3S 5 SHY OF CALIFORNIA LIBRARY OF THE UNIVERSITY OF CALIFORNIA SHY OF CHIFORNU LIBRARY OF THE UNIVERSITY OF CALIFORNII ERSITY OF CALIFORNIA LIBRARY OF THE UNIVERSITY OF CALIFORN fERSITY OF CALIFORNIA LIBRARY OF THE UNIVERSITY OF CALIFORH BUILDING MATERIALS WORKS BY THE SAME AUTHOR. Crown 8vo, cloth, price 45. 6d. net. STRESSES AND THRUSTS. A TEXT-BOOK FOR STUDENTS. Third Edition, Revised and much Enlarged. Illustrated with 170 Diagrams. CONTENTS : Elementary Principles. Loads on Supports. Vertical Shearing Stresses in Cantilevers and Beams. Stresses in Flanges. Rectangular Beams. Method of Designing a Rolled Steel Joist. Method of Designing a Steel Plate Girder. Columns and Struts : Wooden Pillars. Framed Canti- levers. Framed Beams and Girders. Method of Designing a Steel Lattice Girder. Roofs : Dead Load only. Roofs : Wind Pressures and Combined Loads. Method of Designing a Steel Segmental Roof. Walls and Chimneys to Resist Wind Pressure only. Foundations. The Con- struction of a Factory Chimney. Retaining Walls Subject to Earth Pressure. Retaining Walls Subject to Water Pressure. Resistance to Sliding. Arches and their Abutments. Buttresses, Etc. Demy 8vo, cloth, price 2s. 6d. net, A CONCISE BUT COMPREHENSIVE TEXT-BOOK. THE PRINCIPLES OF ARCHITECTURAL PERSPECTIVE. Prepared chiefly for the use of Students. With Chapters on Isometric Drawing and the preparation of Finished Per- spectives, illustrated with Drawings by various well-known Architects. Large crown 8vo, cloth, price 45. 6d. net. THE DRAINAGE OF TOWN AND COUNTRY HOUSES. A PRACTICAL ACCOUNT OF MODERN SANITARY ARRANGEMENTS AND FITTINGS. A TEXT-BOOK FOR THE USE OF STUDENTS AND OTHERS. Illus- trated by 87 Diagrams and 6 Plates, showing- the drainage of a Country House, etc., the Bacterial Disposal Works of a Country Mansion, and the Septic Tank System. B. T. BATSFORD, 94 HIGH HOLBORN, LONDON. BUILDING MATERIALS THEIR NATURE, PROPERTIES AND MANUFACTURE. A TEXT-BOOK FOR STUDENTS AND OTHERS. BY G. A. T. MIDDLETON, A.R.I.B.A., AUTHOR OF "STRESSES AND THRUSTS," "THE DRAINAGE OF TOWN AND COUNTRY HOUSES," "SURVEYING AND SURVEYING INSTRUMENTS," "THE PRINCIPLES OF ARCHITECTURAL PERSPECTIVE," ETC. ILLUSTRATED WITH 197 DIAGRAMS AND TWELVE PLATES FROM PHOTOGRAPHS. ' "^ K OF THF UN/VERS1T / ^U LONDON : B. T. BATSFORD, 94 HIGH HOLBORN, 1905. BRADBURY, AGNEW, & CO. LD., PRINTERS, LONDON AND TONBRIDGE. PREFACE. FOR many years past I have had in contemplation the preparation of a book in which building materials should be described and their present methods of manufacture explained. As time went on, the need for such a book a modern book at a moderate cost was more and more forcibly brought home to me, owing to the extreme difficulty which my students found in obtaining reliable and recent information. In undertaking to prepare such a book I knew the task would be no light one, and it has proved even more arduous than I had anticipated. For more than eighteen months every moment which I could spare has been devoted to collecting and arranging notes, inter- viewing manufacturers, inspecting works, and to a lesser extent to actually writing the book which is now about to see the light. At one time the notes alone more than filled a large drawer made for double-elephant paper; while hundreds of letters and post-cards have been written for the purpose of obtaining at first-hand the information which is contained in the volume often compressed into tabular form. Wherever possible, too, I have seen things for myself, visiting the slate quarries of North Wales, the stone quarries of Somerset, Gloucestershire and Rutland- shire, the iron and steel works of Middlesbrough, the terra-cotta works of Ruabon, Portland cement works at Greenhithe and near Leamington, and numerous brickfields and lime-kilns, and important manufacturing premises, in and around London. Wherever I have visited, and however searching my enquiries have been, I have been received with the utmost VI PREFACE. courtesy ; everybody I have met has shown the utmost readiness to help me. Without particularising, which would be impossible where so many are concerned, I would here desire to express my thanks to all who have assisted me, from the manufacturers who have thrown large works open to my inspection, to the working " hand " who by a few quiet words has explained some point which was puzzling me at the moment. I am greatly indebted, also, to those who have permitted me to quote from their writings or catalogues, many im- portant points being in this way added to the book. For my own part, I have striven to express myself clearly and without redundancy. At times it has been difficult to restrain a tendency to enlarge, and at others to know when and where to stop ; and yet at others to decide what to illustrate and what to leave to verbal description only. My aim has been to include all information that possibly could be of value or interest to English users of building materials, and to exclude all else. Personally I have learnt a great deal during the prepa- ration of this book, and all that I have learnt I have endeavoured to express therein for the benefit of others ; but fresh knowledge comes to me almost every day. The subject is by no means exhausted ; in fact upon each separate branch of it whole volumes have been, and doubt- less will continue to be, written. Those who wish to inves- tigate more deeply should go to such specialised books; and all should do as I have tried to do they should visit works and see things for themselves, and should make for themselves labelled collections of the principal materials used in building. G. A. T. MIDDLETON. LONDON, Jamiary, 1905. TABLE OF CONTENTS. Chapter Page I. GEOLOGICAL INTRODUCTION . ... . . I II. INTRODUCTION : CHEMISTRY AND PHYSICS ... 8 III. STONES : PRACTICAL CLASSIFICATION AND GENERAL DISTINCTIONS . . . . . . .23 IV. STONE : ITS SELECTION, DURABILITY AND PRESERVATION NOTES FOR USERS . . . 33 V. BASALT AND GRANITE . . . . . .40 VI. SLATE . . . ... . . -49 VII. MARBLE . . . . . . . . . 62 VIII. LIMESTONE ......... 69 IX. SANDSTONES . . . . ... ^ . . . -83 X. BITUMEN AND ASPHALT . . *< . . . .96 XI. LIME AND LIME-BURNING SOME MINOR LIME PRODUCTS: WHITEWASH, WHITING, PUTTY ..... IO5 XII. PORTLAND CEMENT . . . 114 XIII. PORTLAND CEMENT: ITS MANUFACTURE . . . . I2& XIV. MORTAR FIRE CEMENT 132 XV. LIME PLASTER PLASTER OF PARIS SIRAPITE KEENE*S, MARTIN'S AND PARIAN CEMENT STUCCO ROUGH-CAST 140 XVI. CONCRETE ... . . . . . . 148 XVII. ARTIFICIAL STONE . . . . . '. . . 155 XVIII. SAND GRAVEL BALLAST CORE FLINT ... - . l6l XIX. BRICKS : THE PRINCIPAL VARIETIES FIRE-BRICK EARTHENWARE STONEWARE TERRA-COTTA NOTES FOR USERS . . . . . * .-. . 167 XX. BRICK, TERRA-COTTA AND TILE MAKING .... l82 XXI. BRICKS, TILES, PIPES : THEIR MOST COMMON SHAPES AND SIZES . . . ... . . . 197 XXII. ARTIFICIAL BRICKS AND MISCELLANEOUS WALLING SUBSTANCES . . . . . . . . 2O7 XXIII. TIMBER : ITS GROWTH AND STRUCTURE NATURAL DEFECTS DESTRUCTIVE AGENCIES MARKS AND MEASURES 211 XXIV. TIMBER CONVERSION 225 VI 11 TABLE OF CONTENTS. Chapter Page XXV. TIMBER SEASONING AND PRESERVATION . . . 235 XXVI. TIMBER CLASSIFICATION : SOFT WOODS NOTES FOR USERS 246 XXVII. TIMBER CLASSIFICATION : HARD WOODS NOTES FOR USERS . . '. . . . . . 254 XXVIII. IRON ORES AND THEIR REDUCTION .... 269 XXIX. MAIN VARIETIES OF IRON : THEIR IMPURITIES, STRENGTH AND TESTS 275 XXX. CAST IRON AND CASTING NOTES FOR USERS . . 282 XXXI. WROUGHT IRON NOTES FOR USERS . . . . 288 XXXII. MILD STEEL 2Q2 XXXIII. COPPER . . . . . 305 XXXIV. LEAD . . . . . . . . . 309 XXXV. ZINC GALVANIZED IRON . . . . . 3 r 5 XXXVI. ALLOYS I BRASS AND BRONZE PEWTER AND COMPOSI- TION . . . .... . . . 320 XXXVII. PAINTS : BASES, VEHICLES, DRIERS, SOLVENTS ADUL- TERANTS AND THEIR DETECTION KNOTTING AND STOPPING REMOVING OLD PAINT . ... . 325 xxxvui. PAINTS: PROPORTIONS FOR VARIOUS COATS DURA- BILITY CLEANING METAL BEFORE PAINTING . . 338 XXXIX. COLOURING PIGMENTS . . . . . 345 XL. SPECIAL PAINTS ENAMELS IRON PRESERVATIVES ENAMELLING STONE PRESERVATIVES AND DAMP WALL SOLUTIONS FIRE-RESISTING PAINTS . . 353 XLI. VARNISH FRENCH POLISH AND LACQUERS ENAMEL PAINTS AND JAPANS STAINS ..... 359 XLII. ENAMELLING AND JAPANNING GILDING WHITEWASH COLOURING WATER PAINTS . . * . 371 XLIII. GLASS 377 XLIV. WALL AND CEILING PAPERS STAMPED LININGS FABRIC LININGS METAL LININGS . * 286 XLV. SUNDRY MATERIALS OF LESSER IMPORTANCE : ASBESTOS URALITE SLAG - WOOL EUBOLITH LIGNOLITE RUBEROID LATHS EXPANDED METAL COMPO- BOARD FELT WILLESDEN PAPER VULCANIZED RUBBER THATCH GLUE SIZE PASTE RUST CEMENT TAR ........ 392 INDEX 403 BUILDING MATERIALS. ERRATA. I'. 21. Line 15. For "the mat" read "them at." P. 64. Line 20. For "Serverezza" read " Serravezza." P. 172. 5th line from bottom. For "Machine burnt" read " Machine made." P. 182. Fig. 45 is upside down and reversed. P. 276. In the first Table, under Cast Iron, for "No elasticity " read " Almost perfect elasticity." P. 355. For " Carbolizing Coating" read "Carbonising Coating." C*YV<4. \Jl. V4011 UJlVJil for its deposit. Sometimes these deposits contained in themselves a cementing material such as rendered them hard, and in other cases they were hardened by the extreme pressure exercised during subsequent bucklings, or by the heat then generated, or by a combination of these. Such rocks M.M. B V^ Vlll TABLE OF CONTENTS. Chapter Page XXV. TIMBER SEASONING AND PRESERVATION . . . 235 XXVI. TIMBER CLASSIFICATION : SOFT WOODS NOTES FOR USERS 246 XXVII. TIMBER CLASSIFICATION : HARD WOODS NOTES FOR USERS 254 BOARD FELT WILLESDEN PAPER VULCANIZED RUBBER THATCH GLUE SIZE PASTE RUST CEMENT TAR 393 INDEX , BUILDING MATERIALS. Chapter I. GEOLOGICAL INTRODUCTION. THE mineral wealth of Great Britain, and incidentally the amount and variety of the natural building materials found in the country, is mainly due to the fact that, in one district or another, almost every known geological forma- tion occurs within workable distance of the surface. How- ever the earth may have been originally formed, it is now generally accepted that for an incalculably long period it has been gradually cooling and simultaneously shrinking. While cooling a crust has formed upon the surface, but this crust is so thin in comparison to the whole mass that it has buckled like a deflated hollow rubber ball during the consequent shrinking. Thus hills were formed ; and rain falling upon the hills washed away any soft material with which they were covered, depositing these in the greater depressions which contained the seas. Subsequent shrink- ages of the earth caused subsequent bucklings, different from the first, depressing the former hills and raising the former sea levels, exposing fresh surfaces of soft material, for washing away, or detrusion, and providing fresh seas for its deposit. Sometimes these deposits contained in themselves a cementing material such as rendered them hard, and in other cases they were hardened by the extreme pressure exercised during subsequent bucklings, or by the heat then generated, or by a combination of these. Such rocks M.M. B 2 BUILDING MATERIALS. would resist subsequent detrusion, while generally retaining signs, by occurring in regular layers or strata, of their original aqueous origin, and would become more hard and compact as time went on and further pressure was exercised. Thus, roughly speaking, it may be expected that the oldest rocks would be the hardest, the softer portions of the older deposits being continuously washed away to form fresh strata ; and, with many exceptions and variations, this may be accepted as the rule. The building up of the earth's surface to its present condition has probably been perfectly uniform and without intermission, but geologists have found it convenient to divide geological time into epochs corresponding with breaks in the continuity of their earlier discoveries. Five great divisions are recognised : Acute Primary, Primary, Secondary, Tertiary, and Post Tertiary. Each of these, except the Acute Primary, is again subdivided, in some cases with great minuteness, but it will suffice for present purposes to give only the table on the opposite page. Of the materials mentioned in this list, the sandstones are of purely sedimentary origin, consisting of grains of quartz or sand washed down from earlier deposits and solidified either by deposit in a calm water highly charged with silica in such a form as to cement the silica (or sand) grains ; or more often the accumulated heaps of sand, covered by great thicknesses of other rocks, have been slowly raised into dry land by gradual upheaval, and then penetrated by water holding the cementing material in solution. Iron also is generally present, and no doubt assists in the cementation, for when present it occurs as an extremely thin covering to the sand grains, to which it imparts any colour which the stone may have, the pure silica being white. The independent sandstone rocks found lying upon the surface in some parts of the country, notably in Dorsetshire and Wiltshire, and known as Sarsen Stones, are the remains of beds of which only these lumps were ever converted into GEOLOGICAL INTRODUCTION. TABLE OF GEOLOGICAL FORMATIONS IN WHICH BRITISH BUILDING MATERIALS OCCUR. Formation. Series. Example of Material found in it. H 2J Recent ... Sand ~ O H * Pleistocene ... Brick earths and Thames gravel. . Pliocene ... Suffolk brick earths P5 Miocene ... Sands H W H Eocene Pottery clay ; Roman and Medina cement ; brick earths. SECONDARY. (Upper Cretaceous - 'Lower , , Upper ( Oolitic j Jurassic-i (Lower JLiassic Triassic Chalk; Gault clay for bricks and cement. Kentish rag. Purbeck marble ; Port- land stone. Bath stone. Cleveland iron ore ; Hy- draulic lime. Runcorn stone ' Alabaster Magnesian limestones and PRIMARY. Coal Measures Carboniferous Mill - stone rit Carboniferous ! limestone J Devonian ... Silurian Dolomites ; Stafford- shire brick earths. Coal ; Clay ironstone ; York flag-stones ; Fire- clays. Yorkshire grit stones ; Dinas fire clay. Derbyshire marble ; zinc and lead ore; Haema- tite iron ore. Cornish slates ; Devon- shire marble. Westmorland slates. Cambrian Welsh slates. BS o S < a PH Fundamental Gneiss ... Road metal. B 2 BUILDING MATERIALS. solid rock. All else has been washed away, together with immediately underlying strata, and the blocks have thus been gradually lowered until they rest upon an entirely different, harder and earlier formation, which now forms the surface. Slate also is originally of sedimentary origin, being formed of clay deposited in shallow water in thin layers. Subsequent buckling of the earth's surface, however, brought great pressure and accompanying heat to bear upon the soft clay, compressing it into a hard mass, obliterating all generally observable signs of the original stratification and substituting another at right angles to the direction of the pressure thus exercised, this artificial strati- fication being known as "slaty cleavage." Many of the comparatively homogeneous limestones are sedimentary, especially such as contain clay or silica and were deposited in compara- tively shallow water ; but others are composed almost wholly of fossil shells and fish bones, and must have been formed very slowly in deep water, being compacted by the superincumbent weight of water. Such is chalk, whose absorbent power is so great that a cubic foot will hold a gallon of water without super-saturation. It is composed of most beautiful shells, microscopic in size, corresponding to the shells of minute organisms still living in abundance in oceanic waters (see Fig. i). Others, even such hard, compact crystalline limestones as, taking a high polish and being ornamental, are called Marbles, are of coral origin, similar rock now being formed in the tropics, where recently formed coral is being so altered by water as to become a compact rock ; while those Fig. i. Structure of Chalk (after Sorby). Magnified 100 diameters. GEOLOGICAL INTRODUCTION. 5 of the oolite class must have been formed from a limestone sand or coral detritus of very fine grain rolling about in a shallow water highly charged with carbonate of lime. Each small grain of limestone would thus become coated with more, each grain presently approximating to an onion in structure, and eventually the grains would adhere to one another and form a mass of stone with a structure like that of a fish's roe (see Fig. 2). The exceedingly fine-grained dolomites and magnesian limestones, on the other hand, are probably chemically deposited rocks. Streams of water containing the salts of lime and magnesia in solu- tion (as distinguished from mechanical washing) have emptied into salt lakes kept at their normal level by evaporation, and not by overflow along an outgoing stream. The natural result of the evaporation has been super-saturation of the lake water with the salts and the precipitation of the surplus as an impalpable powder. This has compacted into stone from its own power of adhesion and the weight of the water above it. Many of these stones contain mechanically deposited silica also. The Italian limestone known as Travertin is similarly a chemical deposit of pure carbonate of lime in the lakes of the Campagna, which are fed by streams from hills of a cretaceous limestone. True Oriental alabaster, a carbonate of lime, is of stalagmitic origin, having been the filling of cavernous hollows in limestone rocks by percolation of water con- taining carbonate of lime ; while most of what is now called alabaster, a sulphate of lime, is another salt-lake deposit. Fig. 2. Microscopic Structure of Oolitic Limestone (after Sorby). Magnified 30 diameters. 6 BUILDING MATERIALS. True marbles are, like slate, metamorphosed or changed rocks. Any limestone, on being heated to redness in such a position that the carbonic acid gas which it contains cannot escape, will on cooling become marble by crystallisa- tion much harder and more compact than before, and quite different in structure, but of the original chemical com- position. Thus marble has been formed at almost all geological periods from previously existing limestones ; and it is geologically dated according to the original deposit, which can be ascertained by sequence ; and not by the time of metamorphosis, which is generally indeter- minable (see Fig. 3). Granites, it will be noticed, are not mentioned at all in the Table, for they are eruptive rocks, which have been formed at all geological periods. Sometimes when the crust of the earth has buckled, vents have occurred and the Fig. 3. Microscopic Structure of molten mass beneath the White Statuary Marble (after , lir f arfk l f^ linr i ~ v ; f Tf Geikie). Magnified 50 diameters. surtace nas tound exit. If this has burst out, as in a volcanic eruption, it has become mixed with air, and has poured out as lava streams, or has formed pozzuo- lana or pumice all chemically akin to granite. If, however, this molten mass, instead of bursting out, has cooled, its constituents have formed themselves into crystals while the whole has become a solid rock, and this rock is granite. Sometimes this occurs in large masses, and sometimes, as in the Auvergne district of France, as pillars of rock standing out above a plain the solid rock cores of old volcanoes from which all the surrounding softer earth which formed the conical hills has been washed away. Lava streams, on cooling, develop a remarkable columnar GEOLOGICAL INTRODUCTION. 7 structure, which is well displayed at the Giant's Causeway in Ireland, and at the Isle of Staffa in the Hebrides, this being due to shrinkage of the homogeneous mass resulting in vertical splitting. Such lava rocks are known as Basalt and Dolerite, the basalt being a compact rock whose com- ponent minerals are so intimately intermingled that they are separately indistinguishable to the eye, while the dolerite is coarser in texture though similar in com- position, in which the intermingled minerals of which it is composed can be readily seen. Chapter II. INTRODUCTION: CHEMISTRY AND PHYSICS. MATTER is capable under certain conditions of under- going various changes, all of which are distinguished either as chemical or physical. If water is mixed with fragments of limestone no alteration is noticed in the stone or the water, but if the lime is first burnt in a kiln and water is thrown upon it, a violent action is seen to take place in the mixture. It is obvious that some material change has taken place in the limestone, that is to say it no longer exists as limestone, but as something quite different. Wherever a substance is influenced in such a way as to produce something essentially different, a chemical change is said to have been brought about. Chemistry is the science which investigates the nature of such changes. If water be heated, it commences after a while to boil and passes away in the form of steam, which when cooled again becomes liquid water. In this case the heating has simply had the effect of dividing the water up into very small particles, which on cooling have collected again in the form of drops. In this case no essential change has taken place in the water, that is to say it is still the same kind of substance, whether in the form of water or steam, but it has merely passed from the liquid state to the gaseous state and back again to the liquid state. Whenever a change is brought about without affecting the composition of a substance so altered, a physical change is said to have occurred. It should be noted, too, that such properties as appearance, weight, hardness, resistance to tension and compression, etc., are termed physical properties. INTRODUCTION : CHEMISTRY AND PHYSICS. 9 THE CONSTITUTION OF MATTER. Molecules. To the mind of a chemist or physicist no substance is absolutely homogeneous, but consists of a vast aggregation of minute particles called molecules. These molecules in any particular substance are all alike ; thus in lead the molecules are all of one kind, while in water the molecules are all of another kind, the properties belonging to the substance being the properties belonging to the molecules in each case. A fragment of ice, a drop of water, or a volume of steam, each consists of an aggregation of molecules. What constitutes the difference of state is explained as follows : When the ice is heated the spaces between the molecules become enlarged, that is to say the molecules are thrust further apart so that they are freer to move. Thus the solid ice becomes liquid water. If now the water is still further heated the molecules become thrust still further apart and the substance assumes the gaseous condition. In the process of cooling the molecules are drawn closer together again. In all substances the molecules exert a force upon one another, which force may be either repellent or attractive. When the attractive forces are in the ascendency the mole- cules are drawn tightly together and the substance appears in the solid state. Where the repellent forces get the upper hand of the attractive forces the substance appears in the gaseous state. A liquid may be regarded as a substance in which the attractive and repellent forces are just counterbalancing one another. Atoms. -1 'o the chemist's mind the molecule is not an indivisible particle of matter, but is itself composed of smaller particles held together by the action of a force known as chemical affinity or chemical attraction. There is a striking analogy between the appearance of a molecule and that of a solar system, the atoms forming the molecule revolving about one another independently of the motion of the whole molecule, just as in a solar system the various members perform certain movements relatively to 10 BUILDING MATERIALS. one another but independently of the motion of the whole system along its prescribed orbit. We can now conceive more clearly the difference between a chemical and a physical change. If a molecule is so LIST OF THE CHEMICAL ELEMENTS WHICH MOST FREQUENTLY OCCUR IN BUILDING MATERIALS. Non-Metallic. Element. Symbol. Hydrogen H Carbon C Nitrogen Oxygen O Silicon Si Phosphorus ... p Sulphur S Chlorine Cl Arsenic As Metallic. Sodium Na Magnesium j Mg Aluminium ... ! Al & Potassium K Calcium . ... ... Q a Manganese .'.'.' M n Iron ... ... p e Nickel . xfi Cobalt . ... ..', " m \ Co Copper I Cu Zinc Zn Silver Ag Cadmium ... Qd jm. ;:; Sn Barium B a L ad '.'.'. Pb Bismuth Atomic Weight, neglecting decimals I 12 14 16 28 3i 32 35 75 23 24 27 39 40 55 56 59 59 63 65 1 08 112 118 J 37 207 207 acted^ upon as to overcome the force of chemical affinity, that is so as to expel one or more of the atoms bound together by the action of this force, then a chemical change has been brought about. Thus with the limestone already INTRODUCTION : CHEMISTRY AND PHYSICS. 1 1 mentioned, the molecule of which consists of one atom of the metal calcium, one atom of carbon, and three atoms of oxygen, the heat generated in the kiln by the combustion of coal partly overcomes the affinity of these atoms and splits up each molecule into two different molecules one of lime, containing one atom of calcium and one of oxygen, the other of invisible gas (carbon dioxide), consisting of one atom of carbon and two of oxygen. A change would be called physical when the motion of the molecules is affected without affecting the arrangement of the atoms in the molecules. Thus if we place a piece of iron in a fire it soon glows with a red colour, but it is still iron, a physical change only having taken place. ELEMENTS AND COMPOUNDS. In the molecules of certain substances the atoms are all of one kind. Such substances are distinguished as elements. There are about 70 elements known to the scientific world, but new ones are discovered from time to time. A list of those which most frequently occur in building materials is printed on p. 1O. Other substances are built up of molecules in which the atoms are of different kinds. Such substances are termed chemical compounds. D ALTON'S ATOMIC THEORY. The theory that matter was composed of atoms, too small to be seen and in a state of continual motion, was propounded by the Greek philosophers Leucippus and Democritus (460 400 B.C.). This conception, however, was not gained by experimental proof, but was purely a matter of opinion which happened to be coincident with truth. Itwasnotuntil the beginning of the nineteenth century that John Dalton, a Manchester school- master, in order to account for the then recently discovered fact that all compounds have invariably the same composition, revi v^ed the theory. An account of his theory was published in his " New Principles of Chemistry" in the year 1808. This theory may be expressed as follows : (i.) Matter is capable of division up to a certain point only, the ultimate particles being called atoms. In the 12 BUILDING MATERIALS. case of the same element the atoms are all alike, but in the case of different substances the atoms differ in weight and chemical properties. (2.) When chemical combination takes place between two substances the combination actually takes place between the atoms. SYMBOLS. It has been universally agreed by chemists to denote the atoms of the various elementary forms of matter by means of symbols. These symbols are given in the second column of the list on p. 10. In many cases the initial letter of the name of the element is used to denote its atom e.g., Hydrogen, H ; Sulphur, S : but where the initial letters of two elements are the same, then the initial letter and another letter most prominently heard in pronouncing the name is used to denote one of them e.g., Chlorine, Cl ; Magnesium, Mg. In other cases the prominent letters heard in pronouncing the Latin name of the element is used e.g., Pb (Plumbum), lead ; Cu (Cuprum), copper. It must be strictly understood that it is not correct to say " two tons of Fe " when " two tons of iron " is meant, for the symbol Fe stands for one atom of iron, and is not merely a shorthand sign for iron. ATOMIC WEIGHTS. It is found, also, that the different kinds of atoms have different weights. Of course, it is impossible to determine the absolute weight of so small a particle as a separate atom, but it is possible to find the weight of the atoms relatively to some standard atom.* This standard is the hydrogen atom, hydrogen being the lightest substance known. The third column of the list (P- I0 ) gi ves the approximate relative weights of the atoms. FORMUL/E. It has been mentioned already that a molecule is regarded as a system of atoms. The question that naturally arises is How many atoms are there in a molecule ? The number of atoms which compose the * The determination of atomic weight is in many cases a very complex matter, and is a subject which scarcely comes within the province of a book on building materials. INTRODUCTION: CHEMISTRY AND PHYSICS. 13 various elementary molecules is not the same in all cases. The molecules of sodium, potassium, zinc, cadmium, and mercury contain only one atom, the terms molecule and atom being in these cases synonymous, and such molecules as these being termed mon-atomic molecules. In the case of hydrogen, bromine, chlorine, oxygen, and nitrogen the molecules are composed of two atoms, and are termed di-atomic. The molecules of ozone contain three atoms, and are therefore termed tri-atomic, while arsenic and phosphorus contain four atoms to the molecule, and are therefore said to form tetra-atomic molecules. The terms mon-atomic, di-atomic, etc., are only applied to elementary molecules. Compound molecules may be formed of practically any number of atoms. According to the chemical system of notation the mole- cules of elementary substances are represented by the symbol for its atom followed by a small numeral e.g., the hydrogen molecule is represented thus : H 2 . The molecules of ozone and phosphorus are respectively represented by O 3 and P 4 . When it is desired to represent a molecule of a compound substance, the symbols for the component atoms are placed in immediate juxtaposition, and thus HC1 represents the molecule of hydrochloric acid. If a molecule contains more than one atom of any particular element, the small numeral is used, as in the case of an element. Thus H 2 O represents water, K 2 Cr 2 O 7 potassium bichromate. Sometimes it is necessary to represent molecules which contain a group of elements acting as a single element. Such groups are placed between brackets with the numeral (if necessary) after it. Thus (NH 4 ) 2 SO 4 represents ammonium sulphate. Such groups are called compound radicals. There are a vast number of instances where simple molecules unite together to form more complex molecules. Thus, aluminium sulphate A1 2 (SO 4 ) 3 ; potassium sulphate K 2 SO 4 and twenty-four molecules of water 24 H a O 14 BUILDING MATERIALS. combine together and form a molecule of a substance known as potassium alum, having the formulae A1 2 (SO 4 ) 3 , K 2 SO 4 , 24 H 2 O. Felspar forms a molecule of the same kind : 6 SiO 2 , A1 2 O 8 , K 2 O. It should be carefully noted that since an atom is the smallest particle into which matter can be divided, it is impossible to have less than a whole atom of any element in a molecule. Such a formula as Cu J SJ would be absurd. CHEMICAL EQUATIONS. Chemistry, we have said, deals with a certain class of changes. It is therefore very desirable to have a system which represents these changes in a simple and comprehensive manner. For this purpose chemical equations are used. Suppose iron filings and sulphur are mixed together in the proportion of their atomic weights and strongly heated ; the two elements combine to form a yellowish-grey com- pound. In the action which has taken place, each molecule of iron has united with a molecule of sulphur to form a substance known as ferrous sulphide. These facts are expressed thus : Fe + S = FeS . . (i). In the extraction of copper it is found necessary to treat the sulphide ore Cu 2 S with a solution of a ferric salt e.g., Fe 2 Cl 6 , the cuprous sulphide reducing the ferric chloride with the formation of cuprous chloride and free sulphur. This change is expressed thus : 2 Cu a S + Fe 2 Cl G = FeCl 2 + 2 Cu 2 Cl 2 + 2 S . (2). If, again, ammonium cyanate is gently heated, the atoms in its molecule arrange themselves differently, so that an entirely new substance is formed with exactly the same atoms in its molecules. The action is expressed thus : (CN)0(NH 4 ) = (NH 2 ) 2 CO . (3). It should be noted that in the above three examples of chemical equations both sides balance that is to say, there INTRODUCTION: CHEMISTRY AND PHYSICS. 15 is the same number of atoms on each side of the = sign. Equations must always balance, for matter is indestructible. THREE TYPES OF CHEMICAL EQUATION. All known instances of chemical action can be referred to one of three modes in which the rearrangement of the atoms can take place : (a) By the direct combination of two molecules to form a more complex molecule. Equation (i) is an example. (If) By a mutual exchange of atoms in two molecules. See equation (2). (c) By the rearrangement of the atoms in the molecule. See equation (3). QUANTITATIVE SIGNIFICANCE OF CHEMICAL EQUA- TIONS. Not only does an equation express the qualitative nature of a chemical change, but a quantitative meaning can also be attached to it. We have already seen that the weights of the elementary atoms have been found in rela- tion to the weight of an atom of hydrogen. The symbol stands for one atom of an element. Now, from the list of elements (p. 10), we see that the atomic or relative weight of iron is 56, of sulphur 32 ; then in the equation (i) it is obvious that 56 parts by weight of iron combine with 32 parts by weight of sulphur, and form (56 + 32) = 88 parts by weight of ferrous sulphide. If, therefore, we heated 56 tons of iron with 32 tons of sulphur, we should form 88 tons of ferrous sulphide. The following question and solution will show the use of this quantitative notation : What weight of quicklime would be obtained by burning 5 tons of limestone ? How much carbon dioxide would be driven off? Solution : The equation of change is : CaCO 3 = CaO + CO 2 Tons. Tons. Tons. (40 + 12 + 3 x 1 6) = (40 + 1 6) + (12 + 2 x 16) 100 == 56 + 44- 1 6 BUILDING MATERIALS. IOO tons of limestone produce 56 tons of lime .'. 5 5 - 6 I( 5 tons of lime = 2 tons 1 6 cwts. Weight of carbon dioxide driven off = 5 tons 2 tons 1 6 cwts. = 2 tons 4 cwts. DIVISION OF ELEMENTS. It is found that certain properties are common to a large number of elements, and it is on account of these properties, which are chiefly physical in character, that the elements are divided into two classes, known as metals and non-metals. The metals are opaque, and their surfaces are capable, when smooth, of reflecting light to a high degree, giving them the appear- ance known as metallic lustre. They also conduct heat and electricity. The metals and non-metals are shown in the list on p. 10. ACIDS AND ALKALIES. With the exception of fluorine and bromine all elements combine with oxygen and form compounds called oxides. The oxides of the alkali metals (soda, Na 2 O ; potash, K 2 O) readily combine with water, forming the hydro-oxides NaOH and KOH ; and those of the alkaline earths (lime, CaO ; strontia, SrO ; baryta, BaO) likewise form hydro- oxides Ca(OH) 2 , Sr(OH) 2 , and Ba(OH) 2 . They are all readily soluble in water, and the solution has a soapy feeling, and the property of imparting a blue colour to litmus, a vegetable colouring matter. A substance which turns litmus blue is called an alkali and is said to have an alkaline reaction to litmus. Such oxides are called salt- forming oxides, or basic oxides, or simply bases. On the other hand, oxides of the non-metallic elements (e.g., SO 2 , SO 3 , CO 2 , N 2 O 5 , and P 2 O 5 ) combine with water to form compounds called acids, which are often corrosive, possess a sour taste, and turn litmus red. INTRODUCTION : CHEMISTRY AND PHYSICS. 1 7 SALTS. When chemical action takes place between an acid and a base a class of compounds is formed called salts e.g. : Base + Acid = Salt + Water ZnO + H 2 S0 4 = ZnS0 4 + H 2 O Fe 2 O 3 + 3 H 2 SO 4 = Fe 2 (SO 4 ) 3 + 3 H 2 O As having a very important bearing upon many of the materials to be considered later in this book, the following note on the nature of solutions particularly of solid solu- tionsis extracted from a Paper by Mr. Clifford Richardson, of the New York Testing Laboratory : " Solutions may be defined as the merging of two or more substances in one another in such a way that it is impossible to recognise them by any physical means. In this respect they differ from the elements and definite chemical com- pounds. The elements cannot be or have not been differentiated by any chemical or physical means into other substances. Definite chemical compounds can be differentiated by chemical means into their constituent elements, but at the same time are always composed of these elements in a definite mathematical ratio, involving only whole numbers and depending upon the combining weight of each element. " Mixtures of gases,gases dissolved in liquids,liquids which are mixed together and salts dissolved in liquids, are types of solutions. In the preceding paragraph mention has been made of solid solutions. We owe our conception of such solutions to Van't Hoff, a Dutch chemist, who, in 1890, having observed some abnormal features in the behaviour of certain solutions of solids in liquids when they were frozen, was led to believe that the solid which separates on freezing is not the pure solvent, but a mixture of the solid solvent and the dissolved substance forming a solid solution. Investigations have proved that the conception was justified. Roozeboom has shown from a study of mixtures of fused salts that, on cooling, solid solutions are often formed, M.M. C I BUILDING MATERIALS. especially if the salts have the same crystalline form and habit. " The constitution of our igneous rocks may best be explained by considering them as solid solutions, which, when the original liquid magma, from which they are derived, is cooled to a temperature at which freezing sets in, are formed by the crystallization of such mineral species as the constitution of the magma may permit, and which we recognise as quartz, mica, felspar, etc., the composition of which, while in approximately definite proportions, is more or less modified by the substances which they may retain in solution. " The structure of alloys has also been most satisfactorily explained by considering that different metals are soluble in each other in different proportions under different states of concentration and at different temperatures ; that of steel has been especially thoroughly worked out in the same way, and it has been shown that it consists of a solid solution of carbon in pure iron, while that of cast iron is explained by the fact that the amount of carbon soluble in the molten iron is so great that a portion separates out, as graphite, on cooling. " Another type of solid solution is glass. In this material we have a solid solution of silica, lime and alkalies, in indefinite proportions, in which none of the constituents can be detected, and out of which nothing separates on freezing. This is regarded as a homogeneous solid solution, and corresponds closely to a homogeneous liquid solution. " In some mixtures of fused salts and in some of the alloys we have heterogeneous solid solutions, as more than one solid solution may separate on freezing. Such a separation is due to what is known as selective freezing. This is well illustrated by the freezing of a solution of salt in water. That portion of the solvent which becomes solid first con- tains less salt than anything subsequently separated. If we take a 15 per cent, solution of salt in water as an example, as has been done by Howe in his excellent book INTRODUCTION : CHEMISTRY AND PHYSICS. 19 entitled ' Iron, Steel and other Alloys,' to which the reader is referred for an exhaustive explanation of the theory of solid solutions, and to which the writer is much indebted, it will be found that the solid matter that first freezes out is nearly pure water, and that there is a corresponding increase in the concentration of the mother liquor. The solid which subsequently separates will contain progressively more and more salt in solid solution in the ice, and there will be a progressive fall in the freezing point of this liquid, until when the temperature has reached minus 22 degrees C. and the proportion of salt in the mother liquor is 23*6 per cent, further concentration will not occur, and the two elements, water and salt, solidify without selection and form what is called an eutectic. The freezing point remains constant at 22 degrees C. until the entire material is solid. The solid originating in this way is a mixed mass of crystals of water and of salt inter-stratified, the salt forming 23^6 per cent, of it and ice 76'4 per cent. The same result would happen with a 20 per cent, solution of salt, the selective freezing going on until the concentration of 23*6 per cent, had been obtained and eutectic ratio had been reached. If the original solution contained 23*6 per cent, of salt it would not freeze until a temperature of minus 22 degrees C. had been reached, and then it would all become one uniformly mixed mass of the solid known as the eutectic. If the percentage of salt is greater than the eutectic ratio, 23-6 per cent., then the material which first freezes will be salt con- taining some water in solution, and the concentration in relation to salt would be reduced until the eutectic ratio is reached. That is to say, the composition of the eutectic is constant, no matter what the initial ratio is between the solvent and that which it dissolves. " Again, many alloys are quite parallel in their constitution to that of the solid salt water series. Tin and lead form an eutectic constituting 31 per cent, of tin and 69 per cent, of lead of constant freezing point. Any tin-lead alloy of other than the eutectic proportion will consist C 2 20 BUILDING MATERIALS. of lead with tin in solution and the eutectic, or tin with some lead in solution and the eutectic, in accordance with whether the lead or tin are in excess over the eutectic ratio. " In some cases, however, where metals or salts are not mutually soluble in the solid state, unselective freezing may take place, that is to say, the elements of the fused solution may solidify separately, and this may be regarded as an eutectiferous mixture. "The term eutectic means well melting, because the eutectic is usually the material which freezes out at the lowest temperature, no matter what the proportions may be of which the mixture may happen to consist. " Two salts which crystallise in the same form may separate from aqueous solutions in such a crystalline form containing more or less of both substances, depending upon the concentration, and in the same way a crystal consisting entirely of one salt may be built up with another by immers- ing it in a solution of a so-called isomorphous salt of proper concentration, that is to say, of a salt which crystallises in the same form. These crystals are known as isomorphous mixtures, or mixed crystals. " Exceptionally a substance which crystallises in a different form from another may assume the form of the latter, and crystallise with it as a so-called isodimorphous mixture or solid solution. The salt which has changed its form must of course, be under a certain tension in such a solution. Such a state of affairs will be found to be the case in a Portland cement clinker, and an example of such an isodimorphous mixture among simple well-known salts will be instructive. The orthorhombic sulphate of magnesia, MgSO 4 , 7 H 2 O, for instance, can take up and hold in solution in the form of orthorhombic crystals as much as 1878 per cent, of the monoclinic ferrous sulphate, Fe 2 SO 4 , 7 H 2 O, while the iron salt can take up 46-00 per cent, of the magnesia sulphate, and hold it in solution in the monoclinic form. Between these limits we find both forms of solid solutions or crystals present. The relation of the INTRODUCTION : CHEMISTRY AND PHYSICS. 21 isotropic aluminates of lime to the anisotropic silicates will be found to be, in Portland cement clinker, similar to that which has been described. " The relation of materials to each other which are not soluble or mixable with each other in all proportions may be also illustrated by mixtures of ether and water. In such mixtures, if they are shaken, and the amount of ether present is not greater than what the water can dissolve, a homogeneous solution is formed. As soon as the proportion of ether reaches a point where it will not dissolve on shaking, an emulsion will form, and this will continue to be the case with the increase in the proportion of ether until the latter reaches an amount where it can dissolve the water present. If it were possible to cool ether-water mixtures so rapidly as to solidify the mat once, we should find, for certain concentrations where the ether was only slightly in excess of what could dissolve, a solid solution of water and ether and an emulsion of water and ether corre- sponding in structure to an eutectic ; but here the eutectic would not consist of separate particles of ether and water, but of separate particles of ether saturated with water and water saturated with ether. This is a structure which is met with in Portland cement clinker. Whether it is an eutectic or not is unimportant. It is the structure itself which is illustrative of what takes place when the com- ponents of the mixture are not soluble in each other in all proportions. In Portland cement clinker of certain concentration similar emulsions are found. " Steel is a solution of carbon in pure iron. Carbon dissolves in the molten iron to a very considerable extent, and remains in solution as long as the metal is molten. If cooling and freezing takes place, the structure of the solid metal will be found to depend upon the proportion of carbon which was dissolved in the original iron, and the temperature at which it was cooled. If carbon amounts to but a few hundredths of I per cent., the solid metal will be wrought iron ; if it does not exceed that amount which will 22 BUILDING MATERIALS. remain in solution in iron after cooling it is steel ; if the carbon is greater than this some of it will separate as graphite, and the solid metal will be cast iron. " The structure of the metal in the solid state under these different conditions may be determined with the microscope, but, of course, not in thin sections, as in the case of clinker, but by the examination of polished surfaces, which have been etched in some appropriate way. "When molten iron containing carbon in solution, in amount insufficient to cause a separation of graphite on cooling, is rapidly cooled from a very high temperature, the solid metal will be found to have definite properties, depending on the percentage of carbon present, the lower percentages furnishing mild steel, the higher tool steel, with a structure which is so definite that it has been named austenite. It will be also found that when the steel in this condition is reheated, as in tempering, the austenite structure is lost, the metal being transformed into a material. of quite a different structure, with resulting changes in its physical properties." Chapter III. STONES: PRACTICAL CLASSIFICATION AND GENERAL DISTINCTIONS. THE classification of stones as BASALTS, GRANITE, SLATES, MARBLES, LIMESTONES, and SANDSTONES, though in some respects unscientific, is so convenient and so generally accepted and suited to practical needs, that it must perforce be adopted by all users of stone. The distinctions between the classes are well marked, and such as are discernible in most cases at sight, the occasional practical inclusion in one class of a stone which scientifically belongs to another being due to this fact that in practice a stone is classed as that which it appears to be rather than as that which scientific investigation proves it to be. The term BASALT, for instance, is made to include all black, heavy, homogeneous, or nearly homogeneous, stones, like the Trap or Greenstone. The true BASALT is an Augitic stone, named after the mineral Augite or Pyroxene, of which, with Labradorite Felspar (a silicate of alumina and lime), it is composed Augite having magnesia for its base, and being of a dark or black colour. There is much of it in the British Islands, including the whole county of Antrim, several islands of the Hebrides, and parts of Wales, Cumberland, Shropshire, and Stafford- shire; but it is so difficult to quarry and hard to work that it is little used, save locally as road metal. BASALT was, how- ever, largely employed by the Egyptians for sculpture, there being several specimens of its use for this purpose in the British Museum ; while in the volcanic district round Naples it has at all times been much used for paving pur- poses, as in the Via Sacra and the Appian Way at Rome. 24 BUILDING MATERIALS. Of the Diosites, or Greenstones, which are, correctly Fig. 4. Lithological Map of England. speaking, not BASALTS, but Hornblendic stones, the most used in England are the Penmaenmawr stone of North STONES : CLASSIFICATION AND DISTINCTIONS. 