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Author: Subject: Newbie with soxhlet, lots of questions...
ptr
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wink.gif posted on 2-8-2010 at 18:22
Newbie with soxhlet, lots of questions...



Hi.
I recently bought this two small fellows
http://www.labx.com/v2/adsearch/Detail3.cfm?adnumb=418052
http://www.labx.com/v2/adsearch/Detail3.cfm?adnumb=418051

By accident I bought the smaller one first, when I realized the size - 2.5cl I also gave a bid at the larger one.

I have _no_ chemistry skills, not studied it in high-school (now i am middle age +) and i would like to get some basic training for what you can do with a soxhlet.

Now to some of my questions.

0.First I would like to put them each on a test run, just with water, or something silly, maybe brewing coffee or something ;) . I would like to get suggestions for what I should look after to possible adjust.

1. Does the size matter :D (maybe the small one would be good for small extractions- tests, before doing a batch of something with more material and liquid)

2. For the bigger one there is no flask, is it possible to substitute the flask with a jar and a hole in the lid.?

3. I also would like to do some experiments together with my son, extracting colors and odors from flowers. Links highly appreciated.

4.I would like to get suggestions for other basic equipments and liquids.
So far i have a magnetic stirrer with heater, some cheap test tubes - probably not heat resistant, and one iron that i will put upside down and use as a secondary heating device so i can choice temperature from silk and up :D .

Well, I suppose I have more questions, but this will be enough for be in the first post.

/ps - I have not got them yet - they are still waiting for dispatch.
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[*] posted on 2-8-2010 at 20:16


I used similar with absolutely no training - I didn't do chemistry until the day I was put in front of one and told to get to work.

Hence, if you think about what you do - you should be fine.

1: Size mainly matters depending on how much, how fast, and how pure you want to do.

2: Maybe. It depends how good your moulding skills are. That said, whatever you make the connection out of may react with what you're trying to extract.

3: Can't think of any off the top of my head, but it sounds like an awesome idea to start with!

4: Upside down iron - I hadn't thought of that :D

Also, welcome to SM.




“If Edison had a needle to find in a haystack, he would proceed at once with the diligence of the bee to examine straw after straw until he found the object of his search.
I was a sorry witness of such doings, knowing that a little theory and calculation would have saved him ninety per cent of his labor.”
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[*] posted on 2-8-2010 at 20:56


> Links highly appreciated.

Here's a blog which describes how to make hot pepper extract
in alcohol along with a video.

http://aonomus.wordpress.com/2010/02/17/extraction-of-capsai...
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[*] posted on 3-8-2010 at 05:23


Quote: Originally posted by psychokinetic  
1: Size mainly matters depending on how much, how fast, and how pure you want to do.
Here i speculate a little, just want to understand the process - pls correct me where I am wrong.

I think that if i want to do a small extraction (mainly as a test) it is ok with the little one because with the larger one I need to use more solvent.?

If i run them side by side, with the same solvent and the same material and 1/10 of the material in the smaller one (which is 2.5 cl, the other is 2.5 dl) , 10 times the size=equal 10 times longer cycles.?)

My idea is something like this. (here I assume the soxhlets are proportional 'clones' of each other - the same type and brand of condenser etcetera - just the size differs)

Time 0 Is where they both are heated up to the same temperature.
Time 1 They both get the chamber filled.
Time 2 The siphoning action kicks in.
Time 3 It starts all over again.

There are - afaik, two opposite things that we have in count
1. The time it takes to fill the chamber, more solvent-but also more pressore from the flask.(?)
2. The time it takes to perform the siphoning action, more solvent and material - but also more pressure from the above.(?)

