LMU (Latin Monetary Union, 1865 to 1926)
History of the LMU on Wikipedia
Note: The mistake of the LMU was that its planners fixed the ratio of silver to gold. Market forces saw to it that the momentarily rarer metal disappeared from the market.
The right thing would have been to introduce gold francs and silver francs onto the market without fixing their relative prices. In that way the two money metals would have kept each other in check, as it were. When market participants value silver more highly, they exchange gold for silver, and vice versa.
The all-important liquidity would thereby also have been ensured. When gold and/or silver are simply hoarded, they can no longer help boost the economy as loan collateral.