GIFT OF ftbe "Westminster" Series LIQUID AND GASEOUS FUELS LIQUID AND GASEOUS FUELS AND THE PART THEY PLAY IN MODERN POWER PRODUCTION VIVIAN B. LEWES, F.I.C. F.C.S. &c. PROFESSOR OF CHEMISTRY AT THE ROYAL NAVAL COLLEGE, GREENWICH ; CHIEF SUPERINTENDING GAS EXAMINER TO THE CORPORATION OF THE CITY OF LONDON ; ASSOCIATE MEMBER OF THE COUNCIL OF THE INSTITUTE OF NAVAL ARCHITECTS, &c., &c. LONDON ARCHIBALD CONSTABLE & CO. LTD. 10 ORANGE STREET LEICESTER SQUARE W.C. 1907 -r \> <* BRADBURY, AGNEW, & CO. LD., PRINTERS. LONDON AND TONBRIDGE. INTRODUCTION. THE subject of Liquid and Gaseous Fuels has, during the last decade, assumed such importance that no apology is necessary for the present attempt to treat the subject from a popular but comprehensive point of view. The develop- ment of the internal combustion motor, the coming of the automobile, and the important part played by liquid fuel in the Navies of the world, make the present time one of the most interesting epochs in the history of power pro- duction, and it is hoped that by bringing together the history and practical development of the use of various forms of combustible liquids and gases for the generation of energy this book may do some service in the advance- ment of the subject. Although the book is only supposed to treat of fuel in its liquid and gaseous form, it is so absolutely impossible to divorce these from the subject of solid fuel, which is in most cases the parent from which the others have sprung, that in order to retain the necessary sequence in treatment solid fuel has also been considered, in some cases, as with peat, at considerable length. There is not the slightest desire or intention in the author's mind to produce a book which shall in any way take the place with the student of such works of reference as Sir Boverton Eedwood's " Petroleum and its Products," Mr. E. Dowson's " Producer vi INTBODUCTION. Gas," or Mr. Booth's " Liquid Fuel," but rather to give a general sketch of the whole subject and its bearings on the power problems of the day, and to leave the student to refer to such standard works as may be necessary for the detail of various applications. In order to facilitate the study of any special branch of the subject a short bibliography is added, which it is hoped will prove of use for reference, and in which are included many works to which the author owes a debt of gratitude. The first three chapters of the work deal with the phenomena of combustion and the part played by the atmosphere, the formation of fuel in its various forms, and the methods by which we determine its value as a source of heat energy. In the next following chapters will be found an account of the production, properties, and use of the liquid fuels and their adoption as an auxiliary to coal in European Navies, whilst the subject of coal gas and the factors which have made it one of the most important of domestic fuels will also be found treated at considerable length. Water gas, both as a help to the coal gas maker and the engineer, receives due attention, whilst those gases which, although the poorest in thermal value, have proved themselves the most valuable in cheapening power production, are fully treated with in the section dealing with poor fuel gases and the suction plant. The last chapter deals with the future of the fuel problem and the probable lines on which a world, bankrupt in fuel, will find means of regenerating the energy which is essential to life and prosperity, and it is hoped that the short disc'ussion on the value of alcohol as a fuel in the INTRODUCTION. vii internal combustion motor may lead to an increase in the experimental work in this direction. Some of the matter utilised in preparing this book has appeared before in lectures and papers given before various Institutions by the author, but where such has been used, it has been brought up to date, and the author desires to express his indebtedness to those who have assisted him with photographs of plant and material for diagrams. V. B. L. GREENWICH, 1907. TABLE OF CONTENTS CHAPTER I. Lavoisier's discovery of the nature of combustion and the part played by the atmosphere Air a mixture of the two gases oxygen and nitrogen -Oxygen as a supporter of combustion The properties of nitrogen Slow and rapid combustion The ignition point The effect of condition on ease of ignition Products of com- bustion Water vapour Carbon dioxide and its properties Incomplete combustion Carbon monoxide and its formation The toxic action of carbon monoxide and its treatment The phenomena of combustion Incandescence Flame and smoke The formation of smoke and its nature The effect of smoke on the atmosphere, and the part it plays in inducing the formation of fog pp. 1 23 * CHAPTER II. The cycle of animal and vegetable life The growth of vegetation Cellulose Wood as a fuel Charcoal Peat The formation of coal Checked decay Variation in composition due to geological change The influence of hydrogen in coal Methane or marsh gas Fire damp and choke damp Safety lamps Coke Mineral oil American and Russian oil Fuel oils Gaseous fuel Pro- ducer gas Water gas Carburetted water gas Coal gas Natural gas Hydrogen The elements The three states of matter Molecules and atoms Symbols and their use Carbon and its combinations ...... pp. 24 57 CHAPTER III. Methods of determining calorific value The calorie and British thermal unit Heat of combustion factors Latent heat of steam Calculation of calorific value from chemical composition Evaporative duty Objections to calculated results Direct determination of thermal value Calorimeters The Mahler bomb, and the method of using it The William Thomson calorimeter The Fischer apparatus The Lewis Thompson calorimeter The use of the bomb for liquid and gaseous fuels The heat of com- bustion of gases The Junker calorimeter Correction of volume for temperature and pressure pp. 58 83 x TABLE OF CONTENTS. CHAPTER IV. The discovery of petroleum in America The Russian oil fields The distribution of petroleum The conditions under which it occurs The nature of petroleum, and the products obtained from it The amount available for fuel purposes The flash point, and how it is determined The Abel test The Pensky- Marten The requirements in a fuel oil Shale oil as a fuel The shale oil industry Coal tar and its composition Creosote oil Blast furnace oil Shipping regulations for oil fuel Petroleum spirit and its dangers The testing of atmospheres likely to contain explosive mixtures of petroleum vapour and air The Clowes- Redwood apparatus ...... pp. 84 107 CHAPTER V. Oil lamps, and the conditions on which their satisfactory working depends Heating and illuminating power of oil The history of the use of oil as a fuel Nobel's troughs Gasification before combustion Foote's burner Simms and Barff process Eames furnace Diirr apparatus Methods of atomising or pulverising oil before combustion Injectors Injection under pressure Korting injector Swensson burner Injection by steam The Holden burner Rushden and Eele's injector The Orde burner Air injection Furnace arrangements Conditions of combus- tion The formation of smoke Merits of steam injection as opposed to air or pressure Furnace space Liquid fuel for marine use Advantages for naval use Employment as an auxiliary to coal United States Naval Board experiments Liquid fuel for use in locomotives Comparative value of liquid fuels in practice pp. 108140 CHAPTER VI. The history of coal gas Murdoch, Lebon, and Winsor The coals used in coal gas manufacture Gas retorts and carbonisation Retort settings Charging and drawing Sloping and vertical retorts Crude coal gas, and its purification Ammonia liquor Sulphur compounds in gas The effect of sulphur in gas on its use for domestic lighting Lime and ore purification The compo- sition of coal gas The enrichment of coal gas Cannel Oil gas Hydrocarbon vapours Oven gas The cause of luminosity in flame The chemical changes taking place in a gas flame Gas burners .,....,.. pp. 141 181 TABLE OF CONTENTS. xi CHAPTEK VII. Calorific value of coal gas and its constituents The relation between illuminating power and thermal value Effect of enrichment on calorific value The inception of the atmospheric burner Early forms of burner The cause of non-luminosity in the " Bunsen " flame Ratio of air to gas in the flame Effect of diluents on the flame Effect of the specific heat of gases in the flame The structure of the atmospheric burner flame, and the chemical changes taking place The temperature of the flame The Le Chatelier thermo-couple and its use Gas stoves, and their relative efficiency as compared with coal Methods of heating, and the effect on the air of rooms Regenerative gas stoves Flueless stoves The necessity for leading away the products of com- bustion Coal gas in the internal combustion motor pp. 182 218 CHAPTER VIII. The history of water gas The " European " water gas plant The introduction of carburetted water gas Thermal considerations in the manufacture of water gas Blow and run processes Dellwik water gas Chemical changes taking place in the generator The application of water gas The Kramer and Aarts process Car- buretted water gas The early forms of plant The Lowe process, and its recent modifications The Humphreys-Glasgow system The poisonous properties of water gas Carburetted water gas as an enricher and diluent of coal gas Blue gas as an adjunct to coal gas works Various methods by which it is used Auto-carburetting "Methane-hydrogen" . pp. 219 253 CHAPTER IX. Incomplete combustion The principle of the gas generator Thermal considerations Bischof generator Siemens and his work Air- producer gas Blast furnace gas Dowson or semi-water gas The Dowson type of generator Anthracite as a fuel, and the considerations governing the size used The composition of Dowson gas Mond gas and its production The Buire-Leucau- chez generator The growth of the internal combustion motor Suction gas plant The Berrier suction generator Pintsch suc- tion plant Dowson suction plant The adoption of the suction plant and gas engine for marine purposes The Emil Capitaine plant The use of bituminous coal for suction plant, and the troubles to be overcome The Duff-Whitfield generator The Boutillier plant pp. 254282 xii TABLE OF CONTENTS. CHAPTER X. Comparison of the thermal values of our fuels, solid, liquid, and gaseous The internal combustion engine as a measure of efficiency with gaseous fuel The future of the fuel question The life of our liquid fuel supply The era of gaseous fuel The utilisation of the peat deposits of the world Modern methods of making peat a valuable fuel The calorific value of peat briquettes as compared with other fuel The problem of the future The fixation of solar energy and its regeneration by combustion Fermentation, and the production of alcohol from vegetation Alcohol as a fuel Denaturated, or methylated spirit Its calorific value Alcohol v. petrol as a source of power in the motor engine . . ' pp. 283 313 PAGE APPENDIX . . . . . . . . . . . 315 BIBLIOGRAPHY 323 INDEX 327 LIST OF ILLUSTRATIONS FIG. PAGE 1. MAHLER BOMB (SECTION) 65 2. MAHLER BOMB WITH FITTINGS 66 8. WILLIAM THOMSON CALORIMETER 70 4. FISCHER CALORIMETER ... 7 .... 71 5. LEWIS THOMPSON CALORIMETER . .."..'. . .72 6. JUNKER CALORIMETER (SECTION) . . . . .75 7. JUNKER CALORIMETER . . . . . . . .76 8. SIMMANCE-ABADY CALORIMETER 80 9. ABEL FLASH-POINT APPARATUS . . . . . .93 10. PENSKY-MARTEN FLASH-POINT APPARATUS .... 94 11. THE CLOWES-REDWOOD TESTING LAMP 106 12. CLOWES-REDWOOD SAMPLE-COLLECTING APPARATUS . . 107 13. NOBEL'S TROUGHS . . . 112 14. COLONEL FOOTE'S FURNACE . 114 15. EAMES' OIL FURNACE 115 16. THE DURR SYSTEM " 116 17. KORTING'S INJECTOR 117 18. SWENSSON BURNER '._'.' 118 19. HOLDEN INJECTOR (LOCOMOTIVE) . . . . . .119 20. HOLDEN INJECTOR (MARINE TYPE) 120 21. RUSHDEN AND EELE's BURNER 121 22. ORDE BURNER 122 23. SMALL GAS WORKS. ... . . 147 24. RETORT HOUSE, GRANTON WORKS 151 25. CANDLE FLAME ... 174 26. COCKSPUR AND COCKSCOMB BURNERS 177 27. OLD FLAT FLAME BURNER 179 28. CANDLES AND CALORIES . ... 185 29. ORIGINAL FORM OF BUNSEN BURNER . ... 190 30. BUNSEN BURNER (SECTION) ... ... 191 31. BUNSEN FLAMES 193 32. SMITHELLS' TUBE CENTRAL CONE IN POSITION . 199 xiv LIST OF ILLUSTEATIONS. FIG. PAGE 38. SMITHELLS' TUBE CONES SEPARATED ..... 201 34. LE CHATELIER'S THERMO-COUPLE AND ARRANGEMENT . . 202 35. HOLDER FOR THERMO-COUPLE 204 36. TEMPERATURES IN BUNSEN FLAME WITH DIFFERENT AERATION 205 37. " EUROPEAN " WATER GAS GENERATOR 222 38. DELLVVIK WATER GAS PLANT . . . . . . . 232 39. WELDING BOILER FURNACE WITH WATER GAS . . . 234 40. FAHNEHJELM COMB 236 41. HUMPHREYS AND GLASGOW CARBURETTED WATER GAS PLANT. 240 42. "METHANE-HYDROGEN" PLANT 251 43. BISCHOF GENERATOR . . . . . . . 257 44. SIEMENS PRODUCER 258 45. DOWSON GENERATOR 264 46. MONO GENERATOR ......... 265 47. MOND PLANT 269 48. PINTSCH SUCTION PLANT 272 49. DOWSON SUCTION PLANT . . . . "X . . 273 50. CAPITAINE SUCTION PLANT 275 51. DUFF-WHITFIELD PLANT ........ 279 52. BOUTILLIER SUCTION PLANT 280 53. EFFECT OF MOISTURE ON THE THERMAL VALUE OF PEAT . 294 54. ALCOHOL CURVE 301 LIQUID AND GASEOUS FUELS, CHAPTEE I. COMBUSTION. Lavoisier's discovery of the nature of combustion and the part played by the atmosphere Air a mixture of the two gases oxygen and nitrogen Oxygen as a supporter of combustion The properties of nitrogen Slow and rapid combustion The ignition point The effect of condition on ease of ignition Products of combus- tion Water vapour Carbon dioxide and its properties Incom- plete combustion Carbon monoxide and its formation The toxic action of carbon monoxide and its treatment The pheno- mena of combustion Incandescence Flame and smoke The formation of smoke and its nature The effect of smoke on the atmosphere, and the part it plays in inducing the formation of fog. ALTHOUGH it was not until the eighteenth century was nearing its close that a true conception of the actions taking place during combustion was arrived at, the fact that heat was most economically obtained by the burning of certain substances, mostly of vegetable origin, was realised from the era when fire worship constituted one of the world's most important beliefs, and the slowness of the advance which was made during the centuries that have elapsed since then is shown by the time it took for the displacement of wood as the universal fuel by coal. When, however, this point was reached, the use of fuel quickly increased, and the past century marks a period L.G.F. B GASEOUS FUELS. which will always stand forth as being that in which the energy locked up in our coal deposits was first laid under contribution for the generation of steam power as well as for ordinary heating, with the result that the wealth and power of nations fortunate enough to possess coal fields have grown with startling rapidity, and the last fifty years have been the most prosperous the world has ever known. It was in 1781 that James Watt patented the first rotary engine, and so initiated a method by which heat energy could be translated into mechanical work, whilst it was not until 1807 that Fulton made the first steam-boat that was a commercial success, and Stephenson only gave the world the locomotive in 1829. During the past quarter of a century liquid and gaseous fuels have been added to our energy creators, and have been firmly established as rival heating agents in cases where their ease of application, under special conditions, has rendered their use economically advantageous. Whether heat energy is obtained by the combustion of such solids as wood or coal, or by the burning of fuel oils, or gases, a knowledge of the chemical and physical actions causing the combustion and governing the course which it takes, is essential to its successful application, and a short description of the researches which, in the latter half of the eighteenth century, revealed the true nature of com- bustion, will best lead to a clear conception of its nature. Antoine Laurent Lavoisier was born in France in 1743, and living at a period when the old alchemical ideas were merging into the true science of chemistry, he did much to justify the title the French nation is so fond of bestow- ing on him, "The Father of Modern Chemistry," and between the years 1765 and 1794, when the guillotine of Kobespierre cut his memorable career short at the early age of .51, he gave to the world a true explanation of the actions taking place during combustion. COMBUSTION. 3 Early in his career Lavoisier noticed that air was neces- sary for combustion, and that if a candle were placed in an enclosed space with a limited supply of air, it gradually burnt dimmer and dimmer, and in a short time went out. Noticing this fact he continued to experiment, and amongst other things found that if he took a candle and enclosed it in such a way that all the products of combustion which came from it were collected and weighed, the gases developed weighed more than the candle itself had done. The discovery that air was needed for combustion and that the products of combustion weighed more than the body burnt enabled Lavoisier to attack and overthrow the phlogistic theory of Stahl, which had ruled supreme during the earlier years of the eighteenth century, and which attributed combustion to the escape of something pre- existing in the combustible material. The discovery of oxygen by Priestly in 1774 enabled Lavoisier, a few years later, to explain the actions which take place when substances burn in air, and led him to the great discovery of the fact that air was not an element, as up to that time had been supposed, but contained two perfectly distinct gases, oxygen and nitrogen. Although the researches of Priestly and Lavoisier showed conclusively that air was not an element, but contained the two gases oxygen and nitrogen, it had still to be shown whether these two gases were present in it in the state of mere mixture, or whether they were combined together as a definite chemical compound. When in mechanical mixture the distinctive properties of the substances present are retained, although often modified by the properties of the other constituents : but in a chemical compound the properties of the original factors entirely disappear, and are merged into new characteristics distinctive of the compound formed. In determining whether a given substance be a compound or merely a B 2 4 LIQUID AND GASEOUS FUELS. mixture, a most important point to be ascertained is whether it varies in composition or not. A chemical compound is unalterable in composition, so that if a substance be a true compound it will always consist of the same elements combined in exactly the same proportions. During the years that Priestly and Lavoisier were making their memorable experiments on the composition of air, the Hon. Henry Cavendish was also devoting his life to the cause of science, and these three men did much to make the close of the last century the most remarkable epoch in the history of both chemical and physical science. Cavendish, who was one of the wealthiest men of his day, devoted his whole life and wealth to scientific lesearch, and it is to him that we owe the first exact determination of the relation existing between the oxygen and nitrogen in air. In the year 1781 he made nearly four hundred determinations of the composition of air in order to find whether the amount of oxygen in it varies to any appreci- able extent. For this purpose he determined the amount present under every possible condition of weather ; but no matter if the weather were fair or clear, wet or foggy, no" 1 difference of which he could be certain could be detected. He likewise experimented to see whether the air in London differed from the air in the country ; but the results of all his experiments so closely agreed that fhe differences came well within the limit of experimental error found in the rough processes of analysis then in use. He finally came to the conclusion that 100 volumes of air con- tain 20'83 parts by volume of oxygen. The remarkable constancy of his results naturally led him to the conclusion that air was a chemical compound, an opinion which was shared and strongly upheld in the succeeding years by Prout, Dobreiner, and Thomson, all of them maintaining that air was a chemical compound of one volume of COMBUSTION* o oxygen with four volumes of nitrogen. Chemists were, however, not wanting to oppose this idea, and foremost among these was John Dalton, the father of our present system of chemical theory, who held that air was merely a mechanical mixture kept in a constant condition by cer- tain natural forces. He also propounded the theory that, because nitrogen is lighter than oxygen, there must be a larger proportion of oxygen present in the air near the earth's level than at an altitude from its surface. In this, however, he was wrong, for as Gay-Lussac and Thenard afterwards showed, the air at a considerable height con- tains the two gases in exactly the same proportion as at sea level a fact which they proved by going up in a balloon and collecting samples of air at a considerable altitude. Their results have since been corroborated by Brunner, who analysed air taken at the bottom and at the top of some of the highest of the Swiss mountains. Before, however, this war of compound versus mixture could be brought to a satisfactory conclusion, it became necessary to institute newer and more accurate methods of analysis, and when this was done the researches of Bunsen, Leroy, and Eegnault demonstrated that the atmosphere shows sensible, though very small, variations in its com- position normal air containing 20*9 to 21 per cent, of oxygen, although under abnormal conditions, more especially in warm and swampy countries, the percentage sometimes falls as low as 2O3 per cent. It was from the observation of these small discrepancies in composition that, in the middle of the last century, the conclusion was finally arrived at that the atmosphere was a mechanical mixture and not a chemical compound, and that the ratio in which its two main constituents exist is By weight. By volume. Nitrogen. . . . 76'9 79'1 Oxygen .... 23'1 20*9 6 LIQUID AND GASEOUS FUELS. It is usual to speak of all gases besides oxygen and nitrogen which are present in the atmosphere as impuri- ties, but this is manifestly incorrect, as there are several compounds present to a greater or less extent, which are absolutely essential for the carrying out of nature's laws, and which do not become real impurities unless they rise above a certain limit. These compounds are carbon dioxide, water vapour, ammonia, and nitric acid ; the water vapour being almost as essential as oxygen and nitrogen for animal and vegetable life, whilst the others are needed for certain phases of plant life. Inasmuch as the atmosphere entirely\ enfolds the world in a vast aeriform mantle, it is evident that all gaseous impurities escaping from the surface of the earth must find their way into it, and we can form a very sound judg- ment as to which of these constitute the real impurities, and which are only impurities after a certain limit is reached, by noticing their distribution in nature. The impurities pure and simple only exist at those spots where the causes which give rise to them are to be found, whilst the natural impurities, or, more correctly speaking, " minor constituents," are equally distributed throughout the atmosphere. The average composition of atmospheric air may be taken as being Oxygen ... . 20*61 Nitrogen 77*95 Carbon dioxide . . . . 0'04 Water vapour .... 1*40 Nitric acid ..... trace Ammonia trace 100*00 COMBUSTION 7 All the marked characteristics of air are derived from the oxygen, which is a colourless, odourless, and tasteless gas, possessing the property of entering into vigorous chemical combination with such substances as are generally spoken of as being combustible, whilst it will combine with all the elements with the exception of fluorine. The nitrogen, on the other hand, is marked by extreme inertia in its power of combining with other elements, and in the atmosphere one of its chief functions is diluting the too vigorous oxygen. Nitrogen neither supports combustion nor does itself burn in the ordinary acceptance of the term, but inasmuch as it forms no less than five compounds with oxygen, it is evident that this phenomenon is due to our inability to produce a sufficiently high temperature to bring about a direct combination. That this is the true explanation is manifest from the fact that compounds of oxygen and nitrogen are to be found in the atmosphere after thunder- storms or other electrical disturbances, whilst an electric spark passed for some time through a confined volume of air soon causes it to assume a brown tint from the forma- tion of some compounds of nitrogen and oxygen, so that at the temperature of the electric spark it is evident that the nitrogen becomes inflammable. Nitrogen gas can be collected over water, as it is only very sparingly soluble, 100 volumes of water only dissolving 1 volumes of gas at ordinary temperatures. It is a taste- less, odourless, and colourless gas, which, although so inert in its behaviour towards most substances, combines with some of the rarer elements, such as tungsten and titanium, with such energy that they become incandescent when thrown into the pure gas. In comparing the weights of gases, hydrogen, which is the lightest gas known, is always taken as unity, and the weight of equal volumes of other gases measured off at the g LIQUID ANi) GASEOUS FUELS same temperature and pressure are compared with hydrogen, in order to give what is called the density of the gas, which expresses how many times it is heavier, volume for volume, than hydrogen. Oxygen is found to have a density of: 16, whilst nitrogen is 14, and the atmospheric mixture of the two gases is 14*47 times heavier than an equal volume of the standard gas. Lavoisier, having ascertained many of the more impor- tant of these facts with regard to the atmosphere, then continued his experiments upon combustion, and using oxygen as a medium, burnt in it such bodies as phosphorus, sulphur, and charcoal, and noticed the great increase in brilliancy and vigour of combustion brought about by the absence of the diluting nitrogen, and further found that not only did such substances as burn in air burn with exaggerated effect in oxygen, but that many substances not generally looked upon as combustible will, under its exciting influence, undergo vigorous combustion, zinc and steel burning in the gas with the most brilliant effects. In all these cases the phenomena observed are dependent upon the formation of combinations of oxygen with the bodies burnt, the phosphorus yielding phosphorous pent- oxide, the charcoal carbon dioxide, the sulphur the gas known as sulphur dioxide, whilst the steel, the only one of these substances, be it noted, which burns absolutely without flame, gives the solid oxide of iron as the result of the chemical action. During these combinations energy is developed, and owing to its intensity by concentration into a short space of time, this energy manifests itself as heat and light. Here, then, is to be found the key to all the actions which we speak of under the general term of " fire," and further experiment soon shows that in order to start this rapid combination between the substances oxidised and the COMBUSTION. b oxygen of the air, it is only necessary to heat the combining bodies to a temperature known as the " ignition point," a temperature which varies very widely with different sub- stances, but which is a constant factor in all bodies of the same composition. Some substances, such as certain organic compounds with zinc, ignite below the ordinary air temperature, and such bodies are called " spontaneously inflammable," whilst others, like phosphorus, have only to be slightly warmed in order to produce the rapid combina- tion known as combustion. Others, again, like coal, have to be heated to a temperature of a little over -500 C. before their ignition point is reached, whilst bodies like steel, having their ignition point above the temperature reached in ordinary combustion, are looked upon, as a rule, as non-combustible. The spread of ordinary fire and flame is due to the fact that when combustion is started by the ignition point being reached, the combustion raises the temperature generally well above the ignition point of the burning body, so that as one particle burns it ignites the next, and this action continues until the burning body has entirely combined with oxygen, but if the heat generated be insufficient to raise the body to the ignition point, combustion ceases as soon as the external heat is withdrawn. In the case of a watch spring burning in oxygen gas, the combustion of a piece of German tinder attached to the end of it is sufficient under the exciting influence of the pure oxygen to raise the spring to the point of ignition, and then the temperature developed by the oxidation of the metal in the oxygen is sufficient to continue the combustion until the whole of the spring is burnt away. If, however, instead of allowing the action to go on in the pure oxygen the spring, whilst still vividly burning, is withdrawn from the jar of oxygen into the air, combustion ceases after a few moments, owing to the dilu- tion of the oxygen in the atmosphere by nitrogen lowering 10 LIQUID AND GASEOUS FUELS* the intensity of the combustion, so that the ignition point of the metal is no longer reached. Although the igniting point of any substance is a fixed and unalterable temperature, the size of the mass to be ignited plays a very important part, as the smaller the mass the more easy .it is to raise it to the ignition point. For instance, iron ignites at about 1,500 C., and gun- powder at a little over 250 C., yet if some alcohol in a dish be ignited and finely divided iron dust be thrown into it, the iron burns brilliantly in the flame, whilst grains of gunpowder may be thrown through the flame without igni- tion and will remain unacted upon in the alcohol until it is nearly all burnt away, when the flame, burning down to them and being in contact with them for some time, heats them to the necessary temperature, and so ignites them. In the same way a very small flame held in contact with a block of wood fails to ignite it, whilst a splint or shaving cut from the block is easily ignited by the same flame. So far we may summarise the facts with regard to com- bustion by saying that combustion is the generation of energy as heat by extremely rapid chemical combination, which is brought about by the ignition point of the substances entering into combination being attained. Although the ignition point marks the temperature at which ordinary combustion gives rise to the phenomena of light and heat, the same chemical action may be pro- ceeding at temperatures short of the ignition point, but at so slow a rate that the energy developed is able to spread itself to the surrounding objects, and so escapes notice. All those processes utilised by Nature for the cleansing of the surface of the earth and the conversion of waste matter back into carbon dioxide and water vapour, which are the food of Nature, and from which she can reconstruct everything anew (processes which are generally spoken of as decay) are actions of this character. It must, however, COMBUSTION. 11 be remembered that for a given weight of material con- verted by chemical combination into the same compounds, whether the action be slow, as in decay, or rapid, as in ordinary combustion, the total amount of heat generated is the same, the only factor in the action which varies being the length of time over which the development of energy is spread. A tree left to rot upon the ground gradually disappears in the course of years, being mainly oxidised into gaseous products such as carbon dioxide and water vapour, and yet scarcely any evolution of heat is observed, although the same amount of heat is generated as if the tree had been cut into logs and burnt. It has been seen that if a steel watch-spring be taken, and a small piece of German tinder attached to the end of it is ignited and plunged into a vessel of oxygen gas, the combustion of the tinder ignites the watch-spring, which burns away in the gas with the greatest brilliancy, and the evolution of heat is sufficient to fuse the metal, the final result being that the watch-spring is converted into a chemical compound of iron and oxygen. The amount of heat developed in this experiment can be approximately judged by the fact that the steel watch- spring is fused as it burns, and it is known that this requires a temperature of 1,500 C. If, however, a second watch-spring be taken, of the same weight as the first, and exposed to moist air for two or three months, it would also be converted into oxide, but in the slow rusting away of the metal no appreciable heat could be distinguished, it having been dissipated to the earth, the air, and the surrounding objects as rapidly as it was generated. If, however, one could construct a calorimeter sufficiently delicate to measure all the heat evolved during the slow rusting away of the metal, it would be found that exactly as much heat had been developed as would have been the case had it been 12 LtQtflD ANi) GASEOtfS FUELS, burnt away in pure oxygen. Indeed the atmospheric rusting of iron may become so rapid as to create a tem- perature sufficiently high to attract attention : as for instance, when a mixture of sawdust and iron filings is swept up from a workshop floor and the heap moistened with water. After a few hours it is found that steam is being evolved, the heat of oxidation having been kept in by the non-conducting sawdust until the temperature had risen to the evaporation point of the water. The more finely the iron is divided the larger will be the surface which it will present to the oxidising influence of the air, and if by chemical means we prepare extremely finely divided iron in an atmosphere devoid of oxygen, on throwing the powdered iron into the air it rusts so quickly as to become red hot. The action taking place below the ignition point is chemi- cally identical with the action taking place during rapid combustion, and only differs from it by being spread through a longer space of time, and is therefore called " slow combustion." In our fuels, be they solid, liquid, or gaseous, we find that the elements entering into combination with oxygen during combustion and generating the heat energy are hydrogen and carbon, the former burning to water vapour, whilst the latter produces either carbon dioxide or carbon monoxide, according as there is an abundance or shortage of atmospheric oxygen present. These gases, because water vapour at the temperature of combustion may be looked upon as a gas, are called " the pro- ducts of combustion," the water vapour and carbon dioxide being products of complete combustion, and the carbon mon- oxide the product of incomplete combustion, the latter being capable of a further combustion with a fresh supply of air. Whenever hydrogen, or any compound containing hydro- gen, such as paper, wood, coal, oil, coal gas, etc., burns in COMBUSTION. 13 air or oxygen, the hydrogen and oxygen combine in the ratio of 2 parts by weight of hydrogen to 16 parts by weight of oxygen to form water ; and weight for weight the com- bustion of hydrogen produces a greater amount of heat than any other known substance, 1 Ib. of hydrogen in com- bining with 8 Ibs. of oxygen giving out sufficient heat to raise 34,500 Ibs. of water through 1 C. The Centigrade scale differs from the Fahrenheit in that the point at which water freezes is called " zero " in the Centigrade, and " 32 " on the Fahrenheit scale : and the boiling point on the former is 100, whilst with the latter it is 212, and tables will be found in the Appendix facilitating the translation of temperatures and heat values from the one scale to the other. When carbon or carbon compounds burn in a free current of air so that ample oxygen is present to complete the com- bustion, 12 parts by weight of carbon unite with 32 of oxygen to yield carbon dioxide, and the heat generated by the combination of 1 Ib. of carbon with 2*65 Ibs. of oxygen is sufficient to raise 8,137 Ibs. of water through 1C. The gas so produced, carbon dioxide, is a clear colourless gas, possessing a peculiar slightly acid taste and smell : it is a heavy gas, being twenty-two times as heavy as hydrogen, and can be poured from one vessel to another like water. It does not burn or support combustion in the ordinary sense of the term, but a piece of the metal potassium healed in an atmosphere of the gas will burn in it, decomposing it, and forming potassium oxide and depositing flakes of carbon. Carbon dioxide is very soluble in water, the water, under normal conditions of temperature and pressure dissolving its own volume of the gas : that is to say, with the barometer at 30 inches and at a temperature of 1 5 C one pint of water will dissolve one pint of the gas. If a change be made either in the temperature of the water or the pressure a corresponding alteration will take place in the amount of 14 LIQUID AND GASEOUS FUELS. gas dissolved, a lowering of the temperature or an increase in the pressure causing the solution of a greater quantity of gas. When however the standard conditions are restored the excess of gas will escape, causing the water to effervesce. The gas can be condensed to a liquid by extreme cold and pressure. Carbon dioxide in its chemical properties very much resembles nitrogen, but can be distinguished from it by its giving a white precipitate when agitated in contact with a solution of lime in water, when a white precipitate of chalk or calcium carbonate is formed from the combination of the carbon dioxide with the lime or calcium oxide ; the weight of the gas also serves to differentiate it from nitrogen. When a mass of incandescent carbon is fed with an insufficient supply of air or carbon dioxide is passed over incandescent carbon, a lower oxide of carbon, containing only one half the quantity of oxygen found in carbon dioxide, is produced, and 12 parts by weight of carbon unite with 16 of oxygen to form carbon monoxide. In the combustion to the lower oxide a far less amount of heat is developed : when 1 Ib. of carbon burns with 1,325 Ibs. of oxygen to produce it the heat generated would only raise 2,489 Ibs. of water through 1 C. The gas differs very widely in its properties from the dioxide. It is colourless and tasteless, it does not itself support combustion, but is inflammable, burning with a pale blue flame, in which process it takes up another atom of oxygen and becomes carbon dioxide : it has no action on lime water, and is only 14 times heavier than hydrogen. Owing to its capacity for combining with more oxygen to form the higher oxide of carbon, the gas has a powerful reducing action, and will take the oxygen from several of the metallic oxides under the influence of heat, leaving the metal free. This action is utilised in many commercial processes for the reduction of different metals from their ores. COMBUSTION. 15 Carbon monoxide has such powerful poisonous properties that less than 1 per cent, of it in air causes death when inhaled, and many fatal accidents have arisen from its being formed during checked combustion, as when metal surfaces cooled by water are exposed to a gas flame, as is the case in some forms of " water heaters " : also by the imperfect combustion taking place in kilns, in slow combustion stoves, and in charcoal pans. The gas acts as a poison by forming a compound with the haemoglobin of the blood, and pre- venting it from carrying on its natural function of taking up oxygen during respiration and carrying it to the capillaries of the body. Dr. J. S. Haldane, who has made a special study of the toxic action of carbon monoxide, gives the following data as to the effect of the gas on man : Percentage Of Wffpota nn Man Carbon Monoxide. l Man ' 0'05 . After half-an-hour to two hours, giddiness on exertion. O'l . ,, ,, ,, inability to walk. 0'2 . ,, ,, ,, loss of consciousness and perhaps final death. 0*4 . ,, ,, ,, probable death. I'O . After a few minutes loss of consciousness, followed before long by death. The treatment for carbon monoxide poisoning or "gassing," as it is usually termed, is to apply artificial respiration without a moment's delay, if the breathing has ceased or is feeble. The use of oxygen is a valuable adjunct to recovery. Whilst artificial respiration is being applied, the oxygen should be supplied to the patient from a cylinder of compressed oxygen, provided with a length of rubber tubing terminating in a metal mouthpiece which is placed loosely in his mouth, and the oxygen supply should be continued for at least ten minutes. A person who has been 16 LIQUID AND GASEOUS FUELS. seriously gassed, even if he is not unconscious, should be kept warm, and protected as much as possible from cold air, which often causes sudden and dangerous fainting. He should also be prevented from exerting himself by walking, and should be kept lying down for some time. If there is any tendency to spontaneous fainting a little brandy or whisky should be given. The ordinary phenomena of combustion consist of incan- descence, flame and smoke, and, as has been shown, these are caused by the heat energy liberated during the combina- tion of the burning body 'with the oxygen of the air. If the substance burnt be a solid, which is non-volatile at the temperature of combustion, or is not decomposed by it into gaseous products before burning, incandescence alone is the result of the combustion, and the colour of the light given by the glowing fuel is a fair indication of the temperature of the burning mass. With most ordinary solids the power of emitting light seems to differ but little, i.e., they mostly emit light of the same intensity and character when heated to the same temperature. The following table, giving roughly the character of the light for different degrees of heat, is the one most usually quoted, although the higher temperatures are open to doubt. Just glowing in the dark 525C. 977F. Dark red ... 700 1292 Cherry red . . . 908 1666 Bright cherry red . . 1000 1832 Orange . . . 1150 2102 White .... 1300 2372 Dazzling white . . 1500 2732 Flame, the second phenomenon of combustion, is in all cases caused by the combustion of gaseous matter. We know that if bituminous coal or resinous wood be burnt COMBUSTION. 