T 
 
 AND-PHYSICS-OF 
 BUILDING-MATERIALS 
 
 :: ALAN-E-MUNBY :: 
 
Class No fJooR Xo- 
 
 FRANKLIN INSTITUTE LIBRARY 
 
 PHILADELPHIA, PA. 
 
 REFERENCE 
 
Introduction to the 
 Chemistry and Physics 
 of Building Materials 
 
The "Westminster" Series. 
 
 Crown 8vo. Fully Illustrated. $2.00 net each. 
 
 The Chemistry and Physics of Building Materials, 
 
 By Alan E. Munby, M.A., Cantab. 
 The Manufacture of Paper. By R. W. Sindall 
 
 F.C.S. 
 
 Timber. By J. R. Baterden, A.M.I.C.E. 
 Electric Lamps. By Maurice Solomon, A.C.G.I., 
 
 A.M.I.E.E. 
 
 Textiles and their Manufacture. By Aldred 
 
 Barker, M.Sc, Technical College, Bradford. 
 
 Gold and Precious Metals. By Thomas K. Rose, 
 
 D.Sc, of the Royal Mint. 
 Ornamental Glass Work. By A. L. Duthie. 
 The Railway Locomotive. By Vadghan Pendred, 
 
 M.I.Mech.E., late Editor of " The Engineer." 
 Iron and Steel. By J. H. Stansbie, B.Sc. (Lond.), 
 
 F.I.C. 
 
 Town Gas for Lighting and Heating. By W. H. Y. 
 Webber, C.E. 
 
 Liquid and Gaseous Fuels, and the Part they play 
 in Modern Power Production. By Professor Vivian B. 
 Lewes, F.I.C, F.C.S. , Prof, of Chemistry, Royal Naval 
 College, Greenwich. 
 
 Electric Power and Traction. By F, H. Davies 
 
 A. M.I.E.E. 
 
 Coal. By James Tonge, M.I.M.E., F.G.S., etc., 
 Lecturer on Mining at Victoria University, Manchester. 
 
 India-Rubber and its Manufacture, with Chapters 
 on Gutta-Percha and Balata. By H. L. Terry, F.I.C. 
 Assoc.Inst.M.M. 
 
 The Book: Its History and Development. By 
 
 Cyril Davenport, F.S.A. 
 Glass. By Walter Rosenhain. Superintendent of 
 the Department of Metallurgy in the National Physical 
 Laboratory. 
 
 Patents, Trade Marks and Designs. By Kenneth 
 R. Swan, B.A. (Oxon.), of the Inner Temple, Barrister-at- 
 Law. 
 
 Precious Stones. With a Chapter on Artificial 
 
 Stones. By W. Goodchild, M.B., B.Ch. 
 Electro- Metallurgy. By J B. C. Kershaw, F.I.C. 
 Natural Sources of Power. By Robert S. Ball 
 
 B. Sc, A.M.I.C.E. 
 
 Radio-Telegraphy. By C. C. F. Monckton, M.I.E.E. 
 
 * Further volumes mill appear at short intervals. 
 
Introduction to the 
 Chemistry and Physics 
 of Building Materials 
 
 BY 
 
 Alan E. Munby, 
 
 M.A. (Cantab.) Associate of the Royal Institute of British Archi- 
 tects ; Fellow of the Chemical Society; Member of the R.I.B.A. 
 Standing Committee on Science ; Lecturer on the Chemistry and 
 Physics of Materials to the L.C.C. School of Building; Author of 
 " Simple Experiments in Magnetism and Electricity " ; Joint Author 
 of "Practical Notes for Architectural Draughtsmen" 
 
 NEW YORK 
 D. VAN NOSTRAND COMPANY 
 
 23 MURRAY AND 27 WARREN STREETS 
 1909 
 
PREFACE 
 — ♦ — 
 
 The great advances in science in recent years and the 
 increasing use of scientific methods have not left the field 
 of work connected with building materials untouched, and 
 developments in technical training have made it essential 
 that the elementary principles of science which underlie 
 this study should be readily accessible. 
 
 Great powers and, therefore, great responsibilities are 
 placed in the hands of those whose duty it is to select and 
 specify the materials used in buildings, and while a know- 
 ledge of the principles underlying such use is an essential 
 part of their educational equipment, these principles must 
 be equally familiar to the manufacturers and even the 
 workers in the building trades who wish to be prepared 
 to meet competition, and combat causes of failure in 
 materials. 
 
 The rule of thumb methods which did duty in the past 
 are incapable of meeting the needs of increasing knowledge, 
 and while the specialist and expert are always ready to 
 advise and are now necessary factors in dealing with the 
 complex problem of modern building, those who consult 
 them should be, at least, in a position to direct and control 
 their assistance. 
 
 178G7 
 
vi 
 
 PEEFACE 
 
 There are many workers in the field under discussion 
 who, either through lack of training in elementary science 
 or owing to the lapse of time since such training was 
 acquired, find it difficult to digest with facility the legion 
 of technical books dealing with materials. Again, other 
 occupations often make it impossible to devote time to any 
 general study of pure science as a preparation for such 
 technical reading, and it is with the object of enabling 
 those interested to attain such knowledge without recourse 
 to a series of general text books that these pages are put 
 together. 
 
 The author's aim is, in fact, to enable anyone with 
 no knowledge of natural science whatever to appreciate 
 something of the chemical and physical principles which 
 underlie the use of building materials. 
 
 The first part of the book endeavours to explain the 
 principles of chemistry, physics, and geology by drawing 
 only on such parts of these sciences as are directly 
 applicable to the production, use, and decay of materials, 
 while in the second part, which comprises more than two- 
 thirds of the volume, these principles are applied to the 
 study of stones, brick clays, limes and cements, the metals, 
 timber, and paints. 
 
 In the space at disposal it has been impossible to do 
 more than generalise, and to review such substances in 
 classes, and all details of manufacture, statistics of pro- 
 duction, and even tabulated data, have been suppressed as 
 far as possible. Such matters are readily accessible in 
 many excellent text books on individual subjects. The 
 object kept in view has been rather to point out the 
 
PEEFACE 
 
 vii 
 
 composition, characteristics, general nature of tests applied 
 to, and causes of failure in, materials, as giving a means 
 of discriminating upon their employment and preservation, 
 or as an introduction to further study. 
 
 Short cuts to knowledge are always open to criticism; 
 this book, however, makes no attempt to create scientists, 
 but merely to inculcate an appreciation of the uses of 
 science. 
 
 In putting together these pages the writer has naturally 
 contracted great obligations to many authors, among whose 
 works he especially wishes to acknowledge : — Johnson's 
 "Materials of Construction"; Eckel's "Cements, Limes 
 and Plasters " ; Eies' " Clays : Their Occurrence, Properties 
 and Uses " ; Harris' " The Science of Brick Making " ; Le 
 Chatelier's " Constitution of Hydraulic Mortars " ; Michaelis' 
 "Hardening Process of Hydraulic Cements";^ Hiorns' 
 "Metallography"; Hurst's "Chemistry of Paints and 
 Painting " ; Hall's " Chemistry of Paints and Paint 
 Vehicles." 
 
 He has also contracted obligations by reference to works 
 by Professors and Messrs. Unwin, Blount and Bloxam, 
 Sexton, Charpentier, Schnabel and Louis, Redgrave, Dibdin, 
 Sabin, Davies, Bauerman, H. B. Woodward, Abney, Dent, 
 and other writers, and to L'Association Internationale pour 
 I'essai des Materiaux de Construction, The Quarry, The 
 R.I.B.A. Journal, The Journal of the Society of Chemical 
 Industry, The Journal of the Chemical Society, The Journal 
 
 ^ For a copy of the American translation of Dr. Michaelis' paper, 
 the writer is indebted to the kindness of Mr. Bower-Hopkinson, of 
 the Associated Portland Cement Manufacturers, Ltd. 
 
viii 
 
 PEEFAOE 
 
 of the American Chemical Society, The Builders' Journal, 
 Cement and Engineering News, Engineering News, and other 
 publications, for information contained in these periodicals. 
 
 If omissions in references and acknowledgment are 
 found in the text, the writer hopes that they will be regarded 
 as inadvertent errors, and he would like to conclude by an 
 expression of thanks to the officials of the Patent Office 
 Library for their courtesy and assistance on many 
 occasions, and to add that in no place in this country is 
 technical literature concerned with the subject of these 
 pages so readily accessible as in this well-arranged 
 institution. 
 
 Alan E. Munby. 
 
 28 Martin's Lane, 
 
 Cannon Street, E.G. 
 January, 1909. 
 
CONTENTS 
 
 PAET I 
 
 ELEMENTARY SCIENCE 
 CHAPTEE I 
 
 PAGE 
 
 NATURAL LAWS AND SCIENTIFIC INVESTIGATIONS ... 1 
 
 I. — Uses and Divisions of Science .... 1 
 
 1. Introductory. 2. Brandies of Science. 
 
 II. — Natural Laws ^ 
 
 III. — Methods of Investigation 4 
 
 1. Chemical and Physical Changes. 2. Heat 
 produces Changes. 3. Moisture aids Change. 
 4. State of Division affects Changes. 
 
 IV. — Simple and Complex Substances .... 7 
 
 1. Elements. 2. Combinations of Elements. 
 3. Characters of Compounds. 4. Complex 
 Compounds. 
 
 V. — Matter is Indestructible 9 
 
 CHAPTEE n 
 
 ON MEASUREMENT AND THE PROPERTIES OF MATTER . . 11 
 
 I. — Standards H 
 
 1. Importance of Standards. 2. Fundamental 
 Units. 
 
 II. — The Metric System 12 
 
 III. — Derived Units 13 
 
X 
 
 CONTENTS 
 
 Chapter II. — continued. 
 
 PAGE 
 
 IV. — Specific Gravity 14 
 
 1. Definition. 2. Determinations for Solids. 
 
 3. Determinations for Liquids. 4. Numerical 
 Example. 
 
 V. — Nature and Properties of Matter .... 18 
 1. Nature of Matter. 2. Solids. 3. Liquids. 
 
 4. Gases. 
 
 CHAPTER III 
 
 THE AIR AND COMBUSTION 22 
 
 I. — The Air : Physical Aspects 22 
 
 1. Material Nature. 2. The Barometer. 3. Boyle's 
 Law. 
 
 II. — Chemical Properties of Air 26 
 
 1. Composition of Air. 2. Preparation of Oxygen. 
 
 III. — Minor Constituents of Air 28 
 
 1. Moisture. 2. Carbonic Acid Gas. 
 
 IV. — Combustion 29 
 
 1. Combustion Defined. 2. Conditions for Com- 
 bustion. 3. Instantaneous Combustion. 
 4. Practical Bearings. 
 
 CHAPTER IV 
 
 HEAT : ITS NATURE AND MEASUREMENT .... 33 
 
 I. — Nature of Heat 33 
 
 II. — Temperature 34 
 
 1. Meaning of the Term. 2. Measurement of 
 Temperature. 3. Construction of a Ther- 
 mometer. 4. Scales of Temperature. 
 
 III. — Measurement of Heat Quantity .... 37 
 
 1. Unit of Heat. 2. Specific Heat. 
 
 IV. — Change of State 39 
 
 1. Latent Heat. 2. Melting Points. 3. Change 
 of Volume with Change of State. 
 
CONTENTS xi 
 CHAPTEB V 
 
 PAGE 
 
 HEAT AND ITS EFFECTS ON MATEEIALS .... 43 
 
 I. — Expansion of Solids 43 
 
 1. Dimensions and Structure. 2. Linear Expan- 
 sion of Solids. 3. Co-efi&cient of Linear 
 Expansion. 4. Practical Importance. 
 
 II. — Expansion of Liquids 47 
 
 1. Expansion of Water. 2. Circulation of Water. 
 
 III. — Expansion of Gases 48 
 
 1. Charles' Law. 2. Ventilation. 
 
 IV. — Transmission of Heat 49 
 
 1. Conduction. 2. Convection. 3. Radiation. 
 
 CHAPTER VI 
 
 CHEMICAL SIGNS AND CALCULATIONS 53 
 
 I. — Atomic Theory 53 
 
 II. — Atomic Weights and Symbols .... 54 
 
 1. Relative Weights of the Atoms. 2. Symbols. 
 3. Table of Symbols and Atomic Weights. 
 
 III. — Combinations of Symbols or Formulse ... 55 
 
 IV. — The Assigning of Formulae 57 
 
 V. — Chemical Equations 59 
 
 1. Meaning of Equations. 2. Calculations. 
 
 VI. — Chemical Nomenclature 61 
 
 1. Names indicate Composition. 2. List of 
 Popular and Scientific Names. 
 
 CHAPTER VII 
 
 WATER AND ITS IMPURITIES 64 
 
 I. — Composition of Water 64 
 
 1. Decomposition by Metals. 2. Decomposition 
 by Electricity. 3. Properties of Hydrogen. 
 
xii 
 
 CONTENTS 
 
 Chapter VII. — continued. 
 
 PAGE 
 
 II. — Solvent Power of Water 65 
 
 1. Solution of Solids. 2. Solution of Gases. 
 
 III. — Water of Crystallisation 66 
 
 1. Meaning of the Term. 2. Efflorescence. 
 3. Deliquescence. 
 
 IV. — Impurities in Natural Waters .... 68 
 
 1. Air and other Gases. 2. Mineral Matters. 
 
 3. Organic Impurities. 4. Suspended Matter. 
 
 V. — Hardness of Water 70 
 
 1. Temporary Hardness. 2. Permanent Hardness. 
 VI. — Effects of Water on Materials .... 72 
 1. Scale in Pipes. 2. Use of Lead. 
 
 VII. — Analysis of Water 74 
 
 1. Total Solids. 2. Chlorine. 3. Hardness. 
 
 4. Ammonia and Nitrates. 5. Poisonous 
 Metals. 6. Good and Bad Water. 
 
 CHAPTER VIII 
 
 SULPHUR AND THE NATURE OF ACIDS AND BASES . . 77 
 
 I. — Occurrence and Preparation of Sulphur . . 77 
 1. Occurrence. 2. Properties of Sulphur. 
 
 II. — Sulphur Compounds 78 
 
 1. Sulphides of Iron. 2. Sulphuric Acid. 
 3. Sulphuretted Hydrogen. 
 
 III. — Other Common Mineral Acids .... 81 
 
 1. Spirits of Salt. 2. Aqua fortis. 
 
 IV. — Acids, Bases, and Salts 82 
 
 1. Acids. 2. Bases. 3. Salts. 4. Acid-forming 
 Oxides. 
 
 CHAPTER IX 
 
 COAL AND ITS PRODUCTS 86 
 
 I.— Coal 86 
 
 1. Introductory, 2. Varieties of Coal. 3. Com- 
 position of Coal. 4. Uses. 
 
CONTENTS xiii 
 Chapter IX. — continued, 
 
 PAGE 
 
 II. — Distillation of Coal 88 
 
 1. Coal Gas. 2. Coal Tar. 3. Coke. 
 
 III. — Carbon and its Oxides 90 
 
 1. Charcoal. 2. Lamp Black. 3. Graphite. 
 4. Carbon Dioxide. 5. Carbon Monoxide. 
 
 CHAPTEE X 
 
 OUTLINES OF GEOLOGY 93 
 
 I.— Earth History 93 
 
 1. Introductory. 2. Erosion. 3. Deposition. 
 
 II. — Arrangement of Strata 96 
 
 1. Layers not continuous. 2. Dip. 3. Faults. 
 
 III. — Identification of Strata 99 
 
 1. Characters. 2. Names and Order of Strata. 
 
 IV. — Eocks not formed under Water .... 101 
 V. — Conclusion 104 
 
 PAET II 
 
 BUILDING MATERIALS 
 INTEODUCTION 105 
 
 CHAPTER XI 
 
 THE CONSTITUENTS OF STONES, CLAYS, AND CEMENTING 
 
 MATERIALS 107 
 
 I.— Mineral Constituents and their Characters . . 107 
 1. Composition of Natural Materials. 2. Minerals 
 Defined. 3. Characters of Minerals. 
 II. — Use of the Microscope in Examining Materials . Ill 
 1. Principles of Construction. 2. Use of 
 Polarised Light. 
 
xiv 
 
 CONTENTS 
 
 Chapter XI. — continued. 
 
 PAGE 
 
 III. — Individual Minerals connected with Materials . 112 
 
 1. Silica. 2. Calcium Carbonate. 3. Calcium 
 Sulphate. 4. Alumina. 5. Magnesium Car- 
 bonate. 6. Potash and Soda Compounds. 
 7. Compounds of Iron. 
 
 IV. — Silicate Minerals 115 
 
 1. Constitution of Silicates. 2. Felspars. 3. Micas. 
 4. Hornblende and Augite. 6. Chlorite. 
 6. Serpentine. 
 
 V. — Table of Common Minerals 119-120 
 
 CHAPTER XII 
 
 CLASSIFICATION OF STONES 121 
 
 I. — Introductory 121 
 
 II. — Igneous Stones 122 
 
 1. Granites. 2. Elvans. 3. Syenites. 4. Other 
 Igneous Stones. 6. Objectionable Minerals. 
 
 III. — Sedimentary Stones 125 
 
 1. Limestones. 2. Sandstones. 3. Objectionable 
 Minerals. 4. Weathering. 
 
 IV. — Metamorphic Stones 129 
 
 1. Definition. 2. Marbles. 3. Slates. 
 
 CHAPTER XIII 
 
 THE EXAMINATION AND TESTING OF STONES . . . 134 
 
 I. — Introductory I34 
 
 II. — Individual Tests I35 
 
 1. Specific Gravity. 2. Porosity. 3. Elasticity. 
 4. Adherence. 5. Expansion. 6. Conduc- 
 tivity. 7. Hardness. 8. Crushing Stress. 
 9. Microscopic Tests. 10. Chemical Analysis. 
 11. Solubility. 12. Characters m situ. 
 
CONTENTS 
 
 XV 
 
 CHAPTER XIV 
 
 PAGE 
 
 BRICK AND OTHER CLAYS 147 
 
 I. — Geological Formation 147 
 
 II.— Varieties of Clay 148 
 
 1. Residual Clays. 2. Transported Clays. 
 3. Varieties of Transported Clays. 
 
 III. — Physical Properties of Clay 149 
 
 IV. — Mineral Composition of Clay 150 
 
 1. Kaolin. 2. Felspars. 3. Mica. 4. Quartz. 
 5. Iron Pyrites. 6. Iron Oxides. 7. Calcite. 
 8. Selenite. 9. Dolomite. 10. Carbonaceous 
 Matter. 
 
 v.— Drying of Clays 153 
 
 VI.— Fusibility of Clays 154 
 
 1. Combinations causing Fusion. 2. Mixtures of 
 Fluxes. 3. Molecular Proportion and Fusion. 
 4. Stages of Fusion. 
 
 CHAPTER XV 
 CLAYS (continued), kiln reactions and the propbetibs 
 
 OF BURNT CLAYS 158 
 
 I. — Kiln and Subsequent Behaviour of Minerals . 168 
 1. Compounds of Ammonia. 2. Water. 3. Car- 
 bonaceous Matter. 4. Magnesium Carbonate. 
 5. Magnesium Sulphate. 6. Calcium Car- 
 bonate. 7. Calcium Sulphate. 8. Ferrous 
 Oxide and its Compounds. 9. Ferric Oxide. 
 10. Iron Pyrites. 11. Potash and Soda. 
 12. Summary of Temperature Changes. 
 
 II. — Removal of Defects in Clays 166 
 
 III. — Examination and Tests 167 
 
xvi 
 
 CONTENTS 
 
 CHAPTEE XVI 
 
 PAGE 
 
 PLASTERS AND LIMES 168 
 
 I. — Binding Materials Classified 168 
 
 II.— Plasters 169 
 
 1. Plaster of Paris. 2. Flooring Plasters. 
 3. Keene's and similar Cements. 
 
 III. — Non-Hydraulic Limes 171 
 
 1. Fat Limes. 2. Lean Limes. 3. Dolomitic 
 Limes. 4. Strength of Lime Mortars. 
 
 IV. — Hydraulic Limes 174 
 
 1. Characters. 2. Feebly Hydraulic Limes. 
 3. Selenitic Limes. 4. Eminently Hydraulic 
 Limes. 5. Grappiers. 
 
 V. — Testing of Hydraulic Limes 178 
 
 1. Chemical Analysis. 2. Mechanical and other 
 Tests. 
 
 CHAPTEE XVII 
 
 CEMENTS 182 
 
 I. — Eelations between Limes and Cements . . . 182 
 
 II. — Natural Cements 183 
 
 1. General Characters. 2. Varieties. 3. Strength. 
 
 III. — Portland Cement Manufacture .... 185 
 
 1. Introductory. 2. Details of Manufacture. 
 
 IV. — Portland Cement Tests 187 
 
 1. Introductory. 2. Fineness. 3. Specific 
 Gravity. 4. Expansion. 5. Tensile Strength, 
 6. Chemical Composition. 7. Eate of Setting. 
 8. Microscopic. 9. Other Tests. 10. Actual 
 Strength of Portland Cement. 
 
 V. — Pozzuolana Cements 194 
 
 1. Natural Pozzuolanas. 2. Artificial Pozzuo- 
 lanas. 3. Properties and Strength. 
 
CONTENTS 
 
 xvii 
 
 CHAPTER XVIII 
 
 PAGE 
 
 THEORIES UPON THE SETTING OF PLASTERS AND HYDRAULIC 
 
 MATERIALS 197 
 
 I. — Cohesion and Adhesion 197 
 
 1. Cohesion. 2. Adhesion. 3. Effect of 
 Aggregates. 
 
 II. — Introductory Remarks on Setting .... 199 
 1. General Causes. 2. Crystalloid and CoUoid 
 Theories. 
 
 III. — Theories of Setting Developed .... 201 
 
 1. Crystalloid Theory. 2. Colloid Theory. 
 3. Effects of Magnesia and Ferra. 4. Sum- 
 mary of Views held. 
 
 IV. — Rate of Setting of Plasters and Cements , . 207 
 V. — Failure of Hydraulic Materials .... 209 
 
 1. Expansion. 2. Efflorescence and Solution. 
 3. Defects due to Sea-vs^ater. 4. Defects due 
 to Aggregates. 
 
 CHAPTER XIX 
 
 ARTIFICIAL STONE ; OXYCHLORIDE CEMENT ; ASPHALTE . 213 
 
 I. — Artificial Stone 213 
 
 1. Ransome's Process. 2. Lime-sand Bricks. 
 
 II. — Stone Preservation 215 
 
 III. — Oxychloride Cements 216 
 
 IV. — Bitumen and Asphalte 217 
 
 1. Bitumen. 2. Asphalte. 
 
 CHAPTER XX 
 
 THE METALS : THEIR GENERAL PROPERTIES AND OCCURRENCE 221 
 
 I. — Introductory 221 
 
 II. — Micro structure of the Metals 222 
 
 B.M. h 
 
xviii 
 
 CONTENTS 
 
 Chapter XX — continued. 
 
 PAGE 
 
 III. — Physical Properties of the Metals .... 225 
 1. Malleability. 2. Ductility. 3. Hardness. 
 4. Elasticity. 5. Fusibility. 6. Expan- 
 sion, etc. 
 
 IV. — Occurrence and Extraction of the Metals . . 228 
 1. Occurrence. 2. Metallurgy. 
 
 CHAPTER XXI 
 
 IRON AND STEEL 232 
 
 I. — Ores, Metallurgy and Definitions .... 232 
 
 1. Ores of Iron. 2. Metallurgy of Iron and Steel. 
 3. Definitions of Iron and Steel. 4. Con- 
 dition of Carbon in Iron and Steel. 
 
 II.— Cast Iron 237 
 
 1. Preparation. 2. Subsidiary Constituents. 
 3. Grades and Properties. 4. Conclusion. 
 
 III. — Wrought Iron 241 
 
 1. Preparation. 2. Subsidiary Constituents. 
 3. Grades and Properties. 
 
 IV. — Steel 244 
 
 1. Preparation. 2. Subsidiary Constituents. 
 
 3. Grades and Properties. 
 
 V. — Corrosion of Iron and Steel 248 
 
 1. Oxidation. 2. Electrolytic Decay. 3. Com- 
 parative Decay. 
 
 CHAPTER XXII 
 
 OTHER METALS AND ALLOYS 251 
 
 I.— Copper 251 
 
 1. Ores. 2. Extraction. 3. Properties. 
 
 4. Impurities. 5. Corrosion. 
 
 II. — Lead .255 
 
 1. Ores. 2. Extraction. 3. Properties. 
 4. Impurities. 5. Corrosion. 
 
CONTENTS xix 
 Chapter XXII — continued. 
 
 PAttB 
 
 Ill.-Zino 258 
 
 1. Ores. 2. Extraction. 3. Properties. 
 4. Impurities. 5. Corrosion. 
 
 IV.-Tin 260 
 
 1, Ores. 2. Extraction. 3. Properties. 
 4. Impurities and Corrosion. 
 
 V. — Aluminium 
 
 1. Ores. 2. Extraction. 3. Properties. 
 
 4. Impurities and Corrosion. 
 
 VI.— Alloys 264 
 
 1. Introductory. 2. Brass. 3. Bronzes. 4. Lead- 
 tin Alloys. 5. Fusible Alloys. 
 
 CHAPTER XXIII 
 
 TESTS UPON AND STRENGTH OF THE METALS . . • 270 
 
 I.— Nature of Tests applied to Metals ... 270 
 1. Introductory. 2. Tensile Tests. 3. Com- 
 pressive Tests. 4. Cross-Bending Tests. 
 
 5. Cold-Bending Tests. 6. Hardness Tests. 
 7. Shear and Torsion Tests. 8. Impact 
 Tests. 
 
 II. — Actual Strength of Metals 278 
 
 1. Introductory. 2. Cast Iron. 3. Wrought 
 Iron. 4. Mild Steel. 5. Conclusion. 
 
 CHAPTER XXIV 
 
 TIMBER 282 
 
 I.— General Characters and Structure .... 282 
 1. Introductory. 2. Classification. 3. Structure. 
 
 II —Moisture and its Effects 287 
 
 1. Occurrence of Water in Wood. 2. Shrinkage. 
 
 III. — Mechanical and Other Properties .... 290 
 
 1. Composition. 2. Specific Gravity. 3. Mecha- 
 nical Properties. 
 
 IV. — Decay of Wood 292 
 
 1. Wet Rot. 2. Dry Rot. 3. Decay due to 
 Insects. 
 
CONTENTS 
 
 Chapter XXIY— continued. 
 
 v. — Preservation of Wood 
 
 1. Seasoning. 2. Impregnation. 3. Eendering 
 Wood Uninflammable. 
 
 CHAPTEE XXV 
 
 PAINTS : GENERAL CHARACTERS. OILS, THINNERS, AND 
 VARNISHES 
 
 I. — General Characters 
 
 1. Introductory. 2. Composition of Paint. 
 3. Essential Qualities. 4. Adulteration, 
 Fillers and Thinners. 
 
 II.— The Oils 
 
 1. Varieties of Oil. 2. Linseed Oil. 3. Other 
 Oils. 4. Tests for the Oils. 
 
 III. — Thinners 
 
 1. Introductory. 2. Turpentine. 3. Turpentine 
 Substitutes. 
 
 IV. — Varnishes 
 
 1. Gen eral Characters. 2. The Eesins. 3. Varieties 
 of Eesin. 
 
 CHAPTEE XXVI 
 
 PAINTS : THEIR SOLID INGREDIENTS— BASES, PIGMENTS, AND 
 DRIERS 
 
 I- — White Ingredients ....... 
 
 1. Introductory. 2. White Lead. 3. Zinc 
 White. 4. Other White Ingredients. 
 
 II. — Coloured Ingredients 
 
 1. Causes of Colour. 2. Use of Pigments. 
 3. Beds. 4. Vermilions. 5. Yellows. 
 6. Browns. 7. Blues. 8. Greens. 9. Blacks. 
 10. Special Pigments or Coatings. 
 
 III. — Driers 
 
 1. Use of Driers. 2. Varieties. 
 
 PAGE 
 
 296 
 
 300 
 300 
 
 304 
 
 309 
 
 311 
 
 315 
 315 
 
 321 
 
 332 
 
 INDEX 
 
 335 
 
INTRODUCTION TO THE 
 CHEMISTRY AND PHYSICS 
 OF BUILDING MATERIALS 
 
 PART I.— ELEMENTARY SCIENCE 
 
 CHAPTBE I 
 
 NATURAL LAWS AND SCIENTIFIC INVESTIGATION 
 
 I. Uses and Divisions of Science. 
 
 1. Introductory. — A reproach often levelled against this 
 country is the lack of co-ordination between the workers 
 in pure and applied science. The man in the laboratory 
 patiently labours to establish abstract principles, and his 
 time is absorbed in researches which have for their object 
 the elucidation of the laws of Nature. The user of Nature's 
 materials, on the other hand, is chiefly concerned with the 
 economic aspect of the vast range of products which comes 
 under his consideration. 
 
 The scientist often complains of the lack of interest 
 displayed by the practical man in his laborious researches, 
 while the latter pronounces the former an idealist who 
 gives him none of the tangible things which concern his 
 daily requirements. The fields of these two workers are 
 so essentially different that it is impossible to expect com- 
 plete sympathy between them, and thus it is that the 
 
 B.M. B 
 
2 OHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 mediator Technology has come into existence to carry the 
 work of pure science into practical channels on the one 
 hand, and on the other to bring home to the practical man 
 the value, not only educative, but also financial, of a know- 
 ledge of the properties of those things which concern his 
 work : knowledge whereby he can alone expect to be able to 
 grasp the trend of new developments, and thus find him- 
 self ready to meet competition. Though the exigencies of 
 present-day existence leave but little time for the cultivation 
 of fields beyond the limits of the "daily round," an acquire- 
 ment of some knowledge of the elementary principles of 
 science is not difl&cult, and while "short cuts," as generally 
 tending to superficiality, are to be deprecated, a modicum 
 of scientific training on the part of the practical man is of 
 the greatest value if properly used. Such training will 
 not, and should not attempt, to make him a scientist, but 
 will enable him to understand and appreciate the work of 
 the scientist and to utilise and direct such work to his own 
 material advantage. 
 
 These pages are devoted to the application of science to 
 building materials in connection with which the manu- 
 facturer, the builder, and most of all the architect under- 
 take great responsibilities which can only be conscientiously 
 accepted with some knowledge of the principles which 
 underlie the preparation, use and specification of such 
 materials. 
 
 2. Branches of Science. — Science is the English rendering 
 of the Latin word for " knowledge," and the term is there- 
 fore correctly applied quite generally. The knowledge of the 
 things of Nature — that is, the tangible things which compose 
 the earth and its surroundings, and of the forces which 
 control these bodies — is distinguished as Natural Science. 
 
 This study offers so wide a field that it is necessary to 
 divide natural science into many branches, to a limited 
 number of which any individual can alone devote attention ; 
 
NATURAL LAWS AND SCIENTIFIC INYESTiaATION 3 
 
 but it should be observed that this is merely a matter of 
 convenience attributable to the limitations of life and 
 mental capacity, and not because there are any real breaks 
 in the continuity of Nature. Among such branches may 
 be mentioned — 
 
 (a) Physics. — The study of the action of mechanical force 
 upon substances, and the transient effects of heat, light and 
 sound and of magnetic and electrical energy, are relegated 
 to the branch of science known as Physics. 
 
 (b) Chemistry. — The investigation of the ultimate compo- 
 sition of bodies, most of which can be split up into simpler 
 substances, and the way in which such bodies combine and 
 act upon one another, form the branch of science known as 
 Chemistry. 
 
 (c) Geology. — The study of the earth's physical character 
 beneath its surface, where materials are found to be arranged 
 in layers or strata possessing distinguishable characteristics, 
 is known as Geology. 
 
 (d) Other Branches. — Thus the list may be continued — 
 the study of minerals, known as Mineralogy ; of plant life. 
 Botany ; of animal life, Biology. All, however, are parts of 
 one great whole, and merge into one another as their study 
 is advanced. 
 
 It is with the first three of the above-mentioned branches 
 of science that a knowledge of building products is chiefly 
 concerned, and in the first part of this book it is proposed 
 to record a few simple facts culled from such sources 
 centred, as far as may be, round concrete examples bear- 
 ing upon the actual materials to be discussed in the later 
 chapters. 
 
 II. Natueal Laws. 
 
 All applied knowledge is based upon the assumption that 
 under a given set of conditions certain definite things will 
 recur. To know the conditions necessary to produce a 
 
 B 2 
 
4 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 particular result requires the collection, study and arrange- 
 ment of a large number of facts and an investigation of the 
 effect of each factor in producing the result attributable to 
 them all. If the relations thus established between cause and 
 effect are found to be of wide application, the generalisation 
 arrived at is termed a Natural Law. 
 
 Thus the statement that all chemical compounds have a 
 definite and constant composition is not a mere speculative 
 announcement suggesting a probable truth, but is the result 
 of the analj'sis of countless bodies prepared in many 
 different ways, and thus rests on experimental evidence. 
 For example, water, chalk and zinc white are chemical com- 
 pounds. A knowledge of the above law therefore enables 
 the certain prediction to be made that whatever means are 
 utilised for preparing these bodies, their chemical properties, 
 such as their action upon other substances and tendency to 
 change under given conditions, will always be the same. 
 This knowledge obviously supplies a broad basis of fact 
 which, as it is applicable to all chemical compounds, must 
 be of the greatest service. 
 
 III. Methods of Investigation. 
 
 1. Chemical and Physical Changes. — Natural knowledge 
 is obtained by making trials or experiments. From infancy 
 our surroundings have been investigated by experiments, 
 sometimes disastrous, always salutary. So also to know 
 materials experiments are essential ; indeed, only by them 
 has natural science found an existence. The procedure 
 need not be elaborate. An experiment is scientific and 
 valuable if (a) the conditions under which it takes place 
 are carefully noted ; (6) the results are properly recorded ; 
 (c) the conclusions therefrom are drawn with discretion, 
 which rapidly increases with experience. 
 
 In making an experiment, if any happens at all, some 
 
NATUEAL LAWS AND SCIENTIFIC INVESTIGATION 5 
 
 change in the substance under investigation takes place, 
 and it is this change which must be studied. 
 
 The substance may change its shape, or colour, it may 
 break up, or alter in many other ways ; but these changes 
 may be divided into two main classes : (a) Those which 
 only last as long as the cause of the change operates, as 
 when a spring is bent and flies back to its original position 
 when released ; (b) Those which are permanent, as when 
 concrete sets owing to the rearrangement of its constituents. 
 The former are called physical changes, and their investiga- 
 tion belongs to the science Physics. The latter are called 
 chemical changes, and their study is relegated to Chemistry. 
 Upon these changes the whole question of the manufacture, 
 stability, and decay of building materials depends. 
 
 2. Heat produces Changes. — One of the best agencies for 
 producing changes in bodies, and thus of investigating their 
 properties, is Heat. Heat results in the throwing of the 
 little particles (or molecules, as they are called) of which 
 all substances are composed, into such violent vibrations 
 that they often lose their hold of one another, so that the 
 substance splits up into simpler bodies which thus reveal 
 its composition. 
 
 If a few scraps of wood be heated in a thin glass tube, 
 known to chemists as a test-tube, water is first evolved as 
 steam, some of which settles down as dew on the cool upper 
 part of the tube. Then yellow gases appear, and darker oily 
 drops condense on the glass. These gases can be lighted, 
 and burn with a bright flame. When no further gases are 
 evolved the remains of the wood, still retaining its original 
 shape, are found as charcoal. 
 
 Wood, therefore, consists of at least three things, or 
 possibly more, since some of these may themselves be 
 capable of further subdivision. 
 
 3. Moisture aids Change. — Another frequent cause of 
 change is to be found in the presence of moisture, of which 
 
6 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 fact the comparative rate of decay of materials inside and 
 outside a building gives ready evidence. A substance 
 affected by moisture may simply dissolve or, as it is 
 expressed, pass into solution, or it may enter into chemical 
 combination with the water and thus become permanently 
 altered. 
 
 If a little powdered sugar be dissolved in water and the 
 solution be allowed to evaporate by exposure to the air, the 
 whole of the sugar will be left behind in its original condi- 
 tion, though possibly if evaporation has been slow it may 
 appear in larger regular fragments known as crystals. 
 This is a case of simple solution. 
 
 If a few zinc clippings or iron nails be placed in spirits 
 of salt the metal will dissolve in the liquid, but in this case 
 with brisk effervescence. On allowing the clear liquid to 
 evaporate, which may be accelerated by heating it, no 
 metal will reappear. The metal and part of the liquid have 
 combined to form a new substance. This is an instance of 
 chemical solution. The metal remains in the solid mass 
 finally obtained, from which its extraction is possible, but 
 only by some further chemical action. 
 
 So important a factor is water in enabling substances to 
 act, or, as the chemist would say, to react upon one another 
 that it is almost true to say that no chemical change or 
 process of decay takes place unless moisture is present. 
 There are many substances which, while entirely without 
 action one upon the other when in a dry state, readily enter 
 into combination in the presence of water, and the more 
 important instances of such changes will be subsequently 
 considered. 
 
 4. State of Division. — Ordinary experience indicates that 
 action takes place between bodies most readily when they 
 are intimately mixed in a fine state of division. The fine- 
 ness of various grades of cement as influencing setting and 
 strength forms a striking instance of this fact. Chemical 
 
NATUEAL LAWS AND SCIENTIFIC INVESTIGATION 1 
 
 forces can only act across very minute distances, and many 
 chemical actions can be accelerated and even induced by 
 effective sub-division and intermixture of the component 
 substances. 
 
 IV. Simple and Complex Substances. 
 
 1. Elements. — In order to understand and guard against 
 the various changes which result through the combinations 
 and decay of materials, it is necessary to become acquainted 
 not only with the history of the formation of the bodies in 
 question, but also with their ultimate chemical composition 
 and physical structure. Fortunately almost every known 
 substance has been dissected or submitted to analysis by 
 the chemist, and it is found that where complex bodies are 
 broken up and the parts thus obtained repeatedly submitted 
 to chemical dissection, a stage is at length reached at which 
 no new and simpler substances are obtained. These final 
 bodies, which have resisted all the devices at the command 
 of science for the separation of substances into their com- 
 ponent parts, are known as Elements. Many of the elements 
 are well known ; included in this class, for example, are the 
 common metals such as iron, lead and zinc ; sulphur, and 
 the two mixed gases which mainly compose the air, are also 
 elements. 
 
 The total number of elementary bodies of which all known 
 substances are composed is not very large ; some eighty of 
 such bodies have been isolated, but more than half of them are 
 never found in familiar substances, while hardly more than 
 one quarter of them are ever found in building materials, 
 which are therefore composed of only about twenty different 
 things. 
 
 2. Combinations of Elements. — If the elements in materials 
 were merely mixed together, an investigation of such 
 materials would be a fairly simple matter. A little reflec- 
 
8 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 tion, however, must make it evident that some more subtle 
 combination than simple juxtaposition exists in most sub- 
 stances of a complex nature. That white lead, for example, 
 contains the metal lead is readily admitted ; the substance 
 is heavy like lead and lead is easily extracted from it, as by 
 painting therewith a red-hot pipe ; but no mechanical 
 division of the material will reveal lead, no microscope 
 will make it visible, the lead has none of its ordinary 
 metallic properties. The metal is, in fact, interlocked or 
 combined with the other elements, carbon, hydrogen, and 
 oxygen present, in some intimate and yet hardly under- 
 stood manner, which gives the substance a new and definite 
 character very different from a mere mixture of the metal 
 with the other elements cited. 
 
 3. Character of Compounds. — Substances containing 
 elements thus combined are termed Chemical Compounds, 
 and possess characteristics which entirely distinguish them 
 from mere mixtures. These are (a) constancy of compo- 
 sition, i.e., a given compound always consists of the same 
 elements, and the amount of each present is definite and 
 fixed ; (b) The properties and characteristics of a given 
 compound are definite and distinctive and are always in 
 many respects different from those of the elements which 
 compose it ; (c) Some chemical change is always neces- 
 sary for the production or decomposition of a compound ; 
 (d) Heat is evolved when compounds are formed from 
 simply bodies, though sometimes delicate instruments 
 are necessary to detect this fact. 
 
 As an example of these characters, quicklime is a 
 compound of the metal calcium and the gas oxygen, and 
 is always composed of five parts of metal to two parts of 
 gas by weight. It is entirely unlike either the metal or the 
 gas which comprise it. Its caustic nature, white colour, 
 and other properties are always retained. It cannot be 
 decomposed by any mere mechanical process. It combines 
 
f I NATURAL LAWS AND SCIENTIFIC INVESTIGATION 9 
 
 with water to form a more complex compound, and great 
 heat is thereby evolved. 
 
 4. Complex Compounds and Mixtures of Compounds. — 
 
 Compounds, as has just been shown, may themselves com- 
 bine to form more complex substances which still possess 
 the characteristics cited above. In spite of this, however, 
 the number of elements present in any compound is usually 
 quite small. It is seldom that more than four or five 
 elements are found in combination. 
 
 The ordinary substances of every-day life are occasionally 
 elements or simple compounds, but most usually they are 
 mixtures of several compounds which can often be separated 
 by mechanical means, or by suitable solution. Quartz, for 
 example, can be picked out from crushed granite and 
 sand removed from mortar by dissolving the remaining 
 constituents in spirits of salt. 
 
 V. Matter is Indestructible. 
 
 The word " destruction," as used popularly, involves the 
 negation of a most important principle which underlies 
 every chemical investigation. Destruction is in reality the 
 antithesis of creation, and it is no more possible to destroy 
 than to create. The amount of material in the earth, for 
 example, is a constant quantity, and none of it can be 
 made non-existent. Apparent cases of destruction involve 
 chemical rearrangement and the production of some in- 
 visible or easily-overlooked substance which, mixing with 
 the air, is lost to notice. A candle, for example, on burning 
 away is converted into a colourless gas and water vapour, 
 so that its constituents are not made non-existent. This 
 truth may be realised by considering the following possible 
 experiment. A very small piece of lighted candle is placed 
 in a large glass globe and the vessel sealed up. If the 
 globe (which contains the necessary air) is sufficiently 
 
10 CHEMISTKY AND PHYSICS OF BUILDING MATEEIALS 
 
 large, the candle will completely disappear, but nothing 
 has been lost, which might have been proved by weighing 
 the sealed globe at the beginning and at the end of the 
 experiment. In this case the products of combustion of the 
 candle have b^en prevented from escaping. No destruction of 
 material has resulted, but mere chemical rearrangement. 
 
 This great truth, known as the Law of the Indestructibility 
 or Conservation of Matter, was discovered at the end of the 
 eighteenth century by the French chemist Lavoisier, 
 aided by the work of the English scientists Priestley and 
 Cavendish. 
 
CHAPTEK II 
 
 ON MEASUREMENT AND THE PROPERTIES OF MATTER 
 
 I. Standards. 
 
 1. Importance of Standards. — As organisation and exacti- 
 tude in any subject gain ground they proceed along the 
 science of measurement, facilities for which are indeed an 
 index to state of civilisation. The interchange of com- 
 modities of all kinds involves measurement, and the more 
 intricate and valuable such commodities become the more 
 accurate and perfectly defined must such measurements be. 
 
 The first essential in any form of measurement is an 
 unalterable standard which shall be generally accepted. 
 This standard must be defined in every particular in which 
 variations are likely to occur for the special class of thing to 
 which it refers. In certain cases the standard is a material 
 tangible thing, such as a pound weight ; in others it is neces- 
 sary to define it by reference to motion or energy, as in the 
 case of time or electric power. Standards are usually purely 
 arbitrary, that is, they are anything agreed upon at will, and 
 owing to the necessity for standards before the days of 
 scientific method, many of them are ill-chosen. Moreover, 
 through the difficulties in past times of intercommunica- 
 tion several standards for the same thing are recognised 
 in different countries, and even in different parts of the 
 same country. Some of these will readily suggest them- 
 selves, such as the kilogram and pound, which latter may 
 be the pound avoirdupois or the pound troy, while such a 
 standard as the bushel not only varies with the produce to 
 
12 CHEMISTRY AND PHYSICS OF BUILDING MATEEIALS 
 
 which it is appUed, but even for the same produce in 
 different counties. 
 
 The power of custom and the great but temporary incon- 
 venience involved in changes of standards is responsible for 
 the retention of many cumbrous methods of measurement 
 which involve enormous waste of labour, but the aim of all 
 thinking people should be the acquisition of one universal 
 set of standards which would be accepted by all civilised 
 nations alike. 
 
 2. Fundamental Units. — There are three fundamental 
 units or standards from which all others are derived. 
 These are the units of Length, Weight (properly called 
 Mass) and Time. 
 
 In this country the standard of length is a certain 
 distance known as one yard (a standard yard is to be seen 
 affixed to the north wall of Trafalgar Square). For mass a 
 certain weight of metal called one pound. For time, which 
 obviously cannot be materialised, the standard is the interval 
 which elapses when the earth rotates through a certain angle, 
 which is called one second. 
 
 II. The Meteio System. 
 
 In most European countries and universally in all 
 scientific work what is known as the metric system of 
 units is adopted. In this system the unit of length is 
 one metre, which is equal to 39*37 English inches. For 
 mass, one kilogram, equal to 2*20 EngHsh pounds. For 
 time, the second, which is the same in value as our own. 
 Association with this last fact makes it difficult to realise 
 the inconvenience which would be involved did the second 
 possess different values in different places, or, conversely, 
 the immense gain which would be derived were the other 
 two units respectively universal. 
 
 The advantages of the metric system lie in the facts : 
 (a) that it is a decimal system — that is, the multiples of the 
 
ON MEASUEEMENT AND PEOPERTIES OF MATTEE 13 
 
 units are always in tens, hundreds, or thousands, and 
 parts of the units in tenths, hundredths, or thousandths, 
 hence all the usual labour of multiplication and division is 
 dispensed with ; (b) One set of units is applied to all kinds 
 of produce and materials — thus the manifold tables of 
 weights and measures in our own system are non-existent ; 
 (c) There is a simple connection between many of the 
 units employed which much reduces calculation. A dis- 
 advantage of this system is that the number ten is only 
 divisible by two once, hence the halving of numbers 
 involves the use of parts of whole numbers, and therefore 
 of more figures in many simple cases than does the British 
 system. The adoption of the metric system, however, does 
 not preclude the use of simple fractions. 
 
 Metric Tables and Equivalents. — For most purposes the 
 only necessary parts of metric tables of length and weight 
 are the following : — 
 
 Length Table. 
 10 millimetres (mm.) = 1 centimetre (cm.). 
 100 centimetres (cm.) = 1 metre (m.). 
 1,000 metres (m.) = 1 kilometre (kilom.). 
 
 Weight Table. 
 
 1,000 milligrams (mg.) = 1 gram (gm.). 
 1,000 grams (gm.) = 1 kilogram (kilog.). 
 
 As an indication of the value of these units in British 
 measures the following may be cited : — 
 
 1 inch = 2'54 cm., hence 1 mm. = about of an inch ; 
 1 metre = 39*37 inches ; 1 kilometre = about f of a mile ; 
 1 oz. = 28'36 grams, 1 kilogram = 2*20 lbs. 
 
 III. Derived Units. 
 
 Units formed from the fundamental trio cited above are 
 known as derived units. That for area, for example, is 
 
14 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 derived from the unit of length, being a length multiplied 
 by another length. Similarly the unit of volume is formed 
 by multiplying the unit of area by another length. 
 
 The square yard and the cubic yard are thus the rational 
 British units, and the square and cubic metres the metric 
 units of area and volume. 
 
 The British system, however, possesses special and quite 
 unnecessary units of area and volume, such as the rod and 
 the gallon, which bear no simple relation to the fundamental 
 units. The unit of volume in the metric system is, as 
 stated, the cubic metre, but since this is somewhat large, 
 one thousandth part of it, namely, a cube 10 centimetres 
 each way, forms a more useful starting point. This volume 
 is called a liti-e and is equal to 1*76 pints. 
 
 A litre of water weighs one kilogram. The metric units 
 of weight are, in fact, based upon the weight of unit volume 
 of pure water. Hence the calculation of the weight of water 
 in vessels is directly obtainable from their capacity in this 
 system of measurement. For example, the weight of the 
 contents of a cistern of water 1 square metre on the base 
 and half a metre deep, and therefore possessing a volume of 
 half a cubic metre, is 500 kilograms (about ^ a ton). This 
 is one of the many instances of the simplicity of the metric 
 system. To find the weight of water in a cistern when 
 measured in feet requires a calculation on paper. 
 
 The use of the metric system is extending, and its uni- 
 versal adoption is only a matter of time, hence an acquaint- 
 ance with it is highly desirable. 
 
 IV. Specific Gkavity. 
 
 1. Definition. — A derivation from the fundamental units 
 of great importance in connection with many materials, is 
 Specific Gravity. Popularly this expression is equivalent to 
 the term " heaviness" ; thus lead would be said to have a 
 greater specific gravity, or to be heavier, than wood. This, 
 
ON MEASUEEMENT AND PEOPERTIES OF MATTEE 15 
 
 however, implies something in reference to heaviness which 
 is not stated, for were an endeavour made to disprove such 
 a statement by demonstrating that a cubic inch of lead 
 weighed less than a cubic foot of wood, the immediate 
 objection would be raised that the pieces of material com- 
 pared were not of the same size. In this matter of size or 
 volume lies the whole definition of specific gravity. One 
 piece of lead can be heavier than another piece of smaller 
 size, but two pieces of identical material cannot have different 
 specific gravities, and it is in the former restricted sense 
 only that the term " heaviness " should be used. Specific 
 gravity expresses, then, the relation between weight and 
 volume, and the most correct popular term equivalent to it is 
 " bulkiness." This relation may be stated thus : — 
 
 Specific gravity = 
 
 It is a matter of indifference which system of units be 
 adopted for measurement of the weight and volume, pro- 
 vided the same system be retained throughout any series of 
 comparisons. Thus if the ounce be taken as the unit of 
 weight and the cubic inch as the unit of volume, the 
 numbers expressing the weights in ounces of one cubic 
 inch of different materials will be the relative specific 
 gravities of such materials. For such a comparison it is 
 not necessary to provide actual cubic inches of the sub- 
 stances ; any convenient volume may obviously be employed, 
 the piece weighed and the weight of one cubic inch found 
 therefrom by simple proportion. 
 
 Water the Standard. — In all comparisons of solid and 
 liquid substances water is taken as the standard or unit ; 
 that is to say, the specific gravity of water is called 1. Thus 
 the statement that the specific gravity of lead is 11 means 
 
 ^ Strictly mass, though this fact need not be considered in 
 calculations. 
 
16 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 that any given volume or bulk of lead is eleven times as 
 heavy as the same volume of water. 
 
 2. Determinations for Solids, — Although very accurate 
 determinations of specific gravity require numerous con- 
 siderations, the approximate values usually necessary in 
 dealing with building materials can be ascertained by 
 anyone with but little apparatus. The specimens examined 
 should not be too small, since the smaller the weight and 
 volume the greater in proportion will be any errors in the 
 determination. The weight in all cases is found by the 
 ordinary process of weighing on a delicate pair of scales. 
 If the material is a solid of regular shape its volume may 
 be obtained by cubing it up with a rule ; if it is an irregular 
 fragment or a powder this is determined by immersing the 
 weighed quantity in some liquid ^ standing at a given height 
 in a measuring vessel marked, say, in cubic inches or cubic 
 centimetres, and noting to what higher division the liquid 
 is raised thereby, when the rise or displacement of the 
 liquid must evidently be the same as the volume of the 
 specimen. If the material floats it may be depressed 
 beneath the liquid by two or three fine stiff wires, the 
 additional displacement due to these being neglected. 
 
 The liquid usually employed is water, but in the case of 
 limes and cements oil is utilised, as combination would 
 take place with water in such cases. If a porous material is 
 under examination and its specific gravity with the pores 
 full of air is required, as would generally be the case, it 
 may be coated with a thin film of varnish before 
 immersion. 
 
 3. Determinations for Liquids. — Liquids, since they assume 
 the shape of any vessel in which they are placed, lend 
 themselves very readily to specific gravity determinations. 
 In this case it is merely necessary to counterpoise a measur- 
 ing vessel on a pair of scales with sand or other convenient 
 
 ^ The liquid must not, of course, dissolve or act upon the solid. 
 
ON MEASUREMENT AND PROPEETIES OE MATTER 17 
 
 material, and to compare the weights of water and the 
 liquid when the vessel is filled to a given mark. The 
 specific gravity of liquids, however, is determined in 
 practice by a hydrometer. This is a glass tube weighted 
 at the bottom so that it floats vertically in the liquid. It 
 contains a graduated scale whereby the depth to which it 
 sinks can be noted. This depth will be less in a heavy 
 than in a Hght liquid, and will in fact be proportional to 
 the liquid's specific gravity. For convenience in reading 
 the scale and to avoid decimal places the height at which 
 the tube floats when in water is marked 1,000 instead of 1, 
 and other numbers give the specific gravities of other 
 liquids directly. Thus if in a certain oil the reading on the 
 scale is 935, the specific gravity of this liquid is 0-935. 
 
 4. Numerical Example. — Suppose it is required to deter- 
 mine the specific gravity of a 6-inch cube of stone. The 
 volume, in this case determined by direct measurement, is 
 6x6x6= 216 cubic inches. The weight of the block 
 proves to be, say, 324 ounces, hence one cubic inch weighs 
 324 
 
 == li ounces. Now one cubic inch of water weighs 
 
 roughly J ounce ; hence, volume for volume, the stone is 
 three times as heavy — that is, its specific gravity is 3. The 
 above reckoning, however, is too rough for the result to be 
 of value. One cubic inch of water weighs more nearly 
 0-6'^ ounce, but in all cases the procedure is the same : the 
 weight of a cubic inch of the substances is divided by the 
 weight of a cubic inch of water and the result is the specific 
 
 1'5 
 
 gravity. Thus in this case — = 2*5 = the specific gravity 
 of the stone. 
 
 If metric measures are used the calculation is even 
 simpler. In this case the volume of the specimen is 
 
 ^ 0*6 is not exact, but the object of this example is merely to show 
 the method of calculation. 
 
 B.M. 0 
 
18 CHEMISTKY AND PHYSICS OF BtJILDINa MATEEIALS 
 
 measured in cubic centimetres and its weight ascertained in 
 grams. Then, as before, by dividing the weight of the 
 specimen by its volume, the weight of one cubic centimetre 
 is deduced. Now, one cubic centimetre of water weighs by 
 definition exactly one gram, hence the specific gravity of the 
 stone is obtained by dividing the weight of one cubic centi- 
 metre of it by 1 ; in other words, this weight of unit volume 
 of the stone is its specific gravity. Thus a piece of pine 
 20 X 35 X 2 cms. weighs 700 grams, 20 X 35 X 2 = 1,400 
 
 c. cms. = 0-5, the specific gravity required. 
 
 V. Nature and Properties of Matter. 
 
 1. Nature of Matter. — By the term " matter " is under- 
 stood any ponderable substance, which may be solid, Hquid 
 or gaseous. All matter is characterised by the possession 
 of weight and requires force to set it in motion, and all 
 matter occupies space. 
 
 Thus air is matter, whereas light is not material. A 
 vessel full of air weighs more than the same vessel 
 exhausted, but not more in light than in the dark. Again, 
 to move air requires force, but to move a heliostat reflecting 
 a beam of light requires no more effort than would be 
 necessary in the dark. 
 
 Matter is not absolutely continuous, but is built up of 
 very minute particles, called " molecules," which have spaces 
 between them even in the case of the most compact solids. 
 That these molecules are very small is evident from the 
 thinness to which many substances may be brought, and 
 which must be necessarily at least one molecule thick if 
 they are to hold together. "Water in the film of a soap 
 bubble, and gold leaf, the latter easily obtained goCcJoo ^^'^^ 
 in thickness, suggest themselves. 
 
 Molecules are usually complex bodies consisting of two 
 or more similar or dissimilar particles known as atoms. 
 
ON MEASUEEMENT AND PROPERTIES OF MATTER 19 
 
 Physical changes usually involve displacement of the 
 molecules as such, but in chemical changes the molecules 
 are broken up individually, which results in the interchange 
 of their constituent atoms. 
 
 That spaces between molecules do exist in matter is 
 indicated by the fact that many substances which possess 
 no apparent porosity can be compressed. Milled lead, for 
 example, has a higher specific gravity than cast lead. 
 Conversely, when a body is stretched it appears to be the 
 interspaces and not the molecules themselves which are 
 enlarged. The pull of one molecule upon another, which 
 accounts for the power of retention of shape in solid bodies, 
 explains the tendency to return to the original form 
 possessed in greater or less degree by solids under deforming 
 forces. 
 
 It has been said that matter can exist in the solid, liquid 
 or gaseous state. The characteristics of these conditions 
 will now be touched upon. 
 
 2. Solids. — All solids possess size and shape ; that is to say, 
 a given amount of any solid occupies a definite space while 
 its internal constitution is such that it retains its shape 
 without support from outside agencies. This retention of 
 shape is dependent upon what is called rigidity, a property 
 possessed in varying degree by all solids in virtue of which 
 they resist forces tending to displace their molecules. The 
 resistance called out by any such deforming force is called 
 a stress. The amount of deformation produced measures 
 what is known as the strain. A body which offers great 
 resistance to deformation, that is, one in which great internal 
 stress is called out by a given strain, is said to possess high 
 elasticity. Elasticity may, then, be defined as stress divided 
 by strain. This definition differs somewhat from the 
 popular idea of elasticness. It is not the amount which a 
 body can stretch and yet recover which is the true measure 
 of this property, but to what extent it can withstand efforts 
 
 G 2 
 
20 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 at deformation. Glass and steel, for example, are highly 
 elastic bodies, though not possessed of the india-rubber- 
 like nature which is the essence of the popular conception 
 of this property. Bodies which show a marked absence of 
 elasticity are termed plastic. Wet clay and lead are 
 examples of such bodies which possess very small power of 
 recovery under forces acting upon them. 
 
 Other distinctive properties possessed in a greater or 
 lesser degree by solids are malleahility, the property in 
 virtue of which they may be beaten into sheets ; ductility, or 
 powers of attenuation, as wire ; hardness, which may refer 
 to power to resist either abrasion or indentation. Much 
 standardisation yet remains to be done in connection with 
 many of these properties. 
 
 3. Liquids.— Though liquids, like solids, possess definite 
 size they have no shape, and this involves some funda- 
 mental distinctions. This lack of shape is due to an entire 
 absence of rigidity in liquids, and from this limpness it 
 follows that the slightest inequality of pressure upon a 
 liquid is able to cause movement. If two vessels contain- 
 ing the same liquid be connected the level in each will 
 become the same whatever the form or distance of the con- 
 necting pipe— a fact well recognised where actual pipes are 
 concerned, but often overlooked when water areas separated 
 by porous soils are in question. 
 
 Liquids are practically incompressible, and transmit any 
 pressure put upon them equally in all directions, which 
 renders them very valuable as media for pressure trans- 
 mission in all forms of hydraulic machinery. 
 
 Any force, however small, will change the shape of a 
 liquid; for example, a stone dropped into a pond moves 
 the whole of the water therein. The rate of this change, 
 however, varies with different liquids. Those in which 
 change of shape proceeds slowly are termed viscous, while 
 limpid liquids are termed mobile. 
 
ON MEASUREMENT AND PEOPERTIES OF MATTER 21 
 
 4. Gases. — The term gas includes not only bodies popu- 
 larly so described as coal gas and carbonic acid gas, but 
 all matter which is neither solid nor liquid. The most 
 important gas is thus ordinary air. Gases have much in 
 common with liquids, and the two are indeed classed together 
 as fluids. Gases possess, however, two important distinc- 
 tions : they have not only no shape but no size, and they 
 are very easily compressed. 
 
 Lack of size may be realised by considering the effect of 
 admitting, say, a cubic foot of air into a vacuous room, 
 The air admitted would immediately expand and fill the 
 whole room in a very attenuated form. The space occupied 
 by a gas is thus entirely dependent upon the limits set 
 upon it. 
 
 Gases possess the simplest constitution of any of the 
 forms of matter. While solids and liquids differ much 
 among themselves, the physical properties of all gases are 
 remarkably similar. Some of the laws relating to gases 
 will be dealt with in succeeding chapters. 
 
CHAPTEK III 
 
 THE AIR AND COMBUSTION 
 
 I. The Air. 
 
 1. Material Nature. — Physical Aspects. — Air though 
 invisible is material, it possesses weight, and no little energy- 
 must be expended in pushing it on one side in moving 
 through it. The actual weight of air may be ascertained 
 by counterpoising an exhausted vessel on a delicate pair of 
 scales, and then admitting air, when the vessel will require 
 to be balanced by weights which will be equal to the 
 weight of air then contained in it. 
 
 All gases vary in volume so largely with variations in 
 temperature and pressure that it is essential to observe and 
 state the conditions in these particulars in dealing with the 
 weight of gases. Under ordinary circumstances, however, 
 a cubic foot of air weighs about 1 J ozs. 
 
 The air in a building may, therefore, weigh many tons 
 and thus exert considerable pressure. When still, this 
 pressure, since it acts in all directions, may be neglected, 
 but when air is in motion unbalanced pressures are pro- 
 duced, which are often of considerable magnitude. 
 
 2. The Barometer. — If one end of a pipe be dipped below 
 the surface of a liquid, and suction be applied to the other 
 end, the liquid rises in the pipe. The height to which a 
 liquid can thus be drawn is limited, however great the 
 suction power applied, and is found to depend upon the 
 specific gravity of the liquid. The heavier the liquid 
 the shorter will be the column raised ; in fact, the weight of 
 
THE AIR AND COMBUSTION 
 
 23 
 
 columns of different liquids drawn up in a given tube will 
 be in all cases the same. 
 
 The liquid rises in the pipe owing to the withdrawal of 
 air, which leaves an unbalanced pressure due to the air 
 outside ; and it is the weight of this external air upon the 
 exposed surface in the vessel which forces the liquid up the 
 pipe. All cases of so-called " suction " are in reality cases 
 of unbalanced air pressure. 
 
 A convenient means is in this way provided for measur- 
 ing air pressure, since when the column of liquid in the pipe 
 is sufficiently long to balance the full weight of the air it 
 will on further suction rise no higher. 
 
 It is found that water can be raised in a pipe by suction 
 some 33 feet in height above the level of that in which 
 the pipe is standing, and this gives the extreme limit 
 (never quite attained in practice) to which water can be 
 raised by lift pumps or other suction appliances, such as 
 syphons. 
 
 The liquid mercury (quicksilver), which is 13 J times 
 
 33 
 
 as heavy as water, reaches its limit of height at feet or 
 
 about 30 inches, and as such shorter column is more 
 convenient than a column of water, a tube thus filled with 
 mercury is used for measuring air pressure which is not 
 quite constant but undergoes small though important 
 variations. The tube need not, of course, be filled by 
 suction. If sealed at one end the mercury may be poured 
 into it, and it may then be temporarily closed and inverted 
 in a dish of mercury, beneath the surface of which its open 
 end is retained. Such a tube of glass some 33 inches long, 
 either standing in mercury as described or with its open 
 end bent round so as to present a surface upon which the 
 air can press, is known as a barometer. 
 
 Variations in the height of the mercury in a barometer 
 are due to several causes. The higher the situation above 
 
24 CHEMISTET AND PHYSICS OF BUILDING MATEEIALS 
 
 the earth's surface the less is the depth of the ocean 
 of air above, and hence the less the air pressure. Thus 
 the height of the barometer decreases with increased 
 altitude, falling about 1 inch for every 900 feet ascended for 
 moderate heights. Heights, even those of lofty buildings, 
 may be measured with considerable accuracy from barometer 
 readings. 
 
 Winds, by accumulating or dispersing air, cause local 
 variations of pressure, and moisture by expelling air usually 
 causes a reduction of pressure and hence a fall in the 
 barometer. 
 
 It has been stated that any force, however small, is 
 sufficient to move a liquid, hence the barometer forms 
 a very delicate instrument, and indicates changes of 
 pressure long before these are evident to the senses. 
 
 3. Boyle's Law. — It has been stated that gases show 
 much more similarity among themselves in their physical 
 properties than do liquids or solids. All gases, for example, 
 expand and contract to the same extent under the influence 
 of heat and pressure. Since the volume of a given 
 quantity of gas is dependent on the temperature and 
 pressure to which it is subjected, any change in volume 
 must involve a change in specific gravity. The relations 
 between temperature pressure and volume are important, 
 because the motion of gases in warmed rooms, chimneys, 
 and flues, and their flow under pressure, are the result of 
 variations in these factors. 
 
 It is here proposed to investigate the relations between 
 the pressure upon a gas and the volume it occupies. 
 Changes in temperature will be considered in a subsequent 
 chapter. 
 
 If the tube shown in Fig. 1a be filled with mercury 
 sufficiently to seal up the air contained in the shorter 
 closed limb and the mercury be made to stand at the same 
 height on each side of the bend, the enclosed air will 
 
THE AIE AND C0MBUSTI(3N 
 
 26 
 
 be under the same pressure as that of the air outside, 
 which would otherwise push the mercury up the tube or 
 allow the enclosed air to push it down. Let a mark be 
 made on the closed limb where the mercury level stands 
 and the length of the enclosed air column be measured. 
 This enclosed air is supporting the atmospheric pressure, 
 to be actually ascertained by reading off the height of the 
 
 Volumes 
 0 _ 
 
 Fig 1. — Eelation between the Volume of a gas and the Pressure 
 sustained by it. 
 
 barometer. Suppose this to be 30 inches. Now let 
 mercury be poured into the open end of the tube until the 
 difference in level between the open and the closed side 
 is 30 inches, as shown in Fig. 1b. The enclosed air is now 
 under twice the original pressure, namely, one 30-inch 
 column equal to the weight of the atmosphere and another 
 actually carried in the shape of the mercury added. It will 
 be found that the mercury has risen halfway up the closed 
 limb, in other words, that the volume of the air (the tube 
 
26 CHEMISTRY AND PHYSICS OF BUILDINQ MATERIALS 
 
 supposed to be of regular bore) has been halved. Thus by 
 doubling the pressure the volume is halved, and had the 
 tube been long enough, by adding another 30 inches of 
 mercury and thus trebling the pressure the volume would 
 have decreased to one-third, and so on in proportion. The 
 result may be expressed generally by the statement that 
 the volume varies inversely as the pressure, and this is found 
 to be true for all gases. This fact, which lies at the 
 root of all gaseous calculations, is known, after the name 
 of its discoverer, as Boyle's Law, and may be stated thus : 
 The volume of a given quantity of any gas varies inversely * 
 as the pressure upon it. 
 
 II. Chemical Properties of the Air. 
 
 1. Composition of Air. — If air be enclosed in an inverted 
 glass vessel standing in water and some clean iron wire be 
 pushed under the water into the vessel, the rusting of this 
 wire, which will readily take place, will be found to be 
 accompanied by a diminution in the volume of the enclosed 
 air, and this decrease will continue (perhaps over a long 
 period) until one-fifth of the air has disappeared, as 
 evidenced by the rise of the water in the vessel. No 
 further diminution will then take place. On taking out 
 the wires they will be found, though much rusted, by no 
 means entirely corroded away.^ 
 
 ' The expression " varies inversely as " is a useful one for convey- 
 ing any such relationship as the above. If one thing gets bigger in 
 the same proportion as another gets bigger, the one is said to vary 
 "as" or "directly as" the other. If one thing gets bigger in the 
 same proportion as that in which another gets smaller, the one is 
 said to vary "inversely as " the other. 
 
 ^ To perform this experiment successfully, a narrow, graduated 
 glass cylinder should be used to contain the air. The level of the 
 water should be the same inside and outside the cylinder to begin 
 with when the volume of the enclosed air is noted, and again after- 
 wards (secured by pouring water into the open vessel in which the 
 cylinder stands). The temperature should also be as nearly as 
 possible the same at the beginning and end of the experiment. 
 
THE AIR AND COMBUSTION 
 
 27 
 
 Some important deductions may be made from this 
 experiment. The presence of unrusted iron on removal 
 shows that the absorption of the air by the iron did not 
 cease owing to the want of material on which to act. It 
 must, therefore, have ceased because the active principle 
 in the air which is responsible for rusting had completely 
 expended itself. Air must, then, consist of two different 
 gases in the proportion of 1 to 4 by volume, ^ of the whole 
 an active gas, | an inert gas. The active gas, which 
 combines with the metals to form rust, is called oxygen, the 
 inert gas is called nitrogen. 
 
 The experiment does not show whether these gases are 
 chemically combined or merely mixed together, or whether 
 more than two different kinds of gas exist in the air. 
 Although air contains small quantities of other gases it is, 
 however, substantially composed of oxygen and nitrogen, 
 and further experiments have shown that these gases are 
 merely mixed together in the atmosphere. 
 
 2. Preparation and Properties of Oxygen. — A further proof 
 that oxygen is the active constituent of the air may be 
 made by extracting this gas from the air and observing its 
 properties when alone, or more readily by utilising other 
 sources for its preparation, such as red lead, nitre, or 
 chlorate of potash, compounds which all contain oxygen 
 obtainable in a free gaseous state by the action of heat on 
 these bodies. 
 
 In pure oxygen rusting and decay take place with 
 increased activity, while substances which merely smoulder 
 in air burn in oxygen with great brilliancy. The chemical 
 activity of oxygen, however, is dependent, as are nearly all 
 chemical actions, upon the presence of a small quantity of 
 moisture. Air or oxygen, if absolutely dry — a condition 
 never attained without special chemical precautions — have 
 no action whatever on ordinary substances. If, for example, 
 some pieces of quicklime, which absorb moisture, are allowed 
 
28 CHEMISTEY AND PHYSICS OF BUILDINO MATEEIALS 
 
 to stand in a well- stoppered bottle into which some bright 
 iron nails are subsequently introduced, the iron will be 
 found to retain its lustre indefinitely. That rusting is not 
 due solely to water, but to both air and moisture together, 
 may be proved by placing some pieces of bright iron in a 
 stoppered bottle filled with water from which all dissolved 
 air has been expelled by boiling briskly for some minutes. 
 
 When oxygen combines with other bodies, whether actual 
 rusting or other chemical change takes place, the process is 
 known as oxidation, and the combination of any element 
 with oxygen is known as an oxide. 
 
 III. Minor Constituents of the Air. 
 
 All air contains, in addition to oxygen and nitrogen, 
 small quantities of moisture and carbonic acid gas, and 
 often floating organic matter and mineral acid vapours. 
 
 1. Moistxire. — Water vapour in air is essential for 
 respiration. The amount present in the atmosphere 
 depends upon geographical and meteorological conditions 
 and upon temperature. At summer temperatures air can 
 carry about per cent, of its weight of water, but at the 
 freezing point J per cent, is sufficient to cause saturation ; 
 hence if warm air laden with moisture come in contact 
 with a cold body water is deposited. The deposition of 
 dew upon cold surfaces, such as pipes conveying cold water 
 and upon windows of inhabited rooms, is attributable to 
 this cause. In the latter case such deposition is much 
 aggravated by inefficient ventilation, since respired air and 
 the combustion products from illuminants contain large 
 quantities of moisture. Although the amount of moisture 
 present in air is very variable, it is seldom that actual 
 saturation is reached under normal conditions, and on the 
 other hand, even the driest winds contain more than 
 one-tenth of the amount of water necessary to produce 
 saturation. 
 
THE AIE AND COMBUSTION 
 
 29 
 
 2. Carbonic Acid Gas and Organic Matter. — This gas, 
 more modernly called carbon dioxide, is produced by com- 
 bustion or decay in air of all animal and vegetable sub- 
 stances, and is also found in respired air as a waste 
 product from the process of food assimilation. In fact, 
 whenever carbon or any of its compounds undergo free 
 oxidation carbon dioxide is formed. Fresh air contains 
 some four volumes of this gas in 10,000 volumes of air, 
 but in inhabited buildings less than six volumes in this 
 bulk of air are seldom possible, and in badly-ventilated 
 rooms ten, or even twenty, volumes have often been 
 recorded. 
 
 The gas itself is not injurious in quantities even much 
 larger than that last cited, but when it results from 
 respiration its amount becomes a measure of floating 
 organic matter, always evolved during breathing, which 
 taints the air and is injurious to health. The estimation 
 of this organic matter directly is not easy, while the means 
 for finding the amount of carbon dioxide which is pro- 
 portional thereto is comparatively simple ; hence such latter 
 estimation is commonly made, and in such terms the 
 purity of the air is expressed. 
 
 Further reference to the action of carbon dioxide when 
 dissolved in water, and to mineral acid vapours and the 
 important part they play in connection with changes in 
 materials, will be found in subsequent chapters. 
 
 IV. Combustion. 
 
 1. Combustion Defined. — When oxidation, or other 
 chemical action, takes place with such energy that the 
 heat thereby evolved raises the substances concerned to 
 incandescence, that is, produces light, the process is 
 termed " combustion." Broadly speaking, the only differ- 
 ence between the combustion of bodies in air and slow 
 
30 CHEMISTEY AND PHYSICS OF BUILDING MATEEIAiS 
 
 oxidation or decay is one of time. The same ultimate 
 chemical changes and the same amount of heat are pro- 
 duced, but in the latter case the production of heat is 
 so gradual that no change of temperature may be observ- 
 able. Occasionally slow oxidation will develop into active 
 combustion owing to the heat generated, as when a hay- 
 stack fires or oily cotton waste ignites " spontaneously." 
 Again, from the remarks in Chapter I. it will be evident 
 that bodies in a fine state of division will oxidise much 
 more readily than the same substances in large pieces. 
 Fires in flour mills and coal mines resulting from the 
 heat generated by the rapid oxidation of fine particles of 
 materials raised as dust are by no means unknown. Even 
 iron may be prepared in such a minute state of division 
 that it takes fire on exposure to the air. These facts are 
 not without some bearing on the design of many buildings. 
 
 2. Conditions for Combustion. — In order that combustion 
 may take place, three conditions must be satisfied. The 
 first, an obvious one, is that there shall be something 
 capable of burning, that is, a substance not already in 
 an oxidised condition. The second, that air (or some other 
 substance with which combination can occur) shall be 
 present. The third, that these two substances shall be 
 raised to a certain temperature, different for different 
 bodies, at which combination can take place, which is 
 known as the " kindling point." 
 
 The proper way of regarding combustion, therefore, is 
 not as a mere inflaming of some perishable material but as 
 an act of chemical combination between two equally neces- 
 sary bodies — the perishable substance and the air. A 
 lighted match, for example, will be extinguished if plunged 
 into a vessel full of coal gas, and the gas will only burn at 
 the aperture exposed to the air. This necessity for air can 
 be strikingly shown by leading an air supply into a vessel 
 filled with coal gas, when the air will burn if lighted. The 
 
THE AIE AND COMBUSTION 
 
 31 
 
 union is, of course, the same as when gas is burnt in air : it 
 is in both cases the two gases which burn together. 
 
 The necessity for raising the substances to be burnt to a 
 certain temperature before any action can take place between 
 them may be readily demonstrated by placing a combustible 
 substance in contact with a flame and withdrawing the heat 
 from it by means of some heat-absorbing material. A piece 
 of paper pressed against a flat-iron may be held in a gas 
 fiame without damage, or if water be placed in a paper bag 
 the bag may be heated over a naked flame until the water 
 has entirely boiled away, provided that the strength and 
 texture of the paper are suitable for retaining the water. 
 
 3. Instantaneous Combustion. — The rapidity with which a 
 body burns and the nature of the products of combustion 
 have an important bearing on the effects of such action 
 upon surrounding materials. If the combustion is prac- 
 tically instantaneous and gases are produced which have 
 no immediate means of escape an explosion results. It 
 follows that the more nearly the combustible body and the 
 air are present in proportions necessary for chemical com- 
 bination the more violent will be such explosion. The 
 disruptive effects of an explosion are due to the sudden 
 expansion of the air and gaseous products of the combustion 
 resulting from the heat of the chemical action. 
 
 4. Practical Bearings of Foregoing Principles. — The pre- 
 servation of buildings from fire can alone be considered 
 intelligently in the light of the above principles, and safety 
 may be assured if it can be arranged that under no circum- 
 stances can the three conditions required for combustion be 
 fulfilled at one time. Thus if combustible materials must 
 be employed it is obviously necessary to so place them that 
 in presence of air they will never be raised to their kindling 
 points, or to exclude the presence (actual or possible) of air 
 in the likely event of their becoming overheated. This 
 latter alternative has not received the consideration it 
 
32 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 deserves. If, for example, the windows and other aper- 
 tures of a building were provided with closely-fitting iron 
 shutters, these when closed would limit the possibilities of 
 internal combustion to the supply of oxygen contained in 
 the air enclosed within the structure. The use of solid 
 wooden floors, and of hard wood in which the pores are 
 filled with solid matter, for stairs and similar structures as 
 safeguards against fire, is based upon the same principle. 
 
CHAPTEE IV 
 
 HEAT ITS NATURE AND MEASUREMENT 
 
 I. Nature of Heat. 
 
 The power of causing chemical changes possessed by heat 
 has already been referred to. In this and the succeeding 
 chapter it is proposed to discuss the nature of heat, and 
 more particularly the physical changes which it produces 
 in materials. The means described in Chapter III. of 
 recognising a material body, if applied to heat would show 
 it to possess a non-material existence. A hot body is no 
 heavier than the same body when cold, neither does 
 increase in heat of a body add to the necessary force 
 required to move it. 
 
