INDUSTRIAL CHEMISTRY 
 
 BEING A SERIES OF VOLUMES GIVING 
 A COMPREHENSIVE SURVEY OF 
 
 THE CHEMICAL INDUSTRIES 
 
INDUSTRIAL CHEMISTRY 
 
 BEING A SERIES OF VOLUMES GIVING A 
 COMPREHENSIVE SURVEY OF 
 
 THE CHEMICAL INDUSTRIES 
 
 EDITED BY SAMUEL RIDEAL, D.Sc. LOND,, F.I.C. 
 
 FELLOW OF UNIVERSITY COLLEGE, LONDON 
 ASSISTED BY 
 
 JAMES A. AUDLEY, B.Sc., F.I.C. R. S. MORRELL, M.A., PH.D. 
 
 W. BACON, B.Sc., F.I.C., F.C.S. J. R. PARTINGTON, M.A., PH.D. 
 E.DE BARRY BARNETT, B.Sc., A. I.C. ARTHUR E. PRATT, B.Sc., Assoc.R.S.M. 
 
 M. BARROWCLIFF, F.I.C. ERIC K. RIDEAL, M.A., PH.D., F.I.C. 
 
 H. GARNER BENNETT, M.Sc. W. H. SIMMONS, B.Sc., F.I.C. 
 
 F. H. CARR, F.I.C. R. W. SINDALL, F.C.S. 
 
 S. HOARE COLLINS, M.Sc., F.I.C. HUGH S. TAYLOR, D.Sc. 
 
 H. C. GREENWOOD, O.B.E., D.Sc., ARMAND DE WAELE, B.Sc. 
 
 F.I.C. C. M. WHITTAKER, B.Sc. 
 &C., &c. 
 
INDUSTRIAL GASES 
 
 BY 
 
 HAROLD CECIL GREENWOOD 
 
 O.B.E., D.Sc. (MANCHESTER), F.I.C. 
 
 SCIENTIFIC ADVISER, MUNITIONS INVENTIONS DEPARTMENT 
 FORMERLY BEYER FELLOW AND 1851 EXHIBITION SCHOl AR-,QV- ,1 - 
 THE UNIVERSITY OF MANCHESTER 
 
 NEW YORK 
 D, VAN NOSTRAND COMPANY 
 
 25 PARK PLACE 
 1919 
 
PRINTED IN GREAT BRITAIN 
 
a 
 
 GENERAL PREFACE 
 
 THE rapid development of Applied Chemistry in recent years 
 has brought about a revolution in all branches of technology. 
 This growth has been accelerated during the war, and the 
 British Empire has now an opportunity of increasing its 
 industrial output by the application of this knowledge to the 
 raw materials available in the different parts of the world. 
 The subject in this series of handbooks will be treated from 
 the chemical rather than the engineering standpoint. The 
 industrial aspect will also be more , prominent than that of 
 the laboratory. Each volume will be complete in itself, and 
 will give a general survey of the industry, showing how 
 chemical principles have been applied and have affected 
 manufacture. The influence of new inventions on the 
 development of the industry will be shown, as also the 
 effect of industrial requirements in stimulating invention. 
 Historical notes will be a feature in dealing with the 
 different branches of the subject, but they will be kept 
 within moderate limits. Present tendencies and possible 
 future developments will have attention, and some space 
 will be devoted to a comparison of industrial methods and 
 progress in the chief producing countries. There will be a 
 general bibliography, and also a select bibliography to follow 
 each section. Statistical information will only be introduced 
 in so far as it serves to illustrate the line of argument. 
 
 Each book will be divided into sections instead of 
 chapters, and the sections will deal with separate branches 
 of the subject in the manner of a special article or mono- 
 graph. An attempt will, in fact, be made to get away from 
 A, v 72 
 
 458*793 
 
vi GENERAL PREFACE 
 
 the orthodox textbook manner, not only to make the treat- 
 ment original, but also to appeal to the very large class of 
 readers already possessing good textbooks, of which there 
 are quite sufficient. The books should also be found useful 
 by men of affairs having no special technical knowledge, but 
 who may require from time to time to refer to technical 
 matters in a book of moderate compass, with references to 
 the large standard works for fuller details on special points 
 if required. 
 
 To the advanced student the books should be especially 
 valuable. His mind is often crammed with the hard facts 
 and details of his subject which crowd out the power of 
 realizing the industry as a whole. These books are intended 
 to remedy such a state of affairs. While recapitulating the 
 essential basic facts, they will aim at presenting the reality 
 of the living industry. It has long been a drawback of our 
 technical education that the college graduate, on commencing 
 his industrial career, is positively handicapped by his 
 academic knowledge because of his lack of information on 
 current industrial conditions. A book giving a compre- 
 hensive survey of the industry can be of very material 
 assistance to the student as an adjunct to his ordinary text- 
 books, and this is one of the chief objects of the present 
 series. Those actually engaged in the industry who have 
 specialized in rather narrow limits ^will probably find these 
 books more readable than the larger textbooks when they 
 wish to refresh their memories in regard to branches of the 
 subject with which they are not immediately concerned. 
 
 The volume will also serve as a guide to the standard 
 literature of the subject, and prove of value to the con- 
 sultant, so that, having obtained a comprehensive view of 
 the whole industry, he can go at once to the proper 
 authorities for more elaborate information on special points, 
 and thus save a couple of days spent in hunting through the 
 libraries of scientific societies. 
 
 As far as this country is concerned, it is believed that 
 the general scheme of this series of handbooks is unique, 
 and it is confidently hoped that it will supply mental 
 
GENERAL PREFACE vii 
 
 munitions for the coming industrial war. I have been 
 fortunate in securing writers for the different volumes who 
 are specially connected with the several departments of 
 Industrial Chemistry, and trust that the whole series will 
 contribute to the further development of applied chemistry 
 throughout the Empire. 
 
 SAMUEL RIDEAI,. 
 
FOREWORD 
 
 BY 
 
 DR. J. A. HARKER, F.R.S. 
 
 t 
 
 IT is with the deepest regret that, on the eve of publication 
 
 of this book, I have to record the untimely death of the 
 author. 
 
 For the past three years Dr. Greenwood had been in 
 charge of the division of the Research Laboratory of the 
 Ministry of Munitions at University College, dealing with 
 the synthesis of ammonia from its elements. As Director 
 of the Laboratory, I have come into close contact with him 
 for more than three years past, and have therefore had a 
 unique opportunity of forming a judgment of the high value 
 of the work he has accomplished. It is undoubtedly largely 
 due to his untiring energy, research ability and wide know- 
 ledge, that a sure foundation has been laid for the future 
 development of the synthetic ammonia industry in this 
 country. 
 
 Although only thirty-two years of age, he had lived long 
 enough to establish a scientific record of which a man of 
 more advanced years might well be proud. Among the 
 long list of his published researches may be cited those on 
 the reduction of refractory oxides, the production of ferro 
 alloys and the determination of the boiling-points of metals 
 at high temperatures and under varying pressures. All these 
 were carried out at Manchester University. As 1851 
 Exhibition Scholar Greenwood worked ten years ago under 
 Professor Haber at Karlsruhe on the study of catalysts for 
 ammonia synthesis. 
 
FOREWORD 
 
 He was awarded the degree of D.Sc. from Manchester 
 University in 1912 at the early age of twenty-five, and the 
 Fellowship of the Institute of Chemistry in 1918, and the 
 O.B.E. in the present year. 
 
 The contents of this volume testify to the thoroughness 
 of his knowledge in an important branch of modern chemis- 
 try, but only those who have had the privilege of working 
 with him can fully realize the great loss which science has 
 suffered by the sudden termination of so brilliant a career. 
 
 J. A. HARKER. 
 
 MINISTRY OF MUNITIONS, 
 24, OLD QUEEN STREET, 
 
 LONDON, S.W. i. 
 
 Novembei; 1919. 
 
AUTHOR'S PREFACE 
 
 THE main aims of this book on Industrial Gases are to give 
 a general account of the manufacture and technical manipu- 
 lation of gases, to describe briefly the development and 
 general principles of industrial gas technology and to present 
 a collection of data likely to be useful in connection with 
 such technology. 
 
 Many branches of gas manufacture are still in course of 
 vigorous development, the war having been responsible for 
 much progress, e.g. in the production of hydrogen, for 
 aeronautical purposes and also for industrial processes such 
 as the manufacture of synthetic ammonia. On this account 
 it is difficult to give in all cases a final picture of the subject, 
 an indication of the present trend being all that is practicable. 
 
 This and other considerations have caused me to con- 
 centrate more on the elucidation of general principles than 
 on very detailed treatment of the various processes involved. 
 Indeed, the latter alternative would have been impracticable 
 in the present volume on account of the enormous field to 
 be covered. 
 
 Special attention has been paid to the question of gaseous 
 equilibria ; the ever-growing importance of heterogeneous 
 catalytic gas reactions is a feature of the present situation. 
 
 In the introductory chapter the more important general 
 considerations relating to the manufacture and use of gases 
 are briefly discussed, while tables of reference data in the 
 form required for immediate use in technical practice are 
 appended. 
 
 From this book have been excluded certain gases such 
 as hydrogen chloride, chlorine, ammonia, etc., which are 
 treated elsewhere in this series. In view of the dependence 
 on fuel gases of most of the important industrial gases for 
 their manufacture and on account of the intimate connection 
 of the methods of production of fuel gases with the general 
 
x AUTHOR'S PREFACE 
 
 question of industrial gases, a concise survey of the manu- 
 facture and applications of gaseous fuels has been included. 
 The subject is not treated exhaustively as it will be further 
 elaborated in a later volume of this series. 
 
 Throughout the book considerable attention has been 
 devoted to patents where such patents relate to differences 
 in principle ; although much of the subject-matter of patent 
 literature is superficial and crude, there is valuable historical 
 and technical information to be obtained from the same. 
 
 A word may be said here with regard to units. While the 
 metric system has many undoubted advantages in dealing 
 with gases as in other connections, it is not in common usage 
 in this country and consequently all gases have been con- 
 sidered on the basis of 1000 ft. 3 at 15 C. under a pressure of 
 one atmosphere. As regards thermal quantities, since all 
 modern chemical works now use the Centigrade thermometer, 
 the usual B.T.U. has been replaced by the more convenient 
 C.H.U. (Centigrade Heat Unit). 
 
 Free use has been made in some cases of many excellent 
 existing textbooks, from which matter and references have 
 been drawn. 
 
 Further, I desire to express my thanks for information 
 received from various sources, especially to the following : 
 Sir George Beilby, Messrs. A. Boake, Roberts & Co., I/td., 
 Mr. E. M. Boote, Messrs. The Carbonic Acid Gas Co., 
 Messrs. R. & J. Dempster, L/td., Dr. R. L,essing, and Dr. 
 B. B. Maxted. Assistance was also given by the late 
 Thos. Tyrer. 
 
 Finally, I must record my indebtedness to my wife, 
 Mary G. Greenwood, B.Sc., for her constant help in the 
 collection of information and the revision of the MS. 
 
 H. C. G. 
 
 LONDON, 
 
 October, 1919. 
 
CONTENTS 
 
 PAGE 
 
 GENERAL PREFACE ......... v 
 
 AUTHOR'S PREFACE ......... i x 
 
 CONTENTS ..... ...... x i 
 
 INTRODUCTION .......... ! 
 
 Avogadro's Hypothesis. Laws of Gay Lussac and Dalton. Boyle's Law. 
 Law of Charles and Gay Lussac. Absolute zero of temperature. 
 Solution : Henry's Law ; Dalton's Law. Sorption. Diffusion. Per- 
 meability of materials. Critical temperature and pressure. Permanent 
 gases and vapours. Joule-Thomson Effect. Specific heats of gases. 
 Latent heats of vaporisation and fusion. . Thermochemistry. Thermo- 
 dynamical principles governing chemical equilibria in the gaseous state ; 
 the chemical constant. Velocity of reaction. Heterogeneous catalytic 
 gas reactions : reaction velocity ; output and completeness. Viscosity 
 of gases : stream-line and turbulent motion. Resistance to flow of 
 gases. Influence of difference in level. Physical methods of testing 
 the purity of gases : gas interferometer ; density ; effusion ; acoustical 
 methods. Separation of gaseous mixtures. Separation of liquid or solid 
 particles from gases. Methods of measuring volumes and rates of flow 
 of gases. Automatic safety and purity tests. The compression of 
 gases : work of compression ; adiabatic compression ; isothermal com- 
 pression. Notes on compressed gases : safety precautions. Liquefied 
 gases. Heat-interchange. Desiccation of gases. The storage of gas. 
 Reference data. References ... I 
 
 PART I. 
 
 THE GASES OF THE ATMOSPHERE 
 SECTION L AIR. 
 
 Property of air. Composition of the atmosphere ..... 58 
 
 The liquefaction of the permanent gases (air). Theory of cooling by the 
 
 Joule-Thomson Effect : expansion at 100 C. ; the case of hydrogen . 60 
 
 MANUFACTURE OF -JUo^uiD AIR : Useful constants. Hampson system. 
 
 Linde system : effect of pre-cooling. Claude system .... 69 
 
 Properties of liquid air. Applications of liquid air. Separation of the con- 
 stituents of liquid air : theoretical considerations .... 77 
 
xii CONTENTS 
 
 PAGE 
 
 MANUFACTURE OF OXYGEN AND NITROGEN. Linde system : Oxygen 
 plants Nitrogen plants. New Linde system. Claude system. Pictet 
 system . ........ 81 
 
 Separation of the rare gases ......... 92 
 
 References ............ 92 
 
 SECTION II. OXYGEN. 
 
 Properties of oxygen .......... 93 
 
 MANUFACTURE : 
 
 General ........ ... 94 
 
 By the fractionation of liquid air ....... 94 
 
 By electrolysis 94 
 
 By alternate formation and decomposition of higher oxides, etc. . . 95 
 
 By auto-combustion methods ........ 98 
 
 By the action of water on peroxides and the like ..... 98 
 
 By physical methods (in the gaseous state) ...... 99 
 
 Compression of oxygen . . . . . . . . .100 
 
 Comparison of costs of production and purity attainable by different processes 101 
 Applications of oxygen : scientific and laboratory uses ; therapeutic uses j 
 
 welding and cutting of metals ; other applications .... 102 
 
 Oxygen-enriched air : use in the blast furnace ; use in the arc process for 
 
 nitrogen fixation ; use in the Hausser process ; other applications .106 
 
 Estimation and testing of oxygen ........ 108 
 
 References ............ 109 
 
 SECTION III. NITROGEN. 
 
 Properties of nitrogen ... ...... 1 10 
 
 MANUFACTURE: 
 
 General .... ... . . in 
 
 By the fractiouation of liquid air 112 
 
 By direct chemical removal of the oxygen from air . . . ."112 
 From producer gas and products of combustion . . . . .114 
 By physical methods (in the gaseous state) . . . . . 115 
 
 By direct chemical methods 1 16 
 
 Purification of nitrogen : from carbon monoxide ; from carbon dioxide ; 
 
 from oxygen j from sulphur compounds . . . . . .116 
 
 Comparison of costs of production and purity attainable by the different 
 
 processes 117 
 
 Applications of nitrogen nitrogen fixation : cyanamide process ; the 
 synthesis of ammonia ; the formation of metallic nitrides ; the direct 
 production of cyanides ; the Hausser process ; comparison of the 
 power requirements in various nitrogen fixation processes ; other 
 applications . . . . . . . . . . u/ 
 
 Estimation and testing of nitrogen . . . . . . .122 
 
 References . . . . . . . . . . . .122 
 
CONTENTS xiii 
 
 
 
 PAGE 
 
 SECTION IV. THE RARE GASES OF THE 
 ATMOSPHERE. 
 
 General ............ 123 
 
 History of the discovery of the rare gases . . . . . .123 
 
 ARGON. Occurrence. Manufacture. Properties and applications . .124 
 
 NEON. Occurrence. Isolation. Properties and applications . . .128 
 
 HELIUM. Occurrence. Manufacture. Properties and applications . .130 
 
 KRYPTON AND XENON. Occurrence. Isolation and properties . . 132 
 
 Niton . . . . . . . . . . . . 132 
 
 References . . . ... . . . . . 133 
 
 SECTION V. OZONE. 
 
 Occurrence ............ 134 
 
 Properties of ozone . . . . . . . . . -134 
 
 Production of ozone: general; by chemical methods; by thermal treat- 
 ment of oxygen ; by electrolysis ; by photochemical means j by the 
 electric discharge . . . . . . . . . .136 
 
 MANUFACTURE : general principles of ozonizers : influence of the character 
 of the discharge ; influence of dielectrics ; relation between energy, 
 concentration and production ; influence of moisture ; influence of 
 temperature ; materials of construction. Construction and production 
 of the various commercial types of ozonizers . . . . .140 
 
 Applications of ozone : water sterilization ; air purification ; chemical 
 
 applications ; other applications 145 
 
 Detection and estimation of ozone ........ 149 
 
 References ............ 150 
 
 PART II. 
 
 HYDROGEN, CARBON MONOXIDE, 
 CARBON DIOXIDE, SULPHUR DI- 
 OXIDE, NITROUS OXIDE, ASPHYX- 
 IATING GASES. 
 
 SECTION VI. HYDROGEN. STATIONARY 
 PLANTS. 
 
 Occurrence ............ 152 
 
 Physical properties. Liquid hydrogen ; properties. Chemical properties . 152 
 MANUFACTURE (STATIONARY PLANTS): 
 
 General ........... 155 
 
 From water gas replacement of carbon monoxide by hydrogen . . 156 
 B.A.M.A.G. continuous catalytic process : theory of the B.A.M.A.G. 
 
 continuous catalytic process . . . . . . 159 
 
 Griesheim-Elektron process : theory of the Griesheim-FJektron process 164 
 
xiv CONTENTS 
 
 MANUFACTURE (STATIONARY PLANTS) : continued. PAGE 
 
 From water gas by liquefaction of the carbon monoxide : the Linde- 
 
 Frank-Caro process 168 
 
 By the action of water or steam on iron or carbon . . . .174 
 
 General . . . . . . . . . . .174 
 
 Iron oxide processes : Lane process ; Messerschmitt process ; pro- 
 cess of the Internationale Wasserstoff A.G. ; Strache process . 175 
 Dieffenbach and Moldenhauer process . . . . . .185 
 
 Bergius process 187 
 
 By the decomposition of hydrocarbons : Carbonium Gesellschaft pro- 
 cess ; Rincker and Wolter process ; Oechelhauser process ; 
 
 B. A.M. A.G. (Bunte) process 189 
 
 By electrolysis . . . . . . . . . 194 
 
 General. Principal electrolytic processes used in practice : Schuckert 
 process ; Schmidt process ; Garuti process ; Schoop process ; Inter- 
 national Oxygen Co.'s processes ; other processes. Danger limits 
 as regards intermixing in electrolytic hydrogen and oxycen. 
 Hydrogen as a by-product . . . . . . 194 
 
 Other processes for the manufacture of hydrogen .... 203 
 
 By the action of acids or alkalis on metals 203 
 
 Separation from water gas and the like by physical methods . . 204 
 Through the intermediary of formates ...... 205 
 
 Miscellaneous methods ........ 205 
 
 Production of a mixture of nitrogen and hydrogen for use in synthetic 
 
 ammonia manufacture ....... 207 
 
 Methods of final purification of hydrogen. From carbon monoxide : by 
 
 soda-lime ; by caustic soda solution ; by cuprous chloride solution ; 
 
 by conversion into methane ; by calcium carbide. From carbon 
 
 dioxide. From sulphur compounds. From other impurities . . 207 
 
 Comparison of costs of production and purity attainable by the different 
 
 methods 212 
 
 Applications of hydrogen : hydrogenation of oils and fats ; manufacture of 
 
 synthetic ammonia ; other applications . . . . . .213 
 
 References . . . 221 
 
 SECTION VII. THE PRODUCTION OF HYDROGEN 
 FOR MILITARY PURPOSES. 
 
 Field processes . 223 
 
 Portable apparatus for use in the field ....... 224 
 
 Silicon and "Silicol" processes: the Schuckert process; the Silicol 
 
 process - 224 
 
 Hydrogenite process ........ .227 
 
 Hydrolith process 228 
 
 By the action of acids and alkalis on metals : action of sulphuric acid 
 on iron or zinc ; action of caustic soda on aluminium ; action of 
 
 activated aluminium on water 229 
 
 Other processes . . . . -231 
 
CONTENTS xv 
 
 PAGE 
 
 Adaptations of stationary types of plant to field purposes .... 232 
 
 Semi-portable plant .......... 232 
 
 Stationary plants .......... 233 
 
 General : Lifting power of the hydrogen ; effect on fabrics ; costs by the 
 
 different processes .......... 233 
 
 Estimation and testing of hydrogen ....... 235 
 
 References 236 
 
 SECTION VIIL CARBON MONOXIDE. 
 
 Properties of carbon monoxide ........ 237 
 
 MANUFACTURE : 
 
 Applications of carbon monoxide : general ; the Mond nickel process 
 metallic carbonyls the refining of nickel by the Mond process ; the 
 production of formates, oxalates and acetates j the production of gases 
 rich in methane ; the manufacture of phosgene properties and uses 
 of phosgene ; other applications . . . . . . .241 
 
 Estimation of carbon monoxide . . . . . . . . 254 
 
 SECTION IX. CARBON DIOXIDE. 
 
 Occurrence ............ 256 
 
 Properties of carbon dioxide ; liquid carbon dioxide j solid carbon dioxide 256 
 MANUFACTURE : 
 
 General .... 259 
 
 Generation of pure carbon dioxide . . . 259 
 
 Utilization of natural sources . .... 259 
 
 By the thermal decomposition of carbonates . ... 260 
 
 By the action of acids on carbonates ... . 261 
 
 Production as a by-product in fermentation processes . . . 262 
 
 By other methods . 262 
 
 Concentration of carbon dioxide from mixtures with other gases . 263 
 
 By means of water under pressure ...... 263 
 
 By the alternate formation and decomposition of alkali bicarbonates 
 
 in solution .......... 264 
 
 By liquefaction . . ... 264 
 
 Production and concentration of dilute carbon dioxide from products 
 
 of combustion j Siirth system . ... 264 
 
 Production and concentration of dilute carbon dioxide from lime-kiln 
 
 gases ........... 267 
 
 The production and transport of liquid carbon dioxide .... 268 
 
 The production and transport of solid carbon dioxide . . 268 
 Applications of carbon dioxide : in the Solvay ammonia soda and the Glaus- 
 Chance sulphur recovery processes; in the manufacture of artificial 
 
 mineral waters ; in refrigeration plant ; other applications . . . 269 
 
 Estimation and testing of carbon dioxide . . 272 
 
 References . . 2 73 
 
xvi CONTENTS 
 
 SECTION X. SULPHUR DIOXIDE. 
 
 PAGE 
 
 Properties of sulphur dioxide ........ 274 
 
 MANUFACTURE : 
 
 General ... 275 
 
 Production of dilute sulphur dioxide . . .. . . . .277 
 
 Concentration of dilute sulphur dioxide : the Hanisch and Schroder process 278 
 
 Transport of liquid sulphur dioxide 279 
 
 Applications of sulphur dioxide : manufacture of sulphuric acid, sulphuric 
 anhydride and sodium sulphate j manufacture of wood pulp ; in 
 refrigeration plant ; as a solvent j for bleaching purposes ; as a 
 
 disinfectant ; other applications . . . . . . 280 
 
 The estimation and testing of sulphur dioxide ...... 283 
 
 References 284 
 
 SECTION XL NITROUS OXIDE. 
 
 Properties of nitrous oxide 285 
 
 MANUFACTURE. From ammonium nitrate ; by other methods . 286 
 
 Purification 288 
 
 Applications of nitrous oxide ........ 288 
 
 SECTION XII. ASPHYXIATING GASES. 
 
 Introduction ....... ... 291 
 
 The development of gas warfare ,291 
 
 PART III. 
 
 GASEOUS FUELS. 
 SECTION XIII. 
 
 General considerations . . . . . . . . 295 
 
 Fundamental principles relating to the use of gaseous fuels : table of 
 
 constants ; calorific value ; the mechanism of flame ; calorific value 
 
 of technical air-gas mixtures ; ignition temperature ; explosive limits 
 
 and the velocity of propagation of explosion 296 
 
 Fundamental principles of the production of gaseous fuels of low calorific 
 
 value : action of air on carbon ; action of steam on carbon ; action 
 ~^f a mixture of air and steam on carbon ; action of carbon dioxide on 
 
 carbon ........... 301 
 
 TECHNICAL PRODUCTION OF GASEOUS FUELS OF Low CALORIFIC 
 
 VALUE : 
 Air producer gas .......... 313 
 
 General. General principles of operation j applications . . . 313 
 
CONTENTS xvii 
 
 PAGE 
 
 Water gas 316 
 
 General. General principles of operation . . . . . 316 
 
 Blue water gas plants ; the Lowe system of operation ; Dellwik- 
 
 Fleischer system ; Kramer and A arts process . . . .318 
 
 Carburetted water gas ......... 322 
 
 Applications of blue water gas ....... 325 
 
 Semi-water gas ....... ... 325 
 
 General. General principles of operation. Choice of fuel : nitrogen 
 content of coal ; sulphur "content of coal ; other deleterious con- 
 stituents of coal. The saturation temperature of the blast. The 
 
 rate of gasification . . . 325 
 
 Semi-water gas plants : general ; pressure plants ; ammonia recovery 
 
 and cleaning of semi-water gas ....... 335 
 
 Mond process . , . . . . . . . 339 
 
 Use of semi- water gas for furnace operations ..... 340 
 
 The production of power by the combustion of semi-water gas in gas 
 engines : general ; plants for power production ; suction plants ; 
 use of suction gas in internal combustion engines . . -341 
 
 Coal gas as a fuel .......... 347 
 
 General . . . . . . . . . . . 348 
 
 Applications of coal gas : furnace operations; power production; other 
 
 applications .......... 348 
 
 Coke-oven gas . . . . . . . . . . . 352 
 
 Blast-furnace gas ... 353 
 
 Natural gas . . . . . 354 
 
 Surface combustion . . . ... . . . 355 
 
 Gas calorimetry . . . . ... . . . . 357 
 
 References . . . . . 358 
 
 INDEX OF SUBJECTS 359 
 
 INDEX OF NAMES OF AUTHORS . . . . . .365 
 
 ERRATA 
 
 Page 144, line 25, for 7000 to 9000 volts rtad 4000 volts. 
 Page 273, References, for Goosman read Goosmann. 
 
INDUSTRIAL GASES 
 
 INTRODUCTION 
 
 THE object of this introductory chapter is to outline and 
 emphasize some of the more important fundamental physical 
 and physico-chemical principles forming the basis of 
 technical gas reactions. In no branch of modern chemistry 
 is the importance of a knowledge of the development of 
 physical chemistry more important than in the study of 
 reactions and phenomena of the gaseous state of matter. 
 This is largely to be attributed to the greater ease of appli- 
 cation of generalizations to the gaseous state, owing to its 
 simple physical condition as compared with the liquid and 
 solid states. It is to be feared that many technical gas 
 processes have been worked without due appreciation of 
 the thermodynamical principles determining their success 
 or failure. A most vital factor contributing to this state 
 of affairs is the fact that in many cases, e.g. in the coal-gas 
 industry, the responsibility and control are delegated to 
 engineers and not to chemists; at the same time, the 
 engineering aspects of the operations must receive careful 
 consideration. 
 
 No attempt will be made in the present volume to give 
 a detailed theoretical treatment of the various physico- 
 chemical generalizations and data to which reference is 
 made ; for such information, works on physical chemistry, 
 etc., must be consulted. The intention is rather to draw 
 attention to the salient points of importance in the investi- 
 gation and control of technical operations relating to the 
 manufacture or utilization of gases. 
 
 Avogadro's Hypothesis. This generalization states 
 
 A. I 
 
/?*'. :/;"*: j : .^[INDUSTRIAL GASES 
 
 that equal volumes of different gases contain equal numbers 
 of molecules under similar conditions of temperature and 
 pressure. As a practical consequence of this law, it may be 
 stated that, to a fairly close approximation, the molecular 
 weight in grams of any permanent gas, i.e. a substance 
 above its critical temperature, at o C. and 760 mm., occupies 
 22*38 litres. The volume at 15 C. will consequently be 
 
 22-38 X 288 v 
 
 litres = 23-61 litres. 
 
 273 
 
 A useful figure is the corresponding volume of a pound 
 molecule, which is equal to 
 
 358-5 ft. 3 at o C. 
 or 378-2 ft. 3 at 15 C. 
 
 With vapours, i.e. gases below their critical temperatures, 
 the volume is usually slightly lower, e.g. 22*26 litres at o C. 
 and 760 mm. in the case of carbon dioxide. 
 
 Laws of Gay Lussac and Dalton. According to these 
 well-known generalizations, chemical combination between 
 gases takes place in definite proportions and the volume 
 of the product or products bears a simple relation to 
 the volumes of the reactants, under like conditions of 
 temperature and pressure. This, of course, is intimately 
 connected with Avogadro's Hypothesis. 
 
 Boyle 's Law. Law of Charles and Gay Lussac. 
 Boyle's Law states that pv = a constant, where p and v 
 represent the pressure and volume of a given mass of gas, the 
 temperature being maintained constant. 
 
 The Law of Charles and Gay Lussac enunciates that the 
 effect of variation of temperature under constant pressure 
 is to vary the volume in direct proportion to the (absolute) 
 temperature variation, or, conversely, if the volume be kept 
 constant, that the pressure varies as the absolute temperature. 
 The combined result of these generalizations may be 
 expressed thus 
 
 i>v 
 
 Z a constant (K) 
 
 or pv = KT. 
 
INTRODUCTION 
 
 When pv refers to one gram molecule at N.*T.P., the 
 equation is usually written pv => RT, R being termed the 
 gas constant and having a numerical value of 1*98 calories. 
 Since gram molecules are inconvenient units for industrial 
 use, the more general form will be adopted. 
 
 This relation, however, is only approximately correct, 
 particularly as regards the constancy of the product pv, 
 as even the permanent gases are not " perfect " ; vapours 
 show very considerable divergencies. Due recognition of 
 this fact is of importance in dealing with compressed gases, 
 and the extent of the deviation from perfection for different 
 gases will be found in Table 12 (A), under the heading of ft. 3 
 of free gas contained in a cylinder of i ft. 3 capacity at a 
 pressure of 120 atmospheres, 121 atms. absolute. The 
 values are obtained as follows : e.g., in the case of hydrogen, 
 the variation of the product pv with v at a temperature 
 
 of 15-5 C. is 
 
 TABLE i. 
 
 AMAGAT. COMPRESSIBILITY OF HYDROGEN. 
 
 p (atmospheres absolute) 
 
 t>v . 
 
 i 
 
 I 
 
 50 
 1*0340 
 
 100 
 
 1-0689 
 
 150 
 
 I'lOII 
 
 2OO 
 1*1342 
 
 blbv 
 
 i 
 
 4.8-36 
 
 Q3'^6 
 
 136*23 
 
 176* 34 
 
 
 
 
 
 
 
 (cf. Amagat, Annales de Chim. et de Phys., [6], 29, (1883), 68). 
 The ratio ~- represents the ratio of the mass of gas 
 
 (or the volume of free gas) contained in a given reservoir 
 at the particular absolute pressure to that at one atmosphere 
 absolute pressure, assuming no change in the volume of 
 the container. The curves in Fig. i give the variation of 
 pv with p for a number of permanent gases. Most of the 
 values are taken from Amagat's investigations (Annales de 
 Chim. et de Phys., [5], 19, (1880), 345 ; [5], 22, (1881), 353 ; 
 [6], 29, (1883), 68, 505) and have been arranged in all cases 
 so that the product pv equals unity at o C. at atmospheric 
 pressure ; at the particular temperature of the determination 
 the product is greater in accordance with the coefficient of 
 expansion of the gas in question. In the case of oxygen, 
 
4 INDUSTRIAL GASES 
 
 1-20 
 
 0-80 
 
 50 IOO ISO 2OO 
 
 PRESSURE ATMOSPHERES (ABSOLUTE) 
 FIG. i. Compressibility of Gases at the ordinaryvTemperature. 
 
INTRODUCTION 5 
 
 only three points are available, namely, i, 100, and 200 atms., 
 consequently the intermediate points of the curve are a 
 little uncertain. 
 
 The capacity of a given cylinder at the (absolute) 
 
 225 
 
 200 
 
 HYDROGEN 
 
 175 
 
 800 
 
 25 50 75 100 125 150 
 
 PRESSURE ATMOSPHERES (ABSOLUTE) 
 
 FIG. 2. Capacity of Cylinder for Compressed Gases. 
 
 pressure p x can readily be determined from these curves by 
 evaluating the expression 
 
 where (^w)! and (pv) x represent the values at the pressures 
 of one and p x atmospheres respectively. Curves on this 
 basis have been plotted in Fig. 2, the ordinates representing 
 the volumes of free gas contained in a given cylinder at the 
 pressures denoted by the abscissae. 
 
INDUSTRIAL GASES 
 
 This variation in the value of pv is due to the joint 
 action of two opposing factors : (i) the attraction between 
 the molecules, acting in the direction of lowering the 
 product pv, and (2) the departure from perfect compres- 
 sibility owing to the actual dimensions of the molecules, 
 operative in the opposite direction. Thus, nitrogen at first 
 shows a decrease in the product pv with rising pressure 
 and subsequently an increase. In order to allow for the 
 very considerable divergence from Boyle's I,aw, even at 
 moderate pressures, of gases such as carbon dioxide, various 
 more complete equations have been proposed. The growing 
 imperfection of air as the temperature is lowered is well 
 shown by the measurements of Witkowski (Phil. Mag., [5], 
 41, (1896), 288), given in Table 2. The values are taken so 
 that pv = i *ooo at N.T.P., as in Fig. i. 
 
 TABLE 2. 
 WITKOWSKI. COMPRESSIBILITY OF AIR. 
 
 Pres- 
 sure 
 
 atras. 
 
 Temperatures C. 
 
 + 100 
 
 + 16 
 
 o 
 
 -35 
 
 -78-5 
 
 -103-5 
 
 -130 
 
 -135 
 
 -140 
 
 -145 
 
 I 
 
 1-367 
 
 1-0587 
 
 I'OOOO 
 
 0-8716 
 
 0-7II9 
 
 0-6202 
 
 0-5229 
 
 0-5046 
 
 0-4862 
 
 0-4679 
 
 10 
 
 1-3678 
 
 I-0550 
 
 0-9951 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 15 
 
 1-3685 
 
 0529 
 
 9923 
 
 
 
 
 
 
 
 
 
 
 
 "495 
 
 3786 
 
 20 
 25 
 
 1-3691 
 1-3698 
 
 -0509 
 0488 
 
 -9897 
 9869 
 
 
 
 6778 
 6689 
 
 5697! H4IO 
 '5559 | '4 l8 3 
 
 ___ 
 
 3808 
 3476 
 
 "3447 
 3 i5 
 
 30 
 
 i'374 
 
 0468 
 
 9842 
 
 
 
 6599 
 
 '54*7 
 
 3936 
 
 3502 
 
 3063 
 
 2444* 
 
 35 
 
 I-37I3 
 
 0449 
 
 9816 
 
 
 
 65IO 
 
 5270 
 
 3650 
 
 3115 
 
 2419 
 
 
 40 
 
 I-3725 
 
 433 
 
 9793 
 
 
 
 6423 
 
 -5125 
 
 -3329 
 
 2598 
 
 1128 
 
 
 45 
 
 I-3738 
 
 0419 
 
 9772 
 
 - 
 
 -6335 
 
 4980 
 
 2963 
 
 1942 
 
 
 
 50 
 
 1*3754 
 
 0408 
 
 "9754 
 
 8288 
 
 6252 
 
 4839 
 
 2544 
 
 1605 
 
 
 
 55 
 
 I- 377 
 
 0399 
 
 9738 
 
 8253 
 
 6170 
 
 4701 
 
 2171 
 
 1553 
 
 
 
 60 
 
 1-3784 
 
 0390 
 
 9723 
 
 8219 
 
 6089 
 
 4567 
 
 2013 
 
 1556 
 
 
 
 65 
 
 1-3802 
 
 0384 
 
 9710 
 
 8187 
 
 6011 
 
 '4439 
 
 1985 
 
 1576 
 
 
 
 70 
 
 1-3821 
 
 0381 
 
 9701 
 
 8158 
 
 '5937 
 
 43i8 
 
 1989 
 
 
 
 
 75 
 
 1-3842 
 
 0379 
 
 9694 
 
 8132 
 
 5863 
 
 4206 
 
 2013 
 
 
 
 
 80 
 
 1-3866 
 
 0379 
 
 9688 
 
 8105 
 
 -5796 
 
 4103 
 
 2043 
 
 
 
 
 85 
 
 1-3887 
 
 0380 
 
 9684 
 
 8o8l 
 
 "5734 
 
 4014 
 
 
 
 
 
 90 
 
 1-3908 
 
 0382 
 
 9681 
 
 8058 
 
 5680 
 
 3948 
 
 
 
 
 
 95 
 
 1-3929 
 
 0386 
 
 9680 
 
 8038 
 
 -5634 
 
 3903 
 
 
 
 
 
 IOO 
 
 i'395i 
 
 0390 
 
 9681 
 
 8023 
 
 5600 
 
 3881 
 
 
 
 
 
 i5 
 
 !-3977 
 
 -0397 
 
 9685 
 
 8013 
 
 5568 
 
 3874 
 
 
 
 
 
 no 
 
 1-4004 
 
 0406 
 
 9690 
 
 8006 
 
 '5544 
 
 3877 
 
 
 
 
 
 "5 
 
 i"434 
 
 0418 
 
 9699 
 
 8004 
 
 5530 
 
 3892 
 
 
 
 
 
 I2O 
 
 1-4065 
 
 0432 
 
 9710 
 
 8006 
 
 5520 
 
 3914 
 
 
 
 
 
 125 
 
 
 -0448 
 
 9722 
 
 8012 
 
 5520 
 
 3944 
 
 
 
 
 
 I 3 
 
 
 0467 
 
 9738 
 
 MM 
 
 5528 
 
 398i 
 
 
 
 
 * Corresponds to 29 atms. 
 
INTRODUCTION 
 In the more complete equation of Van der Waak 
 
 the quotient of the constant a divided by v 2 representing 
 the cohesion effect, and b, another constant, representing the 
 actual dimensions of the molecules, the constants may be 
 evaluated by the following expressions : 
 
 6-| = approximately^ 
 
 where 
 
 T c and p c are the critical temperature and pressure, 
 p and v represent the pressure and volume of the 
 gas at the absolute temperature T , 
 
 and K is a constant. 
 
 The value of this equation in correlating the very 
 different behaviour of various gases under varying conditions 
 of temperature and pressure is well seen if the equation is 
 written in the following form, substituting the above values 
 for a and b 
 
 where TT, <f> and 6 represent the multiples or submultiples 
 of the critical values, pressure, volume* and temperature, 
 respectively. If, now, we plot TT< curves instead of pv 
 curves we obtain practically identical curves for all gases ; 
 for equal values of TT, ^ and 6 two gases are said to be in 
 corresponding states. 
 
 This and other equations, e.g. that of Dieterici, give closer 
 but still incomplete agreement with experimental results. 
 
 Absolute Zero of Temperature. According to the 
 L,aw of Gay L,ussac and Dalton, which may be expressed 
 
 KT 
 
 * The critical volume of the mass of gas under consideration is the 
 volume at the critical temperature and pressure. 
 
8 INDUSTRIAL GASES 
 
 the volume of a gas should become equal to zero when 
 T=.o. 
 
 The observed coefficient of expansion of gases, i.e. about 
 ^fj of the volume at o C. per C., indicates that the 
 absolute zero of temperature, i.e. the temperature at which 
 the molecules have ceased to have relative motion, is 
 approximately 273 C. below the freezing point of water. 
 More exact computations, e.g. from the Joule-Thomson 
 effect (see below), indicate a probable value of 273-13 C. 
 
 Solution: Henry 's Law; Dalton's Law. It was 
 shown by Henry that the solubility of a gas is proportional 
 to its pressure, and by Dalton, shortly afterwards, that with 
 gaseous mixtures the solubility of each constituent in a 
 liquid is proportional to the partial pressure of the con- 
 stituent, the other gases behaving as a vacuum. I4ke 
 many other "laws," these generalizations are only approxi- 
 mately correct, especially for a gas with a high degree of 
 solubility. 
 
 The principle of partial pressures applies to man}- 
 processes besides that of solution, e.g. the temperature at 
 which a particular constituent of a gaseous mixture will 
 liquefy out as the temperature is progressively lowered is 
 dependent on its partial pressure. Generally speaking, it 
 may be stated that the solubility of gases in water falls off 
 as the temperature is raised ; with other solvents, however, 
 this is not always the case. 
 
 Sorption. When gases are taken up by solids, the 
 phenomena are much less simple. It becomes necessary 
 to differentiate between absorption, i.e. solution or uniform 
 distribution throughout the structure of the solid, and 
 adsorption, which is essentially a surface condensation. 
 The combined effect is sometimes termed sorption. Thus, 
 when hydrogen is brought into contact with charcoal at 
 liquid-air temperatures, there is a rapid fall in pressure 
 occupying only a few minutes, attributed to adsorption, 
 followed by a slow fall over several hours, considered by 
 McBain (Z. physik. Chem., 68, (1909), 471) to be a slow 
 penetration into the structure of the charcoal. Similar 
 
INTRODUCTION 9 
 
 effects were observed by Richardson (/. Amer. Ctyem. Soc., 
 39, (1917), 1828) in the sorption of carbon dioxide and 
 ammonia by charcoal. In some cases there is evidence of 
 the formation of a chemical compound, e.g. with oxygen 
 and charcoal (Rhead and Wheeler, Chem. Soc. Trans., 
 (1913), 641). In adsorption phenomena, the relation 
 between pressure and the^ extent to which the gas is taken 
 up is much more complex than in ordinary solubility. 
 
 Gases are taken up in appreciable quantities by many 
 metals, in the solid and especially in the liquid state, the 
 sorption usually increasing with the temperature ; at the 
 fusion point there is a sudden increase in the sorption in 
 the case of most metals. Thus, metallic iron takes up 
 0-000035% by weight of hydrogen at 416 C. and 0*000108% 
 at 1450 C. (Jurisch, Stahl und-Eisen, 34, (1914), 252). 
 Between 23 and 750 mm. the weight of hydrogen absorbed 
 varies as the square root of the pressure for a given allotropic 
 modification of the iron. With nitrogen, the sorption by 
 weight is 0-00158% at 878 C., 0-02103% at 981 C., falling 
 off to 0-01885% at 1136 C., the amount varying as the 
 square root of the pressure (Jurisch, I.e.}. 
 
 Diffusion. The diffusion of one gas into another takes 
 place with considerable rapidity under ordinary conditions. 
 The rate is inversely proportional to the total pressure of 
 the two gases, and approximately proportional to the 
 square root of the absolute temperature. The effect of 
 increased pressure is very noticeable if a mixture of two 
 gases, e.g. nitrogen and hydrogen, be made by successive 
 compression of the two gases into a cylinder, particularly 
 if the cylinder be in a vertical position, and the lighter gas 
 be introduced second. If, however, the cylinder be disposed 
 in a horizontal position, diffusion is almost complete on 
 standing 12 to 24 hours. 
 
 It is interesting to note that diffusion is scarcely affected 
 by the presence of a perforated partition, although the 
 aggregate area of communication may be greatly reduced. 
 
 Permeability of Materials. A point of some practical 
 importance, in dealing with gases, is the permeability of 
 
10 
 
 INDUSTRIAL GASES 
 
 materials. Thus, hydrogen diffuses through heated palla- 
 dium or platinum and to a lesser degree through heated 
 iron. Quartz is appreciably permeable to hydrogen above 
 1000 C., while indiarubber is fairly permeable to gases. 
 According to Dewar (Proc. Roy. Institution, 21, (1918), 
 813) the rate of diffusion of various gases at 15 C. and 
 760 mm. pressure through a rubber membrane of 0*01 mm. 
 thickness is as follows : 
 
 TABLE 3. 
 RATES OF DIFFUSION THROUGH RUBBER. 
 
 Gas. 
 
 Air 
 
 Nitro- 
 
 Carbon 
 
 Helium 
 
 Argon 
 
 Oxy- 
 
 Hydro- 
 
 Carbon 
 
 
 
 gen 
 
 monoxide 
 
 
 
 gen 
 
 gen 
 
 dioxide 
 
 Rate of diffusion 
 
 
 
 
 
 
 
 
 
 cm. 3 /cm. 2 /diem. 
 
 2'0 
 
 1-38 
 
 1-88 
 
 3'5 
 
 2-56 
 
 4-0 
 
 II'2 
 
 28-0 
 
 The rate of diffusion increases rapidly with temperature 
 but does not appear to be directly related to any chemical 
 or physical property of the different gases. When dealing 
 with mixtures of gases, it is obvious that the effect of 
 such diffusion will be to produce a change in composition. 
 
 Critical Temperature and Pressure. Permanent Gases 
 and Vapours. It was found by Andrews that for each gas 
 there is a certain temperature above which it is impossible 
 to effect liquefaction by simple compression, however great. 
 This temperature is termed the critical temperature, and 
 the pressure of the system at this point, i.e. the pressure 
 required to effect liquefaction at the critical temperature, 
 is termed the critical pressure. The values of the critical 
 pressures are comparatively low and fall off as the value 
 of the critical temperature decreases ; thus, for hydrogen, 
 the critical pressure is only about n atmospheres. 
 
 Joule-Thomson Effect. If a compressed gas be allowed 
 to expand to a lower pressure through an orifice without 
 the production of external work, there is, as was observed 
 by Joule and Thomson, a certain slight cooling effect with 
 most gases. With a perfect gas there should be no change 
 in temperature ; the observed effects are therefore due to 
 
INTRODUCTION n 
 
 deviations from Boyle's and Joule's I^aws, Joule's L,aw 
 stating that 
 
 U=>the internal energy of the gas=>KT 
 
 where K is a constant and T the absolute temperature. 
 
 The cooling effect is due mainly to the work of separation 
 of the molecules and will, therefore, be greater as the 
 temperature of the gas is lowered ; similarly the effect will 
 be greater with gases which are not much above or are 
 below their critical temperatures. Thus, the effect is much 
 greater for carbon dioxide than for air, while with hydrogen 
 a heating effect is actually observed (cf. p. 67). On 
 lowering the temperature of the hydrogen, however, an 
 inversion point is reached at 80:5 C. It was found by 
 Joule and Thomson that the fall in temperature could be 
 represented by the expression 
 
 where AT=the fall in temperature in degrees Centigrade 
 and A =a constant, 
 
 while according to the more exact formula of Rose-Innes 
 (Phil. Mag., 45, (1898), 227) 
 
 where A and B are constants. The latter formula indicates 
 the existence of an inversion point. 
 
 The Joule-Thomson effect forms the basis of the L,inde 
 process for the liquefaction of air and is dealt with more 
 fully on p. 61. 
 
 Specific Heats of Gases. The specific heats of gases 
 will be found to be of fundamental importance in many 
 questions of plant design as well as in thermodynamical 
 calculations. The specific heat of a gas varies according 
 as to whether the rise or fall in temperature takes place at 
 constant pressure or at constant volume, i.e. with or without 
 the performance of external work, against the atmosphere. 
 The former, C p , is, of course, greater than the latter, C,, the 
 
12 INDUSTRIAL GASES 
 
 difference being constant and equal per gram molecule of 
 gas to R, the gas constant, R, being also expressed in calories 
 per gram molecule of gas. 
 Thus 
 
 p C v = R= 1-98 calories 
 
 where C^ and C v are the molecular heats. 
 
 It is often convenient in plant design to express thermal 
 quantities in terms of pounds and degrees Centigrade and 
 to denote the resulting units as C.H.U. (Centigrade heat 
 units), this procedure having many advantages over the 
 B .T.U. system using Ibs. and degrees Fahrenheit. It should be 
 noted that i C.H.U./lb.=i calorie/gram=i kilocalorie/kilo. 
 
 Further, as the heat capacities of most diatomic gases for 
 equal volumes are equal to within, say, 15 %, it is often con- 
 venient to express the same in terms of C.H.U./iooo ft. 3 / C. 
 Thus 
 
 The specific heat at constant pressure of air at 20 C. 
 = 0-2417 cals. /gram. = 0-2417 C.H.U. /lb. 
 = 0-2417 X 76-49 C.H.U./iooo ft.s/C. at 15 C. 
 = 18-49 C.H.U./iooo ft.3/C. 
 
 It is important to note that in many cases the specific 
 heats of gases vary very considerably with temperature and 
 pressure. The effect of increased temperature in general 
 is to produce a slow increase in the specific heat ; at very 
 low temperatures, however, approximating to the point of 
 liquefaction of the particular gas, there is a sudden and 
 very marked increase in the specific heat. 
 
 The effect of increased pressure is also to produce an 
 increase in the specific heat, thus, the specific heat at constant 
 pressure of air increases from 0-2415 at i atmosphere to 
 0*2925 at 200 atmospheres (Holborn and Jakob, Z. Verein. 
 deut. Ing., 58, (1914), 1429), an increase of 21 %. The 
 very high pressure coefficients found by I/ussana (dm., [3], 
 36, (1894), 5, 70, 130) are undoubtedly incorrect. It has 
 been found that the ratio C P /C V is a constant for gases 
 containing the same number of atoms in the molecule. 
 The approximate value for monatomic gases, e.g. argon, 
 
INTRODUCTION 13 
 
 mercury vapour, etc., is i'666, for diatomic gases, e.g. 
 nitrogen, 1*41, and for triatomic gases, e.g. carbon dioxide, 
 i '30. This ratio, usually denoted by y, is of importance in 
 connection with adiabatic compression, and with the 
 propagation of sound in gases, etc. 
 
 Latent Heats of Vaporization and Fusion. When 
 dealing with the liquefaction or solidification of gases, a 
 knowledge of the quantities of heat required to effect the 
 change in question is necessary. Particularly is the thermal 
 change demanded by the condensation and vaporization 
 of gases important in connection with the production of 
 cold by mechanical means, e.g. through the intermediary 
 of ammonia or carbon dioxide. The values of the latent 
 heats of vaporization of substances decrease with rise in 
 temperature. 
 
 Thermochemistry. In connection with plant design, an 
 important question is that of the thermochemical quantities 
 concerned in the different reactions, and, in the case of new 
 processes, it may be necessary to make special determina- 
 tions of the same. When dealing with simple combustion, 
 this can be easily effected by means of the Junker calorimeter 
 (cf. p. 357) or other like instrument ; if the gas undergoing 
 combustion contains hydrogen, the heat of combustion may 
 be expressed in two ways : (i) gross, i.e. including the latent 
 heat of vaporization of the water formed, or (2) nett, in which 
 case this quantity is deducted. The latent heat of vaporiza- 
 tion of water at 15 C. is about 590 C.H.U./lb., or 10,600 
 C.H.U./lb. molecule. 
 
 It is sometimes the custom in English technical practice 
 to consider the water as separated at 100 C. with the heat 
 evolution of 538 C.H.U./lb. water and to deduct this quantity 
 plus the heat capacity of the water down to ordinary atmo- 
 spheric temperature (6oF. =15-5 C.), equivalent in this case 
 to 84-5 C.H.U./lb. water, making a total of 622-5 C.H.U./lb. 
 water (1120 B.T.U.). 
 
 In French practice, the latent heat alone, i.e. 538 C.H.U., 
 is deducted. 
 
 Of course, neither of these procedures has a very precise 
 significance. 
 
14 INDUSTRIAL GASES 
 
 An accurate knowledge of the heats of reaction is also 
 of fundamental importance in connection with calculations 
 of gas equilibria. 
 
 Thermodynamical Principles Governing Chemical 
 Equilibria in the Gaseous State. It is often of consider- 
 able importance to be able to make an approximate forecast 
 of the course which will be followed by a reversible gas 
 reaction of which the equilibrium data have not been 
 determined. To take an example, consider the reaction 
 represented by the following equation 
 
 2CO^CO 2 + C + 39,300 calories 
 
 and suppose it is required to know without further data, 
 what equilibrium would be set up at a temperature of 800 C. 
 under atmospheric pressure, assuming the presence of an 
 adequate catalyst and sufficient time for the attainment of 
 equilibrium. 
 
 The theoretical solution, largely due to Nernst, requires 
 more space than can be allotted in the present volume. It 
 may be stated, however, that Nernst deduced the following 
 formula 
 
 . (i) 
 
 applying to an equation such as 
 
 mA -f m'E ^ nC + n'D + H calories. 
 
 If, for the sake of simplification, we adopt the convention 
 that the heat of reaction, Q, is taken as that written on the 
 same side of the equation as the substances occurring in 
 the numerator of the fraction representing K, e.g. in the 
 above instance, Q T = H when 
 
 _ ' 
 
 PS 
 
 p A representing the partial pressure in atmospheres of the 
 constituent A in the final equilibrium, and similarly for 
 B, C, andD. 
 
 Then Q = heat of reaction at absolute zero 
 
 ' T-^j3T2 .... (2) 
 
INTRODUCTION 15 
 
 Sv = the algebraic sum of the volumes, those on the right 
 being taken as positive and those on the left as 
 negative, 
 T = the absolute temperature, 
 
 2T 
 
 being the molecular heat of each constituent at tempera- 
 ture T), and 
 
 3 the algebraic sum of the chemical constants corre- 
 sponding to each volume of gas participating in the 
 reaction, those on the right being taken as positive, 
 those on the left as negative,. 
 
 For most purposes, however, it is permissible to neglect 
 the terms correcting for the effect of temperature on Q 
 (equation (2)), and to omit the third term in (i), especially 
 as the data for such refinements are, in many cases, lacking. 
 We then have- 
 log K = ^___ + 27vi 75 log T + ZvC . (3) 
 
 where Q = heat of reaction at the ordinary temperature. 
 
 If one or more constituents be solid or liquid with no 
 appreciable vapour pressure, e.g. carbon in the above example, 
 the pressures of these constituents do not appear in the 
 fraction representing K, and the chemical constants are not 
 included in the term 2vC. 
 
 When no change in volume occurs during the reaction, 
 the term ^175 log T disappears. 
 
 The Chemical Constant. The undetermined integration 
 constant, known as the chemical constant, can be evaluated 
 by considerations into which it is unnecessary to enter here, 
 and values as follows are obtained for the different gases 
 (cf. also I^angen, Z. Elektrochem. , 25, (1919), 25) : 
 
16 INDUSTRIAL GASES 
 
 TABLE 4. 
 CHEMICAL CONSTANTS. 
 
 Gas. Chemical Constants. 
 
 Hydrogen ............. r6 
 
 Methane .............. 2-5 
 
 Nitrogen .............. 2'6 
 
 Oxygen .............. 2'8 
 
 Carbon monoxide ........... 3-5 
 
 Chlorine .............. 3-1 
 
 Iodine .............. 3-9 
 
 Hydrochloric acid ........... 3-0 
 
 Hydriodic acid ............ 3-4 
 
 Nitric oxide ............. 3-5 
 
 Nitrous oxide ............ 3-3 
 
 Sulphuretted hydrogen ......... 3-0 
 
 Sulphur dioxide ............ 3-3 
 
 Carbon dioxide ............ 3-2 
 
 Carbon disulphide ........... 3-1 
 
 Ammonia .............. 3*3 
 
 Water ............... 3-6 
 
 Carbon tetrachloride .......... 3-1 
 
 Chloroform ............. 3-2 
 
 Benzene .............. 3-0 
 
 Ethyl alcohol ............ 4-1 
 
 Ether .............. 3-3 
 
 Acetone .............. 3-7 
 
 Propyl alcohol ............ 3-8 
 
 Returning to the equation in question, and substituting 
 the appropriate values in the expression 
 
 log K = - + a* 75 log T + 
 we have 
 
 log q=i = zi3 -- j.^- i 1,073 + (3*2 2 X V 
 ' X 1,073 
 
 = 8-013 5-304 3-8 
 
 = 1-091 
 
 therefore K = o-o8ii 
 
 Boudouard's experimental value for this temperature was 
 7% carbon dioxide, i.e. 
 
 P 2 co 0-932 
 
 representing a satisfactory agreement, the closeness of which 
 is accidental. In most cases, the agreement is considerably 
 less good but a valuable, if approximate, idea of the equili- 
 brium may be obtained in this way. 
 
INTRODUCTION 17 
 
 Velocity of Reaction. The velocity of chemical re- 
 action is very sensitive to changes in temperature, and, as a 
 rough average rule, it may be taken that the velocity doubles 
 itself with each 10 C. rise in temperature. 
 
 Further, the concentrations of the react ants are operative 
 as follows, e.g. in the homogeneous bimolecular reaction 
 
 A + B=^C or D + B 
 
 if a and b are the initial molar concentrations of A and B, 
 and x the amount of either which has undergone combination 
 at time t, then 
 
 dx 
 
 ^=*k T (a-x)(b-x) 
 
 where & T is a constant for temperature T. 
 
 Heterogeneous Catalytic Gas Reactions. Reaction 
 Velocity Output and Completeness. By heterogeneous cata- 
 lysis it is implied that there is a discontinuity between the 
 reactants and the catalyst. Nearly all the important cases 
 of technical gas catalysis belong to this category. 
 
 In most heterogeneous catalytic gas reactions, e.g. in 
 the direct synthesis of ammonia, we are dealing with the 
 dual effects of equilibrium and reaction velocity. Thus, 
 on working with a fixed pressure and a moderate gas flow, 
 and gradually raising the temperature from, say, 300 C. 
 to 900 C., we find the percentage of ammonia in the effluent 
 gases increases from practically zero to a maximum value 
 in the region of 500-600 C. (the exact temperature depending 
 on the catalyst and the rate of flow), and then falls off again. 
 At 900 C., even with an indifferent catalyst, equilibrium 
 about 07% NH 3 at 100 atmospheres is almost completely 
 established, whereas at a low temperature, such as 300 C., 
 although the equilibrium value is some 52 % at 100 atmo- 
 spheres, the reaction velocity is so low that practically no 
 ammonia formation takes place. This example is typical 
 of the phenomena occurring in heterogeneous catalytic 
 reactions. 
 
 Another important point in the control of heterogeneous 
 catalytic gas reactions is the relation between the velocity 
 A. 2 
 
i8 INDUSTRIAL GASES 
 
 of passage of the reacting gases over the catalyst, the rate 
 of formation of the product, and the volume occupied by 
 the catalyst. It will be found convenient to denote the 
 ratio of gas velocity per hour to the gross catalyst volume 
 by " space- velocity," and the ratio of the production per 
 hour to the gross catalyst volume by " space- time-yield." 
 Using these terms we find that as the space- velocity is 
 increased there is often a steady increase in the space- time- 
 yield, although the approach to equilibrium in the reaction 
 products falls off. Thus, taking again the case of ammonia, 
 as the space- velocity is increased the percentage of ammonia 
 falls off but the production per unit time increases (cf . p. 215) . 
 This is important as the output of a plant is thereby 
 raised, although this, of course, is not the only practical 
 consideration. 
 
 For a proper understanding of these phenomena it will 
 be necessary to examine the facts a little more closely, and 
 to study the progress of such reactions with time. In an 
 investigation of the catalytic reaction 
 
 2SO 2 + O 2 = 2SO 3 
 
 Bodenstein and Fink (Z. physik. Chem., 60, (1907), i, 45) 
 found that the rate of reaction was practically independent 
 of the concentration of oxygen, was proportional to the 
 concentration of the sulphur dioxide and inversely propor- 
 tional to the square root of the concentration of the sulphur 
 trioxide 
 
 dx , (a x) 
 
 lit ~ x* 
 
 where a is the initial concentration of the sulphur dioxide 
 and x is the concentration of the sulphur trioxide, i.e. we 
 have a modified monomolecular reaction, whereas, according 
 to the laws governing homogeneous reactions, it should be 
 ter molecular. 
 
 This behaviour was explained by Bodenstein on the so- 
 called "diffusion theory," which supposes reaction on the 
 surface of the catalyst to be extremely rapid but that access 
 of the reactants thereto can only occur by diffusion through 
 
INTRODUCTION 19 
 
 an adsorbed film of the reaction product in this case' sulphur 
 trioxide. The rate of reaction, therefore, is dependent on 
 the rate of diffusion of the component with the lower coefficient 
 of diffusion, namely, sulphur dioxide, unless a sufficient 
 excess of this gas be present when the rate of diffusion of 
 the oxygen begins to play an appreciable part. In dealing 
 with such reactions it is difficult to formulate any general 
 rules as to the reaction kinetics ; thus, in the reaction 
 
 2CO + O 2 = 2CO 2 
 
 Bodenstein and Ohlmer (Z. physik. Chem., 53, (1905), 166) 
 found that the rate of reaction was, roughly, inversely pro- 
 portional to the concentration of t ne carbon monoxide, a 
 case of negative catalysis. 
 
 In the case of the catalytic combination of the con- 
 stituents of electrolytic gas, Bone and Wheeler (Phil. Trans., 
 A, 206, (1906), i) found 
 
 where C OH ^ and C/ H are the concentrations of hydrogen at 
 the beginning and at time t respectively ; this observation is 
 not in accordance with the requirements of the diffusion 
 theory, which demands that the rate should be proportional 
 to some function of the oxygen concentration, this being 
 the gas of slower rate of diffusion. 
 
 Taking again the example of ammonia synthesis, a mental 
 picture of the effect of velocity of passage of the gases over 
 the catalyst may be formed as follows : imagine the speed 
 of passage to be suddenly increased ; if we assume the 
 rate of diffusion of the reactants through the ammonia 
 film to remain constant momentarily, the rate of production 
 will be unaltered and the percentage of ammonia in the 
 gases will fall off. The thickness of the film, being a function 
 of the concentration of the ammonia, will now diminish as 
 a result and thus permit the production to rise. The 
 degree of turbulence of the gas current will exert a certain 
 influence by its effect in reducing " pocketing " and conse- 
 quent local formation of thick ammonia films. 
 
20 INDUSTRIAL GASES 
 
 Similar considerations apply to any reaction in which 
 a solid catalyst is used to promote the combination of 
 gaseous substances ; in some cases the point of importance 
 is not the hourly quantity of the resulting product or products, 
 but the closeness with which equilibrium is approached, e.g. 
 in the B.A.M.A.G. continuous catalytic hydrogen process 
 (cf. p. 159) the elimination of carbon monoxide is the most 
 important consideration, being balanced by the desirability 
 of treating a given volume of gas in the least possible 
 catalyst space. 
 
 In catalytic operations the question of catalyst surface 
 is of great importance, the output of a given gross volume 
 being enhanced by the increase of the surface of the catalyst, 
 e.g. by subdivision of the catalyst mass, although the 
 increased resistance set up thereby makes a compromise 
 necessary. Calvert, in B.P. 10612/12, suggests increasing 
 the rate of catalysis by whirling the catalyst inside a closed 
 vessel traversed by the gas current, also Walter, in D.R.P. 
 295507/17, proposes to agitate the catalyst grains by 
 magnetic means. In each case the gain in output is secured 
 without the usual disadvantage of increased dilution, or, 
 conversely, a close approximation to equilibrium is facilitated 
 without the necessity for such slow passage of the gases. 
 The application of such ideas, however, is not very easy in 
 practice, and in the case of the magnetic agitation, the mutual 
 attrition of the catalyst grains would be prejudicial. 
 
 In the patent literature relating to catalysis considerable 
 attention has been paid to the question of electrostatic 
 activation of catalysts, but nothing of practical importance 
 would appear to have been evolved in this direction. 
 
 Viscosity of Gases Stream-Line and Turbulent 
 Motion. When a gas (or other fluid) flows through a 
 conduit under certain conditions see below the gas moves 
 at a higher velocity in the centre than in the layers nearer 
 the walls, while the layer contiguous to the walls is 
 stationary. 
 
 Viscosity is defined as the tangential force exerted per 
 unit area between two layers in the fluid i cm. apart, 
 
INTRODUCTION 21 
 
 when the difference in velocity is i cm. /sec. for flow 
 through a tube, the viscosity (p,) is given approximately 
 by the expression 
 
 where p = the pressure drop in dynes/cm. 2 , 
 r = radius of tube in cms., 
 t time in seconds required for the passage of V c.c. 
 
 of fluid (measured at the mean pressure), 
 / = length of the tube in cms. 
 
 The viscosity of gases increases considerably with rise 
 in temperature, cf. Table 12 (c). 
 
 An interesting fact is that the viscosity of gases is approxi- 
 mately independent of the pressure, i.e. the volume of gas 
 at, say, 200 atmospheres pressure, flowing through a given 
 tube with a certain pressure drop will be approximately the 
 same per unit of time as that observed for an equal pressure 
 drop with gas at atmospheric pressure ; the weight of gas, 
 however, will be some 200 times as great. 
 
 The above observations hold only for stream-line motion 
 through conduits, i.e. in the complete absence of turbulence. 
 When a fluid passes through a straight smooth circular 
 tube, the motion remains of the stream-line type until a 
 certain definite velocity known as the critical velocity is 
 reached, when turbulence sets in abruptly and increases 
 steadily in degree as the velocity is further increased. The 
 pressure drop increases sharply with the inception of turbu- 
 lence and is no longer defined by the expression just given, 
 being now determined by the surface friction. 
 
 The critical velocity is given by the following expression 
 
 25001* 
 
 v c = J 7 r cm. /sec. 
 dp 
 
 where ju, = the viscosity of the fluid in C.G.S. units, 
 d =3 diameter of the tube in cms., 
 p = the density of the fluid in grams/cm. 3 , 
 v c = the critical velocity (mean linear velocity) in 
 cm. /sec., 
 
22 INDUSTRIAL GASES 
 
 i.e. v c is directly proportional to the viscosity of the fluid 
 and inversely proportional to the diameter of the tube and 
 to the density of the fluid. This applies generally to all 
 fluids (cf. Stan ton and Pannell, Phil. Trans., A., 214, (1914), 
 199). 
 
 In some cases it may be more convenient to express 
 partly in terms of British units, thus 
 
 2000/A ,. . 
 
 v c = -f- ft. /sec. 
 
 pa 
 
 or Q c = 40,000 ^ ft. 3 /hr. 
 
 P 
 
 where v c = critical velocity (mean linear velocity) in ft./sec., 
 ft => viscosity in C.G.vS. units, 
 p density of the fluid in lbs./ft. 3 , 
 d = diameter of the tube in inches, 
 Q c = the minimum gas flow, measured at the tem- 
 perature and pressure used, at which turbulent 
 motion obtains, in ft. 3 /hr. 
 
 It must not be imagined that the flow in a given conduit 
 is necessarily stream-line motion because the velocity is 
 below that given in the above formula ; unstable turbulence 
 may be set up by local irregularities, bends, etc. The 
 turbulence will die away, however, if sufficient time be 
 allowed and the re-establishment of stream-line motion may 
 be accelerated by the insertion in the stream of a series of 
 perforated grids. 
 
 Resistance to Flow of Gases. In technical gas 
 manufacture and usage, the calculation of the pressure 
 drop in a given pipe-line is an important point, the resistance 
 to flow often constituting the source of a considerable power 
 expenditure. The following formula gives fairly good 
 results for turbulent motion in smooth, straight, circular 
 pipes (cf. Newbiggin's "Handbook for Gas Engineers and 
 Manufacturers " : Condon, 1913, p. 276) : 
 
 dp =--&%- -Ibs./in.* 
 ^ II X I0 6 X rf 5 ' 
 
INTRODUCTION 
 
 where Q = ft. 3 /hr. of gas, measured at the temperature and 
 pressure in question, passing through the tube, 
 p = density of the gas in lbs./ft. 3 
 Iv = length of the tube in feet, 
 d = diameter in inches. 
 
 The formula assumes that the pressure drop is propor- 
 tional to the square of the linear velocity, which assumption 
 is not strictly correct especially as no account is taken of the 
 state of turbulence or otherwise of the fluid. Thus, with 
 stream-line motion the pressure drop is proportional to the 
 first power of the linear velocity. A more exact treatment 
 is furnished by an experimental investigation by Stanton 
 and Pannell (loc. cit.) giving rise to a general curve which 
 connects 
 
 R ., 2Vrp i 2Qp 
 
 -vj-v I _ - 1 s^r* ***** 
 
 
 (Fig. 3) 
 
 0-007 
 0-006 
 0-005 
 0-004 
 
 & 
 
 0-003 
 0002 
 0-001 
 
 \ 
 
 
 
 
 
 \ r 
 
 ^ 
 
 
 
 
 \! 
 
 
 
 
 
 
 
 \^ 
 
 
 
 
 _1^_ 
 
 
 ^^ 
 
 - 
 
 
 
 
 
 
 3-Q 
 
 5-5 
 
 4-0 
 
 4-5 
 
 5-0 
 
 5-5 
 
 FIG. 3. Stanton and Pannell's Surface Friction Determinations. 
 
 and covers the whole range, including the transition from 
 stream-line to turbulent motion, and, moreover, is applicable 
 to all fluids, whether liquid or gaseous. 
 
 R => resistance per unit area of the internal surface of 
 
 the circular tube, 
 p = density of the fluid, 
 
24 INDUSTRIAL GASES 
 
 V = mean linear velocity, 
 
 r =j radius of tube, 
 
 /z = viscosity of the fluid, 
 all in absolute units. 
 
 The pressure drop in a given circular tube is given by 
 the expression 
 
 , . 2/oQ 2 /C - 2pQ 2 /C 
 
 dp = r ~ 6 dynes/cm. 2 = approximately g 2 6 atms. 
 
 where p = density of the fluid in grams/cm. 3 
 Q =3 flow through the tube in cm. 3 /sec. 
 V =i mean linear velocity of the fluid in cm./sec. 
 / = length of tube in cms. 
 r = radius of tube in cms. 
 C R/pV 2 as read off from the curve (Fig. 3). 
 p viscosity of the fluid in C.G.S. units. 
 
 The above observations apply only to smooth and straight 
 circular conduits. The effect of abrupt bends, valves, local 
 constrictions, and also of enlargements in the section of the 
 pipe is to introduce large effects which may be equivalent to 
 many feet of the plain conduit, and often constitute the 
 most important cause of pressure drop in technical opera- 
 tions. The theoretical treatment of such effects is a difficult 
 matter, although certain rough empirical generations can 
 be deduced from experience. 
 
 A good opportunity of testing the validity of a general 
 formula, such as that of Stanton and Pannell, is afforded by 
 application to the little investigated question of the loss of 
 head in the flow of high-pressure gases through tubes ; in 
 the experience of the author, this formula gives valuable 
 indications of the resistance under these conditions. 
 
 Influence of Difference in Level. When making 
 allowances for the drop in pressure due to dynamic effects, 
 due consideration should be given to the static head if any 
 considerable difference in level occurs, especially with very 
 light or heavy gases. 
 
 Consider a pipe, open at one end and filled with a gas of 
 
INTRODUCTION 25 
 
 density pi, while that of the surrounding medium* e.g. air, 
 
 Then, in absolute units, the pressure difference due to 
 the difference in weight of the gases 
 
 = hg (Pi P2> dynes, 
 
 where h = the vertical difference in height in cms., 
 and g =3 the gravitational constant in C.G.S. units, 
 = h (p 1 p 2 ) grams. 
 
 Expressing h in ft., and p x , p 2 in lbs./ft. 3 , and taking 
 the case of a difference in level equal to 100 ft., with hydrogen 
 in the pipe, at 15 C., we have 
 
 pressure difference = -^(5 : 32-76'49) lbs /ft 2 
 
 1000 
 
 = 7-117 lbs./ft. 2 
 = 0-494 lbs./in. 2 
 = 13*7 inches of water. 
 
 Physical Methods of Testing the Purity of Gases. - 
 
 In special cases it is advisable to be able to determine the 
 quantity of some specific impurity present in a particular 
 gas, by physical means, either from reasons of speed or for 
 purposes of automatic recording. Among such methods 
 may be mentioned the following : 
 
 Gas Interferometer. This instrument was worked out by 
 Haber and Iy6we (Z. angew. Chem., (1910), 1393). Its action 
 depends on the formation of interference fringes by two 
 columns of gases, one containing the impurity to be deter- 
 mined, e.g. carbon dioxide in air, and the other free from this 
 impurity. The apparatus can be made extremely sensitive 
 but is somewhat cumbersome and does not lend itself readily 
 to the production of mechanical records. For technical 
 adaptations, cf. "U.S. Bureau of Mines," Tech. Paper, 
 No. 185 (1918), by Siebert and Harpster. 
 
 Density. The density of a gas is often a good guide to 
 its purity, particularly in the case of hydrogen, and a 
 convenient apparatus for indicating the same is the " gas 
 balance," which consists of a balance beam, one arm of which 
 
26 INDUSTRIAL GASES 
 
 carries a ball supplied with a continuous current of gas 
 by means of mercury cups near the fulcrum of the beam, 
 while the other carries a pointer. The balance is brought 
 into equilibrium by means of riders. 
 
 Effusion. The purity of a gas, e.g. the percentage purity 
 of hydrogen containing small quantities of nitrogen, oxygen, 
 carbon monoxide, etc., may also be ascertained by the rate 
 of effusion through a fixed small aperture. For this purpose 
 an inverted glass cylinder, immersed in a cylinder containing 
 water, or a small water-sealed metal gasholder provided with 
 a balance weight (this form being made by Messrs. Wright 
 & Co.), is filled to a fixed mark with the gas in question, 
 and the time required for the gas to flow out through a fine 
 orifice in a piece of platinum foil, i.e. the time for the cylinder 
 or bell to fall to another fixed mark, is noted. A comparison 
 with a standard gas, e.g. air, or preferably a sample of the 
 pure gas, say hydrogen, if this be the gas under examination, 
 gives the density on the basis 
 
 p oc t 2 
 
 where p = the density of the gas, 
 t = the time of outflow. 
 
 Determinations with this apparatus occupy only a few 
 minutes ; the results, of course, are not of a high degree of 
 accuracy. 
 
 Acoustical Methods. A method was worked out by Haber 
 and L,eiser (J. Soc. Chem. Ind., (1914), 54) for the detection 
 of methane in mine gases, depending on the difference in 
 sound produced by two whistle tubes filled with pure air 
 and mine air respectively, but separated by means of thin 
 mica plates from the actual whistles, both of which are 
 operated by the mine air. 
 
 Separation of Gaseous Mixtures. Special cases of 
 separation will be dealt with in particular instances, e.g. 
 the separation of air into its various constituents, but a 
 short jforecast here of the possible methods will be useful. 
 It is interesting to note that a certain irreducible amount 
 of work must be expended on a gaseous mixture to separate 
 
INTRODUCTION 27 
 
 it into its components, equal to the work of fsothermal 
 compression of each constituent from its original partial 
 pressure to atmospheric pressure or whatever the final 
 pressure may be; cf. p. 80. 
 
 Among the various methods of separation, the following 
 are the most important : 
 
 (1) Chemical methods': 
 
 (2) By liquefaction of one of the constituents. 
 
 (3) By fractional solution in water or other medium. 
 
 (4) By fractional diffusion through platinum or porous 
 
 earthenware, etc. 
 
 (5) By centrifugal action. 
 
 It may be noted that (i) and (2), and in some cases (3), 
 are the only methods which have any technical importance. 
 
 Separation of Liquid or Solid Particles from Gases. 
 In the technical manipulation of gases it is frequently 
 necessary to free a gas from some suspended liquid or solid 
 impurity, e.g. in the manufacture of coal gas, the separation 
 of the " tar fog " is a matter of considerable difficulty, 
 while in the concentration of sulphuric acid in Gaillard 
 towers, the exit gases are liable to contain sulphuric acid in 
 suspension. Without entering into details it will be useful 
 to indicate the methods used in practice for the elimination 
 of liquid or solid particles from gases. 
 
 This object may be achieved by direct filtration through 
 sawdust, or by wetted gauze. A method frequently adopted 
 for the separation of suspended matter present in considerable 
 quantity, e.g. in the manufacture of white arsenic, is to subject 
 the gases to centrifugal force by causing them to traverse a 
 circular path or by means of a special fan ; this throws out 
 the bulk of the dust, the centrifugal separation being usually 
 followed by bag filtration. The centrifugal separation in 
 the fan is sometimes assisted by the injection of water. 
 
 Other methods depend on the use of gas velocities 
 sufficiently low to allow precipitation of heavy dusts to 
 occur, while considerable success has attended the use of 
 abrupt changes in direction by means of baffles, the action 
 being parallel to that occurring with centrifugalization. 
 
28 INDUSTRIAL GASES 
 
 In the case of " tar fog " and the like, passage through a 
 number of small orifices or slits, followed by scrubbing with 
 liquids, is often adopted. 
 
 Another mode of attack is to precipitate the dust by 
 the formation of a mist on producing a condition of super- 
 saturation in the gas, e.g. in the removal of dust from the 
 gases leaving mechanical pyrites burners by addition of 
 steam and sulphur trioxide, the resulting mist being subse- 
 quently removed by electrostatic precipitation or by other 
 means (Holler, D.R.P. 270757/12).* 
 
 The most searching method, however, is that depending 
 on electrostatic action, rendered practical by Cottrell, and 
 at the present time attracting considerable attention. On 
 passing a dust-laden gas in proximity to two highly charged 
 electrodes, the gas is ionized and the particles becoming 
 charged move in the direction of the electrode of opposite 
 charge. If one electrode is pointed the particles tend to 
 become charged with the polarity of this electrode and, 
 consequently, to move to the other electrode. 
 
 The usual method of operating is to pass the gases with 
 linear velocity not exceeding about 12 ft./sec. through metal 
 tubes of, say, about i ft. in diameter, enclosing axially 
 disposed wires, a unidirectional potential difference of from 
 25,000 to 250,000 volts being applied. The dust is deposited 
 on the tubes and periodically dislodged by interrupting the 
 gas current and the electrical supply and by jarring the tubes. 
 
 The process is largely used in the removal of dust from 
 the gases leaving pyrites burners ; for the precipitation of 
 cement dust, which contains valuable quantities of potash ; 
 for the precipitation of white arsenic, avoiding the handling 
 necessary in " bag-houses " ; in treating the effluents of 
 Gaillard towers, etc. Some trouble is experienced in the 
 presence of solids and liquids in conjunction. The uni- 
 directional current is best obtained by means of a rotating 
 commutator, operated in synchronism with a high tension 
 
 * An ingenious proposal is made by Mond in B.P. 112153/16, to effect 
 the removal of constituents from gaseous mixtures by first injecting a 
 suspension of some solid which combines with or absorbs the constituent 
 in question and subsequently separating the dust by suitable means. 
 
INTRODUCTION 
 
 29 
 
 transformer; the power consumption is of the 'order of 
 from 1-8 K.W.H. per million ft. 3 of gas treated (cf. Bush, 
 /. Soc. Chem. Ind., (1918), 38911). The process is applicable 
 to gases at fairly high temperatures ; it is important to 
 avoid conditions leading to the condensation of moisture. 
 
 Methods of Measuring Volumes and Rates of Flow 
 of Gases.- One of the most convenient methods of measuring 
 the volumes or rates of flow of gases through a given conduit, 
 when the quantities are not too large, is that depending on 
 the use of the familiar rotary (wet) meter or the reciprocat- 
 ing (dry) meter. The former consists of a series of inverted 
 buckets, mounted on a wheel with a horizontal spindle, and 
 immersed in a tank of water, the wheel revolving at a rate 
 proportional to the volume of gas entering the buckets. 
 Such meters are constructed in sizes up to about 150,000 
 ft. 3 /hr. They are very sensitive to the level of the water 
 and calibration at frequent intervals is important when 
 using for accurate laboratory work. If accuracy be required, 
 it is necessary to allow for the volume of water vapour 
 present, the effect of saturating the gas with water vapour 
 at 15 C. being to increase the volume by 17 %. Rotary 
 meters of the anemometer type are convenient when dealing 
 with large gas flows, especially as very little pressure drop is 
 introduced. Meters capable of measuring the volume of 
 the gas at pressures greater than atmospheric, e.g. "high- 
 pressure " coal gas, natural gas, etc., are also constructed. 
 
 In many technical operations, however, one has to deal 
 with very large currents of gases, e.g. in chimneys, or it may 
 be desirable to measure or to record continuously the rate 
 of flow in a given conduit of large diameter ; in such cases 
 it is necessary to make use of some kind of flow-meter. 
 The measurement for relatively small conduits may be 
 effected by the use of an " orifice meter," which consists of 
 a perforated diaphragm introduced into the conduit and 
 depends on observation, usually by means of a U-tube 
 containing a suitable liquid, of the pressure drop caused by 
 the constriction. The pressure drop varies roughly as the 
 square of the gas flow and is rather sensitive to temperature 
 
30 INDUSTRIAL GASES 
 
 variations. The Ventuii meter employs, instead of a 
 simple orifice, a stream-line constriction. The increase in 
 velocity gives rise to a fall in pressure in the constriction, 
 but to only a very slight difference across the same ; the fall 
 in pressure varies roughly as the square of the gas flow. 
 
 When the size of the conduit becomes great, say more 
 than i ft. in diameter, the use of an orifice meter is in- 
 convenient, especially as it introduces into the system a 
 pressure drop which may involve the expenditure of con- 
 siderable amounts of energy. In such cases it is possible 
 to employ an anemometer, i.e. a series of vanes with a 
 train of recording dials, or to measure the " drag " on a 
 bucket or plate suspended in the path of the stream, or, 
 more commonly, use is made of a Pitot tube, of which the 
 indications are more easily converted into velocity figures ; 
 if made of glass, it is unaffected by corrosive gases or vapours. 
 
 This apparatus consists of tubes arranged as in Fig. 4 
 (cf. Pannell, Engineering, (1919), 261). The side openings 
 (3 rows of 7 holes 0-04" diameter) are under the static 
 pressure existing in the conduit, while the central tube has, 
 in addition, the dynamic head due to the local arrestment 
 of the current ; consequently, by connecting the ends A and B 
 to a suitable manometer, a pressure difference is registered 
 which is connected with the linear velocity of the current 
 
 as follows : / - 
 
 v = v 2gh 
 
 where v = the linear velocity at the point of the Pitot tube, 
 
 in cm. /sec., 
 
 g = 0,81 cm./sec. 2 (the gravitational constant), 
 h => the height of the gas column equivalent to the 
 
 head of liquid in the manometer. 
 
 If the indicating liquid be water and the moving gas be 
 air, both at 15 C., the expression becomes 
 
 x 
 
 G'001226 
 
 = I264'5'\/A' cm./sec. 
 where h' is the head of water in cm. 
 
INTRODUCTION 
 
 Converting into the more practical units of ft./sec. and 
 inches of water, we have 
 
 t ._ 1264-5 V*"X 2-54 f 
 
 12 X 2'54 
 
 = 66-1 VF' ft./sec. 
 
 where u => the linear velocity in ft.-sec. 
 h" => the head of wafer in inches. 
 
 I* 
 
 -0-307 
 
 FIG. 4. Pitfit Tube. 
 
 Thus, a linear velocity of 20 ft./sec. of air at 15 C. would 
 give a head of water equal to 
 
 20 
 
 . 
 
 m. -0-092 in. 
 
 It is easy to see how corrections for density, temperature 
 and pressure of the gas, or for density of the indicating 
 liquid must be applied. In any case the readings do not 
 give the mean linear velocity in the conduit as the velocity 
 
32 INDUSTRIAL GASES 
 
 varies from point to point, being greatest at the centre and 
 zero at the walls. With stream-line motion the mean 
 linear velocity is about 0-5 that of the axial velocity ; at 
 the critical velocity the ratio increases sharply to a value in 
 the neighbourhood of 0'8 (cf. Stanton and Pannell, loc. cit.). 
 
 The Pitot tube has many disadvantages : it involves 
 the use of a delicate manometer, i.e. a tilting gauge in which 
 a differential brine (S.G., i'o6) and castor-oil combination 
 is often used instead of water for the measurement of the 
 very small pressure difference (cf. Stanton, Proc. Inst. Civil 
 Eng., Civ VI., (1904), 78), the readings being unsuitable for 
 observation by a workman. 
 
 Recently, considerable attention has been directed, 
 therefore, to the question of " hot-wire anemometry." A 
 general description by Thomas of the relative advantages 
 of this system of measurement will be found in /. Soc. 
 Chem. Ind., (1918), i65T. A thin wire, preferably of plati- 
 num, about 0*003 in. in diameter, is mounted either in the 
 centre or at some other point in the conduit at which the 
 relation of the actual to the average linear velocity is known. 
 The wire, heated electrically, preferably to about 200 C., 
 forms one arm of a Wheatstone bridge and the temperature 
 fall produced by the gas current may be determined by 
 measurement of the resistance which, of course, decreases 
 with fall in temperature. 
 
 Calibration may be effected by checking against measure- 
 ments obtained by other means or by calculation (cf . Morris, 
 Engineering, (1912), 892). The expression for the heating 
 energy (co) for a particular temperature is Ceo = \/v -+- k, 
 where v linear velocity and C and k are constants. Small 
 changes in the pressure or temperature of the gas have no 
 appreciable influence on the results if these be expressed 
 in terms of mass of gas, not of actual linear velocity. The 
 measurements are easily taken by a workman and can be 
 recorded automatically, if desired. 
 
 Since the indications of the apparatus are considerably 
 affected by turbulence of the gas under examination, it is 
 desirable that the hot wire should be removed from proximity 
 
INTRODUCTION 33 
 
 to any bends or valves which often introduce o'r modify 
 existing turbulence in a marked degree. 
 
 When gases which are decomposed by even gentle 
 heating in contact with a heated metal surface, e.g. coal 
 gas, are to be dealt with, the platinum wire may be coated 
 with glass which, although it introduces a lag, does not 
 affect the validity of the relation between the resistance 
 of the wire and the gas velocity. By using two wires 
 disposed transversely in the stream, one close behind the 
 other, the direction of motion can be followed, as the down- 
 stream wire is partly shielded from cooling by being swept 
 by the heated gas leaving the other. 
 
 Automatic Safety and Purity Tests. In the routine 
 control of technical gas reactions or treatments it is often 
 desirable to make automatic tests preferably capable of 
 giving continuous records of the percentage of specific 
 impurities at different points of the plant. A familiar 
 example of a recording gas analysis apparatus is the carbon 
 dioxide recorder, which is chiefly used as a check on the 
 combustion in boilers and the like. The most usual form, 
 e.g. the Sarco apparatus, depends on the automatic measure- 
 ment by the position of a small balanced gasholder, of a 
 sample of gas before and after exposure to caustic soda 
 solution. A filter pump or a stream of water is used to 
 provide the necessary power for sucking in and ejecting 
 the gases ; the result of each analysis is registered by a pen 
 attached to the little gasholder on a drum rotated by clock- 
 work, the intervals between successive analyses being about 
 five minutes. 
 
 In another form, a bi-meter recorder, made by the 
 Cambridge Scientific Instrument Co., a continuous stream 
 of gas is passed through two gas meters, between which is 
 interposed a lime or soda-lime absorber. The difference in 
 the readings gives the percentage of carbon dioxide. On 
 similar lines is the form of apparatus in which two orifice 
 gauges are used with soda-lime interposed (/. Gasbeleucht., 
 1914, 548). Other methods operate through the measure- 
 ment of the heat of absorption of carbon dioxide by alkalis. 
 A. 3 
 
34 INDUSTRIAL GASES 
 
 For the automatic detection or determination of either 
 oxygen or combustible gases in admixture with each other, 
 e.g. the oxygen content of electrolytic hydrogen or the 
 presence of methane in mine air, methods have been pro- 
 posed, depending on the measurement of the rise in tempera- 
 ture produced by catalytic combination in the presence 
 of platinum black or the like at the ordinary temperature, 
 by means of air thermometers or by the change in resistance 
 of wires coated with a catalyst (cf. lounge's " Gas Analysis," 
 1914). Hither method can be adapted to giving an alarm 
 automatically or to furnishing a continuous record. These 
 methods have some disadvantages, to overcome which 
 an apparatus has been devised by Greenwood and Zealley 
 (/. Soc. Chem. Ind., (1919), 87 T), depending on the automatic 
 measurement of the contraction resulting from the inter- 
 mittent heating of a platinum wire in the gas mixture. 
 
 Only a few examples have been given above, but they 
 are typical and will serve to indicate the general mode of 
 attack in special cases. 
 
 The Compression of Gases. This is a very important 
 consideration, since most of the gases prepared technically 
 are put on the market compressed to 120 atmospheres. 
 
 Work of compression. It will be well to consider the 
 principles determining the expenditure of energy required 
 to effect the compression of gases as this energy con- 
 stitutes an important item in the cost of the market- 
 able gas. 
 
 In the first place it may be stated that in technical 
 practice the compression approximates rather to adiabatic 
 than to isothermal compression although efforts are 
 made to minimize the increase in power involved thereby 
 by adding water, the vaporization of which reduces the 
 temperature rise, and by effecting the compression in a 
 number of stages, which, as explained later, operates in the 
 same direction. 
 
 Adiabatic compression. Consider a volume of gas v\ at 
 a pressure^ when the temperature (absolute) is Tj. 
 
 Assume this gas to be compressed in an adiathermic 
 
INTRODUCTION 35 
 
 
 cylinder to a pressure of p%, the volume falling to v% and 
 
 the temperature rising to T. 
 
 Now in this process the product pv y will remain constant, 
 where 
 
 equals the ratio of the specific heats at constant pressure 
 and constant volume respectively, or 
 
 where C is a constant. 
 
 The work of this adiabatic compression (Wj) equal 
 
 C 
 
 .dv = (v 1 l -v v 2 *~v) 
 i y v 
 
 Substituting C ^piV^ =*ptf)$ we have 
 
 v i 
 p. 
 
 w l 
 
 Rut 
 
 We have now compressed the gas to the required pressure, 
 but its temperature is 
 
 in accordance with the law for the effect of adiabatic com- 
 pression from pi to p%. 
 
 In order to reduce its temperature to T x , the initial 
 temperature, we will consider the walls of the cylinder to 
 become conducting. To prevent the pressure falling, it 
 will be necessary to follow up the contracting gas with the 
 
36 INDUSTRIAL GASES 
 
 piston, a further amount of work (W 2 ) being thus performed 
 on the gas. 
 
 The volume after cooling to TI will be - 
 
 Pi 
 
 *\ 
 
 assuming Boyle's I,aw to be valid. 
 
 Therefore, the volume before cooling, i.e. at T 2 , will be 
 
 Pi ?2 
 */jk -*F 
 
 P2 J-l 
 
 and the contraction 
 
 Since the pressure remains constant at p z , 
 
 Total work performed 
 
 y-i 
 Further 
 
 Therefore Wx + W 2 = 
 
 For practical purposes it will be convenient to express 
 p in atmospheres and v in ft. 3 , when the result will be in ft. 3 
 atms., i ft. 3 atm. * representing the work done in moving a 
 
 * i ft. 3 atm. = 28-317 x io 3 x 1-0132 x io ergs 
 
 = 2-8690 x io 10 ergs. 
 i K.W.H. = 3'6 x io 8 watt seconds 
 = 3-6 x io 6 x io 7 ergs 
 = 3-6 x io 13 ergs. 
 
 /. i K.W.H. = 3' 6 X IQl3 , ft. 3 atms. 
 
 2-8690 X IO' 
 
 = 1255 ft. 8 atms. 
 or i H.P.H. = 1255 x 0-746 ft. 3 atms. = 936 ft. 8 atms. 
 
INTRODUCTION 37 
 
 piston i ft. 2 in area through i ft. against ar pressure 
 difference of i atm. For further simplification, take p\=i 
 atm., and v l =iooo ft. 3 . Then 
 
 ~* 
 Wj+Wa^: \(^r) i> ft. 3 atms. 
 
 and for diatomic gases 
 
 , , ATT 1000 X i'4i(/^ 2 \ ' 29 ) ' 
 
 Wi+W 2 =i 3J(c?i if ft. 3 atms. 
 
 0-41 \\fij 5 
 
 IOOO X 1^ 
 
 As an example, let us take the compression of 1000 ft. 3 
 of air from i atm. to 201 atms., starting and finishing the 
 operation at the same temperature, e.g. 15 C. 
 
 Work then equals 
 
 t /orjT\' 2 9 "i 
 
 3-6 74 j(52) - i j H.P.H. = 13-4 H.P.H. 
 
 It is interesting to see the effect on the efficiency of 
 compressing in a number of stages, e.g. consider the operation 
 to be effected in three stages, the pressure in each phase 
 rising to 201* times (5*86 times) the starting pressure with 
 intermediate cooling to the initial temperature. Thus, 
 In the first stage the pressure rises from i to 5-86 atms. 
 
 second 5-86 34-3 
 
 third 34-3 201*0 
 
 It is obvious that the temperature rise in each stage 
 will be 
 
 Q'39 
 
 Consequently the work done in each case will be the same 
 and equal to 
 
 3-674 ( 5 -86' 2 9- i) H.P.H. =-2-462 H.P.H. 
 
38 INDUSTRIAL GASES 
 
 while the total work of compression will be 
 3 X 2-462 H.P.H. 7-386 H.P.H. 
 
 The general form of the expression for multi-stage 
 compression, where n = the number of stages, is 
 
 y I 
 
 or, per 1000 ft. 3 of a diatomic gas measured at i atm. 
 pressure 
 
 0*29 
 
 W=3'674{@" -ij H.P.H. 
 
 Isothermal compression. Consider a volume of gas v\ 
 at pressure pi to be compressed to p 2 . If the com- 
 pression be performed in such a way that the heat produced 
 escapes so rapidly that no increase in temperature occurs, 
 the work performed is given by the expression 
 
 W = 
 
 r 
 \ 
 
 J 
 
 .dv 
 
 v 
 
 * 
 
 assuming Boyle's L,aw throughout. 
 
 In this case the number of stages has no influence, and 
 taking again the case of 1000 ft. 3 of gas at i atm. pressure 
 to be raised to 201 atms. 
 
 W = 1000 log, aji ft. 3 atms. 
 = 5300 ft. 3 atms. 
 = WG- H.P.H. = 5-66 H.P.H. 
 
 In actual practice, with large multi-stage (35) com- 
 pressors, the overall efficiency allowing for friction losses, 
 etc., is some 80 % of that calculated as above for adiabatic 
 compression. 
 
INTRODUCTION 39 
 
 Thus, with three-stage compression, the power for the 
 compression of 1000 ft. 3 of air to 200 atmospheres would 
 be 
 
 JI p H B.H.P.H. 
 
 O'o 
 
 equivalent to 6*89 K.W.H. 
 
 Allowing for an efficiency of, say, 85 % in the electric 
 motor driving the compressor, the actual energy expenditure 
 would be 8-n K.W.H. 
 
 The power demanded in practice is found to vary from 
 about 12 to 8 K.W.H. per 1000 ft. 3 , according to the size 
 of the plant. 
 
 Notes on Compressed Gases Safety Precautions. 
 In dealing with compressed gases, due regard should be paid 
 to the question of the strength of materials and to the 
 correct engineering design of the containers and conduits 
 employed. In fact, an elementary knowledge of the methods 
 of calculating the factors of safety of the various parts of 
 the apparatus used, of the mechanical properties of the 
 steels and other materials used in the construction of high- 
 pressure plant, and of the influence of mechanical work and 
 heat treatment on the same may be said to be a sine qua 
 non. The material for the construction of the weldless 
 steel cylinders employed for the commercial transport of 
 compressed gases is legally defined in this country as steel 
 containing not more than 0*25 % carbon. For further 
 details, mechanical tests, etc., cf. Recommendations of the 
 Parliamentary Committee on the Manufacture of Compressed 
 Gas Cylinders, 1895. 
 
 When dealing with inflammable gases, it is very important 
 to make sure by analysis that oxygen is absent from the 
 gases undergoing compression, or at any rate is present 
 only in small quantities well below the limit of inflamma- 
 bility, since the momentary temperature rise on the com- 
 pression stroke is often sufficient to cause explosion ; similarly, 
 it is important that the compressor should be specially 
 designed for use with inflammable gases, i.e. it should be 
 
40 'INDUSTRIAL GASES 
 
 of the enclosed type not open, as in the ordinary Whitehead 
 " liquid air " compressor, for example. 
 
