whether the fibrous texture of wrought iron can be equaled in this
respect by the granulated texture of steel or ingot iron. In this
connection it is interesting to note that the fibrous texture referred to
is imparted to wrought iron by the presence in it of a small proportion
of slag from the puddling furnace, and that this can be secured in the
Bessemer converter also if desired. The so-called _Klein-Bessemerei,_
carried on at Avesta in Sweden for several years past, produces an
exclusively soft, fibrous iron by the simple device of pouring slag and
iron together into the ingot mould. This requires however a very small
charge (usually not more than half a ton), and a direct pouring from the
converter, without the intervention of a ladle, which would chill the
slag."

The effect of the introduction of slag would seem to be to retrace the
steps usually taken in producing steel, viz., to separate the iron from
its impurities, and then to add definite quantities of carbon and such
other ingredients as are found to neutralize the effects of certain
impurities not fully removed.

The most intelligent engineers, after ascertaining by exhaustive physical
tests what they need, present their "requirements" to the iron and steel
makers, whose practical experience and science guide them in the
protracted metallurgical experiments necessary to find the exact process
required. The engineer verifies the product by further tests, and by
practical use may find that his "requirement" needs further
modifications. As a result of all this care, some degree of certainty is
secured as to what the material may be expected to do.

No doubt the chemical composition of the slag used at Avesta was known
and met some equally well known want in the iron, and thus the result
arrived at was one which had been definitely and intelligently sought.

An important factor in selecting material for the cables of suspension
bridges is its _true elastic limit_. By this term we mean the percentage
of the total strength of the material which it can exert continuously
without losing its resilience, i.