Tonic water

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Tonic water; at right under ultraviolet light, quinine, even in negligible quantity, makes the liquid fluorescent.

Tonic water (or Indian tonic water) is a carbonated soft drink flavoured with quinine, which gives it a distinctively bitter taste.

The drink has garnered its name from the medicinal effects of this bitter flavouring. The quinine was added to the drink as a prophylactic against malaria, since it was originally intended for consumption in tropical areas of South Asia and Africa where that disease is endemic. The mixed drink gin and tonic originated in British colonial India when the British population would mix their medicinal quinine tonic with gin to make it more palatable.

Medicinal tonic water originally contained only carbonated water and a large amount of quinine. However, most tonic water today contains a less significant amount of quinine, and is thus used mostly for its flavour. It is consequently less bitter, and is also usually sweetened. Sweet tonic water may contain corn syrup or sugar, making it less bitter. Some manufacturers also produce diet tonic water which may contain artificial sweeteners. Traditional style tonic water with little more than quinine and carbonated water is less common but may be preferred by those who desire the bitter taste. In the United States, the Food and Drug Administration limits the quinine content in tonic water to 83 ppm^[1] (83 mg per litre if calculated by mass), which is 0.25% to 0.50% of the concentration used in therapeutic tonic. Still, it is often recommended as a relief for cramps. Dr. Jim Mitterando states that "Quinine is one of the few treatments shown to help reduce nocturnal cramps. Quinine is found in low concentrations in tonic water (one-tenth of prescription dose). Drinking eight to 16 ounces at night can be a simple remedy."^[2]

Tonic water is often used as a drink mixer for cocktails, especially those made with gin or vodka (for example, a gin and tonic). Tonic water with lemon or lime flavour added is known as bitter lemon or bitter lime, respectively. Such soft drinks are more popular in Europe than in the United States.

Tonic water will fluoresce under ultraviolet light, owing to the presence of quinine. In fact, the sensitivity of quinine to ultraviolet light (UV) is such that it will fluoresce in direct sunlight.