 The means whereby heat may be generated throw some 
 light on its nature. If a rope attached to a falling weight 
 be allowed to run through the hand, heat is readily pro- 
 duced, and since the effect of the hand is to check the weight 
 in its fall and thus deprive it of some of its energy, it seems 
 reasonable to assume that some connection exists between 
 the energy thus lost and the heat so generated. Careful 
 experiments have shown that the whole of the energy 
 possessed by a falling weight may be converted into heat, 
 and the conclusion arrived at is that heat is itself a form 
 of energy into which other forms of energy may be easily 
 converted. 
 
 It has already been pointed out that the molecules of 
 which material bodies are composed are in a state of motion, 
 and it has been shown that the effect of heat energy is to 
 
 B.M. D 
 
34 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 increase the vibratory (or gyratory) motion of these mole- 
 cules so that they move more rapidly and through greater 
 distances as more heat is imparted to them. Heat may 
 thus be looked upon as a form of internal or molecular 
 motion, and if sufficient heat is imparted the molecules 
 may so far lose their relative positions as to break away 
 from one another, which explains the liquefaction and 
 vaporisation of bodies by heat. 
 
 The term "cold" is merely a relative term implying 
 " less heat." All bodies have some internal motion, and 
 thus possess some heat. Ordinary ice, for example, is hot 
 as compared with liquid air. No heat in a body would 
 mean absolute molecular rest, and recent improvements in 
 the means of producing intense cold have almost enabled 
 such a condition to be reached. At very low temperatures 
 not only the physical properties but also the chemical 
 activity of bodies are materially altered, and in a state of 
 molecular rest it is probable that no chemical combination 
 would take place even between the most active substances. 
 
 II. Temperature. 
 
 1. Meaning of the Term. — When a body from any cause 
 gets hotter it is said to rise in temperature. Temperature 
 is not heat. It bears the same relation to heat that the 
 height of a weight bears to the energy or work obtainable 
 by letting it fall. A very small weight may drop from a 
 great height and yet not be able to give as much energy or 
 perform as much work as a heavy weight falling through a 
 moderate distance. Similarly, a small body may be at a 
 very high temperature but possess less heat than a large 
 body only moderately hot. 
 
 Temperature may be called heat level, and the difference 
 between this and heat (energy) should be carefully 
 considered. 
 
HEAT— ITS NATUEE AND MEASUREMENT 35 
 
 2. Measurement of Temperature. — Bodies expand when 
 heated, and in most cases the increase in bulk caused is 
 directly proportional to the increase in temperature of the 
 body. Expansion thus gives a useful means of measuring 
 temperature. 
 
 Liquids expand more than solids, hence when a liquid is 
 heated its level will be raised in spite of the simultaneous 
 expansion of the vessel containing it. If the liquid is con- 
 fined in a narrow tube slight increases in temperature will 
 readily make themselves apparent, and if the tube have a 
 regular bore the increase in the height of the column of 
 liquid will be proportional to the increase in its volume. 
 By placing such a tube of liquid in contact with various 
 bodies possessing known temperatures and marking the 
 heights at which the liquid stands, to correspond to such 
 temperatures, the tube may be used for determining the 
 temperatures of other bodies. Such an instrument is 
 known as a Thermometer. 
 
 3. Construction of a Thermometer. — The liquid employed in 
 thermometers is preferably mercury, and the tube is of glass 
 and has a bulb at its base in order to admit of the use of a 
 sufficient bulk of liquid to render expansion readily visible. 
 In making a thermometer the tube is highly heated until 
 the contained mercury fills it, and it is then sealed up ; thus 
 all air is expelled, and nothing exists above the level of the 
 cooled liquid to impede its subsequent expansion when 
 used. The instrument is then placed in melting ice, and 
 a mark made upon the tube where the mercury then stands, 
 after which it is placed in steam above boiling water, and 
 the increased height of the mercury recorded by another 
 mark. These marks register the freezing and boiling 
 points of water, and are known as the fixed points. 
 
 The length of the tube between these marks is then 
 divided into a number of equal divisions known as 
 "degrees," and these may be continued above and below 
 
 D 2 
 
36 CHEMISTEY AND PHYSICS OF BUILDINa MATERIALS 
 
 the fixed points to enable a greater range of temperature 
 to be recorded. 
 
 4. Scales of Temperature. — The simplest method of 
 dividing up the space between the freezing and boiling 
 points is to mark this off into one hundred equal divisions, 
 and to number them from 0, as the lower point, to 100, as 
 the higher point, continuing the numbers above 100 as 
 desired, and marking those below 0 as minus 1, minus 2, 
 etc., down to the bulb of the thermometer. This is the 
 scale always used in scientific work and for general pur- 
 poses in some places abroad, and is known as the Centigrade 
 scale (C). The word "degree" is generally expressed by a 
 small hollow circle placed at the right hand top corner of 
 the number ; thus if the mercury stood at the division 23, 
 as it might do on a hot summer's day, the temperature would 
 be registered as 23° C. 
 
 Unfortunately, owing to causes explained under the dis- 
 cussion of standards in Chapter II., the numbers above 
 assigned to the fixed points are not employed universally, 
 and two other scales are in common use, though only one of 
 them, that used popularly in this country, need be referred 
 to. This, known as the Fahrenheit scale (F.), adopts the 
 number 32 instead of 0 for the freezing point and 212 
 instead of 100 for the boiling point of water, and the space 
 between the two is divided into equal parts, of which, how- 
 ever, there will be 180 (viz., 212 — 32). Degrees on the 
 Fahrenheit scale are therefore less — that is, represent a 
 smaller rise of temperature — than those on the Centigrade 
 scale. It is, however, a very simple matter to convert one 
 set of readings into the other, just as metres might be con- 
 verted into yards or vice versa ; and as technological books 
 sometimes give temperatures in one scale and sometimes 
 in the other, it is most necessary to be able to effect this 
 conversion in order to make comparisons of various 
 data. Since 180 degrees F. are equal to 100 degrees C, 
 
HEAT— ITS NATUEB AND MEASUREMENT 37 
 
 1 degree F. = or f of a degree C. Hence, a Fahrenheit 
 temperature, or "reading" as it is termed, may be converted 
 into a Centigrade reading by multiplying by f , provided 32, 
 the difference in the numbering of the freezing point, is first 
 subtracted to put this point on the same footing in each 
 case. Conversely a Centigrade reading may be turned into 
 Fahrenheit by multiplying the reading by f and then 
 adding 32 to the result. This conversion is very easily 
 remembered if it is borne in mind (1) that if the numerical 
 result is to be larger (C. to F.) the fraction must be used 
 with the 9 above, and vice versa; (2) that the 32 never 
 takes part in the multiplication, i.e., it is subtracted before 
 or added afterwards, as the case may be. A few examples 
 worked out will give immediate facility in this simple 
 change of unit, thus 100° C. = 100 X f = 180 + 32 = 
 212° F. 
 
 III. Measurement of Heat Quantity. 
 
 1. Unit of Heat. — The amount of heat contained in a 
 body is dependent upon (1) the weight, or, more properly, 
 mass of the body in question ; (2) the temperature of the 
 body ; (3) what the body is. The unit of heat therefore 
 should be, and is, the amount of heat required to raise unit 
 weight of some standard substance through unit rise in 
 temperature. The standard substance universally accepted 
 is water, and the unit of heat is the amount of heat required 
 to raise through 1° C. 1 pound, or 1 gram, of water, 
 according to whether the British or Metric system is 
 adopted. It does not follow that this amount of heat is 
 the same for all parts of the temperature scale, i.e., that 
 the same heat, for example, is required to raise a pound of 
 water from 0° C. to 1° C. as is required to raise it from 
 68° C. to 59° C, but it has been found that the amount is 
 so very nearly the same that the above definition of the 
 unit is quite accurate enough for ordinary purposes. 
 
88 CHEMISTRY AND PHYSICS OF BUILDING MATEEIALS 
 
 It follows from the above statements that to raise 2 lbs. 
 of water 1°C. requires two units of heat, and that two 
 units of heat will also raise 1 pound of water 2° C. To 
 find the number of units of heat, therefore, necessary to 
 raise any weight of water to any given temperature, the 
 weight of the water must be multiplied by the rise in 
 temperature. 
 
 The unit of heat might of course be defined in reference 
 to the Fahrenheit scale of temperature, namely, as the 
 amount of heat required to raise 1 pound of water 1^ 
 Fahrenheit. In engineering work it is often so defined, 
 but the definition as given, employing the Centigrade 
 scale, is always used in scientific work. When water, or 
 any other substance, cools, heat is given out to the air or 
 surrounding bodies, and it would be equally correct to 
 define the unit as the amount of heat given out when unit 
 weight of water cools through unit temperature. 
 
 2. Specific Heat. — The mention of a specific substance — 
 water — in the above discussion implies the tacit assumption 
 that different substances require different amounts of heat 
 to heat them up. This question may be investigated as 
 follows : — Let a pound of iron and a pound of lead be 
 placed for some minutes in boiling water until they have 
 acquired the temperature of the water (100° C). Now let 
 each be rapidly removed and placed in separate similar 
 vessels each containing half a pint of cold water at the 
 same temperature (say, the temperature of the air). The 
 metals will give out their heat to the water, which will thus 
 be raised in temperature ; but if the rise in each vessel be 
 ascertained by a thermometer, it will be found that the 
 water containing the iron is considerably hotter than that 
 containing the lead. Since the iron has given out more 
 heat than the lead it must have absorbed more heat from 
 the boiling water ; in other words, it takes more heat to heat 
 up iron to a given temperature than it does lead, weight 
 
HEAT— ITS NATURE AND MEASUEEMENT 39 
 
 for weight. This fact is expressed scientifically by the 
 statement that iron has a greater specific heat than lead. 
 
 By definition the specific heat of water is 1 and the 
 specific heats of other substances are numbers showing 
 the relative amounts of heat necessary to heat them up 
 as compared with water. Iron only requires about -|th 
 as much heat as water and lead as little as ^^o^^- Thus 
 the statement that the specific heat of iron is Oil means 
 that, weight for weight, iron only requires '11 units of 
 heat for every 1 unit required by water when each is raised 
 through the same range of temperature. 
 
 Water possesses a much higher specific heat than any 
 ordinary substance known. A knowledge of the capacity of 
 bodies for heat has much practical utility. In the extraction 
 of metals from their ores, which necessitates usually a 
 number of heating processes, the amount of fuel required 
 will be, among other things, dependent upon the specific 
 heat of the materials. Again, the rate of cooling of bodies, 
 which merits consideration in many heating problems, is 
 proportional to their specific heats. 
 
 IV. Change of State. 
 
 Change of temperature is not the only effect produced in 
 bodies by heat, and though a body generally gets hotter 
 when heated, this is not always the case. Apart from 
 change of temperature and chemical change, heat energy 
 may be expended upon producing (1) a change of state in 
 the process of melting or boiling ; (2) a change of volume ; 
 (3) a change of internal stress. Two or more of these effects 
 often occur simultaneously. 
 
 1. Latent Heat.— If some lumps of ice be placed in water 
 in sufficient quantity to bring the temperature down to 0° G. 
 and the mixture of ice and water be then heated and kept 
 well stirred, it will be found that, although heat is being 
 
40 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 absorbed, as evidenced by the rapid melting of the ice, a 
 thermometer placed in the liquid will remain at 0° C. until 
 the whole of the ice is melted, after which a regular rise in 
 temperature will occur until the water boils, when the 
 thermometer will again remain stationary at 100° C. while 
 steam is generated. 
 
 Heat is thus evidently used up in melting and in boiling — 
 that is, in changing the state from solid to liquid and from 
 liquid to gas. Admitting that heat is a form of molecular 
 motion, this conclusion seems reasonable, since to confer 
 increased freedom of motion upon the molecules, necessitated 
 by conversion into the liquid and gaseous condition, must 
 involve the expenditure of a definite amount of heat energy. 
 
 Heat thus expended in changing the state of a body is 
 known as Latent Heat, and the amount of heat necessary 
 to produce such change of state in a given weight of any 
 particular substance can be measured in ordinary heat units. 
 Thus the latent heat of water is 79, that is to say, that to 
 just melt unit weight (a pound) of ice requires 79 times as 
 much heat as is required to raise a pound of water 1°C., i.e., 
 79 units of heat. Similarly, to Just boil away a pound of 
 boiling water requires 537 units of heat, i.e., the latent heat 
 of steam is 537. 
 
 It should be remembered that all these physical changes 
 are reversible. Thus when a pound of steam condenses 
 into boiling water 537 units of heat are liberated and 
 actually available for heating surrounding bodies, which 
 accounts for the very rapid heating of water into which 
 a jet of steam is passed. 
 
 Similarly 79 units of heat are given out when a pound 
 of water is frozen, which considerably retards the natural 
 formation of ice. 
 
 2. Melting-Points. — A pure chemical compound (or 
 element) melts and boils at fixed temperatures; hence a 
 determination of the melting or boiling point often serves 
 
HEAT— ITS NATURE AND MEASUEEMENT 41 
 
 as an aid to identification, and as an indication of purity, 
 since an impure substance will show a gradual rise of 
 temperature during changes of state as its various con- 
 stituents (each possessing its own melting and boiling 
 point) undergo this change. 
 
 Commercial substances are, it is true, seldom, if ever, 
 pure compounds, but when a probable adulterant has a 
 melting or boiling point much removed from that of the 
 genuine constituents, an indication of its presence may be 
 made by observing the temperature at which the change of 
 state begins to take place. Thus good mastic melts at 
 about 125° C, but if it is adulterated with coal-tar residues 
 the temperature of fusion observed will be much lower. 
 
 3. Change of Volume with Change of State. — Change of 
 state is always accompanied by some change in volume. 
 When a liquid is converted into a gas a very large increase 
 in volume takes place. In the case of water, for example, 
 the expansion is about 1,700, i.e., any volume of water will 
 produce some 1,700 times its bulk of steam. In the case 
 of solids turning into liquids no general rule can be laid 
 down, though most solids expand slightly on passing into 
 the liquid form, and hence such liquids contract on solidifi- 
 cation. Obviously no such bodies can be used for making 
 sharp castings, as such solidified liquids will fail to fill the 
 moulds in which they are formed. Cast iron and certain 
 alloys, however, expand on solidification, as does also water. 
 
 The expansion of water on solidification has many 
 important effects on natural phenomena. The disintegra- 
 tion of many materials may be traced to this cause. Water 
 finds its way into the pores or cracks in a material, or is 
 stored in a closed water pipe, and when cooled to the freezing 
 point it must either secure additional space for the forma- 
 tion of ice by bursting asunder its confining walls or remain 
 liquid below the ordinary freezing point as the result of 
 compression. As the expansive force involved in solidification 
 
42 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 is much greater than the cohesive power of the particles 
 of most substances, fracture results if the confinement is 
 complete, and often if means of egress are much restricted. 
 Some idea of the force of expansion may be gathered from 
 the fact that to prevent the freezing of water at a tempera- 
 ture of 7 degrees below its ordinary temperature, i.e., at 
 - 7°C., a surrounding pressure of about 14,000 lbs. per 
 square inch would have to be sustained. 
 
CHAPTEE V 
 
 HEAT AND ITS EFFECTS ON MATERIALS 
 
 In this chapter it is proposed to deal with the expansion 
 caused by heat in cases where changes of state in materials 
 are not concerned, and, as a conclusion to this subject, 
 with the means whereby heat is transmitted from place 
 to place. 
 
 I. Expansion of Solids. 
 
 1. Dimensions and Structure. — Solids when heated expand 
 in all directions, and if they have the same structure 
 throughout they expand in all directions equally, or, more 
 correctly, in proportion to their linear dimensions. Thus 
 a cubic inch of lead will, when heated, expand to the same 
 extent along its length, breadth and thickness, but a piece 
 of lead three inches long and one inch square will expand 
 three times as much along its length as in the other direc- 
 tions, simply because each linear inch expands separately. 
 The expansion of a body is therefore proportional to its 
 length. 
 
 If a body is not homogeneous — that is, if its properties are 
 not the same in different directions — a cube of such substance 
 will not expand equally in all directions. Thus the expan- 
 sion of a piece of timber along the grain is not the same 
 as that across the grain. 
 
 2. Linear Expansion of Solids. — It is often convenient to 
 consider the expansion of a body in one direction only, if 
 one of its linear dimensions exceeds the other two. A steel 
 joist, for example, when heated expands, of course, in all 
 
44 OHEMISTEY AND PHYSICS OF BUTLDINa MATERIALS 
 
 directions, but the expansion along its length is so much 
 greater than along its breadth and thickness that the 
 increase to the two latter directions may usually be 
 neglected. 
 
 That expansion does take place for even moderate eleva- 
 tions in temperature may readily be shown by heating a 
 metal rod or tube fixed at one end and resting across a 
 sewing-needle on a flat smooth surface at the other. If a 
 long paper spill or a straw be speared on the point of the 
 needle placed to overhang its support for this purpose, the 
 rotation of the needle caused by the rolling out of the heated 
 metal rod upon it will be made readily evident by the move- 
 ment of the pointer. 
 
 This experiment might be utilised for comparing the 
 expansions of different materials, by heating to the same 
 temperature rods of equal length of various materials and 
 noting the angle through which the needle pointer was 
 rotated in each case. This would be found to be different 
 in different cases — that is to say, the linear expansion of 
 different materials is not the same. 
 
 3. Co-eflBcient of Linear Expansion. — The natural unit of 
 expansion would be the amount of increase in length which 
 the unit length of a substance would acquire when heated 
 through 1° C. The fraction of the original length gained 
 when a body is heated 1° C.'- is known as its co-efficient of 
 expansion, or, more correctly, as its co-efficient of linear 
 expansion. As an example the co-efficient of expansion of 
 lead in terms of degrees Centigrade will be found stated in 
 tables of physical data as 0'000028, which means that a 
 piece of lead of any given length increases by 0-000028 of 
 this length for each degree C. through which it is heated. 
 Thus 1 yard of lead heated 1° C. will become 1-000028 
 yards, and 7 yards will become 7 + (7 X 0*000028) 
 
 ^ Strictly speaking, when heated from 0° C. to 1° C, but the above 
 definition serves for practical purposes. 
 
HEAT AND ITS EFFECTS ON MATERIALS 45 
 
 yards. To find the increase in length when the tem- 
 perature is raised more than 1° C. it is merely necessary 
 to multiply the above result by the rise in temperature. 
 Thus 1 foot of lead heated 25° C. becomes 1 + 0-000028 
 X 25 feet, and 18 feet heated 25° C. becomes 18 + (18 X 
 0'000028 X 25) feet. To determine, then, the increase in 
 length in any case it is only necessary to multiply the 
 number of units of length in question by the co-efficient of 
 expansion and this result by the rise in temperature ; the 
 product added to the original length gives the new length 
 under the altered conditions of temperature. 
 
 If the Fahrenheit scale be adopted the numbers repre- 
 senting the co-efficients will be smaller, because degrees F. 
 do not represent so great a rise in temperature as degrees C, 
 but the method of calculation is the same as that just given. 
 
 4. Practical Importance of Expansion. — The expansion of 
 bodies is of considerable importance in many constructional 
 problems where long lengths of rigid materials are employed 
 or when different substances of a fragile nature are united. 
 A steel joist 30 feet long is, for example, about | of an 
 inch longer in summer than in winter, hence long steel 
 structures must not be rigidly fixed at both ends. The 
 Forth Bridge, which is a yard longer in summer than in 
 winter, forms a striking example of expansion. 
 
 When hot liquids or gases are conveyed in pipes the great 
 change in temperature which such pipes have to undergo 
 often renders special expansion joints necessary. In such 
 cases freedom of motion is essential, and the casing of such 
 pipes in brick or concrete would lead to disruption of such 
 materials. 
 
 The methods employed for attaching lead and zinc to 
 roofs and flats are intimately related to the subject under 
 discussion. The co-efficient of expansion of these metals is 
 very great, about 2J times that of steel. If permanently 
 fixed in large sheets, therefore, they must necessarily 
 
46 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 buckle when exposed to the sun's heat and eventually either 
 tear themselves free from restraint, or fracture. The high 
 specific gravity of lead coupled with its great expansion 
 confers a tendency to work down a sloping roof, as when 
 contraction occurs as an expanded sheet cools this tends to 
 take place more at the upper than the lower end of the 
 sheet, inasmuch as shrinkage at the lower end involves work 
 in raising the metal to a higher level against the attraction 
 of gravity. 
 
 When a substance consisting of two or more bodies which 
 have different co-efficients of expansion undergoes any 
 change of temperature, it is subjected to stresses, since its 
 various parts cannot expand freely. Thus Portland cement 
 has a co-efficient of expansion of O'OOOOll, and cannot 
 therefore make a reliable joint under varying temperatures 
 with lead (co-efficient 0*000028) . On the other hand, the 
 co-efficient for steel fortunately approaches very closely to 
 that of concrete, so that these materials behave well in 
 contact. In the case of brittle substances fixed together 
 this unequal expansion is a frequent source of fracture. 
 The cracking of glaze upon tiles and terra cotta may often 
 be attributed to a lack of appreciation of the principles here 
 cited. 
 
 The force of expansion is very great, and to prevent 
 expansion or contraction, which would occur with change 
 of temperature, requires a force equal to the tensile or 
 compressive stress which would be necessary to lengthen or 
 compress the material to the new lengths which it tends to 
 assume. This is occasionally taken advantage of for 
 straightening the walls of buildings. An iron rod is 
 attached at one end to some rigid structure and the other 
 passed through the bulged wall, the rod is heated and then 
 tightened up to the wall by a nut and washers externally. 
 In order to assume its original length on cooling, the rod 
 has to draw the wall inwards. 
 
HEAT AND ITS EFFECTS ON MATEEIALS 47 
 
 It will have been observed that the foregoing remarks on 
 the importance of expansion have been devoted chiefly to 
 the metals. Allowance for expansion in non-metallic bodies 
 such as stone, brick or concrete is not usually of importance. 
 The reason for this is partly because such bodies have, as a 
 rule, smaller co-efficients of expansion and higher specific 
 heats, and thus require more heat to produce a given rise in 
 temperature than the metals, but mostly on account of their 
 poor conductivity, which, in ordinary cases of change of 
 temperature, makes them exceedingly slow in adapting 
 themselves as a whole to temperature variations to which 
 they may be exposed. 
 
 II. Expansion of Liquids. 
 
 It has been pointed out that liquids as a class expand 
 more than solids. Many instances of this fact present 
 themselves : for example, mercury or spirit would not rise 
 to the stem of a thermometer did not these liquids expand 
 more than the glass tube containing them. The expansion 
 observed in all such cases is in reality the excess of expan- 
 sion of the liquid over that of the containing vessel. 
 
 1. Expansion of Water. — The only liquid of any import- 
 ance in this discussion is water, which behaves in a quite 
 exceptional way at low temperatures, actually contracting 
 in volume when its temperature is raised from 0° C. until 
 4° C. is reached, after which it expands continuously, though 
 not very regularly, until it reaches its boiling point. Water 
 has, therefore, a greater specific gravity at 4° C. than at any 
 other temperature, and if a quantity of water is cooled the 
 cold layers will sink to the bottom as their specific gravity 
 increases, and finally the temperature of the lowest layers 
 will be found to be 4° C. After the whole of the water has 
 assumed this temperature further cooling will result in the 
 
48 CHEMISTRY AND PHYSICS OF BUILDINa MATERIALS 
 
 colder layers remaining at the surface. Hence the tempera- 
 ture of all deep undisturbed water approximates to 4° C. 
 
 When cold water is raised to its boiling point it expands 
 by about 4 per cent. : a fact which must be allowed for in 
 estimating the capacity of vessels which contain water 
 which is likely to be heated. 
 
 2. Circulation of Water. — The circulation of water in 
 pipes is entirely dependent upon the difference of specific 
 gravity of water at different temperatures. The water in 
 contact with the lower heated surface of a boiler expands 
 and rises through the colder layers above it, and the heavier 
 displaced water will fall and in turn be heated. Thus a 
 continuous circulation is set up. It follows that the water 
 will be heated with much greater rapidity if the heat be 
 applied to the bottom of the boiler than if applied at the 
 top. If pipes are attached to the boiler the circulation and 
 consequent distribution of heat to surrounding bodies may 
 be correspondingly extended. If the heated water be 
 allowed to follow a continuous upward path to the furthest 
 positions from the boiler, and to return (cooled) downhill, 
 eventually entering the boiler again near the bottom, circu- 
 lation will obviously be most rapidly effected. 
 
 III. Expansion of Gases. 
 
 1. Charles' Law. — Gases when heated expand very much 
 more than solids or liquids, and, whereas the expansion in 
 the case of solids and liquids varies with each individual 
 substance, all gases expand to the same extent for any 
 given increase in temperature. 
 
 If a bottle of known capacity filled with air be heated in 
 boiling water and then rapidly inverted in cold water, water 
 will enter it as the expanded air is cooled, and the volume 
 of water which enters will be a measure of the air expelled, 
 
HEAT AND ITS EFFECTS ON MATEEIALS 49 
 
 or of the expansion which has taken place between the 
 temperatures of the boiling and cold water. 
 
 Experiments based on these lines have shown that a 
 given quantity of any gas if heated from 0° C. expands of 
 its original volume for each degree C. through which its 
 temperature is raised. The discovery is known, after the 
 name of the investigator, as " Charles' Law." This law, and 
 that of Boyle previously explained as giving a general 
 relation between the pressure and volume of gases, stand 
 at the foundation of all calculations dealing with the 
 distribution and flow of air and other gases. 
 
 2. Ventilation. — To the great co-efficient of expansion of 
 air its movement in heated and inhabited rooms is chiefly 
 due. The warmed air from persons or heated materials 
 rises. This may be looked upon as the ordinary behaviour 
 of a light body tending to float upon a heavier body, or 
 — and this has a deeper significance — as movement due to 
 two columns of air of unequal weight. If the heated air be 
 considered to be enclosed in a column, say, the height 
 of the room, this air is lighter than a similar column of 
 cold air outside, and an unstable condition is set up as in 
 a syphon discharging water. No longer able to balance the 
 cold external air, that in the room will be pressed upwards 
 and will escape through suitable outlets at the top of the 
 room, provided that, and only provided that, the cold air is 
 allowed to exert its pressure freely through inlets of suffi- 
 cient area at low level. This forms the basis of a system 
 for effecting what is known as natural ventilation. 
 
 IV. Transmission^ of Heat. 
 
 There are three distinct ways in which heat may pass 
 from one body to another, known as (1) Conduction, 
 (2) Convection, (3) Eadiation. 
 
 1. Conduction. — Heat is said to pass from one body to 
 
 B.M. B 
 
50 CHEMISTRY AND PHYSICS OF BUILDING MATEEIAXS 
 
 another in contact with it or from one part of a body to 
 another part of the same body by conduction when this 
 transference takes place without any motion (other than 
 molecular vibration) of the body or bodies themselves. 
 Thus heat received by water in a boiler passes from the fire 
 through the boiler walls by conduction. 
 
 All substances conduct heat to some extent, though this 
 power is vastly different in different bodies. 
 
 (a) Measurement of Conductivity. — If a piece of iron and a 
 piece of copper wire of similar diameter be coated with wax 
 (which may be effected by warming them and then drawing 
 them across a candle), and if one end of each be placed 
 in a flame, it will be noticed that wax will melt along the 
 copper wire to a greater distance than along the iron wire. 
 Since the heat reaches the wire by conduction, the experi- 
 ment shows copper to be a better conductor than iron. 
 The point at which the melting stops on each wire will be 
 that at which the air robs the material of its heat suffi- 
 ciently rapidly to reduce the temperature to a point below 
 the melting point of the wax, and the position of this point 
 on the wire will depend upon the rate at which heat can 
 flow through the material from the flame. The actual con- 
 ductivity may be shown to be proportional to the square of 
 the distance along which the wax is finally melted. 
 
 (h) Good and Bad Conductors. — The metals as a class 
 are the best conductors ; non-metallic mineral substances 
 such as stone and concrete, and such bodies as wood, water, 
 and glass, are bad conductors, while most carbonaceous 
 substances, such as oils and woollen fabrics, are still worse 
 conductors. Some idea of the variation of this property 
 in different substances may be obtained from the statement 
 that silver, the best-known conductor, possesses a con- 
 ductivity some 20,000 times as great as that of dry air, 
 which is one of the worst conductors. 
 
 (c) Practical Importance. — Conductivity has many 
 
HEAT AND ITS EFFECTS ON MATERIALS 51 
 
 bearings of practical importance. The use of felt for roofing 
 and other coverings, and the lagging of pipes, will suggest 
 themselves, and since the rate of transmission of heat by 
 conduction is inversely proportional to the thickness of the 
 material, the thickness of any such layer of bad conductor 
 specified should be based upon a knowledge of its conducting 
 power. 
 
 (d) Conduction for Heat and Electricity. — Good heat 
 conductors are always good electrical conductors, and vice 
 versa. The actual conducting powers for heat and electricity 
 possessed by a given substance are not, however, identical. 
 
 2. Convection. — Heat is said to be transmitted by con- 
 vection when the heated body or a part of it actually moves 
 from one place to another in the process of transmission. 
 Thus if a hot body be carried from one room to another, 
 heat has reached the latter room by convection. 
 
 The passage of heat in liquids and gases (nearly all of 
 which are very bad conductors) takes place almost entirely 
 by this method of transference. Hot water and hot air 
 systems are practical examples of the use of convection. 
 The heated particles of liquids and gases rise through the 
 colder particles owing to expansion, thus compelling the 
 latter to take their place and to come into contact with the 
 source of heat, while the first heated particles eventually 
 give up their heat by conduction, and are thus in turn 
 brought again to the source of heat, and this cycle of 
 operations results in a continuous circulation. 
 
 3. Radiation. — It is evident that heat is transmitted in 
 some other manner than by conduction and convection, 
 since it readily passes though a vacuum. A glow lamp, for 
 example, becomes hot though the filament glows in empty 
 space ; and the heat of the sun reaches the earth across a 
 vacuous space of many millions of miles. 
 
 (a) Nature of Radiant Heat. — In such cases heat is said 
 to be transmitted by radiation. The chief peculiarity of 
 
 B 2 
 
52 CHEMISTEY AND PHYSIOS OF BUILDING MATEEIALS 
 
 this form of transmission lies in the fact that the inter- 
 mediate space between the source of heat and the substance 
 thereby heated is not raised in temperature. The heat is 
 in fact propagated as waves of energy which only become 
 heat as ordinarily recognised when they strike some object, 
 and for practical purposes the object must be a liquid or 
 solid ; in other words, radiant heat passes through gases 
 without sensible conversion into effective heat. 
 
 Although the hotter a body the greater the amount of 
 heat emitted by radiation, such emission is by no means 
 confined to bodies hot enough to emit light. 
 
 (&) Practical Value of Radiant Heat. — The aim of all 
 artificial systems of heating should be to provide as large 
 a proportion of radiant heat as possible, thus taking the 
 sun, admittedly the healthiest source of heat, as a model. 
 The chief advantage of radiant heat lies in the fact that by 
 it persons and things are warmed directly, while the air 
 surrounding them remains cool and suitable for respiration, 
 whereas heated air is not only undesirable for respiratory 
 purposes, but by promoting more rapid evaporation of 
 moisture from the body produces, as does all evaporation, 
 cold. It must thus be supplied at an unnaturally high 
 temperature if the sensation of warmth is to be thereby 
 established. The ideal method of artificial heating might 
 possibly prove to be a sphere maintained at a white heat in 
 each room, with means for ventilation above it, whereby 
 any chance organic particles, produced in the surrounding 
 atmosphere, might be rapidly removed, which would 
 prevent their charred remains from vitiating the air. 
 
CHAPTER VI 
 
 CHEMICAL SIGNS AND CALCULATIONS 
 
 I. Atomic Theory. 
 
 In some brief comments upon the constitution of matter 
 reference was made in Chapter 11. to atoms and molecules' 
 and the atom was defined as the smallest particle into 
 which matter is divisible. This atomic theory— that is this 
 presumption that matter can only be divided up to a fixed 
 degree of fineness— is a very old one; but a century ago it 
 received at the hands of John Dalton an important exten- 
 sion which at once raised it to a position of the greatest 
 utility, and coupled it with his name. His addition to 
 the theory lay m the discovery of the fact that all atoms of 
 a given element have the same weight. This discovery 
 forms the basis of all chemical calculations, and upon it 
 modern chemical theories have been built up. 
 
 At the present time it seems likely that the atomic 
 theory is about to experience another great development 
 owing to the discovery of radium and the resulting work 
 since achieved by chemists in the field of radio-activity and 
 It is now suggested that the atoms are in combination with 
 bodies which have been named ''electrons," which them- 
 selves possess weight, though the weight of an electron is 
 exceedingly minute even as compared with the almost 
 inexpressibly small weights of atoms. These electrons 
 appear to give a measure of the chemical activity or power 
 of entering into combination possessed in very varvine 
 degree by different elements. 
 This addition to the atomic theory, though of great 
 
54 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 interest, is hardly likely, however, to affect any of the 
 chemical considerations discussed in these pages for some 
 time to come. 
 
 II. Atomic Weights and Symbols of the Elements. 
 
 1. Relative Weights of the Atoms.— The actual size of 
 atoms and hence their weights, are, as has been stated, 
 exceedingly small. Lord Kelvin has supplied a popular 
 conception of this size by the statement that one drop of 
 water contains more molecules than the number of cricket 
 balls which would be required to make a sphere as large as 
 the earth ; each of these molecules of water, moreover, 
 consists of three atoms. 
 
 It may well be asked, therefore, What is the value ot a 
 knowledge of the weights of atoms ? The actual weights 
 of these minute bodies are of no practical interest, but their 
 relative wei^/ite— that is, information as to how much heavier 
 the atoms of one element are than those of another— are ot 
 great value, and these relative weights are known as the 
 atomic weights of the elements. 
 
 As in other comparisons, some element must be selected 
 as a standard and the weight of its atom called 1. The 
 element usually taken is that of the gas Hydrogen, which is 
 the lightest common substance known. Thus the statement 
 that the atomic weight of zinc is 65 means that the atom of 
 the element zinc weighs 65 times as much as the atom ot 
 
 hydrogen. , 
 
 2. Symljols. — Instead of writing the names of the 
 elements in full it is customary to designate them by their 
 initials; thus C stands for Carbon and 0 for Oxygen. Inas- 
 much, however, as many of the elements have the same 
 initial letter, a second letter of the name is appended where 
 necessary and is written as a small letter alongside the first- 
 just as, for example, the letters St. " are used to represent 
 
CHEMICAL SIGNS AND CALCULATIONS 
 
 the word " street." Thus S stands for Sulphur and Si for 
 Silicon. These chemical initials are known as Symbols. 
 
 Many of the elements were discovered and named in 
 early times when books were written in Latin, and though 
 the^ English names have now replaced the original Latin 
 designations, the symbols of the Latin names are in many 
 cases retained, which accounts for many symbols possessing 
 no apparent connection with the names of the elements as 
 now used. For example, the symbol for Iron is Fe, from 
 the Latin for iron — Ferrum. 
 
 Although symbols have been described above as a species 
 of chemical shorthand, they possess a much more important 
 significance, since the symbol of an element when written 
 is always taken to represent one atom. Thus Al does not 
 imply an indefinite quantity of Aluminium, but one atom of 
 the metal, or 27 parts by weight (its atomic weight) as 
 compared with 1 part by weight of Hydrogen, represented 
 by the symbol H. This aspect of the use of symbols 
 is of the greatest importance in dealing with chemical 
 equations. 
 
 3. Table of Symbols and Atomic Weights.— The table on the 
 following page shows the symbols and approximate atomic 
 weights of the elements found in building materials, 
 arranged in the order of such weights. Those elements 
 possessing the physical characters distinctive of metals are 
 marked with an asterisk, while the elements of lesser 
 importance are printed in smaller type. 
 
 III. Combinations of Symbols, or Formul-e. 
 
 It has been said that the symbol of an element expresses 
 one atom ; if two atoms are in question, instead of writing 
 the symbol twice over, the number 2 is placed either 
 in large type before the symbol or in small type after and 
 
56 CHEMISTRY AND PHYSIOS OF BUILDING MATEBIALS 
 
 Table of Elements used in connection with Building 
 Materials. 
 
 Name. 
 
 Hydrogen 
 
 Boron 
 Carbon 
 Nitrogen 
 Oxygen 
 Fluorine 
 ^Sodium 
 ♦Magnesium 
 ^Aluminium 
 SUicon 
 Phosphorus 
 Sulphur 
 Chlorine 
 ♦Potassium 
 ♦Calcium 
 *Chromium 
 
 Symbol. 
 
 Approx. 
 At. 
 Wgt. 
 
 Name. 
 
 Symbol. 
 
 Approx. 
 At. 
 Wgt. 
 
 H 
 
 1 
 
 *Manganese 
 
 Mn 
 
 55 
 
 B 
 
 11 
 
 ♦Iron 
 
 Fe 
 
 56 
 
 C 
 
 12 
 
 ♦cobalt 
 
 Co 
 
 58 
 
 N 
 
 14 
 
 ♦Nickel 
 
 Ni 
 
 58 
 
 0 
 
 16 
 
 ♦Copper 
 
 Cu 
 
 63 
 
 F 
 
 19 
 
 ♦Zinc 
 
 Zn 
 
 65 
 
 Na 
 
 23 
 
 Arsenic 
 
 As 
 
 75 
 
 Mg 
 
 24 
 
 ♦Silver 
 
 Ag 
 
 108 
 
 Al 
 
 27 
 
 ♦cadmium 
 
 Cd 
 
 111 
 
 Si 
 
 28 
 
 ♦Tm 
 
 Sn 
 
 118 
 
 P 
 
 31 
 
 *Antimony 
 
 Sb 
 
 120 
 
 S 
 
 32 
 
 ♦Barium 
 
 Ba 
 
 136 
 
 CI 
 
 35^ 
 
 *Gold 
 
 Au 
 
 196 
 
 K 
 
 39 
 
 *Mercury 
 
 Hg 
 
 199 
 
 Ca 
 
 40 
 
 ♦Lead 
 
 Pb 
 
 205 
 
 Cr 
 
 52 
 
 •^Bismuth 
 
 Bi 
 
 207 
 
 below the symbol ; thus 2 H or H2 stands for two atoms of 
 hydrogen, and larger numbers of atoms are expressed 
 similarly. Chemical compounds can be represented in 
 the same manner by writing the symbols of the elements 
 they contain side by side with the numbers (if more than 
 one) of the atoms of the elements present. Thus the 
 symbols PbO standing together represent litharge, or lead 
 oxide, which consists of one atom of lead combined with 
 one atom of oxygen. In the case of the common red oxide 
 of iron, two atoms of iron are combined with three atoms 
 of oxygen, and the compound is therefore expressed as 
 FeaOs. 
 
 The use of the word " symbol " is confined to elements; 
 when these are combined as above the expression is always 
 referred to as a Formula. Thus chemists speak of the 
 symbol for iron, and of the formula for iron oxide. In 
 
CHEMICAL SIGNS AND CALCULATIONS 
 
 57 
 
 formulae the numbers expressing the number of atoms are 
 always written as small numerals below the right-hand side 
 of the symbols as shown above ; numbers in large type in 
 front of a formula always mean that the whole formula is 
 referred to taken so many times over. Thus 2 PbO indicates, 
 not two atoms of lead and one of oxygen, but two of both 
 elements, that is, two complete molecules of lead oxide, or 
 2 (PbO), the bracket being always understood. Again, 
 H2O is the formula for water, and 10 H2O represents ten 
 whole molecules of water, or twenty atoms of hydrogen and 
 ten atoms of oxygen. If a compound consists of complex 
 parts which can be separated as such, or sometimes if 
 doubt exists as to the exact manner in which these parts 
 are combined, they are often written as separate compounds, 
 in the manner described above, but making one formula, 
 with each part separated by a dot or full stop. Thus wash- 
 ing-soda crystals are partly composed of carbonate of soda 
 and partly of water which can be removed. These crystals 
 have the formula Na2C03. IOH2O. Again, cement is com- 
 posed of lime, CaO, and silica, Si02. If two molecules of 
 the former are combined with one molecule of the latter, 
 the formula might be represented as 2CaO.Si02. It 
 should be carefully observed in such a formula that the 
 number 2 only qualifies that part standing before the dot, 
 which is sometimes emphasised by placing this part in 
 brackets, thus, 2 (CaO). Si02. This formula might also be 
 written Ca2Si04 by adding all the oxygen atoms together, 
 but usually the former method of expression gives a better 
 insight into the structure, and to adopt the second method 
 in the case of washing-soda crystals by writing the formula 
 Na2C03. 10 H2O as Na2CH2oOi3 would be very misleading. 
 
 IV. The Assigning of Fokmul^. 
 
 The formula proper to any compound can only be ascer- 
 tained after a chemical analysis, showing not only what 
 
58 CHEMISTEY AND PHYSICS OF BUILDING MATEKIALS 
 
 elements it contains, but the proportion of each present, 
 when, on dividing the amount of each element by its atomic 
 weight, the number of atoms of each will be obtained. 
 
 Thus water contains hydrogen and oxygen ; its formula, 
 however, is not HO, because analysis shows that for every 
 sixteen parts of oxygen there are two parts of hydrogen 
 present. Since the atomic weight of oxygen is sixteen and 
 that of hydrogen one, it is evident that one atom of oxygen 
 is combined with two atoms of hydrogen, and that the 
 simplest formula for this compound is therefore H2O. 
 
 Analysis merely gives the proportion of each element 
 present, which is most conveniently expressed as the per- 
 centage. As an example of the construction of a formula 
 which is obtained by dividing the percentage of each element 
 present by the atomic weight of that element, the compound 
 chalk may be taken. This body is found to consist of 
 40 per cent, of the metal calcium (Ca), 12 per cent, of 
 carbon (C), and 48 per cent, of oxygen (0). 
 
 On referring to the previous table of atomic weights, it 
 it will be seen that Ca =: 40, C = 12, 0 = 16, and on 
 dividing the percentages by these weights the following 
 numbers of atoms are obtained: — 40 -r- 40 = I for 
 calcium, 12 -f- 12 = 1 for carbon, and 48 -r- 16 = 3 for 
 oxygen. The compound therefore consists of one atom of 
 calcium, one atom of carbon, and three atoms of oxygen, or 
 is CaiCiOa, or, since the symbols themselves represent 
 single atoms, the formula is CaCOa. 
 
 Naturally, all calculations are not quite so simple, but 
 the principle utilised is always the same, and since common 
 compounds seldom contain more than three or four atoms 
 of any one element in their molecules, the assigning of a 
 formula in such cases is a fairly easy matter. 
 
 It may be argued that by the above determination the 
 formula for chalk might be any multiple of the formula 
 CaCOs. This is true, but does not affect the use of the 
 
CHEMICAL SIGNS AND CALCULATIONS 
 
 formula in calculations, and for the purposes of this book it 
 may be taken that the simplest formula which will give 
 whole atoms is that adopted. Since mixtures of elements 
 or compounds have no definite composition, they can have 
 no formula, and it is often possible to tell whether a sub- 
 stance is a true compound or not by finding out whether 
 the elements it contains are present in a proportion repre- 
 senting whole numbers of atoms. Thus air, though fairly 
 uniform in composition, does not contain oxygen and 
 nitrogen in atomic proportions ; it is a mere mixture of 
 these two gases and possesses, therefore, no formula. 
 
 V. Chemical Equations. 
 1. Meaning of Equations.— "When a chemical change takes 
 place, either owing to the action of heat or some other form 
 of energy on a compound, or to the action of one body on 
 another, the change may be expressed by writing the 
 formula of the compounds affected and of the new com- 
 pounds produced in the form of an equation, just as would 
 be done in algebra. The bodies taken are always repre- 
 sented on the left or those resulting on the right of the 
 equation, with the sign =, indicating the word "gives," 
 placed between the two sides of the equation, and the 
 sign -f- between each body. Thus, if some litharge (lead 
 oxide) be heated with charcoal (carbon), metallic lead and 
 an oxide of carbon result, which is expressed as follows :— 
 Lead Oxide. Carbon. Lead. Oxide of Carbon. 
 
 Pbo -h C = Pb -t- CO 
 
 Again, when chalk or limestone is heated, quicklime is 
 formed and carbonic acid gas (CO2) is driven off thus :— 
 Chalk. Quicklime. Carbonic Acid Gas. 
 
 CaCOs = CaO + CO2 
 If an equation really expresses the changes which take 
 
60 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 place, it is obvious that everything taken must be accounted 
 for and must appear in some new form of combination on 
 the right-hand side of the equation. It is sometimes of 
 value in more complex examples to check this by counting 
 up the total number of atoms on each side, which should 
 always be equal. 
 
 2. Calculations. — Since these equations represent definite 
 chemical reactions with definite weights of bodies, they 
 give the most valuable information as to the amount of a 
 given substance which can be produced from a given 
 quantity of another substance. To obtain such informa- 
 tion, the equation representing the chemical reaction is 
 first necessary, then atomic weights of the elements present 
 are written below their symbols, and where more than one 
 atom^ is present the atomic weight of such element is 
 multiplied by the number of its atoms. The weights thus 
 obtained are added together for each compound, giving the 
 weight of the molecule of the compound or the "molecular 
 weight." The weights of the bodies produced from the 
 weights taken are thus obtained, and the relation between 
 the two will be true whatever unit (the gram or the pound, 
 etc.) is adopted for expressing such weights. Finally, if 
 the weight of one or more of the bodies required to be 
 produced is given, the weights of the bodies necessary for 
 the purpose can be ascertained (or vice versa) by a simple 
 proportion sum. This reasoning may be applied to the 
 first equation given by writing the atomic weights below 
 the elements, thus : — 
 
 PbO + C =r Pb + CO 
 205 + 16 + 12 = 205 + 12 + 16 
 221 + 12 = 205 + 28 
 
 or, in words, 221 parts by weight of lead oxide heated with 
 12 parts by weight of carbon produce 205 parts of lead 
 and 28 parts of oxide of carbon. From 221 pounds (or 
 
CHEMICAL SIGNS AND CALCULATIONS 61 
 
 tons or ounces) of lead oxide, therefore, 205 pounds (or tons 
 or ounces) of metallic lead would be produced. 
 
 As a second instance, the following question may be 
 answered. What weight of quicklime (CaO) can be 
 obtained from j&ve tons of pure chalk (CaCOs) ? 
 
 CaCOg = CaO + CO2 
 
 40 + 12 + (3 X 16) = 40+16 + 12 + 32 
 100 = 56 
 
 100 tons of chalk would produce 56 tons of quicklime, 
 consequently 1 ton would produce of this or tons, 
 
 56 X 5 
 
 and 5 tons five times as much, namely, — Jqq~~ ~ ^'^ tons, 
 
 or 2 tons 16 cwt. 
 
 In each of these equations only single molecules are 
 involved, but the solution is no more difficult in other 
 cases. When more than one molecule of a compound is 
 present the whole weight of such molecule must be naturally 
 taken the number of times over the molecule is present ; 
 thus when spirits of salt, HCl, acts upon zinc the equation 
 and summation of weights is as follows : — 
 
 Zn + 2 HCl = H2 + ZnCla 
 65 + 2(1 + 35^) = 2X1 + 65+(2X35J) 
 65 + 73 = 2 + 136 
 
 The practical value of a knowledge of chemical equations 
 will be obvious even from these simple examples quoted. 
 
 VI. Chemical Nomenclature. 
 
 1. Names indicate Composition. — The names assigned to 
 chemical compounds are not given haphazard, like the 
 majority of popular names in use, but generally convey a 
 good deal of information as to composition, and often an 
 indication of the proportion of some of the elements present. 
 Thus all bodies which are termed oxides contain oxygen, 
 
62 CHEMISTRY AND PHYSIOS OF BUILDING MATERIALS 
 
 and those termed sulphides, sulphur, while carbides, car- 
 bonates, and hydrocarbons all contain the element carbon. 
 The termination ** -um " is usually confined to elements 
 which are metallic in character — for example, aluminium 
 and calcium — while the ending "-a" is found in the old and 
 still used names for certain oxides, such as alumina and silica. 
 
 The termination " -ide " indicates the presence of only 
 two elements in a compound. Thus lead oxide consists 
 only of lead and oxygen, sodium chloride of only sodium 
 and chlorine. The termination " -ate," as in carbonate 
 and sulphate, indicates the presence of three or four atoms 
 of oxygen in a compound of three or more elements. 
 
 As several different compounds containing the same 
 elements but combined in different proportions are often 
 found, a further distinction is necessary in such cases. 
 Thus there are two oxides of carbon, CO and CO2. In such 
 case the prefixes "mono-" or ** mon- " and " di- " are 
 generally added to indicate the presence of one and two 
 atoms of oxygen. Thus CO is carbon monoxide, and CO2 
 carbon dioxide. 
 
 The terminations " -ous " and " -ic " indicate respectively 
 a smaller or larger proportion of non-metallic element in a 
 compound. Thus the oxide of iron, FeO, is termed ferrous 
 oxide, and the better known, red oxide, FesOa, ferric oxide. 
 Many old or popular names for such compounds are, 
 however, still in general use, and these should be remem- 
 bered. Thus carbon dioxide is also known as carbonic 
 acid gas. The modern chemical name for the compound 
 Na2S04 is sodium sulphate, the older and still used name 
 is sulphate of soda, and the popular name Glauber's salts. 
 Similarly sodium carbonate is also called carbonate of soda, 
 and, popularly, washing soda. 
 
 In order to aid the student, a short list, showing the 
 chemical and popular names of some commonly occurring 
 compounds relating to building materials, is appended. 
 
POPULAE AND SCIENTIFIC NAMES FOB COMMON 
 SUBSTANCES. 
 
 Popular Name. 
 
 Chemical Name. 
 
 Formula. 
 
 Mineralogical 
 Name. 
 
 Ammonia (hartshorn) 
 
 Ammonium hydrate . 
 
 NH4OH 
 
 
 Sal volatile 
 
 Ammonium car bon ate 
 
 (NH4)2COs . 
 
 
 Sal ammoniac 
 
 Ammonium chloride . 
 
 NH4CI 
 
 
 Alumina 
 
 Aluminium oxide 
 
 AI2O3 
 
 Corundum 
 
 
 
 BaCOs 
 
 (Emery) 
 
 Carbonate of baryta . 
 
 Barium carbonate 
 
 Witherite 
 
 Heavy spar 
 
 Barium sulphate 
 
 BaSOi 
 
 Barytes 
 
 Carbonate of lime 
 
 Calcium carbonate 
 
 CaCOa 
 
 Calcite, chalk, 
 
 
 
 
 marble, lime- 
 
 
 
 
 stone 
 
 Quicklime 
 
 Calcium oxide 
 
 CaO 
 
 
 Slaked lime 
 
 Calcium hydroxide . 
 
 CaOgHg 
 
 
 Sulphate of lime . 
 
 Calcium sulphate 
 
 CaSOi 
 
 Gypsum, selenite 
 
 
 
 CaS04 2H2 0 
 
 Chloride of lime . 
 
 Calcium hypochlorite 
 
 CaOCla 
 
 
 Chrome green (real) . 
 
 Chromium oxide 
 
 CraOg 
 
 
 Carbonate of iron 
 
 Ferrous carbonate 
 
 FeCOs 
 
 Ironstone 
 
 Black oxide of iron 
 
 Triferric tetroxide 
 
 
 Magnetite 
 
 Green vitriol 
 
 Ferrous sulphate 
 
 FeSOi. 7H2O 
 
 Red oxide of iron 
 
 Ferric oxide 
 
 FeaOg 
 
 HEematite 
 
 Litharge 
 
 Lead monoxide 
 
 PbO 
 
 
 Eed lead 
 
 Red lead 
 
 PbsOi 
 
 
 White lead (Dutch) . 
 
 Lead carbonate and 
 
 PbCOg and 
 
 
 hydrate 
 
 PbOaHa 
 
 
 Chrome yellow 
 
 Lead chromate . 
 
 PbCr Oi 
 
 
 Magnesia 
 
 Magnesium oxide 
 
 MgO 
 
 
 Carbonate of magnesia 
 
 Magnesium carbonate 
 
 MgCOs 
 
 Magnesite 
 
 Epsom salts 
 
 Magnesium sulphate . 
 
 MgSO^.THzO . 
 
 
 Black oxide of man- 
 
 Manganese per- or di- 
 
 MnOa 
 
 Pyrolusite 
 
 ganese 
 
 oxide 
 
 
 
 
 KNO3 
 
 
 Alum (common) . 
 
 Potassium, aluminium 
 
 K2S04.Al2(S04)8 
 
 sulphate 
 
 24H20 
 
 
 Silica 
 
 Silicon oxide 
 
 SiOg 
 
 Quartz, Flint 
 
 
 
 
 (Sand) 
 
 Washing soda 
 
 Sodium carbonate 
 
 NagCOa 10 H2O 
 
 Caustic soda 
 
 Sodium hydrate 
 
 NaOH 
 
 
 Chill nitre . . , 
 
 Sodium nitrate » 
 
 
 Chili saltpetre 
 
 Glauber's salt 
 
 Sodium sulphate 
 
 NaaSO^ 10 H2O 
 
 
 Salt 
 
 Sodium chloride 
 
 NaCl 
 
 Rock salt 
 
 Borax 
 
 Sodium borate . 
 
 Na2B407 10 H2O 
 
 
 White vitriol 
 
 Zinc sulphate . 
 
 ZnS04 7H2O 
 
 
 Zinc white . 
 
 Zinc oxide 
 
 ZnO 
 
 
 Spirits of salt 
 
 Hydrochloric acid 
 
 HCl + water 
 
 
 Aqua fortis . 
 
 Nitric acid 
 
 HNOs 
 
 
 Oil of vitriol 
 
 Sulphuric acid . 
 
 H2SO4 
 
 
 Vinegar 
 
 Acetic acid 
 
 HC2HSO2 
 
 
 Carbonic acid gas 
 
 Carbon dioxide 
 
 CO2 
 
 
 Carbolic acid 
 
 Phenol 
 
 CeHgOH . . 
 
 
CHAPTBE VII 
 
 WATER AND ITS IMPURITIES 
 
 The physical characteristics of water have already been 
 touched upon, but in the present chapter it is proposed to 
 discuss the chemical composition of water and impurities 
 contained in water as obtained from natural sources. 
 
 I. Composition of Water. 
 
 1. Decomposition "by Metals. — If steam be passed through 
 a red-hot iron pipe the issuing vapour is found to contain a 
 gas which will burn, and an examination of the interior of 
 the pipe will further show that the iron has been consider- 
 ably oxidised. The steam has been decomposed into its 
 constituent gases, namely, oxygen, which has attacked the 
 iron ; and hydrogen, the inflammable gas which issues 
 from the pipe. 
 
 Most metals will decompose water under suitable condi- 
 tions owing to their tendency to oxidise, and if a solvent 
 for the oxide formed be present, fresh surfaces of metal are 
 constantly exposed, and the evolution of hydrogen may be 
 made continuous. 
 
 The "killing" of hydrochloric acid (spirits of salt) by 
 zinc for making soldering fluid is an instance of the decom- 
 position of water by zinc in the presence of an acid, and 
 forms the ordinary means of producing hydrogen gas in the 
 laboratory. 
 
 Analysis has shown that the molecules of water are 
 composed of two atoms of hydrogen combined with one 
 of oxygen. The formula for water is therefore H2O. 
 
WATEE AND ITS IMPUEITIES 
 
 66 
 
 The chemical equations representing the action of water 
 upon zinc, and the solution of the resulting zinc oxide 
 hydrochloric acid are 
 
 Zn + H2O = ZnO + H2 
 ZnO + 2HC1 = Zn CI2 = H2O. 
 
 2. Decomposition by Electricity. — When a current of 
 electricity from two or three electric cells is passed 
 through water, the water is decomposed, and if the 
 wires conveying the current to the water consist of 
 unoxidisable metals such as gold or platinum, both the 
 oxygen and hydrogen are liberated in a free state. When 
 decompositions due to the passage of electricity take place 
 the process is known as Electrolysis, and the compound 
 thus decomposed is called an Electrolyte. 
 
 3. Properties of Hydrogen. — Hydrogen gas is almost the 
 lightest substance known. It is colourless and invisible, 
 and burns in air with an exceedingly hot flame to form 
 water, which accounts for the water deposited upon cold 
 surfaces when ordinary combustible illuminants such as 
 oil or coal gas are burnt, since such bodies contain 
 hydrogen. 
 
 II. Solvent Power of Water. 
 
 The changes which are brought about in materials through 
 the agency of water are largely due to its great solvent 
 powers. No substance is absolutely insoluble in water, 
 and though many may be considered to be so for all 
 practical purposes, water, more especially when armed with 
 its ordinary impurities, possesses much greater solvent 
 power than is generally imagined, and it is this fact which 
 renders it so potent an ally in cases of chemical action. 
 
 1. Solution of Solids. — The amount of a solid body capable 
 of solution in a given quantity of water increases (with one 
 
 B.M. F 
 
66 CHEMISTEY AND PHYSICS OP BUILDING MATERIALS 
 
 or two exceptions) with increase of temperature, though by 
 no means necessarily in proportion to the rise in tempera- 
 ture. In all cases, however, the amount of a given sub- 
 stance which can be dissolved by a given quantity of water 
 at a stated temperature is limited, and when this limit is 
 reached the water is said to be " saturated." Lowering of 
 temperature or removal of some of the water, as by evapora- 
 tion, result in deposition of a dissolved solid from a saturated 
 solution, usually in a crystalline form, and the shape of such 
 crystals of deposited solid, and more particularly their size, 
 is greatly influenced by the rate of their formation. The more 
 slowly this proceeds the larger are the crystalline fragments 
 deposited. 
 
 Deposition of solids from solution accounts for the forma- 
 tion not only of many minerals, but also for not a few of the 
 changes which occur in building materials. 
 
 2. Solution of Gases. — Many gases dissolve in water, but 
 unlike solids, the amount which a given quantity of water 
 can absorb is less at high than at low temperatures. Unless 
 any chemical action takes place between the gas and the 
 water the former is always completely expelled when the 
 water is boiled. The solution of air and carbon dioxide in 
 water are matters of considerable importance in connection 
 with materials. 
 
 III. Water of Crystallisation. 
 
 1. Meaning of the Term. — When substances crystallise from 
 solution it is found that in many cases water is taken up by 
 the solids in the process, not in the form of liquid acciden- 
 tally entangled in the solid mass, but as a part of the solid 
 itself, definite in amount and forming an essential in 
 determining that regularity of form which is the charac- 
 teristic of a crystallised compound. Water thus combined 
 with solids is known as " water of crystallisation." 
 
WATEE AND ITS IMPURITIES 
 
 67 
 
 Thus if dry powdered carbonate of soda be dissolved in 
 water until a saturated solution is obtained, and this solution 
 be then cooled or evaporated, ice-like crystalline masses 
 appear which may be removed and dried ; but if they be 
 then heated a large amount of water will be driven off, 
 resulting in the breaking up of the crystals, which will 
 thereby be reduced to a shapeless powder and leave the 
 original substance dissolved. 
 
 The dry carbonate of soda has the formula Na2C03, while 
 the crystals deposited from solutions possess the composition 
 NaaCOs IOH2O. 
 
 2. Eflaorescence. — All compounds containing water of 
 crystallisation can be deprived thereof by the action of heat, 
 though not always quite so completely as in the preced- 
 ing instance, and in many cases so feeble is the state of 
 combination that a warm or dry atmosphere is alone 
 sufficient to remove this water. Both carbonate and 
 sulphate of soda lose some of their water of crystallisation 
 on exposure to a dry atmosphere, which results in the 
 colourless transparent crystals of these compounds falling 
 into a white opaque powder. Bodies which thus readily 
 part with their combined water are said to be Efflorescent. 
 
 The unsightly deposits, known as " white- wash," often 
 seen on the face of brick or stone work are usually the result 
 of the efflorescence of soluble compounds contained in these 
 materials, as to which more information will be found when 
 such materials are discussed. 
 
 3. Deliquescence. — Many compounds when deprived of 
 their water of crystallisation show a very strong tendency 
 to re-absorb water from any available source, and in some 
 cases this absorption will continue, not only until sufficient 
 water has been taken up to enable such bodies to re- 
 crystallise, but until actual solution in considerable excess 
 of absorbed water takes place. The result of this is that such 
 substances, when exposed to the air, which is always more 
 
 F 2 
 
68 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 or less moist, will become wet. Bodies which behave in thig 
 manner are termed Deliquescent. Calcium chloride (CaCla), 
 largely used to absorb moisture from air or other gases, 
 and magnesium chloride (MgCl2), always present in common 
 salt, are instances of deliquescent bodies. Such substances 
 are naturally very objectionable adjuncts to building 
 materials, more particularly where such materials have 
 to be treated with decorative coverings. 
 
 IV. Impurities in Natural Waters. 
 
 The foregoing remarks apply to water considered as a 
 pure chemical compound, but owing to its solvent power 
 it is never found pure in nature. A brief consideration of 
 the history of water as found will be sufficient to make this 
 evident. 
 
 Evaporated by warm air or the direct heat of the sun 
 from the oceans or other free surface, water is constantly 
 rising as vapour into the colder air strata above the earth, 
 where it condenses into drops which form clouds. Eventually 
 these drops become by successive additions so large that 
 the air is unable to support them, and they fall as rain, 
 which immediately begins to exert its solvent action. 
 
 1. Air and other Gases in Water. — Air is soluble in water 
 to the extent of about 2 per cent, by volume at ordinary 
 temperatures. In its fall through the atmosphere, there- 
 fore, water dissolves some air and thus arrives on the earth's 
 surface with some oxidising power, and this solution of air 
 is also continually taking place at every free water surface. 
 
 Oxygen is more soluble in water than nitrogen, and 
 since these gases forming the air are merely mixed, each 
 can dissolve separately, and as a result it is found that 
 about one-third of the gas from air dissolved in rain water 
 is oxygen, whereas it will be remembered that only one-fifth 
 of the air consists of this component. 
 
WATEE AND ITS IMPUEITIES 
 
 69 
 
 Besides oxygen and nitrogen, air contains carbon dioxide, 
 and since this gas is very soluble in water, it is always to 
 be found among the gases in solution, and where water has 
 come in contact with decaying vegetable or animal matter 
 the quantity of this gas is very much increased, and the 
 free oxygen directly diminished, since it is itself converted 
 into carbon dioxide in the process of oxidising such organic 
 matters. 
 
 Under certain local circumstances water also contains 
 acid gases derived from the atmosphere, the most important 
 of which is that formed by the combustion of sulphur always 
 present in coal, which with water and oxygen forms sulphuric 
 acid. 
 
 2. Mineral Matters Dissolved in Water. — As soon as water 
 touches the ground it adds to its impurities by the solution 
 of substances from the soil or underlying strata through 
 which it passes. The character of these dissolved bodies 
 necessarily varies with the nature of the ground. For 
 example, water which has flowed through marshy land 
 over a clay soil will not be found to contain the same 
 impurities as water which has traversed a limestone 
 district. 
 
 The direct solvent power of water enables it to take up 
 such compounds as sodium chloride (salt), calcium sulphate, 
 magnesium chloride and sulphate and sodium carbonate 
 and sulphate, which commonly result from the disintegration 
 of various kinds of rocky strata. 
 
 The presence in water of carbon dioxide (CO2) adds very 
 materially to its power of solution, chiefly in enabling it to 
 dissolve calcium carbonate (CaCOa), whether in the form of 
 chalk, limestone or marble, and armed with this gas water 
 can also dissolve the carbonates of iron and magnesium. 
 The "hardness" of water (see Section V.) is due to the 
 presence of calcium and magnesium compounds. 
 
 3. Organic Impurities. — Water usually contains small 
 
70 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 amounts of organic impurities derived from the decay of 
 vegetation, or animal matters, or possibly from sewage 
 contamination. This results in the eventual production of 
 small quantities of nitrates (compounds of nitric acid (HNO3)) 
 and of smaller quantities of ammonia, which provide the 
 analyst with a means for detecting and estimating such 
 impurities. Sodium chloride (salt) is also found in animal 
 excretions, hence the presence of abnormal quantities of 
 salt gives, in the absence of its production from mineral 
 sources, a valuable indication of sewage contamination. 
 
 4. Suspended Matter. — Water containing all the above 
 impurities may be perfectly bright, clear and tasteless, 
 hence little indication as to the character of water can be 
 obtained by simple inspection. Certain waters, particularly 
 those of river origin, contain, in addition to dissolved 
 matters, suspended solid particles, such as sand or mud, 
 and these alone can be removed by ordinary filtration 
 processes. 
 
 V. Hardness of Water. 
 
 The objection to " hard water " for many domestic 
 purposes and the deposits to which it gives rise in vessels 
 in which it is heated, are well known. Hardness is usually 
 spoken of under two headings : {a) that which can be 
 removed by raising the water to its boiling point and 
 keeping it boiling for a few minutes ; {h) that which cannot 
 be so removed. The former is known as temporary, the 
 latter as 'permanent, hardness. 
 
 1. Temporary Hardness. — This kind of hardness is due to 
 the presence of calcium carbonate (CaCOa) and occasionally, 
 to a small extent, to iron and magnesium carbonates. As 
 explained in the last section, these compounds are only 
 soluble in water containing carbon dioxide (CO2), and since 
 this gas is expelled when the water is boiled, they are 
 
WATEE AND ITS IMPUEITIES 
 
 71 
 
 deposited as solids after such expulsion, which chiefly 
 accounts for the furring of pipes and vessels conveying 
 hot water. The deposit, owing to its gradual formation 
 in successive layers, is usually very hard and tenacious. 
 
 Any other means by which carbon dioxide can be 
 removed from water will naturally be equally efficacious 
 in producing deposition which, while it has disadvantages 
 when occurring in hot water systems, has at times to be 
 resorted to in appropriate vessels for the purpose of softening 
 the water. 
 
 The cheapest and most effective means for softening, 
 temporarily, hard water consists in adding to it quick or 
 slaked lime, which combines with the carbon dioxide in 
 solution forming calcium carbonate, which is itself deposited. 
 Thus— 
 
 Quicklime. Carbonate Dioxide. Cal. Carbonate. 
 CaO + CO2 = CaCOa 
 
 And after such withdrawal of the solvent, the "hardness" 
 is removed by the inevitable deposition of the calcium 
 carbonate originally present. 
 
 Evidently the lime must be added in the proper proportion 
 to just combine with the carbon dioxide present, which can 
 be readily calculated from the above equation, every 44 parts 
 by weight of the gas present requiring 56 parts of quicklime. 
 
 The deposition of calcium carbonate in steam boilers is 
 sometimes prevented by the addition to the water of sal 
 ammoniac (NH4CI), which converts the insoluble carbonate 
 into highly soluble calcium chloride, which remains in 
 solution in the boiler, while the ammonium carbonate 
 simultaneously formed is volatilised and carried off in the 
 steam. 
 
 The equation representing this reaction is — 
 
 Am. Chloride. Cal. Carbonate. Am. Carbonate. Cal. Chloride. 
 2NH4CI + CaCOg = (NH4)2C03 + CaCla 
 
72 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 Water treated in this manner is not, however, suitable for 
 human consumption. A more satisfactory method of 
 preventing scale depends upon the mechanical action of 
 certain vegetable substances which when mixed with the 
 water form a film upon the walls of the boiler to which scale 
 will not adhere. 
 
 2. Permanent Hardness. — This term refers to the hardness 
 of water due to the presence of calcium and magnesium 
 compounds dissolved therein without the agency of carbon 
 dioxide, and which are, therefore, unaffected by boiling the 
 water or by the addition of lime. 
 
 No means exist for the removal of permanent hardness 
 the application of which is practicable on a large scale. 
 Substances present in water, owing to its direct solvent action 
 can only be completely removed by distillation, i.e., by 
 boiling away the water and condensing the steam formed, a 
 process much too costly for any but special purposes. The 
 addition of certain compounds which can, by chemical action, 
 convert the calcium and magnesium compounds present into 
 insoluble bodies and thus withdraw them from the water, 
 is used for domestic purposes. The most important of 
 these is washing soda, the reaction of which with calcium 
 sulphate is as follows : — 
 
 Washing Soda. Cal. Sulphate. Cal. Carbonate. Sodium Sulphate. 
 1 NaaCOa + CaSO^ = CaCOg + . Na2S04 
 
 VI. Effects of Water on Materials. 
 
 The nature and amount of the impurities contained in a 
 given water have considerable bearing upon the choice and 
 arrangement of the materials employed for its conveyance 
 and use. 
 
 ' Water of crystallisation, since it mixes with the water of the 
 ^solution, need not be represented in actions between dissolved bodies. 
 
WATER AND ITS IMPURITIES 
 
 73 
 
 1. Scale in Pipes and Boilers. — The greatest deposition of 
 scale in a hot water system will naturally take place where 
 the inflowing water is first heated, for it will be here that 
 most of the dissolved gas will be expelled, and hence this 
 statement is particularly true for water possessing much 
 temporary hardness. The flow pipe where it adjoins the 
 boiler should, therefore, be of large dimensions and capable 
 of replacement, while the bottom of the boiler especially 
 should possess as continuous a surface, as free from sharp 
 angles and corners, as possible. Scale is a very bad con- 
 ductor ; hence, if allowed to form a coating of any thickness 
 heat is prevented from readily passing through the boiler 
 walls, which may even become red-hot, which will result in 
 a serious loss of strength, and in the event of a flaw arising 
 in the scale, will probably lead to fracture. 
 
 The air dissolved in water will on expulsion oxidise the 
 interior of boiler and pipes, and though these may be soon 
 protected by the deposit of scale, the constant introduction 
 of fresh water into a large service of piping may lead to 
 sufficient internal rusting to produce marked discoloration 
 of the water. The softer the water the more likely, of 
 course, is such a result. 
 
 From the above remarks it will be evident that the com- 
 bination of hot water systems, both for warming a building 
 and for domestic supply, must generally be undesirable. 
 
 It is found that scale settles much less readily upon 
 copper than upon iron. This may be partly due to the 
 rough internal surface usually found in an iron pipe, but is 
 probably also to be attributed to the greater difference in 
 the co-eSicients of expansion of copper and scale than iron 
 and scale, which, aided by changes of temperature, will 
 prevent good adhesion. 
 
 2. Use of Lead Pipes and Cisterns. — The hardness of 
 water is a great safeguard where lead is employed for its 
 conveyance or storage, since the deposit of scale, even to 
 
74 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 the slight extent to which it occurs in a cold water service, 
 prevents oxidation and solution of the lead. 
 
 Lead, as is well known, readily becomes covered with a 
 film of oxide when exposed to a moist atmosphere, and the 
 same effect is produced in water owing to the dissolved air 
 which the water contains. Lead oxide dissolves in water, 
 forming lead hydroxide, and since all soluble lead com- 
 pounds are poisonous, and produce in small quantities a 
 cumulative, and therefore particularly insidious, effect upon 
 the human system, the slightest solution of lead must be 
 guarded against. 
 
 Soft waters are, therefore, particularly unsuited for con- 
 veyance in lead pipes, and in water which contains ammonia, 
 particularly in the presence of large quantities of nitrates 
 (usually derived from decaying vegetation), the amount of 
 lead dissolved is especially large. 
 
 The formation of lead hydroxide takes place as follows : — 
 Lead. Oxygen dissolved in Water. Lead Oxide. 
 
 Pb + 0 = PbO 
 
 PbO + H2O = PbOaHs lead 
 
 hydroxide. 
 
 Even in the absence of any deposit or protecting scale in 
 the pipes, the presence of carbon dioxide in the hard water 
 results in the formation of lead carbonate from the lead 
 hydroxide first formed, and since this lead carbonate is 
 insoluble it soon forms a protective coating. 
 
 Lead Hydroxide. Lead Carbonate. 
 
 PbOaHa + CO2 = PbCOa + H2O. 
 
 VII. Analysis of Water. 
 
 From the above discussion it will be evident that some 
 knowledge of the amount and nature of the impurities 
 contained in water is of considerable practical value. The 
 
WATEE AND ITS IMPUEITIES 
 
 75 
 
 methods whereby such information is obtained cannot be 
 dealt with in these pages, for they involve a knowledge of 
 analytical chemistry ; but the headings under which a 
 chemical analysis is submitted may be briefly referred to 
 in order that the reports of experts may be understood. 
 These are usually as follows : Total Solids, Chlorine, 
 Hardness, Free Ammonia, Albuminoid Ammonia, Nitrates 
 and Nitrites, Poisonous Metals. 
 
 1. Total Solids. — Suspended matter (if any) is usually 
 filtered off from the water and its amount ascertained by 
 weighing the deposit on the filter when dried. The " total 
 solids" comprise all dissolved substances, and are estimated 
 by boiling away a known quantity of water and weighing 
 the residue. 
 
 2. Chlorine is one of the constituents of salt, and hence 
 by its determination the amount of salt present can be 
 calculated^. It is estimated by adding to a given quantity 
 of the water a solution of nitrate of silver of known 
 strength when turbidity is produced, and increases until the 
 whole of the salt has been acted upon, when its amount 
 can be calculated from the amount of standard silver nitrate 
 solution used. 
 
 3. Hardness. — This is estimated by finding out how much 
 solution of soap of a given strength is required to make a 
 lather with a given quantity of the water. In order that a 
 lather may form, soap must freely dissolve, but when added 
 to hard water soap immediately combines with the calcium 
 and magnesium compounds present and is thus withdrawn. 
 The amount of soap necessary to produce a lather, therefore, 
 gives a measure of " hardness." 
 
 4. Ammonia and Nitrates. — These constituents from 
 organic sources are determined by removal of ammonia 
 as gas on distilling the water alone, and subsequently 
 
 > Salt is NaCl (Na = 23, CI = 35|) ; therefore every 35| parts of 
 chlorine found represent 58^ parts of salt. 
 
76 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 with oxidising and with reducing agents, and observing 
 the tint produced by the gas dissolved in water on the 
 addition of a specially prepared reagent which is thereby 
 turned yellow. 
 
 5. Poisonous Metals. — These usually comprise lead and 
 copper, and should be entirely absent in all good waters. 
 They are estimated by a colour test similar to the above. 
 
 6. Good and Bad Water. — Whether a water is to be con- 
 sidered good or bad will naturally be largely dependent 
 upon the use for which it is required. For domestic 
 purposes the hardness and for consumption the organic 
 matters are respectively the most important factors. A 
 water which contained, say, five grains of hardness-pro- 
 ducing compounds per gallon would be regarded as rela- 
 tively soft. London water contains some fifteen grains per 
 gallon, and waters supplied for use containing as much as 
 thirty grains per gallon are known. Organically the 
 albuminoid ammonia should certainly be less than one 
 part in ten million parts of water, and the free ammonia 
 in most cases much less. Lead and copper should be 
 absent, and as regards the other constituents so much 
 variation exists that it would not be wise to attempt any 
 general statement. The study of actual analyses must be 
 made for further information. One is given below to 
 show the form often adopted in stating results. This 
 water was reported upon as of high organic purity but 
 exceedingly hard. 
 
 Analysis of water from a spring in the Stebbing Koad, 
 Essex, made October, 1895 : — 
 
 Grains per gallon. Parts per million. 
 
 Total solids . . 80-0 Free ammonia . . 0-001 
 
 Hardness (reckoned as Albuminoid ammonia 0-024 
 
 CaCOg) . . . 26-3 Nitrates and Nitrites 
 
 Chlorine . . .1-3 (reckoned as HNOg) 11-9 
 
CHAPTEE VIII 
 
 SULPHUR AND THE NATURE OP ACIDS AND BASES 
 
 I. Occurrence and Preparation of Sulphur. 
 
 1. Occurrence. — Sulphur is one of the few elements which 
 are found naturally in an uncombined state; it also 
 enters into the composition of many common substances. 
 Volcanic districts, particularly that at the southern extremity 
 of the Apennine Chain in Sicily, form the chief source of 
 the element commercially. The formation of sulphur in 
 such regions is probably due to the mutual decomposition 
 of gaseous sulphur compounds ejected from the earth. 
 Easily melted, the fine deposit of sulphur lodges among the 
 warm rock and cinder in the neighbourhood of its formation 
 and has become interstratified among the Tertiary beds of 
 the district, in which it forms veins or basin-shaped deposits, 
 whence it is quarried from open workings or mined like 
 coal, but usually in a very primitive fashion. It is separated 
 from the intermixed rock by stacking the collected fragments 
 in kilns resembling lime kilns, and lighting the sulphur, 
 when a small quantity burns and melts the rest, which 
 flows out and is afterwards purified by distillation. In this 
 manner the element is obtained in its familiar form as a 
 yellow brittle solid, or if the condensation of the vapour is 
 allowed to take place without subsequent melting, as a light 
 yellow powder. 
 
 2. Properties of Sulphur. — Sulphur is exceedingly brittle 
 and a very bad conductor of heat and electricity. In a 
 molten condition it readily acts on all metals producing 
 
78 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 sulphides, which, as far as their chemical constitution is 
 concerned, much resemble the oxides. 
 
