We continue with chapter 11 of Maseches Terumah, dealing with the last remnants of Terumah and how one must treat them. Mishnah 8 discusses someone pouring oil from one vessel into another: the first vessel held Terumah oil, and now he is emptying it into a different vessel. The question is how careful he must be to extract every last drop from the first vessel.
Three drops:
The Mishnah teaches that it is enough to let three drops fall. As we know, when oil is being poured out, the amount coming from the vessel steadily decreases until it emerges drop by drop. Once it reaches three drops, the vessel is considered empty enough, and from that point one may refill it with chullin without any concern.
"Hirkinah u'mitzah":
The Mishnah continues: if the vessel was tilted onto its side and the oil collected at the bottom, there is once again a significant amount of oil that can be removed with a spoon or with a straw - and that oil has the status of Terumah, which cannot be denied. The leniency was stated only where no significant quantity of Terumah gathered, in which case one may fill the vessel with fresh oil and the remnants are nullified; but once a meaningful quantity has reappeared, it has the status of Terumah.
As for the precise translation of the words, there is some difficulty here: "hirkinah" - tilting onto the side, which allowed the oil to gather. "Mitzah" - a term of squeezing out, like the wringing out of the blood upon the altar. According to this it sounds as though he tilted the vessel after it had emptied completely, and even so oil gathered in it anew, and perhaps the intention is that the walls were squeezed and the oil collected in one place. Although we cannot be certain of the exact meaning of the word, the law is entirely clear: after tilting the vessel onto its side the oil gathers together, and that gathering has the status of Terumah.
Terumas maaser of demai:
Mishnah 9 moves to an entirely different subject. True, we are still dealing with items that have the status of Terumah and with remnants, but the direction has changed: here the subject is terumas maaser, and specifically terumas maaser separated from demai.
Demai is produce purchased from an am ha'aretz, regarding which there is a concern that it may not have been properly tithed. Most produce in the Second Temple era, in the times of the Mishnah, was properly tithed, but a significant minority among the amei ha'aretz, the simple people, did not separate all the tithes. The concern was for maaser sheni, and above all - and this is the more serious matter - for terumas maaser.
Terumas maaser is the tithe taken from the tithe: a person gives a tithe from his grain to the Levi, and the Levi separates a tenth of the tithe he received and gives it to the kohen. Many of the amei ha'aretz reasoned that since they had not separated the tithe for the Levi, there was as yet no obligation to separate terumas maaser for the kohen - and they were mistaken. Terumas maaser has the full status of Terumah, and it carries with it the severe penalty of death at the hands of Heaven, dying before one's time.
Therefore Chazal ruled that even though most demai has been properly tithed, we do not treat the matter leniently: one who buys produce from amei ha'aretz must separate again, in practice only one percent - a tenth of a tenth - and give it to the kohen.
Hence the question: with oil fit for eating there is no exemption for a minimal amount, and whatever oil he received - the tenth of a tenth of it, the hundredth of it, the one percent of it - he is obligated to bring to the kohen. But what is the law with impure oil, which in any case is not fit for eating? If a tiny, thimble-sized amount of impure oil remained in his hand, must he bring that too to the kohen? In other words, what is the minimum measure below which one is exempt from bringing impure demai oil to the kohen as terumas maaser?
"Sheminis shebishminis":
The Mishnah's answer: the measure is an eighth of an eighth. The Bartenura explains that we are speaking of oil of demai that became tamei, and from this quantity and upward one must bring it to the kohen.
Just as "revi'is," which means a quarter, refers to a quarter of a log, so here we are speaking of an eighth of an eighth of a log. The measure of a log is about the size of a small cola bottle, roughly 500 cc; a revi'is is a quarter of that, roughly 125 cc, a child-sized cup. An eighth of an eighth is therefore one sixty-fourth of a log - about eight milliliters.
It emerges that if a person has about eight milliliters of tamei oil from demai, he need not bring it to the kohen; with more than that, he is obligated to bring it. That eighth of an eighth, one sixty-fourth of a log, has a name: a kortov, and it is the smallest measure of volume in the words of Chazal. Even so, the kortov matters and must be brought to the kohen - certainly when the obligation is from the Torah, and even in a larger quantity than this when the oil is tamei.
In summary: in Mishnah 8 we learned that one who pours out Terumah oil from vessel to vessel needs only three drops, and from that point on he may fill the vessel with chullin; but when he tilted the vessel and drained it, and the oil collected in a significant quantity, it has the status of Terumah. In Mishnah 9 we moved on to terumas maaser of demai, we noted the mistake of the amei ha'aretz who did not separate terumas maaser and the seriousness of the matter, and we learned that the exempt measure for tamei oil is an eighth of an eighth of a log - which is the kortov, about eight milliliters.