How to Seal a Barometer

The barometers that most people are familiar with use a bi-metal strip to indicate the barometric pressure of the air, but it's possible to make a functional barometer out of items that you have at home as well, By cutting the small end off of a balloon and stretching it over the mouth of a jar, you can create the main component of a barometer. Glue a plastic straw onto the balloon so that it is attached to the center of the balloon and stretches out over the side. As the barometric pressure of the air changes, it will press down or pull up on the balloon and this will cause the straw to angle up or down, indicating whether the pressure is high (by angling up) or low (by angling down). In order for your homemade barometer to work correctly though, it's important that it has an airtight seal on it. The reason that the barometer will work is that the pressure of the air in the jar will remain constant while the outside air pressure will change. If there's even a small hole in the balloon or along the edge, then the pressure won't be constant and the barometer won't work. Here is how to properly seal the barometer and ensure that no air will be leaking.

Difficulty: Easy

Instructions

Things You'll Need:

• Homemade barometer (or the necessary items to make one)
• Rubber band
• String or other long fastener
• Rubber cement

1. When you cut the tip off of the balloon, make sure that you use a single cut and that it is even. This will not only let you have an even edge to seal but will also help prevent the balloon from developing small tears as the pressure changes where more than one cut would have met.

2. Once you have stretched the balloon over the neck of the jar and have a decently tight fit, use the rubber band or string in order to make the seal even tighter. Make sure that you get it as tight as you can, being careful not to accidentally cause any holes in the balloon. If you are using a large twist tie or other fastener with wire in it, be careful as you twist it tight.

3. After you have secured the rubber band, string or other fastener, carefully pull the balloon rubber beneath it just enough that you can brush some rubber cement onto the jar. Do this a little bit at a time, being careful not to dislodge The fastener in the process. Continue until you've placed rubber cement all the way around the jar. Press the balloon rubber into the rubber cement slightly, then brush along the outside of the rubber where it meets the jar in order to give even more of a seal. This second application of rubber cement should overlap from the rubber onto the jar.

4. Let the rubber cement dry while you glue the straw onto the balloon. When the rubber cement has fully dried, you will have a completely airtight seal on your homemade barometer.

Tips & Warnings

• Different jar shapes and sizes as well as different types of rubber balloons can produce slightly different results when measuring barometric pressure; you might want to try several different combinations until you find the ones that work best