A Chemical Mystery - Can You Solve It?

My wife and I were able to use our chemical knowledge this past week to solve a perplexing problem. I'll post first what we observed and then let you try and figure it out.

We have a gas cooktop in our house here in Minnesota. A couple of weeks ago, the flames on it started burning more orange-like so we called in a repair guy. Non-blue flames are indicative of a rich fuel/oxygen mixture, one that can potentially put out CO, although it is less of a danger for cooktops than furnaces as the former are used for shorter periods of time often with the vent fan running too. But in any case, the regulator was failing and instead of feeding 3-4 inches water column of gas, it was feeding 6-8. A new regulator was installed and the pressure of the gas was reduced to the normal levels, but the orange flames persisted.

We tried adjusting the Venturi openings that let the air into the burners, but that didn't do anything. Besides, it would be freaky odd for all four burners to suddenly have their Venturi openings block at the same time. And then my wife (a Ph. D. in chemistry) found the solution, one which we have been able to positively confirm: by making an adjustment elsewhere in the house, we can on demand change the flames from blue to orange and back again. Neat, huh? And we also know now not to worry about the color of the flame.

Here's some other information that may or may not be helpful to finding the solution. The house is in Minnesota and is sealed up tight for the winter (it was -16 ^oF this morning!). Since the air is so dry, we run ultrasonic humidifiers in a couple of rooms in the house. About the same time as the problem occurred, we brought a real Christmas tree into the house. We have a dog (a Welsh Terrier), and had house guests staying on and off over the past few weeks. To make meals easier on the cook, we have been using a crockpot (electric slow cooker) a lot the last few weeks. We have hard water and soften it. Speaking of water, we have a gas water heater. Speaking of gas, we have a gas furnace and we also have a gas fireplace on both levels of the house.

With your knowledge of undergraduate chemistry, you now have enough information to solve the "Mystery of the Orange Flame". I will also tell you that the answer has nothing to do with polymers science so to make up for that, I've included a picture of a cute kitten playing with a random polymer coil. (If we had cats at our house (we never will), they would play with random polymer coils and not balls of yarn.)

Why are the flames on the cooktop burner orange and not blue? Start with the water softener. It replaces the calcium and magnesium in the hard water with sodium. That water then goes into the ultrasonic humidifiers. (Distilled water would be a better option, but since these things go through gallons of water a day, it isn't too practical of an option to be trucking in that much distilled.) The humidifier then tosses the sodium into the air where it spreads through the house. Some of it ends up in the feed air to the burner where it burns it's characteristic yellow. Combine that small amount of yellow with a rich blue flame and you get an orange flame.

To further convince ourselves of this, we shut of the humidifiers and after 4 hours, the flames went blue. Turned on the humidifiers and the flames went back to orange. Mystery solved. We were running a good old-fashioned flame test.

My wife then found a video that shows these changes in a most dramatic fashion:
Ignore the audio in the video, as it gives a wrong rationale for the color change. Just look at the pictures. Just that tiny bit of sodium is enough to significantly color the flames.