Amount of substance in use in chemical engineering in the United States is the pound-mole, having the symbol lb-mol. One pound-mole is . When quoting an amount of substance, it is necessary to specify the entity involved, unless there is no risk of ambiguity. One mole of chlorine could refer either to chlorine atoms, as in 58.44 g of sodium chloride, or to chlorine molecules, as in 22.711 liters of chlorine gas at STP. The simplest way to avoid ambiguity is to replace the term "substance" by the name of the entity or to quote the empirical formula. For example: Amount of substance
Composition of matter may be produced by mechanical or chemical operations, and its result may be a compound substance resolvable into its constituent elements by mechanical processes, or a new substance which can be destroyed only by chemical analysis. A newly synthesized chemical compound or molecule may be patented as a composition of matter. Patents have been allowed on transitory products, such as short-lived chemical intermediates. In "Diamond v. Chakrabarty", the United States Supreme Court held that a genetically-altered living microorganism was patent-eligible subject matter. The "Chakrabarty" Court said that "we must determine whether respondent's micro-organism constitutes a 'manufacture' or 'composition of matter'