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Bulk density procedure


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In a recent thread the bulk density of a meteorite was mentioned by Mike. I remembered seeing a video posted here that really laid it out well. I went back and found the thread but the video won't work.

http://www.nuggetshooter.ipbhost.com/index.php?showtopic=19685&hl=%2Bbulk+%2Bdensity

Jim? Is this video available? I would love to see it again!

Could one of you smart fellows compare and contrast bulk density to specific gravity for me?

Edited by Bedrock Bob
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The steps I outlined in the other thread are pretty straight forward, not sure you need a video to do it. :P

Density is a ratio of mass and volume, specific gravity (also known as relative density) is a ratio of density of one substance to that of another control substance.

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Hi Bob!

Ah! Archimedes' Principle!

I dumped pretty much all my how-to videos about a year ago. I actually had two videos on bulk density. One for testing rocks/meteorites and the other for determining the amount of gold in a specific rock.....quartz for example. I also created a calculation spread sheet using my method and another method others seem to like.

It's a 3 step process if water is used.

With an electronic scale set for grams:

1. Weight the object. Record that as 'Weight A'

2. Find a small beaker or glass that the specimen can hang in without touching the sides or bottom. The smaller, the better. Fill it with distilled water and plate it on the scale and tare the scale so it read zero weight.

3. Take a thread and tie it around the specimen. Hang the specimen fully submerged in the water and read the weight. Record this as 'Weight B'.

Then just do the math.. Weight A / Weight B = Bulk Density in grams per cubic centimeter (g/cc).

Here is one video that might help. Don't bother with all this hanging BS and you can ignore the second half of this video.

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Thanks Jim!

I have a bunch of Boy Scouts interested in the natural sciences and I needed a quick and dirty "show and tell". I have been doing bulk density on soils, asphalt and aggregate for years but I was having problems explaining it in terms they could relate to.

A picture is worth a thousand words. Thanks again Jim!

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Bob,

Sounds good. You might share with them the fact that every known rock on earth has been measured for Bulk Density. And, streak too, for that matter.

Having young ones build up a field geology rock id kit would be a good project for them and not break the bank. Learning to use it will stay with them for their lifetime and beyond.

Jim

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The little whippersnappers and scallywags ask so many questions in so many directions it is a full time job focusing them on the task at hand.

We started out knapping an arrowhead and discussing the fused silicates. I contrasted obsidian with perlite and the discussion became density. From there I answered a barrage of questions about why things weighed less in water, and so on and so forth.

By the time I put the notches in the tail of the arrowhead I was commited to another lesson on weight, density and specific gravity.

I have an old triple beam scale with the hole in the bottom so you can hang a wire underneath. I drilled a hole in a little table and I have a small graduated cylinder to baptize the specimens in. I have both formulas written down and a calculator. I'm going to show them your electronic scale method with the automatic tare function first. Then I am going to throw the old school scale at them and let them figure it out.

We will do the arrowhead, a meteorite and a nugget.

Four little hellions that call themselves the "Flaming Arrow Patrol".... No doubt future evil geniuses and sooner or later they will take over the world.

Edited by Bedrock Bob
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Bob,

Another good cheap project is to have the kids make a spectrometer. You will have to be

ready for a ton of questions about what they see, but the project is very simple to build.

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Bob and Jim,

I bought a 2 KG digital fish scale for my SG numbers. You just hold the specimen with the scale in the air (dry weight) and then you just submerge it in water (wet weight) and you have your difference you can use in your formulas.

It is not exactly the 'mass' way of calculating it but one way.

Mitchel

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LOL! I have a trigger pull scale. It uses the formula factors; 'live' weight and 'dead' weight! :brows:

Edited by Desertsunburn
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As long as you have gold in quartz and nothing else is present a specific gravity test is almost accurate.

Most gold is in a matrix of quartz, hematite, arsenic, and sulphides. Then the gold itself is alloyed with silver, copper and other metals.

A specific gravity test on most gold ore is pointless. For a single hand specimen in quartz a specific gravity test is a way to spend an hour playing with your new rock.

Just like an acid test on a solitary piece of low grade float. It is something that is rather pointless.

Understanding specific gravity is useful in many endeavors but trying to estimate the amount of gold in a piece of ore would be one of the least practical uses for it.

Freezing points, boiling points and saturation of solubles is where specific gravity calcs will get you the gold. Qeighing rocks to keep from crushing them is like trying to get an egg yolk in a skillet without breaking the shell. It just makes no sense in almost all cases unless a rookie gold buyer is really interested in the amount of elemental gold in a rock....then it is only a rough ballpark in most cases.

You can take a fishing weight in a block of wax and do the specific gravity test and use the numbers for gold and quartz. If the test showed % of Au you could get rich weighing lead candles.

Edited by Bedrock Bob
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