 When heated, sulphur behaves in a remarkable manner. 
 It melts at a temperature slightly higher than that of boil- 
 ing water to a limpid liquid, but if further heated it becomes 
 almost solid at about 230° C, and again liquefies at a still 
 higher temperature, though it is then much darker in 
 colour and more viscous. Finally it boils at about 444° C. 
 If when the boiling point is approached the liquid is 
 poured into water the solidified mass will be found to be 
 quite plastic, but will, after an interval of a day or two, 
 return to its original brittle condition. 
 
 These changes are due to the breaking up of complex 
 molecules into others containing smaller numbers of atoms, 
 and are worthy of consideration when the element is melted 
 for running joints or similar purposes. 
 
 II. Sulphur Compounds. 
 
 Some of the most important ores of such metals as lead, 
 copper, and zinc are combinations of these metals with 
 sulphur, and many other metals similarly combined are 
 of wide distribution. Sulphur also occurs combined with 
 metals and oxygen as sulphates, such as calcium and 
 sodium sulphates, which have already been referred to. 
 
 1. Sulphides of Iron. — There are two naturally occurring 
 sulphides of iron, both represented by the formula FeS2 
 through want of knowledge as to their molecular structure. 
 One is called iron pyrites (pronounced py-ri-tees), the other 
 marcasite. Both possess the yellow colour of sulphur and 
 are also metallic in appearance, though the former is 
 usually brighter owing to its lesser tendency to tarnish. 
 Iron pyrites, unless in a fine state of division, is remarkably 
 stable even in a moist atmosphere, but marcasite rapidly 
 disintegrates, to the detriment of any materials which 
 
SULPHUE AND THE NATUEE OF ACIDS AND BASES 79 
 
 contain it. Both these minerals occur very commonly in 
 many stones and slates, and in coal. 
 
 When strongly heated in the air the sulphur from these 
 compounds burns away, leaving eventually only iron 
 oxide Fe203. 
 
 2. Sulphuric Acid. — When sulphur from such sources as 
 the above, or as an element, burns in the air, a gas possessing 
 the pungent smell characteristic of burning sulphur, known 
 as sulphur dioxide (SO2), is produced. This gas is readily 
 soluble in water and combines therewith to form a substance 
 known as sulphurous acid, thus : — 
 
 Sulphurous Acid. 
 SO2 + H2O = H2SO3. 
 
 Sulphurous acid has valuable bleaching properties and 
 also arrests fermentation, but is not stable if exposed to the 
 air, since it absorbs oxygen and is converted thereby into 
 sulphuric acid, thus : — 
 
 H2SO3 + 0 = H2SO4. 
 
 This acid is the most important chemical substance 
 manufactured, and about one million tons are produced 
 annually in this country alone. It is used in the produc- 
 tion of nearly all acids, to a decreasing extent in the 
 manufacture of alkalis, in connection with artificial manures, 
 the refining of petroleum, in dyeing and the preparation 
 of dyes, in soap and paper manufacture, in electric cells, 
 and in many other trades directly or indirectly. 
 
 Its manufacture is carried out on the lines indicated 
 above. The sulphur dioxide gas from burnt pyrites is led 
 into very large leaden chambers and there mixed with 
 steam and air, when the sulphuric acid produced falls to 
 the bottom of the chamber with a large excess of condensed 
 steam. This dilute acid is run off and the excess of water 
 expelled by evaporation, when a heavy oily liquid containing 
 
80 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 some 98 per cent, of H2SO4 remains. The concentrated 
 acid is extremely corrosive, chiefly owing to its great 
 tendency to absorb water, which extends even to the 
 extraction of hydrogen and oxygen as water from bodies 
 containing these elements. Nearly all animal and vegetable 
 substances contain hydrogen and oxygen combined with 
 carbon, hence the withdrawal of the two former elements 
 from the carbon which is not acted upon, results in the 
 charring of such substances by this acid. 
 
 The heat evolved by the combination of sulphuric acid 
 with water is very considerable, and therefore the dilution 
 of the strong acid requires care and must be effected by 
 slowly pouring the acid into an excess of water. 
 
 Sulphuric acid has also, when mixed with water, a direct 
 solvent action upon a very large number of substances. 
 Most metals are attacked by it, all carbonates are readily 
 decomposed by it, and many other chemical compounds 
 and common substances yield to its action with greater or 
 less rapidity. 
 
 Pyrites occurs commonly in coal, which may be taken to 
 contain on an average some 67 pounds of sulphur per ton. 
 When coal is burnt sulphuric acid is finally produced owing 
 to the oxidation of the sulphur dioxide in the moist atmo- 
 sphere. The great consumption of coal in large towns 
 renders the amount of sulphuric acid produced in this 
 manner very considerable. In Greater London, for example, 
 probably some 10,000,000 tons of coal are burnt annually, 
 resulting in the production of some 300,000 tons of 
 sulphuric acid, a large part of which descends in rain or 
 fog upon the buildings which so recklessly emit it. 
 
 3. Sulphuretted Hydrogen. — When carbonaceous com- 
 pounds which contain sulphur decompose in the absence 
 of a free supply of air, part of the sulphur may combine 
 with some of the hydrogen present in the substance to form 
 a compound known as hydrogen sulphide, or sulphuretted 
 
SULPHUE AND THE NATUEE OF ACIDS AND BASES 81 
 
 hydrogen. This compound, a poisonous, inflammable gas, 
 is characterised by a smell resembling that of rotten eggs, 
 to the production of which gas in decomposing eggs this 
 smell is, in fact, due. A small proportion of the sulphur 
 contained in coal often finds its way into coal gas in this 
 form, and has a ready action upon certain compounds 
 of lead, producing lead sulphide, which is black. Sul- 
 phuretted hydrogen when burnt is converted into sulphur 
 dioxide and water, thus : — 
 
 H2S+ 30 = H2O + SO2. 
 
 In the presence of atmospheric moisture the sulphur di- 
 oxide is converted into sulphuric acid, as already explained ; 
 hence coal gas containing sulphur compounds exercises 
 a deleterious effect upon the decorations and fittings of 
 rooms in which it is used, even in the absence of any 
 leakage. 
 
 III. Other Common Mineral Acids. 
 
 1. Spirits of Salt. — If strong sulphuric acid is poured 
 upon salt, dense white fumes possessing an irritating odour 
 are produced. This evolved gas is known as hydrochloric 
 acid, and results from an interchange of hydrogen in the 
 sulphuric acid with the metal sodium in the salt. The 
 completed reaction is as follows : — 
 
 Salt. HydrocUoric Acid. 
 
 2 NaCl + H2SO4 = 2 HCl -f Na2S04. 
 
 The gas is very soluble in water, one volume dissolving 
 at ordinary temperatures some 500 volumes of gas, and the 
 solution thus produced is known as spirits of salt or hydro- 
 chloric acid. As sold it contains about 39 per cent, of the 
 acid, the remainder being water. 
 
 The action of this acid upon zinc, producing " soldering 
 fluid," has already been referred to. The zinc chloride 
 
82 CHEMISTET AND PHYSICS OF BUILDINa MATEEIAIS 
 
 formed possesses great powers of absorbing oxygen, which 
 enable it to decompose films of tarnish or oxide upon metals 
 and thus allow solder to adhere. 
 
 Like dilute sulphuric acid, hydrochloric acid readily 
 dissolves many common substances, and on account of its 
 solvent power upon lime and carbonate of lime it is useful 
 in a diluted state for certain cleaning-down processes. 
 
 Though it readily acts upon zinc and iron, hydrochloric 
 acid has no action upon copper, though it dissolves copper 
 oxide in common with most other oxides of the metals. ^ It 
 thus forms a valuable and effective agent for cleaning 
 copper, though it must not be used upon pewter or similar 
 alloys. 
 
 2. Aqua Fortis. — If strong sulphuric acid is heated with 
 nitre (saltpetre), yellow oily drops condense on the sides of the 
 vessel, and if suitable means be taken to collect the liquid 
 formed, as by distilling the mixture in a retort, a highly 
 corrosive acid known as aqua fortis or nitric acid is 
 obtained. The reaction may be represented as follows :— 
 Nitre. Nitric Acid. 
 
 2KNO3 + H2SO4 = 2 HNO3 + K2SO4. 
 
 Nitric acid is occasionally present in small quantities in 
 the atmosphere, while nitrates, which may be looked upon 
 as derivatives of the acid, have been referred to as existing 
 in most natural waters. 
 
 No ordinary metals withstand the corrosive action of 
 nitric acid, and in a concentrated form it has been known 
 to oxidise combustible substances with sufficient rapidity to 
 set them on fire. 
 
 IV. Acids, Bases, and Salts. 
 
 The compounds above discussed have been termed 
 " acids," and represent an important class of bodies which 
 
SULPHUE AND THE NATUEE OF ACIDS AND BASES 83 
 
 bear a relation to other classes of compounds, which in any 
 study of the chemistry of materials it is essential to make 
 clear. 
 
 1. Acids. — Popularly, an acid is regarded as a sour 
 corrosive liquid, but acids can exist in other states. Hydro- 
 chloric acid has been shown to be in reality a gas ; again, 
 oxalic acid, tartaric acid, and many other bodies belonging 
 to this class are solids. 
 
 All acids have the power when in solution of changing 
 the tint of certain vegetable matters, such as the juice of 
 beetroot or an extract from lichens known as litmus, and 
 these colour changes are used for detecting the presence of 
 acid substances. 
 
 Chemically, all acids contain hydrogen and have the 
 power of nullifying or neutralising the properties of 
 another class of bodies known as bases, which involves an 
 exchange of hydrogen for some metal. The three best 
 known mineral acids have been described above. 
 
 3. Bases. — These bodies may be defined as metallic 
 oxides. Most bases are insoluble in water, and, therefore, 
 have not the power of displaying such marked physical 
 characters as are possessed by the acids. Those which 
 dissolve, however, display properties which are the exact 
 opposite of the properties possessed by acids. They are 
 caustic or soapy to the touch, and restore the colour of 
 vegetable tints altered by acids, or change such natural 
 colours to different tints. Thus natural litmus is violet ; 
 it is turned red by acids, and blue by soluble bases. 
 
 Certain bases which possess the above characteristics in 
 a very marked degree are called "alkalis." Such bases 
 which concern this discussion are : Potash (K2O), Soda (Na20), 
 and Lime (CaO). 
 
 3. Salts. — When an acid and a base are brought together, 
 the one neutralises or destroys the characteristic properties 
 of the other, and a new class of compounds which have 
 
 G 2 
 
84 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 neither corrosive nor caustic properties is produced. These 
 compounds are known as Salts, inasmuch as ordinary 
 common salt is one of the best known representatives of 
 the class. In the action of acids upon bases, the hydrogen 
 from the acid and the oxygen from the base always com- 
 bine to form water, which is, therefore, the invariable 
 product of such neutralisation. The following equations, 
 showing the action of acids upon common bases, will make 
 their relations clearer : — 
 
 Base. Acid. 
 Lime . . CaO + H2SO4 
 Soda . . Na20 + 2HC1 
 Lead oxide . PbO + H2CO3 
 PbO +H2Si03 
 CaO +H2Si08 
 
 Magnesium 
 oxide . . MgO + 2HN03 
 
 Water. Salt. 
 
 = H2O + CaSO^ (sulphate of lime). 
 = H2O + 2NaCl (common salt). 
 = H2O + PbCOs (carbonate of lead). 
 = H2O + PbSiOs (silicate of lead). 
 = H2O + CaSiOs (silicate of lime). 
 
 =: H2O + Mg(N03)2 (nitrate of mag. 
 
 nesia). 
 
 By far the largest number of the compounds found in 
 materials belong to the class of bodies called salts, which 
 from their formation may be regarded as consisting of an 
 acid part and of a basic part. Thus silicate of lime (CaSiOa) 
 may be looked upon as composed of CaO, lime, and SiOa, 
 which is silicic acid less water, formed as shown in the 
 reaction given above. 
 
 Since stability in most materials is generally best 
 obtained by the use of such chemical reactions as shall pro- 
 duce neutral compounds, i.e., salts, with neither base nor 
 acid left over, an appreciation of the proportions of acids 
 and bases necessary for such production is not without 
 importance. 
 
 It should always be remembered that the more unlike 
 bodies are the greater will be their tendency to combine 
 and the more stable will be the compound formed. Acids 
 have no tendency to combine with acids, nor bases with 
 bases, neither have salts with salts, though, of course, 
 
SULPHUR AND THE NATUEE OP ACIDS AND BASES 85 
 
 innumerable chemical actions take place in which an 
 interchange of component parts of such bodies occur. 
 
 4. Acid-forming Oxides. — It sometimes happens that 
 salts are formed without the intervention of any actual 
 acid. Certain acids may be looked upon as consisting of a 
 non-metallic oxide combined with water. Thus the solu- 
 tion of carbon dioxide gas in water, known as carbonic acid 
 and possessing the formula H2CO3, may be regarded as 
 CO2.H2O, similar silicic acid H2Si03, may be written 
 Si02.H20. 
 
 Oxides such as these are known as acid-forming oxides, 
 and can themselves combine with bases directly to form 
 salts. The equations for such reactions are similar to those 
 previously cited, with the omission of water. Thus : — 
 
 Base. Acid-forming Salt. 
 Oxide. 
 
 Potash . K2O -f- CO2 = K2CO3 (potassium carbonate). 
 Lime . CaO + CO2 = CaCOg (calcium carbonate). 
 
 CaO -1- Si02 = CaSiOa (calcium silicate). 
 Zinc oxide ZnO + SO3 = ZnSO^ (zinc sulphate). 
 
 CaO + AI2O3 = CaAl204 (calcium aluminate). 
 
 It may be objected that in the last example AI2O3 
 (aluminium oxide) is the oxide of a metal, and, therefore, a 
 base. This is true in many reactions, but in the presence 
 of strong bases, namely, the alkalis (potash, soda, and 
 lime), it acts like an acid-forming oxide. In the clays 
 combined with silica it is found acting as a base, but in 
 limes and cements always as an acid. There is only one 
 other oxide of importance— oxide of iron — which has the 
 power of acting in this dual capacity, according to 
 circumstances. 
 
CHAPTER IX 
 
 COAL AND ITS PRODUCTS 
 
 I. Coal. 
 
 1. Introductory. — The wide occurrence of the element 
 carbon as an essential constituent of all animal and 
 vegetable matter, and its existence combined with oxygen 
 in certain minerals, such as limestone, have been already 
 referred to. The greatest mineral supplies of carbon are 
 found in coal, and the importance of this substance as the 
 commercial source of all forms of energy, apart from the 
 immense number of compounds derived from its distillation, 
 render some account of its nature desirable. 
 
 Coal is the result of the partial decay of vegetation 
 under conditions admitting of but little oxidation : that is, 
 it is the result of decay out of contact with the air, by a 
 process analogous to the formation of peat at the present 
 day. Coal occurs in one definite geological formation, and 
 was formed under sub-tropical conditions of climate which 
 the luxuriant character of its plant remains show to have 
 then existed. Since thousands of feet of rock have been 
 formed over the coal deposits, and since earth movements 
 have produced great heat and pressure in some coal areas 
 while affecting others comparatively little, not only is it to 
 be expected that coal will differ in chemical composition 
 from the original woody substances from which it is formed, 
 but also that it will possess different characters and com- 
 position in different localities. 
 
 2. Varieties of Coal. — The two most important varieties 
 of coal are anthracite, which forms the greater part of the 
 
COAL AND ITS PEODUCTS 
 
 87 
 
 large fields of South Wales, and bituminous coal charac- 
 teristic of the Newcastle and Midland coalfields. The 
 former contains but little gaseous matter, and is composed 
 almost entirely of carbon, while the latter often possesses 
 sufficient volatile matter to make it cake on burning, owing 
 to the distillation of tarry products. Anthracite, since it 
 gives, on burning, an intense heat and but little flame, is 
 used for raising steam and similar purposes, and is also 
 known as steam coal; while bituminous coal is used for 
 ordinary domestic purposes and for making gas. A third 
 variety, known as cannel coal (the name is a corruption of 
 "candle"), is found in irregular and more local masses. 
 It resembles jet in appearance, and owing to the large 
 amount of gaseous matter it yields it is used for enriching 
 coal gas, the luminosity of which, when consumed without 
 the use of mantles, it much improves. In later geological 
 formations a carbonaceous substance, known as lignite (or 
 in Germany as brown coal), is also found, which may be 
 looked upon as a link between true coal and peat, since 
 it partakes of the characters of both. 
 
 3. Composition of Coal.— The main constituents of coal 
 are carbon, oxygen and hydrogen, and the effect of the two 
 latter elements in determining the characters described 
 above is well exemplified by the following table, showing 
 the proportion of oxygen and hydrogen present to every 100 
 parts of carbon : — 
 
 
 Carbon. 
 
 Hydrogen. 
 
 Oxygen. 
 
 Wood 
 
 Peat 
 
 Lignite .... 
 Bituminous coal . 
 Anthracite .... 
 
 100 
 100 
 100 
 100 
 100 
 
 1218 
 9-85 
 8-37 
 6-12 
 2-84 
 
 8307 
 55-67 
 42-42 
 21-23 
 1-74 
 
 (Percy). 
 
88 CHEMISTEY AND PHYSICS OP BtTILBlNG MATEEIALS 
 
 When burnt, coal always leaves a certain amount of 
 mineral ash, as would be expected from the method of its 
 formation. It also as a rule contains some nitrogen and 
 sulphur, the latter generally in the form of iron pyrites. 
 In illustration of more complete analyses of coal two 
 examples are appended : — 
 
 
 Sp. 
 Gravity. 
 
 Carbon. 
 
 Hydro- 
 gen. 
 
 Oxygen. 
 
 Nitro- 
 gen. 
 
 Sulphur. 
 
 Water. 
 
 Ash. 
 
 Bituminous 
 
 1-28 
 
 78-6 
 
 5-3 
 
 12-9 
 
 1-8 
 
 0-4 
 
 11-3 
 
 10 
 
 (Stafford- 
 
 
 
 
 
 
 
 shire) 
 
 
 
 
 
 
 
 
 
 Anthracite 
 
 1-39 
 
 90-4 
 
 3-3 
 
 2-9 
 
 0-8 
 
 0-9 
 
 2-0 
 
 1-6 
 
 (S. Wales) 
 
 
 
 
 
 
 
 (Eoscoe). 
 
 It should be stated that the amount of ash, which consists 
 chiefly of silica and alumina, is often much greater than 
 that shown in the above analyses ; indeed, ten per cent, of 
 ash is by no means uncommon. 
 
 4. Uses. — Some 200 million tons of coal (a rapidly increas- 
 ing quantity) are now annually raised in Britain, and a very 
 large proportion of this is converted into coke, specially for 
 blast furnace use in the iron and steel industry. A much 
 smaller quantity undergoes a similar conversion, but with 
 greater regard to the preservation of the volatile products 
 liberated, in the manufacture of coal gas. 
 
 II. Distillation op Coal. 
 
 For the preparation of coal gas, coal is heated in long 
 tubular retorts attached to a large pipe partially filled with 
 water in which most of the condensable volatile products 
 are retained. The gases evolved pass on and are further 
 purified from vapours condensed on cooling, and from 
 sulphur compounds by passage over lime. 
 
Coal and its peoducts 
 
 89 
 
 1. Coal G-as. — The gas finally obtained is a mixture the 
 composition of which varies not only with the kind of coal 
 employed, but with the temperature at which the distillation 
 has been ejBfected. Its usual composition is, by volume, 
 somewhat as follows : Hydrogen 50 per cent., methane, or 
 marsh gas, CH4, 35 per cent., carbon monoxide 5 per cent., 
 olefines (compounds of carbon and hydrogen, such as 
 ethylene C2H4) 5 per cent. The remaining 5 per cent, is 
 made up of nitrogen, carbon dioxide, and many other gases 
 in small quantities. 
 
 To the presence of hydrogen and methane coal gas owes 
 its lightness, to the carbon monoxide its poisonous proper- 
 ties, and to the olefines its illuminating properties when 
 burnt in the ordinary way. 
 
 2. Coal Tar. — The tar which collects under the water 
 in the pipe to which the gas retorts are connected is itself 
 distilled and yields many valuable products. This dis- 
 tillation is effected in retorts, and each fraction of the 
 liquid, which passes over between certain temperatures, 
 is collected separately. This process is known as 
 " fractional distillation," and when this vaporising and 
 condensing process involves the splitting up of a liquid 
 into new substances, the process is known as " destructive 
 distillation." 
 
 The liquid which passes over when the tar is heated to 
 about 105° C. is known as " first runnings," and consists 
 mainly of water, crude naphtha, and ammonia. When the 
 temperature of the tar rises beyond 105° C. the distillate is 
 separately collected until 210° C. is reached, and this frac- 
 tion, known as "light oils," yields principally naphtha. 
 From 210 to 240° C. "carbolic oils " come over, from which 
 carbolic acid is obtained, and from 240 to 270° C. " creosote 
 oils," which form a valuable preservative for timber, and 
 from which naphthaline is also extracted. Finally " anthra- 
 cene oils " are obtained, from which many valuable coal tar 
 
90 CHEMISTRY AND PHYSICS OP BUILDING MATERIAI.S 
 
 dyes are manufactured, and the distillation is stopped at 
 380° C. 
 
 The substance left in the retort at the end of this process 
 is known as "coal tar pitch." It is sometimes used for 
 adulterating asphalte ; its more legitimate purposes for 
 employment are for making up coal dust briquettes and for 
 preparing cheap varnishes. 
 
 3. Coke. — After all volatile matter has been extracted from 
 coal, coke remains in the gas retorts, and in this coke the 
 mineral ash of the coal naturally exists. This residue from 
 gas manufacture is used as a domestic fuel, but coke is also 
 specially prepared from coal on a large scale in coking 
 ovens, as fuel for blast furnaces used in the manufacture of 
 iron and steel. 
 
 III. Carbon and the Oxides of Carbon. 
 
 Apart from mineral ash, coke is pure carbon, which is the 
 final product when any animal or vegetable substance is 
 heated out of contact with the air. 
 
 1. Charcoal. — When wood is thus heated, the soft highly 
 porous form of carbon which results is known as charcoal. 
 It is used as a fuel for certain purposes. Charcoal acts as 
 a powerful oxidiser, and is often used in this capacity for 
 removing organic impurities from water. This is owing 
 to the intimate contact brought about between the air 
 contained in its pores and the water passing through it. 
 It is necessary that charcoal thus employed should be 
 periodically ridded of accumulated matters by thorough 
 immersion in boiling water. 
 
 2. Lamp Black. — Soot obtained by allowing oil lamps to 
 smoke, is, when freed from oily matters which volatilize in 
 the process, a very pure form of carbon, and is known as 
 Lamp Black, it is used for making black paints and 
 certain oil inks. Bone black and ivory black, prepared by 
 
COAL AND ITS PEODUCTS 
 
 91 
 
 charring bones and ivory, though they contain large 
 quantities of mineral matter, are put to similar uses. 
 
 3. Graphite. — The mineral graphite, also known as black 
 lead and plumbago, is another form of carbon, and is formed 
 artificially in certain processes. Most of the carbon con- 
 tained in grey cast iron, for example, exists in the form of 
 graphite. 
 
 From the above description of the forms of carbon it will 
 be seen that this element can display many physical differ- 
 ences. The most striking of these is found in the diamond, 
 which is the purest form of natural carbon known. 
 
 None of the forms of the element have ever been melted, 
 though evidence exists that carbon would melt at about 
 4,400° C. were any means known for attaining such a 
 temperature. 
 
 4. Carbon Dioxide. — All forms of carbon, when heated in 
 air or oxygen, burn with the formation of carbon dioxide gas, 
 about which compound much has already been said. 
 
 This gas is some two-and-a-half times as heavy as air, 
 and as a product of combustion it neither burns nor sup- 
 ports combustion. When found in vitiated air, the expan- 
 sion which it has undergone prevents it from settling at low 
 levels, but when produced in sewers or wells in situations in 
 which it is neither heated nor disturbed, it may accumulate 
 in a layer of quite definite depth. 
 
 When its presence is suspected a naked light should be 
 lowered into the cavity, and if this is extinguished respira- 
 tion is not to be attempted until the gas has been pumped 
 out or removed by lowering into it some hot body large 
 enough to cause sufficient expansion to enable the gas to 
 rise through the air above. 
 
 Carbon dioxide is not only obtainable from animal and 
 vegetable sources. All carbonates are decomposed with the 
 liberation of this gas when acted upon by acids, and this fact 
 provides a useful means for the recognition of carbonates. 
 
92 CHEMISTEY ANi> PHYSICS OF BUILDING MATEEIALS 
 
 e.g., carbonate of lime, and for the preparation of the gas 
 for compression or carbonating processes. 
 
 This action, in the case of carbonate of lime and hydro- 
 chloric acid, is as follows : — 
 
 Calcium 
 
 Carbonate of lime. HydrocUoric acid. chloride. 
 
 CaCOs + 2 HCl = CaCla + CO^ +H,0 
 
 A few drops of dilute acid placed upon a carbonate will 
 produce effervescence, and since no materials of a stony 
 nature effervesce with acids from any other cause, the 
 fact furnishes a simple and readily applied test for distin- 
 guishing limestones and marbles from siliceous stones and 
 for detecting carbonates in granites and slates, where their 
 presence generally indicates decay. 
 
 5. Carl)on Monoxide. — When carbon burns in a limited 
 supply of air or whenever it has to obtain its oxygen for 
 combustion by the decomposition of some other compound, 
 it only partially burns. The gas formed in such cases is 
 known as carbon monoxide, and has the formula CO. 
 
 This compound, as stated, is present in coal gas and is 
 very poisonous, its action in this respect amounting to 
 physiological suffocation, since it absorbs oxygen from the 
 blood. 
 
 Carbon monoxide burns with an exceedingly hot flame, 
 and is the chief component of " producer gas " and similar 
 gaseous fuels. The lambent blue flame often seen over a 
 red fire is due to this gas, which undergoes combustion 
 thus : — 
 
 CO + 0 = CO2. 
 
CHAPTER X 
 
 OUTLINES OF GEOLOGY 
 
 I. Earth History. 
 
 1. Introductory. — Just as a knowledge of the properties 
 of manufactured materials involves some acquaintance with 
 the methods adopted in their production, so a knowledge of 
 natural materials necessitates some insight into the methods 
 of Nature's workshop. 
 
 Such an inquiry into the arrangement and structure of 
 the accessible materials of which the earth is made, and the 
 elucidation of the history of their bringing together, form 
 the work of the geologist. 
 
 There is strong presumptive evidence that the earth some 
 millions of years ago was a molten mass and that its 
 solidification has been a very gradual process. The universal 
 rise in temperature observed in deep mines, and the 
 existence of hot springs and volcanic outbursts in widely 
 separated districts, is evidence that the earth's interior is 
 hot,^ and as this heat is radiated into space and is not 
 returned, a general cooling must be in progress. It has 
 been pointed out that most bodies contract on solidifying 
 and cooling, and as the earth is not a perfectly rigid body 
 this process is accompanied by a wrinkling of its surface, 
 and often also by cracks and sudden subsidences. 
 
 * Some new hypotheses suggesting that radium may be an impor- 
 tant factor in the earth's internal heat will be found in reports of the 
 British Association meeting of 1908. 
 
94 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 2. Erosion. — When the earth's exterior first fell below 
 100° C. surface depressions formed settling grounds for 
 condensed water, and with the presence of liquid water 
 a ceaseless wear and tear of material was initiated. Pulled 
 out of shape by the sun and the moon's attraction, and 
 lagging behind the earth in its rapid rotation, this water, 
 which now forms the oceans, is in constant motion and 
 dashes itself against its shore lines in its ebb and flow. 
 Evaporated by the sun and again condensed in the cool air, 
 it descends as rain and finds its way, charged with soluble 
 and eroded matters, back to the ocean along spring and river 
 courses carved by its own efforts. The changing seasons, 
 the heat and cold of day and night, the winds produced by 
 varying temperatures and the earth's rotation, all exercise 
 a wearing effect upon the earth's crust. The exposed rocks 
 split by heat or frost, the wind-borne cloud bursting upon 
 the land and washing it away to expose fresh surfaces, even 
 the forms of life themselves, the growing roots of plants, 
 and the teeming microbes of the soil, all aid in this constant 
 breaking down of material and produce a ceaseless wear 
 and tear. If these changes are not very apparent, it must 
 be remembered that in dealing with the earth's history 
 vast lapses of time are in question, periods compared with 
 which the length of human history is as nothing. But the 
 erosion of the earth even in short intervals is by no means 
 inappreciable, in proof of which it may be cited that the 
 solid matter carried to the sea by such a river as the 
 Mississippi is sufficient in a single week to raise an area of 
 a square mile more than five feet in height. 
 
 3. Deposition. — The result of this constant deposition of 
 eroded material is seen in the formation of river deltas. 
 Gravel, sand and mud thus slowly deposited form new land 
 surfaces, and such materials are arranged in layers or 
 strata, and as these deposits accumulate the lower layers 
 become compressed and hardened. This investigation of 
 
OUTLINES OF GEOLOGY 
 
 95 
 
 Nature's present processes, which there is every reason to 
 believe have gone on continuously since the earth possessed 
 a cool solid surface, gives the key to the formation of the 
 rocky strata which form the crust of the earth at the present 
 time. 
 
 This eroding power of water, or more correctly the erosion 
 of rock particles one against the other through the agency 
 of water, is not, however, alone sufficient to account for the 
 vast thicknesses of strata known to geologists. Obviously 
 the accumulation of sediment in the manner described must 
 cease when the deposits reach the surface of the water in 
 which such deposition occurs. The land and the ocean bed, 
 however, are constantly subjected to slow but continuous 
 motions of upheaval and depression, producing effects which 
 may be quite marked within human remembrance. If 
 examples are wanted, the change in the coast lines near 
 such places as Blackpool and Cromer will give striking 
 proof of the truth of this assertion. If subsidence, then, 
 takes place as fast as the deposition of eroded matter pro- 
 ceeds, deposits thousands of feet in thickness may in time 
 be formed. As soon as these accumulations reach the sur- 
 face of the water, which may be due to continued deposition 
 of sediment or to some reversal of earth movement con- 
 verting depression into upheaval, the eroding action of 
 the forces of Nature at once recommences. Streams and 
 rivers again in process of time carve out their courses 
 and the very valleys through which they flow, and frost, 
 wind and tide join in the attack upon the new land areas. 
 Thus an endless cycle of operations involving destruction 
 and rebuilding is ever in progress. The slowness of these 
 changes, however, enables the geologist to investigate the 
 various strata and to study their present characters and 
 geographical limits without any fear that his landmarks 
 will be seriously interfered with, and this study is of great 
 economic value. 
 
96 CHEMISTEY AND PHYSICS OF BUILDING MATERIAIiS 
 
 II. Arrangement of Strata. 
 
 1, Layers Not Continuous. — It might appear at first sight 
 that the various deposits would lie horizontally one over the 
 other, perhaps occasionally thinning out against some older 
 land surface where a deposit was of a limited and local 
 nature. Thus the land might be expected to be built up of 
 more or less continuous horizontal layers, the uppermost 
 representing the final deposit. This is, however, by no means 
 the case. In one district limestones are found ; in others, 
 slates, chalk or sandstones, all of obviously different origin 
 and age ; and further, if such beds of rock are examined they 
 will in many cases be found to lie in positions so much 
 removed from horizontality that it would have been quite 
 impossible for their formation to have taken place at such 
 inclinations. 
 
 2. Dip. — There is little doubt that such strata were 
 originally deposited in approximately horizontal layers, 
 but the great earth movements, already referred to, 
 resulting in wrinkles and dislocations in the earth's crust, 
 have subsequently displaced these strata and tilted them, 
 and actual fracture, or more generally subsequent erosion, 
 has thus exposed the strata once buried thousands of feet 
 below the surface. This is illustrated in Fig. 2, where A 
 shows the original beds as formed by deposition, B their 
 possible upheaval due to earth movement, and C the surface 
 exposure of the beds due to subsequent erosion. 
 
 The angle which the general planes of deposition or 
 "bedding" make with a horizontal plane is known as the 
 dip of such strata, and the determination of this angle is 
 obviously of great importance to the miner and quarryman. 
 
 Strata are occasionally much contorted and broken, but 
 apart from local and always recognisable exceptions, 
 deposits are invariably found to lie one upon the other in the 
 order in which they were originally laid down, that is to 
 
OUTLINES OF GEOLOGY 
 
 97 
 
 say, the oldest rocks ^ are the undermost, and are regularly 
 succeeded by those of later date. 
 
 Dip and subsequent erosion resulting in the exposure of 
 once buried deposits are of great value to the geologist, for 
 were all deposits found in their original horizontal position 
 
 o/i/a/m si/pmce 
 
 /7 
 
 Fig. 2. — Explanation of irregular appearance of strata on the 
 earth's surface. 
 
 vertical borings could alone procure information as to the 
 strata below the earth's surface, whereas under existing 
 conditions, by measurement of the extent of the exposed 
 
 1 The geologist uses the term " rock " not only as popularly applied 
 but as indicative of any deposit, such as a bed of clay or gravel, and 
 the word is so used in these chapters. 
 
 B.M. H 
 
98 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 edges of the deposits and then making allowance for the 
 dip, the thickness of the strata can be ascertained directly, 
 while their characters on a large scale can be investigated 
 on the earth's surface, as will be apparent from a study of 
 Fig. 3. 
 
 Fig. 3. — Measurement of dip or inclination of strata from 
 surface exposure. 
 
 3. Faults. — Strata are not only bent and eroded, but often 
 actually broken, and this usually results in considerable 
 change of level between the separated portions. Erosion 
 may then remove the beds on the higher side of the frac- 
 ture, or subsequent deposition may introduce new deposits 
 upon the beds on the lower side. These dislocations are 
 known as faults, and may be displayed as small local dis- 
 turbances or extend over many miles. A study of Fig. 4 
 will make it evident that faults may have a considerable 
 bearing upon the quarrying of stone. A here shows the 
 condition of the beds after dislocation, and B the section of 
 the same beds after erosion. It will be observed that the 
 building stone, which, from an examination of the beds on 
 the left, might have been expected to be continuous, has 
 disappeared on the right of the fault owing to erosion. 
 
 A consideration of the above facts will make it evident 
 that, although a certain deposit may originally have covered 
 a wide area, it does not necessarily follow that it will always 
 have a present existence over the whole of such area. 
 
OUTLINES OF GEOLOGY 
 
 99 
 
 Many upheavals and submergences of the land, and many 
 wrinklings and breakages, have taken place during the 
 formation of the great series of rocks which form the 
 earth's outer crust, and in places exposure to erosion has 
 continued sufficiently long to admit of the removal of the 
 
 ElG. 4. — Eaults or dislocations in strata, showing how a building 
 stone may suddenly terminate against worthless materials. 
 
 whole of certain deposits, with a corresponding lack of con- 
 tinuity in beds subsequently formed upon such eroded 
 areas. 
 
 III. Identification op Stkata. 
 
 1. Physical and Biological Characters. — On recalling the 
 general characters of the land surface as now existing, laid 
 out as most of it is in the service of agriculture, or for 
 
 H 2 
 
100 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 human habitation, it might appear hopeless to endeavour 
 to trace the geological strata and identify the various beds 
 in different places. It must be remembered, however, that 
 the surface soil, which consists of the disintegrated beds 
 below it mixed with the remains of decayed vegetation, is 
 very superficial in character, usually not exceeding a depth 
 of two or three feet, while in many places the natural rocky 
 stratum is actually exposed. Aided by such exposures and 
 natural sections obtained on cliffs and in quarries and by 
 well-sinkings, geological maps have been constructed 
 representing the country denuded of its superficial soil and 
 artificial excrescences. Further, by noting where certain 
 beds disappear beneath the surface and where they again 
 reappear, and the angle at which they dip, tolerably 
 accurate sections can be produced showing the form of the 
 vertical exposure which would be obtained were the country 
 cut into two between different points. It is true that the 
 physical characters of a given layer of stratum often show 
 considerable variation in different places, particularly in the 
 case of gravelly beds formed in ancient river estuaries, while, 
 again, subsequent local earth movements may have further 
 modified their characteristics ; on the other hand, strata 
 which have been formed in deep water, as for instance chalk, 
 are very constant in their general characters and appear- 
 ance, even in widely-separated districts. The geologist, 
 however, possesses a most important aid to the identifica- 
 tion of his deposits in the existence of the remains of plant 
 and animal life found in them. These life remains are 
 termed fossils, and their value lies in the fact that many 
 of them are characteristic of the beds in which they occur. 
 The fossils, again, differ in organisation : some have evi- 
 dently a marine origin ; others, as proved by similar existing 
 species, lived in fresh water ; and this offers a further means 
 of distinguishing the surrounding strata. The oldest rocks 
 contain only simple forms of life, later fishes are found, 
 
OUTLINES OF GEOLOGY 
 
 101 
 
 hen luxuriant plant life, reptiles, higher forms of shell 
 fishes, then in more recent deposits mammals and birds, 
 and quite in the latest beds remains of man himself occur. 
 The whole series of formations thus exhibits the wonderful 
 process of gradual evolution. 
 
 2. Names and Order of Strata. — Geologists have found it 
 possible, by utilising the means of identification described, 
 to classify and arrange the layers of the earth's crust in a 
 tabular form in the order of their deposition — the main 
 divisions of which are known as formations. The chief 
 members of this table, arranged in descending order — that 
 is, headed by the latest deposits — and the more important 
 economic products derived from these layers, are appended 
 (pages 102 and 103). Aided by such a table, geological 
 maps showing in what part of the country the various strata 
 are exposed may obviously be studied with advantage. 
 
 IV. EOCKS NOT FOBMED UNDER WaTER. 
 
 Although the preceding description has accounted for 
 the formation of by far the greater part of the earth's 
 crust, but little consideration is required to show that some 
 of the rocks found in this country and elsewhere cannot be 
 regarded as having been laid down under water by gradual 
 deposition. Granite, for example, and rocks allied thereto, 
 present no planes of bedding or stratification, contain no 
 remains of animal life, and are found to occur in irregular 
 masses, breaking through the water-formed strata, to which 
 they bear no relation either in character or position. These 
 rocks might represent the original and once molten crust 
 of the earth, and such an origin has indeed been attributed 
 to granite rocks in certain districts, as that of Malvern, in 
 this country ; but their occurrence among strata of all ages 
 calls for some wider explanation of their existence. The 
 resemblance of these irfiegulsw: masses to rocks erupted 
 
102 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
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OUTLINES OF GEOLOG-Y 
 
 103 
 
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104 OHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 from or found solidified beneath ancient volcanoes leaves 
 little room for doubt that they were similarly once molten, 
 and were either poured out upon the land surface, or cooled 
 very slowly, and gradually solidified and crystallised beneath 
 the surface, which has been subsequently eroded away, and 
 this has resulted in their exposure. Eocks possessing such 
 an origin are known as igneous rocks. 
 
 V. Conclusion. 
 
 From this brief introduction to geology it will be evident 
 that the value of this branch of science is not confined to 
 mere localisation of surface exposures, but extends to actual 
 predictions as to the extent of strata underground. 
 
 In mining operations, in the search for coal, building- 
 stones, and indeed any material characteristic of any given 
 beds, a knowledge of the principles of geology is indis- 
 pensable. For example, the dip or inclination of a bed of 
 freestone must obviously have a direct bearing upon the 
 quarrying and market price of such stone, and a slight 
 variation in dip may easily convert an open quarry into a 
 costly working underground. 
 
 The investigation of faults, again, is of great importance, 
 for if beds to be worked end abruptly against valueless 
 rocks owing to dislocations, quarrying must necessarily 
 cease in the working thus affected. 
 
 The nature of the soil, and thus its suitability for agri- 
 cultural products, depends largely upon the strata imme- 
 diately beneath it. The rich plain land, the barren moor, 
 the rounded chalk hill, all owe their characteristics to the 
 rocks below them, while the desirability of a site for 
 building purposes, the nature of the foundation requisite, 
 and the quantity and character of water likely to be 
 obtained thereon, are all matters ultimately connected with 
 the study of geology. 
 
PAET II— BUILDING MATEEIALS 
 
 INTEODUCTION 
 
 In this section of the book it is proposed to deal with the 
 applications of the foregoing principles to the materials 
 used in building. 
 
 In discussing so wide a subject wherein each class of 
 product may form the basis for a small library of text- 
 books, it is obviously impossible to do more than generalise 
 on broad lines within the limits of what is essentially 
 meant to be a small and readily assimilated work. 
 
 Thus the object which will be kept in view is not that 
 of enabling a mastery of the properties and means of 
 identification of any individual stone, brick, or piece of 
 timber, to be acquired, so much as to point out chemical 
 and physical characteristics of these bodies as classes of 
 materials, and to indicate from a consideration of the 
 history of their formation, natural or artificial, and of the 
 conditions surrounding their use, the nature and value 
 of their structure, and of the tests whereby their properties 
 may be assessed. 
 
 For this reason accounts of manufacturing processes and 
 manipulatory and statistical details of tests have been 
 reduced as far as an intelligible presentation of the subject 
 will allow. All these matters are readily accessible in 
 many excellent text-books dealing with individual sub- 
 stances, and it is by the further study of such books and 
 
106 CHEMISTRY AND PHYSIOS OF BUILDING MATERIALS 
 
 of the materials themselves in actual use, that a com- 
 plete knowledge of their practical value can alone be 
 acquired. 
 
 If these few pages serve to show how such further study 
 may be profitably undertaken, they will amply fulfil their 
 intended purpose. 
 
 Arrangement of Subjbct-Matter. 
 
 This section of the book will be found divided up into 
 chapters dealing with materials as ordinarily classified as 
 Stones, Brick Clays, Limes and Cements, Metals, Timber 
 and Paints ; but since the first three of these groups contain, 
 or are derived from, a comparatively small number of com- 
 pounds which occur naturally in the form of minerals, a 
 general account of such minerals and the means employed 
 for their identification will form the initial chapter, after 
 which some account of the natural occurrence or pre- 
 parative principles, properties and composition, tests 
 upon, classification of, and defects arising in, the groups 
 above cited, will be dealt with. 
 
CHAPTEK XI 
 
 THE CONSTITUENTS OF STONES, CLAYS AND CEMENTING 
 MATERIALS 
 
 I. Mineral Constituents and their Characters. 
 
 1. Composition of Natnral Materials. — All the natural 
 mineral materials employed in building — stones and slates, 
 brick-clays, limes and similar substances — although they 
 differ much in origin, physical structure and minor con- 
 stituents, consist essentially of a comparatively small 
 number of bases combined with an equally small number 
 of acid-forming oxides. 
 
 These bases are : potash (K2O), soda (Na20), lime (CaO), 
 magnesia (MgO) , and the acid oxides are alumina ( AI2O3) and 
 ferra^ (FeaOa) (which in the absence of the above bases act as 
 bases themselves), silica (Si02) present alone or in silicates, 
 carbon dioxide (CO2) in carbonates, sulphur trioxide (SO3) in 
 sulphates. 
 
 2. Minerals defined. — The above acids and bases (generally 
 in combination as salts), which constitute natural materials, 
 are found as isolated chemical compounds, or, more usually, 
 as several compounds mixed together. Such naturally 
 occurring compounds are known as minerals.^ 
 
 1 The writer has ventured to coin the word " ferra," which is 
 analogous to and consistent with the common designation of other 
 oxides. The term oxide of iron, by which FcqOs is usually known, 
 besides breaking up terminological continuity, is not always sufl&ciently 
 definite, as there are several compounds of iron and oxygen. The 
 name ferra will be confined to Fe^Og, and the oxide FeO will be 
 referred to by its ordinary chemical name as ferrous oxide. 
 
 ^ Minerals need not be compounds ; e.g., sulphur and gold are 
 minerals, but no elements found naturally concern the present 
 discussion. 
 
108 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 Although minerals are thus defined as chemical com- 
 pounds, from the nature of their formation it is hardly to 
 be expected that they will be found in materials in a state 
 of absolute purity. Small quantities of impurities are often 
 mechanically included within them, and again, chemical 
 reactions sometimes lead to the partial replacement of one 
 base by another, resulting in groups of compounds somewhat 
 difficult to define individually, and conveniently referred to 
 under one designation, which is particularly the case with 
 mineral silicates. Notwithstanding this, most minerals 
 possess distinctive and definite properties whereby they may 
 be recognised, as, for example, quartz and mica in granite. 
 Some of these characteristics will now be referred to. 
 
 3. Characters of Minerals. — {a) Regularity of Shape. — The 
 molecules of most compounds tend to arrange themselves 
 in a regular manner when they can come together freely 
 and they "grow" by the addition of successive layers 
 derived from dissolved or melted material, and under 
 favourable circumstances produce masses which have flat 
 faces separated by definite angles. Such growths are 
 known as " crystals," a term which is used quite irrespective 
 of glassy appearance or transparency; for example, the 
 yellow metallic mineral iron-pyrites and black opaque oxide 
 of iron are found as crystals. 
 
 Owing to the restrictions of surrounding bodies it is but 
 seldom that characteristic crystal forms can be distinguished 
 in building materials, but mere evidence of an attempt on the 
 part of a mineral to crystallise as shown by the sparkling 
 under light of a fractured surface, is of value, since 
 crystalline materials have much more stability than those 
 possessing an earthy structure. Marble and chalk, for 
 example, are both composed of carbonate of lime, and the 
 superior weathering power of marble is entirely due to its 
 crystalline structure. 
 
 (h) Cleavage. — Cleavage is the property in virtue of 
 
STONES, CLAYS AND CEMENTINa MATEEIALS 109 
 
 which bodies split along certain planes, and owes its origin 
 to molecule arrangement. Slates and some stones possess 
 this property, which is developed to a remarkable degree in 
 such a mineral as mica. Cleavage takes places in minerals 
 along definite planes, and often in more than one direction. 
 Crystallised carbonate of lime can be readily distinguished 
 from quartz by its cleavage, since the latter mineral does 
 not cleave but breaks with an irregular fracture like a piece 
 of glass. 
 
 (c) Hardness. — The ease with which a mineral can be 
 scratched forms a useful means of estabHshing its identity. 
 In order to make comparisons of hardness, a scale has been 
 agreed upon represented by minerals numbered from 1 
 to 10 in increasing order of hardness. These minerals are 
 as follows : — 1 talc, 2 selenite, 3 calcite, 4 fluorspar, 5 apatite, 
 6 felspar, 7 quartz, 8 topaz, 9 corundum, 10 diamond. The 
 statement, then, that the hardness of a mineral is, for 
 example, 7, means that it has the hardness of quartz ; thus 
 it will be scratched by a fragment of topaz but will itself 
 scratch felspar. 
 
 (d) Streak— T}he true colours of many minerals are 
 often masked by surface oxidation, but may be revealed 
 by scratching through the external layers with a pen- 
 knife or any harder mineral fragment. The colour 
 presented by the scratch is known as the streak of the 
 mineral, and often aids identification. 
 
 (e) Other Physical Properties. — Further distinctions lie in 
 differences in specific gravity, colour, appearance (whether 
 earthy, glassy, or metallic), and in differences of crystalline 
 form, which study is a special branch of mineralogical 
 science known as crystallography. 
 
 (/) Chemical Analysis. — The ultimate composition of 
 minerals as ascertained by chemical analysis gives a means 
 of identification which requires the services of a chemical 
 expert. Some account of the objects to be aimed at by 
 
llO CHEMISTRY AND PHYSIOS OF BUILDING MATERIALS 
 
 such analyses and of a few simple tests for certain 
 constituents will be found in subsequent pages. 
 
 II. Use of the Miceoscopb in Examining Materials. 
 
 1. Principles of Construction. — The microscope provides 
 such a rapid and effective means of obtaining an insight 
 into the mineral and structural character of many materials 
 that a short description of its use may profitably be given. 
 When an object is viewed through any transparent sub- 
 stance possessing curved faces — a lens — it appears altered 
 in size. The rays of light from the object falling on the 
 lens are bent in their passage through its substance, and if 
 the surface is convex these rays converge to a point on 
 the opposite side of the lens and subsequently diverge and 
 form an image of the object at a definite position. If the 
 matter be investigated by holding different " reading 
 glasses " between a lighted candle and a vertical sheet of 
 paper in a darkened room it will be observed that the size 
 and clearness of the image of the flame formed upon the 
 paper depends upon the distances of the candle and paper 
 from the glass and upon the amount of curvature on the 
 faces of the latter. 
 
 In a microscope an image of the object to be examined 
 is formed by a small lens at the bottom of the instru- 
 ment, known as the " objective," and this image, which 
 is produced in the tube of the microscope, is observed 
 through another lens at the top, called the " eye-piece," 
 which increases the magnification due to the objective 
 in the same way as a simple image of a candle flame 
 on a sheet of paper might be magnified by observing 
 it through another lens held between this image and 
 the eye. 
 
 The position of the objective and eye-piece are adjustable 
 by means of sliding tubes or rack and pinion motion to 
 
STONES, CLAYS AND CEMENTING MATEEIALS 111 
 
 admit of the use of different lenses and to allow for different 
 foci of vision. 
 
 The object to be viewed is placed on what is known as 
 the " stage " of the instrument, which is perforated to 
 allow a strong light, necessary to produce an enlarged 
 image of sufficient brightness, to be thrown upon it from a 
 mirror, sometimes supplied with a concentrating lens of its 
 own below, or if the object is opaque arrangements must be 
 made for throwing light on its upper surface and causing 
 this to be reflected up to the objective. 
 
 2. Use of Polarised Light. — A valuable adjunct to a 
 petrological (rock investigating) microscope consists of two 
 specially constructed prisms known as " Nicols prisms," 
 which are suitably mounted in frames, one below the object 
 viewed, the other in the tube of the instrument above the 
 objective. These prisms are capable of rotation about the 
 axis of the tube of the microscope, and have the effect 
 of filtering out the light so that instead of passing 
 through the object and lenses in a bundle of rays, it is 
 restricted to one plane, and is then said to be " polarised." 
 If one of the prisms is rotated so that the plane along 
 which it transmits light is at right angles to that for the 
 other prism, all light will be cut off from the eye-piece and 
 hence from the observer. 
 
 It is found, however, that certain transparent minerals, 
 if placed on the stage of the instrument, have the effect of 
 allowing some light to pass when the prisms are placed 
 with their transmitting planes at right angles as described, 
 or, in scientific language, "between crossed Nicols." Further, 
 when fragments of certain minerals so placed are rotated 
 on the stage the colour of the light transmitted shows dis- 
 tinct changes in tint, and minerals which possess this 
 property are said to be dichroic (two-coloured) or to exhibit 
 dichroism. 
 
 It is obvious that a knowledge of these facts must be of 
 
112 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 value in aiding identification. For example, a certain 
 kind of mica often present in granite, and which does not 
 weather very well, is strongly dichroic ; if, therefore, a thin 
 section of the granite, mounted for convenience on a strip 
 of glass, be rotated under polarised light, such change of 
 colour in certain parts of the "field," i.e., the magnified 
 image observed, may indicate the presence of this mineral. 
 
 III. Individual Minerals connected with Materials. 
 
 A short description will now be given of the chief 
 minerals which compose the materials now under con- 
 sideration. It will be found most convenient to classify 
 these bodies according to their chemical composition, 
 except in the case of the silicates, where each mineral will 
 be dealt with separately. 
 
 1. Silica (Si02). — Forming as it does more than one half 
 of the entire crust of the earth, silica is of immense 
 importance, and not only do many sandstones consist almost 
 entirely of this compound, but in combination with bases 
 in the form of silicates (salts, described at the end of this 
 chapter), it has a very wide distribution in such bodies as 
 granitic rocks, clays, and slates. 
 
 Silica, besides occurring in rounded or angular grains 
 in sand and sandstone, is found associated with many 
 minerals in rocks and metallic ores, as quartz. In this 
 form it is sometimes milky in appearance, or coloured 
 owing to the presence of oxides of iron or manganese, but 
 generally, as in granites, it is glassy and colourless. Under 
 favourable circumstances it forms six-sided, prismatic 
 crystals with pointed pyramidal ends, as found in certain 
 Cornish granitic stones. Common flint is a form of silica 
 particularly associated with the chalk formation, while agate, 
 jasper, and opal (the last containing water) are other less 
 common varieties of the compound. 
 
STONES, CLAYS AND CEMENTINa MATEEIALS 113 
 
 Silica is exceedingly infusible and has a small co-efficient 
 of expansion. When specially prepared from a molten condi- 
 tion it stands sudden changes of temperature remarkably 
 well, and is likely to replace glass for many special purposes. 
 
 The absence of cleavage and the hardness (7) of mineral 
 silica form useful characteristics for identification. Since 
 the hardness of ordinary steel is below 7, quartz (or sand 
 grains) cannot be scratched by a penknife. The specific 
 gravity of silica is about 2" 6. It is insoluble in all ordinary 
 acids and hence exceedingly durable. It, however, dissolves 
 in alkaline solutions, combining readily with such bases as 
 soda and potash. This solution is of importance and 
 explains the formation of many silicate minerals. 
 
 Quartz generally occurs in stones of the granite class as 
 a transparent infilling between other minerals and shows 
 no regularity of outline in rock sections viewed under the 
 microscope. With high power objectives numerous minute 
 inclusions arranged along definite planes may often be 
 observed in transparent fragments. 
 
 2. Calcium Carbonate (CaCOa). — This compound is also 
 very widely distributed and is known in several mineral 
 forms. In a crystallised condition it occurs as calcite or 
 calc-spar, commonly found in limestone districts. In this 
 form it is usually white or colourless, and possesses a pearly 
 lustre. Its excellent cleavage in two directions and its 
 hardness (only 3) render it easily distinguishable from 
 quartz. Its specific gravity is about 2*7. 
 
 Other forms of calcium carbonate are marble, which 
 shows a distinctly crystalline structure ; chalk, which is 
 the remains of shell fragments, and is generally soft and 
 amorphous (without form, i.e., not crystalline) ; and lime- 
 stone, the commonest and least pure variety of this 
 icompound. 
 
 All forms of calcium carbonate are easily soluble in all 
 (dilute mineral acids and even in many vegetable acids, such 
 
 £.M. 
 
 I 
 
114 CHEMISTRY AND PHYSIOS OF BUILDINO MATERIALS 
 
 as vinegar, and the effervescence produced by such action has 
 already been cited as a useful means of identification. 
 
 3. Calcium Sulphate (CaSO^). — Combined with water of 
 crystallisation this compound is found in flat-pointed 
 crystals, possessing the formula CaS04.2H20 as the mineral 
 selenite which is common in certain clays, and is known 
 among workmen as "petrified water." It occurs in larger 
 masses often possessing a fibrous and silky texture as 
 gypsum or satin spar, which possesses the same composition 
 as selenite and is used as a source of plaster of paris. 
 
 4. Alumina (AI2O3). — Next to silica, alumina is the most 
 plentiful and widely distributed compound known. Ordinary 
 clay contains more than 25 per cent, of this oxide. It is 
 found associated with iron in the mineral Bauxite which 
 forms a source of metallic aluminium, and it also occurs 
 alone as corundum, which in an impure form is the emery 
 of commerce, and owes its value to its great hardness, which 
 is 9. In a mineral form aluminium oxide is quite insoluble 
 in water and acids. 
 
 Alumina, in the presence of bases such as lime, always 
 occurs in combination in building materials as an acid, 
 forming aluminates, but in the absence of other bases it 
 itself acts as a base, forming salts with acid oxides such as 
 silica, e.g., aluminium silicate. In this latter form it is 
 found in clays. 
 
 6. Magnesium Carbonate (MgCOa). — All magnesium com- 
 pounds bear a strong similarity, both chemically and 
 physically, to those of calcium, but since magnesia (MgO) 
 is a less powerful base than lime (CaO), magnesium com- 
 pounds are less easily formed, and when formed are more 
 easily decomposed. This carbonate is found to a limited 
 extent alone as the mineral magnesite, but in larger quantity 
 in dolomite, which is a limestone in which magnesium and 
 calcium carbonates are mixed together. 
 
 6. Potash and Soda Compounds. — The compounds of these 
 
STONES, CLAYS AND CEMENTING MATEEIALS 115 
 
 two bases resemble one another in a very marked degree. 
 Apart from certain silicates referred to in a later paragraph, 
 all compounds of these bases are readily soluble in water, 
 and are therefore seldom found in large quantities in the 
 solid state. Sodium and potassium chlorides NaCl and 
 KCl, the carbonates, NaaCOa and K2CO3 and the sulphates 
 Na2S04 and K2SO4 are among the commonest compounds 
 found, and of these the sodium compounds are much 
 commoner than those of potassium. In the nature of 
 things such bodies cannot enter largely into the composi- 
 tion of stable materials. Eeference has already been made 
 to eflflorescence and deliquescence due to these salts, which 
 are further characterised by their comparatively ready 
 fusibility. 
 
 7. Compounds of Iron. — Two common minerals, iron 
 pyrites and marcasite compounds of iron and sulphur, 
 have already been described in Chapter VIII. These 
 minerals are readily recognised under the microscope as, 
 since they are quite opaque, they always appear black 
 when viewed by light transmitted from below them, but if 
 light is reflected from their surfaces the yellow colour they 
 possess becomes at once apparent. 
 
 Two oxides of iron, ferrous oxide (FeO) and ferric oxide 
 (Fe203), are of common occurrence in building materials, and 
 account for nearly all the natural colours possessed by 
 stones and clays. The former is always found in combina- 
 tions, as for instance, in ferrous carbonate (FeCOa), and thus 
 acts as a base resembling lime and magnesia. The latter is 
 found as the valuable ore of iron haematite, or disseminated, 
 often as a mere coating film (a rust), upon the grains of 
 other materials. 
 
 IV. Silicate Minbkals. 
 
 1. Constitution of Silicates. — The silicates may be regarded 
 as salts of silicic acid. As, however, there are several silicic 
 
 I 2 
 
116 CHEMISTEY AND PHYSICS OF BUILDINO MATEEIALS 
 
 acids there are several series of salts. These acids, them- 
 selves unstable compounds, may be regarded as combina- 
 tions of one, two or more molecules of water with one 
 molecule of silica. The acid HaSiOs or H20.Si02 is known 
 as metasilicic acid, and that having the formula HiSiOi or 
 2H20.Si02 is known as orthosilicic acid. The lime salts of 
 those acids are respectively calcium metasilicate OaSiOs, 
 and calcium orthosilicate CaaSiOi- 
 
 Other bases, such as ferrous oxide and magnesia, form 
 similar silicates, as do potash and soda, and as these silicates 
 are often found in combination and also associated with 
 alumina, a very complex series of minerals results therefrom. 
 
 As the exact composition of many of these compounds is 
 uncertain the bases and acids are usually written side by 
 side in the more complex cases. Thus felspar may be 
 represented as K2Al2Si60i6 ; it is, however, preferable to 
 write the formula as K20.Al203.6Si02. 
 
 2. The Felspars. — The felspars are a group of minerals 
 composed of the bases potash, soda, and lime combined with 
 alumina and silica. They are usually of a dull opaque white 
 or grey colour, but some varieties are pink or red and other 
 colours are known. These minerals show a fairly good 
 cleavage, have a specific gravity of about 2*5 and a hardness 
 of 6 to 7. 
 
 (a) Orthoclase Felspar (K20.Al203.6Si02).— This variety, 
 also called potash felspar, is more often red in colour than 
 the other varieties, and is found in certain stones, such as 
 Shap granite, in large, well-defined, bluntly-pointed crystals 
 often two or three inches long and interlocked in a charac- 
 teristic manner. More frequently it occurs in smaller 
 masses without any distinguishable outline. 
 
 (&) Plagioclase Felspars. — In the minerals included under 
 this title the bases soda and lime are present in place of 
 potash shown in the formula given for orthoclase. The 
 felspars, if not white or grey, are at least not strongly 
 
STONES, CLAYS AND CEMENTING MATEEIALS 117 
 
 coloured. Under the microscope they sometimes show a 
 series of fine parallel lines, and these markings, if present, 
 serve to distinguish them from orthoclase. 
 
 When felspars decay the bases are removed in solution 
 and the remaining aluminium silicate remains as kaolin or 
 china clay. 
 
 3. Micas. — There are two micas commonly found in 
 stones and clays — Muscovite or potash mica and biotite 
 or magnesium mica, which are aluminates and silicates of 
 the bases named. Micas are characterised by remarkably 
 perfect cleavage ; this allows them to be split into exceed- 
 ingly thin pieces which possess much elasticity and the 
 faces of which have a pearly lustre. Under the microscope 
 the fine parallel cleavage lines are readily seen, unless, of 
 course, the piece of the mineral viewed is lying parallel to 
 its cleavage plane. The specific gravity of the micas is 
 about 3 and their hardness 2 to 3. 
 
 Muscovite, the commonest variety, is silvery white or 
 brownish in colour. In sections parallel to the cleavage 
 plane it exhibits bright colours under polarised light. It is 
 found in some quantity in granites and other stones, and 
 weathers well. 
 
 Biotite is usually brown or black and exhibits marked 
 dichroism under polarised light. It weathers badly, assuming 
 a greenish tint when partially decomposed, owing to the 
 formation of chlorite. 
 
 4. Hornblende and Augite. — These two minerals are com- 
 plex silicates and aluminates of iron, magnesium and calcium, 
 and have a specific gravity of 2'9 to 3*5 and a hardness of 
 5 to 6. As found in rocks, such as granite, they are usually 
 dark green or black in colour and occur in opaque irregular 
 masses possessing fairly good weathering properties. Many 
 varieties of the minerals showing very different physical 
 characters are known, however ; the valuable silicate asbestos 
 is, for example, a variety of hornblende. 
 
118 CHEMISTEY AND PHYSICS OP BUILDINa MATEEIALS 
 
 Hornblende is a frequent constituent of many granites 
 and often presents under the microscope crystals showing 
 a corroded outline, it is also strongly dichroic. 
 
 5. Chlorite. — This mineral, a hydrated silicate and 
 aluminate of magnesium and iron, is essentially an altera- 
 tion product, and its presence indicates decay. It occurs in 
 scaly fragments possessing no elasticity and somewhat 
 greasy to the touch. Under the microscope it presents 
 a radiating fibrous or earthy structure, and under polarised 
 light usually appears grey or dull blue in colour and exhibits 
 dichroism if sufficiently transparent. 
 
 6. Serpentine. — This is another decomposition product 
 formed from a mineral termed olivine, found in certain rocks 
 rich in bases and sometimes also from augite or hornblende. 
 Its specific gravity is 2*5 to 2*7 and its hardness 3 to 4. In 
 colour it is dull green (though red varieties are known) and 
 shows a mottled or interlaced structure under the micro- 
 scope. This mineral readily decays on exposure to the 
 weather and is found in large masses alone (when it is often 
 erroneously termed "marble ") and also in certain granitic 
 rocks. 
 
 As a conclusion to this chapter, the following list of 
 minerals, arranged according to chemical composition, show- 
 ing their respective characters, may prove useful, and therein 
 are included metallic ores and other minerals which concern 
 materials dealt with in succeeding chapters. 
 
119—120 
 
 COMMON MINERALS. 
 Occurring in, or Uskd in the Production op, Building Materials. 
 
 02 
 
 o 
 
 -2 
 
 cS 
 
 o 
 
 Name. 
 
 Graphitk 
 Sulphur 
 
 Iron Ptritks 
 Marcasite . 
 Copper Pyrites 
 Galena 
 Blende . 
 
 Bauxite 
 
 Corundum 
 
 Cassiterite 
 
 LiMONITE 
 H«MATITK 
 
 Maqnetiie . 
 Pyrolusite 
 Quartz . 
 
 Composition. 
 
 FeS2 
 FeS.2 
 CuFeS2 
 PbS 
 ZnS 
 
 Specific 
 Gravity 
 
 2—2-3 
 2-0 
 
 4-9— 5-2 
 4-6- -5'9 
 4 1— 4-3 
 7-2— 7-7 
 3-7— 4-2 
 
 Spathic Iron Ore 
 Ca lcite 
 Dolomite 
 Calamine 
 Witherite . 
 
 Barytes 
 Gypsum . 
 
 % j Orthoclase . 
 I I Oligoclases . 
 Mica (Muscovite) 
 
 AUGITE . 
 
 horneblende 
 
 Olivine 
 
 Chlorite 
 
 Asbestos 
 
 Kaolin 
 
 Al203.Pe203 
 AI2O3 
 SnOa 
 2 FeaOs.S H2O 
 Fe208 
 FegO^ 
 Mn02 
 
 Si02 
 
 FeCOs 
 
 CaCOs 
 
 CaCO;! and 
 MgCO 
 ZnCOs 
 
 BaCOs 
 
 3-6—4 
 6-8—7 
 
 3- 4—3 
 
 4- 5—5 
 4-9—5 
 
 4-8 
 2-6 
 
 Hard- 
 
 NESS. 
 
 1—2 
 
 1-5—2-5 
 
 6—6-5 
 6—6-5 
 3-5-4 
 
 2-5 
 3-5—4 
 
 naS04 
 CaSOi.2 H2O 
 
 K2Al2 8ifi0i6 
 Ca, Na, Al, Si, O 
 K, H, Al, Si, O 
 
 Mg, Ca, Al, Fe, 
 
 Si, O 
 Mg, Ca, Al, Fe, 
 
 Si, O 
 Mg, Fo, Si, O 
 
 Mg,Fe,H,Si,0 
 
 Mg.Ca, H, Si,0 
 
 Al, H, Si, O 
 
 3- 7- 3-9 
 2-6—2-8 
 2-8—2-9 
 
 4—4-5 
 
 4- 2—4-3 
 
 4-3— 4-7 
 2—2-4 
 
 2-5— 2-6 
 2-5— 2-7 
 
 2-9 
 2-9—8-5 
 
 2- 9— 3-5 
 
 3- 2-3-5 
 2-6—2-9 
 
 2-2—2-6 
 
 9 
 6—7 
 5 
 
 3—5 
 5-5- 6-5 
 1—2 
 7 
 
 Colour. 
 
 Black 
 Yellow 
 
 Yellow 
 
 Light 
 yellow 
 Yellow 
 
 Lead grey 
 
 Black 
 
 Brown 
 
 Violet 
 
 Black 
 
 Brown 
 
 Red to 
 black 
 Black 
 
 Black 
 
 White, 
 violet 
 
 Appear- 
 ance ON 
 Fracture. 
 
 Cleavage 
 Irregular 
 
 Conchoidal2 
 Irregular 
 Conchoidal 
 
 Good 
 cleavage 
 
 Good 
 cleavage 
 
 3-5—4-5 
 3 
 
 3-5—4-5 
 5 
 
 3—3-5 
 
 3—3-5 
 
 1-5—2 
 
 2—3 
 5-6 
 
 6-7 
 
 Grey to 
 
 brown 
 Colourless 
 
 or white 
 White 
 
 White 
 
 White or 
 colourless 
 
 White or 
 colourless 
 
 White or 
 colourless 
 
 Irregular 
 
 Irregular 
 
 Irregular 
 
 Irregular 
 
 Irregular 
 
 Cleavage 
 fibrous 
 Conchoidal 
 
 Appearance. 
 
 Massivel 
 
 Massive and 
 crystals 
 
 Massive and 
 crystals 
 
 Massive and 
 crystals 
 Massive 
 
 Massive and 
 crystals 
 
 Massive and 
 crystals 
 
 Cleavage 
 
 Very good 
 cleavage 
 Irregular 
 
 Irregular 
 
 IiTegular 
 
 Irregular 
 
 and 
 cleavage 
 Cleavage 
 
 White to 
 
 red 
 White to 
 pale tints 
 Colourless 
 or brown 
 Green or 
 
 black 
 Green or 
 
 black 
 Green or 
 
 brown 
 Light green 
 to black 
 White to 
 
 grey 
 White to 
 
 Irregular 
 
 Irregular 
 
 Very perfect 
 cleavage 
 Irregular 
 
 Irregular 
 
 Irregular 
 
 Cleavage 
 
 Cleavage 
 
 A clay 
 
 Massive, 
 granular 
 Massive and 
 
 crystals 
 Massive and 
 
 granular 
 Massive and 
 
 crystals 
 Massive and 
 granular 
 Massive, 
 earthy 
 Massive and 
 good crystals 
 
 Metallic, scaly 
 Resinous . 
 
 Metallic 
 Metallic, dull 
 Metallic 
 Metallic, light 
 Resinous to metallic . 
 
 Nodules (crys- 
 tal masses) 
 Massive and 
 
 crystals 
 Rock masses 
 and crystals 
 Rounded 
 masses 
 Compact 
 masses 
 
 Massive and 
 crystals 
 
 Fibrous 
 masses 
 
 Earthy 
 
 Vitreous, translucent 
 Vitreous, dull . 
 Earthy, dull, fibrous . 
 Metallic 
 
 Metallic, dull . 
 Semi-metallic . 
 Vitreous, transparent 
 
 Occurrence. 
 
 Ceylon, Cumberland . 
 
 Sicily and other vol- 
 canic districts 
 
 Very widely diffused 
 
 Very widely diffused . 
 
 Cornwall, Cape, Chili . 
 
 Derbyshire, North 
 
 Wales 
 With ores of lead 
 
 Pearly lustre 
 
 Pearly, vitreous 
 
 Pearly or stony . 
 
 Vitreous or chalky . 
 
 Greasy or vitreous 
 lustre 
 
 Interlocked 
 
 crystals 
 Crystalline 
 
 masses 
 Crystalline 
 
 masses 
 Massive and 
 
 crystals 
 Massive and 
 
 crystals 
 Granular 
 
 masses 
 Irregular 
 
 masses 
 
 Fibrous 
 
 masses 
 
 A olay 
 
 Vitreous or granular . 
 Silky lustre, vitreous 
 
 Vitreous, opaque 
 Vitreous, opaque 
 Vitreous, transparent 
 Vitreous, dull 
 Vitreous, dull . 
 Vitreous, translucent 
 Soft scaly flakes 
 Silky texture 
 Earthy, greasy touch 
 
 Aries (France) 
 
 Widely distributed 
 
 Cornwall, Straits Settle- 
 ments 
 
 Sweden, and many other 
 countries 
 
 Spain, Sweden, Cum- 
 berland 
 
 Norway, Sweden, 
 Russia 
 
 Spain .... 
 
 Very widely di stributed 
 
 Remarks . 
 
 Also known as black lead, or plumbago. 
 
 Marks paper. 
 Melts easily and burns. Very brittle. 
 
 Weathers well, unless finely 
 
 Rather brittle, 
 divided. 
 
 Spear-like crystals ; often whitish or brown. 
 
 Weathers b.adly. 
 Chief ore of copper. 
 
 Chief ore of lead. Crystals generally cubes. 
 
 Chief ore of zinc. Sometimes yellow or red, 
 and semi-transparent. 
 
 Prussia, Staffordshire, 
 Yorkshire 
 
 In all limestone dis- 
 tricts 
 
 Sunderland, Permian 
 
 formation 
 Vieille Montague, Spain 
 
 With lead ores 
 
 With lead ores, Shrop- 
 shire 
 
 Bristol, Retford, Derby 
 
 1 Irregular masses, often 
 8 In this and 
 
 The normal felspar of 
 
 granite 
 In granite and many 
 
 rocks 
 
 Siberia. Granites gener- 
 ally 
 
 In many igneous rocks 
 
 In many igneous rocks 
 
 In Basalts and Dolerites 
 
 In many decomposing 
 
 rocks 
 Canada, Italy 
 
 Cornwall, Dartmoor . 
 
 Chief ore of aluminium. Water and other 
 
 impurities i)resent. 
 Impure as emery. Forms many gems : as 
 
 ruby, sapphire. 
 Chief ore of tin. Arsenic often associated. 
 
 Streak white. 
 An iron ore. With clay forms ochre, umber, 
 
 and siliceous earths. 
 Important iron ore. Rounded fibrous 
 
 masses. Streak red. 
 The richest iron ore, and most valuable 
 
 when pure. 
 Chief ore of manganese. 
 
 Crystals six-sided pyramid-t ; varieties : 
 avanturine, agate, jasper, flint .sand. 
 
 Seldom pure ; sometimes with manganese. 
 
 Clay ironstone common impure variety. 
 Crystals in many forms, breaks into rhombs. 
 
 Used as a building-stone. Crystals hare 
 
 curved faces. 
 A valuable zinc ore. Often formed from 
 
 blende. 
 
 Used in brick manufacture as a corrective. 
 
 Known as heavy spar. Used in paints. 
 
 Varieties : selenite (clear crystals), alabaster, 
 satin spar. 
 
 Crystals often large, flat and bluntly pointed 
 
 at ends. 
 Distinct crystals rare. 
 
 Often popularly called talc. A good insu- 
 lator. 
 
 Granular masses, crystals columnar and 
 short. 
 
 Fibrous masses. Very similar to augite. 
 
 Occurs in volcanic rocks. Changes into 
 serpentine. 
 
 Replaces other minerals in igneous rocks. 
 
 Often laminated. 
 A variety of hornblende. Very flexible. 
 
 Also called china clay. Results from 
 decomposition of felspars. 
 
 of considerable size. 
 
 the following minerals the elements present 
 
 2 Resembling the fracture shown by a lump of glass, 
 are alone indicated, as the formulas are very complex. 
 
CHAPTER XII 
 
 CLISSIFIOATION OF STONES 
 
 I. Introductory. 
 
 In Chapter X. it was shown that the majority of stones, 
 or rocks as they are termed by the geologist, which compose 
 the earth's crust, are the fragmental remains of older rocks 
 which have been deposited under water, but that intruded 
 among them are other rocks, such as granite, which have 
 solidified from a molten condition, and which are easily 
 distinguishable by the absence therein of planes of bedding, 
 fossils, and by their general structure. The former class 
 are called Sedimentary (also Stratified or Aqueous) rocks, 
 and the latter, in reference to their origin. Igneous rocks. 
 
 It has further been stated that earth movements and the 
 earth's heat have in various localities caused great changes 
 in many deposits subsequent to their formation, and rocks 
 which have thus been altered may conveniently be relegated 
 to a separate class, and are known as Metamorphic rocks 
 (rocks of changed form). 
 
 The only rocks not accounted for under the above headings 
 are certain limestones which have been deposited from 
 solution, that is chemically precipitated, but since such 
 deposits resemble the sedimentary rocks in all but their 
 mode of origin they are properly included in this group. 
 This simple classification, which conforms both to the 
 geological and utilitarian aspects of the subject, may be 
 
122 CHEMISTRY AND PHYSICS OF BUILDINa MATERIALS 
 
 conveniently adopted and the members of these groups 
 discussed under the following headings : — 
 
 Igneous Stones. Sedimentary Stones. Metamorphic Stones. 
 
 Granites and Limestones Slates 
 allied stones Sandstones Marbles. 
 
 II. Igneous Stones. 
 
 1. Granites. — The name granite is popularly applied not 
 only to most stones of igneous origin but often to hard 
 sedimentary stones used for road coverings. Such ter- 
 minology is very misleading. Granite is an igneous rock 
 which has never flowed out upon the earth's surface as a 
 lava but has consolidated slowly at some depth, hence it is 
 always entirely crystalline in character. 
 
 The normal constituents of granite are quartz, felspar, 
 and micBi. Quartz is always present in quantity — in fact, 
 the total amount of silica present as quartz and combined 
 in the silicates felspar and mica often reaches 70 per cent, 
 of the whole rock. The predominating felspar and mica 
 are generally orthoclase and muscovite, but plagioclase and 
 biotite are also generally present. The quartz and felspar 
 are commonly found in about equal quantities, and the 
 mica in smaller quantity than either of the above 
 constituents. 
 
 The minerals hornblende and augite are often associated 
 with granites, and when present in quantity such rocks are 
 known as hornblende or augite-granites. 
 
 Again, numerous accessory minerals are common in small 
 amounts. Those which are objectionable are referred to 
 at the end of this section. 
 
 The structure of granites varies very much on account of 
 the different rates at which solidification has taken place in 
 different examples. In Shap granite, for instance, large 
 porphoritic crystals of orthoclase felspar several inches long 
 
CLASSIFICATION OF STONES 
 
 123 
 
 occur, while in some other stones of very similar chemical 
 composition all the minerals are so finely divided that they 
 are with difficulty distinguished. As a rule finely grained 
 granites weather better than those of coarser structure, 
 apart from questions of defects. 
 
 2. Elvans. — This name, of Cornish origin, is given to 
 certain igneous rocks which much resemble granite in 
 composition, but which present a very different structure 
 and appearance. Finely grained granites which show no 
 distinctive minerals are sometimes placed in this category. 
 An important member of this group of stones is quartz- 
 porphory, a rock containing well formed crystals of quartz 
 (never found in distinguishable crystals in granite) in a fine 
 ground mass of quartz and felspar. Sometimes crystals of 
 felspar are also present. Very little mica is found in these 
 stones. Some of the Cornish elvans have considerable local 
 use, since they are comparatively easy to work and harden 
 on exposure. 
 
 3. Syenites. — These rocks may be looked upon as granites 
 without quartz, or at least as containing quartz only as a 
 minor constituent. The name Syenite is properly confined 
 to rocks in which the felspar present is orthoclase ; those 
 which contain plagioclase felspars are called Diorites. 
 Syenites are only found in England in Leicestershire, and 
 their chief use from this locality is for road " metalling." 
 
