04-05-99 08:34
No 91411
hey there-
I like using an oil bath on my hotplate/stirrer. there seems area for great improvement though in the actual oil vessel.
I have been using pyrex bowls and even tried a large measuring cup. they all seem to have a little circular rim on the bottom, forming a shallow but noticeable depression. ideally, i'd like to have a perfectly flat vessel to get better heat transfer from the hotplate.
is there some sort of castable substance i could use to fill in the depression? or should i just change to a metal vessel like a large saucepan?
ideas?
(Member)
04-06-99 09:10
No 91413
yeah right after i posted that, i was wondering, won't this interfere with my mag stirring? i know stainless would. i know a lot of the bees are big fans of overhead stirring but not me.
(Moderator)
04-06-99 18:33
No 91412
Use stainless or aluminum pot.
(Member)
04-07-99 02:52
No 91414
The pyrex crystallizaton dishes work great, if you have access to a glassware supplier.
(Member)
04-07-99 06:42
No 91415
Niels- i do indeed! I am looking at one of their dishes right now. This one says it's 75x140 (I'm assuming millimeters) but I was looking for something that's a bit wider and deeper. In fact, a squarish vessel would be ideal for me.
I was thinking of asking a glassmaker to fashion a few up for me, maybe of various heights. Anyone have a rough idea of the cost involved in this low-tech sort of glass labor?
(Moderator)
04-07-99 19:09
No 91416
Aluminum and stainless do not interfere with magnetic stirring.
(Member)
04-07-99 20:30
No 91417
well shut my tater trap! no magnetic currents or eddies? ok i'll try it. empirical is best, no?
(Member)
04-07-99 23:27
No 91418
cheap stainless will. test first see how high you can have flask above the bowl before bar gets loose. if only a little bit get another manf. bowl. also check height before placing bowl under the flask, then you'll have something to judge by.
(Member)
04-08-99 07:26
No 91419
thanks for the inspiration, Os, I guess I should have just TRIED it. I've learned a bigger lesson here, sounds corny, but true.
ok so both stainless and aluminum work, but alumnium seems to interfere less (at least my assumptions weren't totally out to lunch). What I really like are the pans that are the lower half of a double-boiler/Dutch oven set. They have an extremely flat bottom to them.
LN--yes there is a bit of a dropoff going above the bottom but it seems to my untrained eye that i get a bit better rotation an inch or so above the surface of the pan. could this be right? luckily, it appears i have a pretty decent model with a strong magnet. it's also got the nice smart-speed-up, smart-slow-down feature so that the little spinbar doesn't start breakdancing all over the place.
(Member)
04-08-99 10:36
No 91420
Ok, just a little question from someone who has never tried a distillation in an oil bath. The ones (distillations) we did in school we used as some have suggested, flat bottomed flask(s) on a hotplate stirrer. So the question is, does it speed things up, and if not why use one?
(Member)
04-08-99 13:25
No 91421
I like the oil bath because of the temprature hold. I can put a thermometer in the oil and moniter it's temprature. It gives more time to heat up and cool down. Easier on glass.
(Member)
04-08-99 19:07
No 91422
have tried sand, and dot 5 brake fluid. dot 5 works good for sfrole, but when i needed higher for the good stuff I had to go direct to the hotplate. kinda a bitch with a rb flask, just wrapped a bunch of AL foil around bottom and keep the flask about 1/4" form the plate. worked like a charm, left the hot plate on 10 the whole time, i think it might be a problem if plate was to cycle on and off at a lower setting. was able to distill real high bp oil under vac real quick. Dot 5 is real messy! I'm gonna try some silica sand and see what happens, last time i think I had it too thick. and was using regular sand, took 2 hours just to get hot and then never got hot enough to get sassy done. Any comments about sand.
(Member)
04-08-99 19:50
No 91423
i've heard bad things about sand and high temps on hot plates. Apparently, the reflectivity of the sand is too high and is better suited to microscale or low temp operations. anyway, the docs that accompanied my h/s recommended not using a sand bath over a certain setting. LN, have you tried peanut oil? very high flash/ignition point. it's definitely easier than pouring brake fluid all over the kitchen...er..lab
if someone asks about the smell, you say you're having a Jimmy Carter Honorary Fondue party.
(Member)
04-09-99 03:06
No 91424
How about polyethylene glycol with a molecular weight >1000? It has a high boiling point (>210 deg C?) and is water soluable and non-toxic.
(Member)
04-09-99 03:57
No 91425
haven't tried penunt oil yet, what is the bp. whith my shitty vac. some times i think i need over 210c. stir/plate goes to 400c i think.
( )
04-13-99 05:08
No 91426
Your local college chem lab will occasionally supply glass to students who leave the glass in backpack and forget to ask permission to leave.
(Newbee)
12-12-02 18:32
No 388794
Been thinking about sand + oil paste for a while. The sand supports the round bottom well and the oil increases how quickly it heats up. Messier I am sure.
Not a chemist I just follow directions on the box mix
(Hive Addict)
12-12-02 23:23
No 388894
Just a thought, but I'd bet that if you used something like heavy mineral oil with some sand, it might be viscous enough to support the sand in the shape of the flask after you took out the flask. Pretty convenient. Don't know how good heavy mineral oil is for using as a heating element, though.
It is seductive, way too seductive. -Eleusis
(Newbee)
12-13-02 02:57
No 388972
Smokes, Stinks awful. This despite a claimed 350F smoke point on an msds for baby oil. No where near 350F. Lousy cheap mineral oil source.
Not a chemist I just follow directions on the box mix
(Title on BackOrder)
12-13-02 16:22
No 389106
I prefer aluminum pots because you can use a hotplate/stirrer combo with them without distorting the magnetic field to the stirbar in the flask. You can't use magnetic stirring with a stainless steel pot.
If at first you don't succeed, try, try again. Then give up. There's no use being a fool about it.
(Hive Bee)
12-13-02 17:58
No 389119
I sometimes use a stainless steel bowl for oil bath. Stirring is not a problem and never has.