The transition metal nickel is used in the hydrogenation of
vegetable oils to make margarines and soft-spreads.
Hydrogenation means adding hydrogen to a substance.

Liquid vegetable oils that are unsaturated will react with hydrogen
at about 60 °C in the presence of a nickel catalyst.
This is an example of an addition reaction where hydrogen
adds across the double bond leaving only single bonds.
The picture below shows hydrogenation of a double bond.

Hydrogenation raises the melting point above room temperature
and makes the liquid oil become solid in a process called hardening.
The solid product is used as a margarine or spread.

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