Foam in the sterlising solution

 

I poured hot water on the sterilising powder and got a lovely foam. I've never stopped to consider foam. I realised that the fizzing sound was the popping of many tiny bubbles and that the foam is when a lot of very tiny bubbles form together as the carbon dioxide gas is released from the chemical reaction. https://en.wikipedia.org/wiki/Foam has been a good starting point for thinking about what goes on. Work is clearly done blowing a bubble. I will have to start by thinking about the process of forming an individual bubble.