Is it farther or further?
mercaptan mer·cap·tan (mər-kāp'tān')
Any of a class of organic compounds in which the oxygen of an alcohol has been replaced by sulfur and which have distinctive, often disagreeable, odors. Also called thiol.
any of a class of organic chemical compounds similar to the alcohols and phenols but containing a sulfur atom in place of the oxygen atom. Thiols are among the odorous principles in the scent of skunks and of freshly chopped onions; their presence in petroleum and natural gas is objectionable because they have disagreeable odours, interfere with catalysts used in refining processes, and produce sulfur dioxide upon combustion.