Re: how to get measurable data

Hi Bill,

Thanks for your question. I think your idea of measuring the increase in rust is a good one. Rust is basically hydrated iron oxide, so if you use pure iron, it should increase in weight as iron plus oxygen is heavier than just iron.

There are a few things to think about in an experiment like this. First, you will need quite a sensitive balance to weigh the iron, as the increase in weight will be quite low-probably only milligrams or tens of milligrams. Second, you will need a way to ensure that the sample without bacteria is really without bacteria! You might try boiling the water in which you place the iron, but remember that this will remove dissolved oxygen from the water and oxygen is needed for rust to form. The oxygen will diffuse back in from the air after boiling though. Third, remember statistics. It's probably best to have lots of small samples, then you can take an average and compare plus/minus bacteria. You'll also need to be sure that you are measuring all of the rust-some of it might fall off the iron and into the solution.

These are just a few ideas for you. I'm sure that as you think carefully about your experiment, you will think of more things that need to be considered. It's up to you to decide how important these other factors might be! If you think hard, I'm sure you will think of other ways to measure the rate of rust formation too.

Best of luck with your experiment,
Neil Saunders