The Quinto Real or the Quinto del rey, the "King's fifth", was a 20% tax

Tax

To tax is to impose a financial charge or other levy upon a taxpayer by a state or the functional equivalent of a state such that failure to pay is punishable by law. Taxes are also imposed by many subnational entities...

 established in 1504 that Spain

Spain

Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

 levied on the mining

Mining

Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...

 of precious metals. The tax was a major source of revenue for the Spanish monarchy

Spanish monarchy

The Monarchy of Spain, constitutionally referred to as The Crown and commonly referred to as the Spanish monarchy or Hispanic Monarchy, is a constitutional institution and an historic office of Spain...

. In 1723 the tax was reduced to 10%.

Rather than levy the tax on the basis of the amount of silver

Silver

Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

 or gold

Gold

Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...

 produced, the government tracked the amount of mercury

Mercury (element)

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 used. Mercury was essential for the refinement of silver and gold in the patio process

Patio process

The patio process was a process used to extract silver from ore. The process was invented by Bartolomé de Medina in Pachuca, New Spain , in 1554. The patio process was the first process to use mercury amalgamation to recover silver from ore. It replaced smelting as the primary method of extracting...

 (see also amalgam

Amalgam (chemistry)

An amalgam is a substance formed by the reaction of mercury with another metal. Almost all metals can form amalgams with mercury, notable exceptions being iron and platinum. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore.The...

ation). The Spanish government had a monopoly

Monopoly

A monopoly exists when a specific person or enterprise is the only supplier of a particular commodity...

 of mercury production, through its mines at Almadén

Almadén

Almadén, Spain, is a town and municipality in the province of Ciudad Real, within the autonomous community of Castile-La Mancha. The town is located at 4° 49' W and 38° 46' N and is 589 meters above sea level. Almadén is approximately 200 km south of Madrid in the Sierra Morena...

 in Spain and at Huancavelica

Huancavelica

Huancavelica is a city in Peru. It is the capital of the Huancavelica region and has a population of approximately 40,000. Indigenous peoples represent a major percentage of the population. It has an approximate altitude of 3,600 meters; the climate is cold and dry between the months of February...

 in Peru

Peru

Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....

. In 1648 the Viceroy

Viceroy

A viceroy is a royal official who runs a country, colony, or province in the name of and as representative of the monarch. The term derives from the Latin prefix vice-, meaning "in the place of" and the French word roi, meaning king. A viceroy's province or larger territory is called a viceroyalty...

 of Peru declared that Potosí

Potosí

Potosí is a city and the capital of the department of Potosí in Bolivia. It is one of the highest cities in the world by elevation at a nominal . and it was the location of the Spanish colonial mint, now the National Mint of Bolivia...

 and Huancavelica were "the two pillars that support this kingdom and that of Spain." Moreover, the viceroy thought that Spain could, if necessary, dispense with the silver from Potosí, but it could not dispense with the mercury from Huancavelica.

Popular culture

• The King's Fifth
  The King's Fifth
  The King's Fifth is a children's historical novel by Scott O'Dell that was the inspiration for the cartoon TV series The Mysterious Cities of Gold...
  
  is a novel by Scott O'Dell
  Scott O'Dell
  Scott O'Dell was an American children's author who wrote 26 novels for young people, along with three novels for adults and four nonfiction books...
  
   in which the protagonist
  Protagonist
  A protagonist is the main character of a literary, theatrical, cinematic, or musical narrative, around whom the events of the narrative's plot revolve and with whom the audience is intended to most identify...
  
  is accused of stealing the King's Fifth. Sangano