Oxy-Acetylene Welding and Cutting | Page 4

makes the
cheapest steel.
[Illustration: Figure 3.--An Open Hearth Furnace]
Open hearth steel is made by placing the molten iron in a receptacle
while currents of air pass over it, this air having itself been highly
heated by just passing over white hot brick (Figure. 3). Open hearth
steel is considered more uniform and reliable than Bessemer, and is
used for springs, bar steel, tool steel, steel plates, etc.
Aluminum is one of the commonest industrial metals. It is used for gear
cases, engine crank cases, covers, fittings, and wherever lightness and
moderate strength are desirable.
Aluminum is about one-third the weight of iron and about the same
weight as glass and porcelain; it is a good electrical conductor (about
one-half as good as copper); is fairly strong itself and gives great
strength to other metals when alloyed with them. One of the greatest
advantages of aluminum is that it will not rust or corrode under
ordinary conditions. The granular formation of aluminum makes its
strength very unreliable and it is too soft to resist wear.
Copper is one of the most important metals used in the trades, and the

best commercial conductor of electricity, being exceeded in this respect
only by silver, which is but slightly better. Copper is very malleable
and ductile when cold, and in this state may be easily worked under the
hammer. Working in this way makes the copper stronger and harder,
but less ductile. Copper is not affected by air, but acids cause the
formation of a green deposit called verdigris.
Copper is one of the best conductors of heat, as well as electricity,
being used for kettles, boilers, stills and wherever this quality is
desirable. Copper is also used in alloys with other metals, forming an
important part of brass, bronze, german silver, bell metal and gun metal.
It is about one-eighth heavier than steel and has a tensile strength of
about 25,000 to 50,000 pounds per square inch.
_Lead._--The peculiar properties of lead, and especially its quality of
showing but little action or chemical change in the presence of other
elements, makes it valuable under certain conditions of use. Its
principal use is in pipes for water and gas, coverings for roofs and
linings for vats and tanks. It is also used to coat sheet iron for similar
uses and as an important part of ordinary solder.
Lead is the softest and weakest of all the commercial metals, being very
pliable and inelastic. It should be remembered that lead and all its
compounds are poisonous when received into the system. Lead is more
than one-third heavier than steel, has a tensile strength of only about
2,000 pounds per square inch, and is only about one-tenth as good a
conductor of electricity as copper.
_Zinc._--This is a bluish-white metal of crystalline form. It is brittle at
ordinary temperatures and becomes malleable at about 250 to 300
degrees Fahrenheit, but beyond this point becomes even more brittle
than at ordinary temperatures. Zinc is practically unaffected by air or
moisture through becoming covered with one of its own compounds
which immediately resists further action. Zinc melts at low
temperatures, and when heated beyond the melting point gives off very
poisonous fumes.
The principal use of zinc is as an alloy with other metals to form brass,

bronze, german silver and bearing metals. It is also used to cover the
surface of steel and iron plates, the plates being then called galvanized.
Zinc weighs slightly less than steel, has a tensile strength of 5,000
pounds per square inch, and is not quite half as good as copper in
conducting electricity.
Tin resembles silver in color and luster. Tin is ductile and malleable
and slightly crystalline in form, almost as heavy as steel, and has a
tensile strength of 4,500 pounds per square inch.
The principal use of tin is for protective platings on household utensils
and in wrappings of tin-foil. Tin forms an important part of many
alloys such as babbitt, Britannia metal, bronze, gun metal and bearing
metals.
Nickel is important in mechanics because of its combinations with other
metals as alloys. Pure nickel is grayish-white, malleable, ductile and
tenacious. It weighs almost as much as steel and, next to manganese, is
the hardest of metals. Nickel is one of the three magnetic metals, the
others being iron and cobalt. The commonest alloy containing nickel is
german silver, although one of its most important alloys is found in
nickel steel. Nickel is about ten per cent heavier than steel, and has a
tensile strength of 90,000 pounds per square inch.
_Platinum._--This metal is valuable for two reasons: it is not affected
by the air or moisture or any ordinary acid or salt, and in addition to
this property it melts only at the highest temperatures. It is