Reference for Bava Metzia 4:1
הַזָּהָב קוֹנֶה אֶת הַכֶּסֶף, וְהַכֶּסֶף אֵינוֹ קוֹנֶה אֶת הַזָּהָב. הַנְּחֹשֶׁת קוֹנָה אֶת הַכֶּסֶף, וְהַכֶּסֶף אֵינוֹ קוֹנֶה אֶת הַנְּחשֶׁת. מָעוֹת הָרָעוֹת קוֹנוֹת אֶת הַיָּפוֹת, וְהַיָּפוֹת אֵינָן קוֹנוֹת אֶת הָרָעוֹת. אֲסִימוֹן קוֹנֶה אֶת הַמַּטְבֵּעַ, וְהַמַּטְבֵּעַ אֵינוֹ קוֹנֶה אֶת אֲסִימוֹן. מִטַּלְטְלִין קוֹנִים אֶת הַמַּטְבֵּעַ, וְהַמַּטְבֵּעַ אֵינוֹ קוֹנֶה אֶת הַמִּטַּלְטְלִין. זֶה הַכְּלָל, כָּל הַמִּטַּלְטְלִין קוֹנִין זֶה אֶת זֶה:
Gold acquires silver, and silver does not acquire gold. Copper acquires silver, and silver does not acquire copper. [Everything which is regarded as currency and passes readily in trade has the status of money and does not acquire its counterpart which is not regarded as currency and does not pass as readily in trade. The latter has the status of fruit, and pulling it is an act of confirmation. Therefore, when one pulls dinars of gold, the other acquires dinars of silver wherever they are, and neither of them can back out. For dinars of gold are fruits relative to dinars of silver. And silver does not acquire gold. For dinars of silver, which pass readily in trade, have the status of money relative to dinars of gold. So that if one of them pulled dinars of silver, the other does not acquire a dinar of gold until he pulls it, for money does not effect acquisition. And this is the reason, too, that copper acquires silver. For p'rutoth of copper, which are not so readily accounted currency, are fruits relative to dinars of silver, and silver does not acquire copper.] Bad [i.e., invalidated] money acquires good money, and good money does not acquire bad money. An asimon [(a metal piece) shaped as a coin, but, as yet, unstamped with a design] acquires a coin, and a coin does not acquire an asimon. Mitaltelin (movable objects) acquire a coin, but a coin does not acquire mitaltelin. This is the rule: All mitaltelin acquire each other. [If one were exchanged for the other, pulling the one effects acquisition of the other. "All" comes to include even (an exchange) of one pouch full of money for another.]