03-22-04 06:44
No 496564
SWIM was wondering what the best way would be to go about this. SWIM UTFSE and found posts stating that the vacuum hose should be disconnected completely, flasks changed, hose reconnected.
This seemed like it would cause a drastic pressure change quickly, which is what SWIM thought was to bee avoided. What is the best way to do this? Since SWIM is using a water aspirator, could water flow be reduced slowly, then disconnect hose, change flasks, connect hose and raise water flow again? Or should SWIM actually reduce heat and let system cool before switching? Any help appreciated...
(Stranger)
03-22-04 07:49
No 496571
Buy a cow adapter. You'll never look back. Yields will be higher, and distillations will go smoother. It's the best way to go, and well worth the expense.
Thank god for the music.
(The Archetypical "Good Guy")
03-22-04 10:02
No 496593
Could you elaborate on what a cow adaptor is? I have never heard of the expression...
Nuke the whales!
(Newbee)
03-22-04 11:17
No 496604
i don't get it though, you still will break vacuum when you remove one of the flasks from it (usually they've got 4)... so they are intended to be spun around. i can see how it would be helpful in atmospheric distillation though. the cow bits would have to have vacuum valves to be useful to vacuum distillation.
(Hive Bee)
03-22-04 13:02
No 496612
The cow adapter is like a normal vacuum distillation adapter (it has a vacuum connection). rather than having a Ground glass joint for one receiving flask, it has three joints for three receiving flasks. These joints come off at different angles, so that when the glassware is rotated on the end of the condensor, the distillate will fall into a different receiving flask. It is called a cow adapter because it is a bit like a cow's udder I think. They are excellent.
(Stranger)
03-22-04 20:38
No 496679
Thanks for the input all - I was already familiar with the cow adapter, but was hoping the answer would be something besides "buy more glassware".
Is there a proper procedure to do this by literally putting a new flask onto the apparatus? Hasn't anyone ever done this? I was pricing out the cow adapters. Not horrible but not cheap either.
(Hive Bee)
03-22-04 20:54
No 496681
Since SWIM is using a water aspirator, could water flow be reduced slowly, then disconnect hose, change flasks, connect hose and raise water flow again?
Reducing the water flow/interrupting the water flow completely can/will lead to water sucked into your receiving flask ruining your precious distillate. If you use a water aspirator as vacuum source it might be a good idea to have a wash bottle connected between your vacuum adaptor and your aspirator.
Always disconnect your vacuum tubing to release the vacuum.
For Research Use Only
(Hive Bee)
03-22-04 21:49
No 496685
there is a video of a cow adaptor in use
wanted: witty signature...pm with details
(Hive Bee)
03-22-04 22:21
No 496687
If you don't have a cow adapter, just disconnect the vacuum, then change the BF with a clean one, apply the vacuum again and continue. Things will get a bit cooler, then you will have to wait again till it heats up again and resume distillation.
The cow adapter is a much better option, besides saving time ( distillation not interrupted, since you just turn the cow to switch flasks ). I have two, one with a vacuum inlet and the other whithout. All 24/40. Very good for ketone and freebase.
I strongly suggest you to distill your freebase, final product much cleaner. Before I was getting kind of beige powder, almost white, now got real clean, white, powdery stuff.
03-22-04 22:40
(Rated as: misinforming)
(Hive Addict)
03-22-04 22:46
No 496693
do not turn off the vacuum while still connected!
remove the vacuum hose, then turn off the vacuum.
doing otherwise can result in nasty suckback of water/oil.
filter(lambda W : W not in 'ILLITERATE','BULLSHIT')
(Hive Bee)
03-22-04 23:00
No 496695
suck back is usually associated with vacuum filtration but the same rules apply to distillation
wanted: witty signature...pm with details
(Hive Bee)
03-23-04 00:01
No 496703
(Rated as: good read)
Another option is to use a so called Fraction cutter:
With this you can collect your fractions in a barrel and release them into a flask ocasionally. The Vacuum can than be cut off from the flask without breaking the vacuum in your distillation system and thus the flask can be changed while the next fraction collects in the barrel. This is done w/ the aid of 3-4 stoppcocks.
