How can you tell that a 1 kg bar of gold has not been poured out and filled with a worthless metal?

Jean Louis, Since 2009, trader, buyer, seller of scrap and recycled gold

That is basic physics that you have already been learning in the school. To determine if gold that you have in front of you, is really gold, provided you have the access to that gold, and you have opportunity to do the experiment, then I am suggesting you the following:

PROCEDURE WITH THE SCALE AND MEASURING GOLD IN WATER (SPECIFIC GRAVITY):

Equipment:

1) Use the scale that is very precise, preferred with 0.001 digital precision and at least 0.001 deviation from precision. In case you don’t find such scale, you can find 0.01 scale. Scale of 0.1 precision is absolutely not workable for this experiment. You do not need expensive scales that are priced US $2,000 for this same experiment.

2) Find a bowl that may fit onto the scale, and which you may fill with the water.

3) Find smaller container that may float in that water, like a small boat, which you may use to float the 1 kilogram gold inside. If container is plastic or some small bucket of 2 inches diameter, it will be good enough.

Procedure:

1) Measure the gold on the scale, obtain the value, it should be 1 kilogram or 1000 gram precisely. Good companies may give you 1000.5 grams in the gold bar of 1 kilogram, because gold is worn out through the time, and they add little bit to it. You need to calculate it precisely what you get, as the scale will give you the true result. You will obtain the Weight in Air be measuring the weight of gold on the scale.

2) Now put the bowl on the scale, fill it with the water and put the small container or other floating container in the water. Reset the scale to zero (TARE). Put the gold inside of that container, so that container floats in the water together with the gold. Measure the Weight in Water.

The expected result of the weight in water, provided and under condition that gold measured was exactly 1000 grams, and depending of its purity, if the purity is claimed to be 99.99% then the weight in water will be 948.185 grams.

The formula is Purity is equal to division of Weight in Air divided by the difference between the Weight in Air and Weight in Water. Or P = Weight in Air / ( Weight in Air - Weight in Water)

Monday 2017-02-20 (GMT+3) 12:33:45 - Specific Gravity Estimate

Weight in air: 1000.000

Weight in water: 948.185

Specific gravity: 19.299 grams per cubic centimeter

Gold purity: 1.0000 or 99.9971%

PROCEDURE WITH THE GRADUATED CYLINDER:

When you cannot measure it with water, but you can still use the scale, there is the procedure with the graduated cylinder.

Equipment:

Graduated cylinder, big enough and precise enough for the quantity of gold you have to measure.
Scale of precision, minimally 0.01 and without deviations.

Procedure:

Put water in the cylinder, and see that you have for example 100 milliliters
Put the gold in the cylinder, and see how much water you have displaced with the gold.
Put the gold on the scale and see what exact weight you get.
It is expected that you displace 51.813 grams of gold if gold is pure. There may be small differences, but you should rather use formulas to see if it is correct.
The formula is that the displacement in cubic centimeters multiplied with the specific gravity of gold 19.3 multiplied by the purity of gold such as .99 should give you the weight of gold on the scale. If it does not, it may not be gold.

PROCEDURE WHEN YOU DO NOT HAVE THE ACCESS TO THE SCALE OR OTHER LABORATORY INSTRUMENTS:

Often you wish to make the visual check, to make sure that gold purity is right. This procedure is not accurate, however, it may help with the gross differences of gold and other metals.

Equipment required:

Ruler, as you wish to measure all three dimensions of the gold bar. Because the gold bar itself is of uneven dimensions and has deviations, you can just measure it “around”. See here: First Steps for Purchase of Gold from Africa
You need to know the expected purity, if expected purity is 99.95% pure gold, you know that specific gravity should be 19.29 grams per cubic centimeter.
You need to know the weight of gold, if it is 1 kilogram of gold, you would make sure on the scale it is 1 kilogram.
At this point you would calculate the 3 dimension of the gold, for example 1 centimeter thickness X width of 3 centimeter X length of 17.28 centimeter results with 51.84 cubic centimeters multiplied by the expected specific gravity of 19.29 and the result is 999.99 grams, which indicates good gold. However, if the result is in general too many cubic centimeters, like 55 cubic centimeters, and often 80–100 cubic centimeters in case of fake gold, you will simply immediately know it is fake.

The only known metals that may be used to make fake gold is tungsten, coated with the gold, as it could be possible to create same specific gravity as the gold. Such professionally made fake gold with the gold coat and tungsten inside is not to be easily spotted or found. To verify such, you would need to use more precise instruments, that may look inside of the gold, maybe the XRF machine.

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