A chemical substance usually corrosive to common metals (iron, aluminum, zinc). Acids are generally divided into two classes:

a. strong mineral or inorganic acids such as sulfamic, sulfuric, phosphoric, hydrochloric or nitric.
b. weak organic or natural acids such as acetic (vinegar), citric (citric fruit juices), oxalic and fatty acids (oleic, palmitic, stearic, etc.).