As we learned on yesterday’s daf , people’s possessions cannot be taken beyond 2,000 cubits of the city limits (called tehum Shabbat) on Shabbat and Yom Tov, just as the person himself is limited by the tehum. Thus, if a woman lends water and salt to her friend to bake bread on Yom Tov, the final product will be limited in that it can only be taken as far as the borrower and the lender could go themselves. In the Mishna (37a) Rabbi Yehuda argues that this rule does not apply to water, since it becomes part of the baked product and is no longer considered as having independent significance. Therefore we will not restrict its movement by the limits of the original owner; the borrower who baked the bread can take it wherever she is allowed to go.
The Gemara on our daf asks why Rabbi Yehuda differentiates between water, which loses its independent significance when baked into bread, and salt which apparently retains its status. Furthermore, a baraita is introduced in which Rabbi Yehuda clearly states that both water and salt become batel – negligible – when baked or cooked and are now part of food.
To explain the different statements of Rabbi Yehuda, the Gemara explains that there are different types of salt – melah sedomit and melah isterokanit. Melah sedomit is thick and retains its shape, so it can be seen even when baked or cooked. Melah isterokanit is softer and combines with the food to the extent that it can no longer be identified. Thus melah sedomit retains its independent status, while melah isterokanit is considered batel in the food.
Although many define melah sedomit as sea salt, the Ge’onim identified it as salt that is mined on Mount Sodom itself, and not salt that is taken from the Dead Sea. Such stone salt does not dissolve easily and is readily seen even in cooked products. Melah isterokanit (which was most likely given that name because of the place where it was produced) was made by means of channeling sea water into canals and extracting the salt by means of evaporation. In the time of the Mishna melah isterokanit was much softer and dissolved more readily that the stone salt.