What Is The Liquid In A Spirit Level? (And Why Is It Green?)

There are tools in every tool chest that get used so often they can legitimately be labeled as essential. But there are many other tools tucked away in most kits whose usefulness may not always be acknowledged, at least not until you really, really need them. Some might argue that the spirit level should be ranked high on that latter list because, well, they are often the first and last line between you and hanging things or building things that are not precisely straight. 

If you're unfamiliar with the trusty spirit level, it's that rectangular device in your tool kit that has three liquid filled tubes inset with little lines drawn around them. You are supposed to use a spirit level whenever you need to ensure the project you're working on is aligned perfectly straight. They are most often used when hanging pictures on a wall, though carpenters also frequently use them to ensure whatever they might be building is not crooked.

The general idea is that a fixture is dead straight when the bubble set within those tubes is settled precisely in the middle of the little corresponding lines. And yes, as simplistic in design as they are, spirit levels are almost never wrong. As for the liquid inside those tubes, you might be surprised to learn it is not water, but alcohol, hence the "spirit" level name. That liquid was selected due, in part, to its low freezing point, but also because alcohol possesses a clarity that water typically does not.    

Just FYI — If you're interested in adding a spirit level to your arsenal of tools, you'll find options a-plenty on Amazon these days, with prices ranging from a few bucks to more than $100. But amid all those options you will not find many spirit levels that utilize a liquid that is colored anything but green. The reason for the color is pretty simple, as the "spirit" within those little tubes can, theoretically, best be seen in any hue other than clear.

More specifically, a yellowish-green hue has essentially been designated as the de facto color for use in most spirit levels, as studies have shown that particular color range is the most visible to the human eye. While the color within a spirit level's alcohol-filled vials is largely the same, there are dramatic disparities in the size of the levels themselves, so you want to be sure that you purchase a size that best suits your needs. There are, however, also spirit level combo kits that package several different sizes together if you're looking to cover all your bases.

You can also find levels that do not utilize liquids to function. Those include digital models, as well as some that use magnets and still others like Ryobi's AirGrip model that utilize lasers. Heck, these days you can even turn your iPhone into a level if need be. But whatever style of level you select, make sure you keep it handy — even if it spends considerable time at the bottom of your tool box, it will one day prove itself essential.