Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Methylene blue is a heterocyclic aromatic chemical compound with molecular formula: C16H18N3SCl. It has many uses in a range of different fields, such as biology and chemistry. At room temperature it appears as a solid, odorless, dark green powder, that yields a blue solution when dissolved in water. The hydrated form has 3 molecules of water per molecule of MB. Methylene blue should not be confused with methyl blue, another histology stain, new methylene blue, nor with the methyl violets often used as pH indicators. The terms "methylthioninium chloride" and "methylene blue" are sometimes used interchangeably.