Then - I wonder if the smaller material in the smaller soxhlet is expected to be more purified in the same number of cycles.?
Quote: Originally posted by psychokinetic  
2: Maybe. It depends how good your moulding skills are. That said, whatever you make the connection out of may react with what you're trying to extract.
Yes you are absolutely right, I should think before I ask :)
Quote: Originally posted by psychokinetic  
4: Upside down iron - I hadn't thought of that :D
lol - yes it works quite well for small quantities, - I use to tighten it in my workbench but you have to clam the flask well else it easily slip off. And as you for sure allready know, it is not intended to use this way -always have an eye on it.:)
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[*] posted on 3-8-2010 at 05:25


Quote: Originally posted by microcosmicus  

Here's a blog which describes how to make hot pepper extract
in alcohol along with a video.

http://aonomus.wordpress.com/2010/02/17/extraction-of-capsai...
Thank you - very good stuff, This could be one of my first experiments.
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[*] posted on 3-8-2010 at 07:57


The Soxhlet extractor apparatus is used for the lab-scale extraction of essential oils (mainly terpenes and low-melting lipids), and alkaloids and other compounds, from plant materials, with various volatile solvents including n-hexane and water, being similar in principle to a coffee percolator. However, the technique is somewhat outdated now, especially for larger quantities. Sigmaaldrich.com sell a range of the apparatus.

See:
http://en.wikipedia.org/wiki/Soxhlet_extractor

PDFs:
http://www.erowid.org/archive/rhodium/pdf/soxhlet4dummies.pd...
http://www.epa.gov/osw/hazard/testmethods/sw846/pdfs/3541.pd...
http://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/140.%...
http://www.buchi.com/uploads/media/Best_buchi_47_Soxlet_Hot_...
http://www.cem.de/documents/pdf/RE/RE027.PDF
http://cobweb.ecn.purdue.edu/~lorre/16/research/LAP-010.pdf
http://ccsenet.org/journal/index.php/ijc/article/view/5080/4... (PDF)

HTML:
http://stason.org/TULARC/science-engineering/chemistry/16-6-...
http://www.rsc.org/chemistryworld/Issues/2007/September/Clas...
http://www.whonamedit.com/doctor.cfm/3041.html
http://chem-ilp.net/labTechniques/SoxhletExtraction.htm
http://www.oilgae.com/algae/oil/extract/che/che.html
http://www.ncbi.nlm.nih.gov/pubmed/16439256
http://www.astm.org/Standards/UOP602.htm
http://www.cyberlipid.org/extract/extr0010.htm
http://mybuchi.com/Extraction-Solutions.11132.0.htm
http://www.cgerhardt.co.uk/pages.php?page_id=104

Videos:
http://www.youtube.com/watch?v=_fxwp4KcbEE
http://www.youtube.com/watch?v=2L6MDOW88zc
http://www.youtube.com/watch?v=_fxwp4KcbEE

Someone please retrieve the following additional PDF papers on the subject, not available to the general public, and upload them to References:
http://www.jbc.org/content/99/1/289.full.pdf
http://www.springerlink.com/index/N52MR3121145X258.pdf
http://pubs.acs.org/doi/abs/10.1021/ac50077a055
http://linkinghub.elsevier.com/retrieve/pii/S000326709800233...
http://www.plantphysiol.org/cgi/reprint/37/3/357.pdf
http://www.jstor.org/stable/25580942
http://www.ingentaconnect.com/content/els/08891575/2001/0000...
http://www.informaworld.com/index/769225241.pdf

[Edited on 3-8-10 by JohnWW]
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thumbup.gif posted on 3-8-2010 at 09:39


Quote: Originally posted by JohnWW  
However, the technique is somewhat outdated now,
What that you got me thinking about is the Gregar Extractor, the price is not to bad either ~ 470$
http://www.anl.gov/pse/glassblowing/gregar_extractor.html - but I think that if I use a soxleth it's more as learn from the ground and up.(?)

I am very interested in what you should suggest instead of a soxhlet. :)

And -WoW, there was a lot of links you had for me :cool: , I will just go grab a cup coffee so I have time to dig through them, lol - do you think How many cops do you think I got to drink before I am done with them all.? ;)

Thank you a lot for all the links...
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[*] posted on 3-8-2010 at 10:52


It's basically the same as a coffee maker, it just recycles the solvent via distillation so you are extracting into pure solvent and the dissolved material concentrates in the boiler.
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[*] posted on 3-8-2010 at 11:00


I understand that part - but how is it compared to an soxhlet..? In therms of efficiency and versatility.?

