peach
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Why do they do this to filter flasks?
I see this all the time on these composite filter funnels, the flask has a male adaptor.
What's odd about that is all the sintered funnels I see, and own, use a female socket on the flask. It's made more odd as this one is sold by
QuickFit, who certainly use the male funnel into a female flask arrangement for the rest of their glass.
Some furnace tubes use it as well.
Looks strange to me, but there you go. I'm guessing there's some logic behind it and it's not simply an attempt to make me buy another filter flask.
Not quite as expensive as a pair of plastic titties, but nearly...
I like the little cap nipples on these.
[Edited on 2-9-2010 by peach]
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ScienceSquirrel
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It is a safety thing.
The filter will not fit on to a standard flask but only a special thick walled one that will not implode under vacuum.
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peach
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But then...
And these are from QuickFit, who also sell the one at the start of the thread;
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watson.fawkes
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I'm guessing here, but if you're using heat to separate a stuck joint, it's easier to heat a lower thermal mass piece than a higher one. Since heat
causes expansion, you put the female joint on the part that will be heated. I can only imagine that this happens often enough that they went
reverse-polarity to cope with it, and that it's more common with vacuum flasks because the joint pieces are more tightly pressed together from the
ΔP.
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peach
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I figured it'd be heat as well, particularly with the furnace tubes in mind; that it's easier for the female to slide off when it's on top.... .. ....
. ( o ) ( o )
Furnace tubes are about the trickiest things to grease as well, meaning you'll be relying on them not jamming when dry.
That, or it's all part of the global bad credit conspiracy.
I've spent quite a while gazing at that picture trying to think of other reasons, to avoid a face slap moment, but am still wondering.
I would be surprised if there wasn't some reason, and I'd think a lot of glass companies would purposefully do it the other way round to get customers
buying their funnels to match.
Which kind of ties in with QuickFit selling both variations, which aren't compatible with each other.
Never had a funnel jam, or any taper that's been greased properly for that matter.
Follow the MIT advice on greasing your tapers, and they'll jam.
"BEE,UUUUUUUUUtiful money!"
[Edited on 2-9-2010 by peach]
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zed
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Just because some knuckle heads have decided to manufacture such a thing, doesn't mean I have to buy it.
That stuff looks expensive. Expensive and fragile.
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peach
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Quote: Originally posted by zed  | Just because some knuckle heads have decided to manufacture such a thing, doesn't mean I have to buy it.
That stuff looks expensive. Expensive and fragile. |
Ha ha ha, what are you talking about Zed? The weird taper arrangement, sintered funnels or the amber plastic gear?
I think it's a shame they do this with the clampable funnels, because those have nifty replaceable membranes that can filter bacteria and spores, so I
could use the same glass for biology if it wasn't laid out that way. The membranes can either be binned after each use and a new, sterile disc dropped
it or users can dry them and determine the cell mass, or use it to inoculate plates to look at what's in water samples and whatnot.
The amber plastic is from Nalgene, so it's designed for repetitive autoclaving in biology labs, keeping oxygen away from cakes of cells and reducing
the light they're exposed to.
[Edited on 2-9-2010 by peach]
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aonomus
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We use those filters at work with 0.45um nylon membranes for HPLC mobile phase filtration. I suspect the joints are reversed so when you pour, your
mobile phase does not contact the joint, and any potential grease/dirt it might have. In fact we've never had a stuck joint, and they're all
ungreased.
I also suspect that because of the tendancy for organic solvents to boil off like ACN under strong vacuum, the cooling effect on the top portion won't
affect the joint's gas-tightness as much as if it were the normal orientation (ie: the joint becomes tighter instead of looser).
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peach
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It's good to see someone else knows about those membrane filters, they're funky little things hey!
If you look at the Chemglass and QuickFit sinters though, you'll see they both have spouts that stick down, away from the taper, for the grease
reason.
And, if the cooling is uniformly present, it shouldn't matter which way round they are right? I would guess watson may be the closest with his freeing
stuck joints idea. But then, why use the opposite version on everything else?
Tapers aren't going to jam often around solvents alone, it's once something precipitates in them or starts working on the surface of the glass.
For example, I greased a taper to store some Lewis acid, as per the MIT suggestion, and it was fused beyond repair not long after. Three weeks of
messing with it each day, it needed a screwdriver and a hammer in the end. Because the acid had gotten onto the tip of the taper.
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aonomus
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Probably another reason why they use ground glass joints at all in these style flasks is to avoid any plastic, since mobile phases for RP columns can
happily leach out trace contaminants such as plasticizers that you would find in neoprene stoppers/cones for filter funnel adapters.
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virgil53
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As I recall from my readings, this conformation is used in some special syntheses. The male joint on the flask would be useful for cases where the
filtrate is the component of interest.
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MagicJigPipe
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I have one of these. I have used it several times for vacuum filtrations (because I don't really have a good alternate setup; don't understand why?
Because this was really cheap when I got it on eBay and that's just how it happened) but could never really figure out the reason for its odd design,
though. I am very certain it has something to do with HPLC or some other type of chromatography as we also have one in the lab underneath the HPLC
device.
Filtering solvents for HPLC?
[Edited on 11-14-2010 by MagicJigPipe]
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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aonomus
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It is used for HPLC mobile phase filtration, I use one of these almost every day.... I'm not sure why there is a reverse taper... read the thread...
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