 Much syenite is imported into this country from Scan- 
 dinavia, under the name of granite. The rock is usually 
 of a mottled grey tint or almost black, due to the presence 
 of large quantities of augite, and the variety of mica is 
 chiefly biotite. Some of these syenites (or more correctly 
 syenite-dioritee, since both felspars are present) display 
 iridescence, due to the arrangement of the felspars in 
 parallel layers, and are termed popularly Labradorite, 
 though the particular felspar from which this name is 
 derived is not really present. 
 
124 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 The small proportion of quartz and the presence of biotite 
 mica are features which render the weathering properties 
 of these stones not likely to be so great as those of the 
 granites. 
 
 4. Other Igneous Stones. — Few other stones of igneous 
 origin are in general use, though many are employed for 
 local purposes. Of these the most important are the 
 Basalts, which are ancient lavas very rich in iron. The 
 rapid cooling which necessarily takes place in rocks which 
 have flowed out upon the earth's surface has resulted in 
 the production of a very finely grained rock. Basalts are 
 black or very dark in colour. Their high specific gravity 
 and the six-sided columnar form assumed by the rock in 
 certain localities render it valuable for such structures as 
 sea walls. 
 
 5. Objectionable Minerals in Igneous Stones. — Iron pyrites 
 as a constituent of igneous or any other stones is objection- 
 able owing to its tendency to weather, when iron oxide is 
 produced, which is accompanied by expansion. Evidences 
 of rusty stains round pieces of this mineral indicate that 
 its decay has already set in. 
 
 Kaolin, the residue left after the removal of the bases 
 from felspars, naturally indicates advanced decay, and will 
 render the felspars soft and earthy in proportion to the 
 amount present. A test for the hardness of the felspar is 
 therefore valuable. 
 
 Chlorite has been described as essentially a product of 
 decay of several mineral constituents of igneous stones. 
 
 Calcite — crystallised carbonate of lime — is, in igneous 
 stones and in slates, the product of lime freed by decom- 
 position of felspars and other lime minerals, with carbon 
 dioxide obtained from air and water to which such rock 
 may have been exposed. The presence of this easily 
 recognised mineral, therefore, indicates that changes of an 
 undesirable character have taken place in such stones. 
 
CLASSIFICATION OF STONES 
 
 125 
 
 Since decay invariably reduces the hardness of stones, it 
 naturally increases the ease and cheapness with which 
 they can be worked. It should be borne in mind, however, 
 that many partially decayed stones, which usually con- 
 tain much calcite, as, for example, serpentine, may prove 
 perfectly satisfactory for internal work while decaying 
 rapidly in external situations. 
 
 III. Sbdimentaky Stones. 
 
 Stratified rocks have not received, at the hands of petro- 
 logists in this country, the attention which has been devoted 
 to those of igneous origin although they are much more 
 important commercially. The fragmental origin of these 
 stones certainly renders their microscopic examination 
 less interesting, but their structure and the cementing 
 materials of which they are composed are of the highest 
 importance, and not infrequently remains of many of the 
 foregoing minerals which have escaped complete decom- 
 position may be detected. 
 
 1. Limestones. — Under this heading are comprised all 
 stones which consist essentially of calcium carbonate, 
 except such metamorphic stones as the marbles. The 
 variation in composition and structure of limestones is very 
 great, while some consist of little else than calcium 
 carbonate, others contain much silica (siliceous limestones) 
 or clay (argillaceous limestones), some are associated with 
 magnesia (dolomitic stones) or with iron (ferruginous 
 stones), while those impregnated with organic matter 
 are termed bituminous limestones. 
 
 These stones may again be classified from a structural 
 aspect as granular, oolitic, shelly, or crinoidal limestones. 
 
 (a) Common Limestone. — Ordinary limestone is found in 
 layers or beds, which are often of great thickness and cover 
 large tracts of country, as in the North of England and 
 
126 CHEMISTKT AND PHYSICS OF BUILDING MATEEIALS 
 
 Ireland. The rocks of the carboniferous and Hassic for- 
 mations belong largely to this class, and these stones usually 
 possess a bluish grey colour, present a fine grain, and are 
 often distinctly crystalline in structure. Many common 
 limestones were probably originally deposited from solution, 
 and since they are generally highly fossiliferous and often 
 very argillaceous, they are more suited for the production of 
 hydraulic limes than for use as building-stones. 
 
 (b) Oolitic Limestones. — These stones have a chemical 
 origin, their characteristic structure, which presents yery 
 perfectly rounded grains connected by cementing material, 
 is assumed to be due to the constant motion of such grains 
 in shallow water during the deposition of coatings upon 
 them. The oolites can be traced through this country 
 continuously from Yorkshire to Dorset, and comprise such 
 important building-stones as those of Portland, Bath, 
 Ancaster, and Ketton. These stones are lighter in tint 
 than the limestones found in the older rocks. The variation 
 which they show in their weathering powers must be 
 attributed to differences in structure since they vary very 
 slightly among themselves in chemical composition, and 
 consist of little else but calcium carbonate. 
 
 (c) Dolomitic Limestones. — These stones, also called 
 magnesian limestones, consist of calcium and magnesium 
 carbonates mixed together, or possibly to some extent 
 combined, in varying proportions. The stones designated 
 by this name, however, are only such as contain an amount 
 of magnesium carbonate comparable with that of the 
 calcium carbonate present. As all the limestones (at least 
 in this country) which contain any magnesium show either 
 trifling or quite large percentages of magnesium carbonate, 
 this definition of a dolomitic limestone is sufficiently deter- 
 minate. These stones are characteristic of the Permian 
 formation, which presents good exposures in the north of 
 England. 
 
CLASSIFICATION OF STONES 
 
 127 
 
 Structurally the dolomites vary considerably : some are 
 compact and crystalline and possess great durability, while 
 others are porous and shelly and weather badly. A high 
 percentage of magnesium is regarded as an indication of 
 good quality. Anston stone and Woodhouse Mansfield 
 stone are examples of building-stones which come under 
 this category. 
 
 (d) Other Limestones. — Other stones belonging to this 
 class find a limited use as building-stones. Kentish rag is 
 an example of a hard siliceous limestone which weathers 
 well, but its use is generally confined to random work. 
 Ham Hill stone is a shelly ferruginous limestone possessing 
 a warm tint and very attractive appearance, but is some- 
 what difficult to work. Chalk is a soft variety of stone, 
 consisting almost entirely of minute shell fragments 
 deposited in deep water, and its marine origin confers upon 
 it great constancy of structure and composition, but owing 
 to its porosity and the lack of cohesion between its 
 particles it is not suitable for external work. 
 
 2. Sandstones. — Sandstones consist of fragments of 
 quartz cemented together by silica deposited from solution, 
 or by alumina, carbonate of lime or magnesia, or one of the 
 oxides of iron. In some stones, however, no cementing 
 material is discernible and the grains hold together as the 
 result of partial vitrification. 
 
 Since quartz is entirely unaltered by atmospheric 
 agencies the weathering power of sandstones must depend 
 upon the nature of the cementing materials, the shape of 
 the quartz fragments, and the amount of porosity possessed 
 by the stone. 
 
 The commonest of these cementing materials consists of 
 hydrated oxide of iron, which gives the yellow, brown or 
 red tint so associated with these stones. If carbonates are 
 present they may be either crystalline or amorphous, and 
 if alumina, the material will usually be soft and clayey. 
 
128 OHBMISTEY AND PHYSICS OF BUILDING- MATERIALS 
 
 In the strongest and most durable stones the quartz 
 grains are fritted together owing to partial fusion, as in the 
 famous Craigleith sandstone. Such stones are, however, 
 very hard and difficult to work, and if the fusion has taken 
 place to any marked extent they are termed quartzites, and 
 must be regarded as metamorphic stones. 
 
 Some sandstones possess distinct planes of bedding, as, 
 for instance, the well-known York stone. These bedding 
 planes, which give the stone a cleavage, are generally due to 
 the presence of mica, which forms layers between the 
 quartz grains, and thus disturbs their continuity. In 
 other varieties, such as the Bramley Fall stone of Leeds, 
 these laminations are conspicuously absent. 
 
 Finely grained sandstones stand sudden changes of 
 temperature better than other natural stones, owing to their 
 homogeneous structure. 
 
 3. Objectionable Minerals in Sedimentary Stones. — The 
 remarks upon iron pyrites, made in connection with igneous 
 stones, apply equally to those of sedimentary origin, and 
 though, perhaps, seldom present in quantity, the sister 
 mineral marcasite is not uncommon, disseminated between 
 the planes of bedding. The oxidation of these sulphides 
 of iron not only produces staining and disruption due to 
 expansion, but also, owing to the formation of sulphuric 
 acid, solution of any carbonate of lime or magnesia present 
 with the production of sulphate of lime and a corresponding 
 loss in cohesion. 
 
 Other iron compounds, such as ferrous carbonate (FeCOa), 
 if present in quantity are also objectionable owing to their 
 tendency to oxidise, while alumina, the usual source of 
 which is clay, by destroying the continuity of crystalline 
 structure or of some cohesive cementing material may 
 prove a source of great weakness. 
 
 4. Weathering. — The weathering of igneous and sedimen- 
 tary stones differs in that, while the decomposed products 
 
CLASSIPIOATION OF STONES 
 
 129 
 
 remain in situ in the former they are generally removed 
 by surface scaling in the latter, which renders an estima- 
 tion of the process of decay in a stone of sedimentary origin 
 not very amenable to microscopic investigation. No serious 
 attempt, however, has yet been made to carry out micro- 
 scopic examinations of weathered stones, and a most 
 useful field in this direction awaits the labours of the 
 petrologist. 
 
 The chief product of the weathering of sedimentary 
 stones, apart from iron compounds, is sulphate of lime 
 resulting from the action of sulphuric acid upon carbonate 
 of lime, and causing a surface efflorescence often of some 
 thickness. Where such deposits are maintaining the stone 
 in a damp condition and thus causing further damage they 
 should be removed ; but in certain circumstances they may 
 act as a protective coating, when their removal may be 
 doubtful policy. 
 
 IV. Metamoephic Stones. 
 
 1. Definition. — Eeference has been made to the crushing 
 effects of earth shrinkage and the change produced by the 
 heat from intruded rocks in explanation of the alteration 
 in characters which make it desirable to include certain 
 originally sedimentary deposits in a special category. 
 
 So far has this baking action gone in many cases that 
 all remains of original structure, planes of bedding and 
 contained fossils have disappeared, but all stages of meta- 
 morphosis are known down to the slightest alterations 
 which have merely produced incipient crystallisation. 
 
 Water also plays a large part as a metamorphic agent. 
 Under the pressure of great rock masses confined water 
 may reach a temperature far above its normal boiling 
 point while still remaining liquid, and then possesses greatly 
 enhanced solvent powers. When the pressure is released 
 
130 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 through some earth movement this water will turn into 
 steam and deposit its dissolved matter in a form which may 
 be essentially different from that which it originally 
 possessed. 
 
 2. Marbles. — The marbles are composed of carbonate of 
 lime which, subsequent to its deposition, has been rendered 
 entirely crystalline, thus giving the material a compact 
 structure which enables it to take a high polish, and also 
 confers upon it great strength and durability. Since, how- 
 ever, acids attack all forms of carbonate of lime, no marble 
 will withstand exposure to a town atmosphere without 
 detriment, which, owing to the fine arrises and polished 
 faces generally conferred upon marble, makes itself readily 
 conspicuous. 
 
 The colours of marbles are due to the presence of iron in 
 various states of combination. Hydrated ferric oxide 
 confers yellow or brown tints, and this oxide in an 
 anhydrous state (without water) gives red markings. Iron 
 combined with silica in the mineral glauconite accounts for 
 green colourings, while black marbles generally owe their 
 absence of colour to the presence of organic matter derived 
 from bituminous limestones. 
 
 Marbles sometimes contain finely disseminated sulphides 
 of iron, which are particularly to be avoided in the white 
 varieties, since on oxidation of the iron the stone will 
 acquire a pink tint. 
 
 Varieties. — No attempt can be made here to deal with 
 the many varieties of marble used for decorative purposes, 
 which range from the polished fossiliferous and only 
 slightly altered limestones to the much-prized Greek 
 and Italian marbles, which are wholly crystalline in 
 character. 
 
 The term "marble" should be confined to stones composed 
 of carbonate of lime, and not applied to serpentines or 
 similar stones. Some of the Irish Connemara marble, for 
 
CLASSIFICATION OF STONES 
 
 131 
 
 instance, is correctly so called since it is an altered dolo- 
 mite, but other stones included under this designation are 
 serpentines, and therefore of igneous origin. 
 
 Alabaster is a variety of marble characterised by its 
 transparency ; this statement, however, is only true of 
 Oriental alabaster. The material produced in this country 
 under the name of alabaster is not the carbonate but the 
 sulphate of lime, and may be regarded as a variety of the 
 mineral gypsum. 
 
 3. Slates. — (a) Formation. — The term "slate" is properly 
 confined to metamorphic rocks derived from clays which, 
 originally laid down as sedimentary deposits, have been 
 subjected to the action of heat and great lateral pressure 
 while still confined, by the vertical pressure of deposits 
 above them. This has resulted in an alteration of the 
 position of the particles forming the clay, which, originally 
 deposited in horizontal layers — that is, with the longer axes 
 of the particles lying flat — has been transformed into layers 
 with such axes at right angles to the lateral pressure, the 
 thrust upon the particles having turned them round until 
 they occupy as little space from side to side as possible. 
 As an analogy, a crowd of people standing side to side may 
 be taken. If such persons were crushed laterally by crowds 
 pressing upon them on either side they would tend to move 
 individually through a right angle, as they would then, 
 standing face to back, have more space in the direction of 
 the pressure. An important effect of this change is the 
 cleavage which is thereby induced in planes at right angles 
 to the direction of the lateral pressure, since it is naturally 
 easier to separate layers of particles lying side by side than 
 to split the material in other directions, which would 
 involve the fracture of individual particles ; and when thin 
 platey minerals, such as mica, occur in the clay this 
 induced cleavage may be developed in a very perfect degree. 
 From the above considerations it will be obvious that all 
 
 B.M K 
 
132 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 traces of the original planes of bedding will generally be lost 
 when slates are formed. 
 
 (h) Composition. — Clays are decomposed felspars from 
 which the bases have been removed, hence clays and slate 
 formed from them are chiefly composed of silicate of 
 alumina. Since, however, this felspathic decomposition 
 has been seldom complete, and as quartz, mica, and other 
 minerals originally associated with the felspar may have 
 escaped complete removal, slates always contain small 
 quantities of lime and other bases, and are often very rich 
 in iron. Silica is usually present in amounts ranging from 
 some 60 to 60 per cent., and alumina from some 10 to 20 
 per cent. The bases, lime and magnesia, together account- 
 ing for some 3 to 12 per cent., and potash and soda 2 to 5 
 per cent., may be present as part of the original minerals, 
 such as felspar and mica, or in the form of secondary 
 minerals, chiefly as carbonates. In the former condition 
 they are not likely to prove disadvantageous, but their 
 presence as carbonates is, as previously explained, an 
 indication that changes have taken place in the slate sub- 
 sequent to its formation, and coupled with any sign of 
 a soft and friable condition, may be taken as evidence of 
 advanced decay. 
 
 Iron occurs in a fully oxidised condition as Fe203, and 
 also in larger amounts, reaching some 7 per cent, as ferrous 
 oxide (FeO) in combination. In this form, unless combined 
 with silica, it is liable to undergo further oxidation, with 
 resulting expansion as previously explained, and unless 
 well disseminated may cause local disruption. Iron pyrites 
 and marcasite are often found in slates ; the former, when 
 it occurs in crystals, so situated that they are not liable to 
 fall out and leave holes in the slate, are not in the least 
 liable to change, and form a charming feature. When 
 occurring in veins or small grains pyrites is to be looked 
 upon as objectionable. Marcasite, which may usually be 
 
CLASSIFICATION OF STONES 
 
 133 
 
 distinguished by its duller appearance and often by its 
 earthy surroundings, should always cause the rejection of 
 slate, as it decays very readily. The nature of the changes 
 which occur when sulphides of iron decompose has already 
 been discussed. 
 
 (c) Occurrence. — Slates occur only in the older rocks, 
 such as those of the Cambrian and Silurian formations. 
 Since the metamorphic action which has produced them 
 has seldom had a crisp termination in any locality, the 
 quality of slates must be expected to rapidly deteriorate 
 towards the borders of a slate-bearing district, and a 
 gradual passage into shales and clays may in many places 
 be looked for. Shales may always be distinguished from 
 slates by their property of forming plastic clays when rubbed 
 up with water. They also usually possess bedding planes 
 and exhibit very poor cleavage. Poor slates smell earthy, 
 fail to ring when struck, absorb water readily, and possess 
 little crushing and transverse strength, properties developed 
 in good slate to a very high degree. 
 
 Artificial Stone. 
 
 The principles involved in the production of artificial 
 stone, and the methods employed for preserving stone, will 
 be better understood after the discussion of the properties 
 of limes and cements. A short article on this subject will 
 be found in Chapter XIX. 
 
 K 2 
 
CHAPTEE XIII 
 
 the examination and testing of stones 
 
 1. Introductory. 
 
 The examination of stones may be approached from a 
 purely scientific or from a commercial aspect ; but since the 
 latter aspect necessarily calls upon information obtained 
 from scientific investigation, it is very desirable that a 
 complete knowledge of the chemical and physical proper- 
 ties of all stones suitable for commercial use should be 
 obtained. No organised comprehensive scheme for such 
 investigation has yet been attempted in this country, 
 although valuable work in this direction is extant for the 
 building stones of America. Stone is a natural product, 
 and, like all such products, it fails to comply with the 
 rigid standard of constancy which may be demanded in a 
 material made artificially. At the same time there are 
 many building stones which are remarkably constant in 
 composition and properties, and many interspersed beds 
 among them which should be precluded from acceptance 
 in the same category. More precise nomenclature in certain 
 cases would undoubtedly benefit users and ultimately also 
 vendors of stone. 
 
 Scientific tests should be carried out with the greatest 
 accuracy and refinement upon specimens of known origin, 
 in order to serve as a collection of standard data in which 
 every possible factor affecting any use of the stone should 
 be taken into consideration. Commercial tests, the fair- 
 ness of which can only be assessed with a knowledge of 
 
THE EXAMINATION AND TESTING OF STONES 135 
 
 such scientific data, may be of a simpler character, and 
 need relate only to the particular calls which will be made 
 upon the stone in use. 
 
 Thus, for example, the elasticity, hardness and solubility 
 of all building stones may be advantageously recorded, 
 although a determination of the elasticity of a paving-stone, 
 the hardness of a lintel, or the solubility of a marble for 
 internal decoration, would have no value commercially 
 when the use of the materials for these respective purposes 
 was in question. 
 
 The examination of stone may be conveniently discussed 
 under the following headings : 
 
 Specific gravity Hardness 
 Porosity Crushing strength 
 
 Elasticity Microscopic tests 
 
 Adherence Chemical analysis 
 
 Expansion Solubility 
 Conductivity Characters in site. 
 
 II. Individual Tests. 
 
 1. Specific Gravity. — The methods of determining specific 
 gravity have been explained in Chapter II. In making 
 such determinations in the case of stone, it must be reaHsed 
 that this property as assessed for freshly-quarried, for 
 dried stone and for the stone reduced to powder, will not 
 be the same. 
 
 No stone is entirely free from porosity, and when quarried 
 the pores are always partially filled with water, which 
 evaporates on exposure, when air takes its place and thus 
 decreases the specific gravity. On account of porosity, 
 again, many stones have a markedly higher specific gravity 
 when this determination is made with the material in the 
 state of a powder, for in this case the volume added by the 
 intervening pores is excluded. When a stone is composed 
 
136 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 of several mineral constituents it is obviously necessary 
 that a sufficiently large specimen to form a fair sample of 
 average composition must be dealt with if the result is to 
 be of any value. 
 
 Any statement of the value of specific gravity should 
 therefore be accompanied by information as to the condi- 
 tion of the stone at the time of its determination, but as 
 ordinarily understood it refers to its weight per unit volume 
 in bulk after exposure to air of ordinary dryness, and 
 therefore the air-filled pores are included. 
 
 The determination of this property seldom has any direct 
 value, as, except in certain marine works, the stability of 
 stones is seldom influenced by their relative weights. 
 Since, however (at least among sedimentary examples), the 
 individual minerals of which stones are composed differ 
 themselves but slightly as regards this property, differences 
 in specific gravity as determined when in bulk give valuable 
 indications as to porosity. 
 
 2. Porosity. — Tests for porosity are usually made by 
 immersing a given volume of the stone in water and 
 observing the increase in weight of the specimen when 
 no further absorption takes place, when, from a knowledge 
 of the weight of unit volume of water, the volume absorbed 
 by the stone is ascertained. 
 
 The only means of ascertaining whether absorption has 
 ceased, is to weigh the stone at intervals until no further 
 increase in weight is observed. It is obvious that the 
 absorption must be complete if the test is to be of any 
 value, and the time taken to attain this will be partially 
 governed by the configuration of the specimen; a thin 
 slab, for example, will naturally reach saturation more 
 rapidly than a cube of the same weight. 
 
 Even made as suggested, the test is far from satisfactory, 
 since it is almost impossible to remove all air, and thus to 
 fully admit water to the pores of the material, though the 
 
THE EXAMINATION AND TESTING OF STONES 137 
 
 operation may be facilitated by placing the stone in a vessel 
 connected to an exhausting pump. 
 
 Further, any air remaining will be altered in volume 
 quite precisely by barometric changes in pressure and by 
 change in temperature. The water used may, with advan- 
 tage, be previously boiled, as it will then be in a position to 
 dissolve some of the air which it has failed to expel. 
 
 Since porosity represents the ratio of interspaces to solid 
 material, this quality may be assessed by comparing the 
 specific gravity of the stone in bulk, i.e., including the 
 pores, with that of the stone as powder ; but even in this 
 case it is difficult to remove every particle of air from the 
 powdered substance. 
 
 A more satisfactory test for porosity is a practical one 
 based on the rate of soakage, though in the absence of 
 any standard yet agreed upon the results obtained can 
 only have a comparative value, and for this reason, as in 
 the case of many other tests, gives but little assistance in 
 specifying requirements. 
 
 Soakage tests are carried out by placing a piece of the 
 stone of known area and thickness under a known and 
 constant head of water at a constant temperature (hot 
 water is more limpid than cold water), and weighing the 
 water which soaks through in a given time, due precautions 
 being taken to prevent loss by evaporation. 
 
 3. Elasticity.— Defined in a previous chapter, this property 
 is an important one even in the case of stones, as when 
 stones fail from mechanical causes it is generally through 
 bending that fracture occurs. 
 
 Elasticity in stones presents anomalies, and its determina- 
 tion is beset with some difficulties, though these facts are 
 hardly an excuse for the indifference to this property 
 generally displayed in use. The difficulty of the test arises 
 chiefly from the very small amount of deformation apparent 
 under stress, and in obtaining uniformity in the specimens 
 
138 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 to be experimented upon. Professor Unwind has given an 
 interesting account of the investigations of Bauerehinger 
 on this subject, and has himself confirmed the conclusions 
 of this savant by his own experiments. 
 
 The specimens under test were submitted to compression, 
 and the deformations resulting in the stones were measured 
 by optical magnification. A permanent "set" was found to 
 take place in the materials when sustaining but quite light 
 loads, and in the case of hard and dense stones the com- 
 pression was observed to be proportional to the load right 
 up to the final crushing of the test piece. 
 
 In the case of the more porous stones, the compression 
 at first increased more rapidly than the load, but finally, 
 with heavy loads, less rapidly, as would be expected. 
 
 Similar relations between force and deformation were 
 obtained in a series of experiments upon stones under 
 tensile and bending stresses. A stone, then, under stress 
 takes a permanent set, and this process is repeated with 
 each additional load right up to the breaking point. Stones, 
 therefore, possess no elastic limit in the sense that up to a 
 certain stress they will recover their original form on the 
 removal of the force calling out this stress, as is found to be 
 the case with the metals. Their limit of elasticity, if indeed 
 it is wise to use the expression in a different sense, must be 
 regarded as reached at the point of failure. 
 ^ Hard stones appear to possess the greatest elasticity, and 
 limestones as a class to have very similar elastic powers, 
 which are greater than those of sandstones. 
 
 In the case of stones used for lintels and arches, especially 
 when called upon to bear variable loads, as in bridges, a 
 knowledge of elasticity is of importance and can seldom 'be 
 looked upon as useless, since this property is bound up with 
 all causes of mechanical failure. 
 
 » "The Testing of the Materials of Construction." Unwin. 
 
THE EXAMINATION AND TESTING OF STONES 139 
 
 4. Adherence. — Upon the power of the particles of a stone 
 to hold together, the probability of disintegration by 
 freezing water or expanding minerals to some extent 
 depends. Power of adherence over a given sectional area 
 of the stone is necessarily influenced by porosity, as air- or 
 water- filled voids represent area which is a direct decrease 
 in the effective points of contact. 
 
 Adherence is usually tested by artificially freezing water 
 contained in the pores of the material, and is assessed by 
 the weight of the fragments, which are split off as the result 
 of this internal expansion, when this process has been 
 several times repeated. Such a test has little scientific 
 value, but until more research is undertaken upon adherence 
 and coherence it is impossible to formulate suggestions for 
 a standard. 
 
 Some further remarks on these properties occur in 
 Chapter XVIII. 
 
 5. Expansion. — The co-efficient of linear expansion of a 
 bar of stone may be determined as has already been 
 described for the metals in Chapter V., but the result 
 obtained will be found to depend largely upon the amount 
 of moisture contained in the stone, which must therefore be 
 ascertained. Owing, however, to the low conductivity and 
 high specific heat of stones, expansion as thus measured is 
 not of great importance. 
 
 By an expansion test is more generally meant an investi- 
 gation of the relation between temperature and disintegra- 
 tion, and the factors mainly involved are the relative 
 co-efficients of expansion of the different minerals com- 
 prising the stone and the adherence and size of the 
 particles. The behaviour of a stone under sudden increase 
 in temperature can thus be to some extent predicted. A 
 stone composed of very different ingredients, such as granite, 
 must necessarily be subjected to enormous internal stresses 
 when heated, owing to the unequal expansion of its various 
 
140 CHEMISTEY AND PHYSICS OP BUILDING MATEEIALS 
 
 constituents, and will fly to pieces in the heat of a burning 
 building, whereas a sandstone composed almost wholly of 
 one compound may resist the ordeal. 
 
 The tests usually made from the above aspect are not of 
 great scientific accuracy. The time during which the 
 stone withstands a given temperature is naturally an 
 important factor, and this will depend upon the configuration 
 of the test piece, the rate of heating, and in a minor degree 
 upon the specific heat and conductivity of the material. 
 
 In this country such tests are of value in relation perhaps 
 solely to fire risks, but in some climates where very rapid 
 atmospheric changes of temperature occur, much shelling of 
 stone surfaces may take place through consequent sudden 
 expansion or contraction. 
 
 6. Conductivity. — All stones are bad conductors, and 
 although they differ as regards this property the difference 
 is not of great importance in practice. Some data on this 
 subject have been obtained by finding the rates at which 
 heat flows through plates of the same area and thickness of 
 different stones when the two sides of the plate are kept at 
 different known temperatures. 
 
 7. Hardness. — By the "hardness " of stone, resistance to 
 abrasion is usually implied. Abrasion tests are naturally 
 of most interest in connection with stones used for steps 
 and pavements. A standard is again lacking in respect to 
 this quality. Various forms of abrasion machines have 
 been devised ; these usually consist of a weight attached to 
 some gear by which it may be moved over the surface of the 
 stone to be tested, and the actual abrasion is caused by 
 emery fed on to the surface. Possibly a standard might be 
 contrived by the use of a given weighted hemisphere of 
 corundum made to pass at a given rate along a certain 
 length of the specimen, with and across the grain (if any), 
 a certain number of times, after which the abraded material 
 would be weighed. 
 
THE EXAMINATION AND TESTINa OE STONES 141 
 
 The hardness of a stone generally increases considerably 
 on exposure after quarrying, for the " quarry sap " or water 
 in the stone evaporates upon the exposed surfaces and there 
 deposits solids, such as silica, which are contained in the 
 water in solution. The surface pores of the stone are then 
 filled, and the face hardened. It should be remembered, 
 however, that since the evaporation and deposition of solids 
 only takes place on the surface, the interior of the stone 
 does not benefit in the same manner, and that the process 
 of face hardening is not repeated if this skin is removed — 
 a fact which should cause reflection before the surface of 
 old stone is submitted to dragging operations. It must 
 be admitted, nevertheless, that this explanation of the 
 hardening of stones leaves something to be desired, as 
 some stones become hard in course of time to considerable 
 depths beneath their surfaces. This might conceivably be 
 due, in the case of limestones, to gradual solution in moisture 
 charged with carbon dioxide and subsequent deposition of 
 such dissolved material in a crystalline form in the pores of 
 the stone. 
 
 8. Crushing Stress. — It is seldom that the snperincumbent 
 pressure on stones used in buildings, or even the thrust 
 upon such stones, exceeds a tenth of the load necessary to 
 produce failure by crushing. The lightest building stones, 
 for example, will sustain a pressure of some 250 tons per 
 square foot, and even in columns about three quarters of 
 this weight. Notwithstanding which fact this test is the 
 one usually adduced before all others by merchants anxious 
 to substantiate the good quality of a stone. A knowledge 
 of crushing stress, however, has some indirect value as in- 
 dicating the elastic and adherent properties of the material. 
 Such tests as usually made, leave, nevertheless, something 
 to be desired, for the cube, though generally used, has 
 been shown to be less suitable for ascertaining the value of 
 this property than a rectangular block half as great again 
 
142 CHEMISTRY AND PHYSIOS OF BUILDING MATERIALS 
 
 in the direction of the crushing pressure than in its other 
 dimensions. 
 
 The test is applied by submitting opposite and parallel 
 faces of the block to compression in a hydraulic press. 
 Eepresentative results are difficult to obtain without the use 
 of a powerful machine, and since there are but few presses 
 at disposal capable of dealing with specimens presenting a 
 face area exceeding 6x6 inches, the actual load which 
 can be carried by any area of jointed masonry is seldom 
 really ascertained, for it is not probable that this can be 
 correctly assessed from the proportionate area of a small 
 specimen. 
 
 For the reason given above this is perhaps not of much 
 moment, and it would probably be more useful to utilise 
 crushing tests as adjuncts to tests on elasticity and 
 adherence instead of attempting to give them a direct 
 significance. 
 
 9. Microscopic Tests.— The examination of thin slices of 
 stone or rock sections,^ as they are termed, under the 
 microscope gives more information as to the quality of the 
 material than perhaps any other test, and can, moreover, be 
 carried out with rapidity. In the nature of things, micro- 
 scopic analysis must be of a qualitative rather than a quanti- 
 tative character, and it requires an expert petrologist to 
 elucidate the meaning of many of the features displayed by 
 this instrument ; but much may be learnt even by the layman 
 with a little practice. Anyone, for example, can gain some 
 insight into the nature and proportion of the cementing 
 material between the grains of a sandstone, determine 
 whether such grains are rounded or angular, and detect 
 certain minerals, such as iron pyrites, by the use of a 
 
 ^ Rock section cutting forms a small distinct branch of lapidary 
 work, and is accomplished by grinding chips of the stone until thin 
 enough to transmit light when they are mounted on glass slides. 
 Sections of ordinary building stones can be prepared for about Is. 6d. 
 each. 
 
THE EXAMINATION AND TESTING OP STONES 143 
 
 simple instrument devoid of polarising prisms or^ other 
 accessories. Again, incipient decay in igneous rocks as judged 
 by earthy felspars, the presence of carbonates, chlorite 
 and other minerals of secondary origin, is not usually a 
 difficult matter to discover microscopically. 
 
 The microscope has yet to be accorded its due place as a 
 commercial instrument, and a great aid to its popularity 
 would be the production of a standard set of rock sections 
 of the commoner building stones fully identified and 
 described, and a similar set showing the effects of weathering 
 under defined and practical conditions. In the case of the 
 sedimentary stones the preparation of sections showing 
 weathering presents considerable difficulty, but a well-known 
 geologist has expressed to the writer his belief that it is 
 practicable. 
 
 10. Chemical Analysis. — Though a few simple tests 
 which will indicate the presence of certain constituents in a 
 stone may be undertaken by the layman, chemical analysis 
 is essentially the work of an expert, and the preparation 
 of a complete statement as to the nature and amounts of the 
 constituents of any stone involves, except in the case of 
 those of very simple composition, considerable skill and 
 labour. 
 
 Much misconception appears to exist upon the subject of 
 analyses, which usually give the percentage of bases and 
 acids present in the stone with little, if any, regard to their 
 true relations. Such analyses may have some value as 
 showing the presence and amounts of wholly undesirable 
 constituents, and do not give rise to ambiguity in the case 
 of stones of very simple composition. Generally speaking, 
 however, a chemical analysis should be preceded as far as 
 possible by a mineral analysis, for since many of the 
 minerals present usually contain the same acids and bases, 
 a mere statement of the total amounts of such components 
 can give, in such cases, no conception of composition. 
 
144 CHEMISTEY AND PHYSICS OP BUILDING MATEEIALS 
 
 A complete separation of the minerals composing a stone 
 is admittedly a matter of great difficulty, but, making full 
 allowance for the complexity of the problem, the fact 
 remains that much valuable work is thrown away by 
 the stereotyped manner in which the analyst too often 
 approaches his work. 
 
 Different stones require different methods of procedure. 
 As an illustration, the analysis of a calcareous sandstone 
 and a granite may be considered. In the former stone the 
 microscope has revealed grains of silica cemented by 
 carbonate of lime. The chemist submits an analysis 
 showing the percentage of silica (SiOa), lime (CaO) and 
 carbon dioxide (CO2) which accounts for everything present. 
 This is perfectly intelligible. The carbon dioxide could not 
 have been combined with anything but the lime ; hence, since 
 44 parts (the molecular weight) of CO2 combine with 56 parts 
 of CaO, 44 parts of CO2 must involve the presence of 100 
 parts (56 + 44) of calcareous matter, namely, CaCOs, and thus 
 from the percentage of CO2 given, theCaCOa can be calculated 
 by simple proportion. 
 
 The analysis of the granitewhich will probably be presented 
 in the same manner will show the percentage of siHca, 
 alumina, lime, potash and soda. Now both felspar and mica 
 are silicates and aluminates of potash ; in felspar, however, 
 the ratio of alumina to potash is about 4 to and in mica 
 this ratio is about 4 to 1. Suppose that an inspection of 
 the analysis showed that the percentage of potash was low 
 as compared with other analyses of good stones, this might 
 indicate the presence of a large percentage of mica, but it 
 might equally well imply that the felspar had lost much of 
 its potash owing to decay, which would involve a very 
 different conclusion as to the suitabiHty of the stone for use. 
 Identical ultimate analyses are therefore possible for stones 
 possessing wholly different structural values. 
 
 What is wanted in the case of all heterogeneous rocks 
 
THE EXAMINATION AND TESTING OE STONES 145 
 
 is the composition of the individual minerals present. The 
 amount of each mineral, which is not easily ascertained, 
 may be often gauged with sufficient accuracy by microscopic 
 investigation. 
 
 Attempts at mineral separation have been made by 
 crushing the stone and placing the powder in liquids of 
 different specific gravities, so that one constituent of the 
 stone may float while another will sink. This has not 
 proved very satisfactory, and in the case of stones possessing 
 minerals in distinguishable pieces a better plan would 
 possibly be to fracture rock sections and remove the 
 individual minerals while still in position by mechanical 
 separation under the microscope. 
 
 11. Solubility. — Experiments upon the solubility of stones 
 refer chiefly to the effects of acids, such as sulphuric acid 
 present in town atmospheres. In the neighbourhood of 
 certain industries hydrochloric acid is also often found 
 in the air. Both these acids readily dissolve carbonate 
 of lime, and therefore it is among the limestones and 
 calcareous sandstones that their greatest ravages are to be 
 looked for. The structure of the stone is found to influence 
 its behaviour very materially in regard to solubility. 
 
 As usually recommended, the test consists in immersing 
 a known weight of the stone in a weak solution (about 
 1 per cent.) of sulphuric or hydrochloric acid and ascer- 
 taining the amount dissolved after a given period. To 
 obtain results of any accuracy specimens of the same size 
 and configuration should be used, and these must be 
 weighed in the same condition (say dried at 100° C.) before 
 and after the experiment. 
 
 In the case of stones to be placed under water it may 
 occasionally be desirable to make other solubility tests 
 if an analysis of the water indicates the probability of any 
 solution taking place. 
 
 12. Characters in Situ. — The examination of stone by 
 
146 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 actual inspection at the quarry is of great value. This has 
 two objects : an inquiry into (1) Weathering qualities ; 
 (2) The probability of obtaining uniformity in the material 
 supplied. 
 
 In the former investigation actual working faces which 
 have been exposed to the weather should be examined, due 
 allowance being made for weather stains produced by 
 surrounding vegetation. It does not, however, follow that 
 a stone which presents a satisfactory appearance in the 
 quarry will weather equally well in the situation proposed 
 for its use, and every advantage should be taken of possible 
 investigations of the condition of buildings erected in the 
 stone in the locality proposed. It is to be hoped that a 
 register may some day be compiled showing the stone 
 employed, age and locaHty of accessible buildings, with 
 notes upon aspect, weathering and local conditions. This 
 would be invaluable to stone users. 
 
 The question of uniformity to be expected in the supply 
 of stone is naturally of importance in proportion to the 
 amount required, and though in the case of many well- 
 known stones uniformity from reputable vendors may be 
 expected without investigation, this matter assumes a 
 different aspect in the case of stone supplied from new 
 sources. 
 
 A knowledge of local geology and of the investigations 
 which have been undertaken by the quarry owners can 
 alone answer such inquiry, and such owners would do much 
 both for purchasers and themselves by strictly defining the 
 beds of their quarries and publishing such evidence of 
 probable uniformity as they have acquired. 
 
CHAPTEE XIV 
 
 BRICK AND OTHER CLAYS 
 
 I. Geological Formation. 
 
 Clays are universally secondary deposits ; that is, they are 
 the result of the decomposition of older rocks. They are 
 found in all geological formations, though in the lower 
 series of deposits earth movements and the compression 
 due to overlying strata have usually converted clays into 
 shales or slates. 
 
 Clays owe their origin chiefly, but not entirely, to the 
 decomposition of felspars contained in igneous rocks. Such 
 disintegration may be due to ordinary weathering, but 
 since masses of decomposed felspars some hundreds of feet 
 in depth, evidently still situated in their original positions, 
 are known, some further explanation of this decomposition 
 seems to be called for, as it is not conceivable that weathering 
 should have extended to so great a depth without the 
 removal of the larger part of the friable materials so 
 produced. 
 
 It is believed that these deep clay deposits have been 
 formed by the decomposing action of vapours penetrating 
 the felspars from below, and particularly by the action of 
 hydrofluoric acid, a gas which resembles hydrochloric acid, 
 but which possesses greater chemical activity and can 
 dissolve silica. The solution of part of the silica from the 
 felspars sets free the bases, which are themselves then 
 removed in solution, and leaves silicate of aluminium, which 
 constitutes the clay. 
 
 B.M. L 
 
148 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 This theory of the formation of certain clays is borne 
 out by the presence in them of secondary minerals, such 
 as tourmaline, which contain the element fluorine as one 
 of their constituents, and by the fact that hydrofluoric acid 
 is producible from fluorides in the presence of superheated 
 water, which is known to occur in the earth's crust at 
 great depths. 
 
 II. Varieties of Clay. 
 
 Clays may be residual or transported, the latter being 
 the more common. 
 
 1. Residual Clays. — Eesidual clays are those which have 
 been left in situ after the decomposition of the rocks giving 
 rise to them, and may be distinguished by the evident 
 relation in character and composition which they bear to 
 the rocks which they overlie. Such clays generally merge 
 into the underlying rocks without any definite plane of 
 separation. Kaolin or china clay belongs to this class. 
 
 2. Transported Clays. — Transported clays, among which 
 all the ordinary brick clays must be included, form stratified 
 deposits which resemble in their mode of deposition the 
 sedimentary rocks ; that is to say, they have been laid down 
 in beds under water and can be traced by their relations to 
 neighbouring deposits and by their characteristic fossils. 
 These facts, the wide areas often covered by such clays and 
 the sharp line of demarcation between them and the strata 
 on which they rest, to which they bear as a rule no relation 
 in character, make transported clays easily distinguishable 
 from those of residual origin. 
 
 3. Varieties of Transported Clays. — Transported clays 
 present varieties in their mode of occurrence similar to 
 those found among stones of sedimentary origin. Some — 
 the marine clays — have been deposited in deep water, cover 
 wide areas, and show great constancy in composition ; such 
 
BRICK AND OTHEE CLAYS 
 
 149 
 
 clays consist of fine particles, since only such material can 
 be carried out from river courses or cliff erosion far into the 
 ocean. Other clays less extensive and constant in character 
 have been laid down in lakes ; the London clay is an 
 example of this class. Finally, estuarine clays deposited 
 at the mouths of rivers and streams are still more local in 
 character and are often found in lenticular (lens-shaped) 
 deposits which present marked physical variations at, it 
 may be, distances of a few yards. Such clays are often 
 mixed with, or broken up by, layers of sand and gravel. 
 Another extensive clay deposit is the boulder clay, formed 
 from detritus scraped up by the great ice sheet which once 
 spread over the northern part of E urope. Such clay is found 
 in the eastern counties of this country, but is too full of 
 stones and boulders to admit of its being put to much 
 practical use. 
 
 III. Physical Propbetibs of Clay. 
 
 The distinctive property of clay is its plasticity, and most 
 of its uses depend upon this property and upon the fact that 
 it is entirely lost when the material is heated to a certain 
 temperature, when it acquires rigidity of form. 
 
 Plasticity is usually attributed to the presence of kaolin, 
 which is hydrated aluminium silicate ; but since the display 
 of this property bears no relation to the amount of kaolin in 
 a clay which may be exceedingly plastic while containing 
 but 5 or 10 per cent, of this mineral, some further explana- 
 tion seems to be called for. 
 
 Any exceedingly finely grained substance which is wetted 
 by a liquid may be expected to display some powers of being 
 moulded, as, owing to what is called " surface tension," the 
 liquid will tend to stick to the solid particles. Clays contain 
 particles which are stated by Eies^ to be in many cases not 
 
 1 Eies, " Clays : their Occurrence, Properties, and Uses." John 
 Wiley, 1906. 
 
 L 2 
 
150 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 more than i^j,^ou ^ millimetre in diameter, and the plas- 
 ticity of the mass is found to increase with the fineness of 
 the particles, though no direct relation between these 
 properties appears to exist. 
 
 In a valuable summary upon the theories put forward to 
 explain plasticity, the above writer refers to that based on 
 molecular attraction which, where such small bodies are in 
 question, may not unreasonably be supposed to exercise 
 some effect in holding the particles together while still 
 allowing them to slide round one another. 
 
 The effects of kaolin in producing this property are 
 probably due to the colloidal (glue-like) nature of hydrated 
 silica and alumina ; such bodies, to which must be added 
 hydrated oxide of iron and organic matters frequently 
 found in clays, undoubtedly exercise an important effect, 
 on account of their jelly-like nature, which is largely due 
 to their powers of absorbing large quantities of water 
 mechanically. 
 
 IV. Mineral Composition of Clay. 
 
 Though clay results from the decomposition of felspars, 
 it has naturally often happened that the weathering action 
 has been arrested before such decomposition was completed. 
 Hence clays are often very complex in character, and contain 
 not only remains of felspar as such, but other constituents 
 of igneous rocks, such as quartz and mica. The presence of 
 such minerals, again, accounts for the existence in clays of 
 further " secondary minerals," such as caicite and gypsum, 
 formed by later chemical changes. 
 
 The following may be regarded as the commonest con- 
 stituents of clays : kaolin, quartz, mica, felspars, pyrites, 
 iron oxides, gypsum, caicite, dolomite, carbonaceous 
 matter, and water chemically combined and as mere 
 moisture. Many other minerals are often present in 
 small quantities. 
 
BEICK AND OTHEE CLAYS 
 
 151 
 
 The above-named minerals have already received con- 
 sideration in Chapter XI., and the following account of them 
 will therefore be confined to their effects upon the properties 
 of clay and the ware made therefrom, while the behaviour 
 of these constituents in the kiln when clays are " burnt " 
 will form the subject of the succeeding chapter. 
 
 1. Kaolin. — This mineral is referred to as kaolinite by 
 American writers, who confine the term " kaolin " to 
 clays consisting largely of this substance in an impure 
 condition. 
 
 Kaolin, which is found crystallised in very minute 
 hexagonal plates, has the composition Al2O3.2SiO2.2H2O, 
 a specific gravity of 2*2 to 2*6, and a hardness of about 2. 
 It results from the removal from orthoclase and other 
 felspars of the whole of the bases potash, soda, and lime, 
 and of about two-thirds of the silica, but it is never found 
 in a pure condition. Chemically kaolin is usually dis- 
 tinguished as that part of a clay which is soluble in hot 
 sulphuric acid and also in a solution of sodium carbonate. 
 
 2. Felspars. — Felspars are occasionally present in a 
 sufficiently undecomposed state to admit of their identifica- 
 tion when much magnified under the microscope. Orthoclase, 
 which is less liable to decomposition than the felspars 
 possessing lime and soda as bases, is more frequently found 
 than these latter varieties. 
 
 3. Mica. — Mica, particularly muscovite, which withstands 
 much weathering action, is often found in clays, but is by 
 no means universal. 
 
 4. Quartz. — Free quartz is often present in sufficient 
 quantity to seriously decrease the plasticity of clays. As 
 it does not absorb water, however, it decreases the shrinkage 
 which occurs when clays are dried. 
 
 5. Iron Pyrites. — This mineral and also marcasite are 
 fairly common in clays and are very objectionable. On 
 weathering these sulphides of iron undergo oxidation, with 
 
152 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 the eventual production of sulphuric acid, which leads to 
 the formation of gypsum and other undesirable minerals. 
 
 6. Iron Oxides. — Ferra (Fe203) results from the final 
 decomposition of most iron-bearing minerals, and it is to 
 this oxide that the clays, particularly when burnt, owe 
 their various colours. When hydrated, the oxide, then 
 known as limonite, gives a yellow or brownish colour, and 
 when anhydrous (without water), as haematite, it confers a 
 red colour on the clay in its natural state. Iron is also 
 found in a partially oxidised condition, as ferrous oxide 
 (FeO). 
 
 7. Calcite. — Carbonate of lime in this form results from 
 the action of carbon dioxide contained in percolating water 
 upon lime freed by the weathering of plagioclase felspars. 
 Carbonate of lime is also often present as intermixed chalk, 
 or as the shells of fossil organisms. If finely disseminated 
 through the clay it may be harmless or beneficial, but 
 more usually it occurs in lumps, or nodules, which must be 
 removed unless thoroughly crushed and intermixed. 
 
 8. Selenite. — Crystallised calcium sulphate, CaS04. 2H2O, 
 which has already been referred to as the clay worker's 
 " petrified water," results from the action of sulphuric acid 
 on lime, or carbonate of lime. Its presence in the clay is 
 objectionable for reasons given hereafter. 
 
 9. Dolomite. — Certain minerals containing magnesium, 
 such as biotite mica, lead to the production of dolomite — 
 calcium-magnesium carbonate — to which the remarks made 
 upon the presence of calcite may be applied. In making 
 certain bricks for furnace linings the presence of magnesia, 
 properly disseminated, is of value. 
 
 10. Carbonaceous Matter. — Vegetable and animal remains 
 are naturally not uncommon in clays, and often largely 
 account for the natural colours they possess. Usually such 
 matter is found in the form of leaves or twigs, or sometimes 
 as peaty layers. In some clays the organic remains are 
 
BEICK AND OTHEE CLAYS 
 
 153 
 
 present in such quantity that the combustion of this 
 material in the kiln is sufficient to provide the whole of 
 the heat necessary after firing has been started. This is 
 the case, for example, in the Oxford clay, as used at Peter- 
 borough for the manufacture of Fletton bricks, where the 
 material almost assumes the character of an oil shale. 
 The effect of such matter on the plasticity of clay has been 
 commented upon, but there are objections to, as well as 
 advantages in, its presence in the case of clays of low 
 fusibility, as will be shown. 
 
 V. Drying of Clays. 
 
 The drying of moulded clay as a preliminary to its 
 treatment in the kiln is an operation which requires con- 
 siderable care, as any defects there developed will probably 
 be accentuated on burning. 
 
 Drying is the removal of such water as will evaporate 
 at ordinary air temperatures, and the rate at which this 
 can be safely effected depends upon the size and configura- 
 tion of the moulded material, the amount of water it con- 
 tains, the quantity of colloidal constituents present, the 
 power of adhesion possessed by the particles, and the 
 porosity of the material. Clays in their natural state may 
 contain, without any special appearance of wetness, as 
 much as 30 per cent, of evaporable moisture, which 
 increases with their porosity, and as far as composition is 
 concerned., particularly with the amount of hydrated iron 
 oxide and carbonaceous matter present. 
 
 When this moisture is removed, a contraction, which 
 may exceed 5 per cent, of the original volume of the clay, 
 takes place, and since the exterior parts lose water more 
 quickly than the interior, the clay must be submitted to 
 some internal strain, and the rate of drying, which will be 
 a measure of the internal stresses involved, must not 
 
154 CHEMISTRY AND PHYSIOS OF BUILDING MATERIALS 
 
 exceed the adhesive power of the particles, or rupture 
 will result. 
 
 For this reason tensile tests on dried unburnt clay are 
 often made in order to gain an insight into the comparative 
 power of different clays of resisting strains produced in 
 drying. These tests are carried out in the same manner 
 as similar tests upon cements, which will be referred to 
 under this heading. The results of such tests show that 
 the clays capable of resisting the largest strains are those 
 which contain particles which vary in size. This is true 
 generally of binding materials in which graded aggregates 
 are found to be stronger than wholly j&ne or wholly coarse 
 particles. 
 
 Colloidal bodies part with water extremely slowly, as 
 they form therewith a kind of emulsion. Their presence 
 also, by decreasing the general porosity of the material, 
 retards the evaporation of water not actually entangled in 
 such bodies. The presence of large quantities of non- 
 absorbent minerals, such as quartz, much increases the rate 
 of loss of water on exposure, and though clays of this 
 character possess low tensile strength, inasmuch as the 
 shrinkage which they undergo is small, drying may be 
 safely allowed to proceed in them with greater rapidity. 
 Though the washing and subsequent drying of clays is 
 necessary, generally speaking, certain clays which are 
 quarried in a dry state may be reduced to powder and 
 moulded directly in suitable machines. Pressed bricks, such 
 as Flettons, are produced in this manner, which is obviously 
 exceedingly economical when practicable. 
 
 VI. Fusibility of Clays. 
 
 The fusibility of a clay, upon a knowledge of which 
 correct firing must be largely based, is dependent upon its 
 composition and fineness of grain, and it is upon the 
 
BEIOK AND OTHER CLAYS 
 
 165 
 
 temperature of fusion, coupled with considerations of 
 colour, that the acceptance or rejection of a clay for a 
 particular purpose must chiefly rest. Clays for the pro- 
 duction of china, terra cotta, earthenware, stoneware, fire- 
 bricks, common bricks, slips for glazes, and other purposes 
 naturally differ much in composition and mode of treat- 
 ment. It is only possible here to present some general 
 facts connected with the physical and chemical changes in 
 clay burning, but since an endeavour will be made to deal 
 with all the minerals of importance likely to be present, 
 given the analysis of any particular clay, some knowledge 
 as to its behaviour will, it is hoped, be obtainable. 
 
 1. Combinations Causing Fusion. — The melting point of a 
 clay is determined by a very complex set of conditions. 
 Certain compounds invariably confer this property and are 
 known as fluxes, and the most important of these are the 
 non-silicate compounds of the bases potash and soda. The 
 chemical changes which occur in " burning " often result in 
 the production of new substances which have lower melting 
 points than the orignal constituents, and no doubt largely 
 for this reason clays of fine grain melt more readily than 
 those composed of coarse particles, for the smaller the 
 particles the more readily will reaction take place between 
 them. 
 
 When the more infusible minerals unite to form com- 
 pounds possessing lower melting points the proportions in 
 which such minerals are present naturally influence the 
 resulting temperature of fusion. Thus both lime and silica 
 are individually quite infusible at any kiln temperature, but 
 when heated together they form fusible silicates. In a 
 certain proportion the most fusible silicate will be produced, 
 but if either the amount of lime or silica be increased less 
 fusible compounds or possibly uncombined lime or silica 
 will result. It will thus be seen that the fluxing action 
 of any ingredient is not by any means necessarily an 
 
156 CHEMISTRY AND PHYSICS OE BUILDING MATEEIALS 
 
 individual property to be assessed in proportion to the 
 amount of such ingredient present. 
 
 Similarly the oxides of iron, aluminium, and magnesium, 
 and also the carbonates and sulphates of these metals, are all 
 quite infusible individually, but in the presence of silica they 
 may form fusible silicates. The amounts of lime, magnesia, 
 and iron oxides are usually small as compared with silica, 
 hence these compounds may be generally rightly regarded 
 as fluxes, and since silicates of iron melt at a lower 
 temperature than those of lime or magnesia, iron is a more 
 powerful flux and its presence in quantity often precludes 
 the use of clay for burning. 
 
 2. Mixtures of Fluxes. — When two substances are melted 
 together the melting point of the mixture is usually much 
 lower than that of either of the substances alone. Fluxes 
 have thus the power not only to help the general fluidity of 
 the material owing to their molten condition, but, as it 
 were, to induce fusion in other bodies to some extent, and, 
 further, by the increased freedom of molecular motion which 
 they enjoy as liquids they promote chemical actions which 
 in their absence might not be able to take place. 
 
 3. Molecular Proportion and Fusion. — Eichter^ has endea- 
 voured to show that the molecules of all fluxes when 
 present in small quantities have an equal effect in pro- 
 ducing fusibility : that is, for example, that one molecule of 
 lime (CaO), i.e., 56 parts of weight, would lower the melting 
 point as much as one molecule of ferra (FeaOs), i.e., 160 parts 
 by weight, or one molecule of potash (K2O), i.e., 94 parts by 
 weight. It is known that the freezing and boiling points 
 of solutions are equally altered by molecules of different 
 compounds, and therefore this experimenter's conclusions 
 are not unlikely to be well-founded. 
 
 Assuming the truth of the above contention, the conver- 
 sion of the iron in a clay from the ferric to the ferrous 
 
 ^ Beferences will be found in Eies' book previously referred to. 
 
BEICK AND OTHEE CLAYS 
 
 157 
 
 condition, that is, from Fe203 to FeO, will, as pointed out by 
 Eies, double its effective amount, since one moleeule of Fe203 
 will form two molecules of FeO. Such a change may be 
 brought about by an undue exclusion of air from the kiln 
 on burning owing to but partial combustion of the fuel 
 resulting in the formation of carbon monoxide, thus : — 
 
 FeaOg + CO = 2FeO + CO2 
 
 The above forms an interesting example of the direct 
 practical bearing of what may appear a somewhat abstruse 
 chemical consideration. 
 
 4. Stages of Fusion. — Ries classifies the stages of the 
 melting of clays into: (1) Incipient fusion; (2) vitrification; 
 (3) viscosity. The stage to be aimed at is to some extent 
 dependent on the ware to be produced ; in common bricks, 
 for example, incipient fusion is usually sufficient, but in the 
 case of stoneware, vitrification must be attained. Viscosity 
 is to be avoided, since the material naturally loses its shape 
 when it reaches the temperature initial to liquefaction. 
 
 Though no very definite line of demarcation can be 
 drawn between these stages, their recognition is of value 
 because upon the temperature intervals between them the 
 ease or difficulty of burning a given clay depends. 
 
 The above writer points out that in extreme cases 
 incipient fusion and viscosity may be separated by so small 
 an interval as 24° G. Such a condition, which might be 
 expected in a clay very rich in potash and soda, iron or 
 lime, would involve extreme difficulty in correct firing and 
 almost certainly result in the production of under-burnt 
 (slake-baked) materials in the endeavour to avoid the loss 
 which attaining the viscosity temperature would involve. 
 
 In good classes of ordinary clays three or foar times this 
 range of temperature may be looked for, while in fireclays, 
 though incipient fusion takes place at about 1,300° C.,the pro- 
 duction of viscosity requires a temperature of over 1,600° C. 
 
CHAPTER XV 
 
 CLAYS (continued). — kiln reactions and the properties 
 
 OF BURNT CLAYS 
 
 I. Kiln and Subsequent Behaviour of Minerals. 
 
 An introduction to the problems connected with burning 
 clay has formed the subject of the preceding section in 
 Chapter XIV. The probable changes which take place in the 
 various components of clay in the kiln must be also con- 
 sidered, and such changes will be arranged as far as may 
 be in the order in which they seem likely to occur, though 
 it will be evident from the remarks upon fusibility that 
 no definite lines of demarcation can be expected for such 
 re-actions. 
 
 1. Compounds of Ammonia. — When nitrogenous organic 
 matters decay out of contact with air, various salts of 
 ammonia are formed on the application of heat. These 
 compounds are, like those of potash and soda, powerful 
 fluxes, but they are ail easily volatilised, and if present in 
 clay they are expelled as gases before they can produce any 
 effect in promoting fusion. 
 
 2. Water. — Dried clays often contain 10 per cent, of water 
 chemically combined and, therefore, incapable of evapora- 
 tion. Such water is contained in carbonaceous matter, 
 limonite (hydrated ferric oxide), gypsum, kaolin, sodium 
 sulphate and carbonate, mica, and sulphate of iron, pro- 
 duced by decomposed pyrites. This water, which is all 
 finally expelled, is liberated at very different temperatures. 
 From carbonaceous matter and such compounds as limonite 
 
KILN EEACTIONS— PEOPERTIES OF BUENT CLAYS 159 
 
 and gypsum, it is evolved at temperatures not much 
 exceeding 100° C, whereas kaolin and mica must be heated 
 to redness (600° or 700° C.) before such expulsion occurs. 
 Since this water is evolved as steam, firing must be con- 
 ducted with special discretion through the ranges of its 
 most abundant escape, as otherwise the ware may be 
 injured in the same manner as by too rapid air-drying. 
 
 During the escape of this steam it is very important that 
 an efficient draught be maintained to prevent the forma- 
 tion of sulphuric acid from the pyrites, as explained in 
 Chapter VIII. 
 
 3. Carbonaceous Matter. — All organic matters in clay 
 undergo in the kiln decomposition and distillation similar 
 to that described as taking place when coal is heated, and 
 an oxidising atmosphere, that is, efficient supply of air, is 
 most necessary during such distillation. 
 
 Carbon itself is quite non-volatile and infusible, and in 
 the absence of air may be heated indefinitely without 
 change ; hence even the highest temperatures will fail^ to 
 remove it in a closed kiln, and the discolouration thus pro- 
 duced in the ware might be very serious. Much greater 
 evils, however, may result from such incomplete combus- 
 tion. The tarry matters distilled from such sources may, 
 if unoxidised, be unable to pass out through the pores of 
 the clay before surface vitrification has taken place, par- 
 ticularly in the case of clays possessing low melting points. 
 Such matters will then become permanently enclosed, and 
 from such ware used in a fractured condition (as, for instance 
 in the case of half bricks in walling) these tarry substances 
 will be likely to exude and to find their way through plaster 
 and decorations. It is hardly necessary to point out the 
 importance of attention to such considerations as these 
 when mural painting or other elaborate forms of decorative 
 treatment are in prospect. 
 
 4. Magnesium Carbonate. — Magnesium compounds are 
 
160 CHEMISTHY AND PHYSICS OF BUILDING MATEEIALS 
 
 not usually found in clays in quantities much exceeding 
 1 per cent., unless the material is distinctly dolomitic. 
 Carbonate of magnesia decomposes into magnesia (MgO) 
 and carbon dioxide at a much lower temperature than is 
 necessary to effect a similar decomposition in carbonate 
 of lime. 
 
 Eecent experiments have shown that magnesia and lime 
 are not at all similar in their effects upon burnt clays. 
 Magnesia does not appear to exert the bleaching action 
 upon the colour of the ware, nor to produce sudden vitrifi- 
 cation characteristic of calcareous clays ; it seems rather to 
 separate the points of incipient fusion and viscosity, and to 
 counteract any tendency towards warping. 
 
 No explanation of these characters seems to be forth- 
 coming. Possibly they are due to the less basic character of 
 magnesia, which should result in a lesser tendency to com- 
 bine with silica than is displayed by lime. The observed 
 effects of its presence are certainly such as would be 
 expected if this base remained uncombined. 
 
 5. Magnesium Sulphate. — This salt, unlike calcium sul- 
 phate, is very soluble in water and is, therefore, hardly 
 likely to be found in washed clay. It may, however, be 
 produced in the same manner as calcium sulphate (see 
 p. 161). Its presence is likely to result in efflorescence. 
 
 6. Calcium Carbonate. — Ordinary clays seldom contain 
 more than 3 or 4 per cent, of carbonate of lime, though in 
 many marls the amount is much higher, and clays contain- 
 ing as much as 20 per cent, have been successfully employed 
 for brickmaking.^ 
 
 The state of division of this compound is of vital import- 
 ance in considering the percentage permissible. When 
 heated, evolution of carbon dioxide begins at about 400° C, 
 
 1 "The Clays of Alabama." H. Ries. Geological State Bulletin, 
 U.S.A. 
 
KILN REACTIONS— PEOPERTIES OF BURNT CLAYS 161 
 
 but the expulsion of this gas and the consequent con- 
 version into free lime (CaO) is probably incomplete below 
 950° C. 
 
 The objection to free lime in burnt clays is due to the 
 great heat and consequent disruption caused when slaking 
 occurs. In minute fragments partial combination with 
 silica may occur, and the porosity of the ware is usually 
 sufficient to admit of the expansion of the free lime with- 
 out damage, while the local rise of temperature is too 
 slight to be destructive ; but when particles of any size are 
 present the heat and expansion resulting from the access 
 of water in any moist situation have been known to cause 
 disruption sufficient not only to split and shell brickwork, 
 but to throw a wall built of such defective bricks out of 
 the perpendicular. 
 
 Lime has a bleaching effect on the colour of well-fired 
 bricks. This is probably due to the withdrawal of some of 
 the iron oxide with silica to form complex silicate minerals. 
 
 7. Calcium Sulphate. — This objectionable compound may 
 be present in the original clay as a secondary mineral, as 
 explained, or may be formed owing to the action of sul- 
 phuric acid resulting from the weathering of pyrites or 
 marcasite upon carbonate of lime. Another possible source 
 of calcium sulphate is use of water possessing much 
 permanent hardness for clay washing. 
 
 Though clay may be absolutely free from sulphate of 
 lime, this compound may yet be produced in the kiln, either 
 due to the decomposition of iron pyrites contained in the 
 clay, when the formation takes place in a similar manner to 
 that which occurs on weathering, or due to the presence of 
 sulphur compounds in the coal used for firing. 
 
 This latter source of calcium sulphate often fails to 
 receive the attention it deserves. Coal has been shown to 
 contain varying amounts of sulphur, usually in the form of 
 iron pyrites (Chapter IX.), and when burnt the sulphur 
 
162 OHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 therein is converted into sulphur dioxide (SO2) gas. In the 
 presence of air and moisture sulphuric acid is produced, 
 which acts upon lime or carbonate of lime in the heated 
 clay, as follows : — 
 
 CaO + H2SO4 = CaSOi + H2O 
 CaCOa + H2SO4 = CaS04 + H2O + CO2 
 
 In the absence of water it is doubtful whether any action 
 between lime and oxidised sulphur takes place, hence the 
 importance of guarding against a stagnant atmosphere in 
 the kiln when water is being evolved. 
 
 Coals used for firing should be submitted to an analysis 
 for sulphur, and only such varieties used as contain but 
 small quantities of this element. 
 
 The objection to sulphate of lime lies in the fact that it 
 produces efflorescence. Slightly soluble in water, it finds 
 its way in solution to the surface of the material exposed to 
 a moist atmosphere, and when evaporation takes place, 
 owing to heat or dryness, it forms an unsightly salt-like 
 incrustation, which constantly repeated removal can alone 
 at last eradicate. 
 
 8. Ferrous Oxide and its Compounds. — Iron is found in 
 clay partially oxidised, that is, in the ferrous condition, and 
 also fully oxidised as ferric oxide. 
 
 Ferrous oxide (FeO) never occurs uncombined, but is 
 often found in small quantities in combination with carbon 
 dioxide as carbonate of iron (FeCOs), which is decomposed 
 at a low temperature with the momentary formation of 
 FeO, which, in the presence of a good air supply in the 
 kiln, is oxidised to Fe203 ; thus 2 FeO + 0 = Fe208. 
 
 In the absence of sufficient air, however, its tendency 
 will be to combine with silica to form ferrous silicate — 
 
 FeO + SiOa = FeSiOa 
 
 Since silicate of iron is easily fused, ferrous iron is especially 
 liable to act as a flux in clays. 
 
KILN EEAOTIONS— PEOPEETIES OF BUENT CLAYS 163 
 
 An intermediate stage of oxidation between ferrous and 
 ferric oxides is known, in which one molecule of each of 
 these oxides is combined to form a compound FeO.Fe203 
 or FeaPi. 
 
 This oxide is black and it may be produced in burnt 
 clay by a premature cessation of the oxidising process 
 due to rapid heating, if this causes incipient fusion of the 
 outer layers of the material, while ferrous oxide still exists 
 in the interior. The black cores often found in ill-burnt 
 bricks are generally due to the presence of this inter- 
 mediate oxide, though often erroneously attributed to 
 carbon. As this oxide is quite insoluble no ill effects 
 similar to those to be expected from enclosed tarry matters 
 need be feared from it. 
 
 The presence of carbonaceous matter naturally tends to 
 keep the iron in the ferrous condition, as it itself absorbs 
 the oxygen in the kiln atmosphere during its combustion. 
 
 9. Ferric Oxide. — Present in a hydrated state as limonite, 
 or anhydrous, as haematite, this oxide (FeaOa) is often 
 abundant in clays, and accounts almost entirely for the 
 colour of the burnt ware. The colour increases in intensity 
 in proportion to the amount of this oxide present ; 2 to 3 
 per cent, result in a yellow tint, 4 or 5 per cent, will pro- 
 duce a red tint, but the actual colour obtained will be 
 modified by the presence of other compounds, particularly 
 by lime, and, in a lesser degree, by alumina, which, by 
 forming with the iron oxide less highly coloured compounds, 
 exert a bleaching action upon the ware. 
 
 Iron in a fully oxidised state, as Fe203, does not combine 
 directly with silica, and thus its fluxing power is negligible. 
 This is only true, however, if it does not undergo reduction 
 (de-oxidation), which may be brought about by insufficient 
 air in the kiln atmosphere, as explained under the section 
 on Fusibility of Clays in the last chapter. 
 
 At a high temperature also decomposition may take place 
 
 B.M. 
 
 M 
 
164 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 in the presence of silica, resulting in the liberation of 
 oxygen, which may cause blistering, and the ferrous oxide 
 which results then combines with the silica, forming a flux, 
 as already explained — 
 
 FeaOa + SiOa = SFeSiOa + 0 
 
 10. Iron Pyrites. — The sulphides of iron are, in the 
 absence of oxygen, very stable, even when highly heated, 
 but in an oxidising atmosphere they lose half their sulphur 
 at a red heat and the remainder at a temperature approach- 
 ing a white heat. The products of such decomposition are 
 the oxides FeaOs and SOa. The conversion of the gas SOa 
 into sulphuric acid, and its action upon lime, has already 
 been explained. If iron pyrites occurs in the clay in pieces 
 of any size its decomposition will be attended with disruption 
 not only due to the evolution of gas but because the oxide 
 of iron formed is greater in volume than the original pyrites. 
 
 11. Potash and Soda. — Potash and soda (KaO and NaaO) are, 
 when present, always found in combination as silicates, 
 chlorides, sulphates, carbonates, or phosphates. The silica 
 compounds are very infusible. Orthoclase felspar, for 
 example, melts at about 1,200° C, and mica remains unfused 
 even at 1,400° C. Other compounds of these bases, however, 
 have comparatively low melting points, and act as powerful 
 fluxes, as already stated. Though the presence of such 
 compounds in quantity precludes the use of clays for burn- 
 ing, a small amount is often advantageous, since this, on 
 melting, frits the less fusible minerals together. The 
 molten salts of these bases are readily attacked by silica 
 with the formation of silicates. Thus in the case of sodium 
 carbonate the reaction may be given as : — 
 
 NaaCOs + SiOa = NaaSiOs + COa 
 
 If potash and soda are present as soluble (non-silicate) 
 compounds, even in very minute quantities, it is most 
 
KILN EEACTIONS— PEOPEETIES OF BURNT CLAYS 165 
 
 necessary that they should be converted into silicates as 
 above shown, since otherwise they will undoubtedly give 
 rise to efflorescence, the formation of which has been 
 referred to as also due to sulphate of lime. 
 
 12. Summary of Temperature Changes. — From the above 
 attempted outline of the behaviour of compounds in the 
 burning of clay it will be evident that many of the changes 
 enumerated must go on simultaneously or be dependent 
 upon the fulfilment of certain conditions. Under this 
 reservation, and even then, doubtless, open to some criti- 
 cism, the following changes may perhaps be considered to 
 take place with advancing kiln temperature : — 
 100° C. Volatilisation of certain compounds of ammonia 
 and expulsion of water from some sodium salts. 
 200° C. Loss of water by calcium sulphate, limonite, car- 
 bonaceous matter, and in part from kaolin. 
 800° C. Carbonates of magnesium and iron begin to 
 decompose. 
 
 400° C. Above decomposition complete. Calcium carbonate 
 begins to decompose, evolution of water from 
 kaolin and carbonaceous matter continues. 
 
 500° C. Ferrous oxide in presence of air oxidised to ferric 
 oxide. SO2 from furnace gas acts on lime in 
 presence of moisture and air. 
 
 600° C. Above changes continue. Organic matter under- 
 goes combustion. 
 
 700° C. Iron pyrites decomposed with combustion of half 
 its sulphur. Dehydration of kaolin complete. 
 
 800° C. Sodium chloride and sodium carbonate melt. 
 
 900° C. Potassium carbonate and sodium sulphate melt. 
 
 Iron pyrites entirely burnt to Fe203. Expul- 
 sion of CO2 from calcium carbonate complete. 
 Carbon from carbonaceous matter burnt away. 
 
 1,000° C. Ferric oxide attacked by silica, forming ferrous 
 silicate ? 
 
 M 2 
 
166 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 1,100° C. Calcium and sodium sulphates decomposed into 
 free bases and SO3. Melting point of ordinary 
 brick-clays. 
 
 1,200° C. Orthoclase felspar melts. Vitrification of more 
 refractory clays. 
 
 II. — The Eemoval of Defects in Clays. 
 
 Where clays of variable composition are to be found in 
 one brick-field the proportions of certain constituents which 
 may be unsuitable in a single clay may often be advan- 
 tageously modified by making suitable mixtures with the 
 clay from other workings. 
 
 Excess of soluble salts of potash and soda may be some- 
 times removed by prolonged weathering, though this is not 
 an attractive process commercially. 
 
 Eflorescence due to the presence of calcium or magnesium 
 sulphate may be to some extent alleviated by the addition 
 to. the clay of barium carbonate before burning. This 
 compound is found as the mineral witherite (BaCOs), which 
 much resembles calcium carbonate (CaCOa), but is not 
 decomposed by heat. In the kiln it reacts with calcium 
 sulphate (or magnesium sulphate) as follows : — 
 
 CaS04 + BaCOa = BaS04 + CaCOg 
 
 The barium sulphate (BaS04) thus formed is quite insoluble, 
 and hence does not give rise to efflorescence in the finished 
 ware. The amount of witherite necessary may be calculated 
 from the amount of calcium sulphate which would otherwise 
 be present, but excess must be used, as the whole does not 
 come into contact with the calcium sulphate. Witherite 
 further reacts with sulphur dioxide, air and moisture, 
 forming sulphate BaSOi, and thus helps to prevent the 
 action of kiln gases upon the lime compounds. 
 Barium chloride (BaCl2) has been employed in place of 
 
KILN EEACTIONS— PEOPERTIES OF BUENT CLAYS 167 
 
 the carbonate because, being soluble, it is more easily 
 disseminated through the clay ; but since it produces soluble 
 deliquescent calcium chloride, which remains in the burnt 
 material, it merely removes one objection to add another. 
 Its reaction upon calcium sulphate is as follows : — 
 
 BaCl2 + CaS04 = BaSO* + CaCl2 
 
 III. — Examination and Tests upon Clay Ware. 
 
 Nearly all the tests described in Chapter XIII., in 
 reference to building-stones, are also applicable to bricks 
 and other materials composed of burnt clay ; but few of such 
 tests are usually carried out, and some of them would have 
 but little commercial value. 
 
 Mechanical tests upon bricks are usually confined to the 
 determination of crushing strength, but as bricks do not 
 bear stresses individually but in connection with a vast 
 number of interspaces more or less filled with mortar, the 
 results of experiments upon single bricks do not give much 
 indication of the strength of brickwork. The results of a 
 series of tests upon the crushing strength of brick piers, 
 carried out by the Eoyal Institute of British Architects,^ 
 have shown that the quality of the workmanship in the 
 building of brickwork is capable of producing the most 
 marked differences in the strength of brick erections, so that 
 a generous factor of safety or very rigid supervision in 
 building must be allowed for. 
 
 Many of the defects in bricks and tiles cited as possible 
 owing to faulty composition or firing are open to visual 
 detection, and enough has been said to show the value of 
 chemical analysis or at least of the determination of the 
 presence, amount, and dissemination of certain possible 
 constituents. 
 
 1 R.I.B.A. Journal, April, 1896 ; December, 1896 ; December, 1897. 
 
CHAPTER XVI 
 
 PLASTERS AND LIMES 
 
 I. Binding Materials Classified. 
 
 Under the title of " binding materials " are to be included 
 some of the most important and interesting substances con- 
 nected with building products, namely, the various limes, 
 plasters, and cements which to so large an extent deter- 
 mine the permanency of any structure. These substances, 
 presented as they are to the user in the form of powder, 
 do not admit of the direct judgment as to their characters 
 which is possible in the case of stones and bricks; and 
 it is, therefore, the more necessary to carefully consider 
 their chemical compositions and reactions in preparation 
 and use. 
 
 Binding materials may be classified according to their 
 composition, uses, and the strength they display as cement- 
 ing media, and may be briefly described as follows : — 
 
 (a) Plasters. — Though fat limes are used for plaster work, 
 all plasters proper consist mainly of sulphate of lime in a 
 dehydrated condition, and set owing to the absorption of 
 water. 
 
 (b) Limes. — All limes are characterised by containing 
 free lime (calcium oxide), and slake on the addition of 
 water. The non-hydraulic varieties contain little else, and 
 harden largely by mere mechanical drying. The hydraulic 
 limes contain in addition silicates which, when decomposed 
 by water, set in a manner similar to that observed in 
 cements. 
 
 (c) Cements. — All cements are distinguished from limes 
 
PLASTEBS AND LIMES 
 
 169 
 
 by the fact that in them excess of lime is absent, and 
 that since no slaking action takes place with water they 
 must be finely ground before use. The most important 
 cements are formed artificially by heating together chalk 
 and clay. 
 
 (d) Pozzuolanas. — These bodies are siliceous and argil- 
 laceous materials which develop hydraulic properties when 
 mixed with lime. They may be natural volcanic products, 
 or slags produced in various industries. 
 
 The following tabular arrangement will make the rela- 
 tions between these materials clearer : — 
 
 Binding Materials 
 
 Plasters 
 I 
 
 Limes 
 
 Cements 
 
 Plaster Flooring 
 of Paris Plaster 
 
 Non-Hydraulic 
 
 Natural 
 
 Roman Natural 
 Portland 
 
 I 
 
 Hydraulic 
 
 Pozzuolanas 
 
 Artificial 
 Portland 
 
 I I 
 Natural Artificial 
 
 III I I 
 
 Fat Lean Dolomitic Feebly Strongly 
 
 Hydraulic Hydraulic 
 
 Selenitic Grappiers 
 
 I I 
 Clay Slag 
 
 II. Plastees. 
 
 Plasters are essentially composed of sulphate of lime, and 
 are prepared from the mineral gypsum (GaS04.2H20) which 
 is found in rocks of all ages, but in this country chiefly in the 
 Triassic formation. Gypsum often occurs remarkably free 
 
170 CHEMISTEY AND PHYSICS OP BUILDING MATEEIALS 
 
 from impurities ; but is sometimes discoloured by iron 
 which, in the form of oxide, remains in the plaster prepared, 
 and thus decreases its value. 
 
 1. Plaster of Paris, — When gypsum is heated to a tem- 
 perature between 120° and 130° C. it loses three-quarters of its 
 water of crystallisation, and the partially dehydrated sul- 
 phate formed is known as " plaster of paris," which, on the 
 addition of water equivalent to that removed, re-crystallises 
 as gypsum and thus " sets." 
 
