chemical compound containing the nitrate (NO₃) radical. Nitrates are salts or esters of nitric acid, HNO₃, formed by replacing the hydrogen with a metal (e.g., sodium or potassium) or a radical (e.g., ammonium or ethyl). Some important inorganic nitrates are potassium nitrate (KNO₃), sodium nitrate (NaNO₃), silver nitrate (AgNO₃), and ammonium nitrate (NH₄NO₃). Calcium nitrate is used in fertilizers; barium and strontium nitrates are used to color fireworks and signal flares; bismuth nitrate is used in making pharmaceuticals. Nearly all metal nitrates are readily soluble in water; for this reason they are often used when a water soluble salt of a metal is needed. The presence of nitrates in the soil is of great importance, since it is from these compounds that plants obtain the nitrogen necessary for their growth. Nitrogen-fixing bacteria are important in keeping the soil supplied with nitrates. Organic nitrates are esters formed by reaction of nitric acid with the hydroxyl (−OH) group in an alcohol. Nitroglycerin is the trinitrate of glycerol; guncotton is a nitrate of cellulose. In chemical analysis, a test for nitrates involves the addition of a solution of ferrous sulfate to the substance to be tested, followed by the addition (without mixing) of a few drops of concentrated sulfuric acid; the presence of a nitrate is indicated by the formation of a brown ring—of Fe(NO)⁺² complex ion—where the sulfuric acid contacts the test mixture.

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