A type of packing material used in packed columns and towers (see Fig. 50). It consists of a hollow cylinder whose length is equal to its diameter. Raschig rings are made from various materials such as plastic, glass, and ceramic. Raschig rings made from borosilicate glass are sometimes used in vessels containing nuclear materials such as uranyl nitrate to act as neutron absorbers to prevent the possibility of a criticality incident. They are named after German chemist Fritz Raschig (1863–1928).