Sciencemadness Discussion Board - Myth busted - Epsom not good source of Mg Sulphate

Myth busted - Epsom not good source of Mg Sulphate

CHRIS25 - 8-5-2014 at 12:51

MgSO₄ - a very much needed dssicant and I have tried to use it a number of times, became suspicious when absolutely zero moisture found in my "magnesium sulphate" (which I dehydrated many weeks ago), after a week in a place where it should have by now been soaked.

Magnesium sulphate is soluble in water 30g/100mLs at 20c approx and it did dissolve in water; and magnesium oxide is not soluble in alcohol. Because the box says "Epsom Salts magnesium Sulphate" and then in Contents says Magnesium Oxide (no percentage or w/w given at all), I was surprised since the oxide is not a cheap chemical. Here is an image of the white offender in 38% alchohol (no I don't drink the stuff it was a gift years ago and I have used it only for chemistry and nasty cuts). Anyway It refuses to dissolve. It dissolved with vigorous stirring in a 1.8M sulphuric acid concentration giving more credence to a large source of Oxide, so it does appear that this foilage growth Epsom salt is not a good source of Magnesium sulphate for the chemist as is popularly suggested, maybe for the plants yes. The end result is that it simply does not absorb moisture at all - so how much of this stuff is actually sulphate is questionable.
Anybody have any comments? and don't mourn the waste of dry gin it's not good for you anyway.

blogfast25 - 8-5-2014 at 13:14

Hmmm... Epsom salt is a hydrate of magnesium sulphate. As such it's not a desiccant. To make it one, strong heating is needed to obtain the anhydrous form, which is strongly hygroscopic and used as a desiccant.

MgO is probably present in very small amounts, as an anti-caking agent. 0.5 % or so. It's used also in washing soda, to prevent lumping (caking).

Gin is only about 40 % ethanol so shouldn't be described as 'alcohol' (drinking alcohol yes, 'pure ethanol' not)

To obtain purer MgSO4 hydrate from garden grade Epsom salts, dissolve in hot water and filter off the MgO. Then crystallise. Acc. wiki MgSO4 has a decent dependence of solubility on temperature, so thermal recrystallizing is possible.

Also, next time you desiccate it: weigh before and after. The calculate if weight loss more or less corresponds to MgSO4.7H2O === > MgSO4 + 7 H2O

[Edited on 8-5-2014 by blogfast25]

Magpie - 8-5-2014 at 13:18

Quote: Originally posted by CHRIS25

... (which I dehydrated many weeks ago), after a week in a place where it should have by now been soaked.

If you did indeed dehydrate it then it would be a white powder. When it absorbs water to the heptahydrate then it is still a white powder. How do you know that it is not absorbing water?

see http://en.wikipedia.org/wiki/Magnesium_sulfate

CHRIS25 - 8-5-2014 at 13:25

Yes I know, but I did think that I had dehydrated it because it was in an oven at 110c for about 1 hour and it certainly changed appearance from crystals to a fine powder after a little crushing. Anyway I will try what you suggested.

Metacelsus - 8-5-2014 at 13:26

My epsom salts (a different brand) work just fine for dehydrating and using as a drying agent. They also are reasonably pure (>98%) magnesium sulfate. I think the remainder is mostly sodium sulfate, based on a flame test.

CHRIS25 - 8-5-2014 at 13:32

Quote: Originally posted by Magpie

Quote: Originally posted by CHRIS25

... (which I dehydrated many weeks ago), after a week in a place where it should have by now been soaked.

Well because after a few weeks I would have expected at the least, not to have been able to shake the 'powder' around so freely on the glass, plus I used it as a desicant to absorb moisture from precipitated silicon dioxide when I put it into a homemade hot chamber - after one hour I became suspicious, so I swapped this for sodium sulphate that I had made and within another 30 minutes the sodium sulphate was already half its volume with moisture.

Magpie - 8-5-2014 at 13:47

My information says that dehydration should be at "200°C and red heat." I would try 200°C overnight.

[Edited on 8-5-2014 by Magpie]

S.C. Wack - 8-5-2014 at 14:01

Quote: Originally posted by CHRIS25

Yes I know, but I did think that I had dehydrated it because it was in an oven at 110c for about 1 hour

You have to weigh.

CHRIS25 - 8-5-2014 at 14:06

Ah this is the first time I did not search on this forum: http://www.sciencemadness.org/talk/viewthread.php?tid=9429 and then here: http://www.lycaeum.org/mv/mu/MgSO4.html I simply forgot, actually believing that I knew what I was doing when I 'tried' to dehydrate the product. I never bothered doing a research on this thinking that it was straightforward - that will teach me, when I think I know it....double check.

[Edited on 8-5-2014 by CHRIS25]

S.C. Wack - 8-5-2014 at 14:09

PS: In advance, disappointing results on drying your gin with very dry MgSO4 should not come as a surprise, but good luck anyways.

Magpie - 8-5-2014 at 14:26

I have not tried dehydrating spirits with drying agents on the first dehydration. 62% water is a lot of water and it would take a lot of anhydrous MgSO4 even if it does work. Do the math and you will see (hint: use the molecular wts at the bottom of your tech info link).

