תרומות פרק ד משנה ד
The Halacha is that if one סאה of תרומה falls in a vat of 100 סאה (acc. to one שיטה) it becomes בטל and one may take off תרומה from anywhere within the vat, as the original תרומה is בטל.
There is a מחלקת if the vat has half black תרומה and half white תרומה and a piece of white תרומה falls in. One שיטה holds it becomes בטל.(Rabbi Yehoshua). Another holds it does not become בטל.(Rabbi Eliezer). Another שיטה holds that it depends on if we know the color of the תרומה that falls in. If we know the color of the תרומה that falls in it does not become בטל as he can just eat from the other color of תרומה. If we do not know the color of the תרומה that falls in is becomes בטל.
My understanding of Rabbi Yehoshua who holds that it does become בטל is that it does not matter that we know where the תרומה is in the mixture. It is not dependent on our knowledge. As long as it is mixed in that is enough. My understanding of Rabbi Eliezer who says that even we don't know if what fell in was white or black it does not become בטל perhaps he understands that if the color is separate and what fell in belonged to one group that is not considered a mixture at all. Rabbi Akiva is troubling to me: Why does it matter if he knows which color fell in or not. Whether something becomes בטל should be dependent or our own knowledge? Either it became mixed up or it did not become mixed up? Any thoughts of any more understanding of this Mishnah or certainly welcome.