25 Wales, and the Bardon Hill stone of Leicestershire both excellent paving stones ; while the Napoleonite of Corsica is a handsome ornamental stone. Of the same hornblendic class, too, is the Rowley Rag of Staffordshire, which in addition to its use for paving purposes, has been melted and cast into ornamental articles. GRANITES comprise all stones of independent crystals of differing materials, which are so intimately connected as to form a homogeneous whole, and include most of the felspathic and hornblendic stones. All true granites contain felspar and quartz, and the ordinary typical granite consists of felspar, quartz, and mica, while many contain hornblende also. Of these constituents, the felspar is generally of that description known as Orthoclase, which is a silicate of alumina and potash, though the Labradorite felspar is also found. Felspar varies in colour, being sometimes white, sometimes grey, sometimes pink, and sometimes a deep rich red, and the colour of the granite, of which it forms a large part, varies accordingly. The quartz crystals also vary in tint, though they are frequently white. They are almost pure oxide of silicon (SiO 2 ), otherwise known as silica ; and it is found that they contain minute cells partly filled with water. The grains of felspar and mica are partly embedded in the quartz grains, and hence it is concluded that the quartz was the last to solidify. The mica occurs as small flakes of dark colour, which flash as they catch the light. It is a source of weakness, as it is liable to decay. Hornblende, otherwise known as Amphibole, is a silicate of magnesia and lime, with iron and manganese. It is a very tough mineral, of a dark green or black colour, and frequently occurs in granites in small distinct crystals. Granites which contain hornblende in place of or in addition to mica, are called Hornblendic or Syenitic granites, while other stones which contain felspar and 26 BUILDING MATERIALS. hornblende alone, without either quartz or mica, are not granites at all, scientifically speaking, but Syenites, though in practice they are included among the granites. The crushing resistance of an ordinary granite varies from 5 to 12 tons per square inch, as tested on small cubes, and its weight from 160 to 190 Ibs. per cubic foot. The principal granite districts in Great Britain are the North of Scotland, a great part of Ireland, Cornwall and Devonshire, Leicestershire, and the Channel Islands (see map), while much is also imported from Scandinavia and Russia. Under the term GRANITE are commonly included other igneous rocks, little used for building purposes, such as the Porphyries, Elvan (of fine grain and free from mica), and Gneiss, which is constituted like granite, but has the mica more in layers, along which it splits easily, coming out in slabs from a few inches to a foot in thickness. True SLATES are argillaceous in composition that is, they are composed of clay (silicate of alumina) and little else. The chemical elements of all clay, shales and slates are aluminium, silicon and oxygen, and the origin of all alike is to be found in the natural production of Kaolin, a pure white clay, by the decomposition of the felspar of felspathic rocks such as granites. This is washed into streams and rivers and so is conveyed to the sea, where, consisting of matter in an extremely fine state of division, it is carried further from the shore than the other in- gredients of the original granite, and so is deposited separately, forming a clay bed. This forms material for newer clays, and so on ; while clay beds which have long been subjected to vertical pressure have been compacted into shales and mudstones, and when these again are subjected to great lateral pressure and high temperatures they have been changed into the hard and strong material known as slate. Owing to the extremely high temperature at which the change takes place, slate, like all other meta- morphic and igneous rocks, contains no organic remains. STONES : CLASSIFICATION AND DISTINCTIONS. 27 It is practically non-absorbent, and as it can be split into exceedingly thin parallel layers of considerable size, it is a most valuable roofing material. The crushing resistance of slate varies from 6 to as much as 14 tons per square inch, and its weight from 165 to 1 80 Ibs. per cubic foot, while its transverse strength is greater than that of any other stone. True slates are found in large quantities in North Wales and in Westmorland and Lancashire, and to a smaller extent in the south-west and south of Ireland, in Corn- wall, and in the south-west of Scotland (see map). Many other stones, both sandstones and limestones, which naturally occur in thin enough layers to be used for roofing purposes, are locally known as " slates," or some- times as " slate-stones," or " tile-stones." These, however, split along their planes of bedding, and not along planes of metamorphic cleavage, and so are not true slates, having, in fact, each the characteristics of the class of stone to which it belongs. Coly weston " slates," for instance, found in Rutlandshire, near Stamford, though used as roof coverings, are really limestone of a dark grey colour. The stone is obtained in the form of a block, or slate log, showing no sign of lamina- tion. The logs are quarried in the summer and exposed to the weather through the winter, being watered daily except when hard frozen. If the winter be one of succes- sive frosts and thaws, the block splits into thin slabs, while continuous frost with few alternations will produce thick slabs only, the splitting being done entirely by the weather, and the "slates" being ready for use when the spring arrives. Stone slabs for roofing purposes are also obtained in Somersetshire, but they are thicker and heavier than those from Colyweston. All such, however, are more absorbent than true slates, and require strong roof timbers to carry them, while they foster lichen growth ; but their colour is pleasing, and some architects use them to a considerable extent. 28 BUILDING MATERIALS. The term MARBLE has come to include in practice not only marbles proper, but all limestones and even some other stones which are capable of being highly polished, and which then superficially look like marbles. True marbles are composed of practically pure carbonate of lime (CaCO 3 ) in a highly crystalline form, resembling lump sugar in structure. This resemblance is so strongly marked in the white that it has been given the name of " saccharine marble." The white marble has been meta- morphosed from pure white limestones, while the coloured marbles derive their colour from impurities, mostly oxide of iron, in the original limestones from which they have been changed, the colour having run into beautiful veins and markings during metamorphosis. Almost all colours are represented, and all combinations of colour. The crushing resistance of marble is about equal to that of granite, while its weight varies little from i/olbs. per cubic foot. Like granite and slate it is also an excellent weathering stone, and can be obtained in large blocks ; though it does not, as a rule, retain its polish for any length of time if exposed to the weather. The combination in the same stone of strength, size of block and beauty of colour and texture, renders marble one of the most valuable of building materials. White marbles are imported from Greece, Italy, and Norway, yellow marble from Italy, and veined marbles from Portugal and the Pyrenees ; while Great Britain pro- duces marble of many delicate tints in Devonshire and Cornwall, and rich black and red marbles in the South of Ireland. Of other stones generally known as marbles the most valuable are the Green Serpentines, especially the mono- lithic Verde Antico from Larissa, in Turkey, and the Conne- mara marble from Ireland. These are metamorphic igneous rocks, produced by the alteration under heat of igneous rocks rich in olivine, which contains some 84 per cent, of STONES : CLASSIFICATION AND DISTINCTIONS. 29 silicate of magnesia. This is frequently found intermingled with carbonate of lime formed by water percolation, and the result is a stone having a beautiful mottled surface. Though heavy and capable of carrying heavy loads, it is soft and easy to work, but it weathers badly, and so cannot be used externally with success. Lithologically, serpen- tines are Paleose stones, the mineral talc, which consists of silicate of magnesia and occurs in other forms as French chalk, steatite and asbestos, being its basis. ALABASTERS are also commonly and wrongly classed among the marbles. The true Oriental Alabaster, obtained from quarries in Egypt, Assyria and Algeria, is a beautiful translucent and nearly white limestone, often now errone- ously called onyx marble, whose circular markings indicate its stalagmitic origin. It is difficult to obtain, and is replaced in general use by the softer sulphate of lime, also known as alabaster, the two being superficially similar. This is found in considerable quantities near Paris, and in England in Derbyshire, Cheshire, Westmorland and Nottingham- shire ; while recently a sulphate alabaster has been imported from Mexico for ornamental use under the name of Mexican onyx. Alabaster should only be employed internally and for ornamental purposes. Derbyshire, Dorsetshire and Sussex produce formaniferal and encrinitai compact limestones which take a good polish, and, owing to the fossils they contain, are beautifully marked. The polish, however, is not long retained on exposure to weather or wear, and so the ornamental use of these stones is restricted to certain internal positions only. They, also, are erroneously called marbles. The term LIMESTONE, which properly includes the true marbles, is in practice restricted in its use to such stones, composed mainly of carbonate of lime, as are of so open a texture as to prevent their taking a polish. Even so, a wide range is covered, and many sub-divisions are possible. In physical structure alone there are wide divergences, ranging through all grades from the loosely compacted 30 BUILDING MATERIALS. chalk, which consists of the shells of minute formaniferae, to the homogeneous Kentish Rag, the oolites occupying a middle position. Of these, chalk occurs in Kent, Surrey, Sussex and Hampshire, and the Kentish Rag in Kent, while the oolites, which contain many of the best English building stones, extend over many counties, occurring principally in Dorsetshire, Wiltshire, Somersetshire, and Lincolnshire. None are of very great weight or strength, the oolites weighing from 125 to 145 Ibs. per foot cube, and having a crushing resistance of from J ton to 2 tons per square inch. Oolitic stone as a rule is easy, and consequently inex- pensive, to quarry and work, and is therefore known as a " freestone," while it possesses uniformity of colour (generally a light cream or brown), comes to a good surface, and weathers satisfactorily. Of sedimentary origin, it lies in beds, often of considerable thickness, though the " bedding " is still visible in the blocks. Sometimes this is shown by the position of fossil shells, which always lie flat on the beds, and sometimes by markings which, if of clay, are sources of weakness. Other markings, however, frequently traverse the beds, and are due to the vertical percolation of water through fissures ; and these are not to be mis- taken for bedding marks. Frequently the effect has been for the water to convey carbonate of lime to a fissure, which from being a source of weakness has become a source of strength on being filled with a crystalline substance; and in other cases a similar result has been achieved by percolation of silica, though silica veinings of this sort render a stone comparatively hard to work. Lias Limestones which, practically speaking, do not necessarily occur only in the lias formations are such as include a considerable proportion of clay in their com- position. They occur generally in thin beds only, and are more useful for street pavings than for building purposes, though they look well as "shoddies"/'.*., rough ashlar facing blocks with freestone dressings, on account of the STONES: CLASSIFICATION AND DISTINCTIONS. 31 contrast of colour, the lias stones being generally of a dull and somewhat deep blue. This decorative use in contrast is noticeable in Glastonbury Abbey, in which the bases and bands are in several instances of lias, which has withstood some centuries of exposure admirably. Such stone occurs in Somersetshire, in South Wales, and near Rugby. The Dolomites or Magnesian Limestones are also exceed- ingly important impure limestones. While magnesian limestones vary greatly in composition, the true dolomite is of a peculiar granular and crystalline structure, and is known to mineralogists as Bitter-spar, consisting of 54 parts of carbonate of lime to 46 parts of carbonate of magnesia in indivisible crystals. As a rule a dolomite is fine of grain, and uniform in colour and texture, moderately easy to work, and an excellent weathering stone. The weight is about 140 Ibs. per cubic foot, and the crushing resistance from 3 to 4 tons per square inch. Such stones are found in Derbyshire, Nottinghamshire and York- shire. Some of them contain a considerable proportion of silica in the form of sand grains, and so are, perhaps more properly, classed among the sandstones by many writers. The SANDSTONES include all stones whose grains are composed of silica (SiO 2 ). This mineral, the most abun- dant in Nature, assumes various forms, in some of which it is known as rock crystal, flint, chalcedony, agate, and amethyst, and constitutes not only the sands of the sea shore and the desert and the pebbles of shingle beaches, but the framework of many tropical sponges. This silica, or quartz as it is also called, being practically insoluble and of great hardness, endures when associated minerals are dissolved, decomposed, or reduced to impalpable dust. Thus the sand of which sandstones are composed has been derived either from quartzose igneous rocks such as granite, from the quartz veins of the older sedimentary rocks, from flints (which occur in chalk as lumps of silica deposited by water percolation in hollows originally formed by sponges in the chalk), and from the destruction of older 32 BUILDING MATERIALS. sandstones and beds of sand. The grains consequently vary much both in size and angularity, some sandstones being composed of grains both larger and angular, while others have very small and rounded grains, worn down to their present condition by long-continued rubbing by the action of moving water ; and all degrees between these two extremes are met with. Some tropical sandstones, notably that of which the island of Bermuda is composed, consist entirely of micro- scopical diatoms, or the siliceous framework of minute marine organisms, of marvellously beautiful forms. It is thus evident that the terms hard and soft, as applied to a sandstone, have no reference to the material of which the grains are composed, but only to the stone as a coherent mass, and so depend upon the character and amount of the cementing material. This varies also. It may, like the grains, be of silica, in which case the resulting stone is white and may be very hard ; or it may be of peroxide of iron (Fe 3 O 4 ), familiarly known as rust, forming a thin red coating to the grains, and giving a red, brown or yellow colour to the stone, which may be very soft or very hard ; or it may be of clay, or of carbonate of lime ; or it may be a combination of two or more of these substances. The sandstone deposits in Great Britain are extensive and valuable. The best are found in the Carboniferous series, in Yorkshire (near Bradford and Halifax), near Newcastle-on-Tyne, at Bristol, in the Forest of Dean, in South Wales, in mid-Scotland (near Edinburgh), and in the west of Ireland (co. Clare). The Trias yields the sandstones, mostly red, of Warwickshire, Cheshire and Lancashire, while a fine-grained pink sandstone is quarried from the Permian of Westmorland, and yellow and brown sandstones of comparatively little value are found in the Cretaceous formation of Kent and Surrey. The weight of sandstone varies from no to 165 Ibs. per cubic foot, and its crushing resistance from 2 to 4 tons per square inch. Chapter IV. STONE: ITS DURABILITY, SELECTION AND PRESERVATION NOTES FOR USERS. To all stone users the selection of the most suitable stone for the immediate purpose of the moment is a matter of supreme importance. That the information needed may always be at hand when required, it is well to keep a cabinet of labelled specimens, each label containing not only the generic name of the stone, but a brief record of its principal characteristics, the name and address of the quarry owner, the locality of the quarry, facilities for transport, and the price of the stone on rail or ship. Such a collection may take years to acquire, but its possession will often prove invaluable. There is scarcely a stone produced that is not frequently specified to be used in a position for which it is entirely unsuited, while the same stone might in another position, and for another purpose, be the best which could be utilised. Such improper specifying leads either to sub- stitution or dissatisfaction, and could generally be prevented by the possession of an accurately-labelled sample, which a quarry owner will generally supply if there is a genuine likelihood of the stone being used. COLOUR, in particular, is a point upon which actual inspection is infinitely more valuable than description, as in all colours the various shades are innumerable. Even samples often fail here, however, for many stones vary in tint not only between different beds of the same quarry, but even in different parts of the same block. Thus if strict uniformity is required it should be ascertained in advance whether it be obtainable. ORNAMENTAL MARKINGS, as in the veined and the M.M. D 34 BUILDING MATERIALS. fossiliferous stones, stand in this respect upon the same footing as colour ; and in the case of some of the English marbles even the quarrymen do not know till it is cut what will be the colour or the marking of the next block they bring out. In other cases the markings are quite different according to the plane along which the stone is cut, some stones, like the Greek Cippolino marble, being exceedingly beautiful along some planes and quite dull and lifeless along others ; while the fossiliferous stones often show circular markings if the fossils are cut directly across and irregular or rectangular markings if they are cut longitudinally. TEXTURE depends not only on the size of the grains of which a stone is built up, but on their character and the homogeneity of the mass, and is frequently of considerable importance. Most of the very hard stones, like the granites, marbles, and compact limestones, can be brought to a smooth surface, and in that condition be left plain or be highly polished, the latter being the more usual and dis- playing to perfection their marking and colouring. Granite, however, may be left with a roughly chiselled or even a hammer dressed surface, when its coarse and angular grain gives an effect of great solidity and strength. A somewhat similar effect can be conveyed by the use of the coarser sandstones, but it is missing with the coarse limestones, which suggest crumbling weakness if left rough, through the roundness of the oolite grains or the fragmentary stratification of the shells which they contain. Hard smooth limestones, however, like the lias, look strong when hammer dressed, exposing smooth chipped faces separated by sharp arrises ; while smooth rubbed surfaces can be produced on the fine-grained sandstones and lime- stones alike. HARDNESS is one of the qualities in a stone which most considerably affects its cost in use ; for it is generally not so much the raw material which varies in price, as the value of the labour which has to be spent in working it. Thus STONE : ITS DURABILITY AND SELECTION. 35 where economy is a principal object for consideration, the softest stone which will serve the purpose should be used. Elaborate carving, for instance, can be indulged in, where it is protected from the weather and from wear, without great expenditure if a very soft stone be used ; while it would very likely cost three times as much if executed in a sufficiently hard stone to withstand exposure to weather or friction. WEAR, however, in many positions demands something more than mere hardness to withstand it successfully. When used as stairs, landings, or pavements, many of the more compact stones become slippery, while others, like the lias limestones, wear into holes. An angular grit prevents slipperiness, and this is possessed as a rule by granite and the coarser sandstones. Those sandstones which, like the Yorkshire " flags," occur naturally in slabs of from ij ins. to 6 ins. in thickness with true surfaces, are much used for these purposes ; but their layers of deposit are so clearly marked that if subject to heavy foot traffic they are liable to wear away in flakes, and the more homo- geneously bedded sandstones, like that from Liscannor in co. Clare, the thicker Yorkshire stones, and the Forest of Dean and Pennant stones, are then to be preferred, especially for stairs. STRENGTH in stone is not often a matter requiring great consideration, as under ordinary circumstances any stone is capable of bearing the slight load brought upon it ; but where, as in vault groining, church pillars, columns, and girder bearings, great thrusts and loads are brought to bear upon small surfaces, strength becomes of supreme import- ance. In this matter care is necessary, for the results of tests upon small sample cubes are extremely deceptive, except in the case of the higher grade stones of uniform structure. CORRECT BEDDING is, in the case of most of the laminated stones (*>., those deposited in layers or lamina- tions) an absolute necessity. In ordinary walling, bearing D 2 BUILDING MATERIALS. a vertical load only, the beds should lie horizontally. Were horizontal bedding attempted, however, with undercut mouldings, the undercut portion would flake off, as shown by dark lines in the illustration (Fig. 5), and so edge moulding is resorted to, with the bedding parallel to the vertical joints. Face-bedding, as it is called when the bedding lies vertically and parallel to the face of the wall, should never be used, as the surface tends to peel off. In the case of stones resisting heavy thrusts, the bedding must be at right angles to the thrust, as it is in this position that all stone is strongest to resist. A skilled mason can generally detect the bedding of a stone at sight, by noting that fossils lie flat on the bed, or by small bed markings ; or if these fail he can "feel" the bed when he works the surface with his chisel. The inex- perienced, however, are likely to be deceived by mere water veinings. THE SIZE of slab and depth of bed obtainable are important factors in determining the selection of stones for many purposes, where large sizes are needed. Many otherwise excellent stones are obtainable only in comparatively thin beds. As a rule special inquiry upon this point is necessary, else much trouble and delay may result. Very few quarries, even those owned by wealthy firms and containing blocks of any size likely to be required, have the means of hoisting or of transporting stones weighing as much as 10 tons, and many limit their output to blocks of 100 cubic feet in bulk. THE DURABILITY of a stone used externally seems to be a matter which can properly be determined by experience only. Where subject to the action of water and of marine insects, as in sea walls, weight and hardness are essential to durability, but in general building work this is not the case, many stones of comparatively light weight and open Fig. 5- STONE : ITS DURABILITY AND PRESERVATION. 37 structure being known to be excellent weathering stones. Water may penetrate into the pores of some stones, freeze, expand, and blow off fragments ; but this is an infrequent occurrence, except with the very softest, which few would think of using. Similarly, in theory, limestones should not be able to resist the action of the acids contained in the air of all large towns ; yet there are many nearly pure lime- stones which experience shows can be used with perfect safety in such places as London and Birmingham. Tests, whether mechanical, chemical, or microscopic, seem to be of little value. It is better not to trust to them, but to be guided by the results of the many experiments which men of previous generations have made, assuring yourself that you really are using practically the same stone as that in the building you trust to, and from the same quarry bed. Most quarries produce stone of several qualities, usually, though not invariably, the better weathering and harder stone underlying that of less value. Even ABSORPTION is not an entirely reliable test of durability, and certainly not as between class and class of stone. Still, granite should not absorb more than J per cent, of its dry weight of water, slate not more than \ per cent., sandstone and dolomites not more than 5 per cent, and oolite limestones not more than 8 per cent. Walls built of absorbent stones are, it must be remembered, liable to be damp walls, especially if the stones be compact of structure as well as absorbent, and so of a nature which prevents their parting readily in fine weather with the water they have absorbed during rain. Such a stone will probably, on microscopic examination, be found to contain minute fissures along which water will be absorbed to a considerable depth by capillary attraction. A wall built of such stone will be more permanently damp than one com- posed of stones of more open grain, which absorb even a larger proportionate weight of water ; for water penetrates further and is retained longer in fine cavities than in larger ones. 38 BUILDING MATERIALS. Several means of PRESERVING the less durable stones have from time to time been suggested, painting either with lead paint or with oil being the most common, and requiring periodic renewal. Two liquid preparations of secret composition Szerelmey's and the " Fluate " of the Bath Stone Firms have also been much used for this pur- pose ; but they are more valuable for rendering absorbent stones somewhat waterproof than for preserving them. It is better to use a durable stone in the first instance than to trust to these or any other preservative. They have, how- ever, the advantage over other preparations of being colourless and not affecting the appearance of the stone to a material extent. Of DESTRUCTIVE AGENCIES, water is the most to be feared, either from its proverbial " wearing " action, which is mechanical, and whose effect is seen in sea walls and on the " weather " side of buildings in exposed situations, or from its action as a solvent carrying destructive acids present in the air of large towns into the body of the stone, or from its expanding just previously to freezing after having been absorbed, and so splitting off small fragments of stone. Lichens, mosses, ferns, and creepers are also highly destructive, especially to limestones, both through the pene- tration of roots into the pores of the stone, and through the vegetation holding water like a sponge, and so giving time for any acid the water may contain to act. Water is thus again the actively destructive agent. Lodgment for it should never be provided, and such things as hollow mouldings, water-holding carving, and soffits unprotected by drips should be studiously avoided in external stone- work. NOTES FOR USERS. Keep within the natural limits of size. You cannot obtain a stone 12 ins. thick from a quarry whose deepest bed is only 11 ins. Stone is a weight-carrier, with little transverse and less STONE : NOTES FOR USERS. 39 tensile strength. Use it, therefore, freely in compression, with caution as lintels, and never in tension. Bring pressure upon it at right angles to its natural bed, or, in the case of slate, to its cleavage. Arrange that each stone may be cut with as little waste as possible out of a roughly rectangular block, such as is obtained from the quarry. Mouldings and carvings cannot be planted on. The effect must be obtained by sinking the hollows below the natural surface. , Avoid elaborate and undercut detail in the harder and in the laminated stones. Avoid sharp arrises in the more friable stones, and where exposed to rubbing or weather. Chapter V. BASALT AND GRANITE. BASALT, being hard and difficult to work, and mostly found in places from which transport is difficult, is little used structurally ; and, as it has never been worth while to put down expensive plant, the method of quarrying is elementary. Owing to its columnar structure, it comes out of the quarry in long prisms. These, if placed on their sides and bedded in cement, make an excellent facing for sea-walls, where weight and indestructibility are primary considerations, and for this purpose they have been used in some parts of Ireland. A decorative dark green Basalt is found near Exeter, however, which comes out in large beds, splits readily, and polishes well. Used structurally, it makes good hammer- dressed walling, especially for plinths and basements. GRANITE, generally considered as igneous and intrusive, is, however, thought by many to be of sedimentary origin. It is a holo-crystalline aggregation of quartz, felspar and mica, its chemical composition varying with its mineral contents ; and no less than 44 accessory minerals occur in it in varying proportions. Orthoclose, or potash felspar, is generally its principal constituent ; its colour varies from white to flesh-red, and its grains are irregular and sharply defined. It is usually thought to be a weather stone of un- doubted quality ; but this is not by any means always the case. Some granites are no better weather stones than the softer oolites, crumbling in the hand after a few years' exposure, and although most English and Scotch granites are reliable in this respect, the opinion of PLATE ABERDEEN GRANITE. DEVONSHIRE GRANITE (Blackenstone Quarry). CORNISH GRANITE (De Lank Quarry). [To face p. 40. BASALT AND GRANITE. a mason 'accustomed to granite working should be sought where doubt exists. If exposed to fire it disintegrates badly. GNEISS is a rock which has the same mineral constituents as granite, but is more or less stratified. It is very little used in building. GRANITE is extensively worked, generally in large, open quarries. The beds as a rule are very thick ; but still, horizontal beds do occur at intervals, and these often contain a very thin layer of sulphur. If, as sometimes happens, vertical joints of the same nature are found, the great natural blocks can be wedged apart. Otherwise, and more frequently, it is necessary to blast. Vertical holes are driven downwards NEW FACE OF QUARRY-> Fig. 6. (see Fig. 6), close against the new quarry-face which it is desired to expose, the quarry being worked in rough steps, as shown on sketch. These holes are made with a "jumper," which is a tool like a long bar of iron, weighted at about one-third of its length from the point with an attached ball of iron, and having a chisel edge. This the workman merely lifts, turns slightly, and drops, so that drilling a blasting hole is a slow process. After the circular hole has been made to the required depth, a notch is cut throughout its whole length in each direction in which it is desired for the rock to split. The number and position of these holes vary according to the block required, the charge, generally blast gunpowder, is proportioned so as to split the rock where required and lift it forward without unnecessarily breaking it up, and all the charges are exploded simultaneously. BUILDING MATERIALS. In many quarries, if the blocks have not been thrown over the old quarry-face by blasting, they are now levered to the edge till they fall over, and are removed from its foot by cranes and trucks, or by a more elementary system of wood rollers ; while in other quarries it is necessary to use large cranes and lift the blocks to the top for transport. Rough irregularities are, however, always first knocked off with a heavy hammer, or the stone is split up into smaller blocks or slabs by making a series of holes, less in depth, larger in size, and closer together than the blast holes, and driving peculiar wedges into these. Two " feathers " are first inserted, these being of steel and re- sembling shoe-horns in shape, and then a steel " plug," in the shape of a truncated cone, is driven in between the feathers, as shown in sketch. The several plugs in a series have to be tapped in succession to ensure even driving and an uniform split. Sawing, such as will be after- wards described when dealing with marble, is sometimes re- sorted to for producing slabs, but it is a tedious operation ; and the same may be said of turning. After splitting roughly to size with the plug and feathers (see Fig. 7), the next process is that of reducing surface irregularities with the scabbling hammer (see Fig. 8), which weighs about 22 Ibs., and has a short handle. The flat, or "spalling," face is for knocking off irregular lumps and angles, or for roughly " hammer-dressing " the surface, while the pointed or " pick " face is applied vertically to the surface, being just lifted and allowed to drop of its own weight, this action being repeated rapidly by a skilled Fig. 7. Plug and Feathers. KA *lSv THF * ERSITY 1 UNIVERSITY BASALT AND GRANITE. 43 workman and soon reducing a rough to a comparatively smooth surface, chips flying off in all directions. If the Fig. 8. Scabbling Hammer. Fig. 9. Serrated Pick. Fig. 10. Axe. scabbier has two pick faces, and is known as a scabbling pick, it is somewhat lighter in weight, finer work being possible with it, while finer work still can be done with a pick having toothed edges, known as a ser- rated pick (see Fig. 9), or with an axe, such as is shown in Fig. 10, which only weighs about 9 Ibs. Itis this tool whichis gene- rally used to produce the so-called "draughted margins," with their parallel tool marks close together, though the same effect can be produced more tediously by means of a chisel (see Fig. 11)- The finest face, short of polishing, is obtained on Granite by the patent axe, which consists of a bundle of steel plates bound together, so that they can be taken apart and their edges sharpened when necessary. Heavy machinery is necessary for polishing economically Fig. ii. Hammer Dressed with Draughted Margin. 44 BUILDING MATERIALS. on a large scale. The fine axed surface has to be ground down by rubbing on a revolving or travelling table in sand, the weight of the granite, which lies on the table, applying sufficient pressure. This rubbing is repeated, with material of finer and finer grain, until the surface becomes of that absolute smoothness known as high polish, the granite, during these later processes, being fixed, and movement being imparted to the rubbers. Granite is used largely in building operations wherever stone is required to carry a heavy load or resist constant friction, as in plinths, columns, and pavings, while much is also employed for merely decorative effect. The waste blocks and chippings are commonly utilised also, the larger as road metal, and the smaller as the aggregate for concrete and artificial stone, so that the ultimate proportion of waste from a granite quarry is small. DEVONSHIRE AND CORNISH GRANITES (see PL I.) are mostly grey in colour, with distinct black and white crystals, that from the De Lank quarry, six miles from Bodmin, being typical, very hard and durable, and with a well compacted grain, in which hornblende abounds. Farther west, however, near PENZANCE and the LAND'S END, the granite is of a more yellow colour, and contains large felspathic crystals known as " horses' teeth." This is known as PORPHYRITIC GRANITE, and is highly decorative when polished. That from the Blackenstone quarry is typical. Granite from the CHANNEL ISLANDS is close in grain, sometimes of a bluish tinge (though several colours are found), and generally very hard. LEICESTERSHIRE GRANITE is a true syenite. It makes excellent road metal, but except locally is not much used for building, being tough and compact, except as the aggregate for artificial stones and concrete. It is often green in colour. The SHAP GRANITE of Westmorland is one of the most beautiful found in England, containing large red felspar crystals, and taking a high polish. BASALT AND GRANITE. 45 Most of the SCOTCH GRANITE is blue-grey, and it is generally admirable for all purposes for which granite is used. There are extensive quarries in Argyleshire, Kirk- cudbrightshire and Kincardineshire, but the principal ones are in Aberdeenshire, in which county are also found the beautiful red Peterhead and Cruden granites. The Peter- head is particularly well known, both the colour and polish being admirable. The grey granite fades more or less after continued exposure. It is composed of small grains. IRISH GRANITE is not much used except locally, though a great deal exists in the counties of Dublin, Donegal, Louth, Galway and Mayo, most of it being grey, though some of a red colour is found in Galway and Donegal. A large amount of excellent granite, grey, blue and red, is now imported from NORWAY and RUSSIA, as, owing to the low rate of wages obtaining in those countries, it can be put upon the London market at a low price. Amongst this is a granite, nearly black in colour, containing large crystals, which have a peculiar " flash " when polished, which, if introduced sparingly, may be used amongst other stones with good effect. There is doubt, however, whether these foreign granites will retain their polish and colour well externally. BUILDING MATERIALS. 8*3 .JSSSJ I f I .1 - ' Q a -s Ill ? K? M* . 8 3 0-Q fii , oo ifti if 111 0^3 a)-d o^a o^ G *fli 5 O ^ "rti w "Jn w O III i -C o-^ i C/5 .^H (/] : : 2 "3^3 5 I 2.2 : ' =l! || 5 >* T3X1 1 |a|| |I|S -M"<1) S-2 G -0 S CO ^ *"* -fl rrt* O o U* t^ T3 jD G *" [S Q; T3 i a I" 1 f^'P ^1il Ifilr 2" .- vS "5 - oj rt g*rt ^T! -2 o,2 g's s> remely hard urposes. T3 p 0) 'G >-. ||| 111 3p Pi C/5 ' sc^ _G <2 **" 2 ^ G bc-^" T3 'O o ^ ^ , ;*. ^j |3 O) *T3 4) "2 4) .Q be qj i c ^"8 0? | U O S o *S> "3 u O P o Q Q Q 3 S PQ tf w * , '. : > 1 . H i R S O eg R J? S S- p* g 5 ffi H M o I 1 ^ H O ?> S 6 * c-2 c G c Is IS o"iSs S^ S. g ea 5; ^j CJ < * <: < : : o ct; E-c S G O.S o Jrs Tt- i- 1 i 2| S | cxg aa >-, G 3 >-, G < b|!i c -z o ^ > 1 hfe 48 BUILDING MATERIALS. 1 8 d rt a; "5 c> en en 1 "rt 1^ 1 is 3 ^ "S K 22 <2 O) ,jj Illl 2'gu.s 3 CO p 8 I j A Ul t^ u 2 rt 3 frt rt 0>0 I SH^llII w 12^I 6 I B < : 1 o u ii 1 1 I ! up il ! all S i J a? if " & S 5 ^ - Q- Chapter VI. SLATE. THERE are two methods of obtaining slate by open quarrying and by mining. Of these, the open quarry is the more usual except in and around Festiniog, the open quarries at Bethesda and Llanberis being well known as some of the largest of any sort in the world. Whichever system is employed for reaching the slate, however, the process of dislodging it is that of blasting. When a quarry face has been exposed, a vertical channel about 3 ft. square has to be chipped out throughout its height. A horizontal hole has now to be made at a con- venient depth, known as a " split hole" along the cleavage and preferably in a natural joint, and a carefully pro- portioned blast exploded in this just to lift the rock. Then another hole, known as a "pillar hole" is driven in at right angles to the cleavage and down to the " split " caused by the previous charge, thus bursting the stone out at the split and towards the already exposed channel along an imper- fect cleavage, perfect enough for this purpose, called the "pillaring line" which always runs north and south. The blast holes are made with the jumper when vertical, and when horizontal or nearly so with a long chisel (with shield) and a hammer, the men having often to let them- selves down by ropes to their work. At the Bettws-y-Coed slate quarry, the one which was inspected for the purpose of writing this description, natural joints occur in an erratic fashion, crossing one another so sharply as to produce razor-like edges, and yet each continuing, beyond the crossing, in its own plane. Around Festiniog the slate generally underlies granite, M.M. E BUILDING MATERIALS. PEAT SECTION and has to be mined. Almost invariably a tunnel is driven in from the outcrop under the granite roof, with branches at convenient depths, from which chambers are worked under one another, the chambers being 30 ft. wide with 30 ft. pillars of solid rock left be- tween. Thus only half the rock con- tained in a slate mountain is ever removed, owing to the necessity of leaving these pillars to support the roof above. This is known as the descend- ing system (see Fig. 12). At the Rhiw- bach quarry, near Blaenau-Festiniog, which produces roofing slate only, an attempt is being made to reduce the enor- mous waste often 14 tons of rock having to be re- moved to produce one ton of finished slates by working on an ascending system and using a machine wire saw instead of blasting. A steel wire rope, J in. in diameter, running in granulated slate and worked by compressed air, is made to take off a clean slice of rock PLAN ON LINE: AB Fig. 12. Slate Mine. SLATE. face no less than 150 ft. in length, and this, once cut, may be split up into convenient sections along the cleavage and the pillar line with heavy broad-edged wedges. The blocks thus dislodged are split along the cleavage, by wedges or plug and feathers, into slabs of not more than 13 ins. thick and then taken to the workshops or " mill." There the slabs are first sawn into lengths, according to the purpose for which they are required. Circular machine saws are used, the stone being brought to them on travel- ling tables. Thin slabs can be cut by toothed saws running in water, but the thicker slabs are cut by a saw having steel Fig. 13. Tooth of Circular Saw. Fig. 14. Hand Saw. scupper nails set into the blade to serve as teeth, the rotation being so arranged that the head of the nail first meets the slate and acts as a cutting edge, forming a broad groove (see Fig. 13). V^hichever form of blade is used, there are two blades on each spindle acting simultaneously E 2 BUILDING MATERIALS. against the same slab, and so cutting exact lengths, which are adjustable. A hand saw, having a few V-shaped notches in place of teeth, and working in water, can also be used, but its employment is more tedious (see Fig. 14). For many purposes for which slate is used, such as for shelving, cisterns, hearths, paving and urinal sides and backs, the widths as well as the lengths are sawn, and Fig. 15. Slate Ridge in Two Pieces. Fig. 16. Mallet. Fig. 17. Chisel. one or both faces arc planed. This is done by passing the slabs, resting again on a travelling table, under a broad plane iron, 8 ins. or more wide, set in a frame so as to take off any desired thickness of shaving, and the surface thus produced can if required be further smoothed, or "polished" as it is called, though no really polished face results, by rubbing with pumice stone. By altering the planing iron any desired moulding or groove can be cut; and it is in this way that slate ridge rolls are made (see Fig. 15). Chamfers, and mouldings also, can likewise be cut by hand with a large-headed wooden mallet (Fig. 16) and steel chisel (see Fig. 17), such as is used by masons for softer stones, and finished with a file and emery paper or rounded nosings are even filed only, without previous chiselling. When required for roofing, the slate slabs sawn to length SLATE. 53 are split along the cleavage to not more than 3 ins. thick, and then " pillared," or split across the cleavage with a pillaring chisel, having an edge about an inch wide, driven with a heavy iron hammer. The slabs thus roughly re- duced to size are now taken between the knees of the splitter. He gauges the thickness of a slate by eye, vary- ing it according to the class of rock he is dealing with, and drives in a splitting chisel (see Fig. 18), having a thin, wide blade, along the edge with a light iron- bound wooden mallet (see Fig. 19). Very thin slabs of the Fig. 18. Splitting Chisel. Fig. 19. Light Iron- bound Wooden Mallet. Fig. 21. Travel. Fig. 22. Measuring Stick. higher quality slates are obtainable, and the splitting is, as a rule, readily done by a trained man. The slates thus obtained are trimmed to market sizes with a dressing knife (Fig. 20) acting against a travel 54 BUILDING MATERIALS. (Fig. 21), this last being a tool resembling a door scraper with a knife edge the sizes being first marked on the slate by a nail in a notched measuring stick (Fig. 22), the notches being graduated to give every inch from 6 to 18, and then 20, 22 and 24 ins. In many quarries trimming is now done by machinery, with what look like gigantic scissors whose lower blade is fixed horizontally while the upper blade is made to rise and fall. A fixed plate against the side determines the N Fig. 23. Diagram of Slate Cleavage. right-angle, and against this the notched measuring stick is also fixed. A diagram showing roughly how a block may be split along cleavage and pillar is given in Fig. 23. Roofing slates are sorted at quarry according to size and weight, and not according to the trade names by which certain sizes have become known ; and the sizes obtainable are much more varied than is generally supposed, as the following list will show. While the larger sizes only are used in London to any extent, they are scarcely known in SLATE. 55 the North of England and Scotland, where small sizes are much preferred : TABLE OF ROOFING SLATES FROM THE BETTWS-Y-COED QUARRIES. Size in inches. Weight per 100 in cwts. Trade Name. Size in inches. Weight per looincwts. Trade Name. 24 X 14 24 X 12 22 X 12 22 X II 2O X 12 2O X IO 20 x 9 18 x 12 8 \ 6 4i 4i 5 Princess. Duchess. Small Duchess. Countess. 16 x 9 16 x 8 14 x 12 14 x 10 14 x 9 14 x 8 14 x 7 3i if 3i 2| 2 I 2 I Ladies. 