Re: Bucket cap question

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Original poster: "Dr. Duncan Cadd by way of Terry Fritz <twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>

Hi Weazle, All!

>Has anyone done any experiments with different electrolytes for
>a bucket cap?  I know that brine is the favourite, but wondered
>how copper sulfate might work, especially when using copper for
>the electrodes.  Comments and suggestions welcomed.


No experiments, but here's some numbers from the "Handbook of
Chemistry and Physics" 42nd edn, 1960-61:

For 15g of the salt dissolved in 100ml water, electrical resistance of
a 1cm cube:

Ammonium chloride 3,86 ohms
Copper nitrate 11,7 ohms
Copper sulphate 23,7 ohms
Silver nitrate 14,64 ohms
Sodium chloride 6,1 ohms

The main part of the reason for the poorer conductivity of copper
sulphate solution is that it has a higher molecular weight than sodium
chloride i.e. for the same amount of common salt you are getting more
ions i.e. more current carriers, and the ratio of the conductivities
is approximately equal to the ratio of the numbers of ions in 15g.
(Incidentally, I wouldn't recommend the use of ammonium chloride
solution - it's too corrosive, especially with copper wires.)

Whether you would see the difference in TC service is of course
another question, dielectric losses in the glass may far outweigh the
resistive loss difference between brine and copper sulphate, and the
colour of the liquid in the bottles may have some perfectly legitimate
aesthetic appeal.  There might also be an absence of corrosion of the
wire in copper sulphate solution, whereas I recall someone posted that
it had occurred with copper wire in brine, and if corrosion of the
wire in brine was a problem this might go some way to offset the
resistance difference in the solution.  Maybe this is what you were
thinking?

Dunckx
Geek#1113 (G-1)