Keilim, Chapter 7, Mishnah 3. Our Mishnah stays with the earthenware cooking installations of the kitchen in the world of the Mishnah, and it presses a practical question: at what point does such an installation cease to count as a utensil? The kirah was built with a pair of openings in its upper surface, one for each pot; the fire burned in the space below, and the heat climbed through those openings to cook the food. The Mishnah looks first at a kirah that has cracked into pieces, and afterward at a broad earthenware base that was sometimes formed together with it.
A kirah split along its length
The Mishnah begins: "Kirah shenechleka le'orka tehorah" - a kirah that split lengthwise is tahor. Imagine a crack descending from the upper surface all the way down, running the long way. A break in that direction travels through both openings and halves each of them. Neither opening survives intact, and there is no longer a full ring of clay to surround a pot and keep it steady. Two half openings cannot do the work for which the installation was made, and once it can no longer perform its function it has forfeited the status of a utensil altogether. Tumah that it had already received now departs, and it is closed to any tumah in the future as well.
A kirah split along its width
"Ul'rochba temeiah" - but if the split runs along its width, it remains tamei. Here the break falls between the two openings rather than through them, so each opening stays whole. The result is two pieces, each one with a complete opening that can still hold a pot over a fire. In effect each half has become something like a kupach, the single opening stove. It is now more exposed than before and it will not retain heat as well, but if the fire is directly beneath the opening and a pot sits on top, it will still cook. Since it still functions, it is still a utensil, it remains tamei if it was tamei, and it can contract tumah.
A kupach that split
The Mishnah continues: "Kupach shenechlak", a kupach that broke apart, "bein le'orko", whether the break runs the long way, "bein le'rochbo", or across, "tahor", it is tahor. The reasoning needs little elaboration: the kupach was made with a single opening. A fracture in either direction must pass through that one opening and ruin it, leaving nothing capable of holding a pot. Once broken it will never again function as a kupach, so it sheds tumah and is beyond receiving any.
The courtyard of the kirah
A kirah was at times set upon a broad earthenware platform whose surface extended out beyond the stove on every side, with a low lip running around the outer edge, rather like a tray placed underneath. Where this base was formed together with the stove as one piece from the outset, the ledge that projects beyond the walls is termed the chatzer hakirah, the stove's courtyard. The Mishnah now takes up the tumah status of that courtyard.
"Chatzer hakirah": "bizman shehi gevoha", when its lip rises to a height of "shalosh etzba'ot", three fingerbreadths, we are dealing with the minimum height of a kirah, and the courtyard is granted the standing of a kirah in its own right. Hence "mitamei bemaga uv'avir": it receives tumah both by contact and through its airspace. A tamei object that touches the courtyard's floor renders it tamei, and so does a tamei object that enters the space enclosed by the lip without touching anything at all. Tumah that takes hold of the courtyard spreads to the stove as well, and the reverse holds too: let tumah reach the kirah, and the courtyard is tamei along with it.
"Pechuta mikan" - should the lip fall short of that height, the space it encloses is too slight to carry halachic weight. A courtyard like this does not hold the standing of a kirah, and it receives no tumah independently, not even by contact. "Mitamei bemaga ve'eina mitamei be'avir" - it does turn tamei when tumah strikes the kirah, and thereafter it passes tumah on to whatever touches it, though never through its airspace. The reasoning: a shallow courtyard is regarded as a handle attached to the kirah. Handles share the tumah of the vessel they serve, and they convey that tumah by contact alone, never by air.
Measuring the airspace of the courtyard
So a courtyard whose lip stands three fingerbreadths tall receives tumah through its airspace, that is, through the open area bounded on one side by the lip and on the other by the outer wall of the stove. How high does that airspace reach? The stove sits at the center of the tray and its walls climb well above the encircling lip, so the boundary is genuinely unclear: is the enclosed air reckoned up to the top of the stove's wall, or only up to the level of the lip?
The Mishnah asks: "Keitzad mesha'arin ota?" - by what method is it measured? "Rabi Yishmael" answers: "notenet hashapud milma'ala lemata", one lays a shapud, a spit, at an angle, its upper end resting on the edge of the stove's wall and its lower end coming down onto the lip that encircles the tray. A shapud is the long metal skewer used for roasting a sizable cut of meat over the flames. "Uchenegdo mitamei be'avir": the region lying beneath that sloping line, on the side facing the stove, counts as the courtyard's airspace, and a tamei object that enters it conveys tumah to the courtyard through its air.
Rabbi Eliezer ben Yaakov's view
The ruling stated until now moved tumah in both directions: a courtyard that received tumah by itself drew the stove into tumah, and tumah striking the stove reached the courtyard too. A dissenting opinion is now recorded. "Rabi Eliezer ben Yaakov" holds: "nitmeit hakirah, nitmeit hachatzer" - once the stove has contracted tumah, the courtyard is tamei with it, since the courtyard is merely tafel, subordinate, to the stove. "Nitmeit hachatzer", however, where the tumah reached only the courtyard, then "lo nitmeit hakirah": the stove remains tahor, for it is in no sense subordinate to its courtyard.