Its got to do with density
Water- lets call it your test
Salt water-Essentially water with salt in between particles, so its heavier
Distilled water- Nice pure H2o without any naughty extra particles

well it depends on weather simon thought of that in coding r just coincidence

I would really like to make "mixtures" where the elements don't separate as fast as they do, I want to make solutions of like NITR and water to make a weak explosive without using a concentrated amount that loses flavor quickly

Rconover
Uh, thats a little too much to ask for in powder toy, unless you want it to be like saltwater=salt+water
But then you just make a dissolving nitr... Just ask one of the modder, pijojo, tian thers lots

trystanr
What I meant was, I wanted heterogeneous mixtures, where the NITR would be visibly separate.

that might be a bit hard to code, because you would have to change the source to ignore the density in some situations, and still allow it in some others. but a good way to implement this would be to check and see:
1. Are the particles the same state of matter? (Solid, Liquid, Gas)
2. Do the particles have the same state at room temperature?
If both of those questions are answered, ignore density and have the two elements mix heterogeneous(ly) (if you dont know chemistry, heterogeneous means "mixed without dissolving") so that we could achieve oil + water does not make oil on bottom and water on top, rather, it will result in 1px oil, 1px watr, 1px oil, etc. Kind of like a mesh of the two liquids.

the ability to make solutions would be nice but unlikely. although antb has implemented c types or something like that with his X element and this could be used to alter properties of that existing element like say nitro ( water) burns slower and releases some steam. but since i am not a coder i am not quite sure this would be an easy task.

distilled is pure water
water has minerals so its slightly denser then distilled