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# Is your gold ring really pure gold?

### You will need:

• 1 gold ring.
• 1 'cheap' metal ring that looks like gold
• 2 glasses of water, filled to the brim.
• Good scales or a beam balance.
• Permission to use someone's ring!

### Instructions

1. You are doing 2 separate calculations, so record your results for ring experiment 1 and 2 separately.

2. Weigh both rings.. write each mass down next to the letter A in each separate calculation.

3. Weigh the full glasses of water (it should be about to spill)
... write each mass down next to the letter B in each calculation.

4. Tie the cotton thread around each ring and slowly dip the ring into the water.

5. Let the water spill over the glass.

6. Take the ring out of the water. Re-weigh the glass... write the mass down next to the letter C.

7. For each experiment perform the calculation .... (B - C) / A = Specific gravity of the ring.

8. Are there any sources of error?
Eg. It's easier to measure greater volumes of displaced water. Why not try comparing iron vs rock?

9. If the 'cheap' ring is real gold, it's specific gravity should be the same as for the real gold ring. Of course, this experiment would be much easier to measure with a larger gold piece!

Is this ring pure gold?

Be Amazing!
How to teach science, the way primary kids love

#### Why Does This Happen?

Specific gravity is the ratio of an objects mass in a given volume, compared to water.
Gold is a very heavy metal, with it's specific gravity being about 19.3... more than twice Lead!

There is a story that the Greek philosopher Archimedes who once used the displacement of water to work out if the King's crown was made of real gold... he found out that it was partly fake!

How?
He compared the king's gold crown against another gold crown with the same weight.
He found that the king's crown displaced more water than the other crown.

Why?
The king's crown had some silver in it, making it less dense.
So for the king's crown to weigh the same as a real gold crown it's volume had to be bigger.
i.e. the king's gold crown had a specific gravity lower than the real gold crown.

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