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Registered Member #1822
Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300
I am trying to make some iron oxide for use in thermite which by the way, is legal where I live and just about everywhere else. So I mix some water, salt, apple vinegar and iron shavings together and then run 110VAC through the concoction and a 75Watt bulb in series. At first the bulb would light but now, 4 hours later it wont light and the water has over 30K ohms of resistance. Clearly the resistance is initially lowish in the area of 180 ohms estimated.
Registered Member #2123
Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312
You've coated your electrodes with sodium acetate? Try measuring the resistance of the solution by immersing the ohmeter probes directly into the solution.
Registered Member #2123
Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312
What does that last sentence mean exactly?
The sodium acetate thing is just a flip guess that likely isn't correct since sodium acetate is fairly soluble. Why don't you just buy iron oxide from a pottery supplies store? Saves a lot of messy hassle.
Registered Member #1911
Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165
cduma wrote ...
I did. Whats even more strange is that the resistance goes up and down for no aparent reason. If it was sodium acetate build up how would I stop it?
The meter I was using seems to be broken. My new meter gives a consistant reading similar to the old one.
[Edit: Double post]
Is your last sentence meant to give us the impression that your previous meter was flawed and because of that this thread is now useless to you, or is the 30KOhm resistance still there?
Registered Member #1822
Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300
It was actually a mistake the meter is fine. The resistance is going up and down rapidly. I have seen this happen on three diferent meters when measuring the resistance of the mixture. If the mixture is given time to rest then the resistance is more stable if not completly so. When high current is applied (2A to 5A) the resistance becomes unstable and high. Is this a common occurance?
Registered Member #1822
Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300
The electrodes are high and dry. At first I had the problem of erosion on the electrodes due to electroplating so, I made two piles of shavings that are only partially submerged in water and placed the electrodes on top.
Registered Member #10
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
If your electrodes were aluminium you will progressively increase the resistance to a very high value as you make an electrolytic capacitor like this. Needs an alkaline pH though.
Registered Member #2040
Joined: Fri Mar 20 2009, 10:13PM
Location: Fairfax VA
Posts: 180
cduma wrote ...
...When high current is applied (2A to 5A) the resistance becomes unstable and high. Is this a common occurance?
How are you getting currents of over 2A with a resistance of 30K ohms?
Am I reading this wrong or are you measuring the resistance at the same time you are energizing the liquid? Because that will not work.
A better way would be to insert a ammeter in series with the liquid, then with another meter measure the voltage drop across the liquid. Then you could figure out what the resistance is from these two values.
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Water + Salt + Iron shavings = 30,000 ohms?! Why?
