Chinese discoveries and inventions

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Across
  1. 3. an explosive consisting of a powdered mixture of saltpeter, sulfur, and charcoal.
  2. 4. individual characters made of wood or metal that can be arranged to create a printing job and then be used over again
Down
  1. 1. to make quantities of an item by using standardized designs and dividing steps of production among the workers
  2. 2. to protect against disease by transmitting a disease-causing agent to a person, stimulating the body’s defensive reactions