I remember two stories, and I believe they may be from the same book.  One story is of some kids that get “hired” by a local scrap metal company to figure out how to crack open metal cannonballs.  They first try burying it in the snow, but find that the snow acts as an insulator, preventing the cannonball from getting cold enough to crack.  The kids then re-try by leaving the cannonball in the open (at least that’s what I remember), at which point the metal is cold enough to crack.

The other story also involves children, this time on a beach.  They collect up seawater, rig up a distilling system, and then boil the water to make steam.  The steam is collected up as drinkable water.

Thanks in advance!