Calcium hydroxide
Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca(OH). It is a colorless crystal or white powder and is obtained when calcium oxide (called "lime" or "quicklime") is mixed, or slaked with water. It has many names including hydrated lime, caustic lime, builders' lime, slack lime, cal, or pickling lime. Calcium hydroxide is used in many applications, including food preparation, where it has been identified as E number E526. Limewater is the common name for a saturated solution of calcium hydroxide.
Oxidase test
The oxidase test is a test used in microbiology to determine if a bacterium produces certain cytochrome c oxidases. It uses disks impregnated with a reagent such as "N,N,N′,N′"-tetramethyl-"p"-phenylenediamine (TMPD) or "N,N"-dimethyl-"p"-phenylenediamine (DMPD), which is also a redox indicator. The reagent is a dark-blue to maroon color when oxidized, and colorless when reduced. Oxidase-positive bacteria possess cytochrome oxidase or indophenol oxidase (an iron-containing
hemoprotein). These both catalyze the transport of electrons from donor compounds (NADH) to
electron acceptors (usually oxygen).
The test reagent, TMPD dihydrochloride acts as an artificial electron donor for the enzyme oxidase. The oxidized reagent forms the colored compound indophenol blue.
The cytochrome system is usually only present in aerobic organisms that are capable of using oxygen as the terminal electron acceptor. The end-product of this metabolism is either water or hydrogen peroxide (broken down by catalase).