Sulaiman - 30-6-2017 at 18:35
I have c73ml / 991g of mercury that I intend to distill to ensure the accuracy of a barometer / manometer,
I bought the mercury via a private eBay auction, claimed to be triple distilled.
I would like to determine the purity of the mercury before and after distillation,
but how ?
so far I have considered two methods:
1) Using one of my 50ml burettes, and weighing scales, I should be able to measure the density to <= 0.25%
which would only be useful if there is gross contamination.
2) I could measure the boiling point to within 1oC,
but how sensitive is the b.p. of mercury to contamination ?
How else can I test the purity of mercury ?
Assume unknown contaminant(s)
unionised - 1-7-2017 at 03:45
Freezing point?
It's an option if you can get dry ice.
Also, if you freeze most of it then any soluble impurities will be left in the last bit to freeze, and you can pour that off leaving purified frozen
mercury behind.
However, the effect of impurities on mpt or bpt is small.
There's some data for melting point depression here.
http://www.omega.com/techref/pdf/z158-185.pdf
There's also the idea of shaking it up with ozonised air which oxidises many impurities which then form a scum on the surface which can be skimmed
off.
The classic way to determine the purity of mercury isn't very environmentally sound- you boil off a small sample of the metal and see how much stuff
is left behind.
Sulaiman - 1-7-2017 at 07:23
My minimum purchase for dry ice is £35 + delivery/pickup so freezing point is not economical for me,
when I distill the mercury I guess I'll see what is left behind 
I have already rinsed the mercury in dil. HNO3 which gave negligible visible residue when evaporated,
a little surface crud was collected by passing the mercury through a pinhole in filter paper prior to the nitric acid rinse.
After cleaning the mercury had a nice shiny surface,
which now two years later has a little crud on top due to exposure to the atmosphere/air in the jar that I keep it.
I need to at least de-crud the mercury again as tiny streaks of it now stick to the inside of clean glass tubing,
but I fancy doing a full vacuum distillation just to try it.
Does distilling mercury remove all impurities / does it distill in clearly defined fractions,
or can impurities in a mercury amalgam distill over like azeotropic mixtures ?
Most importantly, how can I determine the purity of my mercury with amateur facilities?
.....
I'm beginning to think that mercury is just distilled a certain number of times for a desired purity level,
hence distilled, or in my case, triple distilled - to be distilled again.
(although lab grade, I guess that my nitric acid could have contributed some heavy metal contamination to the mercury ?)
[Edited on 1-7-2017 by Sulaiman]
UC235 - 1-7-2017 at 07:37
I'm pretty sure the mercury distills separately. There's also the "steam distillation" effect that could occur. But considering that even something
like zinc is still solid at mercury's boiling point and 553C away from it's boiling point, I think there would be very little vapor pressure to
contribute.
Sulaiman - 1-7-2017 at 07:57
I think that the nitric acid rinse should have digested any 'reactive' lighter metals such as Zn, Al etc
leaving mainly heavy stuff like Pb, Sb, etc.
I may be over-thinking this one ...
I'll just do a nitric wash and simple vacuum distillation.
It would be nice to actually determine how pure my mercury is, other than 'pure enough'
but I have enough other things to do so never mind.
unionised - 1-7-2017 at 12:05
You could dissolve a little of it in acid then analyse the solution by classical wet chemistry - which doesn't need much equipment (mainly test tubes)
but does need reagents and some skill, or you could get someone to analyse the solution for you.
Distilling it will remover practically all the impurities.
Electrolytic refining would also work.
Neither is exactly the sort of thing to do in the kitchen.
Boiling mercury bumps rather badly and it's heavy- so that can do a lot of damage.
Heavy Walter - 2-7-2017 at 12:25
Hi Sulaiman
Strong (Procedures in experimental physics) details a procedure in several steps to clean mercury. I agree with others that distilling will give you a
nice pure mercury.
AJKOER - 2-7-2017 at 14:11
Per Wikipedia on electrical resistivity (https://en.m.wikipedia.org/wiki/Electrical_resistivity_and_c...):
"Secondly the impurity of the metal is relevant as different ions cause irregularities too.[7]"
diddi - 2-7-2017 at 14:56
I have used vac distillation for cleaning kg scale Hg in the past. very useful when receiving gifts with possible alloyed metals like Al and Zn etc.
The scum in the RBF at the end is easily removed with HNO3