 The limits between which explosion is possible are given 
 below for a number of gases. The values are for atmo- 
 spheric pressure. 
 
 TABLE 5. 
 EXPLOSIVE LIMITS. 
 
 Gas. 
 
 Minimum % air in gas 
 for explosion. 
 
 Minimum % gas in 
 air for explosion. 
 
 Hydrogen . . 
 
 
 
 2 5 -8* 
 
 0* 
 
 Carbon monoxide . 
 
 
 
 2 5 -8* 
 
 12-5* 
 
 Methane 
 
 . 
 
 
 84-6* 
 
 5-3* 
 
 Coal gas 
 
 . . 
 
 
 79 t 
 
 7t 
 
 Blast furnace gas . 
 
 . f 
 
 
 35 t 
 
 36 t 
 
 Water gas (Bunte, 1901) . . 
 
 
 33'25 
 
 12-4 
 
 With electrolytic gas which may contain oxygen un- 
 diluted by nitrogen the limits are considerably smaller 
 (cf . p . 202) . Increased pressure appears to have no noteworthy 
 effect on the limits of inflammability (cf . Burrell and Ganger, 
 loc. cit.) . Further investigations carried out by Burrell and 
 Robertson (Technical Paper, No. 121) with methane show 
 that reduction of pressure has the effect of narrowing the 
 explosive limits ; thus, no methane-air mixture will ignite 
 at pressures below 275 mm. On the other hand, the same 
 investigators found that in the case of methane the limits 
 were widened by increase of temperature ; the minimum 
 percentage of methane in air for inflammation is lowered 
 from 5*5 % at the ordinary temperature to 375-4 % at 500 C. 
 
 According to Terres and Plenz (J. Gasbeleucht., 57, 
 (1914), 990, 1001, 1016), in the case of mixtures of rrydrogen, 
 carbon monoxide and methane with air, the effect of in- 
 creased pressure is to narrow the explosive limits, especially 
 for carbon monoxide mixtures, the upper limit of methane 
 being an exception. Increase of temperature widens the 
 limits. 
 
 * Coward, Chem. Soc. Trans., (1914), 1859; Coward, Carpenter and 
 Payman, Ib., (1919), 27. 
 
 t Burrell and Gauger, Technical Paper, No. 150, Bureau of Mines, 
 U.S.A. 
 
INTRODUCTION 41 
 
 A propos of the danger of explosion from the possibility 
 of meeting with explosive mixtures in cylinders the following 
 precautions are desirable in the manipulation of compressed 
 gases : 
 
 (1) The avoidance of sudden opening of valves leading 
 to gauges, etc. By the adiabatic compression of the first 
 portion of gas, sudden opening of a valve may raise the 
 temperature to the ignition point and a similar effect may 
 be produced by friction in closing a valve, or by the presence 
 of finely divided iron, etc. 
 
 (2) Consistent analysis of the contents of cylinders 
 before exposing to conditions which might initiate an 
 explosion while still under high pressure, also if the con- 
 tents of several cylinders are to be mixed under high 
 pressure. 
 
 When compression of an inflammable gas is performed 
 the compressed gas should be tested for the presence of any 
 oxygen which may have been introduced accidentally 
 during the compression. 
 
 In order to avoid any confusion and to guard against the 
 possibility of such disastrous mistakes as the filling up with 
 oxygen of a cylinder partly filled with an inflammable gas, 
 or vice versa, rigid rules are observed by all filling works 
 that each cylinder shall be emptied before recharging and 
 that all cylinders containing inflammable gases shall be 
 fitted with left-handed screw connections ; oxygen, air, 
 nitrogen, etc., are carried in cylinders with right-handed 
 connections. Further, the cylinders are painted distinctive 
 colours : thus, hydrogen is contained in red cylinders, oxygen 
 in black, and nitrogen or air in grey cylinders. To guard 
 against the possibility of deposits from coal gas and the like, 
 cylinders which have been fitted with left-handed valves 
 are always annealed before being fitted with right-handed 
 valves. All cylinders, of course, are annealed and re-tested 
 at regular intervals. 
 
 For a discussion of the results of carelessness in respect 
 of the above-mentioned precautions, cf. Wohler, Z. angew. 
 Chem., 30, (1917), 174. Manometers and the like should 
 
42 INDUSTRIAL GASES 
 
 be provided with gas checks, i.e. constrictions to minimize 
 the effect of sudden admission of gas. 
 
 (3) The insertion of explosion traps, e.g. tubes packed 
 with copper gauze or steel wool, may often be advisable in 
 cases where explosion is possible. 
 
 Oxygen is a dangerous gas to compress unless proper 
 precautions are taken, while manipulation of the compressed 
 gas requires care, as in the presence of oil, etc., an explosion 
 is easily initiated in various ways, as indicated above. All 
 oxygen pressure gauges and connections should be scrupu- 
 lously free from oil or other organic matter, and only water 
 can be used for the lubrication of the compressors (cf. 
 Rasch, Z. fur komp. u. fliissige Gase, (1904), 141). Acetylene, 
 being an endo thermic compound, is very dangerous to 
 compress by reason of its liability to detonate. 
 
 It has been observed in the rapid release of compressed 
 hydrogen that ignition occasionally occurs. The origin of 
 the phenomenon is somewhat uncertain; possible sources 
 a v re electrical sparks due to dust disturbed from the valve, 
 etc., or the catalytic or pyrophoric action of finely divided 
 iron oxide or metal present in the cylinder or valve passages. 
 
 A feature of compressed gases which should be borne 
 in mind is the almost complete dryness of a gas at, say, 
 100 atmospheres pressure. Thus, at 15 C. the percentage 
 of water vapour will be about 
 
 12*8 x 100 
 
 P per cent. = 0*017 per cent. 
 
 760 x ioo * 
 
 as compared with a possible ioo times this amount at the 
 ordinary pressure. 
 
 Cylinders of compressed gas should be kept in a cool 
 place as a rise in temperature of, say, 20 C. would raise the 
 pressure from the normal value of 120 atms. to some 128 atms, 
 
 Liquefied gases. Reference has been made to the necessity 
 of keeping cylinders of compressed gases cool ; much more 
 does this consideration apply to cylinders containing liquefied 
 gases, especially if the cylinders have been somewhat over- 
 charged with liquid. The following table, adapted from 
 
INTRODUCTION 
 
 43 
 
 Teichmann, Komprimierte und verflussigte Gase, 1908, shows 
 the way in which the sensitivity to warming varies with the 
 degree of filling. 
 
 The figures are based on Regnault's vapour-pressure 
 measurements (cf. Table 7). The "normal fillings" are 
 those given in the third column and are according to German 
 regulations. 
 
 TABLE 6. 
 
 RELATION BETWEEN DEGREE OF FILLING AND PRESSURE IN CYLINDERS 
 CONTAINING LIQUEFIED GASES. 
 
 Gas. 
 
 Volume of i kilo, of 
 liquid at 15 C. 
 
 Minimum cylinder 
 space per kilo, of 
 liquid (litres). 
 
 Absolute pressure (atms.) exerted at temperatures given (C.). 
 
 Normal filling. 
 
 5 % over-filling. 
 
 10 % over-filling. 
 
 
 
 10 
 
 20 
 
 3<> 
 
 40 
 
 o 
 
 10 
 
 20 
 
 30 
 
 40 
 
 o 
 
 10 
 
 20 
 
 30 
 
 40 
 
 Sulphur 
 dioxide 
 Carbon 
 dioxide 
 Nitrous 
 oxide 
 
 0-716 
 
 I'230 
 I'2O5 
 
 0-8 
 i'34 
 i'34 
 
 i'53 
 35'4 
 36-1 
 
 2-26 
 46*0 
 44'8 
 
 3*24 
 588 
 55'4 
 
 4*52 
 
 98-5 
 79-8 
 
 6*15 
 138 
 126 
 
 i'53 
 34'4 
 36-1 
 
 2*26 
 46*0 
 44'8 
 
 3'24 
 66'4 
 55'4 
 
 4' 52 
 no 
 
 99' 5 
 
 6-15 
 151 
 152 
 
 i'53 
 35'4 
 36-1 
 
 2'26 
 
 46 o 
 44-8 
 
 3-24 
 76-6 
 68-1 
 
 13 at 
 23-9 C. 
 
 I2O 
 I2O 
 
 162 
 177 
 
 The rises in pressure are greater than the vapour pressures 
 of the respective liquids at the temperatures in question, as 
 is seen from the following table : 
 
 TABLE 7. 
 VAPOUR PRESSURES OF LIQUEFIED GASES. 
 
 
 Absolute vapour pressure (atms.) at temperature given. 
 
 Gas. 
 
 oC. 
 
 10 C. 
 
 20 C. 
 
 30 C. 
 
 40 C. 
 
 
 Sulphur dioxide { 
 
 r52 
 l'$l 
 
 2*26 
 2'35 
 
 324 
 
 3'3 
 
 4'52 
 4-60 
 
 6-15 
 
 6'20 
 
 Regnault, 1862. 
 Pictet, 1885. 
 
 Carbon dioxide | 
 
 35'4 
 34'3 
 
 46*0 
 44-2 
 
 58-8 
 56-3 
 
 73'8 
 70-7 
 
 91*0 
 
 Regnault, 1862. 
 Amagat, 1892. 
 
 Nitrous oxide . . < 
 
 36-1 
 30-8 
 
 44-8 
 
 55'3 
 49*4 
 
 68-0 
 
 83-4 
 
 Regnault, 1862. 
 Villard, 1897. 
 
 Note. At 40 C. both carbon dioxide and nitrous oxide 
 are above their critical temperatures. The difference is 
 due to the bottle becoming filled with liquid, of course, and 
 
44 
 
 INDUSTRIAL GASES 
 
 the temperature at which this would occur at the above 
 cited degrees of filling is given in the following table 
 (Teichmann, loc. cit.) : 
 
 TABLE 8. 
 
 Gas. 
 
 Temperature (C.) at which completely full with 
 
 normal filling, 
 i.e. as in 
 column 3, 
 Table 6. 
 
 5 per cent, 
 over-filling. 
 
 10 per cent, 
 over-filling. 
 
 Sulphur dioxide 
 Carbon dioxide 
 Nitrous oxide 
 
 64-6 
 21*2 
 24'9 
 
 45'3 
 18-1 
 20-5 
 
 23-2 
 I 4 '2 
 I6'I 
 
 In the case of carbon dioxide, the question is discussed 
 very fully by Stewart (Trans. Amer. Soc. Mech. Eng., 30, 
 (1908), mi), according to whom the temperature at which 
 the cylinder becomes completely filled with liquid is connected 
 with the amount of the charge as follows : 
 
 TABLE 9. 
 
 Cylinder volume in litres per kilo. 
 
 
 
 
 
 carbon dioxide 
 
 1-8 
 
 r6 
 
 1*4 
 
 I'2 
 
 Temperature at which the cylinder 
 
 
 
 
 
 becomes full. C. 
 
 30-31 
 
 28-30 
 
 26 
 
 15-20 
 
 An allowance of about 1*6 litres/kilo, carbon dioxide 
 (or 39 lbs./ft. 3 ) is recommended by Stewart as a result of 
 his calculations and experiments. 
 
 As the cylinder becomes full of liquid the pressure rise 
 becomes much steeper, although the rate of increase is of 
 a different order from that obtaining with water, for example. 
 When the liquid gas is very near its critical temperature, 
 e.g. carbon dioxide, T c =3i'i C., the coefficient of expansion 
 becomes relatively very large, but the compressibility also 
 increases, causing the pressure curve to be less steep than 
 might have been expected. 
 
 In this country the recommendation of the Parliamentary 
 Committee on the Manufacture of Compressed Gas Cylinders, 
 
INTRODUCTION 
 
 45 
 
 1895, is that the charge of carbon dioxide shall not exceed 
 0*75 Ib. per Ib. of water capacity, while a figure of f Ib. is 
 given for tropical use, corresponding to 46*9 and 41*7 lbs./ft. 3 
 respectively ; for ammonia, 0*5 Ib. per Ib. of water capacity 
 is recommended as a maximum ; no specific recommendations 
 are made for sulphur dioxide and nitrous oxide. The 
 Committee recommends attest pressure of 224 atms. for the 
 cylinders in the case of carbon dioxide ; attention is drawn to 
 the regulations in force on the German railways, given below 
 
 TABLE 10. 
 GERMAN RAILWAY REGULATIONS FOR CYLINDERS OF LIQUEFIED GASES. 
 
 Gas. 
 
 Minimum cylinder 
 volume per kilo, 
 (litres). 
 
 Test pressure 
 (atms.). 
 
 Carbon dioxide 
 
 J< 34 
 
 250 
 
 Nitrous oxide 
 
 
 250 
 
 Ammonia 
 
 r86* 
 
 100 
 
 Chlorine 
 
 0-9 
 
 50 
 
 Sulphur dioxide 
 
 0-8 
 
 30 
 
 Phosgene 
 
 0-8 
 
 30 
 
 In the filling of cylinders with liquid gases the complete 
 exclusion of air is important, since the presence of a permanent 
 gas has a considerable effect on the pressure set up in the 
 cylinder. 
 
 When sampling liquefied gases the sample is best taken 
 with the cylinder in an inverted position, using a fine 
 regulation valve ; either liquid or gas can thus be withdrawn 
 without contamination with any air which may be present 
 in the space above the liquid ; compare, however, remarks 
 relating to nitrous oxide on pp. 289, 290. 
 
 Heat-Interchange. The cost of nearly all technical 
 operations depends on the fuel consumption which, in turn, 
 is determined by the operations of heating or cooling to 
 which the gases, or their parent substances or products, are 
 subjected. In almost all cases the final temperature is 
 the same as the initial temperature, i.e. that of the atmo- 
 sphere, and therefore, apart from heat usefully employed in 
 
 * 2'o litres/kilo, recommended by British Committee. 
 
46 INDUSTRIAL GASES 
 
 effecting endothermic reactions, the heat is theoretically 
 capable of regeneration. 
 
 It will therefore be well to examine now the factors 
 which influence the transfer of heat between gases and 
 gases (through a partition) or between gases and solids. 
 
 Suppose one to require a knowledge of the rate of transfer 
 of heat per unit surface per degree C. temperature difference 
 per unit of time over a very short length of tube, and also of 
 the relation between this quantity and the linear velocity of 
 a gas, initially at a temperature t lt passing through a metal 
 tube the outer surface of which is maintained at a lower 
 temperature, t 2 . 
 
 The rate of transfer does not depend, to any great 
 extent, on the thermal conductivity of the metal tube as 
 might at first be thought, the gas itself offering so much 
 resistance to heat flow that the resistance of the metal is 
 almost negligible in comparison. If the gas be flowing with 
 stream-line motion, the rate of transfer will be very low indeed, 
 since it can only occur by conduction from layer to layer of 
 the gas, and gases are very poor conductors of heat. 
 
 When, however, the critical velocity is exceeded, we 
 have an approach to temperature equilibration across the 
 bore of the pipe ; but, although very much better, the heat 
 transference still falls far short of that which is possible, 
 as far as the thermal conductivity of the walls is concerned. 
 This is due to a stagnant film of gas on the walls of the 
 conduit. The effect of increased linear velocity is to 
 decrease mechanically the thickness of this film with con- 
 sequent increase in the value of the heat transfer coefficient. 
 
 According to Porter (Trans. Institution of Engineers 
 and Shipbuilders in Scotland, Nov. 19, 1918), following 
 Osborne Reynolds, the coefficient of heat transfer from a 
 given fluid to the walls of the tube through which it is 
 flowing (or vice versa) for turbulent motion may be expressed 
 in general terms as follows : 
 
 K=MC/^Y >~ 2 
 
INTRODUCTION 47 
 
 where K => the coefficient of heat transfer, 
 
 C ==> the thermal conductivity of the fluid, 
 
 v = mean linear velocity of the fluid, 
 
 p = density of the fluid, 
 
 [j, =3 viscosity of the fluid, 
 
 d = diameter of the tube, 
 
 M =3 a constant, 
 all in absolute units. 
 
 Since a survey of experimental measurements indicates 
 that n may be taken as about i'75, the equation becomes 
 
 The main inferences to be drawn from this relation are 
 
 (1) The heat transfer coefficient will vary as the 0*75 
 power of the linear velocity. 
 
 (2) Except for stream-line motion, the thermal con- 
 ductivity of the fluid is not of itself the determining factor 
 as regards heat interchange ; thus, although hydrogen has 
 a high thermal conductivity as compared with air, its 
 density is relatively small, while the viscosit)^ is about half 
 that of air. The relative values are seen to be in the ratio 
 
 Kair CairVair [ 
 
 for turbulent motion, and equal values of v and d 
 
 ^41-65 x i o~ 5 /o -000089873 x I 73 x io 6 \' 75 
 3 5'67"X lo- 5 \ 0-0012928 X 86 X io~ 6 / 
 atoC. =1-68 
 
 (3) The coefficient of transmission will slowly fall off 
 as the diameter of the tube increases, thus, an increase in 
 diameter from i to 6 inches with otherwise unchanged 
 conditions of linear velocity, etc., results in the decrease in 
 the coefficient in the ratio of 
 
 In an investigation with water, Stanton (Phil. Trans., A, 
 (1897), 67) found the index of the power of d to be O'i6). 
 
48 INDUSTRIAL GASES 
 
 (4) The coefficient will increase rapidly with increase 
 in the pressure of the gas, since the density is approxi- 
 mately proportional to the pressure, while the viscosity and 
 thermal conductivity * are almost independent of pressure. 
 Thus one would expect the coefficient for a pressure of 100 
 atms. to be some ioi*=> 32 times that at atmospheric pressure 
 for equal linear velocity. 
 
 Further, since in regard to pressure variations 
 K oc ( V p)f oc (PV)* 
 
 where P = pressure and V = volume, it is evident that K 
 will be practically constant for all pressures, provided that 
 vp or PV is constant, i.e. provided that the quantity of gas 
 flowing through the conduit in unit time remains the same. 
 
 The above considerations apply equally to liquids ; 
 the values of the coefficient, however, are much higher, 
 namely of the order of several hundred times those observed 
 with gases at atmospheric pressure for equal linear velocity. 
 It will be found convenient to express the coefficient K in 
 terms of C.H.U./ft. 2 /hr./C. temperature differenced 
 
 There are three principal types of heat transfer, as regards 
 gases, to be considered 
 
 (1) Heat passes from a gas to a solid, or vice versa. Here 
 we need to consider the heat transfer coefficient for one 
 gas film only. 
 
 (2) Heat passes from a gas through a thin metal partition 
 to a liquid, or vice versa. In this case, let 
 
 k g =3 the coefficient of transfer between gas and metal for 
 
 the rate of flow obtaining, 
 k w => the coefficient of heat transfer between liquid and 
 
 metal for the rate of flow obtaining. 
 
 Then K = 
 
 neglecting the effect of the tube itself. 
 
 * The thermal conductivity of a gas may be expressed as r6o^C v , and, 
 since the viscosity and specific heats are not greatly affected by changes 
 of pressure, the thermal conductivity may be taken as approximately 
 constant 
 
INTRODUCTION 49 
 
 A little consideration will show that it is almost correct 
 to neglect k w and to take the coefficient of the gas alone, 
 this being the determining factor. An example of this type 
 of interchange is the cooling of air by passing over cold 
 brine pipes. 
 
 (3) Heat passes from one gas through a thin metal 
 partition to another gas. - 
 
 This is the state of affairs in the usual gas heat-inter- 
 changer, e.g. in the B.A.M.A.G. continuous catalytic process 
 for the production of hydrogen (p. 161). In such a case 
 the coefficient 
 
 will be of the order of half the value of k gi or k Sz if these 
 are fairly similar, i.e. if similar conditions of motion and 
 pressure obtain in both gas currents. 
 
 If, however, one gas be at a high pressure and the other 
 at atmospheric pressure, as, for example, in a liquid air 
 machine heat-interchanger, the conditions will resemble 
 those in case (2), the low pressure gas determining the 
 situation although the coefficient of heat exchange between 
 the compressed gas at, say, 100 atmospheres pressure, 
 and the metal is of the order of 30 times that obtaining in 
 the case of the low pressure gas for similar conditions of 
 motion. 
 
 A propos of the investigation of existing plant and the 
 design of new, it is important to note that the mean tem- 
 perature difference is not the mean of the initial and final 
 temperature differences, except in the case of a heat- 
 interchanger with counter-current flows of equal thermal 
 capacities, when the temperature gradient is constant. The 
 mean temperature gradient may be calculated for all cases 
 as follows : 
 
 A. 
 
50 INDUSTRIAL GASES. 
 
 where ^ = the temperature difference at one end of the heat 
 
 transfer process, 
 
 t 2 =i the temperature difference at the other end of the 
 heat transfer process. 
 
 Some values due to Josse are given by Hausbrand 
 (" Verdampfen, Kondensieren und Kiihlen," Berlin, Fiinfte 
 Auflage, 1912) for air at a pressure of 1*034 alms, traversing 
 a pipe 0*9 in. diameter, the outside of which was kept at 
 100 C. by steam. Since saturated steam gives a high 
 coefficient of heat transfer, the values may be taken as 
 applicable to a single air film. The values are adapted 
 from a smoothed curve. 
 
 TABLE ii. 
 HEAT- INTERCHANGE COEFFICIENTS FOR AIR (SINGLE FILM). 
 
 Mean linear velocity of air in ft. /sec. 
 K. in C.H.U./ft.*/hr./ C 
 
 1-6 
 
 2-9 
 
 20 
 
 30 
 6-8 
 
 8-5 
 
 50 
 9-9 
 
 60 
 n'2 
 
 The relation between K and the linear -velocity is 
 approximately that given on p. 47. 
 
 NOTE. The calculated critical velocity for this case is 
 about 5 ft. /sec. 
 
 Desiccation of Gases. It is often necessary to carry 
 out the operation of desiccation on large quantities of gas. 
 Thus, all the air which enters an air liquefaction plant must 
 be scrupulously dried and similarly with the gases for the 
 manufacture of hydrogen by the L,inde-Frank-Caro process 
 (cf. p. 172). In both cases, as will be described later, the 
 desired effect is best secured by refrigeration. 
 
 A less obvious example of need for desiccation is that 
 of the air supplied to blast furnaces, the reason lying in 
 the endothermic nature of the reaction between water 
 vapour and carbon. The water present in the air at 15 C., 
 if, say, 75 % saturated (vapour pressure of water at 15 C. 
 being 12 '8 mm.) 
 
INTRODUCTION 51 
 
 
 
 I2'8 X 075 X 100 
 ^ - ' - per cent. = 1*26 per cent. 
 
 by volume of the air, or 6*0 % of the oxygen present. 
 
 The heating effects, assuming combustion to carbon 
 monoxide only, are 
 
 H 2 O + C => CO + H 2 29-1 kilo, calories, 
 2 C + O 2 = 2CO + 58 kilo, calories. 
 
 Heating effect of 100 gram-molecules of oxygen => 5800 K. 
 Cooling ,, ,, 6 ,, water vapour 
 
 => 174*6 K. 
 
 But coke consumed is equivalent to 103 gram-molecules 
 of oxygen which would have given 5974 K. 
 
 Th r heat actually produced 5800 174*6 
 possible heat production ~ 5974 
 
 6253 a o /o 
 
 5974 
 
 So far we have considered only the number of heat 
 units produced from a given weight of coke without reference 
 to the efficiency of their utilization. In actual practice, 
 the economy effected is considerably greater than that 
 represented by the above comparison, amounting to a 
 saving of the order of 30 % of the fuel required per ton of 
 iron produced. The reason for this fact probably lies in 
 the greater ease of reduction due to the higher temperature 
 attained and possibly to the different equilibria established 
 in the furnace in the absence of water vapour, also in the 
 greater regularity of operation. 
 
 The most practical way of effecting the dehydration 
 (first carried out on the large scale by Gay ley (Trans. Amer. 
 Inst. of Mining Engineers, 35, (1904), 746 ; 36, (1905), 3*5) 
 in America, plants having been installed also in this country) 
 is to cool the air to a temperature of about 5 C. by means 
 of ammonia refrigeration machines. For the most economical 
 working, the bulk of the water is separated above o C. in 
 
52 INDUSTRIAL GASES 
 
 order to avoid the energy demanded by the absorption of 
 the latent heat of solidification. The vapour pressure at 
 5 C. is about 3 mm., i.e. the percentage of water vapour 
 left in the air, 
 
 0-395% by volume. 
 
 A heat-inter changer is used, of course, to minimize the power 
 expenditure. 
 
 An alternative method is to pass the air up a tower, 
 down which cooled, concentrated calcium chloride liquor 
 is sprayed ; the weakened liquor is re-concentrated, re- 
 frigerated and returned to the system (cf. Chem. Trade ]., 
 62, (1918), 113). Besides that of diminished fuel con- 
 sumption, the drying has further advantages, such as the 
 decreased air blast required and diminution in the dust 
 present in the exit gases ; but the high cost of the cooling 
 plant must be taken into consideration in computing the 
 economics of air desiccation. 
 
 The Storage of Gas. In most operations relating to 
 gases, it is necessary to store considerable quantities of gas 
 to serve as a balance against irregular operation of the gas- 
 producing plant, or variable demand, as in the case of coal 
 gas. In such cases it is usual to store the gas in holders 
 consisting of a bell or a series of bells rising and falling in a 
 water seal. Such gas holders have been constructed up to 
 a capacity of about 17 million ft. 3 . It is, however, sometimes 
 convenient to store gas at a pressure of about 20 atmospheres 
 in cylindrical vessels of about 3 in. diameter, while similar 
 vessels are used for railway transit. 
 
 Reference Data. In the following tables will be found 
 collected data which are useful in connection with technical 
 gas problems. The data for the table of physical constants 
 have been selected from the best modern determinations. 
 
INTRODUCTION 
 
 53 
 
 3 
 
 O H 
 
 OJ -g 
 
 ll 
 
 g^S 1 1 I 1 1 II S3 1 1 IS, 
 
 ^- t> CO CO M >OOO U">' 
 
 o oo o TJ- IN t>oo jo I I o *o u"i i ? *o\o 
 co M co c^ oo V 'N V oo coco noo co 
 
 MMHMON COM W 
 
 M 
 
 O^O O >OOO VO i I M OAOO M lO 
 
 O V '<* io co O >O ON O COWD N O N 
 
 t^CO ^S 10 ^ 1 ^^ ^H^M'* 
 
 CO 
 
 ts. 
 
 00 O ** N *O CO Tj-00 vO t^ 
 
 co b> b M M N M b 
 
 CO O O t^ 
 
 lOHOO O N OOOOONco 
 O O 00 O N O\ O O O O O O O O 
 
 o '"t- *o> b V b N N oo M cb Vj- Vf Vo 
 
 M H CO N COOO N Tt- N Tf VO Tj- M 
 
 'Sol : 
 
 B I; 
 
 ^M 
 
54 
 
 INDUSTRIAL GASES 
 
 PI 
 
 M 1 1 1 1 1 1 
 
 tO iO IO 1 1 1 1 1 1 
 
 O.'o d 
 
 <N 2 S 
 
 1 1? 2 +1 ' ' ' 
 
 Mir ^!! 
 
 ft 
 
 00 O CO ^ M O ON 
 
 1 T T 1 3f?7 ' 
 
 ^ IV 
 
 iO O vO I s * O 00 
 
 INN MM 
 1 1 1 1 1 1 1 
 
 i 
 
 Tf" M 
 | | 
 
 ON N - 10 P r* -* 
 M to ONOO M CO VO 
 
 *o 
 
 m 
 
 ^o^o | | | | 1 | 1 
 
 M O 
 
 I 1 i 1 1 1 1 
 
 ||| 
 
 *~~" iO .0 
 ON f "P <* ON .^ . N f ! 
 
 O O 
 1 O O ON tOO 
 
 sP 
 
 CO ON CO Jx INtNCOrfN 
 
 1 M Vf COCO K 'iO 
 
 "2 J 
 
 O O vO ^ 
 
 N t^M TJ-CO 00^ 
 
 Ifi 
 
 ^ H ^M V^vb'Mt^ 
 
 M M M M iMMOt^ 
 
 1 1 1 1 Q 1 1 * 
 
 <i 
 
 O H CO M lOCO N 
 O rf CO CO O COCO 
 
 TTT " ' 
 
 ypt 
 
 5 l",gHlli 
 
 CO M O -^ CO 
 ON O O O vO 'N M 
 N <* Tf CO N CO co 
 
 ipj 
 
 
 
 rt c -^ 
 
 lift 
 
 d d 
 
 iO o o vO 
 M O C00 O r- . , , . . 
 J>. O 00 vO O l> 
 
 M M M M O O ' 
 
 b ? b b V b 
 
 
 
 
 
 M 00 
 IO i O i i i 
 j 1-5 1-1 1 
 
 b b 
 
 *?* 
 
 JO Tj- 0. . IS , , , 
 
 o 
 
 i N ONVO O & M 
 
 1 &' 
 
 CO 00 t^ CO 1 N 1 1 
 
 M M M M IO 
 
 co i^'covb V <o 
 
 M M M N N N 
 
 jrg 
 
 ^ M | g I Si 1 I 
 
 cT <S N M 1 ON 1 1 1 
 
 i N N N ^f CO 
 N Tf O v~> M ON 
 1 ^ N W M N iO 
 
 #0, d 
 
 O O O O Tj- 
 
 CO O O O O O 
 
 
 
 
 
 
 ' '-s ; ' ' 
 
 . .1=81* . 
 
 o 
 
 d d 
 
 S & fl Sd2 a 
 to p j d.2 o Ag 
 
 .h! x' & ? S^ b.- 
 
 **< O ^5 "^J ^5 ffi ^ W ^ 
 
 sllllll 
 
 |^||-|| 
 
INTRODUCTION 
 
 55 
 
 O *O CO t 1 ^ O 00 vO O i i vO *OOO i 01 i 
 O t^ * O N Tf rf- TJ- | I vO co O | t^ | 
 
 .S3-I M 
 
 ^ 
 
 1 MlOCOHNt^N 
 
 OOO 
 H M 
 
 X 
 
 I 1 00 t^ Tf CO ^t- M 
 
 o 
 
 f I ! I I? I ? I I I 
 
 I * 
 
 I I 
 
 Tf 00 
 
 CO rj- ON O >A M 
 
 CO co -^-^O M ^J- 
 
 H CO rt-vO in rj- 
 
 
 O 
 >O 
 00 
 
 CO O 
 
 1 i v 1 *"^ O^ CO 
 vp O\ O co iO <M 
 
 M V CO CO CO K 
 
 Solubility in water at 
 15 C. C.c. of gas at 
 N.T.P. in i c.c. water 
 at i atm. pressure, (A) 
 including, (B) exclud- 
 ing water vapour. 
 
 OTt'l^O'^'COi,,,- 
 
 p p*p p"p p M "B "S pp o PJN en 
 
 b b b b b bob b b M Kb b 
 
 . 
 
 1 
 
 t/i ,xS 
 
 ^fi S JS ^i ^S? 1 vo-2;? 
 
INDUSTRIAL GASES 
 
 TABLE 13. 
 
 
 Heat of combustion. C.H.U. 
 
 
 
 
 per looo ft. 3 at 15 C. 
 
 Heat of formation. 
 C.H.U. per Ib.mol. 
 
 Coefficient of 
 expansion of the 
 liquid. 
 
 
 
 
 Net. 
 
 Gross. 
 
 
 
 Ozone 
 
 
 
 X I0 3 
 
 68-0 
 
 
 Hydrogen 
 
 153,300 
 
 l8l,2OO 
 
 
 
 
 
 Carbon monoxide 
 
 180,500 
 
 
 
 ( 29 from 
 \ amorphous C. 
 
 
 
 Carbon dioxide . . 
 
 
 
 
 
 ( 97'3 from f 
 \ amorphous C.\ 
 
 15 C. O'OIOI2 
 20 C. 0*01308 
 
 Sulphur dioxide . . 
 
 
 
 
 
 ( 70 from f! 15 C. 0*00186 
 \ rhombic S. \\ 20" C. '00192 
 
 Nitrous oxide 
 
 : 
 
 
 
 19'5 { 
 
 15* C. 0-00852 
 
 20* C. 0-OIII2 
 
 Methane 
 
 506,000 
 
 562,000 
 
 | 2 1 '7 from 
 \ amorphous C. 
 
 
 
 TABLE 14. 
 USEFUL CONVERSION FACTORS. 
 
 inch 
 metre 
 ooo ft. 3 
 m. 3 
 m. 3 
 gallon 
 in. 3 
 Ib. 
 
 gram. 
 
 atmosphere 
 C.H.U. 
 ft. 3 atm. 
 K.W.H. 
 K.W.H. 
 K.W.H. 
 H.P.H. 
 H.P.H. 
 H.PH. 
 Ib. coal 
 Ib. coke 
 0-25^,/KW.H, 
 
 2*5400 cm. 
 3-281 ft. 
 28*317 m. 3 
 
 35 3i ft. 8 
 220*0 gallons. 
 4-5460 litres. 
 16*387 cm. 3 
 453-6 grams. 
 15-432 grains. 
 14-690 lbs./in. 2 
 1-800 B.T.U. 
 1-511 C.H.U. 
 1255 ft. 3 atms. 
 860-2 kilo, calories, 
 1896 C.H.U. 
 0-746 K.W.H. 
 936*0 ft. 3 atms. 
 1415 C.H.U. 
 about 7000 C.H.U. 
 about 8000 C.H.U. 
 Years. 
 
 REFERENCES. 
 
 General Theory. Travers, " The Experimental Study of Gases." London, 
 
 1901. 
 
 Chwolson, " Traits de Physique." Paris, 1906-13. 
 Haber, " Thermodynamics of Technical Gas Reactions." London, 1908. 
 Nernst, " Experimental and Theoretical Applications of Thermo- 
 dynamics to Chemistry." London, 1907. 
 Gas Analysis. Lunge, " Technical Gas Analysis." London, 1914. 
 
INTRODUCTION 57 
 
 Heat Transfer. Hausbrand, " Verdampfen, Kondensieren und Kiihlen." 
 
 Berlin, Fiinfte Auflage, 1912. 
 
 Physical Constants. The values in the table are partly selected from 
 Landolt-Bornstein-Roth, " Physikalisch-Chemische Tabellen." 
 Berlin, Vierte Auflage, 1912, and from Kaye and Laby, " Physical 
 and Chemical Constants," London, Third Edition, 1918. Many 
 values, however, are taken from the original sources, and special 
 reference may be made to the following : 
 
 Specific Heats of Oxygen, Nitrogen and Hydrogen at Constant 
 Pressure : 
 
 Scheel and Heuse, Annalen [4], 40, (1913) 473, 492; Escher, 
 
 Annalen, [4], 42, (1913), 761. 
 Specific Heats of Nitrogen and Carbon Dioxide at Constant Volume : 
 
 Crofts, Chem. Soc. Trans., (1915), 290. 
 
 Critical Temperatures and Pressures of Oxygen, Nitrogen, Hydro- 
 gen, Carbon Monoxide and Methane : 
 
 Cardoso, /. Chim. Phys., 13, (1912), 312 ; Bulle, Physikal. Zeits., 
 
 14, (1913), 860. 
 Thermal Conductivity : 
 
 Weber, Annalen, [4!, 54, (1917), 325. 437- 
 Boiling and Melting Points : 
 
 Table of melting points and standard temperatures issued by 
 the American Bureau of Standards, /. Soc. Chem. Ind., 
 (1919), 67 R. 
 General References. Thorpe, " A Dictionary of Applied Chemistry." 
 
 London, 1912. 
 
 Martin, " Industrial Gases." London, 1916. 
 
 Roscoe and Schorlemmer, " Treatise on Chemistry." London, 1911. 
 Molinari, " Treatise on General and Industrial Chemistry," vol. i., 
 Inorg. (Feilmann). London, 1912. 
 
PART I. THE GASES OF THE ATMOSPHERE 
 SECTION I. AIR 
 
 Properties of Air. In view of the complex nature of air 
 it is not proposed to enter, at this stage, into a discussion 
 of its properties, as these are best defined by a consideration 
 of the following sections ; the more important physical 
 constants will be found in Table 12, pp. 53-5. 
 
 According to Holborn and Austin (Sitzungsber . Kgl. 
 Preuss. Akad. Wiss., (1905), 175), the mean specific heat at 
 constant pressure varies with temperature as follows : 
 
 Temperature C. 
 
 S 
 
 20-440 
 20-630 
 20-800 
 
 0-2366 
 0-2429 
 0-2430 
 
 According to Witkowski, the mean value of C^, between 
 102 C. and 17 C. is 0*2372. 
 
 The influence of pressure over the range 1-300 atms. on 
 the specific heat is seen from the formula given by Holborn 
 and Jakob (Z. Verein. deut. Ing., 61, (1917), 146) for a 
 temperature of 60 C. 
 
 io 4 Cj = 2414 + 2'86p + o'ooo^p 2 o'ooooio6/> 3 
 
 p being in atmospheres. 
 
 Composition of the Atmosphere. The composition of 
 the atmosphere is not absolutely constant, but the following 
 table will serve to indicate the general composition, according 
 to the most recent experiments. It is obvious that the 
 
AIR 59 
 
 atmosphere is by no means such a simple mixture as is 
 sometimes imagined. 
 
 TABLE 15. 
 COMPOSITION OF THE ATMOSPHERE. 
 
 Component. Percentage (by volume). 
 
 Nitrogen , . . . . . . . . . 78*05 
 
 Oxygen . . . . . . . . . . . . 2i"o 
 
 Argon . . . . .1 0-93236 
 
 Neon . . . . . . . . . . . . . . 0-00181 
 
 Helium 0-00054 
 
 Krypton . . . . . . . . 0-0000049 
 
 Xenon 0*00000059 
 
 Carbon dioxide . . . . . . . . . . 0-03-0-3 
 
 Hydrogen . . . . . . . . . . . . 0*019 * 
 
 Methane 0-0121 * 
 
 C 6 H 6 and similar hydrocarbons . . . . . . 0*0017 * 
 
 Carbon monoxide, together with hydrocarbons of 
 
 the type C w H 2w _ 2 and C n H 2M . . '. . . . 0-0002 * 
 
 Formaldehyde 0-002-0-005 
 
 Ozone . . . . . . . . . . . . \ 
 
 Hydrogen peroxide . . . . . . . . I 
 
 Ammonia .. . Variable traces 
 
 Nitric acid, oxides of nitrogen 
 
 Sulphur compounds 
 
 Chlorine compounds 
 
 Water vapour . . . . . . . . . . Variable 
 
 iiJ 
 
 The percentage of oxygen is not quite constant, but 
 varies slightly according to the locality and the altitude ; 
 the maximum variations being of the order of 0*1 %. The 
 carbon dioxide content is usually about 0*03 %, rising to 
 some two or three times this value in towns during fogs, 
 while in badly ventilated rooms the concentration may rise 
 to about 0-3 %. 
 
 In this connection it is interesting to note that the 
 composition of exhaled air is somewhat as follows : 
 
 Per cent. 
 
 Nitrogen . . 79*1 
 
 Oxygen . . . . . . . . 16*5 
 
 Carbon dioxide . . . . . . 4 '4 
 
 TOO'O 
 
 * The values marked with an asterisk are due to Gautier (Annales de 
 Chim. et de Phys., [7], 22, (1901), 5). Rayleigh gives a lower value for 
 hydrogen, viz. 0-003 %. The presence of the oxygen-nitrogen compounds 
 is probably due to electrical action, while the sulphur compounds are 
 mostly derived from household and industrial contamination. A certain 
 amount of sodium chloride is to be found in suspension in the atmosphere 
 in the neighbourhood of the coast. 
 
6o INDUSTRIAL GASES 
 
 The Liquefaction of the Permanent Gases (Air). 
 
 The liquefaction of permanent gases is a subject which 
 claimed the attention of scientists and inventors for many 
 years before any degree of success was attained. 
 
 A permanent gas is distinguished from a vapour in that 
 the critical temperature of the former is below the ordinary 
 temperature, that of the latter above. With gases of the 
 latter category, of which sulphur dioxide and carbon dioxide 
 may be taken as representative examples, the mere applica- 
 tion of sufficient pressure at the ordinary temperature is 
 all that is required to produce liquefaction. When one 
 considers that the critical temperatures of nitrogen and 
 oxygen are 145 C. and 118 C. respectively (as was 
 subsequently discovered) , the difficulties encountered by the 
 early experimenters are not surprising. Progress was 
 facilitated by Cailletet's discovery, in 1877, of the principle 
 of cooling by adiabatic expansion through the (accidental) 
 sudden expansion of compressed acetylene in a glass tube, 
 with the momentary formation of a mist. Repetition with 
 oxygen and nitrogen (at a pressure of 200 atmospheres) and 
 even with hydrogen (at 300 atmospheres), employing a 
 constant external temperature of 28 C., yielded a similar 
 result. 
 
 The cooling effect of adiabatic expansion is expressed 
 by the formula 
 
 Although of great scientific interest, these brilliant 
 experiments contributed but little to the practical solution 
 of the problem of liquefying permanent gases in bulk. 
 Some further progress was made by Pictet, the so-called 
 " cascade " method being employed. Carbon dioxide was 
 first liquefied under slight pressure at a temperature of 
 65 C., produced by the ebullition of liquefied sulphur 
 dioxide under reduced pressure. The carbon dioxide was 
 in turn evaporated under diminished pressure, yielding a 
 
AIR 61 
 
 temperature of 130 C., and was then used to cool a tube 
 supplied with oxygen at a pressure of some 300 atmospheres. 
 On opening the exit valve a transient stream of liquid was 
 observed ; here again the yields were very minute. By the 
 evaporation of liquid ethylene, care being taken to provide 
 efficient thermal insulation, Olszewski and Wroblewski, in 
 1885, obtained a temperature of 152 C., at which tempera- 
 ture both oxygen and nitrogen were liquefied under pressures 
 in the neighbourhood of 25 atms. The cascade method 
 was elaborated further by Kammerlingh Onnes, using, 
 (i) methyl chloride, (2) ethylene, and (3) oxygen. By the 
 evaporation of the oxygen under reduced pressure a tempera- 
 ture of 200 C.,was reached and, finally, 270 C. was 
 realized by the addition of (4) a helium system. 
 
 The problem of producing liquid air technically was 
 solved almost simultaneously by Hampson in England 
 (B.P. 10165/95), lyinde in Germany (B.P. 12528/95), and 
 by Tripler in America (B.P. 15235/99). All these investi- 
 gators made use of the Joule-Thomson Effect (cf. p. 10), in 
 conjunction with the principle of the heat-interchanger first 
 propounded by Siemens in 1857. 
 
 This effect is not to be confused with the adiabatic 
 expansion of a gas performing external work ; the fall in 
 temperature being mainly due to the internal work involved 
 in the separation of the molecules. 
 
 The approximate fall in temperature in the case of air 
 can be evaluated from the expression 
 
 *T = 0-276^ ~P2) degrees C. 
 
 where pi and p 2 are the initial and final pressures respec- 
 tively, when^ is not far removed from atmospheric pressure. 
 
 When this property of imperfect gases is utilized in 
 conjunction with the principle of heat-interchange one 
 obtains a progressive fall in the temperature of the expanded 
 air until the point of liquefaction is reached. 
 
 Theory of Cooling by the Joule-Thomson Effect. 
 Some reference to the Joule-Thomson Effect has been made 
 
62 
 
 INDUSTRIAL GASES 
 
 on p. 10 in the Introduction, but a more complete exami- 
 nation will be necessary for a thorough understanding of 
 air on liquefaction processes. 
 
 Consider a volume of gas v under a pressure of p Q atmo- 
 spheres at an (absolute) temperature of T . L,et the gas be 
 compressed to a higher pressure pi at a temperature T x 
 (the volume becoming Vj). Imagine the compressed gas 
 at pressure pi to be disposed in a cylinder A (Fig. 5), closed 
 by a frictionless piston B, which is kept in position by 
 another frictionless piston F of suitable area exposed to a 
 
 FIG. 5. Production of cold by the Joule-Thomson Effect. 
 
 constant pressure p 2 on the side marked H (e.g. in contact 
 with the atmosphere), the space B being vacuous. By 
 means of the valve C the gas is allowed to expand to pressure 
 p 2 into the cylinder D, closed by a frictionless piston G 
 working against a pressure p 2 . We will suppose, further, 
 that any temperature change which may occur on expansion 
 is rectified in the course of passage through the connecting 
 tube so that the whole operation is isothermal. 
 
 Now the work performed by the gas on the piston 
 Q^p 2 V2, while that performed by the piston B on the gas 
 (= work performed by the gas at H on the piston F) 
 
 * In actual practice, this work p^v^ is performed by the piston of the 
 compressor in addition to that demanded by the actual compression of 
 the gas. Since, however, the compressor is fed with gas at pressure p 2 , 
 the power absorbed by the compressor is approximately equal to that 
 calculated on pp. 34-9. 
 
AIR 63 
 
 Since most gases show a greater or less deviation from 
 Boyle's Law, p\v\ is not necessarily equal to ptfJ^, and the 
 work performed by the system on the external gas at 
 pressure p% (which will generally be one atmosphere) 
 
 ~H. e representing the cooling (or, if negative, the heating) 
 produced by external work. In addition, we have to consider 
 the internal work due to the separation of the molecules, 
 which will, in all cases, operate in the direction of producing 
 a cooling effect (H t -). 
 
 f- 
 
 v* 
 
 J v t 
 
 when a is the constant representing the cohesion of the 
 molecules in Van der Waals' equation 
 
 Now a may be derived from the following relation 
 (cf. p. 7) : 
 
 27 
 
 T c and p c being the critical temperature and pressure 
 respectively. Thus, in the case of air, if we take as units 
 cubic feet and atmospheres and consider a volume of 1000 ft. 8 
 measured at i atm. pressure and 15 C., i.e. p Q => i, ^0=1000, 
 TO -288, 
 
 _ 27 
 
 64 X 39V 288 
 We will now consider the cooling effect in C.H.U. 
 (cf. p. 12) of an expansion of this mass of air from 200 atms. 
 (absolute) to i atm. at a temperature of 15 C., assuming 
 the temperature to be kept constant by external supply or 
 abstraction of heat. 
 
 Now for 15 C. and i atm. p Q v Q =>p2 v 2 =* IOO 
 
 1000 X 1*0855 
 
 200 
 
 1 . 0587 
 
 1025-3 
 
64 INDUSTRIAL GASES 
 
 => 1000 1025*3 ft. 3 alms. 
 
 ="- 253 X 1-511 C.H.U. * 
 
 =--38-23 C.H.U. 
 
 H, is seen to be negative, consequently a heating effect will 
 be produced if the external work alone be considered. 
 
 _ 
 
 /I025'3 \ 
 
 2307 ( 1000 ) 
 
 = - V 20 I ft.3 atms. 
 
 1025-3 X 1000 
 
 200 
 
 ^2307X994-87 ft 3 atms . =4477 ft. 3 atms. 
 5126-5 
 
 =.447-7 X 1-511 C.H.U. 
 =676-5 C.H.U. 
 .-. .total cooling effect = 676 -5 38-2 C.H.U. 
 
 -3 638 -3 C.H.U. 
 
 Since the specific heat at constant pressure of air at 15 C. 
 is equivalent to 18-5 C.H.U./iooo ft. 3 / C., this cooling is 
 equivalent to a fall in temperature of 
 
 This agrees sufficiently well with the values experi- 
 mentally determined by Bradley and Hale (Phys. Review, 
 29, (1909), 258), who, for a pressure drop from 204 atms. to 
 i atm. at o C., found a temperature fall of 44*6 C. ; especially 
 as their more favourable conditions would give a greater 
 cooling effect to the extent of about 5 C. 
 
 As the compression of 1000 ft. 3 of air at 15 C. to 200 atms. 
 requires in practice a power expenditure of the order of 
 10 K.W.H. (cf. p. 39), the cooling effect per K.W.H. 
 power expenditure is 638-3/10 = 63*83 C.H.U. 
 
 * i ft. 8 atm. = 2*8690 x io 10 ergs. (cf. p. 36) 
 i C.H.U. = 453-6 gram calories 
 
 = 453*6 x 4-185 X io 7 ergs 
 
 = 1*8983 x io 10 ergs. 
 /. i ft. 8 atm. = 2-8690/1-8983 C.H.U. 
 
 = 1-511 C.H.U. 
 
AIR 65 
 
 Expansion at 100 C. We will next consider the effect 
 of performing the above isothermal expansion after a 
 preliminary cooling of the compressed gas to, say, 103 C., 
 down to which temperature the pv values have been deter- 
 mined by Witkowski (loc. cit., cf. Table 2, p. 6). This is 
 about the temperature to which the air is cooled before 
 expansion in the simple type of machine such as the Hampson 
 plant (cf. Bradley and Hale, Physical Review, 19, (1904), 
 391) ; the temperature does not fall below the critical 
 temperature and, consequently, no liquefaction occurs 
 before expansion. 
 
 As Witkowski's experiments were not extended to 
 pressures exceeding 130 atms., we will take the values at 
 this pressure. 
 
 Considering, as before, 1000. ft. 3 of air at 15 C. and 
 i atm. (in these calculations Witkowski's values are multi- 
 plied by 273/288, since p Q v Q is taken at 15 C.) 
 
 for 15 C. and i atm. p Q v => 1000 
 
 103-5 C. i ^a = 587-9 
 -103-5 C. ,,130,, ^i=> 377-4 
 We have thus a very considerable deviation from per- 
 fection, the gas being now more compressible than a perfect 
 gas ; consequently H, will be positive. 
 
 H, ="#t P\VI => 587'9 377*4 ft. 3 atms. 
 
 = 210-5 ft. 3 atms. == 318-1 C.H.U. 
 
 2307(3^-587.9) 
 _ a(vi _ Vz} 7 V I3Q ) JJ 
 
 377-4 X 587-9 
 130 
 
 ^ 2307 X 585-0 ft 3 atms . 
 I706-7 
 
 => 791 ft. 3 atms. = 1195 C.H.U. 
 Total cooling effect, therefore, 
 
 => 1195 + 318-1 C.H.U. =* 1513 C.H.U. 
 A similar calculation for the expansion of the same 
 quantity of air from 130 atms. to i atm. at a temperature 
 A. 5 
 
66 INDUSTRIAL GASES 
 
 of 15 C. gives a corresponding cooling effect of 470 C.H.U. 
 (H. - 15-4 C.H.U. ; H, = 454'3 C.H.U.) 
 
 The cooling effect is thus found to be considerably 
 greater at the lower temperature. 
 
 Turning to the actual practical operation of liquid air 
 plants, it should be noted that the above observed difference 
 of 1513 470 C.H.U. (= 1043 C.H.U.) is not usefully avail- 
 able for the production of liquid air, since the additional 
 cooling effect is balanced exactly by the extra heat evolution 
 in the heat-inter changer of the incoming gas ; this prevents 
 the temperature of the compressed gas arriving at the 
 expansion valve from falling below about 100 C. The 
 additional cooling is absorbed in lowering the temperature 
 of the expanded gas to that at which the cold gas enters the 
 interchanger, viz. the boiling point of air. It would only 
 be available if the compressor were operated at the same 
 temperature of 103 C. Consequently, the value of pv at 
 the temperature of entry of the compressed gas into the 
 interchanger, or, more strictly, the difference between the 
 values of pv for the gases entering and leaving the inter- 
 changer respectively, assuming the heat-interchange to be 
 perfect, determines the amount of cooling produced. Since 
 the heat-interchange is not perfect the heat required to heat 
 up the exit gases to the inlet temperature must be deducted 
 from the cooling effect. 
 
 We shall see later the effect of a preliminary pre-cooling 
 of the gas. 
 
 The heat evolution of the incoming compressed gas, 
 alluded to above, has the effect of making the temperature 
 gradient between the two fluids in the heat-interchanger 
 increase as the temperature falls. Obviously, the growing 
 imperfection of the compressed gas will be accompanied 
 by an increase in the specific heat, the effect being very 
 marked near the critical temperature at high pressures. 
 
 The outcome of the above considerations is, that we get 
 the same cooling effect with a low temperature expansion, 
 accompanied by a considerable fall in temperature, as in 
 the example given above, in which a temperature of 15 C. 
 
AIR 67 
 
 and isothermicity were assumed. Consequently, we may 
 take the cooling effect under actual working conditions as 
 being of the order of 638 C.H.U. for a working pressure of 
 200 atmospheres. 
 
 When liquefaction sets in the external work performed 
 on the atmosphere by the issuing air diminishes. The 
 decrease is compensated for, however, by the absorption 
 of heat due to external work performed by the air which 
 escapes liquefaction on the portion liquefied. 
 
 We have already seen that the power expenditure is of 
 the order of 10 K.W.H. per 1000 ft. 3 of air compressed. 
 Therefore, cooling effected by i K.W.H. (measured on the 
 switchboard) = about 64 C.H.U. , equivalent to the pro- 
 duction of about 0-29 litre of liquid air. The above 
 estimate is, of course, based on the (incorrect) assumption 
 that there are no thermal losses ; the efficiency falls off in 
 proportion to the extent of such leakages. 
 
 Before leaving the subject it will be worth while to examine 
 the case of hydrogen, which, as stated above, gives a 
 heating effect at the ordinary temperature. 
 
 The case of Hydrogen. Taking 1000 ft. 3 of hydrogen at 
 15 C. and i atm. and, after compression to 200 atms. 
 (absolute), expanding to i atm., we have 
 
 H, 
 
 1000 x 1*198 ,, . 
 =v - V = 1000 --- - ft 3 atms. 
 
 = 1000 1134 ft. 3 atms. 
 
 = 134 ft. 3 atms. = 202 C.H.U. 
 
 27 /iooo X 3i'95\ 2 taking p e as equal 
 / 
 
 4721 iooo ) 
 
 ""64 X ii'O\ 288 / to 11*0 atms. 
 = 472 
 
 1134 x iooo 
 
 200 
 
 ft.3atms. 
 
 = 472 X 994'3 ft3atms . 
 
 5670 
 = 82-8 ft. 3 atms. = 125 C.H.U. 
 
68 INDUSTRIAL GASES 
 
 Therefore total cooling effect 
 
 = _ 202 + 125 C.H.U. = - 77 C.H.U. 
 
 Heating effect per atm. pressure drop => -= C. 
 
 18-20 X 199 
 
 (since specific heat = 18-20 C.H.U./iooo ft. 3 /C.) 
 
 = 0-0213 C. 
 
 The value determined experimentally by Joule and 
 Thomson was 0*03 C. for 6*8 C. and pressures near atmo- 
 spheric ; if the above calculation be repeated for 20 atms. 
 the value obtained is 0-018, not greatly different since the 
 pv curve is practically a straight line between i and 200 atms. 
 
 As the temperature is lowered, H, decreases and H^ 
 increases owing to the growing imperfection of the gas, 
 with the consequence that at 80*5 C. an inversion point 
 is reached ; below this temperature a cooling effect sets 
 in, but is not very marked until the temperature is lowered 
 to the neighbourhood of 200 C. It is found necessary 
 to pre-cool to this temperature before the liquefaction of 
 hydrogen can be effected by the Joule-Thomson effect. 
 The beneficial influence of pre-cooling will be discussed 
 under the L,inde process of air liquefaction. 
 
 The final improvement in the liquefaction of permanent 
 gases was suggested by Siemens, while its technical develop- 
 ment is due to Claude, who overcame the difficulties of 
 employing expansion accompanied by the performance of 
 external work. With this system of working it is important 
 not to allow the temperature to fall below about 140 C., 
 as the increase in the specific heat, in conjunction with the 
 diminished amount of external work which the gas is capable 
 of performing at lower temperatures owing to its rapidly 
 increasing compressibility, leads to low efficiencies. A 
 more detailed account will now be given of the principal 
 systems of making liquid air. 
 
 As regards patents relating to this subject, the number 
 is so great and the differences in many cases so involved 
 that it is impossible in the present volume to do more than 
 give a resume of the salient features of those which have 
 assumed commercial importance. 
 
AIR 69 
 
 MANUFACTURE OF LIQUID AIR 
 Useful Constants 
 
 Weight of 1000 ft. 3 of air at 15 C. and i atm. pressure 
 = 76*49 Ibs. 
 
 Weight of i litre of liquid air = about i kilo. 
 
 Volume of i litre of liquid air when vaporized = about 
 28 ft.s at 15 C. and i atm. 
 
 Heat uiuts which must be abstracted for the production 
 of i litre of liquid air from atmospheric air = about 
 220 C.H.U. 
 
 Hampson System 
 
 The Hampson system is a convenient one for laboratory 
 use, being usually supplied in 5 K.W. sets which furnish 
 about i litre of liquid air per -hour, equivalent to the ab- 
 straction of about 44 C.H.U. /K.W.H. Although somewhat 
 inefficient, it possesses an important advantage for such 
 experimental purposes in its simplicity. Air is compressed 
 to 175-200 atmospheres, being first freed from carbon 
 dioxide by passage over a series of trays filled with lime. 
 After depositing the lubrication water in a separator, the 
 gases are freed from residual traces of carbon dioxide and 
 water vapour in a purifier, consisting of a steel cylinder 
 charged with sticks of caustic potash, and are then allowed 
 to expand at a fine adjustment valve, finally flowing 
 through a heat-interchanger back to the compressor. 
 
 Some 5 % of the compressed air is liquefied at each cycle 
 when the apparatus has once become thoroughly cooled 
 down. Complete removal of the carbon dioxide and water 
 vapour is important, as otherwise blockages may occur in 
 the liquefier. Working for about 10 minutes is sufficient 
 for the production of liquid air to commence. 
 
 The apparatus, as made up by the British Oxygen Co., 
 is shown in Fig. 6. The compressed air entering at A 
 traverses the heat-interchanger coils B, and undergoes 
 expansion at the valve C, which is adjusted by the hand 
 wheel B. After expansion, the air passes over the coils, its 
 path being determined by baffles, to the outlet F. The level 
 
INDUSTRIAL GASES 
 
 of the liquid in the receiver, which holds some 100 c.c., is 
 indicated by the glycerol gauge H ; the liquid air is periodically 
 withdrawn by the valve T. A thick layer of lagging, e.g. 
 sheeps' wool, is disposed around the central portion. 
 
 Linde System 
 
 The Ivinde system (cf. 
 B.P. 14111/02) is perhaps 
 the system most commonly 
 used in large scale practice. 
 It differs from the simple 
 Hampson process, quite 
 apart from constructional 
 details. In the first place, 
 instead of expanding the 
 air from 200 atms. to i 
 atm., I/inde expands only 
 from 200 atms. to . about 
 50 atms. We will ex- 
 amine the diminution in 
 the cooling effect as com- 
 
 FIG. 6. Hampson Liquefier (British Oxygen Co.). 
 
 pared with the decrease in the power expenditure. 
 
 We have seen that with an expansion from 200 atms. 
 
AIR 71 
 
 (absolute) to i atm., the cooling is of the order of 638 C.H.U. 
 for the expansion of 1000 ft. 3 of air measured at 15 C. and 
 i atm. In the present case 
 
 p^i = 1025-3 at 200 atms. and 15 C. 
 p 2 v 2 = 983-3 at 50 atms. and 15 C. 
 
 Therefore H, = (^2^2)^5 (Pi v i)i5 
 
 983-3 1025-3 ft- 3 atms. 
 
 = - 42 ft. 3 atms. = -63-5 C.H.U. 
 
 aW 1025 ' 3 
 
 ^ 2QO _ ft>3 atms . 
 1025-3 x 983-3 
 
 200 X 50 
 = 2307 X I4-542- X 10,000 ft 3 
 
 1025-3 x 983-3 
 
 = 3327 ft. 3 atms. = 502-7 C.H.U. 
 
 Total cooling effect = 502-7 63-5 C.H.U. 
 = 439-2 C.H.U. 
 
 The ratio of the above cooling to that obtained with the 
 full expansion to i atm. = 439/638 = 1/1*45. The power 
 expenditure will also be lower, as follows. 
 
 Assuming the compression to be adiabatic, the power 
 varies as 
 
 0*29 
 
 (cf. p. 38). In the present case we have : (i) single stage 
 compression of ^th of the air from i to 50 atms. (since 
 about xoth of the air is liquefied in each cycle) ; (2) single 
 stage compression of the whole of the air from 50 to 200 atms. 
 (absolute). 
 
 In the straightforward case we have compression of the 
 whole of the air from i to 200 atms. (absolute) in, say, two 
 stages (in large installations three-stage compressors are 
 usually employed). 
 
72 INDUSTRIAL GASES 
 
 The ratio of the power expenditures will be 
 
 5o/ 3 o-i x 2-11+0-495 
 
 2XI " 56 
 
 "3-28 
 
 Consequently, the ratio of output to power expenditure is 
 increased by the Linde system of working in the proportion 
 of 3-28/1-45 =2-26/1. 
 
 Effect of Pre-cooling. Another improvement intro- 
 duced by lyinde consisted in the pre-cooling of the gas fed into 
 the interchanger to, say, 35 C., by means of an ammonia 
 refrigeration system. As referred to above, the enhanced 
 cooling effect produced by effecting the expansion at low 
 temperatures is counteracted by the fact that the compressed 
 gas arrives at the expansion valve at a temperature con- 
 siderably above that of the cold gas entering the heat- 
 interchanger. In other words, the thermal capacity of the 
 compressed gas over the temperature range in question 
 is much greater than that of the same volume of expanded 
 gas. When liquefaction is in progress the cold air enters 
 the regenerator at a fixed temperature, viz. that of the 
 boiling liquid air ; consequently the temperature at which 
 the compressed gas reaches the expansion valve will be 
 determined by the temperature at which it enters the 
 interchanger, as well as by the degree of perfection of the 
 interchanger. 
 
 If, therefore, the incoming compressed air, after being 
 slightly cooled by the interchanger, be diverted therefrom, 
 cooled to, say, 30 C., by means of an ammonia or other 
 system, and subsequently returned to the interchanger, 
 the temperature of the gas arriving at the expansion valve 
 will be lowered by an amount corresponding to the heat 
 units abstracted by the auxiliary cooling plant. In con- 
 sequence, an increased yield of liquid air will result. The 
 exact procedure may be seen by reference to Fig. 7. 
 
AIR 
 
 73 
 
 FIG. 7. Linde 
 System. 
 
 It should be pointed out that the re- 
 frigeration effected by an ammonia system 
 is much more economical than that pro- 
 duced by the Joule-Thomson effect, 
 although, of course, the practical lower 
 limit is in the neighbourhood of 35 C. ; 
 at this temperature the cooling effected is 
 of the order of 1000-2000 C.H.U./K,W.H., 
 as compared with 60-180 C.H.U./K.W.H. 
 by the Joule-Thomson effect. As a result 
 of the p re-cooling the efficiency of the 
 process is raised by some 30 per cent. 
 
 The combined effect of these two 
 modifications is approximately to treble 
 the production of liquid air per K.W.H., 
 this being equivalent to about 0*87 
 litres/K.W.H., taking the previously calcu- 
 lated value of 0-29 litres/K.W.H. for the 
 single cycle and neglecting thermal leakage, 
 etc. In actual practice, 0-65 litres/K.W.H. 
 is about the production. 
 
 I^inde machines on the above lines are 
 made in different sizes, from the laboratory 
 type with a production of some 075 litre/hr. 
 upwards. In large plants three-stage 
 compressors are used and the compressed 
 air, after separation of the lubrication 
 water, is completely dried by cooling with 
 
74 
 
 INDUSTRIAL GASES 
 
 an ammonia refrigeration system to about 25 C., using 
 duplicate cooling systems, which are periodically changed 
 over (three or more times weekly) in order to allow the 
 deposited ice to thaw out. Before compression, the carbon 
 dioxide is removed by means of towers fed with caustic 
 soda solution. Traces of carbon dioxide are usually formed 
 during the compression by the action of the air, heated 
 by the adiabatic compression, on the packings of the pump. 
 
 The diagrammatic representation, Fig. 7, indicates the 
 course of the compressed air. Passing from the compressor 
 A, through the water separator B, and the preliminary heat- 
 interchanger C, to one or other of the ammonia coolers D 
 and D 1 , the dry gas enters the liquefier through the triple 
 heat-interchanger B. (The actual interchanger consists of 
 concentric spiral tubes.) 
 
 Arriving at the valve F, expansion to about 50 atmo- 
 spheres takes place, the gas being returned to the last stage 
 of the compressor. The air liquefied in the separator G, 
 under a pressure of 50 atms., is allowed to expand to ordinary 
 pressure through the valve H, suffering thereby partial 
 evaporation ; the gaseous fraction returns to the inlet of 
 the compressor through the interchanger K. Liquid air 
 is drawn off from the vessel I. The smaller sizes of plant, 
 up to about 3 litres/hr. capacity, are fitted with two-stage 
 compressors, in which case the expansion is from 200 atms. 
 to about 20 atms. 
 
 The outputs and efficiencies of various sizes of plants 
 are indicated in the following table : 
 
 TABLE 16. 
 LINDE LIQUID AIR PLANTS. 
 
 Litres of liquid air per hour with 
 
 
 
 
 
 
 pre-cooling 
 
 '75 
 
 5 
 
 20 
 
 5 
 
 100 
 
 Litres of liquid air per hour with- 
 
 
 
 
 
 
 out pre-cooling 
 
 
 
 
 
 I2'5 
 
 35 
 
 70 
 
 Power K.W. (measured on the 
 
 
 
 
 
 
 switchboard) 
 
 2'6 
 
 14-2 
 
 39 
 
 78 
 
 142 
 
 Litres/K.W.H. with pre-cooling 
 
 0*29 
 
 '35 
 
 0-51 
 
 0^64 
 
 0-70 
 
 Litres/K.W.H. without pre-cool- 
 
 
 
 
 
 
 ing 
 
 
 
 
 
 0-32 
 
 o'45 
 
 0-49 
 
 Cooling water, gallons/hour 
 
 55 
 
 308 
 
 835 
 
 1760 
 
 3300 
 
AIR 75 
 
 Claude System 
 
 The Claude system, as above indicated, depends on the 
 cooling effect produced by expansion accompanied by 
 external work, together with that due to internal work, 
 the latter being, however, small compared with the former. 
 Usually the working pressure does not exceed 40 atmo- 
 spheres. The useful temperature limit which is reached by 
 such expansion of compressed air in an engine cylinder is 
 about 140 C., and much of the initial difficulty in the 
 working out of the process was due to this fact. 
 
 On account of the rapidly increasing imperfection of 
 the air at this temperature in the direction of greater 
 compressibility, expansion at a lower temperature is accom- 
 panied by relatively little work, the cooling effect produced 
 by which may be balanced by the friction of the machine. 
 This temperature is, however, about the critical temperature 
 of air (T c = 140 C. ; p c = 39 atms.) ; consequently, by 
 using the expanded gas to cool a receptacle supplied at 
 40 atms. pressure with air which has been pre-cooled in a 
 temperature-interchanger, liquefaction of the high pressure 
 air ensues (B.P. 27658/02). On release to the ordinary 
 pressure, partial evaporation occurs and the temperature 
 falls to 190 C. By adjusting the height of the liquid 
 in the liquefier-temperature-interchanger, and consequently 
 the rate of liquefaction, the air arrives at the expansion 
 engine at a temperature of about 100 C. 
 
 Considerable trouble was at first experienced in the 
 lubrication of the expansion cylinder, ordinary petrol being 
 employed ; but recently it has been found that suitably 
 treated leathers can be used without any lubrication. 
 
 By the Claude system, an output of about 075 litre of 
 liquid air per K.W.H. (measured on the switchboard) is 
 claimed. The general method of working may be explained 
 further by reference to the diagrammatic representation, 
 Fig. 8. Compressed air, at about 40 atms. pressure, enters 
 through the heat-inter changer M, and suffers expansion 
 
7 6 
 
 INDUSTRIAL GASES 
 
 in the cylinder D, the engine being coupled, either mechani- 
 cally or electrically, to the compressor. The cold expanded 
 gases pass round the tubes of the second inter changer I/, 
 and cause the liquefaction of the compressed air supplied 
 to the inside of the tubes, and finally leave through the 
 interchanger M. The liquid air collects in the header at 
 the bottom of the tubes and is drawn off in accordance with 
 the temperature of the gas arriving at the expansion engine. 
 
 FIG. 8. Claude Liquefaction System. 
 (Claude's " Liquid Air, Oxygen and Nitrogen.") 
 
 A modification of this plan consists in effecting the 
 expansion in two stages ; in the first, the pre-cooled air is 
 expanded in the cylinder, 35 (Fig. 9), so as to produce a 
 temperature, e.g. 160 C., well below the critical tempera- 
 ture. After producing the liquefaction of the compressed 
 air in the temperature-interchanger, 24, 26, being warmed 
 to from 130 to 140 C. in the process, the air undergoes 
 a further expansion in 36, and in turn serves to liquefy the 
 air in a second interchanger, 25, 27. 
 
 To avoid leaks of the very cold air, the two cylinders 
 are arranged in tandem, only the low pressure cylinder 
 having a stuffing box. It is claimed that a production of 
 0*9 litre/K.W.H. (measured on the switchboard) is attained 
 in a moderately large plant. 
 
AIR 
 
 77 
 
 The low working pressure and the rapidity in 'starting 
 up of the Claude plant are both in its favour, and the 
 general tendency of late years has been to instal Claude 
 
 FIG. 9. Claude Liquefaction System. 
 
 rather than L,inde plants. The following table gives 
 particulars of a few sizes of Claude plants : 
 
 TABLE 17. 
 CLAUDE LIQUID AIR PLANTS. 
 
 Production, litres/hr. 
 
 5 
 
 50 
 
 65 
 
 Power (measured on the switchboard) K.W.H.* 
 
 H 
 
 56 
 
 70 
 
 Litres of liquid air per K.W.H. 
 
 0-36 
 
 0-89 
 
 0-93 
 
 With reference to the possible effect of accumulations 
 of solid argon, methane or acetylene in causing explosions 
 in liquid air plants, cf. Bramkamp (/. Soc. Chem. Ind., 
 (1914), 240). 
 
 Properties of Liquid Air. Liquid air is a mobile liquid 
 with a pale blue colour, varying in intensity according to 
 
 * According to Mewes (Z.fur Sauerstoff und Stickstoff Industrie, 5, (1913), 
 317), the power figures given by Linde are the gross values read off on the 
 switchboard, while Claude's figures apply to the power on the compressor 
 shaft. Claude's figures have therefore been increased by 25 per cent., 
 assuming 80 per cent, efficiency in the motor. 
 
78 INDUSTRIAL GASES 
 
 the oxygen content. Its density is about 1*0 and the 
 boiling point varies from 183 to 196 C., according to 
 composition (cf. p. 80). 
 
 Freshly liquefied air usually contains considerably 
 more than 21 % of oxygen, e.g. 50-60 % ; on standing, 
 the oxygen content increases. The specific heat is about 
 0*5, while the latent heat of vaporization is about 50 calories 
 per gram (i.e. per c.c.) = 50 C.H.U./lb. On cooling liquid 
 air, nitrogen separates out at about 213 C. in a compara- 
 tively pure state ; the oxygen does not solidify until a 
 temperature of 225 C. is reached. 
 
 Liquid air has feeble magnetic properties on account of 
 its oxygen content. Its refractive index (/A D ) is 1*2062. 
 On mixing equivalent quantities of liquid nitrogen and 
 oxygen, a contraction of about J % is observed, accompanied 
 by a temperature rise of about 0*5 C. 
 
 Applications of Liquid Air. The principal application 
 of liquid air is in the manufacture of oxygen and nitrogen 
 by fractionation. At the time of its first discovery, many 
 fantastical claims were made for its application as a source 
 of power, etc., but apart from the above, no very extensive 
 use has been made of liquid air. A considerable advance 
 in the possibility of the industrial use is due to the perfection 
 of the metal vacuum vessel. Liquid air can be purchased 
 (at about 55. per gallon) in metal vessels holding up to 
 about five gallons. These vessels are on the lines of the glass 
 Dewar vessel, being furnished with a charcoal tube cooled 
 by the liquid air, for the purpose of effecting the complete 
 exhaustion of the jacket. For a discussion of certain 
 explosions originating from the accidental breaking of 
 liquid air vessels and the consequent contact of the contents 
 with the charcoal, cf. Wohler, Chem. Zeit., Oct. 5, 1918. 
 Liability to explode under these conditions is considered to 
 depend on the presence of catalysts, such as iron oxide, in a 
 highly absorptive charcoal. 
 
 Liquid air of about 60 % oxygen content is used in mine 
 rescue apparatus, some five litres of liquid air being contained, 
 absorbed in asbestos wool, in a vessel with only moderate 
 
AIR 79 
 
 thermal insulation (kieselguhr) ; a slow evaporation results 
 which supplies a stream of air to the breathing apparatus. 
 The advantages over the similar apparatus employing 
 compressed oxygen, are the comparative lightness (the 
 weight is about 30 Ibs.), length of action, and the greater 
 ease of manufacture of liquid air, as compared with com- 
 pressed oxygen, at the pit-head. 
 
 Numerous proposals have been made with regard to 
 the use of liquid air in conjunction with carbonaceous 
 matter or aluminium as an explosive. The usual method 
 of application is to employ a cardboard cartridge with a 
 perforated inner tube ; a mixture of kieselguhr and oil, or 
 soot, etc., is inserted, the cartridge placed in the bore-hole 
 and liquid air injected, after which the charge is fired 
 electrically. This method was used in cutting the Simplon 
 Tunnel. The chief advantages claimed are the absence of 
 fumes and the lack of danger in case of a misfire, as the charge 
 rapidly becomes innocuous. On the other hand, the necessity 
 for firing very rapidly after charging and the difficulty of 
 transportation and storage of the liquid air are against its 
 general application. 
 
 Separation of the Constituents of Liquid Air- 
 Theoretical Considerations. As has already been pointed 
 out, the principal application of liquid air is in the pro- 
 duction of oxygen and nitrogen. 
 
 The separation of the constituents of liquid air by 
 fractionation was propounded by Parkinson in B.P. 4411/92, 
 but was first realized by Dewar. 
 
 To glance first at the theoretical side of the question, 
 we are indebted to the work of lyinde and to the more 
 complete investigation of Baly (Phil. Mag., 49, (1900), 517), 
 for the relation between the liquid and gaseous phases of 
 nitrogen- oxygen mixtures, Fig. 10. 
 
 The curves indicate that starting with liquid air of 
 21 % oxygen content, the percentage of oxygen in the first 
 fraction is about 7 %, rising as evaporation proceeds. It 
 will be noticed that there is no mixture of maximum or 
 minimum boiling point, and that, consequently, application 
 
8o 
 
 INDUSTRIAL GASES 
 
 of ordinary fractionation column principles should result 
 in effective separation as far as oxygen is concerned ; it is, 
 however, impossible by simple fractionation to reduce the 
 oxygen content of the nitrogen fraction to below 7 %. It will 
 be seen later that this can be accomplished by special means. 
 
 DEGREES CENTIGRADE 
 
 -L 1 
 
 D 00 
 3 C/i C 
 
 
 
 
 
 
 
 
 
 ^ 
 
 / 
 
 >* 60 cb cb 
 w o w o 
 
 TEMPERATURE (ABSOLUTE) 
 
 
 
 
 
 ^ 
 
 i 
 
 x 
 
 / 
 
 x 
 
 
 TEMPERATURES 
 
 ' 
 
 i $ a 
 
 / 
 
 / 
 
 X 
 
 
 
 
 
 
 
 
 <^ 
 
 ^ 
 
 
 
 
 
 
 
 
 
 
 
 ' WW 10 20 30 40 50 60 70 80 90 100 
 PERCENTAGE OF OXYGEN 
 
 PERCENTAGE OF OXYGEN 
 
 FIG. 10. Baly's Curves for the liquid and gaseous phases of the system 
 nitrogen-oxygen at atmospheric pressure. 
 
 As regards the minimum energy involved in the separation, 
 it was indicated by Parkinson in the above patent that 
 recuperation of the cold would be desirable, in which case 
 only the losses in the heat-interchanger are involved, apart 
 from the energy required for the actual separation of the 
 gases, a factor liable to be overlooked. This latter quantity 
 corresponds to the isothermal compression of the nitrogen 
 to 079 of its original volume and of the oxygen to 0'2i of its 
 volume, i.e. in each case 
 
 (cf.p.38) 
 
AIR 81 
 
 Taking for example, 1000 ft. 3 of air at 15 C. and i atm., 
 the work involved is 
 
 1000 X 079 X 2-3026 X log - 
 + 1000 X o-2i X 2-3026 X log - - ft. 3 atms. 
 
 = 514-0 ft* atms. =^o H.P.H. 
 
 936-2 
 = 0-549 H.P.H. per 1000 ft. 3 of air. 
 
 Thus each 1000 ft. 3 of oxygen demands a minimum 
 energy expenditure of 
 
 2^49 H.P.H. = 2-61 H.P.H. 
 
 0'2I 
 
 As will be seen below, a considerably greater energy 
 expenditure is demanded in practice. In order to effect 
 the condensation of air by means of a bath of liquid air 
 boiling under atmospheric pressure, a certain compression 
 is required, increasing as the nitrogen boils off from the 
 liquid bath. In practice, a compression of from 3 to 5 
 atmospheres is used. As regards losses in the heat-inter- 
 changers, we may take the efficiency as being of the order 
 of 95%-* 
 
 We will now pass to the consideration of the different 
 systems for the separation. 
 
 MANUFACTURE OF OXYGEN AND NITROGEN 
 Linde System 
 
 The principle of rectification was first applied technically 
 by Linde in 1895 (cf. B.P. 12528/95), but the main features 
 of the Linde plants, except the most recent, are to be found 
 in B.P.s 14111/02 and 11221/03. Since the production of pure 
 nitrogen together with impure oxygen requires a somewhat 
 different procedure from that of the production of pure oxygen 
 together with impure nitrogen, slightly different types of 
 
 * According to Claude, one litre of liquid air is evaporated in the 
 fractionation of the air corresponding to 30 litres of liquid air. 
 A. 6 
 
82 INDUSTRIAL GASES 
 
 apparatus are used for the two purposes. It usually happens, 
 unfortunately, that there are not adequate demands for both 
 oxygen and nitrogen in large quantities in a given locality. 
 
 Oxygen Plants. The operation of the plant consists of 
 two stages : (i) cooling down the air and producing a 
 sufficient quantity of liquid air ; (2) fractionation of such 
 liquid air with sufficient replacement to compensate for 
 thermal leakages. Air, at a pressure of about 135 atms., 
 passes through three small tubes in the heat-inter changer, 
 consisting of the copper tube C (Fig. n, cf. Engineering, 99, 
 (1915), 155) containing the smaller copper tubes, in counter- 
 current to the outgoing gases. After traversing the coils 
 di, expansion occurs at the valve G, the cooled expanded 
 gases being discharged through a rose-ended pipe, d%. As 
 cumulative cooling takes place, liquefaction ensues and 
 liquid flows down the column A, and collects in the chamber 
 B. Presently liquefaction occurs in the coils di themselves 
 and the pressure of the incoming compressed air is reduced 
 by gradually opening G. A steady stream of liquid now 
 falls down the column A, being derived, for the greater part, 
 at the expense of the partial evaporation of the accumulation 
 in the chamber B. This stream of liquid meets the counter- 
 current of gas from the chamber B, and mutual fractionation 
 results. 
 
 As the liquid progresses down the column the tempera- 
 ture gradually rises and the oxygen content continually 
 increases ; consequently, the liquid reaching the bottom is 
 practically pure oxygen, while the ascending gas loses oxygen 
 until its oxygen content is equal to that in equilibrium with 
 liquid air containing 21 % oxygen, viz. 7 %. This means 
 that some 28 % of the total oxygen goes off with the nitrogen. 
 When a steady state is established the working pressure is 
 about 50-60 atmospheres, and the gases leave at a pressure 
 of about 5 lbs./in. 2 , sufficient to overcome the resistance 
 of the heat-interchangers. 
 
 The oxygen leaves the apparatus at e l . As in all similar 
 apparatus, the preliminary purification of the air from 
 water and carbon dioxide is very important. The water 
 
AIR 83 
 
 is often removed by p re-cooling the air with an ammonia 
 plant, using duplicate coolers which are changed over three 
 or more times weekly ; this procedure has the further 
 advantage of increasing the efficiency, the separator 
 
 rr -o 
 
 FIG. ii. Linde Oxygen Plant (Engineering). 
 
 itself runs for about a week before blockage occurs ; it is 
 usually advisable to duplicate the separator in such plants. 
 Instead of producing the liquid air in the separator itself, 
 the latter may be fed with liquid air produced in an 
 independent plant. 
 
8 4 
 
 INDUSTRIAL GASES 
 
 The lyinde patent rights for the United Kingdom were 
 acquired in 1906 by the British Oxygen Co., which now pro- 
 duces most of the oxygen used in this country by the L,inde 
 process. According to Murray, a usual size of plant is one 
 absorbing 100 B.H.P. and producing about 1650 ft. 3 of 
 oxygen per hour (i.e. 60 B.H.P.H. per 1000 ft. 3 oxygen, 
 or, say, 53 K.W.H. if the efficiency of the motor == 85 %). 
 
 The following table gives particulars of various sizes of 
 Ivinde plants as regards power expenditure, etc : 
 
 TABLE 1 8. 
 LINDE OXYGEN PLANTS. 
 
 Oxygen production, 
 
 
 
 
 
 
 
 
 
 
 
 ft. 8 per hour 
 
 35 
 
 70 
 
 175 
 
 350 
 
 700 
 
 i,75 
 
 3.5 
 
 7,000 
 
 I750<> 
 
 35,ooo 
 
 Power (measured on 
 
 
 
 
 
 
 
 
 
 
 
 the switchboard), 
 
 
 
 
 
 
 
 
 
 
 
 K.W 
 
 4'5 
 
 7'5 
 
 15 
 
 26 
 
 4 1 
 
 75 
 
 138 
 
 260 
 
 600 
 
 1,120 
 
 K.W.H./iooo ft. 8 of 
 
 
 
 
 
 
 
 
 
 
 
 oxygen 
 
 129 
 
 107 
 
 86 
 
 74 
 
 59 
 
 43 
 
 39 
 
 37 
 
 34 
 
 32 
 
 Cooling water, gal- 
 
 
 
 
 
 
 
 
 
 
 
 lons per hour 
 
 55 
 
 no 
 
 220 
 
 350 
 
 530 
 
 880 
 
 1,540 
 
 2,860 
 
 6,400 
 
 11,900 
 
 Nitrogen Plants. The I^inde nitrogen rectifier is very 
 similar in general arrangement to that just described for 
 oxygen production, and is shown in Fig. 12 (cf. Engineering, 
 99, (1913), 156). Two gas supplies are used : (i) air at an 
 initial pressure of about 135 atms. to produce and maintain 
 the charge of liquid air ; (2) air at a pressure of about 
 60 lbs./in. 2 . Pre-cooling may be used with advantage, and 
 direct addition of liquid air may be substituted for (i). 
 The liquid air resulting from (i) is fed to the top of the 
 column while the low pressure air is led through coils in B, 
 is there liquefied and then released through the valve G to 
 the central portion of the column. In the column, as before, 
 rectification takes place down to an oxygen content of 7 % , 
 in which state of purity the nitrogen leaves the separator 
 through the pipe C. The high pressure compressor is then fed 
 with part of this effluent, with the result that the liquid at the 
 
AIR 85 
 
 top of the column contains only 7 % oxygen and' can conse- 
 quently reduce the oxygen content of the ascending gas to 
 about 2 % . In this way a cumulative rectification is produced 
 and eventually the gas issuing at C is practically pure nitrogen. 
 
 FIG. 12. Linde Nitrogen Plant. 
 
 The purity of the oxygen fraction is often not very high. 
 The power expenditure is about 14*2 H.P.H. per 1000 ft. 3 
 of nitrogen, according to Murray, equivalent to 12-4 K.W.H. 
 per 1000 ft. 3 if efficiency of motor = 85 %. One of the largest 
 plants in operation before the war was that at the Cyanamide 
 
86 
 
 INDUSTRIAL GASES 
 
 Works at Odda, capable of producing 13,000 ft. 3 (0-43 ton) 
 of nitrogen per hour. 
 
 The following table gives particulars of various sizes of 
 nitrogen plants : 
 
 TABLE 19. 
 LINDE NITROGEN PLANTS. 
 
 Nitrogen pro- 
 
 
 
 
 
 
 
 
 
 
 
 duction, ft 3 
 
 
 
 
 
 
 
 
 
 
 
 per hr. 
 
 210 
 
 4 2 5 
 
 1, 060 
 
 2,100 
 
 4.250 
 
 10,600 
 
 21,000 
 
 42,500 
 
 106,000 
 
 210,000 
 
 Power (mea- 
 
 
 
 
 
 
 
 
 
 
 
 sured on the 
 
 
 
 
 
 
 
 
 
 
 
 switchboard). 
 
 
 
 
 
 
 
 
 
 ! 
 
 K.W. 
 
 4'5 
 
 9 
 
 22 
 
 39 
 
 60 
 
 112 
 
 205 
 
 373 
 
 820 
 
 1,490 
 
 K.W.H./iooo 
 
 
 
 
 
 
 
 
 
 
 
 ft. 8 nitrogen 
 
 21-4 
 
 21'2 
 
 20'7 
 
 18-6 
 
 14-1 
 
 io'6 
 
 9'8 
 
 8-8 
 
 r 75 
 
 7-1 
 
 Cooling water. 
 
 
 
 
 
 
 
 
 
 
 
 Gallons per 
 
 
 
 
 
 
 
 
 
 
 
 hr 
 
 165 
 
 198 
 
 330 
 
 57 
 
 880 
 
 1,650 
 
 2,820 
 
 4,400 
 
 8,360 
 
 16,500 
 
 New Linde System. According to later L,inde patents 
 (D.R.P. 203814/06) rectification is pushed further by effecting 
 a preliminary fractionation under about 4 atms. pressure, 
 and thus obtaining a supply of liquid approximating to 
 pure nitrogen for the final fractionation. Thus, column b 
 (Fig. 13) is fed with air at about 4 atms. pressure at a. The 
 oxygen-rich liquid collecting at the bottom of this column 
 is taken to the vessel e at the top, the pressure being broken 
 down to atmospheric at the valve g. As the gas inside the 
 coil c is under a pressure of 4 atms., complete liquefaction 
 will ensue, the first condensate being thus of 21 % oxygen 
 content. Since the gas in equilibrium with liquid of this 
 composition at 4 atms. contains about 10 % oxygen, the 
 oxygen content of the liquid condensing in c will fall off 
 and eventually almost pure nitrogen will result. A portion 
 of the crude nitrogen from the top of b is led to the spiral 
 d immersed in the tank h at the bottom of the low pressure 
 column k and containing almost pure oxygen. Here 
 liquefaction occurs, the liquid being led via the valve *, 
 where the pressure is released, to the top of the column k, 
 in which further rectification results. The oxygen-rich 
 
AIR 
 
 87 
 
 liquid from / is vaporized in e, the vapours being led to the 
 lower part of k. Pure nitrogen and oxygen leave the 
 apparatus at n and m respectively. According to Martin, 
 when worked specially for oxygen some 85-90 % of the 
 oxygen is obtained as such. The energy consumption is 
 about 37 K.W.H. per 1000 ft. 3 of oxygen. Similarly it is 
 
 FIG. 13. New Linde System. 
 
 possible to produce nitrogen of about 997 % purity with 
 an energy expenditure of about 11-3 K.W.H. per 1000 ft. 3 
 of nitrogen. 
 
 Claude System 
 
 In the Claude system the problem of feeding the 
 fractionating column with a liquid poorer in oxygen than 
 
88 INDUSTRIAL GASES 
 
 that corresponding to ordinary air is attacked by effecting 
 a preliminary rectification, employing what the inventor 
 terms the " backward return," equivalent to a reflux con- 
 denser arrangement (B.P.s 16298/03, 26435/05, 17216/09, 
 etc.). Thus, air at a pressure of about 40 atms. enters the 
 apparatus through the heat-interchangers B and K 1 (Fig. 14), 
 undergoing partial liquefaction in Iy by heat-interchange 
 with the cold gases leaving at the top of M. The residual 
 air enters the rectification apparatus at A and undergoes 
 partial liquefaction in passing up the tubes B, cooled ex- 
 ternally by liquid air. Further liquefaction occurs in the 
 downward path with the production of a nitrogen-rich 
 fraction in A 1 while an oxygen-rich fraction collects in A. 
 These two fractions are fed into the column at different 
 levels, as in other systems. 
 
 The low temperature of the nitrogen issuing at G is 
 utilized for a preliminary liquefaction of the incoming air 
 at I,, as explained above, while thermal leakage into the 
 system is made good by expansion, with performance of 
 external work, of part of the incoming air in the cylinder O. 
 When admitted to the tubes B, the air is at a pressure of 
 about 5 atms., suffering release to atmospheric pressure at R 
 and R 1 respectively. Liquid air from an independent source 
 may be used to charge the apparatus, or, in the latest types, 
 the necessary charge is produced by the expansion device. 
 The pressure at X ranges from about 40 atms., when filling 
 up with liquid air, to a lower value in normal running, 
 varying according to the size of the installation, and being 
 as low as 18 atms. for large plants. The nitrogen obtained 
 in this way contains in practice about 3 % oxygen. Nitrogen 
 of a purity of 99*5% upwards can, however, be obtained 
 (B.P. 7175/10) by preventing the liquid dropping into the 
 chamber surrounding the tubes B from mixing immediately 
 with the main liquid therein, by disposing a separate tray 
 round the upper part of the tubes B. Thus, the entering 
 liquid, at a lower temperature than the main bulk of liquid 
 because of lower oxygen content, is utilized to lower the 
 oxygen content of the gaseous nitrogen. There are at 
 
AIR 
 
 89 
 
 present a large number of plants in operation, the most 
 usual sizes being 175-700 ft. 3 oxygen per hour. 
 
 FIG. 14. Claude Fractionation System. 
 
 The following table indicates the sizes and power 
 requirements of Claude plants (cf. Mewes, loc. cit., 
 
 P- 77) : 
 
90 INDUSTRIAL GASES 
 
 TABLE 20. 
 CLAUDE OXYGEN PLANTS. 
 
 Oxygen production, ft. 3 per hour 
 
 
 i,75o 
 
 3,500 
 
 Power (measured on the switchboard). 
 
 
 
 K.W 
 
 . . 
 
 56 
 
 78 
 
 K.W.H./iooo ft. 3 of oxygen 
 
 
 32 
 
 22 
 
 Pictet System 
 
 The Pictet system for oxygen and nitrogen (B.P.s 
 27463/10 and 9357/13 ; cf. Maxted, J. Soc. Chem. Ind., 
 (1917), 778), which is claimed to be very economical of 
 power by reason of employing only an approximation to the 
 minimum theoretical pressure for liquefaction, operates as 
 follows. Cooled air, at practically atmospheric pressure, 
 is led into the middle of a fractionating column (Fig. 15). 
 A series of coils is arranged, in a number of separate systems, 
 on the plates of the column and is supplied with compressed 
 gas drawn by the pump / from the top of the column at 
 which point the pressure is released from all the coils. Some 
 liquid air being first placed in the column, liquefaction 
 occurs in the coils and presently the gas leaving at the top 
 will contain 7 % oxygen. On liquefaction this will exert a 
 further refining action on the ascending air and pure nitrogen 
 will issue at the top of the column. The liquid collecting 
 at the bottom of the column is practically pure oxygen. 
 
 In order to avoid the employment of more pressure than 
 is necessary for the liquefaction and, further, to ensure 
 uniform fractionation along the length of the column, the 
 coils, as mentioned above, are divided into sections ; the 
 air is admitted at the bottom at a pressure of about 5 atms., 
 while the uppermost section is fed with air only slightly 
 above atmospheric pressure in accordance with the tempera- 
 ture gradient in the fractionation column, the pressure in 
 each case being just sufficient to produce liquefaction of 
 the nitrogen. The usual heat-interchangers are employed 
 and the losses are made good by the liquefaction of part of the 
 
AIR 91 
 
 issuing nitrogen by means of expansion with the production 
 of external work. 
 
 A plant on this system, with a capacity of 14,000 ft. 3 of 
 
 FIG. 15. Pictet System. 
 
 nitrogen and 3500 ft. 3 of oxygen per hour, has been installed 
 at the works of Gas Develop ments, L/td., Walsall. 
 
 Among other systems of importance may be cited the 
 Hildebrandt system, which, in general principle, does not 
 
92 INDUSTRIAL GASES 
 
 differ greatly from the l/inde system. A Hildebrandt plant 
 producing 350 ft. 3 of oxygen per hour absorbs about 27 K.W. 
 in power. 
 
 Separation of the Rare Gases. In the ordinary opera- 
 tion of liquid air fractionation plants, the rare gases divide 
 themselves between the oxygen and nitrogen according to 
 their boiling points. Thus, the oxygen fraction contains a 
 higher concentration of argon than the nitrogen fraction, 
 while the nitrogen fraction is richer in neon and helium. 
 By means of suitable additional fractionation arrangements 
 it is possible to separate the rare gases individually hi a 
 state of much greater concentration, and some account of 
 such methods will be found under the rare gases. 
 
 REFERENCES TO SECTION I 
 
 Claude, " Liquid Air, Oxygen, Nitrogen " (Cottrell). London, 1913. 
 
 Kausch, " Die Herstellung, Verwendung und Aufbewahrung von 
 fliissiger Luft." Weimar, Fourth Edition, 1913. 
 
 Travers, "The Experimental Study of Gases." London, 1901. 
 
 Anon., " The Use of Liquid Air in Industry," Engineering, 99, (1915), 155. 
 
 Linde, "Separation of the Constituents of Mixtures of Gases by Lique- 
 faction," /. Soc. Chem. Ind., (1911), 744. 
 
 Garner, " On the Theoretical Efficiency of the Linde Process of Liquefying 
 Air," /. Franklin Inst., 177; (1914), 305. 
 
 Mewes, "Angaben uber Kraftverbrauch und Leistung von Luftverfliissig- 
 ungs- und Sauerstoff Anlagen," Z.fur Sauerstoff und Stickstoff Industrie, 5, 
 (1913), 317; "Uber die Wirtschaftlichkeit moderner Luftverflussigungs- und 
 Gastrennungs- Anlagen," Ibid., 5, (1913), 175; " Sauerstofferzeugungs- 
 Anlage System Hildebrandt," Ibid., 2, (1910), 134, 160, 204, 281 ; 4, 
 
 (IQI2), 108. 
 
SECTION II. OXYGEN 
 
 Properties of Oxygen. Oxygen is a colourless, odourless 
 and tasteless gas, of which the chief physical properties 
 will be found in Table 12, pp. 53-55. 
 
 According to Holborn and Austin (loc. cit., p. 58) 
 the mean specific heat varies with temperature as 
 follows : 
 
 Temperature C. 
 
 C P 
 
 20440 
 20630 
 
 0-2240 
 0-2300 
 
 Its solubility in water is expressed by the following table : 
 
 Temperature C. 
 
 o 
 
 IO 
 
 15 
 
 20 
 
 40 
 
 C.c. of gas (measured at N.T.P.) 
 
 
 
 
 
 
 
 dissolved by I c.c. of water 
 under a pressure of i atm., ex- 
 
 
 0-049 
 
 0-038 
 
 0-034 
 
 0-031 
 
 0-023 
 
 clusive of water vapour. 
 
 
 
 
 
 
 
 Liquid oxygen is extremely mobile with a faint blue 
 colour, and the density of the vapour agrees with the formula 
 O 2 at 182 C. The liquid is a non-conductor of electricity, 
 but is strongly magnetic. Its refractive index (f* D ) is 1*2236 
 and its specific heat 0-347. It is not easy to obtain pure 
 liquid oxygen by the fractionation of liquid air, as the argon 
 tends to accumulate in the oxygen fraction. 
 