18 x 10 18 x 9 16 x 12 16 x 10 4i 4 4i 3l Small Countess. Also 13 > 12 X 10 X < 10, 13 x f t 8, 12 x 7, 8, 10 x 6, 7, 12 x 10, 12 xg, 12 X 6, 12 X 5, 9 x 8, and 9 x 6. Roofing slates are known as " Firsts," " Seconds " and " Thirds," the quality depending on freedom from flaws as well as upon evenness of colour and thickness, it not being always the thinnest slate which is the best. If good slate be stood in water, the damp should not rise at all perceptibly up its edge above the water line, even in 24 hours ; while in a bad slate it will rise as much as 2 ins. in ten minutes. A bad slate, also, will give off an earthy odour when wetted, and when struck will sound dull, while a good slate gives off a sharp metallic ring. Slates are sold from the quarry by "long tally" that is, per thousand of 1,200, with 60 extra to allow for breakage, making a total of 1,260 to the thousand. By the time they reach the builder, a thousand usually consists of 1,200 only. The following analyses of Bettws-y-Coed and Portmadoc slates are from Davis's " Chemical Engineering," and show both to be good, the former, as containing less oxide of BUILDING MATERIALS. iron and lime, being the better able to withstand the action of acids in chemical works : - Bettws-y-Coed Slates and Slabs. Portmadoc Slate. Silica 61-26 20 -49 58-91 23-08 7*2^ 9'O2 Lime i -08 2'06 Magnesia ... Potash 1-96 2-18 I-I 4 I '92 Soda 2-38 1-02 Water V44 2-85 The specific gravity of slate, like that of all other com- pound minerals, varies slightly, but is about 2*85, and its weight is about 178 Ibs. per cubic foot. The tensile strength, rarely called into play in practice, is about 630 tons per square foot, and its crushing strength varies from 720 to 1,205 tons per square foot. As to its transverse strength, this is difficult to express, and it can only be said that it is such as to render it the best of all stones for use in weight-carrying lintels. Easily split, planed and sawn, it is yet extremely tough and wear-resisting. There is a great amount of wastage both in quarrying and working, no use for the detritus having yet been found, save that the larger blocks of rock which, containing hard veins or otherwise, are useless for conversion, are employed for walling in the locality of the quarries. In some districts, iron pyrites are found in the slate beds, and cause a great deal of trouble to the quarry owners ; but roofing slates and slabs containing them are rarely put upon the market. "Best" or "First" slates, according to the general acceptance of the term, must be thin, of straight cleavage and good colour, and free from spots ; but above all they must be thin. In this respect the classification is SLATE. 57 unfortunate, for while thin slates make very light roofs, they are liable to breakage, and the monotonous smooth- ness is hardly so pleasing, to many architects, as the comparative roughness of a thicker slate. Thin blue slates are principally shipped from Bangor, and are known as " Bangor slates," though obtained from the great quarries at Bethesda and Llanberis, and from smaller quarries in the same district. " Best Bangor" are perhaps the finest slates procurable for perfect uniformity of colour, smooth texture, and extreme thinness. " Portmadoc slates " are also named from the port of shipment, as they are not quarried at Portmadoc, but in the neighbourhood of Festiniog. They are slightly thicker and coarser in grain than " Bangor slates " and of a more purple colour. Bettws-y-Coed slates are shipped from Deganwy. Though free from blemishes they are classed as "Seconds" and " Thirds " only, as they are not thin splitting. Where a little additional weight is not objected to they make admirable roofing slates. The colour is a pleasant dark blue. Very large slabs are obtainable. Blocks can be sawn up to 14 ft. square and planed up to 12 ft. by 6 ft. A green slate with a peculiar permanent red flash upon the surface is quarried at Precelly, in South Wales. Westmorland slates, especially those from the Elterwater and Tilberthwaite quarries, are of a beautiful green colour, thick and rough. They are not arranged in sizes before being sent from the quarry, and so have to be purchased " mixed." Usually the longer slates are laid near the eaves of a roof and the smaller ones near the ridge ; and as the widths as well as the lengths vary, broken jointing results. Laid by skilled hands this can be made to look very well. These Westmorland green slates, it may be mentioned, are not clay formed, but are composed of volcanic ash which has been altered by metamorphism. Though good slates are obtainable from Cornwall, Scot- land and Ireland, they are not much used except locally. 58 BUILDING MATERIALS. Soft, earthy slates are also quarried in Somersetshire, but they are not of great value for roofing purposes. The Irish slates from Valencia and Killaloe are particularly good, and occur in large quantities, but the difficulties of trans- port are great, and seem to prohibit their use to any great extent. They are all purple in colour. The Cornish slates are mostly used for slabs. American slates have been imported and largely used in cheap work of late years. They are mostly blotchy, and of unpleasant purple, green, or red colour. Portuguese slate is imported, mostly for enamelling for it lacks some of the qualities necessary for a good roofing slate. It is somewhat earthy, but is soft to work, is easily brought to a smooth surface, and stands well the temperature of the ovens. Enamelled slate is used principally for chimney pieces. At Messrs. Lee & Brothers' Works at Hayes, the slate, after being planed, is placed on a rubbing bed before the colour is applied. The colour first used is black, and with this the whole surface to be enamelled is covered. As this is done, the slabs are arranged in iron racks so that the air can get all round them, and the racks, running on tram lines, are wheeled into large ovens and subjected to a dry temperature of about 300 degrees F. On removal, any desired colours are applied by skilled enamellers, either to imitate marble veinings, or to produce patterns or even landscapes, the " brushes " used including coarse sponges and feathers. Stoving is repeated, sometimes only once, but usually more often, lower temperatures being used for the colours than for the black groundwork ; and the work is finished by varnishing and polishing with rotten- stone. The various slabs which compose fire-place jambs are fixed together before they leave the works, hook-shaped iron cramps being screwed and leaded into the back of the slabs and these held together with a plentiful supply of plaster of Paris, in which lumps of broken marble are embedded. SLATE. ENGLISH SLATES. 59 Quarry. Nearest Station. Nearest Port. Colour. Remarks. Delabole, Old Delabole, Wadebridge Blue-grey The slate is noted for its L. & S. W. Rly. lightness, durability, N. Cornwall and strength. East Corn- Doublebois, Par Blue Slate very durable. wall G. W. Rly. Cornwall Elterwater Coniston, or Windermere, Barrow-in- Furness Finest light green Rough in texture, but of a durable character. L. N. W. Rly. Lancashire. Honister Keswick, Cumberland. Maryport or Workington Light sea green, Deep olive green, dark sea green Kirkstone Windermere, Barrow Green Very strong and durable. L. & N. W. Rly. Westmorland Launceston South ... Blue Petherwin, Cornwall. Okehampton Wiveliscombe, Watchet Blue and Slate slabs; damp G. W. Rly. variegated courses, etc. Somersetshire Parrock End Coniston, Barrow-in- Light sea green, Slate of rich tint. F. Rly. Furness deep olive Lancashire green, dark sea green Tilber- Tilberthwaite, ... Green thwaite Lancashire Torver Torver, F. Rly. Barrow-in- Blue Lancashire Furness Tracebridge Burlescombe, Dark blue Mostly used for slabs, G. W. Rly., pump troughs, cis- 3j miles Wellington, G. W. Rly., 6 miles terns, hearths, floor- ing, chimney tops, garden edging, etc. Wiveliscombe, G. W. Rly., 6 miles Milverton, 7 miles Somersetshire Treborough Washford, G. W. Rly. Watchet Blue Roofing slates, and slate slabs for all purposes. Somersetshire Yeolmbridge Launceston, Plymouth Blue veined, Chimney pieces, water L. & S. W. Rly. grey hard tanks, sills, steps, & G. W. Rly. paving, etc. Devonshire SCOTCH SLATES. Aberfoyle Aberfoyle, 2i miles, Bowling Blue and green Only roofing slates manufactured. N. B. Rly. Perthshire Balvicar Oban, N. B. &C. Rlys. Glasgow Blue This slate is blue in colour, with small iron Belnahua Argyleshire Oban, Belnahua Blue pyrites. N.B.&C. Rlys. Argyleshire 6o BUILDING MATERIALS. SCOTCH SLATES continued. Quarry. Nearest Station. Nearest Port. Colour. Remarks. Breadalbane Oban, N. B.&C.Rlys. Luing and Talevonochy Blue Craiglea Methven, C. Rly. Perth and Dundee Blue, green and grey Made in all the different sizes. Perthshire Cullipool Oban, Cullipool Blue N. B.&C. Rlys. Argyleshire WELSH SLATES. Aberllefenny Aberllefenny, Aberdovey Dark blue transhipped at Machyulleth, Cambrian Railway Merionethshire Alexandra Dinas Junction, L. & N. W. Rly. Carnarvon Purple Carnarvonshire Bettws-y- Coed Bettws-y-Coed, L.&N.W.Rly. Deganwy Dark blue Carnarvon vein; durable hard slate ; large vein Merionethshire producing largest size slabs and slates; large quantities of slabs for mantel-pieces and slates of all sizes ; strong and durable. Cefn Kilgerran, G. W. Rly. Cardigan Blue Pembrokeshire Cilgwin Nantlle, L.&N.W.Rly. Carnarvon Blue, purple Carnarvonshire Dinorwic Port Dinorwic, Port Dinorwic Grey, blue, red The slate is hard and L.&N.W.Rly. and green very durable. Carnarvonshire Diphwys Blaenau- Portmadoc Blue Casson Festiniog, L.&N.W.Rly. Merionethshire Dorothea Nantlle, Carnarvon Blue and L. & N. W. Rly. purple Carnarvonshire Glynrhonvvy Llanberis, Snowdon Moun- Carnarvon Blue and purple Strong, hard slate. tain Line Carnarvonshire Llechwedd Blaenau-Fes- Portmadoc Dark blue tiniog, L. &N. W. Rly., G. W. Rly., Festiniog & Portmadoc Rly. Merionethshire Moelferna Glyndyfrdwy, Saltney Blue black, blue Roofing slates ; slate slabs for brewery Merionethshire tanks. Oakeley Blaenau-Fes- Portmadoc, Blue The slate is known to tiniog, N. Wales the trade as " Oake- L. & N. W. Rly. leys." Merionethshire 1 SLATE. WELSH SLATES continued. 61 Quarry. Nearest Station. Nearest Port. Colour. Remarks. Penrhyn Bethesda, Purple L. & N. W. Rly. Carnarvonshire Rhiwbach Blaenau-Fes- Portmadoc Blue One of the oldest quar- tiniog, and Deganwy ries producing Port- L. & N. W. Rly. madoc slate; worked Merionethshire from 1812. Votty and Blaenau-Fes- Portmadoc Blue Genuine Portmadoc or Bowydd tiniog, Festiniog slates. G. W. and L. & N. W. Rlys. Merionethshire Wrysgan Tan-y-Grisiau, Portmadoc Blue Festiniog Rly. Merionethshire IRISH SLATES. Fourcoil Skibbereen and Leaf Quay, Dark blue Clonakilty, Glurdere 10 miles each, Harbour Co. B. & S. C. Rly. Cork Garrybeg Nenagh and Limerick Grey Killaloe, G. S. & W. Rly. Tipperary Madrana Skibbereen, 9 miles, Cork, Bandon and Leap, 2fc miles Very dark grey S. C. Rly., Cork Ormonde Carrick-on- Carrick-on- Blue Slate Suir, Suir, 5^ miles, G. S. 6 miles & W. Rly. Valencia Kilkerry Valencia Billiard table beds. Island, Kerry Chapter VII. MARBLE. MARBLE is in some cases easily quarried, as it occurs naturally in blocks of convenient size, needing only to be levered out ; but more frequently blasting or wedging have to be resorted to. In the ancient workings of the quarries near Larissa, from which the Verde Antico was obtained, it has been found that columns were cut with infinite labour out of the solid rock, the stone around them being chipped away so as to leave the rough columns stand- ing, these being finally severed at their bases. Foreign marble generally reaches England in roughly- squared blocks, but the more valuable statuary marble of Italy is sent over just as it is obtained from the quarry, and is invoiced neither by weight nor cubic content, but simply as " One block of Marble," the price being stated in an equally simple manner, as ,100, 150, or 200, as the case may be. Marble masonry is a thing to itself, requiring heavy machinery and infinite patience. At Messrs. Lee & Brothers' large works at Hayes, the blocks are lifted from barges by a crane running on a gantry, and are deposited under cover in a large shed, the power employed for this and all the other machinery being electricity generated by a dynamo driven by a gas engine, the gas for which is made on the premises. When it is required to cut a block into slabs it is put upon a table at ground level and a series of steel blades are suspended horizontally over it in a rocking frame, at such distances apart as correspond with the thickness of the slabs required. As these blades, or saws, swing PLATE II. DEVONSHIRE MARBLE (Characteristic of all true Marbles). [Tc face p. 62 MARBLE. horizontally, they are supplied with fine sand from a hopper in which rollers revolve to crush any coarse particles, the sand passing from the rollers to a fine rocking sieve, through which it is washed with a plentiful supply of water. In this way as many as twenty, or even more, blades can be worked simultaneously upon the same block of marble, but even so the process of sawing is extremely slow. In order to cut the slabs thus produced to their required sizes, several are piled on one another till a depth of about 1 2 ins. is reached, and placed on a slow travelling table in front of a circular saw. This has a steel blade with diamonds set in sockets on its edge, and does its Fig. 24. Marble Hord (Starting of Machine- cut Mouldings). work with compara- tive rapidity, the rate of "feed" being ad- justed according to the total thickness to be cut through. Water only is sup- plied to this saw. The edges are next ground on a revolving iron table in sand and water, and the square slabs are then bedded in plaster of Paris on a wooden frame, to a perfectly true surface, on a setting of brickwork. Over this frame is a revolving arm to which can be attached revolving rubbers of various kinds. The first of these to be used has iron pads, which work in sand to grind down minor surface irregularities and remove any rust stains left by the saws. This acts for eight hours, moving rapidly over the face of the marble and attacking all parts equally, and then is replaced by a rubber having rope pads working in emery for another eight hours, the 64 BUILDING MATERIALS. final polish being applied by a rubber with felt pads working in putty-powder (oxide of tin) for a similar period of time. Straight mouldings, if started by hand as shown in Fig. 24, can be cut by machine on a travelling table under narrow plane irons, but on curves they have to be worked laboriously by chisel and mallet, as must all carving and sculpture. All the various grinding and polishing pro- cesses on such work is also done by hand and exceed- ingly tedious it is sand being first used to remove the tool marks, then pumice-stone, then snake-stone, and finally putty-powder. Columns, however, even up to 16 ft. in length, can be turned and polished by machinery, even the entasis being given in a way which needs little after working to correct ; but breakage sometimes occurs in the machine, entailing heavy loss. Most of the white marble now used for statuary comes from Italy, the Pentellic marble of Greece being no longer worked. Carrara marble is best known, with its sugar-like structure, but the Serverezza marble, which is glassy rather than saccharine in fracture, is almost to be preferred. Of late years a white marble, slightly veined and so not suitable for statuary, has been imported from Norway for use in thin slabs as wall linings and counter tops. Most of the veined marble in common use at present comes from the Pyrenees, whence many colours and most beautiful markings are obtainable, impossible to classify, and only to be selected from samples. The best known coloured Italian marbles are yellow, that from Verona light and pure in tone, and that from Sienna of deeper tint with purple markings. Greece produces a very fine green marble, known as Cippolino, which, however, requires expert cutting if the marking is to be displayed to advantage. The most beautiful marble known, probably, is also green, with crystals of white set in it as if it were a natural mosaic. This is the Verde Antico, which supplied the MARBLE. monolithic columns of Sta. Sophia at Constantinople, as well as most of the decorative marble work of Italy for many centuries. The quarries, which for a long period of time were lost, have recently been discovered near Larissa, in Turkey, and are now being worked by an English com- pany. This marble is often referred to as " porphyry." It is easily distinguished as being a " breccia " of angular fragments of light and dark greens, with pure statuary white, the whole being cemented together with a brighter green, while the snow-white patches usually have their edges tinted off with a delicate fibrous green radiating to the centre of the white. The cement- ing material is also of the same fibrous structure. Another beauti- ful green marble is the Connemara, from Ireland, but it is not obtainable in very large blocks ; and other true Irish marbles are the rich Cork red, the Kilkenny black and white, and the Galway black. Devonshire marble (see PI. II.) lies in a narrow belt which passes from Torquay through Totnes and Ashburton to near Plymouth, avoiding the Moors. Many different colours are obtainable, the tints being as a rule delicate rather than striking, making it suitable for internal wall-linings, chancel floors and steps, and other decorative uses. Purbeck" marble" is really a hard, South of England lime- stone, capable of receiving a good polish, which, however, M.M. F Fig. 25. Appearance of a Polished Specimen of Barton Limestone. 66 BUILDING MATERIALS. it does not retain very well. It is of a deep blue colour, with fossil shells well displayed, and, though little used now, it was empl >y -d largely in the thirteenth and four- teenth centuries for small detached shafts, bases and string mouldings. Somewhat similar stones, though lighter, and sometimes yellowish in colour, are found in Derbyshire, in larger slabs than the Purbeck, rendering them useful for steps, floors and wall linings. Such is the fine-grained Hoptori-Wood stone, which comes out in large blocks and weathers well ; and also the beautiful fossiliferous Barton Limestone (see Fig. 25 and PL III.). The following chemical analysis of the Hopton-Wood limestone was made by Mr. E. W. T. Jones, F.C.S. : Moisture... ... ... ... O'lO per cent. *Lime 55-30 Magnesia ... ... ... 0*45 *Carbonic Acid Gas ... ... 43*60 Oxide of Iron and Alumina ... 0*25 Phosphorus ... ... ... traces only. Sulphur... Siliceous matter ... ... 075 per cent. 100-45 *Equal to Carbonate of Lime ... 98-90 PLATE III. BARTON LIMESTONE. HopTON-VVooD STONE. [To face p. 66. MARBLE. ENGLISH MARBLES. 6 7 Quarry. Nearest Station. Nearest Port. Colour. Remarks. \nglesea Isle of Man Black hudleigh Ohudleigh.G.W. Rly. Teignmouth Dark blue-grey with white Used for chimney pieces. Devonshire. marking Drews- Yeoford.L.S.W. Exeter, I Blue " The marble is burnt for leighton Rly., 7 miles ; Fremington, lime, and is excellent M o r e t on, and Teign- for building purposes G. W. Rly., mouth and road metal. It 7 miles. looks well when used Devonshire. with granite. Ipplepen Stoneycombe Teignmouth, Pink Blocks 1 8 ft. square sent siding. Devon- 8 miles / to London. Used for shire. shafts of columns. National Provincial Bank, Bishopsgate Street. Petit Tor 1 Torre, G. W. Torquay Pink, yellow, Known as Babbicombe Rly. dove, light and marble. Some blocks Devonshire. dark grey consist entirely of fossil corals, and are known Purbeck Swanage, L. & S. W. Rly. Swanage Dark blue or grey as Madrepore marble. It is composed entirely of fossilized shell-fish Dorsetshire. about the size of a pea. It has been largely used in nearly every cathedral in England for columns, and is to be found in many ancient churches for fonts, etc. It occurs in beds from 6 to 9 inches thick. Ramsley Newton Abbot, Torquay Red, grey G. W. Rly. Devonshire. Scarlett Castletown, Castletown Grey Hard and durable. The Manx Northern stone lies in perfect Rly. Isle of Man. layers from 2 in. to 3 ft. in thickness. The famous Castle Rushen was built with stone from this quarry 900 years ago. SCOTCH MARBLES. Tiree Oban, N. British and Caledonian Rly. Hebrides. Scarinish, Tiree White, pink, green, etc. Block for bust of Sir W. de la Becke, Museum of Practical Geology. WELSH MARBLES. Penmon Menai Bridge, Mottled grey For polished and deco- L. & N. W. Rly. rative work ; also in Anglesea. blocks sawn or rough for buildings, etc., and limestone (9875 carb of lime) for fluxing and chemical pur- poses. Britannia Tu- bular Bridge, etc. Depth of bed, 15 ft. F 2 68 BUILDING MATERIALS. IRISH MARBLES. Quarry. Nearest Station. Nearest Port. Colour. Remarks. Ballymore Dunfanaghy Road, Dunfanaghy White and blue ! Polishes well, highly crystalline ; difficult to Donegal. work; chimney- pieces. Clomnacnoise Belmont or Ballinasloe, Dublin. It is carried Blue A good dry limestone for building ; takes a G. S. & W. Rly. King's County. from Shannon Bridge, which splendid polish, with beautiful fossils. is i^ miles from quarry, to Dublin by canal. Firies Castle Island, Tralee Red Solid, sound stone, and G. S. & W. Rly. will stand almost any Kerry. weight ; is easily dressed and takes a very good polish. It can be easily got in almost any size; depth of bed, 20 ft. Kilkenny Kilkenny, Black When dressed the figures G. S.&W.Rly. of shells appear. Kilkenny. Mento Galway, Galway Black Best description of black M. G. W. Rly. marble. Good water Galway. carriage to Galway. There are three beds : the middle is called the "London bed," and exported ; blocks 5 ft. to 10 ft. long and 4 ft. to 5 ft. wide, sawn on the spot into slabs, etc. Tullamore Tullamore, Dublin White, slightly This limestone takes a G. S. & W. Rly. tinged with ; good polish ; makes King's County. blue excellent lime ; is capa- ble of being worked to any shape ; has no " crossway," that is, it works freely to the tools in any direction. Some varieties clouded ; used for polished work, chimney-pieces, etc. Chapter VIII. LIMESTONE. THE method of quarrying limestone necessarily varies considerably, as does the stone itself. Where, like the Keinton stone, it occurs near the surface as a homogeneous stone in thin, well-defined horizontal beds, having good natural joints, little more is needed than to lever it out with crowbars and lift it to the surface, the quarry being worked in floors rather than faces. The subsequent work- ing is equally simple, being mostly done with the hammer, or with mallet and chisel, to produce an approximately fair face, machinery being little resorted to. The detritus can be crushed for road metal or burnt for lime, so that if the quarries were well situated for transport and the lime could be sold at a profit there would be little waste. This not being the case, the waste is considerable. As a contrast to this, the various Bath stones are mined. They occur in deep beds, up to as much as 22 ft. in thick- ness, which rarely outcrop, but have to be reached by long inclined shafts sunk in the hill side. Pillars of hard stone of little value occur at intervals, and these are left to support a natural roof of hard rock, while the bed of free- stone is removed. Between the freestone and the roof, at any rate in the Monk's Park quarry which was visited, there is a thin layer of rubbish, which is first removed with pickaxes, some of which have very long handles, enabling a depth of 5 ft. to be reached. This done, a vertical cut is made down the side, against the hard stone, with a long toothed hand-saw, held horizontally and worked with one hand. A second similar cut is made to form a V groove, wide enough for a man to squeeze into, the stone between ;o BUILDING MATERIALS. the two cuts having to be chipped out as waste if, as is usual, it will not come out solid. Then a man standing in the groove saws downwards at the back of the space picked out, and finally a third saw-cut separates the block, all these cuts being taken down to a natural joint. A roughly rectangular block is thus produced, almost free from waste, and this can be levered out and lifted by cranes on to trucks run- ning on trolly lines through the mines to the foot of the shafts. Bath stone, at least that from quarries Fig. 26. Drag. owned by the Bath Stone firms, which is dislodged during the winter months, is kept in .the underground workings till the spring, so as not to expose it to frost while the quarry sap is in it. When brought to the surface every block is tapped all over with a pebble. If it gives off a ringing sound, the block is a good one, but if the sound be dull a vent is indicated, and its position is then located and it is cut out before the block is sold. There is scarcely any waste from a Bath stone quarry, especially as the " venty " blocks and the smaller pieces are squared and sold as holy-stones for clean- ing ships' decks. In the subsequent working of limestones, the circular, rocking, and hand saws are all used, with or without teeth, according to the hardness of the particular stone, sand washed in with water replacing the teeth when the toothless saw is used. Machinery is not often employed, at any rate for the oolites and dolomites which are soft enough to be profitably worked by hand, except in large works, where Fig. 27. Point. Fig. 28. Boaster. LIMESTONE. 7 1 a circular rotating rubbing bed of iron, on which the stone rests in sand and water, is used to remove saw marks and produce a plane surface. In smaller works, rubbing is done with a piece of sandstone by hand ; or else a plane face, or nearly so, is produced by scraping the surface with a thin metal comb known as a drag (see Fig. 26). Sinking, moulding, grooving, etc., are all performed with chisels, varying from the point to the boaster (Figs. 27 and 28), the latter having an edge 2 ins. wide or more, intermediate sizes alone being known as chisels. These names are, however, liable to local variation. In many parts of the country there exist groups of small limestone quarries, little known beyond their own locality, but producing stone of excellent quality. Of these, the Rutland group may be taken as an example, comprising the Barnack, Ketton, and Casterton stones, whether "free" or " rag " (the rag-stones being shelly conglomerates), of which the Barnack Rag, of which many cathedrals and churches were built, is no longer procurable. The Casterton quarries, near Stamford, were inspected, and may be described as being typical of many other small quarries. They are open workings of no great depth, overlaid with fireclay, which is removed for burning into adamantine clinker, beneath which is a thin layer of useless stone above two beds of good freestone, composed of rounded grains cemented together by carbonate of lime, each with a maximum depth of 3 ft. 6 ins. When first quarried the stone is soft to work, and friable, but it acquires a hard surface on exposure, and weathers well, in a country district at any rate. The bedding is difficult to detect, but im- material, as the stone may be laid equally well in any direction a very useful quality for undercut moulding and carving. The colour varies from white through quiet shades of pink and burf, and the supply is limited to some 200,000 cubic feet per annum, the largest block obtainable containing about 80 cubic feet. The following analyses of true limestones, dolomites, and BUILDING MATERIALS. siliceous dolomites are instructive, bringing into strong contrast the distinguishing characteristics, chemically speaking, of these stones : Typical Stones. Carbonate of Lime. Carbonate of Magnesia. Oxide ot Iron and Alumina. , b oi Water. Bitumen. LIMESTONES. Weldon ... Q . - 0-89 o - o8 r Barnack QV4 r's i -3 I -c trace Chilmark JU T 1 79-0 -J 37 2-0 10-4 * O 4 -2 trace Ham Hill 79'3 8*3 trace Mansfield 93 '59 2-90 0-80 2'0 2- 7 I trace Bath Box 94 '5 2 250 I '20 I 7 8 trace Portland 95-16 I -20 0-50 I '20 1-94 trace Ketton 92-17 4-10 0*90 trace Kentish Rag (homogeneous)... 92*6 trace 7'OO 0-4 DOLOMITES. Mansfield Woodhouse (Yellow) 51-65 42 - 6o 370 2-5 ... Bolsover Moor 40-2 i "8 3-6 3 '3 trace Roach Abbey ... 57 '5 39'4 0-7 0-8 1-6 ... Huddlestone 54 >:[ 9 4 I- 37 0-30 2 '53 1-61 Park Moor 557 41-6 0-4 2-3 ... Newthorpe 55 '4 43 '53 0-36 071 trace SILICEOUS DOLOMITES. White Mansfield 26-50 17-98 1-32 51-40 2-08 Red Mansfield 26-50 i6'io 3-20 49-40 4-80 The three stones known as Mansfield, vary much both in colour and composition, while in other instances the stone from different beds of the same quarry are entirely distinct. It consequently happens that in any classification of limestones, the same name will sometimes occur in two different lists. There are so many varieties of limestone that they have to be distinguished in some way. Custom has based a nomenclature for them, rather irregularly, on their physical condition, mineral contents, and strati- graphical relation to other rocks, and sometimes on the three combined. Limestone can be crystalline or amorphous, compact or fissile ; it may be pisolitic, oolitic, concretionary, LIMESTONE. 73 or shelly ; there are argillaceous, siliceous, bituminous, and dolomitic varieties ; others may be brecciate or coralline, whilst there is no end to the names they derive from their relation to other rocks in the sedimentary strata it will be sufficient to mention the Silurian, Devonian, Carboni- ferous, Lias, and Tertiary limestones as examples of this class of names. Again, limestones are called after the localities in which they are found : these are Woolhope, Wenlock, Derbyshire, Bath, Portland, Purbeck, and Bern- bridge limestone, these local names being in some cases compounded with others, as for instance Bath oolite, Portland oolite, Wenlock concretionary, etc. 74 BUILDING MATERIALS. |l |jiffilliE31j92u|A rries owned by obtained from t as the "Great" group. Of medi r sills, plinths, st tone from the qu Stone Co. are ation known wer Oolitic " ; is suitable f st he st Bath form " Lo grain cour good a *- c .5? o -is LIMESTONE. used principally for esiastical work, tracery, gely used in isth, i6th, uries for church work ; to be seen at present reservation known as ; Ely Cathedral, build- A i! -4-1 ^ ?S .aS-a-Si L ^ 0) 1 2 | ^^s-s&gg^ "CdJOOBP-.C- "oJ "*" ^~ 1 4) Dmpact, one. 3 rt M rt W rt S gS-b8a'S ^-i|C- s |.s Sll'Sllla 5 &o *. SS Hivg aqi asuduioo BUILDING MATERIALS. "3 5 12 g *s ^0 c &J lj O, oo-O J3 T) >, 13 3J S '55 c *S ^- W -3^ | Sg ^^TJ -3 1 :*- 8 -s | 1 111 1 ^ W D (j Monumental and < freely ; can be obt 111 If III | 'c ^^ D /-v j S C i S^ 2* OD rt iT ^ ^ ^D*"^ ^ rr -**1 a 3 Xi y S^^-Eo-l^oW g^ 3 ^ J3-2 S ii 0X1 j &-OQ 0.0 o-g 2 erf 2 8 ; s ; s a : eg w H C/D W 2 hH : : ti -n2. 6(3 "^ . T > ^Sr7.c uq A A ill "5* J J d d s 00 6 o : S M * . : o : : - tO N * S 0) . m x< C ill Si J 5= ^^ s s g - i-a Is 1- 1 |s II cj-o ^ 1 I fa 80 BUILDING MATERIALS. 60 c " S *H . III 1| 1s|l >-) tj CX O 3 gt j? ^^ tfj2 c 13 u% Ij"^ ss'l S " rt "I G Hi al Bf-l Remarks. d lime, road meta for lime burning ; Used for suspensi rushing resistance ; difficult to work, r Killarney, some Muckross Abbey. o ~ s o ..1 II "$ -, u > C a M * - o -1 > 13 ^ ^ v C i 1 -11 & -S f 8 . W 14 : : : : : : : : ; c'c j c c/) 1180 W % UK 3 i 5 i 1 i 8 1 Cork and Tralee o ! w> T5 g OT _S J -s o u ' n c ||p|j| . J? ^ ^> J^ c ^ c'5^ |*s|>j j|L:ife tj^d-Cfrfe iil^j- 1 a^'i 1 rt^j IH g^ C j.2 rtJ3<# ^ h d d 6 -S _ o 02 d S o S < Colour. Jlil 1 111 I 1 1 I 1 1-aR |" a |1 5 s i f & > 3 3 J )STONES st* IS I s sJi- 1* R ; & ; fe ; R ro M en * so H 3 C/D i*. J3 - W^Q ._ IV io M cnpTt-!Oo o o o o\ : MM m D CZ ! ! s ! & 1 L s ^ol yJlMlJ r i m SANDSTONES. *-5 4&1 S.2 S oj'O JQ tc 2 S 54! llMl will! 'O ^ 8J 5 2 C rQ 13^0 *?rf" JS ^ 51 3 fc. rt -Q u c S & ^ 3 r u ( ^- (n/^ OCJ3- ^ _a; to p" '^ S rt d 2 U : WT: Sis U3 *~* 01 s=| O J3 [" llll O D J il a; 2"O 03 Pi If! ill fid.*?] M -2^ rtW s 3>2 i K 55 O ! II- I |lii o ||8 lipPl^ ! ; o o o o o pp 1 00^ ^>^>^>^> ^> o^o > o^-^ :> o> -o I pq 1 J ffi G 1 s [,.:::. rTTTT, sJuarries Fishponds E(2ffi^c ^S Eos ^ ^ SHKOXS NVHQ jo XSHHOJ aq; asijduioo asaqx BUILDING MATERIALS. &OK< g O & c H > K ~ 2 S 2 3 3 111 g $ ill E D *n ai CJ3 S C cS S 3 8 1 13 .^3 S fc" - - J' -S.O r - r^i _8 . ' ^ -5* -o^. 1111 o.>^ SANDSTONES. 91 C si-a J> S M" 3 <0 2n "o G s. u"S - 3 8 S-o c aj i* 01 landings and ste & "2 "u M > :hfield Cathedral ; and sundry ch and sawn slabs. jd for Liverpool a s - i i- ^ c o 'S o a rt DS, landings, etc. shows laminatiol and solid. S "i 'rt ^ wo uc flJi & .*. u good stone f< eatheral Ra ^ -i C U) 1 2 y S| II /) o bo C 'S, 8 1 ^Sa iS S-Sg ^ 5 > y M< >, T oa TJ 3 > aj-g ^-^ e 8 r^c* ^fA - > C _j > en - _42 ^ ^f r W ; ^ . ar^,- c " - ^aT^ 55 ^5 O > .8 J5J J . K o^- K 1 ^ ^5 5 3>n' . 2 'S''*' "n "rt" K ^ j 05 rt 3 o -2 P " S 00 -^ . 0^ 2 ^ "^ ^^ ^ " < oTW 2 r W o y-D .j2 - o y,5'Q3^ ) 'c CO - ^ ^3 "^ rt o "* *u is ss JUi -c a> -fc' cflfc^- jSh4 e ^_ K H " -^ QJ ^6 ^ ft' a; 92 BUILDING MATERIALS. SH a ii ftu .T *J > 4J G ill! ug&d ^3o2 |s 2 w "w ^ w 3 2 II Hfn " 2 r s s p j>> .S re o 1 CS J" ~ a; ..XJ J3 rt"^ o^ c8 CQ O "S 'S *v o^ 00 Cft CO O % vS* i i* HH 11-3" all SANDSTONES. oJ S||||l|| | | 1411 11 rt g w 2 oT y itln^-d * 13 G rt S||a fi 8g ^ii^fll |l a | g4a>o 3^1 Sg i 8 ||l| *| | M- ac OT3 0) g-^^ -J2 CcnoaJu^g^ ^ J? B '3 sjjg pi'l lal 53 sed in New Tec Stobhill Hospital, ll|l|||jj|l iS?g**ill&Ii I s|if5"||'s|'s| ji h ^ W) cx.S 11 a" 3 ll S rt ^fldtf! jilll ocks, Cathedral T ortrose; Invernes well Court ; also for D o < D '3 1 '> >. n _. J " - ^ rt y S >* 10 Q Cs 10 J . CO Th O , . 1 ' 1 1 1 L t d) I L -a > *-i ^ c^> M >> c"* x r^ -^ CM j^ ^ -2 0^ c -5 6C ^ 'S ~ R *n "* ^ f^rv* rt b-^ c .ti c o c T3 ^~* rt r i ^ ^.3 " g||| il 1,1 t/5 T3 !* K t/3 C) Si C ^ . 3 tj &.fq ^ j2 |J|1-J] ~" (j]i> 2^ rt ^ c "Sj^i ^ . ,_} = ! r Q*ig'w> J o u Sc3 O S S ^ Q C c 2 Q H | 1 S o o | rn O ^ M no M fc 5 S c S ^ g C m *5 y^V C -^ I"" a a S D 'bjb'^ ^ *.n " o "5 > C O v> Q Q o * ffl ^ BUILLING MATERIALS. 1 ^ III! 60 OJ D. c '"ID ji t 5 e S c --5 i I J:|j - M * 8 i -a "^2 fS "* . O < '"Q .* o o 1 ^8 S 2 3 -^^ H M _ "' , S rt Cd rt 1 d stone for stai Dundee Water 60 S Jo (U 1 c tiers very we! ing ; very grez ig nearly twice 2e times that o s schist. principally fo principally fc is also suit extensively in ledral, Observ ill 11 lll^l P > 3 r{ o . 00 S 3. S S 1 L 2 1 " if cS 43 52 rt i2 S J u o Q c3 fc fc fc fc 5^. H 60 ""a" $C rt ^ ^ ^'c II u hC U I s a c Arbroath Thurso Arbroath or Dundee Dundee III en N i : 8 i 3 a Pyotdykes 4) _rt C/5 13 U II S S 11 in SANDSTONES. 95 Blocks. S C< OJ bi c 'O .2 B C C rt J5 u very hard. Landings, steps, channels, flags ; very hard. Works well; wears well. All dimensions obtainable. Used for setts. Used for paving blocks for docks and bridge works. Laminated blocks. e "3 PU 2 ll v'B ^3 2 u : : : 10 10 OO Z S M . .00. Antrim Clare 0) U r2 O c O rt 1 111 la f 3 ^ w || ^ 10 % 10 n en N O O M M M I O . i ~ rt barna Cronogort i-S2 E lll ^^0^(2 $" Chapter X. BITUMEN AND ASPHALT. BITUMEN, or natural pitch, though limited for its com- mercial supply to a few districts, is nevertheless by no means of local or limited occurrence. Its origin is somewhat obscure, but it is probably the result of oxidation of the unsaturated hydrocarbons in petroleum. Its specific gravity is I '0924 and it is partially soluble in alcohol and more completely soluble in carbon bi-sulphide, petroleum spirit, chloroform, oil of turpentine, coal-tar, benzol and naphtha. The great reservoir for natural bitumen, commercially, is the Pitch Lake of Trinidad, which seems to be inex- haustible, though it is only about 100 acres in extent. Much of it is used for laying pavements, for damp-coursing, cellar or basement flooring, flat-roofing, bridge-building (both for water-proofing and traffic), and to stop vibration in engine foundations, culverts, tunnels and subways. Electricians find it the best and most effective insulator known. It is elastic (in the popular sense), and is used in various circum- stances where rigid cements fail, and wherever allowance has to be made for expansion and contraction. It is also employed in the manufacture of marine glue, and in its most highly refined state is made into wafers for fastening the tips on billiard cues. All the well-known asphalt firms employ bitumen for purposes for which their own rock asphalt is not so well suited, sometimes alone and sometimes mixed with asphalt rock or grit. Besides the Trinidad lake, there is a similar lake in Texas, at present not very accessible, while bitumen is BITUMEN AND ASPHALT. 97 also found in great abundance on the shores of the Dead Sea in Judea, in Cuba, and in New Grenada. Bitumen, according to Boussingault, on analysis is found to be made up as follows : Carbon ... ... ... ... ... ... 85 Hydrogen ... ... ... ... ... 12 Oxygen 3 IOO COMPOSITION OF TRINIDAD PITCH. Volatile organic matter ... ... ... 7675 Non-volatile organic matter ... ... 1777 Ash 5-48 CHEMICAL COMPOSITION OF BITUMEN OF JUDEA. Carbon 77*84 Hydrogen ... ... ... ... ... 8*93 Oxygen H'54 Nitrogen ... ... ... "* ... 170 Sulphur 3*00 Of late years bituminous sheets have been made (by Messrs. Callender & Co.), by running refined bitumen on to paper bagging, which are capable of being bent in any direction without cracking and yet can be perfectly joined and are impervious to moisture. This material is now very largely used as a damp-course, and also for lining ponds and tanks, for covering arches, and between the inner and outer rings of brick sewers. It is made in various thicknesses, from ^ in. upwards. A modification of this, made by Messrs. Hofler & Co., consists of two layers of bitumen sandwiching a thin sheet of " laminated lead " between them. It is acid proof, and can be cut with a knife and bent in any direction ; and is M.M. H 98 BUILDING MATERIALS. made in 6 ft. lengths and all standard breadths, from J in. thick upwards. An artificial rock asphalt is much used for street paving in the United States, consisting of Trinidad bitumen ... ... ... ... 12*38 Organic matter 0-65 Mineral matter, sand, and other aggregate 86*97 lOO'OO This, it is claimed, is better than the natural rock, as the addition of the sand makes it less slippery. ROCK ASPHALT, used for carriage-ways in Europe, is a natural limestone impregnated with natural bitumen. The rock when quarried is of a chocolate colour, fine in grain, thoroughly and evenly impregnated with bitumen, varying from 6 per cent, of bitumen and 94 per cent, of pure lime- stone to 14 per cent, of bitumen and 86 per cent, of limestone. This is found principally in the Val de Travers (Switzer- land), Laubsann (Alsace), Seysell (Ain, France), Montrotier Seyssel (Haute Savoie, France), Maestu (Spain), Ragusa (Sicily), and Limmer (Hanover) ; but the name of the com- pany supplying it is not always much guide as to its place of origin, the Limmer Co., for instance, having quarries at Ragusa and at Montrotier Seyssel as well as at Limmer ; while on the other hand, unless the name of a well-known company be specified explicitly, inferior asphalt from the same district, legally and correctly, say, Seyssel or Limmer asphalt, may be supplied and no redress be possible. The following information, taken from a paper by Mr. Allan Greenwell, explains the matter very fully : " The method of obtaining this bituminous limestone or rock asphalt is by mining, and the seams are of varying thicknesses from very narrow streaks to 6 ft. and 10 ft. deep. BITUMEN AND ASPHALT. 99 It is found between two layers of white hard limestone either totally unimpregnated with bitumen or else with mere traces of it, which have the appearance of thin smoke or the faint stains in white marble. Sometimes, however, layers of sand and marl are found which have to be propped or held up by rubble. The workings of the Fonticelle Mine in Italy, the property of the Neuchatel Asphalt Co., Limited, are subterranean ; from this mine comes the famous Val de Travers brand of asphalt. COMPOSITION OF ROCK ASPHALTS (DURANT CLAYE). Val de Travers (Switz.). Laubsann (Alsace). Seyssel (Ain, France). Maestu (Spain). Ragusa (Sicily). Water and volatile matter 0'35 3 '4 o'4O 0*40 0-8o Bituminous matter 870 II-QO 9'io 8-80 8-85 Sulphur (free or in organic combn.) 0-o8 4*99 ... trace Iron pyrites O'2I 4 '44 ... Alumina and iron oxide O*3O 1-25 0*05 435 0*90 Magnesia ... O'lO 0-15 0-05 3-85 0-45 Lime 49*5 38-90 50-50 57 49-00 Carbonic acid 40-16 31-92 39'8o 8-15 39-40 Combined silica . ... ii-35 Sand 0-60 3-05 O'lO 57'40 o'6o lOO'OO lOO'OO lOO'OO lOO'OO lOO'OO " At the company's works the rock is treated so as to be formed into COMPRESSED ASPHALT (or COMPRIME) and MASTIC, the two forms in which it is used for the formation of roadways and pavements. For the purposes of the manu- facture of the compressed asphalt the rock is received from the mines in blocks of irregular shape, which are first sub- jected to a crushing process in a steam crusher and broken to the size of walnuts. The material is then passed on to a machine called a disintegrator, which reduces it to powder. The powder issuing from the disintegrator is received on an inclined screen which allows the fine powder to drop through, while any grains too large for the meshes are H 2 100 BUILDING MATERIALS. carried over and conveyed back to the disintegrator to be re-ground. The powder thus obtained is deposited in a covered shed ; when required for use it is heated in slowly- rotating cylinders (very much like a large coffee roaster) over a fire of wood or coal until it reaches the right temperature for laying ; this process takes two or three hours. The object of heating is twofold : (i) to evaporate moisture, (2) to bring the bitumen into such a condition that it may exert the maximum of binding power when subjected to compression by the rammers. If any portion is overheated the bitumen is fused ; if underheated, the asphalt will not be thoroughly consolidated ; hence the utmost care is needed in regulating the temperature, which varies for different kinds of asphalt, since some asphalts will bear a greater heat than others without deteriorating. The extreme limits are, say, 250 to 300 degrees F. " The mastic, which is supplied in blocks, known as Val de Traversor other mastic, is manufactured by pulverising the natural rock in exactly the same manner as for the com- pressed asphalt ; it is then heated in boilers, and from 5 to 10 per cent, of refined bitumen is added, and the whole mass reduced to a mastic or thick liquid state. This is run into moulds, and when cool again consolidates into a hard elastic block, which is used in varying proportions with grit and refined bitumen for laying pavements. " In the laying of roadways with the comprime the method adopted is as follows : The roadway is formed with a bed of good Portland cement concrete, and evenly finished off to the precise contour of the roadway required. When this concrete has become thoroughly set, and become hard and dry, the powder, which has been previously cooked, is brought to the site whilst hot ; and as asphalt in bulk retains the heat undiminished for several hours it can be easily conveyed in properly constructed carts from the cookers to the site, where it is spread and raked over to a uniform thickness, usually two-fifths to three-fifths more than the depth of asphalt prescribed for the finished road. BITUMEN AND ASPHALT. IOI The compression of the powder thus spread is effected by men with iron rammers, which have been previously heated in a fire to about the same temperature as the asphalt powder. After this has been accomplished and the mass reduced down to the finished thickness, the final smoothing is done by an iron instrument of curved form heated to an extent sufficient to soften the bitumen at the surface of the asphalt, and thus gives a fine finish and a glassy appearance to the whole. The work is then complete, and as soon as it is cooled to the temperature of the atmosphere the road can be thrown open to traffic. It can easily be seen that the whole operation of laying is one that calls for much special skill and practical dexterity for its efficient perform- ance. Roadways thus formed are very good, being nearly noiseless, cleanly, and impermeable to moisture. They also diminish to the utmost the force required for traction, and are durable ; but constant traffic is necessary to keep the asphalt compacted, and it is consequently unsuited in this form for roofs, gutters, and many other building purposes. " In the laying of the mastic quite a different process is required. The mastic cakes, which are hexagonal, are manufactured at the works at Travers, and sent in this form to the site to be covered. These blocks are broken into pieces as big as a man's fist, ready to be thrown when required into the heating apparatus in which the mastic is cooked. This apparatus, commonly called a street pot, consists of two parts. There is first the mantle, a round envelope of sheet iron furnished with a chimney and a small door opposite it for firing, the upper and lower rims being strengthened with iron bands ; and this frame forms the furnace in which the fire is kindled. The second part is the kettle proper, a round pot of strong iron with a steel bottom, destined to receive the mastic ; this pot hangs on the upper rim of the mantle by the flange, descending into the furnace for a little more than half its depth, but high enough to allow the flames of the fire to play all round it. The best fuel for heating the whole surface of the pot, thus IO2 BUILDING MATERIALS. giving uniformity to the melting, is peat or hardwood. Sometimes coke is used, but it should be avoided if possible, as it is apt to burn the bottom of the pot and thus tends also to burn the bottom mastic. " Before lighting the fire a small piece of bitumen (half the required proportion) should be placed in the bottom of the pot, and, as soon as the fire has been lighted, the broken pieces of mastic placed on the top of it until the pot is a little more than half full ; the cover should then be put over the top and the mastic allowed to stand for twenty minutes to half an hour, the fire being well kept up. During this time the materials should be watched, and as soon as the mastic commences to melt the cover should be removed and the mass stirred with a long stirrer. "This stirring process finished, the remainder of the mastic should be put in, followed by half the remainder of the bitumen, filling the kettle to the top ; again the cover should be put on and a steady fire kept up. When the mastic round the edges gives signs of melting it should be stirred constantly ; when the whole mass has become pasty and soft, half the required proportion of fine sharp grit should be added with the remainder of the bitumen, spreading the grit evenly over the top. " The proportion of materials generally used in cooking the mastic are as follows : Twelve blocks of mastic, say ... ... 640 Ibs. Refined bitumen... ... ... ... 39 Sharp grit (free from loam) ... ... 335 " The proportion of grit should be varied according to the aspect of the street where the mastic has to be laid. Where it is exposed to the heat of the sun for any considerable portion of the day more grit and less bitumen should be used in mixing. It is an indication that the material is cooked when jets of blue-coloured smoke ascend from the surface ; another and most frequent test is that of thrusting a stick into the mass, and if it comes out clean and the BITUMEN AND ASPHALT. 103 mastic does not adhere to it, the material may be considered cooked. This cooking process takes from four to six hours. " The material being ready for spreading, the mastic is taken out of the pot and put into a wooden pail, which is passed to the man who is termed the spreader, and he empties the contents with a sweeping motion across the path. He then spreads the material with a wooden float to the required thickness. (For illustrations of the utensils Fig. 30. Fig. 32. see Figs. 29, 30, 31, and 32.) It is essential in putting down this material that the second pailful should overlap the first whilst hot, and so on with each successive layer. If the surface on which the mastic is laid is at all damp, blisters will form in the mastic, and it is the business of the man who follows the spreader to prick them with a sharp piece of wood and rub the holes made until the blisters disappear- Sometimes he will also come across a burnt piece of mastic (caused by imperfect or insufficient stirring) ; this must be thrown out at once and hot mastic rubbed into the hole." IO4 BUILDING MATERIALS. It will be again noted that in this mastic a great deal depends upon the method of preparation and laying and the quality of the bitumen used, as any omission of care and skill will render the asphalt when laid inferior and not able to fulfil its purpose. COAL-TAR PITCH is the residue of coal-tar after the separation of naphthas, phenols, creosote and anthracene oils. It amounts to about two-thirds the original weight of the coal-tar before distillation. Its character varies with (i) temperature of distillation ; (2) quality of coal distilled. CHEMICAL COMPOSITION OF COAL-TAR PITCH. Carbon ... ... ... ... ... 