Question:
What is that little glass dish I see next to the tabernacle in St. Francis Xavier Cathedral when I watch TV Mass on Sunday morning? — Appleton
Answer:
The small glass dish with a gold cover that sits to the right of the tabernacle as you view it from the pews is called an “ablution cup.”

Ablution cups (or ablution bowls) used to be more common before the changes in the Mass following Vatican II. However, their use was never abolished and some parishes are starting to use them again.
The word “ablution” comes from Latin words for “wash away.” The presence of the ablution cup near the tabernacle is to allow for the washing away of any stray particles of the Blessed Sacrament that might accidentally get on a priest’s or minister’s hands in touching consecrated hosts that are reserved in the tabernacle. The idea is to rinse off one’s fingers in the bowl after touching the Blessed Sacrament. (It is not required to do so, but the cup is placed there as a convenience.)
The ablution cup’s cover keeps the particles in place until the water is rinsed out. This water should never be disposed of in a regular sink, but only in the special sink called the “sacrarium” which is kept in the sanctuary of every Catholic church and chapel. If, for some reason, the sacrarium cannot be used, the water should be poured out on the ground, so that the earth will take it in. Sacraria do not empty into the water system, but always empty into the ground.
The ablution cup can also be used to hold, and dissolve, a host that may have fallen to the floor after it has been consecrated.
Also present with an ablution cup or bowl is a white cloth called a “purificator.” Purificators are also used to wipe the lip of the chalice and the cups used for holy Communion, as well as to wipe the patens and the ciboria that are used to hold the consecrated bread at holy Communion. Purificators are folded in three parts and may have a cross embroidered on them. When purificators are cleaned, they should first be rinsed in the sacrarium. (While altar linens are made of washable material, they are never made of disposable materials, such as paper.)
Kasten holds a master’s degree in theological studies from St. Norbert College, De Pere.