[Edited on 3-8-2010 by ptr]
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[*] posted on 4-8-2010 at 12:15


P.S. Of the above PDF papers on Soxhlet extraction that I listed as not being available to the general public, it now appears that this one can be downloaded directly without a subscription:
http://www.plantphysiol.org/cgi/reprint/37/3/357.pdf
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[*] posted on 4-8-2010 at 12:49


Soxhlet espresso, anyone?



“If Edison had a needle to find in a haystack, he would proceed at once with the diligence of the bee to examine straw after straw until he found the object of his search.
I was a sorry witness of such doings, knowing that a little theory and calculation would have saved him ninety per cent of his labor.”
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[*] posted on 4-8-2010 at 19:13


Quote: Originally posted by psychokinetic  
Soxhlet espresso, anyone?
Yes, I have had that in mind.
I have a friend that really enjoys her coffee,she buy the best quality coffee and grinds it herself, and she know exactly how to make a good cop of coffee.

I have two small planes for what i would like to surprise her with.

I would like to try to make a cup of coffee in my soxhlet, and i suppose i constantly have to take from the filled chamber because maybe it will be to much tannin (because of heat), in the flask.?

Also if possible, I would like to extract the flavors (eg, dissolve the tannin) - from the product - is there any way do this, and how?

[Edited on 5-8-2010 by ptr]
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[*] posted on 4-8-2010 at 20:53


Is it possible to extract different units of the material by changing the temperature of the condenser so the solvent that fall off will have another temperature.?

Or is it better/more common change the solvent.?

[Edited on 5-8-2010 by ptr]

[Edited on 5-8-2010 by ptr]
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[*] posted on 5-8-2010 at 06:41


JohnWWW deserves a medal for all that linking. ;)

The time it takes depends on how fast the solvent is rinsing through and the amount of material present. There are factors that set those rates.

In your example, assuming the solvent is vaporizing and condensing at a similar rate for each, the 1/10th scaled extractor will work quicker, as the rate of solvent moving through it is the same, but the amount of material to be extracted is an order of magnitude smaller. An extractor that size is still useful. It makes it a lot easier for chemists who only have a small amount of something to work with, or only need a small sample to run through things like chromatography and such. The bigger ones are, obviously, desired more for actual production quantities.

You can't change the temperature of the solvent like that, no. It's one of the properties of boiling or subliming things, they occur at specific temperatures (or in a specific band if it's forming an azeotrope, but that's not something you need don't to worry about for now).

For example, if you put a pan of water on the stove and gently warm it to boiling, then stick a thermometer in, it'll read around 100C. If you then turn the stove up to it's maximum, it'll still read 100C, but the water will be boiling off quicker.

This same thing happens when materials melt. For example, ice. You can cool ice to below 0C. Ice in your freezer will be around -18 to -20C. As soon as you take it out, it will rapidly start warming up, but not melting. Once it's temperature reaches 0C, it'll stop warming up and start melting. The temperature won't change until it's a liquid.

These are called changes of state, or phase changes.

If you take both those examples above and run an experiment, you can actually see the very dramatic effect they have. For instance, stick a thermometer in your freezer cooled ice and then gently warm it to boiling at a constant rate, plotting it's temperature on the Y and the time on the X as it goes.

What you'll see is a graph that quickly goes up, then goes horizontal for a long period. Then starts going up again, then goes horizontal again and won't ever go higher. The first horizontal line is substance melting. The second is it boiling.

To get more technical, there are two phrase you need to know... specific heat capacity and latent heat capacity. The first is the amount of energy it needs to cause a change in state. So there are two, one for melting and one for boiling. The second is how much energy it needs to warm something up by a degree between these two stages.

The specific heat capacities are often HUGE when compared to the latent heat capacity, it takes a ton of energy to melt a lump of ice and an equally gigantic amount to boil it. This is why humans sweat. The layer evaporation of the sweat draws a lot of heat away (again, the specific reasons for why the sweat evaporates even though it's largely water and not at 100C are a bit too technical for now, but it's essentially due to not all the molecules being at the same exact temperature, see; Maxwell Boltzmann curves if interested).