75*32 Hydrogen ... ... ... ... ... 8*19 Oxygen ... ... ... ... ... 16*06 Ash , 0*43 Sulphur and Nitrogen variable traces. Coal-tar pitch may be either soft, hard or medium, according to quality of coal. The hardness depends greatly on the perfection to which distillation has been carried, and it is generally necessary to thin it down before use by addition of various tar oils. Only the heavy oils should be used, or the pitch will lose much of its binding or cementing power. It is obvious, therefore, that artificial pitch is not to be relied upon to the same extent as the natural product. It is, however, largely used for foot pavements to withstand moderate traffic, as the matrix of a kind of concrete, having coarse grit for an aggregate, and generally sprinkled over the surface either with marble chippings or crushed shells, the whole being laid hot and rolled with light rollers. This is commonly known as " tar-paving," though it is pitch, and not tar, which is used. PLATE IV. MERSTHAM LIME WORKS. General View of Quarry. Front and Back View of Kilns. [To face p. 105. Chapter XL LIME AND LIME-BURNING SOME MINOR LIME PRODUCTS : WHITEWASH, WHITING, PUTTY. LlME, or quicklime, is a more or less impure oxide of calcium (CaO) obtained by heating limestone, chalk, shells, coral, or any other substance composed almost entirely of calcium carbonate (CaCO 3 ) in such a position, generally in the open air, that the carbonic acid gas (CO 2 ) and any moisture which it contains are given off and escape. This operation is known as burning or calcining, the chemical changes, neglecting those due to the presence of impurities, being represented by the equation CaCo 3 + heat = CaO + CO 2 . The process of calcining is accomplished in kilns, of which there are two principal varieties. Pure chalk lime whose colour it is important to preserve is burnt in inter- mittent flare kilns (see Fig. 33) in such a way that only the flame from the furnace reaches the stone, which is piled up above the fuel over rough limestone arches ; but much more frequently tall, inverted, cone-shaped draw- kilns (see Fig. 34) are used, the fuel (coal) and stone being piled up in them in alternate layers and worked to a roughly formed cone on top. Such a kiln is generally built on a hillside, so that it can be filled from the top (which is quite open) and emptied from the draw-hole at the bottom when burnt through, the average time taken in burning being about a week. When the fire has burnt out and the lime is cool enough for handling, the furnace bars are removed and the contents of the kiln fall down to io6 BUILDING MATERIALS. the draw-hole, whence they are at once carried in barrows into a shed to be either sold in lump or ground to powder. The lime generally used for mortar in the London district SECTION. SHCO OBAW MOLLS PLAN. Fig. 33. Intermittent Flare Kilns. is the grey stone lime of the Surrey hills- known as Dorking, Merstham, or Hailing Lime, and called " grey " from the colour of the stone from which it is burnt, as after calcination it turns yellow. It is a mildly hydraulic lime, PLATE V. General View. Top View. LIME QUARRY AND DRAW-KILN NEAR FOLKESTONE. [To face p. 107. LIME AND LIME-BURNING. 107 suitable for rapid work, which acquires a moderate degree of hardness in course of time. At the Merstham works of Mr. Peters, the grey stone underlies the white chalk lime, and both are burnt in flare kilns separately. The kilns are filled from a high level door at the back on the hillside, which is closed with rough stones as soon as they are full, and firing takes place from a low level in front. The fires are at first kept low so as not to crack the arches of raw stone directly over them ; but as these stones become hot more small coal is shovelled on, and the fires ^/ N \ kept burning briskly till the whole kilnful is well burnt, when they are al- lowed to cool gradually. The whole process occupies about seventy-five hours. The burnt lime is removed from low-level draw-holes at the side, and at once filled into trucks for re- moval, or ground. Well- burnt lumps should ring well When tapped or hit Fig. 34- Inverted Cone Shaped together ; and those of Draw-Kiln, "stone lime" should be of a bright canary colour, the chalk lime remaining white. Pure quicklime has a great affinity for water, and is extremely caustic, rapidly burning up and entirely destroy- ing any organic matter with which it may come in contact. It is consequently much used as a disinfectant, being freely sprinkled over or dug into the contents of old cesspools or midden pits if such are met with in building operations. If water be added to quicklime it " slakes " that is, it absorbs the water with effervescence, giving out heat, and, if in lump form, tumbles to a fine powder. The caustic properties have been lost and the substance converted into DRAW-HOLE. IOS BUILDING MATERIALS. hydrate of lime (Ca(HO) 2 ), generally known as "slaked lime," as represented by the equation CaO + H 2 = Ca(HO) 2 . Pure slaked lime, known as Rich Lime, has very little strength, and is mostly useful for whitewash and as a base for distemper. It will harden on the surface in course of time by absorbing CO 2 from the air, but if used in bulk or as mortar will remain soft underneath the hardened skin, and it has no cementing value. If the lime contain sand only, no improvement is effected other than would be obtained by the addition of sand. It is rendered more pervious to air, so that the hard skin is deeper. Such a lime is known as a Poor Lime, and is rarely burnt. Other impurities, however, notably clay and to a lesser extent magnesia (MgO) and oxide of iron (Fe 2 O 3 ), affect lime most advantageously by their presence. They reduce the slaking action, rendering it slower at the same time ; the extent to which the impurities are present being well indicated in this way. They also, according to the extent to which they are present, confer upon the lime the property of setting that is, of contemporaneously hardening and coagulating, cementing together substances with which it is in proximity. This action, especially in the less pure varieties, seems to be cumulative, increasing slowly for a very long and at present undetermined period of time, and in such cases is better displayed under water than in air. Limes which show these characteristics are called Hydraulic Limes either " Feebly," " Moderately," or " Eminently," according to the degree to which they appear. As a general rule limes burnt from chalk (known as CHALK LIMES) are only feebly hydraulic, and are suitable for plaster work only; those from ordinary limestone (known as STONE LlMES) are moderately hydraulic ; and those from stones of the lias formation (known as LlAS LIMES) are eminently hydraulic. There are "blue" and "white" lias limes, but LIME AND LIME-BURNING. 109 the terms refer to the colour of the stone from which they are burnt, and not to that of the resulting lime. It is to be noted, however, that the fact that a manu- facturer calls his lime a Lias Lime need, according to a recent legal decision, be no guarantee that it is produced from stone from the lias formation, this fact having to be specifically mentioned if such lime is desired. ANALYSES OF TYPICAL STONE AND LIAS LIMES. Castle Bytham Lime. Harbury Lime ( Warwick- shire}. (Stone lime, moderately (Lias lime, eminently hydraulic.) hydraulic.) SiO 2 14-00 SiO 2 17-53 Fe 2 O 3 + Al 2 O 3 ... 4-25 Fe 2 O 3 2-87 A1 2 O 3 6-83 CaO 77-00 CaO 65-84 MgO 1-25 MgO roo CO 2 0-90 Water and loss . . . 2'6o SO 3 1-36 H 2 O + CO 2 ... 3-85 Insol. matter ... 0*50 lOO'OO 99-78 ANALYSES OF MERSTHAM LIME. Grey Stone Lime ( Yellow). Lime Magnesia ... Oxide of iron and alumina ... Potash and soda ... Insoluble 2 silica ... Combined** water . 80*24 0*50 4-60 1-25 11-40 2'OI lOO'OO Chalk Lime ( White). Lime Magnesia ... Oxide of iron alumina ... Potash and soda Insoluble 2 silica and 91-22 1-50 0-80 0-85 r6o Combined 3 water ... 4*03 1 00 '00 HO BUILDING MATERIALS. When ground, blue lias lime averages eleven 3-bushel sacks to the ton (a striked bushel filled from a hopper averaging about 68 Ibs.). It will be found that two sacks of ground blue lias lime with the addition of sand (in proportion I to 2j) will in the dry state measure roughly one cubic yard, and that one sack of lime with the addition of sand and ballast (in proportion i to 6) will, before water is added, measure about one cubic yard. Ground lime in bags should be kept in a dry place, and if not used within a short time (especially in damp or warm weather) the lime should be shot (under cover) to prevent its bursting the sacks. Briquettes of the Harbury lime and sand have been tested by the owners, Messrs. Greaves, Bull, and Lakin, Limited, under the conditions usual when testing Portland cement, and have given, so far as they have gone, the following results with tolerable uniformity : Broke under 6 parts of sand to i of lime, after ) ,, . , . . . h 3O Ibs. per sq. inch. 2 weeks immersion in water. J 6 parts of sand to i of lime, after ) 52 weeks immersion in water. } I2 lbs " P er s * inch " 3 parts of sand to i of lime, after ) 52 weeks immersion in water. } '^ lbs - P er sc l- lnch - Lime which commences to set on the addition of water, without any appreciable slaking action first taking place, is known as a cement. Stones which burn naturally to cements are to be found to a large extent in some parts of the country, notably as rounded lumps of chalk which have been embedded for long periods in beds of clay, from which the once well-known Roman cement was made ; but the product was so far inferior to the little less costly Portland cement, the process of manufacture of which will be explained in a later chapter, that it is scarcely, if ever, made now. LIME AND LIME-BURNING. Ill The moderately and eminently hydraulic limes may be used in the ground-powder form hot, without slaking, and in any case should be used within a few days of mixing and before material setting commences ; but lump lime and the purer limes must always be slaked. Messrs. Greaves, Bull, and Lakin issue the following directions with regard to slaking their lias lime : Care should be taken in slaking lump lime, and it is recommended that it be first broken into small pieces, then evenly sprinkled with water (preferably through the rose of a watering-can) and covered quickly with sand. It should be left in this state for at least twenty-four hours before being used. Any unslaked pieces may be put into the middle of the next heap to be slaked. No water should on any account be added after slaking has begun. It will be found that the proper quantity of water to be used in slaking is about a gallon and a half to every bushel of lump lime. Only so much lime should be slaked at one time as can be worked off, say, within a week or ten days. SELENITIC LIME is made by this same firm by calcining the lias rock from picked beds, which burn to a quick- setting natural cement, and grinding in raw gypsum with the calcined product, thus slowing down the setting power to within reasonable limits without any liability to slake. The resulting product will carry a large proportion of sand without serious loss of strength. MINOR LIME PRODUCTS. WHITEWASH is a mixture of white quicklime and water. Any lime can be used so far as its efficacy is concerned, but where, as in the case of lias, the lime is slightly tinted, the whiter lumps are picked out for conversion into white- wash. The lime should be mixed up while " hot " with 112 BUILDING MATERIALS. plenty of water, and applied at once with a large brush to the surface to be coated. The process, known as lime- whiting) is exceedingly inexpensive, and is almost universally employed where, for sanitary reasons, frequent re-application is desirable. Whitewash is by no means durable, as it rubs off easily, is washed away by rain, and does not adhere well to smooth surfaces. Constant renewal is therefore necessary, and it should not be used at all in exposed situations in its pure state. A moderately permanent whitewash for external use can, however, be made by thoroughly slaking lime in boiling water and adding sulphate of zinc and common salt, the proportions being i bushel of lime, 4 Ibs. zinc sulphate, and 2 Ibs. salt, with enough water first to slake the lime and then to dissolve it. WHITING is a name for powdered chalk which has not been calcined. To prepare it for use, 6 Ibs. of this powder is covered with v/ater for six hours, when it is mixed with I Ib. of double size and left in a cool place to become like jelly, when it is ready to be diluted with water and used. It is commonly applied to plaster ceilings where better work than that obtained by lime-whiting is desired, the process being known as " whitening." It will not stand the weather. Thus to limewhite a ceiling is to coat it with whitewash, only one coat being possible ; while to whiten a ceiling is to coat it with whiting and size, several coats being possible and two being usual. PUTTY is made by mixing dried and finely-ground whiting, free from grit, with raw linseed oil. After being mixed it should be left for twelve hours, or it is made and sold in bulk, a small portion being taken and further kneaded up by hand as required. Where unusual adhesiveness is required, as in glazed fanlights with small lap, a little white-lead may be added to the putty with advantage ; while a hard putty can be MINOR LIME PRODUCTS. 113 made by using turpentine instead of some of the oil ; and an even harder putty by introducing white-lead, red-lead, and sand. These hard putties should, however, be painted soon after they are applied, as they are liable to crack. Soft putty is made by mixing I Ib. of white-lead and J gill of the best salad oil with every 10 Ibs. of whiting and the necessary linseed oil, the white-lead strengthening its adhesive properties, while the salad oil keeps it soft enough to prevent hardening, cracking, and consequent falling off. Much the same result is achieved by mixing tallow with putty, rendering it " thermo-plastic," as it is called that is, sufficiently pliable not to be loosened by the expansion and contraction of glass in large sheets under different degrees of temperature. To soften old putty for the purpose of removing it, it is only necessary to apply heat in the form of a piece of heated metal, using it as a laundress uses an iron. M.M. Chapter XII. PORTLAND CEMENT: ITS PROPERTIES, CONSTITUENTS, AND TESTS. PORTLAND cement, by far the most valuable of the lime products, is formed by drying, burning, and subsequently grinding to powder an artificial mixture of clay and chalk, or of shale and limestone. The resulting material, on the addition of water, has the property of setting, either in air or water, to rock-like hardness while at the same time binding or cementing together any materials with which it is in contact. It is also, when set, almost impervious to water. By means of recent microscopic investigations, four distinct mineral constituents, known as Alit, Belit, Celit, and Felit, exist in Portland cement clinker, and of these alit and celit are the most important ; the clinker being a highly complicated solid solution of these substances formed by "sintering" that is, by diffusion at a tempera- ture below that of the melting point. Perfect diffusion, by exposure to the proper heat for the right period of time, is essential for the production of good clinker ; and this explains why clinker turns to dust which has not attained as high a temperature as that in the hottest part of the kiln. Thus a proper chemical composition is not of itself any guarantee that the cement will be a satisfactory one, as the materials of which it is composed may not necessarily have attained thorough diffusion, and consequently may not be in equilibrium. According to Mr. Clifford Richardson, of New York, PORTLAND CEMENT. the true Portland cement ratio, neglecting extraneous substances, may be regarded as extending from : Pure tri-calcic silicate ... to 7(SiO 2 3CaO) (3A1 2 O 3 , 2CaO) Si0 2 26*4 1 8*9 A1 2 O 3 CaO O-Q 73*6 13-6 67-5 Beyond the latter degree of concentration he considers that the solutions or clinkers have not the structure of Portland cement, and cannot be regarded as such, although they are hydraulic. Setting begins to take place almost directly water is added. It is therefore essential that it should be used at once, only so much being mixed as is required immediately, for if cement be beaten up which has definitely begun to harden it loses a great part of its ad- hesiveness and cohesiveness, becom- ing little better than so much sand, and fit for nothing else than to be thrown away ; for though these pro- perties can be restored by reburning and regrinding, this is not economi- cally practicable. The period occupied in setting varies considerably ; for though it is rarely less than one hour or more than seven, both quicker and slower setting cements can be made if required by varying the constituents and the manufacture slightly. As a rule this is not a matter of very great importance, except that the slower setting cements allow of greater latitude in mixing, and give time for any particles of free lime to be acted upon and slaked ; but occasionally, especially in tidal work, quick setting is imperative, and in such a case the manufacturer should be informed and should not be tied to too rigid an analysis so long as other requisite qualities are not impaired. The correct test for setting is that of no perceptible impression I 2 Fi g- 35- Vicat Needle. Il6 BUILDING MATERIALS. being made by the point of a Vicat needle (see Fig. 35) having an ^ in. point of '015 square inch area and weighing io'5 ozs., this being allowed to rest lightly on the briquette, or on a mass of cement I J ins. thick placed in a glass dish having a diameter of 3 ins. ; setting being con- sidered to have commenced when the needle no longer sinks to the bottom of the dish. Many users, however, employ the rough-and-ready test of thumb-nail pressure. Fresh cement, when first emptied from the casks or sacks in which it is sold, is generally "hot" that is, it slightly stings the bare hand or arm if plunged into it, or if a paste be made with water and the bulb of a thermometer inserted in the paste, a considerable rise of temperature will take place, up to as much as 12 Fahr. in an hour. Some rise is essential, for it shows that the necessary chemical changes which take place during setting are going on; but a rise of more than 6 indicates that the cement contains unburnt, or at any rate unslaked, particles of free lime whose presence may have very serious results. Hot cements will expand from this cause, sometimes at once, sometimes not till long after the work in which they have been used has been finished, and so are very par- ticularly to be avoided, except occasionally in underpinning work, when a little expansion may be useful. A concrete upper floor has been known to expand and burst the building it was inserted in a year after completion. According to tests made by the Cement Users' Testing Association, a first-class fresh cement, mixed with 20 per cent, water, expanded, on mixing, ^ in. per looins. in one day and J in. per 100 ins. in seven days, or at the rate of i in. in 33ft. 4 ins. Hot cement should therefore always be cooled by being spread on a wooden floor under cover to a depth of not more than 12 ins., with a good current of air passing over it, and turned over occasionally, until the rise of tempera- ture of a sample made into a paste with 20 per cent, of its weight of water is not more than 6 Fahr. in an hour PORTLAND CEMENT. after mixing. Hotter cement than this is unfit either for use or testing. On the other hand, cold cement, which shows little or no rise of temperature, is inert and valueless, having lost its power of setting. Cement may become cold by too long exposure to air in too thin layers. Expansion may also be due to over-liming, and in this connection the following analyses of satisfactory material and product may be valuable : FINISHED WARWICKSHIRE CEMENT. Made by Messrs. Greaves, Bull and Lakin, Limited : H 2 O and CO 2 0-29 Insol. matter ... ... ... ... 0*34 SiO 2 ... 20-44 A1 2 3 Fe 2 O 3 CaO ... MgO... S0 3 . 9-30 370 62-16 174 i '97 WARWICKSHIRE Authority, D. B. Butler, Cement " : LIAS STONE. Silica Alumina and oxide of iron ... Lime Magnesia ... Sulphuric acid Alkalies Carbonic acid 99-94 RAW MATERIAL. A.M.Inst.C.E., on "Portland 372 30-05 1070 S'SO 26-80 3'68 i '43 20'08 0-19 0-13 100-08 LIAS SHALE. 873 Organic matter Silica 878 Alumina 43'95 Oxide of iron 1-8; Lime . 74 Magnesia ... trace. Sulphuric acid 36-20 Carbonic acid Potash Soda I00'27 BUILDING MATERIALS. MEDWAY RAW MATERIAL. Mud (or Clay) from Gillingham. Authority, C. Spackman, F.C.S. : Silica 38*413] As sand in an ex- Alumina with trace of \ tremely fine state iron Silica... Alumina Ferric oxide Lime... Magnesia Potash Soda ... Water 14-244 6744 O'Sio 1727 2-957 0773 Iron pyrites . 0'2 of division. As hydrated sili- cates. Chalk. This substance commonly contains 92 94 per cent, of pure carbonate of lime, with very small amounts of silica and alumina. FINISHED MEDWAY CEMENT. Made by Messrs, J. C. Johnson & Co. Authority, Cement Users' Testing Association : Moisture ... ... ... ... ... 0*37 Alumina ... ... ... ... ... 7'35 Insoluble matter ... ... ... ... 2*37 Combined water and organic matter ... 0*95 Ferric oxide ... ... ... ... 3'47 Sulphuric acid ... ... ... ... 1*25 Magnesia ... ... ... ... ... 0*99 Carbonic dioxide ... ... ... ... 0-93 Lime ... ... ... ... ... 60-39 Soluble silica ... ... ... ... 21*41 Undetermined ... ... ... ... 0*52 100*00 PORTLAND CEMENT. 1 19 According to the Cement Users' Testing Association, a first-class cement should not contain more than 1*25 per cent, of magnesia, 175 per cent, of sulphuric acid, i per cent, of carbon dioxide, or i'5 per cent, of insoluble residue, nor more than 61 nor less than 56 per cent, of lime. These, however, are severe demands, with which neither of the above analyses comply, though both cements are recognised as being good and reliable. Another great enemy to the soundness of a cement, though it quickens its setting properties, is the inclusion of any material proportion of underburnt clinker. This, which is bright yellow in colour, should be picked out during manufacture, and its presence is usually easily detected by the yellow colour of the cement powder, which ought to be a dull grey. An underburnt cement, too, has a low specific gravity. When properly cooled to a rise of temperature of 6 Fahr. in an hour after mixing, good cement should have a specific gravity of at least 3*08 ; but newly burnt cement is heavier, and should have a specific gravity of at least 3*125. The test is rather a difficult one to apply, and should be done in oil, in a Schuman's or Keate's bottle ; but it is at least reliable, which is more than can be said for any test of the mere weight of a measured sample. The great test for absolute soundness is that of boiling. A circular pat of neat cement, which it is essential shall be properly cooled, about J in. thick and 3 ins. in diameter, is made up on glass with 20 per cent, of its weight of water. This is kept in moist air for twenty-four hours, and then immersed in cold water, which is raised slowly to boiling point and kept at that temperature for three hours. Under this test a bad cement will turn into soup, while an unsound one will crack from expansion or curl up at its edges from contraction. Only a thoroughly good cement will retain its form under this severe test, which requires great care, and should only be applied by an expert possessing the proper apparatus. Even 120 BUILDING MATERIALS. Erf the best cement, too, will not stand it if tested while "hot." The effect of boiling is to accelerate the changes which take place in a cement in use, expansion taking place in a few hours instead of several months. A modification of this test, which may be safely relied upon in most cases and used by the comparatively unskilled manipulator, can be made by means of an appliance like an incubator, in which the temperature is maintained within a degree or two by a cleverly arranged valve (not shown in the illus- tration) which regulates the supply to the gas burner. It also is based on the principle that moist heat accelerates the set- ting of cement, and that if judiciously applied, the age of several days may be artificially given to a cement in a few hours. A sound cement ac- quires great hardness in a short time when treated in this apparatus, but an unsound one, or one that would under ordinary conditions "blow" when used in work, is caused to develop this characteristic in a few hours ; and hence, by use of this apparatus, a definite opinion may be formed as to whether a cement is a safe one to use or not ; independently, of course, of its tensile strength, which may or may not be equal to that required. The apparatus (see Fig. 36) consists of a covered vessel Fig. 36. PORTLAND CEMENT. 121 in which water is maintained at an even temperature of from 1 10 to 115, or even by some authorities up to 120 Fahr. ; the space above the water is therefore filled with the vapour arising therefrom, and is at a temperature of about 1 00. Immediately the pat is gauged it should be placed on the rack in the upper part of the vessel, and in five or six hours it may be placed in the warm water and left therein for nineteen or twenty hours. If, at the end of that period, the pat is still fast to the glass, or shows no signs of blowing, the cement may be considered perfectly sound ; should, however, any signs of blowing appear, the cement should be laid out in a thin layer for a day or two, and a second pat made and treated in the same manner, as the blowing tendency may only be due to the extreme newness of the cement. A tendency to " blow," or expand after setting is often caused by the inclusion of coarse particles in the cement, which contain free lime within them. Such particles have little strength or cementing value, and their presence is therefore highly undesirable, especially as it is exceedingly difficult, by the ordinary process of air-slaking which cools the finer particles of free lime and renders them innocuous, to similarly get at the lime concealed in a metamorphic condition in coarse lumps of hard cement. Fine grinding is therefore essential for safety, and it has the added advantage of putting the cement into a condition in which its quality of adhesion can be most highly developed, giving it great "covering" power, and enabling it to penetrate the tiniest crevices ; and this even though extremely fine grinding reduces its cohesion. All good cement is now reduced to an impalpable powder. The actual results, taken at random from the records of Messrs. J. and C. Johnson, with two different mills, were as follows, the percentage residues by weight being ascertained after sifting through meshes of 2,500, 5,625, 10,000, and 14,400 holes per square inch respectively : 122 BUILDING MATERIALS. TABLE OF RESIDUES. MESH. RESIDUES. Percentage by Weight. Standard Diameter No. of Holes of Wire. per Sq. In First Sample. Second Sample. ins. 2,500 O'O2 O'OI 0068 5.625 2'OO no 0044 IO.OOO 9-40 6-30 0032 14,400 14*00 10-50 0024 It is extremely important that testing sieves should be uniform, with the mesh of standard wire whose diameter is equal to half the breadth of the hole. The diameter of wire for all the ordinary sieves is given in the last column of the above Table ; but much finer sieves, with cor- respondingly finer wire, are occa- sionally made and used, down to one with 36,000 holes per square inch. According to the Cement Users' Testing Association, a first-rate cement should leave a residue of not more than 5 per cent, on a sieve of 5,625 meshes, nor more than 12 per cent, on a sieve of 14,400 meshes per square inch. The same Association suggests, as a test of adhesion, that a pat of cement 3 ins. in diameter and J in. thick should, after the expiration of seven days, adhere firmly to the natural cleft surface of a Welsh slate, the slate to be soaked in water prior to the application of the cement, and the whole to be kept slightly moist during the interval. A very high resistance to tension, or power of cohesion, is not necessarily an advantage, as it may be due to the Fig. 37. Briquette Mould. PORTLAND CEMENT. 123 cement being "hot" or to its containing an excess of lime ; but it is a highly valuable quality in a finely ground and properly cooled cement which will stand successfully the boiling or the incubator test. According to the Cement Users' Testing Association, neat cement should bear a tensile stress of 400 Ibs. per square inch after seven days' immersion in water, 500 Ibs. after fourteen days, and 600 Ibs. after twenty-eight days ; while a mixture of i part of cement to 3 of " standard " (Leighton Buzzard) sand should bear a stress of 100 Ibs. after seven days, 1 50 Ibs. after fourteen days, and 200 Ibs. after Fig. 38. Faija's Testing Machine. twenty-eight days ; the increase in all cases to be uniform. Most manufacturers will undertake to supply much stronger cement than this, but in the majority of building works excessive tensile strength is by no means so important as absence of expansion, cracking and shrinkage. For the purpose of testing cohesion, the neat and properly cooled cement is mixed with 20 per cent, of its weight of water, or the cement and sand with 10 per cent, of water, and pressed into iron moulds, of which one of the most usual forms is given in Fig. 37, having a sectional area of one square inch at the narrowest part, where fracture will 124 BUILDING MATERIALS. occur. Thumb pressure only should be used, as any artificial pressure or ramming will result in a much higher resistance ; and as the thumb pressure of different individuals varies, it is best that any series of tests should be conducted if possible by the same person and under similar conditions. The briquette thus made should be kept in a moist atmosphere at a temperature of at least 50 Fahr. for twenty-four hours, and then should be removed from the mould and placed in water at not less than 55 nor more than 60 until the period at which the test is to be applied. The briquette is then inserted in the clips of a testing machine, of which there are many patterns, Faija's being shown in Fig. 38. Strain is gradually applied, at the rate of about 400 Ibs. per minute, by turning the handle, the amount being shown upon the dial, which has two hands, one of which is loose and remains to record the breaking strain, while the other flies back to zero when the tension is released by the snapping of the briquette. Great care must be taken that the briquette is put in truly and evenly, else the pull will be unequal and the fracture be diagonal instead of straight. The following results bear out the generally received opinion that cement should be used as soon as possible after being mixed, the delay of only one hour producing very serious deterioration. The experiments were made upon briquettes composed of 2 parts of sand to i of cement, mixed with 10 per cent, of water : Ultimate tensile stress after two months. Lbs. per sq. in. Mixed one hour before putting into moulds 83 Put into moulds at once ... ... ... 220 On the other hand, the effect of colouring matter is advantageous, so far as experiments have yet gone to prove it. PORTLAND CEMENT. 125 The effect of colouring matters. Briquettes made with standard sand and cement 2 to I : Ultimate tensile stress after two months. Lbs. per sq. in. Coloured with 5 per cent, ultra-marine ... 304*5 Coloured with 7*5 percent, oxide of iron... 325 Coloured with 4 per cent, lamp black ... 286'5 Uncoloured cement mortar ... ... 276 It is also worth noticing that a highly aluminous cement which, after plastering, will set in an hour, has often been found to set in three minutes when stored in closed freight cars for some time in a hot summer's sun. Chapter XIII. PORTLAND CEMENT: ITS MANUFACTURE. THERE are at present three principal methods employed for the manufacture of Portland Cement, these being exemplified by the works of Messrs. J. C. Johnson & Co., at Greenhithe ; those of Messrs. Greave?, Bull and Lakin, Limited, at Harbury, in Warwickshire ; and those of the Associated Portland Cement Manufacturers (1900), Limited, at Swanscombe, in Kent. Though probably no two firms work on exactly the same systems, these may be considered as typical of what, for want of better names, may be termed the "Ordinary," and the "Semi-Dry," and the " Rotary" processes respectively. The clay is brought in barges to Messrs. J. C. Johnson & Co.'s works, and the chalk is quarried on the spot. These raw materials, which naturally vary somewhat, are con- stantly analysed, and the proportions in which they are mixed are altered from day to day accordingly. The chalk and the clay are filled into banows of different sizes, and each barrowful is weighed and then tipped into a circular pit with ample water in it, about three of chalk to one of clay. The pit has a vertical axle carrying arms like wind- mill sails, only with blade attachments in place of sails, and these being given a rotary motion, beat up the contents of the pit into a creamy liquid, which is driven out through a grating. The " slurry," as this mixture is called, is next passed between horizontal grindstones, like those used for grinding corn, which reduce it to such a degree of fineness that all will pass through a sieve of 2,500 holes per square inch, and only 5 per cent, be retained on a 32,ooo-hole mesh. PORTLAND CEMENT : ITS MANUFACTURE. 127 At one time the slurry was run into large open-air " backs," or shallow reservoirs, to settle, but this has now been entirely abandoned in favour of artificial drying by the aid of the spare heat from the kilns (see Fig. 39). The hot air passes over the slurry, of which the drying FUEL DOOR BRICK CO UP DURING BURNI PLAN Fig. 39. Johnson's Portland Cement Kiln. chamber contains just enough with which to charge the kiln, then down through holes in its iron floor, circulating between dwarf walls as shown by the arrows on plan, and thence to a long continuous flue the entry to which is con- trolled by a damper. This flue serves for a long range of kilns, and leads to a large central chimney. The dried slurry, now known as " slip," is filled into the 128 BUILDING MATERIALS. kiln, mixed with small coal to act as fuel, the kiln being piled right up to its arched roof. As soon as it is full, and the drying chamber empty, a rough wall of slip is built round the kiln edge, and a fresh charge of slurry is pumped on to the floor of the chamber. All openings are then bricked up with fire-bricks set in slurry, except a small hole in the fuel door left for purposes of inspection which is temporarily closed with a dry brick, and the kiln is fired from beneath, as much air as possible being allowed to get to it through the fire-bars. An intense heat is generated, and it takes about a week to burn through a kiln, and to convert a chamberful of slurry into slip. At the end of that time the kiln is allowed to cool down, and it is found that its contents have been reduced to one-half their former bulk, and have been converted into a hard metallic clinker of honeycomb structure. The fire-bars are now removed and the clinker falls into the draw-hole. It is there filled into barrows, any yellow (underburnt) lumps being put on one side to be passed through the kiln again, while the good clinker is taken to powerful grinding mills. This final product is again tested, by all the principal analytical and mechanical tests, and a check thus kept upon the working from start to finish. Ball and tube mills are generally used for grinding, the clinker being fed through a hopper to the ball mills, passing out as a powder, which goes through the tube mills afterwards to reduce it to the impalpable condition in which it is sent to market. The Ball-mills are large hollow cylinders con- taining a number of steel balls which grind against one another as the horizontally placed cylinders revolve on their axes ; while the Tube-mills long steel tubes set to a slight incline are half full of flint pebbles, which in a similar manner rub against one another, grinding the clinker and powder as the tubes revolve. The " Semi-dry " Process, as exemplified at the works of Messrs. Greaves, Bull and Lakin, differs only from the above so far as is necessitated by the raw materials being PORTLAND CEMENT : ITS MANUFACTURE. 129 hard instead of soft ; blue lias limestone taking the place of chalk, and a hard shale that of the clay. Crushing is consequently the first operation, and then grinding under an edge runner so as to pass through a J in. mesh formed in the pan of the mill. Mixture then takes place with only a little water, so as to pass the ingredients between hori- zontal grindstones, producing a dark-coloured slurry of about the consistency of porridge. This is pumped on to the dry- ing floors of Johnson kilns, and the subsequent treatment is exactly similar to that already described, except that the heated air from the kiln, after passing over the contents of PIPE TO TANK- Fig. 40. Mechanical Slurry Sieve. the drying chamber, is carried under iron plates on which is spread a thin (3 ins.) layer of slurry. When a kilnful of slip has been heated through and collapsed, slip from this supplementary drying chamber is introduced to fill it up again, without any more fuel ; and as this burns in the heated kiln just as thoroughly as does that which is first inserted, a distinct economy is effected. At the Swanscombe works of the Associated Portland Cement Manufacturers (1900), Limited, the slurry, after being mixed in small pug-mills or "wash-mills," and ground between French Burr-stones, is pumped into a mechanical sieve (see Fig. 40), consisting of a circular basin in which beaters or fans revolve at considerable speed, throwing the liquid forcibly against an inclined sieve of 1,225 holes per M.M. K 130 BUILDING MATERIALS. square inch. Any materially coarse particles are thus retained, while what passes through would leave a residue of but 5 per cent on a 32,000 mesh. This sifted product, little denser than milk, is collected in an external annular trough and passes in a continuous stream through a large pipe to one of several great mixing tanks, each capable of holding 1,200 tons of slurry. These also are circular, with massive beaters slowly revolving in them to thoroughly incorporate the contents and prevent settlement. The effect of this complete mixing of large quantities of slurry is the production of a cement of almost uniform analysis, the variations which inevitably occur in mixture in small Fig. 41. Rotary Portland Cement Kiln and Cooling Cylinders. amounts being compensated when mixture takes place in bulk. The subsequent processes by means of which the slurry is converted into clinker ready for grinding are shown in rough diagrammatic form in Fig. 41. The slurry is pumped directly into the end of A, a large ROTARY KlLN, in the form of a steel cylinder, 70 ft. long and 6J ft. in diameter, set to a slight fall from A to B, lined with fire-bricks internally, and revolving on rollers at any desired speed. At the open lower end B, a jet of coal dust, ground in Griffin mills to a fine powder, is injected by the aid of steam and compressed air, falling in a light spray and being converted into flame at once, generating a temperature of some 3,000 Fahr., the products of combustion passing up the kiln from B to A while the slurry passes through it PORTLAND CEMENT: ITS MANUFACTURE. 13! from A to B, entering at A as liquid slurry and passing out at B as red-hot clinker of about pea-grit size, after about an hour and a half. In this short space of time the moisture has been evaporated from the slurry, passing up the chimney as steam, and the " slip " thus produced has been rendered bone-dry about the middle of the kiln and burnt to clinker at the lower end. The rotary motion, throwing the slurry into drops and the slip into small lumps, greatly facilitates the burning, which can be rapid as well as thorough, the small pieces becoming quickly and completely calcined. The burnt clinker, which is entirely free from dust, falls over the edge of the kiln at the lower end B, as it rotates, into a hopper, and passes thence into another long revolving cylinder through which a current of cold air passes and thence to another similar cylinder in the same way. These cooling cylinders are rifled with deep grooves throughout their length, so that as they revolve the lumps of clinker are caught and dropped, to assist in cooling them ; while the air which enters at the lower end of the cooling cylinders, having been gradually warmed as it passes over the hot clinker, is then introduced into the kiln though the way in which this is done is not shown on the accom- panying diagram. The Cement Clinker is subsequently ground in the usual way by means of Ball and Tube Mills. K 2 Chapter XIV. MORTAR FIRE CEMENT. MORTAR is the substance used for filling up the inter- stices between the blocks of solid material of which a wall is built, forming at the same time a soft and level bed for the blocks to lie upon, so distributing the load evenly over the surface of the lower blocks, and to a greater or less extent cementing the blocks together so as to form one homogeneous whole. It is generally composed of lime and sand, or of substitutes for these materials, in varying proportions, roughly gauged by bulk, so that the matrix (lime or cement) may just fill up the natural interstices between the particles of the aggregate (sand). Pure and poor limes should not be used ; but the following list gives the proportions of different materials in general use for different classes of work : Ordinary brick or stone wall- ) I part of stone lime to ing. j 3 of sand. /- j r f I part of selenitic lime to Good walling ... ... ... \ r ( 4 of sand. Very good walling and piers, to carry considerable loads slowly applied, or light I part of lias lime to of sand. machinery. Quick setting walling, and piers ^ i part of Portland cement and walls to carry heavy loads. J to 4 of sand. Exceedingly strong work, and \ watertight work such as I Neat Portland cement. pointing. J MORTAR. 133 Lime mortar should be used where shattering or swaying motion has to be resisted, as in tall chimney stacks and church spires, a certain amount of " play " being advisable under such circumstances ; but for rigid resistance there is nothing to equal cement. Thin walls, such as half-brick partitions, should also be built in cement mortar, although lias lime mortar is admissible if they are not more than about 9 ft. high and are supported by cross-walls pretty frequently. Careful mixing of the ingredients of mortar is quite as important as the use of proper proportions. On small works this is done by hand, and the following instructions issued by Messrs. Greaves, Bull and Lakin may be taken as being equally applicable under such circumstances to mortar composed of any moderately or eminently hydraulic lime : GROUND LIME should be used in the proportion of I bushel of lime to 2\ or 3 bushels of clean, sharp sand, free from dirt or loam. This should be first thoroughly mixed in its dry state, which may be done by turning them over together several times with a shovel, and afterwards, to ensure a more perfect mixture, passing the whole through a riddle. (It should be borne in mind that a complete incorporation of the ingredients is most essential.) After this has been done the mixture should be left in a heap for a day or two. Mortar may then be made from the heap as required by the addition of water, and a further mixing in the wet state. When LUMP LIME is used instead of Ground, special attention should be given to the instructions for slaking (see p. in), and the slaked lime and sand should be passed together through a riddle. The amount of water required for mixing mortar will depend on the quantities and nature of the materials used, but in the above mixture (say I to 3 of sand) it would be from ij to 2 gallons per bushel of lime and sand. This is in addition to that used in slaking the lime. 134 BUILDING MATERIALS. Much more perfect incorporation is, however, secured by the use of a MORTAR MILL, and as it is more economical to employ one than to mix by hand on even a moderate scale, it is generally used, especially where power is available. There are two types those which are self-delivering, these being most suitable for hard, rough grinding ; and those which have revolving pans passing beneath edge runners. Of these the latter is in more general use, one (the " Century," made by the Glendon Engine Works Co.) being illustrated in Fig. 42. There is a false bottom-plate of hard iron to Fig. 42. The " Century " Mortar Mill. the pan, which can be renewed when it wears away from contact with the heavy metal rollers. Where there is a Mortar Mill, Messrs. Greaves, Bull and Lakin's instructions are as follows : Either Lump or Ground Lime can be used, and the mortar may be made in proportion of I part lime to 3 or 4 parts sand. The sand must be thoroughly clean and sharp, and where this is not readily obtainable, excellent results may be had by substituting (either wholly or in part, according to the selection made) good old broken bricks (clean and well burnt), well burnt ballast, stone chippings, furnace cinders or slag. It is most essential in all cases that the materials used MORTAR. 135 should be perfectly clean and free from loam, clay, or other impurities. The mortar should be left in the mill until thoroughly reduced and incorporated, but excessive grinding is detrimental. When Lump Lime is used, it should, for the sake of economy of time and power, be wholly or partially slaked before being put into the mill ; and if this, either from want of space or otherwise, is not found convenient, Ground Lime should be used in preference, as the small extra cost is in most cases more than compensated for by the greater con- venience in handling, and the saving of labour and room required in slaking. If unslaked lime be passed direct into the Mortar Mill, more water and mixing will be required, and the mortar should stand for a few hours to allow the lime to slake. Mortar made with SELENITIC LIME has to be treated in an entirely different manner. If prepared in a Mortar Mill, pour into the pan of the edge runner two full-sized pails of water, then gradually add one bushel of Selenitic Lime, and grind to the consistency of a creamy paste, then throw into the pan 4 or 5 bushels of clean, sharp sand, burnt- clay ballast, or broken bricks, which must be well ground until thoroughly incorporated. If necessary, water can be added to this in grinding, which is preferable to adding an excess of water to the prepared lime before adding the sand. N.B. The water and the Selenitic Lime must be mixed together first, and, if Self-discharging Mortar Mills be used, the lime and water are preferably mixed in a tub, as explained hereunder, adding the paste to the sand proportionately as required in the Mortar Mill. Where there is no Mortar Mill, an ordinary tub or trough (containing about 40 or 50 gallons), with outlet or sluice, may be substituted. In this case, pour into the tub six full-sized pails of water, and gradually add a 3-bushel sack of Selenitic Lime, which must be kept well 136 BUILDING MATERIALS. stirred till thoroughly mixed with the water to the con- sistency of a creamy paste. Form a ring with half a yard of clean sharp sand, into which pour the mixture from the tub. This should be turned over three or four times, and well mixed with the larry or mortar hook, adding water as necessary. One 3-bushel sack of selenitic lime requires about 18 gallons of water. There are 12 sacks to the ton. CEMENT MORTAR needs still different treatment. It should not be mixed in a Mortar Mill because of the great risk run of grinding being prolonged after setting has com- menced. The ingredients should first be mixed dry in a small heap, being turned over at least twice. Just sufficient water (about 15 per cent.) should then be added through the rose of a watering can, the mixture turned over once again and used immediately at any rate, within half an hour of mixing, and much sooner than this if the cement be quick setting. Neat cement is generally mixed with just enough water on his palette by the bricklayer himself only a few minutes before it is needed. The bulk of mortar is about 25 per cent, less than that of the ingredients of which it is composed when separate and in their dry state. This is due to the interstices between the grains of sand being filled with the lime or cement and water, which are almost, and sometimes entirely, absorbed in this way. Once mixed, all mortar should be placed in a tub or on a wooden platform to keep it clean until required for use. Only so much should be mixed at one time as can be used before it commences to set, and any which has begun to stiffen should be rejected. Unfortunately it is easy to throw into a mortar mill any which has been exposed through a night and has thus begun to set, and to mix it up with a little fresh lime and use it, and a good deal of indifferent work is traceable to this cause. Moisture assists the setting action of all hydraulic limes and cements, while if deprived of its moisture before setting MORTAR FIRE CEMENT. 