Just working through the Betts Specific Gravity Test Greenhornet linked to in his post on “OLD LEAD PIECE"
At first I didn’t quite believe that it would work then afterwards just felt so dumb that I had been doing the SG test the hard way for all my prospecting life.
The difficulty I had with the method, was how could the weight of a bowl of water sitting on a set of scales increase just by dangling or holding something submerged in it. Even a ping pong ball for that matter, It just didn’t seem logical.
A quick trip to the kitchen, filled a small bowl with water, set it on some scales, stuck my finger in and lo and behold the weight increased even though I did not touch the bottom or sides of the bowl.
Googling this phenomenon, it seems that the explanation is that the scales are not measuring the weight of the water directly but the force caused by the pressure of the water exerted on the bottom of the container. Whenever something is put in the water which causes its level to be raised, additional hydrostatic pressure is created at the bottom and it is this increase in force that is transferred to the scales via the container walls.
So even if you stick a finger, ping pong ball or a gold speci in the water to increase the water level an increase in weight will be seen on the scales
Furthermore this increase in pressure will logically be proportional to the volume of water raised ie the volume of the object submerged.
So no more tricky and fiddly devices to suspend a specimen from a set of digital scales in the air while a cup of water is brought up from below.
Just my morning cup of coffee sitting on a set of scales, a thin bit of stiff wire to dangle my speci in it and I can have all the info I need to calculate the SG.
At first I didn’t quite believe that it would work then afterwards just felt so dumb that I had been doing the SG test the hard way for all my prospecting life.
The difficulty I had with the method, was how could the weight of a bowl of water sitting on a set of scales increase just by dangling or holding something submerged in it. Even a ping pong ball for that matter, It just didn’t seem logical.
A quick trip to the kitchen, filled a small bowl with water, set it on some scales, stuck my finger in and lo and behold the weight increased even though I did not touch the bottom or sides of the bowl.
Googling this phenomenon, it seems that the explanation is that the scales are not measuring the weight of the water directly but the force caused by the pressure of the water exerted on the bottom of the container. Whenever something is put in the water which causes its level to be raised, additional hydrostatic pressure is created at the bottom and it is this increase in force that is transferred to the scales via the container walls.
So even if you stick a finger, ping pong ball or a gold speci in the water to increase the water level an increase in weight will be seen on the scales
Furthermore this increase in pressure will logically be proportional to the volume of water raised ie the volume of the object submerged.
So no more tricky and fiddly devices to suspend a specimen from a set of digital scales in the air while a cup of water is brought up from below.
Just my morning cup of coffee sitting on a set of scales, a thin bit of stiff wire to dangle my speci in it and I can have all the info I need to calculate the SG.