Wednesday, 7 October 2009

Rocks fizz

Everyone knows what happens if you leave a dirty 2p coin in a glass of cola overnight. In the morning there is a clean and shiny 1p piece in the glass and a mouse has drunk the juice with a straw. Or might have. I've never stayed up to watch.

I often leave rough rocks in cola overnight to clean them up. Yesterday there wasn't any cheap cola, so I got some Irn-Bru instead and dumped a load of rubies in a bowl of it. I don't know if it worked as well. It's hard to tell. I can't remember if it's the sugar or the acid or a combination. Does anyone know?


Andrew said...

It's the phosphoric acid in Coke and Irn Bru that cleans the rock. The acid (0.05% of the pop, so half a cc, or a few drops, in a litre bottle) drops the pH to about 2.5 (close to the acidity of lemon juice), giving the pop its tang. The phosphoric acid cleans away oxides by reacting with the surface to form phosphates which are insoluble and collect as silt in the pop bath. The sugar is there to disguise the sourness: tangy and sweet equals pop.

Matt Dale said...

There you go. Science.