Halifax’s famous fog is becoming more common with the weather warming up, and there is no better way to investigate it than making your own at home – in a bottle!
You will need a clear plastic bottle with a cap, some hot water and optionally, a match. A funnel may also help, but is not necessary. Your water need not be boiling but ensuring it’s hot enough to at least see steam rising from it will help you along. Of course, be very careful when working around hot things with kids – we recommend ongoing supervision.
Pour a small amount of hot water into your bottle: a few centimetres in the bottom is plenty, and don’t worry about the plastic becoming deformed, that’s normal. There are two ways to produce a cloud using this setup. You may be able to produce fog by simply capping the bottle and squeezing it as hard as you can. Alternatively, light and blow out a match, drop it quickly into the bottle and then put on your cap.
The bottle will get warm when full of hot water, but it should be safe to touch above the waterline.
Fog is essentially a cloud that we see at ground level, and these clouds are formed through two processes: evaporation and condensation. Water transitions most visibly from liquid to gas (water to steam) at 100°C, but this process of evaporation happens in small amounts all the time when water is relatively warm (even only as warm as lakes and rivers). This water vapour in the air will turn back to tiny droplets of liquid when the air pressure around it increases sharply, or when it is given a small particle to stick to – this can happen with particles as diverse as smoke, dust and pollution in the atmosphere or even the salty spray from the ocean (that’s our infamous “salt fog”). Squeezing your bottle increases the air pressure inside, and adding a smoking matchstick offers plenty of particles for water to stick to. Both create perfect environments for clouds (fog!) to form.
If fog and April showers chase you inside, bring the family down to Discovery Centre. Our most popular exhibit ever Grossology is only here until May 13!