What is rubbing alcohol?
Q: I would like to know what rubbing alcohol is and how it differs from alcohol in beer or wine.
HS, Boston
A: The word ''alcohol," used colloquially, usually means a rather specific chemical called ''ethyl alcohol" or ''ethanol." This is the alcohol that makes wine and beer ''alcoholic" beverages.
There are many chemicals known collectively as alcohols, and they are all characterized by some big molecular structure made of carbon and hydrogen atoms, with an oxygen-hydrogen atom pair stuck on somewhere.
In ethanol the ''big molecular structure made of carbon and hydrogen atoms" is made of two carbon atoms and five hydrogen atoms. In methanol, or ''wood alcohol," the structure is smaller, with just one carbon atom and three hydrogen atoms. Rubbing alcohol is usually mostly made of isopropyl alcohol, also called isopropanol, and the ''big molecular structure" this time is made of 3 carbon atoms arranged like the letter ''V" plus 7 hydrogen atoms.
If you noticed that the world ''isopropyl" looks like it might have something to do with propane, which you know from gas barbecues and propane torches, then well-spotted. Propane is made of three carbon atoms strung in a row with 8 hydrogen atoms attached. Poke an oxygen between a hydrogen and the carbon in the middle of the row and you get isopropanol.
Any of the alcohols we've been talking about will evaporate quickly carrying away heat with it, so they are useful to cool and soothe the skin. They are also all good at dissolving oils and greases and therefore good for cleaning all sorts of things. Isopropyl alcohol is also readily turned into acetone, which you probably know as nail polish remover.
Sometimes rubbing alcohol contains ethanol as well as isopropyl alcohol. When rubbing alcohol does contain significant amounts of ethanol, more poisonous and evil-tasting substances are added so that people won't drink it -- a process called ''denaturation." Often the poisonous additive is methanol, which, in addition to being toxic, can blind you if it doesn't kill you.
In other words, under no circumstances should you ever consider drinking any sort of rubbing alcohol!
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