Gallic acid reagent

The Gallic acid reagent is used as a simple spot-test to presumptively identify drug precursor chemicals. It is composed of a mixture of gallic acid and concentrated sulfuric acid.{{cite web | url=https://www.unodc.org/documents/scientific/SCITEC21_07fin.pdf | title=Colour Tests for Precursor Chemicals of Amphetamine-Type Substances | publisher=UNODC | date=December 2007 | accessdate=28 November 2015 | pages=38 }}

0.05 g of gallic acid is used for every 10 mls of sulfuric acid.Rapid Testing Methods of Drugs of Abuse. Manual for use by national law enforcement and narcotics laboratory personnel (ST/NAR/13/REV.1), United Nations, New York, 1994. The same ratio of gallic acid n-propyl ester in sulfuric acid can also be used.{{cite journal | url=http://www.dea.gov/pr/microgram-journals/2012/mj9-1_27-32.pdf | title=Color Tests for the Preliminary Identification of Methcathinone and Analogues of Methcathinone | author=Toole, Kaitlyn E | journal=Microgram | year=2012 | volume=9 | issue=1 | access-date=2015-12-11 | archive-date=2017-05-13 | archive-url=https://web.archive.org/web/20170513130316/https://www.dea.gov/pr/microgram-journals/2012/mj9-1_27-32.pdf | url-status=dead }}

Because of its short shelf life (changing to pale violet color) it is sometimes prepared by dissolving gallic acid into ethanol and adding the sulfuric acid at the time of testing from a separate bottle. In this case 100 mL ethanol is used and one drop of sulfuric acid is used per drop of gallic acid in ethanol.