Specific Gravity Test
A Specific Gravity Test is used to calculate the amount of gold contained in a gold nugget that contains a mixture of gold and other materials. For the sake of this example we are weighing a piece of gold in quartz.
You need two pieces of information to do the calculation. You need the weight of the specimen in air and you need the weight of the specimen when it is suspended in water. Weighing the specimen in air is easy, just put the specimen on the scale and write down the weight (dry weight). Weighing the specimen in water is a little more complex and you will need a few things to do it:
- Electronic or Digital Scale
To set up for weighing the specimen in water, first place the 36" long piece of wood on a table and hang about 8" of the wood over the edge of the table. Put something of weight on the other end of the piece of wood to hold in firmly in place.
Then place the scale on the part of the wood that is hanging over the edge of the table. Tie a piece of string about ½" back from one end of the 7.5" piece of wood, then thread the string through the key ring and tie the other loose end of the string about ½" back from the other end of the 7.5" piece of wood. Leave approximately 24" of string hanging loose between the two places where it is tied onto the wood.
Tie a piece of string to one end of a metal picture hanger or piece of bent wire.
Place a container of water on the floor below the scale.
Now turn on your scale. Place the stick on the center of the scale with the string hanging down. Hook the picture hanger or bent wire onto the key ring so the end of the string hangs down into the container of water. Let the string that is attached to the picture hanger soak up water until it is saturated.
Lift up the stick slightly off the scale and turn on the scale. Set the stick back down on the scale and press "Tare" to zero out the scale. Tie your specimen to the string hanging from the picture hanger and re-hang the picture hanger on the key ring. Make sure the specimen is totally submerged in the water and that neither the specimen or the string is touching the sides or the bottom of the water container.
Note the weight of the specimen (wet weight).
Now you have the dry weight and the wet weight of the specimen. Use the following calculation to calculate the amount of gold in your specimen.
- Subtract the wet weight from the dry weight and note the difference (D).
Below is an example using the formula above:
Specimen dry weight: 35.8 Grams