Plumbers, painters and electricians work weekends, en liquide, for cash under the table.

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In the end, operations in Germany, North America and Britain were sold to Air Liquide, to make it the biggest industrial-gas producer in Europe.

ECONOMIST: Face value

Companies like long-term player Ballard Power Systems, Linde, UTC Power and Air Liquide (which has built 50 big hydrogen generators) have made this a big business.

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