17 flame is formed, whilst if coke or charcoal be used as the fuel no flame accompanies the primary combustion, this being due to the fact that in the former case hydrogen and carbon in various forms of combination are driven out from the coal or wood by the temperature generated in the combustion, and being in the form of gaseous or vaporous products, burn with flame. When these hydrocarbons have been got rid of however in the gas-maker's retort or the charcoal burner's heap, it is the residual carbon alone that burns, and being non-volatile at the temperature employed, no flame results, save under certain conditions which lead to the formation of carbon monoxide. The smoke which accompanies most ordinary forms of combustion is a product of great complexity, and differs very widely with the nature of the substances being burnt. Of the three gaseous products of combustion steam alone plays an important part in the formation of smoke, whilst the other important constituents are tar vapour, minute particles of unburnt carbon, and ash, drawn upwards by the draught created by the fire. The popular idea held by many is that smoke consists mainly, if not entirely, of particles of carbon rendered slightly adhesive by tarry matters, and that it is in fact like the soot found deposited in the chimney. But a micro- scopic examination of smoke reveals a far more interesting condition of things. A very beautiful experiment, first made by Mr. Frederick Hovenden, is to show that if one takes the smoke from a cigar or cigarette, and blows it into a little glass chamber highly illuminated from below by focussing upon it the beam from an electric lantern or limelight, and examines it under a microscope, it presents a most remarkable and wonderful appearance. Such smoke contains no particles of free carbon, but appears to consist of an immense number of little round particles in the wildest condition of commotion and movement, each particle rushing L.G.F. c 18 LIQUID AND GASEOUS FUELS. about and never coming in contact with its neighbour. Indeed, it presents as beautiful a picture as one could imagine of the molecular movement with which theorists have endowed matter. On still further examination these little particles prove to be tiny vesicles, the skins of which are formed of condensed vapour and liquids from the burning substances which give rise to them. These vesicles, being filled with gases, are excessively light, and float in the atmosphere until brought forcibly in contact with some surface, which causes them to burst and deposit the liquid film, so setting the contents free. Whether this cloud of floating vesicles be derived from a cigarette, a coal fire, or other source, if they are collected in such a way as by friction to cause the tiny vessels to burst, one obtains a liquid which comes under the generic heading of " tar," this tar being a highly complex mixture of many different organic liquids formed by the action of heat on the constituents of the burning matter, whilst the gases which escape from the interior of the vesicles on the rupture of the skin consist of nitrogen, carbon dioxide, carbon monoxide, hydrogen, traces of oxygen, and such hydrocarbons as methane. The smoke, however, from the combustion of coal or oil, when burnt with an insufficient air supply, forms a heavy black cloud, the deepening of density and colour being due to the presence in it of minute particles of unconsumed carbon, which have been deposited by premature cooling or during secondary chemical actions taking place in the flame of the burning material. The domestic grate using bituminous coal is the chief cause of the smoke curse which pollutes our town atmo- spheres. Coal of a bituminous character was first intro- duced as a fuel in the thirteenth century, but the smoke it gave rise to appeared so serious a drawback to those unaccustomed to it that in 1306 a decree was passed COMBUSTION. 19 forbidding its use. Time, however, somewhat allaying the apprehensions concerning the various properties of the smoke, coal was again used, only to be again banished as a fuel in the reign of Queen Elizabeth. Its use being once more revived, there were always found reformers to protest against it, and each century since has seen one or more crusades directed against the production of smoke and the pollution by it of our town atmosphere, but there is little chance of success in the abolition of smoke until gas and coke take the place of coal as a general fuel. The idea that smoke means a large waste of fuel is erroneous, and, in point of fact, the carbon wasted as soot is extremely small, and varies in smoke with the state of the fuel which is fed on to the fire. Under the ordinary conditions experienced in an ordinary fire grate, in which the fire has just been made up with bituminous coal, the heavy smoke escaping will contain on an average 1J per cent, of the total weight of fuel consumed, and as the temperature of the mass gradually increases, this falls to less than J per cent., whilst when the fire is burning clear, no smoke at all is given off. In the same way that we have a rapid fall in the carbon given off as soot, so we also find a fall in the hydrocarbons liberated as tar vapour, whilst the gases evolved as products of combustion vary in the same way with the condition of the fire. When the coal is first put on the fire imperfect combustion in its mass takes place, and the gases passing up the flue under these conditions will closely approximate to the following analysis Carbon dioxide ..... 0'70 Methane 0'36 Hydrogen 0'29 Carbon monoxide .... O'Ol Oxygen 19'85 Nitrogen 79*79 c 2 20 LIQUID AND GASEOUS FUELS. showing that the combustion, owing to the cooled surface at the top of the fire and excessive dilution with the inert nitrogen, is very incomplete. Gradually, however, as the temperature rises, less and less combustible matter escapes, whilst as soon as the fire begins to burn clear, the products of combustion are practically simply carbon dioxide and water vapour. This applies to the open fire grate, and also to a great extent to the combustion taking place in a furnace. When we come, however, to examine the solids escaping into the atmosphere under the influence of the stronger draught in the boiler furnace, we find that the solid matter contains large quantities of particles of ash and finely divided organic matter sucked up by the chimney draught. Smoke formed by these processes finds its way from the chimney into the atmosphere, and is rapidly diffused through the air by means of the air currents, and it is manifest that if there were no means of removing it, the air would soon become perfectly opaque from its accumula- tion in large quantities. When, however, rain falls it rapidly washes the air free from such suspended solid and liquid impurities, which constitute the visible portion of smoke. Snow is even more efficacious than rain in doing this : where the snow has fallen on the glass roof of a greenhouse it will be noticed that when it melts it leaves behind a black deposit, consisting of the solid matter it has collected in its passage through the air. An analysis of a deposit of this character formed on glass roofs of some orchid houses at Chelsea gives a very good idea of the constituents of these solid impurities Carbon . . . . 39*00 per cent. Hydrocarbons . . . 12*30 ,, . Organic bases . . . 1*20 Sulphuric acid . . . 4*33 COMBUSTION. 21 Ammonia .... 1*37 per cent. Metallic iron and magnetic oxide .... 2'63 Other mineral matter, chiefly silica and ferric oxide . 31*24 Water not determined. In cases where long drought prevents the rapid clearance of the air by this means, the heavier of the solid particles settle by gravity, whilst the particles of carbon and car- bonaceous organic matter are slowly oxidised by the oxygen and ozone into carbon dioxide, in which form vegetation removes them from the air. There have not been wanting people who have absolutely defended smoke, declaring that its presence in the air of large towns was most healthful and kept down the per- centage of contagious diseases by the absorbent and antiseptic properties of the carbon and hydrocarbons included in its constituents. There are not probably many at the present time who are prepared to take this view of the case, as the amount of free carbon which could exert any absorbent action on deleterious substances is so excessively minute that its action in this direction may be entirely disregarded, whilst the hydrocarbons which may or may not contain substances like creosote are also too limited in quantity to do good in this way. Moreover, if we could credit them with a slight beneficial action in this direction, we must also remember that deleterious action can be proved to be due to their presence. In the first place, solid particles of all kinds set up irritation in the lungs, and so add their iota to the increase of diseases of the chest, whilst the rapid dirtying of buildings and the peculiar characteristics of London fog can undoubtedly be traced to the smoke-laden air. Fog, whether it be in the form of white mist which is 22 LIQUID AND GASEOUS FUELS. found in the country or the yellow abomination which we know so well in town, is formed by the condensation of water vapour in the air, and this is brought about by any cause which rapidly cools a large volume of moist air. If, instead of the surface of the ground and the objects on it only being cooled, the air for a considerable height above it is also lowered in temperature, then the moisture which is deposited from it, instead of forming dew, condenses in the air, forming particles so minute that they remain suspended and floating in the air, and constitute fog or mist. In pure air the mist so formed consists of little else than these minute drops of water, and has no irritating effect on the eyes or lungs. But in a large town like London the air is charged with an enormous number of minute particles, the heaviest of which settle on a horizontal or roughened surface in the form of dust, whilst the lighter particles con- tinue floating in the air. These particles of dust con- sist of a heterogeneous collection of all kinds of matter ground-up particles from the roadway reduced to an impal- pable powder by the incessant traffic, small organic spores, which are the germs of organic decay and disease, and particles of unconsumed fuel which have escaped from our chimneys in the form of smoke, and which in larger masses form " blacks." All these floating solids cool with great rapidity, on account of the smallness of their bulk, and in doing so cause the rapidly cooling air to deposit moisture upon them, and so aid in the formation of the fog. The air of towns in which much coal is used also contains the volatile tarry matter distilled off during the imperfect combustion, and this condensing with the moisture coats it on the outside with a thin film, which does much to prolong the existence of the fog, as when the temperature of the air again rises, the clean mist is once more absorbed by the atmosphere, but the tar-coated yellow fog has its power of evaporation retarded to an enormous extent. Experiments COMBUSTION. 23 made by the late Sir E. Frankland show that the evapora- tion of water in dry air is reduced nearly 80 per cent, by blowing some smoke from burning coal on to its surface. Many proposals have from time to time been made with the idea of abolishing, or at any rate reducing, the polluting influence of improper fuel and faulty combustion on the air, and anthracite, coke, and stoves of weird device have all had their advocates, and it is quite certain that cleansing the atmosphere of our big towns will only become a practical success when bituminous coal is abandoned as a domestic fuel, and is replaced by coal from which the smoke-forming constituents have been eliminated and by gaseous fuel. CHAPTEE II. FUEL, ITS FORMATION AND COMPOSITION. The cycle of animal ancHvegetable life The growth of vegetation Cellulose Wood as a fuel Charcoal Peat The formation of coal Checked decay Variation in composition due to geological change The influence of hydrogen in coal Methane or marsh gas Fire damp and choke damp Safety lamps Coke Mineral oil American and Russian oi] Fuel oils Gaseous fuel Pro- ducer gas Water gas Carburetted water gas Coal gas Natural gas Hydrogen The elements The three states of matter Molecules and atoms Symbols and their use Carbon and its combinations. COMBUSTION being merely the development of heat energy during excessively rapid chemical combination, and fuel being the name which custom has given to the substances which enter into combination with the oxygen of the air with the development of sufficient heat to produce incandescence, it is clear that the name "fuel" might be applied to anything which would satisfy these condi- tions, but usage has limited the term to those bodies which are sufficiently abundant and easily obtainable to allow of their universal employment for the generation of heat, and amongst the solid fuels all are derivatives of vegetable growth. In the whole of Nature there is nothing more beautiful than the wonderful cycle by which matter is kept in circula- tion by the compensating agencies of animal and vegetable life. As was shown in the last chapter, the process of combustion taking place below the ignition point gives in Nature all those phenomena which we call decay, and in FUEL, ITS FORMATION AND COMPOSITION. 25 the vegetable kingdom the actions for the most part set up by certain germ growths convert waste matter into atmo- spheric carbon dioxide and water vapour, while the processes of life carry on an action of the same kind in the living body, the burning up of the tissues of the body by the slow process of internal combustion giving warmth to the body and the energy needed for all actions, voluntary or involuntary. It is in this process that respiration and the circulation of the blood supply blood-borne oxygen to the tissue, and the actions which ensue convert that tissue into carbon dioxide, respired from the lungs, and water vapour, respired from the lungs and also thrown off from the skin, the tissue as used being renewed by the assimilation of food and drink. In this way the tissues of the body are continually undergoing destruction and renewal, and it has been com- puted that a period of something like seven years suffices for the complete renewal of the whole of the body, with the exception of the skeleton, so that during life the constant using up of oxygen from the atmosphere and its conversion into water vapour and carbon dioxide take place. After death the same action continues by a process of decay with even greater rapidity, and the albumen of animal matter containing sulphur, this also becomes dis- engaged in combination with hydrogen and organic matter, yielding those malodorous gases and vapours which mark the progress of decomposition. In the early half of the last century the great chemist Faraday calculated the total amount of oxygen present in the atmosphere, and found that there were present no less than 1,178,158,000,000,000 tons; but enormous as this quantity is, the amount which is daily used up by pro- cesses of animal life, combustion, and decay would rapidly cause a deterioration in the atmosphere. It was Faraday also who first calculated approximately 26 LIQUID AND GASEOUS FUELS. the amount of the life-supporting constituent of the air which is in this way daily used up, and his results are tabulated as follows: Lbs. Kespiration of whole population . . 1,000,000,000 Kespiration of animals. . . . 2,000,000,000 Combustion and fermentation . . 1,000,000,000 Decay and other processes . . . 4,000,000,000 8,000,000,000 8,000,000,000 Ibs. = 3,571,428 tons in a day, or 1,304,642,357 tons in a year, a rate of consumption which would use up the total oxygen present in about 900,000 years : but it must be remembered that the with- drawal of even 1 per cent, of the oxygen present would exercise a serious effect upon the health of men and animals, and that moreover the withdrawal of the oxygen is due to its conversion into carbon dioxide, which would itself rapidly render the air unlit to breathe. It is manifest from this that Nature must have at hand methods not only for the removal of carbon dioxide from the air, but also for the production of oxygen, as otherwise the composition of the atmosphere, instead of being so con- stant as to defy the detection of any considerable variation, would rapidly deteriorate and become unfit to support life. The main factor in this natural regeneration is to be found in the plant world, as it is the growth of vegetation, urged on by the power of the sun, which performs the work of undoing the vitiation of the atmosphere by animal life, and once more liberating oxygen from the carbon dioxide. The surface of every form of vegetation contains innumer- able small openings, called "stomata," which end in little cells filled with a green colouring matter, called " chloro- phyll,", the presence of which gives the distinctive colour to the plant. But little is known of the composition of this FUEL, ITS FORMATION AND COMPOSITION. 27 remarkable substance, which may be extracted by mace- rating grass or green leaves with spirits of wine, when the green colouring matter from the ruptured cells dissolves in the spirit, and yields a green solution which may afterwards be concentrated by evaporation. This chlorophyll appears to consist of two compounds, one of them a yellow sub- stance, the other a blue, and it is generally supposed that the autumn tints are to a great extent due to a gradual disappearance of the blue colouring matter, which causes a change in colour, from green to yellow and yellowish-brown. During the growth of a plant many changes take place. As soon as the seed is germinated it begins to absorb from the soil and the air water and oxygen, and when a certain stage is reached the formation of chlorophyll commences, and from that moment the growth of the plant is as depen- dent upon the air as upon the soil for its nourishment ; for under the exciting influence of sunlight the chlorophyll absorbs carbon dioxide, and this, together with the water vapour partly absorbed from the air and partly drawn up from the soil, forms the constituents from which by a beautiful series of reactions Nature builds up the solid por- tion of the plant, fixes the energy derived from the sun in such a way that it can be regenerated on combustion, and at the same time returns the surplus oxygen to the air, so renewing the amount abstracted by decay, respiration, and combustion. The solid portion of the plant is built up of a compound of carbon, hydrogen, and oxygen, called " cellulose," which has the percentage composition Carbon .... 44*44 Hydrogen .... 6*17 Oxygen .... 49'39 100-00 28 LIQUID AND GASEOUS FUELS. In wood the main constituent, cellulose, is common to all species, the chief differences being in the density and constituents of the sap. As a fuel, the value of wood varies with the amount of moisture it contains and the ash, which is made up chiefly of the mineral constituents of the sap. The moisture in wood varies with many circumstances, such as the season ofjhe year at which it was cut down, the species of tree, and the way in which it has been kept between the times of cutting and burning. When wood is cut in the spring, say during April, it will often contain nearly 10 per cent, more water than the same species of timber cut in the winter. For instance Cut in January. Cut in April. Wood. Water. Water. Ash ...... 28-8 38-6 Sycamore ..... 33-7 40-3 Horse chestnut .... 40-2 47-1 White fir . 52-7 61-0 It also varies in quantity according to the species of tree, the average quantity of moisture present being shown in the following table : Water contained in 100 parts of fresh-cut wood. Hornbeam ....... 18'6 Willow 26-0 Sycamore 27'0 Ash 28-7 Birch 30-8 Oak 34-7 Horse chestnut ...... 38'2 Pine 39-7 Elm 44-5 .Larch 48'6 Poplar 51-8 FUEL, ITS FOEMATION AND CO M POSITION. 29 A certain amount of this moisture can be got rid of by exposing the wood to air and at the same time protecting it from rain, but under favourable circumstances, and after a year's exposure, air-dried wood will still contain about 20 per cent, of moisture, whilst after several years' keeping in a warm room it will often retain 17 per cent, of moisture. For all practical purposes, therefore, wood will, under favourable circumstances, only contain 80 per cent, of combustible matter, whilst the large amount of heat absorbed in heating and evaporating the water present is a serious drawback to its employment as a fuel. The ash left on burning wood varies from J to 5 per cent., and an excess of ash, as it is incombustible, must be looked upon as diminishing the value of fuels for heating purposes. The amount of combined oxygen present in any fuel seriously detracts from its value, as its presence means that some of the combustible constituents of the fuel are already combined with oxygen, and are no longer available for generating heat. Wood, when heated out of contact with air, yields a variety of volatile products and leaves a residue of charcoal. This charcoal is not pure carbon: it always contains oxygen, hydrogen, and a small quantity of nitrogen, in addition to the mineral constituents or ash of the wood ; but the moisture and a large percentage of the combined oxygen having been got rid of, the charcoal is, bulk for bulk, a much more valuable fuel than wood, so that in cases where great local heat is required, it is preferable to convert the wood into charcoal before using. Charcoal which is to be used as fuel is nearly always pre- pared in this country in charcoal heaps, in which the combus- tion of some of the wood subjects the remainder to destructive distillation, air being as far as possible excluded by coating the heap with clay or loam. During the partial burning of the heap, some moisture is distilled off as water, whilst the combined oxygen and most of the hydrogen escape, partly 30 LIQUID AND GASEOUS FUELS. combined together and partly combined with carbon as tar, wood naphtha, and other hydrocarbons, which distil out of the heap and are lost. In foreign countries, however, wood is frequently subjected to destructive distillation almost entirely for the sake of the tar (Stockholm tar) and pyro- ligneous acid which are evolved, and in order to collect these substances the carbonisation is carried on in closed vessels. When the charcoal is to be used for the manu- facture of gunpowder, it must be prepared with great care and at a low temperature, superheated steam being often employed as the heating power. The rate at which the carbonisation takes place has a great effect upon the yield of charcoal obtained : with rapid heating there is a considerable loss, not more than from 17 to 20 per cent, by weight of char- coal being obtained, whilst with careful heating as much as 25 per cent, of the weight of wood taken remains as charcoal. As a fuel, charcoal has about double the calorific value of air-dried wood. Another kind of fuel much employed for domestic pur- poses in certain parts of the world is peat, which is composed of vegetable matter, generally mosses and aquatic plants, which under the combined agency of time and pressure has been converted into the spongy brownish- black substance found in the peat bogs. This peat is cut out in long square blocks, and is piled up exposed to air until dry. The relative heating power of dense, air-dried peat is about the same as wood, but when well dried and converted by pressure into briquettes it may be converted into a really valuable fuel. In composition, peat occupies a position intermediate between wood and coal, and there is no doubt that the formation of peat is a stage in the great natural process by which woody fibre is converted into the most valuable of our fuels coal. When any form of vegetation has ceased growing and is left exposed to moist air, the cellulose begins to decay, the FUEL, ITS FOKMATION AND COMPOSITION. 31 oxygen of the air once again unites with the carbon of the woody fibre, forming carbon dioxide, which mingles with the atmosphere, whilst the hydrogen and oxygen of the fibre combine as water and escape unseen into the atmo- sphere in the form of aqueous vapour. Consequently a tree which has been felled and left on the ground will, in the course of years, be entirely resolved into gaseous con- stituents once more, leaving behind only a small quantity of mineral matter which had been present in the sap sucked up from the soil, and which, had the wood been burned, would have formed the ash left behind by the combustion. If, instead of allowing the wood to decay away in free contact with the atmosphere, this action had been checked by keeping the wood under the surface of water or a sufficient layer of soil to cut off the atmospheric oxygen, a checked process of decay would have taken place, in which the oxygen present in the woody fibre would gradually have combined with carbon and hydrogen to form gaseous constituents, whilst some of the hydrogen and carbon, also combining together, would have yielded small quantities of such gaseous hydrocarbons as methane. We know by experience that if a pool of water, at the bottom of which there is decomposing vegetable matter, be disturbed with a pole, bubbles of gas rise to the surface ; and if we collect and analyse them, we find that they consist of carbon dioxide and methane, which latter has from this fact been given the name of " marsh gas." Where the vegetation undergoing the checked process of decay of this kind is very abundant, a solid residue is left of the character of peat, whilst if the action is continued over a far longer period of time, and also under conditions of pressure and increased temperature, the peat becomes more dense, a larger quantity of gas is eliminated, and a form of coal results. At one time it was supposed that coal was of mineral origin : but it has now been conclusively established that it is entirely formed from vegetable matter. 32 LIQUID AND GASEOUS FUELS. Long before man inhabited the earth, and when the atmosphere was probably far more highly charged than it is at present with carbon dioxide and water vapour, there flourished a monster vegetation, which, in its general characteristics, was not unlike a collection of the marsh plants that are now to be found in any swampy land : but, instead of growjng to a height of a few inches, its exuberant growth would in some cases reach 40 to 50 feet. This vegetation, like the marsh plants of to-day, grew with enormous rapidity, and as rapidly faded away ; and by precisely the same process as that from which we obtain the peat bogs existing at the present time, so beds of far greater thickness were formed from the vegetation of that period. Ample proof of this origin is to be found in the strata immediately above the coal seam, which abound in fossil remains of upwards of 500 different kinds of mosses and ferns ; whilst in the layer immediately below the seam, fossil roots are found in abundance. The three principal varieties of coal are lignite, bitu- minous coal, and anthracite. The lignite, or brown coal, is the least carbonised, and shows indications of organised structure, and also contains considerable proportions of hydrogen and oxygen ; whilst anthracite is the most carbonised, and often contains little else than carbon and the mineral matter which forms the ash. The following table will serve to show the variation in chemical composi- tion due to geological change (Butterfield) : Carbon. Hydrogen. Oxygen. Nitrogen. Sulphur. Ash. Cellulose . 44-4 6-2 49-4 Dry wood 48-5 6-0 43-5 0-5 1-5 (average) Dry peat . 58-0 63 30-8 0-9 trace 4-0 Lignite 67-0 5-1 19-5 1-1 1-0 6-3 Coal . 77-0 5-0 7-0 1-5 1-5 8-0 Anthracite . 90-0 2-5 25 0-5 0-5 4-0 FUEL, ITS FORMATION AND COMPOSITION. 33 The gradual conversion of woody fibre into peat, coal, and graphite, is even better illustrated by the following table, due to Dr. Percy, in which, to show the gradual elimination of hydrogen and oxygen, the carbon is kept as a constant number : Carbon. Hydrogen. Oxygen. Wood 100 1218 88-07 Peat .... 100 9-85 55-67 Lignite 100 8-37 42-42 Bituminous coal 100 6-12 21-23 Anthracite (Wales) 100 4-75 5-28 Anthracite (Pennsylvania) 100 2-84 1-74 Graphite 100 o-oo o-oo The theory that bituminous coal is a "younger" coal than anthracite is not, however, borne out by the fact that in the eastern part of Wales the coal is of a bituminous nature, gradually shading away into the anthracite found in the western portion of the Principality, as it is extremely unlikely that there is any very great difference in the age of the several parts of the Welsh coal field. The quantity of hydrogen present in a fuel exercises an important influence upon the way in which it burns, as hydrogen is expelled at a fairly low temperature in combination with some of the carbon as gases which are inflammable at a moderate temperature. The burning gas surrounds the fuel and continues to heat it, whilst the escape of the gas leaves the remaining and less inflammable carbon in a porous condition, which is favourable to carrying on the combustion. Flame is burning gas, and therefore the nearer to pure carbon that our fuel approaches, the less the amount of flame produced by its combustion, because the smaller will be the quantity of inflammable gas evolved. Lignite contains a larger amount of hydrogen than any L.G.F. D 34 LIQUID AND GASEOUS PUELS. other variety of coal : and it is for this reason more easily ignited, and burns with more flame than any of the others. The next in this respect are the bituminous coals, such as the Silkstone and Wallsend : whilst the anthracites are difficult to ignite, and when lit, can only be kept burning by a strong draught, this rendering them unfit for use in ordinary grates. Our knowledge oT the composition of coal is limited to the total amount of carbon, hydrogen, nitrogen, oxygen, and foreign materials which it contains : and at present we know practically nothing of the way in which these bodies are combined. There can be but little doubt, however, that it is correct to look upon it as carbon which contains, either mixed with it or combined with it, hydrocarbon compounds of much the same character as the paraffins, and also compounds of carbon, hydrogen, and oxygen of somewhat similar kind to the woody fibre from which it has sprung, whilst other compounds containing nitrogen, and probably of more complexity, are also present. As has already been pointed out, methane and carbon dioxide are produced during the process of checked decom- position which leads to the formation of the coal. In the early days of the coal epoch, when the monster vegetation was flourishing, and the surface of the earth had hardly yet hardened, frequent changes of level took place, with the result that many of these beds of decomposing vegetable matter became covered with running water, which, bringing down with it silt and mud, gradually built up over the surface of the rotting mass a dense deposit of soil : and this hardening and undergoing various changes, enclosed the gradually forming coal and kept it under great pressure. Under these conditions the marsh gas or methane and carbon dioxide evolved could not escape, and they created for themselves, in the faults and fissures of the coal, an enormously high pressure, while the coal itself, being FUEL, ITS FORMATION AND COMPOSITION. 35 slightly porous, absorbed these gases in large quantities : so that when, in mining the coal, a gallery is cut through the seam, the occluded gas escapes in considerable quantities into the workings of the mine. In some cases the gas so evolved proves to be nearly pure methane, as is shown by the following analysis : Methane 89'61 Nitrogen 9'61 Carbon dioxide ..... 0'23 Oxygen 0'55 100-00 Methane or marsh gas, when mixed with ten times its volume of air or twice its volume of oxygen, constitutes a mixture which explodes with great violence on the applica- tion of a light, forming carbon dioxide and water vapour. In many coal mines, not only is marsh gas present occluded in the coal itself and ready to issue into the workings when a fall in the barometer takes place, but is also often found accumulated under high pressure in cavities in the coal seams, discharging itself with con- siderable violence into the mines from the fissures made in hewing out the coal. The gas issuing from the fissures would burn quietly if a light were applied to it, since methane is not explosive unless mixed with the air : but when the gas escapes into the workings and mingles with the air, it forms an explosive compound as soon as the proportion of gas amounts to one -eighteenth of the volume of air, the most explosive combination consisting of one volume of methane and ten volumes of air. The explosive mixture of methane and air is called " fire damp," and the gases resulting from the explosion, carbon dioxide, water vapour and nitrogen, are called "choke damp," the latter being often as fatal in its effect as the explosion itself. D 2 36 LIQUID AND GASEOUS FUELS. The mixture of methane and oxygen requires a fixed temperature to ignite it, and unless this temperature be reached, explosion cannot result. If a piece of wire gauze is held over a gas jet, the gas may be ignited above it without the flame passing through and igniting the gas on the under side, the metallic wires composing the wire gauze conducting the heat away so rapidly that the temperature of the gas on the lower side does not rise to the point of ignition. This simple principle was utilised by Sir Humphrey Davy in the construction of the safety lamp for miners. It consists of an oil lamp entirely surrounded with fine wire gauze, through which the air can enter and the products of combustion go out, but no flame can pass from the inside to the outside of the gauze, even if the explosive gases burn in the interior of the lamp. The old form of lamp first used was entirely surrounded with wire gauze, but it gave so feeble an illumination that the gauze immediately surrounding the flame was replaced by a glass cylinder, and until 1887 this was the best form in use. It has been shown, however, that although the flame, when burning under normal conditions, cannot pass through the gauze, yet a sudden disturbance of the air, such as is caused by the blasting of coal in the mine, will some- times jerk the flame by a sudden impulse through the gauze, and so communicate with the explosive mixture outside. To do away with this risk, in the later forms of lamp the wire gauze cylinder is entirely surrounded by a shield of iron plate, which prevents the direct impact of the air upon the gauze, and greatly increases the safety of the lamp. It would considerably decrease the risk of explosion in petrol and oil stores, coal stores, coal bunkers, and coaling vessels if, when a light is required, only such lamps were used, and the employment of a naked flame never allowed, as, besides the gas, it has been shown that the presence of fine dust FUEL, ITS FOKMATION AND COMPOSITION. 37 of coal or other combustible very much increases the liability to explosion. In the same way that charcoal is obtained from wood by destructive distillation, so coke may be obtained from coal, the hydrogen and traces of other substances which it contains being driven off on heating it out of contact with air. When this is done in the manufacture of coal gas, the resulting coke is called gas coke, but for many metallurgical processes coke is specially prepared in ovens from well- washed small coal, temperatures being reached, at which the escaping gases are of no use for illuminating purposes, and can only be used to heat boilers, etc., but at which temperature a very dense and superior quality of coke is produced. This kind of coke is called oven or metallurgical coke. Coke began to be made from coal in the eighteenth century, but it was well into the nineteenth before the depletion of the wood supply turned attention to coke as a substitute for wood charcoal for metallurgical processes, and it was not until 1860 that the subject of coke produc- tion attracted any scientific attention, but since then a large amount of work has been done in coke manufacture, and the means of obtaining the desired results are fairly well known. The drawbacks of coal for such metallurgical processes as the smelting of iron are obvious, as if any coal but anthracite were used, the swelling of the mass under the influence of heat and consequent choking of the blast furnace would result, whilst the smoke, high sulphur, and friability of the coal all unfit it for use for such purposes. Another factor which led to the special coking of coal was that in bringing the coal to the pit's mouth consider- able breakage of the material took place, and that from 30 38 LIQUID AND GASEOUS FUELS. to 50 per cent, of small coal or slack was produced, and that although this only commanded a very low market price as a fuel it answered admirably for making coke from. The characteristics needed to make a good metallurgical coke are 1. Strength, i.e., it must not be friable. 2. Infusibility. 3. Low sulphur. 4. High calorific value. the need for strength depends upon the fact that if the coke easily broke up, in tall columns of mixed coke and ore, such as are used in the blast furnace, a crumbling of the material would take place, which would tend to choke the furnace, whilst freedom from or at any rate low percentage of sulphur is very important, as its presence in the fuel would deteriorate the metal made by its use. Sulphur occurs in the coal largely as iron pyrites or disul- phide of iron, but also as sulphate of lime and organic sulphur, and with coals rich in sulphur this element is reduced in quantity by crushing the small coal and levi- gating it, which gets rid of the heavy pyrites, whilst nearly half the remaining quantity is volatilised during the coking, and of the remainder some escapes as sulphuretted hydrogen when the coke on removal from the ovens is quenched in water. It is not every kind of coal which at the temperature of the coke oven will fuse together before complete decom- position of the hydrocarbons to form a mass of sufficient density, but most bituminous slacks will do so, and when it refuses to do so the admixture of the slack of a good caking coal will often lead to good results and a high coke yield. The composition of some English coking coals and FUEL, ITS FORMATION AND COMPOSITION. 39 the coke yield from them are given in the following table : Percentage Source. Carbon. Hydrogen. Oxygen. Nitrogen. Sulphur. Ash. yield of coke. Durham 83-47 6-68 8-17 1-42 0-60 0-20 62-70 South Wales 83-78 4-79 4-15 0-93 1-43 4-41 72-60 Derbyshire . 79-69 4-94 10-28 1-41 1-01 2-65 59-32 Lancashire . 77-90 5-32 9-43 1-30 1-44 4-88 60-22 whilst a good coke will approximate to- Carbon Oxygen Nitrogen Sulphur ..... Ash , 92*98 1-80 0-23 0-27 5-22 100-00 The heating effects produced from coke are theoretically a little better than those obtained from coal, but in practice the amount of heat obtainable from coal and coke is about the same. It was not until the middle of last century that the oil industry and oil as a fuel may be said to have originated. The first step in the introduction of mineral oil dates back to 1849, when James Young had his attention drawn to the small driblets of oil that ran down from the shale measures in the Biddings colliery near Alfreton. On dis- tilling this oil, he obtained an excellent lubricant, but he soon found that the demand exceeded the supply, and that the source of his oil showed signs of being exhausted. Later on he succeeded in obtaining an abundant supply by distillation from some of the Scotch shales, and in this way he founded the Scotch Oil Industry. In 1859 oil was obtained in enormous quantities in America from wells bored 40 LIQUID AND GASEOUS FUELS. into the oil measures, and the result was that a large supply of oil was soon obtainable all over the civilised world, which was added to when the Eussian oil fields were opened up about 1870, and the supply from this source soon made Kussian oil an important competitor with the American trade. For some years after this Kussia and America practically supplied all the oil, but since that period oil has been dis- covered in many different parts of the world, so that with wider distribution its use as a liquid fuel is rapidly increasing, thus bringing it nearer and nearer to a universal fuel. All forms of mineral oil as they leave the wells are mixtures of hydrocarbons, which, however, vary a good deal in composition, according to the part of the world from which they are obtained. There are several theories to account for the formation of petroleum. One class of theorists insists upon its vege- table origin, declaring that it is the result of distillations from such fossilised vegetation as coal. Another and per- haps a larger class argues that it has been formed from animal remains, whilst a third party is perfectly clear in its views as to these hydrocarbons having been formed by the action of water or steam under considerable pressure upon metallic carbides. Carbides are substances formed by the combination of metals and carbon: there is one carbide perfectly well known calcium carbide and by the action of water it yields acetylene. In the same way as water and calcium carbide give acetylene, so water and some of the carbides of the rare earths will give hydrocarbons of exactly the same composition as many of the hydrocarbons found in the mineral oils. Liquid fuel has now been introduced in nearly all the navies of the world, but as the total supply would at present be a mere fraction of that needed if it were burnt alone, it is mostly used as an adjunct to coal when full power is required. FUEL, ITS FOBMAIION AND COMPOSITION. 41 THE WORLD'S COAL PRODUCTION. 1905, United States United Kingdom . France Germany . Belgium British India Australia New Zealand Canada Transvaal . Natal . Cape of Good Hope LIGNITE. Germany . Austria Hungary United States United States Baku, Russia Austria British India Borneo Canada Germany Italy . Japan . Java . Roumania . Sumatra PETROLEUM. Tons. 350,820,000 236,129,000 34,778,000 119,349,000 21,506,000 8,425,000 7,496,000 1,586,000 7,836,000 2,327,000 1,129,000 147,000 Tons. 47,853,000 21,635,000 5,430,000 5,725,111 Tons. 16,452,000 6,870,000 2,790,000 42 LIQUID AND GtASEOUS FUELS. The small ratio of yield from the Kussian oil fields is due to internal disturbances in the country ; whereas prior to 1903 the amount of Russian petroleum placed upon the market was 51 per cent, of the total output. It is manifest that crude petroleum, being a mixture of many hydrocarbons, will emit inflammable vapour at so low a temperature that its use as a fuel would be attended with danger on land, and would certainly never be permissible afloat, and it is to such residues as are left after the distilla- tion of the more volatile portions and the lamp oil that we must look for the chief source of our liquid fuel, and this further reduces the available supply by about two-thirds. The fuel oils differ but little in the ratio of carbon and hydrogen present, and the following table gives the ultimate composition of the chief available fuel oils : FUEL OILS. Carbon. Hydrogen. Oxygen, etc. American 84-9 13-7 1-0 Russian 86-6 12-3 1-1 Borneo 87-8 10-78 1-24 Texas . . 85-6 11-03 3-51 Caucasus 84-9 13-96 1-25 Burmah 86-4 12-10 1-50 The ease of application and many advantages presented under certain conditions by the use of gaseous fuel in various manufacturing processes have led to considerable attention being paid to the subject, and ever since the dis- covery of water gas by Fontana in 1780, engineers have busily attempted to perfect methods for its economical production. Under the heading of gaseous fuel may be comprised : (1) Coal gas. (2) Water gas, made by the action of steam on incandes- cent carbon. FUEL, ITS FORMATION AND COMPOSITION. 43 (3) Mixed producer and water gases, often called semi- water gas, made by the passage of both air and steam over the highly heated fuel. (4) Generator or producer gas, made by the passage of air through incandescent carbon. Generator or producer gas is a mixture of carbon monoxide and nitrogen, and is the poorest in thermal value of the gaseous fuels. It is formed by passing air through a column of heated coke, when the carbon at the lower surface of the column burns to carbon dioxide, combining with the oxygen of the air : the carbon dioxide, by contact with the heated carbon over which it has to pass, is then reduced to carbon monoxide, and this and the residual nitrogen from the air form the " generator gas." The heating power of such a gas is very low, but its production is inexpensive, and when burnt hot it is a very effective form of fuel for glass melting, the heating of gas retorts, brick burning, pottery kilns, and many processes of this character, in which, used in connection with a Siemens regenerative furnace, it gives splendid results. Siemens gas only differs from generator gas in that small coal or slack is used as the fuel instead of coke, with the result that the gas contains a small proportion of gaseous hydrocarbons, which increase its thermal value. Water gas depends for its formation upon the fact that at high temperatures carbon has a greater affinity for oxygen than hydrogen lias, and that when steam and carbon (in any of its amorphous forms) are heated to such tempera- tures, the steam is decomposed with liberation of hydrogen and either carbon monoxide or dioxide, the oxide formed being to a great extent dependent upon temperature, and the quantities of steam and carbon interacting. The value of the gas produced as a fuel largely depends upon the closeness of approximation to theoretic propor- tions, but the ideal composition is rarely, if ever, reached, 44 LIQUID AND GASEOUS FUELS. water gas consisting practically of a mixture of carbon monoxide and dioxide, hydrogen, and small quantities of methane formed by secondary reactions between liberated hydrogen and carbon oxides. The following analysis will give a fair idea of the composition of ordinary water gas : Hydrogen . . . Carbon monoxide Carbon dioxide . Nitrogen ..... Methane ..... Sulphuretted hydrogen Oxygen ..... 