1) COMPARING "DAVAR SHE'EINO MISKAVEN" TO "MELACHAH SHE'EINAH TZERICHAH L'GUFAH"
QUESTION: The Gemara asks that since Shmuel permits a Davar she'Eino Miskaven, like Rebbi Shimon, he should also permit a Melachah she'Einah Tzerichah l'Gufah. The Gemara answers that the two concepts are not related.
Why does the Gemara initially assume that the two concepts are related when they have entirely different laws? First, a Davar she'Eino Miskaven is permitted on Shabbos, while a Melachah she'Einah Tzerichah l'Gufah is prohibited mid'Rabanan even according to Rebbi Shimon. Second, the concept of Davar she'Eino Miskaven applies to all prohibitions in the Torah, while the concept of Melachah she'Einah Tzerichah l'Gufah is a concept unique to Shabbos, which is derived from the verse of "Meleches Machsheves" (Shemos 35:33). We see that they are two completely independent Halachos. Why does the Gemara compare them?
(a) TOSFOS (DH Afilu) explains that whenever a person does an action that unintentionally results in a Melachah being performed (that is, he does a Davar she'Eino Miskaven), by definition the Melachah that results is not Tzerichah l'Gufah (because the person had no need to perform the Melachah). Hence, the Gemara's initial assumption was that the reason why, on Shabbos, Rebbi Shimon permits a Davar she'Eino Miskaven is because even if a Melachah is done unintentionally, it remains no more than a Melachah she'Einah Tzerichah l'Gufah, which he prohibits mid'Rabanan. Similarly, the Gemara assumed that Rebbi Yehudah prohibits a Davar she'Eino Miskaven because of the possibility that it will result in a Melachah that the Torah prohibits, since he considers a Melachah she'Einah Tzerichah l'Gufah to be a Torah transgression.
(b) The TOSFOS HA'ROSH and TOSFOS in Zevachim (92a) explain that the Gemara initially assumed that if a Melachah she'Einah Tzerichah l'Gufah is forbidden, it is because one's intention does not make a difference (that is, even though he did not intend to perform the Melachah for its normal purpose, he is still Chayav). If one's intention does not make a difference, then it stands to reason that not only does not having intention to perform the Melachah for its purpose not make a difference (and he is still Chayav), but not having any intention at all to do the Melachah also does not make a difference.
2) POURING HOT INTO COLD AND COLD INTO HOT
OPINIONS: Beis Shamai permits pouring hot water into cold water that is in a cup, but not cold water into hot water in a cup. Beis Hillel does not differentiate between hot into cold or cold into hot in a cup (he permits both). Rather, he differentiates between a tub and a cup. In a tub, he agrees that only hot water may be poured into cold water, but not cold into hot.
What is the difference between pouring cold into hot and hot into cold, and what is the difference between a tub and a cup?
There are three basic approaches in the Rishonim.
(a) According to RASHI, the difference between pouring hot into cold and pouring cold into hot is based on the rule that "Tata'ah Gavar" (Pesachim 76a). "Tata'ah Gavar" means that the temperature of the substance on the bottom "overpowers" the temperature of the substance on the top, so that if a hot substance falls into a cold substance, the cold overpowers and cools the hot. (The SEFAS EMES points out that this applies only when the lower and upper waters are roughly equal in quantity. If the quantity of the hot water that is poured into the cold water is much greater than that of the cold water, it is forbidden and "Tata'ah Gavar" does not permit it. Likewise, if the quantity of cold water that is poured into the hot water is much greater than that of the hot water, it is permitted.)
Regarding the difference between a tub and a cup, Rashi explains that a tub is a Kli Rishon, and that is why Beis Hillel is stringent with regard to a tub. As a Kli Rishon, it is inherently hotter than a Kli Sheni and it has the power to cook. A cup, on the other hand, is a Kli Sheni and is not hot enough to cook.
(b) TOSFOS (DH Nosen, DH Ambati) has a different approach. Tosfos explains that the water resting in the container is of much greater quantity that the water that is poured into it. (Tosfos says that this is the normal method used when one pours one liquid into another -- he pours the smaller quantity into the larger quantity). The larger quantity of water (the water on the bottom) is the dominant one.
Regarding the difference between a tub and a cup, Tosfos explains that although a tub, like a cup, is a Kli Sheni, the Rabanan were stringent with regard to a tub, because if they would permit one to pour cold water into a hot tub, people might assume that one may also pour cold water into a Kli Rishon. Since a tub is so hot, they will not distinguish between a tub (which is actually a Kli Sheni) and a Kli Rishon.
(c) The RASHBA explains the difference between hot water poured into cold and cold water poured into hot as follows. While the hot water is being poured, the stream of water cools off and it cannot heat the cold water, regardless of how much hot water is poured. (The hot water is cooled as it flows through the air, as well as by contact with the cold water into which it flows as a thin stream.)
Regarding the difference between a tub and a cup, the reason Beis Hillel permits one to pour even a little cold water into a lot of hot water in a cup is because a cup is a Kli Sheni, and a normal Kli Sheni cannot cook (regardless of how little or how much water is poured into it). The Rashba adds that even if one touches the water after he pours the cold into the hot and it feels like it is boiling hot, nevertheless the cold water was not cooked by the hot. Rather, the heat that one feels is the hot water, and the cold water which was poured in merely became warmed up. In contrast, although a tub is also a Kli Sheni, it is a very hot Kli Sheni. Therefore, it will cook whatever cold water is poured into it (even a large quantity).
3) HALACHAH: PLACING A RAW FOOD INTO A "KLI SHENI"
The Gemara discusses the laws of placing an uncooked food into a Kli Sheni on Shabbos. Two common, practical applications of the Gemara's discussion are as follows.
(a) The Mishnah differentiates between putting spices into a Kli Rishon (that is not on the fire) and putting them into a Kli Sheni. A Kli Rishon cooks them, a Kli Sheni does not cook them. The MISHNAH BERURAH (OC 318:65) points out that this rule does not always apply. A solid object (in contrast to a liquid) that is still very hot (Yad Soledes Bo) will cook regardless of the type of Kli into which it is placed (that is, even a hot Kli Shlishi will cook the food).
(b) The Gemara discusses whether salt can be cooked or not. According to the first version in the Gemara, Rebbi Chiya says that salt does cook in a Kli Sheni. According to the second version, Rebbi Chiya says that it does not cook even in a Kli Rishon.
The Rishonim rule in accordance with the second version, because the second version is consistent with the ruling of Rav Nachman. However, TOSFOS (DH v'Hayinu) and the MORDECHAI conclude that since there is another version in the Gemara, one who refrains from placing salt even into a Kli Sheni "is worthy of blessing." The REMA cites this ruling (OC 318:9).
The Mishnah Berurah adds that the type of salt that is cooked as part of its processing, or sugar that is cooked as part of its processing, may be placed into a Kli Rishon (that is not on the fire), because once an object has been cooked it cannot be re-cooked (Ein Bishul Achar Bishul). However, some people are stringent not to place such salt or sugar into a Kli Rishon, because it appears as though one is cooking. Therefore, it is best not to put salt into a Kli Rishon.