update windows hom pack download

the microscope. Tripoli is similar in origin and com- position. HYDRATED SILICA is not introduced as a raw material, but it may occur in clays, especially those of volcanic origin. Its action in a body, compared to that of crystalline silica, is to increase translucency , shrinkage in air and fire, to lower the temperature of vitrification and to form deposits of silica acid on the surface of the ware. The SILICATES chiefly used in pottery are, besides clay, felspar, Cornish stone, asbestos, water-glass, ganister, marl, cullet, and slag. The employment of silicates is being greatly extended. Granite, syenite, felstone, eurite, volcanic ash, pozzolana, trass, santorin earth, are all making their way into pottery and building ware ; but it is doubtful if the many patents taken out in various countries for mineral silicates could be upheld. FELSPAR in commerce is usually the potash spar, generally of Scandinavian origin. Lime and soda spars do not appear on the market to any extent. According to A. S. Watts (1909), ware made with soda spar gives a wooden ring when tinkled, but such ware may have as much strength a,s that with a brighter sound. A good spar should be free from iron and should contain 14.5 to 16.5 per cent, of K 2 0. The alkalies are estimated by the Lawrence Smith method. Bastard spars containing 9 to 14 per cent, alkali may be utilised on a cheap quotation if the necessary allowance be made in the mixings. We have already