137 has taken place a mortar will revert to its original consti- tuents and become mere inert sand. Consequently in hot weather all brick or stone used in building should be well soaked, else the moisture will be rapidly drawn from the mortar into the thirsty bricks, and setting will not take place this being more apparent in mortars made with slow setting limes than in those made with the quicker setting cements. In all cases work executed in damp earth or under still water becomes eventually harder than that done in air. Frost also rapidly destroys unset or partially set mortar. In frosty weather work must either be stopped or executed in a cement mortar which will set more quickly than it will freeze. Mortar should be used of as stiff a consistency as possible, all beds being even, all surfaces covered, and all joints flushed up that is, in walling. A liquid mortar, known as GROUT, is often poured over the surface of a brick floor and swept over it with a broom so as to penetrate every crevice, but it should not be employed in walling ; for, though excessively rapid work can be done by laying a thick bed of soft mortar and running the bricks along it into place, the practice is far from commendable. FIRE CEMENT. Where mortar has to be employed in a position where considerable heat has to be withstood, either raw fire-clay should be used, or a fire-resisting cement known as " PURIMACHOS " may be employed. Its composi- tion is a secret, but its qualities are unquestionable. The following particulars are taken from the manufacturer's circular : Definitions. The word cement means the moist paste ; the word powder means the dry powder ; the word wash means the moist paste or cement reduced with clean water to the consistency of whitewash. Cement (Moist). The white and dark cements are equally efficacious as fire-resisting materials. The white is generally 138 BUILDING MATERIALS. used for glazing and for other purposes where the colour of the work or surroundings have to be matched. The dark is generally used for general repairs, it being lighter in weight. The cement is sent out ready for use, and may be used for most purposes for which fire-clay is employed. It should, as a rule, be applied in the same manner in the consistency of newly tempered mortar. If too stiff, add a little clean water ; for resisting great heat, add powder (failing it, sifted fire-clay) well mixed together. The cement is not intended to be brought in contact with lime, chemicals, fluxes, etc. Powder (Dry). The powder is not cement in a dry state, which can be converted into plastic cement by wetting it ; it is an entirely different composition, and is not to be used by itself. It is prepared for combining with cement in cases of great heat ; to impart to it greater body ; or to cause it to set more quickly when cold. See also next paragraphs. For moderate heats i.e., not exceeding 1 200 Fahr. (as in open fire-grates, or in pointing round kitchen ranges, etc.) the cement should be used by itself. For very high temperatures (as in modern kitchen ranges, i.e. t in lining the fireholes), the best results will be obtained by the admixture of a sufficient quantity of powder (failing it, sifted fire-clay) ; and, as a rule, the greater the intensity of heat to be encountered, the greater should be the proportion of powder (say I to 3 parts or more of powder to I of cement) : a little experience soon determines the exact proportion in each case. Mixing. The best method of perfectly and readily mixing together the cement and powder is this : In a clean bucket, reduce the required quantity of cement to a batter or wash, to which add gradually the proper proportion of powder (or failing it, sifted fire-clay). With a trowel work up the whole thoroughly well to the consistency of newly tempered mortar. It is absolutely essential that the cement should be first reduced to a batter or wash as FIRE CEMENT. 139 described above ; and then after this batter has been made up, powder (or sifted fire-clay) may be added slowly and by degrees and thoroughly well mixed in and completely blended evenly throughout the whole mass. The mixing, if done in any other way, may produce failure and disappointment. Do not mix more than is required for immediate use. Before applying Purimachos, remove all dirt, dust, grease, grit, carbon, rust, or loose pieces, so that the cement may adhere to a firm surface, and not to any loose substances. Iron surfaces should be similarly cleaned ; and, where upright or sloping surfaces have to be covered with a layer of Purimachos, it is desirable to roughen the metal with an old file, bent to a suitable shape to act as a scraper. Then apply a wash with a clean brush, and let it dry. Upon this a layer may be applied to the required thickness, and thus get a better grip of the iron. Joints in brickwork should be made very narrow with Purimachos. In jointing cracks, work it well in do not merely plaster it outside. In cases of large fissures, etc., and where there is a difficulty in keeping it from falling out as in the arches of furnaces, etc., support it in position until heat is applied, when the whole mass will set quickly with a slight expansion. Wooden supports may be used and allowed to burn away. Purimachos may be applied to a cool or hot surface ; but it is desirable to apply it whilst cool. To ensure a perfect finish, plaster with Purimachos should be as thin as possible. Chapter XV. LIME PLASTER PLASTER OF PARIS SIRA- PITE KEENE'S, MARTIN'S, & PARIAN CEMENT STUCCOROUGH CAST NOTES FOR USERS. ORDINARY plaster is, like mortar, composed of lime and sand, the principal difference between the two materials consisting in the lime for plaster being " pure " or non- hydraulic. No powerful cementitious quality is required, so long as it will adhere to a rough surface and can itself be brought, by the application of successive coats each finer than the last, to a smooth and level surface. On the other hand, it is generally required to be porous and absorptive of moisture contained in the air, which otherwise would condense upon the plastered surface and run down it in unsightly streaks. The lime used must be thoroughly slaked, so that it shall not " blow " (or blister) after being used. A ring of sand is usually made, and the lime well slaked within this ring and left covered with water, the sand being presently mixed with it and the whole heap again left for some weeks to weather before use. There is rather more sand than lime and the mixture is known as COARSE STUFF. When it has to be used on laths, which themselves are comparatively smooth while they have spaces between them into which the plaster is squeezed, ox hair should be mixed with the coarse stuff, in the proportion of about i Ib. of hair to every 2 cubic feet of stuff. The hair should be long, free from grease, and well separated, preferably by immersion in water, and is best incorporated by hand with LIME PLASTER. 141 a rake. If a mortar mill is used the hair should be added at the last minute and the grinding only continued long enough to ensure mixing, as if it is prolonged the hair is broken into short lengths and rendered valueless. This, the first coat, is called " rendering" if on brickwork, and "plastering" or "pricking up" if on laths. The second coat, known as " floating," may also be of coarse stuff, but there is in no case any necessity for it to contain hair. The third, or finishing coat is much thinner than the first or t second and, if it is to be papered, consists of FINE STUFF. This is pure lime which, after slaking with a little water, has been mixed with much, allowed to settle and the surplus water drawn off. The stodgy mass which remains, kept preferably in a large tub, is still left for the contained water to evaporate and the lime to thoroughly cool until it is wanted for use. If the finishing coat is to be whitened or coloured with distemper of any kind, it should be made of PLASTERER'S PUTTY, which is almost identical with fine stuff, only more carefully made, run through a fine sieve, and kept from dirt. For making good defects, and sometimes as a superior finishing coat, GAUGED STUFF is used, this being made by mixing plaster of Paris with plasterer's putty. Generally the proportion of plaster of Paris is about one-fifth of the whole, as a larger proportion may cause cracks to appear in the finished work ; but gauged stuff is also used for running cornices and other ornamental work, when the proportion of plaster of Paris is increased to as much as 50 per cent, of the whole. The addition of this substance greatly hastens the setting (or hardening), so that only very little may be mixed at one time. Selenitic lime can be used in place of pure lime for coarse stuff, it being made, where it is to be employed for rendering, exactly as is selenitic mortar (see p. 135). If for use as a first coat of plastering on laths, however, 9 bushels of sharp sand are added to a mixture, fresh made, of 3 bushels 142 BUILDING MATERIALS. of selenitic lime in 18 gallons of water, and then 3 hods of well-haired fine stuff mixed in. For the second coat the 12 bushels of sand would be used and the hair omitted from the putty. If a hard face is required, prepared selenitic lime may be first passed through a 24 by 24 mesh sieve, to avoid the pos- sibility of blistering, and used in the following proportion : 4 pails of water ; 2 bushels of prepared selenitic lime ; 2 hods of chalk lime putty ; 3 bushels of fine washed sand. This should be treated as trowelled ^ stucco, first well hand-floating the surface and then well trowelling. A smooth and even harder face, if well hand-floated and then well trowelled, is produced by the following mixture : Five pails of water ; I bushel prepared selenitic lime ; I bushel prepared selenitic clay ; 2 bushels fine washed sand ; I hod of chalk lime putty. It is suitable for the walls of hospital wards and public buildings, and, being non-absorbent, it is readily washed. PLASTER OF PARIS is obtained by partially calcining or "boiling" GYPSUM (hydrous sulphate of lime), otherwise known as SELENITE, so that it parts with most of its con- tained water, its composition being then represented by the formula CaSO 4 , 2 H 2 O ; or, in other words, Lime. Sulphuric Water, acid. CaO + H 2 SO 4 + H 2 O. It is mostly used in building operations for small castings applied as enrichments to plaster decorations, its property of slightly expanding while setting making it capable of taking extremely sharp impressions. It is, however, soluble in water, and so can only be used in dry internal situations. It is also occasionally employed as a cement. It does not effer- vesce when treated with acid, and it sets with great rapidity. The best plaster of Paris, setting quickly and hard, is made by the plasterers themselves from the raw stone. This is ground and spread in a layer some 2 or 3 ins. PLASTER OF PARIS SIRAPITE. 143 deep in a shallow metal dish over a fire. When the tem- perature approaches that of boiling water the surface appears to rise up bodily as if suspended by the aqueous vapour given off by the lower layers ; little craters are formed all over the surface and steam passes off freely mingled with fine dust ; and the plaster is stirred from time to time till no further evolution of moisture takes place, as tested by holding a cold plate over it to condense the steam, when the heat is withdrawn and the plaster is ready for use. SlRAPITE is a species of plaster of Paris similarly made from gypsum impregnated with petroleum, which is found at Mountfield in Sussex and Kingston-on-Soar in Derby- shire. It is now largely used either in addition to or in place of chalk lime for ordinary plaster work, being easy to work and rapid in setting, so that a room can be ren- dered one day and finished the next (two coats only being needed), while the resulting surface is hard and smooth, with no risk of bubbles forming. It should be mixed in small quantities at a time, and should not be used upon permanently damp walls, such as retaining walls and basement walls where there is no efficient damp-course. It will keep some time in a perfectly dry store ; but it is better to use it fresh from the works. If it has been kept, or the age is unknown, it should be tested before using in bulk. The work should be thoroughly dry before being decorated upon. The following are the makers' directions for using Sirapite plaster : To be mixed in a banker like ordinary cement. For first coat on walls, one measure of Sirapite to two or three of good clean sand. For first coat on lathwork,two measures of Sirapite to one of good clean sand. Any laths will do, but for economy of material, sawn laths nailed J in. apart are preferable. Finish to be applied neat as soon as the first coat is sufficiently firm. Many users mix the finish in a pail. 144 BUILDING MATERIALS. A small proportion of well-run lime putty may be mixed with the first coat. The lime must be properly burned and thoroughly slacked. One ton of coarse Sirapite and 5 cwts. of finish will cover from 125 to 130 yards super f of an inch thick finished. On metal lathing, for the first coat, Sirapite plaster should be mixed half and half with common hair plaster, the finish to be applied in the usual way. Where the suction ^is great, as on stone walls, Sirapite plaster should be applied half and half with common wall plaster and finished with Sirapite finish in the usual way. The face of the wall should be scored and quite clean. It may also be necessary to size the face before applying the plaster. Many users utilise Sirapite plaster for gauging common lime plaster. Used in this way the latter is so much improved that it becomes equal in most respects to the most expansive hard plasters. It makes excellent and rapid work, is fat and easy to use ; and can be finished in two coats. For walls, use Sirapite plaster half and half with common wall plaster. For ceilings, use Sirapite plaster half and half with common lime and hair plaster. Finishing may be in neat Sirapite finish, or the same mixed with more or less lime putty. KEENE'S, MARTIN'S, AND PARIAN CEMENT are all hardened forms of plaster of Paris, of great use where an impervious, hard and smooth surface is required, and in skirtings, dadoes and angle staves likely to be subject to rough usage. Keene's Cement is made by steeping the calcined stone (gypsum) in a strong solution of borax and cream of tartar. The liquor is composed of I part of borax and I part of cream of tartar, dissolved in about 18 parts of water. In this solution the plaster in the lump, as KEENE'S, MARTIN'S, AND PARIAN CEMENT. 145 withdrawn from the oven, is allowed to remain till it is thoroughly impregnated with the salts, when it is taken out, dried, and reburnt at a dull red heat for about six or eight hours. When cool it is ground to a fine powder and is then ready for use. In making Martin's Cement the solution used is one of carbonate of potash, while for Parian Cement an intimate mixture of powered gypsum and dried borax is calcined and then ground to a fine powder. GYPO is a new plaster, the method of manufacture of which has not been divulged, and for which it is claimed that it is more than ordinarily fire-resisting ; that it adheres firmly to iron and other metals, no key being required ; and that it may be painted or distempered within forty-eight hours. An ASBESTOS NON-CONDUCTING COMPOSITION is made for plastering heated surfaces, the following being the maker's directions respecting it : No. i. For all surfaces of steam pipes, boilers, etc., which are to be free from grease. Surfaces must be covered when hot. Add to the dry compo sufficient water to make it into a good mortar, and apply the first coat very thin to the heated surface with the hand. When dry, other coats should be applied by the hand about half an inch in thick- ness, the last coat should be levelled and finished off with a trowel ; when dry, the covering may be painted, or tarred if exposed to the elements. No. 2. For boiler and steam pipes. May be used as a covering for other boiler-covering compositions that need repair, or as a finishing coat over old asbestos compo, to which it imparts a very hard and smooth surface. Mix in a pail to a fairly thick paste, and empty on covering, smoothing off with a trowel ; it cannot be remixed with water after once setting. No. 3. For gas and water mains, gas purifiers, tanks, stills, or constructional ironwork of any kind, where the temperature does not exceed 150 Fahr., to be applied M.M. L 146 BUILDING MATERIALS. direct to the surface of metal. No key, netting, or wrapping needed. Mix in equal proportions with sand, in small quantities at a time, for immediate use, as it cannot be reworked with water after once setting. May be painted or tarred if exposed to the elements. Plastering used externally is generally known as " STUCCO " if smooth, and as " ROUGH CAST " or " PEBBLE DASH " if rough. Of these, stucco generally consists of I part of hydraulic lime to 3 of sand, trowelled to a smooth sur- face. If it is to be used as an external protective coat to a wall which is likely to be exposed to driving rain, it is frequently in two coats, of which the first is made with Portland cement instead of lime. Rough cast is made, as a rule, in the same way as stucco, coarse grit being used in place of sand, and the surface being gone over with felt after being trowelled, so as to bring out the grit and roughen it ; but an almost better effect is obtained by first rendering with hydraulic plaster, then covering this with a very thin coating of neat Port- land cement, and immediately (before it commences to set) dashing on to this a mixture of grit and coloured lime, with a motion similar to that used when sowing corn by hand. The term " stucco " is, however, also applied to any smooth plaster, carefully worked up, in order that it may be painted on. Perhaps the smoothest and most perfect stucco ever made was that used in the old buildings of Ceylon, in which white of egg formed a principal ingredient ; but its composition and method of working are not absolutely known. NOTES FOR USERS. Plaster is suitable for application in a thin layer on a firm backing, may be brought to a smooth surface over a large area. CEMENT: NOTES FOR USERS. 147 The backing should be rough, in order that the plaster may adhere to it. A backing of lathing on timber is liable to shrink and warp, causing unsightly cracks in the superimposed plaster. Lathing, whether of wood or metal, is too smooth for plaster to adhere to it. Spaces have to be left, and the plaster pressed into the spaces, preferably mixed with hair to assist it to cling. Each coat should partially dry before the next is applied, and all should thoroughly dry before it is papered or coloured. Only hard-surface plasters, such as Keene's or Parian cement, should be used in skirtings, angle staves, and other positions liable to wear. Mouldings can be " run," but undercutting must be avoided, as should also excessively variable thickness of the plaster. Enrichments can be cast, and by attaching the castings to both sides of a hollow moulding the effect of deep undercutting is easily obtained. Shallow trowel-formed and stamped ornament is also possible, while large enrichments can be built up by a clever modeller, but cutting is impossible. L 2 Chapter XVI. CONCRETE. ANY mixture of substances such as will within a reason- able time harden into a compact mass may reasonably be called concrete, but the term is generally restricted in use to a combination of some inert aggregate, such as pebbles, broken stone or brick, with a cementitious matrix such as lime or cement. Such a material, according to its constituents and the proportions in which they have been employed, is useful for foundations, walling (especially retaining walls), damp-resisting floors, lintols, and as a filling between steel framework in fire-resisting floors, and in flat and domed roofs. For ordinary foundations, where there is no excessive weight to carry, Lime Concrete may be used, and a suit- able mixture is as follows : I part of ground stone or lias lime, i part clean sharp sand, and 4 to 5 parts broken stone, bricks, or well burnt ballast, small shingle, or slag. If unscreened Thames ballast be used, care should be taken to see that the proportion of sand in it does not exceed that of the lime. The ingredients should be very thoroughly mixed dry, and again when water is added, which should be through the rose of a watering-can or hose, in just sufficient quantity to penetrate but not to saturate the mass. Concrete may be made with selenitic mortar as a matrix, by using 6 full-sized pails of water, 3 bushels of selenitic lime, and 3 bushels of clean sand. These ingredients should be mixed as before in the edge runner or tub, and then incorporated with from 15 to 18 bushels of broken stone or bricks or burnt ballast, the whole being CONCRETE. 149 turned over two or three times on the gauging floor to ensure thorough mixing with the ballast. When the tub is used the sand must be first mixed dry with the ballast, and the lime poured into it from the tub, and thoroughly Fig. 43. Ganke's Patent Concrete Mixer. mixed on the gauging floor. An addition of one-sixth of Portland cement will be found to quicken the setting. It is of the utmost importance that the mode here indicated of preparing the concrete should be observed, first well stirring the selenitic lime in the water before mixing it with the sand, ballast, or other ingredient, as otherwise the cement will heat and be injured. 150 BUILDING MATERIALS. Where strong foundations are required, and in almost all other cases, it is essential to use Portland Cement Concrete to ensure good work. One part, by bulk, of cement is mixed with (as a rule) six of aggregate, these substances being twice turned over with spades while heaped upon a clean platform of boards, sprinkled with water through a rose, and again twice turned over. Where large works are in progress it has been found both more economical and more satisfactory in result to employ mixing machines, of which there are many kinds upon the market. The pattern shown in Fig. 43, Ganke's Patent, made by Arthur Koppel, for use with steam power, may be taken, therefore, as illustrating one only of numerous similar machines, which can be worked either by hand, steam, or electricity. The aggregate is first shovelled or tipped into the elevator-box A, which is of a size suitable for one charge, and the measured quantity of cement added. The attendant, by pressing a lever, causes the elevator-box to rise in the slides B,B, and discharge its contents into the feeding-hopper C, which in turn passes it into the drum D. This is caused to rotate, and as it contains a central shaft to which blades or paddles are attached, the materials within are intimately mixed. After dry mixing in this way for a sufficient time, water, in an amount which can be exactly regulated, is admitted to the drum from the cistern E, and the mixing is continued. When this is complete, the contents of the drum are discharged into a tipping- waggon F, which runs upon rails below it, or into a barrow. Concrete should not, however, at any time be thrown or dropped into position from a height, as this tends to separate the materials, the heavier particles falling to the bottom ; but it should be rapidly wheeled to the site after mixing, carefully lowered into position, and spread in layers. Ramming has, to some extent, the same effect as dumping from a height, and although it is often advocated as tending to make the substance homogeneous, it ought not to be CONCRETE. 1 5 1 necessary if the materials have been properly proportioned and enough, but not too much, water added. Concrete can also be cast in moulds for many purposes, such as window sills and lintols, being then made with small aggregate and often kept under slight pressure until setting is complete. Many artificial stones, largely adver- tised and sold under high-sounding names, are nothing else than cement concretes. Cement concrete should be used at once, but lime con- crete may be left for a short time before being used to ensure the slaking of all the lime. It is desirable that concrete for foundations should not be built upon until it has been allowed to set for at least seven days. Where more concrete is to be deposited on any concrete face that has become dry, such surface should be thoroughly cleaned and well wetted previous to the application of the new material. One of the great practical difficulties which is met with upon public works is getting concreters to mix materials in small quantities just sufficient for immediate use. If large volumes are mixed at one time they can only be prevented from setting by the addition of excessive quan- tities of water, and this will have a most harmful effect upon the work for all time, as proper crystallization will never take place. If small quantities are used and mixed with just enough water to make them plastic and workable, a first-class concrete is obtained. It should be remembered that chemical action begins with a cement as soon as water is added, and this action is not delayed by the addition of sand or other aggregate. It follows, there- fore, that cement concrete which has partially set should be thrown upon one side. Another matter which needs careful attention is the protection of concrete from frost, and from sun and wind when initial setting is in progress, as bad effects are caused by the sun as by frost ; the latter expands the materials, and so disintegrates them, and the former robs the mixture 152 BUILDING MATERIALS. of the water requisite for crystallization. Work carried out under conditions of extreme cold should be protected by sacking, and the water used should be warm ; or if the work is in the nature of paving, an inch of sand spread over the surface will effectually prevent any but excessive frosts from disturbing the concrete. In the case of heat, it is a great advantage to keep the face of work watered and to cover it up with damp sacking. A properly proportioned concrete should be such that all the interstices between the fragments of aggregate are filled by the matrix, and to secure this sand is sometimes added, though it is rarely necessary with a well-broken aggregate whose fragments are of various sizes. For ordinary foundations, especially in lime concrete, it is most usual to employ ballast, or some other pebbly substance, as an aggregate, only the larger fragments being broken so as to pass in all directions through a 2-in. ring this last being a very necessary stipulation, con- stantly neglected in practice. In no case, however, can such a concrete be really good, as the smooth surface of a pebble is not one to which either lime or cement will readily adhere. Better aggregates for walls or floors are broken stone (either limestone or sandstone), brick or slag, as the fracture is generally clean, having jagged features forming an excellent key for the cement. Round stone, that has been water-worn, is not a good material, especially where the concrete has to bear transverse strains. If gravel must be used, it is a great advantage to use hard, broken brick (preferably well-burnt stocks or broken burrs) in conjunc- tion with the gravel, as a certain amount of cohesion is thereby added to the mass which would otherwise be entirely lacking. Burnt ballast concrete is the worst of any ; it is impossible to obtain a thoroughly vitrified class of ballast until the cores of the ballast heaps are reached. The outsides are entirely unsuitable for use in damp positions, as the baked clay is readily acted upon by the CONCRETE. 153 moisture, and gradually returns once more to its original condition. For floors, the aggregate is generally crushed much more finely, so as to pass through a f-in. or even a J-in. ring, and for upper floors and roofs scarcely any other aggregate is used than broken brick, pumice-stone, or coke-breeze this last being coke from which all the contained gas has not been quite extracted. It is exceed- ingly light, and, strange to say, is an excellent fire-resister when made into concrete with Portland cement so much so that the British Fire Prevention Committee have definitely made up their minds that coke-breeze concrete would last in a fire better than any other. This, however, does not apply to the cheaper clinker or pan breeze, which is comparatively valueless. The average crushing weights for concrete twelve months old, composed I part lime or cement to 6 parts of aggre- gate, is as follows, viz. : Description of concrete. Crushing weight per foot super. Grey stone lime with ballast aggregate 10 to 1 2 tons. Blue lias lime with ballast aggre- gate i8to25 Blue lias lime with brick or stone aggregate 25 to 30 Portland cement with ballast aggregate 70 to 80 Portland cement with brick or stone aggregate 80 to 100 ,, Concrete one month old, and composed of I part Portland cement to 6 parts of aggregate, gives approxi- mately the following results when tested, viz. : Description of concrete. Crushing weight per foot super. Portland cement with ballast aggregate ... 1 4 ton s. Portland cement with brick aggregate ... 20 154 BUILDING MATERIALS. The safe load for ordinary concrete (composed of I part lime or cement to 6 parts of aggregate) is approxi- mately as follows, viz. : Description. Safe load per foot super. Grey stone lime concrete ... ... I to 2 tons. Blue lias lime concrete ... ... 2 to 3 Portland cement concrete ... ... 6 to 8 The average weight of concrete (i to 6) with different aggregates is as follows, viz. : Weight per foot super. / ^s Description. Lime Cement concrete. concrete. Ibs. Ibs. Brick aggregate ... ... 118 122 Limestone aggregate ... ... 130 134 Ballast aggregate ... ... 137 142 PLATE VI. Filling the Mould for a Stair Tread. Rubbing the Face of a Stair Tread. WARD'S SYNTHETIC STONE [To face p. 155 Chapter XVII. ARTIFICIAL STONE. THERE are three classes of artificial stones now made Simple Cement Concretes, Cement Concretes which have been subjected to some hardening process, and Chemical Stones. Of the simple concretes, which include Stuart's " GRANOLITHIC STONE," " GLOBE GRANITE," and Messrs. B. Ward & Co.'s "SYNTHETIC STONE" (see PL VI.), little need be said. Most of them are composed of a granite aggregate with a matrix of Portland cement, and are either laid in situ or cast in moulds for such purposes as steps and window sills. They have the advantage over ordinary concrete that they are made by the skilled workmen of firms who have a specialist's reputation to lose. One of the simple concretes, " BASALTINE STONE," differs from the others in that the aggregate is composed of basalt chippings, while trass, a pumiceous conglomerate of volcanic origin, is mixed with the cement. It has the important property of combining with any free lime in the cement, and consequently upon this is considered to be an essential ingredient in concrete used for sea- defence work by the Dutch Government. The hardened concretes include " VICTORIA STONE," "IMPERIAL STONE," "EMPIRE STONE," "INDURATED STONE," and others. Of these, " VICTORIA STONE," which has an excellent reputation of long standing, may be con- sidered to be typical. The aggregate used is finely-crushed 156 BUILDING MATERIALS. and well-washed Leicestershire granite, having the following analysis : Silica (soluble) 0*55 (insoluble) 65-26 Alumina 13-06 Lime ... 4'55 Magnesia ... ... ... ... ... I'Oi Oxide of iron ... ... ... ... 9*81 Carbonic acid ... ... ... ... 0*03 Soda 2-34 Potash 2-85 Water, etc 0*54 lOO'OO Three parts of aggregate are thoroughly mixed with one of selected and tested Portland cement in a dry state by machinery, and the water then added in a careful manner, so as to avoid the danger of washing out any of the fine and more soluble portions of the cement ; and before any initial set of crude concrete mixture can arise it is put into the moulds, in which it is carefully worked with the trowel, so as to fill up the angles and sides, thus ensuring accurate arrises all round. The moulds are made of wood, which are lined internally with metal, not only to secure accuracy of form, but also to render them durable, and proof against liability to distortion. The moulds, filled thus, are allowed to remain on the benches of the moulding sheds until the concrete has sufficiently set, and a certain amount of the water of plasticity evaporated. The slabs, when sufficiently dry, are relieved from the surroundings of the moulds ; which, being made in pieces, can be readily detached by unscrewing the fastenings. The slabs are then taken to a tank in the silicating yard (pro- tected from the weather), placed side by side, and covered ARTIFICIAL STONE. 157 by a silicate solution of silicate of soda, where they remain for a period of time which depends on the condition of a slab and its capacity of absorption. About fourteen days, under ordinary circumstances, is regarded as sufficient. The slabs, after being taken from the tanks, are stacked in the storeyard, where they remain to season, and are taken away in the order of their age. The machinery required for the conversion of the crude silica into silicate is of a very simple character, consisting of a pair of iron-edged runners to reduce the silica stone, and a series of jacketed boilers, to which steam of the required temperature is supplied, caustic soda obtained from the best sources being added. The resulting " stone" is one of the best paving materials known, being practically non-absorbent, its porosity being only i '3 per cent., and wearing evenly and very slowly under the tread. It has a crushing resistance of over 550 tons per square foot. Though mostly used for pavings, it is also cast into copings, steps, balustrades, and many other forms. The analysis of a piece of Victoria Stone paving slab is : Silica 50'35 Alumina ... ... ... ... ... 11*87 Oxide of iron ... ... ... ... 7-33 Lime ... ... ... ... ... 18*33 Magnesia ... ... ... ... ... 2*03 Potash 178 Soda ... ... ... ... ... 3-81 Carbonic acid ... ... ... ... 1*80 Water, organic matter, etc. ... ... 2*70 100*00 " IMPERIAL STONE " is almost identical with Victoria Stone, the aggregate being washed to remove fractural dust, and so permit of closer adhesion of the cement, and 158 BUILDING MATERIALS. the moulds being filled upon trembling frames, while they are themselves made of stone instead of metal-lined wood, to avoid all risk of warping. The slabs are subjected to steam during setting, thereby quickening the setting process and at the same time testing the cement in a very thorough manner. They are allowed one day in which to set, and are then placed in the silicate tanks for three days, after- wards being stacked in the open for six months before being sent out. Large pipes, as well as paving slabs, are made of this " stone," crushed flint being substituted for granite as the aggregate, and steel wire rings being bedded in them, one to every foot of length. Such pipes are well suited for many purposes, for though slightly absorbent they are almost as impervious as stoneware, and in the larger sizes, from 2 ft. 6 ins. to 4 ft. in diameter, are much more accurate in shape ; and they can be easily jointed, ogee joints being used (see Fig. 44). Whether anything is gained by immersion in a silicate solution is a moot point. The makers of the simple con- cretes deny it, while those who use this bath contend that it is advantageous to do so ; and all endeavour to produce a material suited to the needs of their customers. The "HARD YORK NONSLIP STONE" differs from other hardened concretes in having Silex York stone as its aggre- gate, and in being made under heavy pressure. The stone is not only crushed, but pulverised and reduced to its original sand, the ingredients are run into moulds, and a pressure of over 2,000 tons per square foot is applied, the solid slab being then immediately ready to be carried to the maturing ground, where it is exposed to the weather for at least eight months. Fig. 44. ARTIFICIAL STONE. 159 The only chemically formed stone of importance at the present time is Ford's SlLICATE-OF-LlME STONE. It is made of silica in the form of fine sand and chalk lime in the proportion of from 92 J to 95 per cent of silica, to from 5 to 7j per cent, of lime, mixed dry and rammed dry into a box mould, which for the larger blocks is cylindrical in shape. The box is made of steel, and has an internal copper lining, both the steel and the copper shells being perforated. A vacuum is created in the boxes, and boiling water introduced under pressure, causing the lime to slake and expand. As the water escapes through the perforations it is replaced by superheated steam under a pressure of 1 20 Ibs. per square inch, thus ensuring the slaking of every particle of lime, and its combination with some of the silica, forming a cementitious silicate of lime. The whole process of manufacture only occupies eight hours, and the resulting material closely resembles a sandstone, having grains of silica cemented together with silicate of lime, either coarse or fine, or of almost any colour, according to the sand used in its manufacture. ANALYSIS OF SILICATE-OF-LIME STONE. Silicates ............... 78-65 Silica ... ... ... ... ... 15*12 Lime ... ... ... ... ... 22*2 Alumina ... ... ... ... ... 0*98 Iron ... ... ... ... ... ... 0*75 Combined water ... ... ... ... 2'i8 Undetermined matter ... ... ... trace 99'97 Perfectly homogeneous and free from flaws, it can be worked like freestone, for it is purposely not made harder than is necessary to secure perfect cementing of the particles. OF UNIVERSITY i6o BUILDING MATERIALS. It has a crushing resistance of from 600 to 700 tons per square foot, and its porosity is 8 per cent. It is conse- quently not very suitable, nor is it intended, for paving purposes, but for walling and general stonework, including ornamental carving. It is made in blocks, which vary from the size of bricks up to cubes of 6 ft. side. Samples were then submitted to solutions containing 5 per cent, 10 per cent., and 50 per cent, of sulphuric, hydrochloric, and nitric acids for twenty-four hours, with the following results, which were far superior to those obtained with good weathering limestones under the same tests : SULPHURIC ACID. 5 10 50 Silicate-of-Lime Stone Unaltered. Unaltered. Slightly attacked. HYDROCHLORIC ACID. Do. Unaltered. Unaltered. Slightly attacked. NITRIC ACID. Do. Slightly attacked. Slightly attacked. Slightly attacked. Chapter XVIII. SAND GRAVEL BALLAST CORE FLINT. THOUGH the term SAND may be applied to small grains of any mineral as found in Nature, it is generally confined in its use to those of quartz (almost pure silica), which are found in excessive abundance in the earth's crust. How very close is the approach to purity of white sand will be seen by the following analyses of samples from Messrs. J. Brown's pits in Leicestershire : Rough white. Fine white. Water 2'68 Organic matter ... ... 0*35 Oxide of iron ... ... O'i8 Alumina and salt ... 0*76 Silica 96*03 lOO'OO lOO'OO While a white colour is generally an indication of purity of the quartz, it may possibly be due to the presence of carbonate of lime, usually in the form of chalk, which, however, can readily be detected by its effervescence if some be placed in a saucer and acid (hydrochloric or nitric) be poured over it. Any colour, ranging from the lightest tint of yellow to a deep red, will in almost all cases be due to the presence of oxide of iron (Fe 3 O4) as an impalpably thin coating to the silica grains, the depth of the colour being an indica- tion of the amount of iron oxide which is present. It has no appreciable effect upon the value of the sand for building purposes, except so far as colour is of importance. M.M. M 162 BUILDING MATERIALS. Angularity of grit, or sharpness, is generally considered an essential quality of good sand. Fineness of grain is often also essential, especially for the finishing coats of plaster, and to secure it sifting has to be resorted to ; but for coarser work it is better to have both coarse and fine particles in the sand, that the crevices between the coarse particles may be filled. Good building sand should be of pure quartz only, with grains of known sizes ; for instance, such as will pass through a sieve of 900 holes per square inch, and caught on one of 1,600 holes. It is only by adopting some such specification for a sand that the best results are to be obtained in making mortar. The presence of loam, although it renders sand easier and therefore cheaper to work, if in sufficient quantity to be detected by the touch, or the appearance, or by leaving a stain when rubbed between damp hands, is distinctly harmful, as it will irretrievably destroy even the best cementing material. It should then be removed by washing ; but the effect of washing naturally good sand is scarcely appreciable, as is shown by the following tests made, on briquettes composed of 2 of sand passed through a sieve of 900 meshes per square inch to I of cement, by the Cement Users' Testing Association : Ultimate tensile stress after two months. Lbs. per sq. in. Unwashed. Washed. Sand from Newbury ... 430*2 430*2 Sand from Nuneaton ... 265 320 Sea sand ... ... ... 307 308 Furnace clinker ... ... 320 325 Standard sand ... ... 267 261 Granite dust from Rugby ... 361 356 Granite dust from Nuneaton... 350 351 The best possible way to wash sand for the removal of clay or loam is in a running stream, the force of which is just enough to remove the mud and very fine sand, leaving SAND. 163 the fine grit and coarser particles behind. Sand is some- times sifted and washed by placing it in a sieve held in a tub of water. A quick horizontal motion from side to side causes the smaller grains to pass through the sieve and fall to the bottom ; but much dirt is in this way carried down with the sand, so that the process is not to be recom- mended. It is supposed that the mud remains suspended in the water until it is poured off, and the coarse stuff remaining in the sieve is rejected as being unfit for the work ; as a matter of fact, much of the mud is deposited with the fine sand, rendering it quite unfit for mixing with lime or cement. If sand contain salt it may be removed by constant washing in running clean fresh water. The most con- venient way to effect this is to construct a washing-tank in the ground, about 6ft. square and iSins. deep, lined with brick in cement. The sand should be filled into this to a depth of 10 ins. or 12 ins., and a stream of water turned on it. A brown frothy scum soon rises to the surface. The sand should be constantly stirred. When the water runs off clear, and without having a saline taste, the sand may be removed for use. It is well to bear in mind (i) that the individual grains of sand contain no salt ; (2) that the salt merely coats the grains or lies between them, having been deposited there by the evaporation of salt water ; (3) that the salt is soluble in water, and may be entirely removed by careful washing ; and (4) sea sand so washed is quite as good for building as any pit or river sand of equal fineness and smoothness of grain. Other methods of " killing " or neutralising the effect of the salt in sea water have been tried at various times, but they have hardly proved successful. Salt is the most harmful substance which sand can contain. It has so great an affinity for moisture that a wall in which it is used is rendered permanently damp. Any sand which is salt to the taste, including all sea sand M 2 164 BUILDING MATERIALS. and a good deal of pit sand, dug from comparatively recent under-sea deposits, should consequently be rejected for all purposes other than for use under water, unless it be first properly washed. Sea sand is also generally rounded by attrition, and consequently wanting in sharpness ; and so to a less extent is river sand. Pit sand is of all qualities, it being impossible to lay down any rule. An excellent sand is obtained in the process of washing decomposed granite for the extrac- tion of kaolin, but it is only used locally, the cost of transport being prohibitive. Sand does not absorb water in any appreciable quantity, its bulk is not diminished or increased by cold or heat, and does not contract in drying ; therefore the greater the quantity of sand used in mortar in proportion to lime, the less probability there will be of the mortar shrinking and breaking. In erecting new walls on the site of old ones, it is usual to work up the old mortar as sand ; but this should not be allowed, as in nearly every case the old mortar, through being made with loamy sand, is valueless for the purpose, and will, if mixed with clean sand, only injure it. The use of old mortar has this to recommend it a much smaller quantity of lime will make it into a working paste than will be required from clean sand. Road-scrapings from hard roads are frequently used with lime instead of sand to make mortar ; but as the proportion of grit in them is so small, compared with the mud, horse droppings, and other filth, they do not make good mortar. Scrapings from soft roads are simply mud. Burnt clay, bricks, tiles, and soft stone are frequently broken up and ground to be used instead of sand. These, if free from dust, make a quick and fairly hard-setting mortar ; but, unlike sand, they are porous, and consequently will absorb water Mortar made with them is liable to crack and shrink in drying, and where a waterproof wall is required, they should never be used instead of clean, sharp quartzose sand. GRAVEL BALLAST. 