citric acid or 2-hydroxy-1,2,3-propanetricarboxylic acid, HO₂CCH₂C(OH)(CO₂H)CH₂CO₂H, an organic carboxylic acid containing three carboxyl groups carboxyl group (kärbŏk`sĭl)
..... Click the link for more information. ; it is a solid at room temperature, melts at 153°C;, and decomposes at higher temperatures. It is responsible for the tart taste of various fruits in which it occurs, e.g., lemons, limes, oranges, pineapples, and gooseberries. It can be extracted from the juice of citrus fruits by adding calcium oxide (lime) to form calcium citrate, an insoluble precipitate that can be collected by filtration; the citric acid can be recovered from its calcium salt by adding sulfuric acid. It is obtained also by fermentation of glucose with the aid of the mold Aspergillus niger and can be obtained synthetically from acetone or glycerol. Citric acid is used in soft drinks and in laxatives and cathartics. Its salts, the citrates, have many uses, e.g., ferric ammonium citrate is used in making blueprint blueprint, white-on-blue photographic print, commonly of a working drawing used during building or manufacturing. The plan is first drawn to scale on a special paper or tracing cloth through which light can penetrate.
..... Click the link for more information. paper. Sour salt, used in cooking, is citric acid.

citric acid

Colourless, crystalline organic compound (C₆H₈O₇), one of the carboxylic acids. It is present in almost all plants (especially citrus fruits) and in many animal tissues and fluids. It is one of a series of compounds involved in the physiological oxidation (see oxidation-reduction) of fats, proteins, and carbohydrates to carbon dioxide and water (see tricarboxylic acid cycle). It has a characteristic sharply sour taste and is used in many foods, confections, and soft drinks. It is added to certain foods to improve their stability in metal containers. Industrially, it is used as a water conditioner, cleaning and polishing agent, and chemical intermediate.