04-05-02 11:03
No 292776
OK, what do you guys think is better? Do you think it would be better to have just one big hotplate/stirrer, or a whole bunch of heating mantles to go along with each size RB flask that you use and a really big 9x9 or 12x12 magnetic stirrer? How i've seen it is that heating mantles are easier to control than an oil bath, aren't as messy, and don't require as much attention. but then even str*** book TSII says you should have a hotplate/stirrer. share your thoughts, as i'm about to start buying mantles (500mL, 1 L, and 2 L, the fabric ones). also, how about those 22 L stirmantles, pretty nice, huh? not that i have the money to get one, but if you didn't have one, how would you stir? the only 22 L mantles are aluminum. won't that interfere with the magnetic field?
(Hive Bee)
04-05-02 15:23
No 292824
Id invest several hundred in a large (10x10) kick ass stir-hot plate combo before id ever in several matels. Oil heating is very effective and fits a larger range of glassware sizes and with extra efforts in selecting oils with higher specific heats and insulating the bath you can efficiently heat almost anything, and still have the added benifit of stirring. Also, with LARGE volume heating it is more effective to have an over head stirrer rather than magnetic. Check Rhodium's site for a pictoral on making a ghetto over-head stirrer.
Can a bee be visa vis its entity when half a bee philosophically must ipso facto half not be?
(Hive Bee)
04-05-02 15:25
No 292825
I suggest you to get good magnetic stirrer with a powerful motor. Some can stir up to 100L of liquid. The stirring hotplate is essential for most of organic syntheses and when you have one, then you can buy some heating mantles if you want. You can also get heating mantles with built-in stirrer, but as you already said you would have to get some that would go along with each RB flask you are using.
I agree that 22L mantles are nice, but rather don't try to purchase one, since the DEA likes them so much, that they would come knocking on your door and would ask you some questions. Believe me, you don't want this.
Life without chemistry would be a mistake.
(Hive Addict)
04-05-02 20:47
No 292907
the benefit to mantles is controllable heat... the ability to turn it off easily. oil takes a while to cool down, mantles don't. SWIM gave up on oil baths really quick. aside from that, there's the smell.
on the topic of stirplates, SWIM has used 2 types, a sybron/thermolyne 1000, and shiny new cimarec 2's (both stirrer and combo). SWIM still goes back to the used and abused thermolyne 1000 for it's stronger stirring ability, and it's quick spin down. the cimarec's take forever to spin down, making 'jerking' of the stir bar difficult to get it going when it's covered in foil.
anyone have an comperable comparissons with stirrers?
i learned a thing or two from charlie dontcha know.
(Newbee)
04-05-02 21:14
No 292924
"how would you stir? the only 22 L mantles are aluminum. won't that interfere with the magnetic field? "
aluminum isnt magnetic try to pick up a soda pop can with one. swik seriously doubts aluminum would cause any interference whatsoever.
-kap-
Just say know.
(Stranger)
04-08-02 03:39
No 293939
Aluminum is not ferro-magnetic (sp?) and completely "invisible" to magnetic fields. There is no difference in the strength of a magnetic field passing through aluminum or air. The only reduction of field strength is due to the thickness of the aluminum vessel (distance between the rotating magnet and stirbar).
Worker bees can leave
Even drones can fly away.
The queen is their slave.
(Hive Addict)
04-08-02 10:42
No 294151
Wagrasm;
Not entirely so. While a magnet will "pull" through aluminim, aluminim is not "invisible" to magnetic fields. When a magnetic field moves through aluminum(or vice-versa), eddy currents are induced in the aluminum which in turn cause a magnetic field that opposes the original one.
Wanna see an example? Look on your Ohaus triple beam scale. On the right end of the beam arm there is an appx. 1cm x 4cm x 2mm aluminum plate in a vertical orientation. The right-side stancion of the scale containc two magnets. The aluminum plate moves between the magnets as the balance pivots up and down, providing a damping action via the aformentioned effect.
A more fun example? Go to Six Flags amusement park in New Jersey and go on the Batman & Robin "Chiller" ride. While waiting to board, look at thefront of the car down by the tracks nad check out the linear induction motor that propels it. The cars have horizontal aluminum plates sticking out from the sides, sandwichd closely within the gap of electromagnets running 60 feet down the tunnel. Get into the car. You will soon hear the loud, ominous 60-cycle hum of hundreds of amperes. An instant later, before you have a chance to think about it, you will be rocketed down the tunnel from zero to sixty in about 2.2 seconds. As you shoot skyward into the tight double loop, ponder the aluminum. It is truly quite different from air.
For the home experimenter, build a small electric motor, but wind it with aluminum wire instead of copper. Observe operation.
You ARE right that the magnet will work through aluminum, but the effect is diminished by the aluminum itself.
--Bozakium, Hive Physicist
(Stranger)
04-09-02 02:23
No 294384
Gadzooks! Bozakium, I stand corrected. I didn't take eddy currents and Lens's (sp?) law into account. A spinning stirrer would induce eddy currents wouldn't it? For some reason I was picturing a stationary magnetic field, which obviously isn't the case.
Worker bees can leave
Even drones can fly away.
The queen is their slave.