How much energy in a crisp?

This afternoon 8S were calculating the energy in various crisps. 

First weigh your crisp 

Add water to the boiling tube (known volume)

Take the temperature of the water

Burn the crisp under the tube of water

Measure the rise in temperature. 

Do the maths to find the calories then joules then joules per gram. 

The salt & vinegar sticks have the most energy per gram (but the worst taste according to this commentator)