 Oxygen, being the active constituent of air as regards 
 combustion, supports combustion with great vigour, thus, 
 iron wire will burn freely in oxygen when once started. 
 Oxygen is readily converted into ozone by the action of the 
 silent discharge. Molten silver absorbs some ten times its 
 volume of oxygen, the gas being mostly disengaged on 
 solidification. 
 
94 INDUSTRIAL GASES 
 
 MANUFACTURE OF OXYGEN 
 
 General. The manufacture of oxygen has attracted the 
 attention of many inventors and various methods have been 
 suggested. One of the earliest patents is that of White 
 (B.P. 12536/49), relating to the use of nitre. In the early 
 days of the limelight lantern the oxygen was mainly produced 
 by the classical method of heating a mixture of potassium 
 chlorate and manganese dioxide, while the use of manganese 
 dioxide, either alone or with sulphuric acid, was adopted to 
 some extent. In the production of sulphuric anhydride by 
 the contact process a mixture of sulphur dioxide and oxygen 
 was formerly prepared by the decomposition of sulphuric 
 acid by dropping on a red-hot surface (Squire, B.P. 3278/75). 
 The only processes which have been worked on a really large 
 scale are the liquid air process and the baryta process, 
 No real success has attended work directed to the separation 
 of oxygen from the atmosphere by physical means, except, 
 of course, by fractionation of liquid air. 
 
 Although at present commercial use is only made of 
 oxygen specifically prepared, it is probable that with the 
 advent of various nitrogen fixation processes, e.g. the Haber, 
 Cyanamide, Bucher and other processes, the resulting 
 by-product oxygen will effect a great cheapening of oxygen, 
 not necessarily of a high degree of purity, for many purposes 
 at present out of the question on account of the cost of 
 oxygen. 
 
 (1) Manufacture by the Fractionation of Liquid 
 Air. For a description of this method, see Section I. 
 
 (2) By Electrolysis. Oxygen is liberated, together with 
 hydrogen, in the electrolysis of water. A full description 
 of this subject will be given under electrolytic hydrogen, 
 Section VI., and all quantitative data can be taken from this 
 description, the yield of oxygen being approximately half 
 that of the hydrogen. 
 
 On account of the (past) difficulty of its disposal, the 
 hydrogen produced simultaneously with the oxygen has 
 often been blown to waste or used for heating purposes. 
 
OXYGEN 95 
 
 The hydrogen, in conjunction with the oxygen, ma*y, how- 
 ever, be used profitably for welding. If freed from traces 
 of intermixed hydrogen (which may amount to about 3 %) 
 by passage over a heated catalyst, e.g. palladized pumice, 
 the oxygen is obtained in an extremely pure state. 
 
 On account of its very high purity electrolytic oxygen 
 is eminently suitable for., metal cutting operations (cf. 
 applications of oxygen) . Electrolytic oxygen is manufactured 
 in this country by the British Oxygen Co., L,td., at Wolver- 
 hampton, using the Schuckert cell. 
 
 Many attempts have been made by various inventors 
 to produce oxygen without the simultaneous production 
 of hydrogen ; such efforts, however, do not appear to have 
 met with any technical success. Thus, Coehn (cf. D.R.P. 
 75930/93) proposes the use of (a) cathodes which absorb 
 hydrogen and are subsequently used as elements of a gas 
 cell ; cf. also Brianchon, F.P. 439737/12, who uses a gas cell 
 of hydrogen and air to generate current for the decomposition 
 of water ; (b) the use of depolarizing copper oxide cathodes. 
 The use of depolarizing liquids and of electrolytes such as 
 copper sulphate solution, employing insoluble anodes and 
 effecting the deposition of copper, have been similarly proposed. 
 
 It is interesting to note that the minimum percentage 
 of hydrogen required to produce an explosive mixture with 
 oxygen is 5-5 %, the influence of increased pressure on the 
 limiting percentage being very small (cf. p. 40). 
 
 (3) By Alternate Formation and Decomposition of 
 Higher Oxides, etc. Prior to the introduction of the liquid 
 air method about 1895, the only processes (other than 
 electrolytic) which had been used for the production of 
 oxygen on anything like a large scale come under this cate- 
 gory. The patents relating to the subject are too numerous 
 to be given in full, but allusion will be made to the more 
 important. 
 
 As early as 1864 (B.P.s 2934/64 and 3171/66), Mallet 
 suggested the use of Cu 2 OCl 2 , formed by exposing cuprous 
 chloride to moist air ; on heating to dull redness oxygen is 
 evolved. The alternate formation and decomposition of 
 
96 INDUSTRIAL GASES 
 
 alkali manganates was put forward by Tessie du Motay and 
 Marechal (B.P. 85/66). By heating manganese dioxide 
 mixed with caustic soda to dull redness in a current of air 
 sodium manganate was formed, which on the passage of 
 steam at a bright red heat gave oxygen, the manganate 
 reverting to Mn 2 O 3 and caustic soda. Several works were 
 actually erected in Europe and New York, but the life of the 
 reactant mass was found to be rather short, largely on account 
 of segregation. A number of improvements were patented, 
 e.g. patents having as object the prevention of segregation, 
 while Parkinson (B.P. 14925/90) employed a vacuum instead 
 of steam, the air being pumped in under pressure and the 
 temperature maintained nearly constant. None of these 
 processes, however, met with any special success. 
 
 To take another direction of investigation, the use of 
 alkaline earth plumbates was suggested by Kastner in B.P. 
 1 1899/89. Calcium plumbate is formed on calcining a mixture 
 of calcium carbonate and oxide of lead in air and may be 
 decomposed, yielding oxygen, in a variety of ways, e.g. by 
 treatment with sodium carbonate solution and subsequent 
 heating of the resulting CaCO 3 -fPbO 2 precipitate ; by carbon 
 dioxide in suspension in water or by the action of carbon 
 dioxide without removal from the furnace. None of these 
 processes, however, is very practical. According to a 
 modified form of the process a combination of alkali manga- 
 nate and metaplumbate was used under the name of " Plumb- 
 oxan " (B.P. 12307/11), the mass being treated alternately 
 with air and steam at a temperature of 400-500 C. 
 
 A greater measure of success has attended the use of 
 barium peroxide, the dissociation pressure of which is greater 
 than that of Ca 2 PbO 4 . First suggested by Boussingault in 
 1851, it was developed by Messrs. Brin's Oxygen Co. about 
 1886 (cf. B.P. 1416/80). It was originally operated using a 
 considerable temperature variation, but by means of pressure 
 variation the time of oxygen evolution was shortened from 
 about 4 hours to about 15 minutes, a considerably lower 
 temperature being sufficient. Further, by means of a suitable 
 arrangement of valves (Brin's Oxygen Co. and Murray, 
 
OXYGEN 
 
 97 
 
 B.P.s 4955/89, 4292/91 and 14918/93), the operations were 
 rendered automatic, four cycles per hour being adopted, this 
 procedure tending to greater regularity of working and 
 minimizing wear and tear on the retorts. According to 
 B.P. 17298/91 the baryta is disposed on pumice. 
 
 The baryta used is obtained in a hard, porous state by 
 ignition of the nitrate ; it is important to purify the air 
 from carbon dioxide and from most of its moisture (by lime 
 and then caustic soda) before pumping into the retorts, 
 since both barium carbonate and barium hydroxide are 
 stable at high temperatures. The presence of a little water 
 vapour is necessary since it acts as a catalyst. The vertical 
 steel retorts, containing lumps of about walnut size, are 
 heated to about 600 C. Air at a pressure of about 10 lbs./in. 2 
 passes through the purifiers and then to the retorts, the 
 residual nitrogen escaping through a snifting valve. After 
 about 7 minutes, connection is made to a vacuum of about 
 26 ins. of mercury, the first portion of the oxygen being 
 rejected. The rate of production may be expressed as 
 
 (1) About 0*5 ft. 3 oxygen/lb. baryta/hour. 
 
 (2) About 25 ft. 3 oxygen/ft. 3 retort capacity /hour. 
 (Cf. Murray, Proc. Inst. Mech. Engineers, (1890), 131.) 
 
 The effect of the pressure variation can be readily seen 
 from the following dissociation pressures (Hildebrand, /. 
 Amer. Chem. Soc., 34, (1912), 246), for barium peroxide in the 
 presence of a little water : 
 
 Temperature C. 
 
 618 
 
 655 
 
 697 
 
 737 
 
 794 
 
 835 
 
 853 
 
 868 
 
 Oxygen pressure in 
 
 
 
 
 
 
 
 
 
 cms. of mercury . . 
 
 11-3 
 
 26-8 
 
 6.5-4 
 
 141 
 
 378 
 
 718 
 
 937 
 
 1166 
 
 Water vapour pressure 
 
 
 
 
 
 
 
 
 
 in cms. of mercury 
 
 7'3 
 
 13' 7 
 
 26-3 
 
 47 
 
 98 
 
 159 
 
 195 
 
 231 
 
 Until recent years the baryta process was used extensively 
 in the works of the Brin's Oxygen Co. (now the British 
 Oxygen Co.), e.g. in 1907 three works were producing 30,000 
 ft. 3 of oxygen per day ; it has now been superseded by the 
 liquid air process not only on account of its lower cost but 
 also because of the greater purity of the liquid air oxygen 
 A. 7 
 
98 INDUSTRIAL GASES 
 
 (about 98 % as compared with about 95 % by the baryta 
 process) . 
 
 Other processes on similar lines have been proposed, e.g. 
 the use of hsemoglobin (Sinding-L,arsen and Storm, B.P.s 
 8211/10 and 12728/10), the use of nitrosulphonic acid 
 (Bergfeld, B.P. 21211/13), etc., cf. also Teissier & Chaillaux, 
 see p. 206. 
 
 (4) By Auto-combustion Methods. The development 
 of such methods of preparing oxygen (cf . also the production 
 of hydrogen from " Hydrogenite," Section VII., p. 227) is 
 mainly due to the French chemist, Jaubert, who in a series 
 of patents (B.P.s 24330/05, 12246/06, and 12262/06) 
 proposes the employment of a mixture of perchlorates or 
 nitrates in excess, with a combustible material, an inert 
 diluent being added, if desired. Special apparatus is described 
 in B.P.s 12834/06; 1256/07, 17252/07, and 22034/09. 
 
 Briefly, the apparatus consists of a steel cylinder in which 
 is suspended a perforated cylinder containing the mixture, 
 known as " Oxygenite." The mixture is ignited and the 
 lid rapidly closed when the reaction prop agates itself through- 
 out the mass. Oxygen collects in the annular space sur- 
 rounding the inner cylinder at a pressure of about 12 atms. 
 The yield per Ib. of " Oxygenite " is about 4 ft. 3 and the cost 
 about 5/1000 ft. 3 . It is at once obvious that the process 
 is very expensive in comparison with the liquef action process, 
 but there are advantages for some special cases in the avoid- 
 ance of transport of cylinders, availability for mine rescue 
 work, etc. 
 
 Some slight modifications are due to Harger (B.P.s 
 16693/10 and 17628/10), the mixture of a chlorate and lamp- 
 black, with addition of a catalyst such as manganese dioxide 
 and also of caustic soda if carbon dioxide be produced in the 
 reaction, being used in the form of pencils; a continuous 
 feed of the pencils may be arranged. The hot oxygen is 
 led back through the unused material and through a purifier. 
 
 Other patents relate to alternative mixtures which may 
 be used. 
 
 (5) By the Action of Water on Peroxides and the 
 
OXYGEN 99 
 
 Like. Examination of the patent literature reveals a large 
 number of patents dealing with this method of making 
 oxygen. To take a typical example, sodium peroxide reacts 
 energetically with water according to the following equation : 
 
 2 Na 2 O 2 + 2 H 2 O = 4 NaOH + O 2 
 Thus, Jaubert, in B.P. 11466/01, proposes the use of 
 mixtures of alkali or alkaline earth peroxides with alkali 
 or alkaline earth hypochlorites in the form of pastilles, which 
 generate oxygen on treatment with water. 
 
 CaOCl 2 -f Na 2 2 +H 2 O =Ca(OH) 2 +2NaCl +O 2 
 
 A later patent (B.P. 21122/03) deals with the use of 
 mixtures such as a solution of bleaching powder with the 
 addition of catalysts as copper sulphate and iron sulphate, 
 while Artigue, in B.P. 14848/04, protects apparatus for carry- 
 ing this process into operation. Hanman, in B.P. 9783/03, 
 describes the mixture known as "Oxy lithe/' * while the use 
 of fused sodium peroxide is suggested by Foersterling and 
 Philipp in B.P. 3820/05. Among the various patents for 
 apparatus may be mentioned that of Ransford (B.P. 9785/02). 
 Other patents, e.g. Byk (B.P. 7495/09), describe the use of 
 perborates with the addition of stabilizers and catalysts. 
 
 Preparations on the market such as " Oxy lithe " are 
 useful for laboratory purposes. 
 
 " Oxy lithe " may be used in a Kipp's apparatus, one Ib. 
 giving about 3 ft. 3 of oxygen while " Bpurite " (= bleaching 
 powder + iron sulphate + copper sulphate) is suitable for 
 use on a larger scale, but in either case the oxygen is very 
 expensive. 
 
 Experiments have been made with sodium peroxide 
 preparations for revivifying the air of submarines, oxygen 
 being liberated by the moisture of the breath while the 
 resulting caustic soda serves to remove the carbon dioxide. 
 
 (6) By Physical Methods (in the Gaseous State). 
 In view of the fact that the solubilities of oxygen and nitrogen 
 in water at 15 C. are 0-034 an( i 0*0179 respectively for 
 
 * Sodium peroxide . . 98*32 per cent. 
 Oxide of iron . . . . 1*00 per cent. 
 Copper sulphate . . o - 68 per cent. 
 
ioo INDUSTRIAL GASES 
 
 i atm. pressure, it is obvious that the respective volumes 
 dissolved on shaking water with air are in the ratio 0*034 X z : 
 0-0179x4 = 1 : 2*1, since the partial pressures of oxygen 
 and nitrogen are 0*1 and 0*4 respectively. Consequently 
 the gas evolved on reducing the pressure or raising the 
 temperature is, if all the gas be driven out, of the composition 
 N 2 : O 2 = 2'i : i, i.e. 32 % oxygen, as against the original 
 21 %. Many attempts to effect an economic separation 
 have been made on these lines ; thus, Mallet (B.P. 2137/69) 
 saturated water with air under pressure and afterwards 
 exposed to a vacuum. After some 8 repetitions the gas 
 evolved was 97 % oxygen. Other patents, e.g. Kubierschky 
 (B.P. 17780/99), Humphrey (B.P. 14809/05), Levy (B.P. 
 5931/09), are similar. 
 
 Although the technical prospects of manufacturing 
 pure oxygen by such processes are small there would appear 
 to be some possibility of making oxygen-enriched air economi- 
 cally, e.g. by waterfalls in conjunction with arc processes, 
 etc. The same statement might be made with reference to 
 sundry patents relating to separation by centrifugalization 
 (Mazza, 13598/07) ; by diffusion (Runge, B.P. 3420/14), 
 or by transpiration through indiarubber, etc., (Helouis, B.P. 
 2080/81 ; Neave, B.P. 6463/90 ; de Villepique, Fournier 
 and Shenton, B.P. 19044/96 ; Bartelt, B.P. 24428/06). 
 
 None of these processes appears to have been applied 
 technically, the liquid air process being apparently the only 
 really successful case of the application of physical methods. 
 
 The lyinde-Frank-Caro process for the manufacture of 
 hydrogen (cf . p. 172) may be so operated as to yield oxygen 
 and nitrogen as by-products in connection with the cooling 
 of the water gas (the oxygen = about 25 % of the hydrogen 
 produced). 
 
 Compression of Oxygen. For a discussion of the 
 precautions to be observed in connection with the com- 
 pression of oxygen, see p. 34. In this country oxygen is 
 sold under a pressure of 120 atms., in black-painted cylinders, 
 the capacity of which does not usually exceed ioo ft. 3 . It 
 is most important that no oil or grease of any kind should 
 
OXYGEN 
 
 inr 
 
 be allowed to come into contact with the compressed gas, as 
 serious explosions may thus be caused. Steel should not be 
 used in the construction of the cylinder valves since com- 
 bustion of steel spindles has been known to occur, being 
 started by heat engendered by friction. 
 
 Comparison of Costs of Production and Purity 
 Attainable by Different Processes 
 
 It is difficult to give more than a very approximate 
 comparison of the costs of the different processes which have 
 been described in connection with the manufacture of oxygen, 
 but the following table will serve to give some idea of the 
 advances which have been made in this branch of technology. 
 All costs are on a pre-war basis : 
 
 TABLE 21. 
 COST OF PRODUCTION AND PURITY OF OXYGEN BY DIFFERENT PROCESSES. 
 
 Method. 
 
 Cost per 1000 ft. 3 
 
 Purity. 
 
 From potassium chlorate 
 
 ^8-10 
 
 Liable to contain traces 
 
 
 
 of chlorine. 
 
 
 From manganese dioxide 
 
 *^4-6 
 
 
 
 
 By the Tessie du Motay process 
 
 *^3~4 
 
 
 
 
 By the decomposition of sul- 
 
 *^2-3 
 
 
 
 
 phuric acid 
 
 
 
 
 
 
 Kassner process . . 
 
 
 *High 
 
 
 
 
 Brin process 
 
 
 *7S. tO I2S. 
 
 About 95 %. 
 
 
 By solution in water, et 
 
 
 *>? 
 
 
 
 
 Oxygenite process 
 
 
 
 
 
 
 [Oxylithe.] 
 
 
 L IO 1 
 
 
 
 Epurite process 
 
 
 ? 
 
 
 
 
 By electrolysis . . 
 
 
 t 
 
 Almost perfectly 
 passed over a 
 
 pure if 
 heated 
 
 
 
 catalyst. 
 
 
 From liquid air . . 
 
 * 3 s. 6d. 
 
 About 98 %. 
 
 
 The values of cost marked with an asterisk are taken 
 from Thorpe's "Dictionary of Applied Chemistry," 1912, 
 vol. 4, 40 ; they are apparently exclusive of overhead 
 charges. In the case of the liquid air process the overhead 
 
 f It is difficult to give any cost for electrolytic oxygen, as it depends 
 so much on the price of electric energy and the use to which the hydrogen 
 is put. For any particular case, however, reference to the section on 
 electrolytic hydrogen will supply the desired information. 
 
102 INDUSTRIAL GASES 
 
 charges may be taken as of the order of 1/6 per 1000 ft. 3 
 of oxygen. 
 
 As regards purity, it is important to note that in the 
 liquid air process about half of the argon initially present 
 in the air (about 0-9 %) goes into the oxygen fraction. The 
 percentage of argon is consequently higher in the oxygen 
 than in the nitrogen. A brief consideration of the respective 
 boiling points of the three gases, viz. nitrogen 196 C., 
 oxygen 183 C., argon 186 C., will indicate the reason 
 for this. " Liquid air" oxygen, therefore, usually contains 
 some 2-3 % of argon. Electrolytic oxygen, on the other 
 hand, can be produced in an almost pure state. 
 
 For the influence of purity on the technical applications 
 cf. "Metal cutting," p. 105. 
 
 Oxygen manufactured by the liquid air process contains 
 small quantities of organic matter which are liable to introduce 
 errors in organic combustions and similar operations. When 
 one bears in mind the presence of traces of methane and other 
 hydrocarbons in the atmosphere (cf. p. 59), this fact is not 
 surprising ; such impurities would tend to be concentrated 
 in the less volatile oxygen fraction. 
 
 Applications of Oxygen 
 
 The applications of oxygen are very diverse and it will 
 be well to discuss them under a number of headings as below. 
 Some 150-200 million ft. 3 of oxygen were manufactured 
 in Great Britain in 1913. According to Dewar (/. Soc. 
 Chem. 2nd., (1919), 23 R), the present output of the twelve 
 oxygen factories is about i million ft. 3 /day. 
 
 About 90 % of the above production is absorbed by 
 the welding and metal cutting industries in roughly equal 
 proportions. 
 
 (1) Scientific and Laboratory Uses. Oxygen is used 
 in the laboratory for effecting organic combustions, working 
 quartz or hard glass, making ozone and many other specific 
 purposes. 
 
 (2) Therapeutic Uses. Oxygen is largely used medi- 
 cinally for alleviation in asphyxiation, pulmonary complaints, 
 
OXYGEN 103 
 
 etc. ; and by dentists, in admixture with nitrous oxide, for 
 purposes of anaesthesia. It is also used for diving operations, 
 for mine rescue work (cf. also " Applications of liquid air," 
 p. 78), for smoke helmets, and for aeronautical work at 
 high altitudes. Its use has been suggested for improving 
 the atmosphere of theatres, etc., but at present the cost would 
 be rather prohibitive. 
 
 (3) Welding and Cutting of Metals. As mentioned 
 above, the principal applications of oxygen are in the 
 welding and cutting of metals, particularly steel. 
 
 (a) Welding. The art of autogenous welding is one which 
 has been developed gradually from ancient times. The 
 hydrogen- air, or the much more convenient oxy-coal gas 
 blowpipe, was long used for lead burning, but the industry 
 owes its present standing chiefly to the advent of the oxy- 
 acetylene blowpipe, which came into technical use about 
 1903. Acetylene has the advantage over hydrogen and coal 
 gas of a considerably higher heat of combustion. 
 
 Acetylene, net heat of combustion/ft. 3 . . 815 C.H.U. 
 Hydrogen, . . 153*3 
 
 Coal gas, ,, ,, . . ca. 280 
 
 Apart from its lower heat of combustion the low pressure 
 of coal gas is a considerable disadvantage. Petrol, benzol, 
 etc., may also be used in conjunction with oxygen. 
 
 The equation 
 
 2C 2 H 2 + 50 2 = 4C0 2 + 2H 2 
 
 demands 2,\ volumes of oxygen per volume of acetylene, but, 
 in practice, the best results are found to correspond to about 
 1*0 to 1-5 volumes. This ratio is in accordance with the 
 equation 
 
 2C 2 H 2 + O 2 = 2CO + 2H 2 O 
 
 and this represents the reaction in the inner white cone 
 of the oxy-acetylene flame ; the completion of the com- 
 bustion occurs in the outer cone, this being relatively cool 
 and serving to protect the weld from oxidation. The apex 
 of the cone has a temperature of probably over 3000 C. 
 
104 INDUSTRIAL GASES 
 
 There are two systems of working high and low pressure 
 respectively. The former was the first to be introduced 
 and uses acetylene at about 4-7 lbs./in. 2 pressure from 
 cylinders while the latter is more suitable for acetylene 
 generated directly from calcium carbide. Autogenous 
 welding of steel, aluminium, etc., is employed extensively 
 in connection with the motor industry. 
 
 (b) Cutting. In 1889 Fletcher showed that it was 
 possible to cut metals by introducing excess oxygen into the 
 oxy-coal gas flame. Twelve years later Menne, in Germany, 
 applied the process to opening up tuyeres which had become 
 blocked ; the process was found very convenient and the 
 method gradually became of greater applicability. In the 
 early stages difficulty was experienced from the lack of fluidity 
 of the iron oxide, the cutting being rendered intermittent. 
 
 About 1904, however, on the introduction of the cutting 
 blowpipe (by the Soc. Anon. 1'Oxhydrique Internat. of 
 Belgium), the essential feature of which was the provision 
 of a separate conduit for the " cutting " oxygen, either in 
 the centre of the heating jet or behind it, these difficulties 
 were overcome. 
 
 The method of operating is first to heat up a corner of 
 the article to be cut with a normal flame and then to turn on 
 the " cutting " oxygen, when combustion of the iron com- 
 mences. The fine " cutting "jet has sufficient force to blow 
 away the iron oxide, as it is formed, a thin, regular cut 
 resulting. By means of special guides for the blowpipe it 
 is possible to make a very precise cut. 
 
 As in welding, acetylene gives the best results, although 
 operations may be conducted with hydrogen or even with 
 coal gas. The proportions of combustible gas required for 
 the actual cutting are as follows : 
 
 Acetylene . . 25-10 
 
 ^ - per 100 volumes 
 
 Coal gas . . 50-20 , 
 
 TT j f oxygen 
 
 Hydrogen . . 150-80 
 
 according to the thickness of the work. 
 
 The purity of the oxygen used is of great importance on 
 
OXYGEN 
 
 105 
 
 account of the diluent effect of impurities such as nitrogen 
 or argon. For cutting operations a purity of at least 98 % 
 is desirable ; 95 % gives decidedly inferior results, although 
 quite good for welding. According to the International 
 Oxygen Company, the effect of the presence of 9 % nitrogen 
 is to double the time of cutting, while i % increases the cost 
 of cutting by about 25 %. It is obvious that the presence 
 of a little hydrogen in electrolytic oxygen is no disadvantage 
 from this point of view. 
 
 Some idea of the efficiency of the process may be gathered 
 from the following data (Murray, Thorpe's "Dictionary of 
 Applied Chemistry," 1912), relating to the cutting of nickel- 
 chrome armour plate 
 
 Thickness of 
 armour plate. 
 
 Time per 
 foot cut. 
 
 Oxygen used 
 per foot. 
 
 Oxygen used 
 per hour. 
 
 (in.) 
 
 (rain.) 
 
 (ft. 3 ) 
 
 (ft. 3 ) 
 
 9| 
 
 3i 
 
 30 
 
 530 
 
 12 
 
 4i 
 
 50 
 
 650 
 
 17 
 
 5 
 
 112 
 
 1350 
 
 The advantages of oxygen cutting over mechanical 
 methods are particularly marked in operations of demolition 
 of steel structures, e.g. bridges and the like. 
 
 (4) Other Applications of Oxygen. Among other 
 applications of oxygen may be mentioned the following : 
 
 The use of pure oxygen has been proposed (Pictet, F.P. 
 475528/14) in the manufacture of water gas. By passing 
 a mixture of steam and oxygen into the centre of the charge, 
 it is possible to obtain continuous operation as opposed to 
 the usual intermittent procedure. The employment of 
 oxygen for opening refractory tap-holes and blocked tuyeres, 
 has already been mentioned. Experiments have been made 
 on the operation of Bessemer converters with pure oxygen, 
 while the introduction of oxygen into fluid glass is found 
 beneficial. 
 
 Oxygen is also used, mostly on a small scale, for increasing 
 the temperature of furnaces (cf. also " Oxygen-enriched air "). 
 
io6 INDUSTRIAL GASES 
 
 Oxygen is used for the fusion of platinum ingots (usually 
 in conjunction with hydrogen), and also for the fusion and 
 manipulation of transparent quartz glass. The use of oxygen 
 for producing high power lights, e.g. in admixture with oil 
 gas or coal gas, with or without mantles, has been tried but 
 has not proved a commercial success. Similarly, proposals 
 have been put forward for the addition of oxygen to increase 
 the working pressures of internal combustion engines. 
 
 There are many patents, e.g. Farbwerke, vorm. Meister 
 lyucius and Briining (B.P.s 15948/11 and 13842/13), dealing 
 with the use of oxygen in connection with the conversion 
 of oxides of nitrogen (particularly in the liquid form) into 
 concentrated nitric acid. According to their D.R.P. 249329, 
 compressed oxygen is employed. The use of oxygen in 
 bleaching is said to give good results, effecting a saving in 
 bleaching powder. Milk can be sterilized by exposure in the 
 fresh condition to some 5 atmospheres pressure of oxygen 
 for several hours. Similarly, oxygen is used in the manu- 
 facture of oxidized oils, having the advantage that the process 
 can be effected at a steam heat, and that no " driers " are 
 required ; also for the artificial maturing of spirits, in the 
 production of vinegar, etc. It is claimed (Valon) that by 
 the addition of oxygen (about OT %) instead of air, the 
 elimination of sulphuretted hydrogen from coal gas by the 
 usual iron oxide purifiers is greatly facilitated. Dilution 
 with nitrogen is avoided (which is important when the 
 gas is used as an illuniinant with ordinary batswing 
 burners), and the capacity of the ore for taking up sulphur 
 is increased to 75 % of its weight of sulphur instead of 
 50 %. 
 
 The Vickers process of case-hardening steel consists in 
 effecting a sudden local heating of the surface of the steel by 
 means of an oxy-acetylene flame, on the removal of which 
 the heated layer is quenched by the body of cold metal 
 underneath. 
 
 Oxygen-enriched Air. There are a number of appli- 
 cations of oxygen to technical processes in which even approxi- 
 mate purity of the oxygen is a matter of small importance 
 
OXYGEN 107 
 
 or possibly undesirable ; it will be preferable to deal with such 
 applications under the heading of oxygen-enriched air. It 
 is probable that with the further cheapening of oxygen, many 
 new industrial applications of this character will present 
 themselves. Among such uses may be mentioned the 
 following : 
 
 (1) Use of oxygen- enriched air in the blast furnace. Trials 
 have been carried out by Trasenster at Ougree-Marihaye, 
 Belgium (Engineering, (1913), 374), with a blast furnace 
 supplied with air of 23 % oxygen content instead of the normal 
 21 %. As a result, a diminution of 5 % in the coke con- 
 sumption and an increase of 10-15 % in the output were 
 experienced, the cast iron being of excellent quality and rich 
 in silicon. 
 
 The oxygen was supplied by three Claude plants, each of 
 capacity 70,000 ft. 3 oxygen/hr. Johnson (Metall. and Chem. 
 Eng., 13, (1915), 483) found that an increase of the oxygen 
 content to 50 % resulted in a fuel economy of 33 % when 
 using a cold blast as against the normal dry hot blast. The 
 economy is still greater in the manufacture of ferro-silicon, 
 where a higher temperature is required. 
 
 (2) The use of oxygen-enriched air in the arc process for 
 nitrogen fixation. It has been found that by raising the 
 oxygen content to 50 % the yield of nitric acid in the above 
 process can be increased from 500 kilos./K.W.Yr. to 625 
 kilos./K.W.Yr., the cost of the oxygen being more than 
 balanced by the increased production. Some workers have 
 found as much as 50 % increase in efficiency. It is necessary 
 to work with a closed cycle, as only about 3 % conversion 
 takes place under the most favourable circumstances. 
 
 (3) The use of oxygen-enriched air in the Hausser process. 
 This process depends on the production of oxides of nitrogen 
 by the explosion of a compressed mixture of air and a fuel 
 gas. By increasing the oxygen content of the air to about 
 26 % the yield of oxides of nitrogen is raised from 6*4 Ibs. 
 to 10 Ibs. per 1000 ft. 3 of the combustible gas. According 
 to these experiments (at Wendel in Germany) it was expected, 
 with a supply of 7350 ft. 3 /hr. of coke gas, to make about i ton 
 
io8 INDUSTRIAL GASES 
 
 of nitric acid per diem, by the addition of about 2500 ft. 3 
 oxygen per hour. See also this series Partington, " The 
 Alkali Industry/' p. 174 et seq. 
 
 (4) Other applications of oxygen- enriched air. The use of 
 oxygen-enriched air has also been proposed in the oxidation 
 of ammonia to nitric acid by the Ostwald process ; in the 
 oxidation and absorption of the oxides of nitrogen resulting 
 from this and other operations, and in the manufacture of 
 sulphur trioxide by the contact process. 
 
 Estimation and Testing of Oxygen. Oxygen is readily 
 recognized when present even in small quantities in other 
 gases. If present in hydrogen its estimation is perhaps best 
 effected by means of the so-called " Grisoumeter " by the 
 action of a red-hot platinum wire. The contraction is equal 
 to three times the volume of the oxygen present. For an 
 automatic oxygen detector on this principle cf. Greenwood 
 and Zealley, loc. cit. When the oxygen is present in a non- 
 combustible gas, or where, for various reasons, the use of a 
 Grisoumeter is undesirable, the oxygen is readily determined 
 by absorption by copper gauze in the presence of ammonium 
 hydroxide and ammonium carbonate, by pyrogallol, by sticks 
 of phosphorus, or by sodium hydrosulphite. 
 
 The copper gauze method is very convenient, an absorp- 
 tion pipette taking up large quantities of oxygen without 
 agitation ; after the absorption the gas is freed from ammonia 
 before measurement. If present in the gas. carbon monoxide 
 is also absorbed by this reagent. When using phosphorus 
 the temperature must not be below 15 C. or oxidation does 
 not occur readily ; the presence of certain gases has a similar 
 inhibitive effect. The use of pyrogallol also has some 
 disadvantages as, under certain conditions, carbon monoxide 
 is evolved by the reagent. 
 
 Sodium hydrosulphite used in weakly alkaline solution 
 is an energetic absorbent for oxygen and is free from the 
 drawbacks of the other absorbents mentioned ; it does not 
 absorb carbon monoxide. When present in small quantities, 
 oxygen may be estimated colorimetrically by the red color- 
 ation produced in a solution of pyrogallol or a mixture of 
 
OXYGEN 109 
 
 pyro-catechine, ferrous sulphate and alkali in aqueous 
 solution (Binder and Weinland, Ber., (1913), 255). 
 
 The purity of commercial oxygen is best determined by 
 absorption with one of the above mentioned absorbents, 
 e.g. sodium hydrosulphite, and measurement of the small 
 residue. Small quantities of carbon dioxide are readily 
 determined by absorption with caustic soda, while hydrogen 
 may be estimated by the Grisoumeter method. 
 
 REFERENCES TO SECTION II. 
 
 Engelhardt, " The Electrolysis of Water " (Richards). Easton, Pa., 
 1904. 
 
 Murray, " On the Mechanical Appliances Employed in the Manufacture 
 and Storage of Oxygen (Baryta Process)," Proc. Inst. Mech. Eng., (1890), 
 
 131- 
 
 Richardson, " Autogenous Welding." London, 1913. 
 
SECTION III. NITROGEN 
 
 Properties of Nitrogen. Nitrogen is a colourless, odour- 
 less and tasteless gas, the most important physical properties 
 of which will be found in Table 1 2, pp. 53 -5. The solubility 
 in water is given in the following table : 
 
 Temperature C. 
 
 o 
 
 IO 
 
 15 
 
 20 
 
 40 
 
 C.c. of gas (measured at 
 
 
 
 
 
 
 N.T.P.) dissolved by i 
 
 
 
 
 
 
 c.c. of water under a 
 
 0-0239 0-0196 
 
 0-0179 
 
 0-0164 
 
 0*0118 
 
 pressure of I atm. ex- 
 
 
 
 
 
 clusive of water vapour. 
 
 
 
 
 
 
 The variation of the mean specific heat with temperature 
 has been found by Holborn and Henning (Annalen, (4), 18, 
 (1905), 7139; 23, (1907), 809) to follow the expression 
 C p = 0*2350 + 0-000019^ between o and 1400 C. According 
 to Crofts (Chem. Soc. Trans., (1915), 290), C y =0-1677 -J- 
 o '000014^, where C p is the mean specific heat between t and 
 
 15-5 c. 
 
 Liquid nitrogen is very mobile and quite colourless, with 
 a refractive index (/X D ) of 1-2053 a ^ "the boiling point. Its 
 specific heat is 0*43. For other properties see Tables 12 (B) 
 and 12 (C). 
 
 Nitrogen is generally regarded as a very inactive element. 
 To a very considerable extent, by comparison with such 
 gases as oxygen, this is true, since very few, if any, reactions 
 are known in which nitrogen enters into combination at the 
 ordinary temperature. Given, however, the stimulus of high 
 temperatures or of catalysts, nitrogen is capable of forming 
 directly a great number of compounds. Thus, the endo- 
 thermic compound nitric oxide can be produced by heating 
 air to very high temperatures, and then rapidly chilling, 
 
NITROGEN in 
 
 while the exothermic compound ammonia is easily formed 
 at a moderate temperature in the presence of a suitable 
 catalyst, especially at increased pressures. Nitrides are 
 formed by direct combination with a large number of metals 
 and non-metals at high temperatures. 
 
 According to recent experiments of Strutt, nitrogen can 
 be obtained in an allotropic form known as " active nitrogen," 
 by the passage of an electric discharge, preferably with 
 a condenser and spark gap in parallel, through nitrogen at a 
 pressure of a few mm. of mercury. A yellow glow is set 
 up in the gas and persists for a period varying from several 
 seconds to some minutes according to the conditions ; the 
 rate of disappearance of the glow rises with increase of 
 pressure. While in this state, the nitrogen has the property 
 of combining in the cold with various substances, e.g. with 
 acetylene to form hydrocyanic acid, or with liquid mercury 
 to form mercury nitride. No combination with oxygen or 
 hydrogen has been observed up to the present. It is found 
 that perfectly pure nitrogen does not give the glow, but its 
 formation is induced by the presence of minute amounts of 
 various impurities, e.g. 0-013 % oxygen, o'ooi % methane, 
 traces of sulphuretted hydrogen, ethylene, etc. 
 
 For further information on this interesting subject, 
 cf. Strutt, Chem. Soc. Trans., (1918), 200, and previous papers, 
 also lyowry, Trans. Faraday Soc., 9, (1913), 189. 
 
 MANUFACTURE OF NITROGEN 
 
 General. The production of nitrogen is a subject of 
 great and increasing importance at the present time, chiefly 
 in connection with the various synthetic processes for the 
 fixation of atmospheric nitrogen. In describing this subject 
 it will be unnecessary to make more than a passing allusion 
 to such methods as depend on a direct separation of the 
 constituents of the atmosphere, either by chemical or physical 
 means, since obviously all that has been said with reference 
 to such methods under oxygen, applies also to the case of 
 nitrogen ; moreover, no extensive use appears to have 
 
H2 INDUSTRIAL GASES 
 
 been made of such methods, with the notable exception of 
 the liquid air process. 
 
 (1) By the Fractionation of Liquid Air. The manu- 
 facture of nitrogen by this method, which is the only process 
 worthy of consideration at the present time, if approximately 
 pure nitrogen be required in large quantities, has already been 
 fully described (pp. 81 et seq.). 
 
 (2) By Direct Chemical Removal of the Oxygen 
 from Air. The processes coming under this heading may be 
 divided into two classes : (a) those depending on the alternate 
 absorption and disengagement of oxygen ; (b) those involving 
 the absorption of oxygen with the formation of an oxidized 
 compound which may be regenerated subsequently without 
 the production of free oxygen. 
 
 (a) Practically all that has been said under " Manufacture 
 of Oxygen," Section II., applies equally to nitrogen. The 
 Brin process was the most important, but the nitrogen 
 (cf. Price, B.P. 14213/03) does not appear ever to have been 
 collected and purified technically. 
 
 (b) The only process which has had any important industrial 
 application is that depending on the use of metallic copper, 
 but as many interesting reactions are involved a few of the 
 numerous patents may be mentioned here. 
 
 We find reference to the preparation of nitrogen by passing 
 air over heated iron sponge as early as 1869 (Spencer, B.P. 
 3752/69). The use of copper turnings was proposed by e.g. 
 Welton, B.P. 2559/79. Franke and Finke (B.P. 10718/12) 
 used copper gauze, which was subsequently reduced by 
 methyl alcohol or water gas. According to the Cyanid- 
 gesellschaft (D.R.P. 218671/12), two concentric retorts are 
 employed for this purpose, the charge of one undergoing 
 oxidation, while that of the other is being reduced, heat- 
 interchange thus being effected. 
 
 On similar lines is the process of the New York Nitrogen 
 Co. (B.P. 17666/11) for removing the oxygen by means of 
 molten lead. The use of sulphur (Blagburn, B.P. 25535/08) 
 or phosphorus (Haddan, B.P. 24293/95) has also been 
 suggested. Other inventors have protected the use of wet 
 
NITROGEN 113 
 
 methods, e.g. Wise (B.P. 4359/77) passes air over iron 
 filings moistened with ferrous sulphate solution, and Alder 
 (B.P. 1004/80) uses moist barium sulphide, etc. Similarly 
 Knecht, Perl and Spence in B.P.s 25532/11 and 25533/11, 
 make nitrogen in the course of dissolving cellulose in aqueous 
 ammonia and cupric hydroxide, while Elektrizitatswerk 
 I,onza, A. G. (D.R.P. 362671/16) passes air through a hot 
 solution of ammonium sulphite. 
 
 The " Harcourt " method of passing a mixture of air and 
 ammonia over heated copper turnings forms an excellent 
 means of preparing nitrogen on a semi- technical scale (cf. 
 Hutton andPetaval (/. Soc. Chem. Ind., (1904), 87 ; Marston, 
 B.P. 19074/1900). It is important to. use a considerable 
 excess of ammonia (about twice the theoretical quantity), 
 as otherwise, oxides of nitrogen are formed. After removal 
 of ammonia, the nitrogen contains about 4 % of hydrogen, 
 which can be easily eliminated by copper oxide, if necessary. 
 Nitrogen, prepared in this manner, costs about iyj- per 
 1000 ft. 3 . 
 
 In a series of patents by the Farbwerke vorm. Meister, 
 I,ucius u. Bruning, the manufacture of nitrogen in the 
 oxidation of ammonia is proposed ; excess of air is avoided, 
 nitrogen being obtained after separation of the oxides of 
 nitrogen. If desired, nitrogen may be added to keep down 
 the temperature (B.P.s 3662/13, 28737/13, and 9974/14). 
 
 Of these methods, the " copper " process appears to be 
 the only one which has had any measure of technical success. 
 Vertical cast-iron retorts are usually employed to contain the 
 copper turnings or sponge ; the retorts are heated to redness 
 in an ordinary furnace setting and are fed alternately with 
 air and water gas or other reducing medium. Thus, part of 
 the plant of the American Cyanamide Co. is supplied with 
 nitrogen by this process, the reduction being effected by the 
 gas from the coke-oven plant installed in connection with the 
 carbide production (cf . ' ' Applications of Nitrogen ' ') . Accord- 
 ing to Bucher (/. Ind. and Eng. Chem., 9, 1917, 233), a 
 temperature of 450 C. suffices for the efficient conduct of the 
 operation, and a volume of about 3*3 ft. 3 in the retort 
 A. 8 
 
ii4 INDUSTRIAL GASES 
 
 containing the copper turnings, gave an output during the 
 oxidation phase of some 200 ft. 3 per hour. It was found 
 important to guard against the tendency of the copper 
 turnings to cement together and block the gas passage, by 
 the provision of adequate support among the turnings. 
 
 Nitrogen results, in a more or less pure state, as a by- 
 product from a number of chemical processes, e.g. the 
 effluent from the chamber sulphuric acid process, in the Brin 
 process, in the manufacture of sodium carbonate by the 
 ammonia soda process (cf. p. 269), and also in the manu- 
 facture of wood pulp by the sulphite process. 
 
 The nitrogen present in products of combustion is dealt 
 with in the next section. 
 
 (3) From Producer Gas and Products of Combustion. 
 Since air consists of 79 % nitrogen, it is evident that in the 
 combustion of carbonaceous matter, the reaction products, 
 after separation of the water, will consist in large proportion 
 of nitrogen mixed with carbon dioxide, which gas is very 
 easily removed, or with carbon monoxide if the combustion 
 be only partial as in air producer gas. It will be convenient 
 to deal separately with the nitrogen in the two cases. 
 
 (a) Producer Gas. Air producer gas contains some 
 30 % carbon monoxide, the remainder being mainly nitrogen 
 with a little hydrogen, methane, etc. A description will be 
 found under " Manufacture of Hydrogen " (p. 205) of the 
 production of hydrogen or mixtures of hydrogen and 
 nitrogen from producer gas through the intermediary of 
 formates. 
 
 (b) Products of Combustion. In this case we have a some- 
 what simpler proposition, the gas from which the nitrogen 
 is to be isolated consisting of nitrogen, aqueous vapour, carbon 
 dioxide, with probably carbon monoxide or oxygen or both 
 and perhaps small amounts of sulphur compounds. The 
 removal of the carbon monoxide and/or oxygen, has attracted 
 the attention of a number of inventors, thus L,ance and 
 Blworthy (B.P. 4409/06) complete the oxidation by passage 
 over heated copper oxide ; the use of a heated mixture of a 
 metallic oxide and the corresponding metal, e.g. copper 
 
NITROGEN 115 
 
 
 oxide and copper, is claimed by Frank and Caro (B.P. 
 16963/08), serving the purpose of removing carbon monoxide 
 and oxygen, either alone or separately. According to 
 Riedel (B.P. 20631/09), a small proportion of reducing gas 
 is added to the products of combustion, the better to preserve 
 the balance. The Braun process, founded on the above 
 patent (cf. B.P. 22531/1!), is used on the large scale in Berlin. 
 The Kitzinger process, which is very similar, is stated to be 
 used especially for cyanamide production (cf. Chem. 
 Trade J., 62, (1918), 88). After some purification, the 
 furnace gases containing a certain excess of oxygen, are passed 
 with producer gas into a heated retort where the oxygen is 
 removed. The carbon dioxide is absorbed by passing the 
 cooled gases up towers fed with potash solution, the potash 
 being regenerated by heating the solution (cf. p. 264). 
 Success is stated to depend on an outlet for the large quantity ' 
 of carbon dioxide simultaneously produced. Harger (B.P.s 
 28075/11 and 16855/12) advocates the use of a gas engine 
 exhaust in order to secure a regular combustion, passing the 
 gases over a catalyst, e.g. titaniferous bog iron ore, with or 
 without use of the copper-copper oxide mixture, which 
 may be employed at 100-200 C. under a pressure of about 
 5 atmospheres. The carbon dioxide is removed according 
 to various known methods. Other inventors make use of 
 surface combustion to facilitate exact proportioning of the 
 fuel and air, e.g. McCourt and Ellis (B.P. 25629/12), while 
 Dreaper (B.P. 12927/13) adopts similar methods, but 
 utilizes the heat in the cyanamide or cyanide retorts for 
 which the nitrogen is being manufactured, cf . also Brownlee 
 and Uhlinger (B.P. 5097/15). 
 
 All the above processes are designed to produce, in the 
 first instance, a mixture of nitrogen and carbon dioxide, the 
 latter component being separated in a variety of ways. For 
 a detailed discussion of the removal of carbon dioxide and 
 other impurities, cf. p. 117 ; also for the isolation of the 
 same, cf. p. 264. 
 
 (4) By Physical Methods (in the Gaseous State).- 
 The eminently successful application of physical methods to 
 
u6 INDUSTRIAL GASES 
 
 the separation of the constituents of air by the liquid air pro- 
 cess, has been described. For a discussion of other physical 
 methods, cf. " Manufacture of Oxygen" (p. 94). It may be 
 mentioned that in the production of hydrogen by the L,inde- 
 Frank-Caro process, the cooling of the water gas to 200 C. 
 entails the production of large quantities of more or less 
 pure nitrogen, about equal in volume to the hydrogen 
 produced. 
 
 (5) By Direct Chemical Methods. It should be 
 pointed out that all the processes thus far described give, not 
 pure nitrogen, but a product containing a certain proportion 
 of argon as well as traces of the other rare gases. For 
 example, nitrogen prepared by the liquid air process may 
 contain up to about 0*5 % of argon ; that by the majority 
 of other methods, about 1*2 %. There are few, if any, 
 industrial applications in which absolute freedom from argon 
 is essential.* It is, however, of interest to indicate briefly, 
 possible methods of securing argon-free nitrogen on a fairly 
 large scale. Such nitrogen is easily obtained from a large 
 number of reactions, e.g. from solutions of ammoniacal salts, 
 by passing ammonia over heated copper oxide, by the action 
 of sulphur on cyanamide (Naef, B.P. 14607/12), etc. 
 
 Purification of Nitrogen 
 
 Allusion has been made in the preceding pages to the 
 elimination of specific impurities from nitrogen. It will, 
 however, be of advantage to collect together methods of 
 dealing with the different impurities likely to occur in 
 commercial nitrogen, either in large or small concentrations. 
 
 Purification from Carbon Monoxide. Although many 
 of the processes detailed under the Purification of hydrogen, 
 are equally applicable to the case of nitrogen, it is obviously 
 much cheaper to effect the desired operation by heated 
 
 * Argon content is of considerable importance in such cases as the 
 synthesis of ammonia where the reactants, nitrogen and hydrogen, are 
 circulated continuously over a catalyst in a closed system. Any argon 
 present rapidly accumulates and lowers the output of the plant, cceteris 
 paribus, in proportion to its concentration and necessitates blowing off the 
 gases to waste. Similar considerations apply in cyanamide production. 
 
NITROGEN 117 
 
 . 
 
 copper oxide (cf. p. 114), and subsequent removal of the 
 carbon dioxide produced. 
 
 Purification from Carbon Dioxide. A full account 
 of the different methods of removing carbon dioxide in large 
 or small quantities from hydrogen, will be found on p. 209 
 (cf. also p. 161). All these methods, of course, apply equally 
 to nitrogen. 
 
 Purification from Oxygen. The removal of small 
 quantities of oxygen is effected conveniently with heated 
 metallic copper, etc. (cf. p. 113), or, if the presence of a little 
 reducing gas is not detrimental, by the addition of a slight 
 excess of hydrogen or other reducing gas, and passage over 
 a heated catalyst, e.g. platinized pumice, etc. 
 
 Purification from Sulphur Compounds. In this 
 connection, reference may be made to the information given 
 on p. 210, relating to the purification of hydrogen. All these 
 methods are applicable to nitrogen, with the exception of the 
 Carpenter catalytic hydrogenation method. 
 
 Comparison of Costs of Production and Purity 
 attainable by the Different Processes 
 
 Nitrogen can be manufactured on a large scale, say 
 10,000-20,000 ft. 3 /hr., at a cost (pre-war) not greatly 
 exceeding -/6 per 1000 ft. 3 inclusive of capital charges. On 
 a smaller scale the cost of production will be higher, say i/- 
 per 1000 ft. 3 . The copper process is more expensive. 
 
 As regards purity, reference has been made to the argon 
 content on p. 116. I/iquid air nitrogen usually contains some 
 0*5 % oxygen and up to about 0*5 % argon. 
 
 Applications of Nitrogen Nitrogen Fixation 
 
 The only important industrial consumption of nitrogen 
 is in connection with the fixation of free nitrogen. It is 
 scarcely possible to exaggerate the importance of this rela- 
 tively new branch of chemical technology. The manufacture 
 of explosives without the use of Chile saltpetre, has occupied 
 the attention of belligerent countries during the war, and the 
 war would have been impossible in Germany but for the 
 
n8 INDUSTRIAL GASES 
 
 recent advances in the synthetic production of ammonia and 
 nitric acid : the manufacture of artificial fertilizers in peace 
 time, is of almost equal, if less sensational, national 
 importance. 
 
 A brief description will be given of the chief processes 
 involving the use of free nitrogen. The arc process, which 
 depends on the combination of the constituents of the 
 atmosphere under the influence of a high-tension arc, does 
 not necessitate any preliminary separation of the nitrogen 
 and oxygen. 
 
 Nitrogen is sold in this country in grey painted cylinders, 
 under a pressure of 120 atms. ; there is, as yet, no great 
 demand for nitrogen in this form. 
 
 (a) Cyanamide Process. The inception of this important 
 process is due to the researches of Frank and Caro, about 
 1895. It depends on the direct absorption of free nitrogen 
 by calcium carbide when heated to 1000-1100 C. Re- 
 action does not occur under these conditions with the pure 
 carbide, but proceeds readily with the commercial product. 
 
 CaC 2 + N 2 = Ca=N-N=C + C 
 
 This compound, known as cyanamide or "nitrolim," 
 is stable in dry air and is valuable as a fertilizer ; as a source 
 of ammonia, which is easily produced by hydrolysis with 
 steam under pressure ; in the production of cyanides, and in 
 the production of various dye-stuffs ; in the manufacture of 
 urea ; in explosives ; case hardening media, etc. 
 
 The usual method of effecting the reaction is to raise 
 the temperature of a relatively small charge of powdered 
 calcium carbide, contained in a lagged closed vessel, to a high 
 temperature by means of an electrically-heated carbon rod, 
 and to supply nitrogen, whereupon the exothermic reaction 
 propagates itself slowly through the mass, the entire opera- 
 tion occupying some 30-40 hours. It is important that 
 the nitrogen should be free from water and oxygen, which 
 would react with the carbide and cyanamide respectively. 
 The product usually contains some 20 % nitrogen ; pure 
 CaCN 2 contains 35 % nitrogen. A little calcium carbide 
 
NITROGEN 119 
 
 (about i %) is usually left unchanged in the product, and, 
 to make transport safe; is removed by partial hydration ; 
 for agricultural purposes, the powder is oiled to minimize 
 its dusty propensities. One of the chief drawbacks to the 
 use of the cyanamide process in this country, is the high 
 power consumption as compared with the Haber and Cyanide 
 processes (cf. p. 121). -With cheap water power, on the 
 other hand, the conditions are more favourable. The first 
 plant was erected at Piano d'Orte in 1905 ; there are many 
 plants in Norway (particularly at Odda), at Niagara, in 
 Switzerland, Germany, etc. 
 
 Some 200,000 tons of cyanamide were produced in 
 1914 ; in 1917, the production in Germany alone is stated to 
 have been 886,000 tons (=5400 X io 6 ft. 3 nitrogen), while 
 similar extensions have taken place in other countries ; 
 according to Marselli, the world production in 1916 was 
 981,500 tons (Chem. Trade J., 63, (1918), 182). 
 
 The nitrogen for cyanamide production was at first made 
 by the copper process, but is now mostly produced by the 
 cheaper liquid air process ; the American Cyanamide Co., 
 however, operates part of its plant by the copper process, 
 the reduction of the oxide being effected by the coke oven 
 gases from the coke plant in connection with the carbide 
 manufacture (cf. p. 113). 
 
 The cyanamide plant in contemplation by the American 
 Air Nitrates Corporation during the war, was to produce 
 350,000 tons of cyanamide per annum, a power plant of 
 60,000 K.W. being necessary. 
 
 (b) The Synthesis of Ammonia. An account of this 
 process will be given under the applications of hydrogen. 
 The probable consumption of nitrogen for this purpose in 
 Germany at the end of the war was of the order of at least 
 3000 million ft. 3 per annum or about 350,000 ft. 3 /hr. Refer- 
 ence has already been made (p. 116) to the influence of the 
 argon content in this application of nitrogen. 
 
 (c) The Formation of Metallic Nitrides. There are 
 a number of processes for the production of different nitrides 
 by direct combination of nitrogen. Chief of these is the 
 
120 INDUSTRIAL GASES 
 
 Serpek process, which depends on the action of nitrogen on 
 a mixture of bauxite (impure alumina) and carbon at a 
 temperature of about 1800 C. 
 
 A1 2 3 + 3 C + N 2 = 2A1N + 3 CO 
 
 Most of the silica of the bauxite is volatilized. The 
 process is carried out in rotary furnaces, electric resistance 
 heating being employed ; it is apparently not necessary to 
 use pure nitrogen, air producer gas, which contains about 
 60 % nitrogen, being adequate. With bauxite, a product 
 containing 20-26 % nitrogen is obtained, while pure 
 alumina gives the pure nitride containing 34 %. The process 
 is best used in conjunction with the production from bauxite 
 of pure alumina for the manufacture of aluminium by 
 electrolysis. Thus, the nitride on decomposition with 
 alkalis yields ammonia and sodium aluminate if caustic 
 soda be employed ; by precipitation of alumina from the 
 latter, a very pure product is secured. 
 
 L,arge scale operations are being carried out in Savoy 
 by the Societe Generale des Nitrures. A Claude nitrogen 
 plant, with a capacity of about 10,000 ft. 3 /hr., was recently 
 put down for this purpose. There are a number of patents, 
 many by the Badische Anilin & Soda Fabrik, dealing with 
 the addition of other nitride-forming substances to the 
 alumina and also with the use of other nitrides in the place 
 of aluminium nitride. 
 
 (d) The Direct Production of Cyanides. There have 
 been many proposals for the fixation of nitrogen by the 
 production of cyanides ; thus, if barium carbonate mixed with 
 carbon be treated with nitrogen at a temperature of about 
 1400 C., barium cyanide results and on treatment with 
 steam gives barium hydroxide and ammonia. The only 
 process, however, which has offered any real prospect of 
 being worked on a large scale is that due to Bucher 
 (loc. cit., p. 113), which has recently attracted considerable 
 attention in the United States. It depends on the 
 action of a mixture of sodium carbonate, carbon and a 
 small quantity of iron, which acts as a catalyst, on air producer 
 
NITROGEN 
 
 121 
 
 gas at a temperature of about 920 C., with the production 
 of sodium cyanide. 
 
 The product can be converted into ammonia if desired, 
 with regeneration of the sodium carbonate and iron. 
 
 This process holds out promise of great advantage over 
 most of the other nitrogen fixation processes, on account of 
 its crudity ; no electric power is required and pure nitrogen 
 is unnecessary. On the other hand, the necessity of external 
 heating of retorts to the requisite high temperature, combined 
 with the corrosive properties of the reactants at high temper- 
 atures, makes transition from a semi-technical scale to large 
 scale working difficult. 
 
 (e) The Hausser Process. This process depends on the 
 production of oxides of nitrogen on the explosion of com- 
 pressed fuel gas-air mixtures (cf. p. 107). 
 
 Comparison of the Power Requirements in various 
 Nitrogen Fixation Processes. Before leaving the con- 
 sideration of this very important subject, it will be interesting 
 to give some approximate figures for the relative power 
 requirements of the different processes described above, in 
 terms of 96 % nitric acid as ultimate product. Where 
 ammonia is the immediate product, nitric acid is obtained 
 by oxidation according to the Ostwald or allied processes. 
 
 
 Arc process. 
 
 Cyanamide 
 process. 
 
 Haber process. 
 
 Serpek process. 
 
 Power required per") 
 ton 96 % nitric [ 
 acid. K.W. years] 
 
 r8o 
 
 0-38 
 
 0-050 
 
 0'2 
 
 Cf. Parsons, J. Ind. Eng. Chem., (1917), 829. 
 
 As regards the costs of production, the following may be 
 taken as an indication of the relative values of the processes. 
 (Norton.) 
 
 Cost per ton of 100 % nitric acid 
 
 (a) from Chile nitrate at 1914 rates . . . . 20 
 
 (b) by the Arc process with power at o'o685^./K.W.H. 
 
 (c) by the Cyanamide process 
 
 (d) by the Haber process 7 
 
122 INDUSTRIAL GASES 
 
 Other Applications. Considerable quantities of 
 nitrogen, small in comparison with the amounts used in 
 connection with the above processes, are utilized in the filling 
 of " half -watt " electric lamps, although nitrogen is rapidly 
 being replaced by the more effective argon. The advantage 
 of a certain amount of gas (about ^ atm.) in the bulb is that 
 the filament can be run at a temperature 400-600 C. 
 higher, with consequent marked increased efficiency, without 
 producing " blackening " of the bulb. 
 
 Nitrogen is used for the storage and transfer from one 
 vessel to another of highly inflammable liquids like petrol. 
 
 High temperature mercury thermometers are filled with 
 compressed nitrogen. 
 
 Estimation and Testing of Nitrogen 
 
 In view of its inertness towards reagents at the ordinary 
 temperature, nitrogen is usually estimated by difference, 
 i.e. by determination of the residue after removal of other 
 gases. Oxygen, carbon dioxide and carbon monoxide are 
 readily estimated separately by the methods described under 
 the individual gases. In admixture with hydrogen or other 
 combustible gas, nitrogen is usually estimated by passing 
 the gas over copper oxide when hydrogen, say, is removed 
 and a residue of nitrogen remains. Mixtures with hydrogen 
 lend themselves well to physical methods of analysis. Occa- 
 sionally it is necessary actually to absorb nitrogen in order 
 to determine the content of rare gases ; in such cases, the 
 absorption is best effected by metallic calcium (cf. Sieverts, 
 Z. Elektrochem., 22, (1916), 15) or by calcium carbide. 
 
 REFERENCES TO SECTION III 
 
 General. Crossley ," The Utilization of Atmospheric Nitrogen," Pharm. / 
 
 (1910), 329. 
 Nitrogen Fixation in General. Norton, " Utilization of Atmospheric 
 
 Nitrogen," Dept. of Commerce and Labour, U.S.A., Special Agents 
 
 Series, No. 52. 
 Summers, " Fixation of Atmospheric Nitrogen," Proc. Amer. Inst. 
 
 Elec. Eng., (1915), 337- 
 Cyanamide Production. Landis, " The Fixation of Atmospheric Nitrogen," 
 
 Met. and Chem. Eng., 13, (1915), 213. 
 Washburn, 13, (1915), 309- 
 
SECTION IV. THE RARE GASES OF THE 
 ATMOSPHERE 
 
 General. The discovery of argon by the brilliant work 
 of Ramsay and Rayleigh, has led to the rapid development 
 of our knowledge of these minor constituents of the atmo- 
 sphere. Recently there have arisen certain applications 
 which confer on them the right to be termed " industrial " 
 gases. It is interesting to recapitulate the approximate 
 volume percentages present in the atmosphere. 
 
 Argon . . . . 0-93236 % 
 
 Neon . . . . 0*00181 % 
 
 Helium . . . . 0-00054 % 
 
 Krypton . . . . 0*0000049 % 
 
 Xenon . . . . 0*00000059 % 
 
 Niton . . . . i 
 
 Thorium emanation/ v ^ mnute amounts - 
 
 History of the Discovery of the Rare Gases. In 
 
 1892, certain discrepancies were noticed by Rayleigh between 
 " chemical " nitrogen and nitrogen produced by removal of 
 oxygen from the atmosphere, the former being some 0*5 % 
 lighter than the latter. 
 
 Two years later Ramsay carried out experiments on the 
 treatment of air, after removal of oxygen, with heated 
 magnesium which absorbs the nitrogen. A reduction to 
 i/8oth of the original volume was effected, and the density 
 increased to 16*1 (O 2 = 16) ; by further treatment the density 
 rose to 19*038. It was at first thought that the new gas, 
 which resisted the action of magnesium, bore the same 
 relation to nitrogen as ozone does to oxygen, but by gradual 
 accumulation of evidence, it was established that a new 
 element had been isolated. 
 
124 INDUSTRIAL GASES 
 
 At this point, Ramsay and Rayleigh carried out experi- 
 ments on a larger scale, with the method originally used 
 by Cavendish, viz. of removing nitrogen by combination 
 with the oxygen of the air under the influence of an electric 
 discharge. A high-tension arc was run (using about 800 
 watts) , in a 5o-litre flask of which the inner surface was washed 
 by a continuous fountain of caustic soda solution, the flask 
 being supplied with a mixture of air and oxygen. Absorption 
 took place at the rate of about 20 litres per hour. The 
 process, if desired, can be pushed to completion, but the 
 final concentration is better effected by other methods. 
 The above investigators also employed the method of passing 
 atmospheric nitrogen over a mixture of metallic magnesium 
 and quicklime (originally used by Maquenne, Comptes Rend., 
 121, (1895), 114), heated to bright redness. 
 
 In 1889, it was found by Hillebrand that a certain mineral, 
 Cleveite, on heating evolved a gas resembling nitrogen. 
 Hearing of this, it occurred to Ramsay that the gas might 
 be argon. On carrying out experiments, however, the gas 
 was found to be not argon, but a new gas, which was subse- 
 quently (1894) termed " helium." Further researches on 
 the fractionation of liquid air, which was just becoming 
 available on a fairly large scale (cf. p. 69), led to the 
 isolation of neon, krypton and xenon. 
 
 ARGON 
 
 Occurrence. Argon is present to the extent of 0*93 % 
 in the atmosphere ; it occurs in mineral springs (e.g. the gases 
 from the Wildbad hot springs contain 1-56 % argon and 
 0*71 % helium), in meteorites, and in a few rare minerals 
 such as malacone (3(ZrO 2 .SiO 2 )H 2 O). 
 
 Manufacture. Reference has already been made to 
 the preparation of argon by the action of magnesium mixed 
 with quicklime on atmospheric nitrogen it is important 
 that the lime used should be free from hydrate and carbonate, 
 as otherwise serious explosions may result. Metallic calcium 
 can also be used with good effect. 
 
 A method which appears to be more suited than most 
 
THE RARE GASES OF THE ATMOSPHERE 125 
 
 for technical operations on a moderate scale, depends on the 
 absorption of nitrogen by calcium carbide. According to 
 Fischer and Ringe (Ber., 41, (1908), 2017), cf. also, Fischer 
 and Hahnel, ib., 43, (1910), 1435, air was passed into an 
 iron retort heated to about 800 C. and containing calcium 
 carbide mixed with about 10 % calcium chloride which 
 facilitates the absorption ~at this comparatively low temper- 
 ature (cf. the " Manufacture of Cyanamide," p. 118). The 
 nitrogen is absorbed with the formation of cyanamide while 
 the oxygen is partly fixed as carbonate, some carbon monoxide 
 being also formed. The retort was first exhausted, then 
 heated up and air admitted until no further absorption 
 was observed ; the contents of the retort were then circu- 
 lated in the sequence copper oxide caustic potash- 
 sulphuric acid phosphorus pentoxide pump gas-holder 
 retort until absorption was complete. Some n litres 
 of fairly pure argon were thus made in two days with a charge 
 of 7 kilos, of calcium carbide. The chief drawback to the 
 process is the fact that the residue of carbide + cyanamide 
 is very difficult to remove from the retort. 
 
 It is obvious that in the manufacture of cyanamide on the 
 large scale, large quantities of argon must be produced in a 
 concentrated state, particularly if the nitrogen be prepared 
 by the copper process, and many thousands of cubic feet 
 of highly concentrated argon are sold annually by the 
 American Cyanamide Co., for lamp-filling purposes (cf. 
 Washburn, Chem. News, 112, (1915), 29). For similar 
 procedure in the fixation of atmospheric nitrogen as cyanide, 
 cf. Bucher, B.P. 4667/13. 
 
 Residues from the synthetic production of ammonia, 
 and from direct nitric acid manufacture using oxygen- 
 enriched air, with closed circulatory systems, are also possible 
 sources of argon. For the latter instance cf. Norsk Hydro 
 Elektrisk Kvaelstofaktieselskab, B.P. 100099/16, according 
 to which the circulation is so conducted that the percentage 
 of rare gases is maintained at about 10 %. 
 
 A convenient method of making argon in the laboratory 
 depends on the high argon content of commercial " liquid 
 
126 INDUSTRIAL GASES 
 
 air " oxygen, which often contains some 2-3 % argon and 
 but little nitrogen. For example, Claude (Comptes Rend., 
 151, (1910), 752) describes apparatus for the preparation 
 of argon at a rate of about 5 litres/hr. from 96 % oxygen, 
 passing the same over heated copper and through an iron 
 tube containing magnesium and heated to redness. 
 
 On similar lines is the patent (F.P. 473985/14) of the 
 
 Griesheim-Elektron Co., according to which oxygen as above 
 
 is burnt with the correct proportion of hydrogen either with 
 
 a flame in a water-cooled vessel, or in the presence of a 
 
 catalyst, e.g. copper. A detailed description of a method 
 
 based on this process, is given by Bodenstein and Wachem- 
 
 heim (Ber., 51, (1918), 265). "liquid air" oxygen is 
 
 burnt with hydrogen in a small quartz combustion chamber. 
 
 After cooling to remove steam, the exit gases are led through 
 
 a sensitive rate gauge, and the respective streams of oxygen 
 
 and hydrogen are adjusted to give the minimum final gas 
 
 stream, indicating that the proportions are correct. The 
 
 argon is freed from traces of oxygen or hydrogen by passing 
 
 through heated copper and copper oxide, and finally nitrogen 
 
 is removed by an iron tube containing calcium turnings 
 
 heated electrically to 600 C. Even in the laboratory it 
 
 is possible to make argon at a rate of about 0*5 litres per 
 
 hour. 
 
 For isolating argon in really large quantities, the fraction- 
 ation of liquid air probably offers the most promise. Remem- 
 bering that the boiling point of argon lies between those of 
 nitrogen and oxygen, it will be understood that the inter- 
 mediate fractions will be rich on argon, and various patents 
 relate to the effective separation of the argon, mostly 
 depending on a further fractionation in a separate column 
 (cf. Claude, B.P. 3326/11; I4nde, B.P. 24735/14; Filippo, 
 Schoonenberg & Naamloze Vennootschap Philips Metal 
 Gloelamp-fabrik, B.P. 101860/16; Fonda, (Gen. Elec. Co.), 
 U.S.P. 1211125/17; Claude, Comptes Rend., 166, (1918), 
 492). Blockages are sometimes caused in liquid air plant 
 by the separation of solid argon, which may lead to explosions 
 on incautious heating to remove the obstruction. The final 
 
THE RARE GASES OF THE ATMOSPHERE 127 
 
 concentration of the argon (e.g. oxygen + 20 '% argon) 
 separated by the liquid air process may, of course, be com- 
 pleted by any of the above-mentioned processes, e.g. by 
 combustion with hydrogen. 
 
 It must be remembered that the gas referred to above 
 as argon, means in most cases a mixture of the whole of the 
 rare gases of the atmosphere. This obtains with chemical 
 means, but when made from liquid air a certain selection 
 takes place. 
 
 As regards purification, this is most readily accomplished 
 by treatment with metallic calcium or with lithium (Schloe- 
 sing) for the removal of small quantities of nitrogen, and 
 by fractional distillation or selective absorption with cooled 
 charcoal (see below) for freeing from the other rare gases. 
 
 Properties and Applications. Argon in common with 
 the other rare gases, is distinguished from most other per- 
 manent gases by chemical inertness, and by monatomicity. 
 Its chief physical constants will be found on pp. 53-55. 
 
 According to Kistiakowsky (1897), argon has the property 
 of diffusing through caoutchouc some 100 times as fast as 
 carbon dioxide ; according to Dewar (1918), however (cf. 
 p. 10), its rate is slower. On passage of the electric 
 discharge through the rarefied gas, a brilliant red colour is 
 obtained with continuous current ; the colour of the discharge 
 may be blue, however, under certain electrical conditions, 
 e.g. with oscillatory currents. The change from red to blue 
 is effected when using a continuous current by the incidence 
 of Herzian waves, and an argon-filled Geissler tube may be 
 used as a detector for electric waves. The spectrum is 
 not very characteristic except when the gas is fairly 
 pure, and is thus not of much assistance in detecting 
 the presence of argon in nitrogen. A good criterion of the 
 purity is to be found in the measurement of the dielectric 
 cohesion. 
 
 Argon shares with the other rare gases the property 
 of offering a low resistance to the passage of an electric spark ; 
 the value is increased to about 2j times by the presence of 
 i % air or other impurity. It has been observed that at 
 
128 INDUSTRIAL GASES 
 
 low pressures, spluttering of the electrodes is more marked 
 in the electric discharge in argon than in diatomic gases, 
 and at a pressure of about 0*005-1 mm., argon causes a 
 marked Edison effect in incandescent lamps, with increased 
 blackening. At higher pressures its action is quite different. 
 Reference has already been made to the use of nitrogen 
 in the " half -watt " metal filament lamp (p. 122). Increasing 
 quantities of argon are now being employed, both alone 
 and in admixture with nitrogen, for this purpose. The 
 proportion of argon in admixture with nitrogen for lamp 
 rilling may be estimated (Hamburger and Filippo, Z. angew. 
 Chem., 28, (1915), 75) by comparing the vapour pressure 
 on cooling in liquid air, with the pressures shown by standard 
 mixtures. 
 
 NEON 
 
 Occurrence. Neon occurs with the other rare gases 
 in the atmosphere and also in mineral springs. In the 
 atmosphere it is present to the extent of 0*0018 % being, 
 next to argon, the chief constituent of the inert gas fraction. 
 
 Isolation. The most convenient method of isolating 
 neon is by the separation from air, either entirely by physical 
 means or by physical treatment of the residue of inert gases 
 produced by the chemical removal of the nitrogen and 
 oxygen. Thus, neon was discovered by Ramsay in 1898 by 
 the fractional distillation of crude argon. 
 
 According to Claude (B.P. 22316/09), neon and helium 
 are separated in the fractionation of liquid air, by effecting 
 the further fractionation of the last portions of the nitrogen 
 fraction, i.e. the most difficultly liquefiable portions, which, 
 still under pressure, are liquefied in a spiral cooled by the 
 released and liquefied nitrogen. The " backward return " 
 is used here as in oxygen and nitrogen production. It is 
 possible in this way to obtain a gas containing some 50 % 
 neon. 
 
 The further purification of the neon is best effected by 
 fractional sorption with charcoal. It was shown by Dewar 
 that at 100 C., argon, krypton and zenon are absorbed, 
 
THE RARE GASES OF THE ATMOSPHERE 129 
 
 while neon and helium can mostly be pumped off (cf. 
 B.P.s 13638/04, 7808/05). By further treatment at 180 
 C., the neon in turn is mostly absorbed, and nearly pure 
 helium can be pumped off. On warming up the neon is 
 disengaged in a fairly pure state. The purification is best 
 followed by the density (cf. Table 12 (A), p. 53). 
 
 Separation from helium can also be effected by cooling 
 in liquid hydrogen, when the neon solidifies, while the 
 helium (B.P. 269 C.) can be pumped off (Dewar, Roy. Soc. 
 Proc., 67, (1901), 329 ; 68, (1901), 362). According to Collie 
 and Patterson, the passage of an electric discharge through 
 hydrogen is accompanied by the formation of traces of neon. 
 Measurement of the dielectric cohesion is 'a good test of the 
 purity. 
 
 Properties and Applications. In the electric discharge 
 tube, neon gives a brilliant orange pink incandescence ; by 
 means of the spectrum, the presence of neon in 0*1 c.c. of 
 air can be detected. Neon has a very low dielectric cohesion, 
 and is much less readily absorbed by the electrodes in a 
 discharge tube than most other gases. It is on account of 
 these characteristics that the chief application of neon 
 arises, viz. its use for the Moore lamp. This lamp consists 
 of a long glass electric discharge tube, e.g. 20 ft. in length and 
 about if ins. to 2 ins. in diameter, filled with neon to a 
 pressure of about 2 mm. of mercury. 
 
 Using a potential difference of about 1000 volts and a 
 current of 0^94 ampere, a spherical candle power of about 
 1300 is obtained. This is equivalent to a power consumption 
 of 072 watt/mean spherical candle power, or 0-9 including 
 the losses in the transformer. The power factor is about 
 0-8. In order to minimize the trouble experienced by 
 absorption at the electrodes, very large cylindrical hollow 
 copper electrodes are used, e.g. 6 cm. X 2*5 cm. By keeping 
 the current density down to i amp./ioo cm. 2 , a life of 400 
 hours or more can be obtained (cf. Claude, Comptes Rend., 
 151, (1910), 1122 ; 152, (1911), 1377 ; lyangmuir and Orange, 
 Amer. Inst. Elec. Eng., (1913), 1913, 1935)- The colour effect 
 can be corrected by using contiguous tubes containing 
 A, 9 
 
130 INDUSTRIAL GASES 
 
 hydrogen. Using nitrogen in the discharge tube, some three 
 times the potential difference is required, and only one- third 
 the light is produced. In the case of a neon-filled tube, 
 the intensity of the light is greatly reduced by the presence 
 of nitrogen. 
 
 Neon is manufactured in Paris on a scale sufficient to 
 fill some 1000 tubes of 1000 candle power, i.e. about i ft. 3 
 of neon, per diem. A liquid air plant producing 1750 ft. 3 
 of oxygen per hour, is stated to yield some 3-5 ft. 3 neon per 
 diem. 
 
 Neon tubes can be used for the detection of Herzian waves. 
 
 HELIUM 
 
 Occurrence. Allusion has already been made to 
 Ramsay's discovery of helium in 1894, by the ignition of 
 cleveite. Its presence in other minerals containing radio- 
 active elements, e.g. uranium and thorium, was subsequently 
 discovered. Such minerals are fergusonite, samarskite, 
 monazite sand, etc. It was discovered by Soddy in 1903, 
 that helium is a product of the disintegration of radio-active 
 bodies, the alpha particle shot off in such disintegration 
 being, in fact, a charged helium atom. 
 
 The presence of helium in minerals has been the subject 
 of much discussion by workers in radio-activity, the chief 
 interest centering round the physical or chemical state of the 
 helium in the mineral. Since the gas is only slowly expelled 
 by heating, etc., the possibility of chemical combination 
 seemed not out of the question. It was, however, demon- 
 strated that practically all the helium could be liberated by 
 very fine subdivision of the mineral ; it appears, therefore, 
 that the gas is imprisoned in very fine cavities, under a 
 pressure of the order of 200 atmospheres. 
 
 Helium also occurs in the atmosphere (isolated by Kayser 
 in 1895), in the sea, in meteorites, in the hotter stars, in 
 mineral waters, e.g. the gases from the Bath springs contain 
 0*12 % helium, and those from the Wildbad springs 0*71 %, 
 and in natural gas, which contains up to about i % helium 
 (cf. Cottrell, /. Soc. Chem. Ind., (1919), 121 T.). 
 
THE RARE GASES OF THE ATMOSPHERE 131 
 
 Manufacture. Probably the most convenient method 
 of preparing helium is from one of the above-mentioned 
 minerals. The elimination may be effected by heating the 
 mineral to redness in an iron tube which has first been 
 evacuated, or freed from air by displacement with carbon 
 dioxide. A temperature of 1000-1200 C. gives better 
 results, a porcelain tube being used. Alternatively, the 
 mineral may be heated with sulphuric acid, which treatment 
 gives twice the yield obtained on heating alone, but has the 
 disadvantage of being very slow ; or it may be fused with 
 potassium hydrogen sulphate in a hard glass tube. With the 
 sulphuric acid treatment, 100 grams of cleveite yield some 
 500 c.c. of helium, which is obtained in a fairly pure state 
 after removal of the carbon dioxide. The cost of production 
 in this way is about i per litre. 
 
 Purification from neon and argon is described under 
 " Neon/' the helium resisting sorption and liquefaction ; the 
 charcoal method gives the best results. Hydrogen may be 
 separated in a similar way by reason of its greater sorption 
 by charcoal at liquid air temperatures. Nitrogen and hydro- 
 gen may be removed by the action of metallic magnesium 
 plus quicklime and of copper oxide respectively. 
 
 Properties and Applications. Helium is the most 
 difficultly liquefiable of all known gases, 1 and was first 
 liquefied by Kammerlingh Onnes (Comptes Rend., 147, 
 (1908), 421), the requisite cooling being effected by the 
 evaporation of liquid hydrogen under reduced pressure. 
 
 Under the influence of the electric discharge, a brilliant 
 yellow incandescence is obtained. As in the case of argon, 
 a helium discharge tube may be used for the detection of 
 electric waves (Dora, Annalen, [4], 16, (1905), 784). 
 
 Next to hydrogen, helium is the lightest gas known, the 
 weight of one litre at N.T.P. being 0-1785 gram. The use 
 of helium for filling balloons has been proposed on account 
 of its non-inflammability and its high lifting power, which 
 is 92 % of that of hydrogen (cf. p. 233). Other advan- 
 tages are the possibility of increasing the buoyancy by 
 electrical or other heating, and the lower rate of diffusion 
 
132 INDUSTRIAL GASES 
 
 through the balloon fabric. During the war, a process of 
 isolation of helium from natural gas by fractional distillation, 
 has been worked out in America. It is stated that plants 
 have been erected with an output of 50,000 ft. 3 /day of 93% 
 helium, at a cost of about 20 per 1000 ft. 3 (Chem. Trade 
 /., 64, (1919), 99; Nature, 102, (1919), 487; Cottrell, loc. 
 cit., p. 130). 
 
 KRYPTON AND XENON 
 
 Occurrence. Krypton and xenon were discovered by 
 Ramsay in the dregs from some 30 litres of liquid air. They 
 are present in very small proportions in the atmosphere 
 (cf. Table 15), also in mineral springs, mine gases, etc. 
 
 Isolation and Properties. Krypton and xenon are 
 most conveniently isolated by the method proposed by 
 Dewar (Roy. Soc. Proc., 68, (1901), 362), which depends on 
 the fractional condensation of these, the most easily conden- 
 sible of the permanent gases of the atmosphere. A tube 
 packed with glass wool is cooled in liquid air, and air drawn 
 through at a sufficiently reduced pressure to prevent conden- 
 sation of other constituents. Krypton, xenon and a little 
 argon are deposited on the glass wool in the solid form. 
 The two elements can be separated owing to the difference 
 in their vapour pressures at the temperature of liquid air, 
 krypton 17 mm., xenon 0*17 mm. ; the former can thus be 
 pumped off, leaving the xenon. Charcoal may be employed 
 at about 120 C. in a similar manner (Valentier and 
 Schmidt, Sitzungsber. Kgl. Preuss. Akad. Wiss., 38, (1905), 
 816). 
 
 Under the influence of the electric discharge, krypton 
 gives a pale violet and xenon a sky-blue colour. There are 
 at present no special applications for these gases. 
 
 Niton 
 
 Radium emanation or niton represents the first stage in 
 the disintegration of radium, and has been shown to belong 
 to the group of inert monatomic gases, having all the 
 characteristics of a true gas. It is present in minute amount 
 in the atmosphere, together with thorium emanation. It 
 
THE RARE GASES OF THE ATMOSPHERE 133 
 
 is slowly converted into helium with increase to three times 
 its original volume, its " period of decay " (to half value) 
 being 3*8 days. 
 
 Niton exhibits a characteristic spectrum, like the other 
 rare gases. Owing to its radio-active nature, niton is used 
 to a considerable extent, though necessarily in very minute 
 quantity, in the treatment of cancer, etc. For further 
 details of this interesting element, reference must be made 
 to works on radio-activity. 
 
 REFERENCES TO SECTION IV. 
 
 Ramsay, " Gases of the Atmosphere." London, 1905. 
 Briscoe, "Textbook of Inorganic Chemistry." Friend, Little, Turner 
 and Briscoe. Vol. i. London, 1914. 
 
SECTION V. OZONE 
 
 Occurrence. Ozone occurs in minute quantities in the 
 atmosphere, particularly in the upper strata. This distri- 
 bution can be explained by the action of ultra-violet light, 
 which is known to produce ozone, and which is largely 
 absorbed before reaching the lower layers of the atmo- 
 sphere. A considerable amount of work on this question 
 has been carried out by Pring (Roy. Soc. Proc., 90, A, (1904), 
 204), who found that at an altitude of 7000 ft. the concen- 
 tration was 0*00025 % by volume (0^005 gram/m. 3 ), and 
 at 11,700 ft., 0-00047 %. 
 
 Ozone is sometimes present in mineral waters, e.g. to the 
 extent of O'2 c.c. /litre of water. 
 
 The presence of ozone in the upper strata of the atmo- 
 sphere is of interest in connection with the colour of the sky 
 on account of the blue colour of ozone. The amount present 
 in the atmosphere at the surface of the earth, never exceeds 
 O'ooooi %. Evaporation of water is operative in the produc- 
 tion of small quantities of ozone. 
 
 Properties. Ozone is a permanent gas of which the 
 physical properties will be found on pp. 53-6. It has a faint 
 blue colour and a powerful and characteristic odour which 
 renders possible its detection by smell at a dilution of the 
 order of 0-0002 % (Pring), while quite small concentrations 
 have an irritant action on the mucous membrane. 
 
 Ozone is an allotropic modification of oxygen, consisting 
 of three atoms of oxygen. Its constitutional formula is 
 probably O = O = O. Its production from oxygen is strongly 
 endothermic, thus 
 
 3O 2 = 2O 3 68,000 calories 
 lyike all endothermic gases, ozone is only stable at a very 
 
OZONE 135 
 
 high temperature. Thus, according to the Nernst Heat 
 Theorem (Nernst, Z. Elektrochem., 9, (1903), 891), the 
 equilibrium in oxygen would be about 10 % at a temperature 
 of 6640 C., whereas at 3230 C. the corresponding value is 
 i % and at 2183 C., 0*1 %. Consequently ozone is in a con- 
 dition of metastability under ordinary conditions. At the 
 ordinary temperature, however, the rate of decomposition is 
 fairly slow. At 100 C. the decomposition is relatively rapid, 
 while at 300 C. it is practically instantaneous. Conversion 
 into oxygen is accelerated by the presence of various catalysts 
 such as metallic oxides, chlorine, etc. According to Chapman 
 and Jones (Chem. Soc. Trans., (1910), 2463 ; (1911), 1811) 
 the rate of decomposition is unaffected 'by the presence of 
 nitrogen, carbon dioxide and possibly water vapour. 
 
 As a consequence of the above characteristics, ozone has 
 very powerful oxidizing properties, generally furnishing one 
 atom of free oxygen, the volume remaining constant, e.g. 
 in the action on potassium iodide in solution, with liberation 
 of iodine 
 
 2KI + O 3 + H 2 O = 2KOH + O 2 + 1 2 
 
 On the other hand, in some reactions, all three atoms of 
 oxygen enter into combination, as, e.g. in the absorption of 
 ozone by turpentine or oil of cinnamon. 
 
 In the presence of water, ozone attacks many metals. 
 Thus, the properties of mercury are completely modified by 
 the action of a mere trace of ozone, the metal becoming 
 drossy, losing its convex surface and adhering to glass. 
 Similarly, most organic substances are rapidly oxidized ; e.g. 
 indiarubber cannot be employed in contact with ozonized 
 air. Paraffin wax or concentrated sulphuric acid may be 
 used as a lute. 
 
 By reason of its unstable nature, ozone has never been 
 isolated in a state of even approximate purity in the gaseous 
 state. The highest concentration which has been realized 
 in the gaseous state, in oxygen, is some 28 % by weight 
 ( = 22 % by volume). Ladenburg (Ber., 31, (1898), 2508, 
 2830), however, by careful fractionation in the liquid state, 
 
136 INDUSTRIAL GASES 
 
 obtained an oxygen-ozone mixture containing about 86 % 
 ozone, on the assumption that the formula is O 3 . 
 
 There is, however, considerable doubt as to the correctness 
 of this assumption, thus Harries (Ber., 45, (1912), 936; Liebig's 
 Annalen, 390, (1912), 235) considers that one-third or more 
 of the " ozone " is really O 4 or possibly O 6 . This conclusion 
 is based on a study of the constitution of certain ozonides. 
 By the action of ordinary ozone, two distinct classes of 
 ozonides are produced, one of which corresponds to the 
 addition of O 4 . On washing the crude ozonized gas with 
 dilute caustic soda solution, the so-called " oxozone," i.e. 
 O 4 , C>6 e tc., is removed and a single ozonide results. Sir 
 Joseph Thompson has shown that at least nine substances 
 are formed by the passage of an electric discharge in oxygen 
 (Chem. News, 103, (1911), 265). 
 
 I/iquid ozone has a dark blue colour, is not very mobile, 
 and is more magnetic than liquid oxygen. It is a 
 dangerous substance, as in contact with organic matter 
 it explodes violently. The solid substance has not been 
 described. 
 
 Ozone has a characteristic spectrum, and its solubility 
 in water is probably of the same order as that of oxygen 
 (cf. p. 93), but considerable uncertainty exists on this point. 
 
 Production of Ozone 
 
 General. The first recognition of ozone was by Van 
 Marum in 1785, while much of the classical work which 
 determined the constitution of this gas is due to Schonbein, 
 Soret and Brodie. The difficulty of investigation was 
 greatly increased by the fact that, except at very low temper- 
 atures, ozone could not be obtained in even an approximately 
 pure state. 
 
 In consequence of the endothermicity of ozone, it is fairly 
 obvious that the conditions suitable for its production 
 from oxygen are the attainment of a very high temperature 
 and then a rapid freezing of the equilibrium. Ozone is also 
 produced in the liberation of oxygen from its compounds 
 at the ordinary temperature. 
 
OZONE 137 
 
 The different methods of producing ozone may be classified 
 under the following headings : 
 (a) Chemical methods. 
 (6) By the thermal treatment of oxygen. 
 
 (c) By electrolysis of aqueous solutions. 
 
 (d) By photochemical means. 
 
 (e) By the electric discharge in air or oxygen. 
 
 In connection with ozone production, it is usual to 
 express the ozone content of air, etc., in terms of grams of 
 ozone per cubic metre, the units being of a convenient order 
 of magnitude. In some cases, however, the concentration 
 is expressed as one part in a certain number of parts of air, 
 and considerable confusion is due to the lack of clearness in 
 many instances as to whether the basis of comparison is 
 weight or volume. 
 
 It is useful to note that since 48 grams of ozone have at 
 15 C. a volume of 23*6 litres, one gram of ozone per cubic 
 metre is equivalent to ^V % by volume, and since one cubic 
 metre of air at 15 C. weighs 1225 grams, to about ^ % by 
 weight. For the sake of simplicity, the formula is here 
 taken as O 3 . 
 
 (a) By Chemical Methods. Ozone is produced in small 
 amount during the slow oxidation of phosphorus in moist 
 air, and by the action of fluorine on water. Better yields 
 are obtained by the treatment of barium peroxide, potassium 
 permanganate or potassium dichromate with concentrated 
 sulphuric acid. With permanganate, the action is dangerous 
 and should not be performed except with very small quantities. 
 According to Malaquin (/. Pharm. Chim., [viii.], 3, (1911), 
 329), good results are obtained by heating carefully to 60- 
 70 C. a mixture of 20 grams of ammonium persulphate 
 and 15 grams of nitric acid of S.G. 1*33, in a flask from which 
 the air has been displaced by a current of carbon dioxide. 
 When freed from carbon dioxide, the gases contain some 
 3-4 % by volume of ozone and 4-4*5 % nitrogen. 
 
 (b) By Thermal Treatment of Oxygen. While, as 
 stated ^bove, the equilibrium concentration of ozone in 
 oxygen is calculated by Nernst as some 10 % at a temperature 
 
138 INDUSTRIAL GASES 
 
 of 6640 C., the equilibrium is so unfavourable at 1000 C. 
 that i % of ozone is reduced to 0*001 % in 0^0007 second 
 (Clement, Annalen, [4], 14, (1904), 334). Any process 
 operating by simple heat treatment must obviously provide 
 for very rapid cooling. Thus the Charpentier process depends 
 on the rapid cooling of a flame by sudden dilution with a large 
 volume of secondary air ; it is claimed that an ozone concen- 
 tration of i gram/m. 3 can be realized in this way. By 
 heating a Nernst filament immersed in liquid oxygen to 2000 
 C. (Fischer and Brahmer, Ber., 39, (1906), 940; Fischer and 
 Marx, Ibid., 40, (1907), mi), an ozone content of 3*9 % by 
 weight was obtained. 
 
 When operating with a Nernst filament in dry air, some 
 oxides of nitrogen may be formed according to the conditions, 
 slow cooling being favourable. Thus with air linear velocity 
 of about 16 ft./sec. for dry air, or 23 ft./sec. for moist air, both 
 ozone and oxides of nitrogen are produced ; below this 
 speed only oxides of nitrogen result, while at a velocity of 
 over 100 ft./sec., only ozone is formed. With a linear velocity 
 of 206 ft./sec., an ozone concentration of 0*23 gram/m. 3 
 has been obtained with a production of i'28 grams/K.W.H. 
 (cf. Fischer and Marx, Ber., 39, (1906), 2557, 3631 ; 40, 
 (1907), 443 ; Fischer, B.P. 3692/07). 
 
 (c) By Electrolysis. For the production of ozone by 
 this method, the best yield is secured by the use of dilute 
 sulphuric acid containing 15 % H 2 SO 4 . The conditions 
 favouring the production of ozone are low temperature of 
 the anode and electrolyte, and a high current density at the 
 anode, e.g. 80 amperes/cm. 2 , a not too easy combination. 
 Thus, by embedding platinum foil in glass and grinding away 
 so as to expose the edge only, a concentration of 23 % ozone 
 by weight (16*7 by volume) in the oxygen evolved was 
 realized (Fischer and Bendixsohn, Z. anorg. Chem., 61, 
 (1909), 13, 153). In another series of experiments the anode 
 was coated with glass except for a small slit, and maintained 
 at a temperature of 14 C., while the electrolyte was kept 
 at o C. In this case the oxygen contained 28 % by 
 weight of ozone (22 % by volume), and the yield was 7-1 
 
OZONE 139 
 
 grams/K.W.H. (Fischer and Massenez, Z. anorg.'Chem.,b2, 
 (1907), 202, 229). 
 
 By superimposing an alternating current on the usual 
 direct current, Archibald and v. Wartenberg (Z. Elektro- 
 chem., 17, (1911), 812) increased the concentration of ozone 
 with reference to the oxygen liberated by the direct current, 
 to 37 % by volume, the improvement being due to the 
 depolarizing action of the alternating current, but dilution 
 by the gas liberated by the alternating current reduced the 
 percentage to 6 %. With a greater ratio of direct current 
 to alternating current, the ozone corresponding to the direct 
 current was, in one case, 15 %, that in the actual gas mixture 
 
 12 %. 
 
 (d) By Photochemical Means. Ozone is produced by 
 the action of ultra-violet light or electrical radiations on 
 oxygen, and as with the silent discharge the action is re- 
 versible. According to Pring the maximum concentration 
 attainable by the action of ultra-violet light is 0*15 % by 
 volume, when using air, and o'2 % with oxygen. 
 
 (e) By the Electric Discharge. The only method of 
 making ozone which possesses any technical importance, 
 is that depending on the action of the so-called " silent 
 discharge " on oxygen or air. On the other hand, the 
 electric spark produces practically no ozone, as the gas is 
 rapidly decomposed by the spark. The first form of ozonizer 
 is due to Siemens in 1857 (wd& infra). 
 
 The precise mechanism of the process is still somewhat 
 obscure. It has been suggested that the action is an effect 
 of ultra-violet light, and that the process is really a photo- 
 chemical one. 
 
 Using this process, the efficiency is enhanced by (i) 
 keeping the temperature low ; (2) using oxygen instead of 
 air ; (3) drying the air or oxygen ; and (4) increasing the 
 pressure. Since the formation of ozone from oxygen is 
 accompanied by a decrease in volume, it follows that an 
 increase in pressure is favourable to ozone production. 
 The question is, however, complicated at pressures above 
 atmospheric by the effect of increased pressure on the 
 
140 INDUSTRIAL GASES 
 
 electric discharge itself. The result appears to be that the 
 optimum pressure is about i atm. The action is a reversible 
 one, and the highest concentration realized in this way at 
 the ordinary temperature is about 25 % by weight = 18 % 
 by volume (cf. also Goldstein, Ber., 36, (1903), 3042). 
 Further details relating to this process will be found below. 
 By operating under reduced pressures at liquid air 
 temperatures, Briner and Durand (Comptes Rend., 145, 
 (1907), 1272) effected a conversion of 99 %. The best results 
 were obtained at a pressure of 100 mm., the ozone lique- 
 fying out as it was produced, with consequent reduction of 
 the pressure to i mm. 
 
 MANUFACTURE OF OZONE 
 General Principles of Ozonizers 
 
 Influence of the Character of the Discharge. It 
 has been mentioned above that the only commercially 
 important method of making ozone is that depending on the 
 action of the silent discharge. Generally speaking, ozonizers 
 consist of two electrodes separated by a gaseous or solid 
 dielectric, and maintained at a potential difference of the 
 order of 10,000 volts while a stream of air or oxygen is passed 
 through the apparatus. Alternating current is usually 
 employed, being obtained by the use of a step-up trans- 
 former with a periodicity up to 500 cycles per second. 
 
 According to Warburg and I,eithauser (Annalen, [4], 28, 
 (1909), i) the current density and consequently the ozone 
 production, are roughly proportional to the frequency. 
 
 If direct current be employed, the use of points on the 
 positive electrodes, combined with high current density, 
 leads to the highest yields with moderate concentrations, 
 e.g. 4 grams/m. 3 , while a reversal of conditions with a low 
 current density favours the attainment of high concentrations 
 e.g. 4-9 grams/m. 3 (Warburg and L,eithauser, Annalen, [4], 
 20, (1906), 734). 
 
 Broadly speaking there are three types of electrodes : 
 (i) large smooth electrodes, e.g. parallel plates or concentric 
 
OZONE 
 
 141 
 
 cylinders ; (2) electrodes with points : and (3) cotnbinations 
 of (i) and (2). 
 
 The production of ozone appears to be proportional to 
 the current and independent of the voltage (Gray, Annalen, 
 \4\, 13, (1904), 477). Increase of capacity in the circuit is 
 favourable to ozone production and large electrode area and 
 short distance of separation operate in the same direction. 
 