 Gypsum. Plaster of Paris. 
 
 2(CaS04.2H20) = 2CaS04.H20 + SHaO. 
 
 2. Flooring Plasters. — When gypsum is heated to 163° C. it 
 loses, according to Le Chatelier, a further quantity of its 
 water, and at 194° C. is completely dehydrated. If maintained 
 for a long time above this temperature, or raised to a red 
 heat, the plaster becomes incapable of absorbing water in, at 
 least, any reasonable period, and is then said to be " dead 
 burnt." The power of absorbing water and setting is not, 
 however, lost after all water of crystallisation is expelled, 
 if heating be continued for a limited time at not too high a 
 temperature. 
 
 Gypsum so treated and subsequently finely ground forms 
 what is known as " flooring plaster," which sets slowly with 
 water, producing a very hard material. 
 
 3. Keene's and Similar Cements. — Keene's, Parian and 
 other plasters, which finish with a hard face, are made by 
 heating very pure gypsum to redness and soaking the 
 resulting dehydrated mineral in a solution of alum (for 
 Keene's) borax, sodium or potassium sulphate, or potassium 
 carbonate. The mineral is then heated a second time and 
 finely ground. 
 
 The quantity of alum or other salt taken up from the 
 solution is quite small, often forming much less than one 
 per cent, of the plaster, which is, therefore, essentially the 
 
PLASTERS AND LIMES 
 
 171 
 
 same in composition as flooring plaster. Some sugges- 
 tions as to the action of the salts taken up from the solutions 
 will be found in Chapter XIX. 
 
 By far the greater number of the many patent plasters in 
 use, such as Serapite and Asbestic plasters, owe their bind- 
 ing power chiefly to the above derivatives of gypsum. 
 
 III. Non-Hydraulic Limes. 
 
 The limes which fall under this heading have been 
 classified as fat limes, lean limes, and dolomitic limes. 
 Though each of these groups shows in typical examples 
 characteristic properties, it must be borne in mind that, 
 as previously emphasised, all natural materials show 
 gradations and merge one into the other ; but a study 
 of typical examples will enable a judgment to be formed 
 upon the qualities of such limes as may be found in 
 practice to possess intermediate compositions. 
 
 1. Fat Limes. — Ideal fat lime consists solely of calcium 
 oxide produced by the decomposition of calcium carbonate 
 (chalk) by heat — 
 
 CaCOg = CaO + GO, 
 
 Although in practice pure calcium carbonate is unobtain- 
 able in quantity, certain stones, such as those used for 
 preparing lime used for the manufacture of calcium carbide, 
 approach this ideal very closely. The usual impurities 
 present consist of alumina, iron oxides, silica and magnesia, 
 and a lime is classed in this group when such total 
 impurities estimated after " burning " do not exceed 5 per 
 cent, of the material. 
 
 The specific gravity of pure lime, although it varies to 
 the extent of about 0*06 per cent, according to condition of 
 burning, may be taken as 3*1, to which the specific gravity 
 of fat limes in the lump should therefore approximate. 
 
172 CHEMISTEY AND PHYSIOS OF BUILDING MATEEIALS 
 
 The chief characteristic of fat lime is the great develop- 
 ment of heat which occurs when water is mixed with it, 
 and the large expansion which the material undergoes on 
 hydration. Indeed, before the discovery of gunpowder 
 lime cartridges were used for blasting purposes on account 
 of this property. 
 
 This slaking action is represented as follows : — 
 
 CaO + H2O = CaOaHa 
 
 So sudden and violent is this action that the hydrated 
 lime produced on the direct addition of water always forms 
 a friable mass quite devoid of cohesion, but under suitable 
 conditions this hydrate may crystallise, when its mechanical 
 properties will be very different. 
 
 Fat limes are only suitable for plastering, and their 
 use for making mortar is quite inexcusable, since they 
 possess no setting powers, and what hardening they 
 undergo is due to mere mechanical drying, and in a very 
 small degree to the formation of a thin surface layer of 
 calcium carbonate owing to absorption of carbon dioxide 
 from the air. 
 
 Sand mixed with fat limes should always be clean and 
 sharp, for the presence of clayey matters by decreasing 
 porosity will prevent the progress of such mechanical 
 hardening and carbonating as would otherwise take place. 
 
 2. Lean Limes. — Lean, or poor, limes are merely fat limes 
 containing additional quantities of the impurities cited 
 above, and show only some 80 per cent, of calcium oxide on 
 analysis. Their use should therefore be restricted to the 
 necessities of certain local conditions. These impurities, 
 which, it will be seen later, must be regarded in another 
 light in other classes of limes, are not in those under this 
 heading sufficiently well distributed to admit of the develop- 
 ment of any hydraulic properties therefrom, and for this 
 reason are an actual objection in burning owing to the 
 
PLASTEES AND LIMES 
 
 173 
 
 danger of the production of inert material by local fusion. 
 Lean limes are thus always liable to be underburnt, and 
 therefore to contain inert carbonate of lime as an additional 
 impurity. 
 
 These limes are usually difficult to work, absorb water 
 less violently than fat limes, and are greyish in colour, 
 whereas good fat limes are white. 
 
 3. Dolomitic Limes. — Dolomitic or magnesian limes are 
 those which contain a considerable proportion of magnesia. 
 As has been pointed out, dolomitic stones usually contain 
 large proportions of this base, and these limestones form 
 the source of this group of materials. 
 
 Magnesia is a much less active base than lime, hence 
 dolomitic limes slake more slowly than fat limes, and they 
 also increase less in bulk and are less workable and plastic 
 than the latter. 
 
 Although these limes acquire but little strength when 
 used in mortars, they appear to be stronger than fat limes, 
 probably owing to the lesser amount of mechanical disruption 
 which takes place in the mass on slaking. 
 
 The decomposition of magnesium carbonate in the pro- 
 duction of these limes resembles that of calcium carbonate, 
 but takes place at a much lower temperature. The equation 
 is as follows : — 
 
 MgCOa = MgO + CO2 
 
 Eckel ^ quotes tests which appear to show that, although 
 dolomitic limes when mixed with sand as mortars are not 
 at first superior in strength to ordinary fat limes, their 
 strength increases with age till after one year they are 
 twice as strong. Briquettes made up of 1 part of lime to 2 
 parts of sand showed a tensile strength after one year of 
 
 1 Eckel, " Cements, Limes, and Plasters." John Wiley & Sons, 
 1905. 
 
174 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 45 pounds for fat lime and 93 pounds for dolomitic lime 
 per square inch. 
 
 4. Strength of Lime Mortars. — The strength of non- 
 hydraulic limes in use depends much upon the character 
 and proportion of the aggregate used with them, but by no 
 means decreases in proportion to the aggregate added; in 
 fact, tests are extant which show greater strengths for 1 to 
 3 than 1 to 2 mixtures, and in Sabin's results for 1 to 6 
 than 1 to 3 mixtures. Perhaps 30 pounds per square 
 inch may be regarded as about the tensile strength of 
 ordinary fat lime mortars, and the strength in compression 
 as about 5 times as great. 
 
 IV. Hydraulic Limes. 
 
 1. Characters. — The term "hydraulic" as applied to 
 binding materials has lost much of its original significance 
 which related to the power of setting under water, since 
 such materials also set, and have a much more extensive 
 use, in air. 
 
 Hydraulic limes and cements owe their characters to the 
 fact that silica and alumina, in the natural materials 
 from which they are made, enter into chemical combina- 
 tion with the lime formed on burning, which results in the 
 production of silicates and aluminates of lime. On the 
 addition of water these compounds are decomposed and 
 their previous mechanical division, which is necessary 
 for such decomposition, is effected by the free lime in the 
 case of hydraulic limes, and by grinding in the case of 
 cements. 
 
 The theories advanced to explain the setting of these 
 materials will be dealt with in Chapter XVIH. 
 
 2. Peehly Hydraulic Limes. — Limes under this heading 
 include the many varieties of grey stone limes used for 
 building work. They contain from 40 per cent, to as much 
 
PLASTEES AND LIMES 
 
 175 
 
 as 80 per cent, of uncombined lime, at which latter limit 
 their hydraulic properties are of a very weak description. 
 
 Chemical opinion is not unanimous as to the composition 
 of the compounds of lime with silica and alumina, to the 
 formation of which the subsequent development of hydraulic 
 properties is due. In the strongest hydraulic compounds, 
 lime, silica and alumina are present in such proportions as 
 would form the silicate 3CaO.Si02 and the aluminate 
 BCaO.AlaOa or 2CaO.Al203. The aluminate is generally 
 present in comparatively small quantity, and is only 
 necessary to admit, by its lower melting point, of the 
 formation of the silicate. Neglecting the aluminate and 
 calculating the proportion of silica and of lime in the 
 silicate, it will be seen that in a hydraulic lime in which 
 80 per cent, of free calcium oxide exists only some 5 per 
 cent, of silica present can be in combination. 
 
 3. Selenitic Limes. — Feebly hydraulic limes may be con- 
 siderably increased in strength by the addition of small 
 quantities of calcium sulphate. Limes so treated are said 
 to be selenitised " and are referred to as selenitic limes, 
 a designation derived from the mineral selenite, which is 
 crystallised hydrated lime sulphate. 
 
 The addition of this sulphate is usually made in the 
 form of some 5 per cent, of plaster of paris, but the 
 sulphate may be formed by the neutralisation of some 
 of the free lime by sulphuric acid, thus : 
 
 CaO + H2SO4 = CaSOi + H2O. 
 
 The increase in strength produced by this treatment 
 may be due to the retardation caused by a thin pelHcle of 
 the but slowly soluble sulphate upon the lime particles, 
 which thus obtain the water necessary for hydration much 
 more slowly, and, therefore, with much less mechanical 
 disruption when slaking takes place. This suggested 
 explanation is due to Schott, but no evidence that this 
 
176 CHEMISTEY AND PHYSIOS OF BUILDING MATERIALS 
 
 coating action really takes place has yet been brought 
 forward. Another explanation, based on the supersatura- 
 tion theory of Le Chatelier (Chapter XIX.), may be 
 possible. The actual increase in strength resulting from 
 selenitising the poorer qualities of hydraulic limes is 
 remarkable, and amply sufficient to repay such treatment. 
 From experiments carried out by Grant, it would appear 
 that the strength of mortars of lime and sand in various 
 proportions is, on an average, doubled by such treatment, 
 it has been shown, for example, that a mortar of 1 part 
 untreated lime to 3 parts of sand has almost the same 
 strength as one consisting of 1 part of the same lime 
 selenitised with 5 parts of sand. 
 
 Selenitic limes, or cements as they are often called, are 
 employed chiefly for plastering, but there seems to be no 
 reason why they should not be more extensively used for 
 ordinary building mortars. The objection is often advanced 
 that the sulphate of lime is soluble in water and thus 
 unsuitable for exposure. One thousand parts of water at 
 ordinary temperatures dissolve about 1| parts of slaked 
 lime and about 2 parts of sulphate of lime. This difference 
 in solubility is not great, and inasmuch as a selenitised 
 lime still contains 10 to 16 times as much free lime as 
 sulphate, such mortars would appear to be likely to lose 
 more free lime than sulphate by solution due to atmospheric 
 moisture. 
 
 The process of selenitising is confined to the feebly- 
 hydraulic limes, as the better classes of these limes and 
 the cements do not show improvement on the addition of 
 calcium sulphate, sufficient to Justify such treatment, and 
 may indeed be injured thereby. 
 
 4. Eminently Hydraulic Limes. — This somewhat cumbrous 
 title is applied to the better class of hydraulic limes which 
 contain, after burning, some 60 to 75 per cent, of calcium 
 oxide, partly in combination with silica and alumina. The 
 
PLASTEES AND LIMES 
 
 177 
 
 limestones from which such limes are prepared may be 
 taken to contain some 70 to 80 per cent, of calcium car- 
 bonate, some 13 to 17 per cent, of silica, and a variable 
 percentage of alumina and ferra, say 1 to 6 per cent, in 
 ordinary cases. 
 
 The ideal hydraulic lime would be that in which the 
 whole of the silica and alumina were in combination with 
 calcium oxide, this base being present in excess just suffi- 
 cient to cause complete disintegration of the silicate and 
 aluminate formed in burning, by the disruption due to its 
 slaking. 
 
 In practice it is not found possible to bring the whole of 
 the silica into combination, though such combination is 
 considerably assisted by the alumina and ferra present. 
 
 The best hydraulic limes thus contain a much larger 
 percentage of free lime than would appear to be the case 
 on the assumption that all the silica is present in the form 
 of the compound 3CaO. Si02 after burning. Thus an analysis 
 of blue lias lime, which belongs to this class, supplied by 
 Messrs. Nelson, of Bugby, shows 61 per cent, of CaO and 
 20 per cent, of Si02. If the relative weights of lime and 
 silica in the compound 3CaO.Si02 be calculated, it will be 
 observed that 61 per cent, of CaO requires about 22 per 
 cent, of SiOa for combination, which in the lime in question 
 would leave no free lime over for slaking action ; and since 
 this action does occur, a considerable percentage of the 
 silica must, after burning, be present in an uncombined 
 condition if the formula SCaO.SiOg is to be accepted. As 
 will be seen, however, in Chapter XVIII., the base and acid 
 oxide possibly form the compound 2CaO.Si02, and this 
 view certainly accords better with the proportions of the 
 constituents found in the best classes of hydraulic limes. 
 
 The well-known lime from Lyme Regis contains some 
 24 per cent, of silica, while the famous limes from Teil 
 (France) contain a similar quantity which, in the presence 
 
178 CHEMISTEY AND PHYSICS OF BUILDINa MATERIALS 
 
 of not too small a percentage of alumina, may therefore be 
 regarded as an indication of a lime of high quality. The 
 efficiency of the burning which such limes have undergone 
 may be judged by freedom from carbonate which evolves 
 the gas carbon dioxide when treated with an acid. 
 
 5. Grrappiers. — Although it would appear from the above 
 remarks that hydraulic limes are completely disintegrated 
 on slaking, this is not actually the case with the better 
 class of such materials. The reactions between the lime, 
 silica and alumina in the kiln result in the fusion of these 
 materials, and owing to the imperfect distribution of these 
 compounds, such fusion is found to vary much locally in 
 its completeness. In places, silica and alumina are found 
 combined with lime with but little intermixed free lime, 
 and here fusion has been too far advanced to admit of the 
 disintegration of such masses by the subsequent slaking of 
 surrounding lime particles, hence such fused masses remain 
 as lumps in the slaked product. These lumps, consisting 
 as they do chiefly of calcium silicate, form a valuable cement 
 when ground ; they are, therefore, separated and reduced 
 to powder, in which form they are known as grappier 
 cements. 
 
 This material resembles natural cement in its formation 
 and general characters, but as even the best varieties con- 
 tain 3 or 4 per cent, of entangled limestone which has 
 escaped decomposition, and as the grinding is not usually 
 carried out to a great degree of fineness, the material is 
 much inferior to Portland cement in strength. 
 
 V. Testing op Hydraulic Limbs. 
 
 1. Chemical Analysis. — It is obvious that the analysis of 
 limes from limestones which are natural products covering 
 wide areas, must often differ in a marked degree even for 
 products which may be placed in the same general category, 
 
PLASTEES AND LIMES 
 
 179 
 
 and further, that if comparable analyses are to be expected, 
 these must be made under comparable conditions. Limes 
 readily absorb water and carbon dioxide from the air when 
 exposed ; hence, unless analysis is possible immediately the 
 material is drawn from the kiln, the samples to be examined 
 should be at once selected and kept in stoppered bottles. 
 
 A great number of analyses of limes and limestones are 
 recorded in works upon cementing materials, but the 
 analysis of the stones is not of much interest to the user. 
 In examining the analysis of limes the completeness of the 
 burning may be judged by the amount of carbon dioxide 
 remaining, and the hydraulicity may usually be assessed by 
 the amount of silica present. 
 
 The following table of limes from the kiln will serve to 
 give an idea of the composition of the materials dealt with 
 in this section : — 
 
 
 (1) 
 
 1 Grey Stone 
 Lime, 
 Mersthara. 
 
 Blue Lias, 
 Eugby. 
 
 (3) 
 
 Lyme Regis 
 Lime. 
 
 (*) 
 
 Typical 
 Grappier 
 Cement. 
 
 Lime (CaO) 
 
 80-24 
 
 61-17 
 
 71-9 
 
 63-0 
 
 SUica (SiOi) 
 
 11-40 
 
 20-04 
 
 24-3 
 
 26-5 
 
 Alumina (AI2O3) . 
 
 
 4-97 
 
 3-7 
 
 2-5 
 
 Ferra (Fe^Os) . 
 
 j 4-60 
 
 6-10 
 
 
 1-5 
 
 Magnesia (MgO) 
 
 0-5 
 
 0-95 
 
 
 1-0 
 
 Carbon dioxide (CO2) 
 
 2-0 
 
 4-03 
 
 0-0 
 
 60 
 
 and water (HgO) 
 
 
 
 
 Alkalis (K2O and^NaaO) 
 
 1-25 
 
 1-08 
 
 CO 
 
 
 1 Authority : (1) Middleton ; (2) Messrs. Nelson ; (3) Blount and Bloxam • 
 (4) Le Chatelier. ' 
 
 2. Mechanical and Other Tests. — No very strictly organised 
 series of tests is demanded by users of hydraulic limes, who 
 are often content to regard any lime which is not termed 
 grey stone lime as necessarily eminently hydraulic. 
 
 Owing to the variable amount of iron which these limes 
 
 B.M. N 
 
180 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 contain, no very satisfactory evidence of quality can be 
 based upon colour, but specific gravity determination will 
 serve to distinguish these materials from Portland cement. 
 The average specific gravity for grappiers may be taken 
 as about 2*7, and for hydraulic limes as about 2-9, whereas 
 that of Portland cement is 3'1. 
 
 (a) Tensile and Compression Strength— The determination 
 of tensile strength as estimated by the force required to 
 produce rupture by pulling, is always given so prominent 
 a position among tests on binding materials that some 
 comment upon its value is called for, inasmuch as such 
 materials are never purposely submitted to tensile stresses 
 but are always used in compression. 
 
 Tests of materials under tension are always more reliable 
 and more easily carried out than tests under compression. 
 The apparatus necessary is less cumbrous and costly, and 
 accurate results are obtainable with smaller specimens. 
 These facts would, of course, not offer any excuse for 
 making tests which bear no relation to the practical use 
 of the materials. It has, however, been ascertained that 
 a fairly constant ratio exists in limes and lime mortars 
 between strength in tension and compression, and Eckel 
 places the compressive strength of hydraulic limes at five 
 to six times their tensile strength, in substantiation of 
 which he quotes experiments by Schoch on mortars com- 
 posed of 1 part of lime to 3 parts of sand. 
 
 Average Strength of good Hydraulic Limb Mortars. 
 
 
 Seven. Days. 
 
 Twenty-eight Days. 
 
 One Year. 
 
 In tension 
 
 In compression 
 
 64 
 356 
 
 100 
 683 
 
 299 
 1920 
 
 As an illustration of the strengths of feebly hydraulic 
 and selenitic limes Kirkaldy's results, given in detail by 
 
PLASTEES AND LIMES 
 
 181 
 
 Eedgrave/ may be cited. An average of the results of 
 experiments on common mortar in proportions of 1 to 2, 
 
 1 to 3, and 1 to 4 showed strengths of : in tension 24 pounds, 
 in compression 122 pounds, and in tension as a joint between 
 stock bricks 8 pounds, per square inch. In the case of 
 selenitic lime mortars of 1 to 4, 1 to 5, and 1 to 6, the 
 same lime selenitised showed, as an average of similar 
 experiments, strengths of : in tension 64 pounds, in com- 
 pression 285 pounds, in tension as a joint between stocks, 
 17 pounds per square inch. 
 
 Some tests by McKenna, quoted by Eckel, place the tensile 
 strength of certain grappier cements at about 650 pounds per 
 square inch neat after one year, which appears to bring 
 their strength nearly to full development. The addition of 
 
 2 parts of sand (1—2) seems to reduce the strength to a 
 little more than one-half of this amount. 
 
 I Redgrave, "Calcareous Cements: their Nature and Uses." 
 1 of lime to 2 of sand. 
 
 N 2 
 
CHAPTER XVII 
 
 CEMENTS 
 
 I. Relations between Limbs and Cements. 
 
 Cements differ from limes in that they are "burnt" at a 
 much higher temperature, which results in more effective 
 chemical combination between the acids and bases and the 
 production of semi-fused lumps. As a result, cements do 
 not slake with water, and must be ground to extreme 
 fineness in order to allow water to effect its full decom- 
 position before the material sets, after which any further 
 slaking action of water only takes place with extreme slow- 
 ness, and tends not towards further strength but disruption. 
 
 These building materials are very much superior to 
 even the best hydraulic limes, but the special plant 
 required for mixing, burning and grinding makes their 
 cost considerable. 
 
 Cements may be classified as natural and artificial. The 
 former, of which Roman cement is the best known repre- 
 sentative in this country,! ^re produced by^ the direct 
 burning of natural argillaceous stones, which usually 
 contain a considerable excess of the acid forming oxides, 
 silica, alumina, and ferra. The latter are practically com- 
 prised in Portland cement made from a mixture of chalk 
 and clay so proportioned that acids and bases are present 
 in quantities to admit of effective combination, in which 
 circumstances the greatest strength is obtained. 
 
 Chemically, then, the natural cements err in containing 
 
 » Some of the so-caUed Uas limes are really natural cements. 
 
CEMENTS 
 
 183 
 
 excess of acids, just as the hydraulic limes err in excess of 
 bases (free lime), and the relations between these three 
 classes may be made clear thus : — 
 
 ^^Geeatbst Stebngth.v^ 
 
 Excess of Bases. Excess of Acids. 
 
 Hydraulic Limes. Portland Cement. Natural Cements. 
 
 II. Natubal Cements. 
 
 1. General Characters. — These cements are prepared by 
 " burning " argillaceous limestones : that is, limestones con- 
 taining a proportion of clayey matter. The process of 
 burning is carried out at a much lower temperature than 
 in the case of Portland cement, and the semi-fused product, 
 or clinker, formed is much more friable and therefore more 
 easily ground. These cements set very rapidly, owing to 
 the large quantity of alumina which they contain. They 
 may be further distinguished from Portland cement by 
 their specific gravity, which seldom exceeds 2*8, and (unless 
 this is artificially disguised) by their colour, since they are 
 very ferruginous and thus possess a yellow or brown tint, 
 very different from the blue-grey colour associated with the 
 artificial product. Natural cements are not capable of 
 bearing much dilution with sand when used as mortars, 
 as great falling off of strength accompanies such additions. 
 
 Though now little used in this country, where their 
 employment is chiefly confined to repairs upon work where 
 strength is of no importance, or for work exposed between 
 tides when rapid setting is essential, these cements are 
 extensively manufactured in America and other countries, 
 where they largely take the place of our hydraulic limes. 
 For general use, in order to decrease the rate of setting, 
 plaster of Paris is often added, but it has been shown that 
 this addition, in the case of cements, if made in any 
 
184 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 quantity produces a considerable reduction in strength. 
 The maximum amount allowable in natural cements is 
 placed at about 1 per cent. 
 
 The classification of the natural stones used in preparing 
 these cements is not easy, as they present great variations 
 in composition. Their products, however, may be regarded 
 as represented by the following two groups. 
 
 2. Varieties of Natural Cements. — (a) Roman Cement. — This 
 material is prepared from ferruginous nodules containing 
 some 30 to 45 per cent, of clay, and is, perhaps, the best 
 known natural cement used in this country. It is charac- 
 terised by its rapidity in setting, and its brown colour. It 
 rapidly deteriorates on exposure to the atmosphere, and is 
 very liable to efflorescence after use. Medina, Whitby & 
 Atkinson's cements resemble Roman cement and have 
 similar uses. 
 
 (b) Natural Portland Cement. — This somewhat unfor- 
 tunate name is given to the product of certain natural 
 stones, the ingredients of which resemble in composition 
 those used in making Portland cement. Since, however, 
 their composition varies considerably, and also because the 
 " burning " is not effected in the complete manner adopted 
 in the case of real Portland cement, this natural product is 
 very inferior in strength to the artificial material. Eckel, 
 quoting from a report on the Belgium cement industry, 
 says in reference to such cement : " Cinders are often 
 added, changing it to a grey colour resembling Portland. 
 . . . This is the product which is purchased by unscrupu- 
 lous exporters and sold by them marked as Portland 
 cement." In fairness to the Belgian manufacturers, a 
 further quotation from the report, pointing out that brand 
 marks have been designed to protect purchasers who 
 take the trouble to make their acquaintance, should be 
 also cited. 
 
 The low specific gravity and the large proportion of 
 
CEMENTS 
 
 185 
 
 calcium sulphate necessary to decrease the rate of setting 
 should make cements of this character easily distinguishable 
 from Portland. 
 
 3. Strength of Natural Cements. — The study of a large 
 number of strength " curves " given in Johnson's " Materials 
 of Construction " seems to indicate that natural cements 
 rapidly increase in strength up to about six months, sub- 
 sequent to which but little improvement is observable. The 
 maximum tensile strength of neat American natural 
 cements appears to range between 300 and 500 pounds per 
 square inch, but it would not be advisable to adopt so high 
 a standard as a safe guide for many natural cements used 
 in this country. 
 
 The ratio of compressive to tensile strength is naturally 
 not easy to obtain satisfactorily in such variable materials, 
 but the average results of twenty-nine experiments made 
 by Sabin, on American cements, show a ratio very similar 
 to that given in the case of hydraulic limes, namely, about 
 5 to 1. 
 
 III. Portland Cement (Manufacture). 
 
 1. Introductory. — Not only is Portland cement the sole 
 representative of any importance belonging to the group 
 of materials known as artificial cements, but it far exceeds 
 in quality and scale of production all other hydraulic 
 materials. The cement, first manufactured in England and 
 named from a fancied resemblance to Portland stone, is 
 now made on a large scale in almost all civilised countries. 
 
 The Portland cement industry, which must be placed only 
 second to the iron and steel industry in respect to the 
 application of scientific method and the attainment of 
 accuracy and uniformity in production, owes its position to 
 a great extent to the rigorous demands of engineers for 
 material which shall comply with an exacting series of 
 
186 CHEMISTRY AND PHYSICS OP BTJILDINa MATERIALS 
 
 tests, and forms a useful object lesson as to what might be 
 achieved in other directions for materials were the value of 
 standardisation more widely appreciated. 
 
 If materials were valued and sold on the basis of the 
 characteristics which are sought for in them, such as strength, 
 permanency and protective power, instead of by the more 
 primitive standards of weight or bulk, very rapid industrial 
 advances in many manufactures might be looked for. 
 
 2. Details of Mamifacture. — The object aimed at in the 
 manufacture of Portland cement may be taken to be the 
 production of material consisting, to as great an extent 
 as is practically possible, of lime and silica in the propor- 
 tion represented by the formula SCaO.SiOa. The manu- 
 facture is carried out by the mixture and fusion of natural 
 calcareous and siliceous materials. 
 
 The substances employed to supply the lime are chalk 
 and sometimes limestone or marl, and to supply the silica, 
 clay and sometimes shale or even slate. These materials, 
 besides lime and silica, which are the preponderating con- 
 stituents, contain (1) alumina, which is a practical essential 
 as a fluxing agent to admit of the combination of the lime 
 and silica ; (2) magnesia and ferra, the influence of which 
 in small quantities is not important ; (3) combined sulphur, 
 which is not without its functions. 
 
 The chalk and clay — the usual materials employed — in 
 the proportion of about 3 to 1 are first mixed in mills 
 containing water by the aid of rotating vanes carrying 
 round iron drags, or in more modern practice when the 
 ingredients are both found in a suitably dry and friable 
 condition they are mixed in a dry state. The "slurry" 
 obtained in the commoner wet process as a very liquid mud 
 is kept in motion in large tanks or reservoirs, whence it is 
 pumped into rotating cylindrical kilns slightly inclined 
 from a horizontal position. These kilns, which are 60 
 to 130 feet in length and some 6 feet in diameter, are 
 
CEMENTS 
 
 187 
 
 lined with refractory firebrick and supplied with a blast 
 of air and coal dust (or gas) at the opposite (lower) end to 
 that at which the slurry is admitted. 
 
 The burning of the coal dust produces an intense heat 
 which evaporates the water from the slurry and drives 
 off carbon dioxide from the chalk. The free lime thus 
 formed combines with the silica and alumina in the clay 
 at the high temperature attained in the lower part of the 
 rotary kiln, which may exceed 1400° C. (a bright white heat). 
 On leaving the kiln the semi-fused grey clinker " passes 
 through rotating cylinders of very similar construction but 
 supplied with internal vanes which, by alternately picking 
 up and dropping the material, cause it to give up its heat to 
 a natural current of air passing through this cooler. The 
 air thus heated is supplied to the kilns in place of cold air 
 with a proportionate saving in fuel. 
 
 The cooled clinker is then ground to a state of extreme 
 fineness by passage through other rotating cylinders half 
 filled with rounded stones, during which process a small 
 quantity of steam is admitted to ensure the complete 
 slaking of any free lime which may have escaped 
 combination. 
 
 Portland cement is also made in stationary kilns which 
 are developments of ordinary lime kilns, but owing to the 
 increased output, powers of regulation and continuous 
 working facilities possessed by the rotary kiln, this is 
 rapidly supplanting the older forms of plant. 
 
 IV. PoKTLAND Cement (Tests). 
 
 1. Introductory. — Some indication of the nature of the 
 tests to which hydraulic materials are submitted has already 
 been given, but only in the case of Portland cement have 
 such tests been systematised. As pointed out in the case 
 of stones, individual tests should have some bearing upon 
 
188 CHEMISTEY AND PHYSICS OF BUILDINa MATEEIALS 
 
 the use of the material. For example, though a knowledge 
 of compressive strength is of value in the case of cement 
 used for foundations, this has no interest when such 
 material is required for lining a water tank. The usual 
 tests by which the quality of a cement is judged are, how- 
 ever, not as a rule differentiated according to the intended 
 use of the material. These tests, which form the headings 
 of the following paragraphs, are for : — 1. Fineness of grain ; 
 2. Specific gravity ; 3. Expansion ; 4. Tensile strength ; 
 5. Chemical composition ; 6. Eate of setting. 
 
 2. Fineness. — Fineness in cements is produced mechani- 
 cally by continued grinding. The finer the material the 
 greater the strength of the mortar produced from it, the 
 more thorough is the action of water upon it, and the less is 
 its porosity when set. 
 
 Fineness is estimated by weighing the residue from a 
 given weight of cement which fails to pass through a sieve 
 containing a specified number of holes of given size per 
 square inch. The meshes of such sieves are sometimes 
 referred to by the number of holes in a row per linear 
 inch, and sometimes by the total number of holes per 
 square inch. Thus what is known as 180 X 180 sieve 
 contains 180 holes per linear inch or 32,400 holes per 
 square inch. This is the finest sieve in ordinary use,^ and 
 so perfect is modern grinding that the higher grades of 
 cement will leave considerably less than 10 per cent, of 
 residue on such meshes. It is obvious that the gauge of 
 the wire used in these sieves will materially affect the size 
 of the holes. The wire employed for the sieve above 
 referred to has a diameter of 0'002 inches. 
 
 The strength developed by a cement depends not only 
 upon its fineness but also on the size of the particles of sand 
 or other inert aggregate with which it is mixed, and if the 
 
 ^ A sieve possessing 200 holes per lineal inch, i.e., 40,000 holes per 
 square inch, has recently been introduced from America. 
 
CEMENTS 
 
 189 
 
 full advantage of the fineness of high class cements is to be 
 taken a suitable aggregate must be used. As grinding is a 
 costly process, a limitation to the degree of subdivision 
 economically obtainable would seem to exist, and some 
 interesting " curves " showing such limit from relations 
 between price and strength developed might be constructed. 
 
 3. Specific Gravity. — The determination of specific 
 gravity, which has now taken the place of the measure- 
 ment of weight per bushel, has no direct interest. 
 Indirectly, however, it gives a valuable insight into the 
 quality of the material, because the limes and lightly 
 burnt natural cements never attain the density of Port- 
 land cement, which may be taken as 3'10 to 3*15, whereas 
 the former materials, as stated, range from about 2*7 to 2'9. 
 
 The methods of determining specific gravity have been 
 dealt with in Chapter II. In the case of cement the volume 
 of the weighed quantity taken is ascertained by placing the 
 material in a graduated vessel filled to a certain mark with 
 paraffin oil and noting the rise in level produced. 
 
 4. Expansion. — No test on cement is more important 
 than that for expansion, by which is meant the eventual 
 increase in bulk which, possibly after a long interval, takes 
 place in cement subsequent to use. All cements swell 
 slowly after setting, and if such swelling, which is due to 
 incomplete chemical action, is appreciable, great damage and 
 disruption may result. Undue expansion is generally caused 
 by excess of lime in the cement or by insufficient grinding 
 or burning. 
 
 By placing cement which has set, in hot water, evidence 
 of expansion, which would normally be displayed only long 
 after use, makes itself apparent in a few hours. 
 
 A simple test is made by gauging with water on a 
 plate of glass, and forming a thin pat of cement, which in 
 shape should resemble a slice off a large sphere, and may 
 be three or four inches in diameter and about half an inch 
 
190 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 thick at the centre. This is allowed to set under cold water 
 and is then placed for six hours in boiling water. If the 
 cement neither leaves the glass nor shows cracks on its 
 edges its soundness may be considered assured. 
 
 A more accurate method, due to Le Chatelier, whereby 
 the expansion may be measured, consists of filling a small 
 split cylinder of sheet metal with cement gauged with water, 
 and after allowing the mass to set and immersing it in boil- 
 ing water as above, again measuring the distance between 
 the adjoining edges of the metal which have by expansion 
 been forced apart. To facilitate this measurement a long 
 
 Fig. 6. — Le Cliatelier's split ring for measuring expansion 
 in cements. 
 
 prong is attached to each side of the opening, and the 
 distance is actually measured between the ends of these 
 prongs (Fig. 5). 
 
 5. Tensile Strength. — Some comments upon the reasons 
 for making tensile tests upon cementing materials have 
 been made on page 180, where it was stated that a relation 
 between compressive and tensile strengths exists. This 
 ratio is not the same as for hydraulic limes and natural 
 cements, and may be taken in the case of Portland cement 
 as 10 to 1, i.e., the results of tensile tests multiplied by ten 
 give the approximate strength of the material under the 
 same conditions and with the same amount of aggregate, 
 under compression. 
 
 Tensile tests are made by observing the force — the weight 
 
CEMENTS 
 
 191 
 
 in pounds — applied at the end of a lever, necessary to pull 
 in halves a briquette of cement of dumb-bell shape of one 
 square inch in sectional area in the middle. The briquette 
 is fixed to a support below and gripped at the short end of 
 the lever above, and the actual pull on the specimen is 
 obtained by multiplying the force in pounds employed by 
 the number of times the greater arm of the lever is longer 
 than the lesser arm (Fig. 6). 
 
 10 
 
 WEIGHT / 
 
 Fig. 6. 
 
 -Principle of the lever as used in machines for 
 tensile tests. 
 
 6. Chemical Composition. — Some account of the role 
 played by the various compounds in cement will be found 
 in Chapter XVIII. It may be said here that analysis is 
 chiefly of value as showing {a) whether the bases and acids 
 are present in proper proportion ; (&) proving the absence 
 of inert and useless material ; and (c) as showing the 
 amount of magnesia and combined sulphur present, which 
 are prejudicial in excessive quantities. 
 
 (a) Portland cement consists substantially of lime (CaO), 
 silica (Si02) and alumina (AI2O3), and it may be taken that 
 there should be three molecules of CaO to every molecule 
 of SiOa, and also three molecules of lime to every molecule 
 of AI2O3. To determine from the percentage of these com- 
 pounds whether this is so merely involves a reference to 
 atomic weights and the working out of a simple proportion 
 
192 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 sum, as explained in Chapter VI. If the lime is found to 
 be less in quantity than this amount a loss in strength in 
 the cement may be looked for, while if the lime is greater 
 in quantity, the cement will be liable to exhibit undue 
 expansion after setting. 
 
 (6) Portland cement should be entirely soluble in dilute 
 hydrochloric acid. This may easily be ascertained without 
 expert aid by placing a small quantity of the cement in 
 powder, in excess (say, ten times its volume) of spirits of 
 salt diluted with four or five times its bulk of water. If 
 the mixture is gently warmed in a porcelain or glass vessel 
 the whole of the cement should dissolve in a few minutes. 
 Any residue is sand or other inert matter which has not 
 entered into combination with bases on burning, and has 
 no value in the process of setting. 
 
 (c) The role played by magnesia in cements is still a matter 
 of dispute, but in this country amounts much exceeding 
 2 per cent, are looked upon with suspicion, probably chiefly 
 on account of the slow rate at which this base becomes 
 hydrated and hence of the probability of expansion, due to 
 such hydration, occurring after setting has taken place. 
 
 A certain amount of combined sulphur in cement is 
 probably advantageous, but its addition in the form of 
 calcium sulphate with the object of retarding setting is 
 considered to be prejudicial when the amount of this salt 
 exceeds 2 per cent. 
 
 Sulphur is generally stated in analyses as "sulphuric 
 anhydride " (SO3) which may be looked upon as the acid- 
 forming oxide which with lime forms CaSOi ; thus CaO + 
 SO3 = CaSO^. Given the percentage of SO3, that of CaSOi 
 is therefore readily calculated.-"^ 
 
 » CaO + SOs = CaSOi, 
 80 - - 136, 
 136 
 
 1 = gQ- = 1'70, that is, 1 per cent, of SOs is equivalent 
 to 1-7 per cent, of CaSOi. 
 
CEMENTS 
 
 193 
 
 7. Rate of Setting. — This test, which is of smaller import- 
 ance than the foregoing, is useful as an indication of the 
 suitability of a cement for a particular purpose. Rate of 
 setting depends partly upon the amount of alumina present, 
 partly upon fineness of grain which increases the speed of 
 chemical action with water. 
 
 The determination of the setting point is made by noting 
 the period which elapses after gauging before a metal weight 
 possessing a blunt point of given area fails to make an 
 impression when placed on the cement. It is found that 
 an initial set (due to the decomposition of aluminate) is 
 first obtained, and that the final setting, which indicates 
 real solidity, takes place subsequently. The test refers to 
 the final stage of the process. 
 
 8. Use of the Microscope. — Le Chatelier has brought 
 microscopic research to bear upon cements, and this method 
 of investigation is likely to develop. If sections of cement 
 clinker cut and mounted in the same manner as rock sections, 
 be examined, several distinct minerals may be observed. 
 This experimenter has given the names alit, belit, celit, and 
 felit to these distinguishable constituents, but whether they 
 are true chemical compounds or, as suggested by Eichardson, 
 merely solutions of one mineral silicate or aluminate in 
 another, has yet to be determined. 
 
 Alit, according to Le Chatelier, appears to be the silicate 
 3CaO.Si02. It is colourless, and gives under polarised light 
 but dull colours as distinguished from the deep brown tint 
 and brilliant polarisation colours of certain other less 
 valuable constituents. 
 
 9. Other Tests. — Tests for compressive strength, porosity, 
 elasticity and behaviour under fire are not usually included 
 in the ordinary examination of cement, but may be carried 
 out in the manner described for stones. 
 
 In the case of reinforced concrete structures, elasticity 
 tests are of great importance and are usually carried out by 
 
194 OHEMISTEY AND PHYSICS OP BUILDING MATEEIALS 
 
 loading actual structures and measuring the deflection 
 observed by the magnifying aid of a beam of light reflected 
 from a mirror, and subsequently the recovery attained when 
 the load is removed. 
 
 10. Actual Strength of Portland Cement.— The British 
 standard specification requires a tensile strength test per 
 square inch of 400 pounds in seven days and 500 pounds 
 in 28 days for neat cement, and 120 pounds in seven days 
 and 225 pounds in twenty-eight days for cement mortars 
 composed of one part of cement to three parts of sand. 
 This is for a cement which may leave a 22^ per cent, 
 residue on a 180 X 180 sieve, hence greater strength may 
 be demanded for many cements now prepared. 
 
 From a table of tests given by Butler^ it would appear 
 that the average strength per square inch in tension for 
 neat cements leaving some 4 per cent, residue on 100 X 100 
 sieve is after seven days 740 pounds and after twenty-eight 
 days 767 pounds and as 1 to 3 mortars, after seven days 
 265 pounds and after twenty-eight days 834 pounds. 
 
 V. PozzuoLANA Cements. 
 
 This name, derived from that of the village Pozzuoli, near 
 Naples, is applied to natural and artificial siliceous materials 
 which when ground and mixed with lime exhibit hydraulic 
 properties without any kiln treatment. These products 
 vary very widely in composition, and consist of some 30 to 
 70 per cent, of Si02, some 10 to 20 per cent, of AI2O3, and 
 some 5 to 20 per cent, of Fe203. A small quantity of CaO 
 and MgO, usually considerably less than 10 per cent., and 
 variable amounts of K2O, Na20, and H2O are also present. 
 
 1. Natural Pozzuolanas. — The most important of the 
 natural pozzuolanas are of volcanic origin, though certain 
 clays and sands have a limited use under this designation. 
 
 » Butler, " Portland Cement." 
 
CEMENTS 
 
 195 
 
 The former, derived from lavas, or volcanic cinders or mud, 
 are represented by the famous Italian deposits which 
 supplied material for mortar and concrete still in excellent 
 preservation in many ancient buildings. These deposits 
 still form the source of hydraulic material. Trass, a vol- 
 canic mud, and santorin, an ash, also have an extensive use. 
 
 These materials, quarried in open workings or some- 
 times mined at considerable depths, are screened and ground, 
 after which they are mixed with the requisite quantity of 
 lime slaked so as to form a powder, that is, free from excess 
 of water. The cement is then ready for use. 
 
 2. Artificial Pozzuolanas. — The most important materials 
 classed under this heading are the slag cements, though 
 burnt clays which have been employed in large under- 
 takings remote from transit facilities must also be regarded 
 as belonging to this group. 
 
 Certain slags produced in various industries, particularly 
 in the manufacture of iron and steel, possess a composition 
 very similar to that of many natural pozzuolanas. The 
 more basic varieties, i.e., those containing a fair proportion 
 of lime, are employed to some extent in the manufacture 
 of cements. The slag is granulated by causing it to flow in 
 a molten condition straight from the furnace into water, 
 which, besides producing great mechanical subdivision, 
 removes a good deal of the sulphur present largely as 
 calcium sulphide. It is then dried by hot air, ground, and 
 mixed with dry slaked lime to which is often added a 
 proportion of Portland cement, which is said to promote 
 soundness in the resulting product. 
 
 3. Properties and Strength of Pozzuolana Cements. — In 
 colour these cements vary much, owing to the great 
 difference in the percentage of iron found among them ; but 
 they are generally of light tint, as would be expected in 
 materials partly composed of free lime. Their specific 
 gravity is about 2'8. 
 
 B.M. 
 
 o 
 
196 CHEMISTEY AND PHYSIOS OF BUILDING MATEEIALS 
 
 Though inferior to Portland cement, the better ground 
 and mixed varieties exhibit a remarkable degree of strength, 
 and results are recorded of slag cements consisting of 3 
 parts of slag to 1 of lime which showed a tensile strength 
 exceeding 600 pounds per square inch. Johnson^ quotes 
 experiments which tend to show that the ratio of compressive 
 to tensile strength is similar to that given for Portland 
 cement, namely, about 10 to 1 ; but Eckel,^ citing fuller 
 details, places this ratio at about 5 to 1, and gives tests 
 which show a strength for these neat cements in tension at 
 seven days as about 460 pounds and at twenty-eight days as 
 515 pounds per square inch, while with sand as 1 to 3 mortar 
 such cements showed a strength of 157 pounds and 209 
 pounds respectively. The materials forming the pozzuolana 
 group possess hydraulic properties apart from the addition 
 of free lime, since they contain a certain proportion of bases, 
 but these are usually small in quantity, except in the case of 
 the slag cements, and the strength is always developed 
 chiefly by the free lime subsequently added. Some views 
 suggesting an explanation of this remarkable effect of the 
 presence of lime will be given in the following chapter. 
 
 One of the chief objections urged against slag cements is 
 their liability to contain sulphur in the form of calcium 
 sulphide,^ a substance which readily decomposes in the 
 presence of moisture with the liberation of sulphuretted 
 hydrogen. This compound (or these compounds, for there 
 are several sulphides of calcium) on oxidation form calcium 
 sulphate, with expansion. A greenish tint on fracture 
 shown by briquettes kept under water, and the evolution of 
 sulphuretted hydrogen, readily recognised by its smell, on 
 the addition of dilute acids, enable the presence of sulphides 
 to be detected. 
 
 1 Johnson, " The Materials of Construction." 
 ' Eckel, " Cements, Limes, and Plasters." 
 
 8 The expansion observed in breeze concretes may possibly be due 
 to this compound in coke. 
 
CHAPTER XVIII 
 
 THEORIES UPON THE SETTING OF PLASTERS AND HYDRAULIC 
 MATERIALS 
 
 The great variations which occur in the strength and 
 stabiHty of the binding materials dealt with in the previous 
 chapters, and the importance of a true understanding of the 
 conditions upon which these characters depend, render it 
 necessary to deal with the views which have been put 
 forward in explanation of these complex phenomena. 
 
 Scientific opinion is by no means unanimous as to the 
 explanation of setting and hardening, and much remains to 
 be done in the realm of pure science on the subject of the 
 cohesion and adhesion of bodies, and upon the exact nature 
 of the chemical reactions which take place on the burning 
 of hydraulic materials and on their subsequent treatment 
 with water. 
 
 I. Cohesion and Adhesion. 
 
 The strength of any material is ultimately dependent 
 upon the power possessed by its particles of sticking 
 together when submitted to disruptive forces. This is due 
 to cohesion and adhesion, the display of which vary very 
 much with the area, closeness of contact and nature of the 
 materials or molecules between which such forces are 
 exerted. 
 
 1. Cohesion.— By cohesion is meant the power of resisting 
 disruption possessed by individual chemical substances. 
 Thus, if a crystal of selenite be pulled into halves, the force 
 of cohesion has been overcome. This rupture is, therefore, 
 
 0 2 
 
198 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 the overcoming of the actual molecular forces which confer 
 upon the substance its rigidity. 
 
 Cohesion is not only displayed in very different degrees by 
 different bodies, but this property varies in the same body 
 in different directions. It is less, for example, between 
 cleavage planes, when such exist, than in other directions. 
 
 2. Adhesion. — Adhesion is the tendency displayed by 
 different bodies to stick together. This is non-existent in 
 the case of many bodies, but is sometimes greater than the 
 force of cohesion, as when materials joined by a cement 
 fracture individually rather than at the joint. Given com- 
 plete contact, the force of adhesion usually increases with 
 the roughness of the adjoining surfaces. This is no doubt 
 due largely to the greater area of contact over any given 
 section which is produced by the sinuosities of such surfaces 
 and because the force tending to overcome the adhesion can- 
 not act normally, that is, at right angles and with greatest 
 effect upon the whole of this sinuous area at one time. 
 
 3. Effect of Inert Aggregates on Cementing Strength. — 
 From the above considerations it will be obvious that 
 problems connected with the setting and strength of 
 cementing bodies will be very materially influenced if, 
 as is usual, sand or other aggregate be mixed with such 
 materials. Those aggregates should be chosen as intrin- 
 sically adhere most strongly to the cementing material 
 employed, upon which subject little information at present 
 exists. The shape of the aggregate particles should be such 
 as to produce the greatest total area across any given cross 
 section, that is, to give the greatest interlocking effect 
 consistent with the limits of size permissible for such 
 particles. The aggregate should be graded in size to 
 preclude the formation of voids in the material, which, 
 whether they be filled with air or water, produce a decrease 
 in adhesive power proportional to their combined area. 
 
 In most aggregates in ordinary use the force of cohesion 
 
SETTING OF PLASTEES AND HYDEATJLIC MATEEIALS 199 
 
 is greater than that of adhesion to the cementing material. 
 As this cohesive force is inherent, and therefore costs 
 nothing, whereas the adherence as developed by the cement 
 is expensive, as much value should be got out of the former 
 as possible by the judicious use of angular aggregates, 
 thoroughly cemented together, of as great a size as circum- 
 stances will allow. Such thorough cementing demands the 
 use of aggregates carefully graded so as to contain particles 
 of sizes suitable for filling all voids, otherwise a wasteful 
 amount of cementing material will have to be employed. 
 Some opinion as to the voids presented by various aggre- 
 gates may be obtained by a complete mixing and ramming 
 of the aggregate alone in a vessel of known volume, when 
 the amount of water which can then be added without 
 increasing the apparent volume of the mass will represent 
 the space which must be occupied by the cementing sub- 
 stance when it reaches its final hardened condition. 
 
 It seems probable that considerable economy might be 
 effected in the use of cementing materials by greater 
 attention to the nature, configuration, and grading of the 
 aggregates mixed with them. 
 
 II. Introductoey Kemarks on Setting. 
 
 1. General Causes. — It is now necessary to consider what 
 explanations can be offered of the setting of cementing 
 materials, and though the theories advanced on the subject 
 naturally differ in the case of different substances, it will 
 be observed that, whether plasters, limes, or cements be 
 in question, the ingredients composing them have all been 
 subjected to heat and have thus been rendered anhydrous, or 
 nearly so. Further, setting power is only developed by the 
 subsequent addition of water, which is absorbed, and thus 
 becomes chemically combined, and this hydration takes 
 place with considerable swelling during the setting process. 
 
200 CHEMISTRY AND PHYSICS OF BUILDING- MATERIAL 
 
 Setting is, therefore, the result of hydration ; cohesion is 
 developed by the pull of the newly-formed hydrated mole- 
 cules one upon another ; and adhesion, if inert aggregates 
 or several cementing compounds are present, by the pressure 
 of the boundary areas of the constituent substances against 
 each other. 
 
 The cohesion developed between the molecules of a given 
 substance depends not only upon the chemical nature of 
 the substance and the hydrate formed from it, but in a very 
 high degree upon the physical conditions under which the 
 hydration takes place, at least in the case of all compounds 
 which endeavour to develop an orderly molecular arrange- 
 ment: that is, which show any tendency to crystallise. 
 Molecules in solution take time to group themselves when 
 assuming the solid condition, and if disturbed during the 
 process cohesion will be diminished or destroyed. The 
 heat developed by the hydration of quicklime produces so 
 much molecular disturbance that hydrated lime in a solid 
 condition is produced long before molecular quiescence is 
 possible, and a friable non-coherent mass is the result ; 
 but by allowing the hydration to proceed slowly the same 
 hydrate may be obtained in a crystallised condition, when 
 it possesses considerable cohesive powers. 
 
 The problem of setting is again further complicated 
 by the fact that a given compound may assume several 
 crystalline forms, according to the conditions under which 
 crystallisation takes place- 
 Gypsum, for example, formed on the setting of plaster 
 of Paris, can crystallise in short columnar crystals or in 
 masses of slender needle-shaped form. The force required 
 to separate one crystal from another is less than that 
 necessary to pull into two an individual crystal, hence the 
 material in the latter form will show a much greater 
 development of strength than in the former. 
 
 2. Crystalloid and Colloid Theories of Setting. — Hydraulic 
 
SETTING OF PLASTEES AND HYDRAULIC MATERIALS 201 
 
 materials, which form by far the most important class of 
 bodies connected with this discussion, owe the strength 
 which they develop to the presence of compounds of silica. 
 These compounds break up on treatment with water, but 
 the composition and nature of the resulting bodies is still 
 a matter of dispute. While there are many individual 
 opinions as to the rdle played by various chemical con- 
 stituents two main schools of thought exist on the general 
 subject of setting. 
 
 (a) One view is that setting is due to crystallisation. In 
 the case of wholly crystalline bodies, such as gypsum, this 
 view is beyond contention, but is also held to explain the 
 setting of hydraulic materials, in which process it is assumed 
 that the silicates and aluminates of lime contained in such 
 materials break up and combine with water to form crystal- 
 line compounds, and that setting is due to the interlocking 
 and adhesion of such crystals. This school is led by Le 
 Chatelier. 
 
 (b) The other view is that the hydration of hydraulic 
 materials results in the production of colloidal (gelatinous) 
 forms of hydrated silicates and aluminates of lime, and that 
 it is the drying up of such gelatinous hydrates into hard and 
 glue-like masses which accounts for setting. Further, that 
 some inevitable crystallisation which takes place on account 
 of the presence of non-gelatinous compounds such as 
 hydrated lime resulting from chemical decomposition, is 
 actually injurious to the strength of the material. This 
 school is led by Michaelis. 
 
 III. Theokibs on Setting Developed. 
 
 1. Crystalloid Theory of Setting. — The advocates of this 
 theory believe that the main and only essential compound 
 in hydraulic materials is tricalcium silicate 3CaO.Si02, and 
 that the alumina always present in small quantity and 
 
202 CHEMISTKY AND PHYSICS OF BUILDING MATEEIALS 
 
 necessary in practice to admit of fusion in the kiln, is com- 
 bined with lime as SCaO.AlaOs, according to Le Chatelier, 
 and as SCaO.AlaOs according to the American view as 
 represented by the researches of Newberry and Eichardson. 
 On the addition of water the above silicate of lime is decom- 
 posed into a similar compound which absorbs water as water 
 of crystallisation, and to which the formula 2(CaOSi02).5H20 
 is given. In this process the rest of the lime from the sili- 
 cate 3CaO.Si02is freed and forms calcium hydrate Ca(0H)2, 
 which crystallises. The set cement is regarded as consisting 
 of interlaced needle-shaped crystals of the hydrated silicate 
 and hexagonal platey crystals of calcium hydrate embedded 
 in them. The calcium aluminate is believed by Le Chatelier 
 to combine with water to form 3CaO.Al2O3.10H2O.^ 
 
 These views on the constitution of hydraulic materials 
 are based partly on optical examination of Portland cement 
 and partly on research, in which an attempt was made to 
 prepare silicates and aluminates of limes artificially by 
 fusion in various molecular proportions, and to determine 
 the stability and characters of the resulting bodies. 
 
 Le Chatelier in France, and Newberry in America 
 (1897), have prepared a variety of such compounds, and 
 the experiments of the latter were later confirmed by Clifford 
 Richardson. Le Chatelier believes the setting to be due 
 to the hydrated silicates and aluminates, but in the 
 American view this is due to the crystallisation of calcium 
 hydrate. 
 
 More recently (1906) Messrs. Day and Shepherd, in 
 America, have conducted experiments on the formation of 
 lime silicates, and deny the existence of the trisilicate 
 3CaO.Si02. According to their view the hydraulic proper- 
 ties are due to basic silicate of calcium 2CaO.Si02 formed 
 by rearrangement or " inversion," at a high temperature, 
 
 ^ The later view of this savant, kindly expressed in a letter to the 
 writer, May, 1908. 
 
SETTING OF PLASTEES AND HYDEAUIJC MATEEIALS 203 
 
 of another silicate composed of lime and silica in the same 
 proportions, a fact previously suggested by Zulkowski in 
 1899. The views of these experimenters are now accepted 
 by Eichardson. 
 
 The original papers^ must be consulted for a further 
 pursuit of this subject. 
 
 2. Colloidal Theory of Setting. — This theory, which for 
 many years has been advocated by Dr. W. Michaelis, in 
 Germany, denies the value of crystallisation in the setting 
 process.^ This experimenter contends that the combina- 
 tions of lime and silica after the addition of water cannot 
 be looked upon as definite compounds of precise compo- 
 sition, but must be regarded as gelatinous hydrated sili- 
 cates, which swell very greatly on formation. The water 
 in such bodies cannot then be regarded as water of crystal- 
 lisation, its amount is indefinite, and it is imbibed by a 
 process of transpiration through the membrane-like walls 
 of the colloidal compounds, which thus swell and even- 
 tually stick together, and finally, on drying, harden, when 
 they lose their powers of imbibing water. Portland cement 
 is to be regarded as composed of silica combined with lime 
 in such quantity that most of such lime is liberated on the 
 addition of water, and this freed lime, when hydrated, 
 results in the formation of colloidal silicate of lime, pro- 
 bably, in the case of all hydraulic materials, CaOSi02 + 
 water. The amount of lime, i.e., whether it is present in 
 
 1 Newberry, J. Soc. Chem. Industry, November, 1897, pp. 887 — 
 894. Richardson, Engineering News (U.S.A.), August, 1904, and 
 January, 1905. H. Le Chatelier, " Le Constitution des Mortiers 
 Hydraulic," Dunod, 2nd ed., 1904; Am. translation, 1st ed. H. Le 
 Chatelier and others, L'Association Internationale pour I'essai des 
 Materiaux de Construction, February, 1902 ; January, 1903 ; April, 
 1903 ; April, 1904 ; October, 1904. Day and Shepherd, J. Am. 
 Chem. Soc, vol. xxviii. , September, 1906, pp. 1089 — 1114 ; also Day, 
 Allen, and Iddings, Am. J. Sci., 19, 93 (1905). 
 
 " " The Hardening Process of Hydraulic Cements," paper read in 
 Berlin, February 21st, 1907, translated, published by Cement and 
 Engineering News (U.S.A.). 
 
204 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 such proportion that the compound 3CaO.Si02 could be 
 formed or not, does not all affect the reaction, though this 
 amount may affect the quality of the resulting material. 
 Hence the fact that lime and silica are found to give the 
 best results in cements in about the proportion of 3 CaO 
 to 1 Si02 must be regarded as a more or less fortuitous 
 circumstance depending on the usual method of employ- 
 ing cements, and not as indicating the existence of the 
 compound 3CaO.Si02. 
 
 To substantiate his view that Portland cement ought to 
 be regarded as a kind of desiccated jelly, Michaelis cites 
 experiments showing that when cement is mixed with 
 about fifty times its weight of water and thoroughly 
 agitated, a gelatinous mass is formed, accompanied by 
 swelling of the cement to from twenty to twenty- five times 
 its original volume, and this, when kneaded into a dough, 
 may even be rolled out into slabs without detriment to 
 subsequent hardening. Such treatment would probably 
 prevent any molecular arrangement such as is essential 
 for development of cohesion by crystallisation. 
 
 It would certainly seem that the development of hydraulic 
 properties displayed by pozzuolanic materials on the addi- 
 tion of lime is more readily explained by the adoption of 
 the colloid theory of setting, since lime in solution has a 
 remarkable power of causing the precipitation of gelatinous 
 silica from bodies such as pozzuolanas which contain 
 silica in a soluble form. In the case of slag cements, Le 
 Chatelier attributes the display of hydraulicity to the 
 decomposition of a double siHcate of lime and alumina 
 owing to the solvent power of calcium hydrate in solution. 
 
 3. Views on the Effects of Magnesia and Iron Oxides. — 
 Almost all hydrauUc materials contain small quantities of 
 magnesia (MgO) and of ferra (Fe203), but the importance of 
 these compounds is small as compared with the main con- 
 stituents above discussed. 
 
SETTING OF PLASTEES AND HYDEAULIC MATEEIALS 205 
 
 Opinions as to whether these oxides enter into combina- 
 tion or not are very much divided. If any combinations 
 exist these are probably composed of magnesia and silica, 
 and of lime and ferra, which last, in the presence of strong 
 bases like lime, always acts as an acid-forming oxide. 
 
 (a) Magnesia. — Magnesia is a much less powerful base 
 than lime, hence it is less likely to combine with the acid- 
 forming oxides, and its hydration takes place with com- 
 parative slowness. It is generally regarded in this country 
 as equivalent to lime in its action when present in small 
 quantities, though there is little evidence for the basis 
 of this assertion. Le Chatelier's experiments indicate 
 that magnesia and silica enter into combination, but 
 Newberry describes attempts to prepare silicates of magne- 
 sium which led to no definite indication of the formation of 
 compounds. 
 
 Perhaps the chief authority on this subject is Dyckerhoff, 
 who places the maximum safe limit of magnesia in cements 
 at 4 per cent., and states that no tests on the properties of 
 this base as affecting cements are of value if undertaken 
 less than six months after setting.^ The safe limit is 
 usually placed at 3 per cent, in this country, but cements 
 are in use in America which contain much larger quanti- 
 ties. Michaelis quotes an opinion that magnesia is an 
 essential for the formation, by fusion, of certain silicates of 
 lime, hence this oxide may yet be discovered to play some 
 part in the formation of cements, 
 
 (6) Ferra. — Le Chatelier's attempts to produce compounds 
 of lime and ferra (calcium ferrites) led to the formation of 
 bodies which merely displayed the properties of free lime 
 on slaking. Newberry and Richardson, however, consider 
 that ferra can enter into combination and display hydraulic 
 properties, while both Le Chatelier and Michaelis are 
 agreed as to its value as a component of cements for use in 
 ' Dyckerhoff, J. Soc. Chem. Industry, 1890, p. 943. 
 
206 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 sea-water. The amount of this oxide present in ordinary 
 cements is so small that further discussion on this subject 
 is unnecessary here, but it seems likely that considerable 
 advantage might be taken of the use of iron in cements for 
 special purposes. Michaelis refers to an industry for the 
 production of iron-ore cement which is developing in 
 Germany, and bases his eulogies of this material upon the 
 fact that calcium ferrites do not crystallise. 
 
 4. Summary of Views on Constitution and Setting. — The 
 following attempt to summarise the diverse views on this 
 subject may be found useful ■} — 
 
 View held. 
 
 Authority. 
 
 That in the kiln treatment of hydraulic materials 
 combination between lime and silica takes place, 
 and that such combined silica is chemically active 
 as distinct from free silica such as sand, which 
 is inert. 
 
 That the silicate of Hme formed is substantially 
 SCaO.SiOa. 
 
 That the silicates of lime formed can only be CaOSi02 
 and 2CaO.Si02. 
 
 That the aluminate of lime formed is SCaO.AlaOs . 
 ,, „ ,, J) )) >> 2CaO.Al203 . 
 
 That magnesia appears to form silicates and 
 aluminates. 
 
 That magnesia does not seem to form silicates and 
 aluminates. 
 
 That hme and f erra do not appear to form hydraulic 
 
 compounds. 
 That lime and ferra enter into combination . 
 
 All. 
 
 Le Chatelier 
 and Newberry. 
 Day and 
 
 Shepherd, 
 Michaelis. 
 Le Chatelier, 
 Newberry and 
 Richardson. 
 Le Chatelier. 
 
 Newberry and 
 Richardson. 
 Le Chatelier. 
 
 Newberry. 
 
 ^ A valuable historical summary on the subject will be found in a 
 paper entitled " The Structure of Cementing Materials," by Prof. 
 Anderson, of Glasgow, given in full in The Quarry, April, 1902, 
 pp. 234 — 242. The author, however, entirely omits any reference to 
 the colloid theories of setting. 
 
SETTING OF PLASTEES AND HYDEAULIC MATEEIALS 207 
 
 View held. 
 
 Authority. 
 
 That setting is due to hydration of lime silicates 
 (and aluminates) accompanied by liberation of 
 lime. 
 
 That setting is due to crystallisation, the water 
 added combining as water of crystallisation, 
 
 That setting is due to the formation of the 
 sihcate 2(CaOSi02)5H20, and in minor degree 
 to the aluminate 3CaO.Al2O3.10H2O. 
 
 That setting is due to the crystals of hydrated 
 lime formed. 
 
 That setting is due to colloidal silicate of lime 
 CaOSi02 with an indefinite quantity of imbibed 
 water. 
 
 All. 
 
 T 1^ n Q "foil Of 
 
 Newberry (and 
 Eichardson?). 
 Le Chatelier. 
 
 Eichardson (?). 
 Michaelis. 
 
 IV. Eate of Setting op Plasters and Cements. 
 
 It has already been pointed out that the character of 
 crystalline compounds formed during setting^ bears an 
 important relation to the strength of the resulting material. 
 
 Le Chatelier has carried out experiments upon which he 
 has based an interesting theory in explanation of the effects 
 of fineness of grain and of the presence of certain com- 
 pounds occasionally added to cementing materials, as 
 influencing the nature of the solids which result after 
 gauging with water. This theory, known as the super- 
 saturation theory, is developed in connection with plaster, 
 but also gives an insight into the physical nature of setting 
 in the case of hydraulic materials on the assumption that 
 the crystalloid theory of setting is the correct one. 
 
 This savant has developed his views on the fact that the 
 solubility of a dehydrated or partially dehydrated compound 
 is greater than that of the same compound combined with 
 its full complement of water of crystallisation. Thus when 
 
 ' Advocates of the colloid theory must admit that the liberated 
 lime crystallises as hydrate of lime. 
 
208 CHEMISTRY AND PHYSICS OF BUILDING MATEEIALS 
 
 plaster of Paris is dissolved in water a saturated solution 
 is produced which is, therefore, supersaturated for the 
 resulting gypsum formed immediately on hydration. As a 
 result part of the gypsum, the fully hydrated sulphate, is 
 immediately deposited in the form of crystals. This with- 
 drawal of matter from the solution leaves the remaining 
 water free to dissolve more of the plaster of Paris, and thus 
 the cycle is repeated until the whole of the water added (if 
 not excessive) becomes combined as water of crystallisation. 
 
 It is evident that the relative rates of solution of the 
 plaster of Paris and crystallisation of the gypsum will fix 
 the concentration, that is, the strength of the solution at 
 any given stage in the process, and since it has been 
 shown that the stronger the solution the greater is the 
 tendency towards the production of needle-shaped and, 
 therefore, firmly interlocked crystals, the rate of solution 
 has a material effect upon the strength of the resulting 
 material. 
 
 This rate of solution will be dependent upon the surface 
 exposed to the solvent action of the water, which explains 
 the increased strength of finely ground cementing materials. 
 It will also depend on the relative solubilities of the 
 dehydrated and hydrated compounds concerned in the 
 action, and this relation may be influenced by adding to 
 the water used for gauging, bodies which increase the 
 solubility of the dehydrated salt. This gives an explanation 
 of the use of " accelerators," such as washing soda, some- 
 times added to cements to hasten setting, and may also 
 possibly explain the increased strength of Keene's and 
 other special cements over ordinary plaster of Paris. 
 Common salt is another instance of a compound which 
 accelerates setting. 
 
 Conversely, the use of certain bodies to retard setting, 
 such as calcium sulphate in Portland cement, may possibly 
 be explained by the decrease in solubility of the dehydrated 
 
SETTING OF PLASTEES AND HYDRAULIC MATERIALS 209 
 
 compounds produced by their presence. This gives an 
 alternative to the theory of Schott in reference to the 
 coating action of such compounds, which is supposed to 
 decrease the rate at which water can reach the particles 
 undergoing solution. Much more information, however, as 
 to the actual solubilities of cementing constituents in solu- 
 tions of salts used is required before any general statement 
 can be made on this subject. 
 
 The effect of such retarders as size or other colloid matter 
 is probably to be explained on the assumption that their 
 action is mechanical and decreases the rate of solution by 
 adding to the viscosity of the liquid. Such substances, by 
 preventing the interlocking of crystal masses, must be 
 regarded as having a detrimental effect. 
 
 V. — The Failure op Hydraulic Materials. 
 
 1. Expansion. — The commonest and most important 
 cause of failure in hydraulic materials must be regarded as 
 due to slow expansion after, and often long after, complete 
 rigidity of the mass has been attained. This is caused by 
 incomplete hydration before setting, which may be due to 
 imperfect mixing of the cement and water, or to the 
 presence of particles so large that the action of water upon 
 them cannot immediately reach completion. Again, an 
 excessive proportion of lime may produce expansion, and 
 the use of insufficient water in gauging the cement might 
 also produce similar results. This subsequent expansion is 
 caused by the gradual hydration of cement which has 
 escaped initial action of water, either by atmospheric 
 moisture or by water entangled in the material on setting. 
 Since the compounds formed on hydration all occupy a 
 larger volume than the original constituents, such hydration 
 results in immense internal strains in the rigid material, 
 
210 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 which may thus undergo disruption, with disastrous results 
 to surrounding structures in confined situations. 
 
 The long intervals, which have been known to reach 
 several years, before the expansion of unsound cement 
 makes itself evident would seem to somewhat favour the 
 colloid theory of setting, since the permeability of colloids 
 approaching a state of dryness is exceedingly small, and 
 once such colloidal films surround material unacted upon, 
 the passage of water to such material must be a very 
 gradual process. 
 
 In cases in which disruptive effects make a sudden 
 appearance, it is probable that slow hydration is still the 
 cause, but that the material has previously withstood an 
 accumulating internal pressure under which it has at length 
 broken down. 
 
 If lime is present in cement materials in excessive 
 quantities, this will, after the high temperatures of burn- 
 ing, be found as a comparatively dense material. In this 
 form it may be assumed that immediate slaking, on the 
 addition of water, will not take place, and that an outer 
 layer of slaked lime may be formed upon such free-lime 
 particles, which will protect the internal core of quick lime 
 until setting is complete. Slow hydration of this Hme core 
 will eventually result in expansion. 
 
 The actual effects of the expansion of hydraulic materials 
 will depend very largely on the situation in which they are 
 used and on their own physical structure ; the more porous 
 the cement, for example, the more internal apertures it will 
 provide for expanding particles, hence the disruptive effects 
 of expansion are less likely to make themselves evident in 
 the case of lightly burnt natural cements or hydraulic 
 limes than in the case of denser materials such as Portland 
 cement. 
 
 2. Efflorescence and Solution. — The hydrated bodies 
 formed when water is added to cement are not efflorescent 
 
SETTING OF PLASTERS AND HYDEAULIO MATERIALS 211 
 
 in the ordinary sense, but when cements are exposed to 
 great heat or draught, or when subjected to the action of 
 fire, loss of some combined water may occur, with con- 
 sequent loss of crystalline form, and hence with the 
 production of white powders which may make themselves 
 evident on the surface of the material. The presence, how- 
 ever, of sulphate of lime or of salts of potash or soda may 
 result in efflorescence and staining of surrounding materials, 
 as previously explained. 
 
 Solution of the hydrated lime formed on the setting of 
 cement is undoubtedly possible under ordinary atmospheric 
 conditions of use, but such loss is largely counteracted by 
 its compact and crystalline nature, and by the action of 
 carbon dioxide, which gives it a surface covering of car- 
 bonate of lime, and any loss of material from this cause is 
 trifling, 
 
 _ 3. Defects due to Sea Water.— In marine works the solu- 
 tion of cement may occur with considerable rapidity, owing 
 to the action of magnesium chloride in sea water upon the 
 lime in the cement, which results in the production of 
 soluble calcium chloride. Thus : 
 
 MgCla + CaOaHa = CaCla + MgO + H2O 
 
 Sea water also contains sulphate of lime and magnesia, 
 which act upon the alumina in the cement and produce a 
 compound known as sulph-aluminate of lime; and since 
 this compound occupies more space than the original con- 
 stituents, expansion and disruption of the cement may 
 result from its formation. 
 
 Le Chatelier and, more recently, Michaelis have carried 
 out experiments which show that, if alumina in cements is 
 replaced by ferra, this deleterious action of sea water is pre- 
 vented. It is stated that the whole of the alumina may be 
 replaced by ferra in manufacture without any detriment. Le 
 Chatelier further states, however, that if the percentage of 
 
 B.M. 
 
CHEMISTEY AND PHYSIOS OF BUILDING MATEEIALS 
 
 lime in the cement be decreased, alumina may still be 
 present without the formation of sulph-aluminate, the 
 quantity of lime being then insufficient for its formation. 
 
 Attempts which have been made to improve the resisting 
 power of cements for marine purposes by the addition of 
 fatty materials on gauging to prevent the entrance of sea 
 water appear to show negative results. 
 
 4. Defects due to Aggregates.— The inert materials em- 
 ployed in the production of concretes may occasionally 
 play a part in the failure of hydraulic materials. Coke, 
 clinker, and slag are all liable to contain sulphur, and 
 when this is present in the form of sulphides, decomposi- 
 tion of those compounds is Hable to occur with expansion, 
 as has been already explained in the chapters dealing with 
 Brick Clays. Again, defective bricks containing lumps of 
 lime, if used as an aggregate, might lead to subsequent 
 expansion. 
 
CHAPTEE XIX 
 
 ARTIFICIAL STONE, OXYCHLORIDE CEMENT, ASPHALTB 
 
 I. Artificial Stone. 
 
 The cementing materials discussed in the previous 
 chapters and the means whereby their constituents may 
 be brought mto combination have been extensively utilised 
 for the production of artificial stones and bricks. 
 
 Some of these materials are mere concretes : that is, they 
 consist of inert fragments of stone or other suitable 
 mgredients cemented together by some hydraulic agent 
 such as Portland cement. Such materials do not call for 
 special discussion. 
 
 1. Ransome's Process. — The manufacture of artificial 
 stone proper was first attempted by Eansome, and his pro- 
 cess consists in the formation of calcium silicate, by means 
 of a chemical reaction, as a binding agent between suitable 
 inert fragments. 
 
 This involves the preparation of sodium silicate, a soluble 
 gelatinous substance made by dissolving silica, usually in 
 the form of flmt, in caustic soda solution under pressure 
 The sodium siHcate is mixed with sand or other clean 
 aggregate which is to form the bulk of the finished material 
 and the plastic mass which results is pressed into moulds 
 of the required shape. 
 
 When the blocks are dry they are placed in a solution of 
 calcium chloride, which gradually acts upon the sodium 
 silicate with the production of calcium silicate and sodium 
 
 p 2 
 
214 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 chloride. The composition of sodium silicate is doubtful.^ 
 If it be assumed for simplicity's sake to consist of one mole- 
 cule of Na20 combined with one molecule of SiOa or to 
 have the formula Na2Si08, the reaction may be stated as 
 follows : — 
 
 Sod. silicate. Cal. chloride. Cal. silicate. Salt. 
 NaaSiOs + CaCla = CaSiOg + 2NaCl. 
 
 This equation shows the inevitable production of salt in 
 this process, and since salt produces efflorescence prolonged 
 washing is necessary before the " stone " can be satisfactorily 
 used. 
 
 The presence of salt in such preparations may be easily 
 detected by the production of a heavy^ white precipitate on 
 the addition of a few drops of a solution of silver nitrate to 
 distilled water with which some crushed fragments have 
 been shaken, and by the fact that this precipitate is not 
 dissolved on the addition of nitric acid. 
 
 2. Lime-Sand Bricks. — The most satisfactory artificial 
 combination, certainly from a scientific and probably also 
 from a practical standpoint, is that of lime and silica 
 directly, which is brought about by the treatment of sand 
 mixed with a small percentage of lime with steam under 
 pressure. The invention of the first successful process for 
 effecting this is claimed by Michaelis, but a great many 
 patents now exist under which such combination of lime 
 and sand is carried out. 
 
 It has never been satisfactorily proved, however, that 
 chemical union really takes place. Eckel, for example, 
 considers that any chemical action is unlikely, and cites the 
 fact that the lime in such materials only amounts to from 
 
 1 Na20.4Si02 or Na2Si409 represents the approximate proportion 
 of soda to silica in the substance known as soluble glass. 
 
 2 This test is a very deUcate one, hence mere cloudiness in the 
 water would not be sufficient evidence of incomplete washing. 
 
ABTIFICIAL STONE, OXYCHLOEIDE CEMENT, ETC. 215 
 
 5 to 10 per cent, of the whole mass, and hence is not at all in 
 the proportion to form silicates ; but it should be remembered 
 that a very small proportion of silicate formed would be 
 sufficient, with the perfect dissemination attained, to cement 
 a large quantity of inert sand," and lime, although it does 
 not possess the combining power of soda, is still an exceed- 
 ingly strong base, and hence its combination with silica under 
 the favourable circumstances supplied by heat and pressure 
 seems by no means impossible. 
 
 These artificial stones or bricks, consisting as they do of 
 some 90 per cent, of fragmentary stone material, may be 
 made to resemble natural stones very closely. They 
 possess the advantage of great homogeneity, and can be 
 worked with tools like natural stones. 
 
 II. Stone Preservation. 
 
 Although the preservation of natural stone has no direct 
 connection with the subject of this chapter, the processes 
 adopted for this end so closely resemble the first of the 
 two cited in the preceding section that a few words on 
 this topic have been reserved for introduction here. 
 
 The use of stone preservatives carries its own condemna- 
 tion as showing that the stone has been employed in a 
 situation for which its chemical or physical nature renders 
 it unsuitable, and no process known can be looked upon as 
 approaching perfection on account of the difficulty in 
 securing effective penetration of the preservatives employed. 
 The object in all cases is the same, namely, to close the pores 
 of the stone by some insoluble and permanent solid, and 
 thus to prevent further damage. 
 
 The most favoured means of effecting this is to cause 
 chemical precipitation in the pores of the stone by the 
 infiltration of one solution and then another, which shall, 
 by precipitation, react with the first. Calcium or barium 
 
216 CHEMISTRY AND tHYSlCS OF BUILDING MATEEIAT.S 
 
 silicate is the solid, the production of which is usually aimed 
 at, and this is effected by brushing over the face of the 
 stone a solution of sodium silicate, followed, after this has 
 penetrated as far as possible, by a solution of calcium 
 chloride. The reaction is precisely that described for the 
 production of artificial stone in the preceding paragraph. 
 In the case of barium chloride, barium silicate and salt are 
 similarly produced — 
 
 NaaSiOa + BaCla = BaSiOg + 2NaCl. 
 
