First of all, what is Subject #1, and what is Subject #2? Are they both MgSO4 extractions, one of them? One NaCl one MgSO4? neither?

Here's the thing. It's possible the magnesium hydroxide is making the emulsions a lot worse. It's not particularly soluble in water and I can't find much information about it's solubility in organic solvents. likely it would have an incredibly low solubility in them. That doesn't mean though that it wouldn't form weird micelles or something at the bi-phasic interface.

So you observed no emulsion with only MgSO4 water and sodium hydroxide with naptha? I may recreate this experiment with say a drop or two of glycerine or vegetable oil to simulate plant fats.

You still were not clear as to whether the control experiment was evaporated or not.

Do magnesium hydroxide emulsions exist? They most certainly do.

[URL unfurl="true"]http://www.drugs.com/uk/liquid-paraffin-and-magnesium-hydroxide-emulsion-bp-leaflet.html[/URL]

The thing with emulsions is they are typically not one component.  So maybe the water, Mg(OH)2, and naptha alone won't cause trouble. However with the addition of plant oils and such they very well could form a vicious emulsion. Hard to say.

or maybe you're just getting a case of the unlucky emulsions and I'm over thinking it.