help - using specific gravity to calculate carat of dust??

[jjphotos]

Sorry if I am being silly but how do you go about using specific gravity to calculate carat of dust sample; would the presence of unknown impurities make using specific gravity an inappropriate technique. I have seen a calculation preformed using specific gravity of a sample to give a 22.15 carat value; I would have thought you needed something more akin to a fire assay for this sort of determination.

Cheers guys for your help.

 

[butcher]

Most methods that use specific gravity of an object measure in air then measure submerged in water, I really do not know how well that would work with powders, also when trying to get an idea how much gold a rock has or how much gold a ring has we also have an idea of the specific gravity of the other ingredients.

If these were powders why not just refine them to pure metals and then weigh them, or take a well mixed portion sample and do this, either with chemicals or in a fire assay and then chemicals.

 

[Anonymous]

It is my understanding that the specific gravity water method is highly innacurate,due to the fact that alloying metals have different specific gravities themselves,which can highly throw off a result.

 

[Harold_V]

It is my understanding that the specific gravity water method is highly innacurate,due to the fact that alloying metals have different specific gravities themselves,which can highly throw off a result.

While it's true that a person can get unreliable results, properly executed, a displacement test can be quite precise. Only a particular combination of elements will displace a given amount of water. Vary any of them and they displace more or less water. Therein lies the problem. The volume of water being displaced must be determined very precisely.

Harold

 

[jjphotos]

cheers for the advice guys, some food for thought

 

[jjphotos]

While it's true that a person can get unreliable results, properly executed, a displacement test can be quite precise. Only a particular combination of elements will displace a given amount of water. Vary any of them and they displace more or less water. Therein lies the problem. The volume of water being displaced must be determined very precisely.

Harold given that the volume of displacement is also dependent on temperature; would this not mean that the error margins are huge? I have been given a sheet with SGs at two decimal places; for example:

DENSITY KARAT
17.00 20.17
17.01 20.19
17.02 20.21
17.03 20.22
17.04 20.24
17.05 20.26
17.06 20.28
17.07 20.30
17.08 20.32

what do you think?

 

[Harold_V]

what do you think?

I think you're right. I was just trying to point out that such a measurement system can be quite reliable, as only particular combinations of certain elements will displace a given amount of water. We're back to the degree of precision of the tests involved, which was my other point. It is most likely beyond the ability of a guy working in his garage with a cheap scale and inadequate measuring devices.

Harold