Pitch Black Mountain Dew

If you haven’t read the first entry in about pitch black mountain dew’s blue foam…
Well, after much eager anticipation, my analysis about why the bubbles on the weird pitch black mountain dew turn blue is complete. At the end of my previous post, I had a couple of ideas for some experiments to help clarify this issue. I’ve now finished my experiments and am happy to report that I think the mystery is solved!
I was able to collect a sample of the blue foam. This was difficult at first, because it doesn’t turn blue until it’s almost entirely gone. However, I discovered that if I shook the bottle up with the cap closed, and then carefully released some air, the soda would foam up inside the bottle. After a few moments, the foam in the bottle turned blue. Then I released some more air by opening the lid a small amount and collected some of the foam that ran out.
I blotted nine drops of the liquid from the blue foam and nine drops of regular soda onto a paper towel and let it dry for several days. Then I scanned the towel into Photoshop and drew rectangles around each drop and looked at the red and blue values for each

The picture doesn’t really do it justice, the difference is far more startling that that looks. But who am I to trust the human eye to discern differences? This table presents the raw data for the red and blue channels’ average pixel value as well as the ratio of the two, the averages of those six data sets and the p value from the Student’s T Test on the ratios.

The T Test comes to the same conclusion as my eye — the colors are different!
The results of a second experiment were negative. When I mixed dish detergent with the soda and whipped it up using my nifty milk frother, the resulting foam bubbles did not turn blue. This suggests that my hypothesis advanced in the first posting about blue dye having the ability to diffuse into bubbles is not correct.
So what does this mean? The conclusion I have come to has to do with a technique known as column chromatography. Column chromatography passes a mixture through a tube that is packed with a material that has an affinity for some of the molecules in the mixture. This will slow the molecules down a little, so as water is washed through the tube the molecules come out the other end at different times. Typically a person will collect a few drops of water into a series of tubes (these are called “fractions”). Then you test each fraction to see what is in it. Using a variety of different columns you can actually purify things pretty well.
Anyhow, I had noticed that the foam only turns blue after the bubbles on top had been bursting for a while. This causes those bubbles near the top to turn back into liquid and flow through the foam underneath. The foam bubbles underneath act like a column, to which the blue dye apparently has a higher affinity than the red dye.
Sorry, I can’t write now – West Wing is starting!