 Influence of Dielectrics. If the dielectric be air, 
 the dividing gap is usually about 13 mm., and must not be 
 decreased below 7 mm. (Vosmaer), and the maximum 
 potential difference used is about 10,000 volts. No apparatus 
 using air as dielectric appears to have had much success, 
 and most modern forms use glass as a 'dielectric, the regu- 
 larity of the discharge being increased and the danger of 
 sparking thus being minimized. 
 
 Sparking is very detrimental as it leads to decrease of the 
 ozone concentration and, moreover, to the formation of 
 oxides of nitrogen. With a single thickness of 1-2 mm. 
 of glass, a potential difference of 10,000 volts may be used, 
 while 20,000-25,000 volts may be employed with double 
 thickness. Using " vitreosil " (fused silica), a potential 
 difference of 30,000 volts is permissible with a thickness of 
 i mm. This material has the further advantage of not 
 losing its dielectric properties with increase in temperature 
 in the manner exhibited by glass (Vosmaer). 
 
 Relation between Energy, Concentration, and Pro- 
 duction. The yields obtained in commercial apparatus vary 
 greatly from one type to another, particularly as the design 
 of some ozonizers is directed towards high efficiency, whereas 
 that of others aims at simplicity and robustness at the 
 expense of output, but when using dry air and keeping the 
 temperature down, it may be taken that the relation between 
 concentration and the yield per K.W.H. is somewhat as 
 follows (cf. Brlwein, Z. Sauerstoff u. Stickstoff Industrie, 
 3, (1911), 130, 143, 164, 181) : 
 
 Concentration of ozone. 
 
 
 
 
 
 
 
 
 Grams/m 3 . 
 
 i 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 Yield. Grams/K.W.H. 
 
 62 
 
 50 
 
 36 
 
 23 
 
 13 
 
 8 
 
 5 
 
142 
 
 INDUSTRIAL GASES 
 
 On account of the rapid falling off of the efficiency with 
 increase in concentration, the latter is naturally kept at as 
 low a value as possible for the particular application in 
 question. With the usual commercial concentration of 
 about 2 grams/m. 3 , and using dry air with efficient cooling, 
 the yield is usually about 40- 60 grams/K.W.H. On 
 substituting oxygen for air, the production increases to 
 120-180 grams/K.W.H., even this being, of course, far below 
 the theoretical yield corresponding to the expenditure of 
 electrical energy (Brlwein, loc. cit.). 
 
 In comparing the costs of production of ozone by different 
 ozonizers, it is important to see that the yields given are ex- 
 pressed in terms of an ozone concentration of 1-2 grams/m 3 . 
 The cost of production from air is consequently of the 
 order of 1/3 to 1/9 per kilo, ozone, inclusive of overhead 
 charges with current at about o^d./K.W.H. 
 
 Influence of Moisture. The presence of moisture 
 in the air or oxygen to be ozonized has a marked influence. 
 Thus, the presence of 7 mm, of water vapour (about i % by 
 volume) lowers the production by about 6 % in the case of 
 oxygen and 30 % with air (Warburg and L,eithauser, 
 Annalen, loc. cit.}. 
 
 Influence of Temperature. The effect of raising the 
 temperature of the air to be ozonized from 20 C. to 80 C. is 
 to decrease the production to about 60 % of its former value 
 (lyinder, Trans. Amer. Inst. Chem. Eng., 3, (1910), 188), 
 while the results given below were obtained by Warburg and 
 I>ithauser (loc. cit.) from ozonizer tests with constant flow. 
 
 
 Temperature C. 
 
 Grams ozone per 
 ampere hour. 
 
 Grams ozone/nr". 
 
 Air 
 
 20 
 80 
 
 467 
 338 
 
 I- 7 6 
 1*26 
 
 Oxygen 
 
 18 
 80 
 
 429 
 425 
 
 0-49 
 0-44 
 
 The following table gives the relation between the percent- 
 age of ozone and the temperature in the case of a particular 
 ozonizer (not operating under commercial conditions), the 
 
OZONE 
 
 143 
 
 conditions otherwise being constant and oxygen being 
 used (Beill, Monatsh. Ghent., 14, (1893), 71). 
 
 Temperature C. 
 
 -73 
 
 -46 
 
 20 
 
 o 
 
 20 
 
 35 
 
 78 
 
 IOO 
 
 132 
 
 Percentage ozone 
 
 
 
 
 
 
 
 
 
 
 (by volume) . . 
 
 10 
 
 9-2 
 
 7*9 
 
 5*2 
 
 4'7 
 
 3 
 
 i'3 
 
 0-8 
 
 0-3 
 
 At liquid air temperatures complete conversion can be 
 realized, the ozone liquefying out as produced. By employing 
 refrigeration in conjunction with an ozonizer, Steynis (cf. 
 lender, loc. cit.) claims to have secured a yield of 105-250 
 grams ozone/K.W.H., at a concentration of 4 grams/m 3 . 
 
 Materials of Construction. In view of the action 
 of ozone on steel, etc., various special alloys have been used 
 in the construction of ozonizers and accessory plant, e.g. 
 chrome steel, nichrome, aluminium alloys, etc. Shellac 
 and " bakelite " also resist the action of ozone. 
 
 Construction and Production of the Various 
 Commercial Types of Ozonizers 
 
 As regards the patent literature relating to the manu- 
 facture and utilization of ozone, the specifications are so 
 numerous and the value of the majority so doubtful, that it 
 is impossible to deal with individual patents in the present 
 volume, and information must be obtained from the Abridge- 
 ments of Specifications, Class 90, for British Patents. 
 
 The first ozonizer was introduced by Siemens in 1857, 
 and is typical of all others. In its original form it consisted 
 of two concentric glass tubes with tin-foil inside the inner and 
 outside the outer tube, the air or oxygen being passed through 
 the annular space. A modification introduced by Berthelot 
 was the replacement of the tin-foil by a liquid conductor, 
 e.g. water, dilute acid, etc. 
 
 The commercial Siemens and Halske system consists 
 of 6-8 glass tubes surrounded by water in a cast-iron casing. 
 Aluminium electrodes disposed inside the glass tubes form 
 one set of electrodes, while the water serves as the other 
 electrode. Using 8000 to 10,000 volts, a yield of some 50 
 
144 INDUSTRIAL GASES 
 
 grams ozone/K.W.H. at a concentration of 2*5 grams/m. 3 is 
 obtained. 
 
 The apparatus of the General Electric Co. is similar to 
 the Siemens and Halske, but instead of aluminium, enamelled 
 iron is used for the inner electrodes. 
 
 The older types of the Otto system employed a rotating 
 central electrode consisting of aluminium discs in an iron 
 cylinder in order to break up any spark discharges, no 
 dielectric being used; in the later forms this method is 
 abandoned and glass is used as a dielectric. 
 
 The Tindal de Frise system employs no dielectric and has 
 a series of serrated semicircular aluminium discs, in a water- 
 cooled iron trough. To prevent sparking, a series of glycerol- 
 water resistances is included in the circuit. 
 
 In the Abraham-Marmier system, glass plates one square 
 metre in area are interposed between water-cooled metal 
 plates connected alternately to opposite terminals. Short- 
 circuiting through the cooling water is prevented by the use 
 of water showers. 
 
 The Ozonair system uses electrodes of aluminium alloy 
 gauze separated by mica sheets, the air being passed between 
 the plates. Several pairs mounted in a case form a unit. 
 The use of the gauze is claimed to prevent sparking, while 
 the open construction leads to efficient cooling without the 
 use of water. The potential difference is about 7000 to 
 9000 volts. 
 
 According to the Howard-Bridge system a glass cylinder 
 has an outer aluminium electrode and an inner concentric 
 metal tube serving as electrode, through holes in which the 
 air enters the ozonizer. 
 
 The original Vosmaer system employed no dielectric, 
 the discharge passing between a toothed electrode and a 
 plate. Sparking was prevented by the insertion of a con- 
 denser in the electrical circuit. A dielectric is used, however, 
 in the later forms which consist of a series of cells in a casting 
 of grid form, the separating walls being lined with glass 
 plates, and each cell enclosing a sharp-edged electrode. In 
 the units of joo-iooo watts capacity, a yield of more than 
 
OZONE 145 
 
 50 grams/K.W.H. at a concentration of i gram/m. 3 is 
 claimed. 
 
 The Gerard system, made by the Westinghouse Co., 
 makes use of a double dielectric consisting of two concentric 
 glass tubes with metallic sheathings inside the inner and 
 outside the outer tube respectively. The air is passed between 
 the tubes. Groups of about 10 elements are mounted in 
 a tank rilled with oil. Very high production, viz. 80 
 grams/K.W.H. at a concentration of 3 grams/m. 3 , is claimed. 
 
 Applications of Ozone 
 
 Water Sterilization. Of the various applications of 
 ozone, the sterilization of potable water is the most important. 
 The problem of the sterilization of drinking water, i.e. the 
 removal of the bacteria, or at any rate most of the pathogenic 
 ones, can be solved in a variety of ways. Among these may 
 be mentioned (i) sand filtration ; (2) treatment with chlorine 
 and subsequent removal of the excess by means of sodium 
 sulphite or other suitable " anti-chlor "; (3) treatment with 
 ozone ; and (4) treatment with ultra-violet light. Of these 
 sand filtration is most commonly adopted when dealing with 
 waters not specially contaminated. The use of chlorine, etc., 
 although very effective as regards sterilization, is not very 
 suitable for the preparation of potable water, except in special 
 cases, as e.g. in the field, on account of the usual residual 
 taste imparted to the water. Ultra-violet light has an 
 effect on the water similar to that of ozone, but the ultra- 
 violet light treatment is useless if the water be even slightly 
 turbid. 
 
 Ozone treatment has many advantages in that the 
 slight excess left in the water is unimportant since it rapidly 
 disappears, also the taste of the water is unaffected either 
 by noxious products or by action on the salts to which 
 drinking water owes its pleasant taste. In treating water 
 with ozonized air, it is important that the water should be 
 free from suspended matter, from organic matter, and iron, 
 as ozone is used up thereb} r . Some 50 % of any organic 
 A. 10 
 
146 INDUSTRIAL GASES 
 
 matter is oxidized by the ozone, all three atoms of oxygen 
 participating in the reaction, while any organic iron is con- 
 verted into ferric hydroxide which separates out and clogs 
 up the plant. The preliminary removal of ferrous iron 
 is effected by aeration, that of ferric iron is difficult except 
 by the ozone treatment, and it is therefore often necessary 
 to remove the precipitated ferric hydroxide by subsequent 
 filtration or by similar treatment. The ozone required 
 varies according to the amount of organic matter in the water; 
 it may lie between 2 and 35 grams/iooo galls, of water, but 
 averages about 10 grams/iooo galls. 
 
 The concentration of the ozone should be from 2 to 2*5 
 grams/m. 3 of air, although a concentration of only i gram/m. 3 
 is sometimes employed, e.g. at St. Maur. It follows that the 
 volume of air is roughly equal to that of the water, when 
 ozone is used in concentration of 2 grams/m. 3 , since 10 grams 
 of ozone are present in 5 m. 3 = noo galls, of air. After the 
 ozone treatment, only the harmless bacteria remain in the 
 water. 
 
 Broadly speaking there are three main types of plant 
 for the treatment of water with ozonized air : (i) those 
 operating with towers filled with packing, down which the 
 water trickles meeting the ascending current of ozonized air ; 
 (2) those depending on the use of a tower fitted either with 
 horizontal perforated plates, the ozonized air and water 
 flowing in co-current upwards, or without baffles and with 
 the water flowing downwards in counter-current ; and (3) 
 those in which the air is injected in the form of small bubbles 
 into a rapidly moving column of water. 
 
 In all cases, the object is to effect very intimate contact 
 between the water and the sparingly soluble ozone, the action 
 of which when once in solution is very rapid. Of the three 
 systems, (2) probably gives the most efficient contact. In 
 most modern plants, a combination of the above systems 
 is adopted, the water being first put through a sand 
 filter. 
 
 In class (i), we have the Siemens and Halske and the 
 Abraham-Marmier systems. Towers packed with stones 
 
OZONE 147 
 
 or the like are employed, and the unused ozone is returned 
 to the ozonizer. 
 
 To class (2) belongs the Siemens de Frise system, being 
 a combination of the Siemens and Halske ozonizer and the De 
 Frise scrubber. In this case, the ozonized air is injected 
 into the bottom of a jtower fitted with perforated baffle 
 plates which serve to break up the air into small bubbles. 
 The Vosmaer system, on the other hand, employs no baffles 
 and has counter-current flow. The Gerard and Tindal 
 systems are similar to the above. 
 
 The Otto system represents class (3), and depends on the 
 emulsification of the air by a Korting injector operated by 
 the water. The injector sucks in the air, the action being 
 completed by continued contact in passing down a vertical 
 pipe, some 15 feet in length. One objection to the Otto 
 system is the comparatively small volume of air taken in, 
 and the consequent necessity for the high ozone concentration 
 of 3 grams/m. 3 . The Howard-Bridge system is similar. In 
 the Ozonair system, the water is first atomized into ozonized 
 air in the upper part of a tower of which the lower part is 
 occupied by packing. The ozonized air is injected through 
 special nozzles into the water in a tank which is fed by water 
 flowing down the tower, and then passes on to ascend the 
 tower. After treatment, the water is exposed to the atmo- 
 sphere by flowing down a series of steps, in order to remove 
 the excess of ozone. 
 
 As regards power requirements, it can be stated 
 that for 1000 galls, of water, from 0*2 to 0*7 K.W.H. is 
 usually required, while the cost (pre-war) varies from \d. 
 to id., plus overhead charges, per 1000 galls. 
 
 There has been little application of the ozone treatment 
 of water in this country, chiefly on account of the high quality 
 of the water used in most English towns. An Ozonair 
 plant has, however, been installed in Knutsford. There are 
 many plants on the Continent and in America. A plant 
 at Paris, for example, treats some 400,000 galls, of water 
 per hour. 
 
 The air to be ozonized is dried by the use of calcium 
 
i 4 8 INDUSTRIAL GASES 
 
 chloride or, preferably, by refrigeration. The ozonize rs are 
 always connected in parallel, about 10,000 volts generally 
 being used. According to Vosmaer, the difficulty of packing 
 materials for the pumps used in the injection of the ozonized 
 air is overcome by the use of celluloid piston rings. 
 
 Portable ozone outfits were used for treatment of water 
 in the field by the Russian Army in the Russo-Japanese war. 
 
 Small apparatus for attachment to any ordinary house- 
 hold water-tap are on the market, mostly working on the 
 filter pump (Otto) system. 
 
 Air Purification. Ozone is used on a considerable 
 scale for freshening the air in crowded buildings, underground 
 railways, hospitals, abattoirs, cold stores, etc. It has also 
 been used with success in breweries for the air of fermen- 
 tation rooms, etc., having a beneficial effect on the yeast, 
 probably due to the elimination of adventitious enzymes. 
 
 On account of the irritant properties of ozone, it is not 
 possible to use concentrations sufficiently high to exhibit 
 any marked germicidal effect. Thus, bacteriological action 
 requires a concentration of about 0-5 gram/m. 3 , while the 
 highest concentration in which breathing is tolerable is of 
 the order of O'ooi gram/m. 3 . Ozone is, however, efficacious 
 in removing the noxious organic exhalations present in 
 crowded rooms, much of the discomfort of " stuffiness " 
 being due to the presence of these organic compounds. At 
 the same time an agreeable freshness is imparted to the air. 
 For the best results, according to Vosmaer, the ozone should 
 be present to the extent of O'oooi gram/m. 3 , and in any 
 case, not more than O'ooi gram/m. 3 is permissible. At 
 such a low concentration the yield is of the order of 100 
 grams/K.W.H. 
 
 The Central L,ondon (Tube) Railway is supplied with 
 ozonized air by the Ozonair system. The procedure in this 
 case, which is typical of similar installations, is as follows. 
 The air is drawn by a fan through a gauze screen filter 
 moistened with a spray of water which retains dust and cools 
 the air. A small fraction of the air is then dried and led 
 through the ozonizer, after which it is returned to the main 
 
OZONE 149 
 
 stream. Most of the plants on the above railway treat some 
 360,000 ft. 3 of air per hour ; the cost is stated to be 17^. 
 per million ft. 3 of air treated (pre-war). Small plants of 20 
 to 25 watts capacity are made for use in rooms of 3000 ft. 3 
 content. 
 
 Chemical Applications. Ozone also finds application 
 in the manufacture of vajrious organic compounds, its function 
 being that of an oxidizing agent. Thus, it is used on a 
 fairly extensive scale in the manufacture of artificial vanillin 
 from isoeugenol, a factory at Courbourg, Paris, employing a 
 100 H.P. plant for making vanillin by the Verley process. 
 A similar plant is also in operation at Niagara. 
 
 Ozone is employed in the manufacture of artificial 
 camphor (Schering) and artificial silk, for the bleaching of 
 oils, waxes, sugars, etc., in the production of ozonides (e.g. of 
 caoutchouc), scents and in many other organic reactions. It 
 has been applied with success to the production of transparent 
 varnish from linseed oil, also to the refining of the same. 
 
 Other Applications. Among miscellaneous appli- 
 cations may be cited the sterilizing of barrels, the bleaching 
 of delicate fabrics, etc. The application of ozonized air to 
 the bleaching of flour has not been successful as the flour 
 is affected adversely. Ozone has been tried for such purposes 
 as the ageing of wines, the maturing of timber, tobacco, etc., 
 but in many cases the success is doubtful. Recent experi- 
 ments on the treatment of wounds with ozone have shown 
 the efficacy to be questionable. 
 
 Detection and Estimation of Ozone. In the absence 
 of other oxidizing agents, ozone is readily detected by its 
 action on potassium iodine paper with liberation of iodine 
 (cf. p. 135). Since, however, other substances such as 
 chlorine, oxides of nitrogen, etc., produce the same effect, 
 it is necessary to have some means of discrimination. 
 
 A simple method is to use paper moistened with both 
 potassium iodide and phenolphthalein. The action of 
 ozone differs from that of other oxidizing agents in that it 
 results in the formation of potassium hydroxide. A better 
 selective test depends on the use of moistened tetramethyl 
 
150 INDUSTRIAL GASES 
 
 di-^tfra-aminophenylmethane paper, which exhibits the 
 following colour reactions : 
 
 Ozone violet. 
 
 Chlorine, bromine . . . . deep blue. 
 
 Oxides of nitrogen . . . . straw yellow. 
 
 Hydrogen peroxide . . . . no action. 
 
 One of the best methods of estimating quantitatively 
 the amount of ozone in air, oxygen, etc., is by potassium 
 iodide, with subsequent titration of the iodine after acidifi- 
 cation. If other oxidizing agents are present the ozone may 
 be estimated by repeating the estimation after passing the 
 gas through a tube heated to about 260 C., and then deter- 
 mining the difference in the iodine liberation due to the 
 decomposition of the ozone, this difference giving the 
 initial ozone concentration. 
 
 A more positive method consists in removing the oxides 
 of nitrogen by means of caustic soda, while hydrogen peroxide 
 may be eliminated by passing over finely divided crystals of 
 chromic acid. 
 
 According to Usher and Rao (Chem. Soc. Trans., (1918), 
 799), ozone present in small quantity is best estimated by 
 drawing the air through (i) chromic acid plus manganese 
 dioxide, (2) chromic acid alone. In both cases hydrogen 
 peroxide is removed and in (i) nitrogen peroxide also is 
 eliminated ; on shaking up with sodium nitrite solution 
 and subsequently estimating the degree of conversion into 
 nitrate, the difference in the two cases gives the ozone 
 content. 
 
 Separation of ozone from oxides of nitrogen may also 
 be effected by passing into liquid air, when the ozone dissolves 
 but the oxides of nitrogen separate out as blue flocks. 
 
 REFERENCES TO SECTION V. 
 
 Vosmaer, "Ozone, its Manufacture, Properties and Uses." New York, 
 1916. 
 
 Fonrobert, " Das Ozon." Stuttgart, 1916. 
 
 Harries, " Untersuchungen iiber das Ozon und seine Einwirkung auf 
 organische Verbindungen." Berlin, 1916. 
 
OZONE 151 
 
 Anon., " The Use of Ozone for Chemical Research and Industries," 
 Chem. News, 113, (1916), 193, 205. 
 
 Erlwein, " Herstellung und Verwendung des Ozons," Z.jur Stickstoff 
 und Sauerstoff Industrie, 3, (1911), 130. 
 
 Ziegenberg, " Die elektrische Ozontechnik." Leipzig, 1910. 
 
 Perkin, " The Industrial Uses of Ozone," Nature, 88, (1912), 551. 
 
 Rideal, " Water Supplies." London, 1916. 
 
 Don, " The Filtration and Purification of Water for Public Supply," 
 Engineering, 87, (1909), 126, 160. 
 
 Anon., " Water Sterilization Plant at St. Petersburg," Engineering, 91, 
 (1911), 656. 
 
0-0215 0-0198 0-0190 0-0184 
 
 PART II. HYDROGEN, CARBON MONOXIDE, 
 CARBON DIOXIDE, SULPHUR DIOXIDE, 
 NITROUS OXIDE, ASPHYXIATING GASES 
 
 SECTION VI. HYDROGEN 
 
 Occurrence. Hydrogen is present in small amount in 
 the atmosphere, 0*019 % according to Gautier, 0-003 % 
 according to Rayleigh, its origin being the fermentation of 
 cellulose, etc., by anserobic micro-organisms. 
 
 Physical Properties. Hydrogen is a colourless, taste- 
 less and odourless gas. It is the lightest known gas, the 
 weight of one litre at N.T.P. being 0*089873 gram. The 
 solubility in water is given in the following table : 
 
 Temperature C. . . . . o 10 
 
 C.c. of gas (measured at N.T.P.) 
 
 dissolved by i c.c. of water 
 
 under a pressure of I atm. 
 
 exclusive of water vapour. 
 
 The mean specific heat at constant volume is given by 
 Crofts (Chem. Soc. Trans., (1915), 290) as 
 
 C y = 2-41 + 0-00032^ 
 
 where C v is the mean specific heat between t and 15*5 C. 
 
 Hydrogen does not show the preliminary decrease, common 
 to other permanent gases, of the product pv as the pressure 
 is increased, but gives a continuous increase, the departure 
 from constancy being very considerable at 200 atms. (cf. p. 
 3). Due allowance for the diminished quantity of hydrogen, 
 represented by the expression p/pv, is important when calcu- 
 lating the volume of gas in a cylinder from the pressure. 
 Thus a cylinder of actual volume of i ft. 3 only contains 
 in -8 ft. 3 of free hydrogen at 121 atms. absolute pressure for 
 a temperature of 16 C., in both cases (cf. pp. 4, 5). 
 
 Hydrogen is occluded to a considerable extent by many 
 
HYDROGEN 153 
 
 metals, such as palladium, platinum, iron, cobalt, etc. 
 Palladium has the property in the highest degree. The 
 volume occluded varies little with pressure" between i and 
 4-6 atms., but is dependent on the temperature. Thus, 
 one volume of palladium sponge occludes 917 volumes of 
 hydrogen at 50 C., the quantity falling off with rising 
 temperature to a minimum of 661 volumes at 20 C. and then 
 increasing to 754 volumes at 105 C. (Gutbier, Ber., 46, ii., 
 (1913), 1453). Palladium black and palladium foil show a 
 closely similar behaviour. 
 
 It was observed by Holt, Edgar and Firth (Z. physik. 
 Chem., 82, (1913), 513) that palladium may be either active 
 or passive according to treatment. These authors conclude 
 that the hydrogen exists in two forms, (i) an adsorbed layer 
 of high vapour pressure and easily removed by evacuation, 
 and (2) an absorbed fraction irregularly distributed through 
 the body of the metal. The sorption is accompanied by the 
 evolution of 4370 calories per gram hydrogen, while the 
 palladium increases in volume by some 10 %. In vacuo, at 
 the ordinary temperature, 92-98 % of the hydrogen is 
 disengaged and expulsion is complete at 440 C. ; with foil 
 most of the hydrogen is lost at 100 C. Under high pressure 
 the hydrogen is retained even at a dull red heat, e.g. Dewar 
 showed that 300 volumes were absorbed at 500 C. under 
 120 atms. pressure (Chem. Soc. Proc., 13, (1897), 192). 
 
 The solubility of hydrogen in other metals is fairly 
 marked, e.g. platinum black at the ordinary temperature 
 dissolves no volumes (Mond, Ramsay and Shields, Phil. 
 Trans., A 186, (1895), 657), spongy platinum only a few 
 volumes, reduced iron 9*4 to 19*2 volumes, reduced cobalt 
 59 to 153 volumes, reduced nickel 17 to 18 volumes (Graham, 
 Phil. Mag., [4], 32, (1886), 503 ; Neumann and Streintz, 
 Annalen, 46, (1892), 431) ; cf. also p. 9. 
 
 Palladium, and in a lesser degree platinum and other 
 metals, show a marked permeability to hydrogen, thus 
 i m. 2 of palladium foil of i mm. thickness permits the passage 
 of 325 c.c. hydrogen per minute at 265 C., and of 3992 c.c. 
 at about 1000 C. (Graham, Roy. Soc. Proc., 16, (1867-68), 
 
154 INDUSTRIAL GASES 
 
 422). Similarly platinum foil i'i mm. in thickness passes 
 489 c.c./min./m. 2 at a bright red heat. (Graham, Phil. Mag., 
 [4], 32, (1866), 401.) 
 
 On account of its high coefficient of diffusion, hydrogen 
 easily passes through slightly porous bodies, e.g. indiarubber 
 is markedly permeable to hydrogen (cf. p. 10), while quartz 
 is appreciably so at temperatures above 1000 C. For 
 other properties see Tables 12 and 13, pp. 53-6. 
 
 Liquid Hydrogen. Hydrogen at ordinary temperatures 
 is distinguished from most other gases by the fact that, on 
 expanding without performing external work, heating takes 
 place (cf. p. 67). Consequently, in the production of 
 liquid hydrogen, the Joule-Thomson effect can only be realized 
 after a preliminary cooling. In the British Oxygen Co.'s 
 apparatus, this is effected by passing the hydrogen at a 
 pressure of about 200 atms. through (i) a heat-interchanger, 
 (2) coils immersed in liquid air, (3) coils cooled by the ebul- 
 lition of liquid air, and (4) a second heat-interchanger, after 
 which expansion takes place. The unliquefied hydrogen 
 passes back over the coils, in counter-current to the incoming 
 gases, to the gas-holder. Liquid hydrogen was first obtained 
 in quantity by Dewar in 1898. 
 
 Properties. liquid hydrogen is a colourless, transparent 
 liquid, a non-conductor of electricity ; it is the lightest 
 known liquid, having a density of 0*070 at the boiling point. 
 The surface tension is 1/35 that of water. Specific heat is 
 6*4. When evaporated under reduced pressure, solidification 
 takes place. 
 
 In spite of its low boiling point, liquid hydrogen is easily 
 preserved, as the residual air in the Dewar vessels is frozen 
 out and the vacuum made more perfect. 
 
 Solid hydrogen is colourless, its melting point is 258 C., 
 the triple point 258 C. at 55 mm. pressure, and the latent 
 heat of fusion 16 calories. 
 
 Chemical Properties. At ordinary temperatures, hy- 
 drogen does not behave as an active element, entering into 
 direct combination with only a few elements and compounds, 
 e.g. the halogens, and even then usually only under the 
 
HYDROGEN 155 
 
 influence of light or of catalysts. On heating, * hydrogen 
 reacts with alkali and alkaline earth metals to give crystalline 
 compounds, e.g. NaH, CaH 2 , which are decomposed by water 
 with evolution of hydrogen. 
 
 Mixtures of hydrogen and air are inflammable within the 
 limits 74-2-4'!% hydrogen (cf. p. 40). 
 
 An important characteristic of hydrogen is its power of 
 acting as a strong reducing agent, e.g. in the reduction of 
 metallic oxides. Under high pressures hydrogen will 
 directly displace many metals from solutions of their salts 
 with liberation of free acid. Many reductions depend on 
 hydrogen being liberated in the so-called nascent state, e.g. by 
 action of metals, metallic couples, amalgams, etc., on water, 
 dilute acids or alkalis. Klectrolytically liberated hydrogen is 
 similarly very active as a reducing agent and its effectiveness 
 is largely dependent on the overvoltage of the cathode used. 
 
 Hydrogen is also active in aqueous solution in the presence 
 of spongy or cqlloidal platinum, osmium and the like thus, 
 chlorate solutions are reduced (Hofmann and Schneider, Ber., 
 48, (1915), 1585), nitrates are converted into ammonia, etc. 
 
 Palladium black induces the combination of a mixture 
 of hydrogen and air so energetically that incandescence and 
 inflammation ensue. 
 
 Sabatier (Ber., 44, (1911), 84) opened out a vast field of 
 possibilities by his researches on organic reductions by 
 hydrogen in the presence of a moderately heated catalyst, 
 e.g. nickel or platinum. Thus, carbon monoxide is reduced 
 to methane by passing over nickel at 250 C., and similarly, 
 unsaturated organic compounds such as oils are converted 
 into saturated compounds. Further reference will be made to 
 this important subject under " Applications of Hydrogen." 
 
 MANUFACTURE OF HYDROGEN STATIONARY 
 
 PLANTS 
 
 General. The manufacture of hydrogen occupies 
 probably the most interesting place in the field of industrial 
 gas technology in the variety of the methods employed. 
 The production of pure and cheap hydrogen, which is now 
 
156 INDUSTRIAL GASES 
 
 required for various recent developments such as the synthesis 
 of ammonia and the hydrogenation of fats, is a matter of 
 very considerable difficulty, and quite a large volume of 
 patent literature now relates to this subject. 
 
 Most of the processes having any technical importance at 
 the present time start from coal (or coke) and water. 
 
 In comparison with gases such as nitrogen and carbon 
 dioxide there are relatively few sources of hydrogen in the 
 form of a waste product, but there are some cases where 
 development is desirable, e.g. the waste hydrogen result- 
 ing from the electrolytic alkali industry and from the 
 manufacture of electrolytic oxygen. Further, large quantities 
 of hydrogen are liberated in the manufacture of oxalates 
 by the fusion of sawdust or corncobs with caustic alkalis. 
 During the war some of these sources of hydrogen have been 
 tapped for aeronautical purposes, but in peace times large 
 quantities of such hydrogen have been blown to waste. 
 
 Hydrogen is also produced as a by-product together with 
 carbon dioxide in the manufacture of synthetic acetone by 
 the fermentation process (cf. /. Soc. Chem. Ind., (1919), 155 T). 
 
 MANUFACTURE FROM WATER GAS REPLACEMENT OF 
 CARBON MONOXIDE BY HYDROGEN 
 
 There are two main methods of effecting the replacement 
 of carbon monoxide in water gas by hydrogen (i) the 
 continuous catalytic process mainly due to the Badische 
 Anilin & Soda Fabrik ; (2) the Griesheim-Elektron process ; 
 both processes depend on the interaction of carbon monoxide 
 with steam giving carbon dioxide and hydrogen. 
 
 Water gas has the following approximate percentage 
 composition : 
 
 Hydrogen 49 
 
 Carbon monoxide . . 42 
 
 Carbon dioxide . . . . 4 
 
 Nitrogen . . . . . . 4-5 
 
 Methane . . . . . . 0-5 
 
 100 'O 
 
HYDROGEN 157 
 
 The reversible reaction 
 
 CO + H 2 O ^ CO 2 + H 2 + 10,200 calories 
 
 gives the so-called water gas equilibrium, provided that 
 sufficient time be allowed. 
 
 #coX 
 
 X 
 
 or, 
 
 Pco_ 
 Pco 2 
 
 This equilibrium is dealt with on p. 309, under "Water 
 Gas." 
 
 From an industrial standpoint the desideratum is to 
 convert as much carbon monoxide as possible into the easily 
 removed carbon dioxide, i.e. to make the fraction pco/Pco^ 
 as small as possible. 
 
 The variation of K with temperature is shown in the 
 following table ; the higher values are experimental but those 
 below 700 C. are based on an extrapolation of the formula 
 
 log K = - - + 0783 log T - 0-00043T 
 which fits those actually observed. 
 
 Temperature C. 
 K 
 
 400 
 O'o6 
 
 500 
 0-16 
 
 600 
 
 O'32 
 
 700 
 0-58 
 
 800 
 0*90 
 
 900 
 1-25 
 
 IOOO 
 
 1-62 
 
 1 
 
 It is evident that at comparatively low temperatures 
 the conditions are much more favourable for the conversion 
 of carbon monoxide into carbon dioxide than at high 
 temperatures. 
 
 Thus, if equal volumes of steam and hydrogen be 
 present in the gas after treatment, a condition secured by 
 taking about 1*4 volumes of steam per volume of water gas, 
 the ratio 
 
 Pco _ -rr PH* _ v 
 
 '~ 
 
158 INDUSTRIAL GASES 
 
 The carbon dioxide production is further enhanced by 
 maintaining a high pH 2 o/Pn 2 ratio up to a certain point 
 above which the dilution with steam lowers the reaction 
 velocity and output so much that the favourable effect on 
 the equilibrium is counterbalanced. 
 
 We have seen that a low temperature is desiiable ; below 
 about 400 C., however, the reaction velocity becomes so 
 small that equilibrium cannot conveniently be attained. 
 Further, it will be seen that even under favourable conditions 
 the removal of carbon monoxide cannot be complete. 
 
 There are two obvious ways of furthering the carbon 
 monoxide removal (i) by working at a low temperature, a 
 sufficiently great reaction velocity being attained by the 
 use of an active catalyst ; (2) by disturbing the normal 
 water gas equilibrium through the introduction into the 
 system of an absorbent for carbon dioxide, e.g. lime. 
 
 On these two principles are based the processes of the 
 Badische Anilin & Soda Fabrik and the Chemische Fabrik 
 Griesheim-Blektron respectively. 
 
 It is clear that variation in the pressure will be without 
 influence on the equilibrium ; it should be mentioned that 
 reaction may take place between hydrogen and carbon 
 monoxide or carbon dioxide in the absence of water. When 
 a mixture of Itydrogen with carbon monoxide or carbon 
 dioxide is passed over reduced nickel at 250 C., the following 
 reactions take place (Sabatier and Senderens, Comptes 
 Rend., 134, (1902), 514, 689) : 
 
 CO + 3 H 2 = CH 4 + H 2 
 CO 2 + 4H 2 = CH 4 + 2H 2 O 
 
 giving a very complete removal of the carbon monoxide if 
 the hydrogen be in excess. These reactions are exothermic 
 and therefore proceed less completely in the direction of 
 methane formation at higher temperatures, e.g. at 500 C. ; 
 a certain amount of methane may be formed, however, 
 unless the catalyst be selected to favour the water gas reaction 
 as is the case in actual practice. 
 
HYDROGEN 159 
 
 (i) B.A.M.A.G. Continuous Catalytic Process 
 
 The main development of the continuous catalytic 
 process is due to the Badische Anilin & Soda Fabrik, but 
 some other important patents are included below. 
 
 According to Hembert and Henry, in B.P. 1193/84, steam 
 is blown through incandescent coke and the resulting water 
 gas, mixed with excess steam, passed into retorts packed with 
 fireproof materials, at a red heat. Carbon dioxide and hydro- 
 gen are thus formed and the former is subsequently removed 
 by lime. Similarly, Read, in B.P. 3776/85, proposes to 
 use heated metallic oxides as catalysts. The carbon dioxide 
 formed is subsequently removed by alkalis, absorption in 
 water under pressure, etc. In B.P. 12608/88, Mond and 
 lyanger prescribe the elimination of carbon monoxide and 
 hydrocarbons from fuel gases by passing with excess steam 
 over metallic nickel or cobalt at a comparatively low tem- 
 perature, namely, 350-400 C. with nickel, 400-450 C. 
 with cobalt. Pumice soaked in nickel chloride solution may 
 be used. Carbon dioxide is removed by known methods and 
 the gas is claimed to be almost free from carbon monoxide. 
 F.P. 375164/06 of the Compagnie du Gaz de I/yons, relates 
 to the use of iron oxide at 600 C., while Naher and Mtiller, 
 in B.P. 20486/11, propose the use of palladium or rhodium 
 asbestos at about 800 C. After three treatments the carbon 
 monoxide is claimed to be reduced to 0-4 %. 
 
 None of the above mentioned patents met with technical 
 success and the commercial development of the process by 
 the use of active catalysts, as set forth in the following series 
 of patents, is due chiefly to the Badische Co. 
 
 According to B.P. 26770/12, hydrogen is manufactured 
 by the interaction of carbon monoxide and steam under 
 pressure in presence of a catalyst at a temperature of e.g. 
 300-600 C. A pressure of 4-40 atms. is used to accelerate 
 the reaction. Iron or nickel may be used as catalyst. Carbon 
 monoxide is almost entirely removed. The process is stated 
 to be specially suitable for gases containing only little carbon 
 monoxide ; in such a case the enhanced heat regeneration 
 
160 INDUSTRIAL GASES 
 
 tinder pressure is a further advantage since the heat evolution 
 is small. The use of pressure does not appear to have been 
 developed in practice. 
 
 B.P. 27117/12 relates to the maintenance of the temper- 
 ature in the above process by the catalytic combustion of 
 small quantities of oxygen added to the gases. Further, 
 the steam required for the reaction may be thus supplied 
 if only a little carbon monoxide be present. In B.P. 
 27955/12, a number of catalysts for the above reaction 
 are described, all with a basis of finely divided iron oxide ; 
 the working range is from 400-500 C. and heating to over 
 650 C. is to be avoided. B.P. 8864/13 deals with catalysts 
 consisting largely of nickel or cobalt ; according to D.R.P. 
 297258/14, the metals should be disposed in small quantities 
 on suitable supports and should be derived from salts free 
 from sulphur and halogens. Further catalysts are given in 
 B.P. 27963/13. When using nickel as catalyst, methane is 
 formed and it is here claimed that such methane formation 
 may be avoided by using catalysts consisting largely of iron 
 in conjunction with nickel, chromium, etc. The catalysis 
 is very rapid and suitable also for small quantities of carbon 
 monoxide. Working temperatures are about 400-600 C. 
 B.P. 16494/14 relates to the use of spathic iron ore as catalyst, 
 heating to above 650 C. being avoided ; a binding agent, 
 such as A1(OH) 3 , may be added for briquetting purposes. 
 In D.R.P. 284176/14, the use of the oxides of rare earths, 
 especially of cerium oxide, in conjunction with other activants, 
 is recommended. 
 
 A different class of catalyst is specified by Buchanan and 
 Maxted in B.P. 6476/14, which protects the use of lixiviated 
 alkaline ferrite. One passage gives a gas containing 28 % 
 carbon dioxide and 2 % carbon monoxide. In another 
 patent, B.P. 6474/14, the same inventors propose the use of 
 metallic couples such as iron + copper, e.g. sodium ferrite 
 treated with a copper salt. The couple is heated to 500 C. 
 and a mixture of carbon monoxide with hydrogen passed 
 over together with excess steam. An iron -j- silver couple is 
 stated to be very active. 
 
HYDROGEN 161 
 
 The process founded on the above Badische patents is 
 claimed by the Berlin Anhaltische Maschinenbau Aktien- 
 Gesellschaft (B.A.M.A.G.) to be the cheapest of all processes 
 for making hydrogen on a very large scale. It is used by 
 the Badische Co. at Oppau for the manufacture of synthetic 
 ammonia. One obvious advantage of the process is the 
 fact that whereas other -methods require 2-5 volumes of 
 water gas per volume of hydrogen produced, little more than 
 i 'i volumes are necessary in this case. Since water gas costs 
 about 4^. per 1000 ft. 3 (pre-war) the effect of this difference 
 may easily be estimated. Further, as the reaction is exo- 
 thermic, it is easy by means of heat-interchangers and care- 
 ful external lagging to make the supply of heat unnecessary 
 except on first starting up. A temperature of 400-500 C. 
 is maintained in the contact mass; little attention is required, 
 there being no valves to operate, and one man can look after 
 several contact sets. Starting with water gas mixed with the 
 desired excess of steam exhaust steam may be used the 
 gases issuing from the catalyst chamber, when freed from 
 excess steam by cooling, have a percentage composition 
 somewhat as follows : 
 
 Hydrogen . . . . 65 
 
 Carbon monoxide . . . . 1-2 
 
 Carbon dioxide . . . . 30 
 
 Nitrogen, methane, etc. . . 4 
 
 The gases are compressed to about 25-50 atms. and freed 
 from carbon dioxide by counter-current scrubbing with water 
 while under pressure, the energy of the water issuing from 
 the scrubber being largely recovered by means of a turbine. 
 For data on the solubility of carbon dioxide in water 
 under pressure, cf. p. 256. Final removal of the carbon 
 dioxide may be effected with alkali solution, also under 
 pressure. 
 
 On passage through the catalyst, all the sulphur com- 
 pounds in the water gas which needs no special purification 
 except from dust and tar are converted into sulphu- 
 retted hydrogen which is removed with the carbon dioxide. 
 
 A. II 
 
162 INDUSTRIAL GASES 
 
 If necessary, the remaining 1*5-3 % carbon monoxide is 
 extracted by an auxiliary process. 
 
 Plants are constructed up to a capacity of about 35,000 
 ft. 3 hydrogen per hour. A life of six months is claimed for 
 the catalyst. Before the war the only plant known to be in 
 operation was that at the works of the Badische Co. It is 
 claimed that the process can produce hydrogen at the low cost 
 of 1/9 per 1000 ft. 3 (pre-war) ; taking into consideration the 
 fact that each volume of water gas produces approximately 
 its own volume of hydrogen, together with the continuous 
 and comparatively simple nature of the operations, this would 
 not seem improbable. It should be observed that the presence 
 of some 4 % nitrogen is a serious disadvantage in certain 
 applications, e.g. in aeronautics. The method is eminently 
 suited from this point of view for the synthetic production 
 of ammonia ; by the addition of air to the steam in the 
 " make " period of the water gas manufacture, any desired 
 nitrogen-hydrogen mixture may be produced (cf. p. 207). 
 A certain amount of methane will always occur in hydrogen 
 made by this method. 
 
 Theory of the B.A.M.A.G. Continuous Catalytic 
 Process. Assuming the water gas to have the following 
 percentage composition : 
 
 Hydrogen 50 ' 
 
 Carbon monoxide . . . . 42 v 
 
 Carbon dioxide . . . . 4 
 
 Nitrogen . . . . . . 4 
 
 100 
 
 and the temperature of the catalyst to be 500 C., it is 
 interesting to calculate the theoretical result of using 100 
 volumes of water gas and 300 volumes of steam, both 
 measured at the same temperature. 
 We then have 
 
 Pco _ K PH* _ fi Pn t 
 
 I " A O ID v 
 
 PC0 2 />H 2 />H 2 
 
 If we express the original condition of the gas mixture in 
 
HYDROGEN 163 
 
 terms of partial pressures in atmospheres, we have the follow- 
 ing values : 
 
 Pu 2 o ...... 0750 
 
 PH. -. - 0-125 
 
 Pco ' I0 5 
 
 pco 2 ..... o-oio 
 
 ~ . . . . o-oio 
 
 I '000 
 
 The equation 
 
 CO+H 2 0-H 2 +C0 2 
 
 indicates that no change in volume takes place during the 
 reaction. 
 
 Consequently, if we take the change in partial pressure 
 of the carbon monoxide in the interaction as being repre- 
 sented by x, it may easily be seen that the final partial 
 pressures of the reactants will be 
 
 Pn z o ...... 0750 - x 
 
 Pn 2 ...... 0-125+ x 
 
 Pco ...... 0-105 -x 
 
 Pco 2 o-oioH- x 
 
 ...... o-oio 
 
 I '000 
 
 The value of x may be deduced from the relationship 
 
 #co a X pu 2 
 
 = (0-105-*) (0750-*) 
 (O'OIO +*)(0'I25 +*) 
 
 which gives the value of 0-09899 atm. for x. The final 
 
 partial pressure of carbon monoxide, therefore, is 0*006 atm. 
 
 On the removal of the steam by cooling, the partial 
 
 pressure of the carbon monoxide rises to atm. 
 
 = 0-0172 atm., since the partial pressure of steam after 
 reaction is 0750 0-099=0-651 atm. and the partial pressure 
 of the non-condensable gases, in consequence, 0-349 
 
164 INDUSTRIAL GASES 
 
 By similar reasoning the final composition of the gas is 
 seen to be 
 
 Hydrogen 0-6418 
 
 Carbon monoxide . . . . 0-0172 
 
 Carbon dioxide . . . . 0*3123 
 
 Nitrogen . . . . . . 0*0287 
 
 i -oooo 
 
 After removal of carbon dioxide this becomes, expressed in 
 percentages 
 
 Hydrogen . . 93-33 
 
 Carbon monoxide . . . . 2-50 
 Nitrogen . . . . . . 4-17 
 
 100-00 
 
 (2) Griesheim-Elektron Process 
 
 A description will first be given of the principal patents 
 on which the process is based. 
 
 In U.S. P. 229339/80, Tessie du Motay describes the 
 production of hydrogen by passing water gas, freed from 
 sulphur, over heated lime. The method is elaborated by the 
 Chemische Fabrik Griesheim-Elektron in B.P. 2523/09, 
 according to which, water gas and steam are passed over 
 caustic or slaked lime at 500 C. in a suitable container which 
 may be provided with stirring gear. The reaction is self- 
 supporting and the chamber is cooled to below the temper- 
 ature of the dissociation of calcium carbonate preferably 
 below 500 C. By the addition of 5 % iron powder the 
 reaction is greatly accelerated. The lime is regenerated by 
 subsequent calcination of the calcium carbonate. In a later 
 patent, B.P. 13049/12, it is claimed that the lime may be 
 advantageously used in the form of lumps, the action not 
 being confined to the surface as might be expected. The 
 material may thus be used in vertical towers and regenerated 
 in situ. The same company, in D.R.P. 284816/14, describes 
 
HYDROGEN 165 
 
 the manufacture of hydrogen by the action of steam under 
 about 10 atms. pressure, on a mixture of lime and charcoal 
 or lignite. With lime, a temperature of 600-800 C. is 
 required, but by using baryta a lower temperature is possible. 
 Among other patents may be mentioned B.P. 7147/13 (Soc. 
 1'Air lyiquide) which relates to the utilization of the carbon 
 monoxide-rich fraction obtained in the separation of carbon 
 monoxide from hydrogen by the Claude liquefaction process 
 (cf. p. 170). This gas, which contains some hydrogen, is 
 partially or wholly converted into hydrogen by the action 
 of heated slaked lime as above, the product being returned 
 to the water gas to be liquefied. 
 
 Bearing on this reaction there is a considerable amount 
 of literature, a brief survey of which now follows. 
 
 Merz and Weith (Ber., 13, (1880), 718) 'describe a lecture 
 experiment in which carbon monoxide is passed over heated 
 calcium hydroxide just below a red heat. Hydrogen with 
 only a small percentage of carbon monoxide is easily obtained. 
 
 The matter was further studied in Haber's laboratory by 
 Engels (Karlsruhe Dissertation, 1911, " Uber die Wasserstoff 
 Gewinnung aus Kohlenoxyd und Kalkhydrat ") who carried 
 out extensive experiments on the reactions underlying the 
 process. Carbon monoxide was passed over lime, the 
 temperature, speed, and CO/H 2 O ratio being varied. Kngels 
 concludes that in the absence of a catalyst the conversion 
 takes place essentially on the calcium hydroxide, although the 
 water gas reaction plays a minor part. On the contrary, if 
 5 % reduced iron be present, the action takes place mainly 
 in the gaseous phase. If pure lime be used the reaction 
 velocity is too low below 500 C., while 540 C. should not be 
 exceeded as the calcium hydroxide has a vapour pressure of 
 I atmosphere at 547 C. ; a greater steam concentration than 
 that corresponding to the vapour tension of lime at the 
 particular temperature is useless and, on account of the dilu- 
 tion of the reaction mixture, to be avoided. The reaction 
 velocity is increased about 10 times by the addition of iron ; 
 thus with an 81/19 H 2 O/H 2 ratio, a gas flow of I2'5 litres 
 carbon monoxide, measured at 20 C., per litre lime per hour, 
 
166 INDUSTRIAL GASES 
 
 gave at 500 0., a gas containing 0*4 % carbon monoxide in 
 the absence of iron, while under the same conditions but using 
 5 % iron, a corresponding velocity of 138 litres per hour gave 
 practically pure hydrogen (0*2 % carbon monoxide). 
 
 According to Vignon (Bull. Soc. Chim., 9, (1911), 18), in 
 treating water gas with lime no action takes place until 
 400 C., when hydrogen is formed together with some methane 
 and ethylene. The proportion of hydrogen to hydrocarbons 
 increases as the temperature is raised, pure hydrogen being 
 formed at 600 C. lyevi and Piva (Ann. Chim. App.,1, (1914), 
 i ; J. Soc. Chem. Ind., (1914), 310) consider the action of 
 carbon monoxide on calcium hydroxide to take place through 
 the intermediate formation of formates and oxalates, and 
 state that on heating sodium formate in an atmosphere of 
 carbon monoxide, hydrogen with carbon dioxide and some 
 methane is formed. In a later paper (Chem. Soc. Abstracts, 
 (1916), ii., 525) the same investigators observe that the de- 
 composition temperature of sodium formate is lowered from 
 375 C. to 260 C. by the presence of slaked lime. With pure 
 lime, carbon monoxide gives rise to formates at 250-300 C. 
 and to calcium carbonate and hydrogen above 300 C. 
 
 Theory of the Griesheim-Elektron Process. It is 
 instructive to calculate what is the lowest possible per- 
 centage of carbon monoxide which can be obtained with a 
 given proportion of steam at say 500 C., below which 
 temperature the reaction velocity is low. 
 
 Consider a gas of the percentage composition 
 
 Hydrogen . . . . 50 
 
 Carbon monoxide . . . . 42 
 
 Carbon dioxide . . . . 4 
 
 Nitrogen 4 
 
 100 
 
 to 100 volumes of which at 100 C., 200 volumes of steam are 
 added. 
 
 Now, since the final volume of hydrogen is approximately 
 equal to the original volume of the water gas, the carbon 
 
HYDROGEN 167 
 
 monoxide being almost completely converted into hydrogen 
 without change of volume, we have after cooling to 100 C. 
 
 ^H 2/ = CH. 2i + VCO, = 50 + 42 = 92 
 
 while 
 
 ^H 2 o 7 = 20 v co. = 200 42 = 158 
 
 where the suffixes i and /denote the initial and final volumes 
 respectively. 
 Thus 
 
 f-= K |^=o*i6 T ^ = 0*093 
 
 #CO, />H 2 158 
 
 The value for the dissociation pressure of calcium carbonate 
 as determined by Johnson (/. Amer. Chem. Soc., 32, (1910), 
 938) is i mm. at 587 C., but taking for simplicity i mm. at 
 the lower temperature of 500 C., 
 
 p co =0*093 p c02 = 0*093 mm. approximately. 
 
 Now, since the final volume of the reaction products is 
 approximately 92 +158 +4 = 254 at a temperature of 100 C., 
 while after removal of the steam it falls to 92 + 4 = 96, the 
 pressure of carbon monoxide in the cooled gas after removal 
 of the carbon dioxide, will be 
 
 0*093 X 254 
 ^ ^- = 0*25 mm. 
 96 
 
 or 0*032 %. 
 
 The hydrogen produced commercially by this process 
 is stated to have the following percentage composition : 
 
 Hydrogen .. 97*5 
 
 Carbon monoxide . . . . 0*0-0*2 
 
 Methane 0*3-0*5 
 
 Nitrogen . . . . . . 1*5-2*0 
 
 The cost of production depends on the size of the instal- 
 lation, but for moderate plants in continuous operation the 
 cost is stated to be 2/2^-2/9 per 1000 ft. 3 (pre-war), while 
 for large plants it falls to 1/8 (I/epsius, Monit. Sclent., (1912), 
 493). As the reaction is exothermic it is only necessary to 
 supply heat at the commencement of the operation. The lime 
 
168 INDUSTRIAL GASES 
 
 container requires to be cooled and the waste heat may be 
 utilized for the generation of the steam for the process. One 
 advantage claimed is the comparatively low temperature at 
 which the operation is conducted as compared with the 
 I/ane and allied processes, for instance, repairs being thus 
 minimized. 
 
 The process does not appear to have been used on any 
 considerable scale the handling of the large amounts of 
 lime presents some difficulty. 
 
 MANUFACTURE FROM WATER GAS BY LIQUEFACTION 
 OF THE CARBON MONOXIDE 
 
 This purely physical method of separating hydrogen from 
 water gas is in use on a fairly extensive scale and was the 
 process installed by the Badische Co. in their first synthetic 
 ammonia factory. It depends on the approximate separation 
 of the carbon monoxide and nitrogen as liquid by cooling 
 under pressure to about 200 C. The general trend of the 
 process may be seen from the following table : 
 
 Gas . . . . . . Vapour pressure of liquid at 
 
 -200 C. 
 
 Hydrogen . . . . (Above critical temperature, 
 
 namely 241-2 C.) 
 Carbon monoxide . . 0-57 atm. 
 Nitrogen . . . . 0*33 atm. 
 
 A brief resume will first be given of the principal patents 
 relating to this process. 
 
 Parkinson, in B.P. 4411/92, deals with the separation of 
 the constituents of gases such as air and water gas by frac- 
 tionation, etc. Some of the other early patents relating to 
 the liquefaction of the permanent gases have a bearing on the 
 separation of hydrogen from other gases, but the most im- 
 portant are those given below. According to B.P. 7205/11, 
 of the Gesellschaft fur Linde's Eismaschinen, A.G., the 
 compressed hydrogen-carbon monoxide mixture is cooled 
 by passing through a heat-interchanger, the cooling effect 
 of which may be augmented by means of liquid air or nitrogen. 
 
HYDROGEN 
 
 169 
 
 Partial liquefaction takes place under pressure 'and the two 
 
 phases are then allowed to expand in separate streams into 
 
 the above mentioned 
 
 heat - interchanger in 
 
 counter-current to the 
 
 incoming gas. The 
 
 hydrogen, before ex^ 
 
 pansion, however, may 
 
 pass through a second 
 
 heat - interchanger in 
 
 counter-current to the 
 
 expanded hydrogen, 
 
 whereby more carbon 
 
 monoxide is deposited 
 
 in a chamber connected 
 
 to the first liquefaction 
 
 chamber, the hydrogen 
 
 being thus rendered 
 
 purer, 
 
 A subsequent patent, 
 B.P. 9260/11, deals 
 with certain modifica- 
 tions : (i) a more 
 thorough fractionation 
 is effected by cooling 
 either the mixed in- 
 coming gases or the 
 hydrogen fraction (as 
 in Fig. 1 6) before its 
 expansion, with liquid 
 air or nitrogen boiling 
 under reduced pressure, 
 a lower temperature 
 being thus secured : (2) 
 the hydrogen may be 
 expanded either with or without the performance of external 
 work, in the former case the hydrogen may be slightly 
 heated by the incoming gases before they are cooled by the 
 
 FIG. 1 6. Linde's system for the separa- 
 tion of hydrogen from water gas by lique- 
 faction of the carbon monoxide. 
 
170 INDUSTRIAL GASES 
 
 evaporation of the liquid carbon monoxide fraction, in order 
 to prevent blocking up by solidification on expansion ; the 
 cooling effect of the external work may be used to cool the 
 hydrogen leaving the chamber in which separation of the 
 carbon monoxide has taken place, further carbon monoxide 
 being deposited : (3) the hydrogen may be led away in the 
 compressed state, the extra cooling necessary being supplied 
 by the liquid air boiling under reduced pressure. 
 
 A simplified apparatus, described by the Maschinenbau- 
 Anstalt-Humboldt in F.P. 445883/12, differs from the above 
 in that the compressed water gas, after traversing a heat- 
 interchanger, passes through a coil immersed in evaporating 
 carbon monoxide and then expands into a chamber where 
 carbon monoxide is deposited. The hydrogen escapes 
 directly through the heat-interchanger, while the carbon 
 monoxide is siphoned off to the above mentioned evapora- 
 tion chamber and after vaporizing enters the heat-inter- 
 changer. B.P. 7147/13 of the Soc. 1'Air lyiquide deals with a 
 combination of the liquefaction process with the Griesheim- 
 Elektron process (cf. p. 164) whereby the production of 
 hydrogen per volume water gas is increased. The carbon 
 monoxide-rich portion, after vaporization, is passed over 
 heated slaked lime and the resulting gas, mainly hydrogen, 
 added to the water gas entering the liquefaction system. 
 An attempt is made by the Badische Co., in D.R.P. 285703/13, 
 to avoid the necessity for supplementary cooling by liquid 
 air, by the addition of excess of carbon monoxide or nitrogen, 
 both of which gases show a positive Joule-Thomson effect. 
 This may be accomplished by returning the more volatile 
 portion of the carbon monoxide fraction, containing hydrogen, 
 to the water gas*supply. 
 
 In B.P. 13160/14, Claude (Soc. 1'Air I^iquide) describes 
 apparatus some what similar to that of I^inde. The compressed 
 water gas is divided into two portions which are cooled by 
 passing through two independent auxiliary heat-interchangers 
 AA (Fig. 17), traversed respectively by counter-currents of 
 the expanded hydrogen and carbon monoxide. After re- 
 union of the two streams of water gas, the carbon monoxide 
 
HYDROGEN 
 
 171 
 
 fraction is deposited in a separation chamber B*, the liquid 
 and gaseous phases being then treated separately in the two 
 portions, B and C (Fig. 18) of the heat-interchanger situated 
 above B 1 ; the hydrogen passes through both sections in 
 vertical tubes. The lower part B contains, under atmospheric 
 pressure, liquid carbon monoxide which is fed in from the 
 separating chamber B 1 .. The liquid carbon monoxide passes 
 
 FIG. 17. Claude fractionation system. 
 
 (1) through a coil S immersed in the liquid contained in the 
 lower part of the heat-interchanger B, being cooled thereby ; 
 
 (2) through a coil S 1 immersed in a small interchanger filled 
 with the liquid released to atmospheric pressure from the 
 same coil S 1 , and (3) after this release of pressure into a tank 
 E surrounding the hydrogen tubes in the upper part of 
 section B of the interchanger, finally overflowing into the 
 main bulk of liquid carbon monoxide below. The object 
 of this rather complicated procedure is to utilize the lower 
 
172 
 
 INDUSTRIAL GASES 
 
 temperature of the carbon monoxide deposited in B 1 (in 
 which carbon monoxide some hydrogen is retained on 
 account of its separation under pressure) to further cool the 
 hydrogen and so cause more complete deposition of the 
 carbon monoxide therefrom. With this method of working, 
 the hydrogen passes through tubes cooled by (i) liquid 
 
 carbon monoxide evaporating 
 under atmospheric pressure ; 
 (2) liquid carbon monoxide 
 containing some hydrogen also 
 evaporating under atmospheric 
 pressure ; and (3) the gases in 
 the upper part C of the inter- 
 changer. Here the hydrogen 
 is still further cooled by passing 
 to an engine D in which expan- 
 sion takes place, the expanded 
 gases being led back to the 
 interchanger. The carbon 
 monoxide deposited in the 
 tubes falls back to the separa- 
 tion chamber B 1 . If desired 
 the cooling effect may be in- 
 creased by the expansion of 
 supplementary compressed hy- 
 drogen. If high purity of the hydrogen is unnecessary, 
 the simpler type of separator shown in Fig. 17 may be 
 employed. 
 
 The Linde-Frank-Caro Process 
 
 Several L,inde-Frank-Caro plants have been installed on 
 the Continent and one, of about 17,000 ft. 3 per hour capacity, 
 by Messrs. Ardol, L,td., in this country. 
 
 Water gas, which contains about 50 % hydrogen, the 
 residue being mainly carbon monoxide with smaller quan- 
 tities of carbon dioxide, nitrogen and methane, passes through 
 a scrubber to a holder and is then compressed to about 
 25-50 atmospheres. Under this pressure it is freed from 
 
 FIG. 18.- 
 
 -Claude fractionation 
 system. 
 
HYDROGEN 173 
 
 carbon dioxide by washing with water Bedford process 
 (cf. also B.A.M.A.G. process, p. 161) and subsequently with 
 caustic soda. After being dried by refrigeration with an 
 ammonia or carbon dioxide plant, the compressed gas enters 
 the separator. Passing first through a heat-interchanger 
 in counter-current to all the outgoing gases, the compressed 
 gas traverses a coil immersed in liquid carbon monoxide 
 boiling under atmospheric pressure. Here the greater part 
 of the carbon monoxide is condensed and a little of the 
 nitrogen. The liquid and gaseous phases are separated in 
 a special vessel and the hydrogen, still containing some 
 5-6 % carbon monoxide and nitrogen, passes on to a tube 
 system cooled to about 200 C. by means of liquid air or 
 nitrogen boiling under reduced pressure. The liquid carbon 
 monoxide and nitrogen separated at this stage flow back to 
 the main portion in the separation vessel from which the 
 liquid passes through a valve to the vessel containing liquid 
 carbon monoxide at atmospheric pressure, used to cool the 
 compressed gases as mentioned above. By means of careful 
 lagging the heat losses are made very small so that only 
 relatively little liquid nitrogen is needed. The hydrogen 
 leaves the apparatus through the heat-interchanger under 
 the same pressure as that of entry, consequently little, if any, 
 energy is required for its subsequent utilization for the manu- 
 facture of synthetic ammonia, the hydrogenation of oils, etc. 
 The arrangement is identical with that represented dia- 
 grammatically in Fig. 16 except that the hydrogen is carried 
 back through the interchanger without release of pressure. 
 After evaporation, the carbon monoxide fraction, which has 
 a purity of 80-85 %> corresponding to a loss of about 15 % 
 of the hydrogen, passes to a gas engine, the power generated 
 being sufficient to drive the whole plant. The hydrogen 
 fraction has obviously a very high degree of purity as regards 
 sulphur and phosphorus compounds, heavy hydrocarbons, 
 etc., and the following percentage composition is claimed : 
 Hydrogen .. .. .. 97-97-5 
 
 Carbon monoxide . . . . 2-1 '7 
 
 Nitrogen i-0'8 
 
174 INDUSTRIAL GASES 
 
 The volume of hydrogen is about 40 % of the original 
 water gas. This purity is sufficient for many purposes, but, 
 if desired, further purification may be effected, see p. 207. 
 
 On account of the fractionation of the liquid air which 
 may be produced in the separator itself, or in very large 
 plants in a separate apparatus, nitrogen and oxygen may be 
 obtained as by-products. The operations may be so regu- 
 lated that the former is produced in the proportion required 
 for combination with the hydrogen to form ammonia. 
 
 The following particulars are given by Sander (Z. angew. 
 Chem., (1912), 2401) for different sizes of plants : 
 
 TABLE 22. 
 LINDE- FRANK CARO HYDROGEN PLANTS. 
 
 Hourly output (ft. 8 of hydrogen) 
 
 880 3500 
 
 17,700 
 
 Water gas used per hour (ft. 3 ) 
 
 2500 8800 
 
 44,000 
 
 Coke used per hour (Ibs.) 
 
 no 350 
 
 1700 
 
 Cooling water used per hour (gallons) . . 
 
 500 1700 
 
 7000 
 
 
 
 
 Plants producing 3500 and 35,000 ft. 3 of hydrogen per 
 hour are stated to cost about 13,000 and 80,000 respectively, 
 while the cost of production of the hydrogen by this process 
 is claimed to be about 3/- to 4/- per 1000 ft. 3 for medium- 
 sized plants (all on pre-war basis). The labour required in 
 working the plant is small on account of the continuous 
 nature of the operations. One advantage of the process when 
 used in connection with the hydrogenation of oils is the ease 
 with which the residual impure hydrogen may be purified 
 again. On the other hand repairs are somewhat heavy. 
 
 MANUFACTURE BY THE ACTION OF WATER OR STEAM ON 
 IRON OR CARBON 
 
 General. The processes falling under this heading are 
 all capable of representation by the following equation : 
 
 H 2 + R = H 2 + RO 
 
 Generally speaking, R may be any substance, usually 
 an element, which has the power of uniting with oxygen, 
 
HYDROGEN 
 
 175 
 
 but in practice only iron and carbon find application for this 
 purpose leaving out of consideration certain methods used for 
 field purposes, e.g. the action on water of sodium or other 
 active elements. 
 
 Iron Oxide Processes. The Alternate Action of Steam 
 and Reducing Gases on Heated Iron 
 
 At a red heat iron reacts with steam according to the 
 following equation : 
 
 4H 2 + 3Fe = 4H 2 + Fe 3 O 4 
 
 The action is reversible and the ratio of pn z o/Pn z f r 
 different temperatures is given below, the equilibrium 
 relations for the two stages of the reaction being separated 
 (Chaudron, Comptes Rend., 159, (1914), 237). The values 
 are taken from a smoothed curve. 
 
 SYSTEM Fe/FeO/H 2 /H 2 O. 
 
 Temperature C. . . 
 
 4OO 
 
 5OO 
 
 6OO 
 
 700 
 
 800 
 
 850 
 
 PR 2 0/P& 2 
 
 0-15 
 
 0-23 
 
 '33 
 
 0-46 
 
 0-61 
 
 0*70 
 
 
 
 
 
 
 
 SYSTEM FeO/Fe 3 O 4 /H 2 /H 2 O. 
 
 Temperature C. . . 400 
 H o/P H '2o 
 
 500 
 0-32 
 
 600 
 0-52 
 
 700 
 0-85 
 
 800 850 
 
 cf. also Wohler and Prager, Z. Elektrochem., 23, (1917), 
 199. 
 
 It is evident that reduction is favoured by increase of 
 temperature. On passing a continuous current of steam or 
 hydrogen over the iron or iron oxide heated to redness, the 
 reaction proceeds to completion giving oxide or metal 
 respectively. 
 
 This method of making hydrogen has long been recog- 
 nized and we find patents dealing with the alternate action 
 of steam and reducing gases on iron as early as 1861 (Jacob, 
 B.P. 593/ 61 ' cf - also Baggs, B.P.s 2719/65 and 1471/73), 
 
176 INDUSTRIAL GASES 
 
 One of the first attempts at technical production by this 
 method appears to have been made by Giffard in 1878, who 
 employed a shaft filled with ore. Water gas was used with- 
 out purification and for this reason, coupled with the irregular 
 temperature distribution in the shaft type of plant, the life 
 of the ore was very short. 
 
 The first patent of commercial importance is that of 
 Lewes, B.P. 20752/90, according to which a retort containing 
 iron turnings or moulded oxide, etc., is heated to bright 
 redness by imbedding in a producer, the air producer gas from 
 which is used in the reduction phase, the metal being then 
 treated with steam. This procedure would obviously give 
 rise to over-heating of the iron oxide. In a later patent, B.P. 
 4134/91, the iron oxide is disposed on pumice or mixed -with 
 asbestos, and semi-water gas is used for the reduction. A 
 number of patents dealing with special forms of plant follow. 
 An important point is touched on by the Dellwik-Fleischer 
 Wassergas G.m.b.H., in B.P. 21479/08, which prescribes the 
 addition of steam to the reducing gases to prevent the 
 deposition of carbon ; the reduction is arrested when only 
 half the oxide is reduced. Burnt pyrites is used as reaction 
 material. In B.P. 17591/09, I,ane describes an arrangement 
 of valves whereby more retorts may be reduced than oxidized 
 at the same time, this being desirable by reason of the greater 
 reaction velocity in the oxidation phase. The first portion 
 of the hydrogen is diverted. Impurities, e,g. sulphur, are 
 removed by occasionally burning out with air, and in a later 
 patent, B.P. 11878/10, a method of purification of the gases 
 from carbon dioxide, sulphuretted hydrogen, and sulphur 
 dioxide, by washing under pressure is described. Proposals 
 have been made to use molten iron, e.g. as in B.P. 23418/10 
 by Gerhartz. The use of roasted spathic iron ore as re- 
 action material is claimed by Dieffenbach and Moldenhauer 
 in D.R.P. 232347/10, while B.P. 6683/12 of the Badische 
 Co. relates to the prevention of loss of activity through 
 fusion of the surface of the iron, by using iron oxide which 
 has been melted in oxygen ; refractory oxides may be added. 
 Dieffenbach and Moldenhauer in a further patent, B.P. 
 
HYDROGEN 177 
 
 12051/12, propose to prevent deterioration by the use of 
 alloys of iron with manganese, tungsten, titanium, etc. 
 Mixtures of nitrogen and hydrogen may be obtained by 
 passing air and steam over the iron, or, alternatively, pure 
 nitrogen may be obtained by using air alone. 
 
 Among various patents describing means of avoiding fall 
 in output may be mentioned B.P. 12117/12 by Messerschmitt, 
 according to whom the effects of fusion of the iron oxide 
 in producing obstruction are avoided by the use of a skeleton 
 of compact iron, and B.P. 27735/12 (Badische Co.), where loss 
 of activity is prevented by the use of spongy iron obtained by 
 imbedding Swedish iron ore in carbon and heating from the 
 outside. We come next to a series of patents by Messer- 
 schmitt. B.P.s 12242/12 and 12243/12 deal with special 
 methods of construction of plant, the latter describing the 
 annular type of ore container detailed later. According to 
 B.P. 17690/13, the reduction of the oxide is effected by gases 
 of high calorific power and the heating by gases of low calorific 
 power, e.g. the spent reducing gases, fusion being thus 
 avoided, while B.P. 17691/13 advocates the reduction of 
 the charge by means of a partly burnt mixture of gas with 
 air in insufficient quantity for complete combustion. Modifi- 
 cations in construction are prescribed in B.P.s 17692/13, 
 in 18942/13 and in D.R.P. 291902/14. B.P. 18028/13 is 
 concerned with the use of iron-manganese ores in order that 
 lower temperatures may be employed, thus avoiding absorption 
 of carbon, sulphur, etc. According to D.R.P. 291603/13, the 
 iron is oxidized to the stage of ferrous oxide, giving hydrogen, 
 and then further with air, giving nitrogen. Among numer- 
 ous other patents may be mentioned B.P. 16893/14 by 
 Dempster, according to whom leakage of gas from one part 
 of the system to another is prevented by suitable water 
 seals, and B.P. 12698/15 by Maxted and Ridsdale, where the 
 deposition of carbon or the formation of carbide from the 
 gases in the reducing phase is prevented by the presence 
 of carbon dioxide to the extent of at least twice the volume 
 of the carbon monoxide ; contamination of the hydrogen 
 in the subsequent treatment with steam is thus avoided. 
 
 A. 12 
 
178 INDUSTRIAL GASES 
 
 This procedure is equivalent, of course, to the addition 
 of steam as set forth in B.P. 21479/08, see p. 176. 
 In B.P. 119591/18, Thorssell and L,unden propose to in- 
 crease the active life of the reaction material by impreg- 
 nating iron sponge with a solution of alkali hydrate or 
 carbonate. 
 
 Of the modifications of this method of producing hydro- 
 gen which are now in extensive use may be mentioned the 
 lyane, the Messerschmitt and the Internationale Wasserstoff 
 A. G. (B.A.M.A.G.) processes. 
 
 Lane Process. This process, or as modified by Dempster, 
 Messrs. Humphrey and Glasgow and others, is the one most 
 commonly adopted in this country for the production of 
 hydrogen on a large scale. Calcined spathic iron ore, 
 disposed in vertical cast-iron retorts, is alternately reduced 
 by water gas and oxidized by steam. 
 
 From the equations 
 
 Fe 3 O 4 + 2CO +2H 2 = sFe + 2CO 2 + 2H 2 O gas - 18,000 
 
 calories 
 3Fe + 4H 2 O gas = Fe 3 O 4 + 4H 2 + 38,400 calories 
 
 it will be seen that the reduction is endothermic while the 
 oxidation is exothermic. As regards the reduction by a 
 mixture of carbon monoxide and hydrogen, the interaction 
 of the latter reducing agent absorbs a large amount of heat, 
 while that of the former is very slightly exothermic ; on 
 this basis Jaubert effects economy in the fuel required 
 for maintaining the reaction temperature by working at a 
 lower temperature so that the carbon monoxide acts 
 preferentially. This method of procedure (L^ane- Jaubert 
 process) has probably corresponding disadvantages in in- 
 creasing the deposition of carbon in the reducing phase 
 and consequently raising the carbon monoxide content of 
 the hydrogen (see below). 
 
 The ore is contained in vertical cast-iron retorts about 
 9 inches internal diameter and nearly 10 ft. long, a plant 
 generating 3500 ft. 3 /hr. having 36 such retorts, arranged in 
 three groups each of 12 retorts (Fig. 19). Since the total 
 
HYDROGEN 179 
 
 internal volume of such a set equals 159 ft. 3 the " space- 
 
 velocity" is ft. 3 hydrogen/ft. 3 /hr. =22 ft. 3 hydrogen/ 
 
 ft. 3 /hr. The ends of the retorts are flanged and closed by 
 
 Front Elevation 
 
 FIG. 19. Lane Hydrogen Plant (The Engineer). 
 
 plates with asbestos joints. Heating of the retorts to 
 650-700 C. is effected either by means of a built-in producer 
 or by the combustion of water gas which, of course, needs no 
 purification. 
 
 The method of operation is as follows : Two of the three 
 
i8o 
 
 INDUSTRIAL GASES 
 
 groups are supplied with water gas for 20 minutes, whereby 
 reduction of the oxide takes place, and then treated with 
 steam for 10 minutes, the reduction occupying more time 
 than the oxidation. During the reduction phase the carbon 
 monoxide and hydrogen of the water gas are only partty 
 utilized and, consequently, the exit gases are used for heating 
 the retorts, first passing through a condenser to remove the 
 
 To 1 Atmosphere 
 
 Hydrogen 
 
 FIG. 20. Diagram of the Lane Hydrogen Retort Furnace 
 (The Engineer}. 
 
 steam. When reduction is complete, the retorts contain 
 water gas which, if passed into the hydrogen gas-holder, 
 would introduce carbon monoxide ; for this reason " scav- 
 enging " is resorted to, i.e. for a short time after admitting 
 steam, the impure hydrogen is passed back into the water 
 gas main and is thus not lost. Connection is then made to 
 the hydrogen main. A convenient arrangement of change- 
 over valves, as shown diagrammatically in Fig. 20, is employed 
 to effect these operations. When changing from the oxidizing 
 to the reducing phase the valve H is operated slightly in 
 
HYDROGEN 181 
 
 advance of the valve K. The spent reducing* gases, still 
 containing some combustible gases, on leaving the retorts 
 pass to condensers in which the bulk of the steam formed in 
 the retorts is separated, and then are led to the combustion 
 chamber. 
 
 It is important carefully to purify the water gas used in 
 the reduction of the ore, as sulphur compounds exert a dele- 
 terious influence causing disintegration and loss of activity. 
 The water gas passes from the generators through a heat- 
 interchanger in counter-current to the steam entering the 
 generator, through a water scrubber to a gas-holder from which 
 it is drawn by an exhauster into a series of purifiers charged 
 with bog iron ore to remove sulphur compounds, and then 
 enters the retorts. Four purifiers form a set, three being 
 in use at once, the gas passing the three in series, entering 
 the foulest first. The thorough elimination of the sulphur- 
 etted hydrogen from the water gas has an important bearing 
 on the life of the reaction material. 
 
 During the reduction phase there is some deposition of 
 carbon arising from decomposition of carbon monoxide. 
 
 2CO = CO 2 + C + 39,300 calories (cf. p. 237). 
 
 (For a fuller study of the complex equilibria of the 
 system Fe/FeO/Fe 3 O 4 /CO/CO 2 /C, reference should be made 
 to Baur and Glassner, Z. physik. Chem., 43, (1903), 354 ; 
 cf. also Carpenter and Smith, Trans. Iron and Steel Inst., 
 September, 1918.) 
 
 On passing steam, this carbon gives rise to carbon 
 monoxide and carbon dioxide in the hydrogen. To minimize 
 this effect and to remove accumulations of sulphur com- 
 pounds, the retorts are periodically " burnt out " by blowing 
 air through them. 
 
 Many attempts have been made, as has been mentioned 
 in the patent synopsis, to prevent the deposition of carbon 
 in the reducing phase. Thus, Maxted, of Gas Developments, 
 I/td., proposes to introduce sufficient carbon dioxide into the 
 reducing gases to give a CO 2 /CO ratio higher than that 
 corresponding to the CO 2 /CO/C equilibrium (cf. p. 237) by 
 
182 INDUSTRIAL GASES 
 
 using instead of ordinary water gas, a " converted " water 
 gas (B.P. 12698/15; B.P. 125112/16, see p. 177). It should 
 be pointed out that the equilibrium ratio of CO 2 /CO is not 
 that given on pp. 238-9 for any particular temperature, e.g. 
 700 C., but varies with the actual joint partial pressure of 
 carbon monoxide and carbon dioxide. By working from the 
 value of K t , which equals pcoJP 2 co> it is, however, easy to 
 calculate the ratio for any particular condition. 
 
 On leaving the retorts the hydrogen passes through a 
 scrubber, then through lime purifiers, where carbon dioxide, 
 resulting from the oxidation of carbon monoxide in accordance 
 with the water gas equilibrium, is removed, into a holder. 
 
 The temperature of the retorts is a matter of considerable 
 importance, on account of its bearing on carbon deposition 
 on the one hand, and on the life of the retorts on the other. 
 The usual practice is to employ a temperature of about 
 650 C. The retorts are stated to last about 12 to 1 8 months 
 and the ore about 6 months. Assuming the life of the retorts 
 to be 12 months, the depreciation is equivalent to a charge 
 of about $d. per 1000 ft. 3 of hydrogen. 
 
 In good practice, 2-3 volumes of water gas are necessary 
 for each volume of hydrogen produced. 
 
 A considerable number of plants have been erected in 
 this country, in France and in Russia. The purity of the 
 hydrogen may be fairly high with careful working, e.g. 
 99'5~99'75 %> the main impurities being carbon monoxide 
 and a little (e.g. 0-25 %) nitrogen. Plants are made with 
 capacities from 250-10,000 ft. 3 /hr. The cost of the 
 hydrogen produced by this method is of the order of 3/- to 
 4/- per 1000 ft. 3 plus overhead charges (pre-war). 
 
 The Messerschmitt Process. This process has come 
 into considerable use in Germany and was largely adopted 
 by the German War Department, which had some fifteen 
 plants of 3500-20,000 ft. 3 /hr. capacity (Barnitz, Met. and 
 Chem. Eng., 15, (1916), 494 ; /. Soc. Chem. Ind., (1916), 
 1136). 
 
 It differs from the I^ane process in having much larger 
 units which are of annular form in order to minimize 
 
HYDROGEN 
 
 183 
 
 variation of temperature. The latest type consists of an 
 upright cylindrical shaft lined with firebrick into which shaft 
 two concentric iron cylinders are built (Fig. 21). Of 
 these, the inner one rests on the floor of the generator while 
 
 FIG. 21. Messerschmitt Hydrogen System. 
 
 the other is raised slightly to afford room for the admission 
 of the gases. The reaction material (iron ore or iron- 
 manganese ore) is disposed in the annular space between the 
 two cylinders. Chequer-work in the inner cylinder and 
 between the outer cylinder and the furnace wall, serves to 
 retain and regenerate the heat. A mixture of water gas 
 
184 INDUSTRIAL GASES 
 
 with insufficient air for complete combustion is burnt in the 
 inner cylinder and the products of incomplete combustion 
 pass downwards through the reaction mass in the annulus 
 and upwards again outside the outer cylinder (secondary 
 air being added at the last stage) and so out to the flue. 
 After some 20 minutes, during which a temperature of 
 700-800 C. is maintained, the water gas and air are cut 
 off and steam is passed into the generator from below. The 
 issuing impure gases are allowed to escape for a few seconds 
 into the flue ; at this point the steam is diverted so as to 
 enter at the top of the outer chamber, passing up through 
 the reduced iron, the hydrogen being taken off at the top. 
 Ten minutes suffices for the steaming operation, whereupon 
 the cycle is repeated. The course of the combustion in the 
 furnace may be reversed or the two directions may be 
 alternated. In the Messerschmitt process the effect of carry- 
 ing out the reduction with the partially burnt gases from the 
 central heating chamber should be to prevent or minimize 
 the deposition of carbon on the reaction material owing to 
 the presence of carbon dioxide and its equivalent for this 
 purpose, steam. The hydrogen is subjected to a final 
 purification as in the I^ane process. 
 
 Among the advantages claimed for the system are the 
 ease of control of the working temperature and the avoid- 
 ance of overheating. The purity of the gas is variously 
 stated to be 98-5 to 99*2 %, while the cost, which varies 
 with the size of the plant, is claimed to be as low as 2/~- per 
 1000 ft. 3 inclusive of capital charges (pre-war). Little 
 labour is demanded. When renewal is necessary the reaction 
 mass is abstracted through Morton doors at the bottom. 
 The apparatus is easily adapted to intermittent working 
 should this be desired. 
 
 Process of the Internationale Wasserstoff A.G. 
 This process differs little in principle from the other processes. 
 In its earlier form the plant consisted of two vertical iron 
 cylinders heated externally to 700-800 C. The process 
 has been taken over recently by the B.A.M.A.G., which uses 
 internally -heated firebrick shafts ; the cycle consists of three 
 
HYDROGEN 185 
 
 periods, namely, heating, reducing and steaming. Water 
 gas of the highest possible calorific power is used for the 
 reduction, the excess being subsequently burnt. As reaction 
 mass, large lumps of burnt pyrites are used. Some carbon 
 is deposited from the gases ; the purity of the hydrogen 
 may be 98-99 % with careful working, the carbon monoxide 
 not exceeding 0*8 %.,. For plants producing 60,000 ft. 3 
 per hour, the cost, inclusive of labour and repairs, is stated 
 to be about 3/4 per 1000 ft. 3 (Sander, /. Gasbeleucht., 58, 
 (1915), 637) (pre-war). 
 
 Strache Process. An older process due to Strache 
 employs three vertical iron cylinders set in firebrick, of which 
 No. i is a water gas generator, No. 2 contains iron oxide 
 and No. 3 is a regenerator. The steam is passed in the 
 reverse direction, i.e. from 3 to i via 2. 
 
 With reference to all the above discontinuous processes, 
 the general statement may be made that the hydrogen is 
 liable to contain variable amounts of carbon monoxide, say 
 O'25 to i '5 %, unless subjected to further purification. 
 
 Dieffenbach and Moldenhauer Process 
 
 When steam is passed through heated carbon, a mixture 
 of carbon monoxide, carbon dioxide and hydrogen is produced. 
 In usual practice, e.g. in making water gas, the operation 
 is conducted so as to give a high CO/CO 2 ratio ; this is 
 effected by working at a temperature such as 1000 C. 
 While the conversion of the carbon monoxide of water gas 
 into carbon dioxide may be realized by the B.A.M.A.G. 
 process, proposals have been made, especially by Dieffenbach 
 and Moldenhauer, to combine the two stages by conducting 
 the actual gasification of the carbon at a relatively low 
 temperature. This is accomplished by impregnation of the 
 coke with a suitable catalyst, such as an alkaline salt, to 
 increase the reaction velocity. 
 
 The idea is an attractive one ; on the other hand, there is 
 no record of any industrial success having been attained by 
 such processes, neither are technical data of the process 
 available. Such a process is unlikely to be of importance in 
 
186 INDUSTRIAL GASES 
 
 the production of pure hydrogen ; the matter is, however, of 
 sufficient interest to warrant a brief synopsis of the main 
 patents. 
 
 According toTessie duMotay andMarechal (B.P. 2548/67) 
 hydrogen is produced, together with carbon dioxide, by 
 heating fuel with caustic soda or lime. B.P. 8426/92 by 
 Krupp is similar. Steam is passed over carbonaceous matter 
 mixed with hydrates, carbonates, etc., which limit the 
 temperature of the operation, thus reducing the percentage 
 of carbon monoxide. By passing over red-hot lime the 
 carbon dioxide is removed ; this lime, as also that used in the 
 generating retorts, being subsequently regenerated by the 
 passage of steam. The same principle is elaborated by 
 Dieffenbach and Moldenhauer in B.P. 7718/10, according to 
 which carbon is impregnated with chlorides, sulphates, 
 sulphides, etc., and heated with steam when the reaction 
 takes place at a low temperature, e.g. at 600 C., producing 
 only a little carbon monoxide. Coal may be impregnated 
 and then coked preparatory to being heated with steam. 
 The operation may be carried out in externally-heated retorts, 
 or oxygen may be added in small quantities to maintain the 
 temperature. According to B.P. 7719/10, charcoal is impreg- 
 nated with salts especially silicates, and treated with steam 
 at 550-750 C. The carbon monoxide content of the hydro- 
 gen is claimed not to exceed a few tenths per cent. In B.P. 
 7720/10 it is stated that better results are obtained by 
 impregnating crushed coal and briquetting the product, so 
 counteracting the tendency of the activity to fall off owing 
 to impregnation being only local. The same inventors, in 
 B.P. 8734/10, advocate the addition of a considerable quantity 
 of lime together with salts in order to take up the carbon 
 dioxide and lower the carbon monoxide content (cf. the 
 Griesheim-Elektron process). For example, coke is first 
 impregnated with 10 % potassium carbonate solution, then 
 mixed with 5 times its weight of lime and heated in steam 
 at 550-750 C. The potassium carbonate limits the disso- 
 ciation of the calcium carbonate by making the reaction 
 possible at a lower temperature. 
 
HYDROGEN 187 
 
 Bergius Process 
 
 This interesting process depends on the action of liquid 
 water on iron or carbon at temperatures in the neighbourhood 
 of 300 C., and consequently under pressures at least equal 
 to the vapour pressure of water, the following values relating 
 to the temperature region concerned : 
 
 Temperature C. '* . . 250 300 350 
 
 Vapour pressure (atms.) 39 89 167 
 
 Above 365 C., i.e. the critical temperature of water, 
 no liquid can be present. 
 
 If carbon is used, the reaction differs from that obtaining 
 in a gas producer in that the conditions for carbon monoxide 
 production are much less favourable at the lower temper- 
 ature in question. When iron is employed, the low temper- 
 ature has in like manner the effect of preventing attack by 
 the water on the impurities in the iron. The principal 
 patents relating to this process are given below. 
 
 According to D.R.P. 259030/11 of Bergius and Chemische 
 Fabrik vorm. Moritz. Milch & Co., carbon is heated with water 
 under high pressure to about 300 C. In an example cited, 
 100 kilos, coke, 200 kilos, water, and i kilo, thallium chloride 
 are heated together to 340 C. The resulting hydrogen and 
 carbon dioxide are blown off at intervals and the carbon 
 dioxide absorbed by lime. B.P. 19002/12 by Bergius relates 
 to the use of iron ; hydrogen is generated by the action of 
 liquid water at temperatures above 100 C. on iron or its 
 lower oxide, preferably in the presence of electrolytes, e.g. 
 ferrous chloride. Metallic couples may be formed by the 
 presence of metals electropositive to iron, e.g. an iron- 
 copper couple may be used. In one example iron shavings 
 are treated with water at 300 C., the pressure being kept 
 at 150 atmospheres ; while in another, sodium chloride and 
 a plate of copper are added, the pressure is allowed to rise 
 to 120 atmospheres and a temperature of 250 C. is employed. 
 In an addition to this patent, namely, B.P. 19003/12, Bergius 
 describes suitable plant for carrying out the operations. 
 In its essentials the apparatus consists of a steel pressure 
 
i88 INDUSTRIAL GASES 
 
 vessel fitted with a reflux condenser, dry hydrogen being thus 
 obtained. D.R.P. 277501/13 describes a pressure vessel 
 containing a central heating tube round which is arranged 
 a series of reaction tubes, each of which may be brought in 
 turn under a feed opening in the cover and by this means 
 frequent removal of the main cover is avoided. A later 
 patent, D.R.P. 286961/13, deals with the use of water in the 
 form of steam at temperatures below 500 C. Electrolytes 
 are preferably added as in the previous patents. 
 
 An experimental plant was erected at Hanover (J. Soc. 
 Chem. Ind., (1913), 462 ; Z. angew. Chem., (1913), i., 517 ; 
 Z.fiir komp. undflussige Case, (1915), 33) to test the Bergius 
 process. The plant consisted of six vessels, each of about 
 i *6 ft. 3 capacity and capable of generating some 150 ft. 3 
 of hydrogen per hour. A charge of iron was used, contained 
 in a vessel inserted from the bottom of the bomb and forming 
 a lining in order to protect the bomb itself from attack. Some 
 90 % of the iron was oxidized in a period of about 4 hours. 
 With carbon the action was rather slow. The carbon and 
 sulphur in the iron are stated to be unattacked. 
 
 In the following table are to be found comparative rates 
 of reaction as influenced by additions : 
 
 Reactanls. 
 
 Temperature C. 
 
 Hydrogen generated per hour. 
 
 Iron 4- pure water . . 
 +FeCl 2 
 + FeCl 2 4-Cu.. 
 + FeCl 2 + Cu . . 
 
 300 
 300 
 300 
 340 
 
 230 c.C. 
 1390 c.c. 
 1930 c.c. 
 3450 c.c. 
 
 On leaving the reflux condenser with which each bomb 
 was fitted, the hydrogen passed through a water separator 
 to storage cylinders. The gases being passed through a spiral 
 cooled in liquid air and the condensate examined, the following 
 analysis, calculated for the original gas, was obtained : 
 
 o/ 
 
 /o 
 
 Hydrogen . . . . . . 99*95 
 
 Carbon monoxide . . . . 0*001 
 
 Saturated hydrocarbons . . 0*04 
 Unsaturated hydrocarbons o*oj 
 
HYDROGEN 
 
 189 
 
 By passage over charcoal at liquid air temperatures, a purity 
 of 99*995 % could be obtained. 
 
 This process has certain attractive features (i) the small 
 floor space required ; (2) its suitability for small plants, 
 e.g. for field work, on account of the low initial cost and 
 the discontinuous nature of the operations ; (3) the fact that 
 only direct fuel heating is required ; (4) the production of 
 compressed hydrogen and (5) the high degree of purity 
 of the hydrogen produced. One would, however, expect 
 repairs to be rather high in view of the intermittent character 
 of the process necessitating very frequent breaking of large 
 high pressure joints. The cost of hydrogen produced by this 
 method is stated to be 1/4 J to i/n per 1000 ft. 3 (pre-war). 
 
 MANUFACTURE OF HYDROGEN BY THE DECOMPOSITION 
 OF HYDROCARBONS 
 
 Under this heading may be described a number of 
 processes all of which depend on the dissociation of hydro- 
 carbons by the action of heat. Such dissociations may be 
 attended either by evolution or absorption of heat. As an 
 example of the first class, acetylene is typical 
 
 C 2 H 2 = 2C + H 2 + 47,800 calories. 
 
 In consequence of the high heat evolution accompanied 
 by no change in volume, the equilibrium conditions give 
 almost complete decomposition except at very high temper- 
 atures. With exothermic hydrocarbons like methane, on 
 the other hand, the degree of dissociation rises more or less 
 rapidly as the temperature is raised. Thus, taking the case 
 of methane, we have the following equilibrium conditions at 
 different temperatures for the equation : 
 
 CH 4 ^ C + 2H 2 21,700 calories, 
 
 Temperature C. . . 
 
 400 
 
 500 
 
 600 
 
 700 
 
 800 
 
 900 
 
 IOOO 
 
 Percentage of me- 
 thane in the dis- 
 
 
 
 
 
 
 
 
 sociated product . . 
 
 86-2 
 
 62-5 
 
 31-7 
 
 in 
 
 4' 4 
 
 2 
 
 I 
 
igo INDUSTRIAL GASES 
 
 the values at 900 and 1000 C. being obtained by extrapo- 
 lation. The effect of temperature on the equilibrium 
 CH 4 +H 2 O^CO + 3H 2 is treated on p. 240. 
 
 It must be borne in mind that methane is a very stable 
 vSubstance and that the equilibrium values are only slowly 
 realized, particularly in the absence of catalysts, until temper- 
 atures in the region of 1000 C. are attained. Further, the 
 influence of increased pressure is greatly to increase the 
 stability, since the dissociation constant K equals 
 
 The question of decomposing hydrocarbons has long 
 received attention. In B.P. 1466/76, St. John describes 
 the decomposition of coal gas hydrocarbons by passage 
 through incandescent coke, while Stern, in B.P. 2787/80, leads 
 naphtha vapour with steam over heated lime. Passing over 
 a number of similar patents we come to the patents of 
 Rincker and Wolter, F.P.s 391867/08 and 391868/08, according 
 to which two coke-filled generators are heated to incandes- 
 cence by the injection of air ; tar, oil, or other suitable 
 hydrocarbon is then introduced into one generator, under- 
 going transformation into hydrogen and carbon which is 
 deposited in the generator. The generators are used alter- 
 nately. A new line is taken by Machtolf in B.P. 14601/06. 
 According to this patent, acetylene compressed to 4 to 6 
 atmospheres and mixed with oil gas, etc., is exploded electri- 
 cally ; hydrogen and lampblack are thus produced. In 
 B.P. 15071/09, I^essing describes the production of hydrogen 
 from coal gas by passing through a retort either empty or 
 containing carbon, and heated to 1000-1300 C. In like 
 manner, Nauss (B.P. 2298/10) passes coal gas over nickel 
 at 250-300 C., whereby the carbon monoxide is converted 
 into methane which is subsequently decomposed by treat- 
 ment with coke at 1000-1200 C. According to Dieffen- 
 bach and Moldenhauer (D.R.P. 229406/09), hydrocarbons 
 mixed with steam are heated and passed through a catalyst 
 consisting of gauze of nickel, platinum, etc., disposed at 
 
HYDROGEN 191 
 
 right angles to the current ; it is claimed that with such short 
 exposure to the catalyst carbon dioxide is formed without 
 the production of carbon monoxide. Oxygen may be added 
 to maintain the temperature. 
 
 We will next consider a series of patents by Pictet, who 
 in B.P. 24256/10 prescribes the passage of acetylene, alone 
 or mixed with other hydrocarbons, under slight positive 
 pressure, through a conduit maintained by cooling at about 
 500 C. If liquid hydrocarbons are added to the acetylene, 
 the cooling may be effected by their evaporation. The heat 
 evolved by the decomposition of the acetylene serves for the 
 decomposition of the exothermic hydrocarbons added. 
 According to B.P. 13397/11, petroleum is distilled into a long 
 tube maintained at 1200-1350 C. by the supply of a certain 
 number of calories, while in an addition to this patent, namely 
 B.P. 14703/11, the admixture of steam with the petroleum 
 is prescribed, so that the carbon is wholly or partially con- 
 verted into carbon monoxide. B.P. 16373/11 relates to the 
 addition of oxygen to the steam-petroleum mixture. The 
 combination of the carbon and oxygen give sufficient heat 
 to enable the reaction, represented by the following equation, 
 
 C + H 2 O = CO + H 2 29,100 calories, 
 
 to proceed. The products in the two last patents are naturally 
 mixtures of hydrogen and carbon monoxide. 
 
 Bosch, in D.R.P. 268291/11, describes the continuous 
 decomposition of acetylene under pressure. B.P. 12978/13 
 (Badische Co.) relates to the passage of a mixture of hydro- 
 carbons and steam over a catalyst consisting of a medium 
 such as magnesia carrying 2-5 % nickel and maintained at a 
 temperature of 800-1000 C. The carbon monoxide 
 formed is subsequently removed. The B.A.M.A.G. (B.P. 
 2054/14) proposes to improve upon the usual practice, 
 in the process for manufacturing hydrogen by cracking 
 oils in a mass of heated coke, of spraying the oil on the coke, 
 by effecting evaporation of the oil in an external chamber 
 heated by the waste gases from the generator during the 
 heating phase. Deposition of difficultly combustible carbon, 
 
192 INDUSTRIAL GASES 
 
 which may choke up the generator, is thus avoided. Ellis 
 (U.S. P. 1092903/14) proposes to add lime to the fuel in order 
 to flux the ash and prevent clinkering difficulties, while 
 Brownlee and Uhlinger (B.P. 5098/15) describe a chamber 
 which contains refractory material and is alternately heated 
 with fuel gases and used to decompose hydrocarbons, the 
 carbon formed being carried along with the hydrogen. 
 
