Saltpetre testing, 1580.

GERMANY - JUNE 10: Woodcut showing a man testing saltpetre (potassium nitrate) which is used to make gunpowder and to preserve meat. Illustration from �Beschreibung aller furnemisten mineralischen Ertzt vnnd Bergtwercks arten� (�Description of the Principle Mineral Ores and Methods of Mining�) by Lazarus Ercker (d 1594) published in Frankfurt-am-Main in 1580. In 1554 Ercker was appointed assayer at Dresden and later became a control tester of coins. This book is a mine of information concerning sixteenth century metallurgy and assaying. It can be regarded as the first manual of analytical and metallurgical chemistry. (Photo by SSPL/Getty Images)