The chief and most generally used of such materials are the goods. The best known deposits of fire-clays in this country are those in the Midlands, Stourbridge, Leeds, and Glasgow districts. In each of these districts the mining of fire-clays and the manufacture of fire-resisting goods for furnace work forms an important industry. The theoretical composition of a true would be a double silicate of alumina, and in this pure state it would be of a very refractory nature. But, naturally, fire-clays show the presence of other bases, such as iron, lime, magnesia, titanium, and alkalies, which, if present to any appreciable extent, lower the degree of resistance to heat or refractoriness of the clay. These other bases may be considered as impurities or natural fluxing agents. The characteristics of a highly refractory clay suitable for glass manufacturers’ requirements would be: (_a_) that such a clay should show no signs of softening at the highest heat of the furnace; (_b_) a squatting point not below Cone 31 or 1690° Centigrade; (_c_) a high alumina content not below 30 per cent.; (_d_) the greatest freedom from impurities; (_e_) a fine-grained texture; and (_f_) a high degree of plasticity. These are the qualities most essential for glass house work. The figures given by the chemical analyses of good fire-clays would probably fall within the following limits— Silica 49% to 65% Alumina 48% to 31% Ferric Oxide 0·5% to 1·5% Titanium Oxide nil to 1·5% Lime nil to 0·5% Magnesia nil to ·2% Total Potash and 0·5% to Soda 1·8% Clays of higher silica content than 70 per cent. would not be considered suitable as pot-clays owing to the case in which glass attacks silicious clays. It is important that chemical analyses of fire-clays should be compared with results obtained from the analysis of fired or burnt samples, or they should be recalculated to allow of such comparison, so as to exclude the figures for the hygroscopic and chemically combined water of the clays. The writer gives the following particulars of a very suitable for glass house pot-making. It is plastic and highly refractory, and is now being considerably used by the trade. The clay is supplied by Mansfield Bros., Church Gresley. The figures are from a report made by Mr. J. W. Mellor, D.Sc., of the County Laboratory, Stoke-on-Trent, and are as follows— Raw Fire-clay Dried at 109° Cent. Silica 46·45 per cent. Titanic Oxide 2·65 per cent.