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The Spanish monetary system in the 18th and 19th centuries.
In the 18th century, it was basically the following:
Gold escudo. Its weight was 3,4 grams. It was worth 16 silver reales.
The Real de plata (made of silver). Its weight was 3,35 grams. It was worth 34 maravedíes.
Maravedí de vellón. It was made of an alloy of 50% copper and 50% silver. Its weight was 1,12 grams.
Obviously, there were multiples and fractions of these coins. For example, the doubloon (a two-escudo coin) or the piece of eight, "real de a ocho" (a eight-real coin).
The coins were worth according to their weight and the metal they were made of.
In the 19th century, coins continue to exist together with the paper money that started to be issued by this time. At the beginning of the century the usual currency unit is the real de vellón. 5 reales de vellon were exchanged by two of silver (2,5 x 1). One real de vellón was worth 16 maravedíes, and one piece of eight ("real de a ocho" o "peso duro") was worth 20 reales de vellon (or 320 maravedíes).
In 1868 the government introduced a new organization of the Spanish monetary system by decreet, based on the decimal metric system. Thus, by 1969 the Spanish monetary system was arranged as follows:
Peseta silver: 5 grams. It was worth 100 copper cents.
Cent: 1 gram of copper.
And based on this basic equivalence, the different coins (multiples of cent and divisors and multiples of peseta):
coin of 5 pesetas: 25 grams of silver. Its weight was similar to the real de a ocho or peso duro, and for that reason the five-peseta coin started to be known as "duro".
50 cents coin: 2,5 grams of silver (half a peseta).
100 pesetas coin: 32,25 grams of gold (the most valuable one in the new monetary system)
The new monetary system overlapped with the old existing system. Thus, a peseta was unofficially worth four reales de vellon (or 64 maravedíes).
The memory of the old coins was in everybody's mind and, therefore, the 25-cent coin was commonly known as "real" until the middle of the 20th century. And in many places of the rural Spain people continued to express quantities in duros (reales de a ocho) and not in pesetas nearly until the disappearance of the peseta.
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