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The Trouble with Bubbles.

A preliminary report on a 0.6m K2CO3+H2O/Ni/Pt gas measuring experiment.

Synopsis:  Gas evolution rate varied up to 30% using a fixed electrical
           current -- calling into question the 1.48*I assumption.

I figured I could do some comparative electrolysis gas production 
measurements with some simple equipment (see apparatus description below.)

I figured I could count bubbles if they were not too fast nor too slow.
My apparatus produced bubbles at the rate of about 1-2 per second, which
was just about ideal for eyeball/wristwatch, lucky me.

I applied 200ma (measured with two different meters both within 0.5% of
each other) in the reverse current direction (Ni as the anode, Pt as
cathode.)  After one hour the bubble rate was 111 bubbles per minute.

I applied 200ma in the forward current direction (Ni as the cathode, Pt as
the anode.)  After eight hours (sleep), the bubble rate was 88 bubbles
per minute.

The bubble rate is in a state of flux just after reversing the current
and takes about an hour or two to settle down. 

*Conclusions* -- Any assumption about a fixed relationship between current
and gas production is (preliminarily) shown to be off by as much as 30%
(with an approx 10% worst case range of measurement errors.)

Other observations:  I continue to get some sort of "fuel cell" effect.
That is, I get an EMF potential after disconnecting the power supply.  It
decays quickly from around a volt or so to about 1/10 of a volt in the
course of about 10 seconds (which probably has something to do with the
load of the voltmeter.)

Furthermore, I continue to get current flow at *all* applied voltage levels.
This implies either parallel current paths in the electrolyte, or the effect
of recombination of the gases.

In either case, the 1.48*I factor is (preliminarily) shown to be unreliable
by a wide margin.

   * * * * *

Apparatus consists of:

1.) A glass test-tube approx 1" x 6" and black rubber stopper (sold as a
    unit as pet mouse water supply.)  The test-tube contains:
    a.) Two wires, one Pt and one nickel plated copper.
    b.) Nickel nodules.
    c.) 0.6 molar K2CO3+H2O
    
2.) An 8" length of clear flexible soft plastic tropical fish air hose, approx
    5/32" O.D. 3/32" I.D.

3.) An old clear glass olive jar approx 2.5" x 6" -- filled with tap water.

4.) Approx 2-3 ounces of Nickel metal spherical "nodules" each on the
    order of 1/4" diameter.

5.) A foot of 22 gauge copper wire with nickel plating.

6.) A 20" length of #30 gauge Platinum wire.

7.) A manual voltage adjust power supply with built in milliamp meter.

8.) A Heathkit digital multimeter.

The power supply is connected to the two wires piercing the rubber stopper.
The nickel plated copper wire descends to the bottom and is in contact with
the nickel nodules also settled at the bottom.  The platinum wire is wound
loosely in the top section of the test tube.  The tube is filled to within
1/2" of the top with the K2CO3 solution.

The plastic hose exits the rubber stopper and descends into the water
filled olive jar.  At 200ma input current, bubbles ascend from the hose
exit in the olive jar at rate of 1-2 per second.

Barometric pressure, ambient temperature, granularity of bubble counts,
accuracy of current measurement, and accuracy of timing operations add to
approximately a total worst case error range of 10%.


- John Logajan MS010, Network Systems; 7600 Boone Ave; Brooklyn Park, MN 55428
- logajan@network.com, 612-424-4888, Fax 612-424-2853