Fritted glass crucibles

Fritted glass crucibles cannot withstand high temperatures and, therefore, should only be dried in an oven at temperatures below 200 °G. The glass fiber mats used in Gooch crucibles can be heated to a maximum temperature of approximately 500 °G. 

Sintered-glass (also called fritted-glass) crucibles are manufactured in fine, medium, and coarse porosities (marked/ m, and c). The upper temperature limit for a sintered-glass crucible is ordinarily about 200°C. Filtering crucibles made entirely of quartz can tolerate substantially higher temperatures without damage. The same is true for crucibles with unglazed porcelain or aluminum oxide frits. The latter are not as costly as quartz. 

Fritted-glass crucible A filtering crucible equipped with a porous glass bottom also called a sintered-glass crucible. Fronting Describes a nonideal chromatographic peak in which the early portions tend to be drawn out compare with tailing. F-test A statistical method that permits comparison of the variances of two sets of measurements. 

Sintered-glass crucible Synonymous with fritted-glass crucible. 

The preparation starts from a-stannic and sulfuric acids. Freshly precipitated a-stannic acid (see p. 737) is dissolved in an excess of hot, dilute sulfuric acid, and the colorless solution is evaporated. White crystals of Sn(S04) 3 2 HsO separate. These acquire a needle-shaped, platelike, or prismatic appearance with increasing acid concentration. After cooling, the salt is suction-filtered through a fritted glass crucible and left for some times in a desiccator, on clay and over PjOg, in order to free it of the mother liquor. The pure product must be stored in sealed ampoules, since it is very hygroscopic. 

Procedure. Place 40 ml reagent G in the thermostat at 20 C and adjust the sample to the same temperature before mixing. After the desired reaction time stop the reaction by adding 25 ml of acid solution A. After 15 sec add 25 ml of solution B from a burette. Cool the mixture to 10-15 C and filter in a fritted glass crucible of porosity G4 wash free of HCl. Disperse the precipitate in water dissolve the residue from the filter with 10 ml 1 Af NaOH, and wash it into the precipitate suspension, which dissolves. Back-titrate with solution D using 5 drops of reagent C. 

---