Gooch crucibles have a perforated bottom and include covers. Crucibles are glazed on inner and outer surfaces except for the outside bottom and rim. Used for determination of total suspended solids.Autoclavable. Withstand temperatures to 1150C. To prevent thermal stress cracks, we strongly recommend a heating/cooling rate not exceeding 200C per hour. United porcelain crucibles offer excellent resistance to acids and alkalies except for hydrofluoric acid.