Most of you know how much I like these things:
These two were purchased last week at the dollar store. Had I not already sent/wrapped the Christmas gifts you may have received one too! I quickly set them up and found they weren’t the most well-constructed of kits:
They are made of porous cardboard with the edges dipped into food colouring (or in the case of the snowman, not dipped). A small packet of liquid is included, which is poured into the reservoir at the bottom.
It doesn’t take long for the liquid to move up the cardboard until it reaches the tips, where crystals begin to form. If the crystallization occurs where the cardboard contains food colouring, the crystals themselves are coloured as well.
So what’s happening? Well it’s actually quite complex. The solution contains water and a mix of alkaline and ammonium salts. Since it is a liquid, capillary action causes it to move into the cardboard. Once the water evaporates (which is most likely at the edges) the remaining salts form crystals. The process is quite quick (less than 6 hours) and once completed the crystals are fairly rigid and the ‘tree’ can survive for years if protected.
We actually have a few (better) ones in our curio cabinet, including a panorama of Mt Fuji that we must have had for a decade now! I sent many of you trees like this a few years ago. I wonder how many of you still have them?
There are many good explanations of the science behind such trees online (this is a good one), and you can even find instructions on how to make your own. If I taught chemistry instead of physics, I think I’d certainly work this into one of the lab experiments!