Nice handles Chas.
The broken chisel can be repaired in the following manner:
If you are able to use arc welding or have someone to weld the parts together you'll have the chisel back to work in a snap.
O yeah! what will happen with the temper? Nothing at all if before welding the parts you just dig the blade into a big potato leaving outside only the 1/2 inch needed for welding.
My grandad was a smith, and he was used to weld using only the furnace, this is the trick he used to weld a knive or a tool that broke without loosing the temper. The water contained in the potato cools down the blade and dissipates the heat, it works with any type of welding.
He used to tell me many things about hand forging, welding, horse shoes fitting, and so forth, and now I'm glad I still remember most of those old tricks.
If you give it a try, just let me know about the results.