Warning about some 3 liter Flat bottom flasks

[scram]

Apparently one used before had worked without problems stirring up to 55 grams al. BUT, another one with the same famous Label one the front which is believed to be a custom made (believed to be so because it has more than 1 neck) did not work. The single neck worked fine at the time 2 years ago. I believed it had a larger than 75mm diameter flat bottom circle sitting surface. But This other 3000ml custom made flask is slightly smaller than 70mm diameter at the bottom. This stirred like a hurricane with 40g al at first until the amalgamation had completed and dripping was read to start. Apparently, after the al becomes amalgamated and the solution turns cloudy grey both 2.75" and 3" octogonal stir bars stop stirring all together. The solution must become more viscous and too much weight on such a small amount of surface area of the flask bottom. Desperate attempt was made to get it stirring again on 2 different stirrers. Both stirrers did well with the previous 3 liter flask but even after dumping up to 75% of 40g al out of the flask it still couldn't stir or even maintain stirring. I guess the difference of 12 to 25mm larger diameter for the flat bottom can make all the difference. So before you go out and blow money and time make sure you amalgate with foil and do a test run on al to be safe.

[scram]

Problem was fixed with 3 inch egg shape stir bar. Apparently only 3 inch egg shape bars go through a 24/40 neck. The smaller egg-shaped bars are too fat. It "cuts" through al much easier than octogonal bars. Dont use the ones with the rounded edges, but the bars that have the sharp flat edges. Still doesn't stir as well as the previous 3 liter fb flask but it now stirs 45grams.

[gabd]

Funny, I cant get a 3 inches egg-shaped bar in a flask with 24/40 here. Smaller ones no problems! Stir bar are so different from a country to another? How many companies make them?

[carcrash]

Nice owner of a 3 inch egg bar that will not fit into a 24 40 neck.
Not a chemist I just follow directions on the box mix

[scram]

You just got to keep ordering them from different suppliers until you get one that actually goes through. I'd hate to be stuck with one of those shitty fat rounded edge 3" egg-shape bars that don't even balance on a FB surface. Of course I guess they are intended to only be used on RB flasks. For FB make sure the bar has a flat side surfaces and no curves. These balance well on FB's. I've only had 1 not go through a 24/40 neck. You just got to keep trying.

[carcrash]

Took a rasp and filed down the eggbar so it fits. Used a file to smooth out the roughness. Make sure you file it down enough that you can get it back out. Filing down just the corners was not quite enough. Damm thing finally fits a 24/40 neck
Not a chemist I just follow directions on the box mix

[baalchemist]

Some 3" eggbars can be shaved ever so slightly in a couple of spots and so they will make it into a 24/40.
    GODISNOWHERE
Shoot Narcs, Not Drugs

[Rhodium]

Do you sign up for liposuction when your pants becomes too small too, or would you then consider alternatives like buying a new pair, or maybe have them enlarged if you are too cheap/poor to afford a new pair?

Instead of bastardizing your lab equipment, perhaps you could something as radical as buying a slightly smaller egg stirbar (It's not like you need to feel inferior just because you don't have the biggest bar), or perhaps you could even buy a flask with a tad larger joint (and an adapter between 24/40 -> 29/24 so that it still will fit the rest of your glassware collection)...

(What amazes me most of all is that dozens and dozens of members have had this problem over the years - not checking the dimensions of the stir bar to see if it fits your glassware before buying it is like failing to try a new pair of shoes on before paying and taking them home...)

[carcrash]

Why toss a 3 inch egg bar and risk getting stuck with another that does not fit.  After I figured out the problem I found out alot of 3 inch bars will not fit in a 24 40 neck. Shaving solved the problem now not in a few weeks.

[pHarmacist]

Why not get a round bottom to begin with? Flat bottom might be very useful, but as far as I can see only in various extractions (Soxhlet). Am I missing something here or are they really readily used as all-around-reaction flasks?

[Rhodium]

Only by lazy clandestine chemists who think round-bottomed flasks are a hassle, as they can neither be put down on a table without some kind of support, or be heated on their hotplate without an oil bath.

My opinion is that is a small price to pay for the increased safety and versatility (ever seen a three-necked fb flask?)