Bava Basra, Chapter 5, Mishnah 8. The Mishnah discusses the sale of liquids, and within it are two separate topics: The first topic - when the kinyan (acquisition) takes effect when pouring liquids; and the second topic - when it is considered that the buyer received the full value for his money, meaning how many drops he must extract from the side of the vessel, whatever vessel it may be.
The first part of the Mishnah is difficult to understand simply, and the Gemara addresses this exact point. The Mishnah discusses someone who sold wine or oil to his fellow, and afterward the price of the merchandise went up or down significantly, so that one of the parties wishes to back out of the transaction. In all the laws of kinyan, the practical difference is one: if the kinyan was completed, the parties cannot back out; and if it was not yet completed, they are permitted to back out. The question here, therefore, is whether the parties can back out.
The Mishnah states: "Im ad shelo nismaleis hamiddah - lamocher" - if before the measure is filled, it is the seller's - as long as the measure was not filled, such as if they are filling a gallon jug and the liquid has not yet reached the full mark, the liquid is still the seller's, and consequently, it is possible to back out of the transaction, since a kinyan was not made and a transfer of ownership did not occur. However, "mishenismaleis hamiddah - lalokeiach" - once the measure is filled, it is the buyer's - once the liquid reached the measure mark, it belongs to the buyer, and there is no longer an option to back out.
The Gemara's Question:
The Gemara wonders about this, since the halachah depends on the ownership of the vessel and its location, and the two possible situations are not consistent with the wording of the Mishnah:
The vessel belongs to the seller and the transaction occurs in his domain: The very fact that the seller measured a gallon of oil does not acquire anything for the buyer. The buyer must perform an act of kinyan, which is hagbahah (lifting). Until the buyer takes ownership by lifting the vessel, the liquid belongs to the seller, and the two parties can always back out (for the seller - perhaps with the addition of "mi shepara," but that is not the point).
The vessel belongs to the buyer and it is placed in a location where the buyer is permitted to acquire: In his private domain, in a domain he shares with the seller, or in an alleyway, as was explained in the previous Mishnah. In this case, something very close to kinyan chatzer (acquisition by one's courtyard) takes effect here, except that it is not actual kinyan chatzer but kinyan keilim - a person's vessels acquire for him. His vessel is placed in his domain in a permitted location, and the liquid is poured into it and is preserved there, and therefore there is no need for hagbahah at all.
It emerges that if the vessel belongs to the buyer and it stands in his domain or a shared domain, every single drop that is poured into it is acquired by him immediately, and there is never an option to back out of the transaction. If so, what is the Mishnah asking, and from where does it reach its puzzling conclusion?
The Gemara's Resolution - A Borrowed Vessel:
The Gemara explains that we are dealing with a buyer and a seller who do not have their own vessel, and they must borrow a vessel for the purpose of the transaction. For example, a broker introduced the parties, and they agreed between them that the buyer will purchase a gallon of oil for one hundred shekels - the conditions were agreed upon, but they have no vessel in their hands. A third party comes, and for the sake of discussion let us say it is the broker (but it could be any person), and he lends a vessel for the purpose of the transaction.
And here the question is asked: To whom does he lend the vessel? If he lent it to the seller, the laws of the seller's vessel apply, and the liquid is never acquired by the buyer until he lifts it. And if he lent it to the buyer, the vessel is his from the outset, and if it stands in his physical domain - on land in which he has a share or in an alleyway - every drop that enters it is acquired by him immediately.
The Gemara's resolution, which is the only fundamental novel teaching of the Mishnah here: The third party lends the vessel to the seller as long as it is not full, but once the vessel is filled the seller no longer has any need or use for it, and from now on its entire purpose is for the buyer to acquire the liquid. Therefore, the moment the vessel is filled with the required measure, the borrowing transfers from the seller to the buyer, and the third party is now lending it to the buyer. And since the buyer is the owner by virtue of the borrowing, he acquires everything poured into the vessel through the law of kinyan keilim (acquisition by one's vessels).
Let us review the wording of the Mishnah so that the matter will be completely clear: "Hamocher yayin veshemen lachaveiro" - one who sells wine or oil to his fellow - Reuven sold his wine or oil to Shimon; "hukru vehuzlu" - they went up or went down in value - and afterward the price went up or down, and the question is whether it is possible to back out. "Im ad shelo nismaleis hamiddah - lamocher" - if before the measure is filled, it is the seller's - as long as the vessel was not filled, it is borrowed to the seller, the transaction was not yet completed, and both parties can back out. "Mishenismaleis hamiddah - lalokeiach" - once the measure is filled, it is the buyer's - once it is filled to the end, the vessel is immediately lent to the buyer, and his vessels acquire their contents for him, and they can no longer back out.
