Specific gravity.
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Specific gravity.
Axtyr Thu Nov 10, 2022 10:05 am
Hi there, I am in a quandry.
I found a specimen the other day and I cannot find the weight of gold contained inside.
The only permanent weight I get is the specimen itself. 62.2 grains, which is 4.02 gram.
I have tried 2 methods to find the WET weight.
The first one is to place a container with water on the platen of the scales and hang the specimen from cotton into the water.
This gives me a wet weight of 16.9 grains, about 1.1 grams.
The second method has me placing a plastic bar across the platen with some cotton hanging from either side to which I hook up the specimen to it. Then I lift up a bowl of water under the specimen until it is completely submerged.
Initially this gave me a wet weight of 47.8 grains, BUT then I lifted the bowl even higher. This then changed the wet weight to 48.5 grains. It seems the deeper the specimen is submerged in the water the more it weighs.
Nonetheless, every way I have weighed it and calculated it, I get more gold in the specimen than it weighs. Usually about 6 grams of gold in a 4 gram specimen.
The only one that came close is 2 grams of gold using the wet weight gained from dangling the specimen in the water whilst sitting on top of the platen.
Some calculations gave a negative number and I would have to insert gold into the specimen. I don't like that.
Something is very wrong somewhere. Any help would be appreciated.
Regards Axtyr.
I found a specimen the other day and I cannot find the weight of gold contained inside.
The only permanent weight I get is the specimen itself. 62.2 grains, which is 4.02 gram.
I have tried 2 methods to find the WET weight.
The first one is to place a container with water on the platen of the scales and hang the specimen from cotton into the water.
This gives me a wet weight of 16.9 grains, about 1.1 grams.
The second method has me placing a plastic bar across the platen with some cotton hanging from either side to which I hook up the specimen to it. Then I lift up a bowl of water under the specimen until it is completely submerged.
Initially this gave me a wet weight of 47.8 grains, BUT then I lifted the bowl even higher. This then changed the wet weight to 48.5 grains. It seems the deeper the specimen is submerged in the water the more it weighs.
Nonetheless, every way I have weighed it and calculated it, I get more gold in the specimen than it weighs. Usually about 6 grams of gold in a 4 gram specimen.
The only one that came close is 2 grams of gold using the wet weight gained from dangling the specimen in the water whilst sitting on top of the platen.
Some calculations gave a negative number and I would have to insert gold into the specimen. I don't like that.
Something is very wrong somewhere. Any help would be appreciated.
Regards Axtyr.
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Re: Specific gravity.
hiluxer Thu Nov 10, 2022 3:38 pm
The Betts method is the easiest:
http://www.johnbetts-fineminerals.com/jhbnyc/articles/specific_gravity.htm
The essence of the Betts method is that instead of weighing a specimen while it is suspended in a container of water, you simply weigh the container of water it is suspended in. Much simpler.
http://www.johnbetts-fineminerals.com/jhbnyc/articles/specific_gravity.htm
The essence of the Betts method is that instead of weighing a specimen while it is suspended in a container of water, you simply weigh the container of water it is suspended in. Much simpler.
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Re: Specific gravity.
adrian ss Thu Nov 10, 2022 4:15 pm
Found this handy little chart just now.
https://www.gold-prospecting-wa.com/support-files/gold-in-quartz-table.pdf
https://www.gold-prospecting-wa.com/support-files/gold-in-quartz-table.pdf
Last edited by adrian ss on Fri Nov 18, 2022 8:46 am; edited 1 time in total
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Re: Specific gravity.
Axtyr Thu Nov 10, 2022 10:20 pm
I broke it open and with some quartz still attached it weighed 1.76 gram.
The closest results I could get with the varying weights were, 1.37 grams and 1.89 grams.
Regards Axtyr.
The closest results I could get with the varying weights were, 1.37 grams and 1.89 grams.
Regards Axtyr.
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Re: Specific gravity.
Kon61gold Thu Nov 10, 2022 10:25 pm
A small length of fine thin cotton sewing string, is all that's required for fully submerging your speci in water Axtyr.
As long as your gold quartz specimen (when submerged in water), is close to & off the bottom not touching any part of the container, is all that's required for a fairly accurate & approx. wet weight figure.
When your talking grains instead of grams, give or take a grain, changes little in the overall gold content weight. Just make sure your tare off the weight of canister containing water on your scale first, before fully submerging your speci & then reading off your wet weight result.
