may not wash her hair with natron or with sand. The reason she may not wash her hair with natron is because natron pulls out hair, and that hair may remain sitting on her head and serve as an interposition between her and the water of the ritual bath. And similarly, she may not wash her hair with sand, because it sticks to her hair and it also serves as an interposition.

And Ameimar said in the name of Rava: A woman washes her hair only with hot water, but not with cold water. But she may wash her hair even with hot water that was heated in the sun. What is the reason that she may not wash her hair with cold water? Because it is cold and causes the hair to harden, and the dirt will remain in the hair.

And Rava says: A man should always teach in his house that a woman should rinse any place with creases, e.g., her armpits, in water before she immerses in a ritual bath, to ensure that they are clean. The Gemara raises an objection from a baraita: Places with creases and any concealed part of the body do not require immersion in water. In other words, the immersion is valid even if the water does not touch those parts of the body. If so, why must she rinse them before immersing?

The Gemara answers: Granted that they do not require immersion in water, but we require that they must be a place that is suitable for immersion in water. This is in accordance with the opinion of Rabbi Zeira, as Rabbi Zeira says: For any amount of flour suitable for mingling with oil in a meal offering, mingling is not indispensable for it, i.e., it is valid even if it is not mixed. But for any amount of flour not suitable for mingling, e.g., if the quantity of flour is so great that the ingredients cannot be properly mixed, mingling is indispensable for it, and such a meal offering is invalid. This teaches a halakhic principle: There are certain actions that prevent the fulfillment of a mitzva if they are impossible, even if the actual performance of those actions are not indispensable to the mitzva.

Ravin bar Rav Adda says that Rabbi Yitzḥak says: There was an incident involving a maidservant of Rabbi Yehuda HaNasi who immersed herself, and she ascended from her immersion and a bone was found interposed between her teeth, and Rabbi Yehuda HaNasi required her to perform another immersion. This demonstrates that according to Rabbi Yehuda HaNasi one may not have a foreign object even inside one’s mouth.

And Rava says: If a woman immersed in a ritual bath and ascended from the water, and she then found on her hair an item that interposes between her and the water, what is the halakha? If she immersed soon after washing her hair, she does not need to wash her hair and immerse in the ritual bath a second time, as it can be assumed that this item was not there when she immersed, since her hair had been cleaned. But if she did not wash her hair immediately before immersing, she must wash her hair and immerse in the ritual bath a second time.

There are those who state a slightly different version of Rava’s statement: If she immersed on the same day that she washed her hair, she does not need to wash her hair and to immerse in a ritual bath a second time. But if she did not wash her hair on the same day that she immersed, she must wash her hair and immerse in the ritual bath a second time.

The Gemara asks: What is the practical difference between these two versions of Rava’s statement? The Gemara answers: The practical difference between them is with regard to washing her hair close to immersion. According to the first version of Rava’s statement, she must wash her hair immediately before immersing, whereas according to the second version she has more time. Another difference between the two versions is with regard to washing her hair during the day and immersing at night immediately afterward. According to the first version of Rava’s statement, provided that she washed her hair immediately before immersing, it makes no difference whether or not she washed and immersed on the same day. Conversely, according to the second version she must wash her hair on the same day or night as her immersion.

§ Rava says: A woman may not stand on top of earthenware utensils that are submerged in the ritual bath and immerse. Rav Kahana thought to say: What is the reason for this? It is because the Sages issued a decree against immersing in this manner, as it appears like immersing in bathhouses, i.e., the purpose of the decree is to prevent women from thinking that it is permitted to immerse in a bathhouse, which contains drawn water and is not valid as a ritual bath. It can be inferred from this reasoning that it is permitted for a woman to stand on top of a plank of wood that is in the ritual bath.

Rav Ḥanan from Neharde’a said to Rav Kahana that this is not the reason for Rava’s statement. Rather, there, in the case of submerged earthenware utensils, what is the reason that she may not immerse? She may not immerse because she will be afraid that she might fall off, and consequently she will not immerse herself properly. By the same logic, she will also be afraid when she is standing on top of a plank of wood, and therefore this is also prohibited.

Rav Shmuel bar Rav Yitzḥak says: A woman may not immerse herself