 The principal processes which are known to be in 
 actual operation are the Carbonium Gesellschaft, Rincker 
 and Wolter, Oechelhauser, and B.A.M.A.G. (Bunte) pro- 
 cesses. 
 
 Carbonium Gesellschaft Process. In this process 
 which is founded on the patent of Machtolf (see p. 190) 
 acetylene is compressed to about 2 atmospheres and ignited 
 electrically. Complete decomposition takes place with 
 production of lampblack which is separated and forms a 
 valuable pigment, about 60 Ibs. per 1000 ft. 3 of hydrogen 
 being formed. After passing through large scrubbers the 
 hydrogen is obtained in an exceptionally pure state. The 
 commercial success of the process depends on a market for 
 the lampblack. A Zeppelin station at Friedrichshafen was 
 supplied with hydrogen made in this way. 
 
 That the process is not free from danger is evidenced by 
 the fact that this factory was largely destroyed by an 
 explosion in 1910. The cost (pre-war) of the hydrogen by 
 this process is stated by Sander to be about 4/- per 1000 
 ft.3 
 
 Rincker and Wolter Process. This method of making 
 hydrogen is due to two Dutch chemists, Rincker and Wolter, 
 and has been developed by the B.A.M.A.G. and the 
 Hollandsche Residugas-Maatschaapij. Two generators of 
 the producer type are filled with coke. After heating the fuel 
 beds to a high temperature by an air blast, the air producer 
 gas from one generator being burnt by secondary air in the 
 other, tar, oil, or other cheap hydrocarbon is sprayed in at 
 the top of each generator for about a minute ; decomposition 
 is complete in about 20 minutes, the hydrogen escaping at 
 the bottom. The " blow " is then repeated, this time in 
 
HYDROGEN 193 
 
 f 
 
 the reverse direction. The carbon formed during the "make " 
 is deposited on the coke and is burnt out in the next " blow " 
 period. After traversing a system of scrubbers, coolers and 
 driers, hydrogen of the following percentage composition is 
 .obtained (Kills) : 
 
 Hydrogen . . . . 96 
 Nitrogen . . . . 1-3 
 
 Carbon monoxide . . 27 
 
 By a further purification with heated soda-lime an 
 analysis as below is obtained : 
 
 % 
 Hydrogen . . . . 98*4 
 
 Nitrogen . . . . i'2 
 
 Carbon monoxide . . 0*4 
 
 A plant producing 3500 ft. 3 /hr. is stated to cost ^550 
 exclusive of erecting expenses (Ellis), while the hydrogen 
 costs 2/6~4/- per 1000 ft. 3 (pre-war). Plants are usually 
 arranged to work normally for the production of illuminating 
 gas, and for hydrogen manufacture when required. Portable 
 plants on the Rincker and Wolter system have been used by 
 the Russian and German Air Services. Two generators lined 
 with firebrick are employed and are mounted on two railway 
 trucks together with a turbo-blower and oil pump ; the 
 plants have a capacity of about 3500 ft. 3 /hr. Some 2-3 
 hours are required to start up ; only coke and oil are used 
 as raw materials, while two men are sufficient to operate 
 the plant. 
 
 Oechelhauser Process. This process, as to the com- 
 mercial operation of which little has been published, depends 
 on passing coal gas through vertical or horizontal retorts 
 heated to 1200 C. and filled with coke. The lampblack 
 formed is partly deposited on the coke and partly carried 
 along with the hydrogen wherefrom it is filtered by wood fibre. 
 After cooling and purification the gas consists of 80-84 % 
 hydrogen. The following analysis indicates the nature of 
 the changes induced (I/epsius, Monit. Sclent., (1912), 
 493) : 
 
 A. I 3 
 
INDUSTRIAL GASES 
 
 
 Coal gas. 
 
 Product of process. 
 
 Heavy hydrocarbons, carbon dioxide, 
 
 % 
 
 /o 
 
 oxygen and nitrogen 
 
 7-8 
 
 
 
 Carbon monoxide 
 
 5' 3 
 
 7' 3 
 
 Methane 
 
 24-7 
 
 6-9 
 
 Hydrogen 
 
 
 80-7 
 
 The cost of production of this impure hydrogen is stated 
 by L,epsius to be about the same as that of the original coal 
 gas since there is an expansion, or about 2/9-3/6 per 1000 
 ft. 3 (pre-war). 
 
 On a modification of this method of making hydrogen 
 is based the 
 
 B.A.M.A.G. (Bunte) Process. This process, arising 
 out of experiments by Bunte, is similar to the Oechelhauser 
 process. Coal gas is freed from carbon dioxide and led 
 over white-hot coke. After removing carbon monoxide 
 by soda-lime the product is stated to be almost pure 
 hydrogen, containing only a little nitrogen. The nitrogen 
 content, however, will be not less than that originally present 
 in the coal gas, making due allowance for the increase in 
 volume. Crude hydrogen may be readily manufactured in 
 this way in ordinary gas works, but purification by soda-lime 
 is not attractive technically. 
 
 MANUFACTURE OF HYDROGEN BY ELECTROLYSIS 
 
 General. Hydrogen is obtained electrolytically (i) by 
 the electrolytic decomposition of dilute acids or alkalis 
 as a special operation, or (2) as a by-product in certain 
 electrochemical operations, e.g. the electrolysis of brine, with 
 the production of caustic soda, the electrolysis of fused caustic 
 soda in the manufacture of sodium, etc. Since, in many 
 cases of the second class, the plant is not adapted to the 
 collection and storage of all the gas evolved, the hydrogen is 
 largely wasted ; in view of the exceptional purity of the gas 
 this is to be deplored. 
 
 It will be well at this stage to give some of the constants 
 
HYDROGEN 195 
 
 to which all electronic processes for decomposing water 
 may be referred. 
 
 i gram-ion 
 
 96,470 coulombs (ampere-seconds) liberate -2 - - grams of an ion. 
 
 valency of ion 
 
 X ionic weight 
 T ampere-hour liberates - alency of ion - grams of an ion. 
 
 418-6 c.c. hydrogen \ _ f N T p 
 209-3 c.c. oxygen / d 
 441*6 c.c. hydrogen) at 15 C. and 760 mm. 
 220-8 c.c. oxygen / pressure. 
 0-01560 ft. 3 hydrogen^ at 15* C. and 760 mm. 
 o 00780 ft. 3 oxygen / pressure. 
 ,1000 ft. 3 of hydrogen at 15 C. and 760 mm. pressure require 64,123 
 
 ampere-hours. 
 Decomposition voltage of water = 1*67 volts. 
 
 1*67 is the lowest voltage at which a permanent current 
 may be passed through water and consequently determines 
 the minimum possible energy expenditure, namely 107*1 
 K.W.H./iooo ft. 3 of hydrogen at 15 C. This efficiency 
 cannot be attained in practice, however, as the resistance of 
 the electrolyte necessitates an increase in the voltage to 
 from 2 to 4 volts according to the electrolyte and the con- 
 struction of the cell, thus raising the energy expenditure 
 from 128 to 256 K.W.H./iooo ft. 3 of hydrogen. 
 
 It may be stated broadly that there are three main 
 aims in the design of electrolytic cells : (i) to obtain the 
 lowest possible resistance ; (2) to prevent intermixing of the 
 gases ; (3) to avoid corrosion of the component parts of the 
 cell. These problems have been solved, as far as the con- 
 flicting nature of the circumstances allows, as follows : (i) by 
 using short columns of electrolytes having high electrical 
 conductivity, the heat produced by the resistance of the 
 electrolyte being conserved so as to maintain a temperature 
 of, say, 70 C., and lower the resistance ; (2) by the provision 
 of partitions or diaphragms, porous or otherwise, between the 
 electrodes, or by the provision of tortuous paths for the 
 current in the electrolyte, also by precautions to maintain 
 equal pressures in the two electrode compartments and 
 (3) by suitable selection of materials and electrolytes. The 
 conditions for (i) and (2) are somewhat in opposition ; thus, 
 diaphragms, etc., increase the resistance. 
 
196 INDUSTRIAL GASES 
 
 A brief survey of the important work on this subject 
 will be given here in chronological order : 
 
 As early as 1881, Barlow, in B.P. 1897/81, proposed the 
 electrolysis of water, while d'Arsonval (Elektrotech. Zeits., 12, 
 (1891), 197) produced oxygen for physiological purposes 
 on a large laboratory scale in 1885, using as electrolyte 30 % 
 caustic potash solution with a linen diaphragm. Appar- 
 ently the first large scale apparatus was constructed by 
 I,atchinoff (B.P. 15935/88). Either an acid or an alkaline 
 electrolyte was used, with asbestos or parchment diaphragms. 
 In another form of apparatus lyatchmoff introduced the use 
 of bipolar electrodes for the electrolysis of water. He also 
 devised an apparatus for conducting the electrolysis under 
 a pressure of 120 atmospheres. Renard took up the question 
 from a military standpoint in 1888 (Soc. de Physique, (1890), 
 224 ; D.R.P. 58282/90) and used alkaline electrolytes, per- 
 mitting the use of iron or steel electrodes. A further advan- 
 tage of alkali is the absence of ozone, thus permitting the use 
 of rubber for connections. An asbestos diaphragm was 
 used, an B.M.F. of 3 volts being required. Inter-connected 
 hydraulic seals were employed to equalize the pressure in 
 the anode and cathode compartments. In 1892 a new 
 principle was introduced by Garuti (B.P. 16588/92) in the 
 use of a metal partition to avoid the disadvantages of high 
 resistance and frequent renewals associated with porous 
 diaphragms. The metal diaphragm does not reach to the 
 bottom of the cell and the E.M.F. is kept below that at which 
 the diaphragm will act as a bipolar electrode, say roughly 
 about 3 volts. The apparatus is submerged in the electro- 
 lyte to prevent mixing of the gases. A modification of this 
 idea is embodied in the patent of Siemens and Obach (B.P. 
 11973/93) in which the use of wire gauze diaphragms is 
 proposed. Garuti and Pompili, in B.P. 23663/96, also try 
 to lower the resistance by the use of diaphragms perforated 
 in the lower parts. In 1899 an important advance was 
 made by Schmidt who, in D.R.P. 111131/99, revived the idea 
 of bipolar electrodes in combination with asbestos diaphragms 
 in a practical way, the plant taking the form of a filter press, 
 
HYDROGEN 197 
 
 in which the respective gases were led away by channels 
 similar to those in filter-press practice. A noteworthy 
 economy in floor space is thus effected. Schoop, in Austrian 
 Patent 1285/1900, describes an apparatus which dispenses 
 with a continuous diaphragm, replacing this by a collecting 
 bell of glass or clay round each electrode. We find another 
 patent by Garuti and^ Pompili, B.P. 12950/1900, where 
 soldering is avoided by a special method of construction 
 of the iron cells. The cells and diaphragms are prolonged 
 below the electrodes. A later patent, B.P. 2820/02, relates 
 to covering the perforations in the diaphragms with gauze, 
 while in B.P. 27249/03, the same inventors describe apparatus 
 for purification of the gases by passing them over heated 
 platinum wire. In B.P. 17981/06, the Elektrizitats Aktien 
 Gesellschaft, vorm. Schuckert & Co. substitutes for the usual 
 diaphragm an insulated bell disposed over one electrode, 
 the cell forming the other electrode ; in later patents, B.P.s 
 3000 and 3000A/07, two bells are used, each in electrical 
 connection with its corresponding electrode and separated 
 from the other by a screen of insulating material which 
 projects well below the bells. Cowper-Coles, in B.P. 14285/07, 
 dispenses with diaphragms and uses tongue-shaped projections 
 (pointing downwards) on the electrodes as guides to the 
 gases, while B.P. 24716/09 by Bycken, I^eroy and Moritz 
 deals with various precautions against mixing, especially 
 when the gases are used under considerable pressure, in an 
 apparatus of the filter-press type, the outlets being con- 
 trolled by floats. In B.P.s 27264/10 and 21600/11, 
 Knowles describes a catalytic purifier with heat regenera- 
 tion and with water seals supplied by the water produced 
 in the purifier. Electrolytic plants of the filter-press 
 type are described by the Soc. Anon. 1'Oxhydrique Fran- 
 $aise and I^evin in B.P.s 18818/13 and 3654/14 respec- 
 tively. The recent patents on this subject are very 
 numerous ; it will perhaps suffice to mention the following : 
 U.S.P. 1086804/14 by Burdett, D.R.P. 275515/14 by Mas- 
 chinenfabrik Oerlikon, B.P. 101598/16 by Churchill and 
 Geeraerd, and U.S.P.s 1239530/17 and 1256067/18 by 
 
198 INDUSTRIAL GASES 
 
 Schriver, as examples of patents which have been developed 
 commercially. 
 
 Principal Electrolytic Processes used in Practice 
 
 The best known processes for the electrolytic decompo- 
 sition of water are the Schuckert, Schmidt (Oerlikon), 
 Garuti, Schoop, Churchill, International Ox}-gen Co., vSchriver 
 and Burdett systems. It may be mentioned that electro- 
 lysis, at any rate in the past, has been used for the production 
 of oxygen rather than hydrogen except as regards hydrogen 
 for military purposes. 
 
 Schuckert Process. In the Schuckert apparatus each 
 cell usually takes 600 amperes. The electrodes are of iron 
 and are covered with iron bells insulated from the electrodes 
 and separated by a sheet of insulating material. As electro- 
 lyte a 20 % caustic soda solution is used. In order to 
 minimize the resistance, the temperature is allowed to rise 
 to 60-70 C. by packing round with sand, when 2*8-3 volts 
 are required. Some corrosion of the electrodes takes place 
 necessitating occasional renewals. For a plant producing 
 some 10,000 ft. 3 of hydrogen per day, the energy expenditure, 
 according to L,epsius (Monti. Sclent., (1912), 493), costs 2/3 to 
 1 1/3 per 1000 ft. 3 hydrogen plus 500 ft. 3 oxygen, while the 
 total cost (not including compression) is 6/- to 15/3 per 
 1000 ft. 3 hydrogen plus 500 ft. 3 oxygen, when electric energy 
 costs 0-1175^. to 0*59^. per K.W.H. By calculation from the 
 above figures, 1000 ft. 3 hydrogen plus 500 ft. 3 oxygen require 
 227 K.W.H. According to Blum (Metall. and Chem. Eng., 
 (1911), 157), 275 K.W.H. are required. 
 
 This process is stated to be expensive and demands 
 a large floor space, but gives very pure gases. The purity 
 of the hydrogen leaving the cells is about 99 %, that of the 
 oxygen about 97 %. The gases pass through scrubbers 
 and then through catalytic purifiers. 
 
 A Schuckert plant was installed many years ago by 
 Herseus of Hanau ; there are plants also at Kehl am Rhein, 
 at Metz, at the Wolverhampton works of the British Oxygen 
 Co. and several plants in the United States. 
 
HYDROGEN 199 
 
 Schmidt Process. Schmidt's multiple cell' takes the 
 form of a filter-press with, for example, 40 bipolar electrodes 
 in series. The electrodes are separated and insulated by 
 asbestos diaphragms, reinforced at the edges with rubber. 
 By means of passages similar to those in a filter-press, the 
 hydrogen and oxygen respectively are led to the two sides 
 and pass to chambers where the spray is separated and caused 
 to flow back to the bottom of the cells. The gases may be 
 taken off under a pressure of some 3 Ibs. per in. 2 , or even up 
 to 35 Ibs. pressure, this being advantageous for long pipe 
 lines. This plant is very compact and free from complicated 
 gas and current connections. The electrolyte is a 10 % 
 solution of potassium carbonate or potassium hydrate. 
 An B.M.F. of about 2*3 volts per cell is required at 60 C. 
 According to L,orenz the current efficiency is 86 % . Energy 
 required per 1000 ft. 3 hydrogen plus 500 ft. 3 oxygen is about 
 170 K.W.H. according to Dammer ; at 0*25^. per K.W.H. 
 the cost for current is 3/6. Purification is effected by passing 
 the gases over platinized asbestos at 100 C. Traces of carbon 
 monoxide, derived from the rubber of the joints, are found in 
 the oxygen. The purity of the hydrogen is 99 %, that of 
 the oxygen, 97 %. A Schmidt plant was installed by the 
 Swedish Navy. 
 
 The manufacture of the Schmidt cell was taken over 
 by the Oerlikon Co., who installed a plant at the Farnborough 
 Air Station, cf. p. 232. Similar apparatus is made by the 
 International Oxygen Co., by Schriver and Co., and by 
 other firms (see below, p. 200). 
 
 Garuti Process. The Garuti cell has an iron diaphragm 
 which is insulated from and projects below the electrodes, 
 not functioning as a bipolar electrode so long as the voltage 
 does not exceed twice the decomposition voltage of water 
 or, say roughly, 3 volts. The absence of a porous diaphragm 
 ensures a low resistance, while to decrease this still further, 
 the diaphragms are perforated opposite to the centres of the 
 electrodes, the holes being covered with gauze. A number 
 of narrow cells are arranged together and submerged in a 
 tank of electrolyte, a hydraulic seal being used to prevent 
 
200 INDUSTRIAL GASES 
 
 increase of pressure and mixing. As electrolyte, 26 % 
 caustic potash solution is used. The gases are purified 
 by passing over heated platinum wire ; the purity attained 
 is 98-99 % for the hydrogen, 97 % for the oxygen. B.M.F. 
 required is about 2*5 volts, and the current efficiency about 
 96 % (Buff a). Electrical energy per 1000 ft. 3 hydrogen 
 plus 500 ft. 3 oxygen is therefore 167 K.W.H., and cost of 
 this at 0-25^. is 3/6. At 0-5^. per K.W.H., the cost per 
 1000 ft. 3 hydrogen plus 500 ft. 3 oxygen is stated to be about 
 9/- uncompressed. 
 
 Garuti plants have been installed in Rome, Tivoli, Terni, 
 lyucerne, Monthard, and by the American Oxhydric Co., 
 Milwaukee, Wis. 
 
 Schoop Process. The Schoop process employs no 
 diaphragm, but each of the long narrow tubular electrodes 
 is surrounded by a collecting tube of glass or clay. Two 
 anodes and two cathodes are mounted in each cylindrical 
 cell. Using iron and an alkaline electrolyte, the voltage is 
 about 2 '25 volts, or if lead electrodes and dilute sulphuric 
 acid are used, 3*6 volts. A high degree of purity is claimed 
 for the gases, namely, hydrogen 97*5 %, oxygen 99 %. 
 
 With an acid electrolyte, which is apparently most com- 
 monly used, the electrical energy per 1000 ft. 3 hydrogen 
 plus 500 ft. 3 oxygen for a voltage of 3*6 and a current effici- 
 ency of 100 %, would be 230 K.W.H., costing 4/10 for power 
 at o-25^./K.W.H. 
 
 With an alkaline electrolyte and a voltage of 2*25, the 
 power would be 144 K.W.H., the cost of which at o'2$d./ 
 K.W.H. would be 3/- ; the cost of the plant is higher in this 
 case. 
 
 Plants have been installed at Kalk am Rhein and else- 
 where. 
 
 International Oxygen Co.'s Processes. The Inter- 
 national Oxygen Co., of Newark, N.J., has two well-tried 
 systems : 
 
 (i) Bipolar Filter-press Type. This is very similar to that 
 of Schmidt ; the large cells use a current of 400 amperes at a 
 voltage of 2, a set of 60 electrodes running on 120 volts. 
 
HYDROGEN 201 
 
 By using electrodes of commercially pure iron, nickel-plated 
 on the anode side, the over-voltage is minimized. The 
 energy is guaranteed not to exceed 127 K.W.H. per 1000 
 ft. 3 hydrogen plus 500 ft. 3 oxygen (measured at 15 C. and 
 760 mm.), with an electrolyte of 29 % caustic potash solution. 
 This corresponds to a cost of 2/8 for current at O'25^./K.W.H. 
 As electrolyte, 14*5 % caustic soda solution may also be used. 
 The purity of the hydrogen is stated to be 99*5 % and that 
 of the oxygen 99 % on leaving the generators. The usual 
 purifying and safety devices are employed. 
 
 (2) Unit Cell Type. Enclosed oval cells are used with 
 hydraulic seals for the cover and diaphragm, the latter 
 being of asbestos. The tank itself forms the cathode, and 
 an alkaline electrolyte is used. Energy consumption and 
 purity of the gases are very similar to those relating to (i). 
 
 Other Processes. Apparatus of the filter-press type is 
 constructed by T. Schriyer and Co., Harrison, N.J., the 
 performance of the plant is very similar to that described 
 above for the International Oxygen Co. type (i). 
 
 The Churchill apparatus consists of narrow cells, the walls 
 of which form the electrodes. No diaphragm is employed 
 and intermixing of the gases is prevented by the provision 
 of a series of glass or earthenware vanes arranged close to the 
 electrode walls at an angle of about 45, pointing downwards. 
 The electrodes may be provided with vertical grooves to 
 allow of the escape of the gases past the vanes. Owing to 
 the absence of a diaphragm, the cell has a low resistance, 
 and works at 2*3 volts. The energy requirements are about 
 155 K.W.H. per 1000 ft. 3 hydrogen plus 500 ft. 3 oxygen. 
 
 The Burdett plant has a number of electrodes in a tank, 
 and the gases are taken off by means of bells divided into 
 compartments by asbestos diaphragms. 
 
 In the above processes an addition of distilled water is 
 made daily to compensate for that decomposed ; about 4! 
 gallons are required per 1000 ft. 3 of hydrogen neglecting 
 evaporation. With alkaline electrolytes, absorption of 
 carbon dioxide is largely prevented by the layer of water 
 vapour on the surface when warm, or a layer of oil may be 
 
202 INDUSTRIAL GASES 
 
 used. Those systems employing light gauge electrodes, 
 as the Garuti and Schuckert types, are liable to corrosion 
 of the anodes at high current densities possibly due to the 
 presence of chlorides or sulphates in the alkali. Such corrosion 
 increases the resistance, while iron may be deposited on the 
 cathode and cause short-circuiting. 
 
 It may be stated in general that the production of hydro- 
 gen by the electrolytic decomposition of water is expensive 
 compared with other processes unless a very cheap source 
 of energy is available ; further, a very large floor space is 
 required. The purity of the gases, after passing over a heated 
 catalyst, is very high (cf. p. 213), and provided that due 
 precautions are taken against intermixing, the process is 
 safe and requires little attention. The prevention of mixing 
 is very important when the gases are compressed, and several 
 cylinder explosions have been traced to neglect in this 
 particular (cf. also p. 39 et scq.). Injury to the diaphragm, 
 blockage in the system, excess voltage on cells of the 
 Garuti type, or too great current density, may cause such 
 mixing. 
 
 The question of automatic apparatus for the detection 
 and estimation of oxygen in hydrogen or vice versa is dis- 
 cussed on p. 33. 
 
 Danger Limits as regards Intermixing in Electro- 
 lytic Hydrogen and Oxygen. The inflammability of 
 mixtures of hydrogen and oxygen depends to a considerable 
 extent on the mode of ignition, but the limits may be taken 
 as 5*3 % oxygen and 5 '5 % hydrogen in hydrogen and oxygen 
 respectively (Fischer and Wolf, Ber., 44, (1911), 2956). 
 According to Burrell and Gauger (loc. cit., p. 40) the effect 
 on the explosive limits of increased pressure up to 100 
 atmospheres is very small (cf. also p. 40). 
 
 Hydrogen as a By-Product 
 
 Hydrogen is produced in large quantities as a waste 
 product in certain electrochemical industries, e.g. in the 
 Castner-Kellner and other processes for the manufacture of 
 caustic soda by the electrolysis of brine. In the electrolysis, 
 
HYDROGEN 203 
 
 a volume of 7230 ft. 3 of hydrogen at 15 C. is theoretically 
 produced per ton of sodium chloride electrolysed. The 
 Griesheim-Elektron works at Bitterfeld and Rheinfelden 
 produced, according toL,epsius (1911), some 250,000,000 ft. 3 , 
 i.e. about 600 tons, of hydrogen per annum, or 700,000 ft. 3 
 per diem, enough to inflate a dirigible balloon of moderate 
 size. The purity of the. hydrogen is 90-97 %. If ingress of 
 air and chlorine be prevented, the hydrogen is, of course, of 
 a high degree of purity. 
 
 On the advent of the Zeppelin in 1898 the gas was 
 collected, hydrogen from this source becoming a commercial 
 article. Hydrogen in a compressed state may now be 
 obtained in England from the Castner-Kellner Co., whose 
 daily production is some 500,000 ft. 3 , but before the war, 
 at any rate, the bulk of the gas was wasted. . Some of the 
 hydrogen has been used by this firm for the production of 
 pure hydrochloric acid for analytical purposes, etc., by direct 
 combustion with the chlorine simultaneously liberated. This 
 may be effected either by actual combustion or by combina- 
 tion in the presence of a catalyst, e.g. charcoal. Special 
 precautions are necessary to prevent intermixing of the gases 
 outside the combustion chamber. 
 
 OTHER PROCESSES FOR THE MANUFACTURE OF 
 HYDROGEN 
 
 Before leaving the manufacture of hydrogen by methods 
 suitable for use in stationary plants, it will be well to consider 
 briefly a few patents, etc., which do not fall under the preced- 
 ing general headings and which, although in most cases of 
 little commercial importance, are mentioned for the sake of 
 completeness. Some of the methods are also of interest in 
 connection with field operations (vide infra}. 
 
 By the Action of Acids or Alkalis on Metals. The 
 use of the action of acids on iron, zinc, etc., has been 
 proposed from time to time, the expense of the processes 
 being, in general, only tolerable where valuable by-products 
 are secured. 
 
204 INDUSTRIAL GASES 
 
 In B.P.s 16277/96 and 15509/07, Pratis and Marengo 
 describe apparatus for the generation of hydrogen from 
 sulphuric acid and iron. Carulla, inB.P. 23702/08, proposes 
 to absorb the hydrochloric acid from salt cake manufacture, 
 by means of towers packed with iron scrap, the ferrous chloride 
 liquor being worked up for iron oxide. In like manner Barton 
 (B.P. 28534/10) suggests the interaction of zinc and sulphuric 
 acid, the zinc sulphate solution being used to produce zinc 
 carbonate for use as a pigment and filler, while Bastwick 
 (B.P. 10228/11) uses the acid-zinc generator as a battery. 
 B.P. 107807/16, by Becquefort and Deguide, relates to the 
 utilization of sodium bisulphate by treatment with iron 
 scrap. Another patent, B.P. 25891/11, by the Chemische 
 Fabrik von Hey den, A.G., deals with the production of 
 hydrogen by the action of ammonia on alloys of the alkali 
 metals in a finely divided state. Further details referring 
 to such methods will be found under Field Processes in the 
 following section. 
 
 Separation of Hydrogen from Water Gas and the 
 like by Physical Methods. The only process of technical 
 importance coming under this category is the I/inde-Frank- 
 Caro process, which has been already described. 
 
 Among other suggested processes may be mentioned that 
 proposed by d'Arsonval (Ann. Chim. et Phys., [7], 26, (1902), 
 446), based on the experiments of Dewar, who showed that 
 coal gas could be freed from hydrocarbons by cooling to a 
 suitable temperature with liquid air. Mazza, in B.P. 12194/02, 
 and Elworthy, in B.P. 10581/06, propose to effect a preliminary 
 separation of hydrogen and carbon monoxide (water gas) 
 by centrifugal action, final purification of the two fractions 
 being carried out according to Elworthy by chemical means, 
 e.g. by cuprous chloride and caustic soda (cf. also B.P. 
 17946/05 by Clamond) . 
 
 Several other patents deal with diffusion methods. Thus, 
 in B.P. 22340/91, Pullman and Elworthy describe the 
 production of a mixture of hydrogen and carbon dioxide 
 by passing excess superheated steam over red-hot coke 
 and subsequent separation of the gases by diffusion through 
 
HYDROGEN 205 
 
 diaphragms of plaster of Paris or porous earthenware. 
 Jouve and Gautier, in F.P. 372045/06, deal with a similar 
 separation of the constituents of water gas by means of 
 unglazed earthenware ; it is stated that the percentage of 
 carbon monoxide is reduced from 25 % to 4-4 % by a single 
 passage. Cf. also Nussow, D.R.P. 295463/13, where liquid 
 (e.g. water) or solid diaphragms are used. Snelling, in 
 U.S. P. 1174631/16, in the separation of carbon monoxide 
 from hydrogen uses a septum of porous earthenware or 
 alundun, with a thin coating of platinum or palladium, 
 heated to above 800 C. The operation is preferably 
 conducted under pressure. 
 
 Through the Intermediary of Formates. A number 
 of patents relate to the production of hydrogen by the 
 decomposition of formates, prepared from producer gas and 
 the like. Thus, Feldkamp, in B.P. 22225/05, prescribes 
 the production of formates from producer gas by the action 
 of alkali solutions (cf. pp. 248, 316), and subsequent heating 
 of such formates with production of oxalates and hydrogen. 
 Similarly the Badische Co., in B.P. 30073/13, and Weise and 
 Rieche, in U.S. P. 1098139/14, deal with the production of 
 formates, using e.g. 20 % caustic soda liquor heated under 
 pressure, with subsequent decomposition of the formate, 
 either in the presence or absence of the residual nitrogen ; 
 in this way (i) a mixture of nitrogen and hydrogen (see p. 207) 
 or (2) hydrogen is obtained. 
 
 Miscellaneous Methods. In B.P. 2080/81, Helouis 
 describes a process whereby carbon monoxide is removed 
 from water gas by passing over calcium sulphate heated to 
 redness : 
 
 CaSO 4 + 4CO = CaS + 4 CO 2 
 
 the carbon dioxide being absorbed by sodium carbonate 
 solution. 
 
 Hutin, in B.P. 23370/94, covers an alloy of sodium and a 
 heavy metal with a layer of concentrated sodium hydrate 
 solution, the water content of which is maintained by supply- 
 ing with steam above . A too violent reaction is thus avoided . 
 
206 INDUSTRIAL GASES 
 
 According to L,ahousse, in F.P. 361866/05, steam is 
 decomposed by passage over red-hot barium sulphide, which 
 is subsequently regenerated by the reduction of the resulting 
 barium sulphate with producer gas or coal. 
 
 The Nitrogen Co., N.Y., in B.P. 17666/11, prescribes the 
 production of hydrogen by the action of molten zinc, 
 antimony, tin, etc., at a red heat on steam. The metal is 
 regenerated by passing the oxide into a solvent where it 
 comes into contact with carbon or other reducing agent. 
 According to Kendall, in B.P. 26896/12, a mixture of sodium 
 chloride or potassium chloride with molybdenum is heated 
 and treated with steam. Hydrogen, hydrochloric acid and 
 alkali molybdate are produced. The molybdenum is 
 regenerated by reduction of the molybdate with coke when 
 carbon monoxide and sodium or potassium vapour are formed 
 leaving metallic molybdenum. Tungsten may be used in 
 like manner. 
 
 Teissier and Chaillaux, in F.P. 447688/12, propose to 
 manufacture hydrogen and oxygen as follows : Barium 
 sulphate is first heated to a red heat with manganous oxide 
 when reaction (i) takes place. On raising the temperature 
 to a white heat reaction (2) occurs, and on treating with 
 steam under pressure, reaction (3) results, giving the original 
 mixture again : 
 
 (1) BaSO 4 + 4MnO = BaS 
 
 (2) 4MnO 2 = 4MnO -f 2O 2 
 
 (3) BaS -f4H 2 O == BaSO 4 
 
 Hooton (B.P. 18007/14) proposes the treatment of iron 
 pyrites with steam, whereby the ore is left almost free from 
 sulphur while a mixture of hydrogen, sulphuretted hydrogen 
 and sulphur dioxide is produced. By interaction of the 
 sulphuretted hydrogen and sulphur dioxide in the presence 
 of bog iron ore, sulphur is deposited, any excess of sulphur 
 dioxide being removed by alkali. 
 
 Siemens and Halske, in D.R.P. 220486/10, describe a 
 process of treating calcium carbide with steam at a high 
 
HYDROGEN 207 
 
 temperature, whereby hydrogen is liberated as represented 
 in the following equation : 
 
 CaC 2 + 5H 2 O = CaO + 2CO 2 + 5H 2 
 
 The carbon dioxide is removed by the lime resulting from a 
 previous operation, and a high degree of purity of the 
 hydrogen is claimed. 
 
 Production of a Mixture of Nitrogen and Hydrogen 
 for use in Synthetic Ammonia Manufacture 
 
 Reference has just been made (p. 205) to the production 
 from producer gas of a mixture of nitrogen and hydrogen. 
 There are a number of industrial applications, e.g. the 
 synthesis of ammonia and the filling of electric lamps, in 
 which a mixture of nitrogen and hydrogen is required, and 
 occasionally it may be convenient to produce the mixture in 
 a single operation. Since in the B.A.M.A.G. continuous 
 catalytic hydrogen process, any nitrogen present in the 
 water gas persists in the hydrogen produced, it is obviously 
 a simple matter by using a controlled semi-water gas instead 
 of water gas to produce a nitrogen-hydrogen mixture of 
 any desired composition. Similarly in the L,ane or Messer- 
 schmitt process, instead of steam, as in the usual method of 
 operation, a suitable mixture of air and steam may be 
 passed over the reduced iron (cf. Dieffenbach and Molden- 
 hauer, B.P. 12051/12, p. 177). According to Messer- 
 schmitt, D.R.P. 291603/13, if steam is passed first and air 
 is substituted when oxidation is partly effected, a more 
 complete oxidation of the iron results. As described in 
 U.S. P. 1123394/15, Scholl obtains a mixture of nitrogen and 
 hydrogen suitable for lamp filling by passing a correctly 
 proportioned mixture of gaseous ammonia and air over heated 
 catalytic material (cf. p. 113). 
 
 METHODS OF FINAI, PURIFICATION OF HYDROGEN 
 
 Certain methods of removal of foreign constituents 
 generally present only in small quantities, not having been 
 
208 INDUSTRIAL GASES 
 
 described previously under the various methods of manu- 
 facture, will be given under this heading. 
 
 Purification from Carbon Monoxide 
 
 The elimination of carbon monoxide from admixtures 
 with hydrogen demands special treatment as the ready 
 oxidation of the hydrogen itself precludes the application 
 of such methods as the simple treatment with red-hot copper 
 oxide used for nitrogen. Generally speaking, the high 
 pressure methods described are only economical in connection 
 with the production of synthetic ammonia. 
 
 (10) By Soda-Lime. In B.P. 10164/89 Crookes and 
 Ricarde-Seaver deal with the removal of carbon monoxide 
 from water gas by soda-lime at a red heat. At this tem- 
 perature carbonate is formed but the reaction may be carried 
 out more advantageously at a lower temperature, e.g. 180 C., 
 with the production of formate, the absorption of carbon 
 monoxide being facilitated by the use of pressure. 
 
 (ib) By Caustic Soda Solution. B.P. 1759/12, by the 
 Badische Co., relates to the removal of the last traces of 
 carbon monoxide from hydrogen, containing, say i %, by 
 passing through a solution of caustic soda at a temperature 
 of 240-260 C. under a pressure of from 50 to 200 atmo- 
 spheres. The reaction is, of course, the same as that 
 occurring with soda-lime. The resulting sodium formate 
 is a valuable by-product, cf. applications of carbon 
 monoxide, p. 248. 
 
 (2) By Cuprous Chloride Solution. Huntingdon, in B.P. 
 15310/84, deals with the removal of carbon monoxide from 
 producer gas by the action of ammoniacal cuprous chloride 
 solution under pressure, the copper solution being freed from 
 gas by subjecting to a vacuum. Cf. also Williams, B.P. 
 19096/89. The use of alternate application of pressure and 
 the release of the same is also claimed by lyinde in D.R.P. 
 289106/14. A series of patents by the Badische Co. follows. 
 In B.P. 8030/14 are described special solutions of cuprous 
 chloride which do not attack iron, containing at least 6 % 
 of ammonia, either free or as carbonate, for use in steel 
 
HYDROGEN 209 
 
 vessels under high pressure. B.P. 9271/14 deals with 
 the employment for a similar purpose of ammoniacal cuprous 
 solutions containing little or no halogen. Weak acids, such 
 as acetic, may be present. According to a further patent, 
 B.P. 20616/14, the addition of oxygen is prescribed in the 
 use of ammoniacal cuprous solutions to prevent the separa- 
 tion of copper and also .to effect oxidation of part of the 
 carbon monoxide to carbon dioxide. 
 
 (3) By Conversion into Methane. It is a simple matter 
 to remove small quantities of carbon monoxide by conversion 
 into methane ; this is only useful in cases where the presence 
 of a little methane is not detrimental. The conversion 
 is effected by means of a nickel catalyst at a temperature 
 of 250-300 C. (cf. p. 240). 
 
 (4) By Calcium Carbide. Claim is made by Frank, in B.P. 
 26808/06, for the purification of hydrogen from carbon 
 monoxide, carbon dioxide, nitrogen and hydrocarbons by 
 passage over calcium carbide at a temperature over 300 C. 
 (Actually a much higher temperature than 300 C. is required.) 
 The carbide may be mixed with other substances to promote 
 the action. A later patent, B.P. 26928/06, prescribes a pre- 
 liminary purification from oxides of carbon and other 
 impurities before this treatment. 
 
 Purification from Carbon Dioxide 
 
 Carbon dioxide is an impurity the removal of which from 
 hydrogen is often necessary, and a brief summary of the 
 different methods proposed will be useful. 
 
 Small quantities of carbon dioxide may be removed by 
 ordinary lime purifiers, i.e. boxes containing trays of slaked 
 lime ; if larger amounts are present, other methods are 
 preferable, the most important being dependent on the 
 action of water under pressure. 
 
 In B.P. 1471/73 Baggs claims the removal of carbon 
 dioxide by washing with water or sodium carbonate solution 
 underpressure, and L,ane, in B.P. 11878/10, abstracts carbon 
 dioxide, sulphuretted hydrogen and sulphur dioxide from 
 hydrogen by water under a pressure of several atmospheres, 
 A. 14 
 
210 INDUSTRIAL GASES 
 
 the energy of the released water being utilized. A process 
 described by Claude, in B.P. 15053/14, depends on the use 
 of lime-water instead of water in the pressure absorption. 
 By adopting a counter-current system the final purification 
 is effected by alkali and the initial treatment by water. 
 
 In the use of water under pressure, it is usually necessary 
 to complete the action with caustic solution, preferably also 
 under pressure. Reference has already been made to 
 the removal of carbon dioxide by the Bedford process of 
 scrubbing with water under pressure in connection with the 
 B.A.M.A.G. continuous catalytic process and the lyinde- 
 Frank-Caro process for the manufacture of hydrogen. 
 
 Solution may also be effected by ammonia liquor (Claus, 
 B.P.s 15173/88 and 50/89), or by alkali carbonate or alkaline 
 earth carbonate solutions (Reissig and L,andin, B.P. 2021/91), 
 the carbon dioxide being subsequently expelled by heating, 
 reduced pressure being also employed in the case of carbon- 
 ate solutions, cf. pp. 264-8. 
 
 Purification from Sulphur Compounds 
 
 Sulphuretted hydrogen may be removed to a considerable 
 degree of completeness by treatment with bog iron ore in 
 purifiers such as are used in ordinary gas works practice. 
 Several patents have been brought forward with the object 
 of effecting a more rigorous purification, e.g. in U.S. P. 
 1034646/12, Rabenalt proposes to remove sulphuretted 
 hydrogen by passing through a solution of iodine which is 
 continuously regenerated by means of an electric current. 
 According to Pintsch,Strache and Killer, in D.R.P. 286374/14, 
 sulphuretted hydrogen is removed by passing rapidly through 
 an ordinary oxide purifier first and then through copper 
 sulphate solution. The residual copper sulphide is reoxidized 
 to sulphate by heating in air of oxygen at a temperature 
 sufficiently high to prevent separation of sulphur. 
 
 The removal of carbon disulphide and organic sulphur 
 compounds is much more difficult than that of sulphuretted 
 hydrogen. Carbon disulphide can be partially removed by 
 passage through foul lime (i.e. Ca(SH) 2 ) as in ordinary gas 
 
HYDROGEN 211 
 
 works practice, but the process is very unsatisfactory. In 
 B.P. 14509/13, the Badische Co. prescribes the action of 
 heated caustic soda solution under a pressure exceeding 
 5 atmospheres for the removal of sulphur compounds, includ- 
 ing organic sulphur compounds. Thus, a temperature of 
 150-225 C. may be used for a 10-25 % caustic soda solution 
 at 50 atmospheres (cf. also pp. 208, 250). 
 
 A very interesting process has been evolved by Carpenter 
 and Evans (B.P. 29673/10 ; Trans. Inst. Gas Eng., (1914), 183) 
 in connection with coal gas and is in use on a very large 
 scale by the South Metropolitan Gas Co., one installation 
 treating 15,000,000 ft. 3 /diem. The carbon disulphide is 
 converted into sulphuretted hydrogen by passing the gas 
 over reduced nickel at a temperature of about 430 C., the 
 sulphuretted hydrogen being subsequently absorbed in the 
 usual way. The carbon disulphide content is reduced from, 
 say 40 grains/ioo ft. 3 , or 0*029 % by volume, to about 1/5 
 of this value. Carbon is deposited on the catalyst and is 
 removed by the periodic passage of air about every month. 
 
 According to Guillet, in B.P. 18597/12 and " Soc. Tech. de 
 1' Industrie du Gaz de France," (1912), 245, carbon disulphide 
 may be removed catalytically by passing the gas, freed from 
 sulphuretted hydrogen, at a temperature of 80-200 C. 
 in the presence of water vapour over iron oxide which 
 absorbs the sulphuretted hydrogen formed. If air also be 
 added, the sulphuretted hydrogen and the carbon disulphide 
 may be removed in a single operation ; in this case the exit 
 gases are preferably washed with alkali. In B.P. 3752/10, 
 Bedford and Williams deal with the removal of sulphur 
 compounds, etc., by cooling the gas to 190 C. The removal 
 of sulphur dioxide is effected by the methods given above 
 for carbon dioxide and will take place at the same time if 
 both impurities are present. 
 
 Purification from Other Impurities 
 
 The removal of arseniuretted hydrogen has been proposed 
 by bubbling through petroleum cooled to 110 C. by Renard 
 (Comptes Rend., 136, (1903), 1317), and according to Wentzki 
 
212 INDUSTRIAL GASES 
 
 (Chemisette Industrie, 29, (1906), 405) the same object may 
 also be achieved by the use of bleaching powder or by passing 
 through a red-hot tube containing copper turnings. 
 
 Reference has been made already to the removal of small 
 quantities of oxygen in connection with the manufacture of 
 electrolytic hydrogen ; when the absence of this impurity 
 is desired, it is very readily secured by passage over heated 
 platinized pumice or other catalyst. 
 
 Comparison of Costs of Production and Purity 
 Attainable by the Different Methods 
 
 The following table will serve to give some idea of the 
 relative merits of the different processes from an economic 
 standpoint. The costs, which are on a pre-war basis, are to 
 be regarded as rough approximations only. Overhead 
 charges are not included. The low prices claimed for some 
 of the processes are to be taken with reserve, especially for 
 those which have not been developed, e.g. the Bergius 
 process. The cost of electrolytic hydrogen is conditioned by 
 the very variable price of electric energy and also by the 
 credit for the oxygen. Reference may be made to Table 25, 
 giving the cost of production by various " Field Processes." 
 
 As regards purity, values have also been inserted in the 
 table. Generally speaking, it may be stated that the electro- 
 lytic process, the Carbonium process and the Bergius process 
 are those which alone give hydrogen of a high degree of purity. 
 Hydrogen from the lyinde-Frank-Caro process is quite free 
 from sulphur compounds, while that made in the B.A.M.A.G. 
 continuous catalytic process is practically equally good in 
 this respect. In both processes, however, an appreciable 
 amount of carbon monoxide is present, as is also the case in 
 a greater or less degree in all the remaining processes. The 
 nitrogen content is of special importance only in connection 
 with aeronautics, in diminishing the lifting power of the hydro- 
 gen. All the usual impurities found in technical hydrogen have 
 roughly the same density and, consequently, the same effect 
 on the lifting power. The impurity of most importance is 
 carbon monoxide, especially when the hydrogen is to be used 
 
HYDROGEN 
 
 213 
 
 for the manufacture of ammonia by the Haber process and in 
 a lesser degree when used for the hydrogenation of oils (cf. 
 "Applications of Hydrogen," p. 214). 
 
 Taking everything into consideration, there can be little 
 doubt that the B.A.M.A.G. continuous catalytic process is 
 the most suitable for use in this country for such purposes as 
 the production of synthetic ammonia, when the cost of the 
 hydrogen is of paramount importance. On the other hand, 
 the purity is not very high and especially for ammonia 
 synthesis, further purification from carbon monoxide is 
 necessary. Electrolytic hydrogen is only likely to be a 
 serious competitor in places where cheap water power is 
 available. For aeronautical purposes the L/ane and allied 
 processes are probably the most satisfactory, as giving a high 
 percentage of hydrogen at a moderate cost ; the elimination 
 of nitrogen from the gas obtained from the B.A.M.A.G. 
 process is not practicable. 
 
 TABLE 23. 
 
 COST OF PRODUCTION AND PURITY OF HYDROGEN BY DIFFERENT 
 PROCESSES (STATIONARY PLANTS). 
 
 Process. 
 
 Cost per 
 
 IOOO ft. 3 
 
 Shillings. 
 
 Purity 
 (% hydrogen). 
 
 Percentage ot 
 carbon 
 monoxide. 
 
 B.A.M.A.G. continuous catalytic 
 
 
 
 
 process 
 
 I'75 
 
 ca. 92 % 
 
 i'5-3 -0 
 
 Griesheim-Elektron process 
 
 2-3 
 
 97'5 % 
 
 0'2 
 
 Linde-Frank-Caro process 
 
 3-4 
 
 97% 
 
 2 
 
 Lane process 
 
 3-4 
 
 98-5-99-5 % 
 
 0-25-r5 
 
 Messerschmitt process . . 
 
 2 
 
 ca. 99 % 
 
 0-25-r5 
 
 Bergius process 
 
 lJ-2 
 
 99-95 % 
 
 O'OO I 
 
 Carbonium process 
 
 4 
 
 very pure 
 
 
 
 Rincker and Wolter process 
 
 2*-4 
 
 96 % 
 
 3 
 
 Oechelhauser process 
 
 ca. 3 
 
 80% 
 
 7 
 
 Electrolytic processes, with cur 
 
 
 
 
 rent at o-25^./K.W.H., assum 
 
 
 
 
 ing no credit for oxygen 
 
 3-4 
 
 very pure 
 
 nil 
 
 Applications of Hydrogen 
 
 Apart from aeronautical requirements, the chief con- 
 sumption of hydrogen in this country is in connection with 
 the hydrogenation of oils and fats ; the synthetic ammonia, 
 
214 INDUSTRIAL GASES 
 
 industry also has assumed importance in Germany and is 
 being developed in the United States. 
 
 The Hydrogenation of Oils and Fats. In 1897, a 
 description was given by Sabatier and Senderens of a general 
 method for the hydrogenation of organic unsaturated sub- 
 stances (cf. resume by Sabatier and Senderens, Ann. de 
 Chim. et de Phys., [8], 4, (1905), 3*9 ; *&<*, PL 16, (1909), 
 70 ; also Sabatier, Ber. t 44, (1911), 1984 ; " La Catalyse en 
 Chimie Organique," 1913). 
 
 Speaking generally, the method consists in passing the 
 organic substance in the state of vapour accompanied by 
 hydrogen over gently heated, finely divided metals nickel, 
 cobalt, iron, platinum, palladium and copper being the most 
 useful and their respective activities somewhat as in the 
 order given. The activity of the catalyst depends on its 
 temperature of reduction, e.g. nickel reduced at a bright-red 
 heat is practically inactive, whereas when reduced at 250 C. 
 it is excessively active but rather sensitive and variable. 
 300 C. is a generally useful reduction temperature. The 
 catalysts are very sensitive to traces of " poisons," of which 
 the most important are sulphur, chlorine, arsenic, antimony, 
 and, in a lesser degree, carbon monoxide. For a discussion 
 of the inhibitive action of carbon monoxide, see pp. 19, 241. 
 Sabatier's work was carried out in the gaseous phase, and the 
 avoidance of any liquid in contact with the catalyst is 
 prescribed. As examples may be cited the reactions : 
 CO + 3 H 2 = CH 4 + H 2 and C 6 H 6 -f 3H 2 = C 6 H 12 
 
 The application of the method to liquids is due to the 
 work of Paal, Willstatter, Ipatiew, and Skita in the first 
 instance, while the technical application is largely due to 
 Norman (1903). The hardening of oils and fats consists 
 in the conversion of the glycerides of the unsaturated acids 
 into the glycerides of the corresponding saturated acids. 
 The effect is to raise the melting point and in most cases 
 to free from objectionable odour, taste and colour, the 
 market value being considerably enhanced. According to 
 Schuck (Chem. Trade J., 63, (1918), 139) deodorization 
 without hardening may be effected by the use of hydrogen 
 
HYDROGEN 215 
 
 without a catalyst. Whale oil is one of the principal oils 
 hardened ; a certain factory in Norway is capable of hardening 
 some 55,000 tons of whale oil per annum, using electrolytic 
 hydrogen. Some 35,000 ft. 3 /hr. of hydrogen from the lyinde- 
 Frank-Caro process alone, are used for fat hardening, equiva- 
 lent to about 100,000 tons of fat per annum, one ton of 
 triolein, for example, requiring about 2700 ft. 3 of hydrogen. 
 The hardened fats are extensively used as edible fats and in 
 the manufacture of soap, candles, etc. 
 
 The catalyst usually employed is nickel, although palla- 
 dium is sometimes used. According to some systems nickel 
 from the sulphate is precipitated as carbonate in the presence 
 of kieselguhr, the mixture filtered, the cake dried, finely 
 powdered, calcined to convert the nickel carbonate into 
 oxide, then reduced in hydrogen and allowed to fall 
 without contact with air into oil with which it is intimately 
 mixed. This mixture is added in the desired proportions to 
 the oil to be hardened ensuring, e.g. 0*5-1 part of nickel 
 to 100 parts of the oil, which is carefully dried before using. 
 Temperatures in the neighbourhood of 150-250 C., with 
 pressures of 5-15 atmospheres, are employed. Instead of 
 metallic nickel the suboxide may be used. For a discussion 
 of the constitution of nickel catalysts, see Erdmann, /. Prakt. 
 Chem., 91, (1915), 469. After the hydrogenation the catalyst 
 is removed by filtration and used again. The products always 
 contain minute traces of nickel. The above remarks relating 
 to catalyst poisons apply equally to treatment of liquids. 
 According to Ellis (U.S.P. 1247516) the poisons present in 
 the oil may be removed by preliminary treatment with 
 copper hydroxide. For an account of modern developments 
 in the manufacture of edible fats, cf. Clayton, /. Soc. Chem. 
 Ind., (1917), 1205. 
 
 The Manufacture of Synthetic Ammonia. The 
 synthetic ammonia industry in Germany has been developed 
 from the work of Haber and collaborators and ranks as one 
 of the finest achievements arising out of the application of 
 physico-chemical methods to industry : 
 
 N 2 -f 3H 2 = 2NH 3 -f- 11,000 calories. 
 
2l6 
 
 INDUSTRIAL GASES 
 
 Many experimenters had previously attempted to effect 
 the synthesis of ammonia, but without much success ; an 
 approximate calculation of the equilibrium constant 
 
 3 H 2 X P* 2 
 
 by the Nernst Heat Theorem is sufficient to show that only 
 a very small percentage of ammonia can exist at temperatures 
 for which suitable catalysts were at that time known, e.g. 
 800 C. 
 
 Since 
 
 where P is the total pressure, it is evident that the concen- 
 tration of the ammonia is almost directly proportional 
 to the pressure. Such considerations led Jost and, at 
 about the same time, Haber and I^e Rossignol to study 
 the effect of high pressures, and the latter investigators 
 worked out a series of catalysts which enabled equilibrium 
 to be attained fairly rapidly at temperatures as low as 
 300 C. 
 
 The following table shows the influence of temperature 
 on the equilibrium values : 
 
 TABLE 24. 
 EQUILIBRIA IN THE SYNTHESIS OF AMMONIA. 
 
 Percentage of ammonia at absolute pressures of 
 
 lemperaiure v^. 
 
 i atm. 
 
 100 alms. 
 
 200 atms. 
 
 200 
 
 I5'3 
 
 80-6 
 
 85-8 
 
 3 00 
 
 2-18 
 
 52' i 
 
 62-8 
 
 4 00 
 
 0-44 
 
 25-1 
 
 36-3 
 
 5 00 
 
 O-I29 
 
 10-4 
 
 17-6 
 
 600 
 
 0-049 
 
 4-47 
 
 8-25 
 
 700 
 
 O-O223 
 
 2-14 
 
 4-11 
 
 800 
 
 O'OIiy 
 
 i'i5 
 
 2-24 
 
 QOO 
 
 0-0069 
 
 0-68 
 
 i'34 
 
 IOOO 
 
 0-0044 
 
 o- 44 
 
 0-87 
 
HYDROGEN 
 
 217 
 
 The advantage of the higher equilibrium values can be 
 only partly turned to account by reason of the accompanying 
 decrease of the reaction velocity. At very high temperatures, 
 a reversal of the equilibrium sets in (cf. Maxted, Chem. 
 Soc. Trans., (1918), 168, 386; ibid., (1919), 113), thus by 
 passing a mixture of nitrogen and hydrogen through a capil- 
 lary tube in which a high tension arc was burning under a 
 pressure of i atmosphere, an ammonia content in the exit 
 gases as high as 2*0 % was observed. 
 
 As in other heterogeneous gas reactions, a rise in the velocity 
 of passage of the gases over the catalyst has the effect of 
 lowering the percentage of ammonia, but of increasing the 
 production ; this is a matter of considerable importance 
 as when using high pressures the available space for the 
 catalyst is necessarily limited. 
 
 As an example of this behaviour may be cited the 
 following results obtained at a working pressure of 114 
 atmospheres and with a catalyst temperature of 515 C., the 
 catalyst employed being uranium carbide (Haber and Green- 
 wood, Z. Elektrochem., 21, (1915), 241) : 
 
 Space velocity (litres of free 
 
 
 
 
 
 gas / litre catalyst space / 
 
 
 
 
 
 hour) 
 
 5800 
 
 31,650 
 
 82,600 
 
 194,000 
 
 Percentage of ammonia by 
 
 
 
 
 
 volume 
 
 7 6 3 
 
 6'42 
 
 4-78 
 
 4-18 
 
 Space-time-yield (kilos, am- 
 
 
 
 
 
 monia/litre catalyst space/ 
 
 
 
 
 
 hour) . . . . 
 
 0-318 
 
 1*46 
 
 2-84 
 
 5-83 
 
 It should be pointed out, however, that the above con- 
 siderations are not the only deciding factors, as the space- 
 velocity is limited by such considerations as regeneration 
 of heat, ammonia absorption, etc. 
 
 Amongst the most efficient catalysts may be mentioned 
 metallic osmium and uranium carbide, the range of useful 
 working temperature being 500-700 C. The process was 
 subsequently taken over and developed by the Badische 
 Anilin und Soda Fabrik. 
 
 Since the percentage of the gases undergoing conversion 
 
2i8 INDUSTRIAL GASES 
 
 is only relatively small even at the pressures employed, f.g. 
 100 to 200 atmospheres, it is necessary to circulate the 
 gases through the catalyst removing the ammonia without 
 releasing the pressure, and passing again over the catalyst 
 reinforced with a fresh supply of nitrogen-hydrogen mixture 
 to replace the portion converted. The ammonia formed is 
 removed from the system either by cooling or by absorption 
 with water. 
 
 As regards catalysts, osmium is too expensive and too 
 limited in amount for use on the large scale, while uranium 
 is very sensitive to traces of oxygen or moisture (cf. Haber 
 and Greenwood, loc. cit.). So far as can be gathered from 
 the patent literature, the catalysts used in practice have a 
 basis of pure iron with the addition of a promoter. Among 
 such promoters may be mentioned potassium oxide, lime, 
 magnesia, alumina, zirconia, molybdenum, vanadium and 
 cobalt as patented by the Badische Co. Other patented 
 catalyst groups are various alkali and alkaline earth ferro- 
 cyanides (F. Bayer & Co.) ; ruthenium and various ruthenates 
 with special supports such as chromic oxide (Centralstelle fur 
 wissenschaftlich-technische Untersuchungen) , and sodamide 
 with different promoters as manganese, cobalt, cerium, etc., 
 by De Jahn. 
 
 It is important to avoid certain catalyst poisons such as 
 sulphur, phosphorus, arsenic, lead, tin, oil, impurities carried 
 mechanically by the gases from steel piping, carbon monoxide, 
 etc. Of these poisons the last mentioned is not the least 
 troublesome. The presence of small quantities of sulphur 
 in the iron used in making up catalysts is sufficient to inhibit 
 or diminish the activity while it is necessary to free the 
 hydrogen, usually prepared from water gas, from sulphur, 
 carbon monoxide, etc. The removal of oxygen and water 
 vapour from the gases is also desirable in most cases. 
 
 If the walls of the vessels containing the catalyst are 
 allowed to become heated, trouble is experienced through the 
 action of the hydrogen on the steel at the high temperatures 
 in question, namely, 500-700 C. Under these conditions 
 the carbon of the steel is converted into methane and the 
 
HYDROGEN 
 
 tensile strength of the steel lowered considerably. The 
 difficulty may be minimized by the use of special steels low 
 in carbon and containing nickel, chromium, tungsten, etc., as 
 hardening agents; or avoided by internal electric heating, the 
 pressure-resisting walls being maintained cold. Other special 
 methods of preserving the steel from attack have been 
 proposed (cf. B.P.s 20127/10, 1490/12, 8617/12, 28200/12, 
 29260/12, 9661/14, and 100216/16). 
 
 It is specially important to employ efficient heat-inter- 
 changers in the case of electric heating, the problem being 
 comparatively simple when dealing with compressed gases ; 
 similarly as regards the separation of ammonia by cooling. 
 
 In order to guard against explosions through accidental 
 admixture of oxygen with the gases (since small quantities, 
 i.e. more than 5 % (cf. p. 203) suffice to produce explosive 
 mixtures) automatic oxygen detectors are preferably 
 employed (cf. p. 34), while the catalyst containers may be 
 disposed in bomb-proof chambers. 
 
 The first Badische plant was erected at Oppau in 1912 and 
 produced some 9000 tons of ammonia per annum, a lyinde- 
 Frank-Caro plant of capacity about 70,000 ft. 3 /hr. being 
 installed for providing the necessary hydrogen ; subsequently, 
 and particularly during the war, the plant has been greatly 
 extended and at the present time the production is probably 
 of the order of 100,000 tons of ammonia per annum. Recently 
 another large works has been erected at I v euna, near 
 Merseburg. There can be no doubt that this process 
 played a large part in providing the German Army with 
 explosives during the war. 
 
 The hydrogen, the cost of which, in the requisite high 
 state of purity, represents a large fraction of the whole, 
 is prepared by the B.A.M.A.G. continuous catalytic process 
 (cf. p. 161). Except in special cases where cheap power is 
 available, the use of electrolytic hydrogen, so eminently 
 suitable by reason of its purity, is out of the question in view 
 of its high cost. The national importance of the fixation 
 of atmospheric nitrogen, involving independence of overseas 
 supplies of Chile nitrate, is obvious, ammonia produced by 
 
220 INDUSTRIAL GASES 
 
 direct synthesis being specially suitable, on account of its 
 purity, for oxidation to nitric acid. The Haber process has 
 particular advantages for this country as the power consump- 
 tion is very small compared with the requirements of other 
 processes for nitrogen fixation, the direct arc process, the 
 cyanamide process, etc. (cf. p. 117). During the war the 
 importance of the Haber process was forced into general 
 notice among the Allied Nations. In this country extensive 
 investigations have been carried out on the synthesis of 
 ammonia (J. Soc. Chem. Ind., (1917), 1196). Similarly in 
 the United States a technical process has been developed 
 by the General Chemical Co. (cf. Parsons, J. Ind. Eng. 
 Chem., (1917), 829 ; also B.P. 120546/18). 
 
 It is unnecessary to dwell on the uses of ammonia, 
 usually as ammonium sulphate, for fertilizing purposes. 
 One objection to this excellent fertilizer, as compared with 
 other sources of combined nitrogen, is its demand for sulphuric 
 acid, which is useless except for the purpose of fixing the 
 ammonia. In order to avoid this point, many patents have 
 been taken out with reference to the use of gj^psum, which is 
 caused to interact with ammonium carbonate (see below), 
 e.g. B.P. 27962/13, of the Badische Co., which relates to the 
 troublesome operation of filtering the resulting calcium 
 sulphate and of washing the same free from ammonium 
 sulphate by means of immersion filters (cf . Bosch, Z. Elektro- 
 chem., 24, (1918), 361). Other recent patents of the Badische 
 Co. are interesting ; they relate to the use of ammonium 
 carbonate as a fertilizer. The use of this compound, 
 containing 36 % combined nitrogen as compared with about 
 20 % in ammonium sulphate, is specially important in 
 connection with the manufacture of hydrogen by the 
 continuous catalytic process, which produces large quantities 
 of carbon dioxide as a by-product. For an interesting 
 discussion by Matignon of the validity of the Badische patents 
 in relation to certain patents by Tellier, the Societe Christi- 
 ania Minekompani, etc., see " Comptes Rendus de la Seance 
 d'Inauguration des travaux de la Societe de Chimie Industri- 
 elle," p. 46 ; Chem. Trade J., 62, (1918), 413. 
 
HYDROGEN 221 
 
 Other Applications of Hydrogen. In addition to the 
 above detailed uses hydrogen has been used extensively 
 for the autogenous fusion of metals, the flame being fed with 
 air or oxygen ; thus, the " lead burning " of the seams of 
 chemical lead work is often conveniently carried out with 
 the oxy -hydrogen blowpipe, similarly with the welding and 
 cutting of iron. The use of the more conveniently gener- 
 ated acetylene is, however, becoming more universal and has 
 practically displaced that of hydrogen for such purposes (cf . 
 " Applications of Oxygen "). There are still points in favour 
 of hydrogen when the oxygen is generated electrolytically and 
 the hydrogen is a waste product. The oxy-hydrogen blow- 
 pipe is used for the fusion of platinum in lime crucibles, also 
 for the working of fused silica. The application of hydrogen to 
 the manufacture of artificial gems was initiated by Verneuil 
 and Paquiet about 1900 and later developed by Wild, 
 Miethe and L,ehmann. Thus, alumina alone gives artificial 
 corundum, while with about 2j % chromic oxide rubies are 
 obtained, similarly sapphires and emeralds may be produced, 
 more than i ton of gems per annum being thus manufactured. 
 Synthetic rubies are valuable for small bearings. 
 
 Another application of hydrogen is in the electric lamp 
 industry ; it is extensively used in the reduction of the 
 tungsten and in working up into drawn wire filaments, also 
 for the filling of the bulbs before evacuation, usually in admix- 
 ture with about an equal volume of nitrogen. The use 
 of hydrogen for aeronautical purposes is dealt with in the 
 next section. 
 
 Hydrogen at a pressure of 120 atmospheres and costing 
 about \d. per ft. 3 is sold in cylinders painted red, with left- 
 handed connections. 
 
 The estimation and testing of hydrogen are discussed 
 at the end of Section VII. 
 
 REFERENCES TO SECTION VI. 
 
 General. Ellis, " The Hydrogenation of Oils, Catalysers and Catalysis, 
 and the Generation of Hydrogen." London, 1915. 
 
 Brahmer, " Chemie der Gase." Frankfurt a. M., 1911. 
 
 Lepsius, " Sur la Fabrication et les Applications de l'Hydrogne," 
 Monit. Scient., (1912), 493. 
 
222 INDUSTRIAL GASES 
 
 Sander, " Neuere Verfahren zur Wasserstoffgewinnung," Z. angew. 
 
 Chem., (1912), ii., 2401. 
 Blum, " New Methods of Obtaining Hydrogen," Metall. and Chem. 
 
 Eng., (1911), 157- 
 Crossley, " The Preparation and Commercial Uses of Hydrogen," 
 
 /. Soc. Chem. Ind., (1914), 1135. 
 Linde-Frank-Caro Process. Linde, " Die Wasserstoffgewinnung," Z. 
 
 angew. Chem., (1913), iii., 814. 
 Linde, " Separation 'of the Constituents of Mixtures of Gases by 
 
 Liquefaction," /. Soc. Chem. Ind., (1914), 714. 
 Lane and Allied Processes. Barnitz, "Production of Hydrogen by the 
 
 Iron Contact Method," Chem. Trade J ., 60, (1917), 547. 
 Anon., "The Generation of Hydrogen." The Engineer, (1917), 546. 
 Electrolytic Hydrogen. Engelhardt, "The Electrolysis of Water" 
 
 (Richards). Easton, Pa., 1904. 
 Applications. Frankland, " The Chemical Industry of Germany," /. Soc. 
 
 Chem. Ind., (1915), 309. 
 Hydrogenation of Oils and Fats. Henderson, " Catalysis in Industrial 
 
 Chemistry." London, 1919. 
 
 Maxted, " Catalytic Hydrogenation and Reduction." London, 1918. 
 Ammonia Synthesis. Haber and Le Rossignol, " Bestimmung des Am- 
 
 moniakgleichgewichtes unter Druck," Z. Elektrochem., 14, (1908), 
 
 181 ; " Uber die technische Darstellung von Ammoniak aus den 
 
 Elementen," ib., 19, (1913), 53. 
 Haber in collaboration with Tamaru, Ponnaz, Maschke, Oehlom and 
 
 Greenwood, Z. Elektrochem., 20, (1914), 597; 21, (1915), 87, 128, 
 
 191, 206, 228, 241. 
 Haber, " Die Vereinigung des elementaren Stickstoffs mit Sauerstoff 
 
 und mit Wasserstoff," Z. angew. Chem., (1913), iii., 323. 
 Bernthsen, " Synthetic Ammonia," 8th Int. Congress of A pp. Chem., 
 
 N.Y., 1912. 
 Lunge, " Coal Tar and Ammonia," Fifth Edition, Part III. London, 
 
 1916. 
 Norton, " Utilization of Atmospheric Nitrogen," Dept. of Commerce 
 
 and Labour, U.S.A., Special Agents Series, No. 52. 
 Partington, " The Alkali Industry." This Series. 1918. 
 
SECTION VII. THE PRODUCTION OF HYDRO- 
 GEN FOR MILITARY PURPOSES 
 
 Field Processes. Of late years, and particularly during 
 the war, the production of hydrogen by portable or semi- 
 portable plants for military purposes has assumed great 
 importance. In the early days of ballooning the only avail- 
 able method of preparing the hydrogen was by the action 
 of sulphuric acid on iron or zinc which process had the great 
 disadvantage of requiring a large weight of material, and 
 although of comparatively little importance with the small 
 balloons at first employed, this disadvantage has now 
 rendered the method quite obsolete. 
 
 The first use of methods involving less weight of material 
 was in the Russo-Japanese war in 1904. In the Soudan war 
 of 1885 and also in the Boer war of 1898-1902 hydrogen 
 was transported from England in cylinders. Some 50 
 horses were necessary for the transport of the cylinders 
 required for a balloon of 14,000 ft. 3 capacity. It is interesting 
 to note that the weight of the steel cylinders is of the order 
 of I Ib. per ft. 3 of hydrogen content. Attention was conse- 
 quently paid to methods allowing of the convenient and 
 rapid generation of the hydrogen in the field. 
 
 The progress of the large dirigible has been dependent 
 on the advance of the chemistry of hydrogen production and 
 has, in turn, served as a stimulus to the evolution of new 
 processes. Since the advent of the Zeppelin in 1898, the 
 capacity of balloons* and the demand for hydrogen in 
 quantity have risen steadily, so that at the present time 
 the various types of military hydrogen plants may be classified 
 under three headings : 
 
 (i) Apparatus of a simple and easily portable nature, 
 
 * British rigid dirigibles having a capacity of 2 to 3 million it. 3 have 
 been constructed ; German Zeppelins of 2 million ft.* capacity were used. 
 
224 INDUSTRIAL GASES 
 
 involving a small weight of material and capable of giving 
 rapid generation in the field, the cost of production being 
 of secondary importance in this case. 
 
 (2) Apparatus for use in permanent camps, forts, aviation 
 depots, etc. Here, again, speed of erection and rapid output 
 may be of more importance than economy. 
 
 (3) Plant suitable for economical manufacture on a large 
 scale with a view to subsequent distribution by means of 
 cylinders. 
 
 Portable Apparatus for Use in the Field 
 
 Progress in this direction is very intimately connected 
 with the name of the French chemist, Jaubert. Some of the 
 most important methods are the following : 
 
 Silicon and "Silicol ' ' Processes. These two processes, 
 which have been extensively adopted for military purposes 
 by the European armies, are very similar, both depending 
 on the action of silicon on alkalis. The former, however, 
 uses commercially pure silicon, while ferro-silicon (rich in 
 silicon) , which has the advantages of being cheaper and more 
 easily produced, is employed in the latter. 
 
 Owing to hydrolytic dissociation of the sodium silicate, 
 less caustic soda is required than that corresponding to the 
 equation : 
 
 Si + 2NaOH + H 2 O = Na 2 SiO 3 + 2H 2 
 
 The International Chemical Co., in B.P. 14124/1900, 
 claims the manufacture of hydrogen by treating silicides of 
 the alkaline earths with water. A substance Si 2 H 2 silico- 
 acetylene produced by treating calcium or strontium 
 silicide with acids, gives hydrogen with alkalis. In B.P. 
 21032/09, the Consortium fur Elektrochemische Industrie, 
 G.m.b.H. describes the production of hydrogen by the 
 action on silicon of caustic soda solution with the addition 
 of milk of lime, less caustic soda being thus required. A later 
 patent, B.P. 11640/11, relates to the attainment without an 
 independent boiler, of the temperature necessary for the 
 reaction (i) by a preh'rninary reaction as, for example, 
 
HYDROGEN FOR MILITARY PURPOSES 225 
 
 the solution of aluminium in the caustic soda, and (2) by 
 adding the alkali to the water in the form of powdered sodium 
 hydroxide or oxide. A further series of patents is due to 
 J aubert, who employs f erro-silicon instead of silicon. Accord- 
 ing to B.P. 17589/11 (cf. also F.P. 430302/10), ferro-silicon, or 
 mangano-silicon, is treated with a concentrated solution of 
 potassium sulphate or sodium sulphate containing alkali. 
 The salts serve to raise the boiling point and so increase 
 the reaction velocity. The same object is attained in F.P. 
 433400/10 by the use of increased pressure. In B.P. 
 7494/13 is prescribed the use of a layer of unsaponifiable 
 oil facilitating the admixture of the ferro-silicon with the 
 caustic soda solution and ensuring very rapid generation 
 of gas ; water is added to replace that lost. Baillio, in U.S. P. 
 1178205/16, combines the production of hydrogen with that 
 of sodium silicate from silicon and caustic soda, the former 
 being used in excess. 
 
 TheSchuckert Process. The Schuckert process depends on 
 the use of silicon itself and has been developed mainly in 
 Germany, as a portable field apparatus. A temperature of 
 80-90 C. is required for the rapid progress of the reaction 
 and the heat of solution of the caustic soda is utilized by 
 building the dissolver into the generator. A feed hopper 
 is provided for the gradual introduction of the finely divided 
 silicon, and the hydrogen passes off through a washer fed 
 with water by a pump driven by a petrol engine. Plants of 
 this type have been constructed with a capacity of 2000- 
 4000 ft. 3 /hr. 
 
 The apparatus was first used by the Spanish in the 
 Moroccan campaign, and was also used by the Italians in 
 Tripoli. Stationary plants, with a capacity of 10,000 ft. 3 /hr., 
 have been set up. The caustic soda solution employed is 
 of 20-25 % concentration ; each 1000 ft. 3 of hydrogen 
 requires 50 Ibs. of silicon, 75 Ibs. of caustic soda, and about 
 190 gallons of water, inclusive of cooling water. 
 
 The Silicol Process. This process, due to the French 
 chemist J aubert, has been largely used by the French military 
 authorities. Instead of silicon, the cheaper ferro-silicon, 
 A. 15 
 
226 INDUSTRIAL GASES 
 
 containing 90 % or more silicon, is employed. Using a 
 35~4 % caustic soda solution, the action takes place ener- 
 getically at 60-80 C. ; the concentrated solution has the 
 effect of conserving the heat of reaction by minimizing 
 vaporization of water, while the initial temperature required 
 for the reaction is easily attained in dissolving up the caustic 
 soda, no external heating being necessary. 
 
 Portable plants, with an hourly output of 14,000 ft. 3 , 
 have been built ; the usual pattern, however, has a capacity 
 of about 2500 ft. 3 /hr. and is mounted on a 3-ton lorry. 
 The general arrangement of the apparatus is almost the same 
 as in the Schuckert plant. 
 
 I^arge stationary plants on these lines have been erected 
 for the British Navy at Chatham and elsewhere during the 
 war, by the Societe Fran9aise 1'Oxy lithe. The plant at 
 Chatham has a capacity of some 50,000 ft. 3 /hr. The caustic 
 soda, broken into small pieces, is stirred with i| times to 
 twice its weight of water in a dissolver, whereby a temper- 
 ature of 60-80 C. is reached ; the solution is then run into 
 the generator. By means of a mechanically-operated distri- 
 butor, the finely powdered ferro-silicon is fed into the gener- 
 ator which is provided with a planetary stirrer. A slow 
 stream of paraffin or naphtha is also admitted to prevent 
 the formation of foam which would hinder the progress of the 
 reaction. The hydrogen is cooled and purified by passage 
 through a scrubber fed with water and containing metal 
 spirals, and then freed from suspended water by traversing, 
 at high speed, a series of tubes with abrupt changes of 
 direction. Two generators are provided, one serving as a 
 standby. 
 
 It is obvious that the hydrogen produced in this type 
 of stationary plant is very expensive compared with that 
 from other processes. The very high speed of gas generation 
 in case of necessity is, however, an important consideration 
 for war purposes. 
 
 These two processes have some disadvantages. On account 
 of the vigorous heat evolution a considerable amount of 
 fairly clean water is required, while the hydrogen is liable 
 
HYDROGEN FOR MILITARY PURPOSES 227 
 
 to contain small amounts of phosphine (according to Soyer, 
 Ann. Chim.Analyt., 23, (1918), 221, some 0*0025 to 0-007 % 
 by volume may be present), arsine, sulphuretted hydrogen, 
 etc., derived from impurities in the ferro-silicon and having 
 an injurious effect on the balloon fabrics. For data on the 
 production of ferro-silicon, cf. Anderson, '/. Soc. Chem. Ind. t 
 
 (1917), 881. 
 
 Hydrogenite Process. This process, also due to M. 
 Jaubert (cf. Rev. Gen. Chim., 13, 341, 357), resembles the 
 silicol process in depending on the action of alkalis on ferro- 
 silicon, but differs in that the reaction is carried out in the 
 absence of water and at a high temperature. 
 
 The basis of all the patents given below is the preparation 
 of mixtures which react by auto-combustion in absence of 
 air when the action is started by local heating, hydrogen 
 being evolved. Similar mixtures are used for oxygen produc- 
 tion (q.v.). Jaubert, in B.P. 17252/07, describes apparatus 
 for the generation of hydrogen under pressure by the auto- 
 combustion method. The actual generator is surrounded by 
 and is in direct connection with the gas reservoir, the pressure 
 being thus balanced inside and outside. The same inventor, 
 in B.P. 153/11, deals with the production of hydrogen by the 
 interaction of ferro-silicon, lime and caustic soda in a closed 
 vessel, the reaction being first started by local heating, 
 According to a later patent, B.P. 9623/11, excess ferro- 
 silicon is mixed with an oxidizing agent and a hydrate. As 
 examples of suitable combinations are given (i) powdered 
 iron 20 parts, soda-lime 10 parts, potassium perchlorate 6 
 parts ; (2) ferro-silicon (75 % silicon) 20 parts, litharge 10 
 parts, soda-lime (two-thirds caustic soda) 60 parts ; (3) ferro- 
 silicon 20 parts, powdered iron 5 parts, wheaten flour 3 
 parts, lime 5 parts, potassium chlorate 3 parts. The reaction 
 may also be effected by steam produced in an annular boiler 
 round the generator. According to B.P. 5005/12, the oxi- 
 dation of the ferro-silicon is effected solely by the steam 
 generated as above, no other oxidizing agent being 
 employed. 
 
 " Hydrogenite " consists of an intimate mixture of 25 
 
228 INDUSTRIAL GASES 
 
 parts of ferro-silicon (90-95 % silicon), 60 parts of caustic 
 soda and 20 parts of soda-lime. The gray compressible 
 powder thus obtained is pressed into blocks which are packed 
 in air-tight cases holding from J to i cwt. ; under these 
 conditions the mixture is quite permanent. When required 
 for use the lid is removed, the box placed in the generator, 
 and the heavy lid of the latter, kept in position by its weight 
 alone and serving as a safety valve, is put on. The mass 
 is then ignited through a small hole in the lid by means of 
 a match applied to a small quantity of priming powder, 
 when the reaction propagates itself throughout the mass, 
 without production of flame, hydrogen being produced very 
 rapidly. The generator is surrounded by a water jacket in 
 which steam is generated. Towards the end of the reaction 
 this steam is admitted to the generator, serving to increase 
 the yield and to quench the mass. The hydrogen is washed 
 with water and dried with coke and sawdust. 
 
 Portable plants have been used by the French Army, 
 consisting of waggons with 6 generators grouped round a 
 central washer ; the capacity is about 5000 ft. 3 hydrogen 
 per hour. The method has the important advantage over 
 other processes of requiring no water, and further, of using 
 the same material as the important silicol process. Each 
 1000 ft. 3 of hydrogen necessitates a weight of about 190 Ibs. 
 of hydrogenite. The gas obtained is very pure. 
 
 Hydrolith Process. Jaubert, in F.P. 327878/02, deals 
 with the preparation of calcium hydride from calcium 
 and waste hydrogen, e.g. from electrolytic alkali manufacture. 
 The hydrogen, freed from water and oxygen, is passed over 
 calcium heated to about 600 C. A later patent, B.P. 
 25215/07, describes an apparatus for producing hydrogen 
 from calcium hydride, consisting of a series of generators so 
 arranged that the moisture from one generator is removed by 
 passing the gas through another generator filled with cal- 
 cium hydride but not supplied with water. A modified 
 process is described in D.R.P. 218257/08, by Bamberger, 
 Bock and Wanz, who use, instead of water, substances 
 containing combined water or carbon dioxide, e.g. gypsum, 
 
HYDROGEN FOR MILITARY PURPOSES 229 
 
 sodium bicarbonate, etc., which only react when heated to a 
 temperature above 80 C. 
 
 Hydrolith reacts with water as follows : 
 
 CaH 2 + 2H 2 O = Ca(OH) 2 + 2H 2 
 
 The calcium hydride is prepared by treating molten calcium 
 with hydrogen and serves as a medium for transporting 
 waste hydrogen to the balloons ; although expensive, 
 its use avoids the great weight of cylinders. A white 
 crystalline powder, consisting of 90 % calcium hydride with 
 some nitride and oxide, is obtained, and on treatment with 
 cold water, 1000 ft. 3 of hydrogen are produced from the 
 exceptionally small weight of 62 Ibs. A waggon, carrying 
 6 generators, yields some 15,000 ft. 3 /hr., while plants with a 
 capacity of 50,000 ft. 3 /hr. have been constructed. Such a 
 plant with a supply of 20 tons of calcium hydride, i.e. capable 
 of producing 700,000 ft. 3 hydrogen, was used in recent 
 French manoeuvres and behaved very well. The generators, 
 carrying the calcium hydride on perforated plates, are 
 supplied with water at the bottom while the hydrogen 
 passes off at the top and is freed from water by passing 
 through another generator containing an untreated charge 
 which is subsequently used. A large heat evolution takes 
 place, which at first caused inconvenience. The hydrogen 
 leaving the generators is purified from a small quantity of 
 ammonia before use. 
 
 By the Action of Acids and Alkalis on Metals. 
 This branch of the subject may be divided into several 
 sections : 
 
 (i) Action of Sulphuric Acid on Iron or Zinc. In this 
 connection there are a large number of patents, among which 
 may be mentioned the following : Pratis and Marengo, in 
 B.P.s 16277/96 and 15509/97, describe apparatus for the 
 generation of hydrogen from sulphuric acid and iron (cf . also 
 Hawkins, B.P. 25,084/97 ; Fielding, B.P. 17516/98, and 
 Praceiq and Bourchaud, B.P. 6075/05). 
 
 The use of such methods for generating hydrogen is very 
 old, and although convenient for relatively small quantities 
 
230 INDUSTRIAL GASES 
 
 on a large laboratory scale, for lead burning and allied pur- 
 poses,* is too expensive and involves too great weight of 
 material for military purposes (cf. p. 234) ; consequently for 
 field work these methods have been abandoned (cf. also 
 p. 223). 
 
 A considerable amount of work was carried out by Renard 
 (1875-1880) in the development of this process for military 
 purposes in France. Acid of some 12 % strength was run 
 on to iron or zinc in a leaden vessel ; the hydrogen was 
 washed with water, freed from sulphuretted hydrogen with 
 Ivaming's mixture (quicklime, ferrous sulphate and sawdust) 
 and then passed over caustic soda, the plant yielding some 
 1000 ft. 3 hydrogen per hour. Hydrogen generated from iron 
 or zinc is liable to have a low lifting power on account of 
 impurities and to contain sulphuretted hydrogen and, when 
 using zinc, arsine ; these impurities have an injurious action 
 on the balloon fabrics, while the arsine is further objectionable 
 by reason of its poisonous properties. Attempts have been 
 made to remove arsenic from the hydrogen by passing through 
 a heated tube containing copper turnings ; by the action 
 of potassium permanganate ; cooling with liquid air, etc. 
 (cf. p. 21 1). Arsenic- free acid should, of course, be used in 
 the preparation. 
 
 (2) Action of Caustic Soda on Aluminium. This method 
 has long been known, but only recently used for military 
 purposes. It was employed by the Russians in the Russo- 
 Japanese war in 1904, two types of portable apparatus 
 being employed : (i) Two generators with a common washer 
 mounted on two cars, the set having a capacity of 5000 
 ft. 3 /hr. (2) Two generators of light pattern carried by 
 a pack-horse for use in mountainous country. The sheet- 
 iron generators were filled with 30 % caustic soda solution 
 in the lower part and a basket containing aluminium sheet 
 clippings was lowered by means of a handle. The hydrogen 
 was washed in a water scrubber. A very vigorous reaction 
 takes place and an ample supply of cooling water is necessary. 
 
 * For useful data on the preparation and compression of hydrogen on 
 a large laboratory scale, cf. Hutton and Petavel, loc. cit., p. 113. 
 
HYDROGEN FOR MILITARY PURPOSES 231 
 
 Reference to Table 25 will show that the weight of material 
 is still rather high although less than that required when 
 using iron or zinc with sulphuric acid. 
 
 (3) Action of Activated Aluminium on Water. Considerable 
 attention has been paid to the activation of aluminium 
 with mercury to ensure rapid evolution of hydrogen on 
 treatment with water alone. A great advantage is the small 
 weight of material requiring transport. Thus, Mauricheau- 
 Beaupre, in F.P. 392725/08, generates hydrogen by the slow 
 addition of water to a mixture of fine aluminium filings with 
 1-2 % of mercuric chloride and 0-5-1 % of potassium 
 cyanide, the temperature being kept below 70 C. One gallon 
 of water suffices for 10 Ibs. of the material, which has a specific 
 gravity of 1*4 and is permanent in absence of air and moisture. 
 Similarly the Chemische Fabrik Griesheim-Blektron, in B.P. 
 3188/09, uses a mixture of finely divided aluminium with 
 i % mercuric oxide and i % caustic soda. This mixture 
 has the advantage of being less poisonous than the above. 
 A patent by Sarason, B.P. 18772/11, prescribes the addition 
 of a salt having an alkaline reaction, e.g. a borate, phosphate, 
 etc., to start the action of the water on the aluminium 
 amalgam. Uyeno (B.P. 11838/12) treats an alloy of aluminium 
 and zinc which may also contain tin, with zinc or tin amalgam 
 and subsequently heats to cause penetration of the mercury. 
 The product yields 'hydrogen on treatment with hot water 
 (cf. also D.R.P. 294910/16 by Blkan Krben, G.m.b.H.). 
 
 Other Processes. A series of patents deals with the 
 employment of metallic sodium, avoiding the usual violent re- 
 action. Thus, Foersterling and Philipp, in U.S.P. 883531/08, 
 propose to treat sodium in small pieces with a spray of water 
 at such a rate that no solution is formed, while, according to 
 U.S.P. 977442/10, sodium is kneaded with aluminium 
 silicide and briquetted. The resulting product gives hydrogen 
 on treatment with water ; cf . also Philipp, U.S.P. 1041865/12. 
 In like manner Brindley, in U.S.P. 909536/09, briquettes an 
 intimate mixture of sodium with crude oil, kieselguhr and 
 also aluminium or silicon, the mass being subsequently 
 treated with water. For a proposal to use lead-magnesium 
 
232 INDUSTRIAL GASES 
 
 and similar alloys, cf. Ashcroft, Trans. Faraday Soc., (1918), 
 July 23. A lead-sodium alloy known as " hy drone," yielding 
 hydrogen on treatment with water, has also been proposed. 
 Another field method based on experiments described by 
 Schwarz (Ber., 19, (1886), 1140) has been developed by 
 Majert and Richter, and depends on the interaction of a 
 heated mixture of soda-lime and zinc dust : 
 
 Zn + Ca(OH) 2 = ZnO + CaO + H 2 
 
 The mixture is disposed in a series of horizontal tubes mounted 
 in a heating chamber. The use of a mixture of glycerol and 
 caustic soda has been proposed. The process is convenient, 
 but is rather dangerous. 
 
 Adaptations of Stationary Types of Plant to Field 
 
 Purposes 
 
 By mounting on railway trucks it has been found possible 
 to use some of the less portable types of plant for field 
 purposes as, e.g. the Rincker and Wolter process (cf. p. 192), 
 plants with a capacity of 3500 ft. 3 hydrogen per hour being 
 thus constructed. The process gives cheap hydrogen, but 
 the lifting power is not very high on account of the nitrogen 
 and carbon monoxide contents (see p. 193). 
 
 Semi-Portable Plant 
 
 Certain of the processes described under (i) have been 
 adopted for use in air stations, etc., although the expense is 
 rather unwarrantable in such cases. Many air stations have 
 been equipped with electrolytic plants (cf. 194). Thus an 
 Oerlikon plant was installed at the Farnborough air station ; 
 plants have also been put down by various European powers, 
 while the U.S. Army had an electrolytic plant of capacity 
 3000 ft. 3 /hr. 
 
 In such cases, the stations are equipped with compression 
 plants and with cylinders for purposes of distribution. The 
 French Army has used very large cylinders, namely, 13 ft. 
 long and io| in. internal diameter, with capacity at 130 
 atmospheres of about 900 ft. 3 . In Germany, special railway 
 
HYDROGEN FOR MILITARY PURPOSES 233 
 
 waggons have been used, each carrying 500 cylinders, all 
 inter-connected by soldered joints to a single discharge 
 valve. Each waggon weighs about 30 tons and carries 
 nearly 100,000 ft. 3 of hydrogen, some 8 such waggons being 
 required for a dirigible of volume 700,000 ft. 3 . 
 
 Stationary Plants 
 
 In this category may be included practically all the 
 processes described in Section VI. The hydrogen may be 
 distributed in cylinders as described above. Utilization of 
 waste electrolytic hydrogen has already been mentioned ; 
 the gas may be piped directly to the aerodrome or may be 
 distributed in cylinders. On account of the much greater 
 economy of production possible by such methods, hydrogen 
 can be so made for aeronautical purposes in large quantities 
 with advantage, provided that the freight costs are not too 
 great. The lyinde-Frank-Caro has the advantage with 
 regard to aviation, that it is adaptable to the recovery of 
 the hydrogen in spent balloon gas, i.e. hydrogen which has 
 to be discarded by reason of its diminished lifting power on 
 account of the diffusion through the fabric of a considerable 
 quantity of air, e.g. 25 %. 
 
 General. There are three important considerations 
 relating to the manufacture of hydrogen for balloons 
 (i) lifting power as determined by purity ; (2) effect on the 
 fabric; (3) cost. 
 
 (i) Lifting Power of the Hydrogen. Since 1000 ft. 3 of 
 pure hydrogen at 15 C. weigh 5*319 Ibs. and 1000 ft. 3 of dry 
 air at 15 C. weigh 76-49 Ibs., it follows that the lifting 
 power of pure hydrogen at 15 C. 
 
 = 76-49 5-32 Ibs./iooo ft. 3 
 = 71*17 Ibs./iooo ft. 3 
 
 A. simple calculation will show that the presence of i % 
 of air derived by diffusion through the envelope, would lower 
 the lifting power by exactly i %, while the presence of the 
 water vapour corresponding to 15 C. would have a like 
 effect. The influence of the saturation of the air is obviously 
 
234 
 
 INDUSTRIAL GASES 
 
 small, saturation at 15 C., for instance, only reducing the 
 lifting power by 07 %. 
 
 (2) Effect on Fabrics. It has been found that sulphuretted 
 hydrogen, arsine and phosphine have an injurious eifect 
 on the balloon fabric, probably due to oxidation of the 
 impurities to sulphuric, arsenic and phosphoric acids re- 
 spectively. Electrolytic hydrogen has an advantage from 
 this point of view over that produced by other methods. 
 
 (3) Costs. The following table shows the relative costs, 
 as far as data are available, of various field methods for 
 making hydrogen, together with the weights of material 
 (water excluded) required per 1000 ft. 3 of hydrogen. The 
 costs must be considered as approximations only and in 
 any case refer to pre-war conditions. 
 
 TABLE 25. 
 
 COST OF PRODUCTION OF HYDROGEN AND WEIGHT OF MATERIALS 
 REQUIRED BY DIFFERENT FlELD PROCESSES. 
 
 Process. 
 
 Cost per 1000 ft. 3 
 Shillings. 
 
 Material required 
 per 1000 ft." 
 
 Lbs. 
 
 Silicon (Schuckert) process 
 
 20 
 
 125 
 
 Silicol (Jaubert) process 
 
 20 
 
 120 
 
 Hydrogenite process 
 
 40 
 
 IQO 
 
 Hydrolith process 
 
 7 
 
 60 
 
 Iron and sulphuric acid 
 
 15-25 
 
 450-500 
 
 Zinc and sulphuric acid 
 
 40 
 
 450-500 
 
 
 (with O. V. (80 %) 
 
 
 
 at 255. per ton) 
 
 
 Aluminium and caustic soda . . . . 
 
 70 
 
 350 
 
 Activated aluminium and water: 
 
 
 
 Mauricheau-Beaupre process 
 
 50 
 
 5 
 
 Griesheim-Elektron process 
 
 5 
 
 60 
 
 Before leaving the subject of balloons, it is interesting 
 to note that proposals have been made to substitute helium 
 for hydrogen on account of the non-inflammability of the 
 former in conjunction with its high lifting power. 
 
 Thus, the weight of 1000 ft. 3 of air at 15 C. = 76-49 Ibs. 
 ,, ,, ,, helium ,, = 10-56 Ibs. 
 
 Consequently the lifting power of 1000 ft. 3 of 
 
 helium at 15 C = 65-93 Ibs. 
 
 or 92 % of that of hydrogen. 
 
HYDROGEN FOR MILITARY PURPOSES 235 
 
 Estimation and Testing of Hydrogen. Hydrogen is 
 not readily estimated in gaseous mixtures by simple 
 absorption, although, if desired, absorption can be effected 
 by means of metallic palladium, by chlorate solutions in the 
 presence of colloidal osmium or by other allied methods (cf . 
 the work of Paal, Hofmann and others, p. 155). 
 
 In general, hydrogen is usually estimated by combustion 
 with excess oxygen ; this operation may be effected in various 
 ways, e.g. by explosion, in a Grisoumeter or over palladized 
 asbestos, or copper oxide may be used without addition of 
 oxygen. When hydrogen and methane occur together, 
 fractional combustion can be effected quite cleanly by 
 attention to temperature, both with palladized asbestos and 
 copper oxide. 
 
 Turning to the examination of commercial hydrogen, 
 the purity can be readily determined to a first approximation 
 by means of physical methods, e.g. by effusion. Impurities, 
 such as carbon monoxide, carbon dioxide and oxygen, are 
 easily estimated by methods described under these gases, 
 while reference has been already made to the automatic 
 detection of oxygen in electrolytic hydrogen, etc. Nitrogen 
 is best determined by combustion with copper oxide and 
 measurement of the residue. Hydrogen made by the 
 B.A.M.A.G. continuous catalytic process contains methane 
 which, in view of the small quantit}^ present, is best esti- 
 mated by complete combustion of a stream of the hydrogen 
 with excess oxygen and determination of the resulting carbon 
 dioxide, due allowance being made for any carbon monoxide 
 present. Alternatively the estimation may be performed by 
 explosion and subsequent measurement of the carbon dioxide 
 formed. The Silicol process gives hydrogen containing traces 
 of phosphine ; according to Soyer (loc. cit., p. 227) the pro- 
 ducts of combustion of from 2-20 litres of the hydrogen are 
 taken up with water and phosphoric acid estimated as phos- 
 phomolybdic acid. Arsenic may be estimated by the usual 
 method of passing the gas through a heated glass capillary 
 and comparing the mirror with standards, or by the Gutzeit 
 method depending on the production of a brown or yellow 
 
236 INDUSTRIAL GASES 
 
 stain on mercuric chloride paper. Sulphuretted Irydrogen 
 and carbon disulphide may occur in hydrogen ; the former 
 may be estimated by its action on lead acetate paper or on 
 iodine solution, etc., while the latter may be similarly deter- 
 mined after its conversion into sulphuretted hydrogen by- 
 passing over platinized pumice at 300-350 C. 
 
 REFERENCES TO SECTION VII. 
 
 Sander, " Zur Geschichte der Wasserstoffgewinnung im Kriege," /. 
 Gasbeleucht, 58, (1915), 637. 
 
 Anon., " Hydrogen for Balloons," Engineering, 99, (1915), 415. 
 
 Boyer, " La Nouvelle Usine a 1'Hydrog^ne de 1'Arsenal de Chatham," 
 La Nature, (1915), i. 144. 
 
 Fourniols, " La Fabrication de 1'Hydrogene pour le Gonflement des 
 Ballons," Rev. Gen. des Sciences, 26, (1915), 339. 
 
SECTION VIII. CARBON MONOXIDE 
 
 Properties of Carbon Monoxide. Carbon monoxide is 
 a colourless gas which, according to Merriman, has a definite 
 metallic odour and taste. The chief physical properties 
 will be found in Tables 12 and 13, pp. 53-56. The solubility 
 in water is given by the following table : 
 
 Temperature C 
 
 o 
 
 10 
 
 15 
 
 20 
 
 4 
 
 C.c. of gas, measured at 
 
 
 
 
 
 
 N.T.P., dissolved by 
 
 
 
 
 
 
 i c.c. of water under a 
 
 
 
 
 
 
 pressure of I atm. ex- 
 
 
 
 
 
 
 clusive of water vapour 
 
 0-035 
 
 0-028 
 
 0-025 
 
 0-023 
 
 o'oiS 
 
 Carbon monoxide is readily formed by the combustion 
 of carbon in a limited supply of oxygen and by a number 
 of chemical reactions. The most important commercial 
 form of carbon monoxide is in admixture with nitrogen, 
 hydrogen, etc., in producer gas, water gas and the like. 
 
