Halacha

הלכה א
הַנִּצוֹק אֵינוֹ חִבּוּר לֹא לְטֻמְאָה וְלֹא לְטָהֳרָה. כֵּיצַד. הָיָה מְעָרֶה מַשְׁקִין טְהוֹרִין לְתוֹךְ כְּלִי טָמֵא וַאֲפִלּוּ עַל גַּבֵּי הַשֶּׁרֶץ הֲרֵי הָעַמּוּד הַנִּצּוֹק טָהוֹר. וְאִם קָלַט מִן הַמַּשְׁקִין הַנִּגָּרִין מִן הָאֲוִיר הֲרֵי זֶה שֶׁקָּלַט טָהוֹר. וְאֵין צָרִיךְ לוֹמַר שֶׁהַמַּשְׁקִין שֶׁמְּעָרֶה מֵהֶן טְהוֹרִין:
כסף משנה
1.
A column of liquid being poured is not considered as joined, neither to an impure entity nor to one that is pure.
What is implied? If one was pouring pure liquids into an impure container or even on the carcass of a crawling animal itself, the column of liquid being poured is pure. If one would collect some of the liquids that are being poured while they are in the air, what he collects is pure. Needless to say, that the liquids in the container from which one is pouring are pure.

הלכה ב
בַּמֶּה דְּבָרִים אֲמוּרִים בְּשֶׁעֵרָה מִצּוֹנֵן לְצוֹנֵן אוֹ מֵחַם לְחַם אוֹ מֵחַם לְצוֹנֵן. אֲבָל הַמְעָרֶה מַשְׁקִין טְהוֹרִין צוֹנֵן לְתוֹךְ מַשְׁקִין טְמֵאִין חַמִּין הֲרֵי הַנִּצּוֹק חִבּוּר וְנִטְמְאוּ הַמַּשְׁקִין הַצּוֹנֵן כֻּלָּן שֶׁהוּא מְעָרֶה מֵהֶן וְנִטְמָא הַכְּלִי שֶׁמְּעָרֶה מִמֶּנּוּ מֵחֲמַת הַמַּשְׁקִין שֶׁבְּתוֹכוֹ שֶׁהֲרֵי נִטְמְאוּ. וּמִפְּנֵי מָה אָמְרוּ הַמְעָרֶה מַשְׁקִין צוֹנֵן לְחַמִּין חִבּוּר מִפְּנֵי שֶׁעֶשֶׁן הַחַמִּין עוֹלֶה כְּתִמְרוֹת עָשָׁן וּמִתְעָרֵב בַּנִּצּוֹק וּבַמַּיִם שֶׁבַּכְּלִי הָעֶלְיוֹן וּמְטַמֵּא הַכְּלִי שֶׁהֶעָשָׁן הָעוֹלֶה מִן הַחַמִּין מַשְׁקִין הוּא חָשׁוּב:
כסף משנה
2.
When does the above apply? When one is pouring cold liquids to cold liquids, hot liquids to hot liquids, or hot liquids to cold ones. If, however, one pours pure cold liquids into impure hot liquids, the column of liquids being poured is considered as joined. The liquids are considered as a primary derivative of impurity. They impart impurity to the container in which they are held.
Why did the Sages say that when one who pours cold liquids into hot liquids, the liquids are considered as joined? Because the vapors of the hot liquids ascend like a pillar of smoke. It becomes intermingled with the column of liquid being poured and the liquid in the upper container, causing it to become impure. For the vapor ascending from the hot liquid is also considered as liquid.