 The removal of the sodium chloride, which can only be 
 effected by washing, is a grave objection to the process. 
 
 Single fluid stone preservatives generally consist of 
 silicates or other compounds which dry up, leaving 
 colloidal solids in the pores of the stone. 
 
 The deposition of pure silica in the pores of the stone 
 would be perhaps the ideal method of effecting preserva- 
 tion. Silica is by no means insoluble in water ; solutions 
 containing five per cent, of SiOa can be readily obtained, 
 and if such solution could be arranged to flow slowly over 
 the face of the stone the silica would be deposited on 
 evaporation of the water or precipitated by the presence of 
 alkaline compounds. 
 
 III. OXYCHLORIDE CeMENTS. 
 
 When magnesium chloride and oxide are mixed in suit- 
 able proportions in the presence of water these compounds 
 combine and form a cement of great hardness. This is 
 due to the formation of magnesium oxychloride, which may 
 be regarded as magnesium hydroxide Mg(0H)2, in which 
 one of the oxygen and hydrogen atoms has been replaced 
 
 by chlorine, thus : Mg^^^ becomes Mg<CoH* '^^^ 
 cement, which contains magnesium hydroxide and water in 
 
ARTIFICIAL STONE, OXYCHLORIDE CEMENT, ETC. 217 
 
 addition, has been assigned the composition : 2MgC10H. 
 4Mg(OH)2.12H20. 
 
 Magnesium chloride is prepared from the natural sources 
 of magnesia, namely, dolomite, or magnesite ; that is, from 
 magnesium carbonate by treatment with hydrochloric acid — 
 
 MgCOa + 2HC1 = MgCla + CO2 + H2O. 
 
 For use it is important that the chloride be free from 
 sulphate, to ensure which barium chloride is added to its 
 solution before it is crystallised by evaporation. 
 
 Eckel gives the following proportions of ingredients 
 necessary for preparing the cement: Equal weights of a 
 45 per cent, solution of magnesium chloride and of solid 
 magnesia (magnesium oxide), containing some 93 per cent, 
 of MgO, are added to an amount of water equal to the com- 
 bined weight of these ingredients. The mixture thus pro- 
 duced is then added to the inert material to be cemented to 
 the extent of about 5 per cent, of the whole. 
 
 This cement is too costly to be used on any very large 
 scale, but its adhesive power is great, and it is said to 
 produce artificial stones which are exceedingly durable. 
 It is employed for such purposes as making up emery 
 wheels, and has more recently been brought into requisition 
 for cementing sawdust in the preparation of certain patent 
 floorings which are floated like other cements, and with 
 which colouring matters,^ are usually mixed. 
 
 IV. Bitumen and Asphalte. 
 
 1. Bitumen. — Asphalte, though it has no connection with 
 hydraulic materials, at least consists of inert matter which 
 is bound together by what are eventually colloidal bodies. 
 
 » See article on " Pigments " in the final chapter. 
 
218 CHEMISTEY AND PHYSICS OP BUILDING MATERIALS 
 
 When vegetable or animal substances which have existed 
 on the earth's surface are precluded from oxidation by the 
 formation of deposits upon them, they become mineralised, 
 and are converted into coal and allied carbonaceous deposits. 
 Heat and pressure caused by earth movements, explained in 
 Chapter X., have resulted in many places in subterranean 
 distillation of tarry products from such deposits. These 
 highly complex distillates form, when in a liquid condition, 
 natural oils, and when consisting of heavier and less volatile 
 constituents, what is known as bitumen, mineral pitch or 
 asphaltum. 
 
 Occasionally bitumen oozes out from surrounding strata 
 and forms natural springs, giving rise to such remarkable 
 phenomena as the Pitch Lake of Trinidad, some ninety 
 acres in extent, situated at the head of the harbour of La 
 Brea. This lake is fed by viscous streams of bitumen 
 expressed from the hillsides, which solidify on exposure due 
 to the loss of the most volatile constituents of the liquid. 
 The bitumen thus produced is a grey somewhat brittle solid, 
 which forms a most valuable commercial source of this 
 material. 
 
 Apart from intermixed mineral matters from surrounding 
 strata (chiefly silica and alumina), bitumen consists chiefly 
 of compounds of carbon and hydrogen. Some of these 
 compounds belong to what is known as the paraffin series, 
 and constitute ordinary burning and lubricating oils, while 
 others are what are termed olefines, which are unsaturated 
 hydrocarbons : that is, compounds which have the power of 
 directly combining with other bodies. 
 
 The hardening of bitumen on exposure is due partly to 
 the loss of the more volatile constituents which leave a 
 residue possessing a higher melting point, partly to direct 
 absorption of oxygen from the air by unsaturated hydro- 
 carbons, which results in the formation of solid bodies, as in 
 the case of the drying oils used for painters' work, and 
 
ARTIFICIAL STONE, OXYOHLORIDE CEMENT, ETC. 219 
 
 partly to "polymerisation," that is, spontaneous aggrega- 
 tion of several molecules of certain compounds into one 
 heavier and more solid molecule, which may be brought 
 about by the presence of other substances such as sulphur, 
 of which as much as 6 per cent, is found in some varieties 
 of bitumen, though this element is not always present. 
 
 The valuable constituents of bitumen are soluble in such 
 liquids as carbon bisulphide, naphtha, and chloroform, and 
 by ascertaining the extent of such solution an estimate of 
 the quality of a sample may be obtained. Some 55 per 
 per cent, of Trinidad pitch is soluble in such liquids, and in 
 the case of bitumen from petroleum residues, which is much 
 freer from mineral matter, a larger proportion is thus 
 dissolved. 
 
 Bitumen is liable to be adulterated by coal tar pitch — the 
 residue left from the distillation of tar — a material which 
 lacks the elasticity and power of resisting changes of tem- 
 perature which renders bitumen so valuable. 
 
 2. Asphalte. — The terms " bitumen " and " asphalte " are 
 somewhat loosely used, but the latter substantive should be 
 confined to mineral deposits impregnated with bitumen, 
 which, when it fails to find an outlet on the earth's 
 surface, is often deposited in the interstices of porous rocks, 
 as the result of the subterranean processes of distillation 
 similar to that referred to above. Valuable asphalte 
 deposits in the form of chalk thus impregnated with some 
 6 to 12 per cent, of bitumen are found in the Khone valley, 
 near Bellegarde, where they are worked at Pyrmount and 
 Seyssel, and on the banks of the Eeuse as at the Val de 
 Travers. The deposits are of Jurassic age. The rock is 
 mined or quarried and reduced to fine powder, and is ready 
 for use after it has been roasted at a temperature slightly 
 above the boiling point of water, which results in the 
 expulsion of moisture and the partial liquefication of the 
 bitumen, which is thus enabled to bind the inert rock 
 
220 ohemistey and physics of building mateeials 
 
 powder when compressed by rammers used in laying the 
 material. 
 
 "Mastic " is a term applied to asphalte which has been 
 enriched by some 10 per cent, of bitumen in addition to that 
 naturally contained. This addition is effected by heating 
 the asphalte and bitumen together. 
 
 Many bituminous deposits ^ occur in this country, but few 
 of them have any commercial value. 
 
 ^ A good account of bituminous deposits, petroleum springs and 
 lignite, extending to some 70 pages, will be found in " Earthjf 
 Minerals and Mining." Davies. (Crosby Lockwood & Son.) 
 
CHAPTEE XX 
 
 THE metals: their general properties and occurrence 
 
 I. Introductory. 
 
 Metals present many obvious distinctions from the 
 materials discussed in previous chapters, and of these dis- 
 tinctions perhaps the most important is the power of 
 undergoing change of shape without rupture on submission 
 to the action of force, suitably applied. This power of 
 extension confers upon metals the properties of malleability 
 and ductility. Other distinctive features are : — Compact- 
 ness of structure, which admits of high polishing ; the 
 possession of a lustre very different from the vitreous lustre 
 of stony bodies when polished ; high specific gravity ; 
 great opacity to light ; large powers of conduction for heat 
 and electricity ; high co-efficients of expansion ; and from a 
 chemical standpoint, a tendency to undergo oxidation in a 
 moist atmosphere. 
 
 It must not be supposed, however, that all metallic sub- 
 stances necessarily possess all the above characteristics. 
 Zinc, for example, is comparatively brittle, gold leaf will 
 transmit some light, aluminium has a lower specific gravity 
 than many stones, while chemically although the metallic 
 oxides are essentially bases, their individual powers of 
 acting in this capacity are also very different, as has 
 already been made clear. 
 
 These variations in properties, again, serve as a reminder 
 that all groups of natural substances tend to shade one into 
 another, and that though such groupings are necessary and 
 useful, they are nevertheless to some extent artificial. 
 
222 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 Indeed, the more the structure of the metals is studied, the 
 greater become the apparent analogies between these bodies 
 and the stony materials already dealt with. 
 
 II. The Microstructurb of the Metals. 
 
 The microscope, which has proved so valuable an ally to 
 the study of stones, has, in recent years, given much assis- 
 tance in extending knowledge as to the structure of metals 
 upon which so many of their important properties depend. 
 
 At first sight an entire absence of form and a perfectly 
 homogeneous structure may appear characteristic of a 
 metal. A piece of lead, for example, exhibits when cut no 
 signs of crystallisation or variation of constituents so 
 noticeable in stones or bricks. 
 
 Metallic bodies have, nevertheless, a highly crystalline 
 and complex structure. Occasionally well-formed crystals 
 of metals are found occurring naturally. Crystals of copper, 
 for instance, are not uncommon. Again, when many 
 metals are melted and allowed to cool slowly, crystals are 
 formed on solidification, and may be removed from the 
 still molten residue in which they have been produced. 
 The tendency of molecules to assume the solid state in an 
 orderly manner seems, indeed, to be quite as great in the 
 case of the metals as in that of non-metallic bodies. 
 A strong analogy thus exists between the structure 
 developed by such rocks as granite and by the metals 
 on solidification, and just as slow or rapid cooling will 
 produce a granite composed respectively of large and well- 
 formed, or small and ill-formed crystals, so variations in 
 the rate of cooling will materially affect the structure of 
 a metal. 
 
 The opacity of metallic bodies, and the lack of dis- 
 similarity between their constituent parts, render it impos- 
 sible to obtain evidence of the truth of this contention as 
 
THE METALS: PBOPEETIES AND OCCUEEENCE 223 
 
 regards structure in the simple manner which can be 
 adopted in the case of stones, but by viewing, by reflected 
 light, sections of the metals specially prepared, ample 
 evidence of crystallisation has been obtained. 
 
 It may be argued that many metals consist wholly of one 
 element, whereas such rocks as granite possess several 
 constituents. Few metals as used in commerce are, how- 
 ever, pure. Thus cast-iron contains small quantities of 
 carbon, silicon, phosphorus, and sulphur ; and zinc, minute 
 amounts of lead, copper, and iron. Moreover, small though 
 the quantity of these extraneous substances may be, they 
 are yet able to produce very marked effects upon physical 
 properties. A difference of as little as 0-1 per cent, of 
 phosphorus in steels may, for example, produce a variation 
 of several tons per square inch in tensile strength. The 
 great effects produced by these impurities, or more correctly 
 these subsidiary constituents of the metals, are due to the 
 fact that they are not usually present as isolated elements, 
 but form in most cases definite compounds with the main 
 metallic constituent, and therefore the amounts of such 
 compounds disseminated through the mass may be com- 
 paratively large. Just, then, as granite consists of a mixture 
 of quartz, felspar, and mica, so steel may be looked upon as 
 composed of various distinct compounds of iron and sub- 
 sidiary elements such as those above enumerated. 
 
 These compounds will possess different properties ; some 
 will be harder than others, while some again will be more 
 soluble in acids, or other reagents than are others. 
 Working upon these lines, it has been found possible to 
 obtain microscopic distinctions showing structure by sub- 
 mitting sections of metals to an exceedingly delicate process 
 of poUshing, whereby one ingredient will be left less eroded 
 than another, just as a hard pebble might be found to stand 
 out in a worn paving-brick. 
 
 This polishing is effected by emery, and finally by rouge 
 
224 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 rubbed on with chamois leather, and in certain cases 
 additional differentiation is obtained by etching the surface 
 with dilute acids, or other solutions, which exert a greater 
 solvent power on one constituent than another. Permanent 
 records of the appearance of these sections under the micro- 
 scope may be obtained by replacing the eye of the observer 
 by a photographic plate. The "minerals" observed in 
 such sections often possess defined crystalline forms, and 
 present planes of separation. 
 
 Although the subsidiary constituents are usually found 
 combined with the preponderating metal, they or their 
 compounds are sometimes observed to form layers between 
 the faces of crystals of the main constituent. This is in 
 accordance with the well-known law that when an impure 
 substance crystallises from solution it tends to reject its 
 impurities, which will not conform to the particular crystal- 
 line shape it assumes. These impurities thus get wedged 
 out and by forming layers between crystal faces, prevent 
 direct contact between these faces and thus may seriously 
 affect the cohesion of the material, in much the same way 
 as the minutest film of oxide tarnishing the surface of a 
 metal will prevent adherence of a melted alloy in the 
 ordinary process of soldering. 
 
 In the light of these researches the effects of impurities 
 upon metals is at once rendered intelligible. Mechanical 
 stress carried beyond a certain point produces a slipping of 
 one crystal face over another, which finally results in 
 rupture, and since the cohesion of any metal is made up 
 of the cohesion of its constitutent " minerals," it is obvious 
 that slight differences in chemical composition, or even rate 
 of cooling on solidification, may produce great changes in 
 elasticity, malleability, and other physical properties. The 
 important process of annealing thus finds some explanation. 
 If a metal permanently strained by mechanical treatment 
 be heated for some time to a temperature which is often far 
 
THE METALS: PEOPEETIES AND OCCUEEENCE 225 
 
 below its melting point, the increased molecular vibration 
 thus conferred upon it enables the molecules to largely 
 resume their original positions and to refill the gaps 
 between the crystal faces which have been produced by 
 distortion. Annealing may also result in chemical re- 
 arrangement where sub-constituents are present. 
 
 III. Physical Pkopertibs of the Metals. 
 
 In this section the most important physical properties of 
 the metals as a class will be dealt with. 
 
 1. Malleability. — Malleability is the power of extension in 
 all directions under force, without rupture, whether this is 
 applied slowly, as by rolling, or suddenly, as by hammering. 
 This property is developed in very different degrees in 
 different metals. Thus whereas gold, with a specific gravity 
 nearly twenty times that of water, can easily be beaten out 
 into sheets thin enough to be blown away by the slightest 
 air current, very limited application of force is sufficient to 
 fracture ordinary zinc. Malleability is greatly affected 
 by the presence of impurities. For example, chemically 
 pure zinc is very malleable. Nevertheless, the inherent 
 differences in this property in the case of different metals 
 are considerable, and, again, are displayed in very different 
 degrees at different temperatures. Thus, zinc which is 
 brittle at ordinary temperatures becomes malleable at 
 about 120° C, and again brittle at a higher temperature, 
 presumably owing to the molecular vibrations then being 
 too great to withstand much mechanical force, which might 
 be expected in the case of a metal of low melting point. 
 
 2. Ductility. — This term expresses power of elongation 
 under tensile stress, that is, of conversion into wire, and 
 though it follows in metals the same order as malleability, 
 the values of these properties are not identical for a given 
 metal. Gold is very malleable and ductile ; but lead, 
 
226 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 though readily malleable, possesses but little ductility. 
 Ductility is also affected by temperature, and, as in the case 
 of malleability, the degree of attenuation obtainable is con- 
 siderably influenced by the rate at which deformation 
 proceeds. 
 
 3. Hardness. — In the case of metals, hardness usually 
 implies resistance to indentation, whereas in stony 
 materials resistance to attrition is as a rule in question. 
 This term in the two cases is not therefore synonymous. 
 Hardness is much affected by the condition of a metal, e.g., 
 whether annealed or not, and usually decreases considerably 
 with rise of temperature, so that this property appears to 
 be connected with molecular vibration. Hardness generally 
 increases with increase in elastic limit, and may be used to 
 give a very fair indication of tensile strength.^ 
 
 4. Elasticity. — Elasticity, which has been defined in a 
 previous chapter, is a highly important property in the case 
 of the metals, which differ from stones in that they possess 
 a definite elastic limit. If metals are stressed below this 
 limit they recover their form completely on the removal of 
 the force calling out such stress ; but should the stress pro- 
 duced exceed this limit permanent deformation results, 
 which involves loss in molecular cohesion, and hence the 
 material is then unable to bear without further deformation 
 even loads which in its normal condition would have been 
 insufficient to call out stresses up to the elastic limit. It 
 is obvious, therefore, that the elastic limit represents the 
 limit of safe usage for the material, and is of much greater 
 practical value than the ultimate strength ascertained by 
 testing the material to the point of rupture. As the ulti- 
 mate strength, however, is more easily determined it forms 
 the objective of ordinary tests. The limit of elasticity of 
 most metals may be taken as from 50 to 60 per cent, of 
 the ultimate strength ; hence, if a factor of safety of 4 is 
 
 1 See also p. 276. 
 
THE METALS: PEOPEETIES AND OCCUEEENCE 227 
 
 employed, that is, if the forces allowed in use be limited to 
 one quarter of the amount required to produce rupture, the 
 material is in reality subjected to stresses about half as 
 great as those which it could safely be called upon to with- 
 stand. Elastic properties may be investigated by submitting 
 the test piece to either compression, tension, or bending, 
 some further comments upon which will be found in 
 Chapter XXIII. 
 
 5. Fusibility. — The melting points of the metals cover a 
 very wide range of temperature. Mercury, for example, 
 melts (or freezes) at — 39° C. and platinum at 1,720° C. 
 Some metals, again, melt sharply without much previous 
 softening, while others pass through a viscous condition : 
 a fact of which advantage is taken in the process of 
 welding. 
 
 The fusibility of metals is affected to an extraordinary 
 degree by the presence of small quantities of other 
 elements. Thus the addition of some 2 per cent, of carbon 
 to pure iron lowers its melting point from about 1,600° C. 
 to 1,200° C. 
 
 Alloys — metallic bodies consisting of more than one 
 metal — generally melt at a much lower temperature than 
 do their individual constituents. Advantage is taken of 
 this fact in the preparation of fusible metals for temporary 
 castings, such as printers' type, and for fusible plugs to 
 admit of the discharge of water in case of fire. An alloy 
 has been prepared which, though quite hard at ordinary 
 temperatures, melts at 60° C. The most fusible of the 
 constituents of this alloy is tin, which has a melting point 
 of 235° C. 
 
 6. Expansion, Specific Heat, Conductivity. — The metals 
 as a class possess large co-efficients of expansion and great 
 conducting powers but low specific heats. Among the 
 metals connected with this discussion lead and zinc have 
 the greatest co-efficients of expansion and copper the 
 
 B.M. Q 
 
228 CHBMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 greatest conductivity, a property which in all metals is 
 modified to a marked extent by the presence of impurities 
 both as regards thermal and electrical conductivity. 
 
 IV. OCCUBRENCE AND EXTRACTION OF THE MbTALS. 
 
 1. Occurrence. — Although some three-quarters of the 
 elements which compose the earth must be classed among 
 the metals but few of them are found in any quantity, and 
 of these but a small proportion are used as isolated 
 materials for commercial purposes. 
 
 Bearing in mind the ready tendency of metals to oxidise 
 and yield to other chemical changes, it is hardly to be 
 expected that they will be found in an isolated state after 
 the ample opportunities afTorded for chemical action before 
 the earth assumed a solid condition. 
 
 One or two metals, such as gold and platinum, are indeed 
 found as such, but this is quite exceptional ; and in accord- 
 ance with the general law that elements have the greatest 
 affinity for those unlike themselves, it is with the non- 
 metalHc elements such as oxygen, silicon and sulphur that 
 combinations are to be expected. Oxides, sulphides and 
 silicates form, in fact, the most important natural com- 
 pounds of the metals. The two former classes of compounds 
 include the most valuable ores from which metals are 
 extracted, but most silicates present difficulties in the 
 matter of metallic separation. Again, secondary changes 
 brought about by weathering or special chemical agencies 
 have produced sulphates and carbonates, some of which are 
 used as metallic ores. 
 
 2. Metallurgy. — An ore may be defined as a mineral 
 which contains a commercially valuable metal in sufficient 
 quantity to repay extraction. Ores are almost invariably 
 oxides, sulphides or carbonates of metals mixed with a 
 variable but large proportion of inert and useless material, 
 
THE METALS: PROPEETIES AND OCCURRENCE 229 
 
 which is usually composed chiefly of silica or silicates and 
 aluminates; but sometimes consist of basic compounds, of 
 which the most common is calcium carbonate in the form 
 of limestone. 
 
 The percentage of metal which admits of the designation 
 
 ore," depends upon the value of the metal. Thus an ore 
 containing 12 per cent, of copper is looked upon as rich, 
 whereas one containing 30 per cent, of iron is but poor. 
 
 The treatment of the ore naturally varies considerably in 
 different cases, but the general principles of extraction may 
 be described as follows : — The material first undergoes a 
 roasting or calcining process at but a moderate temperature, 
 whereby moisture is expelled, sulphur, if present, is largely 
 burnt away, and carbonates are split up with the liberation 
 of carbon dioxide gas. 
 
 It will thus be seen that whether an oxide, a sulphide or 
 a carbonate constitute the ore, the material leaves the 
 calciner substantially in the form of an oxide, since the 
 liberation of sulphur results in the oxidation of the remain- 
 ing metal, and the decomposition of carbonates leave 
 metallic oxides also. 
 
 Only as an oxide is the ore capable of reduction by 
 carbon, which is the agent almost solely employed, either 
 in the form of coal or in a semi-burnt condition as carbon 
 monoxide gas. The affinity of carbon and of carbon 
 monoxide for oxygen is greater than that of any of the 
 common metals except aluminium, hence when heat is 
 applied a reaction leading to the separation of the metal 
 results. Thus if M stands for the general symbol of the 
 metal and MO represents its oxide, the equations showing 
 the extraction by the use of carbon and carbon monoxide 
 may be written as follows : — 
 
 MO + C =: M + CO 
 MO + CO = M + CO2. 
 
 Q 2 
 
230 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 In the absence of impurities no other substance besides 
 carbon would be necessary to effect the reduction of the 
 metallic oxide ; but in the presence of silica the oxide 
 would, on the application of heat, combine therewith to 
 orm a fusible silicate from which extraction of the metal 
 would be exceedingly difficult. To prevent such formation, 
 either siliceous and basic ores must be mixed together in 
 suitable proportions for treatment, or more usually a base 
 with which the silica will combine to the exclusion of the 
 metallic oxide, that is of the ore, must be added. 
 
 The cheapest base, and that at the same time a powerful 
 one, is lime (CaO), and this is added to the charge in 
 proportion to the amount of silica present. In practice, 
 chalk or limestone is generally employed, as this at the 
 furnace temperature is readily converted into lime and 
 carbon dioxide which passes off with the furnace gases. 
 Substances added with the above object are known as 
 " fluxes," and form with the silica the " slags " which 
 constitute so large a part of the material discharged from 
 metallurgical furnaces. 
 
 The furnace reactions (1) showing the production of lime, 
 (2) the withdrawal of silica as slag, (3) the action of coal on 
 the metallic oxide, may be represented as follows : — 
 
 CaCOa = CaO + CO2 
 CaO + SiOa = CaSiOg (slag) 
 MO + C = M + CO. 
 
 Some further details of the methods employed for 
 metallic extraction in individual cases and of other impuri- 
 ties which require consideration will be found in subsequent 
 chapters. 
 
 In conclusion a tabular statement of the values of the 
 more important physical constants of the metals may be 
 given. 
 
THE METALS: PEOPERTIES AND OCCUREENCE 231 
 
 Physical Constants of the Metals.^ 
 
 
 Specific 
 
 Specific 
 
 Melting 
 
 Co-eff. lineal" 
 
 
 Gravity. 
 
 Heat. 
 
 Point. 
 
 expansion. 
 
 xtLiUIlililiUxIi • • 
 
 2"58 
 
 0-22 
 
 625° C. 
 
 0-0000231 
 
 Antimony 
 
 6-71 
 
 0-051 
 
 440° C. 
 
 0-0000105 
 
 Bismuth . 
 
 9-80 
 
 0-047 
 
 268° C. 
 
 0-0000162 
 
 Cadmium 
 
 8-60 
 
 0-057 
 
 320° C. 
 
 0-0000306 
 
 Copper . 
 
 8-5 
 
 0-094 
 
 1050° C. 
 
 0 0000167 
 
 Gold 
 
 19-32 
 
 0-082 
 
 1045° 0. 
 
 0-0000144 
 
 Iron. 
 
 7-86 
 
 0-110 
 
 1600° C. 
 
 0-0000121 
 
 Lead 
 
 11-3 
 
 0-031 
 
 325° C. 
 
 0-0000292 
 
 Manganese 
 
 8-00 
 
 0-120 
 
 1900° C. 
 
 
 Mercury . 
 
 13-59 
 
 0-032 
 
 - 39° C. 
 
 
 Platinum . 
 
 21-50 
 
 0-033 
 
 1720° C. 
 
 0-0000089 
 
 Potassium 
 
 0-87 
 
 0-170 
 
 62° C. 
 
 0-0000841 
 
 Silver 
 
 10-53 
 
 0-056 
 
 945° C. 
 
 0-0000192 
 
 Sodium . 
 
 0-97 
 
 0-290 
 
 95° C. 
 
 0-0000710 
 
 Tin . 
 
 7-2 
 
 0-056 
 
 227° C. 
 
 0-0000223 
 
 Zinc 
 
 7-2 
 
 0 094 
 
 415° C. 
 
 0-0000291 
 
 Most of the above data have been taken from Robert Austen's "Introduction to the 
 Study of Metallurgy." (Griffin.) 
 
CHAPTEE XXI 
 
 IRON AND STEEL 
 
 I. Ores. — Metallurgy and Definitions. 
 
 1. Ores of Iron. — Though compounds of iron are widely 
 distributed and often occur in large quantities, the ores 
 of iron are comparatively restricted owing to the difficulties 
 which beset the removal of certain elements, particularly 
 sulphur, phosphorus and arsenic, which are associated 
 with many iron compounds. For this reason the sulphides 
 of iron are never used as ores. The most important sources 
 of iron are the following minerals : — 
 
 (a) Magnetite (Fe304).— This is the richest ore of iron 
 and contains when pure as much as 72 per cent, of the 
 metal. It is found in masses of easily-separated grains, 
 sometimes almost free from extraneous matter. In colour 
 it is black, or sometimes greyish brown. It is magnetic, 
 i.e., attracted by a magnet. Large quantities of magnetite 
 are found in Sweden and in America near Lake Superior. 
 
 (b) Red Hcematite (F2O3). — Several minerals are included 
 under this title, such as micaceous hgematite, which flakes 
 like mica, specular iron ore, and kidney ore, the latter 
 deriving its name from the shape of the masses in which 
 it is found. These minerals are generally black upon the 
 surface but are red internally, and therefore give a red 
 streak when scratched, a fact of which use is made in their 
 identification. Though slightly less rich than magnetite, 
 red haematite is a very valuable ore, and is usually free 
 from phosphorus. It is found in Cumberland and near 
 
lEOK AND STEEL 
 
 233 
 
 Furness in this country, and in great quantities in 
 America. 
 
 (c) Brown Hcematite (FeaOs + water) —Containing as it 
 does 10 per cent, or more of water, this ore is not so 
 valuable as those above cited. Under this designation the 
 minerals limonite and bog iron ore are included. The ores 
 are brown in colour and give a brown streak when scratched. 
 They occur in Gloucestershire, Northamptonshire, and 
 Lincolnshire in this country, much associated with silica 
 and often with phosphorus, but are found in a very pure 
 form in Spain, whence they are imported. 
 
 {d) Carbonate of Iron (FeCOa).— Carbonate of iron, 
 although a poor ore on account of the great admixture 
 of impurities usually found with it, is the most important 
 source of the metal in this country. It occurs in the 
 Cleveland district of Yorkshire as clay ironstone containing 
 some 30 per cent, of iron and associated with carbonaceous 
 matter as black band ore in Staffordshire and in Scotland. 
 The Cleveland ore is brownish or dull blue in colour and 
 much resembles hard clay in appearance. 
 
 2. Metallurgy of Iron and Steel. — The processes involved 
 in the extraction of iron from its ores are the same whether 
 iron or steel is required as the final product. The pre- 
 liminary roasting referred to in the last chapter is effected 
 in large cylindrical vessels open at the top and bottom, in 
 which the ore mixed with fuel is raised by the combustion 
 of the latter to a low red heat. The contents of this 
 " calciner " are then mixed with about twice their weight of 
 limestone and two-thirds their weight of specially-prepared 
 hard coke, and thrown into the top of a blast furnace, a 
 cylindrical structure some 60 to 90 feet in height, and 
 20 to 30 feet in diameter, built of refractory fire-bricks 
 covered externally by iron plates. The internal diameter 
 of the furnace is, by thickening of the walls, reduced at the 
 bottom and also at the top. Air, previously heated by 
 
234 CHEMISTRY AND PHYSICS OP BUILDING MATERIALS 
 
 means of waste gases from the furnace, is forced in near the 
 bottom by powerful blowing engines when the coke is 
 partially burnt, and reduces the iron oxide probably while 
 this is still in a solid condition and while still at a com- 
 paratively low temperature. This reaction may be stated 
 thus : — 
 
 FeaOg + SCO = 2Fe + 3C0j 
 The iron in spongy masses gradually sinks down to the 
 lower part of the furnace as the fuel burns away and alloys 
 with carbon from the fuel, which renders it readily fusible 
 at a temperature of about 1,200° C, which is easily attained 
 at the bottom of the furnace. 
 
 In the meantime silica present in the ore combines with 
 quicklime resulting from the limestone present in the 
 furnace charge and forms slag— silicate of lime— which also 
 melts and finds its way to the bottom of the furnace, where 
 it floats upon the heavier molten iron. Some of the siHca, 
 however, is reduced to the element silicon, a reduction 
 which is promoted by a high temperature, and this also 
 alloys with the iron, which absorbs further impurities, such 
 as sulphur from sulphides, or reduced sulphates present in 
 the ore or limestone, and phosphorus chiefly derived from 
 fossils, remains of animal organisms, found in the form 
 of calcium phosphate Ca3(P04)2 in the limestone. 
 
 Trom time to time the slag is run off from tapping holes 
 at the base of the furnace, and the molten iron is similarly 
 tapped and run into sand moulds, when it forms what is 
 known as " pig iron," from which all varieties of iron and 
 steel are prepared. 
 
 Some idea of the magnitude of the operations may be 
 gathered from the fact that a single furnace can turn out 
 some 50 tons of pig iron per day, involving a charge of some 
 600 tons of materials and the production of some 75 tons 
 of slag, the balance of the charge being finally dispersed 
 into the atmosphere, mostly in the form of carbon dioxide. 
 
lEON AND STEEL 
 
 235 
 
 3. Definitions of Iron and Steel. — The subsequent sections 
 of this chapter will be devoted to the discussion of cast 
 iron, wrought iron, and steel, which are derived from pig 
 iron. Preliminary to this discussion some definition of 
 these materials may be attempted. Originally a simple 
 distinction based on the percentage of carbon contained in 
 these metals was sufficient. Wrought iron was defined as 
 nearly pure iron, steel as iron containing an intermediate 
 quantity, and cast iron as a variety containing the largest 
 quantity of carbon. All these materials (certain special 
 varieties excepted) contain upwards of 95 per cent, of iron, 
 and their great physical differences, therefore, depend on 
 but small variations in chemical composition. One material, 
 moreover, sometimes grades into the others without any 
 sharp line of chemical demarcation. 
 
 With the advent of mild steel, by far the most important 
 of these bodies as here discussed, this definition on a 
 chemical basis became unsatisfactory, since some of such 
 steels contain less carbon than certain wrought irons, and 
 the now generally recognised nomenclature necessitates 
 a definition based upon the mechanical preparation of the 
 materials rather than upon their composition. Although 
 the subject is an important one, if only from a legal aspect, 
 it cannot be said that opinion as to the exact designation of 
 these materials is yet unanimous. 
 
 (a) Cast iron may be defined as the metal resulting from 
 the refining of pig iron by the process of re-melting and oxida- 
 tion of most of its impurities. It contains 1"5 to 4"5 per cent, 
 of carbon, though the latter limit is seldom approached in 
 commercial cast irons. It also contains silicon, often in 
 considerable quantity, while phosphorus and sulphur are also 
 often present. Mechanically it is distinguished by its low 
 tensile strength. 
 
 (b) Steel is often popularly defined as iron containing 
 less than 1*5 per cent, of carbon, and which hardens when 
 
236 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 heated and then suddenly cooled, as by quenching with 
 water. This definition is suitable for hard but not for 
 mild steels, which do not harden when quenched,^ and 
 which contain less than 0'5 per cent, of carbon. Sexton 
 defines steel as " all forms of iron except wrought iron which 
 contain less than 1*5 per cent, of carbon and only ordinary 
 impurities." A definition which would suffice for all mild 
 steels, and serve to distinguish them from wrought iron, 
 might be ** iron prepared by fusion, which contains less than 
 1*5 per cent, of carbon and but very small quantities of 
 other constituents." 
 
 (c) Wrought iron may be defined as iron containing less 
 than 0*25 per cent, of carbon, which has been formed in 
 a plastic (as disfcinguished from a molten) condition. 
 Wrought iron contains thin films of interleaved slag, and 
 is characterised by its great malleability. 
 
 4. Condition of Carbon in Iron and Steel. — The carbon 
 in the above materials may be in a combined or in an 
 uncombined state. It is found in three forms : (1) as 
 graphite, when it is merely mixed with the iron. This 
 condition is practically confined to cast iron, and only 
 occurs when a large quantity of carbon is present ; (2) As 
 hardening carbon, possibly a compound with the formula 
 Fe24C ; (3) As cementite, also called cement carbon or 
 carbide carbon, a compound with iron FoaC, in which 
 form as much as 0*9 per cent, can be taken up by 
 iron. Steel probably contains both hardening carbon and 
 cementite. 
 
 The state assumed by the carbon depends upon (a) the 
 amount present ; (b) the presence of other elements, par- 
 ticularly silicon, sulphur and manganese; (c) the temperature 
 at which cooling begins and the rate at which it progresses. 
 
 ^ This opinion is not shared by Johnson. Johnson, "The Materials 
 of Construction," p. 500, 1904 ed. Some standard of hardness must 
 probably be agreed upon before this question is finally settled. 
 
IRON AND STEEL 
 
 237 
 
 II. Cast Ieon. 
 
 1. Preparation. — Iron as it issues from the blast furnace 
 seldom contains more than 94 per cent, and sometimes as 
 little as 90 per cent, of metallic iron. The other con- 
 stituents consist of some 2 to 5 per cent, of carbon, 01 to 
 4 per cent, of silicon, and variable quantities of sulphur, 
 phosphorus and manganese in combination. 
 
 Commercial cast iron is prepared by re-melting the pig 
 iron in a small furnance known as a cupola, by the aid of 
 fuel mixed with the iron. This does not decrease the 
 amount of carbon present, which, indeed, if small may be 
 increased by the process, but the silicon is readily oxidised 
 by the air blast supplied to the furnace, and the silica thus 
 formed, together with sand adhering to the iron from the 
 sand moulds, forms a slag, which formation is facilitated by 
 the addition of a small quantity of limestone. The object 
 of the cupola treatment is not, however, to remove the 
 whole of the silicon — which is a constituent not without its 
 value — but rather to admit, by the mixing of pig iron of 
 various compositions and the removal of sand and adherent 
 slag from the blast furnace, of the production of cast iron 
 of suitable composition for various purposes. The per- 
 centage of sulphur and phosphorus in the iron undergoes 
 but little modification during the cupola treatment. 
 
 Cast iron is classified into various grades according to its 
 composition and properties. These will be referred to after 
 the effect of the subsidiary constituents in the material have 
 been dealt with. 
 
 2. Subsidiary Constituents of Cast Iron. — (a) Carbon. — 
 Carbon is usually found in cast iron in both the free 
 (graphitic) condition and also combined with iron. Graphite 
 gives the metal a coarsely crystalline structure and a grey 
 colour, and the name " grey iron " is given to cast iron 
 in which the carbon is chiefly in this free condition. When 
 
238 CHEMISTEY AND PHYSICS OP BUILDING MATERIALS 
 
 combined with the iron in the form of cementite and 
 possibly also as hardening carbon, carbon produces a cast 
 iron which, fine in grain, hard, brittle, and white in colour, 
 is known as " white iron." A mixture of grey and white 
 iron is known as " mottled iron." 
 
 In the greyest irons the combined carbon may not 
 amount to more than O'l per cent., and the whitest irons 
 may contain as much as 3 per cent, of carbon in combina- 
 tion. The total amount of carbon in cast iron seldom 
 amounts to 4*5 per cent. 
 
 (b) Silicon. — This element, unlike carbon, seems to have 
 the power of alloying with iron in unlimited quantity. 
 Ordinary pig iron contains some 1 to 4 per cent, of silicon, 
 but iron made for certain special purposes, known as 
 " silicon pig," contains as much as 10 or 15 per cent. 
 Chemically, silicon has a strong resemblance to carbon, and 
 possibly exists in the iron in both the free and combined 
 states. This element is a distinctly valuable constituent of 
 cast iron, which may often advantageously contain as much 
 as 2*5 per cent., for the following reasons : (1) It tends to 
 keep the carbon in the free state, and thus prevents the 
 formation of white iron ; (2) It tends to prevent the 
 absorption of sulphur from the ore and fuel; (3) It 
 reduces shrinkage and blowholes, due to escaping gases, on 
 casting. The direct effect of silicon on iron is to render 
 the metal hard and brittle, but in the presence of other 
 constituents this effect is not displayed unless the amount 
 of the element present is excessive. 
 
 (c) Sulphur. — This element is objectionable in all forms 
 of iron, and the difficulty in eliminating it prevents the use 
 of all sulphide ores, such as iron pyrites, for the prepara- 
 tion of iron and steel. The effects of sulphur are the 
 opposite of those produced by silicon, and its presence 
 causes the carbon to assume the combined condition which 
 renders the metal hard and brittle. Sulphur is rarely 
 
lEON AND STEEL 
 
 239 
 
 present in cast iron in amounts exceeding 0"15 per cent., 
 and in iron to be used for the production of steel not more 
 than one-third of this quantity is admissible. Sulphur is 
 always found in a combined state, as manganese sulphide 
 (MnS), if the manganese present be sufficient for the 
 absorption of the sulphur, but if excess of sulphur exists 
 then iron sulphide (FeS) is formed. This compound, 
 owing to its low power of adhesion, is a great source of 
 weakness, particularly when it occurs in radiating forms 
 which expose large surfaces. 
 
 (d) Phosphorus. — One of the chief sources of phosphorus 
 is, as has been pointed out, the fossil remains in the lime- 
 stone used in the blast furnace. The amount of this 
 element present in iron therefore shows considerable varia- 
 tions, but 0*5 per cent, may be considered to be the 
 maximum allowable. Phosphorus, which is probably 
 present as phosphide of iron, considerably increases the 
 fluidity of the metal, and therefore facilitates casting, but 
 in quantities greater than that above cited it renders the 
 iron hard and brittle. 
 
 As the refining processes of the cupola furnace have little 
 effect on the amounts of sulphur and phosphorus present, 
 it is necessary to exclude excessive quantities of these 
 elements from the original material used. 
 
 (e) Manganese. — Manganese is a metal very like iron in 
 many of its properties, and is associated with iron in the 
 original ore. It is found in cast iron in variable amounts 
 up to about 2 per cent. The effect of manganese is not 
 great, but since it combines with sulphur more readily than 
 does iron, and since the manganese sulphide thus formed is 
 less objectionable than iron sulphide, it is so far valuable. 
 The direct influence of less than 1 per cent, is said to be 
 negligible, but larger quantities tend to produce hardness 
 and brittleness. 
 
 3. Grades and Properties of Cast Iron. — (a) Refined iron, 
 
240 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 produced by the re-melting of pig iron, is usually placed in 
 four grades, based on the greyness or whiteness of the 
 metal. 
 
 No. 1 is the greyest iron and is suitable for making fine 
 castings, but has a low tensile strength and is very soft, 
 a blow from a hammer readily producing indentation. 
 The total percentage of carbon is high, but the combined 
 carbon is less than 0*3 per cent. The amount of silicon is 
 also usually large. For most purposes this grade is mixed 
 with one or more of those mentioned below. 
 
 No. 2 is harder and stronger than No. 1, and is used for 
 the lighter class of castings. The combined carbon still, 
 however, does not exceed about 0"4 per cent. 
 
 No. 3 is suitable for heavy castings, is harder than 
 No. 2, and may contain 0*6 per cent, of combined carbon. 
 
 No. 4 is " white iron " and is distinctly inferior to the 
 above. It is very hard and brittle, and shows a fine 
 structure and white colour on fracture. It contains about 
 0*9 per cent, of combined carbon. This grade is used for 
 making malleable cast iron and for mixing with the above 
 grades. 
 
 (b) Malleable Cast Iron. — The advantages of an iron 
 which can be cast and yet be rendered sufficiently malleable 
 to admit of subsequent changes in form are obviously great 
 enough to warrant subsequent treatment in certain cases 
 with a view to obtaining such malleability. 
 
 When ordinary cast iron is heated in contact with iron 
 oxide (Fe203), the carbon in the combined condition is 
 slowly oxidised by the oxygen in the surrounding oxide and 
 is evolved as carbon monoxide. This reduction takes place 
 initially at the surface of the iron and gradually extends 
 inwards. The material used for the production of malleable 
 cast iron should be white iron, i.e., iron in which the carbon 
 is very largely in a state of combination, hence the per- 
 centage of silicon should be low. Manganese should be 
 
lEON AND STEEL 
 
 241 
 
 present, and the metal should be as free as possible from 
 phosphorus. 
 
 The result of this process is practically to form over the 
 casting a layer of pure iron possessing the physical pro- 
 perties of wrought iron ; but since the extent to which the 
 elimination of the carbon takes place can never be certainly 
 known in the case of castings of any size, the material is 
 not suitable for use in situations in which large stresses are 
 liable to be called out in it. In the production of intricate 
 castings in which minor modifications have subsequently to 
 be made, malleable cast iron is, however, of great service. 
 
 4. Conclusion. — The above brief account of cast iron will 
 have rendered it evident that the action of one element is 
 so dependent upon the presence of others, that any state- 
 ments as to the individual effects of subsidiary con- 
 stituents are beset with difficulty. Turner states that the 
 best percentage of combined carbon for crushing strength is 
 upwards of 1 per cent., for tensile strength 0*47 per cent., 
 and for transverse strength 0-7 per cent. For silicon these 
 values are given for crushing strength as 0-8 per cent., for 
 modulus of elasticity I'O per cent., for tensile strength 
 1-8 per cent., for softness 2-5 per cent. The effect of the 
 constituents enumerated may be summarised by the state- 
 ment that in cast iron a large percentage of carbon in 
 the free state and a small percentage in the combined 
 state is necessary, that a small quantity of silicon is 
 desirable, that sulphur and phosphorus (particularly the 
 former) are objectionable, and that the effect of manganese 
 may usually be neglected. 
 
 III. Wrought Iron. 
 
 1. Preparation. — Wrought or malleable iron is manufac- 
 tured by melting pig iron on a small shallow hearth lined 
 with iron oxide, by means of a fire placed at the side. From 
 
242 CHEMISTRY AND PHYSIOS OF BUILDING MATERIALS 
 
 the roof of this erection, known as a reverberatory furnace, 
 the heat reverberates on to the charge on the hearth, and 
 by maintaining an oxidising atmosphere and keeping the 
 melted metal stirred,^ the subsidiary constituents of the pig, 
 together with a good deal of the iron itself, are oxidised. 
 The iron oxide formed readily combines with the silica from 
 the sand moulds and that produced by combustion of the 
 silicon in the pig iron, and the resulting silicate of iron 
 forms a slag which floats upon the molten iron and is 
 allowed to flow out of the furnace. As the iron approaches 
 a state of purity its melting point rises from about 1,200° C. 
 to 1,600° C, and since the temperature attained in the 
 furnace does not rise to this latter limit, the charge finally 
 becomes pasty, and is then rolled up into balls known as 
 " blooms," which are removed and subjected, while still red 
 hot, to compression from a steam hammer in order to 
 remove as much as possible of the entangled and more 
 liquid slag which is always present in considerable quantity. 
 After this process the iron is rolled into any desired form 
 while still in a pasty condition. 
 
 2. Subsidiary Constituents of Wrought Iron. — The charac- 
 teristic properties of wrought iron are more marked the 
 greater its freedom from any other elements, hence the 
 percentage of subsidiary constituents is usually exceedingly 
 small, and some high grades of this material contain as 
 much as 99*9 per cent, of metallic iron. 
 
 (a) Carbon. — It is seldom that more than 0*1 per cent, of 
 carbon is found in wrought iron, although 0*25 per cent, 
 has been given as the distinguishing carbon limit between 
 this material and steel. The larger the percentage of this 
 element present the less is the malleability of the metal. 
 
 (h) Silicon. — Silicon is always present to a small extent 
 in the form of slag (silicate of iron) which has escaped 
 
 ^ This stirring process is known as "puddling," and the furnace 
 itself is known as a " puddhng furnace." 
 
lEON AND STEM. 
 
 243 
 
 removal during manufacture and occurs as thin interleaved 
 layers between the crystals of iron. Beyond slightly 
 decreasing the strength of the material, this small quantity 
 of slag has no objections. When the element silicon is 
 alloyed with the iron, more than 0*1 per cent, is detri- 
 mental to malleability, as in cast iron. The total quantity 
 of silicon present seldom exceeds 0*25 per cent. 
 
 (c) Sulphur. — This element is not often found in appre- 
 ciable quantities, since care is taken to exclude its presence 
 from the original materials used in manufacture. It is highly 
 injurious, 0-05 per cent, of sulphur is sufficient to render 
 the metal " red short," that is, brittle when hot, and thus to 
 preclude welding. 
 
 (d) Phosphorus. — The presence of phosphorus particularly 
 affects the malleability of wrought iron when cold — known 
 as rendering it "cold short"; 0-25 per cent, is sufficient to 
 produce this result. The quality of iron containing phos- 
 phorus may be sometimes improved by heating the metal 
 and allowing it to cool very slowly, which probably enables 
 the phosphorus to coagulate, when it is not so injurious as 
 when distributed more evenly through the iron, 
 
 (e) Manganese. — This metal is only present in such 
 small quantities in wrought iron that its effect may be 
 neglected. 
 
 3. Grades and Properties of Wrought Iron. — The essential 
 quality of good wrought iron is its perfect malleability both 
 when cold and hot. The appearance of the metal on 
 fracture does not admit of the ready distinctions cited in 
 the case of cast iron. The fibrous structure generally 
 looked upon as evidence of good quality is really the result 
 of the presence of interleaved slag, without which the metal 
 in a completely crystalline condition would be stronger and 
 more malleable ; but since the presence of a small quantity 
 of slag is inevitable, the structure observed is valuable 
 in showing that the material has been rendered as 
 
 B.M. B 
 
244 CHEMISTEY AND PHYSICS OP BUILDING MATEEIALS 
 
 homogeneous as possible by the thorough intermixture of 
 this impurity. 
 
 Brands upon wrought iron, apart from a knowledge of 
 the branding system adopted by the firm supplying the 
 material, are not of much value, though a crown alone, or 
 with one, two or three " bests " accompanying it, usually give 
 the quality in ascending order from a given maker's supply. 
 The poorest qualities of iron are not branded. 
 
 IV. Steel. 
 
 1. Preparation. — Setting aside cementation and crucible 
 steels prepared in comparatively small quantities for tools, 
 springs, and minor purposes, there are but two methods^ in 
 general use for the preparation of steel, known as the 
 Bessemer, and the Siemens or open hearth, processes. In 
 both methods the starting point and objective are the same, 
 namely, the removal of the carbon and silicon from pig 
 iron by re-melting and oxidation until almost pure iron is 
 obtained, when an additional quantity of carbon is added 
 necessary for the production of steel. The difference between 
 these two processes lies chiefly in the means adopted to 
 effect the oxidation of the carbon and siUcon, and in the 
 form of furnace, source of heat, and quantity of material 
 operated upon at one time. 
 
 (a) Bessemer Process. — In this process, named after its 
 inventor, melted pig iron, or in more modern practice 
 molten iron direct from the blast furnace, is run into a 
 cylindrical vessel hung on horizontal bearings near its 
 centre. This erection, known as a " Bessemer Converter," is 
 closed at its lower and open at its upper end, which is 
 tapered. Molten iron is run into the converter and a blast 
 of air is forced through the liquid by means of a perforated 
 
 1 The new process in use at the DarUngton Forge is at present used 
 on too limited a scale to admit of description here. 
 
lEON AND STEEL 
 
 245 
 
 false bottom, which results in the combustion of the carbon 
 and silicon in the iron, whereby the temperature of the 
 material is maintained sufficiently to keep the iron in a 
 molten condition. When this combustion is complete, as is 
 evidenced by the issuing flame showing signs of burning 
 iron, the air blast is stopped and an alloy of iron, carbon 
 and manganese, known as " spiegeleisen," is introduced. The 
 carbon thus added alloys with the iron, and the manganese 
 rapidly absorbs oxygen which still remains in the metal. 
 The oxide of manganese thus formed combines with the 
 oxidised silicon and forms a small quantity of slag. The 
 conversion into steel is then complete, and the metal is 
 immediately cast into moulds. 
 
 (b) Siemens'' Process. — In this method of production, pig 
 iron is melted on a large open hearth by means of powerful 
 gas furnaces, and the oxidation of the carbon and silicon is 
 effected partly by the oxidising atmosphere and partly by 
 the addition of iron oxide (haematite), which is itself reduced 
 to metallic iron and thus supplies oxygen to the charge. 
 Spiegeleisen is then added, though since the duration of the 
 oxidation is much longer than in the Bessemer process and 
 the operation thus under better control, the addition of 
 carbon is not always necessary, as the combustion of this 
 element in the pig iron can be arrested when its amount is 
 decreased to the percentage required in steel. The action 
 of the manganese is similar to that described above, and 
 when the intermixture of the spiegeleisen is complete the 
 charge is run out and the material cast as before. 
 
 (c) The Above Processes Compared. — In neither of the 
 above methods of steel production as described are sulphur 
 or phosphorus eliminated from the pig iron. No means 
 have been found for the removal of the former, hence only 
 iron containing but little sulphur can be utilised for this 
 manufacture. When phosphorus is present its absorption 
 may be effected by the furnace lining if this is made of 
 
 E 2 
 
246 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 basic materials (lime and magnesia), instead of the usual 
 acid lining such as quartz sand, generally employed. The 
 processes thus modified are known as the " basic Bessemer " 
 and " basic open hearth " processes, while the prefix " acid " 
 is, by way of distinction, sometimes given to these processes 
 as ordinarily carried out. 
 
 The Bessemer process is the cheapest method for steel 
 production, but it is gradually giving way to its competitor 
 owing to the greater reliability of open hearth steel, which, 
 on account of the large quantity prepared at one time and 
 the length of the operation, is under better control. Steel 
 is often specified as " open hearth steel," and unless evidence 
 is forthcoming that the ores used in its production are free 
 from phosphorus, it is further, sometimes, desirable to 
 stipulate that the material should be "basic open hearth 
 steel." 
 
 2. Subsidiary Constituents.— (a) Carbon— The amount of 
 carbon in steel varies from O'l per cent, in the very softest 
 to 1-5 per cent, in hard tool steels. The steels used in 
 constructional work seldom contain more than 0'5 per cent, 
 of carbon. This element is never present as graphite in 
 any steel in ordinary use. If the metal has been cooled 
 slowly, most of the carbon is found as cementite (FosC), while 
 rapid cooling produces hardening carbon. 
 
 (h) Silicon— heBS than 0-3 per cent, of silicon appears to 
 have little effect upon steel, and as larger quantities are 
 seldom present, this element is not important. Opinions 
 as to the effect of larger quantities are divided. 
 
 (c) Sulphur. — Owing to the care taken to exclude 
 sulphur, it is seldom present in appreciable quantity. Even 
 as little as 0*08 per cent, is stated to be injurious, and 
 to make the metal brittle when hot and reduce its mallea- 
 bility. Manganese, as shown in previous cases, appears 
 to have a beneficial effect in neutralising the effects 
 of sulphur. 
 
lEON AND STEEL 
 
 247 
 
 (d) Phosphorus.— Thia is the most objectionable impurity 
 in constructional steel, as it renders the metal brittle under 
 shock, which is especially the case with steels rich in carbon. 
 The structure of the material is rendered coarser by the 
 presence of phosphorus, and although this element may 
 raise the tensile strength of the steel, as little as O'l per 
 cent, must be looked upon as objectionable. 
 
 (e) Manganese. — Though added to steel in its manufac- 
 ture, this element is almost entirely eliminated by its 
 combination with oxygen and silica. Its effect in ordinary 
 steel may be neglected, as less than about 1 per cent, 
 appears to exert little influence. 
 
 3. Grades and Properties of Steel. — Steel may be classi- 
 fied according to the method of its manufacture; it is, 
 however, more useful to regard it from the aspect of its 
 uses, as hard, medium, and mild steel. Hard tool steels 
 may contain as much as 1'5 per cent, of carbon, though 
 the amount is more usually about 1 per cent. Such steel 
 may be " tempered," that is, when heated and quenched at 
 various temperatures (evidenced by the tint of films of 
 oxide which form upon its surface on cooling) various 
 degrees of hardness may be obtained owing to the propor- 
 tion of hardening and cement carbon thus produced. Mild 
 steels, alone used in construction, contain less than 0*5 per 
 cent, of carbon, and do not appreciably harden on quench- 
 ing. Medium steels possess properties intermediate between 
 those above cited. The steel used for railway tracks may 
 be placed in this category. 
 
 A number of steels containing large proportions of other 
 metals are prepared for special purposes, and are generally 
 known by the prefix of the preponderating subsidiary con- 
 stituent. Chromium steel, manganese steel, and nickel 
 steel are examples of such materials, which, however, are 
 not of interest from the standpoint of this discussion, 
 
248 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 V. CoBROSioN OF Iron and Steel. 
 
 The decay of iron and steel is due to oxidation, either 
 brought about directly through atmospheric or other 
 natural agencies, or electrolytically : that is, by the setting- 
 up of electric circuits between the iron and other con- 
 stituents or bodies in contact, in the presence of moisture, 
 when the energy of the current is derived from the solution 
 of the iron, 
 
 1. Oxidation. — Iron is, unfortunately, more than any other 
 common metal prone to deterioration by oxidising, the 
 effects of which are much accentuated by the fact that the 
 oxide formed lacks the property of adherence which, in 
 the case of most other metals, limits oxidation to a mere 
 superficial action, the oxide itself forming a protective 
 coating for the interior of the mass. 
 
 The exact changes which occur when iron rusts have 
 formed the subject of several scientific investigations, but 
 it cannot be said that any agreement as to their precise 
 nature has yet been arrived at. It is a well-established 
 fact that no rusting takes place either in air free from 
 moisture or in water free from air, and it was formerly 
 held that, in addition to air and moisture, carbon dioxide 
 (always present in the atmosphere) was also essential. 
 Recent experiments^ would seem to show that the presence 
 of carbon dioxide is unnecessary, but this conclusion has 
 been disputed. Without attempting to enter into this 
 discussion, for which the original researches must be con- 
 sulted, it may be stated that carbon dioxide undoubtedly 
 increases the rapidity with which rusting takes place, and 
 that the presence of alkaline substances, such as lime, are 
 most effectual in preventing rusting. This latter fact is 
 of the utmost importance in connection with the use of 
 
 ' "The Rusting of Iron," J. Chem. Soc, Dunstan, Jowett and 
 Goulding, October, 1905 ; and later criticisms. 
 
lEON AND STEEL 
 
 249 
 
 iron and steel in concrete, as such materials require no 
 protection : in fact, their adhesion to the concrete is improved 
 by a slight initial coating of rust. 
 
 If carbon dioxide is an essential in the rusting of iron, 
 its action is an indirect one, as rust is substantially a 
 hydrated oxide of iron, and appears to have the formula 
 Fe203H20, or, more properly, Fe202(OH)2. 
 
 2. Electrolytic Decay. — The subsidiary constituents in 
 iron and steel, and the presence of rust films, or even 
 protective coatings, when flaws arise in them, may exert 
 considerable influence in promoting decay. 
 
 "When two different substances are separated at one 
 point by a liquid in which one of them is soluble, and are 
 connected at some other point, an electric circuit is formed 
 similar to that produced when the poles of an electric cell 
 are connected. The electric energy is derived from the 
 solution of material : that is, from chemical action which 
 would otherwise result in evolution of heat. Such "electro- 
 lytic action " has constant opportunities of displaying itself 
 when moisture, impregnated with acids from the atmo- 
 sphere or salts in solution, obtains access to two different 
 constituents of iron or steel, and can even take place 
 between iron and rust, or between iron and paint if the 
 latter is so far deprived of its oily covering as to allow its 
 conducting powers to make themselves apparent. Again, 
 when iron is in contact with another metal, a similar action 
 may take place. It does not follow that the iron will in all 
 cases be the material which is dissolved in electrolytic 
 actions, but in all ordinary cases except when zinc is the 
 metal in contact with it, it is the iron which suffers solution. 
 The rapidity of rusting often observed when protective 
 coatings of other metals deposited upon iron are damaged, 
 resulting in exposure of the iron, may in some cases be 
 traced to electrolytic causes. 
 
 3. Comparative Decay of Iron and Steel. — Cast iron, 
 
250 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 protected by a natural thin coating of slag from the sand 
 moulds, resists oxidation well, but this coating is hardly to 
 be relied upon. Finely grained grey iron is said to resist 
 oxidation under ordinary conditions better than other 
 varieties, while white iron is less affected by acids than 
 grey iron. 
 
 Cast iron is said to corrode more quickly in fresh water, 
 and more slowly in salt water, than does wrought iron. 
 
 Mild steel and wrought iron rust in a manner some- 
 what different from cast iron. Layers of oxide are formed 
 on these latter materials which tend to flake off and expose 
 new surfaces, whereas the rust upon cast iron accumulates 
 in nodular masses which are more adherent. 
 
 In confined situations the question of rusting may assume 
 importance in relation to damage to surrounding materials, 
 since rust is much more bulky than the iron from which 
 it is formed. Eust from wrought iron has been stated 
 to occupy ten times the volume of the metal contained 
 in it. 
 
CHAPTEE XXII 
 
 OTHER METALS AND ALLOYS 
 
 I. Copper. 
 
 1. Ores. — Copper is a very widely distributed metal, and 
 since it is much more valuable than iron, comparatively 
 poor ores repay metallurgical treatment. Although occa- 
 sionally found in workable quantities as an isolated element, 
 the ordinary ores of copper are sulphides or oxides of the 
 metal. 
 
 {a) Co-p^per Pyrites or Chalopyrite (CuFeSg). — This is by 
 far the most important ore of copper, and much resembles 
 iron pyrites in appearance, but it is generally less lustrous, 
 and may be further distinguished by its lesser hardness.^ 
 It is usually found in granular fragments associated with 
 iron pyrites and quartz. It occurs in many parts of the 
 world, and is largely imported for smelting. In this 
 country a limited supply is obtained from Devonshire 
 and Cornwall. 
 
 (b) Cuprite (Cuprous Oxide) (CuaO). — This mineral is 
 found in crystals and in masses, sometimes possessing a 
 fibrous structure. Fractured surfaces present a deep red 
 colour, but weathered faces are usually grey or black. It 
 is found in quantity in New Mexico. 
 
 (c) Malachite {CiiGOa.GniOB.)^)' — This ore, which is basic 
 copper carbonate, is emerald green in colour, and is the 
 result of the weathering of other ores, upon which it is often 
 
 1 Copper pyrites can be scratched by a knife, whereas iron pyrites 
 is harder than steel. 
 
252 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 found as a superficial coating. It is mined in the Ural 
 Mountains. 
 
 (d) Native Copper. — Metallic copper containing 10 to 
 40 per cent, of impurities is found in fine granular masses 
 in Chili. It also occurs in a very pure condition in the 
 neighbourhood of Lake Superior. Its existence as an 
 element is probably the result of secondary actions: 
 that is, is due to the reduction of previously existing 
 compounds. 
 
 2. Extraction of Copper. — Ores from all parts of the 
 world are imported to be smelted in this country. The 
 chief seats of the copper industry are at Swansea and on 
 the Tyne. 
 
 After preliminary roasting in a shaft furnace or calciner, 
 the ore is smelted in a blast furnace of very much smaller 
 dimensions than those used in the iron industry, or more 
 usually it is reduced in a reverberatory furnace similar in 
 general principles of design to, though differing much in 
 detail from, that described for the production of wrought 
 iron by puddling. The product of this smelting is not, 
 however, metallic copper, but copper sulphide. The calcin- 
 ing of the ore converts the iron sulphide, usually present, 
 into oxide, and this on fusion in the second process forms 
 a slag of silicate of iron, while the copper sulphide, known 
 as "matte," is also obtained in a fused condition. This 
 "matte" is usually again roasted and fused, when owing to 
 the combustion of the sulphur, metallic copper is obtained, 
 or it is sometimes treated directly in a small Bessemer 
 converter. 
 
 The resulting copper in either case requires further 
 treatment before it is marketable, and this is effected either 
 by re-smelting or electrolytic refining. In the former 
 process the molten metal is stirred with a pole of green 
 wood until the copper oxide, the chief impurity, has been 
 reduced by the gases evolved by the partial combustion of 
 
OTHER METALS AND ALLOYS 
 
 253 
 
 the wood, when the metal, having acqmred the proper 
 " pitch " to ensure toughness, is cast. 
 
 Electrical refining consists of the immersion of the 
 impure copper, cast into a suitable plate, in a solution of 
 copper sulphate, and the passing of a current of electricity 
 from this plate to a sheet of pure copper also suspended in 
 the liquid. The impure copper dissolves, and the pure 
 metal is deposited on the sheet of copper forming the other 
 " pole " of the cell, while the impurities remain in solution. 
 
 Electrically refined copper is much purer than that 
 prepared by fusion, and a very large quantity is now pro- 
 duced in this manner. Indeed, when copper is required as 
 an electrical conductor, this method of refining is essential. 
 
 3. Properties of Copper. — Copper is distinguished from 
 all other metals by its red colour, and its conducting 
 powers for heat and electricity are second only to those 
 of silver, and far superior to such properties as developed 
 in other common metals. The specific gravity of the metal 
 varies considerably according to its mode of preparation. 
 For ordinary commercial copper this is 8*2 to 8*5, but 
 electrically refined copper may, after rolling, have a specific 
 gravity as high as 8"9. 
 
 Apart from conductivity, the value of the metal depends 
 chiefly upon its malleability and ductility, which, in the 
 absence of impurities, are both very great, and which it 
 imparts to its alloys such as brass and gun-metal. It is also, 
 when suitably prepared, exceedingly tough, and possesses 
 a tensile strength second only among individual metals to 
 that of iron. 
 
 The malleability of copper is rapidly impaired by 
 hammering, but may be completely restored by heating 
 and quenching. A temperature of only 240° C. is said to 
 be sufiicient for this annealing process. 
 
 Copper casts badly, becoming porous on solidification, 
 due to absorption of oxygen. The presence of a small 
 
254 CHEMISTRY AND PHYSIOS OF BUILDING MATERIALS 
 
 quantity of lead and the performance of the operation in 
 the presence of an inert gas, such as carbon dioxide, enable 
 satisfactory castings to be obtained. Copper does not pass 
 through a viscous condition before melting, hence its welding 
 properties are almost negligible. The fracture shown by 
 cast copper is granular, but that of rolled or drawn copper 
 is fibrous, in common with that of other metals similarly 
 treated. 
 
 4. Impurities and their Effects. — The minor constituents 
 of copper do not merit the attention given to these bodies 
 in the case of iron, and they may be looked upon usually 
 as impurities. The amount of foreign bodies in copper, 
 particularly if electrically refined, is usually very small, 
 and as the metal does not appear to combine at all with 
 carbon, no varieties corresponding to iron and steel exist. 
 
 The following is a summary of Hamp's work^ on the 
 impurities found in copper. 
 
 (a) Cuprous Oxide. — Copper readily combines with oxygen 
 at a red heat with the formation of a red suboxide CugO, 
 which is formed when the metal is in a molten condition. 
 This oxide is easily fusible, and thus mixes with the liquid 
 metal. When copper is refined by fusion, the operation of 
 stirring with a pole of wood has the effect of reducing this 
 oxide to metallic copper, while the remaining impurities 
 are retained in the state of oxides, in which form they are 
 not detrimental to the malleability of the metal, and the 
 " poling " operation is stopped before reduction of other 
 impurities takes place. 
 
 "When the percentage of cuprous oxide does not exceed 
 0-5, its effect may be neglected ; 2 per cent, affects the 
 malleability of the metal when cold, and 7 per cent, affects 
 this property when the metal is heated. 
 
 (b) Iron. — In any quantity iron destroys the malleability of 
 copper, but the amount ordinarily present may be neglected. 
 
 1 Schnabel and Louis, " Handbook of Metallurgy," vol. i., 1905. 
 
OTHER METALS AND ALLOYS 
 
 255 
 
 (c) Tin. — This metal, in amounts greater than 1 per 
 cent., reduces the ductility of copper, but is never present 
 in appreciable quantities in the commercial metal. 
 
 (d) Bismuth. — Even as little as 0*02 per cent, of bismuth 
 is injurious in copper, and reduces malleability. 
 
 (f) Lead. — This metal, if present, may be almost entirely 
 removed by heating the copper, when the lead separates 
 in a molten condition. More than 0'3 per cent, of lead 
 decreases malleability. 
 
 Arsenic, antimony and phosphorus may be neglected in 
 amounts not exceeding 0'6 per cent. Large quantities, 
 particularly in the case of phosphorus, decrease the 
 malleability of the metal when hot. 
 
 5. Corrosion of Copper. — At a red heat copper is rapidly 
 oxidised, with the production of black copper oxide (CuO), 
 and oxidation also takes place at a much lower temperature, 
 the oxide forming an adherent and protective coating to the 
 metal. In ordinary moist air the additional action of water 
 and carbon dioxide lead to the production of a basic car- 
 bonate of copper known as "verdigris," which resembles 
 the ore malachite in its composition, and is distinguishable 
 by its green colour. These changes are only superficial, 
 and copper exposed to the atmosphere without any protec- 
 tion is almost imperishable. 
 
 In salt water copper undergoes corrosion with comparative 
 rapidity, especially when exposed alternately to such water 
 and to the air, which results in the formation of a green 
 oxychloride of copper and leads to electrolytic action 
 between this compound and the metal. 
 
 II. Lead. 
 
 1. Ores. — Lead is found widely distributed, and since the 
 ores have, like the metal itself, high specific gravities, their 
 separation from associated siliceous or calcareous minerals 
 
256 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 is effected comparatively easily by submitting the crushed 
 material as mined to a process of washing in running water. 
 
 Galena (PbS). This is the most important ore of lead, 
 and is found in masses or crystals possessing considerable 
 metallic lustre and blue-grey in colour. Associated with 
 the ore is usually sulphide of zinc, while iron and copper 
 pyrites, calcite and barytes are also often present. 
 
 Galena is found in workable quantities in North Wales, 
 Derbyshire, and North Yorkshire, in this country, and 
 much is imported, particularly from Spain. 
 
 Cerussite (lead carbonate, PbCOs), and anglesite (lead sul- 
 phate, PbSOi) are other less important ores of lead. 
 
 2. Extraction. — Lead is usually smelted in reverberatory 
 furnaces, but ores other than galena and slags rich in lead 
 produced from the above furnaces, are often smelted in 
 small blast furnaces. The temperature required to effect 
 the reduction of lead is much lower than that necessary 
 in the case of copper, and the furnaces employed are often 
 very primitive in construction. The reduction of the ore 
 is effected by the partial combustion of the sulphur when 
 the liberated lead is oxidised; at the same time part of the 
 galena is converted into lead sulphate by direct absorption 
 of oxygen, and on further heating the oxide and sulphate 
 react with the rest of the galena, when metallic lead is 
 produced. To facilitate these changes the charge is raked 
 backwards and forwards on the hearth of the furnace. The 
 reactions may be represented as follows : — 
 
 2PbS + 3O2 = 2PbO + 2SO2 
 and PbS + 202 = PbSOi 
 
 Then PbS + 2PbO = 3Pb + SO2 
 
 and PbS + PbS04 = 2Pb + 2SO2. 
 
 Lime is sometimes added to the charge to prevent the 
 lead oxide forming a slag with the small quantity of silica 
 remaining in the ore. 
 
OTHEE METALS AND ALLOYS 
 
 257 
 
 3. Properties of Lead. — Lead is chiefly of value on 
 account of its malleability and chemical inertness. It is the 
 softest of the common metals, possesses little elasticity, 
 and is readily beaten to any desired shape. Its ductility 
 and tensile strength are very small. The specific gravity 
 of the metal, which is but little affected by mechanical 
 treatment, is 11"25 to 11*39. Impurities lower the specific 
 gravity of lead, hence this value may be utilised as an indica- 
 tion of the presence of any other common metal in quantity. 
 The conducting power of lead is for heat only about one- 
 ninth, and for electricity about one-fifth that of copper, 
 while its melting point is 325° C, that of copper being 
 over 1,000° C. Lead becomes viscous before fusion, 
 advantage of which fact is taken in "drawing" lead piping. 
 When absolutely free from tarnish pieces of lead may be 
 welded together even when cold. The high co-efficient 
 of expansion (0'000029) possessed by the metal renders it 
 imperative to leave lead coverings capable of free movement 
 to prevent buckling and fracture, and since any rise in 
 temperature is accompanied by great loss in the small 
 amount of tenacity lead possesses, provision must be made 
 for adequate support of the metal when such increase of 
 temperature is expected, as in the case of lead piping. 
 
 4. Impurities. — The impurities in marketable lead are 
 not usually present in quantity sufficient to merit much 
 attention. 
 
 Small amounts of antimony, iron, copper, and zinc are 
 usually found. The first-mentioned metal renders lead 
 hard, and is intentionally added to produce this effect for 
 certain special purposes. 
 
 5. Corrosion of Lead. — Although lead rapidly tarnishes 
 in moist air with the production of a grey sub-oxide (PbgO), 
 this oxide is very adherent and its presence prevents 
 further action, hence lead is exceedingly permanent under 
 atmospheric influences. Further, the acids found in town 
 
258 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 atmospheres do not attack lead, which chemically is a very 
 inert element. Lead, nevertheless, slowly decomposes in 
 boiling water with the production of soluble lead hydroxide, 
 and soft waters, particularly such as contain nitrates 
 (usually derived from vegetable contamination), readily 
 attack the metal. The importance of this consideration 
 has been referred to in the chapter dealing with water, in 
 Part I. 
 
 III. Zinc. 
 
 1. Ores. — Zinc and lead are very often found together, 
 and many mines produce ores of both these metals. 
 
 Blende (ZnS). Sulphide of zinc is, like sulphide of lead, 
 the most important ore, and is associated with the minerals 
 cited as occurring with galena. The specific gravity of 
 blende is intermediate between that of galena and siliceous 
 and calcareous refuse, and it may be separated by washing 
 the crushed materials raised from the mine, in water flowing 
 at suitable velocities. Blende is usually black, but at times 
 red or yellow, and semi-transparent. It possesses a glassy 
 lustre unlike that of galena. This ore of zinc is produced 
 in this country in North Wales, Cornwall, Cumberland, 
 Shropshire, and the Isle of Man. 
 
 Other ores of zinc are calamine, zinc carbonate (ZnCOs) ; 
 zincite, zinc oxide (ZnO) ; and smithsonite (zinc silicate, 
 ZnSi04) ; they are not, however, mined in this country, 
 and are of comparatively small importance. 
 
 2. Extraction. — Zinc has a very great affinity for oxygen, 
 and its extraction in an economical manner presents 
 difficulties. The ore is first roasted in reverberatory or 
 muffle furnaces, when zinc oxide is formed on the combustion 
 of the sulphur thus : — 
 
 ZnS + 3 0 = ZnO + SO2. 
 
OTHEE METALS AND ALLOYS 
 
 259 
 
 The resulting zinc oxide is then heated with powdered 
 coal in cylindrical fireclay retorts some four feet in length 
 and eight or ten inches in diameter. These retorts, slightly 
 inclined towards their open ends, are raised to a white heat 
 by means of a gas furnace, and the oxide is reduced — 
 
 ZnO + C = Zn + CO 
 
 The metal is allowed to flow out, during which operation, 
 and in spite of precaution, a certain amount of it takes fire 
 and again forms zinc oxide. The zinc of commerce pro- 
 duced in this state is known as *' spelter." 
 
 3. Properties. — Zinc is bluish- white in colour and 
 possesses a high lustre. Its specific gravity is about 7*1 or 
 7*3 if rolled. At ordinary temperatures zinc possesses very 
 little malleability, but this property is markedly developed 
 in the metal heated to 100 — 150° C, though at higher 
 temperatures it again disappears, and at 205° C. the metal is 
 exceedingly brittle. Zinc is harder than tin but not as 
 hard as copper. The tensile strength of the metal (about 
 9 tons per square inch) hardly exceeds half that of 
 copper. Its co-efficient of expansion (0'000029) is as 
 great as that of lead, hence zinc sheets cannot be rigidly 
 fixed in situations in which changes of temperature can 
 occur, though since the specific gravity of the metal is less 
 and its tenacity greater than that of lead, it does not show 
 the same tendency to sag when unsupported. Zinc melts 
 at about 415° C. and takes fire in air at 500° C, burning with 
 a vivid blue flame. Its conducting power for heat is rather 
 more than one-third, and for electricity rather less than 
 one-third, that of copper. 
 
 4. Impurities. — The usual impurities in zinc are lead, 
 cadmium and iron. It sometimes contains also small 
 quantities of tin, copper, antimony, arsenic, sulphur, carbon 
 and chlorine. 
 
 Lead is the only impurity likely to be present in 
 
 £.M. s 
 
260 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 quantity sufficient to affect the physical properties of the 
 metal. Lead makes zinc softer and more fragile, and 1*5 
 per cent, is sufficient to prevent the metal from being rolled 
 into sheets. As has been previously suggested, it seems 
 likely that the brittleness of zinc is due to impurities, since 
 the chemically pure metal possesses considerable mallea- 
 bility. The metal in this state, however, is not an article of 
 commerce. 
 
 5. Corrosion, — Exposed to moist air zinc becomes covered 
 by a film of basic carbonate, which is adherent and therefore 
 protective. Zinc, however, is, of all the common metals, 
 most readily acted upon by chemical reagents; acids, even 
 in a dilute state, readily dissolve it, hence it soon decays 
 in a town atmosphere. 
 
 Electrolytic action (explained under ** Iron ") is parti- 
 cularly prone to occur at the expense of zinc, hence 
 particles of iron, carbon, and other elements which give zinc 
 a blotchy appearance on its surface are most productive of 
 decay in presence of moisture, and for external use the 
 purest zinc obtainable is the most economical. Contact with 
 other metas and with carbon (soot) must also be avoided. 
 
 In presence of strong bases zinc oxide acts as an acid- 
 forming oxide and forms salts, hence lime as contained in 
 mortar and cement rapidly corrodes zinc in contact with it. 
 The zinc oxide formed as the result of atmospheric oxida- 
 tion is absorbed by the lime, and hence fresh surfaces of the 
 metal are continually exposed to corrosion. 
 
 IV. Tin. 
 
 1. Ores. — Though the use of tin as an isolated metal is 
 infrequent in building operations, many of its alloys have 
 wide application. 
 
 The only ore of tin is Cassiterite, which is stannic oxide 
 (SnOa), a mineral found in association with sulphur, arsenic, 
 and antimony, besides quartz. The ore occurs in veins in rocks 
 
OTHEK METALS AND ALLOYS 
 
 261 
 
 or in granules in ancient stream beds below later deposits. 
 Owing to the impurities usually present, the ore as mined 
 frequently contains as little as 2 per cent, of metallic tin. 
 
 Tin is found in Cornwall, and abroad in the East Indies, 
 Australia, and Bolivia. 
 
 2. Extraction. — The high specific gravity of cassiterite 
 enables many of the impurities in tin ores to be removed 
 by washing, after which the ore is calcined, when sulphur, 
 arsenic, and antimony are largely volatilised. Another heavy 
 metal, tungsten, is often associated with tin, and when 
 present in quantity the calcined ore is fused with sodium 
 carbonate or sulphate, when sodium tungstate is formed, and 
 is removed in solution by subsequent treatment with water. 
 This compound has been employed for rendering com- 
 bustible materials non-inflammable.^ After such treatment, 
 and sometimes additional treatment with acids if copper 
 and bismuth are present, the ore, which then contains 
 some 50 to 70 per cent, of tin, is smelted with charcoal in a 
 small shaft furnace or with coal in a reverberatory furnace 
 at a very high temperature. The resulting metallic tin is 
 purified by raising the ingots slowly to the melting point 
 when the fusible metal flows away, leaving most of its 
 impurities behind. This process is known as "liquation." 
 