100-00 The ratio of carbon monoxide and carbon dioxide present depends entirely upon the temperature of the generator and the kind of carbonaceous material employed. Using a hard anthracite coal a temperature can be reached at which practi- cally no carbon dioxide is formed: but with an ordinary generator and a loose fuel like coke, a certain percentage of that gas is generally produced. The sulphur present in gas coke gives rise to the sulphuretted hydrogen, but by using a material like anthracite, practically none is formed. The nitrogen is the result of heating the fuel by air blast, which leaves the pipes full of producer gas nitrogen and carbon monoxide which is carried over into the holder by the first portions of water gas. Water gas so produced is non- luminous, and many attempts have been made to use it as an illuminant by heating with it mantles or combs of some refrac- tory material until they become incandescent and emit light. Water gas forms an effective fuel in many metallurgical operations, and is largely used for welding and other engineering work. FUEL, ITS FOEMATION AND COMPOSITION. 45 It is employed to a considerable extent as the basis of an illuminating gas, by mixing with it the gases formed by the decomposition of various grades of oil : these gases, being rich in hydrocarbons, endow it with illuminating power, and the mixture is generally known as carburetted water gas. In the formation of generator or producer gas heat is evolved by the processes taking place in the generator, whilst in the making of water gas a very large amount of heat is absorbed, so that the temperature of decomposition has to be attained and kept up either by exterior heating, as used in the retort processes of making water gas, or by blowing up the fuel to incandescence by an air blast, as practised in all the successful water gas processes. A large number of gas generators is now made in which air and steam are simultaneously passed through the incandescent fuel in such proportions that the formation of producer gas, by partial combustion of the carbon by oxygen of the air, shall raise the temperature in the same ratio that the decomposition of the steam by the red hot carbon into water gas lowers it, the result being a uniform temperature in the generator and the production of a gas which is practically a mixture of generator or producer gas with water gas, and which has a higher thermal efficiency than the producer gas alone, and answers well in gas engine practice. Producers for making these mixed gases are known by the names of their inventors, and the Wilson, Dowson, Dawson, and Duff processes are all of this character., Mond gas however differs from these inasmuch as, by using an excess of steam in the generator, the temperature of the fuel is kept low, and a large proportion of the carbon monoxide is converted into dioxide, this however being accompanied by an increase in the volume of hydrogen produced, and the low temperature favouring the formation of ammonia from the nitrogen in the slack used as fuel, yields a valuable by-product. 46 LIQUID AND GASEOUS FUELS. Blast furnace gas consists of the gases which until lately were blown to waste from the mouth of the blast furnace during the reduction of iron from its ores, and which has a composition not very different from that of producer gas. Coal gas is year by year rapidly increasing in favour for power purposes, and as a fuel for domestic purposes, such as heating and cooking, the only drawback being the cost of gas as compared with coal as a fuel. When used for such purposes the gas is burnt mixed with air in atmospheric burners, and during complete combustion a very high temperature is attained : but per unit of heat evolved the cost is considerably more than that of coal, against which however must be set the economy of being able to turn on the gas just when required, and to turn it off when the desired effect has been produced, and this, when taken in con- junction with the saving of labour and absence of dirt and smoke considerably decreases the margin in favour of coal. The natural gas issuing from the wells and bores in Pennsylvania, Baku, and elsewhere, has much the same composition as the gas from many coal measures, and contains from 80 to 98 per cent, of methane, but higher members of the paraffin series of hydrocarbons are also frequently present in small quantities, marking the fact that the gas is disengaged from the oil and not from the coal measures. COMPOSITION OF NATURAL GAS. Russian (Baku). American (Ohio). English (Heathfield). Hydrogen . . . . Methane . . , Ethane Carbon dioxide . Nitrogen . . Oxygen . . /, Carbon monoxide 0-98 98-09 3-26 2-18 0-49 o-oo o-oo 1-89 92-84 0-35 0-75 3'82 0-35 o-oo o-oo 93-16 2-94 o-oo 2-90 o-oo 1-00 FUEL, ITS FORMATION AND COMPOSITION. 47 It is the most valuable of the gaseous fuels from a heating point of view, but is unfortunately rapidly diminishing in quantity in most of the districts before rendered prosperous by its presence. Having seen that our fuels, be they solid, liquid, or gaseous, contain hydrogen and carbon as the essential constituents for the production of heat during combustion, it will be well to now consider the chemical properties of these elementary substances, and the methods by which we determine their calorific value, and also the composition and calorific value of the various forms of fuel which contain them in combination. Hydrogen was first discovered by the alchemist Paracelsus in the sixteenth century, although it was not until Cavendish's experiments with it in 1766 that the true nature of the gas was thoroughly understood. Practically, hydrogen does not exist free to any great extent on the earth, as with the exception of small quanti- ties found in the gases escaping from volcanoes it is never found by itself: indeed water, the compound of hydrogen with oxygen, is the great storehouse of hydrogen, whilst it also occurs in combination, although in much smaller quantities, with such elements as chlorine, sulphur, and nitrogen, and forms an important constituent of nearly all organic compounds. The most marked and characteristic property of hydrogen is its wonderful lightness. It is the lightest gas known, and is for that reason taken as the standard to which the weights of all other gases are compared. Pure hydrogen is a clear, colourless gas, having neither taste nor smell, and being practically insoluble it may be collected and stored over water, one hundred volumes of which dissolve less than two volumes of the gas. Hydrogen burns in air or oxygen with a non-luminous but intensely hot flame, water vapour being the only product of its 48 LIQUID AND GASEOUS FUELS. combustion. It does not support combustion in the ordinary sense of the term, and a lighted taper plunged into a jar of the gas is at once extinguished. Hydrogen being one of those bodies that resist further decomposition, it is called an element, and of these simple forms of matter some seventy- eight are at present known (see Table in Appendix). The distribution of the elements in Nature is most irregular. Some are found in very large quantities and very widely distributed, whilst others occur in such minute quantities that their properties are scarcely yet known. Indeed, nearly half the elements known at present might be eliminated without, as far as our present knowledge goes, causing any considerable disturbance of the laws of Nature. The general distribution of the elements is roughly indicated in the following tables : APPROXIMATE COMPOSITION OF THE CRUST OF THE EARTH. Oxygen ...... 45*5 Silicon . . . . . . 29'4 Aluminium ...... 8'2 Iron 6'3 Calcium ...... 2'4 Magnesium ...... 1*6 Sodium 2*5 Potassium 2*0 All the other elements . 2'1 100-0 COMPOSITION OF AIR. Nitrogen . . . 76'9 parts by weight. Oxygen . . . 23'1 100-0 FUEL, ITS FOEMATION AND COMPOSITION. 49 COMPOSITION OF WATER. Oxygen . . . 88*8 parts by weight. Hydrogen . . Ill 99-9 To these elements must be added carbon, which exists in all matter of organic origin, and it is then seen that 99 per cent, of known substances are composed of eleven elements, whilst oxygen alone constitutes upwards of 52 per cent, of earth, air and water. Elements combine to form chemical compounds, cr, more rarely, exist free. By matter we understand anything that has weight, and it may be either solid, liquid, or gaseous in its nature. These three states of matter are entirely dependent upon heat. It so happens that at the ordinary temperature zinc is a solid, water is a liquid, and carbon dioxide is a gas, but if water be cooled down below C. it becomes a solid ice, whilst heated above its boiling point (100 C.) it is converted into gaseous steam. In the same way all substances which are not decomposed by heat can be obtained as solids, liquids or gases. If the size of a bar of zinc at the ordinary air tempera- ture be carefully determined, and it is then heated, it is found that the action of heat is to cause it to increase in bulk, this increase proceeding at a definite rate until the temperature is raised to 423 C., when it becomes liquid. If now the liquid be further heated it will be found to still continue to expand until a temperature of 1,040 C. is reached, when it boils like water and is converted into the gaseous state. If carbon dioxide, which is a gas at ordinary tempera- tures, be cooled down to near the freezing point) of water, and be subjected to a pressure of 36 atmospheres (540 Ibs. L.G.F. E 50 LIQUID AND GASEOUS FUELS. on the square inch), it is reduced to the liquid state, and in this condition can be kept in steel vessels of sufficient strength to resist the pressure necessary to keep it liquid. On allowing some of this liquid to escape suddenly into a small box at ordinary atmospheric pressure, it is instantly converted into gas, and in the change from the liquid to the gaseous state takes up so much heat as to produce a degree of cold sufficiently intense to freeze some of the liquid escaping from the vessel into solid carbon dioxide. From these three experiments it is clear that those bodies which we look upon as solids are simply those which have a melting point above the ordinary temperature, whilst a liquid has a melting point below the ordinary tempera- ture, and a gas its boiling point below the ordinary temperature. It was seen that when the solid zinc was being heated up to the point at which it became liquid, a continuous expan- sion was taking place, and that the expansion continued until the zinc was converted into vapour, the volume of the vapour being enormously greater than that occupied by the original zinc bar. In the same way when water is boiled it is converted into steam, the vapour so formed occupying about 1,700 times the volume of the water taken. Eoughly, a cubic inch of water forms a cubic foot of steam. This enormous increase in volume may be explained in one of three ways : either the cubic inch of water is stretched under the influence of heat, like a piece of indiarubber, until it assumes the dimensions of the cubic foot, or the cubic inch of water is built up of an innumerable host of small particles which, when heated, undergo individual expansion, which mounts up to the enormously increased volume, or else this multi- tude of small particles do not themselves expand, but under the influence of heat tend to repel each other, and by FUEL, ITS FORMATION AND COMPOSITION. 51 spacing themselves further apart give the increase in volume. If the first or second theory be correct, then every part of the cubic foot of steam would be perfectly homogeneous, and without condensing some of the steam it would be impossible for any other vapour to find room in the space so occupied, whilst experiment shows us that one vapour can act as a vacuum to another, so that other vapours can occupy the space already filled with water vapour, a phenomenon which can only be explained on the assumption that the vapours do not completely fill the space they occupy, although equally distributed through it : that is, they are built up of particles, which by the action of heat become widely separated from each other, thus leaving spaces within which the particles of other vapours may find place. It has been seen that these three states of matter are merely dependent upon temperature and pressure, and it is clear, therefore, that if the vapours and gases consist of particles, then it must be assumed that liquids and solids also are built up in the same way, an assumption which is entirely borne out by experiment. In the solid state, these particles, each of which has the same properties as the mass of which it is a part, are held together by the force of cohesion, a force which varies with the nature of the substance : so that when a solid is heated, the particles tend to separate, but in different substances they do so to a different extent. The stronger the force of cohesion existing between the particles, the greater is the work the heat has to do in separating them. At a certain temperature the particles are so far asunder that the force of cohesion is weakened to a certain extent, and the particles become free to move round each other, i.e., they assume the liquid state : continue the heating, the distances between the particles grow greater and greater E 2 52 LIQUID AND GASEOUS FUELS. until a point is reached at which cohesion exerts no influence, the particles move independently of each other, and we have the gaseous state. In the solid and liquid states various substances expand unequally for an equal increment of temperature, whilst in the gaseous state all substances behave alike, an equal increment of temperature producing in each case an equal increase in volume, because cohesion has ceased to act between the particles. These particles, of which all matter is composed, and which have the same chemical and physical properties as the original mass of which they form part, are called mole- cules : but when we investigate the composition of any compound mass, we find that these molecules, although they are ultimate particles as far as the particular substance is concerned, are built up of other kinds of elementary matter held together by chemical affinity. For instance/a molecule of chalk is the smallest particle we can imagine to possess the properties of the mass of chalk : yet inasrmich as we can decompose chalk into quick- lime and carbon dioxide, and these again into calcium, carbon, and oxygen, it is evident that each molecule of the chalk must contain still smaller particles of these elements : and these small particles which go to build up the molecule we call " atoms." We define the molecule as being the " smallest particle of matter which can exist free, and still retain the properties of the mass of which it forms a part, and these particles are built up of two or more atoms." The atom is the smallest particle which can exist in combination, and is the smallest indivisible particle of an element that we can assume. In order to facilitate the expression of chemical reactions, each of these elementary atoms is represented by a symbol, consisting of the initial letter of its Latin name, or in case of two or more elements commencing with the same letter, FUEL, ITS FORMATION AND COMPOSITION. 53 the initial and first distinctive letter are used. For instance : Carbon is represented by C. Calcium ., ,, Ca. Cadmium ., ., Cd. Chlorine ., Cl. Copper ., ,, Cu. (Latin Cuprum). Inasmuch as these symbols stand for an atom of the element which they represent, we can, by experimentally determining the number of atoms of each element present in the molecule of a compound, represent symbolically the molecule by placing together the atomic symbols in the right proportions. We conclude by analogy that the molecule of methane contains one atom of carbon (C) and four of hydrogen (H), and this being so, the molecule can be represented by CHHHH. It would, however, be inconvenient to repeat the symbol for an atom when the same element occurs more than once, and we therefore express the number of the elementary atoms by placing a small numeral after and below them, so that the molecule of methane would be written CH 4 . The symbolical representation of a body is called a "formula," and by experimentally determining the proportions in which substances react upon each other, we can by means of the formulae build up a representation of the changes taking place. When methane is heated to a high temperature, it breaks up into carbon and hydrogen, and the decomposition can be represented as Methane. Carbon. Hydrogen. CH 4 = C + 2H 2 The large numeral in front of the symbol for hydrogen multiplies the molecule, whilst the sign of addition between the carbon and hydrogen shows that they are no longer in 54 LIQUID AND GASEOUS FUELS. chemical combination. Such a symbolical representation of a chemical change is called an " equation." The molecules and atoms are so minute that the mind fails to grasp the immensity of their smallness, but Lord Kelvin gave an excellent picture of it in saying that if a drop of water could be magnified until it was the size of the world, we should then see the molecules that composed it, and they would be between the size of swan-shot and cricket balls. Minute as these particles are, yet we are able by physical and chemical means to find the ratio of weight which the various atoms bear to each other, and this, taking hydrogen as unity, is called their atomic weight : for instance, if the atom of hydrogen weighs 1, then the atom of nitrogen weighs 14, oxygen 16, carbon 12 (see Table of Atomic Weights in Appendix), and these are their atomic weights. In writing the formula for a molecule we represented each atom composing it by the symbol for that atom, so that if we add together the atomic weights of the elements com- prising the molecule we obtain the molecular weight. We found by experiment that the molecule of methane contained one atom of carbon and four of hydrogen : therefore we wrote the formula for its molecule CH 4 , and now, knowing that carbon has an atomic weight of 12 and hydrogen 1, we can say that the molecular weight of methane is 12 + (1X4)= 16. It has also been determined by experiment that all mole- cules in gaseous matter occupy the same space, no matter how many atoms are crowded into them, and that this space is just double that occupied by an atom of hydrogen with its atomic weight of 1. This at once gives us a relation between weight and volume in gaseous molecules, as if we take the unit of hydrogen and call it 1 gram, we can measure the volume that weight of gas occupies at standard temperature and FUEL, ITS FORMATION AND COMPOSITION. 55 pressure (0 C. and 760 mm.), and we find it to be 11-16 litres : now, if we call the units in the molecular weight of any gas grams, the number of grams will occupy 2 X 11 '12 or 22*32 litres, so that, taking CH 4 with its molecular weight of 16, we know at once that 16 grams of CH 4 will occupy 22*32 litres at standard temperature and pressure. If we now burn methane in pure oxygen, we find by experiment that the reaction may be represented by the following equation : Methane. Oxygen. Carbon dioxide. Water. CH 4 + 2 2 C0 2 + 2 (H a O) 1 molecule 2 molecules 1 molecule 2 molecules whilst the weight relations will be (12 + 4) + (16 X 4) = (12 + (16 X 2)) + 2 (2 + 16) or 16 + 64 = 44 + 36 and by volume 22*32 + 2(22*32)= 22*32 + 2(22*32) litres litres litres litres Methane Oxygen Carbon dioxide Water as steam So that not only does an equation give us the means of symbolically representing a chemical action, but also affords us the data from which all the gravimetric and volumetric factors can be ascertained. In the Appendix the relation between the weights and measures employed in the metric system and their English equivalents will be found, so that, if desired, the results can be translated into pounds and cubic feet. Carbon, next to oxygen, is perhaps the most widely dis- tributed of the elements. It occurs in the free state as the diamond and as graphite, substances which, although they are physically dissimilar, yet can be proved to be chemi- cally identical, the dissimilarity of physical properties being probably due to some difference in the atomic arrangement. 56 LIQUID AND GASEOUS FUELS. In Nature, as we have seen, carbon is found combined with hydrogen in coal, bitumen, shale, naphtha, the paraffins and numerous other hydrocarbons. With oxygen it is found as carbon dioxide, which is present in the earth in enormous quantities, and which forms the large class of metallic salts called carbonates. In the vegetable kingdom the dry solids contain nearly 50 per cent, of it, whilst all animal matter is largely made up of it, fat containing as much as 79 per cent. Carbon is insoluble, non-volatile, and infusible at all ordinary temperatures, but signs of volatilisation are apparent in the electric arc. The diamond does not easily conduct heat or electricity, but the other forms of carbon are conductors. Carbon forms an enormous number of compounds with hydrogen, these bodies being known by the generic name of " hydrocarbons." Twelve parts by weight of carbon will unite with four parts by weight of hydrogen, and when these elements are united in this proportion, the body formed is incapable of combining with chlorine or any other element of the same kind, the constituents having formed what is termed a " saturated " compound, but the compound may exchange the whole or part of its hydrogen for other elements. Most elements in forming compounds only exist in the molecule in a very limited number of atoms, but carbon has the property of existing in different bodies to a very large number, so that although the simplest compound of carbon and hydrogen known is represented by the formula CH*, it is only the first of a long series of compounds in which the carbon is saturated with hydrogen, each member of this series containing one atom of carbon and two atoms of hydrogen more than the member of the series preceding it. This series is known as the " saturated hydrocarbon " or FUEL, ITS FOEMATION AND COMPOSITION. 57 "paraffin" series, and all its members contain carbon and hydrogen in the ratio of C 7l H2 7l + 2, n being the number of atoms of carbon. Besides this series there are many others in which the ratio of hydrogen to the carbon is not so high, and which can therefore unite directly with some other elements, and for this reason are called " unsaturated hydrocarbons." As examples of these series may be cited The Ethylene series, having the ratio C n H 2% . The Acetylene series, having the ratio CH2-2. The Benzine series, having the ratio CnH 2n -6. In the paraffin series the lower members are gaseous, whilst as the molecule becomes more complex they assume the liquid state, and become less volatile and more viscid as the series is ascended, the higher members being solids. CHAPTEK III. THE DETEEMINATION OF CALORIFIC VALUE. Methods of determining calorific value The calorie and British thermal unit Heat of combustion factors Latent heat of steam Calculation of calorific value from chemical composition Evaporative duty Objections to calculated results Direct determination of thermal value Calorimeters The Mahler bomb, and the method of using it The William Thomson calorimeter The Fischer apparatus The Lewis Thompson calorimeter The use of the bomb for liquid and gaseous fuels The heat of combustion of gases The Junker calorimeter Correction of volume for temperature and pressure. THE heating value of a fuel, solid, liquid, or gaseous, may be arrived at by one of two methods : (1) By analysis of the fuel and calculation of its calorific value from that of its individual constituents. (2) By direct determination in a calorimeter. The heat generated during the combustion in oxjgen of different elements and compounds was first determined by Andrews, and later by Favre and Silberman, Thomson, and others. Some small discrepancies exist between the values obtained by these observers, which must have an influence on the calculated results, and figures derived from deter- minations made by Berthelot in the bomb calorimeter are now generally accepted in preference to those obtained by older methods. The determinations taken as the basis for all calculations are given in the table on p. 59. The scientific unit of thermal value is the calorie, which is the amount of heat required to raise a unit weight of water 1 C. at the point of maximum density, whilst the THE DETERMINATION OF CALORIFIC YALUE. 59 HEATS OF COMBUSTION (BERTHELOT). Calories. B.T.U. Hydrogen .... 34,500 62,100 Carbon to carbon dioxide . 8,137 14,647 Carbon to carbon monoxide 2,489 4,480 Carbon monoxide 2,435 4,383 Methane ... 13,343 24,017 Ethylene ... 12,182 21,898 Acetylene ... 12,142 21,856 Cellulose ... 4,200 7,560 Peat . ... 5,940 10,692 Naphthalene ..... 9,690 10,842 Sulphur ...... 2,500 4,500 usual English engineering unit is the British Thermal Unit, which is the amount of heat needed to raise a unit weight of water 1 F. As long as the unit weight of fuel burnt to give the increase in temperature of the water is the same as the unit weight of water heated, the relation between the two units will be the same as the ratio between the thermo- metric scales, i.e., a gram or a kilogram or a pound of fuel respectively will heat a like weight of water to the same extent, so that if we find that a kilogram of carbon in burning to carbon dioxide raises 8,137 kilograms of water 1C., we call that the calorific value in calories, and if we desire to convert it into B.T.U. all that has to be done is O1 O QO to multiply the result by - , or by the factor 1 '8, 100 which will give us the rise in temperature expressed in degrees F. when one pound of carbon is burnt in such a way as to impart all the heat of combustion to one pound of water. If, however, we use a constant weight or volume of fuel, say, a pound or a cubic foot, and take the calorie as the amount of heat necessary to raise 1 kilogram or litre of water 1 C., and the B.T.U. as the amount of heat necessary to raise one pound of water 1 F. ? then it is evident that in 60 LIQUID AND GASEOUS FUELS. the calorie not only is there the difference due to the thermometric scales, but also to the fact that the kilogram of water is 2*2 times the weight of the pound, so that to convert the pound or cubic foot calorie to the B.T.U. it must be multiplied by T8 X 2'2, or 3'96. When a fuel consists of carbon and hydrogen only, it is considered sufficiently accurate in practiccil working to determine its composition, and then to multiply the carbon present by 8,137, and the hydrogen by 34,500, the sum of the numbers so obtained being taken as representing the calorific value of it as a fuel. For instance, on analysing methane, we find that it has a percentage composition of: Carbon ...... 75 Hydrogen ...... 25 100 and (75 X 8,137) + (25 X 34,500) = ^^ 100 14,727 would therefore be taken as the calculated calorific value of methane. This value, however, is far higher than the figure obtained by direct determination, and this is due to the heat of formation of the compound being neglected in the calculation. When a chemical compound is formed, heat is either absorbed or given out, and when the compound is again decomposed during combustion, as much heat reappears or is absorbed as was the case during its formation, and to make the calculation of calorific value correct this must be allowed for. The heat of formation of the molecule of methane, which contains 16 units by weight, is + 20,414 calories, and our value for methane so corrected would be 14,727 ' ID THE. DETEEMINATION OF CALOKIFIC VALUE. 61 or 13,451 calories, a number much more nearly approaching that obtained by actual experiment, namely 13,343. When water is one of the products of combustion, it is clear that the available heat will depend on whether this water escapes as steam, as from a boiler, or is condensed to the liquid form, as in most calorimeter determinations. In practice it is usual to assume that the water formed is always condensed, but allowance can readily be made for its escape as steam by taking the latent heat of steam into account. In the conversion of water into steam the enormous expansion that takes place is due to heat spacing the particles or molecules of the water further asunder, and heat which is engaged in doing such intermolecular work disappears as sensible heat and remains in the steam until it is again condensed back to the liquid state, when the latent heat once more appears as sensible heat. If steam be passed into cold water it condenses, and giving up the stored heat within it, rapidly raises the temperature of the water. It is found that where a unit weight of steam at 100 C. is condensed into a unit weight of water at the same temperature, enough heat is given out to raise 536 unit weights of water from C. to 1 C., and we therefore say that the latent heat of steam is 536 thermal units. The calculation of the thermal value of a fuel also becomes rather more complicated when the fuel already contains a certain amount of oxygen in a state of combina- tion, for such elements as are partially oxidised can only yield a certain portion of their total heating value. Further, if moisture be present, a certain amount of the heat will be used up in vaporising this. Taking the case of dry cellulose, there are present 44*44 per cent, of carbon and 6*17 of hydrogen, but there is also present 49'39 of oxygen, and as this oxygen has already 62 LIQUID AND GASEOUS FUELS. entered into combination with the carbon and hydrogen present the quantities of these elements so combined are no longer available for the generation of heat during combustion. Oxygen combines with one-eighth of its weight of hydrogen to form water, and if we look upon all the oxygen present as being combined with hydrogen, the calorific value would be found from the following formula : (C X 8,137) + ( (H - 9) X 34,500") V o / which, if applied to cellulose, would give (44-44 X 8,137) + ( (6'17 - ^^) X 34,500 \ o 100 In other words, the oxygen present in combination is sufficient to entirely use up the hydrogen, and the calorific value of the fuel is practically the value of the carbon present. It is evident, therefore, that the combined oxygen in a fuel means that a certain percentage of it is not available as a fuel. Since in an ordinary analysis the oxygen and nitrogen are usually determined by difference, and the amount of nitrogen in coal approximates closely to 1 per cent., the oxygen present will be (0 + N) 1, and this oxygen is always assumed to be wholly combined with the hydrogen, which requires eight times its weight. A formula suitable for coal, therefore, is L f 8,137 C + 34,500 (H - ( + ^ ~ 1 ) - 600 H 2 o) 1UU \ o / the latter term making a sufficiently close approximation to the loss of heat in vaporising the water present in the coal from ordinary temperatures. THE DETERMINATION OF CALOEIEIC VALUE. 63 An example of the use of such a formula may be cited. A sample of coal gave on analysis Carbon ...... 76'71 Hydrogen ...... 4'67 Water ...... 1*94 Oxygen + nitrogen .... 7'46 then ((8,137 X 76-71) + 1 84,500 X (4'67 - 7 ' 46 8 ~ (600 X 1-94) 7,563 calories per unit whilst the actual determination in a bomb calorimeter gave 7,527 calories. The results expressed in calories or B.T.U. serve for a comparison between different fuels, but to the engineer the evaporative duty of the coal is the important factor, and this is usually stated as " Ibs. of water at 100 C. (or 212 F.) converted into steam at the same temperature " : therefore, by dividing the calories by 536'5, the latent heat of steam on the Centigrade scale or the B.T.U., by 965*7, the latent heat of steam on the Fahrenheit scale, the number of units of water evaporated per unit of fuel is obtained, whether these units be kilos, grams, or pounds. Thus in the example given : 7,563 cals. _ 14' 1 kilos or grams evaporated from and at 53fr5~ 100 C. or in B.T.U.- i Q ~7- = 14-1 Ibs. from and at 212 F. * Amongst engineers the Fahrenheit scale is still in most cases retained, and the evaporative value is often calculated from the percentage composition by the formula 0-15 fc + 4-28 (H - \ = Ibs. from and at 212 F. 64 LIQUID AND GASEOUS FUELS. which is constructed on tlie basis that hydrogen has approximately 4*28 times the heating value of carbon, whilst the factor 015 is obtained by dividing the calorific value of the carbon in B.T.U.'s by the latent heat of steam multiplied by 100 14 ' fi47 =0-15. 966 X 100 Certain calculated and evaporative values are open to objections. In the first place there is the difference in heating value given by various observers for the same combustible. Again, the process of analysis requires expert skill in order to obtain accurate results, any errors becoming largely multiplied in the calculation. As already pointed out, heat is required to break down most forms of chemical combination, and as to the amount of heat used up in this way we have no actual knowledge in reference to most fuels, but recent researches show that coal is slightly exothermic, and that any heat required to break it down may be practically disregarded. Close agree- ment is obtained between calculated and determined values with a large number of coals, but occasionally one meets with considerable differences, which are quite inexplicable, and therefore cast a doubt upon calculated values generally. The most satisfactory method for finding the calorific value of a fuel is undoubtedly by direct determination of the heat evolved during combustion in a calorimeter. In all forms of calorimeter the principle relied on is to burn the fuel to be tested in a vessel entirely surrounded by water, and to calculate its heating power from the increase in temperature of the water. Many forms of calorimeter have been devised, but they may be classified into the following types : (1) Where combustion of the fuel is effected by admixture with a solid oxidising agent, as is done in the Lewis Thompson calorimeter. THE DETERMINATION OF CALORIFIC VALUE. 65 (2) Combustion with oxygen at constant pressure (a) Where the temperature of the escaping gas is undetermined, as in the William Thomson calori- meter. (b) Where the temperature of the escaping gas is under control, as in the Fischer calorimeter. (3) Combustion with oxygen at con- stant volume, as in the Berthelot, Mahler, Mahler-Donkin, or Mahler- Krocker bomb. Of these various types of calori- meter undoubtedly the best and most accurate is the bomb, the chief draw- back to it being the expense of the apparatus, whilst the least accurate and most used is the Lewis Thomp- son, which has gained popularity amongst engineers owing to its ease of manipulation. In Mahler's calorimeter the com- bustion of the material takes place, in a closed bomb or cylinder of steel, in oxygen under a pressure of twenty- five atmospheres. The bomb is of the shape shown in Fig. 1, and is coated internally with a thin lining of porce- lain in order to resist the corrosive action of the trace of nitric acid formed during combustion. The cover of the bomb screws down on to a leaden washer (A), placed in a groove in the rim, thus ensuring a tight joint, whilst a tube through the cover serves for the admission of oxygen and is fitted with a screw-down conical valve (B). Through the cover also passes an insulated rod C to the lower end of which a platinum rod D is fastened by means of a clamp. Attached to the L.G.F. F FIG. 1. Mahler bomb (section.) 66 LIQUID AND GASEOUS FUELS. cover and in electrical contact with it is a second platinum rod, to which is clamped another, carrying the platinum capsule E, in which is placed the substance to be burnt. The two ends of the platinum rods can be connected by a fine iron or platinum wire, which is caused to rest on the combustible material, and serves to ignite it when the wire is raised to incandescence by the current from a battery. FIG. 2. Mahler bomb with fittings. The bomb is placed in the calorimeter vessel, which con- tains about 2'25 litres of water, the volume of water being capable of thorough agitation by means of vanes on a frame worked by a lever through a rod on which a spiral thread is cut, thus causing the vanes to have a reciprocating circu- lar motion. The standard carrying the agitator is also fitted with a small clamp for a thermometer, graduated to read to hundredths of a degree. In actual working the charge of combustible is weighed into the platinum capsule, which is then clamped on to its rod, an'd a fine wire is attached to the platinum rods so that THE DETERMINATION OF CALORIFIC VALUE. 67 it rests on the charge. The cover is screwed down firmly on to the bomb, a wrench being applied to the cover whilst the bomb is held in its special clamp. The connecting tube from the oxygen cylinder is attached to the tube in the cover, and oxygen is slowly admitted until the pressure gauge shows 25 atmospheres. The valve is then screwed down, and the oxygen tube removed. The bomb is placed in the calorimeter, which has been previously filled with the required amount of water, and the water is thoroughly stirred to obtain a uniform tempera- ture. Observations of the thermometer are taken at frequent intervals for a few minutes to determine the rate of change of the temperature of the water, and the charge is ignited by touching the insulated rod in the cover and any part of the bomb with the two wires from a battery. The agitator is kept at work during the whole time, and the temperature of the water is taken at regular intervals until it reaches a maximum and then falls regularly, and for another five minutes to ascertain the rate of cooling. The bomb is now removed from the water, the valve opened, and the cover unscrewed, after which the interior is rinsed out with distilled water to collect any acid formed during combustion, which is then estimated by analysis. The result can then be calculated from the observed rise in temperature of the water, which is corrected for radiation ; the weight of the water equivalent of the bomb, accessories, and gas being added to the weight of the water originally taken. An example of the calculation of the calorific value of a fuel is given below from an actual determination. The formula used is as follows : D = observed rise in temperature a = correction for radiation F 2 68 LIQUID AND GASEOUS FUELS. P = weight of water in calorimeter p = equivalent in water of the bomb and accessories x = calories due to nitric acid formed y = sulphuric acid formed W = weight of coal taken then Calories per gram = (D + *) (P +P> - (* - y). The nitric acid is estimated by titrating the washings from the bomb after combustion with standard alkali containing 3*706 grams of sodium carbonate (Na 2 C0 3 ) per litre. One cubic centimetre of this solution is equivalent to '0044 gram of nitric acid, the heat of formation of which is one calorie, so that the number of calories can be ascertained directly from the number of cubic centimetres of standard alkali used. In the same way the sulphuric acid in the washings is precipitated with barium chloride, and the weight of the barium sulphate formed, multiplied by 100, gives at once the number of calories to be subtracted. The correction for cooling is based on Newton's law which gives results sufficiently accurate for technical work. 1. The decrease of temperature observed after the maximum has been attained represents the loss of heat before the maximum and for any given minute if the mean temperature of the minute so determined does not differ more than one degree from the maximum temperature. 2. If the temperature of the given minute differs by more than one degree, but less than two degrees from that of the maximum, the number that represents the law of decrease at the moment of maximum less 0*005 will give the desired correction. THE DETEEMlNATtOtf OF CALORIFIC VALUE. 69 Taking now an actual example Eeadings per minute in degrees C. Minute. Reading. Minute. Reading. 19-343 5-0 22-180 1-0 21-840 6-0 22-170 1-30 22-200 7-0 22-155 Maximum. 2-0 22-280 8-0 22-145 2-30 22-215 9-0 22-135 3-0 22-200 10-0 22-120 4-0 22-195 Fall in 8 minutes from maximum = "16, or '02 mean per minute. Having thus obtained the necessary factors for the calculation we have D = 2-877 a = 0-020 P + p = 3,000 x = 21 y = 5-6 W = 1-0048 and these give us ( (2-877 + 0-020) XMOO)- (21 -5-6) = 86g4 . 5 ^^ per gram. In the William Thomson calorimeter the fuel is burnt in an atmosphere of oxygen under ordinary pressure. The apparatus consists of a platinum crucible in which the fuel is burnt : this rests on a support, attached to a foot carrying three springs which grip a glass combustion chamber fitting over the crucible, and into which oxygen is passed down a tube. The combustion chamber and foot are immersed in a glass vessel, holding 2,000 grams (4*4 Ibs.) of water, and surrounded by a metal cylinder, down which a slot is cut 70 LIQUID AND GASEOUS FUELS. to allow the action to be observed. Before entering the combustion chamber the oxygen is charged with moisture by being passed through a washbottle containing water and a " tower " filled with moistened pumice, as incomplete combustion often results from the gas being too dry. One gram of fuel is weighed out into the crucible, and combustion is started either by means of a piece of cotton wick impregnated with potassium bichromate or nitrate, or by means of fine platinum wire rendered incan- descent by a gal- vanic current. Combustion takes place in a stream of oxygen, and the escaping products pass through the water. When the combustion is completed, the water is admitted to the interior of the combustion chamber by opening a tap, and thorough mixing and uniform temperature is ensured by raising and lowering the chamber and foot for a short time. The temperature of the water is taken at the commencement and at frequent intervals to the end of the determination, and, when the necessary corrections have been made, the calorific value of the fuel is calculated from the rise observed. The results obtained with this apparatus are not satis- factory, as the combustion of the fuel is generally imperfect FIG. 3. William Thomson calorimeter. THE DETEKMttfATlOtf OF CALOftlFtC VALIfE. 