Czapek medium

Friedrich Czapek's original recipe is as follows:

• 1000 g distilled water
• 30 g cane sugar – energy source and sole source of carbon
• 1 g dipotassium phosphate – buffering agent
• 0.5 g magnesium sulfate – source of cations
• 0.5 g potassium chloride – source of essential ions
• 0.01 g iron sulfate – source of cations

Arthur Wayland Dox added 2 g of sodium nitrate in his version, to provide a sole source of nitrogen that is inorganic. This makes the medium a selective growth medium as only organisms that can use inorganic nitrogen can grow. Czapek and Dox did not add agar but many recipes add 15 g to make a solid medium.