It's mainly to conserve solvent. My samples are small and the ultrasonic bath is big. It also allows me to more easily switch solvents as needed for my routine lab work. Yes, it's a glass beaker.

As I mentioned, the caveat with using these baths for a prolonged time is that the solvent can get hot. More than once I've left something sonicating for over an hour in alcohol. When I came back, the solvent got rather warm! I imagine leaving it for more than two hours may get it hot enough to ignite, but thankfully I can't speak from experience. Therein lies the danger. So regular, attentive use will not pose a fire danger. It's only a danger if it's completely forgotten.

I've also used the bath to clean injectors. We have a success story where one of my technicians got 8 injectors from a junkyard for one of his home projects. None of them worked, they wouldn't spritz. After I showed him how to sonicate and reverse flush the injectors, all of them worked beautifully. We used denatured alcohol for the bath (don't use methanol!) To reverse flush, we attached a length of clear hose over the nozzle end of the injector, fill the hose with alcohol, turn the sonicator on, apply ~5v (use a variable voltage source, not battery voltage) to open the injector, and blow the fluid through. Some rather nasty stuff came out of the other end.

__________________
95 E320 Cabriolet, 169K