Seemingly complex scientific devices are often quite simple to create right out of the home, and a hygrometer is no exception. Created to measure the relative humidity of a room, hygrometers are fairly useful for anyone with a love of climatic science, not to mention budding scientists who like to see how things are made.
To make a home made hygrometer, it’s important, first, to know what a hygrometer measures. ‘Relative’ humidity sounds like a tricky phrase, but the concept is fairly simple: it simply means that the hygrometer is measuring the amount of water being carried in the air by comparing it to the normal state of air, that being air that is not humid. Humidity is not, as commonly thought, a mixture of air and water.
That being said, all the scientific theory isn’t that necessary to create a home made hygrometer. Here’s how it’s done, in a few simple steps.
1.) First, you’ll need to get a few human hairs, around eight or nine inches in length. Get them the same length by plucking them from the same person and from the same spot. Painful, yes, but pain means nothing in the pursuit of science.
2.) You’ll also need a base into which you can build your hygrometer. Depending on how you want to proceed, this can range from a piece of folded cardboard to an emptied milk carton. For the purpose of this experiment, use a milk carton.
3.) A hair hygrometer operates on the principle that hair, when particularly moist, is longer. When dried, it contracts. The humidity in the air will be absorbed into the hair and affect its length. Therefore, you need to create a measuring stick that employs both gravity and the hair’s length to measure the humidity in the air.
There are numerous ways to do this, with or without a milk carton. In this case, you’re going to measure inside the milk carton. Cut out one side so you can see the inside of the carton. Make sure the top, bottom and opposite side remain intact.
4.) Cut a small slit in one end of the carton, on the top. Make sure not to cut all the way to the edges of the carton and upset the stability of your hygrometer. This slit needs to be fairly thin, so use a knife rather than scissors.
5.) Attach your hairs to the top of the milk carton. Anything that will fix them in place and keep them rigid will do. Try and keep them at roughly the same length. Run them down into the carton so the tips are dangling an inch or so below the slit.
6.) Affix a penny to the ends of the hairs. A bit of super glue should do the trick, as will strong tape. Don’t worry, the hairs should be able to hold the penny just fine.
7.) You now need to establish two points: one in which the hairs are completely dry, and one in which they’re saturated with humidity. Place your hygrometer in the bathroom while you’re having a bath or shower, making sure to keep the door closed. Once you’re done, check the length of the hairs and mark off the spot on the side of the carton. Then use a hair dryer to dry the hairs and again note the size difference by making a mark on the carton.
8.) Make more marks between the two extremes, then try your hygrometer out in the still partially humid bathroom by leaving it there for half an hour or so. Though you can’t make numerical conclusions at the amount of humidity based on what you see, you will, at least, be able to roughly guess at the relative humidity by the length of the hairs.
Looking for another way to create a home made hygrometer? There are plenty of methods for doing so, some more or less complex than the one above. Here’s another involving a milk carton, and another that uses an arrow to note the humidity. There’s even one here that uses a silk thread rather than hair. Try them all out and see which works best for you. Have fun!
