[Hocks88]

Hey all,

I'm currently working on solving a problem for a friend of mine but I'm coming up a bit short. He needs to find a way of telling time through some sort of accurate, precise and repeatable reaction or process (WITHOUT using a timer or stopwatch). I'm unable to go into massive detail about the project but generally speaking it's to time how long a particular substance should stay submerged in boiling water for, i.e. Sample A needs to be in the water for 30 seconds, sample B needs to be in the water for 90 seconds, sample C needs to be in the water for 120 seconds and so on and so forth...

My initial ideas included a Galileo thermometer, where the temperature of the water will cause a bulb to sink, but then I realised that all of the bulbs would sink at the same time so long as the required temperature is reached. Do Galileo thermometer bulbs exist whereby they all sink at the same temperature, but take different amounts of time before they start to do so? Changing the density/heat conductivity etc?

I'm open to any and all ideas, no matter how obscure.

Hope everyone's good, and thanks in advance for any input! It will be greatly appreciated!

[Corribus]

How about an iodine clock?

http://en.wikipedia.org/wiki/Iodine_clock_reaction