165 GRAVEL is an extremely coarse sand, as a rule composed to a large extent of rounded pebbles. As found in Nature it generally ranges in the same deposit from fine sand to stones of 3 ins. diameter and more, and in this condi- tion is useful for many purposes ; while for others it is " screened," or thrown against an inclined sieve having a wide mesh of strong wire. If a tolerably fine screen be first used, and then what is retained be again screened, and the process repeated three or more times, sands and gravels of several different degrees of coarseness can be separated out. Further than this, gravel, like sand, can be washed if desired to free it from loam or clay ; and an excellent WASHED GRAVEL is often obtained in this way from brick earth, being separated out in the wash mill and sold as a bye-product. BALLAST means literally any substance of little value which is shot into a ship's hold to give it stability for a voyage when profitable cargo is not obtainable ; but amongst builders the term is restricted to river gravel. This is similar to washed pit gravel, free from loam, and with its particles more or less rounded by attrition. More smooth, and with the further disadvantage of saltness, is SEA SHINGLE, though the salt is not so pronouncedly present as it is among the finer grains of sea sand. A form of ballast, known as BURNT BALLAST, is made by burning clay or brick earth in large heaps, the clay being unprepared in any way, but merely dug, mixed with small coal, tipped into a great heap, set on fire and allowed to burn through. In the middle of such a heap a small proportion will be well burnt to a hard clinker, which, when broken to any desired size, makes an excellent sub- stitute for gravel for many purposes such as for concrete and for the foundations of roads ; but the underburnt portion, of which there is always much, tends to assimilate moisture and return to its original condition as a soft 1 66 BUILDING MATERIALS. clay, and so is useless. Burnt ballast is consequently a dangerous material to specify on account of the difficulty of discarding the bad lumps, which are always in excess. CORE, or HARD CORE, is a name given to any hard rubbish, such as furnace ashes, dust destructor slag, the dry refuse from dustbins, or the detritus from buildings which have been pulled down. This is frequently used for filling up under concrete floors, it being difficult to find anything better provided it contain no vegetable or animal matter, that there be enough small stuff in it to fill up crevices and make it bind, and that it be well rammed. The size of the fragments of which it may consist is of little importance, nor their substance, which may vary from old tin trays to broken crockery and jam pots. FLINTS, which are composed of almost pure silica, and are found in all chalk deposits, occur in curious globular and rounded shapes, and break with smooth surfaces and sharp edges. They cannot be cut with the chisel, but will break under the hammer, and a skilled workman can bring them to rectangular shape and a good face for wall facing. They resist wear excellently and make thoroughly good road metal and filling material under floors. The strange shape and the minute structure of flints show them to be mineral aggregations which were formed round a nucleus of decaying organic matter. Certain organisms, such as sponges and diatoms, provide themselves with silicious skeletons or coverings, the material for which they obtain from the water, and these organisms when decayed furnish silica for the flints. Flints, therefore, grew in the chalk after it was deposited as mud, and they did so by the gradual accretion of silica in an amorphous condition which had previously been held in solution by the sea-water in which the chalk mud was deposited. Chapter XIX. BRICKS : THE PRINCIPAL VARIETIES FIRE- BRICK EARTHENWARE AND STONEWARE TERRA-COTTA NOTES FOR USERS. BRICKS aresmall artificially made building blocks, usually, though not invariably, made of clay in moulds, and raised to a high temperature, with the effect that the soft clay is converted into a hard material, which wears and weathers well, the silica and alumina of which, together with water, oxide of iron and carbonate of lime, the clay is composed combining in very complex manner. As different clays vary greatly from one another, no two being alike, it is not possible to give a general analysis ; nor will analysis always denote how the clay will behave during brickmaking. This can only be determined by experiment, which is often extremely costly. Roughly speaking, however, the alumina gives the plasticity neces- sary to enable the clay to be moulded ; the silica prevents undue hardness and shrinkage ; the oxide of iron helps to bind the brick and is its principal colouring ingredient ; and the carbonate of lime is a binding material. The plasticity also depends upon the water. That with which the clay is mechanically combined can be expelled at a temperature slightly above 212 Fahr. without detriment to its plasticity ; but the whole of the water in the clay cannot be driven off without raising the temperature to dull red- ness, and the clay under these circumstances loses its plastic properties, nor can it be made to re-combine with water so as to recover its plasticity thus, for example, powdered brick will absorb a great deal of water, but it does not by such absorption regain the plasticity possessed 1 68 BUILDING MATERIALS. by the clay of which the brick was made. Of late it has become customary to add about an ounce of carbonate of barium to every cwt. of clay intended to be made into bricks to prevent discoloration, and the appearance of surface scum. One of the chief causes of scumming is the presence of soluble salts in the clay itself, and also in the water used for tempering purposes. These soluble salts, by the com- bined action of the water and heat are driven to the surface of the brick, and cause the white discoloration called scum. The majority of these salts are Sulphuric Acid Salts, the principal one being sulphate of lime or gypsum. Now, if sulphate of lime and carbonate of barium are brought together in the presence of water and heat, a chemical change takes place, and insoluble sulphate of barium and insoluble carbonate of lime are formed, thus : Sulphate of Lime, or Ca 804 Carbonate of Barium, or and in this way the soluble gypsum and scum causing impurity becomes changed and rendered harmless. Sulphate of Magnesia would be decomposed in a similar manner. A thoroughly good brick should be regular in shape, texture and colour, equally and perfectly burnt right through, free from all cracks and flaws, even though they be hair-cracks, and sharp in the arrises ; and should give out a clear ringing sound when struck either with a stone, other bricks, or metal. For many purposes, however, it is unnecessary to insist upon all these qualities. Any hard and well-burnt brick will suffice for foundations and for internal work which is to be subsequently covered ; and for such purposes the cheaper and rougher bricks are BRICKS : THE PRINCIPAL VARIETIES. 169 frequently the more useful, as affording a better key for plastering than those with a smooth surface, and often being better weight-carriers than soft, well-finished, hand- made facing bricks. Sandy and absorbent bricks should not be used in foundations, nor in external walls where likely to be exposed to driving rain. Such bricks are generally soft and do not weather well, being frequently underburnt ; and by retaining moisture they encourage the growth of lichen and climbing plants, which all gather and retain damp. Soft, underburnt bricks are valueless. No brickmaker with a reputation to lose will sell them, preferring to pass them through the kiln a second time, or to crush them for sand. On the other hand a markedly non-absorbent brick, heavily pressed and highly burnt, may have too smooth a face to adhere readily to mortar, especially in summer time, in spite of good wetting. Over-burnt bricks will melt and run together, forming burrs which are useless except to be broken up for road metal or concrete. Faulty bricks are more often met with amongst those which are hand made, hack dried and clamp burnt than amongst those which are modern machine made, chamber dried, and kiln burnt. To tabulate the many different kinds of bricks now made in England would be an almost hopeless task. On the other hand, those which are used in London are commonly, and in a very general manner, classed as either Stocks, Flettons, Sand-faced bricks, Rubbers, Pressed bricks, Blue bricks, Glazed bricks, or Clinkers. The term STOCK BRICK is in use in many parts of the country to denote the particular kind of brick most commonly made for general use in that particular district ; but it is being gradually less and less employed in this way as machine making is supplanting hand moulding, and is becoming recognised as the generic name of a class I/O BUILDING MATERIALS. of brick made largely in the London district and nowhere else, from a thin superficial layer of natural clay. The London stock brick is coarse, hard and strong, and grey or yellow (or occasionally red) in colour. The fuel is mixed with the clay in manufacture, causing it to be exceedingly irregular in structure and colour, and frequently cracked ; but if well burnt it is an excellent brick for general internal walling, backing and foundations, being vitrified right through, and it is frequently blue in the middle, as displayed upon fracture. The following analyses of nominally the same earth that from the Kentish brickfields of Messrs. Eastman & Co. from which stock bricks of similar nature are obtained, are instructive : Sample No. i Silica ... 77'8o Alumina ... 8*51 Oxide of iron ... ... ... 5*15 Magnesia ... ... ... 0*91 Alkalies, etc 2-67 Organic matter, water and loss 3*56 Sample No. 2. 69-01 8-95 5*15 0-99 4-42 6*50 Needless to say, these analyses do not discriminate between the free and the combined silica. The following are the average results of exposing stock bricks from Messrs. Eastman & Co.'s yards (six of each kind) to gradually increasing thrusting stress, the bricks being bedded between pieces of pine f in. thick, and the recesses filled with cement. The extremes varied little from the average : Stress in Tons per Square Foot. Cracked Slightly. Cracked Generally. Crushed. Stock brick, hand made Stock brick, machine made, dried in drier, kiln burnt ... 983 I 47'3 "4*3 192-5 125-9 1947 BRICKS: THE PRINCIPAL VARIETIES. I/I The strength of brickwork, however, as was proved a few years since by experiments conducted by the Royal Institute of British Architects, is much less than that of bricks, and varies so largely with the quality of the mortar, and particularly with the workmanship, that no reliable data can be obtained. The lower qualities of stocks are known as " place bricks," " grizzles " and " chuffs" ; but these are local terms only, and need no definition. FLETTON BRICKS, also known in London as FLITTERS, are machine-made and kiln-burnt bricks from an unpre- pared clay found in a deep bed in the neighbourhood of Peterborough, the quality and colour varying considerably according to the exact locality and the part of the bed from which the clay is obtained. They are cheaply pro- duced in large quantities for ordinary internal work and foundations, being about as hard and strong as stocks. Though some are of a good and even red colour, most of them are khaki-coloured a dirty grey and so unsuited for facing. They have a peculiar and distinct grain, some- thing like that of a coarse oolitic limestone, and a smooth surface to the grains, which are well cemented together, on which account it is sometimes thought that plaster would not adhere to them well, though in practice this objection has hardly been found to hold good. SAND-FACED BRICKS are very largely used in London for facings. They are generally of a red and even colour, often beautiful both in tone and texture ; but they are necessarily soft and absorptive, being made from a light and sandy clay, generally unpressed, or only lightly pressed, in manufacture. As a result, the lower qualities do not weather well, but pit and crumble in the course of a few years, especially when used in the lower courses of a building and subjected either to damp or wear. It is con- sequently necessary to carefully apply the test of tapping, to ascertain the "ring," when it is desired to use such bricks, and to reject all which sound dull ; while an even BUILDING MATERIALS. better guarantee is to use only bricks from a well-known field having a high reputation. That they are not necessarily wanting in strength is shown by the following results of tests upon six specimens of the " T. L. B." (Thomas Lawrence, of Bracknell) hand-made, red-facing bricks : Stress ii i Tons per Squa re Foot. Cracked Slightly. Cracked Generally. Crushed. Ranee no to 215 213 to 232 213 to 232 Average 164*2 224*2 22Q"\ RUBBERS are soft, sandy bricks, invariably hand made, of such a nature as to be uniform in colour throughout, and to be nearly as weather resisting if the outer skin were removed as if it were retained. Thus, as their name implies, they are capable of being rubbed down to any desired shape and to a smooth surface, and even of being carved. Both red and white rubbers are made, but the red ones are the more satisfactory, those from some well-known brickfields, such as the " T. L. B.," having a deservedly high reputation, and almost a monopoly. PRESSED BRICKS are, if red, made as a rule from stiff, plastic clays, and if white from gault clays, the red colour of the one being caused by the presence of oxide of iron and the white colour of the other by the presence of lime. Buff-coloured facing bricks are also made from the Devon- shire stoneware clays, such as those from the Marland pits near Torrington, illustrated in the accompanying photo- graphic plate. In either case the bricks are almost invari- ably machine burnt, artificially dried and kiln burnt at a sufficiently high temperature to secure vitrification right through, with resulting close and uniform texture and great strength. They are also much heavier than hand- made and unpressed bricks, and so are frequently made BRICKS : THE PRINCIPAL VARIETIES. 173 with two frogs, or else are perforated, while they are capable of being stamped with a great variety of patterns in the press. Pressed bricks vary but little in size or shape, and have sharp arrises and a smooth surface. They are conse- quently suitable for all high-class work, making excellent facing, and, where their cost is not prohibitive, backing also, those which are most free from discoloration and from accidental chipping being selected for facings. The following are the results of tests upon samples of white gault bricks made by the Aylesford Pottery Co. : STRESS IN TONS PER SQUARE FOOT. Cracked Cracked Trn^pH Slightly. Generally. 750 885 911 BLUE BRICKS are mostly made in Staffordshire, from a clay containing from 7 to 10 per cent, of oxide of iron. They are burnt at an extremely high temperature until they almost melt, and not infrequently stick together in the kiln. They are extremely hard, with a glassy surface, and of a slightly honeycombed vitreous structure. Other equally strong bricks are made, but as these carry on their face, in their deep blue-black colour and glass-like appearance, a guarantee of thorough burning, they are almost invariably used where great strength is necessary, or where they are to be exposed to heavy wear or to an acid atmosphere. GLAZED BRICKS are of two kinds, " salt-glazed " and " dipped." To produce the former of these salt is thrown into the kiln during burning, a thin glass coating being then formed upon all exposed surfaces of the bricks, care being taken to previously protect all beds and other surfaces which it is not desired to glaze. The bricks retain their natural colour and surface, the glaze pene- trating every crevice, and being extremely thin, though 174 BUILDING MATERIALS. absolutely one with the general structure, so that peeling is impossible. The glaze of a " dipped " brick may, however, be of quite a different colour from its general body, the brick being, as its name implies, dipped into a " slip " of specially prepared clay, either before burning or when half burnt, of such a character that a smooth face is produced, similar to that of china. The preparation of the slip is a very special matter, and great care is necessary in all the processes of drying, mixing the slip, dipping and burning, else discoloration will result, or the glaze will crack or peel, owing to its not contracting uniformly with the rest of the brick when in the furnace. CLINKERS are small, thoroughly vitrified bricks, used mostly, if not entirely, for pavings. Of these the ADAMAN- TINE CLINKERS, made near Stamford, are the best known. They are of light yellow colour, machine made and pressed, and consequently heavy, dense, and almost impervious to moisture. TERRO-METALLIC CLINKERS differ from these in little else than colour, being dark brown or nearly black. FlRE-BRICK is the name given to brick burnt from any highly refractory clay, usually one containing a large pro- portion of silica and little alkali, and capable of withstand- ing great heat. Such bricks are always highly burnt and compact in texture, and generally have a smooth-feeling surface. They vary much in quality, and are made of many shapes and sizes, according to the purpose for which they are required, some of quite moderate heat-resisting power being shaped to form fire-backs for grates ; while others of an exceedingly refractory nature are made like ordinary bricks, or specially moulded to radius, to serve as furnace and chimney linings. A large amount of suitable clay is found near Stourbridge, where much of the fire- brick of this country is made, but in many other places the ordinary brick, terra-cotta and stoneware earths so nearly approximate to fire-clay that they can be used as satisfactory substitutes under moderate conditions. True fire-clay also is found in many parts of the country, UNIVERSITY or FIRE-BRICK. generally amongst the coal measures, and in many cases, either with or without admixture with other substances, is moulded and sold as ordinary building brick or stoneware. It is exceedingly difficult, however, to draw any hard-and- fast line, as the following table of analyses and peculiarities of three well-known clays will clearly show, for they differ widely from one another in almost every particular except the possession of the valuable quality of resistance to fire : Dinas (Glamor- ganshire.) Stourbridge (Worcestershire). Lee Moor (Devonshire). Poole (Dor- setshire). Silica (SiO 2 ) 97-62 63-30 74-02 48-99 Alumina (Al 2 O,s) .. 1-40 23-30 23-37 32' 1 1 Potassa (KO) .. O'lO 0-82 Soda(NaO) O'lO ... 0*09 Lime (CaO) 0*29 o'73 0*40 o'43 Magnesia (MgO) ... ... 0-36 0'22 Protoxide Iron (FeO) 1-80 2'34 Peroxide Iron (Fe 2 3 ) 0-49 1-94 Water (H 2 O) ... 10*30 11-96 Form in nature. Sand to which Stiff black clay Coarser parti- Clay, about i p.c. of under coal cles and re- lime has to be measures. fuse of kaolin added. or china clay, nearly white. Characteristics Resists tempera- Pale brown Dull reddish Mostly used when burnt. ture of 4000 to colour, some- brown to for stone- to 5000 Fahr. times reddish white. Com- ware. Brittle. Frac- or buff, fre- pact, hard ture shows coarse white quently m o t- tled with dark and refrac- tory. particles en- spots. Often closed in light mixed with yellowish common clay to brown matter. resist low tem- peratures only. According to Dr. S. Rideal, refractory fire-clays are of two classes : (i) The silicate of alumina class, in which the alumina is about half the silica, and the latter is mostly in combined form. (2) The silicious class, in which silica predominates up to about 90 per cent, mostly in the free state, and the alumina is low. The former class has the most plasticity for working, and is harder when burnt, but both are refractory in the BUILDING MATERIALS. furnace, provided they contain low percentages of iron oxide, lime, and magnesia, which, especially the two former, are the cause of fusibility. For fire-brick : (a) Lime and magnesia together should not exceed I per cent, (b) Iron oxide should not exceed 2 to 2j per cent, (c) Both should be preferably lower. (d) Alkalies may reach 2\ per cent. The following analyses are also of interest, especially as showing that two samples of nominally the same clay are not necessarily identical, the Stourbridge sample being different from that already given, and the two samples of Turton Moor clay mostly used as "stoneware" for sanitary goods showing a moderate amount of variation : Turton Moor. Dowlais. Stour- bridge. Scotch. No. i. No. 2. Silica 5i'3 59*o 53'02 58-22 5976 Alumina ... i6'9 26-2 32-01 29-46 28-56 Lime 2'6 '3 14-02 1-07 I 03 Magnesia I'O I'O 0'12 0-03 o'oy Iron oxide... n'5 I'O 4'OI I- 4 6 I '21 Water and organic matter 107 10-5 9-42 976 9'37 It is of very little use, as a rule, to build fire-bricks in mortar. They should be laid in fireclay capable of resist- ing as great a temperature as the bricks themselves ; and under many circumstances, especially in furnace building, it is customary to build the structure of lumps of unburnt fireclay, welding it into one homogeneous mass by gradually heating up the furnace itself. EARTHENWARE and STONEWARE are names which are often indifferently applied to clay goods of miscel- laneous character, generally made from mixed earths, or of clays mixed with sand and broken pottery and stoneware. If any distinction can be drawn between them, it is that earthenware is made from milder clays, burnt at a comparatively low temperature, more or less porous, and EARTHENWARE STONEWARE TERRA-COTTA. 1 77 approximating to terra-cotta in character ; while stoneware is made from more refractory clays, burnt at a high temperature, well vitrified, close grained, hard and impervious to moisture, and approximating to fire-brick. Between these two extremes, however, there is every grade and variation. As a general rule, the harder stoneware is of a light straw colour, while the softer earthenware is dark brown, but upon this point, as the others, it is impossible to be didactic. Most ware goods used in building operations, such as drain pipes, sinks, and baths, are used in connection with water, and are glazed. The glaze is itself impervious to water, but it is exceedingly thin, especially the salt glaze usually applied to pipes, so that the main substance should be as non -porous as possible ; and as a salt glaze can be applied to goods when burnt at a high temperature, there is no reason why the necessary degree of vitrification should not be present when it is used. The test is by observation of a fracture, to see that it is compact through- out, and by tapping, when, if underburnt or cracked, it will emit a dull sound, while if well burnt and sound, it will ring true. Correctness of shape is, naturally, tested by observation, and is generally of importance, as warped pipes will not properly fit one another, and warping is by no means uncommon during manufacture. Dipped glazes are thicker than salt glazes, but will rarely stand so high a temperature, so that a perfectly impervious backing is not so generally to be expected, nor is it so necessary with dip-glazed ware. TERRA-COTTA is the name given to any burnt clay or mixture of clays which vitrifies on the face at a moderate temperature with a smooth, hardened surface, and is used in blocks as a substitute for stone, particularly in ornamental work. So long as the outer skin remains intact it is practically indestructible by acids or weathering, and so is an exceed- ingly useful material for external walling in towns and by the sea-side, especially as the hard surface is sufficiently M.M. N 1/8 BUILDING MATERIALS. wear-resisting for it to be used successfully at a low level upon a street frontage, while it is strong enough to carry safely any ordinary load. Its decorative possibilities are also considerable, as it can be obtained of all tints, from a light buff to a deep red, according to the pro- portion of oxide of iron contained in it, this reaching as much as 10 per cent, in the richer tints, and can be made of almost any shape within a limit as to size of about 3| cubic feet. Solid terra-cotta weighs about 122 Ibs. per cubic foot, but it is generally made in hollow blocks, about 2 ins. thick, with connecting webs across the hollow spaces. In this condition it is too light for walling, and the hollows are generally filled with lime concrete, which can be trusted not to expand and burst the blocks. Projecting mouldings and cornices, however, ought not to be filled. Most fire-clays can be made into terra-cotta, with little preparation, and then have excellent texture, colour and surface ; but the interior is rough and porous when the outer skin is removed, whereas it is homogeneous and smooth in the true terra-cotta. In no case, however, ought the interior to be exposed (by rubbing or chipping, for instance, to bring down accidental irregularities), as it is by no means so wear or weather resisting as the surface. Suitable clays for the production of terra-cotta are found near Poole, Watcombe (Devon), Tamworth, and Ruabon. NOTES FOR USERS. BRICKWORK. So far as possible the standard size of a brick, with a sufficient allowance for joints, should be used as the unit for all dimensions. Thicknesses of walls must, consequently, be in multiples of 4^ ins. (half a brick). Lengths may, without cutting unduly, be in multiples of BRICKWORK NOTES FOR USERS. 179 2j ins. (the width of a closer), though any lengths can be obtained by cutting and rubbing. Heights should all be in multiples of 3 ins. (the thickness of a brick), to avoid the necessity of packing with pieces of tile or broken chips of brick. Receding courses, as in footings, are preferably built in headers in 2 J-in. off-sets ; and so are corbel courses if they have any weight to sustain. If backing and facing are of different kinds of bricks, they should be so selected in thickness as to bond properly, due allowance being made for the finer joint used in external work. Unless there be very strong reason to the contrary, all cants, squint quoins, and bird's-mouths should be worked to the angle of 45 degrees. For all other angles the bricks have either to be rubbed or specially made. Bricks of unusual sizes and of special contour are always to be obtained by having them specially made, but as a general rule their cost is prohibitive. Rigid adherence to such mouldings and enrichments as are easily procurable is the only safe rule where means are limited. Keep in mind the standard sizes of the bricks you will use when planning. Thoroughly sound bond can only be secured if the distances between openings, and between cross walls, and the widths of openings, are arranged to brick dimensions. If these be not adhered to, bricks must be rubbed to fit or are more often roughly broken and the bond destroyed. This is particularly necessary when using hard, pressed facing or glazed bricks. Uniformity of colour, where required, is only to be obtained by using bricks from the same maker. Thus it would be unwise to make up a group of mouldings from the catalogue sections of several different firms. All bedded timbers should be to brick dimensions so far as they are enclosed in brickwork. Rubbed and carved work should be so devised that all N 2 i8o BUILDING MATERIALS. bricks can be worked down to fit from the bricks to be used. TERRA-COTTA. Get out drawings full size for manu- facturers or if to a smaller scale, dimension everything exactly. Make no allowance for shrinkage the manufacturer will do this. Work to the dimensions of the particular bricks you intend to use, so as to secure proper bond, allowing for the thickness of Fig. 45- Extravagant Section (requiring; separate right and left hand models). Economical Section (the same model serving for right and left hand). mortar joints. Avoid undercut mouldings and enrichments. Though possible to model, they are difficult and often impossible to mould and cast, and so have to be applied by hand and the risk of non -adherence taken ; or else the manufacturer will alter your detail to make it practicable. Keep all sweeps true, so that they can be struck from a single centre with a running mould. Use repeats as much as possible, remembering that any variation in the size of a block, whether it be plain or enriched, will involve extra expense in the production of special shrinkage-scale drawings and a special model. On the other hand, mouldings and enrichments can be varied in blocks of the same size by the introduction of movable sections in the model. It is an economy to make such things as gable parapets of the same section back and front, as then the same model can be used for both right and left stop ends, mitres and kneeler blocks (see Fig. 45). A certain amount of shrinkage and warping being unavoidable, it is unwise to design too much in straight TERRA-COTTA NOTES FOR USERS. l8l lines and regular curves, unless the mouldings be enriched sufficiently to render any slight twist imperceptible. A large amount of such enrichment is possible without materially increasing the cost, as it would do if it had to be carved in stone. Chapter XX. BRICK, TERRA-COTTA, AND TILE MAKING. BRICKMAKING by primitive methods is an exceedingly ancient industry, and although machinery is now used in most brickfields, the old processes of hand manufacture are still largely employed, especially in temporary brickfields of small extent, and wherever a common brick is made from a surface clay ; and also in some instances where high-class bricks are made which require special personal attention in order to secure some particular characteristic. This is the case with the well-known " T. L. B." (Thomas Lawrence, of Bracknell) rubbers, made at large fields, at Swinley, near Ascot, which are required to be soft enough to be rubbed or carved, well burnt right through that surfaces exposed by carving may weather as well as the outer skin, and of uniform colour throughout their substance. At these works the clay is dug, mixed in a large wash- mill, and run into a back to dry, whence it is again dug and passed into an elementary pug-mill somewhat like a large barrel, standing upright, in which knife blades revolve on a central vertical shaft. This delivers the clay to the moulder much of the consistency of dough, nearly dry and of fine sandy grain. The moulder has in front of him, on a rough table, a board with a raised centre (to form the frog or hollow in one side of the brick) about 10 ins. by 5 ins. in size, over which he places a wooden box or mould with neither top nor bottom, so that the bottom is formed by the board. This box he sprinkles with sand from a heap beside him. From another heap he then takes a lump of clay, kneads and rolls it for a moment, and in a single BRICK MAKING. 183 motion lifts it and drops it into the mould, so as to fill it perfectly without pressure. Then taking a bow, having piano wire for string, he passes it over the top to cut away any superfluous clay, and this he removes by hand, leaving the top smooth. A smooth board (a pallet) is placed on this, and the mould turned over on it and lifted off, leaving the brick on top of the pallet. Several of these "green" bricks are placed on a barrow and wheeled to a dry- ing shed, where they are stacked with many more and left under cover but exposed to the air to be subsequently re- moved to the open and piled in hacks or long rows with sloping boards over them to keep off the rain and the sun- shine. When about half dry, they are restacked, or scintled, into similar rows with more air space between, about fourteen courses high instead of six or eight, as in the drying sheds and hacks. Drying by this means occupies a considerable time, and a good many bricks are spoilt during the process by cracking, warping, or breaking, and have to be sent back to PLAN Fig. 46. Scotch Kiln. 1 84 BUILDING MATERIALS. the pug-mill and remade. The great majority, however, are passed on to be burnt in Scotch kilns. These are large chambers open to the sky (Fig. 46) with a series of fine holes down each side, opposite to one another. The raw bricks are piled up in these kilns in such a way that flues connect the fire holes, and so that the fire can pass freely between and around the bricks from bottom to top, the top being generally formed of old burnt bricks. When the kiln has been filled, or " crowded " as it is termed, it holds, according to its size, from 30,000 to 70,000 bricks. The ends, or doorways, are bricked up and plastered over with clay, and fires lit in the fire holes, the heat being gradually increased till all contained moisture is driven out, when the fires are burnt briskly until the top falls in. This is a sign that burning has sufficiently advanced, and that the fires may be allowed to go out and the kiln to cool. As a rule the bricks will be found to vary in shade, those nearest the eye holes being the darkest in tint, and it is customary to sort them accordingly ; but if the burning has been carefully done there should be but few spoilt through over or under burning. The harder burnt and darker bricks, however, will be found to have shrunk more than those of a lighter colour, the difference in size in the case of unpressed hand-made bricks being often considerable. When bricks of a more common character, such as the London stock bricks, are made by hand, it is more usual to burn them in clamps than in kilns. These clamps are, however, little more than heaps of bricks, themselves having fuel mixed with the clay, built up with a casing of old burnt bricks to somewhat resemble a Scotch kiln, fuel in the form of dust coal being sprinkled between the layers of bricks, and fire holes and flues being roughly formed. The process is slow, extravagant and wasteful, much fuel being necessary, and the resulting bricks being exceedingly rough and unequal in quality, some being soft and value- less, and others in the same clamp so highly burnt as to have BRICK MAKING. I8 5 run together into vitrified masses or burrs, useless for any other purpose than to be broken up for concrete or sold for ship's ballast. Wherever large numbers of bricks have to be made, of good quality, it is necessary to employ ma- chinery. This varies consider- ably, that which is suitable for one kind of clay being unsuitable for another, and it will suffice to de- scribe here three different systems that used by Mr. Fenwick Owen to produce the sand- faced "Osta" bricks from a Ter- tiary clay at Hill End, St. Albans ; that employed by Mr. J. C. Edwards in manufacturing his hard smooth bricks from a Per- mian plastic clay 1 86 BUILDING MATERIALS. at Ruabon ; and that for the production of stock bricks recently introduced by Messrs. Eastwood & Co., at Conyer, near Sittingbourne. At Hill End the clay occurs near the surface, almost like a gravel, containing a great amount of flint, which is sifted out and sold as road metal, while the clay is wheeled and tipped into a circular wash-mill (see plan of works, Fig. 47) containing an ample supply of water, in which it is churned up by revolving beaters. A 11 stones in. or more in diameter which have passed through the sieves settle in this mill as a sediment, and are cleared out once a week, the washed clay, in a liquid state, being driven through an overflow grating, Fig. 48. Sutcliffe's Improved Pug-mill Mixer. which only allows particles less than J in. wide to pass, into a sump-hole 6 ft. deep. This thin slurry is pumped from the sump at a pressure of 20 Ibs. per square inch up a long pipe to troughs, whence it gravitates to large square " backs," or hollows cut in the earth, each of which can be filled in turn. Here the clay is allowed to settle, the surplus surface water being returned to the wash-mill, and the now partially dry clay in the back is covered with a thin layer of "commons," or unwashed clay and sand, and left to evaporate and harden to the consistency of butter, which it considerably resembles. In this state it is dug out, loaded into trollies, and hauled on to an upper floor, where it is mixed with a certain proportion of crushed brick to bring it to a BRICK MAKING. I8 7 proper consistency, and passed downwards through rollers to a pug-mill containing revolving knives and thence to the moulding machine in a lower room (Sutcliffe's Pug-mill Mixer is shown in Fig. 48). The moulds, each for six bricks, are made of wood. They are sanded automatically and passed into the machine where the clay is pressed into them, and as they come out are roughly "struck" by the machine, and then are hand struck to bring them to a level surfacei and are lightly sanded over. The moulds are now turned on to pallets, or boards, which lie on a revolving turntable, and the wood moulds are lifted and returned to be resanded and nnnnnnnnnnnnnnnn passed through the ma- chine again while the pallets are transferred to racks or carriages running on rails, similar to that shown in Fig. 49, and passed into a large drying chamber. There the bricks are subjected to a constant stream of hot air forced in by fans, at carefully regulated temperatures a low temperature when the bricks first enter the chamber, gradually altering as the carriages pass on their rails from end to end of the chamber, till a consider- able heat is attained near the exit doors, each carriage, as it enters, pushing forward those in front of it on the same rails. Thus as each carriageful of raw bricks is introduced at one end, a carriageful of dried bricks emerges at the other, the time between entry and exit being twenty-two hours. Very few faulty bricks are found on emergence from the dryer, and these are immediately taken out and returned to the pug-mill, while the sound ones only are passed on to the kiln, which is a modification of the "Perfected " type. Fig. 49. Deck Carriage for Bricks. Q z LJ _J h * LJ r O LJ L. o: *: QL. CC O O hi 3 E ss m 11 BRICK MAKING. 189 Fig-. 50 shows Warren's "Perfected " kiln, which is of the improved Hoffman type, and serves the double purpose of drying chamber and kiln. If the kiln is in full working the conditions will be somewhat as follows : Chamber 14 has just been stacked with green bricks ; chambers 13, 12, n, and 10 contain bricks in increasing degrees of dry ness, while in chamber 9 the firing has just commenced ; chambers 8, 7, and 6 are in full firing ; chambers 5, 4, 3, and 2 are in various degrees of cooling, the bricks in chamber 2 being ready for unloading ; while chamber I is empty. In crowding a chamber, spaces are left so that when the chamber is fired through the holes in the top the fuel falls onto the floor of the kiln ; spaces are also left between the bricks so that the heat may play all round them, while under the arches between the chambers the bricks are packed closely together so as to form a dividing wall between the chambers. To dry chamber 14 the loading door and damper door are blocked up, and the up draught steam flue, down draught steam flue and hot air flue are opened, and the hot air passes from the cooling chambers through the green bricks, carrying away the water they contain in the form of steam. The up and down draught steam flues are built at opposite ends of the chamber so that the hot air may circulate more thoroughly. It has been stated above that the firing has commenced in chamber 9, by which is meant that the fire has been gradually drawn along the tunnel until the fuel under the first row of fire holes has ignited. The bricks round these fires become heated, and the heat gradually passes along to the next row of fires, and so on. Thus the fire creeps round the kiln, its rate of progress being regulated by means of the dampers. With this kiln it is possible to burn seven chambers per week, or in the event of a breakdown of machinery, any less number, even down to one only. The firing being distributed throughout the kiln enables 190 BUILDING MATERIALS. a very uniform brick to be produced, while only 2 cwts. of coal are used to produce 1,000 bricks. It should be noted that the waste gas from the fuel should not be allowed to come in contact with the wet bricks, as it produces an unsightly stain. At Ruabon the clay occurs as a hard rock in a great open quarry, whence it has to be obtained by blasting, and immediately ground to a coarse grit and stacked in the open for two months in order to weather. At the end of that time it is passed into a pan revolving under rollers for further grinding, and fed from thence to a hopper which passes it between rollers set J in. apart, thence along a mixing chamber containing revolving knife blades which pass the clay forward to other rollers which actually touch, and which, though of the same diameter, travel at dif- ferent speeds, grinding the clay extremely fine. At each opera- tion a little water is added, and the action is very similar to that of a mincing machine, the clay eventually emerging through a shaped die as a plastic band a rectangular die about 9| ins. by 4| ins. being used for ordinary bricks, bull-noses and other sections being formed by varying the shape of the die. A frame set with stretched piano wires 3 ins. apart is now drawn transversely across the ribbon or band of clay, and the separate bricks thus formed are slid on to a table on wheels and carried to the drying chambers, if only common bricks without a frog are needed, and thence to kiln. Hard, compacted bricks are made by passing them through a press before drying. The press (see Fig. 51) is somewhat like the familiar letter-copying press, with heavily-weighted horizontal arms which, on being Fig. 51. Spring Press. BRICK MAKING. swung round, bring an upper die on to the brick previously slid into a sinking beneath it. This sinking has a falling bottom resting on springs with the frog or maker's name raised on it. As the upper die, either plain or with a second frog, descends, it pushes the clay and the bottom on which it rests down to a firm seating at such a depth that the entire brick is enclosed within smooth steel sides. It is thus pressed to an exact size, and as the dies accurately fit the casing it is given sharp arrises. When the upper die rises, the spring raises the lower die and the brick which rests on it up to the level, whence it is removed by hand. Drying is at Ruabon ac- complished by spare heat from kilns and from steam pipes, and the burning is in vaulted or domed kilns, similar to one another in gene al idea. The vaulted kilns are rectangular on plan and are filled from doors at the ends which are bricked up when the kiln is full. There are from eight to ten fire holes along each side, and the heat rises between the inner casing and outer wall, and passes down- wards through the bricks to a perforated floor and thence to an air duct leading to a chimney (see section, Fig. 52). Each kiln is of one chamber only, which has to be inde- pendently filled, burnt and unloaded, occupying a good deal of time, but permitting of careful work. At Conyer, as in many other brickfields, the clay occurs naturally in a condition in which it is fit for conversion into an ordinary brick in this case the well-known yellow London " stock " without washing, grinding, or other preparation. It is dug and tipped at once, mixed with a small proportion of coal dust to act as fuel, into a pug-mill, Fig. 52. Domed Kiln. 192 BUILDING MATERIALS. whence it passes directly to the moulding machine, and thence as moulded bricks to and through a long drying chamber, the operations of moulding and drying being similar to those employed by Mr. Owen at Hill End. So nearly is this the case, that, to avoid redundancy, the deck carriages and drying chamber (see Figs. 49 and 53) used by Messrs. Eastwood & Co. alone are illustrated in this chapter, those employed by Mr. Owen varying from these in minor details only and not in general principle. So thorough is the drying, that even the hygroscopic moisture is driven out, and all irregularities and superficial discolouring due to the presence of water in the kiln is avoided. The kiln used is a long tunnel (see Fig. 54), through Fig. 53. Drying Chamber (Cross Section). which a single line of rails passes. The bricks, fresh and warm from the drying chamber, are reloaded on to larger carriages and passed while still warm into the kiln, which they pass through from end to end just as they had passed through the drying chamber, each as it is introduced pushing along its predecessors. Burning takes place about the middle of the kiln, no fresh fuel being introduced, though a few " live holes " are provided in its arched top for use in case of necessity, and when the kiln is first lit. A current of air is introduced at that end of the kiln from which the bricks emerge, and passes out to a chimney shaft at the end at which they enter, thus cooling the burnt bricks and gradually heating up the unburnt until they, too, reach the temperature at which the fuel they contain ignites. 20 ,, l6 ,, 16 ,, 12 ,, 12 ,, 8 8 4 " Planks from \ to f the above time, according to thickness." If proper precautions be taken against warping and splitting, no process of seasoning is superior to this. 238 BUILDING MATERIALS. WATER SEASONING. Water seasoning is frequently used where there are handy ponds or pools of running- water, especially for log timber before conversion, in order to hasten the subsequent processes. It consists in chaining the timber under water, preferably as soon as it is cut, but more often after its arrival in England from the country of its growth, and leaving it thus, with the butt end up stream, for a fortnight or longer (often for several months if it is not required sooner for use), that the sap may be washed out. For this to be effectual, the timber should be entirely immersed, though frequently the wood is merely allowed to float in stagnant water, injuring it along the water line, and merely soaking the submerged portion, without there being any movement to assist removal of the sap, while stagnant water is also frequently discoloured, and stains result. When properly done the process of seasoning is materially hastened, careful drying in the open air following the water seasoning ; but while it is rendered less liable to warp and crack owing to the lesser period of air seasoning, its strength and elasticity are said to be impaired. This is less notice- able if salt water be used, as it frequently is in harbours ; but for building works salt-water seasoned timber is scarcely admissible, on account of its liability to attract moisture. Timber which, in its country of origin, has been floated to the coast, may be said to have been partially water- seasoned before importation. Such timber, like all other which is water-seasoned, must be thoroughly dried before use, else it will be exceedingly liable to dry rot. Water seasoning can be quickened by using boiling water or steam, but this is rarely done, as it is expensive and tends to reduce the strength and elasticity of the timber. Steaming is, however, employed for the purpose of enabling timber to be bent to any particular shape, and as it effects the seasoning at the same time, nothing more than careful drying is afterwards required to fit it for immediate use. About an hour's exposure to steam is necessary for every inch of thickness. TIMBER SEASONING AND PRESERVATION. 239 HOT-AIR SEASONING (DESICCATION). A considerable amount of timber, especially pitch-pine from the Southern States of America, is " stoved " before it Q i PLAN or Roor OVEN TOR HOT AIR SEASONING or TIMBER GROUND P|LAN O B PERPORATCD FLOOF C DRY AIR INLET D MOIST AIR OUTLET E CONDENSER F" FAN G STEAM COIL Fig. 149. 