Once you've determined your wet weight eg:
Wet weight = 1.1gm,
Dry weight = 4.02gm
1.1 x 2.65 (sg of pure quartz) = 2.91 (quartz content)
4.02 - 2.91 = approx. 1.11gm gold content mixed within quartz specimen
Since no native gold or that of quartz found, is ever found in pure form, my preference is to calculate with a specific quartz gravity of (2.67) instead of (2.65), (allowing more for any other impurities usually associated within quartz or gold content), towards a slightly more accurate gold content reading.
Mind you, all the above results, do depend on an accurate wet weight calculation to start off with, in order to obtain the best possible approximate gold content within your quartz specimen.
Note the above formula, gives only a good approximate of gold content within, but, it is only when a specimen is crushed to fine powder & all gold content removed & weighed, can one achieve the most accurate gold content reading.
Kon
As long as your gold quartz specimen (when submerged in water), is close to & off the bottom not touching any part of the container, is all that's required for a fairly accurate & approx. wet weight figure.
When your talking grains instead of grams, give or take a grain, changes little in the overall gold content weight. Just make sure your tare off the weight of canister containing water on your scale first, before fully submerging your speci & then reading off your wet weight result.
Once you've determined your wet weight eg:
Wet weight = 1.1gm,
Dry weight = 4.02gm
1.1 x 2.65 (sg of pure quartz) = 2.91 (quartz content)
4.02 - 2.91 = approx. 1.11gm gold content mixed within quartz specimen
Since no native gold or that of quartz found, is ever found in pure form, my preference is to calculate with a specific quartz gravity of (2.67) instead of (2.65), (allowing more for any other impurities usually associated within quartz or gold content), towards a slightly more accurate gold content reading.
Mind you, all the above results, do depend on an accurate wet weight calculation to start off with, in order to obtain the best possible approximate gold content within your quartz specimen.
Note the above formula, gives only a good approximate of gold content within, but, it is only when a specimen is crushed to fine powder & all gold content removed & weighed, can one achieve the most accurate gold content reading.
Kon
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Re: Specific gravity.
Axtyr Fri Nov 11, 2022 7:18 am
Kon, that is what I worked out originally, so I must have used that calculation first. I never found it again or just couldn't see it.
Between my wife and I working out the calculations we were both going crazy.
Now that I know which way to get the correct WET weight all should be fine in the future. It was a shame to break open the specimen but it was not a clean white quartz.
Had it been pure white quartz I wouldn't have cracked it open.
Thank you everyone for all your help and now I know exactly how to set up my scales for wet weighing.
Regards Axtyr.
Between my wife and I working out the calculations we were both going crazy.
Now that I know which way to get the correct WET weight all should be fine in the future. It was a shame to break open the specimen but it was not a clean white quartz.
Had it been pure white quartz I wouldn't have cracked it open.
Thank you everyone for all your help and now I know exactly how to set up my scales for wet weighing.
Regards Axtyr.
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Re: Specific gravity.
hawkear Tue Nov 15, 2022 8:39 am
I’d like to second Hiluxer’s suggestion about the Betts method.
So much easier than the method I had been using for years tying fiddly bits of cotton around specis and trying to weigh them whilst dangling them in water all the time keeping things from touching the sides.
At first I had a bit of skepticism so I filled a glass with water, put it on some kitchen scales and stuck my finger in and voila the weight displayed increased even though my finger touched nothing other than the water.
Looking up the physics, the method works in that the water displaced by an object in an open container can go only upwards. Therefore this additional height of water is what increases the pressure on the bottom of the container and fortunately by an amount corresponding to the “wet” weight of the object.
So much easier than the method I had been using for years tying fiddly bits of cotton around specis and trying to weigh them whilst dangling them in water all the time keeping things from touching the sides.
At first I had a bit of skepticism so I filled a glass with water, put it on some kitchen scales and stuck my finger in and voila the weight displayed increased even though my finger touched nothing other than the water.
Looking up the physics, the method works in that the water displaced by an object in an open container can go only upwards. Therefore this additional height of water is what increases the pressure on the bottom of the container and fortunately by an amount corresponding to the “wet” weight of the object.
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Re: Specific gravity.
adrian ss Wed Nov 16, 2022 5:16 pm
The weight of the water displaced by an object in the water is the weight of the amount of water displaced...Not the immersed weight of the object.
This is my little sg rig for testing small gems.
The result from this set up gives the weight in water of the speci....Subtract this weight from the dry weight gives the "Loss Of Weight"
Divide the loss of weight of the speci into the speci dry in air weight multiplied by the sg of the water (1) gives the sg of the speci.
This is my little sg rig for testing small gems.
The result from this set up gives the weight in water of the speci....Subtract this weight from the dry weight gives the "Loss Of Weight"
Divide the loss of weight of the speci into the speci dry in air weight multiplied by the sg of the water (1) gives the sg of the speci.