 Carbon monoxide is a poisonous gas, forming a compound 
 with the haemoglobin of the blood (carboxy haemoglobin), 
 and is only very slowly replaced by the normal oxygen. A 
 concentration of 0-4 % is rapidly fatal. Carbon monoxide 
 burns with a characteristic blue flame to carbon dioxide. It 
 is very stable at high temperatures, especially in the presence 
 of a trace of moisture (Woltereck, Comptes Rend., 147, (1908), 
 460), but in the neighbourhood of 300 C. and in the presence 
 of a catalyst, e.g. metallic nickel, decomposition takes place 
 according to the following equation : 
 
 2CO -F^ CO 2 + 39,300 calories. 
 
 The following table gives the percentages of carbon 
 dioxide in equilibrium with carbon monoxide and carbon 
 at different temperatures and at atmospheric pressure. The 
 
238 
 
 INDUSTRIAL GASES 
 
 values above 850 C. are taken from Rhead and Wheeler 
 (Chem. Soc. Trans., (1910), 2178 ; (1911), 1141) and the 
 lower values from Boudouard (Annales de Chimie et de Phys., 
 [7], 24, (1901), 5). 
 
 TABLE 26. EQUILIBRIUM BETWEEN CARBON 
 
 Temperature C 
 
 450 
 
 500 
 
 600 
 
 700 
 
 Percentage CO 2 1 B. 
 by volume /R. and W. 
 
 98 
 
 95 - 
 
 77 
 
 42 
 
 foo 2 
 pco 
 
 49-0 
 
 19-0 
 
 3' 35 
 
 0-724 
 
 K 
 
 2450 
 
 380 
 
 1 4' 55 
 
 1-25 
 
 Rhead and Wheeler adopt the modified L,e Chatelier 
 formula given below as in agreement with their measurements. 
 
 log 
 
 = 1874 - log,P - 
 
 38,055 + 2'02T 
 
 In view of the decrease in volume as decomposition 
 proceeds, it is obvious that the effect of increased pressure 
 will be to favour such decomposition. Experiments by 
 Briner and Wroczynski (Comptes Rend., 150, (1910), 1324) 
 have demonstrated that at 400 atmospheres carbon monoxide 
 is not decomposed at the ordinary temperature even in the 
 presence of platinized asbestos ; at 320-360 C. slow 
 decomposition occurred, a diminution in volume of 10 % 
 being observed after 20 hours. 
 
 Carbon monoxide reacts with water vapour at quite low 
 temperatures, e.g. 400 C., in the presence of a suitable 
 catalyst, giving the so-called water gas equilibrium 
 
 CO + H 2 O ^ CO 2 + H 2 + 10,200 calories. 
 
 This equilibrium is dealt with elsewhere, see pp. 157 and 309. 
 The equilibrium constant becomes unity at a temperature of 
 about 830 C. ; which means that below this temperature 
 
CARBON MONOXIDE 
 
 239 
 
 carbon monoxide is a more active reducing agent than 
 hydrogen and above this temperature less so. Thus, it is 
 found that carbon monoxide begins to reduce metallic oxides 
 at a considerably lower temperature than does hydrogen, 
 
 MONOXIDE, CARBON DIOXIDE AND CARBON. 
 
 800 
 
 900 
 
 IOOO 
 
 IIOO 
 
 I2OO 
 
 7 
 
 
 
 
 
 
 2'22 
 
 0'59 
 
 0-15 
 
 0'06 
 
 0-0752 
 
 O-O227 
 
 O-OOO593 
 
 0-00150 
 
 0*0006 
 
 o'oSn 
 
 0-0232 
 
 0-00597 
 
 0-001503 
 
 0-0006 
 
 cf. Fay and Seeker, /. Amer. Chem. Soc.,35, (1903), 641, and 
 Fay, Seeker and Ferguson, Polytechnic Engineer, 10, (1910), 
 72, who give among others the following reduction temper- 
 atures : 
 
 
 Carbon monoxide. 
 
 Hydrogen. 
 
 Cupric oxide 
 Mercuric oxide (yellow) .. 
 
 75 C. 
 oC. 
 
 125 C. 
 5 o C. 
 
 Silver oxide is reduced by carbon monoxide at the ordinary 
 temperature. 
 
 On similar lines is the observation of Henry (Phil. Trans., 
 (1824), 266 ; Phil. Mag., [3], 9, (1836), 324), that when a 
 mixture of carbon monoxide, hydrogen and oxygen is 
 exposed to a platinum catalyst at a temperature of 150- 
 170 C., the oxygen attaches itself mostly to the carbon 
 monoxide ; similar results were obtained at the ordinary 
 temperature (cf. also p. 255). 
 
 It is evident that carbon monoxide is an energetic 
 reducing agent and many of its applications, usually as 
 producer gas or water gas, depend on this property. It 
 
240 INDUSTRIAL GASES 
 
 slowly reduces silver nitrate solution, potassium perman- 
 ganate solution, etc., at the ordinary temperature. 
 
 Carbon monoxide reacts readily with hydrogen in the 
 presence of finely divided nickel (Sabatier and Senderens, 
 Comptes Rend., 134, (1902), 514), best at a temperature of 
 250-300 C. according to the equation- 
 
 CD + 3H 2 == CH 4 + H 2 + 5o,8oo calories. 
 It is patent that methane production will be favoured by 
 low temperature consistent with sufficient reaction velocity 
 and high pressure. The reaction, however, goes very com- 
 pletely at the ordinary pressure if excess hydrogen be used 
 at 250-300 C., and a rough calculation according to the 
 Nernst Heat Theorem shows that starting with a mixture 
 containing 80 % hydrogen which with complete reaction 
 would give, after removing water, a product containing 50 % 
 methane and 50 % hydrogen the equilibrium constant at 
 300 C. is equal to 
 
 Pco Xp*n 2 
 
 ,., ( 50,800 ) 
 
 = antilog< -- 3-5 log 573 2'2 > 
 K57IX573 J ^ } 
 
 = 3'5 Xio? 
 
 It is evident that very little carbon monoxide can remain 
 in equilibrium and, approximating, by taking p H ^ = p cli ^ 
 = Pn z o = 0*333 atm., we have 
 
 pco = Q-333XO-333 
 
 3-5 X 10* X 0-3333 
 = 8'6 X io~ 8 atms. 
 = o- 0000086 % carbon monoxide. 
 
 At a temperature of 800 C. a similar rough calculation 
 gives a value of 0*0035 for the equilibrium constant. (The 
 question is, of course, complicated to some extent by the water 
 gas reaction owing to which some of the carbon monoxide will 
 be converted to carbon dioxide.) This corresponds to a final 
 methane content of only about 1*7 % when starting with the 
 above-mentioned mixture. In this connection cf. the 
 
CARBON MONOXIDE 241 
 
 production of hydrogen by the decomposition of hydro- 
 carbons, p. 189. 
 
 As an impurity of technical hydrogen carbon monoxide 
 is important in the synthetic production of ammonia 
 and, in a lesser degree, in the catalytic hydrogenation 
 of oils. For the latter case cf. Maxted (Trans. Faraday 
 Soc., Dec., 1917), according to whom the presence of 
 0*25 % carbon monoxide in the hydrogen effects a reduction 
 in the rate of absorption of about 30 %. The sensitivity 
 to carbon monoxide, however, depends on the conditions of 
 preparation of the nickel catalyst; thus, lyessing (B.P. 
 18998/12) introduces the nickel catalyst in the form of nickel 
 carbonyl. 
 
 The illuminating effect of carbon monoxide as regards 
 incandescent mantles is found by Forshaw to be 48 % 
 greater than that of hydrogen, although the calorific value 
 is only 18 % greater. 
 
 Carbon monoxide forms, with various metals, an interest- 
 ing series of additive compounds, a description of some of 
 which will be given later. 
 
 On cooling, carbon monoxide condenses to a colourless 
 liquid and solidifies to a snowy solid. 
 
 The limits of inflammability of carbon monoxide in 
 admixture with air are as follows : 
 
 Minimum percentage of air in carbon) __ 
 monoxide for inflammation . . j ~ 
 
 Minimum percentage of carbon 1 _ 
 monoxide in air for inflammation ) " 
 
 (Coward, see p. 40). 
 
 Manufacture of Carbon Monoxide. Carbon monoxide 
 is seldom made in a pure state on the large scale, but if 
 required it is readily obtained by passing carbon dioxide 
 through a bed of incandescent coke. The operation 
 may be rendered continuous, if desired, by the addi- 
 tion of oxygen to the carbon dioxide (cf. I^oiseau, B.P. 
 11590/08). Reference to p. 238 will show that a tem- 
 perature of not less than 1000 C. is desirable if comparative 
 A. 16 
 
242 INDUSTRIAL GASES 
 
 freedom from carbon dioxide, without subsequent puri- 
 fication, is necessary. With this ideal in view Benjamin 
 (U.S.P.s 1225048/17 and 1225396/17) proposes the use 
 of local electric heating of the carbon dioxide or coal. 
 According to B.P. 21213/13 of the " Athion " Gesellschaft, 
 the necessary carbon dioxide is obtained by concentration 
 from products of combustion, using alkali carbonate lye 
 (cf.p. 264). 
 
 Carbon monoxide is also obtained in a relatively pure 
 state as a by-product of the lyinde-Frank-Caro process, 
 the liquid fraction usually consisting of 80-85 % carbon 
 monoxide (cf. p. 172) the remainder being hydrogen. In 
 most cases the carbon monoxide is burnt in a gas engine for 
 the production of the necessary power for driving the com- 
 pressors, etc., but could quite well be used for chemical 
 purposes, e.g. in the Mond nickel process (cf. p. 243). 
 
 By far the most important industrial form of carbon 
 monoxide, however, is as producer gas and water gas (cf. 
 Section XIII.), the latter of which contains some 40% carbon 
 monoxide. Coal gas also contains a large amount of carbon 
 monoxide. 
 
 Carbon monoxide may be prepared in a pure state on a 
 semi-technical scale by the action of sulphuric acid on 
 commercial formic acid. Suitable apparatus for this purpose 
 is described by Hutton and Petavel (loc. cit., p. 113) consist- 
 ing of a large glass bolthead half filled with 2 gallons of 
 sulphuric acid of S.G. 173 and heated to 150-170 C. by 
 means of a granular carbon electric resistance furnace. 
 Ninety per cent, formic acid is run in, when carbon monoxide 
 (of 99 % purity after washing with caustic soda solution) can 
 be produced at a rate of about TOO ft. 3 /hr. and at a cost 
 of some 50 /- per 1000 ft. 3 . About 130 Ibs. of the 90 % 
 formic acid are required for 1000 ft. 3 of the gas. 
 
 Applications of Carbon Monoxide 
 General. It is a little difficult to draw any sharp line 
 of distinction between the uses of carbon monoxide as such 
 and the general applications of water gas and semi-water 
 
CARBON MONOXIDE 243 
 
 gas, but among the former may be emphasized the following 
 examples : 
 
 The Mond Nickel Process. Metallic Carbonyls. Be- 
 fore describing in detail this interesting process, it will be 
 well to give a brief outline of the production and character- 
 istics of the additive compounds of carbon monoxide with 
 metals. The first known compound, namely, nickel carbonyl, 
 was discovered by Mond and ganger about 1889 somewhat 
 as follows. At this time a process was in use by Mond for 
 the production of chlorine from ammonium chloride in 
 which nickel oxide was heated in the vapour of the ammo- 
 nium chloride, giving free ammonia and nickel chloride 
 which was subsequently reconverted into oxide and chlorine 
 by heating in air. The nickel was used in the form of balls 
 made up with china clay and was found to deteriorate rapidly, 
 the effect being traced to the use of " inert " gas for the 
 purpose of sweeping out the residual ammonia before admis- 
 sion of air. The " inert " gas consisted of nitrogen containing 
 some carbon monoxide and carbon dioxide, obtained from 
 the ammonia soda plant. In like manner, attack on the 
 nickel valves was noticed. These observations led to 
 the study of the action of carbon monoxide on nickel with 
 the object of making any possible compounds. During the in- 
 vestigation the exit gases from the experimental tube were led 
 to a Bunsen burner to burn up the poisonous carbon monoxide, 
 and to the surprise of the investigators, in one experiment 
 when the tube was cooling down, particularly when below 
 100 C., the flame was observed to become luminous, owing, as 
 was subsequently shown, to the formation of nickel carbonyl. 
 
 Nickel carbonyl Ni(CO) 4 is a colourless liquid of B.Pt. 
 43 C. and M.Pt 25 C. The vapour is liable to explode, 
 even at 60 C., while the liquid slowly decomposes in the 
 air, giving a greenish deposit. On heating to about 180 C. 
 metallic nickel is deposited in the form of a mirror. The 
 compound is very poisonous. 
 
 The equation 
 
 Ni-f 
 
244 INDUSTRIAL GASES 
 
 indicates that the formation will take place more readily 
 at increased pressures. According to Dewar the dissociation 
 pressure of nickel carbonyl varies with the temperature as 
 follows : 
 
 Temperature. Dissociation pressure 
 
 (experimental). 
 
 100 C. . . . . . . 15 atms. 
 
 250 C 100 atms. 
 
 Iron likewise forms compounds under similar conditions. 
 The compound most easily formed is the pentacarbonyl 
 Fe(CO) 6 a yellow liquid of B.Pt. IO2'8 C. By the action 
 of light it is converted into Fe 2 (CO) 9 , an orange red crystalline 
 substance which in turn, when dissolved in toluene and heated 
 to 95 C. in an atmosphere of carbon dioxide, gives Fe(CO) 4 . 
 
 Iron carbonyl is formed in small quantities in cylinders 
 containing compressed water gas or coal gas by the action 
 of the carbon monoxide on the iron of the cylinders and has a 
 deleterious action when such coal gas is used for limelight 
 or for incandescent mantles, the iron being deposited in the 
 form of oxide. The formation of the compound may be 
 minimized by special treatment of the cylinders. 
 
 It was long thought that cobalt gave no parallel compound, 
 but, in 1910, Mond, Hirtz and Cowap (Chem. Soc. Trans., 
 (1910), 798) isolated the carbonyls of cobalt, molybdenum 
 and ruthenium. These compounds have higher dissociation 
 pressures than the corresponding nickel and iron compounds. 
 Thus the conditions for their formation are 
 
 Pressure. Temperature. 
 
 Atms. C. 
 
 Cobalt 100 200 
 
 Molybdenum . . . . 250 200 
 
 Ruthenium . . . . 450 300 
 
 Potassium with carbon monoxide at 80-90 C. forms 
 a black, solid explosive compound (KCO), which detonates 
 at 100 C., or by contact with air or water at the ordinary 
 temperature. The formation of this compound was a 
 source of considerable trouble in the old process of manu- 
 facturing potassium. 
 
CARBON MONOXIDE 245 
 
 The Refining of Nickel by the Mond Process. Following 
 up the results of the above-mentioned investigation Mond 
 developed the process on a technical scale. In a very 
 comprehensive patent, B.P. 12626/90, Mond outlines a method 
 of refining nickel based on the alternate formation and decom- 
 position of nickel carbonyl. A number of patents follow, 
 e.g. B.P. 8803/91 relates to the direct production of nickel 
 alloys by passing the gas containing nickel carbonyl into a 
 molten metal ; B.P.s 23665/91 and 23665A/9I describe 
 the arrangement of the reducer and the volatilizer with an 
 intermediate rotatory feed valve for the ore to prevent 
 intermixing of the gases, while B.P. 1106/98 prescribes the 
 use of pellets as media for the continuous deposition of the 
 nickel with appropriate plant. These patents form the 
 basis of the process as described below. In B.P. 9300/02 
 Dewar deals with the action of increased pressure in the 
 operation of the process, but this modification does not appear 
 to have come into use in actual working ; the enhanced 
 formation of the carbonyl would doubtless be largely offset 
 by the increased cost and difficulty of conducting operations 
 under high pressure. 
 
 An experimental large-scale plant was erected at Smeth- 
 wick in 1892 and after the success of the process had been 
 demonstrated, a large works was put up at Clydach, the 
 present output of which amounts to some 3000 tons of nickel, 
 of 99 '9 % purity, per annum. Details of the present plant 
 are not available, but presumably it is similar to the Smeth- 
 wick plant, of which a description is given by Mond in Revue 
 Gen. de Chim. pure et app., 2, (1900), 121. The scheme of 
 the operations is as follows. Nickel ores containing nickel, 
 cobalt, copper and iron as pyrrhotite (magnetic pyrites), 
 kupfernickel, chalcopyrite, etc., are suitable. That usually 
 adopted is pyrrhotite mixed with copper pyrites and is 
 essentially iron sulphide containing some 3 % nickel and 
 about the same quantity of copper ; the principal deposits 
 are in Sudbury. The bessemerized matte, containing some 
 80 % Ni -f- Cu, is roasted to convert it into oxide when it 
 contains about Ni 35 %, Cu 42 %, Fe 5 %. It is next crushed 
 
246 INDUSTRIAL GASES 
 
 and screened through a 6o-mesh sieve and then enriched 
 in nickel by leaching with dilute sulphuric acid which 
 dissolves out part of the copper, the ore having a final 
 composition of about Ni 51 %, Cu 21 %, Fe 3 %. After 
 drying, the ore passes to the " reducing " and " volatilizing " 
 towers, which are superimposed, the latter being on top. 
 By means of annular flues heated by producer gas, the 
 " reducer," which is some 25 ft. high, is maintained at a 
 temperature not exceeding 300 C. The " reducer " and also 
 the " volatilizer " are provided with shelves and mechanically- 
 operated rabbles revolving round a central vertical shaft, 
 as in a Herreshoff sulphur burner, the ore being fed in at the 
 top, passing from centre to periphery and vice versa; the 
 reducer has about 14 shelves. 
 
 The nickel and copper oxides are thus reduced by a stream 
 of water gas passing upwards as the ore descends the tower, 
 the reduced product is cooled to about 50 C. on the lower 
 5 shelves, this section of the tower being water-jacketed. 
 From the bottom of the " reducer " the reduced ore is passed 
 out through a rotating valve and is lifted by means of an air- 
 tight conveyor to the top of the " volatilizer." This tower, 
 which is about 15 ft. in height, is maintained at about 50- 
 100 C. Here the reduced ore passes down in counter- 
 current to a stream of 80 % carbon monoxide which effects 
 the formation of nickel carbonyl, the carbon monoxide 
 effluent having a carbonyl content of about 2 %. The ore, 
 on the other hand, passes out through a rotating valve, which 
 prevents the intermixing of the two types of gas, and back 
 to the reducer. 
 
 This cyclic treatment is necessary, as the nickel after a 
 time loses its power of yielding carbonyl and requires reacti- 
 vation by further heating to 300 C. in the reducing gases. 
 
 The gases leaving the volatilizer pass through a dust filter 
 and enter the decomposer, which consists of a tower some 
 10 ft. high filled with nodules of nickel previously formed, 
 and heated to 180 C. Entering at the top, the gases pass 
 down through a central pipe reaching to the bottom and 
 perforated along its length, the nickel carbonyl suffering 
 
CARBON MONOXIDE 
 
 247 
 
 decomposition among the pellets of nickel which gradually 
 increase in size ; the pellets pass out at the bottom of the 
 tower through a rotating valve and are automatically 
 screened, the smaller ones being returned to the top of the 
 tower by an elevator while the larger pass out through a 
 valved opening. In consequence of the constant friction, 
 the nodules, as put on the market, have the appearance of 
 burnished bicycle balls of about J in. diameter. This system 
 of operating the decomposer avoids any trouble in the other- 
 wise intermittent removal of the deposited nickel. The 
 disengaged carbon monoxide returns to the volatilizer. 
 To prevent blocking by deposition of nickel carbonyl within 
 the central pipe, the latter is water-jacketed. We have 
 here a very ingenious series of cyclic operations represented 
 graphically in Fig. 22. 
 
 H 8 S0 4 
 
 RESIDUE FROM EXTRACTION 
 = Mi 40% Co 35% Fa 5% (o> t '!r 
 
 FIG. 22. Mond Nickel Process. 
 
 It is important that the temperature of the reducer 
 should not exceed 300 C., especially if much iron be present, 
 as the reduction of the iron oxide would give rise to iron 
 pentacarbonyl with consequent contamination of the metallic 
 nickel. Further, an increase of temperature impairs the 
 activity of the reduced nickel as regards carbonyl formation. 
 Reduction is carried out by water gas containing about 
 60 % hydrogen, from anthracite generators ; under the 
 above conditions the reduction is mostly affected by the 
 hydrogen, of which the issuing gas contains only about 
 5-10 %. Part of this gas, after passing first through a 
 cooler and then through a retort filled with incandescent 
 
248 INDUSTRIAL GASES 
 
 wood charcoal and now containing some 80 % carbon 
 monoxide, is used to make up the losses from the volatilizer- 
 decomposer cycle. The ore is circulated through the volati- 
 lizer until about 60 % of the nickel is removed (residue equals 
 about two-thirds of the original matte), this conversion 
 occupy ing from 8 to 15 days, and is then of similar composition 
 to the original matte. It is returned to the roasting furnace, 
 leached and put into commission again. Some care is 
 required as regards the temperature of the decomposer. 
 If less than 180 C. the nickel is not deposited, and if above 
 180-200 C. catalytic dissociation of the carbon monoxide 
 to carbon dioxide and carbon is induced. 
 
 As stated above, the purity of the nickel is extremely 
 high, the carbon content, which is often of importance, being 
 less than 0*1 %. 
 
 The Production of Formates, Oxalates and Acetates. 
 The action of carbon monoxide on heated caustic soda was 
 discovered by Berthelot in 1856, who showed the action to 
 proceed according to the equation 
 
 CO + NaOH = H . COONa 
 
 and observed that the absorption proceeded more rapidly 
 in the presence of water. 
 
 A more complete investigation of the reaction from a 
 technical standpoint was undertaken by Weber (" Uber die 
 Einwirkung von Kohlenoxyd auf Natronlauge," Karlsruhe 
 Dissertation, 1908). Working with increased pressure and 
 at temperatures up to 180 C., Weber arrived at the following 
 conclusions : (i) that the reaction is of the first order ; (2) 
 that a solution containing 10 % NaOH gives the highest 
 reaction velocity at high temperatures ; (3) that the reaction 
 occurs between the dissolved carbon monoxide and the 
 caustic soda, not between gaseous carbon monoxide and 
 water vapour; and (4) that for constant temperature and speed 
 of stirring the rate of absorption is proportional to the 
 concentration of carbon monoxide. 
 
 The experiments were continued by Fonda (" Uber die 
 Einwirkung von Kohlenoxyd auf I^augen," Karlsruhe 
 
CARBON MONOXIDE 249 
 
 Dissertation, 1910) and are summarized by Haber in his 
 Hurter memorial lecture at lyiverpool (/. Soc. Chem. Ind., 
 (1914), 51). At a comparatively low temperature, stirring 
 had little influence, the liquid being easily kept saturated 
 with gas, but when a temperature of 160-170 C. was 
 reached, the stirring could not be made so fast that an 
 increase in the speed did not cause an increased rate of 
 reaction. Above 100 C., 10 % NaOH gave the best results, 
 e.g. Sit 160 C. the reaction velocity was more than 15 times as 
 great with 10 % as with 43 % solution. It was thought 
 possible that the superiority of the 10 % solution might be 
 explained by a connection with the surface tension, but this 
 hypothesis was not confirmed by measurements of the latter 
 at the high temperatures in question. 
 
 Experiments by Bredig and Carter at temperatures of 
 50-80 C. and pressures up to 40 atms., using different 
 bases, e.g. the alkalis, baryta, tetramethylammonium hydrox- 
 ide, piperidene, etc., showed that the reaction velocity was 
 constant for different bases given equal hydroxydion 
 concentration. 
 
 There are many patents relating to this subject, among 
 which the following may be mentioned : B.P. 17066/95, 
 by Goldschmidt, relates to the production of formate by 
 passing carbon monoxide over caustic soda, or preferably 
 soda-lime, at a temperature of about 230 C., the operation 
 being facilitated by being carried out under pressure. 
 According to Koepp & Co. (B.P. 7875/04) a 35 % solution 
 of caustic soda is run on to a mass of coke at a temperature of 
 220 C. in a closed vessel ; carbon monoxide is passed through 
 the liquid for three-quarters of an hour. In B.P. 772/06, the 
 Elektrochemische Werke, Bitterfeld, prescribe the treatment 
 of caustic alkali in large pieces with carbon monoxide at 100- 
 120 C. under pressure, while Nitridfabrik, G.m.b.H. (B.P. 
 9008/06) deals with the use of caustic soda with the addition 
 of 0-12 % to 0-15 % water, such addition of water being 
 claimed to produce improved absorption. In B.P. i3953/7 
 the United Alkali Co. and others claim an accelerated and 
 more complete absorption when using solid caustic soda, by 
 
250 INDUSTRIAL GASES 
 
 the addition of titanium compounds, e.g. a mixture of caustic 
 soda with about n % titanic acid is used at a temperature 
 of about 150 C. After evacuation, carbon monoxide is 
 admitted with stirring, the pressure being kept low. Ellis 
 and McKlroy (U.S. P. 875055/07) prescribe the treatment 
 of basic mineral substances, e.g. calcium carbonate, suspended 
 in water, with carbon monoxide or producer gas at high 
 temperature and pressure. Dubox, L,uttinger and Denis 
 (F.P. 421227/09) advocate the use of ammonia or organic 
 bases in presence of pumice impregnated with one of a number 
 of metallic catalysts at a temperature of 90-165 C. and at 
 atmospheric pressure. On somewhat similar lines is U.S. P. 
 1212359/17, by Katz and Ovitz, according to whom a stream 
 of carbon monoxide and ammonia ascending a tower, meets a 
 descending stream of finely divided caustic alkali solution, the 
 temperature being 150-200 C. and the pressure 10-20 atms. 
 
 The synthetic production of formates is carried out 
 on a considerable scale, the usual source of carbon monoxide 
 being air producer gas. 
 
 In the manufacture of formates, especially when carried 
 out under increased pressure, the action of caustic soda 
 liquor on steel at high temperatures is of importance from a 
 safety standpoint. Hydrogen is absorbed by the steel, 
 the mechanical properties of which are impaired. Cf. 
 Andrew, Trans. Faraday Soc., 9, (1914), 317 ; Mercia, Metall. 
 and Chem. Eng., 16, (1917), 496, 503 ; Stromeyer, Chem. 
 Trade]., 61, (1917), 533 ; Worsley, Ibid., 62, (1918), 65. 
 
 ProductionofOxalates. On gentle heating, sodium formate 
 is easily converted into oxalate with liberation of hydrogen 
 and the following patents relate to such conversion. 
 
 Goldschmidt (B.P. 26172/97) heats sodium formate 
 mixed with about 125 % of anhydrous sodium carbonate 
 to 400-410 C., the sodium carbonate securing a good yield 
 of oxalate and being subsequently removed. Similarly, 
 Koepp & Co., in B.P. 9327/03, heat sodium formate with 
 e.g. i % of caustic soda which facilitates the decomposition. 
 At 260 C. the molten mixture evolves hydrogen and the 
 reaction is complete at ^60 C. The use of reduced pressure 
 
CARBON MONOXIDE 251 
 
 is prescribed in B.P. 19943/07 by the Elektrochemische 
 Werke, Bitterfeld, the conversion taking place at a lower 
 temperature, preferably about 280 C. 
 
 Other patents have as their primary object the production 
 of mixtures of nitrogen and hydrogen through the intermedi- 
 ary of formates, e.g. B.P. 30073/13 and U.S.P. 1098139/14 
 (cf. p. 205), while B.P. 1759/12 relates to the removal 
 of the last traces of carbon monoxide from hydrogen 
 (cf. p. 208). 
 
 Acetates may be produced in a similar manner to formates 
 by the treatment of sodium methoxide with carbon monoxide 
 at a temperature of 180 C. 
 
 The Production of Gases Rich in Methane. Carbon 
 monoxide reacts readily with hydrogen to form methane in 
 the presence of a suitable catalyst, as stated on p. 240. The 
 method has been used on the large scale for the production 
 from water gas of a gas of high calorific power with some 
 illuminating properties. 
 
 A description is given by Krdmann (/. Gasbeleucht., 54, 
 (1911), 737) of an experimental plant installed in England 
 by the Cedford Gas Producing Co. (cf. B.P.s 17017/09 and 
 22219/09). In order to obtain a gas of suitable composition 
 (as the action is unsatisfactory in the presence of excess 
 carbon monoxide), the water gas was given a preliminary 
 treatment in a lyinde-Frank-Caro plant (cf. p. 172), the 
 valves being so regulated as to give a gaseous fraction 
 containing about 17 % carbon monoxide, e.g. in one 
 test the average percentage composition of the gas was 
 
 Hydrogen . . . . . . . . 80*9 
 
 Carbon monoxide . . . . . . 16*3 
 
 Nitrogen . . . . . . . . 2'8 
 
 lOO'O 
 
 Part of the liquid (carbon monoxide) fraction was used 
 for the driving of the compressors. This preliminary 
 treatment had the advantage of giving a gas completely 
 free from sulphur compounds which exert a poisonous effect 
 
252 INDUSTRIAL GASES 
 
 on the nickel catalyst. The above gas mixture was passed 
 through three vertical quartz tubes of 4! in. internal diameter 
 and about 5 ft. long containing pumice impregnated with 
 about 200 grams of nickel per tube. The tubes were electri- 
 cally heated to 280-300 C., the gas being also preheated ; after 
 working for a little time the operation was self-supporting, 
 leaving through a condenser the gases had the following 
 percentage composition : 
 
 Hydrogen .62 
 
 Methane . . . . . . 31 
 
 Nitrogen . . . . . . . . 6 
 
 Carbon monoxide, carbon dioxide, 
 etc Traces. 
 
 and possessed a calorific value of 263 C.H.U./ft. 3 , (474 
 B.T.U.) as against the initial value of 159 C.H.U./ft. 3 
 (286 B.T.U.) for the original water gas. 
 
 About 450 ft. 3 /hr. of the 16 % carbon monoxide gas was 
 passed through the catalytic chambers, which had a volume of 
 about i "8 ft. 3 , corresponding to a " space velocity " of 250 
 ft. 3 /ft. 3 catalyst space/hour, referred to the 16 % carbon 
 monoxide gas, or of 128 referred to the final gas. The cost 
 of conversion of the water gas into the final product is given 
 as 176^71000 ft. 3 of the latter ; this figure would appear 
 to be low and in any case does not include any overhead 
 charges. 
 
 The Manufacture of Phosgene Carbonyl chloride, 
 or phosgene, is an industrial gas which may be conveniently 
 described at this point on account of its manufacture from 
 carbon monoxide. By passing a mixture of carbon monoxide 
 and chlorine over platinum sponge at 400 C., combination 
 takes place yielding phosgene, according to the following 
 reversible reaction : 
 
 CO + C1 2 ^COC1 2 +22,950 calories. 
 
 The equilibrium is given below for a pressure of one 
 atmosphere, the values being calculated according to the 
 
CARBON MONOXIDE 
 
 253 
 
 Nernst Heat Theorem (cf. Horak, Dissertation, Berlin, 
 1909). 
 
 TABLE 27. 
 PHOSGENE EQUILIBRIUM. 
 
 Temperature C. 
 
 % COC1 2 
 
 % CO 
 
 % CI 2 
 
 3 00 
 400 
 5 00 
 
 92-5 
 
 66-9 
 
 29*0 
 
 3-75 
 
 I6'5 
 35' 5 
 
 3' 75 
 16-5 
 35' 5 
 
 It is evident that a low temperature is favourable to the 
 production of the carbonyl chloride and that increase of 
 pressure would also favour the reaction. The reaction 
 takes place in the presence of animal charcoal as catalyst, 
 either in the dark or, better, in sunlight. Thus, according to 
 a small-scale experiment of Paterno, 70 c.c. of animal charcoal 
 effect the formation of about i kilo, carbonyl chloride in 24 
 hours, corresponding to a " space-time-yield " of about o - 6 
 kilos. /litre catalyst/hour. On the large scale, with coarse 
 granulated charcoal in the dark, a considerably lower space- 
 time-yield is to be expected. Cooling is necessary on account 
 of the heat evolution. 
 
 Phosgene has also been manufactured by heating together 
 electrically a mixture of quicklime, calcium chloride and 
 ground coke 
 
 2CaO + 2CaCl 2 -f icC = 4CaC 2 + 2COC1 2 
 
 Calcium carbide is formed while phosgene distils over and may 
 be at once converted into carbon tetrachloride by passing 
 through a heated catalyst, e.g. coke, bone black, pumice, 
 etc., carbon dioxide being formed at the same time with 
 evolution of heat. (Cf. U.S.P. 808100/05 by Machalske.) 
 
 Properties and Uses of Phosgene. Phosgene is a colourless 
 gas liquefying at 8*2 C. It has a characteristic, unpleasant 
 and pungent odour. The liquid has a specific gravity of 
 1-432 ato C. The substance is decomposed slowly by cold, 
 rapidly by hot water. It is fairly reactive and is used on 
 
254 INDUSTRIAL GASES 
 
 a considerable scale for the preparation of di- and tri-phenyl- 
 methane dyestuffs, etc. It combines with ammonia to form 
 urea and ammonium chloride. Phosgene is sold in the 
 liquid state in cylinders. 
 
 With reference to its use as a poison gas, see p. 292. It is 
 much more insidious in its physiological action than chlorine, 
 being less irritant while its effects are only evident after a 
 considerable number of hours and are then very severe. 
 
 Other Applications of Carbon Monoxide. The use 
 of carbon monoxide has been proposed for the reduction of 
 organic compounds ; cf. B.P. 6409/15 of the Badische Co., 
 according to whom nitro compounds as e.g. nitrobenzene, are 
 vaporized and passed with a carbon monoxide-steam mixture 
 over a copper catalyst on pumice at a comparatively low 
 temperature ; the carbon monoxide is converted wholly or 
 partially into carbon dioxide. 
 
 Estimation of Carbon Monoxide Carbon monoxide 
 
 may be detected by its blackening action on paper moistened 
 with palladious chloride solution, or by examination of the 
 blood of animals, e.g. mice, after air containing carbon 
 monoxide has been breathed by them. Carboxyhaemoglobin 
 has a definite absorption spectrum and the test is sensitive 
 to about O'Oi %. When present in sufficient quantity 
 carbon monoxide may be estimated fairly satisfactory by 
 absorption in cuprous chloride solution after preliminary 
 removal of the oxygen. The useful lower limit of the method 
 is about 0*25 % of carbon monoxide. 
 
 By passing the dry gas over iodine pentoxide heated to 
 about 160 C., any carbon monoxide is quantitatively 
 oxidized to carbon dioxide according to the equation 
 
 I 2 O 6 + 2CO = I 2 + 5CO 2 
 
 (cf. Levy, J. Soc. Chem. Ind., (1911), 1437 ; Graham, Ibid., 
 (1919), 10 T.) By means of this reaction, concentrations of 
 from 0-003 t 0^0003 % may be estimated in air by collecting 
 the iodine formed. In the presence of hydrogen, in which 
 gas the necessity of estimating small quantities of carbon 
 monoxide often arises, the results are complicated by a small 
 
CARBON MONOXIDE 255 
 
 portion of the hydrogen undergoing oxidation ; 'it is conse- 
 quently necessary to remove the iodine first by cooling and 
 then by bubbling through mercury which effectively removes 
 iodine vapour, and to estimate not the iodine but the carbon 
 dioxide formed, by suitable means. Methane is not attacked 
 by the iodine pentoxide, but any unsaturated hydrocarbons 
 present must be removed, best by the action of concentrated 
 sulphuric acid at a temperature of about 165 C. (Weiskopf, 
 /. Soc. Chem.Ind., (1909), 1170). The method is accurate, 
 without any special precautions, to about O'oi %, provided 
 that effective means be adopted for the accurate estimation 
 of the carbon dioxide. 
 
 A similar preferential oxidation of the carbon monoxide 
 may be effected by the action of chlorate solutions activated 
 with colloidal osmium, by precipitated mercuric chromate 
 (Hofmann, Ber., 49, (1916), 1650, 1663) ; by activated 
 copper oxide moistened with alkali, or by activated copper 
 moistened with alkali in the presence of oxygen (Hofmann, 
 Ibid., 51, (1918), 1334) a ^ so by the action of precipitated 
 mercuric oxide (Moser and Schmid, J. Soc. Chem.Ind., (1914), 
 442) . An automatic carbon monoxide recorder, designed for 
 estimation of this gas in hydrogen, has been described by 
 Rideal and Taylor (Analyst, March 1919). It depends on 
 the catalytic fractional combustion of the carbon monoxide 
 and subsequent estimation of the carbon dioxide by a con- 
 ductivity method. 
 
SECTION IX. CARBON DIOXIDE 
 
 Occurrence. Carbon dioxide occurs in large quantities 
 in a pure state, issuing from fissures in the earth, usually 
 in the neighbourhood of volcanoes ; in caverns, especially 
 in limestone districts, and also with water in mineral springs, 
 e.g. the mineral springs of the Volcanic Eifel and other 
 springs in Germany and France, the Saratoga springs in 
 New York, etc. In addition, carbon dioxide is present in 
 small quantities in the air (cf. p. 59), 
 
 Properties of Carbon Dioxide. Carbon dioxide 
 (carbonic anhydride, carbonic acid gas) is a colourless gas 
 with a slight acid odour and taste. It is characterized by 
 being easily liquefiable on simple application of pressure at 
 the ordinary temperature, and by its relatively high solu- 
 bility in water. 
 
 The following table gives the relation between temper- 
 ature, pressure and solubility : 
 
 Temperature C 
 
 o 
 
 5 
 
 10 
 
 i^ 
 
 20 
 
 ,0 
 
 40 
 
 5 
 
 60 
 
 C.c. gas at N.T.P. dissolved by\ 
 
 
 
 
 
 
 
 
 
 
 i c.c. of water under a pressure 
 
 
 
 
 
 
 
 
 
 
 of i atm. exclusive of water V 
 
 I-7I3 
 
 1-424 
 
 1-194 
 
 1-019 
 
 0-878 
 
 0-665 
 
 0-530 
 
 0-436 
 
 o'359 
 
 vapour (Bohr and Bock, 
 
 
 
 
 
 
 
 
 
 
 Annalen, 44, (1891), 318) . . j 
 
 
 
 
 
 
 
 
 
 
 At increased pressures the solubility does not follow 
 Henry 'slyaw closely, being, according to Wroblewski (Comptcs 
 Rend., 94, (1882), 1355), as follows : 
 
 Pressure in atms. (ab- 
 
 
 
 
 
 
 
 
 solute) 
 
 i 
 
 5 
 
 10 
 
 15 
 
 20 
 
 25 
 
 30 
 
 Solubility in c.c. per 
 
 
 
 
 
 
 
 
 c.c. water at i2'4C. 
 
 roS6 
 
 5'i5 
 
 9'65 
 
 13-63 
 
 I 7 -II 
 
 20*31 
 
 23^5 
 
CARBON DIOXIDE 
 
 257 
 
 The specific heat shows a much larger temperature 
 coefficient than that of most other gases being given by the 
 following expression (Holborn and Henning, Annalen, [4], 
 18, (1905), 7139; 23, (1907), 809) 
 
 C = 0'20IO -f 0-0000742 0-OOOOOOOI& 2 
 
 over the range 0-1400 C. where C p = mean specific heat, 
 and t = C., while according to Crofts (Chem. Soc. Trans., 
 (1915), 290) 
 
 C v 0-1500 + 0-000052^ 
 
 where C,, is the mean specific heat between t and 15*5 C. 
 
 Carbon dioxide passes through indiarubber with greater 
 rapidity than do most other gases (cf. p. 10). 
 
 An aqueous solution of carbon dioxide is slightly acid 
 to litmus ; the acid H 2 CO 3 is, however, almost entirely 
 undissociated. Crystalline hydrates are formed at low 
 temperatures. 
 
 On heating to very high temperatures carbon dioxide 
 undergoes dissociation into carbon monoxide and oxygen, as 
 is seen from the following table (*Nernst and v. Wartenberg, 
 Z.physik. Chem., 56, (1906), 548 ; f Bjerrum, Z.physik. Chem., 
 79, (1912), 537) : 
 
 TABLE 28. 
 DISSOCIATION OF CARBON DIOXIDE. 
 
 Temperature C. 
 
 *I02 7 
 
 *II27 
 
 *I205 
 
 t2367 
 
 f26o6 
 
 t26 2 ; 
 
 f26 7 2 
 
 t28 4 3 
 
 Percentage of carbon 
 
 
 
 
 
 
 
 
 
 dioxide which has 
 
 
 
 
 
 
 
 
 
 undergone dissocia- 
 
 
 
 
 
 
 
 
 
 tion . . 
 
 0-00414 
 
 0-01-0-02 
 
 0-029-0-035 
 
 21'0 
 
 51-7 
 
 49-2 
 
 64-7 
 
 7 6-I 
 
 These values are determined experimentally for a pressure 
 of i atmosphere. 
 
 At reduced pressures the dissociation is more pronounced. 
 
 By the action of the silent discharge, or ultra-violet light, 
 dissociation into carbon monoxide and oxygen takes place. 
 For a discussion of the equilibrium between carbon dioxide, 
 carbon monoxide and carbon 
 
 CO 2 -f C ^ 2CO 39,300 calories, 
 cf. pp. 238 and 303. 
 
 A. 17 
 
258 INDUSTRIAL GASES 
 
 The conversion of carbon dioxide into carbon monoxide 
 by the water gas reaction has also been dealt with elsewhere. 
 Carbon dioxide is converted into methane by passage over 
 reduced nickel at 350 C. in like manner to carbon monoxide 
 (Sabatier and Senderens, Comptes Rend., 134, (1902), 514, 689). 
 
 Carbon dioxide is decomposed by heated magnesium 
 with separation of carbon. It is a non-supporter of 
 combustion and on this account is employed as a fire 
 extinguisher. Although its poisonous action is slight, it 
 produces suffocation by lowering the concentration of oxygen. 
 Exhaled air contains some 4-4 % of carbon dioxide, about 
 2 Ibs. being expired daily by an average adult. Carbon 
 dioxide is an important factor in the rusting of iron when 
 oxygen and water are also present. At high temperatures 
 carbon dioxide is an energetic oxidizing agent, thus metals 
 such as iron are attacked rapidly by the gas at a red heat. 
 
 It has been observed by Fischer (/. Soc. Chem. Ind., 
 (1915), 726) that carbon dioxide in the gaseous state behaves 
 as a fertilizer in promoting plant growth. 
 
 Liquid Carbon Dioxide. liquid carbon dioxide is a 
 colourless, very mobile liquid, having the following vapour 
 pressures at the temperatures specified : 
 
 Temperature C. 
 Solid. 
 
 78*2 70 60 50 40 30 20 10 o 10 20 30 40 
 
 Vapour pressure in atms. 
 (absolute) 
 
 35-4 46-0 58-8 73-8 91-0* 
 
 34*3 44'2 56-3 70-7 t 
 roo 1-88 3-92 6-73 9-88 14-21 19-52 25-83 J 
 
 * Regnault, 1862. f Amagat, 1892. \ Zeleny and Smith, 1906. 
 
 The density of the liquid at 15 C. is 0*814 (Amagat). 
 lyiquid carbon dioxide is only slightly soluble in water, but 
 is readily miscible with alcohol, ether, etc. 
 
 For further information as to properties, see Tables 12 
 and 13, also pp. 42-45. 
 
 Solid Carbon Dioxide. Carbon dioxide readily assumes 
 the solid state (about one- third of the whole) on simple release 
 
CARBON DIOXIDE 259 
 
 of the liquid to atmospheric pressure. Solid carbon dioxide 
 is a white, crystalline, snow-like substance, which can be 
 handled with impunity in spite of its low temperature 
 (about 78 C.) if not pressed too much. On account of 
 its high latent heat of vaporization, it may be kept for a 
 considerable period without special thermal insulation. 
 Its vapour pressure is equal to i atm. at 78*2 (Zeleny and 
 Smith, Physik. Zeit., 7, (1906), 670). On reducing the 
 pressure to 2*5 mm. the temperature falls to 130 C. 
 Mixed with ether or chloroform, an excellent refrigerating 
 medium is obtained by means of which temperatures as 
 low as 85 C., or even lower if the pressure be reduced, 
 may be obtained. Its use also forms a convenient method 
 of maintaining moderately low temperature baths in the 
 laboratory, e.g. 20 to 50 C. Thus, an alcohol bath 
 may be readily maintained at a constant temperature in the 
 region indicated by successive additions of small quantities 
 of solid carbon dioxide. 
 
 MANUFACTURE OF CARBON DIOXIDE 
 
 General. It is not difficult to produce carbon dioxide 
 in a practically pure state technically, but, as in the case of 
 sulphur dioxide, it is usually more economical either to effect 
 a concentration of the gas from mixtures containing it, or 
 to use it in the dilute condition. 
 
 Consequently, it will be convenient to deal separately 
 with processes producing pure and dilute gases respectively. 
 
 Generation of Pure Carbon Dioxide 
 
 (i) Utilization of Natural Sources. Carbon dioxide 
 is obtained commercially from the Saratoga springs in New 
 York, also from springs in South Germany and France. In 
 some cases the gas is under considerable pressure as it 
 issues from the ground, e.g. 15 atms. ; the carbon dioxide 
 is usually accompanied by a little sulphuretted hydrogen. 
 
 The procedure is very simple, consisting merely in 
 separating the gas from the accompanying water, washing 
 with water to ; which permanganate may be added in order to 
 
260 INDUSTRIAL GASES 
 
 remove sulphuretted hydrogen, etc., drying with calcium 
 chloride, and finally liquefying by compression. If accom- 
 panied by nitrogen or air, concentration may be effected 
 by absorption by water under pressure, with subsequent 
 disengagement on release of the pressure, the water being 
 circulated for further absorption (cf. also the general dis- 
 cussion of methods of concentration, p. 263). 
 
 Carbon dioxide may also be extracted from natural 
 waters containing the gas in solution by combined evacua- 
 tion and steam heating. Although the gas may be obtained 
 in this way at low cost, the cost of transport makes other 
 methods of production more economical for places at a 
 distance from the springs. 
 
 (2) By the Thermal Decomposition of Carbonates. 
 Carbonates, such as calcium carbonate, are fairly easily 
 decomposed on moderate heating. Thus, the dissociation 
 pressure of calcium carbonate varies with the temperature 
 as shown by the following table (Johnson, /., Amer. Chem. 
 Soc., 32, (1910), 938) taken from a smoothed curve : 
 
 Temperature C 600 650 700 750 800 850 
 
 pcoz (mm. mercury) .. .. 2 8 25 67 170 380 
 
 It will be evident that a comparatively high temperature, 
 say about 800 C., is necessary for the rapid expulsion of 
 the carbon dioxide unless means are provided for main- 
 taining a low carbon dioxide pressure. This is most readily 
 effected by a current of steam, as e.g. in the process of 
 Grouven (D.R.P. 26248/83), according to which limestone 
 is heated to moderate redness in the upper portion of vertical 
 retorts of about 10 in. diameter, in a current of steam 
 admitted at the lower ends of the retorts. The steam is 
 subsequently removed by condensation. On similar lines 
 are the patents of Thorn and Pryor (B.P.s 20102/08 and 
 24332/08). Superheated steam is employed, arrangements 
 being provided for recuperation of heat ; precautions are 
 taken against ingress of air. Instead of limestone may be 
 used dolomite or magnesite, which have the advantage of 
 suffering decomposition at considerably lower temperatures. 
 It has been proposed by Westman (B.P. 10705/00) to effect 
 
CARBON DIOXIDE 261 
 
 the decomposition of limestone by circulating a mixture of 
 steam and carbon dioxide through a heater and then through 
 a shaft containing the limestone, cooling by injection of 
 water, returning to the pump and so forth. 
 
 (3) By the Action of Acids on Carbonates. Carbon 
 dioxide is still prepared by the action of dilute hydrochloric 
 or sulphuric acid on carbonates, such as limestone (whiting), 
 marble, magnesite, etc., e.g. for such purposes as the manu- 
 facture of artificial mineral waters. Magnesite is often 
 employed in Germany, the resulting solution being worked 
 up for magnesium sulphate. A generator for the pro- 
 duction of carbon dioxide in this way consists of a 
 lead-lined cast-iron or copper vessel fitted with stirring 
 gear, acid supply tank, safety valve, etc. Sulphuric acid 
 is usually employed in preference to hydrochloric, as not 
 giving rise to volatile impurities, but has the disadvantage 
 of yielding an insoluble sludge with calcium carbonate. 
 In both cases it is important that the acid should be 
 free from arsenic. Marble often contains organic matter. 
 Sodium bicarbonate is sometimes employed, giving a very 
 pure but very expensive gas. L,ead is always liable to 
 be present and the use of such generators has been largely 
 superseded by the cheap and pure liquid carbon dioxide. 
 If desired the apparatus may be adapted to produce the 
 carbon dioxide under the pressure required for the saturation 
 of the mineral waters, by the employment of an acid reservoir 
 the top of which is connected to the gas exit of the generator. 
 The gas leaving the generator is freed from acid spray by 
 scrubbing with water, which may be distributed on lumps 
 of marble or limestone, Organic compounds and sulphur- 
 etted hydrogen may be removed by washing with per- 
 manganate solution, while complete elimination of acid 
 spray is sometimes ensured by washing with sodium bicar- 
 bonate solution. When the gas is being generated with 
 sulphuric acid, permanganate may be added directly to the 
 generator. 
 
 In order to avoid the use of sulphuric acid, proposals have 
 been made by Mackey and Carrol (B.P. 109511/16) to treat 
 
262 INDUSTRIAL GASES 
 
 calcium carbonate with a solution of nitre cake (the NaHSO 4 
 and Na 2 SO 4 mixture resulting as a waste product in the 
 manufacture of nitric acid from Chile saltpetre), use being 
 made of the mixture of calcium and sodium sulphates 
 produced, for glass manufacture, etc. 
 
 A cyclic process has been proposed by Howard (D.R.P. 
 132623/00) in the production of bisulphite by the action of 
 sulphur dioxide (burner gases) on sodium sulphite solution, 
 half of the resulting bisulphite solution to be used to generate 
 carbon dioxide by interaction with hot sodium carbonate 
 solution 
 
 Na 2 C0 3 + 2NaHS0 3 = 2Na 2 SO 3 + H 2 O + CO 2 
 
 The sodium sulphite solution is re-treated with sulphur 
 dioxide, half of it being returned to the cycle while the 
 remainder is marketed ; the carbon dioxide is cooled and 
 washed with sodium carbonate solution. 
 
 According to Behrens (D.R.P. 305417/17) neutral or 
 basic carbonates are decomposed by heating with water 
 under pressure to 150 C. or over. 
 
 (4) Production of Carbon Dioxide as a By-product 
 in Fermentation Processes. Carbon dioxide is produced in 
 enormous quantities by alcoholic fermentation in the manu- 
 facture of beer, etc. According to Goosmann, i Ib. of carbon 
 dioxide results from each 5-6 gallons of wort. As a rule, 
 the gas is allowed to escape, but in some cases is collected. 
 If the gas be drawn from the vats without access of air 
 the treatment is simple and direct compression may be 
 performed. If, on the other hand, the carbon dioxide is 
 obtained only in the dilute state, concentration must be 
 effected before liquefaction by one or other of the methods 
 described below. The carbon dioxide obtained in this way 
 has an odour of fusel oil, which is not detrimental if the gas 
 is to be used for beer raising ; if for other purposes purifica- 
 tion by permanganate solution, sulphuric acid, etc., is 
 necessary. 
 
 (5) Other Methods for the Production of Carbon 
 Dioxide. Among other methods of producing pure carbon 
 
CARBON DIOXIDE 263 
 
 dioxide may be mentioned that due to Wallace and Ball (B.P. 
 24652/94 cf. also Lane and Pullman, D.R.P. 77150/93). 
 In this cyclic process, air is passed first through a retort 
 containing coke whereby carbon monoxide is generated, and 
 then through a second retort charged with copper oxide. 
 Carbon dioxide is thus formed and reaching again the coke 
 retort, each volume produces two volumes of carbon mon 
 oxide, which in turn give two volumes of carbon dioxide 
 
 CO -> C0 2 -> 2CO -> 2C0 2 
 
 one of which is retained in the cycle while the other is 
 removed to a gas-holder. Nitrogen is eliminated by passing 
 the first portions to waste, or alternatively the apparatus 
 may be filled with carbon dioxide at the outset. 
 
 Concentration of Carbon Dioxide from Mixtures 
 with other Gases 
 
 (i) By means of Water under Pressure. Reference 
 has already been made under the manufacture of hydrogen, to 
 the removal of carbon dioxide : (a) from water gas which has 
 been passed over a heated catalyst and contains some 30 % 
 carbon dioxide, in the B.A.M.A.G. continuous catalytic pro- 
 cess (p. 159) ; (b) from blue water gas containing some 5 % 
 carbon dioxide, as a preliminary to fractionation in the 
 Ivinde-Frank-Caro process (p. 172). Although the recovery 
 of carbon dioxide is not necessarily carried out, it is easily 
 realized on the release of the water from the scrubber, 
 when most of the carbon dioxide is disengaged, accompanied 
 by some sulphuretted hydrogen together with small quanti- 
 ties of nitrogen, hydrogen, carbon monoxide, etc. The 
 utilization of such carbon dioxide for the production of 
 ammonium carbonate, cf. B.P.s of the Badische Co. 23939/14 
 and 24042/14, when the hydrogen is being produced by the 
 continuous catalytic process for the synthetic manufacture 
 of ammonia, is interesting, the quantity of carbon dioxide 
 being more than sufficient for the saturation of the ammonia 
 simultaneously produced (cf. p. 215). Another similar 
 process consists in the preliminary production of ammonium 
 
264 INDUSTRIAL GASES 
 
 carbonate and conversion into ammonium sulphate by 
 interaction with gypsum, thus avoiding the use of sulphuric 
 acid (Badische Co., B.P. 27962/13). 
 
 For other references to this subject cf. " Purification of 
 Hydrogen," p. 207. 
 
 (2) By the Alternate Formation and Decomposition 
 of Alkali Bicarbonates in Solution. Some reference to the 
 use of ammonium hydroxide and of sodium and potassium 
 carbonates for this purpose has been made on p. 210. In 
 the Glaus process (q.v.) ammoniacal liquor is used, carbon 
 dioxide being subsequently expelled without noteworthy 
 loss of ammonia by heating to about 90 C. The process 
 most generally used, however, is that depending on the use 
 of sodium or potassium carbonate solutions. In view of 
 its greater solubility and consequent greater absorptive 
 power, potassium carbonate is usually employed in pre- 
 ference to the corresponding sodium salt. An important 
 consideration in the economics of such a process lies in the 
 proper recuperation of the large quantities of heat involved 
 in changing the temperature of the liquor passing round the 
 cycle. In order to avoid this troublesome point the lye 
 may be maintained at constant temperature and the dis- 
 sociation controlled by variation of pressure. Since, how- 
 ever, the exact procedure is largely conditioned by the 
 particular method of obtaining the dilute carbon dioxide, 
 further details will be given under the different processes. 
 
 (3) By Liquefaction. According to Leslie (B.P. 11902/06) 
 cf. also Windhausen, D.R.P. 45102/87, carbon dioxide is 
 separated from furnace gases by compressing, drying, and 
 subsequently cooling the gases to a low temperature. The 
 carbon dioxide separates out in the liquid state while the 
 other gases pass out through a heat-interchanger. Reference 
 to p. 258 will indicate the partial pressures of carbon dioxide 
 which must be attained before any liquefaction can ensue. 
 
 Production and Concentration of Dilute Carbon 
 Dioxide from Products of Combustion. Attention has 
 already been paid, under the manufacture of nitrogen, to the 
 production of a mixture of carbon dioxide and nitrogen free 
 
CARBON DIOXIDE 265 
 
 from carbon monoxide, hydrogen and oxygen. For some uses 
 further treatment is unnecessary, but when pure carbon 
 dioxide is required for purposes of liquefaction, etc., a 
 process somewhat as follows is adopted, depending on the 
 cyclic alkali bicarbonate system proposed by Ozouf in 1865, 
 and first applied technically by I/uhmann. 
 
 The starting material is usually coke, which is burnt with 
 a mechanical stoker or with other precautions to ensure 
 regular combustion with the minimum excess of air, or 
 alternatively first gasified in a producer, the resulting air 
 producer gas being burnt with a secondary air supply in a 
 combustion chamber (cf. Schmalotta, Z. angew. Chem., 
 (1900), 1284). In the former case secondary air may be 
 admitted behind the bridge of the fire-box to remove any 
 hydrogen, carbon monoxide, and sulphuretted hydrogen. 
 The complete conversion of the last mentioned impurity 
 to sulphur dioxide is particularly important since it would 
 otherwise accumulate in the potash lye with deleterious 
 effect. In either case the heat of combustion is employed 
 for heating a boiler containing potash lye, to which plant we 
 shall have occasion to refer presently. Theoretically, with 
 just sufficient oxygen for complete combustion, the carbon 
 dioxide content of the flue gases should be some 20 % ; 
 in practice about 16 % is realized. After passing through a 
 water scrubber, where dust and sulphur dioxide are removed 
 and which may be packed with lumps of limestone, the 
 temperature of the washing water being about 40 C., the 
 cleansed and cooled gases enter the absorber which may 
 take the form of a coke tower, a suitable capacity of which 
 is some 10 ft 3 ./lb. carbon dioxide/hour according to Goos- 
 mann, or of chambers fitted with baffles and dashers or of 
 such chambers followed by a tower. Counter-current 
 scrubbing with potassium carbonate solution, usually con- 
 taining about 15-20 grams K 2 CO 3 /ioo grams solution, is 
 carried out, the temperature of the liquor being about 
 30-40 C. Only about half the carbon dioxide is absorbed, 
 the exact amount depending on the efficiency of the absorp- 
 tion arrangements, the rest passing to waste with the nitrogen 
 
268 INDUSTRIAL GASES 
 
 which it is heated ; the spent lye flows back through the 
 second heat-interchanger and a cooler to the absorber. 
 
 The Production and Transport of Liquid Carbon 
 Dioxide. Before liquefaction, carbon dioxide must be 
 dried thoroughly, and this is usually accomplished by passing 
 the gas through drying chambers packed with granular 
 calcium chloride, either at the ordinary pressure or after 
 the first stage of compression. In order to avoid intro- 
 duction of moisture in the second or further stages of the 
 compression, glycerol may be used for the internal lubrication 
 of the pump, being subsequently separated. A balancing 
 gas-holder is used before the compressor and should be of 
 the annular water-channel type in order to minimize loss 
 of carbon dioxide by solution. 
 
 lyiquid carbon dioxide is transported in cylinders which 
 may hold about 25 or 66 Ibs. On account of its very high 
 coefficient of expansion, great care must be taken in filling 
 the cylinders to ensure that the proper charge is not ex- 
 ceeded and that the cylinder shall not be exposed to the 
 sun or hot situations. 
 
 The question of the degree of filling is discussed very 
 fully by Stewart (see p. 44), who recommends a filling of 
 62 % by weight of the water capacity or 38-8 Ibs. carbon 
 dioxide per ft. 3 of cy Under space, assuming a maximum 
 possible temperature of 49 C. 
 
 The recommendations of the British Parliamentary 
 Committee on the Manufacture of Compressed Gas Cylinders 
 (1895) are that the maximum charge shall be 47 lbs./ft. 3 for 
 this country and 41*7 lbs./ft. 3 for the tropics, while a test 
 pressure of 224 atms. is specified. The German railway 
 regulation of i kilo. /i -34 litres corresponds with the higher 
 figure. Absence of air in the cylinders is important since 
 each per cent, of air involves an increase in pressure of the 
 order of 4-5 atms. at temperatures between 40 and 60 C. 
 
 The Production and Transport of Solid Carbon 
 Dioxide. In order to avoid the inconvenience of handling 
 and the expense of transport of cylinders, the weight of which 
 is of the order of five times that of the liquid carbon dioxide 
 
CARBON DIOXIDE 269 
 
 itself, the substance is sometimes sent from tne works in 
 the solid state* for use when consumption is to be more or less 
 immediate and the distance of transport is relatively small. 
 The carbon dioxide snow is compressed in wooden moulds. 
 
 Applications of Carbon Dioxide 
 
 (a) In the Solvay Ammonia-soda and the Claus- 
 Chance Sulphur Recovery Processes. One of the most 
 important applications of carbon dioxide is in connection with 
 the manufacture of sodium carbonate, both by the old I,eblanc 
 process and by the newer ammonia-soda Solvay process. 
 We will deal first with the latter process. The dilute carbon 
 dioxide gases, from special kilns and containing some 30 % 
 carbon dioxide, are used without concentration. The 
 process consists in the double decomposition of sodium 
 chloride and ammonium bicarbonate with the production 
 of ammonium chloride and sodium bicarbonate. Ammonia 
 is first passed into saturated brine and the solution then 
 saturated with carbon dioxide in a tower or other absorber 
 at a temperature of 25-30 C. With the high towers 
 which are often employed, the hydrostatic head of brine 
 may cause a pressure of some 2 atms. on the gases entering 
 at the bottom. Conditions are so adjusted that the sparingly 
 soluble sodium bicarbonate separates out ; the ammonia is 
 recovered from the solution by boiling with lime. The 
 bicarbonate is decomposed by calcination, the gases, 
 containing in practice some 50 % carbon dioxide, being 
 collected and returned to the cycle. 
 
 The Glaus-Chance process has been used to some extent 
 in connection with the L,eblanc process and consists in the 
 recovery of the sulphur from the " vat waste " (mostly 
 calcium sulphide) by treatment while suspended in water 
 with gases containing carbon dioxide, when calcium carbonate 
 and sulphuretted hydrogen result. 
 
 (b) In the Manufacture of Artificial Mineral Waters. 
 
 * Solid carbon dioxide is conveniently prepared in the laboratory by 
 tilting a cylinder so that the valve delivers liquid, binding a canvas bag 
 over the aperture and releasing the liquid, preferably in a series of jerks. 
 
266 INDUSTRIAL GASES 
 
 and oxygen. The saturated lye now passes to the boiler 
 through a heat-interchanger in counter-current to the hot 
 lye leaving the same. This boiler, as stated above, is heated, 
 to a little above 100 C., by the combustion from which the 
 carbon dioxide results. After giving up its carbon dioxide, 
 the hot spent lye is taken first to the heat-interchanger and 
 then through a cooler to the absorber again. The moist 
 carbon dioxide leaving the boiler is cooled by a system of 
 coils traversed by water, the condensed moisture being 
 returned to the boiler. The heat of condensation of the 
 steam may also be utilized for heating up the saturated lye. 
 
 Instead of using potassium carbonate, it is possible to 
 operate with a solution of sodium carbonate containing e.g. 
 6 grams Na 2 CO 3 /ioo grams solution, but the results are 
 less favourable. Further, as in the Stirth process (vide 
 infra), the variation in the carbon dioxide content of the 
 lye may be produced by alteration of pressure at constant 
 temperature. It has been found that the addition of froth- 
 producing substances, such as soap, is beneficial both as 
 regards the absorption and the disengagement of the carbon 
 dioxide. According to some systems, producer gas is used, 
 part being burnt under the lye boiler and part in a gas 
 engine providing the necessary power, the carbon dioxide 
 from both combustions being utilized. 
 
 Carbon dioxide produced by concentration in this way 
 has usually a high degree of purity. 
 
 Siirth System. In this instance the exhaust gases from 
 an internal combustion engine are used as a source of 
 carbon dioxide, the engine providing the power required 
 for the concentration process. Working in this way, the 
 combustion is under exact control. Using suction gas 
 e.g. of the percentage composition 
 
 Hydrogen . . . . . . 15*0 
 
 Carbon monoxide . . . . 27*0 
 
 Carbon dioxide . . . . 5*5 
 
 Methane . . . . . . 0*5 
 
 Nitrogen . . . . . . 52*0 
 
CARBON DIOXIDE 267 
 
 and diluting with air to, say 30 C.H.U. net calorific value 
 per ft. 3 (cf. p. 346), the percentage of carbon dioxide in the 
 water-free product would be some 16 %. The sensible heat 
 of the exhaust gas is utilized by passage through a boiler in 
 which the saturated lye is heated ; the cooled gases, after 
 traversing a scrubber, are compressed to about 5 atms. and 
 enter the^ absorber which is fed with potash lye at about 
 100 C. As the lye leaves the absorber, its pressure is 
 released to atmospheric, and on entering the boiler carbon 
 dioxide is disengaged. No heat-interchangers are used, and 
 apart from losses, no temperature changes occur in the lye. 
 It is stated that a fuel consumption of J to f Ib. coke per Ib. 
 carbon dioxide produced is sufficient. 
 
 Production and Concentration of Dilute Carbon 
 Dioxide from Lime-kiln Gases. This method of manufac- 
 ture of dilute carbon dioxide is usually employed in connection 
 with the manufacture of sodium carbonate by the " ammonia- 
 soda " process. For this purpose it is advisable that the 
 concentration of carbon dioxide in the gases should not fall 
 below 30 %, consequently the kilns are made very large. In 
 order to effect fuel economy the kilns are generally internally 
 fired by coke mixed with the limestone, usually in the 
 proportion of about i : 7, the carbon dioxide from the 
 combustion being also utilized. In some cases, however, 
 the kiln is heated by gas from a separate coke producer, the 
 gas being burnt in the kiln by the admission of secondary air. 
 When required for use in the dilute state the gas is freed from 
 dust in a plate washer or in a coke scrubber. The use of 
 magnesite results in a higher carbon dioxide concentration 
 on account of the lower decomposition temperature of this 
 carbonate as compared with limestone. 
 
 In order to effect concentration of the gases, similar arrange- 
 ments to those for dealing with products of combustion are 
 usually adopted. The kiln gases pass through a heat-inter- 
 changer to a coke scrubber and then to the absorption towers. 
 The saturated lye traverses a second heat-interchanger in 
 counter-current to the lye leaving the boiler and then passes 
 through the heat-interchanger mentioned above to a boiler in 
 
270 INDUSTRIAL GASES 
 
 In this important application of carbon dioxide the pure 
 gas is required, and, for reasons to which reference has been 
 made, liquid carbon dioxide is now usually employed in 
 preference to the gas generated by the action of acids on 
 carbonates. The gas is generally taken from a gas-holder 
 and forced by a pump into a saturator vessel of gun metal 
 lined with tin, into which water is also pumped at the same 
 time. 
 
 Any required additions such as sodium carbonate, 
 syrups, etc., are made to the individual bottles which are 
 then rilled with the water saturated with carbon dioxide at 
 the prescribed pressure, means being provided for the 
 escape of air. Complete expulsion of air is important since 
 its presence causes the mineral waters to become " flat " 
 rapidly on opening. According to Mitchell (Thorpe's 
 " Dictionary of Applied Chemistry," 1912) the actual 
 pressure in unsweetened mineral water bottles is usually 
 45-55 lbs./in. 2 corresponding to a bottling pressure of 
 120 lbs./in. 2 . In the case of lemonade and the like the 
 water is saturated at only about 60-80 lbs./in. 2 . Soda 
 water siphons are bottled at a pressure of 150 lbs./in. 2 . 
 
 (c) In Refrigeration Plant. Carbon dioxide is exten- 
 sively used in refrigeration plant, especially on board ship ; 
 the chief advantages in comparison with ammonia, which 
 gives a somewhat more efficient cycle for normal refrigeration 
 temperatures, are the small dimensions of the compressor, 
 the relative absence of danger and nuisance from leakages, 
 the use of copper tubing and the smaller cost of the carbon 
 dioxide. Carbon dioxide plants are capable of working 
 efficiently to a lower temperature than ammonia plants. 
 The small sized compressors are generally constructed of 
 bronze. In view of the high working pressure, the glands 
 on the cylinders are usually sealed with oil maintained at a 
 pressure slightly higher than that of the gas, leakage being 
 thus entirely eliminated at these points. 
 
 (d) Other Applications of Carbon Dioxide. Among 
 the many uses of carbon dioxide may be mentioned the 
 following. 
 
CARBON DIOXIDE 271 
 
 The use of carbon dioxide for the compression of fluid steel 
 in the ingot moulds was introduced by Messrs. Krupp, the 
 liquid carbon dioxide serving as a convenient means of 
 generating enormous pressures. 
 
 Experiments have been carried out recently (cf. J. Soc. 
 Chem. Ind., (1918), 224 R) on the use of carbon dioxide for 
 the destruction of pests In grain by forcing the gas into the 
 air-tight silos in which the grain is stored ; some 14 ft. 3 of 
 carbon dioxide are sufficient for the submersion of i ton of 
 grain. According to Dendy (Nature, 103, (1919), 55) air con- 
 taining 20 % carbon dioxide is more effective than pure 
 carbon dioxide, the spontaneous accumulation of carbon 
 dioxide in an air-tight silo being sufficient. 
 
 Carbon dioxide is employed for fire extinction, usually 
 in the form of an aqueous solution produced when required 
 by the action of sulphuric acid on an excess of sodium 
 carbonate solution in a special generator. 
 
 Iviquid carbon dioxide has been applied as a source of 
 motive power for torpedoes and the like ; for operating 
 pneumatic railway signals in outlying districts, thus avoiding 
 the transmission of compressed air over long distances ; for 
 refloating sunken ships, etc. lyiquid carbon dioxide is also 
 used extensively for carbonating, clarifying and raising 
 beer. In the raising operation, the cylinder is fitted with a 
 reducing valve, the low pressure side being connected to 
 the barrel, keeping the beer saturated with carbon dioxide 
 in addition to avoiding the necessity for pumping. Other 
 applications are the protecting of wines from moulds ; the 
 synthetic production of salicylic acid from phenol (Chem. 
 Trade /., 62, (1918), 337) ; the manufacture of white 
 lead ; the decomposition of calcium or strontium sugar 
 compounds in sugar refining ; the precipitation of pure 
 alumina from sodium aluminate solutions produced from 
 bauxite or cryolite, pure alumina being precipitated and 
 sodium carbonate remaining in solution ; the manufacture 
 of bread ; the production of carbonates, etc. 
 
 An interesting application of carbon dioxide is in the 
 production of formates by interaction with hydrogen in the 
 
272 INDUSTRIAL GASES 
 
 presence of a catalyst (cf. Bredig and Carter, B.P. 801/15, 
 also Ber., 47, (1914), 541 ; Chem. Zeit., 39, (1915), 72). 
 According to these authors potassium formate may be 
 produced by vigorous agitation of a 5 % aqueous solution of 
 potassium bicarbonate containing some 0*75 % by weight 
 of platinum black, with hydrogen at a pressure of 60 atms. 
 and at a temperature of 70 C. For the apparatus used in the 
 early investigations see Stuckert and Enderli, Z. Elektrochem., 
 19, (1913), 570. Under these conditions a 20 % yield of 
 formate is obtained. The same effect is produced by 
 treating a solution of borax with carbon dioxide and hydrogen 
 simultaneously or, alternatively, calcium carbonate may be 
 treated with hydrogen in the presence of platinum black 
 with the production of calcium formate. B.P. 9762/15 
 relates to the production of the free acid by the interaction 
 of water, hydrogen and carbon dioxide. A similar com- 
 bination may be induced by the action of sodium amalgam 
 on an aqueous solution of carbon dioxide (cf. Waygouny, 
 /. Soc. Chem. Ind., (1916), 736 ; Kolbe and Schmidt, Liebig's 
 Annalen, 119, (1861), 251). 
 
 Carbon dioxide has some antiseptic properties and is 
 used for the sterilization of milk and organic liquids. It is 
 used therapeutically for baths either in presence or absence 
 of water vapour, its action being to induce perspiration ; 
 also in aqueous solution. The gas is used for the destruction 
 of vermin, such as rats, etc. On mixing carbon dioxide 
 to the extent of 5-8 % with acetylene, the smoky character 
 of the flame is lessened. 
 
 Estimation and Testing of Carbon Dioxide. Carbon 
 dioxide is perhaps the easiest of all gases to estimate. When 
 present in small quantities it is readily recognized by its 
 action on lime-water or baryta solution. It is usually 
 estimated by absorption in caustic soda solution. In very 
 small amount, e.g. as in the air, it may be determined by 
 passing through excess standard baryta solution and titrating 
 back with oxalic acid, using phenolphthalein as indicator. 
 One of the chief needs for estimating carbon dioxide is in 
 connection with flue gases, and many forms of automatic 
 
CARBON DIOXIDE 273 
 
 apparatus depending both on absorption with caustic soda 
 and also on physical methods (cf. p. 33) have been devised 
 for this purpose. Space will not permit of a full description 
 of these methods here, but reference may be made to lounge's 
 " Technical Gas Analysis," 1914. 
 
 Commercial liquid carbon dioxide is examined by with- 
 drawing a sample of gas from the inverted bottle. The 
 content of permanent gases (air, carbon monoxide, etc.) is 
 found by absorption of the carbon dioxide by alkali. An 
 approximate estimate of the air content of a cylinder may 
 be obtained by determining the air contents of the first and 
 last portions of the gas delivered from the upright cylinder 
 (lounge, loc. cit.}. According to Werder (Chem. Zeit., (1906), 
 1021) the absence of empyreumatic substances may be 
 judged by the smell and taste ; at least 98 % of the gas 
 should be absorbed by alkali ; the carbon monoxide content 
 should not exceed 0-5 % ; the gas should be free from sulphur 
 dioxide and oxides of nitrogen, and should not decolorize 
 potassium permanganate solution or give a precipitate with 
 silver nitrate solution. 
 
 REFERENCES TO SECTION IX. 
 
 Goosman, " The Carbonic Acid Industry." Chicago, 1907. 
 
 Kausch, " Die Kohlensaure, ihre Herstellung und Verwendung." 
 Hanover, 1909. 
 
 Thorpe, "A Dictionary of Applied Chemistry." London, 1912. Articles 
 on " Carbon Dioxide " and " Mineral Waters." 
 
 Lunge, " Sulphuric Acid and Alkali," vol. iii. London, Third Edition, 
 1911. 
 
 Stewart, " The Physical Properties of Carbonic Acid and the Conditions 
 of its Economic Storage for Transportation," Trans. Amer. Soc. Mech. 
 Eng., 30 (1908), mi. 
 
 A. 18 
 
SECTION X. SULPHUR DIOXIDE 
 
 Properties of Sulphur Dioxide. Sulphur dioxide is a 
 colourless gas with a very characteristic and pungent odour. 
 It occurs in volcanic gases and in very small traces in town 
 air, being chiefly derived from the iron pyrites present in 
 coal. The chief physical properties of this easily liquefiable 
 gas will be found in Tables 12 and 13, pp. 53-6. 
 
 vSulphur dioxide dissolves in water to a considerable 
 extent with evolution of heat, the solubility amounting to 
 47*3 volumes of gas measured at N.T.P., at 15 C. and 
 I atm. pressure, including water vapour, equivalent to 12*16 % 
 by weight. Other values are given in the following table : 
 
 Temperature C. .. .. .. o 10 15 20 30 40 
 
 C.c. of gas (measured at N.T.P.)) 
 
 dissolved by I c.c. of water! 7g .$ 56 - 6 4? - 3 39 - 4 27>2 lg .g 
 
 under a pressure of i atm. in-j 
 
 elusive of water vapour J 
 
 Solid hydrates are formed with water under suitable 
 conditions, 9-15 molecules of water being linked up. The 
 aqueous solutions decompose very slowly at the ordinary 
 temperature with the final production of sulphur and sul- 
 phuric acid, the action being rapid in sealed tubes above 
 160 C. (Jungfleisch and Brunei, Comptes Rend., 156, 
 (1913), 1719). The gas is soluble to a considerable extent 
 in sulphuric acid, one volume of which dissolves about 58 
 volumes of sulphur dioxide at ordinary temperatures ; it 
 is also dissolved by mineral oils, the solutions, if dry, having 
 no action on metals. 
 
 According to von Wartenberg (Z. anorg. Chem., 56, 
 (1908), 320) sulphur dioxide undergoes no appreciable 
 dissociation at 2200 absolute ; cf. also Ferguson, /. Amer. 
 Chem. Soc. t 41, (19*9), 69. A slight decomposition takes 
 
SULPHUR DIOXIDE 275 
 
 place at tlie ordinary temperature under the influence of 
 light, sulphur and sulphur trioxide being produced. 
 
 The most characteristic chemical property of sulphur 
 dioxide is its action as a reducing agent, itself suffering 
 oxidation to sulphuric acid ; thus potassium dichr ornate is 
 reduced to chromic sulphate. In some cases, however, it 
 behaves as an oxidizing agent, thus Smythe and Wardlaw 
 (/. Soc. Chem. Ind., (1915), 797) found that titanium 
 trichloride and stannous chloride were oxidized by sulphur 
 dioxide in warm, strongly acid solution ; the intermediate 
 formation of thionyl chloride is suggested as an explanation. 
 
 Sulphur dioxide has an irritating action on the mucous 
 membrane ; according to the Selby Smelter Commission 
 (U.S. Bureau of Mines, Bull. No. 98), 0^0005% sulphur dioxide 
 can be detected by smell, while 0*05 % is practically un- 
 endurable. A concentration greater than 0*003 % is 
 injurious to vegetation (lyunge). 
 
 When dry, sulphur dioxide has no action on iron even at 
 100 C., but in the presence of moisture a slight action is 
 observed (cf. L,ange, Z. angew. Chem., 12, (1899), 275, 303, 
 595). As liquid sulphur dioxide cannot contain more than 
 about i % moisture at the ordinary temperature, the action 
 is slight, but in sulphur dioxide refrigeration plants, where 
 a considerable temperature rise occurs in the compression, the 
 action becomes of importance. liquid sulphur dioxide is 
 miscible in all proportions with sulphuric anhydride, but 
 immiscible with sulphuric acid. 
 
 Sulphur dioxide may be obtained in the solid state by 
 evaporation of the liquid under reduced pressure. 
 
 MANUFACTURE OF SULPHUR DIOXIDE 
 
 General. The manufacture of sulphur dioxide in the 
 pure state is, in most cases, a question of concentration of 
 the more or less dilute gases obtained in various ways. 
 Although the only process which appears to be in use at 
 the present time is that of Hanisch and Schroder (see below), 
 it will be well to consider briefly some other methods which 
 have been worked or proposed. One of the earliest used 
 
276 INDUSTRIAL GASES 
 
 was the Melsens-Pictet method, depending on the action of 
 concentrated sulphuric acid when dropped into molten 
 sulphur at a temperature of 400 C. This process was 
 used by certain French firms. The moist sulphur dioxide 
 was compressed and cooled to about 10 C. when the gas 
 liquefied ; any water present served to produce hydrates, 
 sufficiently stable to allow of all the sulphur dioxide being 
 subsequently pumped off (D.R.P. 22365/82). One dis- 
 advantage of this method of generating sulphur dioxide is 
 the action of the sulphur on the iron retort, and an improve- 
 ment consists in employing boiling sulphuric acid in a cast- 
 iron retort with molten sulphur floating on the top. In- 
 stead of sulphur, carbon has been used with 91 % acid ; 
 in this case carbon dioxide and carbon monoxide are 
 simultaneously produced (D.R.P. 196371/08). In B.P. 
 1427/83 Ramsay proposes the concentration of sulphur 
 dioxide by absorption from the weak gases with sodium 
 sulphite, sodium hydrogen sulphite being produced, which 
 on heating gives off pure sulphur dioxide. According to 
 Hart (B.P. 13950/85) sulphur dioxide is produced by the 
 action of sulphuric acid (S.G. 1*75) on finely divided iron 
 sulphide at 200 C. The Hanisch and Schroder process 
 (patents B.P.s 2621/83, 6404/85 and 6405/85 ; D.R.P. 
 36721/86 and 52025/90) relates to the absorption of sulphur 
 dioxide from burner gases by cold water and subsequent 
 expulsion by heat; cf. also Basset, B.P. 20667/13. 
 Bergmann and Berliner (D.R.P. 160940/02) propose to realize 
 the same objective by the alternate formation of Ca(HSO 3 ) 2 
 and Ca(H 2 PO 4 ) 2 by the action of sulphur dioxide on CaHPO 4 
 and subsequent reversal of the reaction by heating to 100 C. 
 Moulin and Vandoni (F.P. 432431/10) prescribe the isolation 
 of sulphur dioxide by compression to 30 atms. of gases 
 containing 10-12 % of sulphur dioxide followed by cooling to 
 o C. by means of the cold produced by the expansion of the 
 residual gases in a heat-interchanger. Moore and Wolf, in 
 U.S. P. 1091689/14, advocate absorption in calcium chloride 
 solution at o C. and subsequent release by evacuation. 
 Similarly, U.S.P. 1145579/15 of Garner and Metals Research 
 
SULPHUR DIOXIDE 277 
 
 Co., relates to the sorptionof the gas in charcoal and B.P. 
 107589/17 (Kaltenbach) to the use of alcohol for the same 
 purpose. 
 
 It has been stated above that the only process in use on 
 any important scale for the manufacture of liquid sulphur 
 dioxide is the Hanisch and Schroder process, which uses 
 dilute burner gases as -a source of sulphur dioxide ; some 
 account will therefore be given of the possible ways of 
 producing such gases as opposed to practically pure or 
 highly concentrated sulphur dioxide. 
 
 Production of Dilute Sulphur Dioxide 
 
 The production of sulphur dioxide in a dilute state is 
 undertaken on a very large scale in connection with the 
 manufacture of sulphuric acid and sulphuric anhydride from 
 iron pyrites, from elementary sulphur or from zinc blende, 
 and would require more space for an adequate description 
 than can be allotted in the present volume. Reference should 
 therefore be made to special treatises on this subject. It 
 will, however, be desirable to mention briefly some of the 
 more important patents from the point of view of the present 
 problem. 
 
 According to theory, the combustion of sulphur, using 
 the minimum quantity of air, should give rise to a gas 
 containing 21 % sulphur dioxide, but even when elementary 
 sulphur is used, 7-15 % represents the values realized in 
 practice. If less air is used there is a tendency for the 
 sulphur to sublime as such. With pyrites the concentration 
 is smaller. 
 
 Dilute sulphur dioxide may be produced in a variety of 
 ways, e.g. by melting zinc blende with zinc sulphate (Pernell, 
 D.R.P. 1351/77) ; by the combustion of sulphuretted hydro- 
 gen (Pernell and Simpson, B.P. 14711/86) ; by roasting 
 galena with calcium carbonate (Huntingdon and Eberlein, 
 B.P. 8064/96) ; from " spent oxide," and as a by-product 
 from various manufacturing operations, e.g. cement manu- 
 facture (Basset, B.P. 12027/12). The use of zinc blende is 
 discussed by Hutin (Moniteur Scient., 7, (1917), 25) ; the 
 
278 INDUSTRIAL GASES 
 
 residue is more valuable than in the case of iron pyrites, but 
 the operations are more troublesome. The gases from 
 pyrites burners usually contain small amounts of sulphur 
 trioxide formed by the catalytic action of the burnt pyrites. 
 A mixture of sulphur dioxide and oxygen was formerly 
 prepared for the manufacture of sulphur trioxide by dropping 
 sulphuric acid into incandescent retorts. 
 
 Concentration of Dilute Sulphur Dioxide 
 
 The Hanisch and Schroder Process. This process was 
 first taken up in 1885, an experimental factory being erected 
 by Grillo in Germany, making 12 cwt./diem of liquid sulphur 
 dioxide from gases containing 6 % sulphur dioxide. In 
 1886, a plant turning out 6 tons/diem, working on zinc blende, 
 was operated in Silesia. According to Molinari a factory 
 should have a minimum output of 8-10 tons/diem for 
 economical working. The usual method of operating the 
 process is as follows : Gases from pyrites burners of con- 
 centration about 6 % sulphur dioxide (not below 4 %) are 
 passed through a dust-retaining chamber, then cooled 
 thoroughly and passed to the water absorption towers. 
 Two towers packed with coke and plates are often employed, 
 arranged in series with counter-current circulation of the 
 water. The sulphur dioxide content of the issuing gases is 
 reduced to at least 0*05 %, while the water leaving the first 
 tower contains about i % sulphur dioxide. In order to 
 effect the removal of the sulphur dioxide from this weak 
 solution with the greatest economy of heat, the said solution 
 is passed first through a leaden heat-interchanger in counter- 
 current to the mixture of steam and sulphur dioxide leaving 
 the top of the desaturation tower. leaving this inter- 
 changer at a temperature of about 85 C., the liquid traverses 
 a coil immersed in the heated liquid in the sump of the 
 desaturation tower, being further heated, and is then sprayed 
 in at the top of this tower, which, according to D.R.P. 
 52025/90, contains a series of inclined baffles, steam being 
 injected near the bottom. The liquid flowing out is practi- 
 cally free from sulphur dioxide while the mixture of sulphur 
 
SULPHUR DIOXIDE 279 
 
 dioxide and steam passes, as explained above, to the heat- 
 interchanger and then to a cooler, the condensed water, 
 containing sulphur dioxide, from both being returned to 
 the middle of the desaturation tower. 
 
 A variation is described in D.R.P. 36721/86, according 
 to which the mixture of sulphur dioxide and steam evolved 
 on boiling the dilute liquor, in leaden pans heated by the 
 burner gases, is passed up a tower in counter-current to a 
 stream of cold water. The excess steam serves to heat the 
 cold water practically to boiling point ; the hot water passes to 
 a heat-interchanger in counter-current to the liquid entering 
 the boiling-out pans, while the sulphur dioxide leaves at the top, 
 practically dry. In both cases, final drying of the sulphur 
 dioxide is effected by passage up a coke tower, down which con- 
 centrated sulphuric acid flows, the re-concentration of the sul- 
 phuric acid being accomplished by the waste heat from the 
 py ritesburners. The dry sulphur dioxide then passes to a single- 
 stage bronze pump, where it is compressed to 2^-3 atms. which 
 suffices, after cooling, to produce liquefaction ; an oil-sealed 
 gas-holder, or other equilibrator, is employed. The liquid 
 sulphur dioxide collects in a large wrought-iron receiver fitted 
 with a relief valve for the nitrogen and oxygen present, which 
 are led back to the absorption tower. The liquid sulphur 
 dioxide produced in this way has often a purity of 99*8 %. 
 
 The preparation of aqueous solutions of sulphur dioxide 
 demands no precautions except that it is necessary to cool 
 both the gas and the water. 
 
 Transport of Liquid Sulphur Dioxide. Sulphur di- 
 oxide is put on the market in glass " siphons " for laboratory 
 use in steel cylinders holding from 12 oz. to 2 cwt., or, in 
 Germany, in tank waggons holding as much as 10 tons of 
 sulphur dioxide, some such waggons having 3 cylinders about 
 23 ft. long and 2 ft. 3 in. diameter. Cylinders are fitted 
 with bent tubes connected to the inlet valves to deliver 
 either liquid or gas according to the position of the cylinder. 
 These tubes also serve to indicate the correct degree of 
 filling of the cylinder ; when the cylinder is erect and the 
 valve opened, no liquid should be ejected. 
 
280 INDUSTRIAL GASES 
 
 According to German regulations, the cylinders are 
 tested to 30 atmospheres and the maximum degree of rilling 
 is i kilo, per O'8 litres, i.e. 78 lbs./ft. 3 , or according to Italian 
 regulations, i kilo, per litre, i.e. 62-5 lbs./ft. 3 In this country 
 no specific regulations appear to exist, but the practice of a 
 prominent firm manufacturing sulphur dioxide is to adopt 
 a maximum filling of about 70 Ibs. sulphur dioxide per ft. 3 , 
 the cylinders being annealed and re-tested (to 30 atms.) at 
 least once a year. 
 
 Applications of Sulphur Dioxide 
 
 The various applications of sulphur dioxide may, for the 
 sake of convenience, be discussed under the following 
 headings : 
 
 (1) Manufacture of Sulphuric Acid, Sulphuric Anhy- 
 dride and Sodium Sulphate. It is unnecessary here to do 
 more than mention the use, on an enormous scale, of sulphur 
 dioxide in the manufacture of sulphuric acid by the chamber 
 process and of sulphur trioxide by the " contact process," 
 a mixture of sulphur dioxide and air being passed over 
 heated finely-divided platinum supported on magnesium 
 sulphate or asbestos, or over iron oxide. Sulphur dioxide 
 is also used in the manufacture of salt cake (sodium sulphate) 
 by the Hargreaves process, which depends on the action of 
 a mixture of sulphur dioxide, steam and air on sodium 
 chloride at 400-540 C., sodium sulphate and hydrochloric 
 acid resulting. 
 
 (2) Manufacture of Wood Pulp. Sulphur dioxide is 
 largely used in the preparation of wood pulp for paper 
 manufacture, by the bisulphite process; liquid sulphur 
 dioxide was formerly used to a great extent in the prepara- 
 tion of the liquor and for bringing up to strength, but now 
 pyrites gases are mostly used. 
 
 The process consists in boiling fir or pine in small pieces 
 with calcium bisulphite solution containing excess sulphur 
 dioxide under a pressure of 50-80 Ibs. /in. 2 until all the 
 incrusting matter is dissolved, and then mechanically 
 separating the cellulose from the residue by washing and 
 
SULPHUR DIOXIDE 281 
 
 beating. The spent lyes contain sugars which may be 
 fermented with the production of alcohol, it being stated 
 that some 4000 tons of alcohol are produced annually in 
 Sweden in this way. After the bleaching of the pulp, sulphur 
 dioxide is again used for the removal of the last traces of 
 chlorine. It is important that the sulphur dioxide used should 
 be quite free from sulphur trioxide and some manufacturers 
 use brimstone in preference to pyrites on this account ; the 
 former procedure has the further advantage of furnishing a 
 stronger gas. To free from sulphur trioxide it is necessary 
 to wash the gases with water. 
 
 In the manufacture of bisulphite the well-cooled burner 
 gases are brought into contact with lime or magnesium lime. 
 Various systems are used for effecting this operation 
 (cf. Williams, /. Soc. Chem. Ind., (1913), 457) (i) the 
 gases are injected at the bottom of vessels through which 
 a slow stream of milk of lime flows ; (2) the milk of lime is 
 fed into the upper of two closed tanks fitted with stirring 
 gear, while the sulphur dioxide gases are led into the lower 
 tank and flow to the upper one, being assisted by the reduced 
 pressure produced by a pump attached to the latter when 
 the lower tank is saturated with sulphur dioxide its charge 
 of liquid is run off and replaced by that from the upper one 
 which is filled up with fresh milk of lime; and (3) one or more 
 towers constructed, e.g. of reinforced concrete, and from 60- 
 100 ft. high, are filled with limestone and water is sprayed 
 in at the top while the sulphur dioxide gases are admitted 
 at the bottom if two towers are used, counter-current 
 working is adopted. The third system has the advantage of 
 using unburnt limestone and of requiring less pressure to 
 effect the passage of the gases. 
 
 In each case the liquor passes to storage tanks and is 
 enriched by the gases evolved in the digestion of the wood. 
 The following is a typical example of the percentage com- 
 position of such a liquor : 
 
 Calcium oxide 0-98 
 
 Free sulphur dioxide 2-65 
 
 Combined sulphur dioxide . . . . 1-15 
 
282 INDUSTRIAL GASES 
 
 (3) In Refrigeration Plant. Sulphur dioxide is used to 
 a considerable extent in refrigeration plant, although, of 
 course, it is much less convenient for general purposes than 
 the commonly employed ammonia. The use of sulphur 
 dioxide for this purpose was originally developed by Pictet, 
 its chief advantages over other substances, such as ammonia, 
 lie in its non-injurious action on food, etc., if escape should 
 occur, its low working pressure and its applicability to 
 conditions where no cooling water is available. On the 
 other hand, a considerably larger compressor capacity is 
 required than is the case with ammonia, for example ; 
 sulphur dioxide plants are only used for relatively small 
 installations. Reference has already been made to the action 
 on iron of moist sulphur dioxide when warm ; in this 
 connection it is important to avoid, as far as possible, the 
 presence of air in sulphur dioxide systems as formation of 
 sulphuric acid may occur and set up corrosion. Although 
 iron is protected to some extent by an insoluble coating, 
 bronze is often used for the compressors. Sulphur dioxide 
 has some lubricating properties and consequently the use 
 of oil is unnecessary. 
 
 (4) As a Solvent. In spite of the relative difficulty of 
 handling a liquid with a high vapour pressure at ordinary 
 temperatures, for such purposes, liquid sulphur dioxide 
 is used in certain extraction operations, the principal appli- 
 cation being in the extraction of bones in the manufacture 
 of glue. In the extraction of the fat, sulphur dioxide has 
 the advantage over other solvents of greater penetration of 
 the animal membranes. After this operation is completed, 
 calcium phosphate is extracted by an aqueous sulphur 
 dioxide solution. Sulphur dioxide has been proposed as a 
 substitute for the inflammable carbon disulphide or benzol 
 in oil extraction, but no important technical progress appears 
 to have been made in this direction. 
 
 (5) For Bleaching Purposes. Sulphur dioxide is used 
 to a considerable extent as a bleaching agent for delicate 
 fabrics, etc., which would be injured by the action of more 
 drastic agents, such as chlorine. The bleaching action of 
 
SULPHUR DIOXIDE 283 
 
 sulphur dioxide, unlike that of most other agents/ depends 
 not on oxidation but on reduction, resulting in the formation 
 of colourless leuco-compounds, and in being reversible, 
 e.g. by the action of light. The gas is more effective than the 
 solution, but its action is favoured by damping. 
 
 Among substances bleached by sulphur dioxide may be 
 mentioned wool, silk, straw, cereals (action injurious), 
 oils and their fatty acids (cf . Hird and L,loyd, /. Soc. 
 Chem. Ind., (1912), 317). 
 
 (6) As a Disinfectant. Sulphur dioxide has strong 
 germicidal properties and is used for the disinfection of 
 rooms (by combustion of sulphur or, more conveniently, in 
 the form of liquid), in beer and wine manufacture, for the 
 preservation of fruit, meat, syrups, etc., in ships for rapid 
 disinfection and for the destruction of rats. 
 
 It is also used for the interruption of fermentation in wine, 
 etc., and in the treatment of cutaneous diseases. 
 
 (7) Other Applications. Among other applications of 
 sulphur dioxide may be cited its use as an " antichlor," 
 already referred to in the case of wood pulp, i.e. the removal 
 of the last traces of chlorine from bleached material ; the 
 refining of crude petroleum ; the softening of hides in tanning ; 
 the extraction of alum from shale, and in sugar manufacture, 
 where sulphur dioxide is passed through the juices after, 
 and sometimes before, their treatment with lime which is 
 converted into the difficultly soluble calcium sulphite, the 
 juice being bleached at the same time. Sulphur dioxide 
 has only a slight inverting action on sucrose. In admixture 
 with carbon dioxide, sulphur dioxide is used for fire ex- 
 tinction, in the manufacture of tartaric acid, etc. The use 
 of sulphur dioxide has been proposed for improving the 
 efficiency of engines by utilizing the heat of the exhaust 
 steam. 
 
 The Estimation and Testing of Sulphur Dioxide. 
 Sulphur dioxide is readily detected by its characteristic odour 
 or by its reducing action on potassium dichr ornate paper, 
 etc., and may be conveniently estimated by titration with 
 standard iodine solution. 
 