These specific heat capacity, state changes require so much more energy because the structure of the substance is changing at a molecular level. For melting, the molecules have to all let go of each other, which happens at a specific energy (temperature). And for a gas, the liquid has to let go even further so the molecules can bounce around freely. In between, the extra heat is simply making them move a bit quicker, not changing their ordering (way of packing). It's a bit like unpacking a well packed parcel. It may take a fair amount of effort to get through all the tape and bags but, once it's open, it's easy to throw the packing peanuts around.

An interesting fact is that the LATENT heat capacity (the one that determines the amount of energy something needs to warm it up but not change it's state) is what defines that which we experience as 'cool' or 'warm' to the touch, even when something is at the same temperature as the things around it. Your nervous system is being tricked into thinking it's cooler because it draws heat away better. Or a wolly jumper will feel warmer to the touch because it doesn't. Even when they're both the same temperature.

The latent heat capacity also changes a little depending on the specific temperature something is at. Using water as the example again, it takes the least amount of energy to change it's temperature when it's around 37C. The fact that the majority of warm blooded animals happen to keep themselves at this temperature is not an accident, it's the ideal temperature for the body to regulate it's self using the least amount of effort.

The only way to affect the temperature something changes state / phase at is to change the pressure it's under, as this is whats telling the molecules how much energy they need to have to start moving around more. Some examples, water will boil at a lower temperature if you climb a high mountain, as there are less molecules pushing down on it's surface. If you connect that water to a semi-decent vacuum pump, it'll boil at room temperature. All solvents and liquids do this, and chemists exploit the fact by distilling things under vacuum to lower the temperatures; which may harm the glass or the substance inside (as well as removing the oxygen for it to react with). Yet another example, CO2, propane and numerous other gases will turn into a liquid when highly pressurized. Cylinders of the gases use this trick, because you can get orders of magnitude more product into the same sized cylinder if it's a liquid rather than a gas. Another example is steam. It'll boil over 100C provided it's in a sealed boiler where the pressure can't escape, as per a steam strain or turbine at a power plant; where they use the trick to produce mechanical energy from the solvent as it forces it's way out of the container.

The people who fill the cylinders use both tricks together to produce the products. They even call themselves 'liquid air' companies. They suck in air from the atmosphere, dry it very well, then compress the shit out of it, causing a number of the components in it to liquefy. They then let it gently warm up and recollect the specific gases as they boil off at their own specific temperatures.

This is all essentially what you already know in reverse. You will have seen steam condensing on the tops of pans and maybe the experiment where steam is blown into a plastic bottle, then the bottle is submerged in water, causing it to collapse in on it's self as the steam goes back to a liquid. Rather than cooling to reduce the pressure, the cylinder guys are raising the pressure to produce a liquid.

After all that, no you can't change the temperatures. They're defined points at set pressures and you can't pressurize glass like yours over about 14psi; which is dangerous to begin with and not something I'd recommend.

These facts are still used by chemists over precision temperature controlled hotplates or expensive thermometers. By choosing a specific solvent that will work chemically, they can then pick one from that range that boils at a specific temperature. As the solvent usually boils long before the chemicals in the glassware, the temperature will be fixed at the boiling point of the solvent. You'll see people saying "I refluxed this for an hour", meaning they're boiling the solvent, condensing it and dripping it back in, as your soxhlet does. What they're also, indirectly, saying is "I ran the reaction at ...[solvent boiling point]... temperature for an hour".

To provide some more everyday useful help, whilst you can't really change the BP without changing the solvent you're using, you can change the RATE it's boiling at.

There are two main factors affecting this. The rate heat is going into the solvent flask and the amount of surface area the liquid has.

So, using a round bottom flask, you want it about half full, where the surface of the liquid will be at it's maximum. You can also turn up your hotplate. The temperature of the solvent won't rise anymore once it's boiling, but your adding heat to it quicker, allowing it to boil faster. It's often better to think of energy rather than temperatures when thinking about this. By that I mean, think of it as not raising the temperature, but pouring more heat energy into something. It can only escape so fast, and the resulting temperature is the accumulation of the energy. With the BP fixed, the only place the energy can go is into boiling the solvent off quicker.

