Shekalim 19 - Found coins
While putting money into the collection chests we discussed before , one could error and drop them on the floor. If such coins are later found near the chests, we need to know what to do with them - because they had been designated for a specific purpose. The rule is like this: if, for example, the coins were found next to the "Shekalim" chests, we assume that they are for shekalim. If they were found closer to the adjacent "voluntary offerings" chest, we assume that they are for that purpose. If they are exactly in the middle, we take the more stringent view and put them in the voluntary offerings. Thus "close to" is a ruling principle, but in case of doubt we take the most stringent possibility into account.
In general, other coins found in Jerusalem, which might potentially be designated for some special purpose, are governed by similar principles. For example, if coins are found next to animal dealers, we assume they have the holiness of tithe. This is because the people used to bring their tithe money to Jerusalem and buy food or animals and eat it them there. Most likely they did not have the chance to spend all the money, and dropped the coins. However, if the coins are found on the Temple Mount, we assume they have no designation at all - since we have no reason to assume otherwise, and majority of coins in the world are not designated for anything special.
Art: The gold-weigher by Salomon Koninck