Gemara

Question: A verse exempts Kodshim from Shilu'ach ha'Kan. What is the case?

Answer: He saw a Hefker nest and he was Makdish it.

Rejection: "Ish Ki Yakdish Beiso Kodesh" - one can be Makdish only things like his house, which he owns.

Bava Kama 115a (Mishnah): If Levi was carrying a barrel of wine, and Yehudah was carrying a jug of honey, and Yehudah's barrel cracked, and Levi spilled out his wine and saved the honey, he is paid only like a worker.

Question: The honey was going to be lost. It is like Hefker!

(Beraisa): If a man was carrying jugs of wine and oil, and saw that they were breaking, he may not make the wine and oil Terumah to exempt what he has in his house. If he did, it is invalid.

Answer: In the Mishnah, a basket around the barrel holds the pieces of the barrel in place.

Question: In the Beraisa, why is the Terumah invalid?

(Beraisa): If Reuven was carrying coins, and an extortionist approached him, Reuven may not redeem the Kedushah of coins in his house onto the coins he is carrying. If he did so, it takes effect.

Answer: The case is, he can save them from the extortionist (with difficulty).

Tosefta (Demai 8:8, according to Gra's text): If one was carrying jugs of wine and oil, and saw that they were breaking, he may not say 'they are Terumas Ma'aser on Peros in my house.' If he did, Lo Amar Klum (this has no effect). However, he may designate the Terumas Ma'aser in the wine or oil before it reaches the ground.

Rishonim

Rambam (Hilchos Gezeilah 12:5): If Levi was carrying a barrel of wine, and Yehudah was carrying a jug of honey, and Yehudah's barrel cracked, and before it spilled to the ground Levi spilled out his wine and saved the honey, he is paid only like a worker. If the wine spilled to the ground it is Hefker, and whoever saves it saves for himself.

Rambam (Hilchos Terumos 3:17): One must tithe Min ha'Mukaf. If one has 50 Sa'im in this house and 50 Sa'im in another house, he may not make two Sa'im from them Terumah on all 100, for then he tithes on another place. If he separated Lo Min ha'Mukaf, b'Di'eved it is Terumah, as long as what he makes Terumah is guarded. If one was carrying barrels of wine or oil, and they are breaking, if he declared them Terumah to exempt what he has in his house, Lo Amar Klum.

Tosfos (115b DH v'Chol): The Gemara did not ask why it is forbidden l'Chatchilah. Whenever there is a loss to the Kohen, it is forbidden l'Chatchilah. We ask why b'Di'eved, Lo Amar Klum.

Chidushei Riz ha'Levi (Hilchos Terumos, p. 29 DH Bava): In Hilchos Gezeilah, the Rambam says that it becomes Hefker only when it falls to the ground. Why didn't he say so in Hilchos Terumos? There, it seems that even before it spills, he cannot make it Terumah! He connotes that there is a special law that it must be guarded. If not, he did not fulfill his obligation of Terumah and Ma'aser. It is not due to Hefker. Also, he taught this along with the law of Mukaf. This connotes that he cannot separate on Peros in his house, but he can tithe the spilling Peros themselves. This is because the law is based on the obligation to separate Terumos and Ma'aseros, so it is only when he exempts other guarded Peros, but not if he tithes them themselves. This requires investigation, for the Sugya taught it regarding Hefker!

Rashi (115b DH b'Ekel): We answer that a basket around the barrel holds the pieces of the barrel in place. The honey would have dripped out slowly. It could have been saved.

Riz ha'Levi (ibid.): Tosfos says that the question was from oil. It is forbidden to make it Terumah only l'Chatchilah, but b'Di'eved it is valid. The Gemara answered that there is a basket around the barrel. According to the Rambam, this means that it did not spill yet. Then, the Terumah takes effect. The Rambam connotes oppositely! The Tosefta according to the Gra's text is exactly like the Rambam. However, the Sugya equates this to Hefker. Also, it says that when there is a basket around the barrel, one can make it Terumah on other Peros. Why does the Tosefta say 'similarly'? The Gemara establishes the second law to discuss there is a basket around the barrel, and it is not Hefker. The first law discusses Hefker! Also, if a loss to the Kohen causes that the separation does not take effect, we need not mention Hefker! According to the Rambam, this is not difficult. Both Beraisos discuss the same law. Whatever is not guarded and is destined to be lost, one does not fulfill through it the obligation of Terumos and Ma'aseros, so the designation is invalid. This is also the law of the second Beraisa, in which the Kohen loses. This is if he separates on guarded Peros. If both are not guarded, he can separate. The first Beraisa teaches that he may separate on the Peros themselves. The same applies to Tamei wine, for in any case the Terumah will be useless. As long as it is not Hefker, he can tithe it. We asked from the Mishnah, for the Tosefta teaches that once it spills to the ground, he cannot tithe even it itself, for it is Hefker. We answered that there is a basket around the barrel, so it does not spill and it is not Hefker. We then asked from a Beraisa that says that one can designate Terumah when it spills. We answer that there is a basket around the barrel, and it did not spill yet. In such a case one cannot separate on other Peros, due to loss of the Kohen, but one can tithe it itself.