 3. Properties. — Tin is exceedingly permanent ; moist air 
 and many liquids which act on other metals leave it 
 unaffected, and it possesses considerable lustre if pure. It 
 is also very malleable. Its specific gravity is 7*13 to 7'3, but 
 that of commercial tin is usually about 7*5, on account of 
 the presence of slight impurities. Tin of high commercial 
 purity may be recognised by the cracking sound it emits if 
 bent. The melting point of the metal, about 230° C, is 
 much lower than that of any other metal in common use. 
 
 Tin is largely employed for coating sheet iron, which is 
 then known as "tin plate." The pure metal is distinguished 
 
 * But see Chapter XXIV., last paragraph. 
 
 S 2 
 
262 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 from coated metals under the name of " block tin." Besides 
 its use in alloys and as foil ("silver paper "), tin is almost 
 the sole constituent of many modern pewters; it is also 
 employed for lining pipes for special purposes, as for 
 conveying malt liquors. 
 
 4. Impurities and Corrosion. — The best grades of tin do 
 not contain more than O'l per cent, of impurities, the most 
 important of which is iron. Copper and lead, when added 
 to tin to the extent of 1 or 2 per cent., render the metal 
 harder and also increase its tenacity. Tin is in no way 
 subject to corrosion by any of the influences to which 
 materials are usually subjected ; the high price of the metal, 
 however, prevents its general use as a protective covering. 
 
 V. Aluminium. 
 
 1. Ores. — Though this metal, next to silicon and oxygen, 
 is the most abundant element found in Nature, forming, as 
 it does, a considerable percentage of common clay, the 
 difficulty of separating it from silica, with which it is nearly 
 always associated, makes the available ores of aluminium 
 very few. The most important source of the metal is 
 Bauxite, a hydrated oxide of aluminium and iron, and even 
 this often contains much silica. Various analyses of 
 bauxite show it to be composed of some 43 to 78 per cent, 
 of alumina, 1 to 25 per cent, of ferra, and 6 to 34 per cent, 
 of silica. The mineral is found as a clay in the south of 
 France and in Ireland. 
 
 2. Extraction. — The union between aluminium and 
 oxygen in the oxide AI2O3 is so strong that no separation 
 of the metal is possible by smelting with coal. The 
 extraction is effected by passing a very powerful current 
 of electricity by means of plates of carbon through the ore 
 contained in cast iron boxes, when reduction takes place 
 and the oxygen from the alumina burns away the carbon 
 
OTHEE METALS AND ALLOTS 
 
 263 
 
 plates as the metal is liberated. Since the commercial 
 application of this process requires a current of some 
 13,000 amperes (at about 15 volts), this industry can only 
 be profitably carried on where cheap power, such as that 
 obtainable from waterfalls, is available. 
 
 3. Properties. — Aluminium when pure possesses a white 
 colour and lustre resembling tin. The bluish tinge asso- 
 ciated with the commercial metal is due to the presence of 
 silica or to mechanical treatment (rolling). On fracture 
 the metal shows a coarse, woolly structure, but this may 
 become fibrous and silky after rolling. The specific gravity 
 of aluminium is 2"58 when pure, but that of the com- 
 mercial metal, which generally contains 1"5 per cent, of 
 impurities, is 2'6 to 2"74. The metal is fairly malleable 
 and ductile, but, like copper, requires frequent annealing 
 when worked cold. At 200° C. it is easily forged and rolled. 
 It possesses considerable tenacity, and when cast has a 
 tensile strength of about eight tons per square inch. Its 
 melting point is 625° C, its linear co-efiicient of expansion 
 0"000023, its specific heat 0*22 ; its conductivity for heat and 
 electricity is almost identical, the former being rather less 
 than half that for copper. 
 
 4. Impurities and Corrosion. — The valuable properties of 
 aluminium are much impaired by impurities, and particu- 
 larly by silicon, which, as stated, is associated with the ore 
 and is difficult to entirely remove. The metal is quite 
 permanent in the air, and water has no action upon it. 
 Sulphuretted hydrogen does not blacken it, which gives 
 aluminium a great advantage over brass and copper. 
 Unlike copper, nitric acid has little action upon it, whereas 
 hydrochloric acid readily dissolves it. This metal is much 
 more suitable for culinary utensils than brass or copper. 
 Foods, it is true, attack it also slightly in cooking opera- 
 tions, but the soluble compounds formed are not, in the case 
 of aluminium, poisonous. 
 
264 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 VI Alloys. 
 
 1. Introductory. — A metal which consists of two or more 
 metallic elements is known as an " alloy." Such a defini- 
 tion really embraces the commercial metals already dis- 
 cussed, for none of them are entirely free from other 
 metallic constituents besides the preponderating metal to 
 which they owe their designation. As ordinarily under- 
 stood, however, the term "alloy" is only applied to bodies in 
 which the constituent metals are present in proportions to 
 some extent comparable, and this distinction, though not 
 scientific, is convenient in practice. 
 
 Much research work has been conducted upon alloys in 
 recent years, with a view to ascertaining the nature of the 
 combination of constituent metals and how composition is 
 related to physical properties. In certain cases metals 
 when mixed appear to form definite chemical compounds 
 with one another ; in some cases such compounds have 
 been actually isolated, in others their existence has been 
 inferred from physical properties, as, for example, by the 
 display of sudden evolutions of heat at certain temperatures 
 when a molten alloy is allowed to solidify, which indicates 
 chemical combination at such temperatures. Broadly 
 speaking, alloys may be regarded as chemical compounds 
 dissolved in excess of one of the constituents of such com- 
 pounds : that is, as compounds of metals mixed with a 
 further quantity of one of such metals. In no case, how- 
 ever, are the marked differences in physical characters 
 which usually result on the formation of chemical com- 
 pounds, to be observed. Compounds of the metals with one 
 another always retain many of the properties of the 
 elementary metals from which they are formed, which 
 enables some prediction to be made as to the probable effect 
 of adding one metal to another. Thus zinc added to copper 
 will reduce its colour, which will become yellow and finally 
 
OTHEE METALS AND ALLOYS 
 
 265 
 
 white by such addition. Again, lead added to another 
 metal will generally make the latter softer and more easily 
 tarnished. Such changes in properties are, nevertheless, 
 not always proportional to the amount of metal added. 
 
 One change which occurs with remarkable variation in 
 properties is the lowering of the melting point. Alloys 
 usually possess melting points which are much lower than 
 the average of the melting points of their constituent metals. 
 Many alloys have in reality no definite temperature of 
 liquefaction, but gradually become liquid as the melting 
 points of the elements and compounds they contain are 
 approached. This fact renders great judgment necessary 
 in heating alloys (as in annealing), since at a temperature 
 well below that of total liquefaction partial melting or 
 decomposition may occur, and with it great changes in 
 physical properties. Thus, if brass (an alloy of copper and 
 zinc) be heated to a temperature short of actual fusion and 
 be then allowed to cool, it will be found to have altered 
 structurally with much deterioration, and is then said to 
 have been " burnt." 
 
 The nomenclature of alloys is in a very loose and 
 unsatisfactory condition, and a large number of different 
 bodies are often placed under the same designation. There 
 are, for example, some thirty alloys which are termed 
 " brass," while the bronzes are perhaps even more numerous. 
 Any definite information about a particular alloy, therefore, 
 entails first of all a definite statement as to the proportions 
 of its constituents. 
 
 2. Brass. — All brasses are alloys of copper and zinc, with 
 or without small quantities of lead, tin, and iron present 
 in the original metals as impurities or added intentionally. 
 Harder, and therefore more wear-resisting than copper, 
 malleable and ductible, capable of producing good castings, 
 and attractive in colour, brass is used for many purposes in 
 place of copper. 
 
266 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 Common brass consists of about 64 per cent, of copper 
 and 36 per cent, of zinc. Brass suitable for wire-drawing 
 is composed of about 70 per cent, of copper and 30 per 
 cent, of zinc, while that used for rolling into sheets may 
 contain as much as 80 per cent, of copper. The addition 
 of small quantities of lead renders brass softer, and thus 
 more easily worked, but such addition increases the diffi- 
 culty of annealing, which is only effective at a high 
 temperature (about 600° C). 
 
 The tensile strength and other physical characters of 
 brass vary much, not only with its composition but also 
 with mechanical treatment, and the metal soon loses its 
 malleability and gets hard when rolled or hammered, and, 
 like copper, requires annealing. Brass soon tarnishes in 
 a moist atmosphere, and if neglected for a long period 
 eventually becomes black owing to the formation of 
 copper oxide and sulphide on its surface. This alloy 
 much resembles copper in its tendency to undergo change ; 
 it suffers slight solution in the presence of organic acids, 
 and undergoes, especially if rich in copper, corrosion in 
 salt water. 
 
 3. Bronzes. — Bronze consists essentially of copper and tin, 
 the former metal largely predominating. Zinc and other 
 elements are constituents of certain bronzes, while the term 
 is even extended to metals in which tin is absent, as, 
 for example, aluminium bronze, an alloy of copper and 
 aluminium. The bronzes vary in colour, from red (those 
 containing 90 per cent, of copper) through yellow to white 
 (those containing 70 per cent, or less of copper). Some of 
 these alloys are tough and malleable, others are hard and 
 brittle. 
 
 Gun-metal is the most important variety of bronze from 
 the point of view of this discussion. As guns are now made 
 of steel the original significance of the name is lost, and the 
 alloy is chiefly used for fittings as a superior substitute 
 
OTHEE METALS AND ALLOYS 
 
 267 
 
 for brass. Gun-metal contains copper, tin, zinc, and some- 
 times a little lead, while small quantities of iron, manganese, 
 aluminium, phosphorus, and silicon may be present as 
 impurities or by intention. Like brass, the properties of 
 gun-metal vary with the proportion of zinc which it contains. 
 When the alloy consists of 90 per cent, of copper, 8 per 
 cent, of tin and 2 per cent, of zinc it is reddish-yellow in 
 colour and tough, though much harder and more brittle 
 than copper ; 80 per cent, of copper, 5 per cent, of tin, and 
 15 per cent, of zinc produce an alloy yellow in colour and 
 harder and more brittle than the above, though still work- 
 able, while gun-metals exist which contain 7 5 per cent, of 
 copper, 5 per cent, of tin, and 20 per cent, of zinc ; such 
 alloys are, however, hard and decidedly brittle. 
 
 Lead softens bronze, but has a tendency to separate from 
 the alloy on solidification; hence the amount present is 
 usually small. 
 
 Iron appears to form several definite compounds with 
 tin, and in small quantity it is beneficial in increasing 
 hardness and tenacity. 
 
 Phosphorus is employed in alloys known as "phosphor- 
 bronzes," which consist of copper and 4 to 9 per cent, of 
 tin, and usually 0*1 to 1 per cent, of phosphorus. This 
 last element, owing to its great tendency to combine with 
 oxygen, decomposes any copper oxide which may be present 
 in the copper or formed by oxidation during the preparation 
 of the alloy. It thus promotes soundness, and also 
 improves the casting properties of the material. Phosphorus 
 hardens bronze, though at some expense to toughness, and 
 larger quantities than that cited produce brittleness. 
 
 Silicon is used in place of phosphorus when good con- 
 ductivity combined with tenacity is desired. Suspended 
 conductors for conveying electricity are often composed of 
 silicon bronze in place of pure copper. 
 
 Aluminium. — This metal alloyed with copper produces a 
 
268 CHEMISTEY AND PHYSICS OF BUILDINa MATEEIALS 
 
 material possessing remarkable properties. An alloy com- 
 posed of 90 per cent, of copper and 10 per cent, of aluminium 
 is golden yellow in colour, permanent in ordinary air, 
 possesses a tenacity equal to that of mild steel, and is 
 readily workable. The applications of this alloy are only 
 limited by the cost of its component metals. 
 
 4. Lead-Tin Alloys. — The most important alloys of lead 
 and tin are pewter and solder, which are proportional in 
 quality and price to the amount of tin which they contain. 
 A useful indication of the proportion of these metals may 
 be obtained from the fact that such alloys containing 
 upwards of 25 per cent, of lead will make a mark when 
 drawn across paper. 
 
 Lead increases malleability and tendency to tarnish, and 
 tin increases tenacity and toughness. If the amount of lead 
 present does not exceed 10 per cent, the cracking sound 
 referred to, as a characteristic of tin, is audible when the 
 metal is bent, provided the alloy be free from zinc, 1 per 
 cent, of which will nullify this sound. 
 
 Pewter. — Common pewter contains about 80 per cent, of 
 tin and 20 per cent, of lead, and if the percentage of lead 
 exceeds this amount the metal is not safe as a receptacle for 
 food or beverages. Many modern pewters, however, are 
 pure metallic tin. All lead-tin alloys possess low melting 
 points ; that of common pewter is 186° C. 
 
 Solder. — Ordinary solders vary in composition from 67 per 
 cent, of tin and 33 per cent, of lead to 33 per cent, of tin 
 and 67 per cent, of lead, or 2 parts of tin to 1 of lead to 
 1 of tin to 2 of lead. The former possesses the lowest 
 melting point of any of the lead-tin alloys. The propor- 
 tions of the metals may be judged by the fusibility of the 
 alloy, and by its tin-like or lead-like appearance. 
 
 Tinman's solder (2 of tin to 1 of lead) possesses a fairly 
 definite melting point, and thus passes through no viscous 
 stage on solidifying. Plumber's (or common or hard) solder 
 
OTHER METALS AND ALLOYS 
 
 269 
 
 (1 of tin to 2 of lead) has, owing to its excess of lead, two 
 melting points, consequently it solidifies gradually — a fact 
 of practical importance in the wiping of Joints and other 
 plumber's work. 
 
 5. Fusible Alloys. — The lowering of the melting point 
 resulting from the mixture of metals is taken advantage of 
 in the production of certain very fusible alloys utilised as 
 safety plugs in steam systems or to admit the flow of 
 water in case of fire, and for many other purposes beyond 
 the limits of this discussion, as in linotype printing. The 
 metals bismuth and cadmium (elements of no commercial 
 value alone) possess special powers of lowering the melting 
 point of alloys. Two parts of bismuth, 1 of tin and 1 of 
 lead produce an alloy which melts at 94° C, and which, 
 therefore, liquefies in boiling water, while by the addition 
 of cadmium the melting point may be reduced to as low a 
 temperature as 60° C. Alloys containing mercury may be 
 made which melt at still lower temperatures. Such 
 mixtures, generally known as " amalgams," are, however, 
 generally plastic, whereas those cited above are quite rigid 
 at ordinary temperatures. 
 
CHAPTEE XXIII 
 
 TESTS UPON AND STRENGTH OF THE METALS 
 
 I. Nature of Tests Applied to Metals. 
 
 1. Introductory. — From the foregoing description of the 
 metals it will be evident that designation carries with it 
 but little guarantee as to properties, and in the light of 
 the present unscientific nomenclature assigned to metallic 
 materials it is the more necessary to define the standard 
 of quality to be maintained as adjudged by tests. 
 
 The physical effects produced by various minor con- 
 stituents and the evidence of structure to be obtained from 
 microscopic observations have already been discussed. The 
 tests, however, demanded in ordinary practice are confined 
 to those of a mechanical nature, partly because such tests 
 are most readily to be undertaken, and have in many cases 
 been standardised, but chiefly because the properties thereby 
 investigated are those bearing directly on the structural 
 strength of metals, in which connection alone tests are 
 commonly demanded. 
 
 These tests all require the application of mechanical force 
 and the measurement of the relation between the amount of 
 such force and its effect on the material either in producing 
 rupture or deformation. When rupture occurs the quality 
 of the metal is often further Judged by the appearance of 
 the fractured area, and as such appearance cannot be placed 
 in the category of separate tests enumerated below, some 
 valuable comments on this subject by Johnson^ may be 
 here referred to. 
 
 ' Johnson, "The Materials of Construction." 
 
TESTS UPON AND STEENGTH OF THE METALS 271 
 
 Popularly, a fibrous and silky fracture is regarded as 
 evidence of metal of good quality, whereas a crystalline 
 appearance is taken to denote brittleness. The above writer 
 points out that the character of the fracture varies very 
 greatly with the mode of application of the force effecting 
 disruption. It has been shown that the crystalline condi- 
 tion is the normal condition in metals, and though a fibrous 
 appearance is displayed on fracture by many metals as the 
 result of tensile, and particularly of bending, tests, and is 
 good evidence of toughness and power to resist shock, such 
 structure must be looked upon as induced by distorting 
 forces, and not as representing the normal condition of the 
 material. If a specimen of mild steel or even of good 
 wrought iron be nicked all round so as to offer a very 
 definite area of weakness, the fracture produced by sub- 
 mitting the metal to a tensile test will be crystalline. 
 Thus, although it is true that a crystalline fracture in 
 malleable metals usually indicates poor material, because 
 the conditions under which it would take place would 
 generally be such as to induce fibre during failure, such 
 conclusion might be quite erroneous if fracture occurred 
 across an area greatly weakened by some cause other than 
 deforming mechanical force. The above considerations 
 indicate that the assumption that metals become crystalline 
 by continuous use is very probably erroneous. 
 
 The mechanical tests applied to metals usually investigate 
 strength in tension, compression, and cross-bending ; cold- 
 bending, hardness, and, less frequently, shear, torsion and 
 impact. These tests will be briefly referred to under the 
 above headings. 
 
 2. Tensile Tests. — Tests in tension are more serviceable 
 than any other tests, are more easily carried out, and more 
 comparable in their results than most other means of 
 investigation. Such tests are particularly suitable for 
 obtaining information as to the elastic limit of the material, 
 
272 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 which, it has been pointed out, is also the limit of its prac- 
 tical utility under stress ; and since in the case of malleable 
 metals this limit has the same value for both tensile and 
 compressive stresses, the determination of the elastic limit 
 in tension is applicable to the use of the metal in compres- 
 sion. When this limit is reached the elongation of the 
 specimen proceeds much more rapidly than before, and 
 is no longer proportional to the increasing pull upon it. 
 Since the machine used for the tests indicates, usually by 
 means of an increasingly weighted lever, the amount of the 
 pull exerted, the drop of this lever, or " weigh-beam," when 
 this rapid stretching begins, forms a useful means of record- 
 ing the elastic limit. A more accurate but less ready 
 method of investigation is to measure the amount by which 
 the test piece has stretched and the pull then upon it at 
 intervals as the test proceeds, and subsequently to plot 
 the result on a chart just as would be done in the case 
 of barometer readings, substituting pull (say in tons) and 
 extension (say in hundredths of an inch) for days of the 
 week and inches of barometric height. In this manner by 
 joining up the points obtained on such a diagram a bend 
 will be found (corresponding to a sudden drop on a 
 barometer chart) when rapid stretching for little addi- 
 tional pull takes place, thus indicating at what pull the 
 elastic limit is reached.^ 
 
 The actual extension which the test piece undergoes will 
 naturally vary very much with different metals and depend 
 upon their ductilities. In the case of a brittle material 
 such as cast iron the elongation produced before rupture 
 will be almost inappreciable, but in the case of mild steel 
 and wrought iron this is considerable, and its value is often 
 demanded. The measurement is made by comparing the 
 
 1 The elastic limit is in reality more complex than indicated in this 
 paragraph. The question is fully dealt with in works on the testing 
 of materials. 
 
TESTS UPON AND STEENQTH OF THE METALS 273 
 
 original length of the test piece with its length when 
 fractured, after the two halves have been again fitted 
 together. The area of the cross-section at fracture is 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 t L 
 
 ASTIC 
 LIMIT V 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 E — 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 EXTENTION ^ay TENTHS OF AN INCH 
 
 Fig. Y. — Diagrammatic explanation of method of determining 
 elastic limit by laying out the pull and extension along 
 two lines at rigM angles, drawing lines from each, exten- 
 sion observed and from the corresponding pull until they 
 meet in the diagram, and then joining all these points of 
 contact up by a curve. 
 
 also sometimes measured and compared with the area of 
 the original cross-section in order to determine the amount 
 of contraction which has taken place. 
 
 In order to obtain comparable results of tests upon 
 different specimens of metal the geometrical form must 
 
274 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 be the same in all cases. For example, the same ratio 
 of length to diameter or sectional area must be main- 
 tained in all cases, and the shape of the specimens and 
 form of the ends to be gripped in the machine must 
 be similar. 
 
 Metals submitted to tensile tests are, as indicated above, 
 invariably tested to destruction, that is, until rupture 
 occurs. The expert's report embodying the result of the 
 test usually gives (1) the cross-sectional area and the force 
 which produced rupture, and calculated from this, the number 
 of tons required to rupture a specimen one square inch 
 in cross-section ; (2) the extension produced in the fractured 
 test piece calculated as a percentage of a given length 
 measured, usually 8 or 10 inches ; (3) if desired, the per- 
 centage of contraction formed by comparing the original 
 with the fractured area. Information as to elastic limit is 
 not usually included in commercial reports in spite of its 
 obvious importance. As previously stated, this value 
 may for ordinary purposes be taken as from 50 to 60 
 per cent, of the ultimate strength, that is, of the strength 
 at rupture. 
 
 3. Compressive Tests. — Tests in compression are of two 
 kinds : (1) on cubes or short cylinders which give the real 
 compressive strength of the material; (2) on columns or 
 long cylinders which ultimately fail by bending, and show 
 a much smaller strength per square inch in consequence. 
 There is little value in the determination of the compressive 
 strength of malleable metals, the elastic limits of which 
 have already been ascertained by tensile tests. In the case 
 of brittle metals like cast iron, such tests are occasionally 
 employed and are carried out in the same manner as has 
 been indicated in the case of stones. The force required to 
 crush short lengths of metals is, however, so great that 
 failure from this cause is seldom to be anticipated, except, 
 perhaps, in the case of forms of irregular section, such as . 
 
TESTS UPON AND STRENGTH OF THE METALS 275 
 
 ornamental caps ^ of cast-iron columns, now seldom employed 
 as weight carriers. 
 
 ^ In the case of columns tests are only made in special 
 circumstances, since these to be of value should be carried 
 out on the actual columns proposed for use, and as further 
 results depend very largely on the transmission of the 
 crushing force through the exact geometrical centre of the 
 shaft and on the methods adopted for supporting the ends. 
 
 4. Cross-Bending Tests. — These tests are commonly 
 relegated to metals possessing but Httle ductility, such as 
 cast iron, and can be utilised for determining the ultimate 
 strength of brittle metals and the elasticity of those which 
 are malleable. A test is made by supporting a bar of the 
 material upon strong knife-edges at a known distance apart, 
 while the force is applied in the centre until rupture by 
 bending occurs. As in the previous tests, the force should 
 be applied gradually and continuously, and it is essential 
 that the bearings supporting the specimen should be per- 
 fectly rigid, otherwise a portion of such applied force will be 
 employed in causing deformation in the machine itself. 
 Cross-bending tests involve tensional, compressive, and 
 also shearing stresses, the first two greatest in the centre, 
 the last greatest near the supports ; hence the conditions of 
 these tests are more complex than those previously cited. 
 The necessary apparatus, on the other hand, may, for test 
 pieces of moderate size, be comparatively simple in 
 character. 
 
 Cross-bending tests are sometimes employed to determine 
 deflection of girders and concrete beams or floors under 
 actual working loads. Such deflections can be measured 
 with some accuracy by observing the movement of a beam 
 of light reflected from a mirror suspended from the material 
 under test. Minute angular motions of the mirror pro- 
 duced by the deflection are thus enormously magnified by 
 
 1 Even here failure would probably not be due to compression only. 
 
 B.M. m 
 
276 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 the reflected beam of a light which acts like a long pointer, 
 and thus renders such deflections measurable. 
 
 5. Cold-Bending Tests. — The rough workshop tests upon 
 the powers possessed by a metal of bending when cold, 
 though they cannot be placed in the same category as the 
 foregoing, are yet very useful and are also performed in a 
 very simple manner. 
 
 Any material which can be bent double so as to com- 
 pletely fold upon itself without showing cracks possesses 
 malleability in so high a degree that no question can arise 
 as to its sudden failure in construction. In the case, how- 
 ever, of specimens of some thickness, such a test is of too 
 severe a character, and the general requirement for such 
 metals as mild steel is that bending shall take place with- 
 out the exhibition of any cracks round a curve equal in 
 radius to the thickness of the specimen. 
 
 In the case of small pieces of metal the bending may be 
 effected by mere hammering, but is more fairly applied by 
 means of a hydraulic press or by a long lever attached. 
 When complete closing of the fold is not required, the 
 operation is conducted by bending the metal round a 
 mandril of suitable diameter. 
 
 6. Hardness Tests. — By hardness, in the case of metals, 
 is meant the power to resist indentation as contrasted with 
 abrasion. In this sense the property bears some relation 
 to ductility, and, although no very definite connection has 
 yet been established, mild, medium, and hard steels can 
 readily be distinguished by the indentation they undergo 
 with given loads. In a recently designed machine the load 
 is applied by a small hydraulic press and its amount 
 registered by a pressure gauge. The indent is made by a 
 small ball of hardened steel which forms the termination 
 of the ram of the press, and the distance to which it 
 penetrates is ascertained by subsequent measurement of 
 the diameter of the depression formed in the metal. 
 
TESTS UPON AND STRENGTH OF THE METALS 277 
 
 Since the machine referred to can be fixed to an ordinary 
 table and admits of rapid tests, it is not unlikely to prove 
 of great value commercially where an approximate know- 
 ledge of the tensile strength of materials is alone required. 
 
 7. Shear and Torsion Tests.— These tests are but seldom 
 demanded in the case of metals used in construction. Shear- 
 ing is a pure cutting which results in one portion of the 
 test specimen sliding past the rest. The correct estimation 
 of the force required to produce shearing necessitates special 
 precautions to ensure absolute rigidity in that part of the 
 specimen which is to remain in position after shearing has 
 been effected. 
 
 Torsion tests are usually confined to wire, and are carried 
 out by comparing the number of twists which can be given to 
 specimens submitted before fracture occurs. Shearing and 
 torsional stresses are identical, apart from the method of 
 applying the force producing them. Hence the behaviour of 
 a metal under torsion may be used to indicate its capacity 
 to resist shear. 
 
 In constructional problems shear is chiefly of interest in 
 connection with rivets, which, however, are also subject to 
 great tensional stresses, owing to contraction on cooling after 
 they have been closed. 
 
 8. Impact Tests. — Building materials are not normally 
 subject to shock, and in the case of malleable metals failure 
 from this cause need not be anticipated. Impact tests, 
 that is, tests by a blow suddenly applied, are made on 
 brittle metals, such as east iron, and it is sometimes 
 demanded that this metal shall withstand a given blow, as 
 from a known weight dropped from a certain height upon 
 the centre of a bar of given dimensions. 
 
 Power of resisting shock is generally measured by 
 observing what decrease in the length of swing of a heavy 
 pendulum is produced by causing it to fracture a bar of the 
 metal of given section which it strikes during its swing. 
 
 T 2 
 
278 CHEMISTEY AND PHYSICS OF BUILDING MATEKIALS 
 
 The chief difficulty experienced in carrying out such tests 
 is that of obtaining rigidity in the vice or other form of 
 jaws holding the test piece. 
 
 II. — Actual Strength of Metals. 
 
 1. Introductory.— The actual strength exhibited by a 
 metal is ascertained in practice by cutting pieces of suitable 
 or available dimensions from the samples submitted, and 
 calculating from the results obtained the strength per unit 
 area (generally 1 square inch) or the deformation per 
 given length, by simple proportion. This assuniption, that 
 the strength per square inch as thus calculated is indepen- 
 dent of the size of the specimen tested, is practically correct 
 in the case of mild steel, but in the case of wrought and 
 cast iron, test pieces of small section show a greater strength 
 per square inch than those of large section— a fact which 
 should be regarded in specifying quality as assessed by such 
 tests. In the case of plates, strips are cut directly from 
 the samples, and when other forms, such as steel joists, 
 T or L irons, are to be tested, pieces in strip form are cut 
 from flange and web and tested separately, and the results 
 of such tests are given separately or averaged for each 
 sample. Eods of reasonable diameter are tested as such, 
 and in the case of massive materials, or such as possess 
 irregular forms, test specimens in the form of a rod with 
 thicker cylindrical ends to be gripped by the shackles of the 
 machine are prepared by means of a lathe for tension or 
 torsion tests. 
 
 In preparing such test pieces, the opinion is commonly 
 held that the natural surface of the material should be 
 interfered with as little as possible, as the skin of the metal 
 is often stronger than the interior. 
 
 Though it is true that cold-rolling, hammering, and 
 wire-drawing increase strength and elasticity at the expense 
 
TESTS UPON AND STBENGTH OE THE METALS 279 
 
 of elongation, Unwin ^ regards the above objection to the 
 machining of test pieces as devoid of foundation, and 
 certain tests quoted by him appear to bear out his 
 contention. 
 
 2. Cast Iron. — The commonest test to which cast iron is 
 subjected is that of cross-bending, though a test in simple 
 tension is a more valuable one. 
 
 The load sustained by a bar of cast iron is, of course, 
 dependent upon the length of the specimen between supports 
 and on its breadth and depth ; the form of the test piece 
 also affects the result ; thus, circular bars are stronger than 
 those possessing a square section of the same area. The 
 usual form and size tested is a bar 3 feet long between 
 supports, 1 inch wide and 2 inches deep, though bars 1 inch 
 square in section are often employed, and are stated by 
 Keep to give more uniform results than other sections. 
 Different qualities of cast iron of the dimensions cited 
 (3 feet X 1 inch x 2 inches) are stated by Unwin to break 
 with central loads ranging from 6J to 42 cwts. Common 
 iron should carry 20 cwts., and good iron 30 cwts. ; thus 
 25 cwts. may fairly be demanded as the minimum and 
 32 cwts. as the maximum load sustained. 
 
 The tensile strength of cast iron is greater for small than 
 large sections per square inch, though the form of the test 
 piece has but little influence on the result. Unwin quotes 
 the averages obtained in nine sets of experiments on sections 
 varying from J to 4 square inches for iron of good quality, 
 and the mean of these averages gives an ultimate strength 
 per square inch equal to 11'3 tons. In practice 8 to 10 
 tons on rupture may be required for bars one square inch 
 in section. 
 
 The strength in compression for short cylinders may be 
 taken as averaging about 42 tons per square inch. A rapid 
 falling-off in strength is observed when the height of the 
 
 ^ Unwin, '* Testing of the Materials of Construction." 
 
280 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 test piece much exceeds its diameter, as it then fails by 
 bending. A valuable collection of tests on failure of cast iron 
 columns in compression given by Johnson^ seems to 
 indicate, if so broad a generalisation is permissible, that 
 the ultimate strength of hollow columns as ordinarily used 
 in construction may be taken at about 11 tons per square 
 inch of metal in their least sections. 
 
 Cast iron possesses no well-defined elastic limit; its 
 deformation on testing is very small, and consequently not 
 easily ascertained. The strength up to the limit of elas- 
 ticity may, as for wrought iron and steel, be taken as equal 
 to 50 to 60 per cent, of the ultimate strength. 
 
 Owing to local variations in cast iron, makers will 
 generally stipulate that the standard agreed upon is to be 
 shown as the average of tests on a number of test pieces. 
 
 3. Wrought Iron. — Wrought iron is usually only required 
 to be tested in tension. Not only is the strength per square 
 inch greater for small than for large sections, but the 
 material shows, when the pull takes place across the grain, 
 a strength only about three-quarters as great as when tested 
 with the grain.^ The latter direction for testing is the more 
 common, hence the strength as reported will usually be that 
 along the grain, in the absence of any statement upon the 
 subject. 
 
 The ultimate tensile strength in plates or rods up to, say, 
 five-eighths of an inch in thickness may be taken as 22 to 
 26 tons per square inch in iron of good quality, but a 
 somewhat lower figure per square inch must be demanded 
 for larger sections. 
 
 The elastic limit, again, varies considerably with the 
 section in question, and may be taken as about 18 tons per 
 square inch in f -inch rods, but only as some 10 tons in 
 2-inch rods. It should further be noted that the elastic 
 
 ^ Johnson, " The Materials of Construction." 
 
 2 The direction in which the metal has been rolled. 
 
TESTS tlPON AND STEENGTH THE METALS 28l 
 
 limit of built-up girders and rolled iron joists is below tbat 
 of test specimens cut from such beams. 
 
 The percentage of elongation varies with the length over 
 which it is assessed. The greater the length the less will 
 this percentage be. Two lengths, 8 inches and 10 inches, 
 are commonly used in this country. When tested along 
 the grain this percentage varies from 5 to 25, according to 
 the quality of the iron. For wrought iron used in construc- 
 tion 20 per cent, elongation in an 8-inch length may fairly 
 be demanded. 
 
 The contraction of area on rupture naturally depends 
 upon the elongation attained, and may be taken as varying 
 from 7 to 40 per cent, of the original section. 
 
 The compressive strength of wrought iron is only of 
 practical interest in connection with the use of iron stan- 
 chions, which as ordinarily built up may be regarded as 
 possessing an ultimate strength of 13 to 18 tons per square 
 inch. 
 
 4. Mild Steel. — Since the form and dimensions of test 
 pieces for steel have little influence on the calculated 
 strength per square inch, no stipulations are necessary as 
 to these particulars in making commercial tests. 
 
 The tensile strengths of steels generally range from some 
 20 to 70 or 80 tons per square inch, depending chiefly upon 
 the percentage of carbon contained in them. Mild steels 
 used in construction show a tensile strength of, say, 24 and 
 32 tons, and may be specified to give results lying between 
 26 and 31 tons. 
 
 The elastic limit, which is the same both in tension and 
 compression, may be taken at about 60 per cent, of the 
 ultimate strength. 
 
 The elongation in a length of 10 inches may be reasonably 
 demanded to be 20 per cent. 
 
 5. Conclusion. — It is seldom that tests upon other metals 
 than those above cited are demanded in connection with 
 
282 CHEMISTRY AND PHYSICS OP BUILDING MATERIALS 
 
 structural work, as they are hardly ever employed in 
 situations in which their powers of resisting calculable 
 stresses are called upon. No metals or alloys in common 
 use possess the strength of iron and steel. Though 
 copper, after favourable mechanical preparation, can 
 sustain 14 tons per square inch in tension, its elastic limit 
 depends very much on previous treatment, and may be as 
 low as 3 tons per square inch. 
 
 Working stresses or safe loads producing these stresses are 
 usually taken at one quarter the ultimate strength of metals 
 in ordinary constructional circumstances. A more rational 
 method of procedure would be the adoption of a sub-multiple 
 of the elastic limit, which, as already pointed out, is really 
 the limit of utility of a material. 
 
CHAPTEK XXIV 
 
 TIMBER 
 
 I. General Character and Structure. 
 
 1. Introductory. — Wood differs from other materials used 
 in building in that it is the direct product of vital processes. 
 It thus necessarily presents variations, possessed by all 
 living species, which place it in a category somewhat 
 different from that of mineral or manufactured substances. 
 The rigid scientific tests, for example, applicable to such 
 materials as cement and steel cannot be successfully 
 imposed upon a substance of vegetable origin. Thus stan- 
 dardisation in timber is exceedingly difficult. Even in the 
 matter of classification of trees the botanist finds obstacles ; 
 while quite apart from questions of species, the properties 
 of wood from a given tree will vary with its age, with the 
 part whence the wood is taken, with the season at which 
 the selection is made, with the amount of moisture present, 
 and with the way in which the specimen is cut from the 
 tree. 
 
 It will thus be evident that experiments on woods must, 
 to have any comparative value, be carried out under care- 
 fully defined conditions, and, further, that since the greater 
 the number of these conditions the less likely is it that they 
 will in any instance in practice all be similar to those under 
 which a given series of experiments have been made, the 
 direct value of experiments on the physical properties of 
 timber must thereby be much reduced. 
 
 2. Classification. — The botanist divides trees into two 
 
284 CHEMISTRY AND PHYSIOS Oi' BUttDlNG MATERIALS 
 
 groups : (1) those which grow by the addition of external 
 layers, known as exogenous trees ; (2) those in which the 
 growth is internal, known as endogenous trees. 
 
 All trees used for timber are included in the former class. 
 The latter much smaller class is represented by the palm 
 and bamboo, which possess a cellular structure quite 
 unsuitable for conversion into timber. 
 
 Exogenous trees are divided into two groups : (a) Conifers, 
 comprising cone-bearing trees, such as the fir and pine ; 
 (5) Dicotyledons, or broad-leaf trees, such as the oak and 
 sycamore, which bear broad leaves. Speaking generally, 
 the conifers comprise what are termed " soft woods," and the 
 dicotyledons " hard woods." To this rule, however, there 
 are some exceptions : lime and poplar, for example, which 
 yield soft woods, are dicotyledonous trees. 
 
 3. Structure. — An examination of a cross-section of an 
 exogenous tree will disclose at or near its centre a pith 
 surrounded by concentric layers of wood fibres enclosed by 
 a ring of bark. Further inspection may show that the 
 rings of fibre near the centre differ in colour and texture 
 from the external rings, and between the external rings and 
 the bark a soft layer of tissue filled with a sticky liquid will 
 be found. 
 
 The pith is the original life centre of the tree, and consists 
 of cells which carry the nutriment for its early growth. 
 As the tree matures the seat of its life is transferred to the 
 thin layer of tissue immediately within the protecting bark, 
 known as the cambium, which is annually converted into a 
 ring of wood fibre. When the cambium layer is once 
 properly established the function of the pith is at an end. 
 The pith cells then perish, and in a matured tree are usually 
 found in a state of powder. The inner rings of wood fibre 
 also die in process of time, and are often hardened and 
 coloured by the infiltration of foreign matters. They 
 further become compressed as the growth of outer rings 
 
TIMBER 
 
 285 
 
 proceeds. Such inner rings are known as heartwood or 
 duramen, and serve no other purpose than that of giving 
 the growing tree sufficient rigidity to enable it to carry its 
 own increasing weight in security : as witness the healthy 
 growth often displayed by old trees which have become 
 entirely hollow through internal decay. 
 
 The outer layers of fibre are known as sapwood or 
 alburnum. Even these probably play little part in the 
 growth of the tree, though they appear to contain reserve 
 food, in the form of starch, in much the same manner as 
 fat forms a reserve food in animals. The wood in these 
 layers is usually lighter in colour and less dense than the 
 heartwood, and when the tree is felled the contents of these 
 layers are liable to undergo putrefactive changes unless the 
 wood is seasoned. 
 
 The cambium — the layer between the outer ring of sapwood 
 and the bark — is, as stated, the seat of life of the tree. It is 
 here that the sap flows and growth takes place. The 
 addition of material depends on the agency of the soil and 
 the leaves. By means of the roots the soil supplies moisture, 
 nitrogenous constituents and certain mineral ingredients 
 such as potash, while the green colouring matter of the 
 leaves has, in the presence of sunlight, the power of decom- 
 posing carbon dioxide in the air with the assimilation of 
 the carbon. 
 
 Thus supplied with nourishment from above and below, 
 the cambium layer, which extends under the bark through- 
 out the tree, forms new tissue, and periodically, usually 
 annually, all the cells which compose it are converted into a 
 ring of sapwood while a fresh layer of cambium cells is 
 generated upon those so converted. 
 
 The fibres which make up the bulk of the tree are in 
 reality hollow tubes varying from about ^^fcoth to ^ho^^ of 
 an inch in diameter, and partially closed by constrictions at 
 intervals. In general these tubes extend in a direction 
 
286 CHEMISTRY AND PHYSICS OF BUHiDiNG MATERIALS 
 
 parallel to the axis of the tree : that is, they are vertical ; but 
 some of them extend radially from the axis of the tree and 
 therefore at right angles to those just referred to. It is 
 these radial tubes or fibres which form what are known as 
 the medullary rays (Fig. 8). 
 
 In conifers the radial tubes form a very insignificant part 
 of the wood tissue, hence such woods have a simple struc- 
 ture, and in the pines, which 
 constitute an important section 
 of coniferous trees, this simpli- 
 city is intensified by the fact that 
 the tube walls do not fill up and 
 thicken with increasing age ; 
 hence there is in such woods 
 but little difference to be observed 
 between heartwood and sap- 
 wood. In most of the dicotyle- 
 donous trees, on the other hand, 
 the radial tubes form a large 
 part of the wood fibre, which 
 accounts for the well-marked 
 medullary rays in such timber 
 as oak. The structure of the 
 vertical tubes in such woods is, 
 moreover, much less regular ; the 
 walls of these tubes are thicker 
 and infiltration in the older rings of fibre is much more 
 marked than in coniferous woods. Great differences between 
 heartwood and sapwood thus result, and such timbers are 
 more complex in structure. Although the rings of wood fibre 
 are approximately circular, the conversion of sapwood into 
 heartwood is by no means regular, and the amount of each 
 differs much on different cross-sections of the tree. The rate 
 of this conversion is also variable and increases with the age 
 of the tree. The formation of a single ring of heartwood 
 
 Fig. 8. — Structure of timber, 
 showing the main vertical 
 tubes or fibres, and radial 
 tubes producing medullary- 
 rays. 
 
TIMBEE 
 
 287 
 
 from sapwood may indeed take many years, hence it is 
 obvious that treeis at full maturity will usually contain 
 a large proportion of sapwood. In many well-matured 
 pines, for example, not more than half of the fibres are in 
 the condition of lieartwood. To demand all timber free 
 from sapwood is therefore merely to display a lack of 
 discrimination which must lead, in the case of soft woods, 
 to a disregard for the terms of a specification unless a most 
 unjustifiable amount of waste, probably doubling the 
 scantlings necessary, is to be incurred. This fact is well 
 recognised in the timber trade, for soft woods are not even 
 classed in qualities in reference to the amount of sapwood 
 contained in the converted material. 
 
 II. Moisture and its Effects. 
 
 1. Occurrence of Water in Wood. — Water in wood tissue 
 plays a very important rdle in connection with the 
 mechanical properties of timber, and occurs associated 
 with wood structure in three ways : (1) As filling (usually very 
 partially) the tubular fibres of which the tree is mainly 
 composed ; (2) contained in the cellular walls of such tubes; 
 (3) in the life substance, the protoplasm of the living cells 
 in which growth is proceeding. 
 
 The greatest amount of water is found near the bark, and 
 the sapwood always contains more water than the heart- 
 wood, the amount decreasing towards the centre of the tree. 
 In such woods as show distinctive heartwood a sudden 
 falling off in the contained water is observed when such 
 matured rings are reached. 
 
 The quantity of water in green wood is very great. 
 Johnson ^ gives the loss in weight due to evaporation of water 
 
 1 Johnson, " liie Materials of Construction." To the excellent 
 section upon tinnber in this work the writer is indebted for much 
 information contiained in this chapter. 
 
288 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 from 100 pounds of coniferous wood at about 180° F. (82° C.) 
 as 45 to 65 pounds for sapwood and 16 to 25 pounds for heart- 
 wood, and from a like weight of hard wood as 40 to 50 pounds 
 from sapwood and 30 to 40 pounds from heartwood. At a 
 higher temperature more water is evolved, until finally the 
 cellulose and other compounds forming the tissue begin to 
 decompose and the oxygen and hydrogen which they con- 
 tain are expelled in the form of water in such destruction. 
 
 Perfectly dry wood is unknown, for if heated to a point 
 just short of chemical decomposition, wood on cooling 
 immediately absorbs moisture from the air. 
 
 2. Shrinkage with Loss of Water. — Even when wood 
 merely undergoes natural drying in air at ordinary tem- 
 peratures the loss of water results in considerable shrinkage 
 and internal strain. Such drying, owing to the organised 
 structure of the material, differs very much in its effects 
 from the drying of clay or porous mineral substance. The 
 emptying of the tubes which proceeds with evaporation has 
 little effect on the volume of the wood, but when the 
 moisture present in the tube walls is expelled, these walls get 
 thinner though they do not appreciably decrease in length. 
 This individual shrinkage of the fibres produces internal 
 stresses, which may be sufficient to overcome the cohesion 
 of the fibres and to thus produce cracks if drying proceeds 
 too rapidly. Such cracks are most liable to occur at 
 exposed ends of the tubes : that is, at sections across the 
 grain, for here evaporation takes place more readily than 
 elsewhere. Initial end cracks may, however, close up when 
 the timber is dried equally throughout, since the internal 
 pull finally developed between the fibres by loss of water 
 tends to draw these separated ends together. 
 
 The effects of loss or gain of water on the shape of a piece 
 of wood will necessarily vary with the amount and relative 
 disposition of the heartwood and sapwood it contains. If 
 boards, for example, are cut radially from a log so that one 
 
TIMBER 
 
 289 
 
 edge of the board lies at the circumference and the other at 
 the centre of the tree, the board will possess the same cell 
 structure on both sides, and as both sides will thus shrink 
 equally, warping will not occur on drying. If, however, the 
 boards are cut in parallel slices tangentially, as is usually 
 the case with soft woods, a larger amount of sapwood will 
 occur on the top faces of the boards above the centre of the 
 log than on the under faces ; and as sapwood contains more 
 moisture than heartwood, greater shrinkage will occur on the 
 upper faces of these boards than on the under faces ; con- 
 sequently warping is more likely to occur, the upper faces 
 
 Fig. 9. — Warping due to unequal shrinkage when boards 
 are cut tangentially, due to greater quantity of moisture 
 in sapwood. 
 
 becoming concave and the under faces convex. The same 
 thing will of course be true conversely for boards below the 
 centre of the log. 
 
 The tubes forming the medullary rays, since they are at 
 right angles to the main vertical fibres, set up stresses on 
 shrinkage in directions which conflict with the stresses 
 previously referred to. Hence the problem of the successful 
 drying of woods in which such rays are abundant, i.e., 
 hard woods, is much more complex than in the case of soft 
 woods. This fact and their less open structure make it 
 requisite to allow the drying of hard woods to proceed over 
 a considerable period. 
 
290 OHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 III. Mechanical and Other Propeeties. 
 
 1. Composition. — Chemically, wood consists almost 
 entirely of carbon, hydrogen and oxygen. Nitrogen, how- 
 ever, is an important constituent in the growth of the tree, 
 and occurs in the albumen present in the sap. This albumen 
 also contains small quantities of sulphur, while mineral 
 constituents derived from the soil include potash, soda, 
 silica, and often traces of iron and manganese. The ashes 
 from completely burnt wood consist largely of potassium 
 and sodium carbonates. 
 
 The growing cells or tubes are composed chiefly of cellulose 
 (CeHioOs), represented in an almost pure state in cotton wool 
 and untreated paper. As the fibres mature this substance is 
 converted into lignine (C18H24O10). Starch contained in the 
 tube cells also possesses the formula CeHioOg, but is 
 differently constituted. The gums and resins found in 
 many coniferous trees are also compounds of carbon, 
 hydrogen and oxygen. 
 
 2. Specific Gravity. — Since nearly the whole structure of 
 wood consists of cellulose, it is evident that the great 
 difference in the specific gravities of different woods is due 
 to structural rather than chemical variations. It is indeed 
 found that, if any wood be broken up and the specific 
 gravity of the material under comparable conditions ascer- 
 tained, this is about 1*5 in all cases, whether teak or pine be 
 in question. 
 
 That wood itself is really heavier than water is proved 
 by the fact that if freed from air, either by the artificial 
 compression of its fibres or by long immersion in water, it 
 will sink. 
 
 In the determination of specific gravity in the ordinary 
 way it is therefore most necessary to consider the condition 
 of the material as regards dryness. In addition it is found 
 that wood taken from the base of a tree has a greater 
 
TIMBER 
 
 291 
 
 specific gravity than that from the top, and also that 
 heartwood is heavier than sapwood, though, according to 
 Johnson, wood from the centre and from the circumference 
 of a good pine log is less dense than that found in the 
 intermediate rings. 
 
 Heavy woods such as oak and ash have a specific gravity, 
 when measured in the ordinary way, of 0*8 to 0'7, such 
 woods as pitch pine and maple 0'6 to 0'5, while light woods, 
 such as white and red pine and fir, range from 0"5 to 0*3. 
 
 The specific gravity of wood may be taken in general 
 as a measure of its strength, since the greater this value 
 the smaller must be the percentage volume of air-filled 
 pores. Though the structural variations of different 
 species to some extent modify this relation, it is certainly 
 of value in assessing the strength of different specimens of 
 the same kind of wood. 
 
 3, Mechanical Properties. — The preceding paragraphs will 
 be sufiQcient to indicate that mechanical tests on wood are 
 not likely to possess the same value as those upon more 
 homogeneous and definitely constituted materials. The 
 importance of mechanical tests is further minimised by the 
 fact that joints necessary in most timber structures show 
 very great variation in strength according to workmanship, 
 while the importation of converted timber and the conse- 
 quent restriction to a comparatively small number of 
 market sizes in economic practice, still further robs elaborate 
 calculations of much of their utility. 
 
 Many tests, nevertheless, have been made,^ and though 
 the use of timber in constructional work is rapidly decreasing, 
 these are not without interest. 
 
 Most coniferous woods possess a greater strength in 
 compression than in tension, while for hard woods the 
 
 • An interesting paper (illustrated) containing an account of crush- 
 ing tests on full-sized timber trusses, by Major G. K. Scott-Moncrieff, 
 will be found in the B.I.B.A. Journal for January 14, 1899. 
 
 B.M. U 
 
292 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 converse is generally true. Since heartwood is stronger 
 than sap wood, the efficiency of a joist or beam which 
 contains heartwood on one edge and sapwood on the other 
 will be considerably modified by its disposition. Thus 
 a soft wood joist or rafter should be fixed with the sapwood 
 at the top, but if any sapwood is shown on hard woods this 
 should generally be placed on the underside. 
 
 Like the metals, wood possesses a more or less definite 
 elastic limit, which is reached by a load of from 50 to 
 70 per cent, of that required to produce rupture by bending. 
 Nevertheless, loads should in practice be kept well within 
 this limit, since it is found that when applied for a long 
 period much smaller loads may eventually cause failure, 
 probably due to the gradual compression of the fibre. It 
 is much easier to separate the fibres of wood from one 
 another than to break them across, hence shearing takes 
 place much more readily with than across the grain, a fact 
 well recognised in construction. The strength, indeed, is 
 some ten times as great in the latter as in the former 
 direction. 
 
 In comparing the strength of dry and moist timber it 
 should be remembered that the cross-section of a piece 
 of wood when dry will be less than when moist. For a 
 given sectional area dry wood is stronger than moist wood, 
 because the former contains more wood fibre. It is probably 
 also true in a lesser degree that a given piece of wood is 
 stronger when dry than when moist, because drying deprives 
 the fibres of much of their pliability. 
 
 IV. Decay of Wood. 
 
 Wood is not only subject to decay owing to the disin- 
 tegrating influences described as affecting mineral materials, 
 but since it is the product of life processes it is, like other 
 organic substances, also open to the ravages of insects and 
 
TIMBER 
 
 293 
 
 micro-organisms either gettling upon it or produced 
 by its own putrefaction. Decay may thus be classified 
 as due to (1) oxidation and mechanical disruption 
 known as wet rot ; (2) tiie action of fungoid growths 
 known as dry rot ; (3) the ravages of insects terrestrial 
 and aquatic. 
 
 1. Wet Rot. — Preserved -n "pure and dry air or entirely 
 immersed in water, wood is (apart from the attacks of 
 insects) practically imperishable, as timber taken from very 
 ancient buildings has oftea proved. But when wood is 
 exposed alternately to air ar.d water it decays partly through 
 slow oxidation, but probably initially owing to mechanical 
 disruption. The repeated S'^yelling and shrinking of the 
 fibre due to alternate gain and loss of water eventually 
 results in the complete breaking down of cohesion, and the 
 wood is finally converted into powder, which in this state 
 undergoes oxidation with comparative rapidity. This form 
 of decay, known as wet rot, ii which micro-organisms play 
 no part, is often observed at the water-line of timber only 
 partially immersed. It natu:'ally proceeds most rapidly in 
 soft, porous woods, and is most effectively resisted by the 
 heart wood of hard woods (particularly oak and elm), in 
 which the fibres are compressed and filled with solid 
 material. 
 
 Wet rot is particularly liatle to occur in standing timber 
 which has been damaged or in felled timber which is left 
 on sodden ground. Spreadjig trees, especially those of 
 mature growth, often provide lodgment for water and wet 
 vegetation, either owing to ihe form of their growth or to 
 the loss of limbs or other da-nage. 
 
 The decay of trees past rniturity may perhaps be placed 
 in this category. This proceeds from the pith outwards 
 and may be in progress whib new rings of wood are still 
 being added below the bark.. 
 
 2. Dry Rot. — This form oi lecay has a special interest for 
 
 u 2 
 
294 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 the ordinary user of timber because of its possible develop- 
 ment in completed buildings. Dry rot is a disease caused 
 by micro-organisms ; it is, moreover, a contagious disease, 
 and the means adopted for its prevention or cure must 
 be, therefore, of a pathological nature. There appear to 
 be three ways in which this form of decay is initiated : 
 (a) through putrefaction of living tissue— sap— remaining 
 in unseasoned timber; (b) owing to the presence of a 
 forest fungus, usually Polyporus vaporarius, in the timber 
 before use ; (c) by infection due to spores of fungus, usually 
 Merulius lachrymans, carried to the timber in the air or on 
 the clothing or tools of workmen, or spreading from decayed 
 vegetation or other affected timber in proximity. 
 
 The forest fungus referred to is characterised by the 
 production of red patches, distinguished under the name 
 of red rot. The mycelium — the development of the fungus 
 devoted to absorbing and storing nourishment — is in this 
 case white. The commonest fungus, Merulius, is generally 
 initiated by greenish patches which develop a white, wool- 
 like but radiating mycelium which becomes grey or brown. 
 This fungus readily condenses moisture and rapidly spreads 
 even over mineral substances, such as brick, plaster, or 
 even iron, and on full development hangs between joists or 
 other woodwork in festoons, which are generally brown 
 but sometimes form a delicate black network resembling 
 seaweed.^ 
 
 The wood attacked first swells and then shrinks as water 
 is taken up by the fungus. Finally it cracks and presents 
 a charred appearance. If the atmosphere is dry the wood 
 becomes brown and very brittle, and if wet, soft and pulpy. 
 
 The essentials for the development of fungus are mois- 
 ture and an alkali. The presence of ammonia, which 
 with water forms a strong alkali, greatly favours the possi- 
 bility of growth. Since ammonia results from the gradual 
 » Bidlake, " Dry Rot in Timber." (Batsford, 1889.) 
 
TIMBER 
 
 295 
 
 decay of nitrogenous organic matters, it is liable to 
 occur as an accompaniment of faulty drains or insanitary 
 conditions such as sometimes exist in stables and cow- 
 houses. Whether the mineral alkalis potash, soda, and 
 lime found in materials such as mortar influence the 
 growth of the fungus, appears to require investigation. 
 The absence of sunlight and a stagnant atmosphere are 
 further factors which aid fungoid growths, while the more 
 nutriment left in the wood the greater is the means of 
 sustenance. Sap left in wood will itself decay and produce 
 fungus owing to putrefaction of albumen, a nitrogenous 
 substance best known as forming a large proportion of 
 white of egg. Even in the absence of actual sap the 
 fungus can find nourishment by feeding on starch and 
 other bodies stored in the wood fibres, and since such 
 supplies exist chiefly in sapwood this is more readily 
 attacked than is heartwood. Chemically the action of the 
 fungus is the converse of the building-up of wood tissues, 
 the lignine is reconverted into cellulose, and this is then 
 further decomposed. 
 
 3. Decay due to Insects. — Apart from the ravages of certain 
 termites known as white ants, the operations of which 
 are confined to tropical climates, the most important 
 forms of decay in converted timber under this heading 
 are caused by worms. Terrestrial worms sometimes find 
 their way into woodwork, and by boring break down the 
 fibre and reduce it to powder. These insects operate 
 successfully in hard wood, and are often found in old 
 furniture. The progress of decay in such cases is generally 
 slow, but worm-holes should be treated as soon as they 
 are discovered, as otherwise complete rottenness is likely 
 to result eventually. 
 
 Aquatic worms rapidly attack timber below water, and 
 the most active of these is the small crustacean Limnoria 
 terebrans, which thrives both in clear and muddy water, 
 
296 CHEMISTEY AND PHYSIOS OF BUILDING MATEEIALS 
 
 and no timber appears to be secure against its ravages save 
 eucalyptus. Another well-known boring worm is Teredo 
 navalis. The increasing use of concrete piles in place of 
 wood offers a solution to the destruction due to these 
 insects. 
 
 Forest timbers are subject to attacks from many cater- 
 pillars and other insects, a concise account of which will 
 be found in Chapter XVI. of "Timber," by Charpentier 
 (English translation, Joseph Kennell). 
 
 V. The Preservation of Wood. 
 
 The methods at disposal for preserving timber depend 
 to some extent upon the purposes for which it is intended. 
 The most usual means consists in the removal of all 
 matters capable of putrefaction and the maintenance of the 
 material in salutary conditions. When appearance is unim- 
 portant and conditions liable to induce decay are inevitable, 
 some form of impregnation is usually resorted to. 
 
 1. Seasoning. — Seasoning consists in the removal of sap 
 and excess of water, by which process the wood is sterilised. 
 Natural seasoning consists in mere air drying, which is 
 effective, since evaporation of water eventually dries up and 
 kills the living tissue. Complete immersion in water also 
 washes out the sap, provided that stagnant conditions do 
 not prevail, and the excess of water may then be removed 
 by air drying. Artificial seasoning is often resorted to to 
 hasten the process of sterilisation ; this consists of drying 
 the timber in a " kiln," which is often merely an enclosure 
 over a steam boiler supplying power in the saw mill. Here 
 air at about 82° C. (180° Fahr.) is allowed to circulate 
 round the wood suitably stacked. At this temperature 
 drying and sterilisation are rapidly completed, but the opera- 
 tion requires care to obviate damage by splitting and 
 warping, and is in general confined to the treatment of 
 
TIMBEE 
 
 297 
 
 soft woods. Probably the most effective form of seasoning 
 consists of kiln treatment preceded by a partial natural air 
 drying. 
 
 Seasoned wood alone is in a fit condition for paint or 
 other covering, and to paint unseasoned timber is merely to 
 seal up in it the germs of its own decay. As regards 
 situation and surroundings, dryness is the first essential, as 
 no fungoid growths can exist in a dry atmosphere. Further 
 aids to preservation are complete air circulation from one 
 side of a building to the other, effected, if necessary, by 
 pipes under concrete floors, light wherever possible and 
 impervious seatings for timber in contact with moisture- 
 bearing substances. 
 
 2. Impregnation. — The attempts to preserve timber by 
 impregnating it with antiseptic substances have the object 
 (1) of coagulating the albumen of the sap ; (2) filling up 
 the pores of the material. This has been effected by the 
 use of {a) metallic salts ; (h) creosote. 
 
 (a) Metallic salts. — Though some fifteen different com- 
 pounds have been cited for preserving timber, hardly any 
 of them are both effective and practicable. These salts 
 are introduced in solution in water, and if they are to be 
 permanent must act upon the wood tissues and produce 
 insoluble substances, otherwise they will be gradually 
 removed by moisture. Among these compounds may be 
 mentioned zinc chloride, a powerful antiseptic, and mercuric 
 chloride, one of the most effective germicides known. 
 When this latter compound is dissolved in mobile liquids 
 such as methyl alcohol (wood spirit) it can penetrate into 
 timber for some distance and is valuable for local treat- 
 ment, as, for example, for destroying worms in furniture ; 
 but it is expensive and exceedingly poisonous. 
 
 (6) Creosote— Thia is the only preservative now 
 employed on a large scale. Its preparation by the distilla- 
 tion of tar between 180° and 250° C. has been referred to in 
 
298 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 Chapter IX. Creosote is a complex mixture of many 
 carbon compounds, and opinions upon its essential 
 ingredients seem to be divided. It is generally held that 
 its value depends upon the amount of carbolic acid it con- 
 tains, and that this should exceed 5 per cent, of the 
 material ; but Charpentier^ cites experiments which seem 
 to show that the efficacy of creosote is due to a larger 
 extent to naphthalene, a white crystalline compound which 
 is volatilised with the tar oils between 180° and 200° C. and 
 condensed. Though carbolic acid is a much more power- 
 ful antiseptic than naphthalene, it is at the same time both 
 deliquescent and fairly soluble in water, hence it is still 
 possible that naphthalene plays a part in preservation. 
 
 The mere immersion of timber in creosote or other 
 antiseptic liquids results in but the most superficial 
 impregnation of the material, and to produce effective 
 results it is necessary to first expel air and moisture from 
 the pores of the wood by the aid of heat and reduction of 
 atmospheric pressure. This is effected by placing the 
 material in its final form for use in large iron cylinders. 
 Subsequently creosote is admitted and the contents of the 
 cylinders are submitted to pressure, whereby the liquid is 
 forced into the cells of the wood. The value of this treat- 
 ment is proportional to the amount of creosote absorbed, 
 which should form the basis of charges for the process. 
 For ordinary exposed work 8 to 10 pounds of creosote should 
 be absorbed per cubic foot of timber; but for protection 
 against the attacks of worms in water double this quantity 
 is desirable. 
 
 The timbers which best repay creosoting are the soft 
 woods and such as contain much sapwood. Material 
 almost worthless in its ordinary state may by this 
 treatment be rendered proof against decay in very adverse 
 circumstances. 
 
 * Charpentier, "Timber." 
 
TIMBER 
 
 299 
 
 3. Rendering Wood Uninflammable. — The combustible 
 nature of timber is a grave objection to its use for many 
 purposes, not only on account of direct risk of fire, but 
 because its combustion involves the evolution of much 
 smoke and volatile matter which in confined situations 
 may cause suffocation. 
 
 From what has been said in Part I. on the subject of 
 combustion it will be evident that any treatment of wood 
 aiming at reducing its inflammability should result in the 
 filling up of the internal cavities in order to deprive the 
 material of its contained supporter of combustion — air, 
 with which the cavities are normally filled. The reason 
 why oak is less readily inflamed than pine lies not in 
 difference of composition, but in the greater structural 
 compactness of the former wood. Even a combustible 
 substance, therefore, such as starch, filling the wood cells 
 will decrease inflammability. 
 
 Compounds of ammonia appear to be most efficacious in 
 this connection, which is probably due to the ready vola- 
 tility of all ammonium compounds by heat. The gases 
 thus formed, which do not support combustion or them- 
 selves burn, drive out the air which is still contained in 
 the pores of the wood before the igniting point of the 
 material is reached, and also impede the access of air to its 
 surface. 
 
 Tungstate of soda has often been cited as a compound 
 which renders timber and other fabrics non-inflammable ; 
 but in the opinion of Charpentier its value has been over- 
 estimated, and he considers that ammonium phosphate is 
 an essential ingredient of all impregnating mixtures. 
 
 Mere painting of the surface, though it has its value, is 
 naturally less effective than impregnation. Paints employed 
 for the purpose are usually composed largely of silicate of 
 soda (soluble glass) or of asbestos reduced to a fine state of 
 division and mixed with some suitable liquid vehicle. 
 
CHAPTEE XXV 
 
 PAINTS — GENEEAL CHARACTERS — OILS, THINNERS AND 
 VARNISHES 
 
 I. General Characters. 
 
 1. Introductory. — The use of paint results either from 
 the necessity of protecting materials from atmospheric or 
 other destructive influences or from the desirability, real 
 or supposed, of concealing the true nature of materials 
 with a view to adding to their decorative effect. Paints are 
 an assemblage of various substances of vegetable, mineral 
 and manufactured origin. The efficiency of these con- 
 stituents may be regarded from a utilitarian or artistic 
 standpoint, but since the greater the elaboration in their 
 use the more important is their unalterability, permanence 
 really determines their ultimate value. 
 
 The lasting power of paint depends not only upon the 
 chemical nature and proportions of the bodies which 
 compose it, but also to a considerable extent upon the 
 mechanical state of division of solids used in its prepara- 
 tion. Until the state and proportion of the ingredients is 
 defined upon a recognised basis no satisfactory specification 
 which shall safeguard the user and reputable manufacturer 
 can reasonably be expected. The mere requirement that a 
 given number of coats shall be applied is of but small 
 value even with a paint of defined composition, when the 
 extent to which such coats are thinned out by evaporable 
 liquids is left to the discretion of the painter, and it would be 
 very much better when work can be carefully measured and 
 
OILS, THINNERS AND VAENISHES— PAINTS 301 
 
 paints decided upon in advance to require a fixed weight of 
 paint to be laid upon the material to be treated, distributed 
 in the desired number of coats. Though the cost of 
 painters' work may be small as compared with that of 
 other trades in a new building, it becomes a matter 
 of no little importance when considered in the light of 
 periodical renewals, and standardisation in this trade is 
 much needed.^ 
 
 2. Composition of Paint. — Paint consists essentially of 
 two things : (1) a base, which is the paint proper, that is, the 
 solid matter to the covering power of which the protection 
 afforded is mainly due. (2) A vehicle, some liquid which 
 carries the base suspended in it and eventually oxidises and 
 forms a solid film which binds the particles of the base 
 together. When the base does not possess the desired 
 colour some pigment, which usually forms but a small pro- 
 portion of the ingredients, is added, while the viscosity of 
 the paint vehicle may necessitate the addition of some 
 more mobile liquid known as a thinner, which is entirely 
 volatilised when the paint dries. Finally, if circumstances 
 compel the natural rate of oxidation of the vehicle to be 
 hastened, one or two per cent, of some agent which induces 
 oxidation, known as a drier, is added. 
 
 3. Essential dualities of Paint. — It cannot be said that 
 the characteristics of paints have yet been properly defined, 
 much less that any scientific standards have been decided 
 upon in connection with this material. The vehicle must 
 be capable of complete solidification on exposure, and must 
 then possess both toughness and elasticity, while the base 
 appears to owe its efficiency to (a) chemical stability, 
 (b) mechanical fineness, (c) what is termed opacity. 
 
 (a) It is by no means proved that any chemical action 
 
 1 The subject is under the consideration of the Eoyal Institute of 
 British Architects. 
 
302 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 between the vehicle and the base takes place,^ and the pro- 
 perties of the latter may certainly be judged in paint upon 
 those possessed by it alone. Further, admixture with the 
 dried vehicle (oil) only confer partial immunity from 
 destructive influences, hence the protective power of the 
 dried oil film cannot be relied upon to prevent chemical 
 and physical changes in the base. Solution of zinc white, 
 for example, in rain water charged with carbon dioxide 
 takes place in zinc paints, and sulphur compounds in certain 
 atmospheres readily blacken white lead in paint form. 
 
 (b) For a given base the durability of paint increases 
 with the fineness of the particles of that base, and a standard 
 of fineness is much needed, and would probably remove 
 many difficulties in paint specification. Some interesting 
 experiments^ on this subject showed that in the case of two 
 similar paints possessing particles about 0*0080 and 
 0*0004 inch in diameter respectively, the life of the latter 
 was at least twice that of the former under similar 
 conditions. 
 
 (c) Opacity gives paints what is technically termed 
 ** body," and may be judged by the relative exclusion of 
 light produced by films of different paints similarly applied 
 to the surface of a transparent material. Naturally such 
 comparison should be made with bases possessing the same 
 degree of fineness. 
 
 It is not the inherent optical opacity of the solids used in 
 paints which confers durability, but opacity due to the 
 assemblage of masses of solid particles, and it seems not 
 unlikely that specific gravity is really the important factor 
 in this connection. Many of the less opaque bases have 
 low specific gravities, and on applying such bases in oil 
 their greater tendency to remain suspended in the liquid 
 
 ^ Church cites experiments which seem to show that such action 
 exists in the case of white lead and linseed oil. 
 
 2 American tests quoted in 2'he JBuilders' Journal, 1906. 
 
OILS, THINNEES AND VARNISHES— PAINTS 303 
 
 will cause the particles to spread over a larger surface, 
 hence the number of particles per unit area will not be 
 so many as in the case of heavy bases which sink more 
 rapidly. In practice zinc white, for example, is well known 
 to possess more covering power but less body than white 
 lead, and efforts are made to increase its specific gravity in 
 its manufacture. 
 
 If the above hypothesis of ** body " is a correct one, the 
 lighter bases should be more effective when used in oils 
 possessed of low specific gravity and viscosity. 
 
 4. Adulteration and the use of Fillers and Thinners. — 
 Owing to the lax way in which paints are usually specified, 
 it is extremely difficult to define adulteration, and makers 
 taxed with the addition of foreign ingredients will generally 
 contend that they possess beneficial properties. 
 
 It is essential to consider the composition of paints in the 
 light of the use to which the paint is to be put, the neces- 
 sities for renewal and the price paid for the material, and 
 while the best paints are generally the most economical, in 
 certain cases, as for temporary work or rough coverings 
 for walls or fences, second quality paints may be desirable. 
 A definition of adulteration will obviously differ with quality, 
 which must first be standardised. 
 
 When porous substances such as brick are to be painted 
 it is usual to first apply what is termed a filler. This is 
 composed of some inert substance, such as chalk or sulphate 
 of lime, compounds much inferior both in body and cover- 
 ing power to most bases, but provided good adherence is 
 obtained and that the subsequent coats of paint proper are 
 not deteriorated (as by the use of an unsuitable vehicle for 
 the filler or of some filler not chemically inert) such a pro- 
 cedure may be legitimate and much decreases the cost of 
 bringing the final surface to a proper state of finish. 
 
 Adulteration with solid bodies appears to be intimately 
 connected with questions of fineness and specific gravity. 
 
304 CHEMISTRY ANB PHYSICS OF BUILDING MATERIALS 
 
 For example, the addition of barium sulphate to white lead 
 is generally rightly condemned, but this is not because this 
 compound possesses objectionable qualities, for its stability 
 is much greater than that of white lead. The objection lies 
 in the comparative coarseness of the particles prepared 
 by the mechanical crushing of the mineral barytes, and 
 possibly on account of its lower specific gravity. In the 
 case of pigments, adulteration, viewed in the light of 
 chemical stability, becomes even more important, in such 
 cases, for example, organic colouring matters liable to fade 
 may be substituted for stable minerals. 
 
 The excessive use of thinners, though not usually regarded 
 in this light, is a form of adulteration of the worst kind, 
 because this involves an actual decrease in the amount 
 of material which may fairly be expected to be deposited 
 upon the surface painted. 
 
 II.— The Oils. 
 
 1. Varieties of Oil. — By the term " oil " is generally under- 
 stood some greasy liquid which is not miscible with water 
 and which produces a permanent stain on paper ; but as 
 the expression is a popular rather than a scientific one, no 
 very exact definition is to be expected. 
 
 Oils of mineral, vegetable and animal origin are well 
 known, but only those of vegetable origin are used in 
 paints to any extent. Examples of vegetable oils are 
 linseed and olive oil ; of animal oils, sperm and menhaden 
 (fish) oil ; and of mineral oils, petroleum and its refined 
 product paraffin oil. 
 
 Oils, again, may be classified as volatile and fixed oils. 
 The former, those which may be distilled by heat and con- 
 densed unchanged ; the latter, those which break up or 
 suffer destructive distillation when heated. Nearly all 
 animal and vegetable oils belong to the latter class. 
 
OILS, THIKNTEES AND VAENISHES— PAINTS 305 
 
 (a) Mineral oils are mixtures of compounds of carbon and 
 hydrogen, and are derived from coal or other carbonaceous 
 deposits as the result of natural or artificial distillation, and 
 possess characters quite different from oils of vegetable and 
 animal origin. They do not become rancid nor dry into 
 solid films nor re-act with alkalis, and they usually display 
 evidences of iridescence on their surfaces which is not 
 observed in oils of organic origin. 
 
 (b) . Vegetable oils are substantially compounds of carbon, 
 hydrogen, and oxygen, and form a mixture of complex 
 organic salts of organic (carbonaceous) acids. They are 
 obtained from the seeds of plants by mechanical pressure 
 and alter on exposure, some becoming rancid, others drying 
 up wholly or partially when left in the air in thin layers. 
 Heated with alkalis, such as caustic soda, they are decom- 
 posed and form glycerine and soap, hence they are said to 
 undergo saponification under such treatment. 
 
 The vegetable oils admit of an important subdivision into 
 drying and non-drying oils. The former, which are alone 
 suitable as paint vehicles, dry completely when exposed in 
 thin layers into hard resinous films. The latter remain 
 sticky, and in some cases become rancid. 
 
 Vegetable oils, however, do not show any definite line of 
 demarcation in drying properties, and it is difficult to decide 
 into which group certain oils should be placed. As, how- 
 ever, but one oil is used in good paint work, this is not a 
 matter of much moment. 
 
 2. Linseed Oil. — (a) Ratv Oil. — This, the sole oil used to 
 any extent for ordinary paints, is obtained by pressure 
 from flax seed, that from the Baltic being regarded as of 
 the best quality. After filtration and the removal of 
 albuminous matters the oil is sent out into the market as 
 cold pressed raw oil. If the extraction is undertaken when 
 the seed is heated to a temperature approaching that of 
 boiling water, the yield of oil is increased, but the quality 
 
306 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 of such "hot pressed oil" is inferior to that obtained at 
 the ordinary temperature. 
 
 Linseed oil has a greenish yellow colour and its specific 
 gravity is 0*930 to 0*937. It is stated^ to be a mixture of 
 the following organic salts which are allied to glycerine : — 
 
 Per cent. 
 
 Glycerol isolinoleniate, C3H5 (Ci7H29COO)3 . 65 
 „ linoleniate (the above formula, but 
 
 different constitution) . . 15 
 linoleate, C3H5 (CivHaiCOOa . . 15 
 „ oleate, C3H5 (Ci7H33COO)8 . . 5 
 
 The drying of the oil appears to be dependent upon the 
 proportion of the first two of the above constituents, and 
 involves (as in the case of all drying oils) the absorption of 
 oxygen, but the chemical changes which take place in the 
 formation of the solid resin resulting from this oxidation 
 are still but ill understood. 
 
 (b) Boiled Oil. — The rate at which linseed oil dries is 
 much accelerated by heating, when a loss of some volatile 
 constituents (or possibly decomposition products) takes 
 place, and the oil becomes thicker and darker in colour. 
 Sometimes the process of drying is initiated in the oil by 
 blowing air through it during the heating operation. The 
 oil prepared in this manner is known as " boiled oil," and 
 forms a more resistant film as a vehicle than the raw oil. 
 It has a specific gravity of 0'937 to 0*952, and will dry as a 
 thin layer, on a glass plate, in twelve to twenty-four hours, 
 whereas the raw oil seldom dries in two days even in 
 favourable circumstances. 
 
 When the colour of linseed oil is objectionable, as, for 
 example, in making up delicately tinted pigments, it may be 
 bleached by the action of sulphuric acid and steam, after 
 which process all traces of acid must be removed by shaking 
 the oil with water. 
 
 * " Chemistry for Engineers and Manufacturers," Blount and Bloxam. 
 
OILS, THINNERS AND VARNISHES— PAINTS 307 
 
 3. Other Oils. — Since linseed oil is alone used as a paint 
 vehicle in reputable work of an ordinary character, there 
 are few other oils that need be referred to. 
 
 (a) Cottonseed oil is obtained from cottonseed in a 
 manner similar to that above described. It has a deep 
 reddish colour, but this tint may be largely removed by 
 treatment with alkalis. It possesses constituents which 
 easily solidify, hence paints containing it in quantity are 
 apt to become very viscous in cold weather. It is only a 
 drying oil in part, and hence is unsuitable as a paint 
 vehicle, though it is sometimes found as an adulterant in 
 linseed oil. 
 
 (b) Rosin oil is the chief product of the distillation of 
 rosin, which is itself the residue left on the distillation 
 of crude turpentine. This oil is a mixture of compounds of 
 carbon and hydrogen ; and, therefore, although its original 
 source is a vegetable one, it may be regarded as a mineral 
 oil, and often exhibits the iridescence characteristic of 
 mineral oils. Though it contains a proportion of con- 
 stituents capable of absorbing oxygen, and thus partially 
 dries, it is quite unsuitable as a paint vehicle, as it never 
 dries completely. A cheap oil, it is occasionally found as 
 an adulterant in linseed oil. It has a few legitimate uses 
 when a permanently greasy surface is desirable to turn wet, 
 as, for example, for treating roof shingles. 
 
 (c) China wood oil, though hardly likely to be found 
 replacing linseed, may be mentioned here as a suggested 
 efficient and cheap substitute for linseed oil in making 
 varnishes.^ It is obtained from the seeds of a tree native 
 in China, and is a viscous light-coloured oil which dries 
 rapidly to form a tough and elastic film. 
 
 4. Tests for the Oils, — The only tests for oils which 
 can be undertaken by the layman are such qualitative 
 
 ' Hall, " The Chemistry of Paints and Paint Vehicles." 
 B.M. X 
 
308 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 investigations as are involved in noting the rate of drying 
 and characters of film produced. The report of an expert 
 upon the value of a drying oil will probably include the 
 following tests : — 
 
 (a) Iodine Absorption— The drying power of an oil 
 depends upon the amount of unsaturated compounds — that 
 is, compounds capable of direct chemical addition — which it 
 contains. The determination of oxygen absorbed is difficult, 
 but may be measured by the quantity of iodine taken up 
 by the oil. This estimation is made by shaking up a given 
 quantity of the oil with a given quantity of iodine solution 
 of known strength, and by further chemical tests finding 
 out how much iodine still remains unabsorbed. The 
 amount of iodine taken up by the oil is known as the 
 "absorption equivalent," and the higher this value the 
 greater is the drying power of the oil. 
 