When I was making absolute alcohol from vodka I would fractional distill first to obtain the azeotrope which is only 5% water. Then I would dewater further by distillation over lime (CaO) which would take it to ~1% water. Final polishing is then done with 3A molecular sieves which gives very near absolute alcohol.

I later shortened the above procedure by starting with Everclear which is a spirit of 5% water. Praise be to those states selling Everclear!

There are other methods involving elemental Na, etc, but I have never tried those.

CHRIS25 - 8-5-2014 at 14:37

Hey I was not trying to dry Gin! (it says it's dry on the bottle anyway

); ?

blogfast25 - 9-5-2014 at 04:32

Quote: Originally posted by Cheddite Cheese

My epsom salts (a different brand) work just fine for dehydrating and using as a drying agent. They also are reasonably pure (>98%) magnesium sulfate. I think the remainder is mostly sodium sulfate, based on a flame test.

Same here. It's remarkably clean for a garden grade.

Quote: Originally posted by Magpie

My information says that dehydration should be at "200°C and red heat." I would try 200°C overnight.

Red heat??? I've used an electrical hot plate on max. No problem to full dehydration (weight loss verified).

Quote: Originally posted by CHRIS25

Hey I was not trying to dry Gin! (it says it's dry on the bottle anyway

); ?

If you're going to waste perfectly good distilled damnation, please quote me for what you have.

I'm afraid no myth was busted in the making of this thread!

[Edited on 9-5-2014 by blogfast25]

Tsjerk - 9-5-2014 at 05:39

Microwaving is the way to go when drying salts! Works good for Na2SO4 and MgSO4 at least. I always used two glass bowls with the open side against each other. This prevents the violent splattering to leave the containment but allows the water to leave.

Three minutes maximum power, followed by some cooling and you have a bone dry salt. You do have to scrape it from the bowl, so won't get everything off, but if you just use the same bowl every time this shouldn't be a problem.

CHRIS25 - 9-5-2014 at 10:45

Well I guess, as always, I presumed too much, have not quite cultivated the discipline of Empiricism. Anyway, I heated for one hour at 240c, crushed, heated another hour, crushed, then heated another hour - it's anhydrous definitely. It's a fine white powder, disturb it and it really fills the air so I did a good job. You can feel it soak up the sweat on your hand.

Metacelsus - 9-5-2014 at 11:05

I have found microwaving to give inconsistent results with magnesium sulfate -- sometimes it doesn't remove all of the water, sometimes it does. Sodium sulfate works fine, though.

quantumcorespacealchemyst - 12-12-2014 at 09:14

powdering in mortar and pestle and heating in the kettle on moderate flame causes it to melt and puffletting out vapor and turning white gradually till the mass is seemingly all white. the bottom of the cake formed seems to be possibly yellow and that may be due to impurities.

i had a solution of epsom salts used as a water bath in the same kettle that was let to crystallize and poured off the liquid to a cup and seperating most of the mostly dry crystals to a bag, then i put the rest of the liquid logged crystals into the cup, i pipetted out the water that collected in the plastic bag corners to the same cup, then the next night i believe, pipetted out the liquid from the cup to another cup, now having a mosly dry bag of MgSO4, a cup of some and a cup of liquid which is yellowish. if the color isn't from the kettle, the cup, or dropping/spilling something in the water bath (i believe it isn't these, especially the last) then it may impurities from the epsom salt.

the aforementioned dessication was done with non-recrystallized epsom salt

edit: i forgot to add, i am thinking of washing them with acetone, although the ones in the cup, i just washed with distilled water as they were drying and i did not want to combine them with the first separation in the bag and/or have the impurities dry on the crystal surfaces. the crystals lost some mass of course, quite a bit actually, estimating a third no a half (crude estimation).

[Edited on 12-12-2014 by quantumcorespacealchemyst]

[Edited on 12-12-2014 by quantumcorespacealchemyst]

[Edited on 12-12-2014 by quantumcorespacealchemyst]

unionised - 12-12-2014 at 11:53

Quote: Originally posted by CHRIS25

Quote: Originally posted by Magpie

Quote: Originally posted by CHRIS25

... (which I dehydrated many weeks ago), after a week in a place where it should have by now been soaked.

OK, for a start you need to find the difference between hygroscopic (which MgSO4 is) and deliquescent (which it isn't).

Also, unless you dried it before you tried to use it as a drying agent it's simply not going to work.

aga - 12-12-2014 at 12:10

You got CaCl2 dude.

Heat the hell out of it !

subsecret - 12-12-2014 at 16:12

It doesn't really matter if there's MgO in it, as long as you're drying with it. If you're using it as a reagent, there could be larger problems.

dermolotov - 13-12-2014 at 14:00

Quote: Originally posted by aga

You got CaCl2 dude.

Heat the hell out of it !

x2

I just use Calcium Chloride found at the local pool supply shoppe. They come in flakes similar to potassium hydroxide flakes which I bake in an oven at 230deg for 30 minutes and they soak it up almost immediately. On top of the fact that it's much more inert, it's much cheaper, too.