Two friends are testing a design for a barbecue that floats on water. They notice that the barbecue sits lower in the water after it has been loaded with charcoal, due to the charcoal's mass. After the charcoal has all been burned, leaving only ash, the barbecue is lower in the water than when it was empty, but not as low as when it was loaded with charcoal. They conclude that the ash must have less mass than the charcoal and wonder where the extra mass has gone.
Explain the reaction that occurred in the barbecue. Describe the evidence that could be observed that would support or refute the law of conservation of mass.