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in respect of substituting either in a mixing. Whiting should contain 98 per cent. CaC0 3 . Theoretically, whiting is equivalent to 56, dolomite to 30.4, gypsum to 32.5, plaster to 38.5, fluorspar to 71.5 per cent. CaO; but dolomite also contains 21.74 per cent. MgO. Grecian 34 CERAMIC CHEMISTRY. magnesite contains approximately 90 per cent. MgCO 3 and 10 per cent. CaCO 3 . Precipitated barium carbonate may have a loss on drying of 1 per cent. (All raw materials should be periodically tested for moisture during storage.) The mineral witherite may hold some isomorphous stron- tium carbonate and some barium sulphate mechanically mixed. Barium sulphate rarely contains more than 96 per cent. BaS0 4 . It should be tested for loss with hydro- fluoric acid to ascertain clay, etc. Theoretically, the sulphate is equivalent to 65.7 and the carbonate to 77.7 per cent. BaO. BORAX has the composition : H 2 O 47.12, Na 2 O 16.23, B 2 O 3 36.65 per cent. The soda is titrated with methyl orange and normal acid, then glycerine is added to one- third of the total bulk and the boric acid titrated with phenolphthalein and normal alkali (see Schaak, Journ. Soc. Chem. Ind., 1904, 23, 699). B 2 3 is multiplied by 2.731 to convert into borax. Moisture, as apart from water of crystallisation, is obtained by difference. Boric acid is also tested by Schaak' s method. Langenbeck found (1894) 10 per cent. S0 3 as ammonium sulphate in boric