For those whos cats are impatient placing a small amout of a substance in a lets say a pint size wide mouth jar and then immersing that in a few pounds of dry ice in acetone has a wonderful almost instantaneous fallout and allows one to simply pour off their solvent, instead of waiting for evaporation. Using the smallest possible container facilitates removal. Dissolving in the smallest amount of hot sovent and recrystalizing in a very small container serves thee well. Meow!

Thanks for sharing!

One question, what substance exactly are you talking about? Freebase spice? Or something else?

What temperature does dry ice go?

Also, IME usually when one lowers temperature or forces crystallization fast, crystals tend to be less pure. What was the purity like?

I wonder if dry ice can be used to freeze-precipitate spice out of xylene/limonene too, that would be interesting. What about other impurities, do they precipitate too?

What we are talking about is reducing soluability of any solvent by reducing the temperature this is basic chemistry and physics. It applies to any solute in a solvent, many substances dissolved in another affect its freezing point as in antifreeze, or salt in water, and will often raise its boiling and freeze points, well unless you have a endothermic reaction like a cold pack which uses ammonium nitrate or urea in water, or exothermic like an Meal Ready to Eat pack. Our desire is to reduce the temperature to lower solubility of our solvent and effect crystalization and to be able to recycle our solvent over and over.Of particular importance is that the freezing points of naptha and acetone are below the temperature of dry ice -109.3°F or -78.5°C.

Acetone dry ice baths are a common labratory technique as the acetone does not freeze at the temperature of dry ice 109.3°F or -78.5°C and the acetone conducts the heat energy away from your solvent in a sealed container (beware acetone readilly attacks many plastics, so glass or metal is advised)if you have an open container water from humidity can condense and dissolve your crystals after return to room temp and that can require protracted drying.This is often used to prevent boil off (at room temperature)
of low boiling point subtances (like ether/ammonia that have been distilled.Using dry ice in water is not totally ineffective nor dry ice allone but neither conducts heat away nearly so fast.

There is nothing like watching instant snow fallout after the dry ice is added to acetone.

Yes you can have an increase in impurities although not highly significant, so you may desire to use a heated solvent (no Flames please) added dropwise to dissolve, then decant to a smaller container like a shot glass or several shot glasses to perform further recrystallization as the bigger the container the greater the losses to the surface of same.

Thank you for the more coherent second post, but I'm still a little confused. It sounds like you are talking about precipping out of acetone, but maybe you are adding the dry ice directly to acetone, making that a bath for a container with freebase dissolved in naptha? Freeze precipitating out of naptha using dry ice is nothing new, but putting it in an acetone bath with the dry ice is new to me.

You are adding the dry ice in pieces crushed by a hammer blow into the acetone, then putting your sealed acetone resistant container in that, which is full of your solvent you extracted with. Heres how to start get a pint preferrrably or worst case a quart wide mouth mason jar, why worst more surface area equals more loss so unless you have that much volume use the smallest possible container why wide mouth well use a narrow and its a Xitch to scrape out anything. Ok you will need a large 2gt to gallon size or so metal pot or glass bowl or one prefers a giant glass pyrex pitcher, so one can recover and reuse the acetone back into its gallon can you might get by with a quart if you use a pint jar. Now just make sure the lid is on the mason jar snugly and sink into the acetone/dry ice mixture. You will be amazed how well and quickly this works turning a 1-2 day project into a 4-6 hour effort. Getting your stuff now requires pouring off the solvent (save that over and over) and if you like filtering it but that usually results in losses. Just a slow decant works well. If you start off using too much solvent to extract too little you may consider evaping it down some before the flash freeze. If you wait around much after pulling it out of the freezing bath to decant the solvent for usually the required 20-30minutes, you will see stuff disappearing back into solution so work quickly. Also you may need a hot wet wash rag and some big channel lock pliers or a lid removal tool to get the lid off since its cold metal and contracted tight.Drain the Jar upsidedown after draining and spooning out loose stuff. Let Dry and then take some clean solvent thats hot and add a very small amount and rub around with a finger tip to dissolve then pour off into a tall shot glass and follow others notes on recystallizations. Hope this helps someone my cat is like a kid before xmas and likes to get to the catnip before it would normally be made available by waiting patiently! If working on a very small scale using a very large testtube with a taped on rubber stopper works well this also works well in rapid recystallizations and a doctors toungue depressor works well as a cleanout tool sorry doc! hope your not missing any!