iirc one of the people who was in Fusioneers before me said that when we had two solidifiers someone tried using a heated solidifier as a heat source for a second solidifier and the first solidifer was destoyed. your solidifer should not break unless sy uses it as a heat source for the first one. kiley and change were around then one of them might know more about what exactly happened
regarding loading items other than memory stones to be turned into heat stones:
the way the solidifer works is it takes the second word of an item's name and then adds the prefix "heat" to it. "spicy pickle" would become "heat pickle", "angien creature totem" will become "heat creature", "test item" will become "heat item". any "heat *" that the solidifier produces will function exactly like a heat stone
edit:
This being said, it's still a very bad idea to put things into the solidifier that it wasn't meant to handle.