71 and a certain proportion of carbon monoxide is formed, which vitiates the accuracy of the estimation. The combustion chamber in the Fischer calorimeter is made of silver, and the waste gases are drawn off at the bottom, whence they pass through a flattened pipe to the exit tube E, in which a thermometer is inserted. The fuel is placed in a platinum crucible A, into which oxygen is directed from a platinum tube in the cover C of the combustion cham- ber. The latter stands in the water vessel H containing 1,500 grams (3'3 Ibs.) of water, pro- tected against ex- ternal influences by a wood casing, the space between which and the water vessel is packed with glass wool. An agitator F and thermometer G complete the fittings. Like the William Thomson calorimeter, the drawbacks to the use of the Fischer are imperfect combustion, as is shown by a small amount of smoke which escapes, however carefully the determination be carried out. In the Lewis Thompson calorimeter the fuel to be tested is burnt by combined oxygen in a small metal diving bell, under the surface of a known weight of water, and the FIG. 4. Fischer calorimeter. LlQTllD AtfD GASEOUS increase in temperature of the water gives the necessary data for the calculation of the calorific value of the fuel. As supplied for commercial purposes the instruments are graduated for use with the Fahrenheit thermometer, and consequently the latent heat of steam is taken as 967. It follows then that if a unit weight of fuel is burnt under the surface of 967 unit weights of water, and if all the heat is im- parted to the water and raises it one degree, the same amount of heat would have con- verted a unit weight of water at 212 F. into steam at the same tempera- ture. Two grams of the fuel in a finely divided condition are mixed with eleven times the weight of a finely powdered mixture of three parts of potassium chlorate to one of potassium nitrate, and the mixture is pressed, a little at a time, into a small copper crucible. A small piece of wick soaked in potassium nitrate is fixed into the upper surface of the charge, and the crucible is then placed in the FIG. 5. Lewis Thompson calorimeter. THE t)Ef ERMlNATtOtt OF CALOElFlC VALtTE. ?3 combustion chamber, being held in position by means of a brass plate to which three clutch springs are fitted. After igniting the fuse, the whole apparatus is plunged into the cylinder, which contains 967 X 2 = 1,934 cc. of water at a known temperature. The mixture ignites, and the fuel burns at the expense of the combined oxygen present in the potassium chlorate and nitrate, whilst the products of combustion bubble up through the water, escaping through small holes in the base of the chamber. When combustion is complete, the water is admitted to the chamber by opening the tap in the tube of the chamber, and the w r ater is well agitated by raising and lowering the apparatus several times. The apparatus is then withdrawn, and the temperature of the water taken with the thermometer. Ten per cent, is added to the number obtained as the difference between the initial and final temperatures, to allow for heat absorbed by the apparatus, radiation, etc., and the total is looked upon as giving the number of unit weights of water which a unit weight of the fuel would evaporate. As an example Temperature of water before combustion . 62 F. after 75 F. Eise in temperature . . .13 Add 10 per cent. 1/3 Evaporating power . . 14'3 Therefore as a gram of the fuel will evaporate 14 '3 cc. of water, one pound will evaporate 14*3 pounds. The objections to this form of calorimeter are that the fuel is never completely consumed and particles of unburnt carbon are ejected from the crucible during combustion : the products escape through the water too rapidly, and are therefore never properly cooled, and the apparatus is very liable to loss of heat by radiation. 74 LIQUID AND GASEOUS FUELS* The above forms of calorimeter are all designed for solid fuels, and the only one in which the calorific value of a liquid fuel can be determined is the Mahler bomb. In practice, it has been recommended that the liquid fuel should be soaked up by a pellet of absorbent cellulose, and the pellet and oil burnt together, but the objection to this is that the heat of combustion of the pellet has to be allowed for, and it is difficult to get its exact weight owing to its hygroscopic properties. The best method is to fill the platinum crucible or holder with kieselguhr, and to drop the oil on to this. No trouble is experienced in igniting the oil in the bomb, and no allowance has to be made for added cellulose. To determine the calorific value of a gas, the exact con- tent of the bomb must be ascertained. It is filled with the gas, and the pressure is reduced to a few millimetres of mercury by an air pump, when the bomb is again filled with gas under atmospheric pressure and at the ordinary temperature. It may be then taken that the bomb is filled with the pure gas. Care must be taken that the gas is not diluted too greatly with the oxygen, as otherwise combustion will not be secured. With illuminating gas a pressure of 5 atmospheres of oxygen is sufficient, whilst with a poor combustible like producer gas, half an atmosphere only is needed. For the determination of gaseous fuels, however, the simplest and best form of calorimeter is the Junker, in which the heat caused by the combustion of the gas from a suitable burner is transmitted to a current of water flowing at a constant rate. Measurements are taken of the quantity of gas burnt, the quantity of water passed through the apparatus, and the difference in temperature of the water at its inlet and point of outflow. The apparatus consists of two concentric metal vessels connected with one another by a large number of copper FIG. 6. Junker calorimeter (section). LIQUID AND GASEOUS FUELS. tubes, which lead from the top of the inner to the bottom of the outer cylinder, and down which the heated products of combustion pass. A current of water is caused to flow round the tubes in the opposite direction, and in this way the products of combustion are robbed of all their heat, which is taken up by the water. The gas, after passing through a meter and regu- lator, is consumed at the bunsen bur- ner A in the com- bustion chamber B. The water is arranged to flow into a small reser- voir C, which serves to maintain a con- stant level, the ex- cess passing away by the overflow tube, and the head of water being kept in this way at an even pressure. From the reser- voir the water flows down the pipe D to the regulating tap E, where a thermo- meter F is inserted to take the initial temperature ; the water passes up through the calorimeter to the top, where the outlet temperature is taken by the second thermo- meter Gr, the water passing into another small reservoir H, fitted with an overflow pipe of rubber tube, which is so arranged that the water can either be run to waste or into FIG. 7. Junker calorimeter. THE DETEKMINATION OF CALOKIFIC VALUE. 77 a measuring cylinder. In order to collect the water con- densed from the products of combustion, a side tube I is fitted in the base of the calorimeter, down which the condensed water can drip into a graduated vessel. In practice, the cooling water is turned on until it leaves the pipe K at a rate of about one litre per minute, and the burner is lighted and fixed in position, the whole being left until the exit thermometer G indicates a fairly steady temperature, and the condensed water has begun to drip from its tube I. The rate of flow of the gas is now regulated, and, as soon as the index hand of the meter passes the zero, the rubber pipe of the water exit is quickly transferred to a graduated two-litre flask, a small measuring cylinder is placed under the condensed water drip, and the temperature noted at both thermometers. The inlet thermometer will probably remain unaltered throughout the test, but the temperature is taken at frequent intervals at the exit thermometer. As soon as the two-litre flask is filled up to the mark, the gas is turned out and the con- densed water measure removed from under the drip-tube. The amount of gas consumed is read off from the meter, and the rise in temperature determined by subtracting the temperature of the inflowing water from the average of the readings at the exit thermometer. The heat of combustion is then obtained by multiplying the volume of water flowing per minute by the rise in temperature, and dividing the result by the volume of gas burnt per minute, thus : W = quantity of water in litres. T = rise of temperature in water in degrees C. G = volume of gas burnt, in cubic feet. W T Calories per cubic foot = . The result in calories multiplied by 3'968 gives the B.T.U. per cubic foot. 78 LIQUID AND GASEOUS FUELS. The above is the " gross " value of the gas, i.e., includes the latent heat of the steam formed by the combustion of the hydrogen in the fuel, which heat is not used in firing boilers or in the internal combustion engine, as the steam escapes uncondensed. To determine, therefore, the actual available heat, this latent heat must be deducted from the gross value, and the result gives the " net " value. The amount of condensed water in cubic centimetres per cubic foot of gas consumed collected in the measuring cylinder, multiplied by 0'6, will give the calorific value of the latent heat of the steam. To take an actual example : Gas consumed Meter at start .. . . zero. Meter at finish . . . 0'25 cubic feet. Temperature of the water Inlet Thermometer. Exit Thermometer. 10-2 28-5 10-2 28-6 10-2 28-5 10-2 28-4 10-2 28-5 Average 10'2 28'5 Increase of temperature = 28'5 - 10'2 = 18'3 C. Water collected . . . 2 litres. Gross heating value of the gas O -y IQ'Q - - = 146'4 calories per cubic foot. " 2iD Condensed water collected in measuring cylinder 51 cc. from 2 cubic feet of gas. The latent heat of the condensed water, therefore, is ' 6 * 51 - 15-3 calories. THE DETEEMINATION OF CALOEIFIC VALUE. 79 Deducting 15*3 from the gross value, 146*4, the net value is obtained. 146*4 15*3 = 131*1 calories per cubic foot. To obtain the value in B.T.U., multiply the results by 3*968, then CALORIFIC POWER OF THE GAS. Calories. B.T.U. Gross. . . . . 146*4 580*9 Net . . . . 131*1 520*2 In the Simmance-Abady calorimeter, which differs but little from the Junker, the gas to be tested is burnt in a bunsen burner, and the products of combustion are made to pass downwards through a number of tubes set in a vessel through which a constant flow of water is kept running in the opposite direction. The outside of the vessel is lagged with wood to prevent loss by radiation. The thermometers for recording the temperatures of the water at the inlet and outlet of the supply are brought close to one another at the top of the calorimeter, whilst an open glass tube at the outlet serves as a gauge for detecting any changes in the " head " of water passing through the instrument. A thermometer is placed at the exit for the cooled products of combustion. The outlet pipe of the water is provided with a tilting bucket, by means of which the stream of water can be directed either into the measuring cylinder or into the waste funnel. Water is allowed to flow through the calorimeter and run to waste, and the gas to be tested, after passing through a governor and meter is burnt in the special burner in the stand under the calorimeter. The outlet shutter at the exit of the products of combustion is adjusted till the thermo- meter there shows that practically all the heat has been extracted from them. When all the thermometers show a 80 LIQUID AND GASEOUS FUELS. fairly constant temperature and the hand of the gas meter passes zero, the flow of water is directed by means of the tilting bucket into the measuring cylinder, and kept in that position until the meter hand has made one revolution, when the water is again allowed to run to waste by releasing the bucket. The difference in tem- perature between the inlet and outlet ther- mometers multiplied by the volume of water collected in the mea- suring cylinder and divided by the quantity of gas consumed will give the calorific power of the gas. The Simmance- Abady calorimeter is easily modified for de- termining the calorific power of light oils, alcohol, etc. Instead of the gas burner and meter, a small lamp is used, which fits on a FIG. 8,-Simmance-Abady calorimeter. sengitive balance. The lamp is charged with the liquid hydrocarbon to be tested, and whilst water is passing through the calorimeter, is lighted and placed on the balance with its flame or chimney central under the calorimeter. When all the thermometers are steady, the balance is so adjusted that the lamp is slightly heavier than its counterpoise. As the oil burns, the lamp will rise, and as the balance indicator passes the level point, the water is switched into the THE DETERMINATION OF CALOKIFIC VALUE. 81 measuring cylinder, a small measure is placed under the outlet for condensed water, and a gramme weight added to the lamp pan, which will cause it to fall again. With the combustion of the oil the lamp will again rise, and as the balance indicator passes the level point, the water is allowed to run to waste. The collected water is weighed and correction applied for temperature, if necessary. Knowing then the difference in the inlet and outlet water thermometers, the weight of fuel burnt, and the amount of water collected, a simple calculation will give the calorific value of the fuel. The difference in tempera- ture is multiplied by the amount of water in litres and divided by the quantity of fuel consumed, and the result will give the calorific value in grammes per litre. All gases exhibit certain similarities in their physical properties, and it has long been known that within certain limits all gases expand equally under the influence of heat or alteration in pressure. Boyle (1662) showed that the volume of any gas varies inversely to the pressure : thus doubling the pressure halves the volume, or reducing the pressure by one half doubles the volume. Many gases obey this law almost exactly, but show some considerable deviation under high pressures. That the rate of expansion for all gases was the same for the same rise of temperature was first shown by Charles, and it is found that for every rise of 1 C. the volume is increased l/273rd of the original, so that if we raise the temperature of any gas from C. to 273 C. we double its volume, the pressure of course being kept constant. Theoretically then if we measured a litre of gas at C. and the temperature could be reduced to 273 C. the gas would cease to occupy any space, but this is a condition impossible to conceive, and there is no doubt but that at such a low temperature every gas would be condensed to the liquid condition and cease to obey Charles' law. L.G.F. G 82 LIQUID AND GASEOUS FUELS. This temperature of 273 Q C. is therefore taken as the absolute zero. A gas at C. will, therefore, be at 273 on the absolute scale, or generally to arrive at the absolute temperature we must add 273 to each degree Centigrade. 10 C. will, therefore, equal 283 absolute, and 10 C. will equal 263 absolute. From a knowledge of these facts we are enabled to calculate the volume of any gas under any conditions of temperature and pressure. For change of temperature, if we let v = old volume v l = new volume ,, a v X (273 + t l ) t = old temperature 273 + t t l = new temperature The atmospheric pressure is measured by the barometer, in which a column of mercury is supported in a tube by the weight of the superincumbent air, and the normal height of mercury so supported is thirty inches, which approximately corresponds to 760 mm., and as we express the barometric pressure in millimetres, it is evident that we can calculate the increase or decrease in volume due to barometric disturbance by a direct proportion. Suppose a given volume of gas to be measured at a time when the barometer stood at 755 mm., and that the pressure was increased to 768 mm., the volume would decrease in the ratio of 768 to 755, or in other words These variations in volume, due to change of temperature and pressure, have made it necessary to fix a standard temperature and pressure at which all gases shall be measured and for all scientific purposes C. and a baro- metric pressure equal to 760 mm. of mercury have been adopted,- and called the " normal " temperature and pressure. THE DETEKMINATION OF CALOEIFIC VALUE. 83 Now it is evident that it would be practically impossible to secure these conditions, so that the usual method adopted is to measure the gas under ordinary circumstances, and having noted the temperature and pressure, to calculate what would be the volume under normal conditions of temperature and pressure, and this is done by the formula v p __ v l p 1 t T~ where v = original volume. p = observed pressure. t = observed temperature in (273 + x C.). v 1 = required volume. p 1 = normal pressure. t 1 = normal temperature (273 + C.). This formula is adapted for any calculation as to change in volume, etc., by using v\ p 1 , and t 1 , as may be required. G 2 CHAPTEE IV. LIQUID FUEL. The discovery of petroleum in America The Russian oil fields The distribution of petroleum The conditions under which it occurs The nature of petroleum, and the products obtained from it The amount available for fuel purposes The flash point, and how it is determined The Abel test The Pensky-Marten The requirements in a fuel oil Shale oil as a fuel The shale oil industry Coal tar, and its composition Creosote oil Blast furnace oil Shipping regulations for oil fuel Petroleum spirit and its dangers The testing of atmospheres likely to contain explosive mixtures of petroleum vapour and air The Clowes- Redwood apparatus. THOSE districts which now yield so rich a harvest of mineral oil have been celebrated, from the earliest days of which we have record, for the curative powers of certain oils found either as springs or as a scum on lakes and pools. Many hundred years before the American Indians in the valleys of the Allegheny collected the scum from certain pools and streams and used it as a cure for rheumatism, the curative properties of the oil from springs in the Baku district of Eussia had been recognised and used by the Persians for sore heads and mangy camels, whilst at even earlier dates the natural gas issuing from the ground not far from the present site of Baku gave the everlasting fire that made this district the principal stronghold of the fire worshippers. It was in America, however, that the first systematic boring to obtain oil took place, when in 1859 Colonel Drake sank an artesian well on much the same system as had LIQUID FUEL. 85 been previously employed for water. This well was sunk at Oil Creek in Pennsylvania, and oil was obtained at a depth of 69 feet. Although the yield during 1859 only amounted to some 2,000 barrels, yet it led to rapid develop- ment, all the available land down the creek and along the Allegheny being taken up, numbers of wells were sunk, and considerable quantities of oil were obtained, although always at a greater depth than had been the case with Drake's well. In these early wells the oil had to be pumped, but in 1861 a well drilled to a depth of 460 feet yielded oil at such pressure that it rose to the surface and overflowed, and oil to the extent of 300 barrels a day was obtained from it for six months, whilst the Empire well, sunk close to it, yielded 2,500 barrels a day. The oil fever was now at its height, and oil was pros- pected for in every direction : wherever found, wells were sunk, and the most wasteful systems of collection and storage being adopted, the loss of oil was enormous. As a rule these wells were only productive for from six months to two years, and mushroom cities sprung up in the neigh- bourhood of successful wells only to be deserted as the supply failed. Moreover, the glut of oil so created swamped the demand, and prices fell until the barrels were of more value than the oil, and in 1862, in Pennsylvania it is computed that as much as ten million barrels of oil ran to waste. Western Virginia, Kentucky, Tennessee, Illinois, Kansas, and Texas, all proved to be oil-bearing States. About this time also, in the township of Enniskillen, Canada, at Blake Creek, enormous yields of petroleum were obtained, and wells were sunk in large numbers, but as there was no market for the oil most of it ran to waste down the creek, and five million barrels were wasted in 1862. Gradually, however, the supply created an increasing demand, and vast quantities of oil being exported, the prices gradually 86 LIQUID AND GASEOUS FUELS. increased, until in 1872 the great Russian oil fields entered into competition with America for the European trade. Although it had been well known from the earliest dates that in the Baku district oil existed in great quantities, but little importance had been attached to it, and at this period the oil production of the district was practically a monopoly in the hands of a trader named Meerzoeff : in 1872, how- ever, this concession was withdrawn, and the Russian Government substituted a tax on the amount of oil pro- duced, this change quickly resulting in the oil production of the district being increased tenfold. At this period the oil wells of the district were mostly dry, and there were no flowing wells, but in 1873 drilling resulted in getting oil not only to flow, but to spout in such enormous quantities as to be entirely beyond control, with an enormous consequent loss, these fountains often rising to a height of 200 to 300 feet. These enormous deposits were generally tapped at a depth of 400 to 800 feet, and the volume of oil discharged may be imagined from the following description given by Sir Boverton Redwood from a Baku paper : " From the town the fountain had the appearance of a colossal pillar of smoke, from the crest of which clouds of oil sand detached themselves and floated away a great distance without touching the ground. Owing to the pre- valence of southerly winds, the oil was blowing in the direction of Bailoff Point, covering hill and dale with sand and oil, and drenching the house of Bailoff, a mile and a half away. . . . The whole district of Bibi-Eibat was covered with oil, which filled up the cavities, formed a lake, and on the fifth day began flowing into the sea. The outflow during three days was estimated at 5,000 or 6,000 tons daily. . . . On the eighth day the maximum was reached, the oil then spouting at the rate of 11,000 tons, or 2,750,000 gallons, a day After the tenth day it began to diminish, and by LIQUID FUEL. 87 the fifteenth day the engineers had so far got it under control that the outflow was only 250,000 gallons a day. Altogether, over 10,000,000 gallons of oil came to the surface, and most of this was lost for want of storage accommodation." At the present time there is hardly a country in the world that has not yielded small quantities of petroleum, but the Russian and American fields yield about 92 per cent, of the total output, the following table giving an approximate idea of the relative quantities in percentages of petroleum obtained from various countries before unrest in Russia interfered with her output. Out of a total production of some 20,000,000 tons : Russia yielded 51 per cent. America Galicia ,, Roumania India ,, Canada \ Sumatra Java Borneo } Japan Germany Italy 41 2 1 1 100 The form of well and method of driving it varies a good deal with the country and the geological strata through which the shaft has to pass, whilst the depth in some cases may be under 100 feet, and in others over 2,000. Nor is the oil confined to any particular geological formation. The oil is mostly found in strata of conglomerate or sand, and the deposits which have proved commercially success- ful in working are chiefly comprised within the Silurian 88 LIQUID AND GASEOUS FUELS. and Carboniferous epochs in America, and deposits of the Tertiary period in the eastern hemisphere. The conditions under which petroleum and natural gas occur are summarised by Mr. Topley as follows : 1. They occur in rocks of all geological ages, from Silurian upwards. The most productive areas are the Palaeozoic in North America, and Miocene in the Caucasus. 2. There is no relation to volcanic action. 3. The most productive areas for oil in great quantity are when the strata are comparatively undisturbed. Oil, but in less abundance, frequently occurs when the strata are highly disturbed and contoited : but gas is rarely so found. 4. The main requisites for a productive oil or gas field are a porous reservoir (sandstone or limestone) and an impervious cover. 5. Both in comparatively undisturbed and in highly disturbed areas, an anticlinal structure often favours the accumulation of oil and gas in the domes of the arches. 6. Brine is an almost universal accompaniment of oil and gas. As the crude oil comes from the well it is a mixture of many hydrocarbons, and varies considerably both as regards its physical and chemical properties, according to the source from which it was obtained, the American and Kussian oils, upon which the greatest amount of scientific work has been done, differing widely in their chemical composition, although much alike in the physical properties of the products obtained from them. The researches of Pelouze, Schorlemmer, Warren, and others, all show that the Pennsylvanian oil consists of the methane or paraffin series of hydrocarbons, whilst the Russian oil belongs to the naphthene group (C n H2_ e + H 6 ), which in empirical composition is identical with the ethylene group (C n H 2ri ), but which in many properties so closely resembles the paraffins that in considering the LIQUID FUEL. rectification of the oil it will be sufficient to consider the processes employed in dealing with the American oil. The specific gravity of the oil as it leaves the well varies from 0*77 to TOO, although either of these extremes is very rarely met with, and the bulk of the crude oil of Pennsyl- vanian and Russian origin will fall between the limits of 0*844 and 0*899. Where the specific gravity much exceeds this it often means that it is an oil collecting at shallow depths, and which has lost most of its more volatile constituents by evaporation, or else that it contains a high proportion of solid hydrocarbon dissolved in it. The following members of the paraffin series have been isolated from American petroleum : PARAFFINS FROM PENNSYLVANIAN PETROLEUM. Name. Formula. Boiling Point C. Specific Gravity. Condition. Methane CH 4 Gaseous Ethane C 2 H 6 Propane C 3 H 8 jj Butane C 4 Hi Pentane (normal) C 5 H 12 38 0-628 Liquid Hexane ,, C 6 Hi 4 69 0-664 n Heptane C 7 Hi 6 97-5 0-699 Octane C 8 Hi 8 125 0-703 Nonane C 9 H2o 136 0-741 Decane Ci H22 158 0-757 Endecane . CnH 24 182 0-765 i Dodecane . Ci 2 H 2(5 198 0-776 5 Tridecane . CiaH^ 216 0-792 Tetradecane C^HSO 238 9 Pentadecane C 15 H 32 258 Hexadecane CieH 3 4 280 n Octodecane Ci 8 H 38 9 Q JJ 42 9 SlS I'araffin (myricyl) clnl Solid (ceryl) . . CaoHoa 370 " 90 LIQUID AND GASEOUS FUELS. The object of the refiner is to obtain from the crude oil the largest proportion of the most marketable pro- duct, and in most cases the oil is fractionally distilled, so as to separate from it the various grades of petro- leum spirit now, owing to the demand for motor spirit, one of the most profitable products, burning oils, suitable for use in lamps, lubricating oil, and solid paraffin. The proportions in which these products are obtained from American crude oil have been given as Petroleum spirit Gasoline . 1 '5 per cent. C naphtha lO'O B naphtha 2'5 A naphtha 2*5 ,, Lamp oil .... 54'0 ,, Lubricating oil . . . 17 '5 Paraffin solid . . . 2'0 Loss lO'O 100-0 The petroleum spirit and lamp oil after separation have to undergo a process of purification to remove highly coloured traces of tarry matter dissolved in them, as well as other impurities, and this is done by first washing the oil with sulphuric acid, then with water, and finally with caustic soda or sodium hydroxide. Where oil is abundant the distillation is in many cases only continued until the naphthas and lamp oil have been separated, and the heavy oil left in the still and called in America " residuum " is employed as fuel. In Kussia especi- ally, where the crude oil contains a comparatively small proportion of the volatile hydrocarbons, and where there is a good market for the residue, which is called "ostatki," this is done. LIQUID FUEL. 91 The crude Eussian oil yields on an average Petroleum spirit . . ' . 6 per cent. Lamp oil . . . . 20 Solar oil ... . .6 Ostatki . . ... 58 This at once shows the difference in value of an oil as a source of fuel, as with the American oil there is only some 20 per cent, of residuum which could be supplied at a price that would make it commercially possible as a fuel, whilst in the Eussian oil there is nearly 60 per cent, of the Ostatki. In the oil fields which have been more recently discovered, such as those of Texas, Borneo, and California, the oils are comparatively poor in the lighter hydrocarbons, but yield a high percentage of fuel oil, whilst some of the still smaller sources of supply yield oil so poor in volatile bodies that mere exposure to the atmosphere would fit them for fuel purposes. Taking all the sources of oil supply, the amount which could be used as fuel in place of coal would be approximately one- third of the total yield. As has been already stated, the total oil output of the world in round figures is 20,000,000 tons, as against 800,000,000 of coal, and if of the 20 only one-third is available for fuel purposes, we find that there is less than one-hundredth of the liquid fuel to be obtained that would be necessary if it were to entirely replace solid fuel, as some of its more ardent advocates seem to think it should. It may be urged that the supply of oil has steadily increased since its discovery in quantity, but whilst this is perfectly true, it is also a fact that the increase has been due to increase in the number of wells, and that the oil- yielding districts are becoming rapidly exhausted. This is especially the case in America, and whilst, although less visible in Eussia, the last ten years have seen the number 92 LIQUID AND GASEOUS FUELS. of producing wells more than trebled, whilst the production has been hardly doubled. It is quite clear that even if oil is still being produced by natural processes in the underlying strata of the earth, it can only be at a very minute rate as compared with the drain that is taking place on the oil stored in the sand strata from which we take our supplies, and that instead of building our hopes on an ever increasing supply of this valuable fuel we should be rather economising the supplies we can get for use in those branches of industry in which liquid fuel has shown itself to be of the greatest economic advantage. The factor which has cut down our liquid fuel supply to one-third of the total production is the all-important one of safety in transport and use. If it were attempted to use crude oil as obtained from the oil well, those portions which in the rectification of the oil distil over at the lowest temperatures, would evaporate into the air, and with it form an explosive mixture, whilst the vapour, being specifically much heavier than air, would flow from the fuel store to even distant sources of fire, and once ignited the flame would travel back to the oil store itself, hundreds of accidents of this character taking place in the early days of the oil industry before the full danger had been realised. The temperature at which a sample of oil commences to give off inflammable vapour is known as its " Flash Point." For oils suitable for domestic use in heating and lighting the flash point used to be determined by heating a small quantity of the oil in a cup or other open vessel, the tem- perature, as indicated by a thermometer in the oil, being gradually raised until a point was reached at which, when a small flame was passed over the mouth of the vessel, a flash was observed, clue to the ignition of the oil vapour given off. The temperature at which this occurred was called the flash point of that particular oil. LIQUID FUEL. 93 This method of testing gave very discordant results, and was unsatisfactory, as it was easily affected by external influences. These troubles were overcome by using a closed vessel to contain the oil, and the type of apparatus which has been adopted in England was designed by Sir Frederick Abel, and bears his name. In this instrument a metal cup A of standard size is used for holding the oil, the cor- rect quantity being indicated by a bent wire with sharpened point being fixed inside the cup ; a flange near the top of the cup permits it resting in an outer vessel D which forms a water jacket, and which can be heated by a spirit lamp placed be- low. The CUp is FlG> 9> _ Abel flash point apparatus. provided with a close-fitting cover C, which carries the test flame and thermo- meter B. In the cover also are cut three square holes of definite sizes, which can be closed or opened by a sliding piece of metal with perforations to correspond. The test flame may be a small bead of gas at the end of a small tube, or the flame from a small oil lamp, but in either case the 94 LIQUID AND GASEOUS FUELS. burner is so arranged on trunnions that the flame can be lowered into one of the cover openings when the slide is drawn back, and resumes its normal position when the slide once more closes the openings. The thermometer is fixed in a slanting position for ease of observation, and is so arranged that when slipped into its tube in the cover the bulb is a definite dis- tance below the surface of the oil in the centre of the cup. In use the spirit lamp below the outer water jacket is lighted, and the temperature slowly rises. At regular in- tervals the slide on the cover is pulled, thus causing the test flame to be lowered into the opening in the cover, and the moment a flash is seen to occur, the tempera- ture is noted, this point being regarded as the "flash point" of the sample under consideration. If the same oil be tested with the open and the closed cup, it will be found that whereas the oil will flash at, say, 100 C F. with the open, the flash will take place at 73 F. FIG. 10. Pensky-Marten flash point apparatus. LIQUID FUEL. 95 in the closed vessel, the difference being due to various factors, such as absence of draughts, etc. In Germany the authorised apparatus is the Pensky- Marten, which is a modified form of the Abel, and is used in a similar manner. The oil cup is of porcelain, B, and rests in an outer vessel of iron, A, which contains sufficient sand to raise the bottom of the cup half an inch away from the point of contact with the flame. A mechanical device of a rotating fan attached to the rod C in the oil is used to keep the liquid agitated, and ensure an even distribution of the heat. For domestic purposes and use on shore the flash point of an oil has to be 73 F. (22'8 C.), whilst for use as a fuel in the mercantile marine it has to be 150 F. (65*5 C.) : the flash point of oil fuel for the Navy, however, has been fixed at 200 F. (93 C.). In considering the requirements for a really good fuel oil, there are several factors that must be taken into account. Many of the more recent oil supplies contain an objection- able amount of sulphur, and if this were all left in the fuel oil, its action upon copper and copper alloys in the injectors and oil-burning fittings would rapidly corrode and destroy them. The oil, however, can be easily purified to a reason- able extent, and there should not be more than one per cent, left in the oil. The petroleum intended for fuel should undergo filtration or other process to free it from any foreign matters that would be liable to choke the injector whilst burning the oil, and it should be practically free from water, as it has been found that if the oil contains drops of water entangled in it, these will often put out the flame at the burner, and lead to the formation of an explosive mixture of oil spray and air in the combustion chamber. The flash point allowed for a fuel will, of course, vary with the purpose for which it is to be used, and for locomotives 96 LIQUID AND GASEOUS FUELS. it might be as low as 73 F. (22'8 C.) if it were to be used in a cold climate ; but experience shows that it is far safer not to lower the flash point below 150 F. (65'5 C.), as trouble may arise in the preliminary heating of the oil before being brought to the burner, and an oil tank on fire is so serious a matter even on land that no risks should be taken. Many samples of oil otherwise fitted for fuel purposes are so thick and viscid that they will only flow sufficiently freely when heated, and as this gives rise to considerable complication in their use, a good fuel oil should be sufficiently fluid to flow through half-inch tubes, even at the freezing point. SHALE OIL AS A FUEL. Although its wide distribution and the quantity of the supply make petroleum the great liquid fuel, yet there are other liquid hydrocarbons, which are locally obtainable in sufficient quantity to be used in the place of coal, and next to mineral oil in importance comes the oil obtained by the destructive distillation of shale. We have already seen (p. 39) the course of events which led to Dr. James Young attempting the preparation of lubricating oil from the Scotch shales, and although the fact that liquid hydrocarbons could be obtained by distilling coal and other solid hydrocarbons had been known long before, it was undoubtedly Young's experiments that started the shale oil industry as at present it is carried out. During the early years of the industry the shale mostly employed was the Torbanehill mineral, but since 1862 the Broxburn, Midlothian, and Linlithgow shales have been the chief source of supply. The shales differ from coal in that, instead of being a mixture or compound of carbon with hydrocarbons, they contain hydrocarbons with mineral matter, with the result that when heated to redness in a LIQUID FUEL. 97 retort, they do not form coke, as coal does, but leave 70 to 80 per cent, of mineral matter. The distillation of the shales takes place in vertical retorts, the upper portions of which are often of cast iron, and here the shale is exposed to a temperature of 900 F. (482 C.), at which the oil distils over ; the spent shale then passes down into the lower portion of the retort, which is made of brickwork heated to about 1,300 F. (704 C.), and being kept moving downwards is finally discharged into a hopper at the bottom. The process is continuous, and takes about six hours from feed to discharge, fresh shale being fed into the top of the retort as the spent shale is removed below, and steam is passed through the retort during the whole process, the quantity varying with the character of the shale. The action of the steam is to recover the ammonia from the nitrogen present in the shale, and from a ton of shale from 20 to 30 gallons of crude oil and from 40 to 70 Ibs. of ammonium sulphate can be obtained. The crude oil has a specific gravity of from 0'860 to 0*890, and has a dark green colour ; during the process of refining this yields approximately Naphtha 6 per cent. Burning oil . . . 32 ,, Heavy oil .... 24 ,, Paraffin scale . -. .12 ,, Loss 26 100 and it is the heavy oil that is used as a fuel. Tar, formed during the destructive distillation of coal for the production of coal gas, is also used as a liquid fuel, but in its crude condition contains so much solid matter that it can only be employed with very unsatisfactory furnace arrangements. L.G.F. H 98 LIQUID AND GASEOUS FUELS. Tar derived from ordinary bituminous coal is a black, somewhat viscid liquid, varying in specific gravity from 1*1 to 1*2. London tar, made from coal alone, or at most with an admixture of only about 2 per cent, of cannel, has usually a specific gravity of 1*2 ; whilst provincial tar, made from coal with a larger proportion of cannel, is reduced to near the lower limit owing to the greater quantity of light oils yielded by cannel. The ultimate composition of a London tar is approximately as follows : Carbon . . . . . . 77'53 Hydrogen . . . . , . 6'33 Nitrogen T03 Sulphur .... . . . . 0-61 Oxygen . . . . . . 14'50 100-00 These elements in tar are built up into about 140 different compounds, traces of which can be identified, but for all practical purposes we may take those given in the table on page 99 as being the chief constituents. In roughly considering the proportion in which the main constituents occur in coal tar, we can still further simplify the composition, and look upon it as containing benzene, naphtha, naphthalene, anthracene, carbolic acid, and pitch ; and if this tar be carefully redistilled, we find it can be separated into these constituents, which distil over at various temperatures. First, light oils pass over, from which benzene and its homologues can be obtained ; then heavy tar oil, from which carbolic acid is made ; and pitch is left, from which a substance called anthracene can be separated. The benzene obtained is the source from which aniline is prepared, and it is from aniline that most of the coal-tar colours are derived. LIQUID FUEL. 99 Neutral Hydrocarbons. Boiling Point C. Formulae. Specific Gravity. Liquid . Benzene 80 CcHfi 0-88 Toluene 110 H 7 H 8 0-87 Xylene 142 CsHio 0-87 Isocumene 170 CgHl2 0-85 Solid . Naphthalene 217 CioHg Anthracene 360 C^IIio Chrysene Ci 8 Hi2 Pyrene Ci G Hi Alkaline Ammonia NH 3 products Aniline 182-5 C 6 H 7 N 1-02 Picoline 130 C 6 H 7 N 0-96 Quinoline 239 C 9 H 7 N 1-08 Pyridine 117 C 5 H 5 N ^Acids Carbolic acid 180 C 6 H 6 1-07 Cresylic C 7 H 8 Kosolic CioHi 4 02 Brunolic Acetic ,, 118 C 2 H 4 2 1-06 Free carbon The heavy tar oil obtained in this way from the coal tar is often called " creosote," and forms a fairly good liquid fuel. It is called also " heavy oil," from the fact that its specific gravity is over that of water, being as a rule about 1*1. In the fractional distillation of tar it distils over between 392 F. (200 C.) and 572 F. (300 C.), and is rich in phenols and cresols, and also contains large quantities of naphthalene dissolved in it, the latter often being separated from it and purified for use in the albo-carbon light, disinfecting tablets, etc. The oil obtained from blast furnaces is also sometimes used locally for fuel purposes under the name of " Phenoloid," or blast furnace oil, but none of these forms of liquid fuel can be obtained in sufficient quantities to give them any H 2 100 LIQUID AND GASEOUS FUELS. universal value. Tar oil and blast furnace oil have the great drawback as fuels, that in a closed stokehole they give off fumes, probably of acrolin, which painfully affect the eyes of the stokers, making them smart and water. Attempts have been made to use alcohol as a fuel and, according to the German Press, experiments were made in 1902 with it on ships, the spirit being injected on to the surface of burning coal in the boiler furnaces in much the same way as oil fuel is frequently used. If alcohol could be obtained cheaply it would have an advantage in burning without smoke, and as it is made by the fermentation of vegetable matter there would not be the fear that exists with coal and oil of exhausting the supply. During the early years of the oil trade, when the import- ance of the flash point, and the use of proper precautions had not yet been learnt, a good many accidents occurred to cargo ships used in the transport of petroleum or using mineral oil as a fuel, and led to Lloyd's Register of British and Foreign Shipping issuing the following regulations with regard to ships burning and carrying liquid fuel. 1. In vessels fitted for burning liquid fuel, the record "Fitted for liquid fuel," will be made in the Register book. 2. The compartments for carrying oil fuel must be strengthened to efficiently withstand the pressure of the oil when only partly filled and in a sea-way. They must be tested by a head of water extending to the highest point of the filling pipes, or 12 feet above the load line, or 12 feet above the highest point of the compartment, whichever of these is the greater. 