# What’s wrong with my cloud chamber setup?

For my setup, I am using a fish tank, lined with black felt and with one side open for viewing and a slit on a side for the light. I have a pretty bright multi led flashlight. I am using dry ice blocks inside a stryofoam container that is separated from the chamber by a metal cooking sheet. I am using 91% IPA, and taped the bottom of the fish tank to the tray to seal it. I am using some hand warmers to heat the top of the tank.

All that happens (after 4 attempts) is that the IPA begins condensing onto the sheet. I never see mist. I have tried to reposition the light, and have used other lights. It is dark in the room.

• Is IPA the alcohol of this demonstration? youtube.com/watch?v=xky3f1aSkB8 . Ale does not have enough alcohol – anna v Sep 13 '18 at 4:39
• Is IPA isopropyl alcohol? – PM 2Ring Sep 13 '18 at 11:03
• IPA = India Pale Ale in my vocabulary :) – mike stone Sep 13 '18 at 18:07

## 1 Answer

Try and make the black flat metal base which is sitting close to the dry ice (solid carbon dioxide) as horizontal as possible.
If the bottom plate is not approximately horizontal convection currents will be set up within the chamber which will ruin the experiment.

The felt soaked in isopropyl alcohol (IPA) is placed at the top of the chamber.
The sensitive layer in such a cloud chamber is very thin $(\sim \rm mm)$, near the bottom of the chamber $(\sim \rm cm)$ and dynamic in that the alcohol vapour from the top is cooling as it drops and the air becomes supersaturated with alcohol vapour in that sensitive layer.
Once condensed the droplets continue on a downward path so you have a continuous transport of alcohol from the top to the bottom of the chamber.

You will need to wait for several minutes for a stable thermal gradient to be set up within the chamber and also for droplets to form on any dust which is within the chamber.

Do not use a hand warmer as this will introduce unwanted convection currents in the chamber. I have seen a hot water bottle but initially try it without one.