upstream b2 test book download

tures, and fit the iron as nearly as possible. And according to its purpose, it must be more or less acid-proof. In order to lower its melting point, it is made very rich in fluxes, and the ingredients are previously fritted. The coefficient of expansion must be raised as much as possible. Iron has the coefficient of cubical expansion (3a) x 10" 7 of 4 . 2, and copper is greater still. Pottery and glazes, on the other hand, are 2.0-3.0; so that the constituents of an enamel require judicious selection to fit a metal. Winkel- mann and Schott's figures (1894), revised and extended by Mayer and Havas (1911), and confirmed practically by Wolf (1911), are as follows for the expansion of the various oxides in a glaze or enamel, as compared with the 4.2 of iron : Na 2 O 10.0 PbO 4.2 ZnO 2 2.1 K 2 O 8.5 TiO 2 4.1 SnO 2 2.0 NaF 7.4 Fe a O 3 4.0 As 2 O 6 2.0 Na 3 AlF 6 7.0 Nio 4.0 Li 2 O 2.0 Cr 2 O 8 5.1 Sb 2 O 5 3.6 P 2 O 5 2.0 CaO 5.0 BaO 3.0 ZnO 1.8 A1 2 O 3 5.0 CaF 2 2.5 SiO 2 0.8 CoO 4.4 MnO 2.2 MgO 0.1 A1F 3 4.4 CuO 2.2 B 2 O 3 0.1 From these figures the expansion of a glaze which is suitable in other respects may be calculated. 54 CERAMIC CHEMISTRY. It will be seen that very few of these oxides have co-