Man's physical universe

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ELECTRON TRANSFER 595

railroad cars, for electric industrial trucks and tractors, for lighthouses,

for propelling small boats, for store delivery trucks, for mine locomotives,

for electric cap lamps for miners' lights, and many other uses that

are characteristic of modern industrial civilization.

In 1899 E. W. Junger invented the cadmium-nickel battery in Sweden.

This battery has been used industrially in Europe for about ten

years. It is quite similar to the nickel-iron battery in construction

and discharge characteristics.

Displacement Reactions Are Special Examples of Oxidation and

Reduction.

When oxygen combines with any substance, the process is

called oxidation,

and when oxygen is removed from a compound, the process is

called reduction. Thus the rusting of iron is oxidation because this

process, as already mentioned, involves the combining of iron with

oxygen to form iron oxide ; oxygen is an example of an oxidizing agent.

On the other hand, when iron ore is treated with coke in a blast furnace,

the process is reduction because in this case the iron oxide is reduced to

iron; carbon is an example of a reducing agent. The simplest example

of oxidation and reduction is the burning of hydrogen in air to form

water

2H2 + O2 —>- 2HiO

hydrogen oxygen water

In this case the hydrogen is said to be oxidized because oxygen is added

to it to form water. On the other hand, oxygen is said to be reduced

because hydrogen is added to it to form water.

Organic compounds may be oxidized in steps; for example, the following

compounds represent progressive stages in the oxidation of

methane

CH4 —>- CH3OH —>- HCHO —>- HCOOH —>- CO2

methane methyl alcohol formaldehyde formic acid carbon

dioxide

CH4 >- CH4O >- CH2O >- CH2O2 >- CO2

oxygen added hydrogen oxygen hydrogen

removed added removed

In this reaction and many other reactions it is apparent that oxidation

may be the result of either an addition of oxygen or a removal of

hydrogen. Reduction would then be the removal of oxygen or the addition

of hydrogen. Thus the terms oxidation and reduction are extended

to include reactions in which hydrogen is added or removed.

Oxidation and reduction may also be interpreted in terms of valence

changes. Inasmuch as uncombined elements represent no combining

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