(Edit: Great video. Exactly what I was talking about CP! Now, we just need to figure out how to make it so you aren't doing them all and feel like you are having your arm twisted.
And nice job with the camera Mrs. "Mudfoot"
)
Woot! SCIENCE!
I think the common principle of wet detergents is fun to understand, probably more than is healthy for a layman. Swizz explains that it disperses grease (or oil) and thus reduces water tension, which is exactly right but also not the whole picture.
Think of soap as that molecule that both loves water and hates oil. One side of the soap molecule loves water (is strongly attracted) and the other side pushes away from oil, dirt, etc. In doing so, the oil's cohesion is disrupted, and individual oil molecules can't find fellow oil molecules to latch on to because all the oil molecules have been forced to disperse as almost individuals through the full water column (in effect, grease and oils float too because the water molecules are cohesive and acting "together" to hold the oil's weight).
But there is a second benefit: Those water molecules now act as if there was more "space" between each other, which also aided in the oil losing its cohesion. Water, in a physics sense, becomes "wetter" with a detergent because of that extra space between the water molecules. This as a whole makes the surface tension of the water even less than what was needed to just disperse the oil... which is a good thing, because really fine and flat gold can float even without oil present, it just isn't as likely. (You can actually get gold to float in RO/DI water that is typically filtered down to the 1/10,000,000th of impurities.) With your water even wetter than it started, more things drop into the water column because not enough H20 molecules can find a place to stay and attract together under floating objects to support the floaters' weight.
So why doesn't it disrupt how a gravity based trapping system works too? Because gravity remains constant, and the mass of the water remains unchanged, and turbidity is actually slightly aided because more solids fall out. Because the mass of the water remains nominally unchanged, the force it has as it moves isn't different either. Thus the system maintains integrity, and the lessening of attractions between molecules (tension reduction affecting the surface and the column) simply aids in gold recovery.
So what happens with too much soap? Bubbles. Bubbles are simply left over soap that the water column couldn't support, and so they start rebinding and acting with each other because they can't find any free water molecules to attract to. Which is bad, because you essentially made floating/rising/popping islands with more tension capability than the oil (and water!) you wanted to disperse in the first place.
Notice too how Dan pointed out in the video that warm (or hot even) water helps reduce tension too? It is because the water molecules are traveling with enough stored thermal energy to make the water "vibrate" faster, thus imparting even more space between each molecule than if the water was cold. The over all effect is less than what is accomplished with the detergent, but it still adds up and is a very nice principle to work with when cleaning up to get the ache out of your hands from being in COLD Colorado water for days.
I sure wouldn't mind finding out who thought to put these principles to use the first time for prospecting purposes, that was one "fine" leap forward for prospecting.