3. If peak tanks or other deep tanks are used for carrying liquid fuel the rivetting of these should be as in the case of vessels carrying petroleum in bulk. The strengthening of these compartments must be to the Committee's satisfaction. LIQUID FUELS. 101 4. Each compartment must be fitted with an air pipe, to be always open, discharging above the upper deck. 5. Efficient means must be provided by well sparring or lining to prevent any leakage from any of the oil com- partments from coming in contact with cargo, or into the ordinary engine room bilges. 6. If double bottoms under holds are used for carrying liquid fuel, the ceiling must be laid on transverse battens, leaving at least two inches air space between the ceiling and tank top, and permitting free drainage from the tank top into the limbers. 7. The pumping arrangements of the oil fuel compart- ments and their wells must be absolutely distinct from those of other parts of the vessel, and must be submitted for approval. If it is intended sometimes to carry oil and sometimes water ballast in the various compartments of the double bottom, the valves controlling the connections between these compartments and the ballast donkey pump, and also those controlling the suctions of the special oil pump, must be so arranged that the suctions for each separate compart- ment cannot be connected at the same time to both pumps. 8. No wood fittings or bearers are to be fitted in the stokehold spaces. 9. Where oil fuel compartments are at the sides of or above or below the boilers, special insulation is to be fitted where necessary to protect them from the heat of the boilers, their smoke-boxes, casings, etc. 10. If the fuel is sprayed by steam, means are to be provided to make up for the fresh water used for this purpose. 11. If the oil fuel is to be heated by a steam coil the condensed water should not be taken directly to the con- denser, but should be led into a tank or open funnel mouth and thence led to the hot-well or feed tank. ^SVS-** 102 LIQUID AND GASEOUS FUELS. 12. The above arrangements are applicable only to the case of oil fuel the flash point of which, as determined by Abel's closed test, does not fall below 150 Fahrenheit. The use of petrol or petroleum spirit in large quantities for oil motors, and the necessity for storing it in bulk, have of late given rise to a danger which before only existed to a limited extent. Petrol is the first distillate from the crude oil as it comes from the oil well, and largely consists of pentane, C 5 Hi 2 , and hexane, C 6 Hi 4 , the first liquid members of the great paraffin group of hydrocarbons. This liquid is volatile even below the freezing point, and a pint of it poured on a level surface will cover about 80 square feet with an inflammable vapour, through which, on coming in contact with a light, a flame will spread. One pint of the liquid will also give enough vapour to render 100 cubic feet of air highly explosive. These light oils have a wonderful penetrative power, and it is a matter of considerable difficulty to get vessels made for commercial purposes sufficiently vapour-tight to resist the insidious creeping of petroleum spirit. The result is that in stores, cellars, and other places where vessels containing such spirits are kept, slight leakage and evapora- tion into the air are constantly occurring, and as the evaporation of one volume of liquid petroleum spirit would render 5,000 volumes of air strongly explosive, it is clear that special precautions must be taken in dealing with the storage and use of such spirit. Mixtures of air and petrol vapour begin to be explosive when there is 2 per cent, of the vapour present in the air, the strength of the explosion increasing with the quantity of vapour up to about 2*6 per cent, and then gradually falling until with 5 per cent, of vapour the mixture is practically non-explosive. The temperature needed for the ignition of explosive LIQUID FUELS. 103 mixtures of petroleum vapour and air is comparatively high, and experiments made by Colonel Majendie, Sir Boverton Redwood, and Dr. Dupre show that such mixtures were not ignited by the glowing spark on a splint of wood, a red hot coal which had ceased to flame, or a shower of sparks from a flint and steel, and that it needed a temperature of platinum wire raised nearly to a white heat before explosion took place, that is, about 1,200 to 1,400 C. If, however, any inflammable dust is present in the air, even a small spark will cause explosion, as the dust catching fire causes a flame that ignites the explosive mixture. One of the greatest dangers with the vapour of volatile hydrocarbons is that the great weight of the vapour as compared with air will cause it to creep along surfaces for very long distances, and then on reaching a light the flame flashes back along the vapour to the source from which it sprang. It may be accepted that the transport and storage of refined lamp oils and residuum are practically free from danger, the only point to be guarded against being the ignition of the liquids in volume, during fires, whilst the real dangers to be guarded against are to be found in the transport and storage of crude oils containing highly volatile constituents, and with petroleum spirit. In all confined spaces used for the storage of such material, the adoption of the safety lamp, and the constant testing of the atmosphere by the beautiful method devised by Dr. Clowes and Sir Boverton Kedwood would go far towards ensuring safety. In the early days of the last century, when the introduc- tion of coal gas gave rise to an increased demand for coal, explosions in mines became of such frequency that attempts were made to safeguard the miners' lives. As the result of the labours of a Eoyal Commission appointed 104 LIQUID AND GASEOUS FUELS. to enquire into the subject, and the experimental researches of Sir Humphrey Davy and George Stephenson, the safety lamp was installed in all fiery pits. Long before this period, however, the miners themselves had utilised a rough test for detecting the presence of the dread fire-damp in anything approaching dangerous quantities. It was well known that even a small percentage of fire-damp in the air of the pit gave rise to the appearance of a small flame- cap above the flame of the burning candle, and as the miner went down into the workings with the candle fixed at the end of his primitive candlestick a wooden lath in front of him, he would shade his eyes from the glare of the flame, and watching its tip would blow out the flame for very life the moment that the ghostly cap appeared. This flame-cap not only gave an indication of the presence of fire-damp, but according to its length also indicated roughly the proportion that was present, and it is upon a modification of this principle that our most modern and successful methods of detecting explosive gaseous mixtures and roughly estimating the proportion of explosive gas present have been based. With the introduction of the safety lamp it was still found that the flame served to indicate the proportion of combustible gas even when still below the explosive limit, the change in the appearance of the flame giving a very fair guide to an experienced man of the proportion of fire- damp present, whilst when the dangerous limit in the atmosphere had been reached the fire-damp would burn within the lamp, and by its products of combustion rapidly extinguish the flame. In those early methods of judging the nature of an atmosphere that might be explosive by means of a flame- cap it is clear that the flame employed being luminous, and the cap of a faint shadowy nature, the glare of the luminous portion of the oil or candle flame might seriously interfere LIQUID FUELS. 105 with ease of observation. As it was gradually realised that this phenomenon gave the simplest and most convenient method of testing, the apparatus was improved from time to time with a view of making it more accurate, and by the replacement of the gauze in the lower portion of the safety lamp by glass, and by shielding the direct light of the lamp from the eye, considerable advances were made, but it was only when the luminous flame was replaced by a non- luminous hydrogen flame, and mechanical devices were adopted for setting the test flame to an accurate height and maintaining it at this point, that the method attained any degree of accuracy. The miner's test lamp, as devised by Professor Clowes, has been adopted almost universally in mines. When it became clearly evident that the development of the carriage of crude petroleum in bulk, and the carriage and storage of petroleum spirit necessitated analysing the atmosphere in tanks and stores, this method of testing naturally suggested itself, and Sir Boverton Kedwood succeeded in devising a special modification of the lamp, and also an apparatus for collecting samples of the atmosphere in which petroleum vapour was suspected, and testing them under uniform conditions. The apparatus consists of the lamp, the cylinder of compressed hydrogen, and a sampling vessel. The base of the lamp is fitted with two inlet tubes, one for the sample of atmosphere, and the other for the hydrogen, the latter being provided with regulating tap and jet. Immediately above the tube for the inlet of the vapour-laden sample is a series of baffles, on the top of which are three discs of very fine wire gauze, which regulate the flow of gas and prevent any flashing back of the flame into the sampling vessel. The hydrogen jet is partially enclosed by a metal tube, the front of which is removed, and over this slides a chimney, partly of metal and partly of glass, the metallic portion 106 LIQUID AND GASEOUS FUELS. being blackened inside. In the window are lines corresponding to various heights of flame-caps. The collecting vessel consists of a compression pump fitted with a metallic piston fixed inside a strong metal cylinder, which is furnished with a pressure gauge and valve, and also has connections and taps for collecting and delivering the sample. About thirty strokes of the pump suffice to charge the cylinder to a pressure of 30 Ibs. to the Sample Hydrogen- Bottle FIG. 11. The Clowes- Red wood testing lamp. square inch, when it will contain one-third of a cubic foot of the atmosphere sampled. In using the apparatus, the hydrogen cylinder is con- nected to the lamp, and the sliding chimney being raised, the hydrogen is turned on and lighted. The supply is adjusted to give a flame of slightly more than 10 milli- metres in length, and the apparatus is left for a few minutes to warm up, so as to drive off any condensed moisture from the surface of the chimney. The collecting vessel is attached to the other inlet of the lamp, the chimney is closed completely, and the hydrogen flame finely adjusted by the regulating valve till the tip of the flame is just hidden when the eye of the operator is on a level with LIQUID FUELS. 10? the bottom of the window. The lamp and head of the operator are then covered with a light-tight cloth, and the tap of the collecting cylinder turned on. Even with a pro- portion of vapour that is too small to give an explosive atmosphere a cap of a greyish-blue appears on the flame. As the proportion of vapour in- creases the flame-cap becomes better defined, followed by considerable enlargement of the cap, this feature occurring before the atmosphere contains sufficient vapour to render it inflammable. When petroleum spirit has once taken fire it is most difficult to deal with, as, being far lighter than water, even when great volumes are poured upon the fire the spirit rises to the surface and continues burn- ing, whilst the vapour given off pre- vents any cooling of the liquid from proving efficacious. Chemical ex- tincteurs and gases like carbon dioxide and sulphur dioxide can only act upon it if the fire be in a very confined space, as the updraught caused by the fierce flame sweeps them away and sucks in air to the burning mass. Sand or fine mould is the best thing for extinguishing a petrol fire, and if this is not at hand in sufficient quantity, the next best thing is to let the fire burn itself out, and devote one's whole attention to protecting surrounding property. CHAPTEE V. THE USE OF LIQUID FUEL. Oil lamps and the conditions on which their satisfactory working depends Heating and illuminating power of oil The history of the use of oil as a fuel Nobel's troughs Gasification before combustion Foote's burner Simms and Barff process Eames furnace Diirr apparatus Methods of atomising or pulverising oil before combustion Injectors Injection under pressure Korting injector Swensson burner Injection by steam The Holden burner Eushden and Eeles injector The Orde burner Air injection Furnace arrangements Conditions of com- bustion The formation of smoke Merits of steam injection as opposed to air or pressure Furnace space Liquid fuel for marine use Advantages for naval use Employment as an auxiliary to coal United States Naval Board experiments Liquid fuel for use hi locomotives Comparative value of liquid fuels in practice. ALTHOUGH the term " fuel " by custom applies more especially to substances used for heating purposes alone, there are many cases in which liquid fuel at any rate per- forms the dual function of supplying light as well as heat, and the oil lamp is often in the homes of the poor an efficient stove as well as illuminant. In order to secure from the oil lamp high illuminating power, together with a smokeless flame and only products of complete combustion, it is necessary to pay strict attention to several factors which play an important part. In the first place the wick must be so arranged as to supply the right quantity of oil for gasification at the burner head, the flame must be neither starved nor overfed, as if the- former is the case great loss of light is occasioned, THE USE OF LIQUID FUEL. 109 whilst the latter, by supplying more hydrocarbons than the air supply to the flame can completely burn, gives rise to smoke and products of incomplete combustion. The action of the wick depending on the capillary action of the microscopic tubes forming the cotton fibre, nothing but good quality long staple cotton should be employed, and this should be spun into a coarse loose thread with as little twist in it as possible, and from this the wick is built up. Having obtained a wick of soft texture and loose plait, it should be well dried before the fire, and when put in posi- tion in the lamp must fill the wickholder without being compressed ; it should be of sufficient length to reach to the bottom of the oil reservoir, and leave an inch or two on the bottom. Such a wick will suck up the oil in a regular and uniform way, provided that the level of the oil is not allowed to fall too low in the lamp ; but it must be remembered that the wick acts as a filter for the oil, and that if any sediment be present it will be retained by and choke the capillaries upon which the action of the wick depends, so that a wick should not be used for too long a time, a good rule being that the wick should, when new, trail for two inches on the bottom of the oil vessel, and should be discarded when these two inches have been burnt off. When the lamp is lighted the oil burns with a heavy smoky flame, this being due to its not being able to obtain sufficient oxygen to complete the combustion, and not only are soot flakes produced, but products of incomplete com- bustion, such as carbon monoxide and even petroleum vapour, escape into the air, the first being highly injurious to health and the second offensive to the nose. In order to supply the necessary amount of air to the flame an artificial draught has to be created which shall impinge upon the bottom of the flame and sweep upwards 110 LIQUID AND GASEOUS FUELS over its surface, giving it rigidity, and, by completing the combustion in a shorter period of time than could be done otherwise, increasing the calorific intensity, and thus raising the carbon particles in the flame to a far higher incan- descence, so as to secure a greater illuminating power. This in practice has been done in two ways, first, by drawing in the air by the up-suck of the heated and expanded products of combustion in a chimney fitted over the flame, and, secondly, by creating a draught from a small clockwork fan in the base of the lamp. It is necessary in doing this to break the initial rush of the draught, this being done mostly by discs of perforated metal in the base of the burner, called diffusers, whilst the metal dome which surrounds and rises slightly above the wick- holder serves to deflect the air on to the flame. These arrangements also to a certain extent act as regenerators, the air passing over the heated metal surfaces being warmed before reaching the flame, whilst other contrivances, such as discs, cones, buttons, perforated tubes, inner air tubes, etc., have from time to time been introduced with the object of increasing the illuminating power and completing the combustion. In the table on p. Ill the results obtained by testing some of the most popular lamps on the market are given. The amount of heat emitted by our illuminants is a point of importance upon which very little has been said, and which places a distinct limit upon the size and illuminating power of our oil lamps, a lamp such as the 60 line Veritas giving out not only a magnificent illumination, but also an amount of heat which, although acceptable in a cold country chapel on a winter's night, would be unbearable in a dwelling room. Taking the composition of lamp oil as being 86 per cent, carbon and 14 per cent, hydrogen, the combustion of one THE USE OF LIQUID FUEL. Ill pound would give 20,411 British Thermal Units, whilst 50 grains, yielding one candle of illumination, would give 177 British Thermal Units. When the idea of using liquid fuel for steam raising first arose, the methods which had served before for the genera- tion of light and heat would undoubtedly be those to which the early investigators would turn first, and on a small Grains of Oil per Candle Power Total Candle Power. per Hour. Type. Name. American. Russian. American. Russian. Circular Veritas, 60 line . 64-5 112-5 122-5 78-0 Wick. 30 . . 42-5 50-0 60-0 60-0 20 . . 43-75 58-5 40-0 35-0 Ariel, 12 line 52-8 70-9 18'0 18-0 (centre draught) Beading, 14 line 97-9 85-4 12-0 12-0 Kosmos, 10 line 63-9 97-2 , 90 9-0 Wizard, 15 line . 56-9 51-3 18-0 19-0 Flat Wick, Wanzer, no glass 42-6 48-3 17-0 15-0 single. Solid Slip . 84-4 84-4 8-0 8-0 (gauze and cone) Old Slip, fixed gauze 60-9 89-3 7-0 7-0 Duplex. Feeder Wick 56-2 55-7 20-0 22-0 Ordinary . 51-2 46-6 20-0 22-0 American Oil : Specific Gravity, 0'7904 ; Flash Point, 110 F. Russian ,, 0*823; ,, 83 F. scale wicks were employed in the combustion in order to draw up and gasify the oil. These soon proving inadequate, the next step was to make the bed of the furnace of porous material, and saturate that with the oil which was allowed to percolate through it. Such a method was introduced in 1864 by J. C. Kichardson, and was slightly improved in 1866 by using steam to aid the action. The method, how- ever, is only of historical interest, and the results obtained by it were of a poor character. 112 LIQUID AND GASEOUS FUELS. The next step was to burn the oil from a series of open troughs, so arranged that the unburnt oil flowed downwards from trough to trough. This system was generally known as " Nobel's troughs," and gave good results in practice, an evaporative efficiency of as high as 14|lbs. of water being FIG. 13. Nobel's troughs. obtained in stationary boilers. The troughs are generally fitted at the mouth of the boiler, and a strong draught draws the flame together with the requisite quantity of air into a mixing chamber, whence it passes with more air through the furnace, combustion chamber, and flues. This method of burning the oil has also been applied frequently THE USE OF LIQUID FUEL. 113 to metallurgical and other furnaces with considerable success, but it must be remembered that such an arrange- ment would be almost impossible to use with oils of the high density it is necessary now to employ as fuel, and that complete combustion would be very difficult to attain. As early as 1863 the methods which now are most extensively used began to be introduced, and consisted of bringing the oil into the combustion chamber either as a gas or in such a condition of finely divided spray as to ensure its rapid and complete combustion. It is well known that if oil be subjected to the action of heat it can be converted into a gas rich in hydrocarbons with simultaneous formation of tar and deposition of more or less solid carbon, and the various oil-gas processes which have from time to time been introduced for the manufacture of illuminating gas give us a fairly complete insight into the actions taking place, and the best conditions for obtaining gaseous from liquid hydrocarbons. The idea of first gasifying the oil before burning seems to have originated with Colonel Foote, of the United States. The United States gunboat Polos was in 1867 fitted for burning liquid fuel by him, and on her trial trip ran over 14 knots, whereas 8 knots per hour had been her previous best record with coal. It was also found that instead of twenty firemen required with solid fuel, the stokehold staff could be cut down to three. The liquid fuel consisted of petroleum, which was carried in two large iron tanks placed on deck, and from the description given these were fitted with a vent-pipe on top to allow the escape of vapours, so that it is evident that crude petroleum and not residuum was being used. The oil was allowed to flow by gravity through half-inch pipes to a retort placed some little distance inside the furnace, where it was gasified, and the oil-gas was led back towards L.G.F. I 114 LIQUID AND GASEOUS FUELS. the furnace mouth by pipes filled with apertures and giving a large flame which swept back over the retort, keeping it heated to the necessary temperature to continue the decom- position of the oil. The oil-gas so formed was diluted with hydrogen, made by passing steam through tubes filled with Steam FIG. 14. Colonel Foote's furnace. heated iron filings, and the flame was fed with air forced in with an air pump. The combustion is recorded as being very intense and perfectly smokeless, but nothing more was heard of the system, this being probably due to the costly method of diluting the gas and the trouble from choking of the retort and tubes with carbon, which must inevitably have taken THE USE OF LIQUID FUEL. 115 place. There are certain points of interest in the experi- ment, however, which are well worth notice, and will be discussed later on. Soon after, a system of a similar character was patented by Simms and Barff, the oil being injected and vaporised in a retort placed in the furnace, and although satisfactory results were obtained, it was found that considerable trouble was experienced with the retorts, which, being exposed to a very high temperature, had a very short life. Several systems of this kind have been proposed, and FIG. 15. Eames' oil furnace. also others in which the vaporisation of the oil should take place in retorts external to the fire-bars. The best known of these are those processes patented by C. Eames in 1875, and by Diirr. In the Eames system the oil was fed into an externally heated cylindrical retort with round ends, in which it flowed downwards over a series of hori- zontal iron plates whilst superheated steam was passed upwards, and being decomposed by the hydrocarbons at the high temperature, formed a mixture of what was practically oil-gas and water-gas, which was burnt as it issued from the vaporiser at suitable burners. In the Diirr apparatus the oil is supplied by air pressure i 2 116 LIQUID AND GASEOUS FUELS. through a heated retort in which it is vaporised, and the vapour is then gasified in a chamber in the mouth of the furnace heated to a high degree. The gas is led straight for combustion into the furnace. It is, however, quite evident that for the successful use of liquid fuel auxiliary apparatus and sources of heat must be done away with and the furnaces made practically self- contained if anything approaching success is to be attained, FIG. 16. The Diirr system. as it is upon simplicity, ease of working, and freedom from complicated parts that the claim of liquid fuel for supremacy over solid is largely based. The direct pulverisation of the oil so as to drive it direct into the furnace chamber in a spray sufficiently divided to act almost as a gas is the method now practically universally adopted. This pulverising or atomising action may be brought about either by forcing the oil out from a jet at considerable pressure, or by injecting it with steam or air, or by a combination of the two. THE USE OF LIQUID FUEL. 117 The system of direct pulverisation, i.e., by pressure, is perhaps the latest and most promising method of consuming the oil. Korting's injector or burner is the best known arrangement for this purpose, and has been employed with great success on ships of the Hamburg- American line. The oil is heated to a temperature of 130 C., and is then forced into the injector under an air pressure of 50 Ibs. on the square inch. In the injector the oil flows into a chamber feeding the jet, and into this jet is fitted a spindle carrying a spiral screw. The oil, at the pressure of 50 Ibs., is forced down this spiral, and acquires a centrifugal ac- X" ^X-^ tion which / /""* sprays it out of V V- , the jet in a very ^^^s^ finely divided condition. Another form of burner, the action of which also is merely dependent upon FIG. 17. Eorting's injector. the pressure, is the Swensson, in which the oil under pres- sure is heated in a steam-jacketed tube, and is then forced out from a fine jet on to the point of a V-shaped metal cutter, which has the effect of pulverising it into a very fine spray. Perhaps the best known and most used of the burners are those in which the oil is pulverised by steam, a method that was first used by Messrs. Ay don, Wise, and Field in 1865-7, the general principle being that the oil is led down to the injector by gravity, and there meets a steam jet, which drives it out from the nozzle of the injector with high velocity and in a fine, state of division, whilst 118 LIQUID AND GASEOUS FUELS. the outrush of the steam and oil is usually made to suck in air around the jet to aid the combustion in the furnace. Of these burners perhaps at the present time the best known are those of the Holden type, and it is a form of these that is employed in the highly successful installations of liquid fuel that Mr. Holden has fitted up, and which 120 LIQUID AND GASEOUS FUELS. have shown themselves to be of a most satisfactory character. One form of the injector or burner is that used on locomotives, which is made to serve the double purpose of injecting the fuel and also maintaining the vacuum necessary for the brakes. In a second pattern, however, arranged for marine work, valves are designed to supply the oil in two portions to the steam injector, in order that if a change from half speed to full speed, or vice versa, be desired, the supply of fuel can be arranged without any alter- ation in the steam consumption. At the mouth of the burner an ingeni- ous arrangement of a steam ring performs the im- portant function of allowing jets of steam at various angles to catch the oil spray as it .leaves the burner and to more evenly distribute it throughout the FIG. 20. Holden's injector (stationary type). furnace, the steam ring also serving to draw in air for the primary combustion. Another form of steam pulverising burner largely used in practice is that designed by Messrs. Eushden and Eeles, which is the burner employed on the vessels of the Shell Transport Company. This excellent burner has shown itself very successful in working, and in it oil, after having been heated by a steam jet, is sprayed out by the steam, and as the burner is made so as to allow of separate THE USE OF LIQUID FUEL. 121 adjustments of the steam and oil jets the consumption of the fuel can be nicely adjusted to the work which it has to do. The burner used by Messrs. Armstrong, Whitworth & Co. that designed by Mr. E. L. Orde. In this burner is highly superheated steam is employed, 600 F. being probably the temperature at which it works best, and the steam is so arranged as to sweep out and spray the oil with a very high velocity, thus inducing a current of heated FIG. 21. Rushden-Eeles burner. air together with the jet of steam and oil, this being found to help the combustion. Although there have been many other forms of burner employed, these types may be taken as fairly covering the most successful methods of bringing the oil to the point of ignition, and it will now be well to see the arrangements which have been found necessary for the successful use of these burners in practice. When the liquid fuel has been atomised by the injectors and ignited, the burning rush of vapours in most cases is brought in contact either with a layer of fuel or brickwork near the mouth of the furnace ; whilst in some cases, as in the Korting system adopted by the Hamburg- American Line, the furnaces are bricked right round. In building in 122 LIQUID AND GASEOUS FUELS, vl THE USE OF LIQUID FUEL. 123 brickwork to the furnace, it should be so jointed as to leave plenty of play for expansion, as otherwise at the high temperatures obtained it buckles and the projecting surface fuses. The best bricks for use in this way are the Scotch Glenboig firebricks, which, although less refractory than several other kinds of firebrick, stand better the constant changes of temperature found in the furnaces when in intermittent working. The brickwork under these conditions can be made to fulfil several requirements. In- the first place it gets heated to a very high temperature, and serves to ignite the oil vapour and air coming into the furnace; and in the next place, if the oil jet is made to dash straight against it, it serves to disintegrate and gasify it, and also prevents the burning oil and flame being driven too rapidly through the furnace, and saves the plates from the direct impact of the flame. For these latter purposes also various forms of brick baffle are frequently employed. The Holden injector has already been referred to as one of the best in practice, and the methods used in the engines on the Great Eastern Kailway fitted for liquid fuel are somewhat as follows : Steam is first raised in the boiler by a wood and coal fire, and when 30 to 40 Ibs. pressure has been attained, the fire is levelled over and covered with a layer of broken fire brick ; a few pieces of wood or oily waste are then thrown in to make a flame, and the oil injector is started. Combustion is imperfect at first, and smoke is formed, but after a few minutes, the necessary temperature having been attained, the ring steam jet is turned on and induces the necessary air current to complete the combustion, when the fire clears and all smoke ceases. Among the many important questions which have yet to be solved is the best way in which to carry out the 124 LIQUID AND GASEOUS FUELS. combustion taking place in the furnace, and we must remember that our present methods of burning coal are the outcome of a century of practice and experience, and it cannot be expected that the small amount of work as yet done with liquid fuel should in any way approach perfection. When coal is burnt in a furnace a large proportion of the heat transmitted to the water takes place by radiation, and it is clear that in our method of burning oil it will have to be determined whether it is better to so arrange the air supply as to produce almost non-luminous flames, such as those given by the atmospheric burner, or whether the air supply should at first be limited so as to give a highly luminous flame, and the air needed to complete the combustion only added when the combustion chamber is reached. A non-luminous flame gives but little radiant heat, whilst the incandescent particles in a luminous flame give a very considerable amount. It is probably best in order to facilitate the transmission of a portion of the heat as radiant heat that the flame in the furnace itself should be luminous, and that the combustion should be completed by the addition of more air at the entrance to the combustion chamber before the tubes are reached. The transmission of heat from a non-luminous flame in the furnace to the water in the boiler is but small, as the contact of the surface of the furnace crown extin- guishes the flame, and leaves a layer of badly conducting gases between the metal and the flame. This is one reason why, when the mass of radiating fuel on the furnace grate is done away with, and is replaced by the flame of burning hydrocarbons, it becomes necessary to use firebrick or other refractory material in the furnace in order that it may become highly heated, and by its radiation aid the trans- mission of heat to the water in the boiler. THE USE OF LIQUID FUEL. 125 In burning oils there is always a risk that there may be present small particles of solid matter, which may choke the injector, and also water, the latter being present when the oil has been stored in the double bottoms and ballast tanks of the vessel, and also in crude oil. It has been found that the presence of drops of water in the oil is apt to extinguish the flame at the injector nozzle, and if that were to take place, and the finely divided oil spray or oil-gas were to get into the furnace mixed with air in any large quantity, it would give rise to an explosion. In order to get rid of solid particles and water the oil is pumped into settling tanks, fitted with a steam coil, which can be used to raise its temperature, the necessity for this being found in the fact that the specific gravity of the oil generally used as a fuel is only a little below that of water, and that therefore the separation would be very slow, but when slightly warmed the oil expands at a much greater rate than the water, and the separation takes place with much greater rapidity. In some cases two settling tanks are employed, each capable of containing 12 hours' supply, and the one which is out of use, after standing 12 hours, has the water drawn off from the bottom, whilst the oil is pumped out through a wire gauze filter. In other forms of settling tanks a filtering cage of wire gauze is employed, which is kept by a float near the surface of the oil, whilst a steam coil is used as before to aid the separation. The oil is nearly always heated before reaching the injector or atomiser in order to facilitate its flow and disintegration into minute particles. But this preliminary heating must be kept below the point at which the oil generates vapour or decomposes, as otherwise the formation of a break in the column of liquid owing to the generation of gas or vapour might extinguish the flame at the injector nozzle. 126 LIQUID AND GASEOUS FUELS. One of the points with regard to the methods employed for atomising the oil before combustion is the relative merits of mechanical injection and disintegration, or the utilisation of steam as the injecting and atomising power. If steam be used for injecting and atomising the oil 0'2 Ib. of steam per I.H.P. per hour is required, which on a service vessel could not be obtained without extra boilers, and this of course is a strong point in favour of injecting by pressure. There is another side to the question, however, which must not be overlooked, and that is that it is necessary to dilute the oil gas as far as possible during combustion in order to prevent the deposition of carbon, which once formed is very difficult to reburn and is one of the chief causes of smoke. If the effect of the steam were merely the mechanical one of injecting and afterwards diluting the oil gas, and no chemical action took place, the advantage would decidedly be*entirely on the side of such injectors as do their work by pressure and not by steam ; but it must be remembered that as the oil spray is heated in the furnace space in presence of the steam, chemical action takes place and greatly simplifies the decomposition of the hydrocarbons. It may be roughly taken that the petroleum residue chiefly employed will approximate to Ci2H26, that is to say, will be a mixture of hydrocarbons the composition of which is around this point, and if this be brought in contact with sufficient steam in the hot furnace space, the action, if com- plete, would result in the formation of carbon monoxide and hydrogen C 12 H 26 + 12 H 2 = 12 CO + 25 H 2 whilst under ordinary working conditions, the proportion of steam being far less than this, the result would be hydro- carbons of a simpler molecular structure diluted by hydrogen THE USE OF LIQUID FUEL. 127 and carbon monoxide, such a mixture being comparatively easy to burn without formation of smoke, whilst the rich oil gas and oil tar vapours formed by the heating when no steam is there to aid the chemical interactions are exces- sively difficult to burn without considerable formation of smoke. Some observers have tried to argue that the utilisation of steam for direct pulverisation of the oil adds enormously to the heating effect by producing in this way hydrogen and carbon monoxide, but this of course is an utter mistake, as it takes just as much heat to break up the steam as is evolved by the after combustion of the products formed, that is to say, the balance of heat will remain unchanged whether the oil be burnt alone with air or whether it be decomposed by steam and the products then burnt, the great advantage of the steam being to facilitate the com- bustion of the oil without the formation of smoke, and this is the only way in which the steam can act to give increased heat by preventing the escape of unconsumed products. When oil is driven by pressure from an injector of proper construction it spreads out as an inverted cone, and in this condition should be so atomised as to be only one degree removed from a vapour. When this is done in the open air the particles are so minute that they continue to float for some moments after the velocity acquired at the mouth of the injector has practically ceased to act. When this jet of oil is ignited close to the injector mouth it burns for the first few feet with a bright and excessively hot flame, and over this area gives no smoke, the reason being that the velocity at which the oil particles are travelling is sufficient to drag in with them from the surrounding area a considerable amount of air which is sufficient to complete the combustion of the outer portion : the radiation from this bakes the oil particles in the interior, where no combustion is going on, into gases and vapours. 