G. Mahin
THE MICROSCOPIC STRUCTURE OF METALS
1. Malleabilized casting; temper carbon in ferrite (enlarged 50 times)
2. Type metal; lead-antimony alloy in matrix of lead (enlarged 100
times)
3. Gray cast iron; carbon as graphite (enlarged 500 times)
4. Steel composed of cementite (white) and pearlite (black) (enlarged 50
times)]
Another way of protecting iron ware from rusting is to rust it. This is
a sort of prophylactic method like that adopted by modern medicine where
inoculation with a mild culture prevents a serious attack of the
disease. The action of air and water on iron forms a series of compounds
and mixtures of them. Those that contain least oxygen are hard, black
and magnetic like iron itself. Those that have most oxygen are red and
yellow powders. By putting on a tight coating of the black oxide we can
prevent or hinder the oxidation from going on into the pulverulent
stage. This is done in several ways. In the Bower-Barff process the
articles to be treated are put into a closed retort and a current of
superheated steam passed through for twenty minutes followed by a
current of producer gas (carbon monoxide), to reduce any higher oxides
that may have been formed.
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