One of the most difficult commandments to understand is the process of purification involving the ashes of a parah adumah – a red heifer (see Sefer Bamidbar, Chapter 19). A full tractate of Mishnah – Masechet Parah – is devoted to these laws, which require the slaughter and burning of a parah adumah, mixing those ashes with water that is drawn and prepared for this purpose and then applying the water – referred to as mei hatat – to the individual who is tamei met(ritually defiled through contact with the dead).
In the context of discussing issues of mixture and halakhah, the Gemara on today’s daf (=page) quotes a Mishnah that teaches about a case where a small amount of ordinary water fell into the tzelohit – the flask – that held the mei hatat. According to Rabbi Eliezer, the water can still be used for the ritual, all that needs to be done is to apply the water twice to the person who was tamei met. The Hakhamim argues that this does not solve the problem, and that this water cannot be used.
A tzelohit, or flask, was a container – ordinarily made of earthenware, but occasionally made of glass or metals like gold or silver. Such flasks had many uses. They were used as serving utensils at meals, as containers for scents used in different places, e.g. in cemeteries, for body oils and perfumes, for medicines, but mainly for storing and transferring liquids. During the water libation service in the Temple on Sukkot, the water was brought to the Temple in golden flasks like these.
Some such earthenware vessels were made with covers from the same material, but covers were not always made for these flasks, most likely because in those cases the expectation was that the liquid would be kept in the flask for a relatively short period of time. In those cases, when it was necessary to close the flask, they used whatever was readily available, including the paper that they used at that time.