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Re: Specific gravity.
hiluxer Wed Nov 16, 2022 9:35 pm
Determining the SG of a specimen is relevant to distinguishing one type of gemstone from another. eg. topaz from quartz. However it doesn't answer the question asked in this thread, which is how to determine the gold content of a specimen comprising unknown amounts of gold and rock.adrian ss wrote:Divide the loss of weight of the speci into the speci dry in air weight multiplied by the sg of the water (1) gives the sg of the speci.
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Re: Specific gravity.
adrian ss Wed Nov 16, 2022 11:15 pm
You have to know the sg of the speci and the sg of gold before you can start to figure out the weight of the gold in a rock.
Last edited by adrian ss on Fri Nov 18, 2022 8:47 am; edited 2 times in total
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Re: Specific gravity.
adrian ss Wed Nov 16, 2022 11:31 pm
Before you can calculate the answer you need to know the dry and immersed weight of the speci. also the sg of the host rock, the sg of the gold and the total sg of the speci..
If your scales are not accurate to 3 decimal places then there will be big errors when testing species that contain very small amounts of gold.
If your scales are not accurate to 3 decimal places then there will be big errors when testing species that contain very small amounts of gold.
Last edited by adrian ss on Fri Nov 18, 2022 8:56 am; edited 1 time in total
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Re: Specific gravity.
hawkear Thu Nov 17, 2022 2:51 pm
Axtyr wrote:Hi there, I am in a quandry.
I found a specimen the other day and I cannot find the weight of gold contained inside.
The only permanent weight I get is the specimen itself. 62.2 grains, which is 4.02 gram.
I have tried 2 methods to find the WET weight.
The first one is to place a container with water on the platen of the scales and hang the specimen from cotton into the water.
This gives me a wet weight of 16.9 grains, about 1.1 grams.
The second method has me placing a plastic bar across the platen with some cotton hanging from either side to which I hook up the specimen to it. Then I lift up a bowl of water under the specimen until it is completely submerged.
Initially this gave me a wet weight of 47.8 grains, BUT then I lifted the bowl even higher. This then changed the wet weight to 48.5 grains. It seems the deeper the specimen is submerged in the water the more it weighs.
Nonetheless, every way I have weighed it and calculated it, I get more gold in the specimen than it weighs. Usually about 6 grams of gold in a 4 gram specimen.
The only one that came close is 2 grams of gold using the wet weight gained from dangling the specimen in the water whilst sitting on top of the platen.
Some calculations gave a negative number and I would have to insert gold into the specimen. I don't like that.
Something is very wrong somewhere. Any help would be appreciated.
Regards Axtyr.
Hi Axtyr.
Just rereading your post, I had another thought to suggest and that is regarding the units you are using to weigh you speci.
The most important thing here is to determine the VOLUME of the specimen. Settling on grams as the unit of measurement makes things far easier than say grains etc, as the metric system was set up interrelating weight and volume ie 1 cc of water weighs 1 gram.
Of course measurements can always be taken in other units such as grains or ounces but they would always have to be converted back to grams as you have done because the specific gravity of gold or quartz is also expressed metrically as grams per cc.
In the first measurement you quote 16.9grains (1.1gr) as the wet weight. That is NOT the wet weight but rather the DIFFERENCE between the dry weight and the wet weight. This method (Betts) just skips measuring the wet weight and takes you straight to the important volume figure in this case 1.1cc.
In the second method involving measuring the true wet weight, and regarding getting a heavier wet weight when lifting the bowl to have the spec suspended at a deeper level in the water, this should not happen. A mechanism that might explain that could be if the specimen was rough and hackly, it could hide hidden cracks and crevices in which air might be hidden. A deeper submersion could cause this hidden air to compress or perhaps disturb a small bubble resulting in a lower displacement and a greater wet weight. I would therefore take the higher wet weight as closer to the true wet weight ie 48.5 grains or 3.14gr.
Subtracting that from the dry weight gives 0.88 cc as the volume figure.
Even so, the two methods have given somewhat different results for the volume, the first 1.10 cc and the second 0.88 cc. It is quite a small specimen at around 1cc so any imperfections caused by the apparatus eg weight of suspending lines, wicking of cotton threads, and even inaccuracy of scales at low weights can be exaggerated and that may explain the difference.
Nevertheless they are not that far apart, so let’s assume an average of the two say 1.0cc for convenience for the volume.
If the speci was all quartz (sg 2.65) then with a volume of 1.0cc it should weigh 2.65 grams but in fact weighs 4.02. The difference must be gold content ie 4.02 - 2.65 = 1.37gr. That would be a minimum estimate.
