Quinine
This is 100% pure food grade Quinine (quinine hydrochloride) is used as bittering agent for beverages such as Indian tonic water, grape tonic water, bitters and vermouth.
The American Food and Drug administration limits the dosage of Quinine in tonic water to 83 ppm (or 83mg per liter water).
A 20g pack will therefore make at least 240 Liters of Indian tonic water if used at the maximum dosage.
Read more on Tonic water on this Wikipedia link.
Read also more on quinine on this Wikipedia link.
WARNING: Quinine in its concentrated form poses several health risks including severe bleeding, kidney damage, irregular heartbeat and severe allergic reactions. Avoid skin contact with the powder, don't inhale the powder or use it in concentrated forms stronger than the maximum limit of 83 ppm.
With skin contact rinse the affected area under running water for at least 20 minutes. If a skin reaction develops, seek medical attention. On ingestion of high concentration Quinine, seek medical attention immediately.