128 LIQUID AND GASEOUS FUELS. As the circumference of the flame gets larger and larger, and the velocity decreases, the cooling influence of the outer air begins to tell, and the carbon particles within the flame gradually begin to show themselves as black smoke on the exterior. This action being increased the more the flame is cooled, dense black clouds of smoke are produced, a result which always ensues with such a method of combustion in the open air, whilst unburnt oil vapour and oil-gas from the interior of the mass form a bluish white line of smoke, showing up in marked contrast to the black mass of caibon- aceous smoke. The cooling of the flame therefore before combustion is complete gives rise to (1) Black carbonaceous smoke. (2) Oil gas. . (3) Oil vapour. When the injector is fitted in the furnace front and the combustion of the oil takes place in the furnace and com- bustion chamber, the air supply is drawn chiefly from the front of the furnace, passes in alongside the jet of oil, and being heated to a considerable extent before being utilised for combustion, the cooling effect is not nearly so great, but the upsuck of the chimney and the pressure under which the air is in the stokehold, by accelerating the rush of air, also lengthen the combustion area, and the formation of smoke is therefore thrown further from the injector, and with ordinary types of boiler probably takes place to the greatest extent in the combustion chamber. With any rich hydrocarbon gas the carbon particles, when once formed and cooled to the condition of smoke, are excessively difficult to again burn up by air or even oxygen, but steam is far more effective for this purpose, as it acts on the finely divided carbon with enormous rapidity as long as the temperature is near or about 1000C. The heat taken by the decomposition of the steam by the carbon is THE USE OF LIQUID FUEL. 129 again recovered by the combustion of the hydrogen so formed to water vapour once more, whilst the heat which would otherwise be lost owing to the escape of unconsumed carbon where smoke is allowed to form, is now rendered available by the combustion of the carbon monoxide. In the combustion of oil in the various forms of furnace and combustion space found in different types of boiler, the great point to bear in view is that the cause of the smoke is cooling before combustion is complete, and that the arrange- ments made should prevent the contact of the flame with surfaces capable of cooling it before the carbon has been so far consumed as to prevent smoke formation. It is not necessary that before a cooling surface is reached complete combustion should have taken place, but that before that point the carbon should have been burnt to carbon monoxide, which is incapable of yielding smoke in its further con- version into carbon dioxide. In many attempts to ensure smokeless combustion too much air has frequently been added, which is even worse than too little, as its admixture cools the exterior of the flame, whilst the excess of escaping gases takes away so much heat as to seriously reduce the evaporative power of the fuel. As far as fuel goes the blackest smoke only means a loss of about 1 per cent, of the fuel value, whilst it is easy to reduce the evaporation by 15 or 20 per cent, by using undue volumes of air. The only advantage of the uneconomical method of using steam instead of direct pressure injection is that the steam present can act on the carbon particles as soon as they are liberated, but it could never be so effective in preventing smoke as the use of a tenth or a twentieth of the quantity of steam injected into the flame at a later period, as the large volume going in with the oil spray begins to act on the oil even before the carbon begins to be liberated. So endothermic is the reaction that takes place that a serious cooling of the flame is brought about, whilst the formation L.G.F. K 130 LIQUID AND GASEOUS FUELS. of a large volume of carbon monoxide and hydrogen tends to prevent proper access of air to the flame in its earlier stages. Nor could such a high efficiency be got from the combustion, as by the direct injection of oil under pressure the oil spray is burnt at its best during the first few feet of ignition, and is emitting an enormous amount of radiant heat, which in the furnace is largely transmitted to the water, whilst the steam injected at the moment when smoke would otherwise begin to form then fulfils its functions under conditions which do not detract from the efficiency. With land boilers the use of oil has great advantages, but for use on board ship the advantages are greater still. When coal is used it has to be got into the bunkers, meaning an enormous amount of extremely hard labour, everything on the ship being made filthy by the coal dust, necessitating cleaning and polishing up afterwards. As regards the advantages of oil in this direction, there can be no reason- able doubt. Taking the oil in from big storage tanks along- side the wharf, it can either be run into the portion of the ship reserved for storage by gravity, or it can be pumped in, and instead of having the bunkers, as one is obliged to for coal, above the level of the stokehold, the storage tanks for the petroleum, or whatever liquid fuel it may be, may be in practically the ballast tanks, and as the oil is used it can be replaced by water, thus giving an enormous increase in capacity to the vessel. If it be a ship of the mercantile marine, it gives a large amount of cargo room, which means of course greater earning power for the ship ; if it is a man- of-war, it does more it gives the power of storing a much larger amount of energy in the same space as coal would have occupied. Liquid fuel is far in advance of coal as a steam raising- agent, as it is found that one ton of oil is about equal to 1/5 of coal, and the result is that for the same weight an amount of fuel can be carried which will give a very much THE USE OF LIQUID FUEL. 131 greater radius of action, which at the present time in the Navy is a factor of the greatest possible importance. Again, in the feeding of the oil to the furnaces, instead of needing a very large number of stokers for trimming the coal in the bunkers and keeping up the fires, the use of oil will reduce that number to about one-fourth, whilst there being no ash, cinder, and clinker to clear out of the furnaces and throw overboard, another economy in labour is effected. Many of the apparent discrepancies to be found in experimental results with liquid fuel are caused by the different conditions of use. For instance, the results obtained by such vessels as the Murex and the Strojnbus, over very long periods of steaming with coal and with oil, give respectively the ratios of 25 to 16 and 42 to 30 as the relation by weight of coal to oil consumed to give the same I.H.P. and speed to the vessel. The working of the Hamburg-American Co.'s steamer Ferdinand C. Lainer gives a ratio of 3 to 2, and many other vessels could be cited giving even better results. In the Service these results were not at first so easily attained, and this is due to the fact that the conditions existing in the boilers of the Navy and the merchant service are so utterly different that no comparison can be made between them. In the combustion of liquid fuel the oil is practically entirely converted into gas, vapour, and floating particles of finely divided carbon before combustion begins, or at any rate before any large amount has been consumed. This requires a large combustion area, as the volume of air needed to complete the action and prevent smoking is very great, whilst with coal the combustion of the largest pro- portion of the fuel takes place on the furnace grate, and it is only the escaping gases distilled out of the coal and formed by incomplete combustion that have to be burnt in the crown of the furnace and combustion chamber. K 2 132 LIQUID AND GASEOUS FUELS. The result of this is that plenty of combustion space becomes one of the important factors in a furnace for liquid fuel, and with the vessels that have given the best results in the merchant service the combustion of 2J Ibs. of oil per cubic foot of combustion space will give them full steam power, whilst under the conditions of combustion area exist- ing in the naval boilers, a far larger quantity per cubic foot of space would have to be consumed to give the desired result. The question of combustion area and air supply needed for the use of liquid fuel is made clear when one considers in figures the work which has to be done. With a Service vessel under full steam, if the best Welsh coal is used there will be little or no smoke, showing that combustion has been fairly complete, whilst one knows that if a Newcastle or Durham coal be taken there would be abundant black smoke from the funnel, showing that already the combustion area and air supply were insufficient to deal with the work that had to be performed. If the actions taking place with a bituminous coal be regarded as repre- senting the maximum efficiency of combustion that could be obtained by that particular arrangement of boiler and furnace, the efficiency would certainly be overstated and not understated. The action of the heat from the fire in the grate when coal is first charged in very closely resembles the actions that take place in the gas maker's retort, as the red hot fuel below is raising the fresh fuel above to a temperature of about 1000 C., and is preventing any large amount of air from getting through the bed of incandescent carbona- ceous material to it. Under these conditions a ton of bituminous coal would yield 10,000 cubic feet of gas and 10 gallons of tar in the condition of vapour, whilst 75 per cent, of the weight of the coal would be left to burn on the fire grate, a certain proportion of which by incomplete THE USE OE LIQUID EUEL. 133 combustion would yield carbon monoxide to add to the body of gas to be burnt up in the crown of the furnace and the combustion chamber. On the other hand, when a ton of ostatki is converted into gas, on being injected into the furnace it yields double this quantity, i.e., 20,000 cubic feet of gas and about 12 per cent, only of residual tar in the form of vapour and carbon particles. Not only is the volume of gas thus yielded twice as great in the case of oil fuel as in the case of coal fuel, but it is a gas which, being far richer in hydrocarbons, requires a far greater volume of air for its complete combustion than was the case with the gas developed from the coal, so that it can easily be understood that, without considerable alteration in the draught arrangements, a furnace with its combustion area and air draught arranged for coal cannot be expected to deal with nearly the same weight of liquid fuel. It must be borne in mind that the area over which the combustion spreads is governed by the length of travel of the combustible gases before they find the necessary amount of atmospheric oxygen for their complete combustion, and that the conditions of air supply mean, to a great extent, regulation of combustion space and rate of travel of the burning vapour. During the last few years a large amount of attention has been given to the burning of liquid fuel by the naval authorities of all the first class Powers, and it is now firmly established as an auxiliary to coal in the English, German, French, Italian, and American Navies. From the evidence given by the late Sir Gordon Miller before the Koyal Commission on Coal Supplies, the Admir- alty take about 1,000,000 tons of steam coal annually from the 24 collieries on the Admiralty list, and this quantity would be much increased in time of war, so that the amount of liquid fuel available would be far too small to admit of its being used alone. 134 LIQUID AND GASEOUS FUELS. In every case the limitation of the supply of liquid fuel has led to its being fitted as an adjunct to coal, and not as the sole fuel, as it has been realised that until its supply in large quantities is placed upon a more reliable basis than at present, it would be incurring a grave risk to fit a large battleship for burning liquid fuel only, although with smaller vessels, such as destroyers, it is permissible to do so. As an auxiliary to coal it has very great advan- tages, as with a fleet manoeuvring at half speed it gives the power of suddenly increasing to full steam by the mere turning on of the oil supply to the injectors, and it is with this object in view that all the newer English, German and French battleships and cruisers have been fitted for burning coal or a mixture of coal and oil. Many European critics are distinctly adverse to this method of consumption, as they point out that if the furnaces of a vessel are so arranged as to give the best results with coal, it is clear that the conditions will not allow of sufficient air supply to properly consume the oil and develop its full advantages, whilst a dense flame of oil burn- ing above the coal will keep air away from it and deaden the surface combustion. This is perfectly true as far as it goes, but there is not the least doubt that the results obtained are sufficiently good to justify its adoption for this purpose and that, burnt in this way, it has proved and will prove of the greatest value. In the United States many experiments have been made with liquid fuel in the mercantile marine, especially when the opening up of the Texas fields seemed to promise an enormously increased supply, whilst the naval authorities also carried out an extensive series of experiments in 1902, for the full details of which the reader is referred to Mr. W. H. Booth's valuable work on Liquid Fuel, but the conclusions arrived at may be stated as follows : (a) That oil can be burned in a very uniform manner. THE USE OF LIQUID FUEL. 135 (6) That the evaporative efficiency of nearly every kind of oil per pound of combustible is probably the same. While the crude oil may be rich in hydrocarbons, it also contains sulphur, so that after refining the distilled oil has probably the same calorific value as the crude product. (c) That a marine steam generator can be forced to even as high a degree with oil as with coal. (d) That up to the present time no ill effects have been shown upon the boiler. (e) That the firemen are disposed to favour oil, and there- fore no impediment will be met in this respect. (/) That the air requisite for combustion should be heated if possible before entering the furnace. Such action undoubtedly assists the gasification of the oil product. (g) That the oil should be heated so that it could be atomised more readily. (h) That when using steam higher pressures are undoubtedly more advantageous than lower pressures for atomising the oil. (i) That under heavy forced draught conditions, and parti- cularly when steam is used, the Board has not yet found it possible to prevent smoke issuing from the stack, although all connected with the tests made special efforts to secure com- plete combustion. Particularly for naval purposes is it desir- able that the smoke nuisance should be eradicated, in order that the presence of a warship might not be detected from this cause. As there has been a tendency of late years to force the boilers of industrial plants, the inability to prevent the smoke nuisance under forced draught conditions may have an important influence upon the increased use of liquid fuel. ( j) That the consumption of liquid fuel cannot probably be forced to as great an extent with steam as the atomising agent as when compressed air is used for this purpose. This is probably due to the fact that the air used for atomising purposes, after entering the furnace, supplies 136 LIQUID AND GASEOUS FUELS. oxygen for the combustible, while in the case of steam the rarefied vapour simply displaces air that is needed to complete combustion. (k) That the efficiency of oil fuel plants will be greatly dependent upon the general character of the installation of auxiliaries and fittings, and therefore the work should only be given to those who have given careful study to the matter, and who have had extended experience in burning the crude product. The form of the burner will play a very small part in increasing the use of crude petro- leum. The method and character of the installation will count for much, but where burners are simple in design, and are constructed in accordance with scientific principles, there will be very little difference in their efficiency. Con- sumers should principally look out that they do not pur- chase appliances that have been untried and have been designed by persons who have had but limited experience in operating oil devices. The use of liquid fuel for steam raising in locomotive boilers has received a large amount of attention, and various grades of oil, tar, and tar by-products have been exhaus- tively tried with most successful results by Holden, on the Great Eastern Railway, and by Urquhart, on some of the Eussian Eailways, and their classic researches on the sub- ject have led to its introduction for this purpose in every part of the world. The engineering details of such instal- lations are beyond the scope of the present work, and may be found in full in Booth's work on Liquid Fuel. The liquid fuels generally employed do not show as wide a difference in their calorific value as determined by the bomb calorimeter as might be expected, but in practical work such oils as the blast furnace and heavy tar oils, owing to their chemical nature and the difficulty of decom- posing them, give lower evaporative results than the petro- leum oil. The general run of these differences may be seen THE USE OF LIQUID FUEL. 137 from the following table, and gives the practical results obtained with the same boiler : LIQUID FUELS. Calorific Value by Bomb. Actual Evapora- Description. Specific Gravity. Flash Point. tive Power in practice, from Calories. B.T.U. and at 212 C F. American Residuum 886 350 10,904 19,627 15-0 Russian Osfcatki 956 308 10,800 19,440 14-8 Texas 945 244 10,700 19,242 14-79 Burmah . 920 230 10,480 18,864 14-5 Barbadoes 958 210 9,899 17,718 14-2 Borneo 936 285 10,461 18,831 14-0 Shale Oil . 875 288 10,120 18,217 13-8 Blast Furnace Oil 979 206 8,933 16,080 12-0 Heavy Tar Oil . 1-084 218 8,916 16,050 12-0 The best results obtainable with this type of boiler fired with coal would have been an evaporative duty of between 9 and 10 Ibs. of water from and at 212 F., when using the best Welsh steam coal. It must be borne in mind that such evaporative values as have been given here are considerably below many that have been claimed, and it is said that Messrs. Thornycroft have obtained the high evaporative value of 18'95 Ibs. of water per pound of oil fuel, but if this is so the boiler must have been a wonderfully perfect instrument for converting heat into steam. A good sample of oil fuel on analysis gives the following percentage composition : Carbon Hydrogen . Oxygen 87-80 10-78 1-24 and the evaporative power calculated from the analysis is 138 LIQUID AND GASEOUS FUELS. 1 -9J. 0-15 (87-8 + 4-28 (10'78 - )) = 19'9 Ibs. from and at o 212 F. Its calorific value taken in the Bomb is 18,831 B.T.U., and by dividing this by 966 (latent heat of steam in F.) we obtain 19*5 as its evaporative power, so that it is safe to assume that under theoretically perfect conditions the evaporation per pound of oil would be about this quantity. Taking a good sample of coal, analysing it, and calculat- ing the evaporative effect we obtain 14'1 Ibs., whilst by determination in the Bomb we get 14 Ibs. from and at 212 F. Now we know from years of experience with boilers and furnaces specially made and adapted for burn- ing this coal, that an evaporation of 9'5 Ibs. of water will be the most we shall ever get under the very best circum- stances per pound of coal, the difference between the 9 '5 found and the 14 calculated being due to the heat losses inseparable from the system. On the same basis it is hard to understand why one should expect to get a greater pro rata duty from the oil, and if a calculated 14 gives an actual 9'5 Ibs. evaporation, then our calculated 19*5 for oil should only give an evaporation of 13*2 Ibs. If, however, the loss is, as it were, a fixed charge of 4'5 Ibs. per pound of fuel due to the personal equation of the boiler, then our calculated 19'5 Ibs. evaporation would give in practice just about the 15 Ibs. evaporation obtained with this oil in the particular boiler used, and it seems unlikely that when the full steaming power of a boiler has to be developed over a considerable period that this evaporative efficiency will be much increased, although under conditions when smaller quantities of oil can be used to give the required steam power, careful nursing may develop better results for a short period. Where oil fuel is abundant it is also used for smelting ores and other metallurgical operations, for which the comparative freedom from sulphur of most kinds of oil THE USE OF LIQUID FUEL. 139 specially fits it, whilst for many forms of furnace, rivet heaters, etc., its ease of application and the high tempera- ture obtainable by its use make it a convenient and in some cases even economical form of fuel. Internal combustion engines using heavy mineral oil of much the same character as that used for fuel are rapidly finding favour not only on land but for marine purposes ; in these the oil is introduced into the combustible cylinder as the finest attainable spray, and is there exploded with highly compressed air, the heat generated during compres- sion being an important factor in the successful ignition of the charge. In a valuable paper read before the Institution of Civil Engineers by Mr. J. T. Milton in January, 1907, the author thus tabulates the special conditions to be satisfied by marine internal combustion engines if they are to be successful for large vessels: (a) The engine must be reversible. (b) It must be capable of being stopped quickly and of being started quickly either ahead or astern. (c) It must be capable of being promptly speeded to any desired number of revolutions between dead slow and full speed, and of being kept steadily at the required speed for any length of time. " Dead slow " ought not to be faster than one quarter of full speed, and should be less than this in very fast vessels. (d) It must be capable of working well, not only in smooth water, but also in heavy weather in a seaway in which the varying immersion of the propeller causes rapidly changing conditions of resistance. (^ All working parts must be readily accessible for overhauling, and all wearing surfaces must be capable of being promptly and easily adjusted. (/) The engine must be economical in fuel and especially so at its ordinary working speed. 140 LIQUID AND GASEOUS FUELS. In small engines condition (a) is not complied with ; the engines are always run in one direction, the reversing of the vessel being provided for either by a reversing-bladed propeller, or by the intervention of toothed gearing. Condition (b) also, in small engines, is fulfilled by means of a friction clutch arrangement which permits the engine to be kept running while the screw-shaft is stopped. For large sea-going vessels, however, condition (d) practically puts movable-bladed propellers, clutches, and toothed gearing entirely out of question, and necessitates a reversing engine, with a direct drive on to the screw shaft, and a fixed propeller. In large engines also conditions (b) and (c) prohibit the use of a heavy flywheel, and necessitate a fairly equable turning-moment at all working speeds. It must be remembered, however, that for the high powers necessary in large sea-going vessels, and especially in warships, the internal combustion engine for heavy oil is as yet in a purely experimental stage, but for smaller craft it is a distinct success, and it will not be long before it finds its way into the Service for submarines and torpedo boats. CHAPTER VI. THE MANUFACTURE OF COAL GAS. The history of coal gas Murdoch, Lebon and Winsor The coals used in coal gas manufacture Gas retorts and carbonisation Retort settings Charging and drawing Sloping and vertical retorts Crude coal gas and its purification Ammonia liquor Sulphur compounds in gas The effect of sulphur in gas on its use for domestic lighting Lime and ore purification The com- position of coal gas The enrichment of coal gas Cannel Oil gas Hydrocarbon vapours Oven gas The cause of luminosity in flame The chemical changes taking place in a gas flame Gas burners. THE ease of application and cleanliness in combustion of gaseous fuel, together with the recognition of the importance of the gas engine as one of the most economical sources of power, have led to a considerable amount of attention being paid to the subject during the last twenty years, and for convenience and efficiency, if not for cheapness, coal gas claims the first place amongst this important class of fuels. The fact that an inflammable vapour could be obtained from coal by the action of heat was known as early as 1691, but it was William Murdoch who, in the closing years of the eighteenth century succeeded in showing how it could be made a valuable aid to the advance of civilisation. It was in 1779 that Murdoch, a hard-working young Scotch engineer, went to Cornwall as superintending manager to Messrs. Boulton & Watt, in order to introduce their pumping machinery and engines in the tin mines, which were then in their zenith. Having a certain amount of 142 LIQUID AND GASEOUS FUELS. leisure time he occupied it in trying to work out a number of ideas which had occurred to him in his earlier days, and had it not been for the opposition and obstacles thrown in his way by Watt, he would undoubtedly have perfected the locomotive many years before Stephenson ; indeed he did construct a sort of motor tricycle which was the cause of great alarm to the surrounding country. Amongst other experiments tried by him was that of obtaining gas from coal and using it for lighting purposes. Making coal gas in a simple form of retort in his back yard he led the gas into the front office of his house in Cross Street, Eedruth, and there exhibited the wonderful proper- ties of the gas flame to admiring audiences. It must be remembered that at this period the only sources of artificial light were candles and lamps, and to the mind educated by centuries of such forms of illumination it seemed scarcely possible that an illuminating flame could be obtained without a wick, and Murdoch's wickless flame was looked upon in those days with as great wonder as we have bestowed upon Eontgen rays, liquid air, and radium. In the year 1798 Murdoch left Cornwall, and returned to Messrs. Boulton, Watt & Co.'s engine works at Soho, near Birmingham, where he lighted up their principal buildings and made many experiments on the best form of retort to use for the distillation of the coal. These experiments occupied until about 1802, when a great public display was made of gas lighting by the illumination of Messrs. Boulton & Watt's factory in honour of the Peace of Amiens, and it was at this period also that many shops in the neighbourhood of the factory were lighted up by coal gas. Murdoch, however, was not destined to reap the reward of his discovery, and in 1799 a Frenchman named Philippe Lebon took out a patent in Paris for making an illuminating gas from wood, and gave an exhibition of it in 1802, which THE MANUFACTURE OF COAL GAS. 143 excited a considerable amount of attention on the Continent. It was seen by a German, named Winsor, who made Lebon an offer for his secret process for Germany. This offer was, however, declined, and Winsor returned to Frankfort determined to find out how such a wondrous effect as making common smoke burn with greater beauty than wax or oil had been brought about. Having quickly succeeded in finding out how it was to be done, he in 1803 exhibited before the reigning Duke of Brunswick a series of experiments with lighting gas made from wood. Looking upon London as the happy hunting ground for the accumulation of wealth, he came over to England, and at the commencement of 1804 boldly took the Lyceum Theatre, where he gave lectures on gas lighting, or rather had an assistant to read the lecture whilst he looked after the experiments. He then proceeded to float a company, and in 1807 the first public street lighting took place in Pall Mall, whilst in 1809 he applied to Parliament to incorporate the National Heat and Light Company, with a capital of half a million. This application was opposed by Murdoch on the ground of his priority in invention, and the Bill was thrown out, but, coming to Parliament for the second time in 1810, Winsor succeeded in getting it passed in a very much cur- tailed form, a charter being granted in 1812, and the company was called the Chartered Gas Light & Coke Co., and was the direct forefather of the present Gas Light & Coke Co. From that day to this the great gas industry has never looked back, and is at the present moment certainly one of our most important industrial assets. W T e have seen the wide differences which exist in coal (p. 32), and the coals employed for the manufacture of illuminating gas are all of bituminous character, such coals as the Welsh steam coal or anthracite being useless as a source of gas. The districts yielding coals best fitted for gas making are 144 LIQUID AND GASEOUS FUELS. the Northumberland, Durham, South Yorkshire and Derby- shire fields, and the ultimate composition of such coal may be gathered from the following table : c , g d 1 TD e< 1 1 j 'o a m fc O <5 Newcastle gas coal . 82-16 4-83 1-00 1-23 6-82 3-20 0-76 Durham gas coal 84-34 5-30 0-73 1-73 4-29 2-42 1-14 South Yorkshire silk- stone 80-46 5-09 1-66 1-67 6-79 3-30 1-03 Derbyshire silkstone . 76-96 5-04 2-39 1-77 6-92 3-28 3-64 Barnsley gas coal 75-64 4-94 2-84 1-65 7-25 4-28 3-40 For enrichment purposes, cannel or " parrot " coal is largely employed. As before pointed out, our knowledge of the composition of the hydrocarbon compounds present in coal is so limited that the ordinary analysis of a coal affords but little indica- tion of its value for the production of illuminating gas ; but there is one point which is highly suggestive, and which has received but a small amount of the attention it deserves. In a report made by M. Ste. Claire Deville in 1886 upon a series of experiments, extending over 12 years, which were carried out at La Villette (Paris) with 59 different kinds of coal, he clearly established the fact that as the amount of oxygen in the original coal oxygen in combination with hydrocarbons increases, so does the total amount of vola- tile matter present in the coal rise in quantity, whilst the density and illuminating value of the gas produced also increase, and he comes to the conclusion that the best gas coals are those containing from 7'5 to 9 per cent, of oxygen. Less oxygen than this in the coal means that the coke will be plentiful, but the gas poor : whilst if the oxygen is above the standard, the coke is bad. This fact seems to point to THE MANUFACTUKE OF COAT, GAS. 145 the valuable hydrocarbons for gas production in the coal being oxygenated bodies, which, like fatty acids or alcohols, would decompose with formation of efchylene, methane, hydrogen, and oxides of carbon at the temperature of the gas retort, and not, as has been more ordinarily supposed, bodies like paraffins. The effect which the combined oxygen has upon the composition of the gas obtained front the coal is also instructive. Percentage of oxygen in coal . 5 to 6-5 6-5 to 7'5 7-5 to 9 9 to 11 11 to 12 Composition of gas Carbon dioxide . 1-47 1-58 1-72 2-79 3-13 Carbon monoxide 6-68 7-19 8-21 9-86 11-93 Hydrogen . 54-21 52-79 50-10 45-45 42-26 Benzols 0-79 0-99 0-66 1-04 0-88 Methane 34-37 34-43 35-03 36-42 37-14 Ethylene 2-48 3-02 3-98 4-44 4-76 Density of gas . 0-352 0-376 0-399 0-441 0-482 It will be seen from the table that the proportion of oxides of carbon increases with the rise in the oxygen, as also does the ethylene, whilst the hydrogen decreases. In ordinary gas practice the coal is heated out of contact with air in elliptical or D-shaped retorts, set in groups of five, seven, nine, or even more and heated by the same furnace, and the products of distillation are then led off by an ascending tube from the mouth of each retort. This tube, called the ascension pipe, after ascending above the level of the bench of retorts, bends over and descends into a trough-shaped tube, which is about half full of tar ; and into this the delivery tube or dip pipe from the retort just dips, the tar closing the mouth of it gas-tight. This collecting main runs horizontally over the whole of the front of the bench L.G.F. L 146 LIQUID AND GASEOUS FUELS. of retorts and is called the hydraulic main, and all the retorts discharge into it by means of their ascension and dip pipes, each of which is sealed by the tar, kept at a constant level by means of an overflow syphon at the end of the hydraulic main. Each retort is fitted at the end which projects from the furnace with a mouthpiece and lid, which can be removed to allow of the coke being withdrawn and the fresh charge of coal inserted, and the vertical ascension pipes which lead up to the dip pipe and hydraulic main start from the top of the mouthpiece. The reason why these pipes are sealed by dipping under the surface of the liquid in the hydraulic main is that the gas from the other retorts cannot escape down the ascension pipes, as would be the case if they simply opened into the main, and this enables any of the retorts to be opened for recharging, whilst the others are still giving off gas, and also prevents leakage from the whole bench of retorts should one accidentally crack. A large quantity of volatile products escapes as vapour with the gas into the hydraulic main, where much condenses as tarry products and ammoniacal liquor (consisting of ammonia, carbonate and sulphide of ammonium, etc., in solution), and these run off through the overflow syphon to the tar well, where they are collected. The gas passes down from the hydraulic main to the atmospheric condensers, a series of tubes which are exposed to the air, thus cooling down the gas as it passes through them, and causing a further deposition of tar, ammoniacal liquor, and any easily con- densable hydrocarbon which may be present. There is also generally an arrangement for artificially cooling the con- densers in hot weather by means of water. After leaving the condensers the gas next passes through the scrubbers, which consist of towers built of iron plate and filled with coke or brushwood, over which water or diluted ammoniacal liquor is sprayed and trickles down, meeting the gas which L 2 148 LIQUID AND GASEOUS FUELS. is made to pass up them. The alkaline liquor absorbs some of the sulphuretted hydrogen and carbon disulphide present in the gas, and also removes the last traces of tar and ammonia ; the gas, still containing some sulphuretted hydrogen, carbon disulphide, and carbon dioxide, then passes on to the purifiers. When Murdoch first made gas at Eedruth, he employed a cylindrical cast iron pot with a rounded bottom, sunk in the furnace. But it was soon found that the removal of the coke left by the carbonisation of the 15 Ibs. of coal employed caused inconvenience, and in 1802 he constructed a horizontal retort. A little later on, in 1804, he reverted to the vertical pot form, but added a tubulure at the bottom for removing the coke, and it was about this period also that he made an inclined retort with lids at either end. The form of the retort, however, soon settled down to the horizontal. This early period was richer in experiments on the subject of carbonisation than almost any we have had since, as when once the horizontal retort gave satis- factory results, the only alteration made during the next 70 years was in material shape and setting. Since then the "sloper" has been once again introduced, with all its mechanical improvements, and has brought gravity to the aid of labour in charging and discharging, with results that need no discussion. Kotary retorts have also had some short trial, and the vertical retort has now come forward under the auspices of Dr. Bueb in Germany, and Messrs. Settle and Padfield, and Woodall and Duckham, in England. The forms of retort now most in use are made of fire clay : in small country works these are what are termed " single-ended " retorts, and are about 9 feet in length, but in works of any size the more economical double-ended retort is used. The cross-section of the retort has under- gone a considerable amount of experiment, but what is known as the " D " form is now generally adopted, as long THE MANUFACTURE OF COAL GAS. 149 exposure to the heat of the furnace does not affect the shape, and it presents a large amount of heating surface on the base. The conditions of working, the heats employed, and other factors affect the life of the retort, but with ordinary care a retort of D section will last about thirty months. At each end of the retort is fitted a cast iron mouth- piece and lid, and into the mouthpiece is fitted the ascension pipe. A number of retorts, varying from five to twelve, are set together in the furnace, which has the form of an arch, the retorts resting upon the ends of the furnace and upon trans- verse brick walls built in the furnace. This arrangement of retorts and arch is called a " bed," and a number of beds are set in a row, to which the name of " bench " is given. Each bed has its own furnace for the external heating of the retorts, and the heating can either be by direct or regenerative firing, but the latter system possesses so many advantages that it is rapidly superseding the direct method. In the regenerative system producer gas, consisting of a mixture of carbon monoxide with nitrogen, is made by passing air over incandescent coke heated in a generator below the bench, whilst a small proportion of steam is added to the entering air in order to form a small proportion of water gas, and so obtain an increased heating effect. The gas so produced contains about 32 to 38 per cent, of combustible gas. The mixed gases pass into the retort furnace at a high temperature, and there meet with a second air supply in order to complete their combustion, the latter air being heated by having to pass around the exit flue, which carries off the hot products of combustion. With this system of heating the retorts a considerable saving of fuel, amounting to about one-third, is gained over the direct firing, and the retorts can be heated to a higher temperature, whilst the distribution of heat is more even. 150 LIQUID AND GASEOUS FUELS. A great improvement and saving in the retort house has been introduced during the last twenty-five years by labour- saving machinery. The charging and discharging of the retorts by hand has always been laborious and expensive, but now it is only to be found in small gas works, charging and discharging by machinery having taken its place. The machines for this purpose are driven either by com- pressed air, hydraulic, or electric power, and have effected a saving averaging fifteen pence per ton of coal carbonised. With through retorts the charging takes place from both ends, and a scoop, having a capacity of 1^ cwt., enters and discharges its contents twice from each end, and the 6 cwt. of coal is then allowed from four to six hours for the distillation. When the coal has been properly coked, a rake is made to enter the retort, and on its return with- draws the coke, several strokes of the rake being necessary to complete the operation. Such machines, however, are costly, and wear and tear, both of retorts and machinery, is high, with the result that in order to bring gravity to the assistance of the operation inclined retorts have been reverted to. These retorts are fitted in the furnace at such an angle that the class of coal employed will just slip in them, the angle varying between 28 degrees and 34 degrees. In charging an iron stop is placed in the lower mouthpiece, and the coal is charged in from above by hoppers through a shoot, and running down the slope of the retort is arrested by the barrier at the bottom, and forms an even layer of any desired depth throughout the length of the retort. When carbonisation is complete the door of the lower mouthpiece is opened, the barrier removed, and on being gently stirred with an iron rod the red-hot coke rapidly discharges itself, and its course is directed by guides to coke hoppers below the working floor. An 'idea may be obtained of the appearance of a setting THE MANUFACTUKE OF COAL GAS. 151 of these retorts from Fig. 24, which shows the drawing stage in one of the retort houses at the Granton Works at Edinburgh. 152 LIQUID AND GASEOUS FUELS. One of the earliest retorts tried by Murdoch in his experiments was set vertically in the furnace which heated it, but gave such unsatisfactory results that this form was abandoned. During the last few years the idea has again come to the front, and the disadvantages urged against it have been to a great extent overcome. Several systems of vertical retorts have been proposed, and are now under trial. With both the horizontal and sloping retorts the great drawback has always been found in the unequal heating of the gas produced from the coal, the portion near the mouthpiece escaping with but little heating, whilst from the middle of a double-ended retort or the end of a single retort the gas has been exposed to the full baking influence of the hot crown of the retort during its travel to the mouth- piece, this being one of the most prolific causes of naphthalene in the gas. With a properly arranged vertical retort, into which the coal is charged in small portions, as is done in the Settle- Padfield process, the gas is all evolved at the same rate, and not having to pass through a mass of hot material, which destroys a considerable amount of its illuminating and heating value, can escape direct from the coal, and after exposure to a minimum amount of radiant heat in the upper portion of the retort is withdrawn from the heated zone. The evil effect of overheating gas is shown by the retort carbon deposited in the crown of the horizontal retort, this carbon having been all produced at the expense of the illuminating and heating value of the gas, the hydro- carbons, which are the valuable luminants, having been broken up into carbon, which is deposited, and non- luminous hydrogen, which escapes with the gas. Dr. Bueb, who has experimented in this part of the process, gives the following figures as the heating value of gas obtained THE MANUFACTUEE OF COAL GAS. 153 from the same coal by different methods of carbonisa- tion : Vertical retorts 604 British Thermal Units per cubic foot. Inclined 584 ,, Horizontal 570 ,, 1 After leaving the retort and passing through the hydraulic main and condensers the coal gas will still retain impurities which have to be got rid of. The analysis of the gas taken at this point is approximately as follows : Hydrogen 47*40 Unsaturated hydrocarbons. . . 34*50 Saturated hydrocarbons . . . 4*75 Carbon monoxide . . . 6*50 Carbon dioxide 1*50 Nitrogen 3*00 Sulphuretted hydrogen . . . 1'50 Ammonia ...... 0*75 Cyanogen 0'07 Carbon disulphide .... 0'03 100*00 The last six of these constituents are imparities, and the gas manager as far as possible diminishes them by purification. Besides the gas the destructive distillation of the coal also yields as by-products (1) Solids, the coke and retort carbon. (2) Liquids, tar and ammoniacal liquor. The subject of coke has already been dealt with (p. 37) , and the composition of the tar has been discussed under liquid fuel (p. 98). 154 LIQUID AND GASEOUS FUELS. Of the other residues the retort carbon, which forms as a dense layer on the .overheated crown of the retort, is carbon in a very pure form, deposited from hydrocarbons decomposed by heat, and on account of its power of con- ducting electricity, it is much used for making the poles of arc lamps and the negative plates for certain forms of battery. The second liquid product of the destructive distillation of coal is the ammoniacal or gas liquor, which consists of water partly condensed from the hot gas, and partly added to wash the gas in the scrubbers. It contains as its prin- cipal constituents ammonia, partly combined with carbonic acid and sulphuretted hydrogen, forming compounds which are decomposed on boiling with evolution of ammonia gas, and partly combined with stronger acids to form compounds which require to be acted upon by a strong alkali before the ammonia contained in them can be liberated. The ammonia in the first class of compounds is technically spoken of as " free," that present in the latter as "fixed." The following analysis will give an idea of the relative quantities in which these compounds exist in the liquor : Grams per Litre. Free ammonium sulphide . . . 3*03 carbonate . . 39*16 Fixed ammonium chloride. . . 14*23 thiocyanate . . 1*80 ,, sulphate . . 0*19 ,, thiosulphate . ... 2*80 ,, ferrocyanide . . 0*41 From a scientific point of view, the term " free " is absolutely incorrect, and in using it the fact must be clearly borne in mind that in this case it merely stands for ammonia which can be liberated on simply boiling the liquor. THE MANUFACTURE OF COAL GAS. 155 The ammonia is derived from the nitrogen present in the coal combining with hydrogen during destructive distillation, the nitrogen becoming distributed amongst all three classes of products. The following table will give an approximate idea of the proportions which go to each Per cent. Nitrogen as ammonia . . . 14*50 ,, as cyanogen . . . 1*56 ,, free in gas and combined in tar 35-26 ,, remaining in coke . . 48'68 100-00 It might be imagined from the enormous solubility of ammonia in water that the coal gas could easily be freed from this compound by the merest contact with water, but in all purification dilution of the gas to be absorbed by the presence of many hundred times its volume of other gases renders this far from easy. If air containing 5 per cent, of ammonia be bubbled through water, or even strong acid, plenty will be found in the mixture after treatment, whereas if pure ammonia gas had been used, not a trace would have come through. The gas liquor produced is almost always employed in the manufacture of ammonium sulphate, by a process of great simplicity. The free ammonia is first expelled by means of steam, and when this operation is completed, the residual liquor is treated with lime and more steam, in order to expel the fixed ammonia, which, as we have seen, is the term used to denote the more stable compounds. The ammonia and other gases are passed through strong sulphuric acid in lead tanks, and the crystals of ammonium sulphate forming there as the solution becomes saturated are withdrawn from time to time by perforated copper 156 LIQUID AND GASEOUS FUELS. ladles. The process is a continuous one, the stream of gas liquor flowing through the apparatus in one direction, whilst steam passes in the contrary direction. The proportion in which the products are approximately obtained from a ton of gas coal is as follows : 10,000 cubic feet of gas = 380 Ibs. = 17*0 per cent. 10 gallons of tar 115 5'1 Gas liquor 1 177 7'9 Coke 1,568 , 70'0 2,240 100-0 The purification of the crude coal gas consists in entirely freeing it from sulphuretted hydrogen, ammonia, and carbon dioxide. Up to last year (1906) the carbon disul- phide contained in the gas also had to be abstracted as far as possible, but most of the gas companies have now been relieved from the Parliamentary necessity of doing this, and it is hoped that as a result a cheapening in the pro- duction may be possible without the sulphur being increased to a point at which it becomes detrimental to the consumer. It was thought that in relieving the companies from these onerous restrictions the maximum amount of sulphur pre- sent in the gas as carbon disulphide would not rise above 35 grains per 100 cubic feet of gas, and many gas companies have by a partial purification, or by not using excessive heats in retorting, kept down to the limit, but in other cases the amount has risen to over 51 grains, owing to the high temperatures used in carbonising the coals with the view of obtaining a larger yield of gas. The formation of the carbon disulphide vapour found in coal gas is due to the direct action of sulphur vapour upon the red-hot carbon. If powdered charcoal or coke be mixed 1 Liquor condensed from gas alone, without wash water. THE MANUFACTUKE OF COAL GAS. 157 with powdered sulphur, and the mass heated, sulphur vapour distils off, and no carbon disulphide is produced, because the sulphur has all volatilised before the carbon is in a sufficiently heated condition to bring about com- bination ; and if the sulphur in the coal were in the free state, the same thing would happen. When coal is put into the hot retort the portions in contact with the sides are rapidly raised in temperature, and the sulphur liberated by the breaking down of the iron disulphide, pyrites, or " brasses," then vaporises and combines with free hydrogen to form sulphuretted hydrogen. By the time the pyrites in the centre of the mass of coal are sufficiently heated to yield sulphur vapour the outer sur- face of the partly coked mass is at a temperature high enough to form with it small traces of carbon disulphide, and the higher the temperature used the more of the " sulphur compounds other than sulphuretted hydrogen " are produced. In the following table, obtained from experiments made by Mr. Lewis T. Wright, this is shown very clearly, the yield of gas per ton of coal being taken to give an idea of the temperature, whilst the grains per 100 cubic feet of sulphur compounds in the gas are after purification from sulphuretted hydrogen. The same coal was used in each case : Sulphur per 100 Yield of Gas. Cubic Feet. Per Ton. Grains. 