re Sela'im from copper (i.e. coins. The former are forbidden, for they add heat.)
How do you know that these are Selayim Copper "Coins" and the other one is a "Rock" of Silver.
are Selayim of Even, regular rocks that do or dont produce heat.
David Ashear, brooklyn
Rashi (DH ha'Sela'im) writes that the Sela'im (that the Mishnah states one must keep away from the neighbor's wall) are stones that light (or fire) comes out of. These are bad for the wall since they heat it up. Tosfos (DH Sela'im) writes that Sela'im are stones that fire comes out of. So according to Rashi and Tosfos, the Sela'im of Even are special rocks which produce heat. They seem to be fire stones or fire rocks.
So it is not the copper Sela'im that add heat, it is the stone Sela'im that add heat.
Tosfos is not referring to a rock of silver; Tosfos is referring to silver coins.
Best regards.
Dovid Bloom