Period 6 element devices though concerns about the element's toxicity have led to mercury thermometers and sphygmomanometers being largely phased out in clinical environments in favor of alcohol-filled, galinstan-filled, digital, or thermistor-based instruments. It remains in use in scientific research applications and in amalgam material for dental restoration. It is used in lighting: electricity passed through mercury vapor in a phosphor tube produces short-wave ultraviolet light which then causes the phosphor to fluoresce, making visible light. Thallium is a chemical element with the symbol Tl and atomic number 81. This soft gray other metal resembles tin but discolors when exposed to air. The
SN 1885A brightness, which is atypical for Type Ia supernovae. Some astronomers observed the spectrum of the star visually (no photographic spectral observations were made in that time). These observations were made at the limit of visibility, but they were considered to be in good agreement with each other and with modern data on typical supernovae of Type Ia; so SN 1885A had been assigned to this type. Recent studies led by Dovi Poznanski and by Hagai Perets suggest that SN 1885A belongs in a new subclass of Type I supernovae along with SN 2002bj and SN 1939B. The location of the