6,893 13-9 8,370 19-1 9,431 26-7 10,772 36-9 11,620 . 44-1 It will be found that in the crude gas made by most gas 158 LIQUID AND GASEOUS FUELS. companies the sulphur compounds other than sulphuretted hydrogen will average from 30 to 40 grains of sulphur per 100 cubic feet. In considering the effect of these sulphur compounds in the products of combustion it must be borne in mind that when coal gas is burnt the sulphur is liberated in the form of sulphur dioxide, and many most misleading statements and ideas have gained ground as to the quantity of this which becomes converted into sulphuric acid in the atmo- sphere. The experiments of Professor Harold B. Dixon and others all prove that when traces of sulphur dioxide, as minute in quantity as those which are given off in the combustion of gas, are present in the air, they show no tendency to oxidise to sulphuric acid, even though the air is highly charged with moisture, unless the temperature fall to such a point that water is deposited from it. This water then takes up the sulphur dioxide, which slowly becomes oxidised to sulphuric acid. For this reason it is perfectly possible to find traces of sulphuric acid and sul- phates upon window panes where the cold air from outside has caused moisture to condense on the windows, and the same action will take place where ammonia or other alka- line substances present in the air or dust can fix the sulphurous acid. But it is manifestly incorrect to suppose that this action goes on unless the temperature of the room has fallen to the condensing point of the water vapour, for, if this did take place, even with a highly purified gas, there is not a sitting room in which the draperies would not become rotted in a very short space of time, as the smallest deposit of sulphuric acid, no matter how dilute, would by slow and cumulative action become sufficiently strong to burn away the fabric. The test of time has shown the fallacy of any such injurious action. In order to prove the deleterious effects of this hypo- thetical formation of sulphuric acid, certain observers have THE MANUFACTUBE OF COAL GAS. 159 brought forward many experiments to show that, in passing the air through absorbing solutions, sulphates could be detected in them in small and varying quantities. This, however, does not prove that sulphates were present in the air, as directly the sulphur dioxide is absorbed by the liquid the oxidation to sulphuric acid takes place with considerable rapidity. It is this that has given rise to wrong deductions from the observed facts of sulphuric acid, either free or in combination, being found in wetted fabrics or on moistened plates or liquid absorbents exposed to the air of rooms in which gas has been burnt, also on lamp glasses and in ventilating tubes, especially in towns where no limit is placed on the amount of sulphur present in the gas. Exhaustive experiments made by Dr. Eideal and Dr. Otto Hehner also showed conclusively that the alleged damage due to such quantities as 30 to 40 grains of sulphur per 100 cubic feet of gas was entirely mythical. In purifying the gas, the crude gas after leaving the surface condensers is sucked forward by the exhauster or pump for pulling the gas away from the retorts and forcing it through the purifiers to the gas holder. These exhausters are of various kinds, but the most usual form is the rotary, in which a revolving fan rotates excentrically in a cylindrical drum. The exhauster is driven by a steam or gas engine, and is kept so regulated as to maintain a slight vacuum in the hydraulic main, the vacuum not exceeding the extent of the seal given to the dip pipes, otherwise air would be drawn into the retorts and mixed with the gas when the retorts were open. From the exhauster the gas is driven forward through the scrubbers, which are tall towers packed with wooden boards, coke, or brushwood, down which water percolates from a supply on top of the tower, whilst the gas passes upwards. Two or more scrubbers are generally used in series, the first being fed with gas liquor, and the last with 160 LIQUID AND GASEOUS FUELS. clean water. Instead of " scrubbing " the gas some works employ " washers," which are vessels in which the gas is broken up into fine streams and caused to bubble through water, or else the apparatus is half filled with water, and the rotation of a central shaft, fitted with a number of metal discs, continually presents freshly wetted surfaces to the streams of gas. The operation of scrubbing or washing the gas serves to extract from it practically all the ammonia remaining in it after passing the surface condensers ; the gas still contains carbon dioxide and sulphur in the form of sulphuretted hydrogen and carbon disulphide, and to remove these the gas is forced through the "purifiers," a series of large rectangular boxes with movable lids rendered gas-tight by a seal, and generally eight in number, and charged some with slaked lime and others with ferric hydroxide, the latter in the form of Irish bog ore. The iron removes the sulphuretted hydrogen and when exhausted can be revivi- fied by exposure to the air ; the lime removes the carbon dioxide and some sulphuretted hydrogen. In working, the purifying boxes are arranged to work in couples; the first couple remove the carbon dioxide by means of slaked lime, the second couple contain oxide of iron for extracting the bulk of the sulphuretted hydrogen ; in the third couple the bulk of the carbon disulphide is removed with calcium hydrosulphide, whilst the fourth couple act as the final purifying box for the elimination of the last traces of sulphuretted hydrogen. The purifiers are so arranged that they can be worked in five different ways, and allow of any of them being cut out for recharging, etc. The most generally accepted theory as to the chemical action which leads to the purification of the gas in this part of the process is that, as the gases pass through the lime, the latter first takes up carbon dioxide, becoming calcium THE MANUFACTUKE OF COAL GAS. 161 carbonate. Until nearly the whole of the carbon dioxide is removed from the gas the sulphuretted hydrogen is but little acted upon, as the carbon dioxide has under these conditions a greater affinity for lime than the sulphuretted hydrogen ; and if sulphide of lime were formed, carbon dioxide and moisture would again decompose it. As soon as the carbon dioxide is all taken up the lime begins to act upon the sulphuretted hydrogen and absorbs it, forming calcium sulphide and other more complex bodies, and liberating moisture ; and the sulphides so produced have the power of taking up the sulphur compounds other than sulphuretted hydrogen. In this way they are reduced in quantity, and the sulphuretted hydrogen is almost entirely eliminated; to get rid of the last trace of the latter the gas is generally passed through hydrated oxide of iron. The compounds which sulphur forms with lime, and which act in absorbing carbon disulphide, are not thoroughly understood, and there is no doubt that there are many factors in purification which are at present out- side our knowledge, one of the most important of these being the effect of change of temperature and moisture upon the compounds formed by lime, sulphuretted hydrogen, and carbon disulphide. In lime purification of the above character there is very little difficulty in keeping the sulphur down to the pre- scribed limits under normal conditions, especially in the summer, when reduced output allows of a slower flow of the gas through the purifying material ; but in the winter the sulphur compounds are liable to sudden rise in quantity, due to causes which, being at present but little understood, are practically beyond the gas manager's control. These sudden rises are more frequent when the limit aimed at is, say, 17 grains than when it is 22 grains. These unaccountable variations and the nuisance caused to the neighbourhood of the gas works by the removal of L.G.F. M 162 LIQUID AND GASEOUS FUELS. the spent lime made the abolition of the limit for sulphur compounds other than sulphuretted hydrogen a very welcome relief to the gas manager, and at the present time the dry purification of the gas generally consists in passing the crude gas, after leaving the scrubbers, through a sufficient number of purifiers containing slaked lime, to remove all the carbon dioxide and some of the sulphuretted hydrogen, and then through oxide purifiers to remove the remainder of the sulphuretted hydrogen. The lime used for purification is prepared in large quantities by burning chalk or limestone, both of them impure forms of calcium carbonate, in egg-shaped kilns. The limestone is brought to the mouth of the kiln in waggons in fair sized lumps. In the older kilns large pieces were used to form an arch over the fire grate at the bottom, the rest of the kiln being filled up with the smaller pieces mixed with coal or some other combustible material. The fire is then started and kept going for about two days, after which time the lime is allowed to cool, and is removed. In the modern continuous process, however, the limestone is renewed from the top, whilst the burnt lime is drawn from the bottom ; lime and coal in alternate waggon loads being supplied at the top as fast as the burnt lime is removed from the base. By this method of working fuel is economised, and the smoke, so offensive in the old forms of kiln, is greatly reduced. About one bushel of coal is required for the manufacture of six bushels of lime, although some limestones require less. If a large amount of clay is present the lime fuses very readily, and great care must be exercised in order to keep the temperature below the melting point, otherwise a slag is formed. When lime is brought in contact with water great heat is evolved, and some of the water enters into combination with the lime to form calcium hydroxide or slaked lime. This calcium hydroxide is a white amorphous powder, THE MANUFACTUBE OF COAL GAS. 163 sparingly soluble in water, the solution being known as lime water. This has an alkaline reaction and absorbs carbon dioxide from the air, in like manner to caustic soda. Calcium hydroxide is decomposed at a red heat into water and calcium oxide. In oxide purification Irish bog ore is generally employed, which contains as a rule about 32 per cent, of hydrated oxide of iron, but of this only about two-thirds is in a condition in which it can actively absorb sulphuretted hydrogen. The bog ore also contains a large percentage of moisture, sometimes amounting to nearly half its weight, but for successful purification it should not contain more than about 25 per cent, of moisture, as, when the quantity rises much above this it becomes less sensitive, whilst if too dry it gets dusty and works through the grids on which it is placed on the purifiers, and increases the resistance to the passage of the gas. When it is just damp enough not to pass through the grids it is in the best condition for working. As the crude coal gas passes through the hydrated oxide sulphuretted hydrogen is arrested, and forms with the iron two sulphides, ferrous and ferric sulphide, at the same time liberating water. When the material ceases to absorb sulphuretted hydrogen, its original power can be restored by exposing it freely to the action of the air, when the sulphides deposit all their sulphur in the free state, and the iron, taking oxygen from the atmosphere, is rapidly converted once more into oxide of iron. This process of oxidation is called " revivification," and it is effected by simply spreading the foul oxide on the floor, when it becomes warm and gradually changes from black to its original reddish-brown colour. The material can in this way be revivified about sixteen times, after which the accumulation of sulphur interferes with the action, and the mixture of oxide with about 55 per cent, of free sulphur is then sold to the sulphuric acid manufacturers. M 2 164 LIQUID AND GASEOUS FUELS. If traces of ammonia and cyanogen find their way into the purifiers, ferrocyanide of iron is formed, which greatly interferes with its effect, and prevents its subsequent revivification, but this trouble rarely arises when lime purifiers are used before the oxide boxes. After purification the gas is stored in the gas holder, and is ready for distribution. Gas so made is not a definite compound but a mechanical mixture of several gases, some of which are reduced to the lowest limit in order to develop as fully as possible the light-giving properties of the most important constituents of the gas. The following analysis gives a fair idea of the composition of an average sample of gas made from coal and without enrichment : Hydrogen . . . ' . . 52'22 Unsaturated hydrocarbons . . 3'47 Saturated hydrocarbons *. . 34*76 Carbon monoxide . . . 4*23 Carbon dioxide . . . . 0'60 Nitrogen ... . . . 4*23 Oxygen . . 0'49 100-00 These constituents may be divided into three classes : (a) light-yielding hydrocarbons, (b) combustible diluents, and (c) impurities. The hydrocarbons, upon which the luminosity of the flame entirely depends, are divided in the analysis into two groups, saturated and unsaturated, according to their behaviour with a solution of bromine in potassium bromide, which has the power of absorbing those termed "unsatu- rated " but not affecting in diffused daylight the gaseous members of the saturated series of hydrocarbons. They THE MANUFACTURE OF COAL GAS, 165 may be separated in the same way by concentrated sulphuric acid, which has an absorbent effect on the one class, and not on the other. The chief unsaturated hydrocarbons present in coal gas are: Ethylene C 2 H 4 Butylene C 4 H 8 Acetylene ..... Benzene ..... Naphthalene Ci H 8 whilst the saturated carbons consist chiefly of Methane CH 4 Ethane C 2 H 6 The light-giving power of coal gas is undoubtedly entirely due to the hydrocarbons, and the idea held up to sixteen years ago was that the illuminating value depended upon the amount of ethylene present. This, however, is manifestly incorrect, as, if it were true, 4 per cent, of ethylene mixed with 96 per cent, of hydrogen or other combustible diluent should give a 16 to 17-candle gas, whereas a mixture of 10 per cent, of ethylene and 90 per cent, of hydrogen is devoid of luminosity. In 1876 Berthelot came to the conclusion that the illuminating value of the Paris coal gas was almost entirely due to benzene vapour. But here again another mistaken idea arose, owing to a faulty method of estimat- ing the benzene ; and there is no doubt but that methane is certainly one of the most important of the hydro- carbons present, when the gas is burnt in such a way as to evolve from it the proper illuminating power, whilst the benzene vapour, small as the quantity is, comes next in importance, and the ethylene last. It is the combined action of the hydrocarbons which gives the effect, not any one of them acting alone. 166 LIQUID AND GASEOUS FUELS. The illuminating power of a gas made as described from an ordinary gas coal will have a value of from 14 to 15 candles, and this unsophisticated coal gas undoubtedly forms the best supply a town can have. In most cities the Parliamentary requirements, which at one time were mostly that the gas should have an illuminating value of 16 candles upwards, have, owing to the introduction of the incandescent mantle, been reduced to a candle power that can be obtained from the coal gas per se. There still remain, however, towns where the conservative tendency has been sufficiently strong to keep up the idea of high candle power, and under these conditions the gas, as obtained from the coal, has usually to undergo a process called enrichment. This enrichment may be done in several ways : (1) by the admixture of a certain percentage of cannel coal with the original gas coal ; (2) by carburetting the coal gas with the vapours of volatile hydrocarbons ; (3) by oil gas ; (4) by mixing the coal gas with carburetted water gas. It is the custom to call all hard, homogeneous, non- laminated coal <; cannel," and consequently the term applies to coals of very different gas-making qualities. But inasmuch as in practice the worst 'of the cannel coals yields gas having a higher illuminating value than ordinary coal gas, there is some justification in the application of the name to all material of this distinctive appearance. The gas-making value of these hard, homogeneous coals cannot be judged by their outside appearance, as the finest, such as the Australian shale and the Boghead, are brown in colour, whilst others are either dull black or bright black. Good cannel coal gives a large quantity of gas having a high illuminating value, but any considerable admixture with the ordinary coal lowers the quality of the coke, and also to a certain extent alters the composition of the tar produced. During the past twent} 7 years cannel coal has THE MANUFACTUKE OP COAL GAS. 167 so increased in price that the gas managers of this country are practically forced to adopt some method of enrich- ment which, whilst satisfying their requirements, is less expensive. The enrichment of coal gas and other diluents with the vapours of volatile hydrocarbons has been tried from a very early period of the history of coal gas, and the late Dr. Letheby made many experiments upon this method of carburetting gas. There is no doubt that by using an extremely volatile hydrocarbon of definite composition, such as pentane or benzol, it is quite possible to enrich gas to a very great extent, whilst if the gas takes up the hydrocarbon vapour at a temperature below that which it will afterwards encounter, there is no fear of it again depositing. But if gasoline (such as is obtained as the first distillate from American petroleum) is used, the hydro- carbon, being a mixture of many compounds, will yield up its more volatile portions first and gradually lose its enriching power ; whilst if the vapour be driven off from the hydrocarbon by heat, great care must be taken to supply only a very small percentage of the vapour, otherwise it will again be deposited in the gas holder and pipes. The amount of volatile hydrocarbon which will remain as a gas without depositing is purely a question of vapour tension. As this increases with rise of temperature, and falls with diminution of temperature, it is manifest that for a gas to retain its illuminating value it must be a long way from its point of saturation. Gas engineers have got into the habit of speaking of the " carrying power " of various gases, and of looking upon one gas as a good carrier of vapours and another gas as a bad one ; but this is an entire mistake, as a volatile liquid will evaporate into other gases at the same rate, and practically without reference to the properties of the gas. This method of carburetting is very largely used in the 168 LIQUID AND GASEOUS FUELS. smaller towns, and is very convenient, as the gas manager can rapidly and easily bring up the illuminating value of a poor make of coal gas by carburetting it at the outlet of the holder with the necessary quantity of benzol or gasoline vapour. An apparatus designed by Messrs. Maxim and Clark, and largely used for this purpose, is so arranged as to supply each portion of the gas passing through it with its own particular share of hydrocarbon, and does not allow the selective absorption by the gas of the more volatile portions. That oils when heated were decomposed into gases having a far greater illuminating power than coal gas was a fact known even before the introduction of coal gas, and when the use of gas became general, many attempts were made to produce it from liquid hydrocarbons instead of coal. This, however, was abandoned, owing to the price of oil in this country being too high for it to compete with coal, so that oil gas has in the past been restricted to the prepara- tion of gas for compression, as in the Pintsch and other processes, and for lighting up country mansions and public institutions, where the consumption was insufficient to warrant the erection of a coal gas works, but it is also used to a limited extent for the enrichment of coal gas. A large number of various forms- of apparatus has been devised from time to time, many of which have been designed without the slightest knowledge of the changes to which the hydrocarbons are subjected on exposure to high temperatures. The following may be considered as types of the best processes. The Paterson plant consists of a horizontal cylindrical retort built into a furnace containing an oven or flue space, in which the retort is placed. The oil to be decomposed is led to the back of the retort from the oil tank by two straight horizontal tubes, extending from the front nearly to the back. The oil, in flowing along 'these pipes, is partly converted into vapour, and is THE MANUFACTUKE OP COAL GAS. 169 further decomposed after leaving the pipes by passing from the back of the retort to the front, where the outlet tube is situated. The supply of oil is regulated by a tap near the oil tank, and by a separate tap' for each retort. The gas after formation is led through atmospheric condensers, and is then stored in the gasholder. In selecting the material to be employed in an apparatus of this sort, two points must be considered the cost of the crude material, and ease of working. As the result of many experiments it has been found that the best results were obtained with a temperature of 900 F., and that the most suitable oil was Eussian " Solar Distillate," obtained by subjecting the residuum of the Kussian Baku oils, after the lighter kerosenes have been driven off, to further distilla- tion. Nearly as good as this, however, are the blue and green shale oils. The best results obtained from these oils working at a temperature of 900 C. were 98 cubic feet of 50-candle gas per gallon, equivalent to 98 candles per gallon of oil ; besides which there was about 20 per cent. of residuals, which contained a certain amount of benzene as well as paraffins and olefines of lower boiling points. Attempts have been made from time to time to produce oil gas in such a way that there shall be few or no residuals of a liquid nature, and that the whole of the oil shall be converted into gas, or only leave a solid residue in the retort. Hillary, in 1846, was the first to attempt this by placing condenser tubes above his retorts, so that any liquid that condensed ran back into the retort, and became further carbonised ; the result being the production of coke and gas only. His idea was revived and improved by the late Mr. W. Young in his plant for the manufacture of oil gas. The principle of Young's process is dependent upon the washing of the oil gas, retorted at a moderate temperature, by means of the oil which has to undergo decomposition, 170 LIQUID AND GASEOUS FUELS. by which it is freed from all condensable vapours, and only permanent gases are allowed to escape to the purifiers. No loss takes place, as the olefines and other fixed gases which are absorbed to a considerable extent by the oil during the washing of the gas, are again driven out by the action of heat during the retorting. The apparatus consists of two cast iron retorts about 10 feet in length, and set so as to have a downward slope to the back. They are fitted with doors and ascension pipes in the usual way, but in each door there is a small pet-cock, by opening which the colour of the gas can be seen. This should be of the palest lemon, as when any darker colour or approach to brown is produced, decompositions of tar and other troubles com- mence. The oil is admitted by small cocks about 2 feet up the ascension pipe, and falls down through the ascending gas on to steel plates, which extend 3 feet into the retort so as, in a great measure, to prevent the direct impact of the oil on to the bottom of the retort. The temperature is kept about 800 to 900 C. After passing up the ascension pipes the gas flows to the hydraulic main, situated at the back of the bench of retorts, then goes through a coil of horizontal condensing pipes, and on to the scrubber. The oil cistern is situated at the top of the scrubber, and the supply pipe from it is so arranged that the oil can be made to flow into one or all of the sections, as in cold weather the gas needs less scrubbing than in hot. Having passed through the scrubber, the oil is led along the bottom of the horizontal condensers, and into the hydraulic main. It then passes into a small cistern containing a float, which is in connection with an indicator close by the oil-feed taps, so that the supply from the cistern can be regulated in such a way as to keep the flow constant. In this way the oil passing to the retort is always going in an opposite direction to the gas. The oil used is " blue oil," having on an average a specific gravity of about '850. Each retort MANUFACTUEE Otf COAL GAB. 171 makes 500 cubic feet of gas per hour, and 5J cwt. of a very dense graphitic coke is left in the retort for each ton of oil decomposed. The coke collects near the back of the retort and can readily be removed. It forms with a horizontal surface, which seems to point to its having flowed there as pitch and been carbonised, or else that carbon deposited in the ascension pipe and front of the retort has been washed there by the oil. The gas, when tested on the photometer in burners most suitable for its combustion, gives an average of 60-candle power : The composition of the gases made by these two processes are shown in the following analyses, the gas made by the Paterson process being a 50-candle power gas, and the Young gas 60-candle power : Paterson. Young. Unsaturated hydrocarbons . 33*16 43*83 Saturated hydrocarbons . 45'15 36*30 Hydrogen .... 19*65 16*85 Carbon dioxide . . . 0*50 0*63 Carbon monoxide . . 0*50 0*00 Oxygen . ' . . . 0*60 1*14 Nitrogen .... 0*44 1*25 100*00 100*00 The chief objections to oil gas for enriching coal gas are, first, that its manufacture is a slow process, requiring almost as much plant as coal gas ; and, secondly, that although it can be made to mix perfectly with coal gas and water gas on a small scale, yet on a large scale this is a source of difficulty, in spite of the law of diffusion, as the gases form layers in the holder which give rise to wide variations in the illuminating power during consump- tion. The belief has arisen amongst many gas managers 172 LIQUID AND GASEOUS FUELS. that oil gas is not so permanent as coal gas, but this is not the case, as a well-made oil gas depends less upon con- densable vapours for its light-giving power than coal gas, so that there will not be so great a loss of illuminating power when oil gas is exposed to cold or surface friction. In large works the most widely adopted method of enrichment is to mix the poor coal gas with carburetted water gas, a mixture of water gas with oil gas, and as this can readily be made of any desired value, the amount mixed in with the coal gas can be made to raise its candle power to the desired degree. The preparation of carburetted water gas will be found fully described and discussed at page 238, and also the so-called auto-carburetting of coal gas now largely adopted on the Continent, in which the illuminating gas is washed out of the carbonising retorts by a stream of water gas, so preventing the destruction of valuable illuminants by overbaking in the retort. An entirely new departure in the manufacture of coal gas has lately been introduced in America, in which the coal undergoes destructive distillation in by-product coke ovens instead of retorts, the advantages claimed being that in the working day eight times as much coal can be car- bonised in an oven as before was possible in a retort, the process yielding good metallurgical coke instead of gas coke. The gas from the ovens is collected in two portions ; that which comes over first is of good illuminating value and, after purification, is distributed as a town supply, whilst the gas evolved during the latter half of the carbonisation is poor in illuminants and is used for heating the ovens. The gas so available for illuminating purposes only amounts to about 4,000 cubic feet per ton, as against 11,000 obtained by the ordinary retorting, and the economic value of such a process would be entirely dependent upon the price obtainable for the coke and other by-products. THE MANUFACTUEE OF COAL GAS. 173 The use of coal gas for illuminating and heating purposes necessitates the consideration of the structure and properties of flame. When a solid which is incapable of being volatilised burns under ordinary conditions, no flame is produced, but when a volatile solid, a vapour, or a gas undergoes com- bustion in air, flame is formed. Flame may therefore be looked upon as the com- bustion of gaseous matter, and as combustion is merely extremely vigorous chemical combination, it is manifest that the flame can only exist where the coal gas and air meet. If a jet of hydrogen be ignited in air, the conical flame which* is produced consists of a hollow sheath of burning gas, surrounding an inner core of unburnt hydrogen, and flames formed by a simple gas which burns without decomposition and only forms one product from its combustion, all have this simple structure, the sheath of flame being produced where the combining gases meet. The fact that such a flame is hollow can be at once proved by inserting a tube into the hollow cone, when some of the unburnt gas will pass through it and can be burnt at the other end. Compound gases, which undergo decomposition during combustion, or gaseous mixtures, give flames with a rather more complex structure, and it is usual to describe the flame of coal gas or of a candle as consisting of three zones. The first of these, A, is the inner non-luminous zone (Fig 25), in which no combustion is taking place, but where some very important chemical changes are going on ; the second, B, is the zone of luminosity upon which the light-giving power of the flame depends, whilst the third, C, is a thin, non- luminous envelope which entirely surrounds the flame, and which is clearly seen if a small piece of card be held in front of the flame so as to shield the eye from the light emitted 174 LIQUID AND GASEOUS FUELS. by it, and only to leave the edge visible. This latter zone may again be divided into two parts a small blue portion at the base of the flame and the envelope of the upper part of the flame. When a candle is lighted the burning wick melts the wax or material of the candle in contact with it, and then by capillarity sucks up the liquid, and the heat of the burning wick in the first instance, and afterwards the heat of the flame, convert the hydrocarbons into a mixture of gases and vapours of much the same character as a rich coal gas. In each case, therefore, the gases flowing from the wick or the jet contain unsaturated hydrocarbons, methane, and hydrogen as their chief constituents. These gases when ignited burn, but the lighter they are the more rapidly will they diffuse and so reach the outside of the flame ; the result of this is that the hydrogen and the methane are the first to burn, and the heavier hydrocarbons flowing upwards between the walls of flame become highly heated and converted into a mixture of acetylene and methane. Taking ethylene as the type of the unsaturated hydro- carbons in the gas, the change would be represented by- FIG. 25. Candle flame. Ethylene. 3 (C 2 H 4 ) Acetylene. 2 (C 2 H 2 ) Methane. 2 (CH 4 ) and at the top of the inner non-luminous zone 80 per cent, of the unsaturated hydrocarbons present are found to be acetylene. The temperature of the flame rapidly rises the higher the point, and at the spot where the luminosity of the flame commences the temperature is over 1,000 C., and THE MANUFACTURE OF COAL GAS. 175 this causes sudden and extremely rapid decomposition of the acetylene into its constituents- Acetylene. Hydrogen. Carbon. CJH.2 = H 2 + C 2 Acetylene is one of those compounds termed " endothermic " from the fact that heat is absorbed during their formation, and at the moment of decomposition this heat is again liberated, and having no time to dissipate itself amongst the other gases present, heats up the carbon particles to a temperature far higher than the average temperature of the flame, causing them to become incandescent and so render- ing the flame luminous, the incandescence of these solid carbon particles being further aided by the temperature of the flame and by their own combustion, partly by the oxygen of the air and partly by the action of water vapour and carbon dioxide upon them, Carbon Oxygen Carbon monoxide (a) C + CO Carbon Water vapour Carbon monoxide Hydrogen (6) C + H 2 CO + H 2 Carbon Carbon dioxide Carbon monoxide (c) C + C0 2 2 CO and it is the combustion of the carbon monoxide and hydrogen which gives the outer non-luminous envelope to the flame. The small blue portion of the outer envelope at the base of the flame is caused by the rapid inrush of air, the nitrogen so diluting the hydrocarbon molecules at that point that they are burnt up without being first decomposed, and there being therefore no separation of carbon there is no luminosity, and the same blue colour may be observed when 176 LIQUID AND GASEOUS FUELS. a gas flame is rendered non-luminous by dilution with nitrogen or carbon dioxide. This explanation holds good for all luminous hydrocarbon flames, but the combustion of many other substances emits light, such as phosphorus, magnesium, zinc, and arsenic, but in these cases the products of combustion are solid, and in the finely divided condition in which they are formed are rendered incandescent, and, in the case of phosphorus and arsenic, are again volatilised by the heat of their own formation. Flames which can only contain gaseous matter can be rendered incandescent if a sufficiently high temperature can be obtained : for instance, if hydrogen be burnt in an atmosphere of oxygen under a pressure of several atmo- spheres, light is developed, but the temperature of such a flame is many times hotter than an ordinary hydrogen flame burning in oxygen, as pressure acts on flame in the same way as on a gas, and at a pressure of several atmo- spheres several times the amount of hydrogen and oxygen would be consumed as would be the case under ordinary conditions of temperature and pressure. The luminosity of flame may therefore be stated to be due either to the presence of incandescent solid particles or at a far higher temperature to incandescent gases. As may easily be imagined, the first burner used for the consumption of coal gas was the end of the tube from which it was issuing, but Murdoch soon saw that the consumption was far too high and the illuminating value far too low to make this a successful method of burning his new illuminant. Casting about to find a method of retarding the flow he fitted an old thimble over the end of the pipe, and this happening to have several pinholes in the crown, he lighted the gas issuing from them to prevent it escaping into the room. He at once found that several small jets gave a far better light than one big flame, besides causing considerable THE MANUFACTUBE OP COAL GAS. 177 economy in the consumption of gas. But as his experiments progressed the form of his burner was modified, until in 1807, when fitting up the works of Messrs. Phillips and Lee, in Manchester, he used two forms of burner, the one a rough argand, and the other " a small curved tube with a conical end having three circular apertures or perforations about gVth of an inch in diameter (one at the point of the FIG. 26. Cockspur and cockscomb burners. cone and two lateral ones) through which the gas issuing formed three distinct divergent jets of flame, somewhat like a fleur de lys." The latter burner, which from the shape of the jet received the name of the "cockspur" burner, gave a light equal to 2J mould candles of six to the pound, whilst the argands used developed a light equal to 4 candles of the same description. The argand burner had been in use for the consumption of oils for some years before the introduction of coal gas, and in its early form it consisted simply of two concentric tubes L.G.F. N 178 LIQUID AND GASEOUS FUELS. fixed at the required distance apart, the coal gas being fed in between them. Soon however the idea arose of closing the open circular slot by a metal ring pierced with holes, so as to give a circle of small jets ; and even prior to 1816 the main principles of our present argands were found to be in the burners in use. It was about 1816 also that the cockspur burner became converted into the " cockscomb," and then the "batswing," thus marking a distinct advance- in the method of burning the gas, as by spreading the flame out into a thin sheet, instead of having it in a solid mass as in the jet burner, the air was more readily and uniformly supplied to the burning gas, and the higher temperature of the flame, due to the more perfect combustion, increased the light-giving power of the burner to nearly that of the argands then in use. In 1820, Nielson, of Glasgow, whose name will always be remembered as the discoverer of the hot air blast in iron smelting, found that by allowing two flames to impinge upon one another an increase in luminosity was obtained ; and after several preliminary stages the union jet or " fishtail " burner was produced, in which two holes, bored at the necessary angle in the same nipple, caused two jets of gas to impinge upon each other so that they mutually splayed themselves out into a flat flame, the same result being also secured in the chisel-head burner shown in Fig. 27. The batswing flame was a very wide one, of but little height, whilst the fishtail was much higher and more narrow. Although the service yielded by the fishtail for each foot of gas consumed was no better than, even if it was as good as, that given by the batswing, yet its shape, which made it less affected by draughts and enabled a globe to be used with it, ensured a greater meed of success for it than the batswing burner had secured. The next twenty years was a period of the gradual improvement and perfecting of the argand and flat flame THE MANUFACTURE OF COAL GAS. 179 burners, the influence of pressure and regulation of the flow of gas to the burner being gradually realised and arranged for, whilst other structural improvements were introduced. On May 20th, 1853, Dr. Frankland, whilst giving one of the Friday lectures at the Koyal Institution, showed, but did not fully describe, an argand burner in which the idea FIG. 27. Old flat flame burner. was first adopted of utilising the heat, which otherwise would have been lost, to raise the temperature of the air supply. This burner was afterwards described in " Ure's Dictionary," the article, however, not being published till a year or so after it had been written. The burner con- sisted of an ordinary argand, but in addition to the usual chimney it had a second external one, which extended some distance below the first, and was closed at the bottom by a glass plate, fitted air-tight to the pillar carrying the burner, so that the air needed to support the combustion of N 2 180 LIQUID AND GASEOUS FUELS. the gas had to pass down the annular space between the chimneys, and in its passage became highly heated, partly by contact with the hot inner glass and partly by radia- tion. The temperature of the air finally entering the burner Dr. Frankland considered to be about 500 F. In 1854 the Eev. W. E. Bowditch brought out a burner identical in nearly every respect with the one just described, and as this was brought prominently forward, it attracted con- siderable attention, with the result that the inception of the regenerative burner has been generally ascribed to Bowditch, whereas that honour is undoubtedly due to Frankland. In 1879 Friedrich Siemens, of Dresden, brought out his large burner, which, although one of the most effective, was also one of the most unsightly, from its big overhead feed pipe. This burner was really first made for heating purposes, but the light it gave was so far ahead of any effect which had been obtained up to that time that with certain modifications it was adopted for lighting purposes. During the eighties the regenerative burner was perfected and adapted for general use, and such overhead burners as the Wenham, Cromartie, etc., gave not only an excellent duty per cubic foot of gas consumed, but could also be made powerful engines of ventilation, as, fitted to flues in the ceiling space, they could be made to withdraw an enormous volume of vitiated air from the upper part of the room. The discovery by Dr. Auer von Welsbach in 1885 of the method of making the incandescent gas mantle, and the further discovery in 1892 of the use of the oxide of thorium with a trace of oxide of cerium for its composition, gave a method for developing light from coal gas which has so far surpassed any other way of burning it that the old forms of burner are now but little used. This system consists of consuming the gas in an atmospheric or bunsen burner, so THE MANUFACTUEE OF COAL GAS. 181 as to obtain a non-luminous but very hot flame, and then utilising this to raise to incandescence a mantle made of Thorium oxide 99 Cerium oxide . 1 100 a mixture having a far higher power of light emissivity than carbon particles. The mantles are made by saturating a cotton fabric or stocking with a solution of the nitrates of the two metals mixed in the right proportions. The fabrics are then shaped and dried, and an asbestos loop having been sewn into the top, are burnt in a bun sen flame, the organic matter of the original fabric burning away and the nitrates being converted into oxides, which retain the shape of the original structure. The oxide mantle is then shaped and hardened in a blow-pipe flame, and is rendered sufficiently strong for handling and distribution by dipping it in a solution of collodion. When fixed on the burner the collodion is burnt off, and the mantle of oxides, which just fits the outer zone of the bunsen flame, is heated to high incandescence and emits ten times the light that the same amount of gas burnt in a flat flame burner would have given. CHAPTEE VII. THE USE OF COAL GAS FOR HEATING AND POWER. Calorific value of coal gas and its constituents The relation between illuminating power and thermal value Effect of enrichment on calorific value The inception of the atmospheric burner Early forms of burner The cause of non-luminosity in the " Bunsen " flame Ratio of air to gas in the flame Effect of diluents on the flame Effect of the specific heat of gases in the flame The structure of the atmospheric burner flame, and the chemical changes taking place The temperature of the flame The Le Chatelier thermo-couple and its use Gas stoves and their relative efficiency as compared with coal Methods of heating, and the effect on the air of rooms Regenerative gas stoves Flueless stoves The necessity of leading away the products of combustion Coal gas in the internal combustion motor. A GOOD example of the confusion created in the lay mind by scientific utterances is to be found in the calorific value of hydrogen. A pound of hydrogen when burnt evolves more heat than a pound of any other known substance ; and as a rule this has given rise to the impression that this gas must be the most valuable of all gaseous fuels. The fact is overlooked, however, that it is also the lightest known element, and that it takes no less than 178'8 cubic feet to weigh a pound, so that the heat value of the cubic foot is only 325 B.T.IL gross, whilst the fact that water is the only product of its combustion lowers the net value to 272 B.T.U., a lower duty even than that of the product of the incomplete combustion of carbon (carbon monoxide), which yields 330 B.T.U. both net and gross, there being no water to vapourise, and no heat therefore rendered latent during its combustion. THE USB OF COAL GAS FOR HEATING AND POWER. 