It is called a monstrance, also knownas an ostensorium
monstrance
It is a place reserved for the adoration of Jesus Christ in the Eucharist. In such a chapel, the Eucharist is placed in a Monstrance so that it can be seen and worshipped.
The container that actually holds the eucharist is called a ciborium, it resembles the chalice except it has a lid usually topped with a cross, dove, or image of christ. The eucharist is distributed from the ciborium. The container in which the ciborium is reserved is called a tabernacle. The glass disc that contains a large host for adoration is called a Luna, and is kept in a round container called a capsula, the Luna is placed in a monstrance during benediction of the blessed sacrament. Both the capsula and the ciborium are covered with a veil within the tabernacle.
Your question is strangely phrased, so I'm not sure what you mean by "instrument". A Monstrance or Ostensorium is used to hold the Blessed Eucharist for Adoration, it is placed on the altar. During Mass, a corporal must be placed under the Blessed Sacrament, the Precious Blood is held in the chalice and the Host is held in on a paten or in a ciborium.
There are a several, namely the Mass, Benediction, and Adoration, that honor the Real Presence of Our Blessed Lord in the Eucharist.
pyx also pix (pĭks)n. # Ecclesiastical. ## A container in which wafers for the Eucharist are kept. ## A container in which the Eucharist is carried to the sick. # A chest in a mint in which specimen coins are placed to await assay. [Middle English pyxe, from Latin pyxis, box, from Greek puxis.]Taken from The American Heritage Dictionaries. (answers.com)
It is called a Pyx
The eucharist is normally held in a church building although it can be held anywhere.
Roman Catholic AnswerPerpetual Eucharist Adoration is 24/7 exposition of the Blessed Sacrament with at least one adorer always present before Our Blessed Lord in the Sacrament of the Altar.
The Sacrament is kept in a Ciborium. For adoration, the Holy Eucharist is displayed in a monstrance.
solids...
Roman Catholic AnswerThe Blessed Sacrament is placed on the altar, held in a Luna, placed in a Monstrance on the altar.
Adoration, for Catholics, means to be in the presence of GOD Himself in the form of the Blessed Sacrament exposed in a "monstrance." Catholics believe that the bread and wine which are used in the Mass, after the words of Consecration, become the Body, Blood, Soul, and Divinity of Our Lord Jesus Christ (The Second Person of the Trinity). Once the Host (bread) is consecrated it is transformed from its original substance (bread) into a supernatural substance (The Body, Blood, Soul, and Divinity of Jesus) - it is GOD Himself in the appearance of Bread...The essence changes .... though the substance (appearance) remains. This Host is placed in a container called a Luna, which is placed in a "Monstrance" - a a decorated container for exposition - which is placed on an Altar for Adoration. The Adoration which is given is worship, prayer, and communion with The Lord Himself. When one goes to Adoration, with a prayerful mind, one is humbled and awed at that one is in the Presence of the Lord and is still alive - Nothing unclean shall see the Lord - and one is brought into closer communion with the Lord. To sit and worship the Lord is a comfort and a Blessing...where prayers are answered and hopes fulfilled... a quiet place where one knows true love