Australia's Science Forum

Hi ,

I have 22 x 100ml and 250ml volumetric flasks that were used to see how yeast and sugar react to blow up a balloon. They were poorly rinsed by the students and now I can't get some residual yeast muck out of them

I have used detergent and hot water, shaken, soaked then shaken then rinsed - it's still in there. Any ideas? Does the uncooked rice and water thing I've heard about work?

I'll make sure conical flasks are used next time.

Thanks in advance

Have you tried soaking them overnight in Napisan? Make sure they are really, really well rinsed afterwards. And be careful, it makes glassware very slippery. If you're reluctant to use napisan, try just soaking them in detergent and water for a few days.
I would definitely only give them conical flasks next time - much cheaper. I try to keep the volumetric flasks for the "serious" stuff to reduce contamination.

Have you tried 3M HCl? That is my goto soaking agent. It cleans up most glassware and as a bonus it can be reused over & over again.

Good luck!

I had a flask with something in it that I was not going to let beat me. I ended up putting some smallish gravel in it, swirled it around a bit and it came off YAY!!! That was after soaking it to loosen it up a bit.

What about those long-handled bottle brushes? They might work, especially if you bend them a bit at the end.

Milo wrote:What about those long-handled bottle brushes? They might work, especially if you bend them a bit at the end.

I've bent test tube brushes into shape before to clean round bottom flasks. It works really well. You'd have to use a burette brush maybe for a vol flask?

Try some sand.

CC wrote: ↑08 Jun 2017, 09:52Try some sand.

Thanks, the sand worked well.

Would the dishwasher on hot and pot cycle help. I am also a firm believer in nappy san using very hot water. Preferably in a container you could close so it says hot longer. Then there is rice with detergent and hot water, swizzle it, then use a large bottle brush. Pour liquid to next conical fask

Nappy San every time. Oh yes. Hey do not laugh

3M HCl is my goto glassware cleaner. Works every time, and best of all you can use it over and over again! (Just make sure you don't accidentally send it out to the labs for a prac!

Sand and metho. Or dishwashing powder (for dishwashers) and vinegar.

Curious about the sand method.
Do you swish it around or something and if so for typically how long ?

Yeah swish it around quite forcefully. Sugar also works (it doesn't dissolve in the metho and the sharp edges abrade the residue).

Cheers Marama

Or use a magnetic stirrer hot plate, with out the hot plate on, We use to do this with nappy san.