240 BUILDING MATERIALS. is imported into England. This may not be very scienti- fically done, but it is so far effectual that it prevents the sapwood from turning blue, and renders it extremely difficult to detect the difference between sapwood and heartwood. The application of heat is of no harm if the tempera- ture be under 120 Fahr. Precautions must, however, be taken against the pieces twisting, and in rapid seasoning against their cracking radially ; and above all in season- ing at such a high temperature that strength is taken from the wood, leaving it short and brittle. This occurs most markedly if the heat be applied without a current of air. On the other hand, properly performed, hot-air seasoning, besides being rapid, has the added advantage of driving away all valueless matter, the albumen in the timber being made insoluble and the fibres strong and rigid. A section of the oven used by Messrs. James Latham, Limited, is shown in Fig. 149. The timber is carefully stacked in the chamber A, which has a perforated floor B, beneath which is a horizontal coil of steam pipes, supplying the necessary heat. Dry air is admitted by the perforated pipe C along one side of the bottom of the chamber. As it passes through the chamber it becomes charged with moisture from the wood, and is then drawn off by means of a fan through the perforated pipe D, which is suspended along the top of the opposite side of the chamber. Thence the moisture-laden air is driven over a coil of pipes in which cold water is circulating, in a small closed cylinder The moisture condenses on these pipes and is carried away, while the dried air is passed along to enter the pipe C again. This is continued throughout each day, but is stopped at night-time, so as not to keep the timber constantly under tension ; and a regular temperature of 105 Fahr. is maintained. When freshly-sawn timber is inserted in the chamber, however, open steam instead of dried air is admitted into the chamber TIMBER SEASONING AND PRESERVATION. 24! for the first few hours, in order to dissolve the sap and make it more easy to deal with. Freshly-cut oak, one inch thick, takes between three weeks and a month to season by this process, which is hardly applicable to large scantlings, while the length is limited by that of the chamber. If the rate of seasoning be forced, either by quickening the flow of air or raising the temperature, or by keeping it going constantly night and day, the result is not satisfactory, a hard and brittle surface being produced. It may be pointed out here that stoved or desiccated wood is liable to reabsorb moisture from the air and return to its original unseasoned condition. If used for joinery, it should consequently be kept in a warm drying room between the times of being worked up and being finally fixed, and should be painted (primed) before fixing, preferably before leaving the drying room, and certainly before insertion in an unfinished, and consequently damp, house. McNEILL'S PROCESS. Exposure to the products of combustion of a fire, in a chamber which contains a large surface of water, this being known as McNEILL'S PROCESS, is in principle much the same as desiccation, the result being to make damp, warm air circulate amongst the timber. Efficiently performed, it is equally good, and it is somewhat largely used. It is said that this process renders timber harder, denser and tougher, while entirely preventing dry rot, and that it is best to treat the wood in as green a state as possible. If the heat applied be not too great, sound timber will neither split or warp in the slightest degree, and at the same time thorough seasoning takes place ; while subsequent exposure to the atmosphere will not result in any material absorption of moisture at any rate to not the same extent as happens after dry air seasoning. M.M. R 242 BUILDING MATERIALS. SMOKE-DRYING. Occasionally the seasoning of timber is hastened by drying it over a bonfire of straw, shavings or furze. This is said to render it proof against the attacks of worms, and to make it hard and durable ; but the process is rough and somewhat elementary, and is likely to lead to the timber splitting if the heat is not applied very gradually so as to dry out the moisture from the interior. PRESERVATION BY PAINTING, OILING, TARRING, OR CHARRING. The best seasoned timber will not stand exposure to weather in England for more than 25 years unless some further means be taken to preserve it, and although oak in a dry and well ventilated position has been known to last a thousand years, it is customary to paint all exposed timber in ordinary building works. The effect of painting is merely to cover the surface with a thin film which is impervious to moisture, but as paint is itself perishable, it needs to be renewed, generally once every three years if exposed to the weather. This preserves timber for a very long period, provided that it has first been thoroughly seasoned. This is a very important point, for otherwise the filling up of the outer pores only confines the sap, and so leads to decay. In such a case, it is usually the sapwood which decays first, but properly seasoned timber, whether it be sapwood or heartwood, seems to be equally well preserved by painting. Oiling and tarring have precisely the same effect as painting, save that tar is less perishable than paint and rarely needs renewal, except where it is exposed to sun- heat. Tarring is consequently much used for timber which is inserted in the ground or placed close to the ground and out of sight, and for hidden ends and bedded surfaces of timber in constructional work ; but its rough and unfinished TIMBER SEASONING AND PRESERVATION. 243 appearance, its stickiness when exposed to heat, and its inflammability render tar unsuited to many positions. Charring also may be classed with painting and tarring, it being applied to the surface of timber where it enters the ground, with the object of closing the external pores in this instance permanently. CREOSOTING. Many processes for preserving timber by impregnating it with various substances have been put forward from time to time, but the only one which has proved to be practically and commercially successful is that known as CREOSOTING. Commercial creosote is a dark brown, thickish liquid obtained from coal-tar, of which it constitutes from 20 to 30 per cent. It consists of the light and heavy oils of tar, and is produced from coal-tar by distillation, at tempera- tures ranging from 350 Fahr. up to 760 Fahr. Its com- position is very variable, and but little appears to have yet been accomplished in the way of fixing any standard of purity, or of recording the complexity of its many constituents. The timber to be treated should be thoroughly well seasoned, and then artificially dried for twenty-four hours. It is then piled in a cylinder, which is closed airtight, and pumped to a vacuum. Creosote at a temperature of 120 Fahr. is now allowed to enter, and after the cylinder is full pumping is resorted to at a pressure of 120 Ibs. per square inch. The creosote should be such as to be entirely liquid at 120 Fahr., should contain not less than 25 per cent, of constituents which do not distil over at 600 Fahr., and should yield to a solution of caustic soda not less than 6 per cent, by volume of tar acids, while the specific gravity at 90 Fahr. should lie between 1*040 and 1*065, water being roo at the same temperature. The process is exceedingly efficacious for soft woods, R 2 244 BUILDING MATERIALS. and is invaluable where these are employed for fencing, piles, railway sleepers, or the paving of carriage-ways ; but the discoloration produced and the strong odour of the creosote make it unsuitable for use in ordinary build- ing work. Sapwood in particular is improved by creosoting ; but there are several of the hard woods, including pitch- pine, which the liquid cannot penetrate. An imperial gallon of creosote weighs about io| Ibs. The amount usually absorbed by timber is from 8 Ibs. to 13 Ibs. per cubic foot; but dry beech has been known to absorb as much as 24 Ibs. per cubic foot. NON-FLAMMABLE WOOD. Many processes have been put forward for the preserva- tion of timber from fire, with little success till recently. One, the chemicals employed in which are not revealed, which is now used by the Fire Resisting Corporation, Limited, has of late years proved successful, and not only renders the wood highly fire resisting, but has the further advantages of seasoning and drying it at the same time within a month of its being felled if necessary while the chemicals used are antiseptic, odourless and harmless, and do not injure the wood. The following descriptions are taken from the company's pamphlet : " The timber to be treated is stacked on low wheel trollies running on tracks laid from the stacking yard into the treating retorts or cylinders, which are 105 ft. in length and 7 ft. in diameter (see photographic illustration). The loaded trucks are then run into the treating cylinder, more or less trucks being employed according to the quantity of timber to be treated, and the door of the cylinder closed. The load is now subjected to changes of temperature and certain manipulation, by which means the volatile and fermentable constituents of the wood are withdrawn and the pores of the wood prepared for the reception of the fireproofing ingredients. When the timber is ready, the TIMBER SEASONING AND PRESERVATION. 245 latter is presented to it in the form of a solution of a certain definite strength, such strength varying with the description of wood under treatment. Hydraulic pressure is next applied until the wood is thoroughly saturated. The cylinder is then opened and the load withdrawn, which, if the cylinder be full, will consist of 20,000 cubic feet. " The wood, now thoroughly saturated, and, consequently, more than double its original weight, is re-stacked and run into the drying kiln, which is a large room fitted with heat- ing apparatus, and air fans to circulate warm currents of air, and condensing apparatus to condense the vapour arising from the wood. In about thirty days a load of wood of average thickness should be dry ; that is, the aqueous portion of the solution has been drawn off, leaving the fireproofing ingredients closely incorporated with the cellulose in the pores of the wood. " The wood is now ready for delivery, and, owing to the fact that the volatile and fermentable constituents have been driven off and their place filled with antiseptic material, no rot can take place. Besides, as the wood has been equably dried, the possibility of after-warping is avoided ; and since the interstices of the wood are packed with material, no after-shrinkage is possible." Some woods lend themselves more advantageously than others to the process notably the open-grained non- resinous woods ; while those woods that contain large quantities of pitch and resin, such as pitch-pine, and woods that are very oily in their constituents, such as teak, prove to be sometimes more or less refractory to the treatment. Woods of this class after treatment, while liable under conditions of very intense heat to inflame, are, nevertheless, most difficult to ignite, and consequently afford a protection against fire far greater than if the wood was untreated. In the case, however, of non-resinous and non-oily woods, where complete impregnation can be effected, the treated wood is said to effectually and permanently resist the spreading of flame. Chapter XXVI. TIMBER CLASSIFICATION : SOFT WOODS. NOTES FOR USERS. ALL building timber may be broadly classed under two heads, SOFT WOODS and HARD WOODS ; the terms soft and hard, however, being used in a very general sense, some of the so-called soft woods being harder than some of the hard woods. This comes about through the term soft wood being applied, as a popular name, to all timber of the natural order of Coniferce that is, to all timbers which in their growing state are cone bearing, and have spikes instead of leaves all others being known as hard woods. The following classification of timber, which is a modi- fication by Professor Rankine and Mr. Hurst of that originally proposed by Tredgold, is now generally accepted : CLASS I. SOFT WOOD or PINE WOOD (resinous and coniferous), having very distinct annual rings, one part of each ring being hard and dark and the other soft and light coloured, while the pores are filled with resinous matter. Pine, Fir, Larch, Cowrie, Cedar, Cypress, Yew, and Juniper all belong to this class. CLASS II. HARD WOOD or LEAF WOOD (non-resinous and non-coniferous), the various examples of which may be subdivided as on page 247. When more detailed classification is attempted, however, the confusion which exists in nomenclature introduces an element of extreme difficulty, which is accentuated by the fact that, in the ready-converted form, it is often almost impossible to distinguish between even botanically dif- ferent timbers, to say nothing of botanically similar timbers sold commercially under different names and PLATE IX. SEQUOIA. PITCH-PINE. \To face 6. TIMBER CLASSIFICATION : SOFT WOODS. 247 shipped from different ports. This is especially the case amongst the soft woods, which are almost exclusively used for ordinary building work to such an extent that the great forests of Northern Europe have been nearly denuded of well- grown timber, so that large balks, free from sap- wood, are hardly obtainable ; which is scarcely surprising, considering that a well-grown pine tree takes from 180 to 300 years to reach maturity, according to climate, and that the slower-grown timber is generally the best. DIVISION I. With distinct large medullary rays. DIVISION II. Without distinct or large medullary rays. Sub-division I. With distinct annual rings, one side porous and the other compact. Oak. Ash, Elm, Chestnut. Sub-division II. Annual rings not distinct, and the texture nearly uniform. Alder, Beech, Plane, Sycamore. Greenheart, Mahogany, Poplar, Teak, Walnut. The two following trees, whose ages were computed by the number of annual rings, may be compared : The first, grown 680 miles north of London 24^ ins. diameter at 5 ft. above ground ; 85 ft. high ; 216 years old. The second, grown 1,160 miles north of London 23! ins. diameter at 5 ft. above ground ; 59 ft. high ; 365 years old. Of these the first showed the less heartwood, and a balk 14 ins. square was obtainable from it of heartwood only ; while from the second, a similar heartwood balk was only obtainable I2j ins. square. An attempt to remove confusion has been made in the following tables, but the descriptions are necessarily inade- quate, and students are recommended to trust more to 248 BUILDING MATERIALS. experience gained by personal inspection than to anything they may read. It may also be pointed out that the characteristics mentioned as applicable to the timber from any port are due not to any peculiarities of the port, but to the climate and soil of the district where the timber has been grown possibly hundreds of miles distant The following pseudonyms for the general classes of soft woods may be here noticed : Botanical Name. Popular Pseudonym. Abies ... ... Fir Larix ... ... Larch Picea ... ... Spruce Pinus Pine Tsuga ... ... Hemlock North America is much more rich in varieties of fir timber fit for building purposes than is Europe, and as a general rule the American timber now imported is superior to the European, although the effect of reckless felling is being felt, and large sound timber is not always easy to obtain. Much of the American wood is, in its converted form, almost indistinguishable from the European, however, save by the system of branding and the marks adopted ; so that one is frequently substituted for the other. As a general rule, London and the eastern coast of England are supplied from the Baltic, while Liverpool and the western coast are supplied from America. On account of confused nomenclature it is again desir- able to adopt a tabular system of classification, the same timber being frequently known by several names, and, at least in the case of pitch-pine, several different timbers being known by the same name. In each case the first name given will be that in most common use in England. TIMBER CLASSIFICATION : SOFT WOODS. 249 Special Characteristics and Uses. Formerly sound wood of good length and scantling. Not many large trees left. Still excellent timber if obtainable free from sapwood. Suitable for good carpentry. As above. Even the first quality cut with much sap-wood, often with the heart contained and some- times shaky, while small scantlings are commonly all sapwood. The lower quali- ties are mere rubbish. Often as above, but some good wood for joinery purposes. 1 i No timber of any value. i| "o 2J2 I'jJ '3 .S 2 S 00 03 1 <2 03 Port whence Shipped. ll Is o^ S1JOJ 0) tJO III "Cm Hafaranda Niederkalix Lulea Gefle 11 above port opreg PUB' UAA < Biuqjog *i*M jo SJl no i "1 g .2 S rt ll &o I 1 1 C -SS (5 C/5 55 ^ U sflJ-JI c aj 22 ^ 1 ^ jg O A 'g'g'g' 5 rt^"c3 o" ^ ' ^ C *"^ . { i ^ O ^ o 'w '2 T3 e g S w> & *"}. y 5 5 o ^ ;s iti " Co J3 - O 'Si'*-' O :3 m Ja ac-^ C p 3 si 5 i o o hj S T ^ 1 S ~ c c .s g x6 111 a 1 6 _ o 5 i-! 1 ^ ^j rt W .2T *J-=4- J ** TIMBER CLASSIFICATION : SOFT WOODS. c .ts l>^i ^S'g.S.o 2 Si"?' "So i^f ^ ' c PJ< o ^ 5 ^i rt . ll^bjgl g 9 P ~"O'R 1 s g 3 C ^(U " |11| rt rt o >-," Oii olfsll "EIc 5 n two colours, the red being coarse- grained, hard and strong, while th^ yellow is finer grained and more easily worked. The sapwood is nearly white. As it seasons it becomes hard to work and flinty. loft, weak, brittle and coarse grained ; very light in weight (only iSlbs. per cub. ft.), but durable in contact with damp or soil. The sapwood is nar- row and white, and the heartwood a clear red, which darkens in the light to a deeper tone than pencil cedar. It is very straight grained, and the largest timber known, growing up to 400 ft. high and 40 ft. diameter. L highly resinous, tough, and clean wood, difficult to work, but obtain- able up to 30 ft. in length, and of large scantling of a beautiful grain, some- times richly marked and curly. Very durable and with distinct annual rings. Should be specified by quality and not by port, as sound, close-grained timber, free from large and dead knots and sapwood "- 1 uj *s S|8 S. V i UJ . rt ^ 'o o O* t/3 *+2 c ; 1 > rt c a 2 'C oTs c - v iiii.fi ti-g c S O'-4-(O ( _2 if I 2 o3l P|g 1 jH d Kilj |||| 11 S U^3'2 || 1 sllll 'S JS ^"c fe -J *^ S g-g'S'o 2^ > ,^|'c-| 2 rt ^ c j^u ' G C rt JS I ^J ^-g | 03 rt ^ Sb { ^ N aj g ji**" 1 2 OH^ CO 2 2 ^j ^ W) P .. till ,0 03 111 ic j 5 H rttw H rt ' ' S tn" T3 oj C 1 TJ >** 1 o IE ^ i is"! C '"^ CO C ^ ^ *in C ." 'o *-" 1 2 'S.5 5rC c &o 8 I 8 l^i|| i o Is"-! 03 _ 0) rt *- cn^ en 1 Illllll 1 ^ 03 ^co,n i I Popular Name. fllll flltJJ Ijs llli -rfaT P|| i PQ 262 BUILDING MATERIALS. U 1 1 ^ 2 6 2 o c ' i . rt tt 2 : T3 js 2 9 ^ i u M rt w 5 s rt i niture an >truments c ca 1 ery whic inted or si t3 c rt o .Vhitewoc 1 1,8 *"* C fa'" 15 i* < iH |S II ,0 P P p o Ijl ^ C I-S ll w di si rt |*1 - g c G s , i CJ O C 'o 1 -S t| Somewhat like oak, distinct medullary r heartwood, whiter ; broader grain Very similar to Whit see), for which it is c in the trade 3l|l ~ P 60 1 d j|*| l 00 TJ 1 f-ffl! o'g g-l r o co* C/} M ^ o *" M-S W)" a j2 (/) s >J 5 " tj 3 si I d c I III 1- a II S 1 a ^t c ^g 1 o % If : % q V fill t/), rt = H < 0) 1 "2 III i 1 1 rt 2 j j o 1 I a 111 sl rt a l| If 1 l s - ri o C E c? 3 c oi Ij 1 K CQ u g g "g T3 1 if-i! ~ If 1 Popular N i 1 1 8 J CQ CQ 1 Canary-w Cottonw( (see Popl Cucumber TIMBER CLASSIFICATION : HARD WOODS. r~; T3 n G CXG "- 1 G K 'O >>A 1 *S i tl. cS^ - g"3 ill II" 2 '1 1 rt > 11^ a l >^ Q C; T3 'O .ii aJ aT 1 "- " aj'Sb'ctf 3 l^Oi^jJlJ |- s iisi H ^S 4) C.Q ^j | & 1 " .5 cl d) IM - rt S ,/ ^ o u "5 '5 ^ rt.2 . **3^ '"^ t "*' c M ? C G too Ooti2rt^O U ''o CD d) ^ 2 to ! & rt "a o >-S M<8a & ot/3vG >i G > > O T3 . C C D.***. G rt o cd 1&! 2feS.S ft?i Iff^ J -^3 | rown colour, moderate weight, hard, tough, and porous, with large twisted grain. Difficult to split. Must be used fresh cut, certainly within a year. Most durable if kept entirely dry or entirely wet. Soon decays if subject to changes s above. Takes good polish. Warps and twists in drying lean and straight in grain, very heavy and tough, hard, strong, and elastic. In transverse section it looks like cane, being full of minute pores, with annual rings hardly visible. Dark greenish colour; centre often nearly black. Sap and heartwood difficult to distinguish 'hite colour, close, hard, tough, and strong, with minute pores and plainly marked medullary rays Contains no heartwood tard, coarse grained, and beautifully mottled, showing wavy fibres on radial sections. Dark brown, in- clining to red. Contains much resin. Weighs 60 Ibs. per c. ft. as " Ironwood" in different parts of M PQ , a 3 ol G (i; j3 R? a.". *3 j 1 if. i g O* O j. Tj" u . rt ^ ~ h rt 3" J- 1 H M * . ; 6| T) 52* | I 1 ' "* a? rt G +- ^ C/} ^ G ^ So" :.y"S il "S rt G 2 If rt 6 a I S o fe O i w | ifl I ||| 2 w 2 O 1 S 264 BUILDING MATERIALS. . - s!J HI rt-u <3 CCM 0"* A large wa and varied a C *-->(ne^SL I - | S i3 aine ed. s a g 60 rt^! oS2 O COTS *P - He- s rt -9 2 - I^S ^ !E^ 2 JJ * <" M^S H < 5^ as p M rt o" 5 i i I 2 ||- O i, - c M fa 1 1 "5 1 5s PLATE XII. BIRD'S-EYE MAPLE. LACEWOOD. [To face p. 264. TIMBER CLASSIFICATION : HARD WOODS. 26 5 S m | S u'Q U) j"S 1 M O l-c T5 &13 fe 1 " o" Q a Heartwood is bright red, streaked brown and black ; snpwood a grey- ish colour, and very narrow. On exposure to light the heartwood turns to a clayey brown Soft, easily worked, no^ durable. Twists in seasoning. Tangential sections show medullary rays. Satiny lustre. Not a handsome wood Heartwood is hard, close grained, very dark purple, streaked longi- tudinally with black ; sapwood yel- low, forming a narrow ring Heartwood hard and dark brown A remarkably solid wood, with very little sap, and almost entirely free from shakes. Stands exposure well. Liable to contain hidden cross frac- tures of the fibres Yellowish-brown heartwood, strongly scented. Half the diameter is sap- wood, white and scentless. Weighs 60 Ibs. per ft. c. fO) SD U _ 11 c u .- 03 XI bo Is u d .^ M i y ii o ^ .5 *> II Q cn w h" W M '3-w> ~4J O ^ ? ^ 2^: M a "S M 1 uno Pvo *- ci '-*3 * c H H **J H > 03 CO 0.0 ^? (2 OS E 266 BUILDING MATERIALS. 3 |-s SI ^ .C 2 UJ " n l II } ii a ' c 3 > V S.BJ S bi "rt rt c* 1 : g^^ O rt O n oP S fa 00 h >-i in ^ S T3*";g^^ g en jd S o cd C .5 .2 rt ^ & C be G ^ "^ ^ Characteristics. cu gl. & S J3 a s lll^ ifa s iii^ illisisl ja i-c 5 2g,^SS^^ wg2 c U! rt 00^ oT O o C ^ - a >B.Z y .a I |M ^ *+ O o ^ h-4 ' * O CQ o 00 :. j ' ~ en "O E u 2 "S "S S rt jTO D 3 G C c" O C 113 a'' K u 8 1 1 |i5g||f o o ] 1 g|- ^2 'S T! e*"^'^ 0}^?*-^ ^ "rt *rt -S 3 a, CO 00 Irfgi W Cfl"' TIMBER CLASSIFICATION : HARD WOODS. 267 iii!l 2 . 111 bw SrfSl CL h/i fli ^ . .- cnb gjplgi! ,*- i a, , cq -S >2.s.s^;^s | O I rt 'd'c' II Liriodendron Tulipifera Omphalobi Lambert 268 BUILDING MATERIALS. NOTES FOR USERS. Hard woods, having much greater cohesion between the fibres than soft woods, may be used in curved as well as straight pieces. Shrinkage is complicated by the action of the medullary rays, but is generally less than in soft woods. In constructional work, hard wood should always be used where subject to shocks, as in warehouse doors and storey posts. Mouldings may be undercut, and carving may be rich and deep, there being ample cohesion to render this possible. Exposed hard wood may be protected by oiling, var- nishing or polishing ; but so long as it is kept dry and well ventilated it is exceedingly durable even if unprotected. Chapter XXVIII. IRON ORES AND THEIR REDUCTION. MUCH of the iron ore now used in England is imported from Spain, the richer veins of English ore being mostly worked out or nearly so, that which is left having so small a yield of metal as to be unprofitable. The different kinds of ore and the localities in which they occur, or used to occur, are as follows : Name of Ore. Description. Where Found. Yield of Metal. Clay Ironstone A carbonate of iron, of clay-like appear- ance but oolitic structure, with nodules the size of a pin's head in a silici- ous envelope. Very impure, containing clay, pyrites, and sulphur. Coal measures of Derbyshire, Stafford- shire, Shropshire, Yorkshire, Warwick- shire and South Wales, and in the lias formation of the Cleveland District (Yorkshire) ; also largely imported from Spain. 20 tO 30 %. Not profit- able below 24% Blackband Clay ironstone contain- ing 15 to 20% of bitu- minous and carbona- ceous matter, and consequently easy to smelt. Lanarkshire and Ayr- shire. 40% Durham, Staffordshire, North Wales. Variable Red Haematite Oxide of iron, gener- ally in globular or kidney - sh aped masses; red in colour. Carboniferous lime- stone of Cumberland (Cleator Moor, Whitehaven) Ulver- ston (Lancashire), and Glamorganshire. 50 % to 60 % 2/0 BUILDING MATERIALS. Name of Ore. Description. Where Found. Yield of Metal. Brown Haematite Hydrated oxide of iron ; brown colour. Forest of Dean (Gloucestershire), Al- ston Moor (Cumber- land), D urham, Devon, Northamp- tonshire ; and in France and Belgium. 50% to 60% Magnetic ... Devonshire (very little) ; and in large quantities in Scandi- navia. Spathic Crystallized carbonate of iron, generally mixed with lime. Weardale (Durham), Exmoor (Devon), B r e n d o n Hill (Somerset). 37% The most important English ore which is now profitably worked is that from the Cleveland Hills, near Middles- brough. The best seam, 10 ft. thick, yields 30 per cent, of iron, but this is largely worked out, and much now being smelted yields only 26 per cent. As the cost of reduction rises as the yield diminishes, the limit of profitable working must soon be reached. At the works of Messrs. Wilsons, Pease & Co., Limited, at Middlesbrough, which are similar to most other smelting works in the country, the ore is first tipped, together with small coal to act as fuel and limestone, in such proportion as is later on required to combine with the impurities in the ore, into large continuous kilns, and there calcined, the process being the same as that of lime-burning. Coke is similarly tipped into bunkers adjoining the kilns. This roasted ore and limestone and coke is next hoisted to the top of a blast furnace (see Fig. 1 50) and tipped over its edge into a deep circular V-shaped hopper formed between inwardly inclining plates of C.I. and a central steel cone suspended from a chain by a counterbalance. IRON ORES AND THEIR REDUCTION. 271 ORE GAS FLUE When enough has been tipped into the hopper, together with a proportionate amount of coke, the cone is allowed to drop, discharging- all that is lying upon it into the furnace, which is kept full to within about 1 5 ft. of the top, and is only allowed to go out once in several years, for repairs, it being otherwise in continuous work, night and day. Immediately below the level of the cone is a flue, into which pass the gaseous pro- ducts of combus- tion, the valuable part being the in- flammable carbon monoxide (C O) from the coke, and this is carried off to heat an air blast. This, at a temperature of some i,5ooFahr., is forced into the furnace near its floor through small nozzles known as " Tuy- eres," surrounded with coils of W.I. pipe, through which water circulates to prevent the sides of the furnace well burning out. The furnace is built of brick, much in the shape of a soda-water bottle, with a flat bottom or hearth, Fig. 150. Blast Furnace. 2/2 BUILDING MATERIALS. which, like the whole interior, is carefully constructed of fire-brick. Under the influence of the great heat some 2,000 Fahr. which is generated, the ore is reduced and melted, the iron which it contains sinking, from its greater specific gravity, to the bottom and resting directly upon the hearth, while a lighter scum of impurities, known as slag, floats above it, the burning ore being above that again. When the molten matter has reached to a sufficient depth, never so great as to rise to the tuyere holes, a hole is opened at such a level as to allow the slag to escape. This, which is a crude glass in a molten state, is passed along a trough, and, though some of it is utilised for paving bricks (see p. 207), and some is blown into slag wool (see p. 394), the greater part is valueless, /WOOD CORE ROUND and is either deposited WHIChLSANDJS .PACKED in waste heaps or barged out to sea and dropped in deep water. Fig> I5I> Section of Pig Channels. After the slag has been drawn off, the furnace is " tapped " by making a small hole in a fire-clay stopping at its hearth level. Molten iron runs out through this hole into a semi-circular channel made to an inclination in a sand bed (see Fig. 151). With this metal flows some slag, which rises to the surface and is almost immediately diverted along a branch channel, while the iron itself continues its course down the main channel. At the bottom end of this main channel a branch runs off at right angles, which itself has many short branches parallel to the main, each just long enough to hold I cwt. of iron when full, known as " pigs." When the branch and the pigs which it feeds are full, another branch little higher up the main is opened, by breaking down a temporary wall of sand which lay between, and the main itself is blocked with a C.I. "shutter" just below this newly-opened branch; and so on the process continues unti all the molten IRON ORES AND THEIR REDUCTION. 2/3 iron lying in the well of the furnace has been run out into the pigs. The general arrangement on plan is shown in Fig. 152. oafuumn wiiumiu vJ i\INr\Wii TMfUUUUll IIMMIUIMJ uuuifinnnnnnj REITAINING WALL Fig. 152. Plan of Furnace and Sandbed. The channels, both the smaller ones or pigs, and the larger ones, known as sows, are formed by laying wooden moulds on layers of sand, lying on a sloped platform, and ramming damp sand into the spaces M.M. T 274 BUILDING MATERIALS. between the moulds and levelling the surface before the moulds are removed. Initials denoting who are the owners of the furnace, and showing from which furnace of a series the metal is run, are stamped in the sand at the bottom of each pig. When sufficiently cool the metal is roughly broken up into separate pigs and sections of sows. It is brittle and rough when red hot. The raw materials and products of a Cleveland blast furnace are roughly as follows : Raw materials. cwts. Calcined ironstone 48 Limestone ... 12 Coke 21 J Products. cwts. Iron ... ... 20 Slag 35 Waste, which passes off in the form of gas in combination with introduced air 26 Chapter XXIX. MAIN VARIETIES OF IRON : THEIR IMPURITIES, STRENGTH AND TESTS. IT will readily be understood that pig iron, as run from the blast furnace, is necessarily impure and irregular in its composition, from the intimate manner in which ore, fuel, and flux have been mixed. The principal impurity is carbon, but there are also generally present, in small quantities, silicon, sulphur, phosphorus, and manganese. So important is carbon that it is upon the proportion of this element contained in the metal that the principal distinction between cast iron, steel, and wrought iron depends. Roughly speaking Cast iron contains from 5 to 2 per cent, of carbon (ideal between 4 and 2 per cent.) ; steel contains from 2 to "15 per cent, of carbon (ideal between 2 and *5 per cent) ; wrought iron contains less than '25 per cent, of carbon (ideal under *i per cent). Of these three great classes of iron, the following table (on p. 276) shows what may be considered as the leading characteristics again speaking roughly, and remembering that the classes merge into one another and overlap, the distinctions being sometimes rather those of method of manufacture than of chemical composition, while of each class there are important varieties to be mentioned in greater detail in later chapters. T 2 2 7 6 BUILDING MATERIALS. Cast Iron. Steel. Wrought Iron. Cannot be permanently magnetized Can be permanently mag- netized. Can be temporarily magnetized. Open grained crystal- Close grained brilliant Silky fibrous fracture. line fracture. crystalline fracture. Can be melted and Harder varieties only can Cannot be cast. cast. be cast. Cannot be rolled, Softer varieties only can Can be readily rolled, forged, welded or be rolled, forged, forged, welded, and wire drawn. welded and wire drawn. wire drawn. Cannot be tempered... Can be tempered. Cannot be tempered. Snaps suddenly, espe- Harder varieties snap sud- Gives warning before cially under a sudden denly, softer varieties breaking by first blow. buckle or stretch buckling or stretch- before breaking. ing. No elasticity ... High elasticity. Moderate elasticity. When exposed to fire, Buckles, twists, and ex- Buckles, twists, and stands the heat, but pands when exposed expands when ex- snaps suddenly if to fire, but does not posed to fire, but water touches it break. does not break. while hot. The following, though a different classification from that usual in England, may sometimes be useful. It is based upon that which is official in Germany : Crude Iron. Malleable Iron. Contains over 2-3 per cent, of impurities, generally 9 to 10 per cent. , of which Irom 2 to 5 per cent, is carbon and the rest silicon and phosphorus ; melts without passing through any well-marked pasty stage, and is therefore not malleable; brittle at the ordinary temperature. A. Grey Iron. The bulk of the carbon is graphitic, giving a grey fracture. B. White Iron. The bulk of the carbon is com- bined, and is not present as graphitic carbon. C. Spiegel-Eisen and Ferro- Manganese. Contains a smaller proportion than 2-3 per cent, of impurities, chiefly carbon, gene- rally under i per cent.; higher fusing \ point than crude iron, increasing as the impurities decrease ; softens gradually on heating up to its fusing point, and is therefore malleable. Those kinds which are markedly poor in impurities are malleable when cold. A. Puddled Iron. Prepared in a pasty, imperfectly fused state, therefore not homogeneous ; contains intermixed slag. Varieties containing more carbon are called Puddled Steel B. Ingot Iron (Mild Steel}. Prepared per- fectly fluid therefore homogeneous ; con- tains intermixed slag. The harder varieties, containing more carbon and used for large steel castings, may be called Ingot Steel. C. Special varieties, including Malleable Cast Iron and Temper Steel e.g., Cemen- tation Steel. VARIETIES OF IRON : IMPURITIES AND STRENGTH. 2 The effect of imparities other than carbon is worth noting, though of more importance to the manufacturer than the user, who, so long as he obtains a material which will do the work he requires, does not mind much how it is composed. The following table is therefore rather of interest than value to the constructor : _ Cast Iron. Steel. Wrought Iron. Silicon Effect similar to that of carbon. Also makes it more fluid when melted, i.e., less viscous. 02 per cent, makes it cool and solidify without bubbling. More makes it brittle. '5 per cent, makes it unforge- able. Makes it hard and brittle. Phosphorus Reduces tenacity, hardens, renders fusible. i per cent, makes it cold, short and use- less for tools. Most injurious. Injurious, 'i per cent, makes it more weldable. i per cent, makes it too brittle for use. Manganese Tends to produce white variety. Essential in mild steel to counteract sul- phur. Counteracts red shortness. Sulphur Tends to produce white and mottled varieties. More than '2 per cent, unfits it for forging, but makes it more fluid and suited lor coating. 3 per cent, produces red shortness. In ordinary structural work the following are the approximate data upon which calculations for strength should be based : Cast Iron. Cas: Steel. Mild Steel. Wrought Iron. Ultimate resistance to 32 tons. 40 tons. 30 tons. 16 tons. compression. Safe load in compression 8 ,, 10 ,, 7& 4 , Ultimate resistance to ten- 9 >. Not used in 30 ,, 20 sion. tension. Safe load in tension ij n Do. 7* 5 Ultimate resistance to 8" ,, Not used in 24 ,, 20 , shearing shear. Safe load in shear i * Do. 6 5 Elastic limit or yield point Scarcely dis- 20 tons. 15 ., ii tinguishable from ultimate resistance. Modulus of rupture per 40,000 Ibs. 60,000 Ibs. 42,000 Ibs. square inch. Modulus of elasticity per 17,000,000 Ibs. 30,000,000 Ibs. 29,000,000 Ibs. square inch. Weight per foot super one inch thick. 38 Ibs. 43 Ibs. 42 Ibs. 40 Ibs. 2 7 8 B.U I LD I N G M A T K R I A LS . TABLE OF TESTS FOR CAST IRON. Test Bars, 3 ft. 6 ins. long by 2 ins. deep and i in. \vide, set on bearings 3 ft. apart, and the Test-load assumed to be hung in centre of span. N.B. The Test-load should be supported without fracture, the deflection named being that due to this test load. Description of Material. Test Load. Minimum Deflection. Ordinary quality, suitable for medium- sized columns, etc., and steady loadings Good quality, suitable for large or light columns, bressummers, etc. Special quality, where sudden shocks or extra stresses may arise, as in beams carrying heavy live loads, machine cast- ings, high pressure pipes, etc. C\vts. 25 28 30 tin. &in. 1 Castings should also be tested by tapping them lightly with a hammer all over in order to detect, by the sound, the presence of any air bubbles, cracks, or hollows filled with the sand used in casting. TABLE OF TESTS FOR MILD STEEL. ALL SHAPES OF BARS OR PLATES. Quality. Tension. Elongation.! Minimum.* Maximum.* i Good quality Special welding quality, suitable for rivets. 27 26 31 30 per cent. 20 25 * Maximum and minimum tension strains are in tons per square inch of original section. f Elongation is the percentage of increase in a length of 8 ins. NOTE. Contraction of area tests are seldom applied to steel, the elongation being considered a sufficient test for ductility. MAIN VARIETIES OF IRON : TESTS. 279 The following results of a test upon Whitworth fluid pressed steel show, however, that a better material is obtainable when required for special purposes, though the additional expense of producing it is not generally warranted, it being more economical to use more metal of ordinary quality : Diameter of specimen 7979 in. Length acted upon Yielding Ultimate strength Elongation Reduction of area 5 sq. in. area. 2 inches. 22 tons per sq. in, 38 36 per cent. 60 TABLE OF TESTS FOR WROUGHT IRON. N.B. The Tension columns show the Minimum tensile strains in tons per square inch of original section ; the Contraction is measured at per- centage of original sectional area ; and the Elongation at percentage increase in a length of 8 ins. The Medium quality is suited for most ordinary requirements, but where much forging or welding is necessary, " Special Quality" should be specified. Medium Quality. Special Quality. Description. Tension. Contrac- tion. Elonga- tion. Tension. Contrac- tion. Elonga- tion. Rounds, Squares, 2O per cent. 15 per cent. 10 22 to 23 per cent. 22 per cent. 18 and Flats. Angles, Tees, 2O J 5 10 22 20 10 Channels, etc. Plates (to | in. 2O IO 8 21 12 10 thickness) lengthways. 1 Plates across the 18 5 2 18 6 4 fibre. Wrought iron, suitable for rivets, should have a tensile strength of at least 23 tons per square inch with 30 per- centage contraction of area. In addition to this, it is often specified that the rivet should be capable of being bent double without cracking, to further prove its ductility. 280 BUILDING MATERIALS. The test pieces used for these tension tests are circular in section, and, before and after test, have the appearance shown in Fig. 153, which has been made from the actual bar of Whitworth steel referred to on p. 279. In breaking a specimen of ductile material, such as wrought iron or mild steel, by tension, it is found that before fracture takes place the test piece behaves as a viscous substance (such as pitch or toffee), and flows, being drawn out uniformly until a contraction takes place at the weakest point and fracture occurs. The elongation, or extension, which is thus caused is a measure of the duc- tility of the material ; but in judging this quality, regard must be had to the length of the specimen used, as it is found that of two test pieces of the same material, but of different lengths, the Before Test. shorter will give the higher percentage of elongation ; and similarly, other things After Test being equal, the thicker the ._. test piece, the greater is Fig. 153. Piece of Whitworth Steel. * , the percentage of elonga- tion. It is now usual to make the test pieces 8 ins. long and of 7979 in. diameter, having a sectional area of '5 sq. in. Furthermore, ductile materials such as these, when subjected to a gradually increasing load, as in a testing machine, carry the load up to a certain point with trifling elongation, and return to their original dimensions on removal of their load. In other words, they are perfectly elastic up to that certain point, which is generally known as their "elastic limit," or "yield point." On further increasing the load, however, the material " breaks down " : it begins to stretch to a more marked degree and does not come back on removal of the load. The effect appears to be cumulative. If a load, in excess of the yield point, be applied and removed, stretching occurs, and if the load be applied again, further stretching occurs, with the inevitable MAIN VARIETIES OF IRON : TESTS. 281 result of eventual fracture if the process be repeated too frequently. Consequently in considering the strength of materials for structural purposes, the yield point should be taken as the measure of their tenacity and not the ultimate tensile strength, a point which can scarcely be emphasised too strongly ; but ordinary practice is the reverse of this. The use of a sufficiently high factor of safety, and conse- quently of a sufficiently low working or safe load, puts this right. Repeated alternating stresses, the material being alter- nately in tension and in compression, have also a weakening effect, even if they be well below the yield point individually, but the nature of this effect is not yet quite clear. COLD BENDING TESTS FOR SHEETS. (A convenient size for the test pieces is 8 ins. by 6 ins.] Steel. | Thickness of Sheet. Wither : Wrought Iron, across the \ With the [Across the Remarks. Grain. Grain. Grain. No. 22 Birmingham Wire To bend double round Gauge and under. twice its own thickness. No. 16 to No. 21 B. W. G. JSQ 130 80 \ T h e i n n e r radius of Exceeding No. i6B. W. G., 110 IIO 60 curve at up to |in. in thickness. bend not to exceed i Exceeding \ in., up to A in. 90 90 40 times the thickness of , the sheet. Chapter XXX. CAST IRON AND CASTING NOTES FOR USERS. WHEN the crude iron is run from the blast furnace into sand moulds, forming pig iron, a portion of the carbon taken up in the furnaces separates out in the form of graphite. Some of this floats to the surface and is removable, but the rest remains incorporated in the iron. Furnaces which work with silicious ores, and with a large percentage of fuel at a high temperature, produce a metal containing silicon, which assists the crystallization of the contained carbon. The result is GREY CAST IRON, which displays a grey fracture showing distinct crystals of graphite and a large, dark and bright grain. It is readily fusible, runs well into moulds, and is most suitable for delicate castings, but of no great strength. It is also used for conversion into steel. Its specific gravity is 7'i. Where the opposite conditions prevail, of furnaces working with non-siliceous ores, with a low percentage of fuel and low temperature, the resulting metal contains little silicon and the contained carbon does not crystallize. The result is WHITE CAST IRON, having a fracture of silvery hue, hard and brittle, and of little use for castings, except the very commonest, such as sash-weights. It is principally used for conversion into wrought iron. Its specific gravity is 7-5. MOTTLED CAST IRON lies between the grey and the white, or, more accurately speaking, contains both. When treated with nitric acid, the fracture of grey iron shows a black stain, while the stain on white iron will be brown. CAST IRON AND CASTING. 283 Grey iron may be converted into white by suddenly cooling it. It is thus rendered brittle and hard, and advantage of this fact is sometimes taken to give a hard surface to a grey casting by embedding massive cold iron in the sand of the mould, so as to be in contact with those parts which it is desired to " chill." Similarly white iron may to a certain extent be converted into grey iron by reheating and gradually cooling it ; but it must be remembered that these changes do not affect the composition of the alloy, which normally is as follows : Grey. White. Graphitic carbon Combined carbon Silicon ... ... . . Per cent. 3-30 O'2O O-KO Per cent. 3-20 O'64 Phosphorus 0-08 I'32 Sulphur . ... O'O2 C'2O* Manganese 1-^8 o'6o Iron (by difference) 90-42 94-04 lOO'OO lOO'OO NOTE. The percentage of sulphur in white iron is generally greater than this. When it is required to confer toughness on small cast iron articles of complex form, they are embedded in haematite and heated for several days, and are thereby rendered malleable. By modifying the working of the blast furnace, and by the use of different ores, other important forms of crude iron are obtainable, including FERRO-SlLICON, a light coloured glazy iron, rich in silicon, useful for mixing with white pigs in the " cupola " in order to produce grey iron ; and SPIEGEL- ElSEN (mirror iron), an alloy of crystalline structure and lustrous appearance, containing a considerable amount (generally about 10 per cent.) of manganese, and conse- quently more carbon than does the normal pig. When the proportion of manganese is largely increased, up to a 284 BUILDING MATERIALS. possible maximum of 85 per cent, the metal is called FERRO-MANGANESE. These manganitic pigs are both used in steel making, and so also, to a less extent, are FERRO- CHROMIUM, containing 60 to 70 per cent, of chromium ; and PHOSPHORIC IRON, containing as much as 7 per cent of phosphorus. For foundry purposes, pig iron is remelted in a " cupola" this somewhat mis- leading name being given to a small ver- tical blast furnace (see Fig. 154), worked in- termittently with a cold blast. It is about 5 ft. diameter inter- nally, and lined with fire-brick. Almost in- variably advantage is taken of this oppor- tunity to mix pigs of various classes, with the result that any desired quality of cast iron can be ob- tained. The oxidation of silicon would occur in this furnace, to the detriment of the cast- TEEDING DOOR GAL BLAST PIPES ABOUT SIX IN NUMBER TIPPING LADLE Fig. 154. Cupola. ing, were it not prevented by the presence of manganese, which is the first impurity to oxidize when crude iron is remelted ; while grey iron, rich in graphitic carbon, is improved by being mixed with poorer varieties when used for castings. The pigs and coke are fed into an upper door from a gallery, are melted in the furnace, falling on to the hearth, where a scum of slag collects and is removed as in the blast furnace, while the molten metal is poured out through CAST IRON AND TASTING. 