On 27 November 1873 the "Antofagasta Nitrate & Railway Company" signed a contract with the Bolivian government in which it would have authorized to extract saltpeter duty-free for 25 years. In February 1878, The Bolivian Congress and a National Constituent Assembly found the contract incomplete because it had not been ratified by congress as required by the Bolivian Constitution of 1871. Subsequently, the congress would approve the contract only if the company would pay a 10 cents tax per quintal of mineral extracted.