Take off for fores

[twojaythomo]

I don't seem to be able to find a direct answer sorry if it's buried deep in the forum somewhere.

My question is running a bubbler and collecting fores/heads. If I set it to full reflux for 10-20 minutes before anything has come out will the foreshots still be the very first part to come out.

It just looks like all the fores is mixing back through so I'm a bit confused with this.

Sorry if it's a stupid question but I have all ways though about this.

[The Stig]

Fore shots is always the first stuff to come out hence the name

[Doubleuj]

Stigs 100% on the money as usual, fores are what comes off first, but what do you mean when you say “it looks like all the fores are mixing back through?”

[bluc]

Think he means falling reflux. The foreshots are not the falling reflux but the invisible vapour in top of still . When a still hits equilibrium there will be foreshots heads (a number of different compounds) and hearts stacked up the vertical column. The reflux falling liquid is crap water and fussel oils not good stuff...

[twojaythomo]

Wasn't really asking when the fores start but when it comes up to temperature, you have the PC in full reflux and leaving it in that state for 30 minutes to an hour will the fores still be the very first part, do they just sit at the RC till they're allowed to pass by reducing the reflux of the RC.

Sorry I've had a few tonight so don't know if I'm making much sense.

[bluc]

Wasn't really asking when the fores start but when it comes up to temperature, you have the PC in full reflux and leaving it in that state for 30 minutes to an hour will the fores still be the very first part, do they just sit at the RC till they're allowed to pass by reducing the reflux of the RC.

Sorry I've had a few tonight so don't know if I'm making much sense.

Yes
And
The longer you leave it the more compacted and defined each fraction becomes.
The fractions will compress and define without mixing together while in full reflux. When you.open valve and let vapour through after full refluxing you get nice concentrated defined cuts :handgestures-thumbupleft:

[The Stig]

2JT I think you should be asking about the RC not the PC.
RC = reflux condenser
PC = product condenser

[twojaythomo]

Yep Stig I definitely f'd that up I meant the RC.

Thanks for clearing this up for me lads I knew the parts of the distillation got compressed just wasn't sure about the foreshots part of it.

[db1979]

A lot of members like to "bleed off" the fores, which means they set their RC to not quite achieve full reflux allowing the fores to come over to the PC, then let the column reach equilibrium. This means the fores are pretty much all gone and not a part of the dynamic system in the column. I reckon if you're going to spend time waiting for the wash to boil, then spend time waiting for the column to reach equilibrium then you'd be better off doing that with the fores already gone. They're a lot lower in boiling point than heads and hearts so why bother allowing them to hang around?