If you measure the temperature inside the jar, it will be exactly the same as the temperature outside the jar. Any child with any sense and a respectable contempt for authority will tell you this. It's cooler in the jar!
It definitely feels cooler, yet the thermometer says otherwise. What's going on?
(Hint: this wouldn't work in Phoenix.)
Turns out experience is local. No national science curriculum can tolerate the very different results of my pretzel jar demo, a shame, really, because the children in Phoenix can very easily (and cheaply) discuss their results with the children in the humid halls of Bloomfield. Skype, blogs, wikis, heck, even phones.....
The humidity in the jar is much lower than the humidity in most of Jersey. Sodium chloride ("salt") is really good at grabbing water molecules from the air. The salt on the pretzels in the jar assures a low humidity environment, at least as long as you keep on the lid.
2nd graders do not need to know terms like "sodium chloride" or "hygroscopic." They should know, however, that science and intuition are not mates. They should know that science is based on what we call the "natural world" (itself a concept 2nd graders have a shot at grasping). They should know that science is testable.
I really don't give a rat's buttocks if a child can convert Celsius into Fahrenheit--that kind of skill matters, true, but that's not science, and it's something I can easily teach. I do care if a child is curious enough to wonder why her hand feels cool in a bucket of Snyder's Sourdough Specials.
Good Lord, I need curious children.We all do.