"Ve'im hayah sarsor beineihen" - And if there was a broker between them:
Here the Mishnah begins a new section. In the previous line, the middleman was only involved in lending the vessel, whereas here the broker does the work himself and dirties his hands by pouring the liquid. The buyer says to the broker: "I want to buy oil, get me a gallon of oil for one hundred shekels." The broker goes to the supplier and says: "I want to buy oil from you for ninety shekels a gallon", since he must sell it for a hundred, and the ten-shekel difference is his profit. The broker therefore fills his own vessel, intending to transfer it to the buyer.
The implicit question that the Mishnah comes to answer is: Does the middleman have the status of an agent - meaning that he acts on behalf of the buyer, and in such a case the oil belongs to the buyer immediately; or perhaps he acts on his own behalf, and he is like an intermediate buyer who will sell the merchandise onward to the final buyer. The Mishnah adopts the second option: once the middleman enters the picture and pours into his own vessel, the oil belongs to him, and afterward he will sell it to the buyer who authorized him to obtain the oil.
And since this is so, if after the broker filled his vessel, the vessel was broken, lost, or stolen - who bears the financial loss? Not the buyer and not the seller, but the broker in the middle, since he made an acquisition the moment he poured the supplier's oil into his vessel. And this is the wording of the Mishnah: "Ve'im hayah sarsor beineihen" - if there was an intermediate stage where the broker receives the merchandise, "nishberah hechavit - nishberah lasarsor" - if the barrel was broken, it was broken to the broker, and the broker is the one who bears the loss.
When Did the Buyer Receive the Full Measure:
From here onward, the Mishnah begins a completely new topic, so much so that it could have served as the beginning of its own separate Mishnah. Until now we dealt with the question of when the transaction concludes and to whom the product belongs; from here onward, the Mishnah deals with the question of at what stage one can say that the buyer has received the amount of liquid due to him. The concept is this: liquid poured from the vessel, and especially oil, sticks to the sides, and therefore continues to drip in ever-decreasing amounts for a whole day. When one enters a store and asks for a gallon of oil, and the storekeeper pours for him from his vessel into the bucket he brought with him - how long must he stand over the bucket and allow the vessel to empty, waiting for any remainder that stuck to the sides?
This question also applies to wine. While wine is thinner and pours more easily, we must remember that their vessels were earthenware vessels, whose insides are not smooth, and presumably the liquid stuck to their sides even more. Either way, the question remains: how long must the seller stand over the buyer's vessel and let the vessel empty?
The Mishnah says: "Vechayav lehatif lo shalosh tipin" - he must drip three drops for him, meaning the seller must wait until the pouring turns into a drip of individual drops, and from that stage he must wait for the falling of three drops. This is sufficient. The assumption is that the buyer waives his right and relinquishes ownership of all the remaining leftover, and he has no further claim or demand regarding the remnants of liquid on the sides.
And therefore: "Hirkino umitzah - harei hu shel mocher" - if he tilted it and drained it, it belongs to the seller. If, after the three drops came out, the seller rested his vessel on its side, and the oil accumulated at its bottom until, in an additional pour, not only a drip but even a small stream came out of it - this remainder belongs to the seller. Once the three drops have come out, the buyer says: "That is enough, and I waive my right to the final portion", and the remainder once again becomes the property of the seller.
Furthermore, the Mishnah says: "Vehachenvani" - but the storekeeper, meaning the storekeeper working in a grocery store where many things are happening, cannot stand for ten minutes until the final three drops come out. Therefore, he is permitted to pour until the vessel empties, and he is not required to wait even for those few seconds of the three drops, since everyone is waiting in line and he is under pressure. The store buyer therefore waives his right the moment the liquid stops pouring freely.
Rabbi Yehudah disagrees and holds that on all days of the year the storekeeper is obligated to wait for the three drops like any person, and he has no special exemption, and people will wait patiently. But on Erev Shabbos at dusk, when everyone is rushing and no one has time, the storekeeper is exempt from waiting for the final three drops, since everyone waives their right to them out of a desire to get home for Shabbos and speed up the line.
The halachah, on the other hand, was decided in accordance with the opinion of the Tanna Kamma, that the storekeeper is exempt from waiting for the final three drops to fall at all times.