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The Mechanic's Workshop Handybook by Paul H. Hasluck, 1895

   

Preface

The metals constitute about five-sixths of the known elementary bodies. They are distinguished by a peculiar luster, by their opacity, and by their power of conducting heat and electricity.

With few exceptions, metals possess considerable specific gravity, hardness and cohesion, and require a high degree of heat to liquefy them. One, mercury, is liquid at ordinary temperatures; and a very few, as sodium and potassium, are lighter than water, which they decompose with such energy as to produce combustion.

The properties which characterize metals, and by which distinctive qualities are shown, are tabulated on page 2. The various figures are collected from a multitude of sources, the best attainable.

The authorities often differ somewhat widely, but this can be accounted for from the fact that few metals are obtained pure. The peculiarities in the same metals obtained from different localities are often unnoticed, and account for the variable statements of the cohesion in the tables compiled by those who have investigated the properties of metals and published the results.

Iron and steel, though strictly alloys, are usually spoken of by the mechanic as metals; and none are so valuable as these.

A few words on their origin and production will be read with interest by all mechanicians who desire to learn the operations involved in the manufacture of the materials which they are constantly using, not only for the construction of every description of mechanism, but also in the form of tools and appliances by which rough metal is wrought to shape.

 

Pure metallic iron has but little commercial use, and in this state is comparatively unknown ; it is when combined with carbon, sometimes modified by other elements, that pure iron becomes the iron of commerce, and is known as malleable iron, steel, and cast iron, as the proportion of carbon is increased.

Pure iron may be obtained by placing a mixture of magnetic oxide of iron and fragments of commercial iron, such as filings, in a crucible, and heating to a white heat - the crucible being meanwhile covered.

The pure iron thus obtained is softer than ordinary soft malleable iron; it is very tenacious and ductile, and its malleability is not affected by heating and suddenly cooling. Though it does not retain magnetism, its magnetic power is very high.

The more free from impurities, the higher will be the electrical conductivity of the metal and the greater the heat required for its fusion - admixture of carbon reducing the point at which pure iron melts, which is but little below the melting-point of platinum.

Though unaffected by dry air at ordinary temperatures, iron, when in a state of very fine division, is liable to spontaneous combustion.


 
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