We can further refine that estimate by calculating the volume that 1.37gr of gold must occupy. That is 1.37 divided by 19.3 (sg of gold) and that comes to 0.07 cc. As we have already settled on the volume of the specimen to be 1.0cc, the volume of quartz can be no greater than 0.93cc and therefore weigh only 2.46 grams so the weight of gold must be adjusted upwards to 1.56gr.
A further iteration of this calculation ups the gold content to 1.58gr. Any further recalculation would result in only minuscule changes and be meaningless within the context of the measuring methods.
So I think you have made fairly reasonable measurements overall and they support the weight obtained after your smashing it.
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Re: Specific gravity.
Axtyr Thu Nov 17, 2022 7:04 pm
All I can say is "the mind boggles", with all these calculations, yet none were very accurate.
If I find further specimens I will test and then crack open to see which one gets me the closest. I even tried the Betts method using both ways of getting the wet weight and it wasn't anywhere near accurate either method.
So many have, and swear by their own methods and there could be so much discussion. I tried a few methods and found all of them wanting. So my only conclusion is to keep trying in the future. At least now I can set up my scales to get accurate measurements of small specimens. Maybe the calculations will be more accurate on larger specimens.
Thank you everyone.
Regards Axtyr.
If I find further specimens I will test and then crack open to see which one gets me the closest. I even tried the Betts method using both ways of getting the wet weight and it wasn't anywhere near accurate either method.
So many have, and swear by their own methods and there could be so much discussion. I tried a few methods and found all of them wanting. So my only conclusion is to keep trying in the future. At least now I can set up my scales to get accurate measurements of small specimens. Maybe the calculations will be more accurate on larger specimens.
Thank you everyone.
Regards Axtyr.
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Re: Specific gravity.
adrian ss Fri Nov 18, 2022 9:09 am
I have been testing some of the methods mentioned here and on line .
I used qtz pieces of 0.85g to 14g with known weight of 0.15g gold attached using tiny amounts of super glue to fix the gold in contact with the stone.
The results have all been in the minus 38% to 50% range.
Accurate scales are imperative when testing small weights and variations in sg if accurate gold weights are to be obtained. Plus the ident of the host rock is mandatory. Guesstimating the ident and sg of the host rock is not good enough and at the best will give you ball park results if you are lucky.
This chart gave better results than all of the other methods I tested.
No matter what calculating method you use the end result hinges on accurate weight and sg calculations
https://www.gold-prospecting-wa.com/support-files/gold-in-quartz-table.pdf
I used qtz pieces of 0.85g to 14g with known weight of 0.15g gold attached using tiny amounts of super glue to fix the gold in contact with the stone.
The results have all been in the minus 38% to 50% range.
Accurate scales are imperative when testing small weights and variations in sg if accurate gold weights are to be obtained. Plus the ident of the host rock is mandatory. Guesstimating the ident and sg of the host rock is not good enough and at the best will give you ball park results if you are lucky.
This chart gave better results than all of the other methods I tested.
No matter what calculating method you use the end result hinges on accurate weight and sg calculations
https://www.gold-prospecting-wa.com/support-files/gold-in-quartz-table.pdf
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Re: Specific gravity.
hawkear Fri Nov 18, 2022 11:36 am
Agree wholeheartedly about the need for accuracy and especially when dealing with small samples inaccuracies can be magnified by later calculations.
Excellent chart Adrian and would save a lot of maths work.
Back on the subject of measurement, if one would like to check their own ability to accurately make the required measurements, perhaps try out on a clean bit of quartz to see how close calculations come to zero gold content.
Excellent chart Adrian and would save a lot of maths work.
Back on the subject of measurement, if one would like to check their own ability to accurately make the required measurements, perhaps try out on a clean bit of quartz to see how close calculations come to zero gold content.
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Re: Specific gravity.
adrian ss Fri Nov 18, 2022 4:55 pm
Just one example:
Scales are to 3 decimal places.
Citrine gem with .145g bit of gold ( near on 23k) in positive contact with the gem with total weight of 3.131g
Total sg measured at 2.748.
The chart gives a gold content of 4.10 % of the total weight 3.131g which is 0.128g of gold This is 0.017g difference from the actual gold weight of 0.145g. Not too bad for a tiny bit of gold and a set of cheap Ebay scales.
Scales are to 3 decimal places.
Citrine gem with .145g bit of gold ( near on 23k) in positive contact with the gem with total weight of 3.131g
Total sg measured at 2.748.
The chart gives a gold content of 4.10 % of the total weight 3.131g which is 0.128g of gold This is 0.017g difference from the actual gold weight of 0.145g. Not too bad for a tiny bit of gold and a set of cheap Ebay scales.
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