A Fraction cutter is especially usefull when distilling / collecting larger amounts, while the "cow adapter" is preferred for small fractions.
The applicatin of the Fraction cutter, by Xicori can be seen in:
Post 478384 (Xicori: "P2P from Aniline! (Meerwein arylation)", Methods Discourse)
Post 451447 (Xicori: "PCP via enamine intermediate [pictures]", Methods Discourse)
The "cow adapter":
Post 473189 (Xicori: "P2P-Success! (Phenylacetic acid/AA/NaAc)", Stimulants)
Post 475049 (Xicori: "PCM synthesis", Methods Discourse)
OR the film:
../rhodium/archive/vacuum.di
" Unorthodox cooking, illicit cooking. A bit of real science, in fact. "
(Chief Bee)
03-23-04 00:24
No 496708
Also see this makeshift fraction cutter:
(full descriptions in ../rhodium /equipme
The Hive - Clandestine Chemists Without Borders
(Hive Bee)
03-23-04 00:29
No 496711
I agree that this is not the correct technique, but ...
1) My aspirator has a backflow valve, I can safely turn it off, the system will keep the vacuum, no water suck back.
2) With the pump, there will be suck back, but it takes sometime, usually I turn off the pump, then fast, disconnect the hose. Once I forgot, I got pump oil sucked over my ketone. Easy to separate, though.
Indeed, I agree with the comments, I am wrong, sorry.
(Chief Bee)
03-23-04 00:56
No 496718
1) My aspirator has a backflow valve, I can safely turn it off, the system will keep the vacuum, no water suck back.
I relied on such a backflow valve too in my younger days, and got a really hefty suckback with messed up distillate, cracked distillation flask (water was sucked as far back as to reach the 150°C+ distillation flask) and with resultant splattering of the oil bath when water hit it.
After that I learned that the valve is a safety device, and not something which should be used because you don't feel like removing the vacuum hose from your distillation setup before killing the vacuum.
The Hive - Clandestine Chemists Without Borders
(Hive Bee)
03-23-04 01:31
No 496727
Hi! i am also using an wateraspirator. i reduce waterflow about 3/4, so that it is sucking just a little bit, to prevent sucking water back. then slowly and carefully remove vacuumhose, first a little bit on one side so that the vacuum will be released slowly. after a few seconds you can fully remove it and stop waterflow. i did it always like this and had never a suckbackproblem. i tried all steps without chemicals to learn, used just water several times.
(Hive Bee)
03-23-04 05:05
No 496778
Answering DeeMTermined question :
The cow whithout vacuum inlet is used with a short path distillation condenser, that has its own vacuum inlet. The one I have is a bit akward, because the condenser angle is 45 deg. I found out that bending it 30 deg and using a small 24/40 extension lets the cow receiver to be connected properly. Whithout the extension there is no space to fit in the cow and boiling flasks. I have one 250 ml and two 100 ml 24/40 BF's, that I normally use with this setup.
The one with the vacuum inlet is used with a 300 mm Liebig condenser, that has no vacuum inlet. This condenser has a 15 deg ( 105 deg type ) angle with the horizontal. I clamp all the BF's with Keck clips.
(Hive Bee)
03-23-04 06:07
No 496787
you could clamp your vacuum hose, turn off the water driving your aspirator, then slowly release the clamp. it's cheap and easy.
please note, swim has never tried this because he doesn't use an aspirator. this is only a suggestion based on non-practical knowledge.
(Chief Bee)
03-23-04 10:21
No 496818
You forgot to say "disconnect hose from aspirator before releasing clamp".
The Hive - Clandestine Chemists Without Borders