284 INDUSTRIAL GASES 
 
 According to Haller (/. Soc. Chem. Ind., (1919), 52 T) 
 dilute sulphur dioxide is best estimated by absorbing in 
 caustic soda solution, and, after acidifying strongly with 
 hydrochloric acid, titrating with potassium iodate. Sponta- 
 neous oxidation of the sodium sulphite to sulphate is pre- 
 vented by the addition of a negative catalyst, e.g. glycerol, 
 to the caustic soda solution. On titration of an aqueous 
 solution of sulphur dioxide with a strong alkali, such as 
 caustic soda, methyl orange gives the point of conversion 
 of the caustic soda into sodium hydrogen sulphite. 
 
 liquid sulphur dioxide is tested for water by with- 
 drawing a sample of the liquid under pressure and evapora- 
 ting through tared calcium chloride tubes. Sulphuric acid 
 and lubricating oil are determined in the residue. Arsenic 
 also may be looked for when the sulphur dioxide is to be 
 used in connection with food-stuffs. Carbon dioxide and 
 air may be estimated by bubbling a considerable quantity 
 of the gas through chromic acid solution and examining any 
 gas passing through (cf. lounge, "Technical Gas Analysis," 
 1914, p. 361). 
 
 REFERENCES TO SECTION X. 
 
 Teichmann, " Komprimierte und verfliissigte Case." Halle, 1908. 
 Lunge, " Sulphuric Acid and Alkali," vol. i. Ixmdon, Fourth Edition, 
 
 Harpf, " Flussiges Schwefeldioxyd, Darstellung, Eigenschaften und 
 Versendung desselben," Sammlung chem. und chem-techn. Vortrage von 
 Ahrens, Bd. v., 1900. 
 
SECTION XI. NITROUS OXIDE 
 
 Properties of Nitrous Oxide. Nitrous oxide is a colour- 
 less gas with a faint but characteristic odour resembling 
 that of burnt sugar. It is readily soluble in cold water as 
 below : 
 
 Temperature C 
 
 5 
 
 15 
 
 25 
 
 C.c. of gas (measured at N.T.P.) dissolved by i 
 
 
 
 
 c.c. of water under a pressure of i atm., 
 
 
 
 
 exclusive of water vapour 
 
 1-0480 
 
 0-7378 
 
 o'5443 
 
 The gas is found on the market in the form of liquid, 
 the vapour pressure varying with temperature as follows : 
 
 Temperature C C. 
 Vapour pressure in atms. 
 
 /Regnault (1862) 
 \Villard (1897) 
 
 o 
 36T 
 30-8 
 
 10 
 
 44-8 
 
 20 
 
 55*3 
 49' 4 
 
 30 
 68-0 
 
 40 
 83'4 
 
 Liquid nitrous oxide is very mobile and is colourless. 
 The other important physical properties will be found in 
 Tables 12 and 13, on pp. 53-56. 
 
 Nitrous oxide is an endothermic compound 
 
 2N 2 + O 2 = 2N 2 O 38,000 calories. 
 
 It is, consequently, in a metastable condition at the 
 ordinary temperature. According to Hunter (Z. physik. 
 Chem., 53, (1905), 441) nitrous oxide is decomposed at 700- 
 900 C. into its elements with the formation of small quanti- 
 ties of higher oxides, especially at the higher temperatures ; 
 moisture was found to have little influence. A rough 
 calculation of the equilibrium constant, according to the 
 Nernst Heat Theorem, for a temperature of 2000 C. 
 
 38,000 
 
286 INDUSTRIAL GASES 
 
 indicates that at atmospheric pressure the equilibrium 
 condition corresponds to 0*00013 % f nitrous oxide. Even 
 under the more favourable conditions of a pressure of 1000 
 atmospheres and the same temperature the equilibrium per- 
 centage is only raised to about 0*004 % 
 
 It was observed by Wroczynski (1910) chat no decom- 
 position occurred at 420 C. under a pressure of 600 atmo- 
 spheres. 
 
 Nitrous oxide is an energetic supporter of combustion 
 of e.g. carbon or sulphur, provided that a sufficiently high 
 temperature for the initiation be first produced. It forms 
 an explosive mixture with hydrogen while a mixture with 
 carbon disulphide burns with a very actinic blue flame. 
 Its use as an anaesthetic was first suggested by Humphrey 
 Davy in 1800 ; in small amount it produces a kind of 
 intoxication, hence the name " laughing gas." 
 
 Manufacture 
 
 From Ammonium Nitrate. Nitrous oxide may be 
 produced from other nitrogen compounds in a variety of 
 ways, e.g. by the reduction of nitric acid with a mixture of 
 hydrochloric acid and stannous chloride (Campari) and by 
 the reduction of nitrites with sulphur dioxide, sodium 
 amalgam, etc., but the only method of any practical im- 
 portance is that depending on the decomposition of ammonium 
 nitrate by heating 
 
 NH 4 NO 3 = N 2 O + 2H 2 O + 25,000 calories. 
 
 The decomposition begins at 170 C. and is fairly 
 energetic at 215 C. It is important that the ammonium 
 nitrate should be pure, especially as regards chlorine com- 
 pounds, and great care must be taken not to overheat as the 
 decomposition may become explosively violent. 
 
 A description is given by Flagg (" Art of Anaesthesia/' 
 1916) of a plant at the Lakeside Hospital, Cleveland. 
 Ammonium nitrate, in charges of 40 Ibs., is heated in one of 
 two aluminium retorts to 200 C. and the resulting gases 
 passed through a cooling coil to a wash bottle containing 
 
NITROUS OXIDE 287 
 
 potassium permanganate solution in order to remove higher 
 oxides of nitrogen. The nitrous oxide is then washed with 
 caustic soda in a tower packed with coke to remove nitric acid, 
 freed from alkali by passing through sulphuric acid and 
 finally washed with water. The gas passes into a holder 
 and is subsequently either compressed to about 100 atmo- 
 spheres and liquefied or stored as gas at a pressure of about 
 100 lbs./in. 2 in pressure vessels from which it is distributed 
 at a pressure of 5 lbs./in. 2 through meters to the operating 
 rooms. The theoretical yield of nitrous oxide is about 
 4* 7 ft. 3 /lb. ammonium nitrate, whereas about 4 ft. 3 are 
 obtained in practice. On this basis 1000 ft. 3 require about 
 250 Ibs. of ammonium nitrate. Instead of aluminium, cast 
 iron may be used as the retort material. 
 
 According to L,idoff, a mixture of 2 parts of ammonium 
 nitrate, previously dried at 105 C., with 3 parts of sand is 
 heated to 260-285 C., the resulting gas being washed first 
 with a solution of sodium sulphide or a suspension of iron 
 sulphide and then with an emulsion of ferrous sulphate in 
 concentrated sulphuric acid, to remove nitric oxide. The 
 expensive ammonium nitrate may be replaced by a mixture 
 of ammonium sulphate and sodium nitrate (Smith and 
 Blmore, B.P. 9023/91). Specified proportions of the two 
 salts are mixed and heated to not higher than 230 C. at the 
 beginning of the operation, the temperature rising to about 
 300 C. at the end. B.P. 11828/13, of Torley and Matter, 
 prescribes the continuous injection of ammonium nitrate 
 either in solution or as solid in convenient form, into a heated 
 reaction vessel containing sand, shot, molten metal, etc., 
 and fitted with a stirrer. 
 
 By Other Methods. In B.P. 1 9074/00 Marston describes 
 the preparation of mixtures of nitrous oxide and nitrogen 
 by passing regulated proportions of ammonia and air freed 
 from carbon dioxide over heated copper. The use of this 
 method for the preparation of nitrogen has been already 
 described, p. 113. Higher oxides of nitrogen are removed 
 by passing through iron shavings, followed by ferrous 
 sulphate solution and then alkali. 
 
288 INDUSTRIAL GASES 
 
 By rapidly cooling, at the point of maximum nitrous 
 oxide content, a nitrogen- oxygen flame produced by com- 
 bustion (not of hydrogen) or by electrical means, Sodermann, 
 in F.P. 411785/10, claims the production of nitrous oxide, 
 which is separated from nitrogen by liquefaction after 
 removal of the carbon dioxide. On similar lines is F.P. 
 415594/10 of Pictet, according to whom a mixture of 55 
 volumes of oxygen with 45 volumes of nitrogen is forced 
 centrally into a vessel through an oxy-acetylene flame 
 issuing from a flattened annulus. A particular part of the 
 flame is cooled by jets of water which absorbs the nitrous 
 oxide. A yield of 25 % of nitrous oxide is claimed. 
 
 Purification 
 
 As indicated above, nitrous oxide is best freed from 
 nitric oxide by scrubbing with ferrous sulphate solution, 
 while chlorine, which may be derived from ammonium 
 chloride present in the ammonium nitrate used in its pre- 
 paration, can be removed by caustic soda solution or other 
 suitable means. Ammonia may be removed by washing 
 with sulphuric acid. According to Villard, further purifi- 
 cation may be effected by fractional distillation of liquid 
 nitrous oxide, any nitrogen going off in the first fraction, or 
 by the formation of a hydrate (below o C.) and subsequent 
 decomposition by heating. 
 
 Applications of Nitrous Oxide 
 
 The chief use of nitrous oxide is as an anaesthetic, 
 especially for dental operations. The practical application 
 of the anaesthetic property of nitrous oxide is due to Colton 
 and Wells in 1844. It is now administered almost exclu- 
 sively in conjunction with oxygen since with nitrous oxide 
 alone it is difficult to produce sufficiently lasting anaesthesia 
 without danger of asphyxia. The proportion of oxygen 
 used is from 5-25 % ; usually about 10 % at the beginning 
 with subsequent increase according to the susceptibility 
 of the patient. The effect is very evanescent in any case, 
 
NITROUS OXIDE 289 
 
 generally lasting about 40 seconds. On the average the 
 time for the production of anaesthesia is a little less than one 
 minute and about one ft. 3 of nitrous oxide is required. 
 Among anaesthetics it is the one most free from constitutional 
 disturbances, but is only suitable for cases in, which complete 
 muscular relaxation is not essential. 
 
 Nitrous oxide is obtained in steel cylinders containing 
 from about 6 oz. to about 50 Ibs. of the liquid, i.e. from 3-2- 
 430 ft. 3 of the gas. One Ib. of the liquid is equivalent to 
 about 8-55 ft. 3 of gas at 15 C. For purposes of anaesthesia 
 it is important that the nitrous oxide should be free from 
 chlorine, other oxides of nitrogen, combined organic matter, 
 solids, liquids, etc., and should contain at least 95 % nitrous 
 oxide. 
 
 A representative sample of the commercial product 
 appears to have a percentage composition somewhat as 
 follows (Baskerville and Stephenson, J. Ind. Eng. Chem., 3, 
 (1911), 579) :- 
 
 Nitrous oxide 96-99 
 
 Water 0*15 
 
 Carbon dioxide traces 
 
 Ammonia O'0oi-o-oo6 
 
 Oxygen . . traces 
 
 Nitrogen . . . . . . . . O'i6~3'94 
 
 According to the same authors the presence of chlorine 
 and of the higher oxides of nitrogen may be detected by 
 passing some 10 litres of the gas through solutions of silver 
 nitrate and ferrous sulphate. The nitrous oxide may be 
 estimated by passing the dry gas together with hydrogen 
 over heated reduced copper with subsequent reduction of 
 any copper oxide by hydrogen, the water produced being 
 determined in the usual way. In view of the fact that 
 nitrous oxide is an endothermic compound, the stability 
 of the liquid has been the subject of some enquiry (liquid 
 acetylene or even the compressed gas is, of course, a highly 
 dangerous substance owing to its endothermic character). 
 
 A propos of the unexplained explosion of a cylinder of 
 A. IQ 
 
290 INDUSTRIAL GASES 
 
 liquid nitrous oxide, Rasch (Z. fiir komp. u. fliissige Case, 
 (1904), 159) examined the question as follows. By heating 
 platinum or iron wires in the liquid, only local decomposition 
 was observed as a rule when the temperature of the liquid 
 was below 30 C., but occasionally explosion occurred, even 
 with the temperature of the liquid as low as o C. in one 
 instance. Above 30 C. the decomposition propagated 
 itself throughout the mass. Electric sparks produced no 
 explosion even at 80 C. Generally speaking, detonation 
 only occurred with an energetic temperature rise above the 
 critical temperature of the liquid, viz. 38-8 C. ; direct 
 heating of the cylinder produced no detonation, although 
 the cylinder burst owing to the high pressure generated. 
 
 The possibility of the production of sparks from the 
 presence of suspended solid matter is, however, preferably 
 minimized by always opening the valve with the cylinder in 
 a vertical position, thus avoiding the passage of solid particles 
 through the valve. Further, just as in the case of oxygen, oil 
 should be scrupulously excluded from the valves and con- 
 nections. As in the case of other liquid gases, special care 
 must be taken with regard to the degree of filling of cylinders 
 owing to the rapid increase in volume of the liquid with 
 temperature. Reference to p. 45 will indicate the permissible 
 content of a given vessel. 
 
SECTION XII. ASPHYXIATING GASES 
 
 Introduction. During the war the manufacture and 
 use of asphyxiating gases attained such proportions that 
 a book dealing with industrial gases would be incomplete 
 without a brief reference to this branch of the subject. 
 
 Although one hopes that the production of the various 
 gases will never be revived for like purposes, there is no 
 doubt that the knowledge gained as regards the technical 
 preparation and properties of many substances previously 
 unknown except to the few will prove to be of signal service 
 in the industries, particularly in the realm of organic chemistry. 
 Further, a number of the substances may be found useful 
 for such purposes as the extirpation of various pests harmful 
 to vegetation. 
 
 Since most of the gases, such as chlorine, come under 
 subjects treated in other volumes of this series, their prepara- 
 tion cannot be dealt with in any detail ; also, in most cases, 
 the published information in this connection is very meagre 
 at present. 
 
 The Development of Gas Warfare.- The initiation of 
 gas warfare was made by the Germans in April, 1915, con- 
 sisting in the use of chlorine discharged from cylinders of 
 the liquid, disposed at regular intervals along the front line, 
 with far-reaching effects on our unprotected troops. Emer- 
 gency respirators were rapidly improvised and the subsequent 
 development was determined by counter-efforts of a 
 defensive and offensive character respectively. 
 
 For a proper understanding of the subject it will be 
 necessary briefly to consider the factors determining the 
 success or otherwise of the operations. One of the most 
 important points is the maintenance of a high concentration 
 from this standpoint 0*1 % is a fairly high concentration 
 
292 INDUSTRIAL GASES 
 
 while 0*01 % is quite effective with most gases, e.g. phosgene 
 and this is dependent chiefly on the wind, the velocity of 
 which should be between the limits of say, 4 and 12 miles per 
 hour, and also to some extent on the slope of the country. In 
 order to ensure the safety of the attacking troops, especially 
 as the line may often be very irregular, the wind should 
 approach normality to the general direction of the line. 
 According to Auld (J. Wash. Acad. Sci., 8, (1918), 45), 
 the deviation tolerated by the Germans was about 40 
 on either side of the normal. The density of the gas is 
 not so important as is sometimes imagined, since dilution 
 to a concentration of the order of cri % occurs very 
 rapidly and the density of such a mixture does not differ 
 appreciably from that of normal air whatever the density 
 of the gas. 
 
 Perhaps the most important matters from a practical 
 point of view are (i) the toxicity ; (2) the difficulty of 
 providing protection against the gas ; (3) the ease of manu- 
 facture hi the large quantities required; and (4) the con- 
 venience of transport. Condition (4) points to the advantage 
 of non-permanent gases, since a given cylinder filled with 
 liquid contains a considerable weight of poison at a relatively 
 low pressure ; chlorine, although suitable as regards (i), (3) 
 and (4), was soon found wanting as regards (2), being very 
 reactive and easily absorbed by alkalis, thiosulphate, etc. 
 The most important gas for this type of attack has been 
 phosgene (COC1 2 ) (cf. p. 252), which while possessing the 
 other desiderata has also the advantage of being only slowly 
 hydrolysed by alkalis. Phosgene is much less irritating 
 than chlorine but has an insidious delayed physiological 
 action. However, absorbents were soon found in sodium 
 phenate and especially in urotropine hexamethylenete- 
 tramine which two substances in conjunction gave pro- 
 tection against concentrations of O'l % when used in the 
 impregnated flannel type of respirator, a valve being 
 provided for exhalation. This type of respirator was soon 
 entirely susperseded by the box type, which consisted of a 
 chamber filled with granules of specially activated charcoal 
 
ASPHYXIATING GASES 293 
 
 possessing the property of absorbing gases, especially those 
 of high critical temperature in which category practically all 
 the poison gases are to be found. The box is connected to 
 the mouth by means of a flexible corrugated rubber tube 
 ending in a mouthpiece and nosepiece, suitable inspiration 
 and expiration valves being fitted. This type of respirator 
 has the advantage of simplicity combined with effective 
 protection for long duration attacks for practically all the 
 gases used, and is very easily recharged. For short periods 
 concentrations of several percents can be dealt with. Much 
 depends on the previous history of the charcoal, particularly 
 as regards heat treatment, also on the wood from which 
 it has been made. The enclosed oxygen breathing apparatus, 
 while affording an absolute protection, has only a short time 
 of action and is much too heavy and cumbersome. 
 
 Further attempts to use cylinders were made in the 
 direction of increasing the concentration, but the cumber- 
 some and vulnerable nature of the equipment, which was an 
 unwelcome addition to the front line trenches, the need for 
 a special corps of operators, the noise produced by the 
 discharge and the danger of part of the attacking line being 
 gassed, led to their almost complete supersedence by poison- 
 charged projectiles. The shells could be placed with accuracy 
 where required and their use made the operations independent 
 of the wind. Gas attacks by shells are best made with 
 concentration over a relatively small area. Hand grenades 
 have also been used to some extent. In addition to sub- 
 stances which are primarily poisonous, considerable use 
 has been made of " lachrymators," i.e. substances which 
 attack the eyes, producing weeping, and also the mucous 
 membranes, e.g. benzyl bromide, xylyl bromide, chloropicrin 
 (CC1 3 . NO 2 ), phenylcarbylamine chloride (C 6 H 6 . N : CC1 2 ). 
 With some lachrymatories a concentration of O'oooi % is 
 sufficient to affect the eyes seriously. Similar irritants, 
 which are not highly developed lachrymators, may also be 
 used, the best known member of this class being the deadly 
 " mustard gas," j8'-dichloroethyl sulphide (CH 2 C1 . CH 2 . 
 S . CH 2 . CH 2 C1) . This substance, even in the state of vapour, 
 
294 INDUSTRIAL GASES 
 
 has a most extraordinary, inflammatory action on the skin, 
 the more insidious because not immediate, while its after- 
 effects on the eyes and mucous membranes are most serious, 
 blindness often resulting. 
 
 Among other substances may be mentioned trichloro- 
 methyl-chloroformate (Cl . CO . O . CC1 3 ) which is poisonous but 
 not lachrymatory, and diphenyl-chloroarsine (As(C 6 H 5 ) 2 Cl) 
 which, when suspended in the air, causes very violent 
 sneezing in addition to its lachrymatory and very toxic action. 
 The lachrymatory and irritant substances just referred to, 
 being in most cases liquid, were practically always used in shells 
 or hand grenades ; phosgene was also used in shells. Hydro- 
 cyanic acid was apparently not employed by the Germans, 
 probably on account of its temporary action if the dose is 
 insufficient to produce death at once and of its easy arrest- 
 ment ; nickel salts or alkalis may be used as absorbents. 
 
 The number of substances which have been employed is 
 very large, the element of surprise being one of the most 
 important tactical points. 
 
PART III. GASEOUS FUELS 
 
 SECTION XIII 
 
 General Considerations. The subject of gaseous fuels is 
 one which is receiving great attention at the present moment 
 on account of its bearing on the question of thermal efficiency 
 in heating processes generally. This matter is of great 
 importance in connection with the conservation of our 
 fuel resources, and particularly at the present time, in con- 
 nection with the shortage of labour and the restricted supply 
 of oil fuel for industrial operations owing to the reduced 
 tonnage and, during the war, to the demands of the Navy. 
 
 The principal possibilities for increased economy are 
 (i) the utilization of low grade coal with high ash content, 
 and other fuel which would otherwise be useless, e.g. peat, 
 waste wood, straw and other refuse may be used with some 
 types of producers ; (2) the greater ease of effective thermal 
 regeneration with gaseous fuels and the avoidance of the 
 large excess of air necessary with solid fuel, especially when 
 high temperatures are required, enable better thermal 
 efficiency to be obtained in spite of a certain minimum loss 
 of energy in the preliminary gasification of the solid fuel ; 
 (3) the recovery of the greater part, about 70 %, of the 
 nitrogen present in the coal, as ammonia, a valuable national 
 asset both for war purposes, in connection with explosives, 
 and also for use as a fertilizer ; and (4) the much greater 
 efficiency of the gas engine as a source of power in comparison 
 with the steam engine, at any rate for relatively small plants. 
 
 Among other advantages afforded by the use of gaseous 
 fuel, are the much greater ease of control, i.e. the adjustment 
 of temperature or of the reducing or oxidizing nature of the 
 atmosphere of a furnace ; the possibility of shutting off the 
 
296 INDUSTRIAL GASES 
 
 fuel supply immediately when finished with ; the absence 
 of smoke and ash ; and the ease of distribution from a central 
 station. 
 
 The success of various high temperature operations of the 
 highest importance is directly attributable to the introduction 
 of gaseous fuels of low calorific value but cheap, burnt in 
 regenerative furnaces, e.g. in the open hearth furnace, in 
 the heating of coal gas retorts, etc. 
 
 Fundamental Principles relating to the Use of 
 Gaseous Fuels 
 
 In Table 29 are given typical examples of composi- 
 tions, based on averages of the analyses given by a number 
 of authorities, of the various gaseous fuels, together with 
 some of their more important characteristics with which 
 we shall deal presently. 
 
 Calorific Value. An important point in the comparison 
 of gaseous fuels is the question of calorific value. 
 
 Reference has already been made to the necessity for 
 discrimination between " gross " and " net " calorific values, 
 and although the latter term has no very precise significance 
 (cf . p. 13) its use is convenient in connection with most opera- 
 tions of heating. Observations relating to British and 
 French practice have been made on p. 13 ; in the United 
 States it is usual to use the gross value for the comparison 
 of fuels, while in German and Austrian practice the products 
 of combustion are assumed to be cooled to 100 C., the water 
 remaining as steam. 
 
 We shall see, however, that the value of a gas as a fuel 
 cannot be expressed in terms of calorific value alone. 
 
 The Mechanism of Flame. The subject of the pro- 
 perties of flames is an extensive one, and we must confine our 
 attention here to a few of the more practical aspects of the 
 question. Usually the most important characteristic of a flame 
 in relation to furnace work is its temperature. The temper- 
 atures of particular portions of a flame are best determined 
 by using several thermocouples of different diameter wires, 
 
W O ** 
 
 N M M tx *r> 
 
 !S|! 
 
 H ~ 
 
 w CO 
 
 M!* ^ 
 
 
 H0| JJJ13 
 
 ON K tx KoO K O MD O M 
 rj- rJ-Tt*'^"'^' CO CO CO COCO 
 
 fc o a oj 
 
 
 si^i'M 
 
 ''COiOcONO vO H OO^ 
 O ONCO C/J O M M O O *" 
 
 H 3 M 1 ij I 
 
 Q Vj- Vj- f< Vt- M W M W O 
 
 
 
 ^S^? 
 
 
 B 1 
 
 p ."tJ 
 
 b 
 
 ffl 
 
 O OO t^* ^O t^ 00 tx tx t^* 10 
 IO W C< M N 
 
 O jn 
 
 
 
 0o o 
 
 H 
 
 H f>.ioiOco CO O COOM 
 W O Q^ lr> O\ ^O ^1" cO W O 
 
 O *OrfC > '^- M W M MM 
 
 P H 8 
 
 B 
 
 M 
 
 *JJ* 
 
 ill 
 
 K 
 
 o MOOO ON oo c>.r>.o 
 
 O CO CO M CO 
 
 g 2 
 
 S _ | <3\vDooo VT>NWT}- 
 
 S 3 
 
 O M vX ir^ o -^ vP^ if\ * <v^ rt 
 
 o " 
 
 
 H 
 
 M IOOCOO M M M MM 
 
 
 PQ 
 
 
 l-i i O ' 
 
 . .2. 'S fj oO 
 
 
 H IB &> 
 
 1OOOMONO M N ONOOM 
 
 g <fl o "^ Q.+J 
 
 O MWMTf IO M 1OOO 
 
 W 'p ^ a ^ 
 
 IO CO CO ^ ^t" VO *O VO CN* C^ 
 
 Q ii-s^* 
 
 
 a 
 
 o 
 B 
 
 i 
 
 |||j 
 
 1 **l 2 | 111! 
 
 I 
 
 * 
 
 COvDOOLi.0 (S ^M MM 
 rf 10 VO vO 
 
 o 
 
 2 
 
 
 * >0 
 
 1 
 
 S 
 
 ^ 00" MM^fN, fT) fO NM 
 t J M CO CO M 
 
 o 
 
 
 
 9 
 
 
 ..^^ 
 
 & 
 
 O 
 
 ^(MN^-CO . IO 
 
 ? 
 
 
 2 M ^ 
 
 
 
 O 
 
 1 ^^-^ cT 2 $ %$ 
 
 
 
 
 
 I 00 00 OOO T}- O IO >O M 
 
 
 K 
 
 1 ^t" <* "4- CO M M M 
 
 ri 
 
 
 
 Jtiiiliifili 
 
 I 
 
 
 ; uofQuc/) c/3 c/3 < CQ 
 
298 INDUSTRIAL GASES 
 
 plotting the results and extrapolating for zero thickness 
 of wire. 
 
 Turning to factors determining flame temperatures, it 
 is obvious that, assuming the combustion to be adiabatic, 
 the flame temperature will be represented by the following 
 fraction, sometimes termed the calorific intensity : 
 
 Heat of combustion of the components of the mixture 
 
 Mean thermal capacity of the products per degree C. over 
 the temperature range in question 
 
 neglecting any dissociation at the flame temperature. Even 
 non-luminous flames, however, are far from being adiabatic. 
 According to Callendar (B. A. Reports, (1910), 214), 10-15 % 
 of the energy is lost by radiation, the loss increasing with 
 decreasing air supply and consequently increasing size of 
 flame, a maximum of 15-20 % loss being found when a well- 
 defined inner cone is formed. 
 
 The radiation is ascribed by most investigators to the 
 intensely vibratory condition of newly-formed compound 
 molecules (of hydrogen and oxygen or carbon and oxygen, 
 which subsequently revert to the condition of ordinary water 
 or carbon dioxide molecules), a gas in the ordinary state being 
 incapable of transmitting radiation. The measurements 
 of Helmholtz (Beiblatter, 14, (1890), 589) indicate that the 
 radiation from a carbon monoxide flame is some 2*4 times 
 that from a similar hydrogen flame, for equal volumes of 
 gas burnt. This fact probably explains the greater 
 usefulness of carbon monoxide than of hydrogen as a con- 
 stituent of semi-water gas for heating purposes, given equal 
 calorific values in the two samples. The radiation from 
 flames is also of considerable importance in connection with 
 the communication of heat to the cylinder walls in gas 
 engines. 
 
 An important factor in the transmission of heat from 
 flames to cooler surfaces is the velocity of the products of 
 combustion over the surface. Thus, the high temperature 
 which is obtained with a blow-pipe in comparison with a 
 Bunsen burner is due in a considerable measure to the high 
 
GASEOUS FUELS 299 
 
 velocity and consequent high degree of turbulence in the 
 gases. 
 
 Calorific Value of Technical Gas-Air Mixtures. 
 
 Reference to Table 29 will show that although a consider- 
 able variation exists between the calorific values of the 
 different gases, there is much less variation between the 
 corresponding values for the mixtures of the same with 
 the volume of air required for complete combustion, and since, 
 for most technical purposes, it is almost impossible to avoid 
 the use of a certain excess of air, the differences are still 
 smaller in actual practice. 
 
 It must not be forgotten, however, that a small difference 
 in the calorific intensity may make a considerable difference 
 in the efficiency, especially in non-regenerative high temper- 
 ature furnaces. The calorific intensities are more or less 
 in the order of the calorific values of the gas-air mixtures, 
 although not necessarily so ; thus, blue water gas has a 
 higher calorific intensity than coal gas. Calculated values 
 have not been given on account of the variable proportions 
 of air used in practice and the lack of trustworthy data 
 for specific heats at high temperatures. 
 
 Ignition Temperature. Mixtures of various inflam- 
 mable gases with air or oxygen possess, under certain con- 
 ditions, quite definite ignition temperatures ; by ignition 
 temperature is meant the temperature at which combustion, 
 originated at a point, propagates itself rapidly through the 
 mass of the gas. In the exact determination of such ignition 
 temperatures there is considerable difficulty on account of 
 errors, such as those caused by the heating effect due to 
 slower initial combination at a temperature below the true 
 instantaneous ignition temperature. The method used by 
 Dixon and Coward (Ghent. Soc. Trans., (1909), 514) was to 
 spark the point at which streams of the two gases, separately 
 preheated to a given temperature, were brought together, and 
 their measurements, which are given below, were criticized 
 by McDavid (Chem. Soc. Trans., (1917), 1003) on the above 
 grounds. To avoid this error and in order to have a station- 
 ary volume of gas since the mixture is imperfect with a 
 
300 
 
 INDUSTRIAL GASES 
 
 streaming method, McDavid allowed a soap bubble of the 
 mixed gases to impinge on a wire electrically heated to a 
 given temperature ; his values also will be found below. 
 Alternatively, the time factor can be eliminated by performing 
 the heating by means of adiabatic compression (Falk). 
 
 TABLE 30. 
 IGNITION TEMPERATURES. 
 
 f*AC 
 
 Gas + air. 
 
 Gas + oxygen. 
 C. 
 
 
 Dixon and 
 Coward. 
 
 McDavid. 
 
 Dixon and 
 Coward. 
 
 Hydrogen 
 
 580-590 
 
 (10 % H t ) 
 
 747 
 
 580-590 
 
 Carbon monoxide (moist) . . 
 
 644-658 
 
 
 93i 
 
 637-658 
 
 Methane 
 
 650-750 
 
 ^> 
 
 IOOO 
 
 556-700 
 
 Ethane 
 
 520-630 
 
 
 1062 
 
 520-630 
 
 Ethylene 
 
 542-547 
 
 (10 % C 2 H 4 ) 
 
 IOOO 
 
 500-519 
 
 Acetylene 
 
 406-440 
 
 
 
 
 416440 
 
 Sulphuretted hydrogen 
 
 34-379 
 
 
 ' ' 
 
 220-235 
 
 Ignition temperatures are of importance, particularly 
 in connection with power production, as the modern gas engine 
 depends for its high efficiency on the employment of a high 
 degree of compression with a correspondingly high temper- 
 ature production owing to the adiabatic compression (cf. 
 p. 346) ; it is, consequently, necessary for a suitable power 
 gas fuel to be capable of withstanding the required com- 
 pression without pre-ignition. 
 
 Explosive Limits and the Velocity of Propagation of 
 Explosion. The above are important points in the use of 
 fuel gases, the former from a danger standpoint (for values 
 for some of the fuel gases, cf. Table 29), and the latter in 
 relation to questions of back-firing ; thus, in burners of the 
 Bunsen type and in injector blow-pipes, it is necessary for 
 the linear velocity of the explosive gas mixture to exceed 
 the velocity of propagation of explosion in the same. 
 
 Space will not permit more than an indication of the 
 complex nature of the phenomena of the propagation of gas 
 explosions. Broadly speaking, however, it will suffice to 
 
GASEOUS FUELS 301 
 
 state that the explosion originating in a tube results in a 
 period of acceleration of the flame, succeeded by a more or 
 less sudden increase of the velocity of propagation to a very 
 high value of the order of io,oooft./sec. The phenomena, 
 particularly in the preliminary period, depend (i) on the 
 position of the point of ignition, e.g. whether near the open or 
 closed end of the tube ; (2) on the diameter of the tube, 
 and (3) on the composition of the gas mixture. For further 
 information cf. Mallard and L,e Chatelier, Annales des Mines, 
 [8], 4, (1883), 524 ; Dixon, Phil. Trans., A 200, (1903), 315, 
 and other papers. 
 
 Fundamental Principles of the Production of Gaseous 
 Fuels of Low Calorific Value 
 
 Starting from the general standpoint that all processes 
 for the complete gasification of coal depend on the action 
 of oxygen, or water, or of both, on the carbon which consti- 
 tutes the most important part of the coal, it will be well to 
 consider the thermochemical and thermodynamical changes 
 involved. 
 
 (i) Action of Air on Carbon. The combustion of 
 carbon takes place either to carbon monoxide or to carbon 
 dioxide or to a mixture of both according to circumstances. 
 
 2C + O 2 = 2CO + 58,000 calories (a) 
 C + O 2 = CO 2 + 97,300 calories (b) 
 
 Reaction (a) corresponds to the liberation of 2420 
 C.H.U./lb. carbon (4360 B.T.U.). 
 
 Reaction (b) corresponds to 1he liberation of 8110 
 C.H.U,/lb. carbon (14,600 B.T.U.). 
 
 Now, the general ideal in the production of a fuel gas is 
 to have as high a " cold " thermal efficiency as possible, 
 by which is meant the ratio of the calorific value of the 
 gaseous fuel to that of the corresponding quantity of the solid 
 fuel from which it originated, net values being preferably 
 taken. Stated in other words, the principle is to transform 
 as little potential energy as possible into " sensible " heat 
 
302 INDUSTRIAL GASES 
 
 in the gasification process. We shall see later that in some 
 cases it is feasible economically to utilize such " sensible " 
 heat, but in general the gases are used cold, and unless 
 recovered by regenerative operations, the sensible heat 
 liberated in the generator is wasted. 
 
 Considering the " cold " thermal efficiency in the above 
 reactions, we find that here the case is very simple since 
 carbon dioxide is incapable of further combustion and conse- 
 quently the efficiency will vary from 
 
 8no - 2420 _ 5690 _ 
 8110 ~~- 
 
 when only carbon monoxide is formed, to zero when all 
 carbon dioxide is formed. 
 
 If, on the other hand, the gases are utilized in the hot 
 state supposing, for instance, that the gases leave the gener- 
 ator at a temperature of 800 C., about the usual temperature 
 we must add to the heat of combustion of the carbon 
 monoxide the thermal capacity of the mixture of carbon 
 monoxide and nitrogen. 
 
 Assuming that we are dealing with pure carbon, in which 
 case we should have a gas mixture of CO 4- 2N 2 , and neg- 
 lecting the increase in the specific heats with temperature, 
 we see that the quantity to be added is 
 
 785 Cco X + C* N . X C.H.U./lb. carbon 
 
 = 785 (0-242 X 2-33 + 0-243 X 4*66) C.H.U./lb. carbon 
 = 1330 C.H.U./lb. carbon. 
 
 The " hot " efficiency therefore equals 
 
 5690 + 1330 =0 . 866 
 
 8110 
 
 the difference from unity representing the loss by radiation 
 from the generator. 
 
 Up to the present we have been dealing with the ideal 
 case, viz. the production of carbon monoxide only. A 
 
GASEOUS FUELS 33 
 
 consideration of the equilibrium relations of the reversible 
 reaction 
 
 2CO ^ C -h CO 2 + 39,3 calories 
 
 (cf. p. 237) will indicate that this can only be the case 
 (approximately) at temperatures over 1000 C., although the 
 fact that the partial pressure is approximately 0-33 atm. 
 will hinder the decomposition. According to theory the 
 action of air on carbon should result in the production of a 
 gas containing about 33 % (CO + CO 2 ). 
 
 The following table shows the equilibria calculated from 
 the experimental data of Rhead and Wheeler and Boudouard 
 (cf. p. 238) for various temperatures taking p co + p COz 
 equal to 0-33 atm. 
 
 TABLE 31. 
 
 EQUILIBRIUM BETWEEN CARBON MONOXIDE, CARBON DIOXIDE AND 
 CARBON AT 0-33 ATM. PRESSURE. 
 
 
 600 
 
 800 
 
 IOOO 
 
 K (from smoothed curve) 
 
 I4-55 
 
 0-124 
 
 0-00597 
 
 pco in atms. 
 
 0-120 
 
 0-318 
 
 0-329 
 
 pco 2 in atms. 
 pco/pco 2 
 
 0'2IO 
 0-57I 
 
 0-012 
 26-5 
 
 O'OOI 
 
 329 
 
 An important point in the consideration of the attainment 
 of these equilibria is that discovered by Rhead and Wheeler 
 (loc. cit.}, namely, that the rate of reaction is much greater 
 some 166 times at 850 C. in the direction of carbon monoxide 
 formation than in that of its decomposition ; the consequence 
 is that in passing through the hot zone in the neighbour- 
 hood of 1200-1500 C. the gases are practically free from 
 carbon dioxide and on subsequent passage through the upper 
 cooler zones, the reaction in the direction of dioxide formation 
 is sufficiently " frozen " to prevent any considerable amount 
 of carbon dioxide being formed. 
 
 The practical outcome of these considerations is that 
 from this point of view it is desirable to run the producer at 
 as high a temperature as possible. In practice this desider- 
 atum is qualified by the fact that much trouble is caused at 
 excessively high temperatures by " clinkering " and by the 
 
304 INDUSTRIAL GASES 
 
 increase in losses by radiation, etc. If the fuel used is 
 not pure carbon, but contains considerable quantities of 
 hydrogen, as e.g. bituminous coal, the gaseous products will 
 contain appreciable quantities of decomposition products, 
 notably hydrogen and methane, in addition to carbon 
 monoxide, carbon dioxide and nitrogen. 
 
 (2) Action of Steam on Carbon. As in the case of 
 oxygen, the action of water on carbon may take place in either 
 of two ways : 
 
 [C -f H 2 O liquid = CO + H 2 39>7<>o calories (a) 
 
 |C + H 2 ga8 = CO + H 2 - 29,100 calories (a 1 ) 
 
 |C + 2H 2 O Uquid = CO 2 + 2H 2 29,500 calories (b) 
 
 \C + 2H 2 O gas = CO 2 -f 2H 2 18,900 calories (b r ) 
 
 The net calorific values of the resulting gaseous products 
 will be 167 and 102 C.H.U./ft. 3 at 15 C. respectively (cf. 
 Tables 13 and 29) ; it is therefore obvious that the product of 
 (b) is much less desirable as a fuel and, consequently, it will 
 not be considered further. The action differs from that of air 
 in that we have in both the above cases, not an evolution 
 but an absorption of heat. 
 
 Thus 
 
 Reaction (a) involves the absorption of 3310 C.H.U./lb. carbon 
 
 (5960) B.T.U. 
 (') 2420 C.H.U./lb carbon 
 
 (4360) B.T.U. 
 ,; (b) ,, 2460 C.H.U./lb. carbon 
 
 (4430) B.T.U. 
 
 (V) 1570 C.H.U./lb. carbon 
 
 (2830) B.T.U. 
 
 It is therefore evident that the reactions cannot be self- 
 supporting and that the necessary supply of heat must be 
 furnished in some way. External heating of the generator is 
 impracticable, and, consequently, it is found more convenient 
 to adopt the plan of using the fuel itself and the furnace 
 lining as heat accumulators by supplying alternately to the 
 fuel bed an air blast the " blow " period and a steam 
 blast the " make " period, or the " run." 
 
GASEOUS FUELS 305 
 
 We have seen above that the combustion of i Ib. of carbon 
 liberates (a) 2420 C.H.U. if carbon monoxide be formed, and 
 (b) 8110 C.H.U. if carbon dioxide be formed. It will be 
 instructive to make a rough estimate of the thermal balance 
 sheet of the generator. The calculations are made for the 
 sake of indicating clearly the various items in the heat balance 
 sheet rather than for obtaining an accurate evaluation of the 
 coke requirements. For this purpose we will assume the 
 gases both from the " blow " and " make " periods to leave 
 the generator at a temperature of 600 C., and will take no 
 account of the increase in the specific heats with rise of 
 temperature, since the calculations are only approximate 
 and the corrections are not accurately known in all cases. 
 For further simplicity we will neglect the loss by radiation, 
 etc., from the body of the generator ; such losses vary with 
 the type of generator, but may be evaluated for specific cases. 
 
 Blow. (a) Combustion to Carbon Monoxide. Heat 
 of combustion of 12 Ibs. of carbon 
 
 = 12 X 2420 C.H.U. 
 = 29,000 C.H.U. 
 
 Heat lost in products of combustion (28 Ibs. CO and 56 Ibs. 
 N 2 ) 
 
 = 585 (0-242 x 28 + 0-243 X 56) C.H.U. 
 
 = 11,920 C.H.U. 
 
 Total heat available therefore 
 
 = 29,000 11,920 C.H.U. 
 = 17,080 C.H.U. 
 
 Blow, (b) Combustion to Carbon Dioxide. Heat of 
 combustion of 12 Ibs. of carbon 
 
 = 12 X 8110 C.H.U. 
 = 97,300 C.H.U. 
 
 Heat lost in products of combustion (44 Ibs. CO 2 and 
 112 Ibs. N 2 ) 
 
 = 585 (0-202 X 44 4- 0*243 X 112) C.H.U. 
 
 = 21,120 C.H.U. 
 A. 2O 
 
306 INDUSTRIAL GASES 
 
 Total available heat therefore 
 
 = 97,300 21,120 C.H.U. 
 = 76,180 C.H.U. 
 
 For the present purpose it will be most convenient to 
 consider the reaction in the " run " as being carried out 
 with liquid water and to add on the heat carried into the 
 generator by the steam, assumed at 100 C. 
 
 Make. Heat supplied in 18 Ibs. of steam, if at 100 C. 
 
 = 18 (85 X i + 538) C.H.U. 
 = 11,210 C.H.U. 
 
 Heat absorbed in the gasification of 12 Ibs. carbon 
 
 = 12 X 3310 C.H.U. 
 
 = 39^700 C.H.U. 
 
 Heat lost in the gaseous products (2 Ibs. H 2 and 28 Ibs. 
 CO) 
 
 = 585 (3-42 X 2 + 0-242 X 28) C.H.U. 
 
 = 7960 C.H.U. 
 
 Total loss of heat therefore 
 
 = 39,700 + 7960 11,210 C.H.U. 
 = 36,450 C.H.U. 
 
 Considering the two cases (a) and (b) separately we find 
 that the ratios of the carbon consumed in the " blow " and 
 " make " periods respectively would be 
 
 (a} 36,450 _ 2-134 
 W 17,080 i 
 
 th\ 36,450 _ 0-478 
 
 W ^m = ~r 
 
 or the proportions of the total carbon appearing in the useful 
 product, i.e. water gas, would be 
 
 In actual practice the corresponding values are of the 
 order of (a) 0-3, (b) 0-5-0-6. 
 
GASEOUS FUELS 307 
 
 A simple calculation will indicate that i Ib. of carbon in 
 the " make " period should produce 63*0 ft. 3 of water gas at 
 15 C., or conversely, 1000 ft. 3 of water gas should require 
 15*87 Ibs. of carbon in the " make " period. This is equiv- 
 alent to a total of 
 
 (a) 15-87/0-319 = 49-7 Ibs. carbon 
 
 (b) 15-87/0-677 = 23-4 Ibs. carbon 
 
 per 1000 ft. 3 of water gas according to the method of com- 
 bustion in the " blow " period. 
 
 The average values found in actual practice for good work- 
 ing are about (a) 50-60 Ibs., (b) 32 Ibs. coke, or, taking the coke 
 as containing, say, 85 % carbon, (a) 42*5-51 Ibs., (b) 27 Ibs. 
 of carbon, the figures not including the fuel for raising the 
 steam, this item, if 60 Ibs. steam used, being equivalent 
 to some 7 Ibs./iooo ft. 3 of water gas in good boiler practice. 
 
 If, as usually happens in practice, the blow gases from a 
 generator working on system (a) contain a certain proportion 
 of carbon dioxide, the fuel consumption may be considerably 
 lower than that calculated above. 
 
 Theoretical considerations on the above lines would point 
 to the formation of the following volumes of " blow " gases : 
 
 (a) 3200 ft. 3 , (b) 1200 ft. 3 per 1000 ft. 3 of water gas. 
 
 The volumes produced in practice are (a) 3000-4000 ft. 3 , 
 (b) 2000 ft. 3 . 
 
 Similarly the water requirements should be 
 
 I5>8 ; 2 Xl8 lbs./ioooft. 3 ati 5 C. 
 
 = 23-8 Ibs./iooo ft. 3 at 15 C., 
 
 assuming complete decomposition, which is not realised in 
 practice. 
 
 In practice the weight required is about 60 Ibs., including, 
 however, the steam for the blowers. If the " blow " be 
 carried out to give carbon dioxide, the theoretical efficiency 
 of the water gas manufacture should be 100 % ; in other 
 words, the net calorific value of the water gas should be equal 
 to that of the coke used in its manufacture, assuming no 
 heat losses in the generator, blow gases, etc. In practice, 
 however, the " net cold " efficiency is of the order of (a) 
 35 %> (&) 7 %> taking the net calorific value of coke at 8000 
 
308 INDUSTRIAL GASES 
 
 C.H.U. /lb., excluding the fuel for raising the steam, driving 
 the blower, etc. Estimate (a) neglects, of course, the calorific 
 value of the blow gases ; this, if counted, would bring the 
 efficiency up to that of (b). 
 
 Before leaving this section of the subject, it will be 
 instructive to calculate the effect of preheating the steam. 
 Imagine the incoming steam to be heated from 100 C. 
 to 600 C. at the expense of the issuing water gas 
 
 Heat absorbed by 18 Ibs. of steam 
 
 = 18 x 500 x 0-473 C.H.U. 
 = 4260 C.H.U. 
 
 The total heat loss during the " make " will therefore be 
 diminished by this amount and will amount to 
 
 36,450-4260 C.H.U. = 32,190 C.H.U. 
 
 Therefore ratio of carbon consumed in the " blow " and 
 " make " periods respectively is 
 
 17,080 i 
 b] 32,190 __ 0-423 
 
 W 76^85- 
 Proportion of total carbon appearing in the water gas 
 
 = ' 347 
 
 (b) = = 0703 
 1-423 
 
 Total carbon required per 1000 ft. 3 of blue water gas 
 
 (a) 15-87/0-347 = 457 Ibs. 
 
 (b) 15-87/0-703 = 22-6 Ibs. 
 
 In case (a) this value is considerably lower than in that 
 previously considered. 
 
 Thus far we have considered the water gas as being 
 composed of equal volumes of hydrogen and carbon monoxide. 
 In practice this is approximately the case, but a small percen- 
 tage of carbon dioxide is always present, in amount depending 
 
GASEOUS FUELS 
 
 309 
 
 principally on the temperature of the fuel bed. The reason 
 is to be found in the reversible reaction known as the water 
 gas equilibrium : 
 
 CO + H 2 O ^ CO 2 + H 2 + 10,200 calories. 
 
 The following table indicates the results of the equilibrium 
 
 measurements of Hahn (Z. physik. Chem., 42, (1902), 705 ; 
 
 44, (1903), 513 ; 48, (1904), 735), the points being taken 
 
 from a smoothed curve which is extrapolated below 686 C. 
 
 TABLE 32. 
 HAHN. WATER GAS EQUILIBRIUM. 
 
 Tempera tureC. 
 _ pco PH Z O 
 
 500 
 0-16 
 
 600 
 0*32 
 
 700 
 0-58 
 
 800 
 0*90 
 
 900 
 1-25 
 
 1000 
 
 1-62 
 
 1 100 
 
 1-92 
 
 1200 
 
 2-16 
 
 1300 
 
 2-35 
 
 1400 
 
 2-49 
 
 pco z .pa z " 
 
 The exact course of the establishment, in technical 
 generators, of the above equilibrium on the one hand, and of 
 the CO, CO 2 , C equilibrium on the other, have been the subject 
 of much discussion. In a discussion of the investigations 
 of Bunte and Harries (/. Gasbeleucht., (1894), 81) on the 
 results of passing steam over carbon at different temperatures, 
 and to which we shall have occasion to refer later, lyUggin 
 (/&., (1898), 713) finds that the water gas equilibrium is 
 established at temperatures between 760 C. and 1000 C., 
 but that the CO, CO 2 , C equilibrium is not attained, the 
 carbon dioxide being always in excess. It was suggested 
 by Haber that the ash content of the coke is operative in 
 facilitating catalytically the attainment of the water gas 
 equilibrium without the carbon itself coming into equili- 
 brium with the carbon monoxide and carbon dioxide. 
 Recently the question has received experimental attention 
 from Gwosdz (Z. angew. Chem., (1918), i., 137), who found that 
 over the range of 560-855 C., a considerable percentage of 
 carbon dioxide up to 29 % was always formed with gas 
 coke containing 8-5 % of ash. On the other hand, with 
 almost pure carbon lampblack with O'i % ash even at 
 600 C., the water gas contained only 8'6 % carbon dioxide. 
 
310 INDUSTRIAL GASES 
 
 Gwosdz's conclusion is that the carbon dioxide is not formed 
 in the primary reaction, but that in the first instance the 
 carbon reacts with water vapour to give carbon monoxide 
 and hydrogen, the establishment of the water gas equilibrium, 
 in the upper and cooler regions of the generator, following by 
 catalysis through the ash of the fuel. 
 
 In practical operation of water gas plants, the temperature 
 conditions are continually changing during the "make " period 
 and the duration of this period is so arranged that the average 
 percentage of carbon dioxide does not rise beyond the desired 
 limit. 
 
 (3) Action of a Mixture of Air and Steam on Carbon. 
 We have seen above that the action of oxygen on carbon 
 results in an evolution of heat with a consequent tendency 
 to excessive rise in temperature in the producer while the 
 action of water is strongly endothermic, leading to the 
 necessity for discontinuous working and consequent lower 
 efficiency. It is therefore not difficult to see why a combin- 
 ation of the two processes has proved to be the most advan- 
 tageous method of producing a fuel gas for furnace work and 
 for power generation. Such a combination has the double 
 advantage of avoiding the tendency to " clinkering " and of 
 securing a gas with less inert nitrogen and of higher calorific 
 value than air producer gas ; further, owing to the lower 
 temperature, the efficiency is less dependent on recuper- 
 ation of the " sensible " heat of the products. For a proper 
 understanding of the thermal balance it is convenient to 
 regard the process as being carried out in two generators, 
 disposed side by side, and separated by a partition perfectly 
 permeable to heat. If we imagine the " blow " cycle of 
 the ordinary water gas manufacture to be carried out in 
 one generator simultaneously with the performance of the 
 " make " cycle in the other, the resulting gaseous products 
 being united giving " semi-water gas," it is evident that we 
 have much the same thermal balance as that just worked 
 out for water gas production. 
 
 Thus, assuming no heat-interchange, the ratio of the 
 carbon reacting with water to that reacting with air will 
 
GASEOUS FUELS 311 
 
 be 1/2-134, i.e. 0-32 of the carbon reacts with water and 
 0-68 with air. The weight of water per Ib. carbon is seen to be 
 
 Since the volume of i Ib. of water vapour at 100 C. is 
 26-43 ft. 3 , the volume of this water at 100 C. will be 26-43 x 
 0-48 ft. 3 = 12-7 ft. 3 Similarly the weight of the oxygen 
 involved is 
 
 0-68 X 16 
 _ --=0-907 Ib. 
 
 and the volume = '97 X 1000 ft3 ^ c 
 
 04-50 
 
 = 10-7 ft. 3 at 15 C. 
 
 or 10-7/0-21 ft. 3 of air at 15 C. = 51-0 ft. 3 of air at 15 C. 
 or 66-0 ft. 3 of air at 100 C. 
 
 This steam/air ratio corresponds to a partial pressure of 
 
 12*7 X 760 
 
 - , ' mm. mercury 
 12-7 + 66-0 
 
 = 123 mm. mercury, i.e. a saturation temperature of 56 C. 
 
 We have calculated for the case of the action of steam on 
 carbon that a weight of 49*7 Ibs. of carbon should produce 
 1000 ft. 3 of water gas plus 3200 ft. 3 of " blow " gases (air 
 producer gas) at 15 C., i.e. a total of 4200 ft. 3 of gas. 
 Since these data are applicable to the present case, we see 
 that 1000 ft. 3 of semi- water gas should result from 49-7 x 
 1000/4200 Ibs. of carbon = ir8 Ibs. of carbon. The air 
 requirements per 1000 ft. 3 of gas should, therefore, be 
 n-8 x 51 ft. 3 at 15 C. = 602 ft. 3 at 15 C., while the 
 water is similarly evaluated at ir8 X 0-48 Ibs. = 56-6 Ibs. 
 
 If the above ideal conditions were fulfilled, the percentage 
 composition of the gas, when operating with pure carbon 
 and neglecting carbon dioxide formation, would be 
 
 Hydrogen . . . . . . 11*9 
 
 Carbon monoxide ... . . 37*3 
 
 Nitrogen ........ 50-8 
 
 lOO'O 
 
312 INDUSTRIAL GASES 
 
 corresponding to a calorific value (net) per ft. 3 at 15 C. 
 of 85-6 C.H.U. On this basis the thermal efficiency would be 
 
 A somewhat lower saturation temperature than that just 
 calculated would be necessary in practice on account of losses 
 due to radiation, convection, etc. Owing to the diluting effect 
 of products of distillation and partial replacement by carbon 
 dioxide, the carbon monoxide content is not so high in 
 practice. By paying attention to thermal losses, effici- 
 encies of about 80 % may be attained in actual working. 
 
 As regards the establishment of the equilibria in the 
 generator, the remarks on water gas apply also to the present 
 case. From a technical standpoint, low carbon dioxide 
 concentration is desirable in order to secure high calorific 
 value and high gasification efficiency. The most important 
 condition for such low concentration is, of course, the 
 maintenance of a high temperature in the fuel bed by keeping 
 down the steam ratio. On the other hand, as we shall see 
 presently, it is sometimes advantageous to sacrifice efficiency 
 of gasification to the recovery of ammonia, by working with 
 a high steam ratio and consequent low temperature in the 
 producer. 
 
 Since the manufacture of semi-water gas is usually 
 carried out from bituminous fuel, not from coke, there is 
 often present in the gases an appreciable amount of methane 
 of the order of 3 % formed mainly by destructive distil- 
 lation of the fuel in the upper and relatively cool portions of 
 the generator. 
 
 A possible future development of semi-water gas manu- 
 facture lies in the substitution of pure oxygen or oxygen- 
 enriched air for air in admixture with the steam (cf . remarks 
 on the possibilities in the future provision of cheap oxygen, 
 p. 94 and p. 106). Using pure oxygen, the resulting gas 
 would contain only combustibles, possessing, in fact, the 
 advantages of water gas without the inherent drawback of 
 intermittent working. 
 
GASEOUS FUELS 313 
 
 (4) Action of Carbon Dioxide on Carbon. There is 
 still another method of gasifying carbon, namely by the 
 action of carbon dioxide either alone or in admixture 
 with air. 
 
 C + CO 2 = 2CO 39,300 calories. 
 
 If carbon dioxide alone be passed through the producer, 
 the strongly endothermic nature of the reaction, resulting 
 in an absorption of 3270 C.H.U./lb. carbon (5890 B.T.U.), 
 makes it necessary to use an intermittent " blow " as in 
 water gas manufacture. Using a mixture with air, a balance 
 will be struck as in the case of semi-water gas. 
 
 The process was used some years ago in power production 
 on account of the freedom from pre-ignition troubles when 
 using this gas. A portion of the gases from the exhaust of 
 the engine, which operates on very high compression, is 
 returned together with additional air to the generator. The 
 composition of the gas is similar to that of air producer 
 gas. 
 
 TECHNICAL PRODUCTION OF GASEOUS FUELS 
 OF LOW CALORIFIC VALUE 
 
 AIR PRODUCER GAS 
 
 General. The gaseous fuel resulting from the action 
 of air on incandescent carbon, and known variously as 
 producer gas, air gas, air producer gas, straight producer 
 gas, etc., was the first form in which carbon was completely 
 gasified for industrial purposes. A simple form of producer 
 with natural draught was introduced by Bischof in 1839, 
 but the first important advance was made by the Siemens 
 Bros., who used producer gas in connection with the principle 
 of regeneration for steel melting, also introduced by them. 
 Natural draught was at first used, but later air injection 
 was adopted and finally the air was injected by means of a 
 
314 
 
 INDUSTRIAL GASES 
 
 steam blast, air producer gas being no longer used in steel 
 melting. 
 
 General Principles of Operation. A clear insight 
 into the principles governing the operation of air producers 
 is afforded by Wendt's investigations (Stahl und Eisen, 
 26, (1906), 1184), which were carried out in a technical 
 generator using bituminous coal as fuel, the bed being 7' 3" 
 deep. For a summary of the results obtained, see the 
 following table, which represents analyses of gases drawn 
 from different zones of the producer at the stated heights 
 above the grate. 
 
 TABLE 33. 
 WENDT'S EXPERIMENTS ON PRODUCER GAS. 
 
 Height above 
 tuyere. 
 Inches. 
 
 Temperature 
 C. 
 
 H 2 
 
 CO 
 
 C0 2 
 
 CH 4 
 
 N 2 
 
 o 
 
 _ 
 
 _. 
 
 19-6 
 
 8-8 
 
 , 
 
 71-6 
 
 10 
 
 1380 
 
 
 
 34*5 
 
 
 
 
 
 65-5 
 
 20 
 
 
 
 
 
 34' 5 
 
 0'2 
 
 
 
 65-3 
 
 30 
 
 1250 
 
 0-7 
 
 32-7 
 
 0-8 
 
 0-4 
 
 65-4 
 
 4 
 
 
 
 11-9 
 
 28-9 
 
 1*0 
 
 2*0 
 
 56-2 
 
 50 
 
 1145 
 
 IO'O 
 
 26-7 
 
 2'0 
 
 3'8 
 
 57-5 
 
 60 
 
 
 12-3 
 
 27'2 
 
 2'0 
 
 4-2 
 
 54' 3 
 
 Outlet 
 
 610 
 
 6'4 
 
 30-9 
 
 ro 
 
 3-2 
 
 58'5 
 
 Tar was present in the gases at and above the zone 40" above the 
 tuyere. Depth of bed =87". 
 
 An examination of the above analyses will indicate 
 that the equilibrium between carbon monoxide and carbon 
 dioxide is established at or below the point 20" above the 
 tuyere. 
 
 Thus, at 20", pco 2 0-002 atm. (cf. the equilibrium 
 values on p. 303), the rate of reaction being very high at the 
 temperature of this zone. Free oxygen is very rapidly 
 removed in the first portions of the fuel ; no oxygen was 
 found at any of the points. As the highly heated products 
 of combustion ascend through the fuel bed, their temperature 
 is lowered by contact with the cooler fuel and consequently 
 some reversion to carbon dioxide takes place, but a reference 
 
GASEOUS FUELS 315 
 
 to p. 303 will show that equilibrium is by no means attained 
 at say 600 C., in the time available. 
 
 Further, with the bituminous coal used in these trials, the 
 distillation taking place in the upper regions results in the 
 formation of methane and hydrogen. The composition of 
 the gas produced will vary with the fuel used ; with coke the 
 hydrogen and methane will, of course, be lower than with 
 bituminous coal. 
 
 The temperature of the producer tends to rise until 
 limited by the increasing losses through radiation and the 
 sensible heat of the gaseous products ; the practical limit 
 is set by the trouble of " clinkering " which increases rapidly 
 at high temperatures, and also by the action on the lining of 
 the producer. These difficulties and the low thermal effici- 
 ency (cf. p. 302) have led to the almost complete substitution 
 of semi-water gas for air producer gas except in the case of 
 the " blow " period in the manufacture of water gas, where 
 the function of the " blow " is actually to produce a high 
 temperature in the fuel bed and producer lining. 
 
 Some plants have been constructed with the deliberate 
 object of working at the maximum possible temperature and 
 combine the production of CO 2 -free gas with the elimina- 
 tion of " clinkering " difficulties by adding limestone to 
 produce a fusible slag with the ash, this slag being tapped off 
 regularly through a slag notch. According to Bone (Thorpe's 
 "Dictionary of Applied Chemistry," 1912) a gas with the 
 following percentage composition and a calorific value of 
 73 (gross) or 69 (net) C.H.U./ft. 3 at 15 C. is obtained with 
 the Thwaite cupola producer using Lancashire slack coal : 
 
 Hydrogen 5-35 
 
 Carbon monoxide . . . . 29*0 
 
 Carbon dioxide . . . . . . 2*0 
 
 Methane . . 2-05 
 
 Nitrogen . . . . . . . . 61*6 
 
 lOO'OO 
 
 Similar results were obtained by Wiirth and Co. (Stahl 
 und Eisen, (1914), 1135) using small coke, the gas containing 
 
316 INDUSTRIAL GASES 
 
 34 % CO, 1-2 % CO 2 , and having a calorific value of 84 
 (gross) or 75 (net) C.H.U./ft. 3 at 15 C. The iron of the 
 ash is stated to be recoverable with the slag as a high silicon, 
 low sulphur, pig iron (cf. also Markgraf, Stahl und Eisen, 
 38, (1918), 703). 
 
 Applications. Apart from its use as a fuel gas, air 
 producer gas has some chemical applications, among which 
 may be cited the manufacture of formates, the production 
 of nitrogen, carbon dioxide (q.v.}. 
 
 WATER GAS 
 
 Water gas was first made on an industrial scale in the 
 United States in about 1873, the initiation being due to 
 lyowe. No progress was made in this country until 1888, 
 when a plant was installed at the lyeeds Forge operating on 
 the lyowe principle, i.e. with the production of carbon 
 monoxide in the " blow " period. 
 
 In order to effect a distinction from carburetted water 
 gas, really a mixture of water gas and " oil gas " (vide infra), 
 water gas is usually spoken of as "blue water gas" since 
 it burns with a non-luminous blue flame. 
 
 General Principles of Operation. From what has 
 been said in the preceding pages it will be evident that the 
 success of water gas production depends on the maintenance 
 of a high temperature in the fuel bed up to the end of the 
 " make " period. The way in which the CO/CO 2 ratio 
 varies with temperature is well brought out by the following 
 experiments carried out by Harries in Bunte's laboratory 
 (/. Gasbeleucht., (1894), 81), and arranged by lyUggin (Ib., 
 (1898), 713). In these experiments, steam was passed over 
 wood charcoal heated to different temperatures, on a labor- 
 atory scale. 
 
 The values of K in the penultimate column are taken from 
 a curve representing the values given in Table 32. 
 
 Disregarding certain experimental discrepancies, an 
 approximate agreement is seen to exist between the calcu- 
 lated equilibrium and that observed experimentally except 
 at the lowest temperature. 
 
GASEOUS FUELS 
 
 * s 
 
 bi 
 
 H 
 
 ts 
 
 O J 
 
 0) 
 
 O oo 10 
 OICQ o N co co M oo co 
 
 w 
 
 
 b M co co ino o ON w 
 
 M 
 
 / 
 
 X X 
 
 CO 
 
 
 
 rt 
 
 HO CO CO t" 1 U"> IO w ON 
 
 u"> (> o O H '"t'O ON 
 
 o <T 
 
 
 
 From dat 
 
 
 / 
 
 ! 
 
 t^oo O ONOO N M l> '*' 
 
 ^8 
 
 
 
 
 o . 
 
 
 00 O O O> Oi0 *O COO 
 
 ^ 
 
 gl 
 
 o 
 o 
 
 ^ c-T N" ?i <s 
 
 E COMPOSITI 
 REMOVAL OF 
 
 o 
 
 O^OO H H H CO t^ O ^O 
 V|- K CO >OOO O ONOO 00 
 
 a 
 
 
 NN^ONONCOCOtv.ON 
 
 2 
 
 sT 
 
 ir) o w M b> cocio b b 
 
 EAVING THE 
 
 } 
 
 CO 
 N N Oi ">00 H N 00 O 
 HOOOMHMOvCO 
 
 tx io Vj- t> Oi S. CO CO O 
 00 O 10 Tf CO W 
 
 
 
 rj- CO ON w COO O O O 
 00 N M w COO rt- N O 
 
 ss 
 
 2:0 
 
 
 COOiM C< CO*OM H O 
 
 M M H 
 
 Q 
 
 J 
 
 o 
 
 CO t** Tf-O H O O M ^f 
 
 O O O ON O t^ c^ co co 
 
 r 
 
 o 
 
 O NO r*.H NOOOOO 
 
 M CO ^t" ^t" ^* 
 
 o 
 
 H 
 
 
 H 00 00 t^OO CO O ""t" CO 
 
 ^ d O ^^ "^ ^ coco t^ 
 
 5 
 
 A 
 
 do N do N o Vt- i>oo b 
 
 TEMPERATURE. 
 
 ! 
 
 Tj-OO 00 CO w Tt- O O ^ 
 
 t* IT) CO COO O H O N 
 
 O t^CO CO 00 O* O O 
 
 M M M 
 
318 INDUSTRIAL GASES 
 
 It will be noticed that the action at 700 C. results in the 
 formation of very little carbon monoxide and much carbon 
 dioxide, while above 1000 C., only comparatively small 
 amounts of carbon dioxide result ; the percentage of hydro- 
 gen, however, is not greatly affected. An important practical 
 pQint is the completeness of decomposition of the steam ; 
 this is seen to be sufficiently good at 1000 C. 
 
 Water gas is usually made from coke in practice, and 
 consequently its composition is liable to less variation than 
 is the case where coal, with varying hydrogen content, is 
 employed ; for this reason also the methane content is low, 
 viz. from 0*1-1*0%. According to Vignon, the methane 
 content can be increased to some 20 % by addition to the 
 coke of lime in large quantity. 
 
 The general composition and characteristics of blue water 
 gas will be found in Table 29, p. 297. According to Meade, 
 blue water gas usually contains about 100 to 120 grains of 
 sulphuretted hydrogen per 100 ft. 3 , i.e. 0*177-0*194 % by 
 volume, and 10 to 15 grains carbon disulphide per 100 ft. 3 , 
 i.e. 0*007-0*011 % by volume. 
 
 Blue Water Gas Plants 
 
 Generally speaking, a blue water gas generator consists 
 of a cylindrical chamber, lined with fire-brick, and provided 
 with a gas-tight charging device at the top and with suitable 
 air and steam admission conduits. It is important that the 
 steam should be dry, while superheating, preferably at the 
 expense of the hot-water gas leaving the generator if the 
 sensible heat of the "blow" gases is being utilized, is an 
 obvious desideratum. Since the steaming is attended with 
 a marked absorption of heat, causing the temperature of the 
 fuel to fall steadily during the run, the rate of reaction 
 rapidly falls off (cf. Bunte and Harries, Table 34). It 
 would be advisable continuously to reduce the rate of supply 
 of steam, with improvement both as regards heat losses and 
 the content of carbon dioxide, but this procedure is not 
 carried out in practice. 
 
GASEOUS FUELS 319 
 
 Owing to the intermittent character of the bperations 
 it is necessary to provide a gas-holder as a balancer except, 
 perhaps, when a battery of generators is employed. 
 
 Although attempts are made to regenerate heat from the 
 " blow " gases, e.g. in carburetted water gas manufacture with 
 the I,owe system (vide infra) and from the water gas by 
 superheating the steam, in the Dellwik-Fleischer process, there 
 is no doubt that much more might be done in this direction. 
 
 The Lowe System of Operation. The I^owe system, 
 in which the " blow " period furnishes air producer gas, is 
 the one chiefly adopted in this country, since its application 
 to the manufacture of carburetted water gas for which 
 ultimate object most blue water gas is produced admits 
 of economic utilization of the " blow " gases. For working 
 on this system the depth of fuel bed must be fairly great ; 
 a depth of 6^ ft., according to Meade, gives the best result, 
 with the coke not more than 3 in. in diameter. The generator 
 is usually some 20 ft. in total height. In most producers 
 the steam is passed alternately up and down, in order to avoid 
 chilling the bottom layers by the steam below the temper- 
 ature necessary for combustion in the "blow" period; 
 in this way a more uniform distribution is effected. The 
 " blow " and " make " periods in this system of working are 
 generally about 3 and 5 minutes respectively. The fuel con- 
 sumed is usually about 60 Ibs. of coke per 1000 ft. 3 of blue 
 water gas inclusive of the fuel required for raising the steam. 
 
 According to L,ewes, the percentage composition of the 
 " blow " gases is 
 
 Hydrogen 2-5 
 
 Carbon monoxide . . . . 29 
 
 Carbon dioxide 4 
 
 Nitrogen 64-5 
 
 lOO'O 
 
 while Meade gives 
 
 Carbon monoxide . . . . . . 17 
 
 Carbon dioxide 10 
 
 Nitrogen 73 
 
 100 
 
320 INDUSTRIAL GASES 
 
 As stated above, the volume of the " blow " gases is some 
 3-4 times that of the blue water gas produced, about 30 % 
 only of the carbon of the fuel appearing in the water gas. 
 
 Dellwik-Fleischer System. In view of the low thermal 
 efficiency (about 35 %) of the I^owe system when used for the 
 production of blue water gas without regenerative arrange- 
 ments, the more rational system of burning the carbon 
 dioxide in the " blow " period was introduced by Dellwik 
 about 1900 (cf. Dellwik, Trans. Iron and Steel Inst., (1900), 
 i., 123). It is used extensively on the Continent but only 
 to a limited extent in this country. 
 
 In this system of working, a shallow, but frequently 
 replenished, fuel bed about 3 ft. thick is employed, in 
 conjunction with a powerful air blast, the " blow " gases 
 containing some 2 % carbon monoxide (L/ewes) . As in other 
 types of generator, the steam is admitted alternately at top 
 and bottom of the fuel bed, passing through a heat-inter- 
 changer before entering the generator, and so being heated 
 by the effluent hot-water gas. On account of the much more 
 energetic liberation of heat in the " blow " period, this 
 occupies only about 1-2 minutes while the run lasts 4-8 
 minutes. 
 
 According to a test carried out by Bone, using coke of 
 87*4% carbon content (referred to the dry coke), 34-4 Ibs. 
 of the dry coke 30 Ibs. carbon were required per 1000 ft. 3 
 of blue water gas at 15 C. (exclusive of fuel for raising 
 steam), the average percentage composition being 
 
 Hydrogen 49-15 
 
 Carbon monoxide 42-90 
 
 Carbon dioxide 3-90 
 
 Methane . . . . . . . . 0*55 
 
 Nitrogen 3-50 
 
 lOO'OO 
 
 and the calorific value 
 
GASEOUS FUELS 321 
 
 The " net cold " thermal efficiency was 60*5 % (excluding 
 the fuel for raising the steam, etc.), 50*5 % of the carbon 
 appearing in the blue water gas. 
 
 Such high efficiency is, of course, not always realized 
 in common practice. 
 
 Kramer and Aarts Process. The Kramer and Aarts 
 process is a modification of the Dellwik-Fleischer process, but 
 differs in the construction and operation of the generator. Twin 
 generators are used, side by side, and are operated as follows : 
 
 The fuel beds, of 5-6 ft. depth, are " blown " in parallel 
 for about i minute, a powerful air blast being used. The 
 resulting gases, consisting essentially of carbon dioxide 
 and nitrogen, pass out at the top of the generator, together 
 with secondary air to complete the combustion of any carbon 
 monoxide present, to a regenerator consisting of two vertical 
 shafts arranged side by side, packed with chequer-work 
 and interconnected at the upper end, and then into the 
 atmosphere. The fuel having been raised to a high tempera- 
 ture in this way, steam is admitted at the bottom of one of 
 the fuel beds, passing through the bed, up one shaft of the 
 regenerator and down the other (the valve at the top 
 communicating with the atmosphere being now closed) then 
 down through the second fuel bed and escaping through 
 annular ports just above the grate. In this way the gases 
 from the generator, together with any undecomposed steam, 
 are superheated in the regenerator, and, as relatively little 
 heat absorption is thus demanded in the second generator, 
 very complete decomposition of steam and elimination of 
 carbon dioxide take place at the resulting high temperature, 
 the composition of the gas suffering less impoverishment 
 during the " run " than in other systems. After steaming 
 for some 5 minutes the " blow " is repeated, and then 
 steaming is resumed in the opposite direction from that of 
 the previous " make " operation. 
 
 The Kramer and Aarts system has the advantage of 
 
 removing the gas from the fuel bed, i.e. from catalytic 
 
 influences, at the highest temperature zone, thus preventing 
 
 carbon dioxide formation by reversal of the water gas 
 
 A. 21 
 
322 INDUSTRIAL GASES 
 
 equilibrium, and secures passage of the steam through twice 
 the depth of fuel offered to the passage of the air. In a 
 recent test of a Kramer and Aarts plant by Bone, using 
 coke of 87-2 % carbon content (referred to the dry coke), 
 the following data were obtained : 
 
 Dry coke per 1000 ft. 3 of gas at 15 C. = 287 Ibs. =25-0 
 Ibs. carbon, exclusive of the fuel required for raising the steam. 
 The average percentage composition of the gas was 
 Hydrogen . . . . . . . . 45-10 
 
 Carbon monoxide . . . . . . 4370 
 
 Carbon dioxide . . . . . . 375 
 
 Methane . . . . . . . . 0*50 
 
 Nitrogen . . 6-95 
 
 and the calorific value loo'oo 
 
 Gross .. .. 162 j CHU/ft3at o c 
 Net . . . . 149 $ 
 
 The " net cold " thermal efficiency was 0705 (excluding 
 the fuel used for raising the steam). 6o'6 % of the carbon 
 in the fuel appeared in the water gas. 
 
 Figures are also given by Keable (/. Soc. Chem. Ind., 
 (1918), 644 A) ; 29*8 Ibs. of coke were required per 1000 ft. 3 
 of blue water gas. Carburetted water gas may be produced 
 with this plant if desired, the oil being sprayed into the 
 second generator. 
 
 Carburetted Water Gas 
 
 One of the chief applications of water gas is as an inter- 
 mediate product in the manufacture of carburetted water 
 gas for the purpose of addition to coal gas. Carburetted 
 water gas is really a mixture of blue water gas and " oil gas," 
 meaning by the latter term the products of " cracking " 
 petroleum oils at a high temperature. For the production 
 of this mixture, the Lowe system is well suited, and the 
 carburetted water gas in this country is principally made by 
 this system, the best known plant being that of Humphreys 
 and Glasgow, an American firm. 
 
 Briefly described, the process is carried out in the follow- 
 ing manner. The hot " blow " gases, consisting mainly of 
 
GASEOUS FUELS 323 
 
 
 
 carbon monoxide and nitrogen, are led to a " carburettor " 
 down which they pass, a supply of secondary air being 
 admitted at the top. The carburettor consists of a chamber 
 packed with chequer- work, which is heated to a high temper- 
 ature by the combustion of the " blow " gases. I/caving 
 the carburettor the gases pass up a tall " superheater " 
 chamber about twice the height of the carburettor, also 
 packed with chequer-work, a further supply of air being 
 admitted to complete the combustion of the carbon dioxide ; 
 the products finally escape into the stack. During the 
 " run " the blue water gas passes through the chambers in 
 the same direction. Oil is sprayed into the carburettor at 
 the top mostly during the first half of the " run," so as to be 
 swept out before the next " blow " ; in passing down this 
 chamber and up the " superheater " the oil vapours are 
 converted into gaseous products by contact with the brick- 
 work, heated to about 750 C. 
 
 The mixed gases from the top of the " superheater " 
 are led to sulphuretted hydrogen and carbon dioxide purifiers. 
 The sulphur content is much less than that of crude coal gas, 
 and although naturally variable maybe about 100 grains H 2 S 
 per 100 ft. 3 (0-16 % by volume) ; the sulphur is, moreover, 
 mostly in the form of sulphuretted hydrogen which is re- 
 movable by iron oxide, the final sulphur content (CS 2 ) being, 
 according toMeade, 10-15 grains per 100 ft. 3 . The 'Composi- 
 tion of the carburetted water gas is naturally dependent on 
 the proportion of oil used, generally about 2-3 gallons per 1000 
 ft. 3 of carburetted water gas. It is not usual to add more than 
 one volume of carburetted water gas to two volumes of coal gas, 
 in order to keep down the final percentage of carbon monoxide, 
 most town gas containing 15-30 % of carburetted water gas. 
 The coke consumption is usually of the order of 45 Ibs. of 
 coke per 1000 ft. 3 of carburetted water gas, inclusive of the 
 fuel for raising the steam. According to Meade (/. Gas 
 Lighting, 117, (1912), 211), the coke for the generator is about 
 37 Ibs. coke/iooo ft. 3 of carburetted water gas in good practice, 
 lyewes states that the thermal efficiency of the process may be 
 as high as 80 %, Meade gives 61 %. Table 29 gives a 
 
324 INDUSTRIAL GASES 
 
 typical example of the composition of carburetted water 
 gas, the calorific value of which is usually about 300 gross, 
 275 net C.H.U./ftA 
 
 Originally used as an enricher on account of its high 
 illuminating power when burnt in a batswing burner 
 according to Meade about 18 C.P. as compared with 14 for 
 coal gas carburetted water gas is now used principally as 
 a means of coping with " peak " and emergency loads in 
 municipal gas supply stations on account of the ease and 
 speed with which the plant can be started up, and of the small 
 standby costs of producer plant in comparison with coal gas 
 retorts, a bench of which requires about three days for 
 heating up. Carburetted water gas is even used for distri- 
 bution without admixture in the United States. 
 
 Recently, owing to the difficulty of obtaining oil on 
 account of the decreased tonnage and the demands of the 
 Navy, together with the tendency towards the replacement 
 of the illuminating standard by a calorific standard, blue 
 water gas (i.e. uncarburetted) has sometimes been added, e.g. 
 20 %, to coal gas. Such addition has previously been 
 regarded with disfavour in this country, where the percentage 
 of carbon monoxide in illuminating gas does not often exceed 
 1 6 %, on account of the poisonous properties of blue water 
 gas with its high carbon monoxide content. 
 
 The Humphreys and Glasgow plant at the Beckton works 
 of the Gas, Light and Coke Co. produces some 18 million 
 ft. 3 /day of carburetted water gas and consists of twin genera- 
 tors which can be operated in series or in parallel according 
 as to whether the quality or the quantity of the gas is of 
 more importance. 
 
 In the Humphreys and Glasgow and other plants, special 
 interlocking devices are used to prevent the formation of 
 explosive mixtures, etc. 
 
 The carburetting of water gas may also be performed by 
 the " cold " process, i.e. by the addition of benzol, this 
 process being specially suitable when the " blow " gases 
 consist of carbon dioxide and nitrogen only. 
 
 Various proposals have been made for combined systems 
 
GASEOUS FUELS 325 
 
 effecting both destructive distillation of the coal and 
 subsequent complete gasification of the coke with the aid of 
 steam in the lower part of the same generator, the gaseous 
 products being mingled except as regards the " blow " gases 
 from the water gas production. 
 
 Applications of Blue Water Gas 
 
 As explained above, the chief application of blue water 
 gas is in connection with the manufacture of carburetted 
 water gas. It is, however, used in large quantities for 
 heating purposes and in particular for the welding of large 
 steel tubes and plates, as its flame is short and of high calo- 
 rific intensity, slightly greater than that of coal gas. Using 
 preheated air it is even possible to melt platinum. Some 
 care is needed by reason of its poisonous properties and 
 absence of smell, strongly smelling substances such as 
 mercaptan sometimes being added to mitigate this 
 danger. Blue water gas is also used in large and increasing 
 quantities for the manufacture of hydrogen by the I/ane and 
 other allied processes, by the B.A.M.A.G. continuous 
 catalytic process, etc. Blue water gas is seldom used in 
 internal combustion engines on account of its liability to 
 pre-ignition, but may be used if the compression is not too 
 high. To a limited extent, blue water gas is used in furnace 
 work, but is not so convenient for general purposes as semi- 
 water gas, cf. also the remarks on p. 298 anent the bearing of 
 high hydrogen content on the radiation from flames. On a 
 pre-war basis blue water gas could be manufactured at a cost 
 as low as 4^./iooo ft. 3 and carburetted water gas at about 
 8d./iooo ft. 3 . 
 
 SEMI-WATER GAS 
 
 General. The subject of semi-water gas, by which 
 general term we will denote the products depending on the 
 action of a mixture of air and steam on incandescent carbon, 
 is somewhat complex owing to the variety of the ultimate 
 objects of plants in which the essential reaction is the above. 
 
 Generally speaking, semi-water gas plants may be divided 
 into two classes : (i) those operating, usually on bituminous 
 
326 INDUSTRIAL GASES 
 
 coal, for the production of a gas which is used directly, in 
 the hot state without any recovery of ammonia or other 
 products, for furnace operations ; (2) those operated princi- 
 pally for the production of power. 
 
 General Principles of Operation 
 
 Perhaps the most important variables as regards general 
 procedure in the manufacture of semi-water gas are (i) the 
 nature of the fuel ; (2) the saturation temperature of the 
 air blast, i.e. the ratio of oxygen to steam; and (3) the rate 
 of gasification per square foot of grate area. 
 
 (i) Choice of Fuel. The statement already made as to 
 the possibility of utilizing almost any type of low grade fuel 
 in a producer applies particularly to the manufacture of 
 semi-water gas. This, however, should not be taken as 
 meaning that the nature of the fuel has no technical impor- 
 tance ; on the contrary, it is a very important consideration 
 in the design and performance of producers. 
 
 Of special importance are the caking propensities of the 
 fuel, which determine the tendency to choking and channelling 
 and, if highly developed, make the use of the fuel in a producer 
 out of the question ; the nature and quantity of the ash, 
 which affect the difficulty of clinkering and the permissible 
 temperature as determined by the air /steam ratio ; and the 
 carbon content, which influences the physical properties of 
 the fuel and the composition of the resulting gases, the 
 calorific value varying with the proportion of volatile hydro- 
 carbons in the fuel. 
 
 An adequate treatment of the complex subject of the 
 classification of solid fuels is beyond the scope of the present 
 volume, but a brief indication of the different varieties of 
 coal is desirable. A very complete synopsis of the avail- 
 able literature on the subject of the constitution of coal will 
 be found in a monograph by Stopes and Wheeler, published 
 by the Department of Scientific and Industrial Research, 
 1918. Many attempts, none wholly successful, have been made 
 to correlate the properties of coals with their compositions. 
 
 A classification due to Campbell (Trans. Amer. Inst. 
 
GASEOUS FUELS 327 
 
 Mining Engineers, 36, (1906), 324), and adopted by the United 
 States Geological Survey, is given below : 
 
 Group. C : H ratio. 
 
 A. Graphite .. oo -(?) 
 
 Anthracite 
 
 D. Semi-anthracitic . . 26(?)-23(?) 
 
 E. Semi-bituminous . . 23(?)-20 
 
 20 -17 
 
 Bituminous 
 
 . \ 
 
 I. 
 
 17 -14-4 
 
 I2-5-II-2 
 
 J. lignite .. .. .. 11-2-9-3 
 
 K. Peat .. 9 - 3 -(?) 
 
 Iv. Wood, Cellulose . . 7-2 
 
 According to Seyler's classification the carbon content 
 works out as follows : 
 
 Class . . Anthracitic Carbonaceous Bituminous I4gnitous 
 
 P of r c e arbon e l>93-3 W^r* 91*84 8 4 - 7 5 
 
 the carbon being reckoned on the pure coal substance free 
 from ash and sulphur. 
 
 An important characteristic of coals, especially of bitu- 
 minous coals, is the variation in their properties as regards 
 " caking " or agglomeration on heating in absence of air. 
 The exact relation between this property and the composition 
 is not definitely established ; it may, however, be stated that 
 bituminous coals may be classified roughly in the order 
 
 non-caking 
 
 caking 
 
 coking 
 according to the decrease of the carbon/hydrogen ratio. 
 
 Nitrogen Content of Coal. The percentage of nitrogen 
 present in coal varies somewhat, but is usually about 1*3- 
 1 '5 % This i s equivalent to 35-41 Ibs. N 2 /ton coal, or 
 137-158 Ibs. ammonium sulphate/ton coal. It is evident that 
 with a possible 70 % recovery of this nitrogen the quantities 
 of ammonia capable of production would be very large if any 
 
328 INDUSTRIAL GASES 
 
 considerable proportion of the fuel consumed were gasified 
 under suitable conditions. Thus 70 % recovery at 1*3 % 
 nitrogen is equivalent to 96 Ibs. ammonium sulphate/ton coal, 
 the value of which sulphate is an important fraction of that of 
 the fuel. 
 
 Sulphur Content of Coal. Sulphur is present to the 
 extent of 0-5-2-5 % in coal, partly in combination with the 
 mineral constituents of the ash, e.g. FeS 2 , CaSO 4 , and partly 
 in the form of organic compounds. The latter volatilize 
 on heating, but the bulk of the sulphur remains in the coke 
 on destructive distillation. 
 
 Other Deleterious Constituents of Coal. Coal contains small 
 quantities of arsenic and phosphorus ; arsenic may be 
 present to the extent of some O'Oi % by weight (cf. Wood, 
 Smith and Jenks, /. Soc. Chem. Ind., (1901), 437). 
 
 An important point in the choice of fuel for a particular 
 object is the question of tar elimination. The tar produced 
 with different fuels varies not only in quantity but also in 
 quality, the property of chief importance from our point of 
 view being the ease of removal of the fog, which is particularly 
 injurious when the gas is to be used in internal combustion 
 engines owing to its deleterious action by deposition on the 
 valves, etc. Thus, in spite of the small proportion of volatile 
 matter in coke, the tar fog produced in the generator is 
 specially difficult to scrub out. For such reasons, in order 
 to avoid the use of elaborate scrubbers, etc., anthracite is 
 usually employed in preference to the much cheaper bitumi- 
 nous coal in relatively small " suction " power gas plants, 
 Generally speaking, however, bituminous coal is the usual 
 fuel for semi- water gas production on a large scale. 
 
 (2) The Saturation Temperature of the Blast. 
 In our preliminary examination of this question we arrived 
 at a saturation temperature of 56 C. as striking the thermal 
 balance for the ideal case considered. In practice, however, 
 it is possible to operate over a considerable range of the 
 oxygen/steam ratio according to the quality of gas required 
 and the degree of regeneration, if any, of the sensible heat 
 carried off by the gases. 
 
GASEOUS FUELS 329 
 
 A valuable large-scale investigation of the conditions 
 influencing the production of semi-water gas was carried 
 out by Bone and Wheeler (Trans. Iron and Steel Inst., (1907), 
 i., 126 ; (1908), iii., 206), using a Mond type of producer with 
 Lancashire bituminous coal.* The main results of the 
 investigation are summarized in Table 35. 
 
 Among the more important conclusions from this investi- 
 gation may be mentioned the following : (cf . also synopsis 
 of the same by Bone in his article on Fuel in Thorpe's 
 " Dictionary of Applied Chemistry," 1912) : 
 
 (1) The mean final distribution of the carbon of the coal 
 is as follows : 
 
 In the gas 92^4 % 
 
 tar 6-3% 
 
 ash 1-3 % 
 
 lOO'O 
 
 (2) The steam undergoes practically complete decompo- 
 sition at saturations up to 55 C., above which temperature 
 some steam passes through the fuel though the absolute 
 quantity decomposed per unit weight of fuel increases. This is 
 due to the endothermic nature of the carbon-steam reaction 
 which causes a lowering in temperature in the fuel bed 
 until such tendency is balanced by the falling rate of reaction. 
 
 (3) Increasing the depth of the bed beyond 3^ ft. and 
 doubling the rate of gasification have little influence on the 
 quality of the gas. 
 
 (4) The degree of saturation has no great effect on the 
 " net cold " thermal efficiency (including the fuel required 
 for raising the steam) except when the saturation temper- 
 ature exceeds 60 C. Above this temperature a steady 
 decline is observed. The authors conclude that the best 
 compromise between high thermal efficiency and the 
 production of a good furnace gas with high carbon monoxide 
 content is obtained at 45-55 C., consequently 50 C. would 
 appear to be about the best saturation temperature (cf. also 
 
 * For similar experiments cf. also Neumann, Stahl und Eisen, 33, 
 (1913), 394- 
 
330 
 
 INDUSTRIAL GASES 
 
 TABLE 35. 
 BONE AND WHEELER'S EXPERIMENTS 
 
 Average depth of fuel bed . . . . . . 3 ft. 6 in. 
 
 Average rate of gasification (day shift) per "I . , 
 hour per producer J 
 
 
 Steam saturation temperature C. . . 
 
 45 
 
 50 
 
 55 
 
 60 
 
 70 
 
 H 2 
 CO 
 Percentage composition CO 2 
 CH 4 
 
 N a 
 
 Total percentage of combustibles 
 
 11-60 
 31*60 
 2'35 
 3'5 
 51-40 
 
 12-35 
 30-60 
 2-50 
 3-00 
 
 5i'55 
 
 I5-45 
 28-10 
 4-40 
 3-00 
 49'05 
 
 i5'5 
 27-30 
 5-10 
 3*05 
 49-05 
 
 45^5 
 
 I9-75 
 20-85 
 
 9-25 
 3'45 
 46-70 
 
 
 46*2 
 
 49-95 
 
 46-6 
 
 44^5 
 
 Calorific value, C.H.U./ft. 8 \ Gross 
 at 15 C. / Net . . 
 
 94-8 
 89-8 
 
 94-0 
 88-8 
 
 95'2 
 89*0 
 
 94' i 
 
 87-9 
 
 92-4 
 
 84-8 
 
 
 Coal used per TOGO ft. 3 of gas at 15 C. Lbs. 
 
 I5'9 
 
 16-0 
 
 16-0 
 
 157 
 
 
 
 
 Steam added to blast. Lbs. per Ib. coal . . 
 
 0'2 
 
 0'2I 
 
 0-32 
 
 "45 
 
 
 
 
 Percentage steam decomposed 
 
 all 
 
 all 
 
 all 
 
 76-0 
 
 
 
 
 Total percentage carbon losses (tar, ashes, 
 soot) 
 
 7'3 
 
 7'9 
 
 9-I5 
 
 8-0 
 
 
 
 
 Air used per Ib. coal. Ft. 3 at 15 C. 
 
 40-9 
 
 40-7 
 
 38-77 
 
 39' 5 
 
 
 
 
 -. , . , oxygen from steam . 
 Ratio of ^ . -m the semi- 
 oxygen from air 
 
 water gas . . .... 
 
 o'33 
 
 o*3 
 
 0*42 
 
 '44 
 
 
 
 
 Net cold thermal efficiency as in trials,* 
 including steam for blowers 
 
 '73 
 
 0-718 
 
 0-722 
 
 0*725 
 
 
 
 
 Ditto,* including also steam for the washers 
 
 
 
 
 
 
 
 
 
 
 
 
 Net cold thermal efficiency including fuel 
 for raising the steam for the blast (if 
 boiler efficiency =70 per cent.), also steam 
 for the blowers and washers 
 
 
 
 
 
 
 
 Ammonia in the gases. Lbs. ammonium sul- 
 phate/ton coal 
 
 
 
 
 
 
 
 
 
 
 
 
 * In the actual trials exhaust steam was 
 
GASEOUS FUELS 
 
 ON SEMI- WATER GAS PRODUCTION. 
 
 
 7 ft. 
 1 1 '5 cwt. 
 
 60 
 
 65 
 
 70 
 
 75 
 
 so 
 
 
 1 6- 60 
 27-30 
 5'25 
 3*35 
 47*5 
 
 18-30 
 25-40 
 6' 95 
 3*4 
 45-90 
 
 19-65 
 21-70 
 
 9-15 
 3-40 
 46-10 
 
 21-80 
 
 18-35 
 11-65 
 
 3'35 
 
 44-85 
 
 22-65 
 16-05 
 
 I3'25 
 3-50 
 44'55 
 
 47*25 
 
 47-10 
 
 4475 
 
 43'50 
 
 42-2 
 
 
 97'7 
 91-1 
 
 97-6 
 90*6 
 
 93-5 
 86-0 
 
 90-6 
 
 82-8 
 
 89-3 
 8i'3 
 
 
 T5'4 
 
 15-8 
 
 15-0 
 
 14-6 
 
 14-4 
 
 
 0'45 
 
 0'55 
 
 0-80 
 
 no 
 
 i-55 
 
 
 87-0 
 
 80-0 
 
 6ro 
 
 52-0 
 
 40-0 
 
 
 5'8 
 
 7-8 
 
 8-1 
 
 r i 
 
 8-4 
 
 
 38-98 
 
 36-8 
 
 36-7 
 
 38-9 
 
 39-1 
 
 
 0-50 
 
 0*62 
 
 0-65 
 
 0-75 
 
 0-80 
 
 
 0778 
 
 0-750 
 
 0-727 
 
 0-701 
 
 0-665 
 
 
 0-715 
 
 0-687 
 
 0-660 
 
 0-640 
 
 0*604 
 
 
 0-687 
 
 o"655 
 
 0-630 
 
 0-611 
 
 0-578 
 
 
 39' 
 
 447 
 
 5i'4 
 
 65-25 
 
 71-8 
 
 used except at the saturations over 65 C. 
 
332 INDUSTRIAL GASES 
 
 Voigt, /., Gas Lighting, 109, (1910), 168). For this 
 temperature, at which it is found possible to operate 
 continuously, the gas has the percentage composition 
 
 Hydrogen ...... 12*35 
 
 Carbon monoxide . . . . 30*60 
 
 Carbon dioxide . . . . 2*50 
 
 Methane ...... 3-00 
 
 Nitrogen ...... 51-55 
 
 Attention is drawn to the importance of the fact that 
 when used for regenerative furnaces the gas entering the 
 regenerators should be of such composition, including its 
 moisture content, that no change should be set up by establish- 
 ment of the water-gas equilibrium (at any rate in the direction 
 of converting carbon monoxide into carbon dioxide by reason 
 of the presence of too much water vapour) at the temperature 
 in question, namely about 1100-1200 C. Thus, the gas 
 obtained at 50 C. saturation temperature of the blast, when 
 saturated with water vapour at 20 C., and having conse- 
 quently a composition of 
 
 Hydrogen . . . . . . 12*1 
 
 Carbon monoxide . . . . 29*9 
 
 Carbon dioxide . . . . 2*4 
 
 Methane . . . . . . 2*9 
 
 Nitrogen . . . . . . 50-4 
 
 Water vapour . . . . 2*3 
 
 lOO'O 
 
 gives a value of 
 
 K ^29-9 x 2-3 
 2' X I2'I 
 
 approximately equal to that corresponding to the regener- 
 ator temperature (cf. Table 32), and is found to pass 
 unchanged through the regenerator. 
 
 (5) The methane content is independent of the steam/ air 
 ratio, indicating that its presence is due mainly to 
 destructive distillation. 
 
GASEOUS FUELS 
 
 333 
 
 The actual proportion of steam used in practice will 
 depend, of course, on the moisture content of the fuel, thus, 
 peat may require no addition of steam, while lignite requires 
 
 120 
 
 110 
 
 0,100 
 k 
 
 5 90 
 
 
 80 
 
 88 
 
 !- 
 
 $60 
 
 K 
 
 50 
 
 03 
 
 I 4 
 
 5 
 
 30 
 
 20 
 
 10 
 
 0-15 
 0-14 
 
 0'I3| 
 
 x 
 
 0-12 
 
 Ollg 
 
 
 o-ios 
 
 0-9 fc 
 
 0-7 
 
 O 
 -06Q: 
 
 -0-5 
 04 
 0-3 
 0-2 
 0-1 
 
 10 20 30 40 50 60 70 80 90 MOO 
 TEMPERATURE OF SATURATIONS 
 
 FIG. 23. Curve giving water content of air blast for saturation at 
 different temperatures. 
 
 relatively little. As seen in the production of air producer 
 gas, it is advantageous from the point of view of low carbon 
 dioxide content, to run at a temperature not below 1000 C., 
 but, on the other hand, high working temperatures involve 
 
334 
 
 INDUSTRIAL GASES 
 
 greater losses of sensible heat in the gases and of heat by 
 radiation, and also give rise to clinkering troubles. The 
 steam/air ratio will consequently depend on the nature of 
 the ash, its quantity and fusibility, and incidentally on the 
 type of grate, depth of ash, etc. Fig. 23 gives the relation 
 between the saturation temperature and the proportion of 
 steam present in the blast. 
 
 For very low grade fuels with high ash content special 
 producers are constructed. 
 
