substitute lemon for lime
The simple answer is yes, you may use lime juice in place of lemon juice in home canning recipes, as lime juice is slightly more acidic than lemon juice. Some people prefer lime juice, as they feel it has a milder flavor. Of course, if a recipe specifies lime juice, it is not necessarily safe to substitute lemon juice. Realistically, their pH's are so close as to be moot, but I'm just repeating what the food scientists say. Another question is substituting lemon (or lime) juice for vinegar, and vice versa. Notice in the table farther down this page that vinegar is considerably less acidic than lemon juice, so you can substitute lemon juice (or lime juice) for vinegar in recipes that call for vinegar, but you may not substitute vinegar for lemon juice.