A term used variously to describe either a waxlike substance or a group of compounds. The former use pertains to the high-boiling residue obtained from certain petroleum crudes. It is recovered by freezing out on a cold drum and is purified by crystallization from methyl ethyl ketone. Paraffin wax is a mixture of 26- to 30-carbon alkane hydrocarbons; it melts at 52–57°C (126–135°F). Microcrystalline wax contains compounds of higher molecular weight and has a melting point as high as 90°C (194°F). The name paraffin is also used to designate a group of hydrocarbons—open-chain compounds of carbon and hydrogen with only single bonds, of the formula C_nH_{2n + 2,} where n is any integer. This usage is obsolete.