I've been trying to get some PG for my tupperdor without having to spend 20 bucks at Tractor Supply on a gallon of the stuff, just to throw most of it out.

I just off the phone with a pharmacist, who told me PG and PEG (polyethylene glycol) are the same thing.

Any chemists (or chemistry buffs) here who can give me a definitive answer? I've looked at wikipedia, and used my google-fu, and all I see is that they're chemically similar.

So, should I go get some MiraLax and mix that with my distilled water? Or try to find a smaller amount of PG? My spidey sense is tingling on this one.
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Just use distilled water. :-)
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Yeah, I think that may be best. Using it with some wet flower foam right now. Holding humidity at 63-64%.
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careful as flower foam will mold Jason. :-)
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:-) flower foam should be viewed with caution. It's probably okay for a couple months, but I'd try to have an alternative ready by then. Been there, paid that price.
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How big is the humi? Boveda packets are really hard to beat if it's a desktop type rig. About as cheap and easy as it comes.

http://www.bovedapacks.com/catalog.aspx?catid=1
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Propylene glycol and polyethylene glycol are absolutely not the same thing.

Propylene glycol is 3 carbons long with 2 hydroxyl groups, weighing 76 g/mole.

Polyethylene glycol is a polymer of variable lengths and molecular weights.

Polyethylene glycol 200 weighs ~200 g/mole and is liquid at room temperature while polyethylene glycol 20,000 is ~20,000 g/mole and is a white solid at room temperature. They differ in how many ethylene glycol molecules are in the polymer. Miralax is polyethylene glycol 3350, weighing (you guessed it) 3350 g/mole.

PEGs are different from ethylene glycol, which is the poisonous component of antifreeze (PEGs are ethylene glycol polymers).

You want propylene glycol if you're mixing for humidity control, but I prefer and recommend beads.

Bovedas are OK ... they use saturated salt solutions to control humidity the way we use saturated sodium chloride to test hygrometers (at 20-25 C, NaCl --> 75% humidity, NaBr --> 58-59% humidity). I forget what salts Boveda uses.
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They seem simular according the the MSDS for both, but there are differences.

Polyethylene glycol 400 MSDS
http://www.sciencelab.com/msds.php?msdsId=9926620
Chemical Formula: H(OCH2CH2)nOH

Propylene glycol MSDS
http://www.sciencelab.com/msds.php?msdsId=9927239
Chemical Formula: CH3CHOHCH2OH
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The reason propylene glycol reduces humidity is because the water vapor pressure (that controls humidity) is related to the mole fraction of water in a liquid mixture.

So you COULD use a low molecular weight PEG to control humidity, as long as it was soluble in water. Since you are changing the partial vapor pressure of water by decreasing its mole fraction, a large molecular weight compound such as PEG 3350 would be much less effective than propylene glycol (you'd need more PEG 3350 in a water mix than propylene glycol).

http://en.wikipedia.org/wiki/Vapor_pressure

You could even use ethanol to control humidity, but you'd be facing problems because ethanol is volatile. Propylene glycol has low volatility and thus useful in decreasing water vapor pressure and humidity when mixed with water.
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I have plenty of floral foam. I can change it out every coule of months.

I should have an alternative in a couple of months. I think beads will be my best long-term solution.

I have a 2.5 gal. rubbermaid container, sided with spanish cedar sheets, my flower foam humidifier, and my hygro.
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Sounds like a pretty good setup if you can get some beads. I could be wrong but I think that you could get the beads for around $20 for that sized space. You might start researching. I think Heartfelt Industries has some great beads at a great price. Just my two cents though.
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Thanks. I've read good thngs about Heartfelt here and other forums, so I will start researchng.
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Fault the same battles, Jason. Save yourself a lot of time, money, and worry.

One word - beads.

Get more than you need and follow the instructions. Carefree humidity controls.
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Jamie is very wise. :-)
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Also, give kitty litter a try. Its a less expensive alternative.
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:-)
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I have a gallon of 50/50 (PG/distilled water) I'll send you if you just cover shipping. It's about 95% full.
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Shipping might be more than the $10 I would spend at Tractor Supply.

I'm gong to get the beads. After payday.
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Wise decision. :-)
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haha dont laugh at me! my kitty litter holds at a steady 68% :-)
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