sodium_stearate - 4-3-2018 at 12:39
Just recently was asked by a collector of very early Edison
cylinder phonographs, how to activate and
use a Grenet cell.
I do have some reference material about this, but I've never
done any of this myself mainly because I do not have an
old original Grenet cell to use.
According to what the old book says, the Grenet cell is
of a type known as a Bichromate Cell.
The book describes a solution of either sodium or potassium
bichromate treated with sulphuric acid to form chromic
acid. The compound CrO3 it says is not only rich in oxygen,
but it also gives it up to nascent hydrogen, hence the use
of bichromates as depolarizers.
Here is what the old book recommends:
Potassium Bichromate:...77.5 grams
Suphuric Acid:.................78.5 c.c.
Water:.......................... 750 c.c.
Dissolve the bichromate in the water by heating to
boiling. After cooling slowly add the acid. After cooling
again, the solution is ready for use.
It also says that sodium bichromate can be used:
200 grams of sodium bichromate is dissolved in 1 litre
of water, to which 150 c.c. of strong acid gets added.
It goes on to say that when using either type of solution,
that once the cell starts to weaken, another 25 to 50 c.c.
of acid can be added to rejuvinate the cell several times
until the solution is spent.
For reference the Grenet cell is constructed using
2 vertical plates of carbon with a zinc electrode between them.
The carbon plates form the positive electrode and the
zinc is negative. The zinc plate is attached to a rod that
can be held with a thumbscrew. The rod is used to
pull the zinc plate out of the solution when the cell is
not in use.
Anyone here familiar with these reactions or ever
do any experiments along these lines?
I ask because many times I've seen these old Grenet cells
displayed with Edison electric motor driven cylinder phonographs from the 1880s. However, not many collectors
of this old stuff seem to be interested in gathering up
the required materials to actually use these old cells.
Voltage per cell is around 2.0 volts.
Sulaiman - 4-3-2018 at 13:56
Probably this ? https://en.wikipedia.org/wiki/Chromic_acid_cell
notice the requirement to remove the zinc when not in use.
I would expect most people would use Lead-acid batteries as a replacement as they are also 2 V/cell
- and rechargeable.
sodium_stearate - 4-3-2018 at 17:55
Yes, correct, that is what the rod in the center is for.
When the cell is not in use, the rod is pulled up and
locked in position with a thumb screw to prevent wasting
the zinc electrode to "local action".
Yes, also correct in that many other forms of 2 volt DC
power are often used to operate these ancient motors.
Most guys tend to lash up some kind of a power supply
that runs off of the AC mains.
That is not the point though. The point is to actually
operate the old Grenet cell the exact way it was
done in the 1880s.