Irregular Webcomic! #3488

Pure ethanol^[1] has a density of 0.789 grams per cubic centimetre, significantly less than water (at 1.000 g/cm³), so it will float on top of water. However, alcohol and water are highly miscible, so the layers will begin mixing at the boundary easily. In practical terms, what this means is that bartenders need to be very careful when making layered drinks that rely on the differences in density between different ingredients to produce the different layers.

[1] The sort of alcohol that people drink. More generically, "alcohol" refers to a family of organic compounds characterised by having a hydroxyl group (basically, an oxygen atom bound to a hydrogen atom) bound to a saturated carbon atom - i.e. a carbon atom which is atomically bound to four other things (one of them being the hydroxyl group, in the case of alcohols). The three "other things" that the carbon atom are bound to can vary, being either a single hydrogen atom, a chain of carbon atoms (themselves bound to other things), or various other combinations of atoms.

If all three "other things" bound to the carbon atom are hydrogen atoms, you have the simplest alcohol of all, methanol. It has just one carbon atom. Methanol is highly poisonous to humans, as the body metabolises it to formic acid^[2], which directly attacks the nervous system.

If two of the other things are hydrogen atoms, but the third is a carbon atom, itself attached to three hydrogen atoms, then you have ethanol. This is the second simplest alcohol, with two carbon atoms in total, and the sort usually meant when people say "alcohol", as it's the sort in all alcoholic drinks. It has an intoxicating effect on humans, and excess consumption can cause damage to many organs, but it is a popular component of many recreational drinks.

Moving up to three carbon atoms, there are two possible arrangements. The three carbon atoms will be in a chain, and the hydroxyl group can hang off an end one, giving propanol, or the middle one, giving isopropyl alcohol.

From there, things get more and more complicated and the possibilities explode as you add more carbon atoms, as they are no longer restricted to a single chain - instead there can be branches and loops and all sorts of things. Some of the more complex alcohols that you might be familiar with include glycerol (also called glycerine), xylitol (used as an artificial sweetener), menthol (the "minty" compound found in mint), and geraniol (the primary component of rose oil and many other essential oils, having a floral aroma, and used in many fruit flavourings). Despite technically being alcohols, these more complex compounds typically do not have any of the intoxicating effects of simple alcohols. Which is fortunate, really, or else we might get drunk on peppermint and rosehip teas.

[2] Formic acid is so named because it is produced as a defence mechanism in the bodies of many species of ants, and the Latin word for ant is formica. Some ants can even spray formic acid at attackers, which is a good deterrent as it is highly irritating and damaging to other animals. This is also the reason for the name of the Dungeons & Dragons monster race known as the formians.