285 a shoot, in appearance like a stream of golden water, into a tipping ladle, whence it is poured into smaller ladles carried by one, two or more men (according to their size) to the moulds. The preparation of the moulds and the process of casting is long, difficult, and often complicated ; and it is unneces- sary to go into the matter here in detail, though a general description may be useful. In the first place, a pattern or model of the object which it is desired to cast is made of wood (or of metal if a large number of duplicates are required), a trifle larger than the finished object, to allow for shrinkage in cooling. Fre- quently a pattern has to be in several pieces, to allow of its subsequent removal in sections from the sand mould ; and often these pieces are alternative where slight variations from a general model are required. For simple castings of small or moderate size, the pattern is placed on its side in the lower of a pair of square frames without top or bottom, known as flasks, so that half of it rises above the level of the top of the flask ; and then fine, loamy sand in a damp condition is tightly rammed into the flask round it* The surface of the sand is smoothed level with the top of the flask, and sprinkled over, together with the visible half of the pattern, with dry or " parting " sand. The upper flask is then lowered so as to fit upon the lower half, to which it is bolted, and damp sand is again packed in, over and around the pattern. When full, the upper flask can be lifted off, carrying with it the tightly-packed damp sand which it contains, but not the dry parting sand nor the pattern, which can be lifted out carefully. For many purposes the flasks are dispensed with and the pattern is sunk in the floor of the foundry, and there packed round with sand or even roughly built in with brickwork before the sand is packed ; while for special purposes specially shaped flasks are used. * See illustrations, Figs. 173 and 174, to the Chapter on "Brass," where the process is again referred to. 286 BUILDING MATERIALS. In either case, the mould left on removal of the pattern frequently requires touching up and finishing by hand an extremely delicate operation ; and when sharp castings are needed it is dusted with powdered charcoal and care- fully smoothed. This also prevents the iron from being chilled by too close contact with the damp sand, as a cushion of gas is formed when the metal is poured in. Finally, holes are carefully rnade through which the contained air of the mould and any produced gases may escape, and for the pouring in of the metal ; the flasks are closed ; and the metal is poured in great care being exer- cised in the case of large castings, where more than one ladle of metal is used, that the pouring is continuous ; and if more than one pouring hole is used, that two streams of metal shall not meet when in the smallest degree cooled ; otherwise a weak spot, or joint, known as a "cold-shut," will be produced. As bubbles form and rise to the surface during casting, it is well that the metal be poured in to the very top of the mould, and that a " head " of metal, afterwards to be cut off", be cast, into which such bubbles may collect. Hollow objects, such as columns and pipes, have to be cast round a solid core, which frequently itself consists of a pipe perforated with many holes, round which damp sand is carefully worked to the desired shape. Theoretically such objects should be cast vertically, but this is rarely possible, and they are generally laid to a slight inclination and cast with a head. The core is, in large columns and long pipes, difficult to fix and retain in position so as to give uniform thickness of metal throughout. Often the core is connected to the outer sand of the mould with iron wire or nails, which, when the hot metal is poured in, are firmly embedded in it. Castings should be left in the sand mould to cool gradually, else irregular cooling is likely to occur, or too rapid cooling of the outside, eventuating in cracks, as strains are set up in the already cooled portions by the CAST IRON AND CASTING. 287 cooling and consequent contraction of the remainder. Similarly, sudden changes of form, and particularly sudden changes in the thickness of the metal in a casting, are likely to result in breakage, the thinner portions cooling much more rapidly than those which are thicker. So far as is practicable, the same thickness of metal should be retained throughout, but if a change is necessary, it should be made gradually. All angles, particularly internal angles, should be rounded. In cooling, the metal is apt to arrange itself in lines parallel with the adjacent surfaces, so that sharp angles result in indefinite mitres in the metal itself, and these are sources of weakness. NOTES FOR USERS. Cast iron can be made into almost any conceivable form of which a pattern or mould can be made. It is most valuable in positions where continuous com- pression is to be resisted, but its resistance to tension is slight, as is also its resistance to shocks. It cannot be twisted, or worked under the hammer, or welded, or riveted. Pieces can only be joined together by the use of screws, collars or bolts. It is much used for common gates and railings, but is very liable to break, and it is rarely used where special designs are called for, when wrought iron would be cheaper (owing to the cost of preparing a pattern), and more durable. Regular painting is essential as a preservative. It cracks suddenly, with little or no warning, whether failure be due to shock, over-loading, or exposure to fire. Chapter .XXXI. WROUGHT IRON NOTES FOR USERS. WROUGHT IRON has been almost entirely replaced by mild steel for heavy structural work, but it is still much used for conversion into hard steel and for small forgings, and particularly for ornamental work, where a tough material, easily handled, bent, or welded is required. Chemically, even in respect to the quantity of contained carbon, it does not greatly differ from mild steel, and in fact, the two often overlap ; but its method of manufacture is entirely different, and the resulting material has very different properties. White, mottled, or hard grey pig iron is loaded and melted upon the hearth of a reverberatory furnace, such as is shown in longitudinal section in Fig. 155. When molten, slags containing oxide of iron are introduced, with the result that the carbon in the pig iron combines with the oxygen they supply, bubbling or boiling off as CO, which ignites, and so assists to raise the temperature of the furnace, this being necessary as the melting temperature of the metal steadily rises as the proportion of contained carbon diminishes. Before long, however, this can go no further, the boiling ceases owing to the carbon having been nearly eliminated, and the metal collects in lumps in a sticky condition. These lumps are brought together with rakes, worked through a side door, and the ball thus made is withdrawn from the furnace, the whole process being known as "puddling." It is then compressed, either by blows from a steam hammer, or by means of a squeezer which acts like the upper arm of a pair of nut-crackers against a bed-plate. In this way the greater part of the contained slag is WROUGHT IRON. 289 squeezed out, and the bloom thus formed is passed between rollers to further consolidate it, the result being known as "puddled" bar. This is cut into short lengths, which are "piled," or tied together with wire, reheated, again in a c n 3oooli ELEVATION SECTION Fig I 55- Reverberatory Furnace. reverberatory furnace, and again hammered and rolled, when it is known as " merchant " bar. Repetition of the process produces " best " bar, which is followed by "best best," and "best best best." If the puddling be stopped at a stage short of the complete M.M. U 290 BUILDING MATERIALS. elimination of the carbon, " puddled steel " is produced, but this is rarely done, owing to the difficulty of obtaining exact proportions. The temperature in a reverberatory furnace being con- siderably less than in a Bessemer converter or a Siemens- Martin hearth, puddled, or wrought, iron is never perfectly fused, so that after being hammered and rolled it consists of a series of parallel fibres arranged to form laminae, some- what like the flakes of pastry which are similarly produced by piling and rolling. Slag which has escaped being pressed out exists between these fibres and laminae, and the material is consequently not homogeneous. The higher qualities, however, have considerable tenacity, and a silky fibrous fracture of grey colour. Until very few years ago wrought iron thus manufactured was used for almost all purposes for which mild steel is now universally employed. Owing to much of the contained impurities existing as intermixed slag, and not intimately combined with the metal, a larger proportion, as detected by chemical analysis, can be carried without injury than is the case with mild steel. The following may be taken as typical analyses : Puddled Bar. Wrought Iron. Per cent. O'lO Per cent. O'oG Silicon O'T-3 Manganese o - o8 o - o8 Sulphur ... O'O^ O'O 1 ! Phosphorus Iron (by difference) 0-35 99-29 0'20 99-57 lOO'OO lOO'OO NOTES FOR USERS. Wrought iron is obtainable in plates, rectangular bars or circular rods, and may be cut, twisted, and bent in any WROUGHT IRON. 291 direction or hammered out flat, or into bulbous knobs ; but it cannot be obtained in mass. Pieces can be joined together by welding (beating together while hot), or by riveting, or by means of wrought-iron collars, but as a rule the joints form weak spots. Wrought iron shrinks as it cools, and advantage of this can often be taken to produce very tight connections, a collar, for instance, being put on hot and allowed to cool on. Only such forms are obtainable, either for construction or ornament, as can be made by hammering, cutting, and planing. Complicated designs have to be built up of many small pieces, each separately formed. It resists shocks admirably, and so is most suitable for gates and railings ; but it rusts readily, and should be kept well painted if used externally. It should not be used in contact with oak, the gallic acid in which attacks the metal, nor in contact with other metals, such as copper, with which a galvanic circuit would be completed in presence of moisture. It bends and twists if exposed to great heat, but bends before it breaks, and so gives warning at all times of impending failure. U 2 Chapter XXXII. MILD STEEL. THERE is another important method of manufactur- ing hard (or true) steel, such as tool steel, known as the CEMENTATION process, but it is not intended to do more than refer to it here. We may, however, note that by its means steel is produced from wrought iron. Our attention will be confined to the BESSEMER and the SIEMENS-MARTIN processes, which alone are employed for the production of the mild steel (more properly called Ingot Iron) used in structural work. Both these processes can be worked as either acid or basic. As originally designed, the Bessemer converter was lined with ganister, a highly siliceous material, refractory at high temperatures and acid in character. This only allows of the use of pure haematite ores, as others con- tain phosphorus, and this can only be eliminated freely in the presence of a base capable of forming a stable phosphate with the oxidized phos- phorus. As non-phosphoric ores are comparatively rare and costly, a basic lining is therefore more commonly used, consisting of dolomite, and to produce the best results with such a lining the ore should not only contain phosphorus, but this element should be present to a fairly rich extent. In the basic Bessemer process, as seen at the works of Messrs. Bolckow,Vaughan & Co., Limited,at Middlesbrough, Fig. 156. Rocker. MILD STEEL. 293 294 BUILDING MATERIALS. the crude iron is run direct from blast furnaces into ladles of large size, which are conveyed by small engines on trucks along railway metals to a mixer, or rocker (see Fig. 156), into which is poured the contents of several ladles from several different furnaces. The rocker is then set in motion, and the contents, when well mixed, are poured into another large ladle and conveyed to the converter. This is a large pear-shaped contrivance (see Fig. 157), hung to revolve vertically, with a hot blast introduced through "tuyere" holes at or near the bottom. It is first heated by a charge of burning coke, which is raked out, and then, if its lining be basic, a proportion of quicklime, of from 10 to 15 per cent, by weight of the total charge, is introduced, and the molten iron is poured in. If the lining be acid, the quicklime is not needed. The blast is now introduced, and the converter is turned into a vertical position. The blast is continued for about eighteen or twenty minutes, during which time important chemical changes take place, which can be followed by the colour and character of the flame and sparks emitted, resulting in the almost complete removal of impurities, including the carbon, when a stream of white-hot nitrogen from the air of the blast alone escapes. If the lining be basic this is continued for a short period known as the " after-blow," during which the phosphorus is oxidized and combines with the lime to form a basic slag, which is poured off. At this stage the blast is stopped for a moment, and spiegel-eisen, containing a known proportion of carbon and manganese, is introduced ; or, if a metal very low in carbon is required (say '25 per cent.), ferro-manganese is substituted for the spiegel-eisen, as by this means a smaller proportion of carbon is introduced for a given amount of manganese. Blowing is now continued for a few minutes to effect perfect incorporation, and then finally stopped, and the converter turned into the position shown in dotted lines in Fig. 157, so as to pour the contents into a ladle, which is carried on a swinging beam. This is swung round, and the MILD STEEL. 295 contents of the ladle are poured into large iron moulds, which stand upright upon railway trucks. Before long the metal cools sufficiently to stand by itself, when the mould is removed, and the truck is taken away with a glowing " ingot " of red-hot steel standing upon it, possibly 6 ft. high and 18 ins. square. The proportions of impurities present at various stages may be seen from the following table : Bessemer Acid Process. Bessemer Basic Process. III 4 Sulphur Phosphorus .. Iron (by differ- O'lO 0-07 93-96 O'lO 0*07 99-64 o'og 005 98-95 o - o5 i '57 92-39 0-05 0.08 99-87 ox>4 O'O2 99 '52 O'OI 0-06 99-70 ence). lOO'OO lOO'OO lOO'OO lOO'OO lOO'OO lOO'OO 100 00 At the works of Messrs. Dorman, Long & Co., Limited, at Middlesbrough, steel is produced by the Siemens-Martin, or Open-hearth process, from a mixture of pig iron, scrap, and ore. The furnace used is that known as a regenerator (see Fig. 158), heated with " Producer Gas," of which 34-4 per cent, is carbon monoxide (CO) and the remainder nitrogen (N). When in work, heated air and heated gas are introduced where shown on the plan, and pass by way of the passages marked a and g respectively, and then up through the regenerators C and B (which are chambers packed with chequer- work of fire-brick). The air and gas meet as they enter the combustion chamber on Hearth A, which they sweep over in a state of combustion at an extremely high temperature, passing out through the 296 BUILDING MATERIALS. SECTION regenerators D and E to the passages a and g, and thence to the smoke flue F. Every few minutes the valves V and V are reversed, and the blast is thus caused to pass in the opposite direction across the hearth and through the regenerators, which are thus alternately cooled while heating the already hot air and gas, and heated while cooling the products of combustion. The hearth of the fur- nace, A, is made of iron plates kept cool by the circulation of air beneath them, packed, in the acid process, with highly sili- cious sand, or in the basic process with dolo- mite or magnesite burnt and ground with tar. When the furnace is white-hot it is charged with pig iron, and when this is fused scrap iron or ore, or both, is added, the pig iron being phosphoric if the hearth be basic, in which case also lime is added to the bath. Complete control is possible ; and when all impurities have been re- r , _ Fig. 159. Steel-Rolling Mills. moved, ferro-manganese is added, as in the Bessemer process, to give the exact proportion of carbon required, and the metal is then poured into ladles and thence into ingot moulds. PLAN PRODUCER GAS Fig. 158. Regenerator. UPPER ROLLS TABLE OF LL CROSS ROLLERS MILD STEEL. 297 By whichever process the ingots have been produced, they are next reheated to a white heat in either vertical or horizontal furnaces, and are then passed lengthwise between steel rollers, of which a simple set is shown in Fig- 1 59- The ingot is placed on the table of small lower rollers, and guided as they convey it under one of the grooves of the large upper roller. The way in which the rollers revolve is reversed, so that the ingot passes alter- nately forwards and backwards, first through groove I, then through groove 2, and so on, being squeezed to a smaller section and greater length each time. After passing through this simple set of rollers, the " bloom," as it is now called, is cut into suitable lengths, and the lengths passed between further rollers, of which the upper and lower sets are now usually of the same diameter, and both grooved, gradually changing the form of the bar until the finished section is obtained, be it rod, plate, joist, T, or angle iron. The following list of market sizes is taken from the catalogue of Messrs. Dorman, Long & Co., Limited, and may vary with other manufacturers ; but the beams (or joists) are standardised, and should be obtainable anywhere : SIZES OF STEEL BARS. Note. All the dimensions given are in inches. Rounds (see Fig. 160) |, , i, ij, ij, if, ij, if, If, If, 2, 2j, 2 J, 2f , 2j, 2f, 2|, 2$, 3, 3j, 3j, 3f, 3j, ^^ 3tb 3i 3l 4, and rising by J in. to 8 ins. Fig I6o> Squares (see Fig. 161) J, $, i, \\ t I J, ig, I j, if, If, If, 2, 2j, 2, 2|, 2j, 2f, 2f , 2$, 3, 3^ 3i 3 3i, 3|, 3i 3f , 4 ins. Fig> 298 BUILDING MATERIALS. SIZES OF STEEL B^RB continued. Flats (see Fig. 162). Fig. 162. Width. Thickness.. Width. Thickness. Width. Thickness. Width. Thickness. I* | to i 3 to i 5 A*' 10 i to I if .. 3i M 5k \ , II .. 12 2 .. 3^ " 6 " *4 i to i 2i " 3 " 7 i to i 15 (> 2| " 4 " 8 " 16 M af " 4i I 5 6 tO I 9 .. 18 " The following are the British standard sections issued by the Engineering Standards Committee, by whose permission they are published : EQUAL ANGLES. H- ^A >j Fig. 163. Size. Thickness at Correct Standard Profile. Radii. Weight per foot. Sectional area. Minimum. Mean. Maximum. Root. Toe. t t ( n np in. in. in in. in. in. Ibs. Ibs. in. in. I X I 125 .. 250 175 125 So 1-49 234 '437 liXI* 125 .. 250 200 150 I'02 1-92 299 5 t t t ''I r-2 in. Max. Mm. Max. in. in. in. in. in. in. Ibs. Ibs. in. in. 3 X2 250 '375 500 275 200 4-04 7-65 19 2-25 3 X2j 250 375 500 275 2OO 4-46 8-50 '37 2-50 3^X2^ 250 '375 500 300 200 4-90 9-36 '44 2 75 3^x3 250 375 500 325 22 5 5'3i I0'20 56 3'3o 4 X2j 250 '375 500 325 225 5'3i I0'20 56 3-00 4 X3 300 425 500 325 225 6-84 11-05 2'OI 3'25 4 X3i 300 425 500 '350 250 7'34 II-9O 2-16 3 '50 4^x3 300 425 500 350 250 7'34 II-90 2-16 3 '50 4ix 3 300 425 500 350 250 7'85 12-75 2- 3 I 375 5 X3 300 425 500 350 250 7-85 12-75 2- 3 I 375 5 X3i '375 ... 500 '375 250 10-37 13-61 3-05 4-00 5 X4 "375 ... 500 '400 275 1 1 '00 14-46 3^4' 4-25 Six 3 '375 500 '375 250 10-37 13-61 3-05 4"oo 5X3 '375 ... 500 400 275 II'OO 14-46 3'24 4'25 6 X3i '375 ... 500 "400 275 11-64 !5'3i 3-42 4*50 6x4 '375 ... 500 425 3 00 12-27 16-15 3'6i 475 6x 3 i '375 500 '425 300 I2-27 16-15 3-61 475 6ix 4 525 ... '425 3 00 17-81 5'24 6x 4 i 550 ... '45 325 19*54 574 7 X3| 525 ... '425 3 00 17-81 5-24 7 X4 ... 550 '450 325 I9-54 574 8 X3i ... 575 '475 325 21-37 6-28 8 X4 ... 625 ... '475 325 24-18 7-11 9 X4 650 ... 500 '35 27-30 8-02 10 x 4 ... 675 ... 550 '375 30'6O 9-00 Z BARS. u ?. ---A' i \0^ i i v ---* i * i A . i Fig. 165. A ! !*, .^ ^ i 1 MILD STEEL. 301 Z BARS continued. Size. Thickness at Correct Standard Profile. Radii. Web and Flanges. Web. Flanges. Root. Toe. per foot. area. A x B x C ti ti n r-i in. in. in. in. in. Ibs. in. 3 X2*X3 300 400 :325 225 9'8l 2-88 4 X2X3 325 425 350 225 11-53 3'39 5 X3 X3 350 450 '375 250 14-17 4 -I 7 6 X3*X3^ '375 '475 H25 300 17-88 5'26 7 X3|X3* 400 500 '45 300 20-22 5-94 8 X3ix 3 .i 425 525 '45 325 22-68 6-67 9 X3^X3 H50 "550 '475 350 2533 7H5 10 X3^X3 '475 '575 500 350 28-16 8-28 CHANNELS. * 1 jf i j^T T i 2 i i B <-&-> -X-- *"* B i ; i , 2 92\ \j? i / ^7 i 1. ^ * ~7 Fig. 166. Size. Thickness at Correct Standard Profile. Radii. Web and Flanges. Web. Flange. Root. Toe. Weight per foot. Sectional area. A X B X B tl t-2 n r% in. in. in. in. in. Ibs. in. 3 xixi 250 312 312 220 5-27 i*55 3^X2 X2 250 312 312 '22O 6-75 1-99 4x2x2 250 375 '375 260 7-96 2-34 5 X2^X2 3 I2 '375 '375 26O 10-98 3-23 6 X2|X2^ 3 I2 '375 '375 260 12-04 3-54 6 X3 X3 3 I2 '437 437 3 00 14-49 4-26 6 X3 X3 '375 '475 475 325 16*29 479 6 X3^X3| '375 475 '475 325 17-90 5-27 7 X3 X3 '375 '475 '475 325 17-56 5*i7 7 X3x3 4 00 500 500 '35 20-23 5'95 8 X2^X2^ 312 437 '437 3 00 15*12 4'45 302 BUILDING MATERIALS. CHANNELS continued. Size. Thickness at Correct Standard Profile. Radii. Web and Flanges. Web. Flange, Root. Toe. Weight per foot. Sectional area. A X B X B ti t-2 n ft in. in. in. in. in. Ibs. in. 8 X3 X3 '375 500 500 350 19-30 5-67 8 X3^X3^ 425 525 525 "375 22-72 6-68 8 X4 X4 H50 550 550 '375 2573 7'57 9 X3 X3 '375 '437 '437 *35 I937 5-70 9 X3X3 '375 500 500 350 22-27 6-55 9 X3X3 450 550 550 '375 25-39 7'47 9 X4 X4 '475 '575 '575 400 28-55 8-40 10 X3^X3 '375 500 500 350 23-55 6-92 10 X3jX3 '475 '575 '575 400 28-21 8-30 10 X4 X4 '475 '575 '575 400 30-16 8-87 ii X3jX3 "475 575 '575 400 29-82 8-77 ii X4 X4 500 600 600 H25 33-22 977 12 X3^X3j '375 500 500 350 26*10 7-67 12 X3^X3 500 600 600 H25 39-88 9-67 12 X4 X4 525 625 625 425 36-47 10-73 15 X4 X4 525 630 630 440 41-94 12-33 MILD STEEL. 303 BEAMS co ntinued. Reference Mark. Size. Weight per foot. Thickness at Correct Standard Profile. Radii. Sectional area. Web. Flange. Root. Toe. A x B h fe n ''2 in. Ibs. in. in. in. in. in. B.S.B. i 3 xii 4 160 248 260 130 1*176 B.S.B. 2 3 X3 8'5 200 '332 300 150 2-501 B.S.B. 3 4 xif 5 170 '240 270 135 1-472 B.S.B. 4 4 X3 9'5 220 336 320 160 2-795 B.S.B. 5 4 fxi| 6'5 180 325 280 140 1-912 B.S.B. 6 5 X3 ii 220 376 320 160 3 238 B.S.B. 7 5 X4 18 '290 448 390 195 5-290 B.S.B. 8 6 X 3 12 260 348 360 180 3'527 B.S.B. 9 6 X 4 i 20 370 431 470 235 5-882 B.S.B. 10 6 X 5 25 4 IO 520 510 255 7"354 B.S.B. ii 7 X4 16 250 387 350 175 4-709 B.S.B. 12 8 X 4 18 280 402 580 190 5-297 B.S.B. 13 8 X 5 28 350 '575 450 225 8-241 B.S.B. 14 8 x6 35 440 '597 540 270 10-293 B.S.B. 15 9 X4 21 3 00 460 400 200 6-178 B.S.B. 16 9 X7 58 550 924 6 5 325 17-064 B.S.B. 17 10 x 5 30 3 60 552 460 230 8-820 B.S.B. 18 10 x 6 42 400 736 500 250 12-358 B.S.B. 19 10 x 8 70 600 970 700 350 20-582 B.S.B. 20 12 X5 32 350 550 450 225 9-408 B.S.B. 21 12 X 6 44 '400 717 500 250 12-946 B.S.B. 22 12 X 6 54 500 883 600 300 I5-879 B.S.B. 23 14 X 6 46 '400 698 500 250 i3'533 B.S.B. 24 14 x 6 57 500 873 600 3 00 16769 B.S.B. 25 15 x 5 42 '420 647 520 260 12-351 B.S.B. 26 15 x 6 59 500 880 600 3 00 I7-346 B.S.B. 27 16 x6 62 550 847 650 325 18-227 B.S.B. 28 18 X7 75 550 928 650 325 22-066 B.S.B. 29 20 X7-J 89 600 I'OIO 700 350 26-164 B.S.B. 30 24 X7 100 600 1-070 700 350 29-392 j<- T ] B- 3ARS. > 3 i i ^ ^1 \ ?N i -* --> <-Si-> <-^^ / i f \ i .,J) Fig. 1 68. 304 BUILDING MATERIALS. T BARS continued. .. 1x3. Gil. Weight per Sectional Thickness at foot. area. 171 \\7a>1\ riange. WCD. Profile. Root. Toe. Min. Max. Min. Max B A t t t n r-2 in. in. in. in. in. in. in. Ibs. Ibs. in. in. I I 125 187 175 125 82 1-17 24 "34 li If 125 I8 7 .. '2OO 150 1-03 1-49 30 '44 4 I* 187 250 '200 150 1-81 2'35 '53 69 i! If I8 7 250 .. 225 150 2-14 2-79 '63 82 *i 2 250 312 .. 225 150 2'79 3 '40 82 oo 2 2 250 312 '375 250 175 3*22 4-64 '95 37 2* ** 250 312 "375 250 175 3'64 5-28 1-07 55 2^ 2* 250 312 '375 275 '2OO 4-07 5 '92 I'20 74 3 2 312 '375 ... 275 200 5*oi 5'93 I- 47 74 3 2 i 312 '375 275 '20O 5'53 6-56 1-63 92 3 3 312 '375 '437 3 00 200 6-08 8-30 1-79 2-44 3 4 '375 500 325 225 8-48 11-07 2-49 3-26 3ft 3i '375 '437 500 325 22 5 8-49 1 1 -08 2-50 3-26 4 3 '375 500 325 225 8-49 11-08 2-50 3-26 4 4 375 500 ... 350 250 977 12-78 2-87 375 4 5 '375 500 ... 4 00 275 11-09 J 4'5o 3 '25 4-26 5 3 '375 500 350 250 978 1279 2-87 376 5 3^ 500 ... '375 250 13*66 4-02 5 4 500 ... ... 400 275 H'Si ... 4-27 6 3 375 500 ... 400 275 1 1 -08 14 '53 3-26 4-27 6 4 500 425 300 l6'22 ... 477 7 3i 500 ... ... 425 300 17-08 ... 5-02 The DlFFERDANGE BEAMS made by Messrs. H. J. Skelton & Co. are for many purposes better than those of the standard section. They are shallow, with broad flanges, most useful where the depth is restricted, while they can often be used where built-up girders are generally employed and they are made of extraordinary length, the smaller sections up to 82 ft., and even the largest to 49 ft. Chapter XXXI it. COPPER. NATIVE COPPER is found in large masses about Lake Superior, and in veins, distributed in crystalline form through granites and other rocks, in Cornwall. There are also many forms of copper ore, including the red oxide, known as cuprite (Cu 2 O) ; the black oxide (CuO) ; and copper gravel (the sulphide, Cu 2 S), all found in Cornwall; and the carbonates: malachite CuCOs. Cu(OH) 2 , and azurite, 2CuCO 3 . Cu(OH) 2 , found at Burra- Burra, in Australia. The most abundant copper ores, however, are the pyrites, which when pure have the com- position Cu 2 S. Fe 2 S 3 , though they are usually associated with gangue and arsenic and with an excess of sulphide of iron. The methods of reduction are numerous and complex, the three principal being the Dry Welsh Process, in which reverberatory furnaces of different forms are used for calcining and melting the ore alternately several times ; the Wet Process, in which the copper is chemically dissolved from its sulphide ores ; and the Electrolytic Process. Of these the Welsh process alone need be described in detail. Several cargoes of ore are successively deposited in one large heap, and the heap is cut away in vertical slices so as to mix the ores. This mixture is first calcined and so reduced to a black powdery form, and then melted in a reverberatory furnace (see Fig. 169), so constructed that while a great heat is generated, beating down from the arched roof upon the dish of ore, the fuel and the ore do not mix, but the flame and smoke from the fuel pass M.M. X 306 BUILDING MATERIALS. over the ore to the chimney. As the ore melts, the metallic portion drops to the bottom of the dish, and a lighter scum of slag rises to the surface. This is skimmed off with an iron rabble through the door, and its place taken by fresh TAPPING HOLE PLAN Fig. 169. Reverberatory Furnace. calcined ore, and the skimming and filling repeated till the dish is full of metal only, which is then run out through the tapping hole into water and so granulated. The whole process of calcining, melting, skimming and granulating has to be repeated three times before a product COPPER. 307 containing even so much as from 80 to 90 per cent, of copper is obtained, and this is then cast into pigs instead of being granulated. The pigs are again melted, or roasted, under a strong current of air, and again cast into pigs, which are of honeycomb structure internally and covered outside with black blisters. This " blister copper " is refined by re-melting, or refining, under a gradually increasing temperature, and the final slag skimmed off. The surface is then covered with charcoal, and a pole, usually of birch, is held in the liquid matter, causing considerable ebullition ; and this poling is con- tinued, with the addition of fresh charcoal so as to keep the surface covered, until by the assays which are taken from time to time it is found that the grain, which at the commencement of the operation was open, has quite closed, so as to assume a silky, polished appearance in the assays when half cut through and broken. The malleability is then tested by taking out a small quantity in a ladle, pouring it into an iron mould, and when set, and still hot. beating it out flat on an anvil. If it stands this without cracking at the edges, the metal is sufficiently toughened, and may be ladled out in clay-lined ladles and poured into moulds. The reddish-brown sonorous metal thus produced is extremely soft and malleable and considerably ductile, with a specific gravity of about 878 and an ultimate tensile strength of about 7 tons per square inch. Castings are rarely made from pure copper, owing to its extreme softness, but this is corrected by alloying it with zinc or tin (see Chapter on "Alloys"). When hammered and rolled, copper becomes rigid, stiff and hard, and even liable to crack and disintegrate, the change being purely mechanical. The specific gravity increases up to 9*0 and the tensile strength to 15 tons per square inch ; while copper wire, J^th of an inch in diameter, may be worked up to such a condition that it will require a strain of 300 Ibs. to pull it asunder. X 2 308 BUILDING MATERIALS. On exposure to the atmosphere, a protective film of so-called verdigris, a basic carbonate of copper of a green colour,* forms upon the surface, rendering the metal prac- tically indestructible. On this account it is extensively used for masonry dowels ; and, when the first cost is not prohibitive, for glazing bars. It is also used for lightning conductors, being an excellent conductor of electricity, and hot-water piping, geysers, baths and ventilators ; but should be avoided in connection with drinking water, as the verdigris coating just mentioned is highly poisonous. Sheet copper is one of the best roofing materials known, being very light, absolutely impervious, and practically everlasting, capable of being laid flat, as in flats and gutters, or of being worked to any curve, and developing a beautiful colour. The general stock size of sheets is 4 ft. by 2 ft., the Scotch size being 4 ft. by 3 ft. 6 ins. ; but Messrs. Ewart & Son make sheets 5 ft. 3 ins. by 2 ft. 8 ins., specially for roofing purposes. The thickness known as 24 B. W. G., weighing 16 ozs. per foot super, is almost invariably used, for though thinner metal would generally suffice, it is more costly to roll, and anything thicker would be extravagant. Larger sheets are obtainable without extra cost (by weight), but they have to be thicker. Up to 16 ft. super- ficial area they must weigh at least 28 ozs. per ft. super (20 B. W. G.) ; above this up to 24 ft. super they must weigh 32 ozs. (19 B. W. G.) ; and above this up to 28 ft. super they must weigh 48 ozs. per ft. (16 B. W. G.). Hardened copper sheeting has of late been introduced by Messrs. Ewart & Son for rain-water eaves, gutters and ornamental features, such as finials, as being capable of standing with little or no support. Copper wire is used for electric lighting, electric bells, and for ordinary bell-hanging this last from 17 to 19 B. W. G., well stretched before use. * This is not a true verdigris, which is a basic acetate of copper. Chapter XXXIV. LEAD. LITTLE lead ore is now found in England, though at one time lead mining was an extensive industry in the North of England, Derbyshire, Wales, and Scotland. Most of the metal now in use is obtained as a bye-product of silver mining, as at the Broken Hill Mines in Australia, while a good deal is also obtained in the United States, Spain, the Hartz district of Germany, and Peru. The ore is mechanically separated out from the gangue, or spar with which it is mingled, and then roasted and reduced in a cupola or blast furnace. The principal ore is galena (the sulphide, PbS) ; though cerussite (the carbonate, FbCO 3 ) is extensively worked at Leadville, Colorado ; and anglesite (lead sulphate, PbSO 4 ) is occasionally found, especially in combination with silver. Crude lead thus obtained needs refining before it is ready for use, but the following analyses show that after refining it becomes almost absolutely pure : Freiburg Commercial Crude Lead. Lead. Per cent. Per cent. Lead 9772 99*9837 Arsenic ... ... 1*36 Antimony 072 ... 0*0037 Iron ... ,.. 0*07 ... O'OOi6 Copper 0*25 ... 0-0014 Silver 0-59 ... O'OoSo Lead is one of the heaviest substances known, having a specific gravity of u'35. It has a low melting point (617 Fahr.), and is soft and easily bent and worked or 3io BUILDING MATERIALS. beaten out to any desired form ; but it is by no means ductile, and is greatly wanting in strength, being easily crushed, torn, and twisted. At the same time it well resists wear, and is practically impervious to water. This last quality, together with its pliability, renders it a CUP 3WIVEIL- MOUL n Fig. 170. Lead Melting Furnace. most valuable material for use in water-carrying pipes, and for lining cisterns and sinks, while, used horizontally, it is one of the best roofing materials, as only just enough fall need be given to enable the water to flow towards the gutter or outlet and to compensate for accidental irregu- larities in the laying a fall of I in 120, or I in. in 10 ft., being usually considered sufficient. Where good work is LEAD. 311 required it is similarly used, almost universally, in gutters behind parapets and between roofs, in roof valleys, and as apron flashings. Its low melting point, combined with its impermeability, has caused lead to be largely used in a molten state for making joints in iron pipes, and for " running in " iron cramps and the joints of iron railings to stonework ; but not with success except under cover, as in the presence of moisture, and particularly in that of soft rain water, gal- vanic action is set up between the lead and iron, resulting in the destruction of both metals. The lead as received from abroad is melted in a large copper pan with a furnace beneath it, similar to the ordinary domestic copper, only larger in size, and supplied with a valve near the bottom for letting out the molten metal. From this valve it is conveyed to any spot desired in semi- circular troughs, the arrangement when running it into moulds being somewhat as is shown in Fig. 170. The moulds, which contain I cwt. of metal each, and are semi- circular in section, are arranged in fan form round the furnace, and the lead is poured into each in rotation, any scum due to the metal becoming chilled being carefully removed and returned to the furnace. Chilled lead, though pure, is brittle and of little value, so that its use must be avoided. Sheet lead is generally made by casting a plate of lead about 5 ins. thick, weighing about 7 tons, and then passing this under metal rollers until it is squeezed down to the required thickness. Such sheets are known as "milled lead," and can be gauged very accurately, the various thicknesses being known by the weight in pounds per foot super. Such sheets are commonly made in lengths up to 35 ft., and in widths which vary from 5 ft. 6 ins. to 8 ft., but greater lengths and widths can be obtained if desired. Sheets can also be made by pouring the molten metal on to a carefully levelled bed of sand on a wooden bench, and then passing a " strike " over the surface to sweep away 312 BUILDING MATERIALS. any surplus beyond the desired thickness. Such sheets are known as "cast lead," and they are generally thicker than the milled sheets and smaller in size. Many architects, however, prefer cast lead, holding that the natural structure of the metal is broken up in the passage through the rollers, and that milled lead is thus rendered brittle and liable to crack if exposed to changes of temperature, as is inevitable upon roofs. Gauges are procurable for testing the thickness of lead sheets according to UPPER CYLINDER the weight specified ; but if any doubt exists it is best to cut off a rectangular piece from a sheet and weight it care- fully, computing from that the weight of a square foot. In general practice, 4 or 5 Ibs. lead isspecified for aprons and flash- ings ; from 6 to 8 Ibs. for roofs, flats, and gutters ; and from 5 to 7 Ibs. for ridges and hips ; but in exposed situations or on flats liable to wear these thicknesses are hardly sufficient. A very thin sheet is also rolled, known as "laminated lead," which is used as a lining to damp walls underneath the paper. Lead pipes are made (at the works of Messrs T. & W. Farmiloe) in a hydraulic press in a manner shown diagram- matically in Fig. 171. There are two steel cylinders, of which the upper is fixed while the lower is gradually lifted by hydraulic pressure, the lower one exactly enclosing the STEEL DIE HAVING CIRCULAR MOLE EQUAL TO OUTER DIAMETER Of PIPE LEAD LOWER CYLINDER CIRCULAR STEEL MANDRIL WHOSE DIAMETER IS EQUAL TO THE INTERNAL- DIAMETER OF PIPE HYDRAULIC PRESSURE APPLIED UPWARDS Fig. 171. Diagram of Pipe-making Press. LEAD. 3 1 3 upper. In the upper cylinder a steel die is fixed, having a circular opening, whose diameter is exactly equal to the desired outer diameter of the pipe ; while a steel mandril is fixed in the lower cylinder, whose diameter is equal to that of the inside of the pipe. Molten lead is poured into the lower cylinder till it overflows, when the chilled scum is removed, and the metal allowed to partially cool. The hydraulic pressure is then applied to the lower cylinder, which rises, exactly encloses the upper cylinder, and forces the lead upwards between the mandril and the die. Large pipes that is, pipes of 2 ins. internal diameter and more are helped to rise vertically, and are generally cut off in lengths of 10 ft. Pipes from i to 2 ins. in diameter are rolled in coils of 36 ft. long, containing three " lengths " of 12 ft. each ; while the coils of all smaller pipes than this contain four "lengths" of 15 ft. each, or a total of 60 ft. The weight in pounds per "length" is stamped at each end of each coil. All the smaller pipes should be made of perfectly pure, new and unchilled lead, that they may bend readily as desired without cracking ; but large pipes, like soil pipes, require to have more stiffness, and this is imparted by mixing some old lead with the new. Table of lead pipes manufactured by Messrs. T. and W. Farmiloe, Limited : LEAD PIPE. ^ in. 10 Ic , 20 2 1 ) Ibs per is ft ^1 Equal to 2 3 Ibs per yard in. 10 20 10 Ibs per 15 ft Equal to 2 i in. 15 18 4 20 5 22 6 28 ST 40 ... Ibs. ... Ibs. per yard per i z ft. j . Equal to 3 fa in. 1 6 4 22 5 5* 6 7 8 9 ... ... Ibs. ... Ibs per yard per i ^ f t P Equal to 3^ i Ibs per yard c in. i 8 22 2 7 30 :? 4O .. Ibs per i ^ f t **? o Equal to ^4 *1 r> 7 8 Ibs per yard ^ J-l if in. 22 Equal tO4| i in. 28 Equal to 5 J 24 5 36 OC-&. Ot tO C. u*- M W- CM* 28 51 45 9 32 6* 48 36 52 10 J 40 8 56 45 50 9 10 60 64 12 13 55 60 II 12 70 80 14 16 ... Ibs. ... Ibs. ... Ibs. . . Ibs. per 15 ft. per yard per 15 ft. per yard J 3'4 BUILDING MATERIALS. LEAD PIPE continued. ij in. 28 32 36 42 48 52 56 60 64 72 80 88 Ibs. per 12 ft."^ Equal to 7 8 9 ioj 12 X 3 J 4 15 16 l8 20 22 Ibs. per yard T! in of~ 41 A *? 48 <^6 60 72 84 06 Ibs per 12 ft. J 2 m - o Equal to 9 * 4 -, ioj T- 12 D*-" 14 ^j 152 /> 18 U T- 21 yvj . .. 2 4 ... Ibs. per yard T i-n CfS * r?o 8 ft lengths. *i 34 4i 48 55 ... Ibs. per 10 ft." 3 4i 49 57 66 74 82 M 3i i 47 54 57 65 73 67 76 85 76 87 97 86 98 95 109 " ( In 10 ft. lengths. 5 81 94 107 6 ... 128 it J LEAD SOIL PIPE. (As specified by the London County Council.) i. ... 65 Ibs. per 10 ft. length. | 5 in. ... 92 Ibs. per loft, length. ...74 Ibs. no Ibs. Chapter XXXV. ZINC GALVANIZED IRON. THE principal zinc ores are those known as the calamine (the carbonate, ZnCO 3 ), zinc-blende or black-jack (the sulphide, ZnS), and the red oxide (ZnO). These are mostly found in the Ardennes, the Rhine country, Silesia, Greece, France, and the United States, the best known zinc-works being those of the Veille-Montagne Company of Liege, whose English agents are Messrs. Braby & Co. The ore is reduced by roasting, mixing with half its weight of coke or non-caking coal, and then heating in retorts, the metal being driven out as a vapour, condensed, and then refined by melting on a hearth provided at one point with a well, into which any contained lead (generally from i to 3 per cent.) settles out in the course of two or three days. The metal thus produced is brittle and fusible ; but it becomes malleable at about 220 Fahr., and at that tempera- ture can be rolled into sheets which retain their malleability though at a higher temperature, about 400 Fahr., this malleability is again lost. Its melting point is 774 Fahr., and it has a specific gravity of 7. On exposure to the atmosphere a protective film of zinc oxide is soon formed on the surface ; but unfortunately this has not the permanent protective effect that verdigris has upon copper, especially near the sea and in large towns, as sea salt and acids act harmfully and soon destroy the metal. Soot and urine are also destructive to it, and con- sequently zinc should not be used in positions accessible to cats. It is important that zinc should be pure when it is of 3l6 BUILDING MATERIALS. uniform colour (dull grey), tough, and easily bent without cracking ; while if impure, it is darker in tone and blotchy in appearance. If it contain iron to any perceptible extent it will not resist the action of the air, while the presence of lead makes it too brittle to roll. The following analysis of Veille-Montagne zinc shows that it is practically pure : Pure zinc ... ... ... ... 99'5 Traces of iron ... ... ... ... 0*4 Lead and sulphuret ... ... ... o - i lOO'O Sheet zinc is largely used for flat roofs, gutters, and flashings, and is supposed to have a life of about twenty years under ordinary London suburban conditions. It is also stamped into ornamental tiles, ridge cresting, and eaves gutters, and is even used for rain-water pipes ; but its brittleness and want of stiffness prevent its being of much value if so employed. As a lining to drinking-water cisterns it is satisfactory, but its greatest value is as a protective coat to ironwork (see Galvanizing), and as a component of alloys. If zinc be allowed to come in contact with iron, copper, or lead in the presence of moisture, galvanic action is set up, and the zinc is rapidly destroyed. It catches fire at a low temperature, and blazes furiously. The expansion and contraction of zinc under changes of temperature are considerable, being more than those of other metals, not excepting lead, and must be carefully provided for by avoidance of rigid fastenings. Zinc is rolled in sheets of 6, 7 or 8 ft. long by 3 ft. wide ; though longer sheets up to a maximum length of 10 ft. are obtainable by extra payment. The thicknesses are standardised by a special zinc gauge, by which they should always be specified. For roofing purposes, 14, 15, and 16 ZINC. 317 gauges are those mostly used, but 14-gauge zinc is really too thin to be reliable. Thinner gauges than this are mostly used in perforated sheets for ventilation purposes, and the thicker gauges are stamped into eaves gutters, ornamental tiles, etc. ZINC GAUGE. LIST OF WEIGHTS AND THICKNESSES. &D i Approximate Thickness. Approximate weight per square foot. Approximate weight of Sheets. 36 in. x 72 in. 36 in. x 84 in. 36 in. x 96 in. 43 3 11 2 o C rt^ ! i o 24 1880 26 ' i o 6 2170 The Sheets should have 6-in. Laps, and be Double-rivetted at Joints : 3 Ibs of rivets required per Square. Hot galvanizing, as described above, is the process most extensively used to apply a zinc coating to iron and steel. Electro-zincing, or cold galvanizing, is used for special classes of work. A third method, called Sherardizing, has now been developed, and works have recently been com- pleted for carrying it out on a commercial scale. By this new process iron and steel can be coated with a thin even deposit of zinc at a temperature below the melting point of this metal. The first step in the process is to free the GALVANIZED IRON. 319 iron from scale and oxide by any of the well-known methods, such as dipping in an acid solution or sand- blasting. The articles to be rendered rust-proof are then placed in a closed air-tight iron receptacle (exhausted of air to prevent oxidization of the zinc) charged with zinc dust, which is heated to a temperature of from 500 Fahr. to 600 Fahr. for a few hours and allowed to cool. The drum is then opened and the iron articles are removed, when they are found to be coated with a fine homogeneous covering of zinc, the thickness depending on the tempera- ture and the length of treatment The temperature required to bring about this result is about 200 below the melting point of zinc. The low temperature required makes the process cheap as compared with the process of dipping in molten zinc, and has the additional advantage that it does not deteriorate iron or steel of small section to the same extent as hot galvanizing. The whole of the zinc is consumed, and there is no waste of zinc as in the hot galvanizing process. This dry process of coating iron is not limited to zinc, but has been applied to coating iron with copper, aluminium, and antimony, and to coating other metals, such as aluminium and copper, with zinc. Copper and its alloys subjected to this process are case- hardened on the surface, and can be rendered so hard as to turn the edge of a steel tool. The zinc powder used is the zinc dust of commerce, and is obtained during the process of distilling zinc from its ores. One of its peculiar pro- perties is that it cannot be smelted or reduced to the metallic form under ordinary conditions even when heated to a very high temperature under considerable pressure, and this is advantageous in the new process of galvanizing, as it does away with the risk there might be otherwise of melting the finely divided zinc through overheating of the furnace. OF THF UNIVERSITY OF Chapter XXXVI. ALLOYS : BRASS AND BRONZE PEWTER AND COMPOSITION. INTIMATE mixtures, or solid solutions, of metals, made by melting them together, are known as ALLOYS possessing properties which differ widely from those of the metals of which they are composed, and varying in a strange and apparently erratic fashion, according to the proportions of the various mixtures. The most important alloys are those of which copper is the basis Brass, Bronze, Gunmetal, and a few others slightly differing from these to which special names have been given. They are much used for small cast objects, such as taps, door handles, hinges, and minor fastenings of all kinds, while those of harder character are employed for the bearings of machinery. All are prepared similarly. The metals of which they are composed are cM &S melted in crucibles or pots, generally made of plumbago (see Fig. 172), the less fusible metal being melted first, and those with lower melting points added afterwards in rotation. The crucibles are plunged into the heart of the furnace, each lasting for about three meltings, and the contents when incorporated are cast into ingots. These are remelted in the same way, a little old metal being commonly added to assist in perfect incorporation when casting is to take place. The objects to be made being small and in great demand, metal patterns are kept, with projections to represent the ALLOYS : BRASS. 32 1 ends of the cores, as shown in Fig. 173, which is an illus- tration of the pattern for an ordinary tap casing. The cores also are made in hinged metal moulds, of tightly packed loamy sand, slightly damp. As a rule several small objects are cast at once, but for the sake of clearness only one is shown in Fig. 174, which illustrates the "flasks" in which the castings are made. The lower " flask " Fig. 173. Pattern of Tap. nothing else than a metal tray, about 4 ins. deep is filled with sand with the pattern care- fully inserted to half its depth. The pattern is withdrawn, the space it occupied dusted with dry sand, and it is replaced, when the dusting is repeated and carried over the whole surface of the lower flask. The upper flask, which has no top, is then dropped into place and packed with damp sand. When it is lifted it carries with it the sand it contains. The pat- tern can then be removed and the sand core placed in the sockets in the lower flask U which were made for it by ^PATTERN 1 1 the pattern. The upper flask * 7F5\ I i 1 1 is then quietly replaced in position and the metal poured into the space formerly occu- pied by the pattern through "BLOWER FLASK carefully arranged holes, en- Fig.:i 74 . Brass Casting : Arrange- closing the core. When the ment of Flasks. metal cools, the sand is re- moved from the flasks and the casting taken out, the sand core dropping out when tapped. All that is needed is for the rough surface to be smoothed and polished. BRASS, though the name is often given to all copper M.M. Y r-*-e--B-y SAND 322 BUILDING MATERIALS. alloys promiscuously, properly means a mixture of copper and zinc, a little phosphorus being sometimes added to make it fusible. It is a tough alloy, its colour varying from a light to a reddish yellow, according to the propor- tions of its constituents, that containing more copper being TABLE OF COPPER ALLOYS. Constituents. s E (U 13 g o c "H = 1 1 c P .5 | p 03 i 1 'c 1 O < s, PC 1 Name. Purpose for which Used. Proportions by Weight. Brass Ordinary for taps, etc. 2 i M Locks and door handles 3 i _ Turning and fitting (can be filed but not hammered). 3 i A - Engraving name plates, etc. 3 i A little (J Bushes and sockets . 18 i __ . _ Plnmhpr^' nnirm