title: History of patent law
context: The first Patent Act of the U.S. Congress was passed on April 10, 1790, titled "An Act to promote the progress of useful Arts."[19] The first patent was granted on July 31, 1790 to Samuel Hopkins  for a method of producing potash (potassium carbonate).
question: What was the first patented invention?
answers: potash (potassium carbonate)