הלכה ג
לְפִיכָךְ הָאִשָּׁה שֶׁהָיוּ יָדֶיהָ טְהוֹרוֹת וֶהֱגִיסָהּ בִּקְדֵרָה טְמֵאָה וְהִזִּיעוּ יָדֶיהָ מֵהֶבֶל הַקְּדֵרָה נִטְמְאוּ יָדֶיהָ כְּאִלּוּ נָגְעָה בַּמַּשְׁקֶה שֶׁבַּקְּדֵרָה. וְכֵן אִם הָיוּ יָדֶיהָ טְמֵאוֹת וֶהֱגִיסָהּ בִּקְדֵרָה וְהִזִּיעוּ יָדֶיהָ נִטְמָא כָּל מַה שֶּׁבַּקְּדֵרָה כְּאִלּוּ נָגְעָה בַּמַּשְׁקִין שֶׁבַּקְּדֵרָה:
כסף משנה
3.
For this reason, when a woman whose hands were pure was stirring a hot pot that was impure and liquid collected on her hand because of the vapor of the pot, her hands contract impurity. It is as if they touched the liquids in the pot. Similarly, if her hands were impure, she stirred a hot pot, and liquid collected on her hand because of the vapor of the pot, all of the contents of the pot contract impurity, as if she touched the liquids in the pot.

הלכה ד
נְחִיל דְּבַשׁ הַזִּיפִים וּדְבַשׁ הַצַּפַּחַת הַנִּצּוֹק שֶׁלָּהֶן חִבּוּר וַאֲפִלּוּ הָיָה מְעָרֶה מִצּוֹנֵן לְצוֹנֵן מִפְּנֵי שֶׁיֵּשׁ לָהֶן רִיר וַהֲרֵי הֵן נִמְשָׁכִין כְּדֶבֶק. לְפִיכָךְ כָּל הָאֳכָלִין אֵין הַנִּצּוֹק שֶׁלָּהֶן חִבּוּר וַאֲפִלּוּ הָיוּ עָבִים הַרְבֵּה כְּגוֹן הַגְּרִיסִין וְהַחֵלֶב הַמֻּתָּךְ וְכַיּוֹצֵא בָּהֶן. לְפִי שֶׁאֵין לָהֶן רִיר. וְכֵן שְׁאָר כָּל הַמַּשְׁקִין אֵין הַנִּצּוֹק שֶׁלָּהֶן חִבּוּר אֶלָּא אִם כֵּן עֵרָה מִצּוֹנֵן לְחַם כְּמוֹ שֶׁבֵּאַרְנוּ:
כסף משנה
4.
When honey from Zif and Tzapachat is poured, the column of honey is considered as joined even if one is pouring from a cold container to a cold container. The rationale is that the honey remains attached to them and they are extended like glue. Therefore the column of all other foods which are poured are not considered as joined even if they are very thick, e.g., cooked groats, melted fat, or the like, because they do not remain attached. Similarly, with regard to other liquids, a column of poured liquid is not considered as joined unless one is pouring from cold to hot, as we explained.

הלכה ה
הַנִּצּוֹק אֵינוֹ חִבּוּר לְטָהֲרָה. כֵּיצַד. שֶׁאִם עֵרָה מַיִם טְמֵאִים מִכְּלִי אֶבֶן וְכַיּוֹצֵא בָּהֶן לְתוֹךְ הַמִּקְוֶה אֵין אוֹמְרִים מִשֶּׁהִגִּיעַ קְצָת הַנִּצּוֹק לַמִּקְוֶה טִהֲרוּ הַמַּיִם אֶלָּא הֲרֵי הֵן בְּטֻמְאָתָן עַד שֶׁיַּשִּׁיק הַמִּקְוֶה לְכֻלָּן מִצַּד אֶחָד כְּמוֹ שֶׁבֵּאַרְנוּ. וְכֵן הַקְּטַפְרֵס שֶׁיֵּשׁ עָלָיו מַשְׁקֶה טוֹפֵחַ אֵינוֹ מְחַבְּרָן לִשְׁאָר הַמַּשְׁקִין שֶׁבַּמִּדְרוֹן לֹא לְטֻמְאָה וְלֹא לְטָהֳרָה. אֲבָל הַמַּשְׁקִין שֶׁבַּאֶשְׁבּוֹרֶן כֻּלָּן חִבּוּר לְטֻמְאָה וּלְטָהֳרָה:
כסף משנה
5.
Similarly, a column of liquid is not considered as joined to a pure entity.
What is implied? If one poured impure water from a stone container or the like into a mikveh, we do not say that when the edge of the column being poured reaches the water, it is purified. Instead, it is considered as impure until it is all connected to the mikveh from one side, as we explained.
Similarly, when there is an incline that has tangible moisture upon it, the moisture is not considered as joined to other liquids on that incline, neither to render them impure or pure. Liquids that are collected on the ground, by contrast, are all considered as joined, whether this renders them impure or pure.