 (b) Saponification Tesi.— When fatty (non-mineral) oils 
 are treated with caustic soda this alkali combines with part 
 of the oil to form a soap. The amount of alkali taken up 
 by an oil may thus be used to test its freedom from 
 admixture with mineral oils which do not form such 
 combinations. 
 
 (c) Flashing Point. — The ignition temperature of a 
 mixture of air and vapour, given off by an oil through 
 which the air is forced, is known as the " flashing point." 
 This temperature in a standard apparatus is characteristic 
 for different oils, and can thus be used as a test for purity. 
 Boiled linseed oil, for example, flashes at 275° C, whereas 
 for rosin oil the flash point is 140° C. 
 
 (d) Sulphuric Acid Tesi.— Sulphuric acid has a charring 
 effect on most carbonaceous substances, and the increase 
 in depth of tint produced in an oil by such addition may 
 be used to indicate its nature. Linseed oil, for example, 
 under similar conditions, darkens much less than cottonseed 
 and rosin oils. 
 
OILS, THINNEES AND VAENISHES— PAINTS 309 
 
 III. Thinnbes. 
 
 ^ 1. Introductory.— Thinners, as already explained, are 
 liquids used to decrease the viscosity of paints and to 
 render them workable under the brush. Since the more 
 liquid the paint the less is the labour of spreading it over 
 a given surface and the greater the surface it will cover, 
 there is every temptation to use excessive quantities of 
 thinners both on the part of the workman and his employer, 
 who is receiving payment for the area of material covered 
 and not for the thickness of the protective coat he is supply- 
 ing. ^ The limited use of thinners, however, is not only 
 legitimate but necessary, and the characteristic of these 
 liquids is that they evaporate practically entirely during 
 the drying of the paint. 
 
 2. Turpentine. — This liquid, known in the trade as 
 "turps," which has no rivals^ as a thinning agent, is 
 obtained by the distillation of resin collected from growing 
 pines or from the liquids obtained on heating pine waste. 
 Turpentine is a mixture of hydrocarbons, most of which 
 may be represented by the formula CioHie. The specific 
 gravity of turpentine is 0-862 to 0-870, and its boiling point 
 156° to 158° C. It possesses a pleasant resinous smell when 
 free from adulterants, and on exposure evaporates, leaving 
 only a trace of solid residue. 
 
 If a tube, with transparent ends, filled with turpentine, 
 be viewed under polarised light between crossed nicols,^ 
 it is found that its introduction between the nicols enables 
 some light to pass to the eye of the observer, and that to 
 restore darkness one of the nicols must be rotated through 
 a certain angle. Substances which possess this power of 
 "rotating the plane of polarisation" are said to be 
 "optically active," and since under standard conditions ^ 
 ' The subject, however, needs more investigation 
 I mt® • ^! polarised light has been explained in Chapter XI 
 ihe chief condition is a given length of column of liquid; that 
 usually adopted measures 100 mm. 
 
 X 2 
 
310 CHEMISTRY AND PHYSICS OF BUILDING MATERIALS 
 
 the angle through which the nicol's prism must be turned 
 to restore darkness is characteristic of the substance, it 
 forms a useful means of identification.^ This angle, known 
 as the optical rotation of the substance, is designated 
 + or — according to whether the prism must be rotated 
 to the right or the left hand to restore darkness. A micro- 
 scope is hardly suitable for the examination of tubes of 
 liquid in this manner, and therefore these investigations 
 are carried out in a special instrument known as a " polari- 
 meter." The optical activity of turpentine distinguishes 
 it from all its substitutes which have no power of rotating 
 the plane of polarisation. American turpentine, chiefly used 
 in this country, is stated by Hurst to possess in ordinary 
 commercial samples a rotation of + 8° to 16°. 
 
 3. Turpentine Substitutes. — The fact that many limpid 
 liquids easily miscible with oils are cheaper than turpentine 
 has led to the adoption of certain substitutes as thinners. 
 The legitimate amount of thinners in paints is so smalP 
 that there seems very little reason for adopting such sub- 
 stitutes, and any claim for a large saving in price therefore 
 carries with it its own condemnation. If other thinners 
 are employed the amounts allowed should bear some 
 relation to their limpidity and evaporative power. 
 
 (a) Rosin Spirit. — This liquid is the first product of the 
 distillation of rosin, and is much used for making cheap 
 
 ^ In an interesting paper on Turpentine Oils, J. Soc. Chem. Indus., 
 June Both, 1908, Messrs. Richardson and Bo wen state that some 
 turpentines contain a mixture of right- and left- handed turpenes 
 which, by neutralising each other's rotation, seriously decrease the 
 value of the polarimeter test. These experimenters recommend a 
 determination of the Index of Refraction (that is, the amount by 
 which a ray of light is bent from its normal course in passing through 
 a given layer of the material) as a more reliable means of identification, 
 and state that while for turpentines this value is about 1-47, it is lower 
 (1'41 to 146) for hydrocarbon adulterants. 
 
 2 This is true of ordinary paint work, but in some cases, as in 
 carriage painting, the evaporable liquid forms the greater part of the 
 vehicle. 
 
OUB, THINNEES AND VAENISHES-^PAINTS 311 
 
 varnishes. It may be considered the best of the turpentine 
 substitutes when free from the non-drying rosin oil whieh 
 distils from the rosin at a higher temperature. The oil 
 may be detected by evaporating the spirit at a temperature 
 not exceeding 250° C, when any oil present will be left as 
 a residue. 
 
 (h) Shale naphtha forms some 6 per cent, of the distillate 
 obtained from crude shale oils. Hurst describes it as 
 "largely used as a substitute for turpentine and on the 
 whole a good material for the purpose." 
 
 (c) Benzine, also called benzoline and petroleum spirit, is 
 obtained as a first product in the distillation of American 
 natural oils. It is a common and very inferior substitute 
 for turpentine, and owes its popularity to its cheapness and 
 limpidity, which renders it a powerful thinner. Its great 
 inflammability introduces a risk of fire. It tends to flat 
 paints less than turpentine, but its rapidity of evaporation 
 seems unlikely to be beneficial to the homogeneity of the 
 oil film in paints. 
 
 (d) Petroleum Oils. — The objection to the use of benzine 
 has been met by the introduction of heavier oils obtained 
 at later stages of crude petroleum distillation ; thus ordinary 
 paraffin oil is used as a thinner and is certainly preferable 
 to benzine, but it dries slowly. 
 
 In considering the use of the products of natural oils as 
 thinners the possible presence of sulphur compounds such 
 as thiophene, which may have a deleterious action upon lead 
 paints, should not be overlooked. 
 
 IV. Vaknishes. 
 
 1. General Characters. — Varnishes are solutions of natural 
 resins in oils or spirits and are generally applied as final 
 coatings to stained or painted work, but sometimes mixed 
 with paints before application, as in enamels. 
 
312 CHEMISTRY AND PHYSICS OF BUII.BING MATEEIALS 
 
 No brief description of varnishes can be very satisfactory, 
 as they present great variations in composition and some of 
 their components are very ill defined. These facts, and the 
 difficulties attending a scientific examination, make varnishes 
 by no means easy to criticise. 
 
 The qualities to be looked for in a varnish for ordinary 
 purposes are toughness, hardness, gloss, transparency, body, 
 freedom from colour, and rate and completeness of drying. 
 These qualities may be in some measure assessed by the 
 layman by pouring similar quantities of a known varnish of 
 good quality and of that under examination on to glass plates 
 and examining their relative tendency to bruise, splinter, 
 crack, deteriorate on exposure, and so forth. 
 
 Body may be judged by the rate at which thickening with 
 litharge (PbO) takes place, the body possessed by the varnish 
 being inversely proportional to the time taken in thickening. 
 
 A good varnish should dry and be hard enough to touch in 
 ten hours under ordinary conditions. It should resist a 
 moderate blow without showing cracks, and the finger should 
 leave no mark when rubbed over its surface. 
 
 The qualities of varnishes depend quite as much upon the 
 solvent as upon the dissolved resin, and none of such as are 
 made up with wholly volatile solvents, known as spirit 
 varnishes, and which therefore leave merely a thin layer 
 of resin on drying, are capable of resisting wear or exposure. 
 Since the oxidation of the solvent and the binding power of 
 the film thus formed are essential, the best varnishes are 
 those consisting of a resin dissolved in linseed oil. 
 
 Varnishes may thus be classified as oil and spirit 
 varnishes. The former alone are serviceable for general 
 purposes, the latter are used for making French poHshes 
 and lacquers. The inferiority of spirit varnishes is 
 emphasised by the fact that the harder resins cannot 
 be dissolved in spirits. 
 
 2. The Eesins. — The properties of a resin in a coat of 
 
OILS, THINNEES AND VAKNISHBS— PAINTS 31^ 
 
 varnish may be assessed by those of the resin alone, hence 
 the tougher, harder, brighter and more free from colour^ 
 the resin, the greater will be its value for varnish making. 
 
 Resins are of vegetable origin and are found in plants or are 
 produced by the oxidation of turpentine exudations. They 
 are solid amorphous glue-like bodies, more or less trans- 
 parent and very stable, hence they are found covered by 
 deposits long after the trees which produced them have 
 undergone complete decay, and these so-called " fossil 
 resins " form the chief source of these bodies in commerce. 
 
 Chemically resins are closely allied to turpenes, com- 
 pounds represented in an impure form by turpentine and 
 possessing the formula GioHie. The resins are sometimes 
 denoted by the term gum-resins, but the designation is 
 unfortunate, for the gums are another series of compounds, 
 having the general formula CeHioOs of which dextrine is 
 an example. Gums dissolve or become sticky in water and 
 are precipitated from solution by alcohol, whereas most 
 resins are quite unaffected by water, and some of them are 
 soluble in alcohol. 
 
 The manufacture of varnish, necessitating as it does the 
 melting of the resin, its solution in heated oil and sub- 
 sequent thinning with turpentine, involves operations which 
 cannot be undertaken by a building contractor and are 
 seldom attempted by even paint manufacturers, hence the 
 resins themselves seldom come directly under the criticism 
 of those responsible for the quality of painters' materials. 
 But a brief description of these bodies is therefore given. 
 
 3. Varieties of Resin. — Amber. — This is the best of all the 
 resins and is chiefly found in the Greensand (see geological 
 table), but it is much too costly for any ordinary purpose. 
 
 Copals. — Many resins are included under the name copal, 
 
 ' Some resius are white owing to minute air or water inclusions 
 which escape on solution. 
 
314 OHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 and these vary much in quality. The absence of classifica- 
 tion of these resins makes it, further, exceedingly difficult to 
 ascertain what is being supplied under this name. 
 
 The best copal is animi, which is often classed as a resin 
 independent of this group. It is very tough, harder than 
 the finger nail, and highly transparent. Its use is confined 
 to highly finished varnishes exposed to much wear, such 
 as are requisite in carriage work. 
 
 Hard copals, which find a use in the best varnishes for 
 ordinary purposes, are those of West African origin, and 
 an attempt has been made to define the hard varieties of 
 this resin as " true copals." New Zealand and Manila 
 resins are other varieties which (particularly the latter) are 
 inferior to West African copal. 
 
 Dammar is a resin possessed of some hardness but little 
 tenacity, and becomes powdery on slight abrasion. 
 
 Rosin is the solid residue from the distillation of turpen- 
 tine. It is hard, but much too brittle to be durable, and 
 should be excluded from good varnishes. 
 
 Lac is a product of the action of insects upon the sap of 
 certain Indian trees. It is distinguished from other resins 
 by its solubility in water. In its commonest form it is 
 known as shellac, and, dissolved in methylated spirit, or in 
 modern practice in benzine to increase the rate of drying. 
 It is used as a spirit varnish (French polish). 
 
 Asphaltum, — This substance, mineral pitch, described in 
 a previous chapter, can hardly be looked upon as a resin. 
 It may be mentioned here, however, as forming the solid 
 ingredient of japan. 
 
CHAPTEE XXVI 
 
 PAINTS THEIR SOLID INGREDIENTS BASES, PIGMENTS AND 
 
 DRIERS 
 
 I, White Ingredients. 
 
 1. Introductory. — The value and general character of the 
 solid materials in paints have been referred to in the 
 opening paragraphs of the last chapter, and it is here 
 proposed to discuss these ingredients in detail. It is usual 
 to make a distinction between such bodies as are responsible 
 for covering the material painted which are known as 
 "bases" and form the mass of the solids contained in 
 paints, and those which are added to give desired colours, 
 known as pigments. As, however, certain bases, such as 
 white lead and zinc white, also play the part of white 
 pigments, while some pigments, such as iron oxide and red 
 lead, are also used as bases, it may be sufficient after 
 the foregoing remarks upon the relative quantities and uses 
 of these constituents to classify them together merely 
 according to colour. 
 
 2. White Lead. — (a) Manufacture. — This substance, the 
 most important base used in painting (in, at least, this 
 country), is a basic carbonate of lead which may be prepared 
 in several ways, and most simply by precipitating the 
 carbonate from a solution of a salt of lead such as the 
 acetate by means of any soluble carbonate. The method 
 of manufacture, however, which, in spite of its laborious 
 and lengthy nature, produces white lead which is more 
 popular than any other kind, is known as the Dutch or 
 
316 OHEMiSTBY AND J^HYSICS OF BtflLDlNa MATERIALS 
 
 stack process. In this process thin plates of lead are 
 placed over pots containing vinegar (dilute acetic acid), 
 which is caused to evaporate by the heat produced on 
 fermentation of organic matter contained in bark which 
 has been used for tanning (spent tan) with which the 
 pots are surrounded. The vaporised acid attacks the 
 lead, when acetate of lead is formed, and this in turn 
 is decomposed by the carbon dioxide evolved from the 
 decaying tan. In the presence of air and moisture a 
 mixture of hydroxide and carbonate of lead (basic carbo- 
 nate) is produced as a white incrustation upon the lead. 
 The formation of this carbonate regenerates acetic acid, 
 which again exerts its corrosive action on the lead, and 
 this cycle of changes continues until all the lead is converted 
 into carbonate. 
 
 The pots and lead sheets to the number of many 
 thousands are walled up in large chambers, and after two 
 or three months they are unstacked, any remaining metal 
 is removed by hand, and the white lead then ground and 
 washed. 
 
 The purity of the metal used is important in this manu- 
 facture, since traces of iron, antimony and copper impart 
 a yellow colour to the material, and though this may 
 be partially corrected by the admixture of indigo during 
 grinding, this cannot be regarded as a desirable treatment. 
 
 (b) Composition and Properties. — It is very doubtful 
 whether white lead can rank as a chemical compound. The 
 formula 2PbC03.Pb(OH)2 is assigned to it in text books, 
 but this ratio of carbonate to hydroxide is by no means 
 constant, and the material often contains water in addition. 
 
 White lead owes its popularity to its great body and 
 covering power, which is due to its amorphous structure, 
 fine state of division and high specific gravity. The 
 opacity or body is conferred chiefly by the carbonate, while 
 the binding power is regarded as due to the hydroxide, and 
 
PAINTS— INQEEDIENTS— BASES, PiaMENTS, DElEES 317 
 
 the proportions indicated in the above formula are said to 
 give the best combination of these properties. 
 
 This base is by no means free from disadvantages. It 
 is poisonous, costly, and open to the action of many 
 destructive agents, particularly (as far as its appearance is 
 concerned) sulphuretted hydrogen H2S, a gas always liable 
 to be present in the atmosphere where coal gas is in use 
 owing to slight leakage or incomplete combustion. The 
 reaction between these bodies may be represented as 
 follows : — 
 
 3H2S 4- 2PbC03.Pb(OH)2 = 3PbS + 2C02 + 4H2O. 
 
 Lead sulphide (PbS) thus produced is black, hence the 
 discolouration of white lead due to this action. 
 
 The restoration of colour to white lead, though not worth 
 attempting for ordinary painted work, becomes important 
 when artistic work is in question. This may be effected by 
 treating the surface of the paint with a dilute solution of 
 the unstable compound hydrogen peroxide H2O2 : — 
 
 PbS + 4H2O2 = PbS04 + 4H2O. 
 
 Lead sulphate is thus formed, and not the original lead 
 carbonate, but the sulphate, like the carbonate, is white ; it 
 is moreover permanent. 
 
 (c) Adulteration and Tests. — The possible presence of 
 other metals in white lead which result in discolouration of 
 the manufactured material have already been referred to. 
 In addition to these, lead acetate may also be present, due 
 to imperfect washing. This salt is readily soluble in water, 
 and may be easily tested for by shaking the white lead 
 with water, filtering, and adding sulphuric acid to the clear 
 liquid, when lead sulphate will be produced as a heavy 
 white precipitate. 
 
 The most probable adulterants in white lead are barium 
 
318 CHEMISTEY ANB PHYSICS OF BUILDING MATERIALS 
 
 sulphate, lead sulphate, kaolin, calcium sulphate, magne- 
 sium silicate, and chalk. If in powder, the complete 
 solubility of white lead in dilute acetic or nitric acids 
 serves to distinguish it from all these adulterants but the 
 last, which is seldom found. If in oil, the reduction of the 
 substance in the blowpipe flame on charcoal will display 
 the presence of all these adulterants, except lead sulphate, 
 as white incrustations, since lead compounds will eventually 
 produce nothing but globules of metal. 
 
 Any sulphur compound will, when strongly heated with 
 sodium carbonate on charcoal in the reducing flame, pro- 
 duce sodium sulphide, and if the freed mass be placed on 
 silver (a coin) and wetted, a brown stain on the metal will 
 result from the presence of this sulphide. 
 
 White lead may be rapidly distinguished from other 
 white bodies by its ready discolouration with sulphuretted 
 hydrogen. This gas may be easily made by burning 
 sulphur on an iron wire and immersing the wire in strong 
 hydrochloric acid. If this evolution of gas be allowed to 
 take place in any small vessel and a piece of paper smeared 
 with white lead be placed over its mouth, discolouration 
 will take place immediately. 
 
 3. Zinc White. — {a) Manufacture and Properties. — This 
 base, which is zinc oxide (ZnO) is made by highly heating 
 metallic zinc in air, when it takes fire and forms an 
 exceedingly fine white fume, which is allowed to settle in 
 suitable chambers. The zinc employed should be free 
 from cadmium, which on burning forms a brown oxide and 
 thus produces discolouration. Lead is also liable to be 
 associated in small quantity with metallic zinc, and should 
 be avoided, as the permanent character of zinc white would 
 be thereby interfered with. 
 
 When pure this base is intensely white, and is used by 
 artists under the name of Chinese white. It possesses 
 great covering power, but comparatively poor body ; it does 
 
PAINTS— INGEEDIENTS— BASES, PIGMENTS, DEIEES 319 
 
 not work so freely under the brush as white lead and is 
 therefore less popular with workmen. Eequiring as it does 
 some 22 per cent, of oil to bring it into a state for use, it is 
 a slow dryer. The opacity possessed by zinc white is some- 
 what decreased by age, and this base is appreciably soluble 
 in water containing carbon dioxide, which renders it less 
 suitable for external use than white lead. Its merits rest 
 chiefly upon its intensity and permanence of colour. 
 Sulphur compounds do, indeed, affect it, but since the 
 zinc sulphide formed is also white no colour change is 
 apparent. 
 
 Zinc white seems to deserve a more extended use for, at 
 least, internal work than it has yet received. Its use is 
 certainly increasing as an ingredient of white enamels, and 
 its employment as final coatings upon white lead has been 
 advocated.^ 
 
 (b) Adulteration and Tests. — Zinc white is sometimes 
 adulterated, but its ready solubility in dilute acids serves to 
 distinguish it from all probable adulterants except white lead 
 and chalk, both of which on the addition of acid dissolve 
 with effervescence owing to liberation of carbon dioxide. 
 Lead can be found by the blowpipe as described, since zinc 
 yields no globules of metal when heated in a reducing 
 flame. Zinc oxide is characterised by turning a bright 
 yellow when highly heated and regaining its white colour 
 on cooling. 
 
 4. Other White Ingredients. — (a) Lead Sulphate. — Many 
 attempts have been made to substitute for the basic 
 carbonate of lead some other lead compound of a more 
 permanent and less poisonous nature. When galena (PbS) 
 is roasted in a suitable atmosphere it becomes oxidised to 
 lead sulphate, a white and very stable compound which is 
 freed from its other associates in the furnace and ground 
 
 * Jennings, " Recent Improvements in Decorators' Materials." 
 Soc. of Arts J., March 27th, 1908. 
 
320 CHEMISTRY AND PHYSICS OF BUILDING MATEEIALS 
 
 in oil in the usual way. In spite of much energy and 
 capital which has been, and is being, expended in per- 
 fecting processes for this production, the sulphate has 
 never been prepared to produce the body and working 
 qualities of the basic carbonate, and its drying and harden- 
 ing powers are also said to be inferior. Though the quality 
 of different makers' sulphate doubtless varies, this base, as 
 prepared by most recent methods, does not appear to find 
 favour with workmen, who distinguish it in use from the 
 basic carbonate without difficulty. This is to be regretted, 
 since from the standpoint of chemical stability and inno- 
 cuousness this compound is a very desirable one. 
 
 It is worth noting that the relegation of the term " white 
 lead " to the basic carbonate has no legal recognition, and 
 that such designation alone is not, therefore, sufficient as a 
 specific definition. 
 
 (6) Zinc Sulphide. — This white permanent compound 
 (ZnS) mixed with some 70 per cent, of finely-ground 
 barytes and known as Orr's zinc white or, more recently, 
 as Lithophone or Lithopone is, when carefully manu- 
 factured, a valuable and permanent pigment, and is 
 becoming popular as a constituent of enamels. Owing 
 to the sulphide contained, it, in all lead pigments, including 
 even driers, must be avoided in its use. 
 
 (c) Barium Sulphate. — This compound, as the mineral 
 barytes (BaS04), has some use as a paint ingredient, and 
 has been mentioned as an adulterant. A white, heavy 
 compound (Sp.g. 4*5) of extreme chemical stability, entirely 
 unaffected by water, acids and sulphur compounds, it is 
 much to be desired that it could be rendered more suitable 
 as a base for paints. Its crystalline nature, however, is 
 against its minute sub-division, which is the probable cause 
 of its small covering power and tendency to make mixed 
 paints set when kept. 
 
 Its complete insolubility in water and acids and the 
 
PAINTS— INGEEDIENTS— BASES, PIGMENTS, DEIEES 321 
 
 presence of sulphur in it (see test under white lead) enable 
 barium sulphate to be recognised without difficulty. 
 
 (d) Calcium Sulphate.' — This substance (CaSOi) has been 
 referred to as a filler and forms an occasional adulterant 
 of paints. It is very inferior both in body and covering 
 power to the bases previously described, and is quite appreci- 
 ably soluble in water. Other properties of this compound 
 have been discussed in the chapters dealing with clays, limes 
 and plasters. 
 
 (e) Kaolin. — This finely divided and inert clay, a silicate 
 of aluminium (Al2Si05), forms a very cheap material, and 
 may occur as an adulterant. It is too poor in body to find 
 a legitimate use in paint work. 
 
 All aluminium compounds are characterised by the blue 
 colour produced when fused with sodium carbonate on 
 charcoal and subsequently heated after the application of a 
 drop of cobalt nitrate solution. 
 
 (/) Calcium Carbonate. — This compound (CaCOs) as chalk 
 is perhaps the worst of all the inferior materials occasionally 
 added to paints, not only on account of its poor body 
 and covering power, but because it is soluble in water, 
 containing carbon dioxide, is readily acted upon by acids, 
 and is decomposed by heat. Its effervescence on the 
 addition of an acid is (in the absence of lead carbonate, 
 which behaves similarly) a distinguishing character among 
 paint materials, while if heated to redness and placed on red 
 litmus paper the quicklime produced by its decomposition 
 will, when moistened, turn the litmus blue. 
 
 II. Coloured Ingredients. 
 
 1. Causes of Colour. — Although any complete appreciation 
 of the phenomena connected with colour involves a study of 
 optics, a few words on this subject may be given as an intro- 
 duction to the succeeding paragraphs dealing with pigments. 
 
322 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 The colour of a body is not an inherent property, but 
 depends both on the nature of the body and the light in 
 which it is viewed. It is well known, for example, that a 
 scheme of colour which may be harmonious by daylight 
 may be quite discordant by artificial light. 
 
 Light is a form of energy, and travels from bodies emit- 
 ting it in rays composed of exceedingly minute undulations 
 or waves, and upon the length of these waves — that is the 
 distance from hollow to hollow (or crest to crest) — the 
 colour of such emitted light depends. 
 
 "White light, such as sunlight, consists of an assemblage 
 of waves of different lengths possessing individually the 
 colours seen in the rainbow which, propagated altogether, 
 produce an uncoloured mixture. When such light energy 
 falls upon a body part of it is absorbed and is converted 
 into heat ; the rest is reflected and renders the body visible. 
 
 If all the colours of which white light is composed are 
 equally reflected the body appears white, but if it happens 
 that the molecules of the body vibrate in harmony with the 
 waves of a particular length such waves are absorbed, and 
 hence the reflected light is deprived of that particular colour. 
 Thus, if the molecules of a body vibrate in harmony with 
 waves giving the sensation of blue light, these waves are 
 absorbed and the light reflected will be deprived of blue, 
 that is, the red rays (red being one of the primary rainbow 
 colours) will predominate, and the body will in consequence 
 appear red. Many artificial lights are deficient in rays of 
 certain colours ; oil and candle flames, for example, contain 
 few blue rays, hence the colour of a body will change with 
 the light in which it is viewed, since the colours available 
 for reflection will differ in different cases. In oil lamp or 
 candle light yellows appear white and blues green. Among 
 artificial lights acetylene most nearly approaches sunlight 
 in composition, hence colour schemes suitable for daylight 
 are less altered in this light than in others. 
 
PAINTS-INGEEDIENTS— BASES, PIGMENTS, DEIEES 323 
 
 If all the light which falls upon a body is absorbed the 
 body appears black. The above remarks apply not only to 
 the case of opaque bodies reflecting light but to transparent 
 bodies which transmit light. 
 
 When pigments are mixed, the colour of the mixture is 
 not the mean of the individual colours, but is determined by 
 the nature of the colours which are returned unabsorbed 
 by both pigments. Thus a blue pigment absorbs all but 
 the blue and green rays from white light and a yellow pig- 
 ment all but the yellow and green rays, hence when such 
 pigments are mixed green rays will alone be unabsorbed, 
 and green is therefore the resulting colour. 
 
 A certain amount of white light is usually reflected without 
 absorption from the surfaces of bodies on which it falls. 
 For this reason finely powdered pigments are paler in tint 
 than those composed of large transparent particles; for 
 since the directly reflected light is still white it will dilute 
 the coloured light reflected after absorption, and the greater 
 the area of exposed surface presented by the body the larger 
 will the proportion of this reflected light be. For alHed 
 reasons pigments are darker when wetted than when dry, 
 since the liquid aids the light in penetrating the body. 
 
 In the commercial comparison of pigments state of division 
 and dryness are therefore important factors. This com- 
 parison is generally made by noting the reduction in the 
 depth of tint produced by the addition of known quantities 
 of a white powder (zinc white), or in the case of light tints 
 a black powder, to different samples. 
 
 2. Use of Pigments. — In ordinary cases pigments are 
 usually ground in oil during the manufacture of the paints, 
 as only in this way can proper admixture be obtained. 
 The growing tendency of paint users to buy their materials 
 ready mixed, while it has advantages in securing uniformity, 
 makes it more difficult for those who have to approve paints 
 to judge the exact nature of the pigments which they 
 
 B.M. Y 
 
324 OHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 contain. Expert knowledge in this matter is nevertheless 
 necessary, as chemical reactions between certain pig- 
 ments or between pigments and bases are apt to occur 
 with destructive effects upon the colour of the material. 
 Generally speaking organic pigments — that is, those of 
 vegetable or animal origin or prepared from carbonaceous 
 substances {e.g. dyes)— are to be avoided as being much 
 less permanent than mineral colours. 
 
 Pigments mixed with evaporable liquids such as water 
 are known as stains, and if used in this condition require 
 subsequent varnishing to withstand wear. 
 
 Distempers consist of pigments mixed in water containing 
 size (glue), and, when required to be washable, casein or 
 other insoluble binding material is added. 
 
 3. Eed Pigments. — (a) Red Lead. — This oxide, PbaOi, is 
 prepared by the direct oxidation of metallic lead, which is 
 melted and submitted to a current of air. Litharge (PbO) 
 is first formed and, on further oxidation, red lead. The 
 production of this oxide of good colour requires some skill 
 in the regulation of the air current and furnace temperature. 
 
 On account of its drying and filling properties red lead is 
 very popular in priming coats and also for painting iron- 
 work. For these purposes it is mixed with white lead and 
 oil. In common with other lead compounds, it is blackened 
 by sulphuretted hydrogen. 
 
 Adulteration of this pigment owing to its high price is 
 not uncommon. The presence of organic dyes may be 
 detected by shaking the pigment with alcohol, which in 
 their absence will remain uncoloured. Any admixture of 
 iron oxide, silica or similar inert material, will be shown as 
 a powdery residue if the substance is reduced to metallic 
 lead on charcoal. 
 
 (b) Bed Oxide of Iron.— This oxide, Fe203, is used in 
 several pigments, and substantially composes "Indian 
 red," "Venetian red," and "Eed oxide." The finest 
 
PAINTS-INGEEDIENTS— BASES, PIGMENTS, DEIERS 325 
 
 pigment is produced by calcining ferrous sulphate, 
 FeS04.7H20, which leaves pure Fe203 on ignition. As 
 sulphuric acid is produced in this decomposition it is most 
 essential that the operation be very perfectly conducted. 
 Other varieties are made by calcining yellow ochre and are 
 necessarily much less pure (see " Yellow Ochre "), while the 
 commonest reds are produced by grinding the oxide in its 
 mineral form as haematite. 
 
 Very permanent and possessed of good body, iron oxide 
 forms a valuable pigment and is cheap enough to be used 
 as a base, for which purpose it is very satisfactory, provided 
 it is sufficiently finely ground, which is a point requiring 
 attention in its use. 
 
 Adulteration is particularly liable to occur in iron oxide, 
 either through the employment of impure hematite or 
 owing to intentional additions. Grades of this pigment 
 have been cited which contain no more than 10 per cent, of 
 FeaOa. The chief impurity is silica, much associated with 
 haematite, which, though unalterable, is present in particles 
 much too coarse to form a protective coating. Barytes, 
 brick dust and dyes may be also intentionally added. Iron 
 oxide is dissolved by hot strong hydrochloric acid, though 
 after strong ignition such solution proceeds slowly, barytes, 
 and silica (of which brick dust is also largely composed), 
 will remain as a white, sand-like residue, and any colourless 
 deposit after heating the pigment with the acid in a test tube 
 may be regarded as impurity. If dyes have been added to 
 improve the colour, necessarily weakened by other impuri- 
 ties, the colouration of the liquid due to their solution when 
 the pigment is shaken with alcohol will serve to detect their 
 presence. 
 
 4. Vermilion Pigments. — (a) Mercury Vermilion. — Mer- 
 curic sulphide (HgS) has the best claim to the title of 
 vermilion, but as it has been largely replaced by other 
 substances such designation is now no guarantee of 
 
 Y 2 
 
326 CHEMISTEY AND PHYSICS OF BUILDING MATEEIALS 
 
 composition. Originally made by grinding the natural 
 sulphide, cinna,bar, it is now prepared by the direct com- 
 bination of mercury and sulphur. Of fine colour and 
 considerable permanency, this compound forms a good 
 pigment, but its cost is great, and its high specific gravity 
 causes it to settle in paints somewhat too rapidly. 
 
 Adulterants are easily detected, since mercuric sulphide 
 entirely volatiHses when heated. If a small quantity be 
 placed in a dry test tube and gently heated it will volatiHse 
 and become deposited on the cool sides of the tube, while 
 impurities will remain behind. 
 
 (b) Basic Lead Chr ornate. —This compound, PbCr04.PbO, 
 may be made by heating white lead with a solution of 
 sodium bichromate until no further change of colour occurs, 
 after which a little sulphuric acid is added and the resulting 
 pigment is separated by filtration and well washed. Very 
 permanent, but too crystalline to possess much body, this 
 pigment has a fine colour and is not very likely to be found 
 in an adulterated condition, 
 
 (c) Red Lead Vermilion. — This pigment is made by 
 precipitating the dye eosin upon red lead. It has a very fine 
 colour, but, like other pigments containing organic bodies, 
 it is liable to fade. 
 
 (d) Permanent Red. — This is a vermilion similar in 
 character to the above and prepared by the precipitation 
 of dyes upon barium sulphate. It has been described 
 as very permanent and superior to all other vermilions, 
 and is very much cheaper than mercury vermilion. 
 Much, as regards permanence, probably depends upon 
 the completeness of the covering of the pigments by 
 varnishes. In the use of dyes in this manner it should 
 be remembered that they have remarkable penetrative 
 power. In a case which came under the writer's obser- 
 vation, such a vermilion, added accidentally to a 
 priming coat, appeared after a few weeks through five 
 
PAINTS— INaEEDIENTS— BASES, PIGMENTS, DEIERS 327 
 
 subsequent coatings, and eventually the whole paint had 
 to be removed. 
 
 5. Yellow Pigments. — (a) Yelloiv Ochre. — This is a natural 
 earth composed of hydrated ferric oxide associated with 
 a variable and often large proportion of siliceous and clayey 
 matter. The ochre is selected by hand and then washed 
 to free it from large particles and soluble compounds, and 
 finally dried at 100° C, which removes moisture but not 
 the water hydrating the iron. 
 
 Ochre is very permanent and possesses considerable body, 
 and as it is cheap it is a useful priming agent. Adultera- 
 tion is hardly likely to pay the cost of intermixture, but 
 would be difficult to detect in so variable a material. Good 
 samples of dried ochre may contain some 14 per cent, 
 of Fe203 (reckoned without water) and often 65 per cent, 
 of silica and alumina, water of hydration accounting for the 
 remaining percentage. The yellow vegetable colouring 
 matter turmeric is occasionally added to give a false value 
 to the colour of the pigment, but is easily detected by the 
 addition of a little ammonia and alcohol, to which the 
 yellow colour of turmeric will be imparted but not that due 
 to the iron oxide. 
 
 (b) Chrome Yellow. — This compound, lead ehromate 
 PbCrOi, is much the commonest yellow used in ordinary 
 paint work, and it also enters into the composition of most 
 greens. It is formed by precipitation on the addition of 
 a solution of sodium bichromate to a solution of a salt 
 of lead, usually the acetate or nitrate. Like other lead 
 compounds, it is affected by sulphuretted hydrogen. The 
 chromates are somewhat liable to part with oxygen in the 
 presence of any reducing agent, as for example organic 
 colouring matters, and such reduction results in the 
 formation of green chromium oxide. 
 
 Lighter shades of yellow, such as lemon chrome, are 
 made by mixing ehromate of lead with white lead or lead 
 
328 CHEMISTEY AND PHYSICS OF BUHiDING MATEEIALS 
 
 sulphate. Adulteration of chrome yellow is unlikely, but 
 the complete solubility of this compound in nitric acid 
 yielding a deep green solution may be utilised to detect any 
 insoluble ingredients. 
 
 6. Brown Pigments. — Browns used in ordinary painting 
 are nearly all derived from natural minerals allied to the 
 ochres and are prepared in a similar manner. They are 
 very permanent and owe their colour to the presence of 
 manganese. 
 
 {a) Sienna. — This is a rich ochre containing 1 or 2 per 
 cent, of manganese peroxide. It is employed as raw 
 sienna, which is the natural mineral ground, and washed, 
 and as burnt sienna, the calcined material, which loses its 
 water of hydration when heated and as a consequence 
 becomes considerably deeper in tint than the raw mineral. 
 
 (h) Umber. — This pigment is similar to sienna, but 
 contains a larger proportion of manganese. It is also used 
 in a raw and burnt state, in which latter condition it 
 possesses a reddish tint. Adulteration in siennas and 
 umbers is uncommon. 
 
 7. Blue Pigments. — {a) Prussian Blue. — This is the 
 commonest blue used in paints, and is prepared by pre- 
 cipitation from sodium ferrocyanide, by a salt of iron. Its 
 exact composition is doubtful and probably varies, but 
 it may be regarded as a ferrocyanide of iron. The finest 
 variety of Prussian blue is known as Chinese blue, which 
 is made by the action of copperas (impure ferrous sulphate) 
 on potassium ferrocyanide in solution. The precipitate 
 formed produces on oxidation a pigment possessing a deep 
 blue colour. These pigments may be distinguished in 
 powder by their bronze-like tint. 
 
 Adulteration is not common, but starch is said to be 
 occasionally added. This may be easily detected by boiling 
 the pigment with water and adding a drop of tincture 
 of iodine to the clear liquid obtained by filtration. If 
 
PAINTS— INGEEDIENTS— BASES, PIGMENTS, DEIERS 329 
 
 starch is present a deep blue colour will result provided the 
 filtrate be cold. 
 
 (b) Ultramarine. — This compound, which possesses a fine 
 light blue colour, is now made entirely by artificial means, 
 by heating in closed vessels kaolin, sodium sulphate, 
 and sulphur with carbon to effect reduction. The tint pro- 
 duced depends on the proportions of the ingredients, much 
 silicon producing a greenish, and much aluminium a 
 purple tint. Acids decompose ultramarine with liberation 
 of sulphuretted hydrogen, and on account of its contained 
 sulphur it is not a desirable constituent of lead paints. 
 Apart from this it is exceedingly permanent, but is too 
 costly for most uses. 
 
 Ultramarine is not very likely to be adulterated, but may 
 easily be distinguished from Prussian blue as it is not 
 affected by caustic soda, whereas this alkali when warmed 
 with the latter pigment suspended in water produces a 
 brown precipitate resulting from decomposition and 
 precipitation of iron. 
 
 8. Green Pigments. — (a) Brunswick Green. — This name, 
 originally applied to oxychloride of copper, is now always 
 understood in the trade to indicate a green prepared by 
 mixing chrome yellow with a small quantity of Prussian 
 blue. Even in green of deep tint less than 20 per cent, 
 of the pigment consists of these ingredients, the remainder 
 being substantially some inert base, usually barium 
 sulphate. These greens are affected by sulphuretted 
 hydrogen and are readily attacked by lime, hence they are 
 by no means permanent ; nevertheless they are by far the 
 commonest pigments of this colour used in paint work. 
 They are often described as "chrome greens," a designation 
 which should not be countenanced. 
 
 (&) Chrome Green. — This compound, often in self- 
 defence called "real chrome green," is chromium oxide 
 Cr203, and may be prepared by heating a bichromate with 
 
330 CHEMISTEY AND PHYSICS OP BUILDING MATEEIALS 
 
 sal ammoniac. Freed from soluble constituents by washing, 
 the oxide forms a dark green powder which possesses good 
 body and is quite permanent. The depth of tint obtained 
 may be to some extent modified by the temperature at 
 which the reaction involved in this preparation takes place. 
 This green is quite easily obtainable, but under existing 
 trade conditions it requires very definite designation, such 
 as " pure chromium oxide." 
 
 9. Black Pigments. — (a) Ivory and Bone Blacks. — When 
 ivory or bone is heated to redness, in the absence of a 
 free supply of air a charred mass, consisting chiefly of 
 phosphate of lime and a small quantity of carbon, remains 
 after the expulsion of volatile matters. In spite of the 
 large proportion of phosphate, itself white, the residue is 
 intensely black and is used as a pigment. 
 
 (6) Lamp or Gas Black. — When oil or natural gas is 
 burnt in a limited supply of air soot is formed in large 
 quantities. This deposit is prepared in suitable chambers 
 and forms the common pigment in black paints. Though 
 less intense than ivory or bone black, this material is a 
 more effective agent when mixed in oil, probably owing to 
 its fine state of division. Since black consists wholly of 
 carbon, which is unaffected by acids, alkalis or sulphur 
 compounds, such pigments are very permanent. 
 
 Adulteration presents no inducements in black pigments, 
 but volatilised mineral oils are often present, due to faulty 
 preparation, and prevent complete drying. These are par- 
 ticularly objectionable, as the quantity of drying oil neces- 
 sary for making up black paints is very large, and they are, 
 therefore, slow driers to begin with. Mineral oil may be 
 detected in the pigment as a powder by shaking up a small 
 quantity with ether * in a bottle. On allowing the powder 
 to settle and pouring the clear ether on to a sheet of glass, 
 
 ^ Ether is highly inflammable. 
 
PAINTS— INGEEDIENTS- BASES, PIGMENTS, DEIEES 331 
 
 no residue should remain after evaporation of this solvent, 
 which occurs almost instantaneously. 
 
 10. Special Pigments or Coatings. — Of the large number 
 of special paints, chiefly applicable to metallic structures, it 
 is impossible here to give any adequate account, but a few 
 of these may be referred to. 
 
 (a) Graphite. — This form of carbon, familiar in an 
 impure form as ordinary " black lead," forms, when mixed 
 with finely divided silica and linseed oil, a valuable paint 
 in cases in which a dull grey colour is not objectionable. 
 
 Graphite possesses a slippery surface and thus " turns " 
 wet very effectively, hence its use upon exposed surfaces 
 such as iron roofs is to be commended. 
 
 (b) Aluminium Paint. — Metallic aluminium in the state 
 of extremely fine powder, mixed with oil varnish as a vehicle, 
 forms a useful and effective coating for metal work in 
 circumstances in which its objectionable appearance can be 
 tolerated. Jennings ^ states that two classes of this paint 
 are made, one as above described for outside work, another 
 prepared with collodion ^ varnish (which is lighter in colour 
 than ordinary oil varnish), for internal work. Care is 
 necessary in the selection of aluminium paints, as some 
 makes contain free organic acids, which themselves possess 
 a corrosive action upon metals. 
 
 (c) Angus Smith's Solution. — This material, though it 
 can hardly be described as a paint, is constantly specified 
 as a protective coating for pipes and flues conveying acid 
 gases. 
 
 Wood, in whose recent book^ much valuable information 
 on paints will be found, states that the composition of 
 Dr. Smith's original solution is unknown, but that his 
 
 ' Jennings. Soc. of Arts J. March 27th, 1908. 
 ^ Collodion is nitrated cellulose prepared in the manufacture of 
 explosives. 
 
 8 Wood. " Eustless Coatings," John Wiley, 1905. 
 
332 CHEMISTEY AND PHYSICS OF BUILDINQ MATERIALS 
 
 process as satisfactorily followed consists in immersing the 
 material to be treated in coal tar from which the naphtha 
 has been removed by distillation, after the addition of some 
 6 per cent, of linseed oil. The liquid is kept by the aid of 
 external heat at a temperature of about 150° C. (300° F.), and 
 the material to be coated is immersed for fifteen to thirty 
 minutes. He intimates, however, that much of the coating 
 carried out under this designation consists of nothing more 
 than dipping the material in ordinary coal tar, which afifords 
 a much smaller measure of protection. 
 
 III. Drieks. 
 
 1. Use of Driers. — The necessity for increasing the rate 
 of drying of oils has led to the use of bodies, mostly metallic 
 salts or oxides, the presence of which promotes oxidation of 
 the oil.'^ The explanation of this fact, which, as far as is 
 known, does not result in any change of composition in the 
 drier, is yet to be discovered, and all that can be suggested 
 is that these added bodies act as carriers of oxygen from 
 the air to the oil. Many chemical actions (catalytic actions) 
 are known which are brought about or accelerated by the 
 presence of bodies themselves apparently unaltered. 
 
 Driers are not desirable in paints and should not be 
 used unless necessity demands them, and even then but 
 sparingly, since if the drying of an oil be greatly acce- 
 lerated, the film produced on oxidation will not have an 
 opportunity of acquiring that toughness and elasticity 
 which are essential for efficient wear. 
 
 Driers must always be mixed in oil before being added 
 to paint, and are usually ground in oil and often added to 
 the oil during its preparation for the market. While this 
 has the advantage of securing perfect intermixture it 
 makes it very difficult to ascertain the exact composition of 
 
 1 See a paper entitled " The Action of Driers on Linseed Oil," read 
 before the Paint and Varnish Society, printed in The Oil and Colour 
 Trades Journal, November 21, 1908. 
 
PAINTS— INGEEDIENTS— BASES, PIGMENTS, DRIEES 333 
 
 painters' materials, as the paint manufacturer often alone 
 knows the amount and nature of the driers added. The 
 quantity of a drier admissible in an oil varies with the 
 nature of this addition, but one part to every twenty parts 
 of oil is probably to be regarded as the maximum allowable, 
 and the amount should generally be much less. When added 
 to oil, in the process of " boiling," a large proportion of the 
 drier remains in the deposit left from the clarified liquid. 
 
 2. Varieties of Driers. — (a) Lead Compounds. — Lead oxide 
 (PbO) is the commonest and one of the most powerful 
 driers, and red lead is also a drier of some power, but its 
 colour precludes its use for most purposes. 
 
 Lead acetate (sugar of lead) is another lead compound 
 much employed, but it is not very stable. 
 
 Terebene is composed of copal resin dissolved in hot 
 linseed oil, to which litharge has been added, and may, 
 therefore, be looked upon as a lead drier. 
 
 (6) Zinc Compounds, such as the oxide, carbonate and 
 sulphate, also find a use as driers, and are useful when 
 lead is undesirable in paints. Of these zinc sulphate is the 
 least powerful and probably least desirable, although the 
 one most commonly used. 
 
 (c) Manganese Compounds form valuable driers. The 
 oxide Mn02, is an exceedingly powerful agent, but its 
 black colour makes it unsuitable for most paints. The salts 
 of manganese are usually of a pale pink colour, and the 
 acetate is a favourite compound for good paint work. The 
 sulphate is also used, while manganese borate, made by 
 precipitation from solutions of the sulphate and borax, is 
 said to be very permanent and reliable, and to be, in fact, 
 the most desirable metallic drier known. 
 
 Eosin and linseed oil, when heated with caustic soda, 
 form sodium salts of organic acids, which when treated 
 with solutions of other metallic salts, such as those of lead 
 and manganese, form rosinates and lineolates of these 
 
334 CHEMISTEY AND PHYSICS OF BUILDING MATERIALS 
 
 metals. These compounds are used as driers and have the 
 advantage of dissolving completely in oil, and do not there- 
 fore interfere with its brightness. Many patent driers 
 contain such compounds ; their use, however, is generally 
 considered deleterious. Much more observation upon the 
 actual effects of various driers is desirable before any defi- 
 nite judgment can be passed upon the comparative merits 
 of many of them. 
 
INDEX 
 — « — 
 
 AccBLBRATORS in Cement, 208 
 Acid-forming oxides, 85 
 Acids, bases and salts, 83 
 Adherence, 
 
 in cements, 198 
 
 in stones, 139 
 Adulteration of paints, 303 
 See also Pigments. 
 
 Air, 
 
 carbon dioxide in, 28 
 
 chemical properties, 26 
 
 composition, 26 
 
 moisture in, 28 
 
 weight of, 22 
 Alabaster, 130 
 Alloys, 
 
 brass, 265 
 
 bronze, 266 
 
 fusible, 269 
 
 nature of, 264 
 
 pewter, 268 
 
 solder, 268 
 Alumina, 
 
 both acid and base, 85, 211 
 
 forms of, 114 
 
 in cements, 186, 194, 202, 206 
 Aluminium, 
 bronze, 267 
 paint, 331 
 metallic, 262, 263 
 test for in compounds, 321 
 
 Analysis of water, 74 — 6 
 Ancaster stone, 126 
 Angus Smith's solution, 321 
 Aquafortis, 82 
 Artificial stone, 212 
 Asphalte, 217 
 Asphaltum, 314 
 Atomic theory, 53 
 Atomic weights, 
 
 explained, 54 
 
 table of, 56 
 Atoms, 18 
 
 Augite, 117, 120, 122 
 
 Barium carbonate, 
 
 properties of, 120 
 
 use in clays as corrective, 16 
 Barium sulphate, 
 
 in paints, 320 
 
 properties of, 120 
 Basalt, 124 
 Bases, 
 
 defined, 83 
 
 in natural materials, 107 
 
 in paints, 315 
 See Paints. 
 Bath stone, 126 
 Bauerchinger on stones, 138 
 Bedding planes, 96 
 
336 
 
 INDEX 
 
 Bessemer steel, 244 
 Binding materials, 
 
 table of, 169 
 Biotite mica. See Micas. 
 Bitumen, 217 
 Black pigments, 
 
 bone, 380 
 
 ivory, 830 
 
 lamp, 380 
 Blue pigments, 
 
 Chinese, 328 
 
 Prussian, 328 
 
 ultramarine, 329 
 Brass, 265 
 Bricks. See Clays. 
 
 lime in, 161 
 Bronze, 266 
 Brown pigments, 
 
 sienna, 328 
 
 umber, 328 
 
 Calcite, 120 
 
 See Calcium carbonate. 
 
 Calcium carbonate, 
 
 as a mineral, 113, 120 
 
 in clays, 152, 160, 165 
 
 in limes, 171 
 
 in paints, 321 
 
 in stones, 124, 130, 131 
 
 Calcium chloride, 68 
 
 Calcium sulphate, 
 
 as a mineral, 114, 120 
 in cements, 185, 192 
 in clays, 152, 161, 166 
 in paints, 321 
 in plasters, 169, 170 
 in selenitic limes, 175 
 
 Calculations, chemical, 60 
 
 Cambium layer in wood, 284 
 
 Carbolic acid, 89 
 
 Carbonates, tests for, 92 
 
 Carbon dioxide, 91 
 
 Carbon monoxide, 92 
 Cast iron, 
 
 carbon in, 237 
 
 columns, strength of, 280 
 
 grades of, 289 
 
 malleable, 240 
 
 manganese and phosphorus 
 in, 239 
 
 preparation of, 287 
 
 silicon and sulphur in, 238 
 
 strength of, 279 
 Cements, 
 
 accelerators, use of, 208 
 
 adhesion in, 198 
 
 cohesion in, 197 
 
 colloid theory of setting, 201 
 
 crystalloid theory of setting, 
 201 
 
 efflorescence of, 211 
 expansion of, 209 , 
 failure of, 209 
 iron in, 205 
 Keene's, 170 
 magnesia in, 205 
 natural, 183 
 
 " Portland," 184 
 oxy chloride, 216 
 Parian, 170 
 Portland, 185 
 
 See also under 194 
 Pozzuolana, 194 
 relation to hmes, 182 
 retarders, use of, 208 
 Roman, 184 
 strength of, 185 
 sea water, effect on, 211 
 setting, general causes, 199 
 slag, 195, 196 
 
 summary, views on setting, 
 206 
 
 supersaturation theory, 208 
 Centigrade scale, 36 
 
INDEX 
 
 337 
 
 Chalk, 
 
 characters of, 127 
 
 for cement, 186 
 
 for fat Hmes, 171 
 Change of state, 89 
 Changes, physical and chemical, 4 
 Charcoal, 90 
 Charles' Law, 48 
 Chemical 
 
 calculations, 60 
 
 equations, 59 
 
 names, formation of, 62 
 
 nomenclature, 61 
 Chemical analysis of stones, 143 
 Chemistry defined, 3 
 Chlorite, 118, 120, 124 
 Classification of stones, 121 
 Clays, 
 
 calcium svilphate in, 152, 161, 
 166 
 
 carbonaceous matter in, 152, 
 149 
 
 colour of, 152 
 
 defects, removal of, 166 
 
 drying of, 153 
 
 examination of, 167 
 
 formation of, 147 
 
 fusibility of, 154—6 
 
 fusion stages of, 157 
 
 kiln reactions of, 158 — 64 
 
 minerals composing, 150 — 3 
 
 physical properties of, 149 
 
 EiES, authority on, 149 
 
 summary of kiln changes, 165 
 
 tests upon, 167 
 
 varieties of, 148 
 Cleavage, 108 
 Coal, 
 
 formation of, 86 
 
 sulphur in,re clay burning,161 
 Coal gas, 89 
 Coal tar, 89 
 
 Cohesion in cements, 197 
 
 Coke, 90, 212 
 
 Cold bending tests, 276 
 
 Colloid theory of setting, 203 
 
 Colour, causes of, 321 
 
 Columns, tests on, 275, 280 
 
 Combustion, 
 
 conditions for, 30 
 defined, 22 
 instantaneous, 31 
 practical bearing of, 31 
 Compounds defined, 8 
 Compressive tests, 
 
 on cements, 194, 196 
 on metals, 274 
 on stones, 141 
 Concrete, elasticity of, 193 
 Conduction of heat, 49 
 Conductivity of stones, 140 
 Convection of heat, 51 
 Conversion of temperature scales, 
 
 36 
 Copper, 
 
 alloys of, 265—7 
 corrosion of, 255 
 extraction from ores, 252 
 impurities in, 254 
 ores of, 251 
 properties of, 253 
 strength of, 282 
 Craigleith stone, 128 
 Creosote, 
 
 for timber, 297 
 preparation of, 89 
 Cross bending tests, 275 
 Crushing tests on stones, 141 
 Crystalhsation, water of, 66 
 Crystalloid, theory of setting, 201 
 Crystals, natural, 108 
 
 Dalton's atomic theory, 93 
 Decay of wood, 293 
 
338 
 
 INDEX 
 
 Day and Shepherd on lime sili- 
 cates, 202 
 Deliquescence, 67 
 Deposition of strata, 94 
 Dichroism, 111 
 Dip of strata, 96 
 Distempers, 824 
 Dolomite, 120 
 Dolomitic stones, 126 
 Driers, 
 
 lead compounds, 338 
 
 manganese, 833 
 
 rosinates, 883 
 
 use of, 332 
 
 zinc compounds, 833 
 Dry rot, 298 
 Drying of wood, 289 
 
 Earth history, 98 
 Efflorescence, 
 defined, 67 
 
 in artificial stone, 214 
 
 in bricks, 162, 166 
 
 in cements, 210 
 Elastic limit in metals, 273 
 Elasticity, 
 
 defined, 19 
 
 of metals, 226, 272 
 
 of stones, 187 
 
 of timber, 292 
 Electricity, water decomposed by, 
 65 
 
 Electrolysis, 65 
 Elements defined, 7 
 Elongation of iron and steel, 281 
 Elvans, 128 
 
 Equations, chemical, 59 
 
 Erosion of rocks, 94 
 
 Expansion, 
 
 coefficient of, 44 
 in cements, 189, 209 
 of building stones, 189 
 
 Expansion, 
 
 of gases, 48 
 of liquids, 47 
 of solids, 43 
 
 practical importance of, 45 
 
 Fahrenheit scale, 36 
 Faults, geological, 98 
 Felspars, 
 
 in clays, 151, 164 
 in granites, 122 
 properties of, 116, 120 
 Ferra (ferric oxide), occurrence 
 of, 115 
 See also Iron, ores of. 
 in cements, 205, 206, 211 
 in clays, 152, 156, 163, 165, 
 179 
 
 in marbles, 180 
 
 in slates, 131 
 Ferrous oxide, 
 
 in clay, 157, 162 
 
 occurrence of, 115 
 Fillers in paints, 303 
 Fireproofing wood, 299 
 Floors, tests on, 275 
 Formations, geological, 100 — 1 
 Formulae, chemical, 
 
 assigning of, 57 
 
 use of, 56 
 Fossils, value of, 102 
 Fracture of metals, 271 
 Freestones, 125 — 8 
 Freezing, expansion of water on, 
 41 
 
 Fundamental units, 12 
 Fusible alloys, 269 
 
 Galena, 120, 256 
 Gases, properties of, 21 
 Geological strata, table of, 100 — 1 
 
im)Ex 
 
 339 
 
 Geology, 
 
 chapter on, 98 
 
 defined, 8 
 Granites, 122 
 Granitic stones, 101 
 Graphite, 
 
 as a mineral, 91, 120 
 
 in iron, 236, 237 
 
 in paints, 331 
 Grappier cement, 178 
 Green pigments, 
 
 Brunswick, 329 
 
 chrome, 329 
 Gypsum, 114, 120, 169, 170 
 
 See also Calcium sulphate. 
 
 HiEMATITB, 120, 232 
 Ham Hill stone, 127 
 Hardness, 
 
 estimation of in water, 75 
 
 of building stones, 140 
 
 of metals, 226, 276 
 
 of water, 70 
 
 scale of for minerals, 109 
 Heartwood, 285 
 Heat, 
 
 nature of, 33 
 
 producing change, 5 
 
 transmission of, 49 
 
 unit of, 37 
 Hornblende, 117, 120, 122 
 Hot water systems, 73 
 Hydraulic cements. See Limes, 
 
 Cements, and Portland 
 
 cement. 
 Hydrochloric acid, 81 
 Hydrogen, 65 
 
 Ignbous stones, 102 
 Impact tests, 277 
 B.M. 
 
 Indestructibility of matter, 9 
 Iron, 
 
 and steel defined, 235, 236 
 carbon in, varieties of, 236 
 cast, 237—40. See also 
 
 under Cast Iron, 
 corrosion of, 248 
 metallurgy of, 233, 234 
 ores of, 232 
 rusting of, 249 
 strength of, 278—282 
 sulphides of, 78. See also 
 
 under Pyrites, 
 tests upon, 271 — 77 
 wrought, 241 — 44. See also 
 
 under Wrought Iron. 
 Ivory black, 90 
 
 Japan, 314 
 
 Johnson fracture of metals, 270 
 
 Kaolin, 
 
 in clays, 149, 151, 165 
 
 in granites, 124 
 
 in paints, 321 
 
 properties, 120 
 Keene's cement, 170 
 Kentish ragstone, 127 
 Ketton stone, 126 
 
 Lamp-black, 90 
 Latent heat, 39 
 Lead, 
 
 action of water on, 73 
 alloys of, 268, 269 
 corrosion of, 257 
 expansion of, 45, 46 
 extraction of, 256 
 impurities in, 257 
 ores of, 255 
 
 Z 
 
340 
 
 INDEX 
 
 Lead — continued, 
 
 properties of, 257 
 
 sulphate in paint, 319, 320 
 Le Chatblier on plasters and 
 
 cements, 170, 190, 202, 
 
 205, 206, 207, 211 
 Light, 
 
 and colour of pigments, 322 
 
 nature of, 322 
 Limes, 
 
 analysis of, 178 
 
 classified, 169 
 
 constitution of, 177 
 
 dolomitic limes, 173 
 
 Eckel on, 173 
 
 eminently hydraulic, 176 
 
 fat lime, 171 
 
 hydraulic, 174 
 
 lean lime, 172 
 
 mortars, strength of, 174 
 
 non-hydraulic, 171 
 
 selenitic, 175 
 
 tests upon, 180 
 Lime-sand bricks, 213 
 Limestones, varieties, 125, 126 
 Liquids, properties of, 20 
 Litharge, 324 
 Lithophone, 320 
 Litre defined, 14 
 
 Magnesia in cements, 205 
 Magnesium, 
 
 carbonate, 114 
 
 chloride, 68 
 Magnetite, 120, 232 
 Marbles, 130 
 Marcasite, 
 
 in slates, 132 
 
 occurrence of, 78 
 Mastic, 220 
 Matter defined, 18 
 
 Medullary rays in wood, 286 
 
 Melting point, 40 
 
 Metallurgy. See individual 
 
 metals. 
 Metals, 
 
 annealing of, 224 
 
 conductivity, 227 
 
 ductility, 225 
 
 elasticity, 226 
 
 expansion, 227 
 
 fusibility, 227 
 
 general properties, 221 
 
 hardness, 226 
 
 malleability, 225 
 
 metallurgy, principles of, 228 
 
 microstructure, 222 
 
 occurrence of ores, 228 
 
 specific heat, 227 
 
 table of physical data, 231 
 
 tests upon, 270, 278 
 
 See also individual metals. 
 Metamorphic stones, 129 
 Metric system, 12 
 Micas, 
 
 in clays, 151, 164 
 
 in granites, 122 
 
 in slates, 132 
 
 properties of, 117, 120 ' "•" ' 
 MiCHAELis on cements, 201 , 203, 
 
 204 
 Microscope, 
 
 for building stones, 142 
 
 use of, 110 
 Microstructure of metals, 222 
 Mineral oils in black paint, 330 
 Minerals, 
 
 characters of, 108, 109 
 
 defined, 107 
 
 table of common, 119 — 120 
 Moisture produces change, 5 
 Molecules, 18 
 
 Muscovite mica. See Micas. 
 
INDEX 
 
 341 
 
 Naphthaline, 89 
 Natural laws, 3 
 Nicols' prisms, 111 
 Nitric acid, 82 
 Nitrogen, 27 
 
 Oils, 
 
 boiled, 806 
 
 china wood, 307 
 
 cottonseed, 307 
 
 drying, 305 
 
 in paints, 304 — 8 
 
 linseed, 305 
 
 rosin, 307 
 
 tests for, 307, 308 
 
 varieties of, 304 
 Open hearth steel, 245 
 Ores, 
 
 of aluminium, 262 
 
 of copper, 251 
 
 of iron, 232 
 
 of lead, 255 
 
 of tin, 260 
 
 of zinc, 258 
 Oxidation, 28 
 Oxide, 28 
 
 Oxychloride cement, 216 
 Oxygen, 27 
 
 Paints, 
 
 adulteration of, 303 
 aluminium, 331 
 barium sulphate in, 320 
 bases in, 315 
 
 calcium carbonate in, 821 
 calcium sulphate in, 331 
 colour of, 321—3 
 composition of, 301 
 driers in, 332 — 4 
 See Driers. 
 
 Paints — continued. 
 fillers, use of, 303 
 general characters, 300 
 graphite for, 331 
 kaolin in, 328 
 lead sulphate in, 312, 320 
 lithophone, 320 
 oils used in, 304 — 8 
 
 See Oils, 
 pigments in, 323 — 30 
 
 See Pigments, 
 resins in, 312 — 14 
 
 See Eesins. 
 thinners, use of, 303, 309—11 
 
 See Thinners, 
 turpentine in, 309 — 10 
 varnishes, 311 — 12 
 
 See Varnishes, 
 white lead in, 315 — 18 
 
 See White lead, 
 zinc white in, 318—19 
 Parian cement, 170 
 Pewter, 268 
 
 Physical constants of metals, 231 
 
 Physics, defined, 3 
 
 Pigments, 
 
 blacks, 330 
 
 blues, 328 
 
 browns, 328 
 
 greens, 329 
 
 reds, 324 
 
 use of, 323 
 
 vermilions, 325 
 
 yellows, 327 
 Plaster of Paris, 170 
 Plasters, 169 
 Polarised light. 111 
 Popular and scientific names, 
 
 table of, 63 
 Porosity of stones, 136 
 Portland cement, 
 
 chemical composition, 191 
 
342 
 
 INDEX 
 
 Portland cement — continued. 
 
 expansion, 189 
 
 fineness, 187 
 
 manufacture, 185 — 7 
 
 microscopic tests, 193 
 
 rate of setting, 193 
 
 specific gravity, 189 
 
 strength of, 194 
 
 tensile tests on, 190 
 Portland stone, 126 
 Potash and soda, 114 
 Pozzuolana cement, 
 
 artificial, 195 
 
 natural, 194 
 
 strength of, 195 
 Preservation 
 
 of stone, 215 
 
 of wood, 296 
 Pyrites, 
 
 in clays, 151, 164, 165 
 
 in coal, for clay burning, 161 
 
 in freestones, 128 
 
 in igneous stones, 124 
 
 in marbles, 130 
 
 in slates, 132 
 
 properties, 120 
 
 source of acids, 78 
 
 Quarry, examination of stones 
 in, 145 
 
 Quarrying, effects of faults, 99 
 Quartz, 
 
 in clays, 150, 151 
 
 in stones, 127 
 
 properties of, 120 
 
 Radiation 
 
 of heat, 51 
 
 practical value of, 52 
 Ransome's stone, 212 
 Red pigments, 
 
 red lead, 324 
 
 Red pigments — continued. 
 
 red oxide of iron, 324 
 Red rot in wood, 294 
 Red lead, 324 
 Resins, 
 
 amber, 313 
 
 characters, 312 
 
 copals, 313 
 
 dammar, 314 
 
 lac, 314 
 
 nature of, 312 
 
 rosin, 314 
 Retarders in cements, 208 
 Rot in timber, 293 
 
 Salts defined, 83 
 
 Sandstones, 127 
 
 Sapwood, 285, 287 
 
 Scale in boilers, 73 
 
 Seasoning of wood, 296 
 
 Sea water's action on cements, 211 
 
 Serpentine, 118 
 
 Setting of cements, 199—209. See 
 
 Cements. 
 Shearing tests, 277 
 Siemens steel, 245 
 Silica, 
 
 forms of, 112 
 
 in clays, 155 
 Silicates, 
 
 constitution of, 115 
 
 in cements, 186, 194, 201, 202, 
 206 
 
 in limes, 177 
 
 list of common, 120 
 Slag cements, 195 
 Slates, 131—3 
 Sodium silicate, 214, 299 
 Softening water, 71 
 Solder, 268 
 Soldering fluid, 81 
 Solids defined, 19 
 
INDEX 
 
 34$ 
 
 Solubility of stones, 145 
 Soluble glass, 214, 219 
 Solvent power of water, 65 
 Specific heat, 38 
 Specific gravity, 
 
 explained, 14 
 
 numerical examples, 17 
 
 of building stones, 135 
 
 of liquids, 16 
 
 of solids, 16 
 
 of wood, 290 
 Spirits of salt, 81 
 Stains, 824 
 
 Stanchions, strength of, 281 
 
 Standards, 11 
 
 Steel, 
 
 Bessemer process, 244 
 composition of, 246, 247 
 corrosion of, 248 — 250 
 grades of, 247 
 open hearth, 245 
 preparation of, 244 
 Siemens process, 245 
 strength of, 281 
 tests upon, 270 — 8 
 Stones, 
 
 arranged geologically, 100 — 1 
 artificial, 213 
 basalt, 124 
 classification of, 121 
 el vans, 123 
 granites, 123 
 limestones, 125 — 7 
 metamorphic, 129 
 objectionable minerals in, 
 
 124, 128 
 preservation of, 215 
 sandstones, 127, 128 
 syenites, 123 
 tests upon, 234 — 246 
 weathering of, 128 
 Strain defined, 19 
 
 Strata, 
 
 arrangement of, 95 
 
 formation of, 94 
 
 table of geological, 100 — 1 
 Streak of minerals, 109 
 Stress defined, 19 
 Structure of wood, 284 
 Sulphides of iron, 78 
 Sulphur, 77 
 
 Sulphuretted hydrogen, 80, 317 
 Sulphuric acid, 79 
 Supersaturation theory of setting, 
 
 208 
 Syenites, 123 
 
 Symbols of the elements, 54 
 
 Table of geological strata, 
 
 100—1 
 Table of minerals, 120 
 Tables, metric, 13 
 Temperature, 
 
 meaning of, 34 
 
 scales of, 36 
 TensUe strength, 
 
 of cast iron, 279 
 
 of cement, 194 
 
 of steel, 281 
 
 of wrought iron, 280 
 Tensile tests, 
 
 on cements, 191 
 
 on metals, 271 
 Thermometer, 35 
 Thinners, 
 
 benzene, 311 
 
 naphtha, 311 
 
 petroleum, 311 
 
 rosin spirit, 310 
 
 turpentine, 309 — 10 
 
 use of, 303 
 Timber, 
 
 cambium layer, 284 
 
 classification of, 284 
 
344 
 
 INDEX 
 
 Timber — continued. 
 composition of, 290 
 decay of, 292 
 drying of, 289 
 fireproofing of, 299 
 heartwood, 285 
 impregnation of, 297 
 insects in, 295 
 mechanical properties, 291 
 medullary rays in, 286 
 nature of, 283 
 preservation of, 296 
 rot in, 293 
 sapwood, 285, 287 
 seasoning of, 296 
 specific gravity of, 290 
 structure of, 284 
 warping of, 289 
 water in, 287 
 
 Tin, 
 
 alloys of, 268, 269 
 
 extraction of, 261 
 
 impurities in, 262 
 
 ore of, 260 
 
 properties of, 261 
 Torsion tests, 277 
 Transmission oE heat, 49 
 Trass as a cement, 194 
 Turpentine, 
 
 optical activity of, 809 
 
 substitutes for, 310 
 
 Unit of heat, 37 
 Units, 
 
 derived, 13 
 
 fundamental, 12 
 Unwin tests on metals, 279 
 
 Vaenishbs, 
 
 characters of, 311, 312 
 resins for, 312 — 14. See 
 Besrns. 
 
 VentUation, 49 
 
 Vermilion pigments, 
 
 basic lead chromate, 326 
 mercury vermilion, 325 
 permanent red, 326 
 red lead vermilion, 326 
 
 Volume, change with state, 41 
 
 Warping of wood, 289 
 
 Water, 
 
 action on lead, 73 
 air dissolved in, 68 
 analysis of, 74 
 circulation of, 48 
 composition of, 64 
 expansion of, 47 
 impurities in, 68 
 in wood, 287 
 of crystallisation, 66 
 softening of, 71 
 solvent power of, 65 
 
 Weathering of stones, 129 
 
 Wet rot, 293 
 
 White lead, 
 
 adulteration of, 317 
 composition of, 316 
 legal definition, 320 
 manufacture of, 315 
 properties of, 317 
 sulphur, effect on, 317 
 tests for, 317, 318 
 
 Wood. See Timber. 
 
 Wrought iron, 
 
 composition of, 242, 243 
 corrosion of, 248 — 50 
 grades of, 243, 244 
 strength of, 280 
 
 Yellow pigments, 
 
 chrome yellow, 327 
 
INDEX 
 
 345 
 
 Yellow pigments — continued. 
 
 lemon chrome, 327 
 
 yellow ochre, 327 
 York stone, 128 
 
 Zinc, 
 
 alloys of, 265, 266 
 
 Zinc — continued. 
 corrosion of, 260 
 expansion of, 45 
 extraction of, 258 
 impurities in, 259 
 properties of, 259 
 white, 318, 319 
 
 BRADBURY, AGNKW & CO. LD,, PRINTERS, LONDON AND TONBRIDQE. 
 
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 an elementary knowledge of electricity is presupposed, the bearings 
 of the subject can be grasped by every reader. No subject is fraught 
 with so many possibilities of development for the future relationships 
 of the peoples of the world. 
 
 India-Rubber and its Manufacture, with Chapters 
 on Gutta-Percha and Balata. By H. L. Terry, 
 F.I.C., Assoc. Inst. M.M. . With Illustrations. 
 
 List of Contents : Preface. Introduction : Historical and 
 General. Raw Rubber. Botanical Origin. Tapping the Trees. 
 Coagulation. Principal Raw Rubbers of Commerce. Pseudo- 
 Rubbers. Congo Rubber. General Considerations. Chemical 
 and Physical Properties. Vulcanization. India-rubber Planta- 
 tions. India-rubber Substitutes. Reclaimed Rubber. Washing 
 and Drying of Raw Rubber. Compounding of Rubber. Rubber 
 Solvents and their Recovery. Rubber Solution. Fine Cut Sheet 
 and Articles made therefrom. Elastic Thread. Mechanical 
 Rubber Goods. Sundry Rubber Articles. India-rubber Proofed 
 Textures. Tyres. India-rubber Boots and Shoes. Rubber for 
 Insulated Wires. Vulcanite Contracts for India-rubber Goods. 
 
 ( 5 ) 
 
THE "WESTMINSTER" SERIES 
 
 The Testing of Rubber Goods. Gutta-Percha. Balata. Biblio- 
 graphy. Index. 
 
 Tells all about a material which has grown immensely in com- 
 mercial importance in recent years. It has been expressly written 
 for the general reader and for the technologist in other branches of 
 industry. 
 
 Glass Manufacture. By Walter Rosenhain, Superin- 
 tendent of the Department of Metallurgy in the National 
 Physical Laboratory, late Scientific Adviser in the Glass 
 Works of Messrs. Chance Bros, and Co. With Illustra- 
 tions. 
 
 Contents : Preface. Defmitions. Physical and Chemical Qualities. 
 Mechanical, Thermal, and Electrical Properties. Transparency 
 and Colour. Raw materials of manufacture. Crucibles and 
 Furnaces for Fusion. Process of Fusion. Processes used in 
 Workmg of Glass. Bottle. Blown and Pressed. Rolled or 
 Plate. Sheet and Crown. Coloured. Optical Glass : Nature 
 and Properties, Manufacture. Miscellaneous Products. Ap- 
 pendix. Bibliography of Glass Manufacture. Index. 
 
 This volume is for users of glass, and makes no claim to be an ade- 
 quate guide or help to those engaged in glass manufacture itself. For 
 this reason the account of manufacturing processes has been kept 
 as non-technical as possible. In describing each process the object 
 in view has been to give an insight into the rationale of each step, so 
 far as it is known or understood, from the point of view of principles 
 and methods rather than as mere rule of thumb description of manu- 
 facturing manipulations. The processes described are, with the 
 exception of those described as obsolete, to the author's definite know- 
 ledge, in commercial use at the present time. 
 
 Precious Stones. By W. Goodchild, M.B., B.Ch. With 
 42 Illustrations. With a Chapter on Artificial 
 otones. By Robert Dykes. 
 
 List of Contents : Introductory and Historical. Genesis of 
 Precious Stones. Physical Properties. The Cutting and Polish- 
 ing of Gems. Imitation Gems and the Artificial Production of 
 Precious Stones. The Diamond. Fluor Spar and the Forms of 
 Sihca. Corundum, including Ruby and Sapphire. Spinel and 
 Chrysoberyl. The Carbonates and the Felspars. The Pyroxene 
 and Amphibole Groups. Beryl, Cordierite, Lapis Lazuli and the ' 
 Garnets. Olivine, Topaz, Tourmaline and other Silicates. Phos- 
 phates, Sulphates, and Carbon Compounds. 
 
 An admirable guide to a fascinating subject. 
 
 ( 6 ) 
 
THE ''WESTMINSTER" SERIES 
 
 Patents, Designs and Trade Marks : The Law 
 and Commercial Usage. By Kenneth R. Swan, 
 B.A. (Oxon.), of the Inner Temple, Barrister-at-Law. 
 
 Contents • Table of Cases Cited— Pari I.— Letters Patent. Intro- 
 duction. General. Historical. I., II., HI. Invention, Novelty, 
 Subject Matter, and Utility the Essentials of Patentable Invention. 
 IV. Specification. V. Construction of Specification. VI. Who 
 May Apply for a Patent. VII. Application and Grant. VIII. 
 Opposition. IX. Patent Rights. Legal Value. Commercial 
 Value. X. Amendment. XI. Infringement of Patent. XII. 
 Action for Infringement. XIII. Action to Restrain Threats. 
 XIV Negotiation of Patents by Sale and Licence. XV. Limita- 
 tions on Patent Right. XVI. Revocation. XVII. Prolonga- 
 tion. XVIII. Miscellaneous. XIX. Foreign Patents. XX. 
 Foreign Patent Laws : United States of America. Germany. 
 France. Table of Cost, etc., of Foreign Patents. Appendix A.— 
 
 I Table of Forms and Fees. 2. Cost of Obtaining a British 
 Patent. 3. Convention Countries. Part II.— Copyright m 
 Design. Introduction. I. Registrable Designs. II. Registra- 
 tion. III. Marking. IV. Infringement. Appendix B.— i. 
 Table of Forms and Fees. 2. Classification of Goods. Part 
 in —Trade Marks. Introduction. I. Meaning of Trade Mark. 
 
 II Qualification for Registration. III. Restrictions on Regis- 
 tration. IV. Registration. V. Effect of Registration. VI. 
 Miscellaneous. Appendix C. — Table of Forms and Fees. Indices. 
 I. Patents. 2. Designs. 3. Trade Marks. 
 
 This is the first book on the subject since the New Patents Act. 
 Its aim is not only to present the existing law accurately and as fully 
 as possible, but also to cast it in a form readily comprehensible to the 
 layman unfamiliar with legal phraseology. It will be of value to those 
 engaged in trades and industries where a knowledge of the patenting 
 of inventions and the registration of trade marks is important. Full 
 information is given regarding patents in foreign countries. 
 
 The Book ; Its History and Development. By 
 
 Cyril Davenport, V.D., F.S.A. With 7 Plates and 
 126 Figures in the text. 
 List of Contents : Early Records. Rolls, Books and Book 
 bindings Paper. Printing. Illustrations. Miscellanea. 
 Leathers. The Ornamentation of Leather Bookbindings without 
 Gold. The Ornamentation of Leather Bookbindings with Gold, 
 Bibliography. Index. 
 The romance of the Book and its development from the rude inscrip- 
 tions on stone to the magnificent de Luxe tomes of to-day have 
 never been so excellently discoursed upon as m this volume, ihe 
 history of the Book is the history of the preservation of human thought. 
 This work should be in the possession of evey book lover. 
 
 ( 7 ) 
 
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 Gold and Precious Metals. By Thomas K. Rose, 
 
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 Photography. By Alfred Watkins, Past Presi- 
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 London Institute. 
 
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