today was my first attempt at drying Epsom salt in the oven at 400 degress for an hour, to make Anhydrous Magnesium Sulfate. at no point does it turn "gray and ashy", as it's said it would. instead it slightly yellows around the edges of the salt pile, the rest turns super white, and it all hardens to a solid sheet which i break apart in large chunks. Same result at 450 degrees for 2 hours.

so my questions are:
why is it turning yellow? is the yellowing a bad thing? should i fish and toss out the yellowed salt? am i doing something wrong? i feel like i am because i can't find any mention of this in the nexus. is it possible that some brands of epsom salt has additives or impurities that are not listed on the label?

what do i do with the chunks? do i mash them down to a powder? i didn't think the end result of the drying meant the epsom salt would no longer be in chunky salt crystal form as it began, but instead it all "melts" together. if i grind it down to a fine powder, would a fine powder consistency be appropriate for use in drying out solvents. it seems like it would be hard to filter out?

Until your baked epsom salt makes a solid mass,its done, 1 hour is the max Swim puts it in the oven .
The yellow part might mean its burnt. Not sure if its bad or not.

"Too much heat will cause the product to take on an unattractive gray coloration and expel sulfur trioxide." I read that from this website http://www.lycaeum.org/mv/mu/MgSO4.html

It seems like you don't want to make it "gray and ashy" if going by what it says on that site.

I would just toss out the parts that have any yellowish look to them, though they would work and probably not hurt anything.

I can recall in the past when making the stuff on a regular basis, that certain parts of the bottom surface always looked a little "charred" (grey) and I would ignore that and use it. Never any harm from it. It all absorbs water, which is the job it's there to do. (I never saw true yellow, just a sort of off white discolored look.)

Then again I was cooking it on a piece of heavy-duty Al foil, so maybe it was color coming from the Al? It never seemed to contaminate the salts I was making from the solutions the MgSO4 had dried... in fact the product was tested a couple of times on GC/MS and was ultra clean (Al would have showed up).

LB

I think you over cooked it... SWIM just microwaved a small batch (a few tablespoons) and it was done after 5 min. He said he just broke off a small piece and dropped that in the solvent. It took up the few drops of water that got stuck in the bottom, and was easily filtered out since it was mostly one piece.

quoting AVA---
The solvent and alkaloid gets soaked onto the surface, so after you filter the dry solvent, pour through some fresh solvent on top of the epsom salts, to help wash through the alkaloids clinging to the epsom salts.

When the epsom salts stays looking like free flowing powder instead of clumping, that when you know that you've absorbed all the water. So you need to add a bit at a time, then stir for a while and look at it to see what the epsom salts look like.

This same yellowing and clumping happened when I dried MgSO4. Not sure about the yellowing, but i think the clumping comes from water being trapped in the salt, causing it to bind together, and this could be solved by letting the salt cool in the oven while the oven is off (because there will be less atmospheric moisture for the Mg to absorb) until its cool enough to handle, and grinding/smashing the salt up, and then re-heating it for a short period to make sure there is no more moisture.

LB actually used/use it as chunks instead of breaking it up into a powder. That way it was far easier to filter out. Just give it a little longer in the solvent you're drying (15 minutes should do it).

Ah, I guess it depends on which solvent you wish to make anhydrous, Philodendron. I was using acetone, which epsom salt is insoluble in, so it sunk to the bottom after sitting and the top most of the liquid was decanted/pipetted off before use. Disregard my last post if you're using a different solvent then, eh

ur stuff went yellow caus u need to clean ur oven

So it seems like there are different opinion on whether or not one should powderized the cooked epsom cake or break in chunks, each method having its pros and cons.

Also, I found that the caking happens because, from what i observed, as the epsom heats up it releases a good amount of water that melts all the salt crystals together. i tried constant stirring, but there's no way around it.

well that answers the mystery of the yellow, lol! i don't know why it makes me laugh, the way he said it. astralsmity, you need to go clean your oven, ha ha!

thanks phlux!

dg, could you possibly post a link to that thread

update:
i decided to ignore the yellowing on my first batch of dried epsom and use it anyway. with my other batches i found that stirring the salt a few times during the baking prevented the yellowing, or more likely just made it harder to detect. my third batch developed about 5 small, almost black spots, weird. i collected it all together in a sealed metal tin and quickly powderized it in a blender once it cooled.

what i've been trying to do is dry a bottle of 70% isopropyl alcohol. i had no clue as to how much epsom i should add to soak up the water content of a liter of this solution so i added about 3 cups of epsom just to see what happens.

what happened was that the alcohol got fairly hot... and turned yellow. this might be because of the yellow i saw in the oven. also, i was also only able to recover about 1/4th of the alcohol, the rest stayed stuck with the epsom, even after trying to squeeze it out with a french press, which is when i noticed the epsom/alcohol mix got hot. if anyone has any insight as to what might have happened here, please do chime in.

so that was my first attempt. 2nd attempt, i suppose i'll just dry the epsom on the stove until i get around to cleaning the oven, and keep some epsom in chunks to experiment with. also, try Light-Being's and dg's advice to determine how much epsom to use.

I remember it took significantly longer than an hour for mine to finish (or until I thought they were finished? ), and the only visible tinges I eventually got were a slight grey tinge around the edges. However, as long as it hardens and you have to break it up... that should do the trick!

Hey, when getting the Crystal-Water out of the Salt needs heat, it´s endotherm. When you gave the dried Salt to the alcohol/water-mix, binding of the water with the salt was an exothermic reaction. It gets hot. The energy causing the warming is called Hydratation-Energy which is released when water molecules bind to ions.

nvm