You should now see that changing the condenser won't change the temperature of the solvent a lot, as the temperature it turns into a liquid is basically the boiling point and the same rules apply. The glass is also being heated in that region to the same temperature it boils at, so there's nowhere for the liquid solvent to cool. If you wanted to cool it, it'd need to go back down through a separate cooler.

Despite the fixed BP, roasting your glass to run a reaction, distillation or extraction faster is often not a good idea, particularly with organic substances in it, as the surface of the glass can get a lot hotter than the solvent. And, since the substance is in contact with the glass as well, it can ruin it.

You will get cleaner, purer results by turning the iron up to the [just about boiling the solvent] setting. :P For something like water, that'll be the nylon / lycra / acrylic / acetate / synthetic setting. :D

The surface area of the solvent can also be increased by stirring it, which sloshes the solvent up the walls of the flask and deforms it from a smooth surface. If I'm running a distillation or reflux, it's hot and have forgotten to turn my stir bar on, when I flick it on I'll see the solvent momentarily try to push it's way through the condenser. Chemists in well funded labs have things called rotary evaporators to maximize this effect. It spins the flask to continually coat the walls and maximize the solvents surface area. These costs literally thousands new, and are far from anything you'll need for a good while (there are a lot of very good chemists who've never found the need for one). Not many people here have one. Don't try spinning your soxhlet, spin the solvent with a stir bar. ;)

A few more tips.

Don't touch the glass against the hotplate, especially if it's a round bottom flask, as it'll scorch the thing you're extracting into the solvent and risk popping the glass due to the temperature gradient. The glass needs warming uniformly. Suspend the flask a half inch or so above the surface and then make a foil skirt around it. This is called the TP method, and has nothing to do with the toilet. TP stands for Tipi (tee-pee is how I think of it) because the foil looks like a little tent around the flask. You simply wrap the foil around the neck and then drape the rest down over the flask so it forms a big, old fashioned type skirt over the surface of the plate. Don't squeeze it against the flask, that's the opposite of what you want and it won't work, you need a pocket of air between it and the plate. The more of the surface of the plate the base of the tent covers, the quicker it'll transfer heat. This method is a lot safer, quicker to set up, cleaner and less smelly than using oil baths. The first is a serious concern if you're getting your youngin' involved, as there are even chemists on this forum who've burned themselves with hot oil spills, very badly. This TP method works great, produces a very uniform heating profile and can easily get the glass up to hundreds of degrees. It's also very easily to cool the glass down if it's getting out of control, by simply unwrapping the foil. As opposed to playing with the clamp stand and lifting hot, potentially reacting and out of control, delicate glass out of a hot oil bath.

Using a bigger flask with the same amount of solvent and whipping it round really quickly with a stir bar may help give you a bigger surface area. But, if you increasing the flask size and using lots more solvent to fill it, you're kind of defeating one of the points of a soxhlet, which is to use a small amount of solvent.

People designed soxhlets for a few reasons. Firstly, the solvent dripping back down will never 'burn' the organic material, but this is defeated if the glass is run very hot, as the extracted substance will burn in the boiling flask under the same conditions. Next, the solvent dripping back down is fresh, which means it will pull the extractables out of the sample faster; as there's a higher diffusion gradient between the two than there would be if it was simply sat in the solvent in the boiling flask.

Using the minimal amount of solvent possible was useful not long ago (and still is) because it made it easy and quick to remove the solvent when the work was done, leaving the extracted material behind. Now the more expensive labs have rotovaps, the chemist can use a big jug of solvent to quickly remove the material, then stick it on the rotovap and remove the solvent in minutes.

One of the prime reasons for the rotovap is that there'll be 30 students lining up to remove liters of solvent in one lab session, and it lets them get it through in time to do the rest of the work under supervision.

