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

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!