Tutorial on how to do specific gravity

CaptHenway

The original link in this thread no longer works. See tutorial below.

TheBigB

<< <i>I have written a tutorial on how to perform a specific gravity test for silverstackers.com. It can be found here:

SG tutorial linky

This will become more and more important as the Chinese keep pumping out fake bullion ounces.

TD >>



I have one of the Ohaus electronics with a SG kit.

Do you have any special techniques for tying the knot and securing the coin? This part has always been a pain for me.

Timbuk3

Thanks for the links !!!
Very informative.

CaptHenway

<< <i>

<< <i>I have written a tutorial on how to perform a specific gravity test for silverstackers.com. It can be found here:

SG tutorial linky

This will become more and more important as the Chinese keep pumping out fake bullion ounces.

TD >>



I have one of the Ohaus electronics with a SG kit.

Do you have any special techniques for tying the knot and securing the coin? This part has always been a pain for me. >>



I never use string. Use wire.

TheBigB

<< <i>
I never use string. Use wire. >>



Thanks Capt.

Spooly

Thanks for the post.


Can we get a video?

CaptHenway

Not from me. Don't have anything to make one with.

Mesquite

I'm a little confused. Density is mass per unit volume (grams/milliliter). Specific gravity is density of material divided by the density of water (1 gram/milliliter). So, specific gravity is simply unitless density. I don't doubt the results that were shown in the videos - I just don't understand how that procedure yields unitless density. If I had to do this I would first determine the mass of the dry material and then determine the volume of that material by displacement. (Use a graduated cylinder filled to, for example, 50 ml, add the solid material, measure the new level of the water, subtract 50 ml and know that the displaced volume is the volume of the solid). Divide the mass of the solid by its volume to determine its density; eliminate the units grams/milliliter and you have specific gravity.

Maybe it is difficult to get a precise measure of displaced volume with a 2 inch diameter coin in a 500 ml graduated cylinder?

At any rate I have not yet figured out how the procedure shown in the videos yields unitless density. ??

CaptHenway

OOPS.

I see that my link above did not link to my specific post, as I thought it did, but to a thread that had a lot of other stuff in it, including two videos that I do not believe are correct. My bad. Let me try to copy my post in question here.

CaptHenway

Here is a link to the best scale for performing a specific gravity test:

(fixed link down at bottom)

Note the weighing pan to the left. Under that is an adjustable support platform which can be brought up above the weighing pan.

Put your beaker of water on that support platform, with a piece of bent wire hanging down into the water from the hook that is also holding the weighing pan.

(The bent wire should have a large adjustable loop at the bottom to hold the object being tested, and a small simple upside-down J-shaped bend at the top to go around the hook on the scale. You adjust the loop at the bottom by bending the wire in or out. Trial and error is your friend here.)

Balance it out to zero using the adjustable screw weight at the left end of the crossbeam balance bar.

Now weigh your bar or whatever in the weighing pan. Write it down.

Then carefully take the bent wire off of the hook, put the bar or whatever in the loop at the bottom of the bent wire, and lower the bar into the water while slipping the J-shaped bend over the hook. Make sure you didn't splash any water into the weighing pan below, because the scale will weigh that as well.

Determine the weight of the object now suspended in water. Make sure none of it sticks out above the water, and that neither the object nor the wire are touching the side or bottom of your water container. Write it down.

Subtract the wet weight from the dry weight. Write the difference down.

Divide the difference back into the dry weight. The result is the specific gravity, or density, of the object. Pure silver is 10.49.

Tom D.

ohaus link

VikingDude

Very informative! I assume the same would hold true for Morgans? Knowing that the ratio would be different.

Mesquite

It should work with any material - keep in mind that morgans are 90% silver and 10% something else. They will not have the density of pure silver.

CaptHenway

The s.g. of .900 fine silver is about 10.34.

guitarwes

Just curious, have you performed a sg test on that big 'ole hunk of a gold bar you have?

TheBigB

Here is a reference page on s.g. values... Specific Gravity & Melting Point

CaptHenway

<< <i>Just curious, have you performed a sg test on that big 'ole hunk of a gold bar you have? >>



Naw, I'd have to use the bath tub to suspend it in............

guitarwes

<< <i>

<< <i>Just curious, have you performed a sg test on that big 'ole hunk of a gold bar you have? >>



Naw, I'd have to use the bath tub to suspend it in............ >>



That's a good problem to have.

CaptHenway

Bump

Coinstartled

Thank you for the info, Tom.

Certainly timely. One wonders how many bogus bars are in the market.

1630Boston

One of my part time jobs [40 hrs/week] is laboratory manager for materials testing lab.
We do specific gravities daily, mostly on rocks and asphalt mixtures.
We use 'weigh below' scales like this:

But I may try building a setup like the one shown below in the video

https://youtu.be/bvOLke3iy-c

ricko

Good information... have never tried to do SG myself, though my lab (where I worked) often did that for materials....Cheers, RickO