But, as I say, rotovaps are extremely expensive and also easy to break. They require vacuum pumps and often dry ice / acetone baths to condense the solvents which (now under a strong vacuum) won't turn back into a liquid until they're tens and tens of degrees below zero.

Soxhlets are good because you can simply set it up in the morning, then go out and return to find the material has been gently, thoroughly extracted. Labs still use them now, particularly those that do work collecting samples from nature for testing or analysis (like looking for contaminations in soil samples from around rivers, farms, industrial plants, mines and so on). They'll often have a big bank of them so they can go out forging for samples in the wild, drop each into a thimble and then the extractor, start them up and go out again.

As a guide, to speed up solvent removal when it's done, you could try finding a rough solubility for the compound you're extracting in that particular solvent and then use about that amount of solvent. You'll want to use a little extra, as there'll be a number of other things trying to dissolve in it if it's a complex organic sample from the wild.

If your compound of interest is heat stable, you can select a solvent for it that boils at a higher temperature. The extra heat in it will mean the molecules in the liquid at moving quicker, and so the compound will diffuse out into it even quicker.

A lot of chemistry takes times. Hours or days. There is an art to structuring the work such that you can start one thing, then get on with something else, like preparing the next stage or doing the washing up of the things you've used so far.

Commercially, when they want to extract things like essential oils, they'll use the same idea but use something like liquid CO2. It will extract the compounds, cause zero damage to them and violently boils off at room temperature, making it all very quick. But they also need special compressors to catch the gas and recycle it, and special pressure vessels that won't burst in the process. Potentially a lethal process for homebrewed pressure vessels (which many people here will affectionately refer to as a bomb).

When using the iron method, of coarse, be very, very careful to make sure the iron isn't going anywhere. Clamp it in a fixed vice or a make a clamping support for it. It's common for improvised setups to catastrophically fail. E.g. the iron slips, smashes the flask, topples the rest onto the floor and pours potentially toxic or flammable materials out, which are also hot and boiling (making them far, far easier to ignite). A number of people on this forum use portable hotplates for chemistry. As they're already flat, sometimes adjustable and they're not going to topple or fall over. They're also extremely cheap.

I would suggest either running the glassware in a sink or a large, flat pan, where any escape attempts can be contained. Once you start working with flammable solvents, a fire extinguisher is a good idea. As is easy access to a garden hose.

With regards to the Gregor extractor, that's just some glassblowers with an inflated sense of provide in their modifications of a normal soxhlet. It does look handy for some things, but it's no technical masterpiece that takes a leap forwards in extraction rates and such. It's bits of other commonly available glass and knowledge being used to make a soxhlet a bit quicker or allow it to extract liquids with liquids.

There is already a piece of glass that can do the latter, called a Dean-Stark trap. They've just glued the feature to a chamber.

You could produce the same effect as that newer design using a filter flask. Put the liquid you want to extract in there, boil the solvent in another flask, blow it through to a condenser over the filter flask and let it drip in as you stir. The solvent will gradually fill the flask (sitting atop the liquid being extracted) and then start dripping out the side arm, which you can direct back to the boiling flask.

You could also build a continuous extractor by attaching a plain fractionating column to a flask, wadding the end with glass wool, loosely packing it with the sample and fitting a condenser to the top. The solvent will run through, and back down in a similar manner. The drawback here would be that the column may 'flood' with solvent if you can't dynamically control the rate it goes back, with a tap for example, and it may also run down the sides of the sample as opposed to all of it. This is why the soxhlet has the syphon tube. By flooding the thimble, you're sure all of the sample is exposed and, when the flooding gets to be too much, the syphon automatically empties the chamber. A neat piece of mechanized, self driven glassware.

This is an example where improvising could easily produce a poorer, more expensive, more dangerous result and it'll be easier in the long run to get the glass designed to do it most of the time (even in terms of the work you have to do to get the money to buy it versus the extra work the improvised method will cause with the added negatives of risk and poorer results). But I doubt you'll ever even require things like liquid / liquid extraction, and you already have your sexylets on the way.

That was probably my longest post ever to this forum. I hope it's helpful for you and the little guy and gets you going with some fun,
John




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