Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/249

 FIR E-C L 239 materials used in the manufacture of fire-bricks are insufficiently plastic to prevent their being easily moulded, and in the manufacture by the dry jwocess, or the compres sion of the brick out of nearly dry pulverized clay, plasticity is not so essential a quality. As regards chemical composi tion the following analyses indicate its general character, and the variability of the proportion of the constituents of some of the more important fire-clays : Coal-Measure Clays. A. Stourlridye Clay. (Omitting B. Stourbridge Clay. (Analysis the water.) silica 70-no Alumina 2G GO Oxide of iron 2 Lime T40 Magnesia traces. C. Glass House Pot Clay, Tintam Abbey, Stourbridge. (Analysis by A. W. Wills.) Silica 73-82 Alumina 15 88 Protoxide of iron 2 94 Alkalies 90 Water 6 45 by Richardson.) Silica 70-50 Alumina 25 46 Protoxide of iron 2 04 Magnesia 1 05 D. &quot;Best Clay,&quot; Taimcorth. (Analysis by A. W. Wills. ) Silica 71-40 Alumina 2M7 Protoxide of iron 91 Lime 04 Alkalies 82 Water.... .. G 06 F. Fire-Clay from Newcastle. (Excluding the water.) Silica 69-25 Alumina 17 UO Oxide of iron 2 97 Magnesia 1-30 Lime 7-58 E. F ire-Brick Clay from New- castle. (Analysis by ir. Taylor. ) Silica .&quot; &quot; 55-50 : Alumina 27-75 Sesquioxide of iron 2 01 } Lime 0&quot;G7 i Magnesia 75 j Alkalies 2-63 Water 10 53 G. Clay from Glasgow, used for saggars, glass house pots, bricks, &c. (Percy s Metal lurgy.) Silica CG-16 Alumina 22 54 Protoxide of iron 5-31 Lime 1-42 Water a-14 J. Fire-Clay from Dowlais. (Analysis by J. E. Rily. ) Silica G7-13 Alumina 21-18 Sesquloxide of iron 1 85 Lime 32 Magnesia 0-84 Alkalies 2 02 Organic matter 90 Water C-21 A o/e. In comparing the percentages of the individual constituents, it must be noticed that some of the analyses exclude the water. Tertiary Clays of Dorset and Devon used for Fire-Brick Manufacture. II. Dinas Fire-Clay, Smith Wales. (Excluding the water.) Silica 91-95 Alumina 8 05 With traces of iron. K. Welsh Fire-Clay. (Exclud ing the water. ) Silica 80-10 Alumina 17-90 Oxide of iron I O Lime 1-0 L. White Clay, Branksca Island, Dorset. (Analysis by Professor Way.) Silica _ 65-49 Alumina 21-28 Oxides of iron 1-26 Alkalies and alkaline earths .... 7-25 Sulphate of lime 472 IT. Beacon Hill Clay, near Poole. Lower Bagshot Beds. Sflica ... C3-00 Alumina 33 50 Oxide of Iron TOO Magnesia 2 00 M. Black Clay, Branksca Island, Dorset, (Analysis by Professor Way.) Silica 72-23 Alumina 23 25 Oxides of iron 2 54 Alkalies and alkaline earths 1-78 0. Beacon Hill Clay, near Poole. Lower Bagshot Beds, Silica 53-52 Alumina 33&quot;68 Lime 76 Magnesia 14 Oxide of iron 52 Alkalies 0-04 Water 11-34 ?. Blue Ball Clay, Bovey Tracy, Devon. Miocene Lignite For mation. Silica _ 47-00 Alumina, 4800 Oxides of iron, 1-5 Magnesia 2-0 Water, Ac, 1-5 The above analyses indicate a preponderance of silica in the Coal-Measure fire-clays compared with the Tertiary clays of Dsvon and Dorset, in which a larger proportion of alumina occurs. The latter character is accompanied by tenacity and plasticity, and greater contraction in drying and burn ing, which, when excessive, is counteracted by mingling with the clay sand and ground burnt clay or sherds. Contractility. The contraction in burning (excluding the contraction in drying) of several Coal-Measure fire-clays pressed out of nearly dry pulverized clay was ascertained by the writer to be as follows: Fire-clay occurring between the &quot;Penystone Measure&quot; ) and &quot;Vigor s&quot; clay, Shropshire coal-measures, near &amp;gt; 1 per cent. Broseley ) &quot; Two-foot coal&quot; lire-clay, Shropshire coal-nieasures... 5 ,, Ganie coal&quot; fire-clay, Shropshire coal-measures 2 ,, Bewdley Forest fire-clay, from the works of Mr Mob- berley, Bewdley, No. 1 Do. do.&quot; No. 2 Do. do. No. 3 Stourbridge fire-clay, from Messrs Fisher Brothers, &quot;The Hayes,&quot; Stourbridge, No. 1 Do. do. No. 2 &quot;Best&quot; fire-clay, from the earl of Dudley s pits near Dudley Seconds &quot; and offal, from same Fire-clay, Maryport, Cumberland 4 ,, The average contraction of the Coal-Measure fire-clays is thus little over two per cent. A brick manufactured from the best Stourbridge clay without admixture of burnt material contracted seven-eighths of an inch in nine inches, but this would probably represent the contraction both in drying and burning. The contraction in burning of the Tertiary fire-clays used for the manufacture of fire-bricks in Devon and Dorset is much more than that of the Coal Measure clays Contractility of Devonshire Clays. &quot; Best pipe-clay,&quot; Miocene Lignite Formation, Bovey Tracey, from the works of Messrs 12 per cent. Watts, Blake, Bearne, & Co Cutty clay &quot; 8 Household clay &quot; 5 Stoneware clay &quot; 7 Alum-makers clay &quot; 7 Drain pipe clay &quot; 4 Blue ball clay &quot; 13 Black ball clay &quot; 11 Brown ball clay&quot; 11 Black carbonaceous clay &quot; 10 Average contraction a little under 9 per cent. Contractility of Dorsetshire Clays. Beds. Lower Bagshot (Eocene) White clay &quot; from Messrs Pike s works, ) n n _. Wareham ............................................ 10 per 13 6 &quot;T&quot;clay &quot;V&quot; clay &quot;Black&quot; clay 13 Blue &quot; clay 13 &quot;H&quot;clay 15 &quot;P&quot; clay 15 &quot;S&quot; clay 7 Mottled sandy clay, Lower Bagshot Beds, Wareham Clay from Upper Plant Bed, Lower Bagshot Beds, Studland Bay, Dorset The clays above enumerated are not exclusively used for fire-brick manufacture, but fairly indicate the general character of the Tertiary fire-brick clays, which, compared with the Coal-Measure fire-clays, are characterized by a pre ponderance of alumina, tenacity of texture, contractility in the kiln, and an absence of iron and the alkalies, fcc., which tend to vitrification. Tenacity of texture in a fire-brick material is, however, a mechanical condition, which, c&tens paribits, assists vitrification, a coarse open body being more refractory than a close homogeneous brick of similar chemical composition. A well manufactured brick should be of a pale cream or clear buff colour, uniform throughout its mass, and burnt to the full extent of its contractility. The chemical changes which take place in the burning consist, first, of the destruction of the disseminated carbonaceous matter, the dehydration of the silicates of alumina, destroying their plastic character, and the decon&amp;gt; position of the disseminated carbonate of protoxide of iron,