הלכה ו
עֲרֵבָה שֶׁהִיא קְטַפְרֵס וְעָלֶיהָ מַשְׁקֶה טוֹפֵחַ וְשָׁלֹשׁ חֲתִיכוֹת אֳכָלִין טְמֵאִים בִּכְבֵיצָה מֻנָּחִין עָלֶיהָ זוֹ לְמַטָּה מִזּוֹ אֵינָן מִצְטָרְפוֹת. הָיוּ שְׁתַּיִם הֲרֵי אֵלּוּ מִצְטָרְפוֹת. וְאִם הָיָה תַּחְתֵּיהֶם מַשְׁקֶה עוֹמֵד אֲפִלּוּ כְּעֵין הַחַרְדָּל הֲרֵי זֶה מְצָרֵף אֶת כֻּלָּן:
כסף משנה
6.
When a kneading trough is on an incline, there is tangible moisture on it, and there are three impure pieces of food, together an egg-sized portion in size, positioned on it, one below the other, they are not combined. If there are two, they are combined. If there was standing liquid beneath the food, even if the pieces are all the size of mustard seeds, the liquid combines them all.

הלכה ז
כְּבָר בֵּאַרְנוּ שֶׁטְּבוּל יוֹם אֵינוֹ מְטַמֵּא חֻלִּין כְּלָל אֶלָּא פּוֹסֵל אָכְלֵי תְּרוּמָה וּמַשְׁקֵה תְּרוּמָה וְעוֹשֶׂה הַכּל שְׁלִישִׁי. וְכֵן אִם נָגַע בְּאָכְלֵי קֹדֶשׁ אוֹ מַשְׁקֵה קֹדֶשׁ פְּסָלָן וַעֲשָׂאָן רְבִיעִי:
כסף משנה
7.
We have already explained that a person who immersed to purify himself on the same day does not impart impurity to ordinary foods at all. Instead, he disqualifies foods that are terumah and liquids that are terumah, making them all tertiary derivatives. Similarly, if he touches sacrificial foods or sacrificial liquids, he disqualifies them and causes them to be considered as fourth degree derivatives.

