No, all liquids are not wet. Even water is not always wet. It depends on who or what is the “wet-ee.”
Make this inquiry of a linguist, however, and you’ll be told that it is a foolish question. The word wet is so intimately related to the word water in the roots of our language that wet has always meant “coated with water.” Water is “wet” by definition, and the opposite of wet is dry, which means “without water.”
But language is a fickle facsimile of fact. The reason for the linguistic intimacy between water and wetness is simply that no other liquids were known by our primitive ancestors when they needed a word to describe the way you look when you come out of a river. After all, water is not only the most abundant liquid on Earth, it is the most abundant chemical compound of any kind. Even today, most people would be severely challenged to name two or three other liquids. Things like blood and milk don’t count, of course, because their liquid parts are still water.
Innumerable other liquids do exist, however. In principle, any solid material can be melted into a liquid by heating it, and any gas can be condensed into a liquid by cooling it. It just happens that water exists in its liquid form over most of the temperature range at which life also exists. That’s no coincidence, of course; life presumably began in the water, and liquid water is still essential to all forms of life.
Why, though, is this ubiquitous liquid wet? Why does it stick to us when we emerge from the river? Our primitive ancestors would have loved this explanation: It sticks to us because it likes us.
Putting it a little more scientifically, water molecules will adhere to those substances whose molecules hold some form of attraction to them. If there were no attraction between the molecules in a drop of water and the molecules at the surface of our skins, the water would just roll off. Our job, then, is to find out what those attractive forces may be.
At several other places in this book, we talk about the fact that water molecules are polar, and attract each other like tiny magnets. Water molecules are attracted to each other also by hydrogen bonding. If an alien substance comes along whose molecules are also polar or are also subject to hydrogen bonding, the water molecules will be attracted to them as if to their own. In other words, water will wet that substance.
Most proteins and carbohydrates, including the proteins in our skin and the cellulose in wood, paper, cotton, and other vegetable matter, are made of molecules with the right characteristics so that water molecules want to snuggle up to them. They will therefore be wetted by water. Other substances, however, such as oily or waxy materials, do not have either of the two necessary molecular characteristics to be wet by water.
Dip a candle into a glass of water and you will see that water isn’t necessarily wet. Water is sometimes “wet” and sometimes not, depending on what material we are tempting it to stick to.
What about other liquids? Are they always “wet”? We might wonder about such liquids as grain alcohol, isopropyl rubbing alcohol, gasoline, benzene, olive oil, and even liquid metals such as mercury. Like water, these liquids will wet materials to whose molecules they are attracted by a mutual attractive force. As far as human skin is concerned, the first five can find enough in common with “skin molecules adhere to them, and these liquids will wet you. But the atoms of metals have nothing in common with your molecules” and won’t wet them at all.
If you ever get a chance to dip your finger into a pool of mercury you will note that it comes out as dry as that candle that you dipped in water. (Don’t linger over the mercury. Its vapor is toxic.) But dip a piece of clean copper or brass into the mercury and it will wet it eagerly because metal atoms all have similar attractive forces and tend to stick together If you have ever done any soldering, you know that the melted (metal) solder wets the metal parts that you are trying to join together.
Actually, wetness is a relative term. Some liquids are wetter than others; they will spread out and flow more readily over the surface that they are wetting.
Surprisingly, water isn’t a very good wetter, as liquids go. Alcohol, for example is much wetter than water. That’s because water’s molecules adhere to each other so strongly that they tend to ignore other nearby molecules and won’t adhere to them very readily even if they do have the right kind of molecular attractions.
Sprinkle a few drops of water onto your umbrella and they will roll off, unless you force them to wet the material by rubbing them in with your finger. Sprinkle some alcohol onto the umbrella, though, and it will soak right in.
There will make it a better wetter. Soap is the most common one..
All liquids aren’t wet, and even water is sometimes dry.