The Stovebolt Site Forums The Shop Area The Tool Chest What is this for?

My Dad had a 1' x 1' x 4" tall wooden 2 drawer cabinet that he kept on a shelf above his work bench as far back (1952 or so) as I can remember. It contained some specialized tools (a 1" micrometer, a few calipers, a set of dividers, a tire pressure gauge) a length of #35 chain for the go cart we built together in 1957, 5 football inflation needles, a plumb bob, a couple of pocket knifes, etc. Just stuff that needed a good place to be.

I inherited the cabinet when Dad passed in 1994 and keep it in the den of our house as a reminder of him.

Today I went to it to get the bicycle spoke wrench to tweak a neighborhood kids rear wheel. When I put it back I happened across the thing in the picture below.

The glass tube is about 1/2" in diameter and 2 inches long. It is about 1/4 full of what appears to be black metal particles that do react to a magnet. The tube is stored in a 2 piece wooden container that is about 1" OD and 2 3/4" long.

I never asked him what it was for. Do any of you have an idea?

It's a magnetic stirring bar for scientific experiments. It sits in liquid and spins around, mixing the contents of the liquid when a magnetic field is applied.

You put your beaker of liquid on a thing that looks like a hot plate. Instead of heat, it has a rotating magnet in it. This causes the stir bar to spin, keeping the liquid contents mixed together without having to constantly use a stirring rod manually.

At first I thought it was a coherer. Radio signal detector for tube radios. Basically it's the ancestor of a diode. But there are no metal ends on it.

Maybe, but the magnetic stirring bars that Google just showed me had permanent magnets inside the bar. The metal pieces in this one do not stay magnetized once the external magnet is taken away.

Wondering if it’s the opposite type of system. Yours uses the magnet on the spinning motor spinning the tube, and the Google finds use a metal object that spins the magnetic tube. Both say the glass tubes are less cross contamination sensitive than the all metal or ptfe types.

More observation:

I have a really big magnet from an early 1970s Memorex hard drive from a mainframe computer. The magnet probably weighs 15 pounds. I rubbed the glass tube against the magnet and as expected the pieces in the tube were pulled toward the magnet and interacted with each other. But as soon as I moved the tube away the pieces did not retain any magnetism.

The individual pieces in the tube are black. They are irregular in shape, less than 1/32nd of an inch in length and much smaller in the other two dimensions, and have some flat surfaces. Some have "pointed" ends.

I have a magnetic stirring hot plate in my lab. The stirring sticks are much smaller diameter and magnetic. I have different sizes. They also do not float. That looks like it might float. they need to sit on the bottom to be effective. I also don't see how the metal would stay evenly spaced. The ones with permanent magnets in them are finicky enough.

Mine sinks in water.

I'm pretty sure that's a stir bar.

I was reading up on Alnico (Aluminum, Nickel, Cobalt)stir bars from the 40s. They will lose their magnetism if stored improperly. Back in the old days they were stored in pairs, end to end to avoid losing their magnetism.

Alnico stir bars have "high heat resistance but very low coercivity. This means they require reletively little energy to lose their magnetic alignment."

In the 1940s, it was common to store them in pairs north to south. Storing them alone allows the magnets's own external field lines to loop back and slowly weaken its own domains over decades.

Dropping them or causing a physical shock "disrupts the magnetic domains out of their aligned state".

Storing them in a junk drawer or jumble of metal objects exposes them to stray magnetic fields over decades. "Without paired storage, individual domains drift into random , entropy-favored orientations."

Thanks. So much for my idea.

Simple iron filings sealed in a glass tube were used with a spinning magnetic base in the chemistry labs I attended back in college in the 1960s. The tube would follow the magnet and stir the liquid in the beaker or Erlenmeyer flask.
Jerry

They could be iron filings, but wouldn't they tend to retain magnetism after being held up against a powerful magnet?