הלכה ח
יֵשׁ דְּבָרִים שֶׁאֵינָם חִבּוּר בִּטְבוּל יוֹם וְאַף עַל פִּי שֶׁהֵן חִבּוּר בְּכָל הַטֻּמְאוֹת. אֶלָּא אִם נָגַע בָּהֶן טְבוּל יוֹם לֹא פָּסַל אֶלָּא זֶה שֶׁנָּגַע בּוֹ. וְאִלּוּ הָיָה הַנּוֹגֵעַ בִּמְקוֹם טְבוּל יוֹם אָדָם אַחֵר הָיָה פּוֹסֵל הַכּל. אֲפִלּוּ הָיָה הַנּוֹגֵעַ אָדָם שֶׁאָכַל אֳכָלִין טְמֵאִין אוֹ שָׁתָה מַשְׁקִין טְמֵאִין שֶׁהִיא טֻמְאָה קַלָּה הֲרֵי זֶה פָּסַל הַכּל שֶׁלֹּא פְּסָלוֹ טְבוּל יוֹם. וְאֵין צָרִיךְ לוֹמַר שֶׁאִם הָיָה הַנּוֹגֵעַ אַב טֻמְאָה אוֹ רִאשׁוֹן שֶׁהוּא מְטַמֵּא הַכּל. וּמִפְּנֵי מָה הֵקֵלּוּ בִּטְבוּל יוֹם מִפְּנֵי שֶׁכְּבָר טָהַר וְאֵינוֹ מְחֻסָּר אֶלָּא הַעֲרֵב שֶׁמֶשׁ. וְעוֹד הֵקֵלוּ בִּטְבוּל יוֹם שֶׁיֵּשׁ אֳכָלִין שֶׁהֵן מְיֻחָדִין לְאָדָם וּמִתְטַמְּאִין בְּכָל הַטֻּמְאוֹת וְהֵן טְהוֹרוֹת בִּטְבוּל יוֹם. וְאֵלּוּ הֵן. הַשְּׂעוֹרָה וְהַכֻּסֶּמֶת בִּזְמַן שֶׁאֵינָן קְלוּפִין. אֲבָל בִּזְמַן שֶׁהֵן קְלוּפִין וְהַחִטָּה אַף עַל פִּי שֶׁאֵינָהּ קְלוּפָה. וְהַקֶּצַח וְהַשּׁוּמְשׁוּם. נִפְסָלִין בִּטְבוּל יוֹם וְאֵין צָרִיךְ לוֹמַר שֶׁהֵן מִתְטַמְּאִין בְּכָל הַטֻּמְאוֹת:
כסף משנה
8.
There are certain situations where articles are not considered as joined when one of them is touched by a person who immersed that day even though they are considered as joined with regard to all forms of impurity. Instead, if a person who immersed that day touched them, he disqualifies only the article he touched. If, instead of such a person, those articles had been touched by another impure person, he would have disqualified all of them. Even if the person who touched them merely partook of impure foods or drank impure liquids and thus his impurity is light, he disqualifies everything. In contrast, a person who immersed that day does not disqualify it. Needless, to say, if a person is a primary source of impurity or a primary derivative of impurity, he imparts impurity to everything.
Why was leniency granted to a person who immersed that day? Because he already purified himself and he is lacking only nightfall to attain purity.
A further leniency was granted with regard to a person who immersed that day. There are foods that are designated for human consumption and hence susceptible to all types of impurity, but they are pure if touched by a person who immersed that day. They are barley and spelt when they are not shelled. If, however, they are shelled, and, similarly, wheat, even if it is not shelled, black cumin, and sesame seeds are disqualified when touched by a person who immersed that day. Needless to say, they contract all forms of impurity.

הלכה ט
כָּל יַד הָאֳכָלִין שֶׁהֵן חִבּוּר בְּאַב הַטֻּמְאָה הֲרֵי הֵן חִבּוּר בִּטְבוּל יוֹם. וְכֵן כָּל הָאֹכֶל שֶׁנִּפְרָס וּמְעֹרֶה בְּמִקְצָת שֶׁהוּא חִבּוּר בְּאַב הַטֻּמְאָה כָּךְ הוּא חִבּוּר בִּטְבוּל יוֹם. וְכָל שֶׁאֵינוֹ חִבּוּר בִּטְבוּל יוֹם הֲרֵי הוּא חִבּוּר בְּיָדַיִם וְגַם זֶה חֹמֶר בְּטֻמְאַת יָדַיִם מִטְּבוּל יוֹם:
כסף משנה
9.
All of the "handles" of food that are considered as joined to the food with regard to a primary source of impurity are also considered as joined with regard to a person who immersed that day. Similarly, whenever food has been sliced, but is still somewhat connected and thus is considered joined with regard to a primary source of impurity, it is also considered as joined with regard to a person who immersed that day. Whenever leniency is granted and objects are not considered as joined with regard to a person who immersed that day, they are considered as joined with regard to the impurity of hands. This is also a stringency that applies with regard to the impurity of hands that does not apply with regard to a person who immersed that day.

טהרה הלכות טומאת אוכלים פרק ז
Taharah Tumas Ochalin Chapter 7