These low form crucibles are particularly adapted to analytical work where precipitates are dried to constant weight at 110°C. They are also suitable for higher temperatures, in which case it is advisable to heat in an electric furnace. Crucibles should not be subject to sudden temperature changes. In order to avoid strain, they should not be removed from the furnace until the temperature has dropped to 250°C.
These crucibles are available in three different porosities of Pyrex® fritted ware so that precipitates varying in size can be filtered at maximum speed with no sacrifice of retention. Porosity is controlled in manufacture, and discs are individually tested and graded into these classifications: coarse porosity (40 to 60µm), medium porosity (10 to 15µm) and fine porosity (4 to 5.5µm). The porosity for the pore diameter of the filter is determined in the same manner as specified in ASTM E-128 "Maximum Pore Diameter and Permeability of Rigid Porous Filters for Laboratory Use."