 (3) The Rate of Gasification. In the above cited 
 experiments by Bone and Wheeler the rate of gasification was 
 as high as 35 lbs./hour/ft. 2 grate area, and a similar perform- 
 ance is claimed in the " Alma " producer modified Mond 
 type designed by them. 
 
 The rates attained in usual working are, however, more of 
 the order of 15 lbs./hour/ft. 2 grate area. 
 
 The nature of the reactions taking place in the generator 
 is well illustrated by the experiments carried out by Wendt 
 on a technical semi-water gas producer with a fuel bed 
 of 7j ft. depth. 
 
 TABLE 36. 
 WENDT'S EXPERIMENTS ON SEMI-WATER GAS PRODUCTION. 
 
 Height above 
 tuyere. 
 Inches. 
 
 Temperature 
 
 H 2 
 
 CO 
 
 C0 2 
 
 CH 4 
 
 N 2 
 
 2 
 
 
 
 __ 
 
 __ 
 
 . 
 
 11-4 
 
 __ 
 
 79-1 
 
 9-5 
 
 10 
 
 mo 
 
 10-5 
 
 22'0 
 
 9-3 
 
 0-4 
 
 57'5 
 
 
 
 20 
 
 
 
 IS'? 
 
 28-0 
 
 5-5 
 
 0-9 
 
 51-9 
 
 
 
 30 
 
 925 
 
 17-9 
 
 32-7 
 
 3-0 
 
 F2 
 
 45'2 
 
 
 
 4 
 
 
 2r8 
 
 28-7 
 
 5*o 
 
 5'0 
 
 39'5 
 
 
 
 50 
 
 810 
 
 20-7 
 
 28-3 
 
 6-0 
 
 4*8 
 
 40-2 
 
 
 
 00 
 
 
 
 19-0 
 
 28-0 | 5-3 
 
 4' 1 
 
 4J6 
 
 
 
 Outlet 
 
 440 
 
 14-6 
 
 26-8 5-5 
 
 3'4 
 
 49'7 
 
 ~ 
 
 Tar was present at and above the zone 40 in. above the tuyere. Depth 
 of fuel, 7' 5*. 
 
 It will be noted that the temperatures are considerably 
 lower than those in the corresponding tests in the same 
 generator in the absence of steam (p. 314). The carbon 
 
GASEOUS FUELS 335 
 
 monoxide concentration rises to a maximum and the carbon 
 dioxide concentration falls to a minimum at 30 in. above the 
 tuyere, the less favourable water gas equilibrium at the lower 
 temperature in the upper regions causing conversion of 
 monoxide into dioxide. Methane and hydrogen are given 
 off in the upper layer from the bituminous fuel, much of the 
 sensible heat of the gases being absorbed in the process of 
 distillation. 
 
 Semi-Water Gas Plants 
 
 General. The plants for the production of semi- water 
 gas may be described under the two general headings of 
 pressure plants and suction plants according as the pressure 
 in the generator is greater or less than atmospheric. Pressure 
 plants are used for all furnace gas production and for most 
 large power installations (over about 500 H.P.), while 
 suction plants are convenient for relatively small power 
 plants. 
 
 Pressure Plants. A pressure gas plant consists 
 essentially of a vertical cylindrical shaft lined with firebrick, 
 having a fuel bed usually about 3-7 ft. in depth, and suitable 
 arrangements for charging from the top, e.g. by the use of 
 a double cone hopper, without loss of gas. A definite mixture 
 of air and steam is blown upwards through the fuel bed, 
 either by a steam injector or by a fan or blower, the steam 
 in the latter case being introduced either directly or by 
 passage of the air through or over water heated to the 
 appropriate temperature. It is important to have a thorough 
 knowledge and control of the steam/air ratio at all times. 
 
 Uniformity of the blast throughout the fuel bed is all- 
 important. The method of effecting such distribution varies 
 from the practice of using as tuyere a perforated hut-shaped 
 box as in the Duff producer, or some other distributing 
 device at the bottom of the generator, to the method most 
 usually adopted of enclosing the grate in an airtight casing 
 to which the blast is supplied. The grate may consist either 
 of horizontal fire-bars or of circumferentially disposed bars 
 inclined at about 45 C. to the vertical, e.g. as in the Mond 
 
336 INDUSTRIAL GASES 
 
 and Alma producers. The area of the grate should be 
 approximately equal to that of the generator section, other- 
 wise excessive local heating and clinkering are liable to 
 occur. 
 
 A point of great importance is the provision of suitable 
 means for effecting the removal of the ashes. In most 
 types, e.g. the Mond producer, the casing enclosing the grate 
 is open below and is sealed by water, this procedure allowing 
 of the removal of the ashes through the water without inter- 
 ruption of the working. Considerable trouble is caused by 
 the production of clinker, which is difficult to remove and 
 offers resistance to the passage of the blast, and by the 
 adherence of such clinker to the lining in the zone of highest 
 temperature, i.e. just above the grate ; consequently, 
 in some plants, e.g. the Kerpely, the walls of the producer 
 corresponding to the lower third of the fuel bed are water- 
 jacketed. This procedure has also the effect of furthering 
 ammonia recovery (vide infra). In this generator the 
 ashes are automatically removed by means of a special 
 revolving grate. This consists of a perforated eccentrically 
 constructed conical furnace bottom mounted in a circular 
 trough which revolves once in 2-4 hours, a water-sealed 
 joint being made with the furnace casing. The eccentric 
 construction has the effect of breaking up and ejecting 
 clinker. Air may be admitted either uniformly over the 
 whole of the conical surface or preferentially at the 
 centre or the periphery. In order to protect the fire-bars of 
 producers from the high temperatures attending the first 
 action of the air on the fuel and to minimize loss of heat, 
 a fairly deep layer of ashes rests on the actual grate, but for 
 small producers this procedure is not always followed. 
 Arrangements are provided in some types of producer for 
 automatically clearing the fire-bars. According to recent 
 tests by Bunte and Terres (/. Gasbeleucht., 61, (1918), 433, 
 445) with Kerpely-Marischka producers, the thermal 
 efficiency was 8i'6 %, while the loss by radiation was equiva- 
 lent to about 2 % of the total heat, all the steam being 
 generated by the water-j acket boiler. 
 
GASEOUS FUELS 337 
 
 A high rate of gasification is important and depends on 
 adequate grate area and on the avoidance of choking and 
 channelling in the fuel bed. Such troubles may be caused 
 by the fuel being too small or having a tendency to cake. 
 In the Kerpely producer referred to above, four special J- 
 shaped stirrers are arranged in the upper part of the fuel bed 
 and slowly revolve about their axes and also as a whole round 
 the furnace. This type of producer, which is used chiefly 
 on the Continent, is well suited for the gasification of very 
 low grade fuels, in treating which blast pressures up to 30 
 in. of water are employed. It was shown in Bone and 
 Wheeler's experiments (p. 329 et seq.) that a shallow fuel bed, 
 of 3 J ft. depth, gave a carbon dioxide content approximately 
 equal to that obtained with the 7-ft. bed, and in addition 
 gave a higher rate of gasification owing to the decreased 
 resistance of passage. Further, less trouble with clinker 
 and adherence of same to the producer are experienced. 
 Many producers are operated with beds of about this depth, 
 while in others depths up to about 7 ft. are used. 
 
 As regards the influence of the size of the fuel on the 
 reaction velocity, the active surface exposed will be roughly 
 inversely proportional to the size of the lumps of fuel. Dry- 
 ness of the steam is important, and in many producers a 
 pre-heating is effected, either by definite heat-interchange 
 with the hot gases leaving the producer, or by passage through 
 the annular space surrounding the lower part of the producer. 
 The blast pressure in pressure producers is usually about 
 3-6 in. of water, but may be as high as 20 in. or even 
 higher. Some producers have a bell projecting into the 
 upper part of the interior in order to minimize tar production 
 by compelling the products of distillation of the upper layers 
 of fuel to pass through the highly heated zone ; the efficacy 
 is, however, doubtful. 
 
 Useful data relating to the operation of various makes 
 of producers are given by Mills (Trans. Inst. Mining 
 Engineers, (1915), 723). 
 
 Ammonia Recovery and Cleaning of Semi-Water 
 Gas. The extent to which the purification of semi-water gas 
 A. 22 
 
338 INDUSTRIAL GASES 
 
 from suspended matter is carried, is necessarily dependent 
 on the purpose to which the gas is to be put. If to be used 
 directly in furnaces, the 5 % or so of the total carbon going 
 to tar is with advantage left in the gases both on account of its 
 calorific value and to avoid loss of the sensible heat of the 
 gases, the temperature of which is usually about 500-600 C. 
 on leaving the generator. When such purification of the 
 gas is necessary, principally in the production of gas for 
 power purposes, the removal of the tar, except in the case of 
 relatively small suction plants, is usually performed in con- 
 junction with ammonia recovery and it will be advantageous 
 to consider the two operations together. In the first place, 
 when ammonia recovery is to be effected it is necessary to 
 keep down the temperature in the producer (cf. Table 24, 
 p. 216, relating to the concentrations of ammonia existing 
 in equilibrium with nitrogen and hydrogen at high tempera- 
 tures), and this is usually accomplished (i) by the use of a 
 large proportion of steam in the blast, (2) by cooling the walls 
 of the generator. 
 
 The influence of the steam/air ratio is well shown by the 
 experiments of Bone and Wheeler (cf. Table 35), in which 
 the ammonia recovered is seen to rise from 39 to 72 Ibs. 
 ammonium sulphate per ton coal according as the saturation 
 temperature is changed from 60 C. to 80 C., equivalent to 
 a variation of the weight of steam per Ib. fuel from 0*45 to 
 1-55 Ibs. This advantage is, of course, gained at the expense 
 of a considerable increase in the percentage of carbon dioxide 
 and of a greater loss of heat in the gases. 
 
 In the Moore producer for ammonia recovery (cf. 
 Engineering, (1915), 326), by water-jacketing the walls of 
 the producer of which the upper part is air cooled, the water- 
 jacket acting as a steam boiler, it is claimed that effective 
 ammonia recovery can be secured with the use of only about 
 i Ib. steam/lb. fuel, half of which steam is generated by the 
 annular boiler, as compared with ii to 2 Ibs. in usual Mond 
 practice. The gas produced has the percentage com- 
 position 
 
GASEOUS FUELS 339 
 
 Hydrogen . . . . . . 26-0 
 
 Carbon monoxide . . . . 18*4 
 
 Carbon dioxide . . . . ir6 
 
 Methane . . . . . , 2'2 
 
 Nitrogen . . . . . . 40*0 
 
 Water vapour . . . . 1*8 
 
 100*0 
 
 and leaves the generator at a temperature of about 200 C. 
 
 Mond Process. The first attempt at gasification of coal 
 with ammonia recovery and the production of a cheap fuel 
 gas was due to Mond, who erected an experimental plant in the 
 Midlands in 1879 > the success of this experiment led to the 
 construction of the present large plant. In the Mond process, 
 the air-steam blast is led into an annular casing surrounding 
 the lower part of the producer and serving to some extent as 
 a pre-heater. The grate has inclined " fire-bars and is water- 
 sealed. In view of the high steam content about 2 Ibs./lb. 
 coal, equivalent to saturation at about 85 C. only ^ of 
 which is decomposed, it is necessary to arrange for the 
 eificient recuperation of the sensible heat carried away from 
 the producer thereby. The gases, together with the excess 
 steam, leave the generator at a temperature in the region 
 of 500-600 C. and pass first to a heat-interchanger, being 
 cooled to 300-400 C. by the counter-current flow of the 
 air-steam blast entering the generator. Further reduction 
 is effected in a water washer fitted with agitators where also 
 the tar is mostly removed, and ammonia is abstracted by 
 passage up a tower down which a solution containing about 
 36-38 % ammonium sulphate and some 2*5 % of free 
 sulphuric acid is flowing. The gases emerge at a temperature 
 of about 80 C., and are cooled in a further tower with water 
 which is subsequently utilized for the saturation of the blast 
 at about 75 C. in a third tower. In the recent types of 
 plant built by the Power Gas Corporation, the towers are 
 sometimes replaced by horizontal chambers. By rneans of 
 a further quantity of steam the saturation is raised to 85 C. 
 and the wet blast enters the generator after traversing the 
 
340 INDUSTRIAL GASES 
 
 heat-interchanger referred to above, whereby its tempera- 
 ture is raised to about 250 C. 
 
 With bituminous coal containing i*2-i*6 % nitrogen a 
 recovery of about 80-90 Ibs. ammonium sulphate/ton coal 
 can be realized on the Mond system with a yield of gas 
 equivalent to about 160,000 ft. 3 at 15 C. per ton coal (14-0 
 Ibs. coal/iooo ft. 3 at 15 C.) of calorific value about 87 gross, 
 78 net C.H.U./ftA 
 
 A representative analysis of semi- water gas with ammonia 
 recovery is given in Table 29. It will be noted that the 
 hydrogen and carbon dioxide are high and the carbon mon- 
 oxide low. The large plant operating at Dudley Port on 
 the Mond system produces gas of net calorific power about 
 75 C.H.U./ft. 3 at 15 C., which is distributed over an area of 
 about 1 20 square miles, the cost (pre-war) being about 
 if^./iooo ft. 3 . The chief drawbacks of the Mond process are 
 the high percentage of inert matter nitrogen, carbon 
 dioxide present in the gas, and the large capital outlay 
 which renders a plant of turnover less than about 150-200 
 tons coal/week unprofitable. The latter objection, it is 
 claimed, has been met by plants of later date, e.g. the Crossley 
 plant, which claims to work profitably with a weekly fuel 
 consumption of about TOO tons, the lyymn plant (Engineering, 
 (1915), 624), etc. In the Crossley plant the general procedure 
 is similar to that followed in the Mond process, the main 
 difference consisting in the replacement of the towers by a 
 series of chambers fitted with revolving paddles. In these 
 chambers cooling and ammonia absorption are effected, 
 the hot liquor at about 80 C. being circulated to saturate 
 the incoming air at about 60 C. and returned at about 
 40 C., slightly acidified with sulphuric acid, to the absorbing 
 chamber, a portion being periodically removed for evaporation. 
 It is possible to gasify successfully even such fuels as lignite, 
 peat, etc., containing 60 % moisture, by the Mond process. 
 
 Use of Semi-Water Gas for Furnace Operations 
 
 The most important application of semi-water gas for 
 furnace work is in the Siemens open-hearth furnace for steel 
 
GASEOUS FUELS 341 
 
 melting. The hot gases leaving the generator at 500- 
 600 C. and containing a considerable amount of tar, are led 
 to the regenerator which consists of chambers filled with 
 chequer-work. The chambers are traversed alternately 
 by the products of combustion in the furnace and by the 
 incoming gas and air, the two latter entering through 
 separate chambers, of course. The temperature in the 
 regenerator is in the neighbourhood of 1100-1200 C. and 
 the steel is heated to about 1600 C. 
 
 According to Hadfield (Soc. Brit. Gas Industries, Presi- 
 dential Address, April i8th, 1918), the volume of air used 
 in the practical operation of such a furnace is found to be 
 from iJ-2 times that demanded by theory ; the volume 
 of semi-water gas required for the melting of i ton of steel 
 in the open-hearth furnace is stated to be about 48,500 ft. 3 
 or 2i'6 ft. 3 /lb., equivalent to a thermal efficiency of the order 
 of 17 %, taking the net calorific value of semi- water gas as 
 85 C.H.U./ft. 3 
 
 Stress has already been laid on the importance of avoiding 
 excess hydrogen and of maintaining a high carbon monoxide 
 content ; 12-14 % hydrogen is considered the maximum 
 which is desirable (Bone), both on account of the radiation 
 from the flame and the danger of back-firing. 
 
 The Production of Power by the Combustion of 
 Semi-Water Gas in Gas Engines 
 
 Some reference has already been made to the advantages 
 of internal combustion engines for the generation of power 
 especially for relatively small units. Since, as we shall see 
 later, the overall net efficiency, i.e. inclusive of the steam 
 for the generator and the power for operating the blowers, 
 scrubbers, etc., of a gas producer may be safely taken at 
 75 %, then for 7000 C.H.U./lb. coal, we have 5250 C.H.U. 
 in the gas. Now the efficiency of a modern gas engine is 
 about 27 % referred to B.H.P. being practically indepen- 
 dent of size over say 100 H.P. The useful power production, 
 therefore, will be equivalent to 5250 X 0*27 C.H.U. = 1417 
 C.H.U., and since i B.H.P.H. = 1415 C.H.U., to 
 
342 INDUSTRIAL GASES 
 
 1417/1415 B.H.P.H. = roo B.H.P.H./lb. coal ; the overall 
 efficiency being 1417/7000 = 0*202. With 100 % efficiency, 
 i Ib. of coal would produce about 7000/1415 =4*95 B.H.P.H. 
 
 Using steam power, on the other hand, with a boiler 
 efficiency of say 75 %, representative of good practice, and an 
 engine efficiency of say 15 %, a value only obtained with 
 large units, we have a final power production equivalent to 
 7000 x 075 x 0*15 C.H.U./lb. coal = 787 C.H.U. =787/1415 
 B.H.P.H. = 0-56 B.H.P.H. per Ib. coal, or i B.H.P.H. for 
 1*8 Ibs. coal, the overall efficiency being 787/7000 = 0-112. 
 
 It should be pointed out that the above values apply 
 only to very large units. In the case of gas engines, however, 
 the figures are only slightly lower for plants of say 100 H.P. 
 or even smaller, while the efficiency for a similar steam plant 
 may be of the order of half. On the other hand, the very 
 large modern turbine sets now in vogue for electrical power 
 generation give an almost equivalent efficiency, e.g. the 
 35,000 H.P. Parsons turbine plant recently installed at the 
 Fisk Street power station, Chicago, uses steam equivalent, 
 if we take a boiler efficiency of 75 %, to about i Ib. coal per 
 B.H.P.H. ; this represents an efficiency of about 27 % in 
 the steam turbine. Another point in favour of steam plant 
 for large power units is the lower maintenance cost. 
 
 An interesting possibility of increasing the overall thermal 
 efficiency of the power production lies in the utilization of 
 the sensible heat of the exhaust gases of a gas engine, e.g. 
 by passage through Bone-Court or other boilers and utilizing 
 the steam thus produced in the usual way. With such a 
 procedure, from the 40 % or so of the heat units of the gas 
 which leave in the exhaust (= 40 X 075 =30% of the 
 original calorific value of the fuel) taking a boiler efficiency 
 of 075 and an engine efficiency of 0*15, we have another 
 30 X 075 X 0-15 % = 3-4 % to add to the overall thermal 
 efficiency. An alternative scheme is to generate steam by 
 direct combustion of producer gas, produced from very low 
 grade fuel, under the boilers. The foregoing remarks as to 
 efficiency relate also to gas engines working on blast furnace 
 gas (vide infra). 
 
GASEOUS FUELS 343 
 
 Plants for Power Generation. For this purpose we 
 have a choice of pressure plants, either with or without 
 ammonia recovery, and suction plants, and of using as 
 fuel anthracite, coke, bituminous coal, lignite, etc. The 
 respective economics of the alternatives are somewhat 
 complex but it will suffice to give a few generalizations. 
 Suction plants are used up to sizes of the order of 500 H.P. 
 on account of their greater thermal efficiency and are usually 
 operated with anthracite or gas coke for relatively small 
 plants, say 250 H.P., to avoid the troublesome cleansing 
 treatment, with its attendant loss of pressure on the engine 
 suction pipe, necessary with bituminous fuel. When, 
 however, very large plants are required, of 1000-2000 H.P., 
 the importance of ammonia recovery and of the utilization 
 of low grade fuel outweighs the cheapness and convenience 
 of the suction plant. 
 
 In all cases, it is important to remove the tar very tho- 
 roughly and to cool down the gases practically to atmospheric 
 temperature before admission to the engine. Using anthra- 
 cite the problem is comparatively simple and scrubbing in 
 towers containing coke moistened with water is often sufficient, 
 though this is sometimes preceded by passage through atmo- 
 spheric coolers, and, when using coke or inferior anthracite, 
 further treatment in a dry sawdust scrubber may be required. 
 With bituminous coal it is necessary (i) to take steps to 
 minimize the production of tar in the generator, or (2) to use a 
 centrifugal or static extractor after the scrubbers. Method 
 (i), which is not so much in favour as (2), depends on the 
 passage of the gases arising from the distillation of the fuel 
 in the upper layers of the generator, through the zone of high 
 temperature, e.g. in the Dowson plant a supply of secondary 
 air is taken in at the top of the producer and the gases are 
 withdrawn at about the centre of the fuel bed ; in the Duff- 
 Whitfield producer the tarry vapours from the upper part of 
 the producer are drawn away by steam injectors and forced 
 upwards through the lower, high temperature zone of the 
 fuel bed, the gases leaving at about the centre of the bed. 
 The " cracking " of tar proceeds very slowly, however, 
 
344 INDUSTRIAL GASES 
 
 and for this reason method (2) is generally considered 
 preferable. (2) Static tar fog separators usually depend on 
 the principle of bubbling the gas in fairly fine streams through 
 water, as in the Livesey apparatus, the gas passing through 
 narrow orifices or slits ; or in subjecting to abrupt changes 
 of direction by suitable baffles as, e.g., in the Pelouze and 
 Audouin separator. Surfaces covered with a film of tar are 
 much more efficacious in the removal of suspended tar than 
 when moistened with water. In the Smith Gas Power 
 Corporation's separator, the gas is filtered through a glass- 
 wool mat, a pressure drop of from 2-4 lbs./in. 2 being neces- 
 sary. The dynamic types usually rely on centrifugal 
 force. Thus in the Crossley centrifugal fan extractor, the 
 gas, together with water passes over the periphery from one 
 side of a rapidly rotating disc fitted with vanes, to the axis 
 on the other side. Mention may also be made of the method 
 of electrostatic separation which has been found to effect a 
 satisfactory removal of tar (cf. White, Hacker and Steere, 
 /. Gas Lighting, 119, (1912), 825 ; White, Rowley and Wirth, 
 /. Soc. Chem. Ind., (1914), 1000 ; Steere, Ib., (1914), 1145 ; 
 (1915), 415). In Gas /. (1918), August I3th, it is stated that 
 coal gas can be treated with a power expenditure of 0*0008 
 K.W.H./iooo ft. 3 . In all scrubbing appliances for suction 
 plants it is important to make the loss of head as small as 
 possible as pointed out above, hence sawdust filters, etc., are 
 perferably made of disc form rather than long and narrow ; 
 sometimes a booster fan is inserted before the engine. 
 
 Suction Plants. The principle of drawing the gas through 
 the generator by the suction of the engine (originally sug- 
 gested by Benier (1896), the technical development of the 
 modern gas engine operating at high compression on gases 
 of low calorific value being mainly due to the pioneering 
 work of Dowson) has led to the evolution of a very compact 
 and serviceable type of power plant which now plays an 
 important role in power generation and is destined to have 
 even greater importance in the future. 
 
 Suction plants have an advantage in the reduction of 
 risk of carbon monoxide poisoning owing to the prevailing 
 
GASEOUS FUELS 345 
 
 negative pressure. Gas from pressure producers lias usually 
 a slightly higher calorific value than that from suction plants, 
 (10-20 %) ; further, the pressure drop with the latter, of 
 the order of 6 in. of water, renders the power development 
 with a given engine somewhat smaller. In the smaller 
 suction plants the steam is often generated in an annular 
 boiler disposed as a jacket to the generator, loss of heat by 
 radiation being thus minimized ; in other types the sensible 
 heat of the gases is utilized in a multitubular vaporizer ; flash 
 vaporizers are also employed. The result is to make the 
 overall thermal efficiency somewhat greater than for pressure 
 producers with independent boilers. The sensible heat 
 of the exhaust gases may be employed for steam raising as 
 e.g. in the Smith (Ohio) plant. 
 
 A point in connection with suction plants requiring some 
 attention is the lag in the response of the generator to a 
 sudden variation of load on the engine ; if the load has been 
 light for some time the temperature in the fuel bed will fall 
 and, on a sudden rise in the gas requirements, only a poor gas 
 will be available for a period. This difficulty is minimized 
 by the use of a gas-holder and by allowing the gas to go to 
 waste during such " heating up " periods, or alternatively, 
 by making some gas to waste during the light load period. 
 In some cases automatic steam regulation operated by the 
 gas-holder is provided. 
 
 On starting up a suction generator the procedure is to 
 " blow up " the producer with an auxiliary fan, the gases 
 passing to the flue until of sufficiently good quality, as judged 
 from the flame at a test cock. The depth of fuel bed varies 
 from 2-3 ft. according to the size of the plant. According 
 to Burt, the volume of the generator varies from 0-12 to 
 0-18 ft. 3 /B.H.P. as the capacity increases from 20-100 
 B.H.P. ; the grate area is usually some J that of the cross- 
 section. Owing to the necessity for continuous working over 
 long periods, ample capacity must be allowed for the accumu- 
 lation of the large lumps of clinker ; charging of fuel is 
 usually performed only at intervals of say 6-12 hours, 
 adequate fuel capacity being provided. The arrangement 
 
346 INDUSTRIAL GASES 
 
 of a layer of ashes above the fire-bars is usual in suction 
 producers. The rate of gasification is of the order of 15-30 
 lbs./ft. 2 depending on the fuel burnt. Special types of 
 generator are used for small, waste fuels, etc., as, e.g. the 
 Ruston plants for the gasification of sawdust, straw and the 
 like. Even untreated seaweed may be used. Owing to the 
 method of generating the steam in suction plants the satura- 
 tion temperature is liable to vary considerably both from 
 time to time and from one plant to another ; less variation is 
 experienced with flash vaporizers with automatic regulation 
 of the water feed. The net thermal efficiency, allowing for 
 the power of the suction and including the generation of the 
 steam, is usually 75 % to 80 %. Fuel consumption varies 
 from about 12 Ibs./iooo ft. 3 of gas at 15 C. with anthracite 
 to about 1 6 Ibs. with bituminous coal. 
 
 Use of Suction Gas in Internal Combustion Engines. 
 Reference to Table 29 will indicate that although consider- 
 able differences exist between the calorific values of the various 
 fuel gases, e.g. that of coal gas is some 4 times that of suction 
 gas, there is little difference between those of the theoretical 
 mixtures with the necessary air for combustion except in 
 the case of semi-water gas, air producer gas, and blast furnace 
 gas, which have slightly lower values. Further, in practi- 
 cally all cases gaseous fuels are used with a sufficient excess 
 of air (a relatively small excess being required for semi- 
 water gas, blast furnace gas, etc.), to reduce the calorific 
 value of the mixture to about 25-30 C.H.U./ft. 3 , it being 
 specially necessary to keep down the calorific value in very 
 large engines. 
 
 The permissible degrees of compression without causing 
 pre-ignition are given by lyucke as : 
 
 Gas. Coal gas. Semi-water Blast furnace 
 
 Compression (lbs./in.2 > 
 
 excess pressure) ) J 35 J 55 
 
 Trouble experienced with pre-ignition is usually attributed 
 to the presence of excess hydrogen, but considerable doubt 
 appears to exist on the point ; apparently mixtures as rich 
 
GASEOUS FUELS 347 
 
 as 40 % hydrogen can be worked successfully if 'the com- 
 pression be not too great (cf. discussion on paper by Bone 
 and Wheeler, p. 329). There is some evidence to suggest that 
 pre-ignition may be caused by the minor constituents of semi- 
 water gas, e.g. to traces of carbon disulphide, acetylene, etc. 
 
 An interesting discussion of the above mentioned points 
 relating to gas engines will be found in a paper by Tookey 
 (/. Soc. Chem. Ind., (1917), 309). As regards the volume of 
 gas required for the production of i B.H.P.H. = 1415 
 C.H.U., taking the efficiency of the engine at 27 %, the heat 
 units required in the gas 
 
 0*27 
 
 and, taking the net calorific value of suction gas as 
 70 C.H.U./ft. 3 at 15 C., we see that the requirements are 
 
 5250 
 
 ft.3 = 75 ft.3 at 15 C. 
 
 70 
 
 This applies to a fairly large plant. 
 
 According to Brame, coal gas becomes less economical 
 than suction gas when the plant exceeds about 50 H.P. 
 
 We have seen above that the production of B.H.P.H. 
 should require the gasification of about i Ib. of coal, and this 
 amount is closely approached when anthracite is used even 
 in small plants and is improved upon in many. 
 
 Coal Gas as a Fuel 
 
 It is not proposed to enter into a description of the manu- 
 facture of coal gas, an average composition of which may be 
 found in Table 29. The composition varies to some extent 
 with the temperature of carbonization and with the size of 
 the retort and is somewhat different with the modern con- 
 tinuous system. The effect of high carbonization tempera- 
 tures is to raise the percentage of hydrogen and to lower 
 that of methane. The coal required per 1000 ft. 3 of gas at 
 15 C. is usually of the order of 17-20 Ibs. The former 
 legal standard was one of illuminating power, namely 16 candle 
 power per ft. 3 , but with the advent of the incandescent 
 mantle together with the increasing use of coal gas for power 
 
34^ INDUSTRIAL GASES 
 
 and heating purposes this standard became of secondary 
 importance and in some districts has been partly replaced 
 by one of calorific value, namely 276 C.H.U./ftA 
 
 It should be remembered that nearly all town gas contains 
 a considerable proportion of carburetted water gas or even 
 of blue water gas ; the calorific value of carburetted water 
 gas is, however, not greatly different from that of coal gas. 
 
 The sulphur content of coal gas is important in connection 
 with its domestic and industrial uses, e.g. in metal melting, 
 annealing, etc., at least in such cases as the metal is exposed 
 to the products of combustion. The initial high content 
 (according to Meade the H 2 S present in crude coal gas is of 
 the order of 500-800 grains/ioo ft. 3 = 0-8-1-3 % by 
 volume, in addition to some 35-50 grains/ioo ft. 3 of other 
 sulphur compounds) is reduced by methods described else- 
 where to a value of the order of 35-50 grains/ioo ft. 3 , the 
 residue being mostly carbon disulphide. 
 
 General. Applications of Coal Gas. For small 
 plants, coal gas has many advantages over the cheaper 
 producer gas on account of the absence of any overhead or 
 standby costs in the way of generators, gas-holders, and fuel 
 storage, and in uniformity as regards quality, pressure, etc. 
 
 Furnace Operations. Of late years, and especially 
 during the war, gas firing has come into extensive use for 
 metal melting, annealing, and reheating operations. Much 
 useful information on the subject of gas firing of crucibles 
 for the melting of non-ferrous alloys may be obtained from 
 the Annual Reports of the Royal Mint, the results of the 
 working being summarized by Hocking in Trans. Inst. 
 Metals, (1917), ii., 149. The following table, compiled from 
 Hocking's paper, indicates the general result of changing 
 the melting system from one using coke to a gas fired system : 
 
 
 Fuel used Cost of fuel per ton metal 
 per Ib. (coke, 3875. per ton) 
 metal. (gas, ao'ad. per 1000 ft. 3). 
 
 Cost in crucibles 
 per ton metal. 
 
 Coke melting (1905-1909) 
 Gas melting (1911-1916) 
 
 0-55 Ibs. 21-3 shillings 
 5-45 ft 3 . : 20-58 shillings 
 
 39- 8 shillings 
 26-8 shillings 
 
GASEOUS FUELS 349 
 
 If the net calorific value of the coke be taken as 8000 
 C.H.U./lb. and that of the gas be taken as 280 C.H.U./ft.*, the 
 heat units expended per Ib. metal are (i) coke, 4400 C.H.U. ; 
 (2) gas, 1526 C.H.U. 
 
 A reduction in wages from 157 to 10*8 shillings per ton 
 metal was also recorded for the years 1909 and 1913 respec- 
 tively with coke and gas firing. The output per furnace was 
 increased to from 190 % to 260 % of that realized with coke 
 according to the alloy melted. The gain in speed is, of course, 
 most pronounced with the first heat. 
 
 Somewhat similar conclusions are arrived at by Brook, 
 using a Brayshaw furnace (Trans. Inst. Metals, (1917), ii., 
 171). According to Forster (/. Soc. Chem. Ind., (1917), 
 1264), the gas consumption varies from 2*4 ft. 3 /lb., equivalent 
 to some 21 % efficiency, in melting 60/40 brass ingots to 8-5 
 ft. 3 /lb. (efficiency some 7-8 %), in melting cupro-nickel, 
 using the ordinary pit type of furnace. Amongst advantages 
 may be mentioned the ease of recovery of spillings by avoiding 
 the necessity of grinding and washing the ashes, as in the 
 case of the coke-fired furnace, this being important in the 
 melting of brass, nickel silver, cupro-nickel, etc., as well 
 as with precious metals ; further, the metal from an acci- 
 dental breakage of the crucible is easily recovered. As 
 regards crucibles, the economy indicated above can only be 
 secured by the use of (graphite) crucibles of special compo- 
 sition ; with the ordinary variety, as the author has experi- 
 enced in the melting of nickel silver, etc., the life is apt 
 to be shortened by flaking, owing to local oxidation and to 
 sudden heating which do not occur with a coke furnace.* 
 
 The importance of the crucible costs, which a reference 
 
 * It should be remembered, as pointed out by Thornton and Hartley, 
 Trans. Inst. Metals, (1917), ii., 306, that the oxidation of the graphite 
 crucible does not depend simply on the presence of less oxygen than that 
 corresponding to the stoicheiometric requirements for combustion ; the 
 attack on the carbon will depend on the ratio of the carbon dioxide to 
 carbon monoxide at any particular temperature, this ratio in turn being 
 conditioned by the completeness of combustion and by the water gas 
 equilibrium. Even when a considerable excess of gas is used the ratio 
 CO 2 /CO will be fairly high, and a consideration of the CO/CO 2 /C equili- 
 brium at the partial pressures in question (compare e.g. p. 303) will suffice 
 to show that in the case of carbon, oxidation will always tend to occur, 
 
350 INDUSTRIAL GASES 
 
 to the table will show to be greater than that of the fuel, is 
 not always realized in the consideration of non-ferrous 
 melting. 
 
 Amongst other advantages of gas firing may be mentioned 
 (cf. Greenwood and Hutton, Trans. Inst. Metals, (1917), i., 
 237) (i) the greater ease of regulating the heating and of 
 maintenance of a slightly reducing atmosphere ; (2) decreased 
 contamination of the metal by sulphur; and (3) greater 
 ductility of the alloy, demonstrating itself both by the ordinary 
 mechanical tests, e.g. greater elongation and greater endur- 
 ance under torsion, and also in the production of " difficult 
 spinnings/' a matter of great practical importance. There 
 are, however, some disadvantages, such as the noise, increased 
 zinc losses due to the rapid movements of the gases, etc. 
 
 The above remarks apply particularly to the usual 
 practice of intermittent working in non-ferrous melting ; 
 for continuous working on a fairly large scale, regenerative 
 producer gas furnaces are more economical. Thus, Teisen 
 (Trans. Inst. Metals, (1917), ii., 257) reports for a Hermansen 
 counter-current recuperative furnace, a coke consumption of 
 O'i8 Ib./lb. brass melted. In the design of melting furnaces 
 it is important to keep down the combustion space round the 
 crucible, the resulting high gas velocity producing better 
 heat-interchange, cf. p. 45 ; the shape of the inlet nozzle 
 is also important. 
 
 Thus far only melting furnaces have been considered. 
 Turning to the more general aspects of the question, gas 
 furnaces may be divided into three general classes : (i) those 
 operating with gas at a pressure of 2 to 3 in. of water and 
 drawing in air like the ordinary Bunsen burner ; (2) those 
 operating with gas at a pressure of 2 to 3 in. of water and 
 air at i to 3 lbs./in. 2 ; and (3) those operating with gas 
 at a comparatively high pressure, e.g. 12 lbs./in. 2 on 
 the Bunsen principle. System (3), which has been applied 
 on an extensive scale in Birmingham, gas being dis- 
 tributed at a pressure of 12 lbs./in. 2 (cf. Walter, Trans. 
 Inst. Metals, (1917), ii., 185), is more or less equivalent 
 to (2). It has the advantage of dispensing with the use 
 
GASEOUS FUELS 351 
 
 of a blower, the gas consumption is greater than with (2), 
 but the lining suffers less. Various intermediate proce- 
 dures have been adopted, e.g. in the internally-fired reheating 
 furnaces built by the Richmond Gas Stove Company; these 
 are fed with air at a pressure of a few inches of water from a 
 fan, the air not being mixed with the gas before the point 
 of combustion. A luminous flame results. The incoming 
 air passes through fireclay tubes in the furnace bed, in counter- 
 current to the exit gases, and a high efficiency is attained. 
 Thus, 100 to 300 ft. 3 of coal gas are required per cwt. metal 
 annealed, according to its thickness. Much more may be 
 expected in the future from development of the principle 
 of utilizing the heat of the products of combustion for the 
 preheating of the metal and the air. Efforts in this direction 
 have given thermal efficiencies of the order of 20 %. Pre- 
 heating of the gas tends to cause carbon deposits by cracking. 
 One of the best known furnaces of type (2) is the Brayshaw 
 furnace. In many annealing operations, the maintenance 
 of a neutral or reducing atmosphere is of great importance 
 in avoiding surface oxidation, decarburization, etc. ; gas- 
 fired furnaces are eminently suited for such purposes. 
 Further, using gas, uniformity of temperature throughout 
 the furnace is readily secured. 
 
 According to Hadfield (loc. cit., p. 341), the volume of 
 coal gas required for the heating of steel in bulk to 900 C. 
 is 1*23 ft. 3 /lb., equivalent to a thermal efficiency of 32 %. 
 To give an idea of the impetus given by the war to the use 
 of coal gas, it may be mentioned that the consumption 
 during the year 1917 at the works of Messrs. Hadfield, lytd., 
 was 360 million ft. 3 , while in some towns the consumption 
 has been more than doubled. 
 
 Coal gas is used extensively in the heat treatment, forging, 
 etc., of tools, including those of high speed steel, which demand 
 a temperature of about 1300 C. ; also for the annealing of 
 glass and wire ; in the textile industries ; in heating shell- 
 varnishing stoves, and for other purposes too numerous to 
 mention. 
 
 Power Production. Reference has been made to the 
 
352 INDUSTRIAL GASES 
 
 relative advantages of coal gas and semi-water gas for power 
 production. Since the modern gas engine has a net efficiency 
 of some 27 % on full load, the volume required per B.H.P.H. 
 of coal gas with a net calorific value of, say, 280 C.H.U. 
 (504 B.T.U.) per ft. 3 at 15 C. 
 
 = Q I415 ft.8 at 15 C. 
 280 x 0-27 
 
 = 187 ft.3 at 15 C. 
 
 equivalent to 5250 C.H.U. 
 
 Other Applications of Coal Gas. It is hardly necessary 
 to dwell here on the domestic uses of coal gas. One may, 
 however, mention that the modern gas fire has an over- all 
 efficiency up to about 75 %, some 35 to 50 % being directly 
 radiated into the room. 
 
 During the war, owing to the scarcity of petrol, coal gas 
 has been used for motor traction, in flexible rubber containers 
 and also compressed to some 50 atmospheres in steel cylinders 
 or to about 17 atmospheres in the equivalent of a large 
 pneumatic tyre. It is found that in practice 1000 ft. 3 are 
 equivalent to 3 to 4 gallons of petrol. 
 
 Coal gas, preferably after being bubbled through am- 
 monium hydroxide, is used for case hardening (cf. /. Gas 
 Lighting, 132, (1915), 3*2 ; 134, (1916), 691). 
 
 Coke-oven Gas 
 
 In the production of coke for metallurgical purposes, the 
 early " beehive " process which is, one regrets to say, still 
 in use in this country, depends on the partial combustion 
 of the coal (coking) with no recovery of the ammonia, tar 
 products, etc. In the modern type of coke oven, carbonization 
 is effected in very large closed retorts, and the gas evolved 
 after treatment for by-product recovery burnt in part 
 to heat the retorts, reasonable efficiency being secured by the 
 use of regenerators or by passing the hot products of com- 
 bustion through boilers. Some 50 % of the total gas produced 
 is required for the heating of the retorts ; the rest is available. 
 The gas has a composition similar to that of coal gas, but may 
 
GASEOUS FUELS 353 
 
 contain more nitrogen owing to ingress of air. Tie weight 
 of coal required for 1000 ft. 3 , if no gas were used for heating ; 
 the calorific value of the gas ; and the volume required for 
 the production of one B.H.P.H., are similar to the corre- 
 sponding values for coal gas. 
 
 When one considers that some 20 million tons of metal- 
 lurgical coke are produced annually in this country, the 
 possible recovery of gas is seen to be of the order of 13 million 
 ft. 3 per hour, equivalent to about 600,000 H.P. Utilization 
 for power purposes is already in progress on a large scale on 
 the North-east coast, while in some cases, e.g. at I^eeds, 
 Middlesbrough and Sheffield, the gas is piped for municipal 
 supply. In such cases the poorer first and last portions of 
 the gas are often collected separately and used for the 
 heating. 
 
 Coke-oven gas is often used in admixture with blast 
 furnace gas for heating steel furnaces. When used in this 
 way, passage through the regenerators reduces the calorific 
 value per unit volume by some 30 % (Simmersbach, Stahl u. 
 Eisen, 33, (1913), 239, 273), and there are advantages in 
 heating the air alone. By burning under steam boilers an 
 efficiency of 60 to 70 % can be obtained with an evaporation 
 of about 5 lbs./ft. 2 /hr. (cf. Kershaw, Engineer, 124, (1917), 
 28). 
 
 Blast-furnace Gas 
 
 In the smelting of iron ore the necessary temperature is 
 obtained by the combustion of (excess) carbon by air, result- 
 ing in the production of very large volumes of gas similar 
 in composition to air producer gas except that more carbon 
 dioxide is present (cf. Table 29). Originally allowed to 
 burn at the throat of the furnace, the gas was used later 
 (1837) f r the pre-heating of the blast and also for steam 
 raising, but a surplus still remained, increasing as the hot- 
 blast stoves were made more efficient. 
 
 For each ton of pig iron produced, about 150,000 ft. 3 of 
 gas are obtained (according to Hubert), some 60 % being 
 required for the hot-blast stoves and for generating power 
 A. 23 
 
354 INDUSTRIAL GASES 
 
 for the blast, etc. Thus, for each ton of iron we have some 
 60,000 ft. 3 of gas of net calorific value about 57 C.H.U./ft. 3 . 
 Taking as before an efficiency of 0*27 in the gas engine, the 
 power production per ton of iron 
 
 60,000 X 57 X 0-27 
 
 1415 
 = 652 B.H.P.H. 
 
 B.H.P.H. 
 
 In consideration of the enormous quantities of coke 
 used for blast furnaces upwards of 10 million tons/annum 
 in this country the possible power development is obvious. 
 Some power stations on these lines are in operation on the 
 North-east coast. It was predicted by Hutchinson of the 
 Skinningrove Iron Company, that the potential energy of 
 the blast furnace gas would suffice to produce all the power 
 required for the production of finished steel rails from the 
 ore. The high compression of about 155 lbs./in. 2 is used 
 without risk of pre-ignition. 
 
 It is essential to remove very thoroughly the large amount 
 of dust in the gases about 5 grams/m. 3 the removal being 
 effected either dry by bag filters after cooling the gas, since 
 it leaves the furnace at about 250 C., or wet by a Theissen 
 fan (Reinhardt, Trans. Iron and Steel Inst., (1906), iii., 47), 
 the maximum permissible residue being of the order of O'oi 
 gram/m. 3 , or by a combination of the two methods (cf. 
 also electrostatic dust removal (p. 28). With reference to 
 the recovery of potash from the blast furnace gases, see Chance, 
 J. Soc. Chem. Ind., (1918), 222T ; Berry and M'Arthur, 
 Ib., iT. 
 
 Natural Gas 
 
 Natural gas is evolved from petroleum wells in prodigious 
 quantities in the United States and Canada. In smaller 
 amounts it has been found also in Hungary, near Hamburg, 
 and even in England (Heathfield in Sussex). A representa- 
 tive composition is given in Table 29, but there is consider- 
 able variation from well to well and also with the amount 
 drawn from a particular source. Thus, hydrogen may be 
 
GASEOUS FUELS 355 
 
 present to the extent of about 20 % while i % of carbon 
 monoxide may be found in some samples. Up to about 
 i % of helium may be present (cf. pp. 131-3). 
 
 The gas is tapped oft* at pressures up to 40 atmospheres, 
 and is sometimes measured for distribution purposes at 
 this pressure; in this connection the very considerable 
 deviation from perfection of the gas at high pressure is of 
 importance (cf. Burrell and Robertson, U.S. Bureau of 
 Mines, Tech. Paper No. 131). 
 
 In the United States and Canada the gas is distributed 
 over very large areas for heating and lighting, some 900,000 
 million ft. 3 being consumed in 1917. In connection with a 
 recent cyanamide plant in Hungary some 2500 million ft. 3 / 
 annum of natural gas are being utilized for power purposes. 
 If compressed for distribution in cylinders, some of the 
 higher boiling petroleum constituents present are liquefied 
 out and may be separated, the calorific value of the gaseous 
 fraction possibly being lowered by some 20 % (cf. Dykema, 
 U.S. Bureau of Mines, Bull. 151). Natural gas gives a flame 
 of high calorific intensity. 
 
 There would appear to be a promising field for research 
 in the utilization of natural gas for the production of form- 
 aldehyde by catalytic oxidation (cf. D.R.P. 214,165) and 
 of other organic compounds. In D.R.P. 281,084/13 Herman 
 proposes to produce nitric acid by the combustion of methane 
 with oxygen-enriched air under pressure or by surface 
 combustion. 
 
 An excellent discussion of the properties and possible 
 applications of methane is given by Malison and Bgloff, J. 
 Phys. Chem., 22, (1918), 529. 
 
 Surface Combustion. The principle of surface com- 
 bustion, i.e. the flameless combination of two gases on the 
 incandescent surface of a solid, was first suggested by the 
 experiments of Davy in 1817, and has recently been elaborated 
 by Bone as a result of his researches on the catalytic combina- 
 tion of hydrogen and oxygen (Phil. Trans., A 206, (1906), 
 i), and developed on a technical basis in conjunction with 
 McCourt. 
 
356 INDUSTRIAL GASES 
 
 Perhaps the simplest form is that in which a mixture 
 of gas and air in the correct proportions or with slight excess 
 of air, is forced at considerable velocity through a refractory 
 diaphragm, combustion occurring on the other side which 
 becomes highly incandescent ; combination is confined to 
 J" or y below the surface. It is necessary, of course, that 
 the diaphragm be sufficiently refractory to avoid risk of fusion. 
 
 The advantages of such an appliance for heating purposes 
 are : (i) the high proportion of radiant energy, the radiation 
 from a solid surface being proportional to the fourth power 
 of the absolute temperature ; (2) the fact that combustion 
 is effected without the use of more than a slight excess of 
 air ; and (3) that high temperatures may be readily obtained 
 without the aid of cumbrous regenerators. When applied 
 to the heating of a crucible or a muffle, a granular refractoty 
 material such as carborundum or fused magnesia is packed 
 around and the gas mixture introduced with a velocity 
 sufficient to prevent back-firing. 
 
 Most attention has been paid, however, to the gas-fired 
 steam boiler, the efficiency of which is notoriously low 
 (usually not exceeding 60 %, according to Bone), owing to 
 the relatively small radiation and the low rate of transmission 
 of heat from gases to surfaces (cf. p. 45). In the Bone- 
 Court system the usual procedure is to pack the tubes of a 
 multitubular boiler 3" to 6" diameter with a granular 
 refractory ; the heating efficiency is confined mainly to the 
 first portions of the tube (about 70 % in the first third) 
 as combination is complete in a short length, the granular 
 material in the remaining portion of the tubes acting merely 
 to improve the turbulence and so increase the coefficient of 
 heat-interchange. It is stated that the gases leave at 
 130-200 C., a net thermal efficiency of over 90 % 
 being realized. Thus, a boiler with no 3" tubes (4' long) 
 erected at the works of the Skinningrove Iron Company, 
 Ltd., gave an evaporation of 14 lbs./hr./ft. 2 surface at and 
 from 100 C., burning coke-oven gas, and an efficiency of 
 93 % r 94 % l a gg e( l. In other cases an evaporation of 20 
 lbs./hr./ft. 2 is claimed. 
 
GASEOUS FUELS 357 
 
 In the later types wide tubes (about 6") of considerably 
 greater length are used. A specially moulded refractory is 
 used in the tubes, and combustion is not flameless as in the 
 Skinningrove boiler, giving a longer life to the refractory. 
 The air-gas mixture is supplied at a pressure of about 20 in. 
 of water. 
 
 The process works best with gases of high calorific inten- 
 sity, such as coal gas, carburetted water gas, natural gas, 
 etc., but even blast furnace gas may be used by first starting 
 up with coke-oven gas or by using pre-heated air. I^arge 
 hardening furnaces have been constructed with a thermal 
 efficiency of 32 %, while claims are made for the melting of 
 brass with 175 ft. 3 /lb. (cf. p. 349), equivalent to a net thermal 
 efficiency of the order of 29 %. I^ead melting is effected by 
 means of a bent submerged tube packed with a granular 
 refractory, with an efficiency of some 69 %. 
 
 Diaphragms of the type described have found successful 
 application in the evaporation of sugar solutions. 
 
 Gas Calorimetry 
 
 In the control of plant for the production and utilization 
 of gaseous fuels, efficiency and economy are greatly enhanced 
 by the use of calorimetric testing apparatus, especially 
 recording apparatus. The usual type of gas calorimeter, 
 e.g. those of Junker and Boys, consists essentially of a central 
 combustion chamber in which the gas flame burns at a 
 burner without touching the walls, the products of combustion 
 being led through or round coils or tubes in counter-current 
 to a regulated stream of cold water, the temperature rise in 
 which is noted by means of suitable thermometers. In the 
 Boys calorimeter the water content is only about that of the 
 Junker. The thermal efficiency exceeds 99 % under suitable 
 conditions. The condensed water is collected and the 
 necessary correction applied for the calculation of the net 
 calorific value roughly equivalent to a deduction of 600 
 calories per c.c. water. 
 
 It is not difficult to render such an instrument recording ; 
 
358 INDUSTRIAL GASES 
 
 in the Junker instrument this is accomplished by recording 
 the E.M.F. of a differential thermocouple measuring the 
 temperature difference between the inlet and exit water 
 streams respectively, the water and gas rates or their ratio 
 being maintained constant by suitable means. The Sarco 
 instrument depends on the difference in the height of two 
 columns of oil interconnected at the bottom, one of the 
 columns being heated by the gas flame and provided with a 
 jacket carrying radiator fins ; net values are indicated. 
 
 REFERENCES TO SECTION XIII. 
 
 Taylor, "Economic Fuel Production in Chemical Industry." This 
 Series. London, 1919. 
 
 Brame, "Fuel: Solid, Liquid and Gaseous." 2nd Edition. London, 
 1917. 
 
 Bone, " Coal and its Scientific Uses." London, 1918. 
 
 Meade, " Modern Gasworks Practice." London, 1916. 
 
 Thorpe's " Dictionary of Applied Chemistry." London, 1912. Articles 
 on Fuel and Water Gas. 
 
 Dowson and Larter, " Producer Gas." London, 1906. 
 
 Robson, " Power Gas Producers, their Design and Application." 
 London, 1908. 
 
 Clerk, " The Gas, Petrol and Oil Engine," New Edit. London, 1909. 
 
INDEX OF SUBJECTS 
 
 ABRAHAM-MARMIER ozone system, 
 
 144 
 water sterilization system, 146-7 
 
 Absolute zero, 7 
 
 Acetates, synthetic production of. 
 251 
 
 Adiabatic compression of gases, 
 34-8 
 
 Air producer gas, 313-16 
 
 Air, 58-92 ; properties, 58 
 
 Liquid air, useful constants, 
 69 ; manufacture, 69-77 ; 
 properties, 77-8 ; applica- 
 tions, 78-9 ; separation of 
 constituents of, 79-92 
 
 Air purification by ozone, 148-9 
 
 Alma producer, 334, 336 
 
 Ammonia equilibrium, 216 
 recovery, 33740 
 -soda process, 269 
 synthesis. See Haber process. 
 
 Argon, 124-8 ; occurrence, 124 ; 
 manufacture, 124-7 ; pro- 
 perties, 127-8 ; applications, 
 127-8 
 
 Arc process, 107, 121 
 
 Asphyxiating gases, 291-4 
 
 Atmosphere, composition of, 58-9 
 
 Automatic safety and purity tests, 
 33-4 
 
 Avogadro's hypothesis, 1 
 
 BALLOONS, 223 
 
 B.A.M.A.G. (Bunte) hydrogen pro- 
 cess, 192, 194 
 
 continuous catalytic hydrogen 
 process, 20, 49, 159-64, 173, 
 185, 207, 210, 212, 213, 219, 
 235, 263, 325 
 
 Barium peroxide, dissociation pres- 
 sure of, 97 
 
 Bedford process for the removal of 
 carbon dioxide, 173, 210 
 
 Bergius hydrogen process, 187-9, 
 212 
 
 Blast furnace, dry blast for, 50-2 
 gas, 353-4 
 
 ; Bone-Court boiler, 356-7 
 
 Boyle's Law, 2 
 
 Boys' gas calorimeter, 357 
 
 Braun nitrogen process, 115 
 i Brayshaw furnace, 351 
 
 Brin process, 96-7, 112 
 I British Oxygen Co.'s hydrogen 
 
 liquefaction apparatus, 154 
 i Bucher process, 94, 120-21 
 
 Burdett electrolytic process, 198, 
 201 
 
 i CALCIUM carbonate, dissociation 
 pressure of, 260 
 
 Calorific intensity, 298 
 
 Calorimetry, gas, 357-8 
 
 Calorific value, 296, 299 
 
 Carbon dioxide, 256-73 ; occur- 
 rence, 256 ; properties, 43-5, 
 256-9 ; dissociation, 257 
 Manufacture, 259-69 ; pure 
 carbon dioxide, 259-63 ; 
 utilization of natural sources, 
 259-60 ; thermal decom- 
 position of carbonates, 260- 
 61 ; action of acids on 
 carbonates, 261-2 ; by-pro- 
 duct in fermentation pro- 
 cesses, 262 ; concentration 
 from mixtures with other 
 gases, 209-10, 263-9 
 Applications, 269-72 ; estima- 
 tion and testing, 272-3 ; 
 liquid carbon dioxide, 258, 
 268 ; solid carbon dioxide, 
 258-9, 268-9 
 
 Carbon monoxide, 208, 237-55 ; 
 properties, 237-41 ; decom- 
 position of, 237-9 ; equili- 
 brium with carbon dioxide 
 and carbon, 14-16, 237-9, 
 303; manufacture, 241-2 
 Applications, 242-54 ; Mond 
 nickel process, 243-8 ; pro- 
 duction of formates, oxalates 
 and acetates, 248-51 ; pro- 
 duction of gases rich in 
 
360 
 
 INDEX OF SUBJECTS 
 
 Carbon monoxide continued. 
 
 methane, 251-2 ; manu- 
 facture of phosgene, 252-4 ; 
 other applications, 254 
 Estimation, 254-5 
 
 Carbonium Gesellschaft hydrogen 
 process, 192, 212 
 
 Carbonyl chloride, 252-4 
 
 Carbonyls, 243-4 
 
 Carburetted water gas, 322-5 
 
 Cascade method of liquefying gases, 
 60-61 
 
 Castner-Kellner electrolytic process, 
 202-3 
 
 Catalysis, heterogeneous, 17-20 
 homogeneous, 17 
 
 Charles' and Gay Lussac's Law, 2 
 
 Charpentier ozone process, 138 
 
 Chemical constant, 15-16 
 
 Churchill electrolytic process, 198, 
 201 
 
 Cleaning of gases, "27-9 
 semi-water gas, 337-40 
 
 Claude hydrogen system, 165, 170- 
 
 72 
 
 liquid air system, 75-7 
 oxygen and nitrogen plants, 87- 
 90 
 
 Claus process, 210, 264 
 
 Claus-Chance sulphur recovery pro- 
 cess, 269 
 
 Coal gas as a fuel, 347-52 
 
 Coke-oven gas, 352-3 
 
 Compressed gases, safety precau- 
 tions, 39-45 
 
 Compressibility of gases, 2-7 
 
 Compression of gases, 349 
 
 Conversion factors, 56 
 
 Cottrell precipitator, 28-9 
 
 Critical pressure, 10 
 temperature, 10 
 
 Crossley ammonia recovery plant, 
 
 340 
 fan extractor, 344 
 
 Cutting of metals with oxygen, 
 104-5 
 
 Cyanamide, 85-6, 94, 118-19, 121, 
 125 
 
 Cyanide process (Nitrogen fixation). 
 See Bucher process. 
 
 Cylinders, gas, 39, 41-5 ; Parlia- 
 mentary Committee on the 
 manufacture of, 39, 44, 45; 
 maximum charges of lique- 
 fied gases, 42-5, 268, 280 
 
 D ALTON'S Law, 2, 8 
 Dellwik-Fleischer water gas plants, 
 319, 320-21 
 
 Density of gases, 25-6 
 
 Dieffenbach and Moldenhauer 
 
 hydrogen process, 185-6 
 I Diffusion, 9-10 
 | Dowson producer, 343 
 i Drying of gases, 50-52 
 ! Duff producer, 335 
 
 Duff-Whitfield producer, 343 
 
 EDISON effect, 128 
 
 Effusion, 26 
 
 Electrolysis of water, constants, 
 195 
 
 Electrolytic hydrogen, 194-203 
 
 Electrostatic separation of im- 
 purities from gases, 28 
 
 " Epurite," 99 
 
 Equilibrium, 14 
 
 Exhaled air, composition of, 59 
 
 Explosion, velocity of propagation 
 of, 300-01 
 
 Explosive limits, 40, 202, 297, 300 
 
 FAT hardening. See Hydrogena- 
 
 tion of oils and fats. 
 Formates, synthetic production of, 
 
 205, 208, 271-2 
 
 Fuels, classification of solid, 326-7 
 Furnaces, use of semi-water gas in, 
 
 340-41 ; use of coal gas in, 
 
 348-51 
 
 ' GAILLARD tower, 28 
 Gas analysis, 33-4, 56 
 
 cylinders. See Cylinders, Gas. 
 holders, 52 
 
 Gaseous fuels, fundamental prin- 
 ciples relating to use of, 
 296-301 ; composition of, 
 297 ; fundamental principles 
 of production of, 301-13 
 Air producer gas, 313-18 
 Blue water gas, 318-22, 325 ; 
 Lowe system, 319 - 20 ; 
 Dellwik - Fleischer system, 
 320-21 ; Kramer and Aarts 
 process, 321-2 
 
 Carburetted water gas, 322-5 
 Semi-water gas, 325-47 ; choice 
 of fuel, 326-8 ; saturation 
 temperature of blast, 328- 
 34; Bone and Wheeler's 
 experiments, 329-32 ; rate 
 of gasification, 334 - 5 ; 
 pressure plants, 335-7 ; 
 ammonia recovery and clean- 
 ing, 337-40 (Mond process, 
 339-40) ; use for furnace 
 
INDEX OF SUBJECTS 
 
 361 
 
 Gaseous fuels continued. 
 
 Semi-water gas continued. 
 operations, 340-41 ; pro- 
 duction of power from, 
 341-2 ; plants for power 
 generation, 343-4 ; suction 
 plants, 344-7 
 
 Coal gas as a fuel, 347-52 ; 
 coke-oven gas, 352-3 ; blast- 
 furnace gas, 353-4 ; natural 
 gas, 354-5 ; surface com- 
 bustion, 355-7 ; gas calori- 
 metry, 357-8 
 
 Gases, tables of properties of, 53-6 
 
 Gasification in producers, rate of, 
 334-5 
 
 Garuti electrolytic process, 198, 
 199-200, 202 
 
 Gay Lussac's Law, 2 
 
 General Electric Co.'s ozone pro- 
 cess, 144 
 
 Gerard, ozone system, 145 
 
 water sterilization system, 147 
 
 Griesheim-Elektron field process 
 
 for hydrogen, 231 
 hydrogen process, 156, 164-8, 
 170, 186 
 
 HABER process, 94, 119, 121, 213, 
 
 215-20 
 
 Half-watt lamp, 122, 128 
 Hampson system of air liquefaction, 
 
 69-70 
 Hanisch and Schroder sulphur 
 
 dioxide process, 275, 276, 
 
 277, 278-9 
 
 Harcourt nitrogen process, 113 
 Hargreaves process, 280 
 Hausser process, 107-8, 121 
 Heat-interchange, 45-50, 57 
 Heat of combustion, 13 
 Helium, 130-32 
 Henry's Law, 8, 256 
 Hermansen furnace, 350 
 High pressure gas, 350-51 
 Hildebrandt oxygen and nitrogen 
 
 plants, 91-2 
 
 Hot-wire anemometry, 32-3 
 Howard-Bridge ozone system, 144 
 
 water sterilization system, 147 
 Humphreys and Glasgow water gas 
 
 plant, 322-5 
 
 Hydrogen, 152-236 ; Joule- 
 Thomson effect in, 67 - 8 ; 
 
 occurrence, 152 ; properties, 
 
 3, 152-5 
 Manufacture, stationary plants, 
 
 155-207 ; from water gas, 
 
 replacement of carbon mon- 
 
 Hydrogen continued. 
 
 Manufacture continued. 
 
 oxide by hydrogen, 156- 
 68 ; from water gas by 
 liquefaction of the carbon 
 monoxide, 168-74 ; by the 
 action of water or steam on 
 iron or carbon, 174-89 (Iron 
 oxide processes, 175-85 ; 
 Lane process, 178-82 ; 
 Messerschmitt process, 182- 
 4 ; other processes, 184-5 ; 
 Dieffenbach and Molden- 
 hauer process, 185 - 6 ; 
 Bergius process, 187-9) ; by 
 decomposition of hydro- 
 carbons, 189-94 (Carbonium 
 Gesellschaft process, 192 ; 
 Rincker and Wolter process, 
 192-3 ; Oechelhauser pro- 
 cess, 193-4 ; B.A.M.A.G. 
 process, 194) ; by electro- 
 lysis, 94-5, 194-203 ; other 
 processes, 203-7 ; produc- 
 tion of a mixture of nitrogen 
 and hydrogen, 207 
 
 Purification, 207-13 ; from 
 carbon monoxide, 208-9 ; 
 from carbon dioxide, 209-10 ; 
 from sulphur compounds, 
 210-11 ; from other im- 
 purities, 211-12 
 
 Cost and purity of, 212-13, 234 
 
 Applications, 213-21 ; hydro- 
 
 fenation of oils and fats, 
 14-15 ; manufacture of 
 synthetic ammonia, 215-20 ; 
 other applications, 221 
 Manufacture in the field, 223- 
 34 ; portable apparatus, 224- 
 32 ; Silicon and Silicol 
 processes, 224 - 7 ; Hydro - 
 genite process, 227-8 ; 
 Hydrolith process, 228-9 ; 
 by action of acids and alkalis 
 on metals, 229-31 ; other 
 processes, 231 - 2 ; semi - 
 portable plant, 232 - 3 ; 
 stationary plants, 233 ; lift- 
 ing power, 234 ; effect on 
 fabrics, 234; costs, 234. 
 Testing of, 235-6 
 
 Hydrogenation of oils and fats, 
 214-15 
 
 Hydrogenite process, 98, 227-8 
 
 Hydrolith process, 228-9 
 
 IGNITION temperature, 299-300 
 Interferometer, gas, 25 
 
362 
 
 INDEX OF SUBJECTS 
 
 International Oxygen Co.'s electro- 
 lytic process, 198, 200-01 
 Internationale Wasserstoff A.G. 
 hydrogen process, 178, 184-5 
 Iron carbonyls, 244 
 
 oxides, equilibria in reduction by 
 
 hydrogen, 175 
 
 oxide processes for hydrogen, 
 175-85 
 
 JOULE-THOMSON effect, 10-11, 61-8, 
 
 154, 170 
 Joule's Law, 11 
 Junker gas calorimeter, 357 
 
 KERPELY producer, 336, 337 
 Kerpely-Marischka producer, 336 
 Kitzinger nitrogen process, 115 
 Kramer and Aarts water gas plants, 
 
 321-2 
 Krypton, 132 
 
 LANE hydrogen process, 168, 178- 
 82, 184, 213 
 
 Latent heats of fusion and evapora- 
 tion, 13 
 
 Level, influence of difference in, 
 24-5 
 
 Lifting power of hydrogen, 233-4 ; 
 of helium, 234 
 
 Linde oxygen and nitrogen plants, 
 
 81-7 
 
 system of air liquefaction, 73-4 ; 
 theory of, 61-8, 70-72 ; 
 effect of pre-cooling in, 723 
 
 Linde-Frank-Caro process, 50, 116, 
 172-4, 204, 210, 212, 215, 
 219, 222, 233, 242, 251, 263 
 
 Liquefaction of permanent gases, 
 60-92 ; theory of Joule- 
 Thomson effect, 61-8 
 
 Liquefied gases, 42-5 
 
 Liquid air, See Air. 
 hydrogen, 154 
 
 Livesey tar separator, 344 
 
 Lymn ammonia recovery plant, 
 340 
 
 MAURICHEAU-BEAUPRE process, 231 
 
 Measurement of rate of flow, 29-33 
 
 Melsens-Pictet sulphur dioxide pro- 
 cess, 276 
 
 Messerschmitt hydrogen process, 
 178, 182-4 
 
 Meters, gas, 29 
 
 Methane equilibrium, 189 
 
 production from carbon monoxide, 
 209, 240-41, 251-2 
 
 Mine rescue apparatus, 78-9 
 
 Mineral waters (artificial), 269-70 
 Mond gas, 339-40 
 
 nickel process, 242, 243-8 
 
 producer, 334, 335, 336 
 Moore lamp, 129 
 
 producer, 338-9 
 
 NATURAL gas, 354-5 
 
 Neon, 128-30 
 
 Nernst Heat Theorem, 14-16, 135, 
 216, 240, 253, 285 
 
 Nickel carbonyl, 241, 243-4 
 
 Niton, 132-3 
 
 Nitrogen, 110-22; properties, 110, 
 
 111 
 
 Manufacture, 79-92, 111-16; 
 by the fractionation of liquid 
 air, 79, 92, 112; by direct 
 chemical removal of the 
 oxygen from air, 112-14 ; 
 from producer gas and pro- 
 ducts of combustion, 114-15 ; 
 by physical methods (in the 
 gaseous state), 115-16 ; by 
 direct chemical methods, 
 116 
 
 Purification, 116-17 ; cost and 
 purity, 117 ; applications 
 (nitrogen fixation), 117-22 ; 
 estimation and testing, 122 
 
 Nitrogen content of coal, 327-8 
 fixation, 117-21 
 
 Nitrous oxide, 285-90 ; properties, 
 43-5, 285-6 ; manufacture, 
 286-8 ; purification, 288 ; 
 applications, 288-90 
 
 OECHELHAUSER hydrogen process, 
 
 192, 193-4 
 
 i Orifice meters, 29, 30 
 Ostwald process, 108, 121 - 
 Otto ozone system, 144 
 water sterilization system, 147, 
 
 148 
 Oxalates, synthetic production of. 
 
 See Formates. 
 | Oxygen, 93-109 ; properties, 93 
 
 Manufacture, 79-92, 94-100 ; 
 by the fractionation of liquid 
 air, 79-92, 94 ; by electro- 
 lysis, 94-5, 194-203 ; by 
 alternate formation and de- 
 composition of higher oxides, 
 etc., 95-8 ; by auto-com- 
 bustion methods, 98 ; by the 
 action of water on peroxides 
 and the like, 98-9; by 
 physical methods (in the 
 gaseous state), 99-100 
 
INDEX OF SUBJECTS 
 
 363 
 
 Oxygen continued. 
 
 Compression, 42, 100-01 ; cost 
 and purity, 101-2 ; applica- 
 tions, 102-8 ; estimation 
 and testing, 108-9 
 Oxygen-enriched air, 106-8 
 Oxygenite, 98 
 Oxylithe, 99 
 Ozonair air purification system, 
 
 148-9 
 
 ozone system, 144 
 water sterilization system, 147 
 Ozone, 134-51 ; occurrence, 134 ; 
 
 properties, 134-36 
 Production, 136 - 40 ; by 
 chemical methods, 137 ; by 
 thermal treatment of oxygen, 
 137-8 ; by electrolysis, 138- 
 9 ; by photochemical means, 
 139 ; by the electric dis- 
 charge, 139-40 
 
 Manufacture, general principles 
 of ozonizers, 140-43 ; com- 
 mercial ozonizers, 143-5 
 Applications, 145-51 ; water 
 sterilization, 145 - 8 ; air 
 purification, 148-9 ; chemi- 
 cal applications, 149 
 
 PELOUZE and Audouin tar ex- 
 tractor, 344 
 Permeability of materials, 9-10, 
 
 153-4 
 
 Phosgene, 252-4 
 Physical constants, 53-7 
 methods of testing purity of 
 
 gases, 25-6 
 Pictet oxygen and nitrogen plants, 
 
 90-91 
 
 Pitot tube, 30-32 
 Plumboxan process, 96 
 Poison gases, 291-4 
 Power production, from semi-water 
 
 gas, 341-2 
 
 producer plant for, 343-4 
 suction plants for, 344-7 
 from coal gas, 351-2 
 Properties of gas, tables of, 53-6 
 
 RARE gases of the atmosphere, 92, 
 123-33 ; discovery of, 123-4 
 
 Reaction velocity, 17 
 
 Reference data, 53-6 
 
 Resistance to flow of gases, 22-4 
 
 Richmond Gas Stove Co.'s furnace, 
 351 
 
 Rincker and Wolter hydrogen 
 process, 192-3 
 
 Ruston suction gas plants, 346 
 
 SAFETY precautions with com- 
 pressed gases, 3945 
 
 Sarco carbon dioxide apparatus, 33 
 gas calorimeter, 358 
 
 Saturation temperature of air blast, 
 328-34 
 
 Schmidt electrolytic process, 198, 
 199 
 
 Schoop electrolytic process, 198, 
 200 
 
 Schriver electrolytic process, 198, 
 201 
 
 Schuckert electrolytic process, 95, 
 
 198, 202 
 
 (Silicon) hydrogen process, 224, 
 225 
 
 Semi- water gas. See Gaseous fuels. 
 
 Separation of gaseous mixtures, 
 
 26-7, 79-81 
 
 liquid or solid particles from 
 gases, 27-9 
 
 Serpek process, 119-20 
 
 Siemens and Halske ozone system, 
 
 143-4, 147 
 water sterilization system, 146-7 
 
 Silicol hydrogen process, 225-7, 235 
 
 Siemens de Frise water sterilization 
 system, 147 
 
 Smith Gas Corporation's tar separa- 
 tor, 344 
 suction gas plant, 345 
 
 Solubility of gases, 8 
 
 Solvay process, 269 
 
 Sorption, 8-9 
 
 Space- velocity, 18 
 
 Space- time-yield, 18 
 
 Specific heats of gases, 1113 
 
 Storage of gas, 52 
 
 Strache hydrogen process, 185 
 
 Stream-line motion, 20-22 
 
 Suction gas, 344-7 
 
 Sulphur dioxide, 274-84 ; proper- 
 ties, 43-5, 274-5 
 Manufacture, 275-80 ; pro- 
 duction of dilute sulphur 
 dioxide, 277-8 ; concentra- 
 tion of dilute sulphur dioxide, 
 278-9 
 
 Applications, 280-83 ; estima- 
 tion and testing, 283-4 ; 
 liquid sulphur dioxide, 279- 
 80 
 
 Sulphur content of coal, 328 
 
 Surface combustion, 355-7 
 friction, 23 
 
 Siirth carbon dioxide process, 266-7 
 
 THEISSEN fan, 354 
 Thermochemistry, 13-14 
 
INDEX OF SUBJECTS 
 
 Tindal water sterilization system, 147 
 Tindal de Frise ozone system, 144 
 Turbulent motion, 20-22 
 
 VENTURI meter, 30 
 Verley vanillin process, 149 
 Viscosity of gases, 20-21 
 Vosmaer ozone system, 144 
 water sterilization system, 147 
 
 WATER gas, blue, 156, 316-22, 325 
 
 carburetted, 322-5 
 
 equilibrium, 157-8, 238-9, 309 
 Water sterilization by ozone, 145-8 
 Welding autogenous, 103-4 
 Wood pulp manufacture, 280-81 
 
 ZENON, 132 
 
INDEX OF NAMES OF AUTHORS 
 
 ALDER, 113 
 
 Amagat, 3, 43, 258 
 
 American Air Nitrates Corporation, 
 
 119 
 American Cyanamide Co., 113, 119, 
 
 125 
 
 American Oxhydric Co., 200 
 Anderson, 227 
 Andrew, 250 
 Archibald, 139 
 Ardol, Ltd., 172 
 Artigue, 99 
 Ashcroft, 232 
 Athion Gesellschaft, 242 
 Austin, 58, 93 
 Auld, 292 
 Avogadro, 1 
 
 BADISCHE ANILIN & SODA FABRIK, 
 120, 156, 158, 159, 161, 162, 168, 
 170, 176, 177, 191, 205, 208, 211, 
 217, 218, 220, 263, 264 
 
 Baggs, 175, 209 
 
 Baillio, 225 
 
 Ball, 263 
 
 Baly, 79, 80 
 
 Bamberger, 228 
 
 Barlow, 196 
 
 Barnitz, 182, 222 
 
 Bartelt, 100 
 
 Barton, 204 
 
 Baskerville, 289 
 
 Basset, 276, 277 
 
 Baur, 181 
 
 Bayer & Co., 218 
 
 Becquefort, 204 
 
 Bedford, 211 
 
 Behrens, 262 
 
 Beill, 143 
 
 Bendixsohn, 138 
 
 Benier, 344 
 
 Benjamin, 242 
 
 Bergfeld, 98 
 
 Bergius, 187 
 
 Bergmann, 276 
 
 Berlin Anhaltische Maschinenbau 
 A. G. (B.A.M.A.G.), 161, 184, 
 191, 192 
 
 Berliner, 276 
 
 Bernthsen, 222 
 
 Berry, 354 
 
 Berthelot, 143, 248 
 
 Bischof, 313 
 
 Binder, 109 
 
 Bjerrum, 257 
 
 Blagburn, 112 
 
 Blum, 198, 222 
 
 Bock, 256 
 
 Bock, 228 
 
 Bodenstein, 18, 19, 126 
 
 Bohr, 256 
 
 Bone, 19, 315, 320, 322, 329, 334, 
 
 337, 338, 341, 347, 355, 356, 
 
 358 
 
 Bornstein, 57 
 Bosch, 191, 220 
 Boudouard, 16, 238, 303 
 Bourchaud, 229 
 Boussingault, 96 
 Boyer, 236 
 Bradley, 64, 65 
 Brahmer, 138, 221 
 Brame, 347, 358 
 Bramkamp, 77 
 Bredig, 249, 272 
 Brianchon, 95 
 Brindley, 231 
 Briner, 140, 238 
 Erin's Oxygen Co., 96, 97 
 Briscoe, 133 
 British Oxygen Co., 69, 70, 84, 95, 
 
 97, 198 
 Brodie, 136 
 Brook, 349 
 Brownlee, 115, 192 
 Brunei, 274 
 Buchanan, 160 
 Bucher, 113, 120, 125 
 Buffa, 200 
 Bulle, 57 
 Bunte, 192, 309, 316, 318, 
 
 336 
 
 Burdett, 197 
 Burrell, 40, 202, 355 
 Bush, 29 
 Byk, 99 
 
366 
 
 INDEX OF NAMES OF AUTHORS 
 
 CAILLETET, 60 
 
 Callendar, 298 
 
 Calvert, 20 
 
 Campari, 286 
 
 Campbell, 326 
 
 Carbonium Gesellschaft, 192 
 
 Cardoso, 57 
 
 Caro, 115, 118 
 
 Carpenter, C., 211 
 
 Carpenter, H. C. H., 181 
 
 Carpenter, C. W., 40 
 
 Carrol, 261 
 
 Carter, 249, 272 
 
 Carulla, 204 
 
 Castner-Kellner, 203 
 
 Cavendish, 124 
 
 Cedford Gas Producing Co., 251 
 
 Centrallstelle fur wissenschaftlich- 
 
 technische Untersuchungen, 218 
 Chaillaux, 98, 206 
 Chance, 354 
 Chapman, 135 
 Charles, 2 
 Chaudron, 175 
 Chemische Fabrik Griesheim-Elek- 
 
 tron, 126, 158, 164, 203, 231 
 Chemische Fabrik von Heyden, 
 
 A. G., 204 
 Chemische Fabrik vorm. Moritz, 
 
 Milch & Co., 187 
 Churchill, 197 
 Chwolson, 56 
 Clamond, 204 
 Claude, 68, 81, 92, 126, 128, 129, 
 
 170, 210 
 Glaus, 210 
 Clayton, 215 ^ 
 Clement, 138 
 Clerk, 358 
 Coehn, 95 
 Collie, 129 
 Colton, 288 
 
 Companie du Gaz de Lyons, 159 
 Consortium fur Elektrochemische 
 
 Industrie, G.m.b.H., 224 
 Cottrell, 28, 130, 132 
 Cowap, 244 
 
 Coward, 40, 241, 299, 300 
 Cowper-Cowles, 197 
 Crofts, 57, 110, 152, 257 
 Crookes, 208 
 Crossley, 122, 222 
 Cyanidgesellschaft, 112 
 
 DALTON, 2 
 Dammer, 199 
 D'Arsonval, 196, 204 
 Davy, 286, 355 
 Deguide, 204 
 
 De Jahn, 218 
 
 Dellwik, 320 
 
 Dellwik - Fleischer Wassergas 
 G.m.b.H., 176 
 
 Dempster, 177, 178 
 
 Dendy, 271 
 
 Denis, 250 
 
 De Villepique, 100 
 
 Dewar, 10, 79, 102, 127, 128, 129, 
 132, 153, 154 
 
 Dieffenbach, 176, 185, 180, 190, 207 
 
 Dixon, 299, 300, 301 
 
 Don, 151 
 
 Dorn, 131 
 
 Dowson, 344, 358 
 j Dreaper, 115 
 I Dubox, 250 
 
 Durand, 140 
 
 Dykema, 355 
 
 EASTWICK, 204 
 
 Eberlein, 277 
 
 Edgar, 153 
 
 Egloff, 355 
 
 Elektrizitats, A. G., vorm. Sclmckert 
 
 & Co., 197 
 
 Elektrizitatswerk Lonza A. G., 113 
 Elektrochemische Werke, Bitterfeld, 
 
 249, 251 
 
 Elkan Erben, G.m.b.H., 231 
 Ellis, 115, 192, 193, 215, 221, 250 
 Elmore, 287 
 Elworthy, 114, 204 
 Enderli, 272 
 Engelhardt, 109, 222 
 Engels, 165 
 Erdmann, 215, 251 
 Erlwein, 141, 142, 151 
 Escher, 57 
 Evans, 211 
 Eycken, 197 
 
 FALK, 300 
 
 Farbwerke vorm. Meister, Lucius & 
 
 Briining, 106, 113 
 Fay, 239 
 Feldkamp, 205 
 Ferguson, G. E., 239 
 Ferguson, J. B., 274 
 Fielding, 229 
 Filippo, 126, 128 
 Fink, 18 
 Finke, 112 
 Firth, 153 
 
 Fischer, F., 125, 138, 139, 202 
 Fischer, H., 258 
 Flagg, 286 
 Fletcher, 104 
 Foersterling, 99, 231 
 
INDEX OF NAMES OF AUTHORS 
 
 367 
 
 Fonda, 126, 248 
 Fonrobert, 150 
 Forshaw, 241 
 Forster, 349 
 Fournier, 100 
 Fourniols, 236 
 Frank, 115, 118, 209 
 Franke, 112 
 Frankland, 222 
 
 GARNER, 92 
 
 Garners and Metals Research Co., 
 
 276 
 
 Garuti, 196, 197 
 Gas Developments, Ltd., 181 
 Gas Light and Coke Co., 324 
 Gauger, 40, 202 
 Gautier, 59, 152, 205 
 Gay Lussac, 2 
 Gay ley, 51 
 Geeraerd, 197 
 General Chemical Co., 220 
 General Electric Co., 144 
 Gerard, 145 
 Gerhartz, 176 
 Gesellschaft fur Linde's Eismas- 
 
 chinen, A.G. See Linde. 
 Giffard, 176 
 Glassner, 181 
 Goldschmidt, 249, 250 
 Goldstein, 140 
 Goosmann, 262, 265, 273 
 Graham, J., 153 
 Graham, J. I., 254 
 Gray, 141 
 Greenwood, 34, 108, 217, 218, 222, 
 
 350 
 Griesheim - Elektron Co. See 
 
 Chemische Fabrik Griesheim- 
 
 Elektron. 
 Grillo, 278 
 Grouven, 260 
 Guillet, 211 
 Gutbier, 153 
 Gutzeit, 235 
 Gwosdz, 309, 310 
 
 HABER, 25, 26, 56, 215, 216, 217, 
 
 218, 222, 249, 309 
 Hacker, 344 
 Haddon, 112 
 Hadfield, 341, 351 
 Hahn, 309 
 Hahnel, 125 
 Hale, 64, 65 
 Haller, 284 
 Hamburger, 128 
 Hampson, 61 
 Hanisch, 275 
 
 Hanmann, 99 
 
 Harger, 98, 115 
 
 Harpf, 284 
 
 Harpster, 25 
 
 Harries, 309, 316, 317, 318 
 
 Harries, C., 136, 150 
 
 Hart, 276 
 
 Hartley, 349 
 
 Hausbrand, 50, 57 
 
 Hawkins, 229 
 
 Helmholtz, 298 
 
 Helouis, 100, 205 
 
 Hembert, 159 
 
 Henderson, 222 
 
 Henning, 110, 257 
 
 Henry, 8, 159, 239 
 
 Heraeus, 198 
 
 Herman, 355 
 
 Heuse, 57 
 
 Hildebrand, 97 
 
 Hillebrand, 124 
 
 Killer, 210 
 
 Hird, 283 
 
 Hirtz, 244 
 
 Hocking, 348 
 
 Hofmann, 155, 235, 255 
 
 Holborn, 12, 58, 93, 110, 257 
 
 Hollandsche Residugas - Maats- 
 
 chaapij, 192 
 Holt, 153 
 Hooton, 206 
 Horak, 253 
 Howard, 262 
 Hubert, 353 
 Humphrey, 100 
 
 Humphreys & Glasgow, 178, 322 
 Hunter, 285 
 Huntingdon, A. K., 208 
 Huntingdon, T., 277 
 Hutchinson, 354 
 Hutin, 205, 277 
 Hutton, 113, 242, 350 
 
 INTERNATIONAL CHEMICAL Co., 224 
 International Oxygen Co., 105, 199 
 Internationale Wasserstoif A.G., 
 
 184 
 Ipatiew, 214 
 
 JACOB, 175 
 
 Jakob, 12, 58 
 
 Jaubert, 98, 99, 178, 224, 225, 227, 
 
 228 
 
 Jenks, 328 
 Johnson, J. E., 107 
 Johnson, J., 167, 260 
 Jones, 135 
 Josse, 50 
 Jost, 216 
 
368 
 
 INDEX OF NAMES OF AUTHORS 
 
 oule, 10, 11 
 ouve, 205 
 ungfleisch, 274 
 unker, 13 
 
 urisch, 9 \ 
 
 KALTENBACH, 277 
 
 Kainmerlingh Onnes, 61, 131 
 
 Kastner, 96 
 
 Katz, 250 
 
 Kausch, 92, 273 
 
 Kaye, 57 
 
 Kayser, 130 
 
 Keable, 322 
 
 Kendall, 206 
 
 Kershaw, 353 
 
 Kistiakowsky, 127 
 
 Knecht, 113 
 
 Knowles, 197 
 
 Koepp & Co., 249, 250 
 
 Kolbe, 272 
 
 Krupp, 186, 271 
 
 Kubierschky, 100 
 
 LABY, 57 
 
 Ladenburg, 135 
 
 Lahousse, 206 
 
 Lance, 114 
 
 Landin, 210 
 
 Landis, 122 
 
 Landolt, 57 
 
 Lane, 176, 209, 263 
 
 Lange, 275 
 
 Langen, 15 
 
 Langer, 159, 243 
 
 Langmuir, 129 
 
 Larter, 358 
 
 Latchinoff, 196 
 
 Le Chatelier, 301 
 
 Lehmann, 221 
 
 Leithauser, 140, 142 
 
 Leiser, 26 
 
 Lepsius, 167, 193, 194, 198, 203, 
 
 221 
 
 Le Rossignol, 216, 222 
 Leroy, 197 
 Leslie, 264 
 Lessing, 190, 241 
 Levi, 166 
 Levin, 197 
 Levy, 100 
 Levy, 254 
 
 Lewes, 176, 319, 320, 323 
 Lidoff, 287 
 Linde, 61, 79, 81, 92, 126, 168, 169, 
 
 170, 208 
 
 Linder, 142, 143 
 Lloyd, 283 
 Loiseau, 241 
 
 Lorenz, 199 
 
 Lowe, 25 
 
 Lowe, 316 
 
 Lowry, 111 
 
 Lucke, 346 
 
 Luggin, 309, 316 
 
 Luhmann, 265 
 
 Lunden, 178 
 
 Lunge, 34, 56, 222, 273, 275, 284 
 
 Lussana, 12 
 
 Luttinger, 250 
 
 M' ARTHUR, 354 
 
 McBain, 8 
 
 McCourt, 115, 355 
 
 McDavid, 299, 300 
 
 McElroy, 250 
 
 Machalske, 253 
 
 Mackey, 261 
 
 Machtolf, 190, 192 
 
 Majert, 232 
 
 Malaquin, 137 
 
 Malisoff, 355 
 
 Mallard, 301 
 
 Mallet, 95, 100 
 
 Maquenne, 124 
 
 Marechal, 96, 186 
 
 Marengo, 204, 229 " 
 
 Markgraf, 316 
 
 Marselli, 119 
 
 Marston, 113, 287 
 
 Martin, 57, 87 
 
 Marx, 138 
 
 Maschinenbau-Anstalt Humboldt, 
 
 170 
 
 Maschinenfabrik Oerlikon, 197, 199 
 Maschke, 222 
 Massenez, 139 
 Matignon, 220 
 Matter, 287 
 
 Mauricheau-Beaupre, 231 - 
 Maxted, 90, 160, 177, 181, 217, 
 
 222, 241 
 Mazza, 100, 204 
 Meade, 318, 319, 323, 324, 348, 
 
 358 
 
 Menne, 104 
 Mercia, 250 
 Merriman, 237 
 Merz, 165 
 
 Messerschmitt, 177, 207 
 Mewes, 77, 89, 92 
 Miethe, 221 
 Mills, 337 
 Mitchell, 270 
 Moldenhauer, 176, 185, 186 190 
 
 207 
 
 Molinari, 57, 278 
 Moller, 28 
 
INDEX OF NAMES OF AUTHORS 
 
 369 
 
 Mond, A., 28 
 
 Mond, L., 153, 150, 243, 244, 245 
 
 Moore, 276 
 
 Moritz, 197 
 
 Morris, 32 
 
 Moser, 255 
 
 Motay, Tessie du, 90, 104, 180 
 
 Moulin, 270 
 
 Muller, 159 
 
 Murray, 85, 90, 97, 105, 109 
 
 NAEF, 116 
 
 Naher, 159 
 
 Nauss, 190 
 
 Neave, 100 
 
 Nernst, 14, 56, 137, 257 
 
 Neumann, G., 153 
 
 Neumann, K, 329 
 
 New York Nitrogen Co., 112, 200 
 
 Newbiggin, 22 
 
 Nitridfabrik G.m.b.H., 249 
 
 Norman, 214 
 
 Norsk Hydro Elektrisk Kvaelstof- 
 
 aktieselskab, 125 
 Norton, 122, 222 
 Nussow, 205 
 
 OBACH, 196 
 
 Oehlom, 222 
 
 Oerlikon Co. See Maschinenfabrik 
 
 Oerlikon. 
 Ohlmer, 19 
 Olszewski, 61 
 Onnes, 61, 131 
 Orange, 129 
 Ovitz, 250 
 Ozouf, 265 
 
 PAAL, 214, 235 
 
 Pannell, 22, 23, 24, 30, 32 
 
 Paquiet, 221 
 
 Parkinson, 79, 80, 96, 108 
 
 Parsons, 121, 220 
 
 Partington, 108, 222 
 
 Paterno, 253 
 
 Patterson, 12 
 
 Payman, 40 
 
 Perkin, 151 
 
 Perl, 113 
 
 Pernell, 277 
 
 Petavel, 113, 242 
 
 Philip, 99, 231 
 
 Pictet, 43, 60, 105, 191, 282, 288 
 
 Pintsch, 210 
 
 Piva, 166 
 
 Plenz, 40 
 
 Pompili, 196, 197 
 
 Ponnaz, 222 
 
 Porter, 40 
 
 Power Gas Cprporation, 339 
 
 A. 
 
 Praceiq, 229 
 Prager, 175 
 Pratis, 204, 229 
 Price, 112 
 Pring, 134, 139 
 Pryor, 200 
 Pullman, 204, 263 
 
 RABENALT, 210 
 
 Ramsay, 123, 124 128, 130, 132, 
 
 133, 153, 270 
 Ransford, 99 
 Rao, 150 
 Rasch, 42, 290 
 Rayleigh, 59, 123, 124, 152 
 Read, 159 
 
 Regnault, 43, 258, 285 
 Reinhardt, 354 
 Reissig, 210 
 Renard, 196, 211, 230 
 Rhead, 9, 238, 303 
 Ricarde-Seaver, 208 
 Richardson, D., 109 
 Richardson, L. B., 9 
 Richter, 232 
 Rideal, E. K., 151, 255 
 Rideal, S., 151 
 Ridsdale, 177 
 Rieche, 205 
 Riedel, 115 
 Rincker, 190, 192 
 Ringe, 125 
 Robertson, 40, 355 
 Robson, 368 
 Roscoe, 57 
 ! Rose-Innes, 11 
 Roth, 57 
 Rowley, 344 
 Runge, 100 
 
 SABATIER, 155, 158, 214, 240, 258 
 
 Sander, 174, 185, 192, 222, 236 
 
 Sarason, 231 
 
 Scheel, 57 
 
 Schering, 149 
 
 Schmalotta, 265 
 
 Schmid, 255 
 
 Schmidt, O., 196, 199 
 
 Schmidt, R., 132 
 
 Schmidt, Rudolf, 272 
 
 Schneider, 155 
 
 Schonbein, 136 
 
 Scholl, 207 
 
 Schoonenberg & Naamloze Ven- 
 
 nootschap Philips Metal Gloe- 
 
 lamp-fabrik, 126 
 Schoop, 197 
 Schorlemmer, 57 
 Schriver, 198, 199, 201 
 
 24 
 
370 
 
 INDEX OF NAMES OF AUTHORS 
 
 Schroder, 275 
 
 Schuck, 214 
 
 Schuckert. See Elektrizitats A.G. 
 
 vorm. Schuckert & Co. 
 Schwarz, 232 
 Seeker, 239 
 
 Selby Smelter Commission, 275 
 
 Senderens, 168, 214, 240, 258 
 
 Seyler, 327 
 
 Shenton, 100 
 
 Shields, 153 
 
 Siebert, 25 
 
 Siemens, 61, 68, 139, 196, 206 
 
 Sieverts, 122 
 
 Simmersbach, 353 
 
 Simpson, 277 
 
 Sinding-Larsen, 98 
 
 Skita, 214 
 
 Smith, C. C., 181 
 
 Smith, R. F. W., 328 
 
 Smith, R. H., 258, 259 
 
 Smith, W., 287 
 
 Smythe, 275 
 
 Snelling, 205 
 
 Soc. Anon. 1'Oxhydrique Fran9aise, 
 197 
 
 Soc. Anon. 1'Oxhydrique Inter- 
 nationale, 104 
 
 Societe Christiania Minekompani , 
 220 
 
 Societe Fran$aise 1'Oxylithe, 226 
 
 Societe Generate des Nitrures, 120 
 
 Societe 1'Air Liquide, 165, 170 
 
 Soddy, 130 
 
 Sodermann, 288 
 
 Soret, 136 
 
 South Metropolitan Gas Co., 211 
 
 Soyer, 227, 235 
 
 Spence, 113 
 
 Spencer, 112 
 
 Squire, 94 
 
 Stanton, 22, 23, 24, 32, 47 
 
 Steere, 344 
 
 Stern, 190 
 
 Stevenson, 289 
 
 Stewart, 44, 268, 273 
 
 Steynis, 143 
 
 St. John, 190 
 
 Stopes, 326 
 
 Storm, 98 
 
 Strache, 185, 210 
 
 Streintz, 153 
 
 Stromeyer, 250 
 
 Strutt, 111 
 
 Stuckert, 272 
 
 Summers, 122 
 
 TAMARU, 222 
 Tavlor, 255, 358 
 
 Teichmann, 43, 44, 284 
 Teisen, 350 
 Teissier, 98, 206 
 I Tellier, 220 
 Terres, 40, 336 
 Thorn, 260 
 Thomas, 32 
 Thompson, 136 
 Thomson, 10 
 Thornton, 349 
 Thorpe, 57, 101, 270, 273, 315, 329, 
 
 358 
 
 Thorssell, 178 
 Tookey, 347 
 Torley, 287 
 Trasenster, 107 
 Travers, 56, 92 
 Tripler, 61 
 
 UHLINGER, 115, 192 
 United Alkali Co., 249 
 Usher, 150 
 Uyeno, 231 
 
 VALENTIER, 132 
 
 Valon, 106 
 
 Van der Waals, 7 
 
 Vandoni, 276 
 
 Van Marum, 136 
 
 Verley, 149 
 
 Verneuil, 221 
 
 Vignon, 160, 318 
 
 Villard, 43, 285, 288 
 
 Voigt, 332 
 
 Von Wartenberg, 139, 257, 274 
 
 Vosmaer, 141, 148, 150 
 
 WACHEMHEIM, 126 
 Wallace, 263 
 Walter, 350 
 Wanz, 228 
 Warburg, 140, 142 
 Wardlaw, 275 
 Washburn, 122, 125 
 Waygouny, 272 
 Weber, F. A., 248 
 Weber, S., 57 
 Weinland, 109 
 Weise, 205 
 Weiskopf, 265 
 Weith, 166 
 Wells, 288 
 Welton, 112 
 Wendt, 314, 334 
 Wentzki, 211 
 Werder, 273 
 Westman, 260 
 Westinghouse Co., 145 
 
INDEX OF NAMES OF AUTHORS. 
 
 Wheeler, 9, 10, 238, 303, 320, 32'.), 
 
 334, 337, 338, 347 
 White, A. H., 344 
 White, S., 94 
 Wild, 221 
 
 Williams, C. E., 211 
 Williams, F. M., 281 
 Williams, T., 208 
 Willstatter, 214 
 Windhausen, 264 
 Wirth, 344 
 Wise, 113 
 
 Witkowski, 6, 58, 65 
 Wohler, 41, 78, 175 
 
 Wolf, M., 202 
 Wolf, R. B., 276 
 Wolter, 190, 192 
 Woltereck, 237 
 Wood, 328 
 Worsley, 250 
 Wright, 26 
 Wr6blewski, 61, 256 
 Wroczynski, 238, 286 
 Wiirth, 315 
 
 ZEALLEY, 34, 108 
 Zeleny, 258, 259 
 Ziegenberg, 151 
 
 THE END 
 
 Printed byJViUiam Clowes & Sons, Limited, Beccles,for Baillitre, Tindall & Cox, 
 8 Henrietta Street, Covent Garden, W.C. 2. 
 
INDUSTRIAL CHEMISTRY 
 
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 THE CHEMICAL INDUSTRIES 
 
 Edited by SAMUEL RIDEAL, D.Sc. (Lond.), F. I. C, Fellow of 
 University College, London. 
 
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