Possible Clues:

• So the saucepan has been burnt for fertiliser
• K2CO3
• That's what comes of burning the saucepan
• If one burns the bottom off the saucepan, 17 across would be left
• The strange pathos of a potassium compound
• Burn the bottom out of the saucepan and use it in the garden
• Terriers kept in stylish compound
• Potassium oxide
• Remains of the joint?
• A powerful alkali