Rambam (4:2): One cannot tithe Peros that are not his without consent of the owner.

Or Some'ach: The Yerushalmi asked whether the problem is that it is another's Peros, or because it is not his. This affects one who was Mafkir his Peros after final processing. Perhaps the Yerushalmi holds that one can tithe Hefker only to fix those Peros, but not to make all of them Terumah on other Peros. This is because the Peros are destined to be tithed and to permit the Isur Tevel, but not to make all of them Terumah. If a barrel broke, one cannot make it Terumah on elsewhere (Bava Kama 115b). Since it will be lost, one cannot acquire it. It is Hefker. This shows that one cannot tithe Hefker. However, the Yerushalmi discusses only tithing the Hefker. Surely, one cannot declare Hefker Peros to be Terumah on other Peros. If so, there is no proof from Bava Kama. This is almost explicit in the the Gra's text of the Tosefta. Even though the Peros are about to be lost and they are Hefker, one can tithe it itself. However, the Sugya holds that this is because they will be lost. This is worse than Hefker. The Sugya equates Peros that will be lost to an extortionist who will seize money. There, the money will not be lost, just it is not b'Yadecha (in your hand), which is required for Ma'aser. These were taught together in the Tosefta of Ma'aser Sheni (1:6). It says there 'if he did so, it is forbidden.' When the loss is only to the owner, his words take effect. However, regarding Terumas Ma'aser, which belongs to the Kohen, his words are Batel and the Peros are Tevel, if the Kohen would lose. This depends on the argument of Rav Chisda and Rav Noson bar Hoshaya (Yevamos 89a) about one who separated Tamei Terumah to exempt Tahor produce, if we say that when he was Mezid the Peros revert to be absolute Tevel.

Mordechai (Bava Kama 163, citing Maharam): One who buys from a robber acquires only if the owner despaired. If an extortionist was coming and one redeemed his Ma'aser onto his coins, it is valid only if he could save them with difficulty. If he cannot save them, Lo Amar Klum. That discusses a Yisrael extortionist, or even a Nochri extortionist if there is no Siman on the money.

Pnei Yehoshua (115b DH Sham v'Im): The Beraisos themselves are not contradictory. We could say that the reason one cannot separate Terumah is not due to Hefker, rather, lest the Kohen lose. This reason does not apply to Ma'aser Sheni. However, our Sugya assumes that the reason for Terumah is Hefker. If so, the Beraisa of an extortionist is difficult, for also this is like Hefker, since he cannot save it. Maharam asked that even after it was stolen, it is still in the owner's Reshus, for Stam there is no despair. He distinguished between Yisrael and Nochri robbers. I say that there is no difference. Rather, it is invalid because redemption money of Ma'aser Sheni must be "b'Yadecha". This is why one cannot redeem on coins in Har ha'Melech (if he cannot get to them).

Poskim

Shulchan Aruch (YD 331:25): One must tithe Min ha'Mukaf. If one has 50 Sa'im here and 50 Sa'im elsewhere, he may not make two Sa'im here Terumah on the Peros in both places. B'Di'eved it is Terumah, as long as what he makes Terumah is guarded. If one was carrying barrels of wine or oil, and they are breaking, if he declared them Terumah to exempt what he has in his house, Lo Amar Klum. It seems that nowadays that Terumah perishes, due to Tum'ah, it becomes Terumah.

Gra (70): It is Terumah b'Di'eved only when there is a basket around the barrel. (It is not Hefker, for he could save it with difficulty.) The Mechaber means only that it becomes Terumah b'Di'eved, like it says in the Tosefta in Demai.

Gilyonei ha'Shas (115b): If not that they were Hefker, the Terumah would take effect, even though they will be lost. We should say that Kesusei Michtas Shi'urei (it is as if was already lost and it is less than the Shi'ur), for there is a Shi'ur for Ma'aser! Perhaps the Gemara asked from Terumah, which has no Shi'ur mid'Oraisa. Also, this is unlike Isurei Hana'ah that must be burned. Something destined to be burned is inferior. Here, as long as it did not perish, it is intact. If a Sefer Torah fell into an oven, as long as it did not burn, it is Metamei Terumah (Tosefta Shabbos 13:6). This is when there is bread in the oven. Even though the Sefer will be burned, it is Metamei. The Chidush is that Sefer did not lose its Kedushah, or that we do not say Kesusei Michtas Shi'urei. A Sefer must have at least 85 letters to be Metamei hands, and the same applies to Terumah.