183 Taking the main constituents of coal gas and tabulating them according to their calorific value taken in round numbers, we may state them as follows : Calories per cubic foot. B.T.U. per cubic foot. Gross. Net. Gross. Net. Benzene vapour . .. 938-9 902-5 3,718 3,574 Ethylene 404-8 381-3 1,603 1,510 Methane 258-6 232-0 1,024 919 Carbon monoxide 83-3 83-3 330 330 Hydrogen . . . 82-0 68-7 325 272 Taking now an ordinary sample of 16-candle-power coal gas as supplied to London in the city area, and applying these values to its combustible constituents, we have Hydrogen Methane Ethylene Benzene Carbon monoxide 54 per cent. X 325 = 17,550 34 3 1 6 X 1024 = 34,816 X 1603 = 4,809 X 3718 == 3,718 X 330=- 1,980 62,873 or 628*73 B.T.U. gross for a cubic foot ; whilst if the calorific value be tested direct in the calorimeter, we obtain, as the value of the mean of ten determinations by the Junkers calorimeter, 157 calories per cubic foot, or 157 x 3-968 = 623 B.T.U. For every reason the experimental determination of the calorific value of a gas is the most satisfactory, the easiest, and the most reliable method, as calculation necessitates an accurate analysis of the gas, which is very difficult to obtain, and which would not only make the calculation of the calorific value a most laborious operation but would also leave loopholes for so many sources of error that the. 184 LIQUID AND GASEOUS FUELS. results would be open to grave doubts. Given a good analysis, however, calculation enables one to obtain not only the calorific value under conditions where direct deter- mination would be impossible, but also affords an insight into the cause of any abnormal variation in thermal value which might otherwise be difficult to trace. Taking the calculation of the calorific value just given it is clear that more than two-thirds of its heating power are due to the hydrocarbons present in it, and that methane is the factor which makes a good coal gas so superior to all other forms of gaseous fuel with the exception of natural gas. The calorific value of a coal gas varies enormously with its composition, and the saturated and unsaturated hydro- carbons, which are all-important in endowing the gas with illuminating value, play an equally important part in its heating value. As the illuminating value of a town supply is generally a well-known factor it would be a great con- venience to the user of gas for fuel purposes if even an approximate relation between heating and illuminating value could be established. The photometric determination of illuminating values, however, has, until lately, been rendered absolutely fallacious for all qualities of gas, except just about the 16 candle point, by the method employed of burning the gas in a standard London argand at a fixed rate of flow, 5 cubic feet per hour, which properly develops the light from a 16 candle gas, but does a grave injustice to gas of a higher or lower value. Within the last few years, however, a more reasonable, although far from perfect, method has been introduced, and a rough approximation may be arrived at. It is clear that it is not possible to take a calorific value as indicative of any particular illuminating value, or say that such a candle power gas will have a definite calorific value, because a 16 candle gas may be anything between 575 and 650 B.T.U. gross, and will vary between such limits British Thermal Units. British Thermal Units, 186 LIQUID AND GASEOUS FUELS. according to the kind of coal used for its production, or whether it is a pure coal gas or a mixture with carburetted water gas. In fact every alteration in composition is reflected in the calorific value. As, however, calorific tests made on varying grades of coal gas are collected in greater and greater numbers and are entered in diagrammatic form, the more nearly does a line drawn through the centre of the myriad points approximate to a straight line, until now, after several years' testing the calorific value of various grades of coal gas from every part of the country, and made from all sorts and classes of coal, the average relation shown for coal gas, and the second curve for carburetted water gas, in Fig. 28 have been obtained. Taking the original diagram, the lines appear to run through a haze of spots and are only rendered straight by their equidistance from outlying points; whilst those points distant from the main average lines themselves again fall into secondary lines in the same direction, but on different planes to the main lines, and which represent the curves of calorific value for coals of the same kind. This diagram is merely put forward as the average relation between the illuminating power of a pure coal gas and its calorific power, and the variations from the line may amount to 5 per cent., or even more. With this reservation it gives a definite idea of the relation existing between candle power and calorific value. Taking now the chart, the average calorific value may be tabulated for each candle power between 12 and 20 as shown on p. 187. In many of the published results regarding the relation between calorific power and illuminating power the experiments have been rendered useless by the low illuminating power having been obtained by " stripping " the gas, i.e., by taking out the unsaturated hydrocarbons to a greater or less extent by bubbling the gas through THE USE OF COAL GAS FOR HEATING AND POWER. 187 CALORIFIC VALUE OF PURE COAL GAS. Calories. British Thermal Units. Candle Power. Gross. Net. Gross. Net. 12 136-0 120-6 540 480 13 141-0 125-6 560 500 14 147-0 131-2 585 522 15 153-2 136-2 610 542 16 157-0 141-2 625 562 17 162-5 146-2 647 582 18 168-3 151-2 670 603 19 173-3 156-3 690 622 20 178-8 161-3 712 642 CALORIFIC VALUE OF CARBURETTED WATER GAS. Calories. British Thermal Units. Candle Power. Gross. Net. Gross. Net. 12 123-1 113-5 490 452 13 128-1 118-6 510 472 14 132-9 122-8 529 489 15 137-4 127-6 547 508 16 142-4 132-4 567 527 17 147-5 137-4 587 547 18 152-7 142-4 607 567 19 157-5 147-5 627 587 20 162-5 152-5 647 607 petroleum. It is possible, working in this way, to obtain a gas which will remain almost constant in calorific value, whilst the illuminating power descends with great rapidity. This result is due to the fact that the methane, which gives considerably more than half the heating value, remains untouched, whilst the benzene and ethylene, which were the main factors in the illuminating value, are absorbed ; 188 LIQUID AND GASEOUS FUELS. and these representing only a very small percentage of the heat-giving constituents of the gas, the loss is naturally a very slight one as regards the calorific value. This point also shows the effect which various methods of enrichment have upon calorific value. If the candle power of a pure coal gas rises, it is because a larger per- centage of illuminants from the coal is present, and at the same time that one gets an increase in the unsaturated hydrocarbons and a consequent increase in light, a pro rata increase is also obtained in the saturated hydro- carbons, such as methane, and consequently a relative increase in the heating value. But if a poor coal gas be enriched by adding to it, say, benzene vapour, the enrich- ment in candle power takes place without so great an enrichment in heating value. This is at once seen when one considers the relation between the light-yielding and the calorific values of such hydrocarbons as are present in the coal gas. B.T.U. Description of Gas. Illuminating Value per 5 cubic feet. B.T.U. per Candle. Gross. Net. Methane . 1,024 919 5-2 984-6 Ethylene , Benzene vapour 1,603 8,718 1,510 3,574 70-0 820-0 114-6 22-6 It is clear from this that if a coal gas be taken in which a large proportion of the illuminating power is due to the presence of methane and ethylene, for any given illuminating power, it must have a higher calorific value than when the illuminating power is due to the addition of benzene vapour. If no method had been devised for burning coal gas with a non-luminous smokeless flame, little or nothing THE USE OF COAL GAS FOE HEATING AND POWER 189 would have been heard of coal gas as a domestic fuel, as the carbon deposited when a luminous flame is caused to impinge on a surface at a lower temperature than the flame itself would have been an unsurmountable objection. In the historical researches which led to the discovery of the principle of the miner's safety lamp, Sir Humphrey Davy noticed that if ethylene or other gaseous hydro- carbon capable of burning with a luminous flame was allowed to escape from a jet placed a few inches below a piece of iron wire gauze, and was then ignited above the gauze, the flame was no longer luminous, and deposited no carbon upon substances held in it. As years passed by and coal gas asserted its position, some attempts were made to utilise it in burners for heating purposes. For scientific work these early burners were warmly welcomed in spite of their many failings, because, bad as they were, they yet had advantages over the spirit lamp, charcoal furnace, and oil lamp upon which the chemist up to that time had been dependent, but up to the middle of the nine- teenth century only luminous gas flames were employed for this purpose. It was at this epoch that Bunsen, the greatest of Heidel- berg's great men, was planning and fitting those laboratories which have since then given so rich a harvest to the scientific world, and whilst considering the methods of heating which should be adopted on the working benches, his attention was called by one of his assistants, now Sir Henry Koscoe, to Davy's experiment with the gauze and gas jet. Seeing at a glance the enormous convenience of such a source of heat, Bunsen brought his marvellous manipulative skill to bear upon the subject, and in a few weeks gave the world its " bunsen burner," a burner which has done more for the gas industry in the past decade than almost any discovery or invention connected with it ; which has made coal gas possible and successful for fuel purposes, and has enabled 190 LIQUID AND GASEOUS FUELS. it, in conjunction with the incandescent mantle, to hold its own against the threatened rivalry of the electric light. The names of Davy, Bimsen, and Koscoe will always awaken in the mind a long list of benefits which their labours have conferred upon the world ; but for practical utility the simple atmospheric burner will always remain one of the most success- ful achievements to be placed to their credit. Starting from the simple forms left to us by Bun- sen, the skilled craft of such masters of the trade as Fletcher has given us convenient modifications in form for endless uses ; whilst the utilisation of the atmospheric burner as the heat supply for the incandescent mantle has, during the last few years, given rise to many altera- tions and some improve- ments in producing the non-luminous flame in the most effective form. FIG. 29. Original form of Bunsen T ,, , burner. In the early form of burner made by Bunsen the gas issued from either a flat flame or an argand burner head into a metal cylinder open at the bottom and closed at the top by means of a disc of fine wire gauze, so that the gas issuing from the burner head passed upwards through the air in the cylinder and mixed with it, the mixture burning on the top of the gauze. The difference between this class of burner and those which succeeded it was that the uprush THE USE OF COAL GAS FOE HEATING AND POWER 191 of the gas and its mingling with the air was due simply to the velocity with which it left the burner, and to the fact that the specific gravity of the gas is less than half that of air. Very soon however it was found that a more rigid flame and one more easily under control could be obtained by utilising the pressure under which the gas was delivered at the burner to produce the effect of an injector, causing the uprush of the gas to drag the air in through side holes arranged in the bottom of a vertical burner tube placed above the gas nozzle. In order to do this a small jet or series of orifices discharged the coal gas into a small chamber surmounted by the upright burner tube, and either the walls of the chamber or the lower portions of the tube were perforated with an opening or openings in connection with the air. On opening the gas tap the coal gas is discharged through a jet with a velocity dependent upon the pressure of the supply, and rush- ing upwards and impinging upon the sides of the tube above, it acts in the same way as the steam in a Giffard's injector. By drawing up from the chamber the air which is present there it forms in it an area of low pressure, and so sucks in more air through the lateral holes to re-establish equilibrium, this action con- tinuing, and the formation of the mixture of gas and air in the tube going on as long as the gas continues to flow. In this arrangement it is manifest that by regulating the size of the hole in the gas jet and the lateral air holes it is possible to adjust the mixture of gas and air formed in the tube with the greatest nicety, and to obtain a perfectly non- luminous and fairly rigid flame at the top of the burner. FIG. 30. Section of Bunsen burner. 192 LIQUID AND GASEOUS FUELS. After burners have been in use for some time, no matter how well they may be regulated at first, the partial stoppage of the injector tip by dust particles, and other causes acting upon the air supply, frequently deranges the ratio of the two supplies, and the result is that in a laboratory or other place where a large number of bunsen burners are used a wide discrepancy can be noticed in the flames given by the burner?. In some the gas is burning with a slightly luminous top and the inner zone is barely visible : in others the normal conditions exist, and there is a well- marked violet inner zone and a non-luminous lilac outer zone : in others again the flame is somewhat shortened, showing a distinct greenish tint in the inner zone, with a pale lilac outer zone, and it is generally found that when this point has been reached the flame has more or less a tendency to roar, and will often show a tendency to flash back in the burner tube and ignite the gas as it issues from the jet. These appearances all mark different ratios between the air and gas in the mixture passing up the tube. When one sees a slightly luminous tip it means that the gas is mixed with less than twice its own volume of air, whilst with the normal conditions obtained with the ordinary 16 candle gas, one volume of gas is drawing in 2*3 volumes of air: the violet inner zone begins to show a tendency to green when the ratio has become one of gas to 2'5 of air, whilst another tenth of a per cent, causes the green to become most marked, and the roaring to commence. With the ordinary bunsen burner as used in the labora- tory it is not possible to push the admixture of air and gas beyond this point, as the admixture of air and gas in the tube is now explosive, and the flame is only prevented from flashing back to the jet below by the rate of propagation of the explosive wave being less than the upward rate of flow of the mixture, and any further increase in the quantity of air present increases the rate of the explosive wave, and so THE USE OF COAL GAS FOE HEATING AND POWER. 193 causes flashing back. If however the head of the burner tube be covered with a layer or layers of fine wire gauze, the power of conduction which the fine metal filaments possess, and the fact that they reduce slightly the area of the tube, and so increase the rate of flow through the orifices of the mesh, prevents the downward propagation of the wave, and under these conditions the ratio of air to gas can be raised to over three volumes of air to the one volume of gas; the green zone shrinks down on to the surface of the gauze, and shows itself as a seething layer in which the green colour has reverted to a very pale blue. The importance of the regulation of the ratio between the gases having been recognised, the air holes in most of the burners used for laboratory and heating purposes were then fitted with cut- off rings, consisting of loose rings of metal with holes in them, which could be slid round over the holes in the side of the chamber, so that when the two sets of holes coincided the full air supply could be obtained, whilst by drawing the solid metal of the ring more or less over the under holes, the area of the air supply could be reduced. In this way it was possible to adjust the condition of the flame to the work required of it. L.G.F. o FIG. 31. Bunseri flames. 194 LIQUID AND GASEOUS FUELS. It will be evident that it will be the admixture of air with the coal gas before combustion that causes the production of a non-luminous flame, and the old theory to account for this phenomenon was that the oxygen burnt up the hydrocarbons in the gas before their decomposition set free any solid particles of carbon to render the flame luminous. Knapp and others, however, showed that oxygen was not necessary for the production of a non-luminous flame, but that the luminosity could be destroyed by diluting the gas before combustion with such non-inflammable and inert gases as nitrogen, carbon dioxide, and steam, and the experi- ments of Blochmann, Landolt, and Heumann showed that nitrogen in the air sucked in by the burner also played a most important part in the action. The relative importance of the oxygen and nitrogen in rendering the flame non-luminous can be readily deter- mined experimentally by taking a bunsen burner, fitted at the bottom of the tube with two supply pipes instead of the ordinary gas jet and lateral air holes. Each pipe is con- nected with a. small meter, so that the flow of gas and air can be measured. The amount of air required to render the flame non-luminous was found to be 13*5 volumes of air for 6 volumes of gas ; and 13*5 volumes of air contain roughly 2*7 of oxygen and 10*8 of nitrogen. When 6 volumes of coal gas are passed into the burner with 10*8 volumes of nitrogen, a flame is obtained which has only a slightly luminous tip, whilst with 2*7 volumes of oxygen and 6 volumes of coal gas a luminous flame is obtained which flashes back unless the burner is provided with a gauze top. A bunsen burner burning coal gas alone gave on the photometer with 5 cubic feet per hour 5'6 candles, but with the addition of 2*2 cubic feet of oxygen 3'1 candles ; using nitrogen, however, in the proportion of 9 cubic feet to 5 cubic feet of gas the luminosity was so feeble that it THE USE OF COAL GAS FOE HEATING AND POWER. 195 could not be read. It follows, therefore, that the amount of oxygen in the air necessary to destroy the luminosity does less than one-half the work. On making another experiment with varying amounts of oxygen, the results obtained are as follows : Candle Power. 5 cubic feet of gas alone 5*6 5 ,, ,, to 1*1 oxygen 5*4 5 to 1-5 8-0 5 to 2'2 3'1 (gauze used) 5 to 2-5 0-0 ( ) With a coal gas flame burning at the rate of 6'2 cubic feet per hour it is found that 14*2 cubic feet per hour of nitrogen are necessary to bring about complete non- luminosity by dilution only, an amount which is practi- cally the same as that of the air required in the previous experiment. 1 vol. of gas required 2*30 vols. of nitrogen 1 2-29 of air This seems to show that the oxygen acts merely as a diluent, but if this were so then mixtures of oxygen and nitrogen containing a larger percentage of oxygen than ordinary air should have the same effect on the luminosity of flame as air, but this is disproved by the results shown on p. 196. From this it will be seen that until the percentage of oxygen reaches the amount present in air, the diluting influence of the nitrogen overpowers the effect of the oxygen in the destruction of the luminosity, but with 25 per cent, and over of oxygen the retarding influence of the nitrogen has no effect on the activity of the oxygen. The effect of various gases in bringing about non- luminosity was then tried, but the employment of a wet o 2 196 LIQUID AND GASEOUS FUELS. VOLUMES OF VARYING MIXTURES OF OXYGEN AND NITROGEN RE- QUIRED TO RENDER ONE VOLUME OF COAL GAS NON-LUMINOUS IN A BUNSEN BURNER. Gas Volume. Volume of Mixture required. Composition of Mixture. Volume of Oxygen present in amount required. Nitrogen. Oxygen. 1 2-30 1 nil. nil. 1 2-30 5 1 0-38 1 2-27 4 1 0-45 1 2-02 3 1 0-50 1 1-49 2 1 0-50 1 1-00 1 1 0-50 1 0-50 nil. 1 0-50 meter for measuring purposes rendered the number of these limited. Volume of Gases required to render One Volume of Coal Gas non-luminous. 1 vol. of coal gas requires 0*50 vol. of oxygen 1 1'26 carbon dioxide 1 2'27 air 1 2'30 nitrogen 1 5*11 carbon monoxide 1 12*40 hydrogen So that a combustible diluent which increases the temperature of the flame is required in far larger quantity than a non-combustible diluent in order to render the flame non-luminous. The varying effects of diluents have been attributed to the influence of density, but it has been shown by Heumann that a flame can be rendered non-luminous by cooling as well as by dilution. If a luminous flame be caused to spread itself over a cold surface it becomes non-luminous, but the luminosity can be restored by heating the surface THE USE OF COAL GAS FOR HEATING AND POWER. 197 over which the flame plays. If, therefore, a diluent had the power of extracting more heat from a flame than another, it would be more active in reducing the luminosity, so that a smaller quantity would be required to render the flame non-luminous. On comparing the specific heats of the gases used in the last experiment the reason for the small quantity of carbon dioxide is at once seen : Specific Heats of Equal Volumes. Oxygen ..*... 0'2405 Carbon dioxide .... 0'3307 Nitrogen 0'2370 Air ../... 0-2374 Carbon monoxide .... 0*2370 Hydrogen 0'2359 Experiments show that this is in all probability the true explanation, as in the flames rendered non-luminous by diluents the inner cone for the first 1J inch is decidedly cooler than in the luminous flame, owing to the cooling action of the nitrogen or carbon dioxide. Above this point, however, the influence of the oxygen begins to be felt, and the non-luminous flame is here hotter than the luminous flame, whilst the hottest portion of the flame is to be found half-way between the tip of the inner and outer cones. With inert diluents, however, the hottest points are found at the side and tip of the outer cone, where the air necessary for the combustion is obtained. With a bunsen burner in which the mixed gas and air give a green inner cone, although a low temperature, due to the excess of air, is found at the bottom of the inner cone, yet the increased quantity of oxygen causes a rapid oxida- tion in the upper portion, and a smaller and hotter flame is produced. From these experiments and also from the researches of 198 LIQUID AND GASEOUS FUELS. Heumann, it will be seen that several causes aid in the destruction of luminosity in a flame, chief amongst which are oxidation, dilution, and cooling. The chemical changes taking place in the bunsen flame are far more simple than those which are going on in the luminous flame. Taking an ordinary coal gas having the composition Hydrogen 52'16 Unsaturated hydrocarbons . . 3*50 Saturated hydrocarbons . . 36*25 Carbon monoxide . . . . 3*68 Carbon dioxide .... O'OO Nitrogen ..... 4*10 Oxygen . . . . . 0'31 Sulphuretted hydrogen . . . O'OO 100-00 It is found that the gas of this composition requires about 5*0 times its own volume of air for its complete combustion. When a bunsen burner burns with a blue non-luminous flame, the ratio of air to gas is about 2*3 to 1, less than half the amount necessary to complete combustion, whilst with the green inner cone 2'5 of air mix with 1 of gas, so that the bunsen flame obtains from the mixture only about one- half the air necessary for its complete combustion, the remaining portion being obtained from the exterior of the flame during combustion. This is the cause of the double cone in the flame, the inner cone being caused by the incomplete combustion of the gas with the admixed air, and the outer cone by the combustion of the products of this incomplete combustion by means of the external air. This can be proved by the use of an apparatus devised by Mr. Lewis T. Wright and perfected by Professor Smithells, in which the two parts of the flame can be separated. THE USE OF COAL GAS FOE HEATING AND POWEE. 199 The apparatus consists of a glass tube, about 16 inches long and about 1 inch in bore ; over the bottom end is a piece of rubber tubing through which slides easily an inner glass tube 20 inches long, kept central with the outer tube by a ring of brass carrying three outspreading springs. Both tubes at their tops are sur- rounded by a ring of platinum foil to prevent the heat of the flame cracking the glass. The lower end of the inner tube is placed over a bunsen burner, and the gas turned on and lighted at the top of the tubes, the tops of the tubes being level. The flame is much shorter than the ordinary bunsen flame and of a greenish colour. If now the outer tube is raised, bringing its mouth above the top of the inner tube, the outer cone of the flame will be lifted away from the inner, which latter will continue to burn at the orifice of the inner tube. On altering the ratio of either the gas or the air, the inner flame can be made to ascend to the mouth of the upper tube, or recede down the inner tube to the bottom ; with increase of gas the inner flame ascends, and with increase of the air supply it descends. The dual action of the flame is practically complete when Fio. 32. Smithells' tube central cone in position. 200 LIQUID AND GASEOUS FUELS. the ratio of air to gas is 2*6 to 1, when the green cone is produced. The action of the mixture in the inner cone may be approximately expressed by the following equations : Hydrogen. Oxygen. Water. H 2 + = H 2 Ethylene. Oxygen. Carbon monoxide. Water. Hydrogen. C 2 H 4 + 30 = 2 CO + H 2 + H 2 Methane. Oxygen. Carbon monoxide. Water. Hydrogen. CH 4 + 2 = CO + H 2 4- H 2 The resulting carbon monoxide and hydrogen in about equal proportions diluted with twice the quantity of steam and the unchanged nitrogen burn at the expense of the oxygen of the external air, forming the outer cone. A small quantity of carbon dioxide is also always found, probably due to the oxidation of some of the carbon monoxide by the steam, and the gaseous mixture which forms the outer cone has the approximate composition of : Water vapour ..... 16 Nitrogen . . . . . .60 Carbon monoxide .... 9 Hydrogen ...... 10 Carbon dioxide . 5 100 It does not seem possible that such a mixture, containing as it does less than 20 per cent, of combustible gas, should burn and produce the intense heat found in the outer cone of the burisen burner. But Professor Smithells has shown that under ordinary conditions the heat of the inner cone is added to that of the outer, so that in the combustion the outer cone is always hotter than the inner. That this is so can be clearly shown by using the Smithells tube, and having widely separated the two cones THE USE OF COAL GAS FOE, HEATING AND POWER. 201 of the flame, holding an incandescent mantle in the outer zone. The mantle is not then heated to incandescence, but on now allowing the inner cone ,to rise in the tube the mantle becomes more and more luminous until the zone has reached its proper position in the centre of the flame, when the mantle gives its full incandes- cence. It is clear that the temperature of the flame must be to a very great extent governed by the degree of oxidation due to air drawn in by the gas, as this governs the size of the flame. A mixture of coal gas and air which is under- aerated forms a longer flame than one which contains more atmos- pheric oxygen, as the flame has to travel further before it can obtain from the air the surplus oxygen to com- plete its combustion, and it must be clearly borne in mind that as long as combustion is complete, a cubic foot of gas burnt either as a luminous flame, or an under-aerated, or fully aerated bunsen flame, gives the same total of heat, but the bunsen flame is hotter than the luminous flame because the combustion is quicker, the flame therefore smaller, and the intensity greater. The best method for measuring the temperature of flames FIG. 33. Smithells' tube cones separated. 202 LIQUID AND GASEOUS FUELS. that is practically available is the thermo-couple, devised by Le Chatelier, and although it is open to certain objec- tions as a recorder of absolute temperature, still when properly used it gives a nearer approximation to the truth than any other method of measurement. In this instrument the measure of the electromotive force developed by the rise in temperature of a junction of two dissimilar metallic wires is utilised, and affects a " dead-beat " galvanometer in circuit with the couple. The FIG. 34. Le Chatelier's thermo-couple and arrangement. wires best suited for the purpose are composed one of platinum and the other of platinum alloyed with 10 per cent, of rhodium, the thickness of each being about 0'4 to 0*5 millimetre. The galvanometer B is of very sensitive character, and the moving coil carries a small mirror, which serves to reflect a beam of light from a lamp on to a scale at F placed at the focus of the mirror, a distance generally of about a metre. In front of the lamp is a tube with cross wire, so that the shadow of this wire is projected on to the scale in the centre of a disc of light. In this way the smallest movement of the galvonometer coil is magnified THE USE OF COAL GAS FOB, HEATING AND POWEE. 203 and rendered visible by the travel of the spot of light on the scale. The galvanometer and lamp are so adjusted that when at rest the line of the cross wire rests at zero in the centre of the scale. On subjecting the junction of the wires A to heat a current of electricity is generated, which increases with rise of temperature, and this small current affects to a greater or less degree the moving coil of the galvanometer. The junction of the wires is best made by fusing together the ends in an oxy- hydrogen flame, so as to form a minute bead ; the circuit includes a definite resistance B (to keep the spot of light within the limits of the scale) and a reversing switch C, the latter being used in order to obtain readings on both sides of the scale from zero, the mean of the two readings being taken as correct. All joins of the connecting wires should be soldered and kept at a uniform temperature, otherwise opposing currents might be set up which would vitiate the results. To calibrate the thermo-couple various substances are employed whose melting points are accurately known, and from the results so obtained the temperature curve of the junction can be plotted out. The substances usually employed, together with their boiling or freezing points, are given in the following Table :- Boiling. Freezing. Water .... 100-0 Naphthalene . . . 218'0 Sulphur .... 444*6 Tin 232 Zinc 419 Silver .... 962 Gold 1065 In order to protect the couple from any action which the materials used might have upon it the wire and junction 204 LIQUID AND GASEOUS FUELS. can be encased in thin glass tubes, made by drawing out a piece of wider bore. With substances whose boiling point is desired, the couple is immersed in the vapour above the liquid and out of range of any chance splashings, whilst with metals the material is melted in a small crucible, and the protected couple sunk well below the surface to about the centre of the mass. The heating flame is withdrawn, and the disc of light on the scale carefully watched ; the disc gradually descends, remains stationary for some few seconds, and then continues to de- scend, or makes a sudden rise. The point at which the disc remains station- ary is the freezing point of the substance under test. The points obtained by standardising with these materials are plotted on squared paper, and should approximate or fall on a straight FIG. 35. Holder for thermo-couple. the lowest to the highest temperature line drawn from used. In utilising the thermo-couple for the determination of temperatures in various parts of a flame, various correc- tions must be made and precautions taken, such as allowing for radiation of heat at the junction, whilst in order to avoid as far as possible any disturbance of the flame it is neces- sary to use wires of the smallest diameter that will stand the heat of the flame. The stand shown in Fig. 35 will be THE USE OF COAL GAS FOE HEATING AND POWEE. 205 1560 1595 1635 1635 1610 found of great use for work of this kind. It consists of a stout metal pillar, which is threaded to carry a large milled nut, and over which slides a metal tube having the table fixed to it ; on the table are the clamps between which lies the thermo-junction with its wires horizontal, the clamps being mounted on a horizontal slide. In this way the junc- tion can be given vertical as well as horizontal move- ment, and by attach- ing scales to the rising table and the clamps - slide any definite point in the flame can be arrived at. When the tempera- ture existing in a bunsen flame is mapped out by the Le Chatelier thermo- couple with all pos- sible precautions the general range of temperature is found to vary with the degree of aeration as shown in Fig. 36. So far only upright bunsen or atmospheric burners have been mentioned, but for cooking and heating many modifi- cations have been introduced, such as ring burners and slot burners, in which the gas is generally injected horizontally, drawing in air from an air port in the under side of the burner tube. In all forms of atmospheric burner careful regulation of 1695 Air 4. 3 Gas 1.0 Air 3.8 Gas I FIG. 36. Temperatures in Bunsen flame with different aeration. 206 LIQUID AND GASEOUS FUELS. the air port is one of the chief essentials for successful working, and as the quantity of air required varies with the composition of the gas used, many burners are fitted with ring baffles, by which the air port can be altered to the dimensions necessary to give the best results. From the point of view of health, cleanliness, conveni- ence and comfort, gas is immeasurably superior to coal for fuel purposes. Not only would the general adoption of coal gas as a fuel do away with the heavy pall of smoke which hangs over a big town and prevents the sun's rays from carrying out the beneficent work which Nature intended them to perform, but it would also reduce to a minimum the number of fogs from which a big town suffers, and would in this way quickly reduce the death rate due to lung diseases. The only point which militates against the use of gaseous fuel is the assumption that it is much more expensive than solid fuel, and, if the ccst of the thermal units developed by ordinary bituminous coal and by coal gas be calculated out, coal has a very substantial advantage. A good bituminous coal could not be obtained in London under ordinary conditions for less than 18s. 6d. per ton, and at this price one pound would cost O'l of a penny, and would have a calorific value of 15,000 B.T.U. Taking now an average coal gas yielding 600 B.T.U. per cubic foot, and costing 2s. per 1,000, it is clear that 25 cubic feet of the gas will contain the same heating value as one pound of the coal, and will cost six times as much, i.e., 0'6 of a penny for the 25 cubic feet. It does not by any means follow from this that heating by gas will be six times as costly as heating by coal, as this will largely depend upon the efficiency of the stoves used and the way in which the heat is imparted to the air of the room. Gas stoves may be classified in three groups 1. Flueless stoves, in which the products of combustion THE USE OF COAL GAS FOR HEATING AND POWER. 207 either before or after condensation of water vapour are discharged into the air. 2. Eadiant heat stoves, in which refractory bodies are heated to incandescence, and the heat is radiated into the room, the hot products and some unburnt gases escaping by Hue. 3. Stoves of the same kind as Group 2, but in which by means of air chambers, regeneration, or passing the pro- ducts through a length of metal pipe, most of the heat is withdrawn from the products of combustion before dis- charging into the flue. In the first class of stoves all the heat of the burning gas passes into the air of the room, and practically the whole of the heating is done by hot air and convection. In the second class of stoves the heat is mostly discharged into the room by radiation, whilst in the third class both radiation and air-heating come into play. There is not the slightest doubt, from a hygienic point of view, that heating by radiation is infinitely preferable to effecting the heating by warming the air, and this is one of the factors that make the English open fire so superior in comfort to the closed stoves and other air-heating devices so popular on the Continent. A good gas stove, like the open fire, should not depend too much for its heating effect upon discharging warm air into a room, but should distribute a considerable proportion of its heat by radiation, and so raise the temperature of the floor and furniture in the lower parts of the room. Kadiant heat does not directly raise the temperature of the air, but is radiated to the floor, walls, and furniture of the room, which again slowly part with their heat to the air in contact with them and to the inhabitants, so that the walls and other solid bodies in the room are at a higher temperature than the air. Apart from its being much more healthy to breathe cool 208 LIQUID AND GASEOUS FUELS. than hot air, there is another important point to consider. The normal temperature of the body is 98F., or 36.8C., and this temperature is maintained by the slow combustion processes going on in the body. By the laws of radiation a heated surface parts with its heat more or less rapidly according to the temperature of the surrounding bodies, so that if a person be sitting in a room filled with warm air, but near a wall colder than the air, his body will rapidly part with heat by radiation to the wall, and a sensation of chill is the result. But with the open fire this is never the case, as the radiant heat from the fire heats the walls of the room to a temperature higher than that of the air. When however a room is heated by means of warm air the walls not being heated in the same proportion, though the air may feel warm, the walls will remain cold : so that the heat of the body would pass by radiation to the walls and give rise to a chill. When gas stoves were, first introduced the desire of the manufacturers was to as nearly as possible imitate the open stove, and this was done by filling the existing fire-grate with balls made of fireclay, asbestos lumps, or other refractory material, and heating this mass to as high a temperature as possible by means of a series of atmospheric burner flames arranged along the bottom of the front of the grate. This method, however, was found very wasteful of gas, as most of the heat went up the chimney, and the gas stove was then made to stand in front of the grate with a short tube and elbow discharging the products of combustion into the chimney, whilst a row of six or eight atmospheric burner flames played upon asbestos fibre, refractory metal work, or asbestos fireballs in such a way as to heat the material to a temperature at which it would radiate its heat into the room. Whenever an atmospheric flame is used to heat substances like asbestos in a gas stove, a considerable percentage of THE USE OF COAL GAS FOR HEATING AND POWER. 209 inflammable products of incomplete combustion escape unburned, and that this is so may be seen by disconnecting the stove from the short flue pipe that leads into the chimney, and after the gas has been burning a short time in the stove, and the exit pipe has become hot, the products of incomplete combustion will burn at the exit with a pale blue flame, unless the gas supply has been very carefully regu- lated, which is hardly ever done by the consumer. The effect of these products on health will be fully discussed under gas cookers and water heaters, but it is now thoroughly recognised that it is impossible to do away with the pro- ducts of incomplete combustion as long as the heating flame is brought in contact with any surface cooler than itself. In other words, the only way to get complete com- bustion is to allow the flame to burn itself out without con- tact with any other body, and the only forms of stove in which this has been attempted were those in which flat luminous flames were burned in the top of the stove, and the light and radiant heat were reflected out into the room by a concave copper reflector placed below the flames. The amount of heat, however, radiated by a luminous flame burning under ordinary circumstances was so small that this form of stove was never very efficient, but when regeneration was also used, a very fine result was obtained. Many forms of stove which heat the room rapidly depend on either hot air chambers or a certain length of flue between the stove and the flue, in order to utilise a propor- tion of the heat which would otherwise escape up the chimney, but such stoves have two important drawbacks. In the first place, the thin iron of which the flues or air chambers are made soon gets heated to a high temperature, and under these conditions carbon monoxide, which is the most deleterious of the products of incomplete combustion, freely diffuses through it and escapes into the room, vitiat- ing the air and quickly giving rise to a feeling of oppression L.G.F. P 210 LIQUID AND GASEOUS FUELS. and headache. This principle therefore should only be used for stoves in which flame burns unchecked, and where consequently combustion is perfect. Secondly, the largest part of the heating is effected by warming the air of the room, and not by radiant heat, which is wrong. Whatever views may be held on the subject, the author feels very strongly that the idea that some forms of stove can be used without being attached to a proper flue is not only dangerous to health, but also militates against the use of gas as a fuel, by encouraging the idea that gas stoves are unpleasant and unhealthy as sources of heat. It cannot be insisted on too strongly that a gas fire whether used for heating or cooking must be connected with a flue, as the products of combustion are just as deleterious, if not so dirty, as those given off by the combustion of solid fuel. The author has on many occasions protested against the sale of flueless stoves, but freely admits that in spite of protests and preachings they continue to flourish, and have indeed multiplied in number more than any other form of gas heater. Some of these stoves are small stoves of the ordinary types, whilst others, known as condensing stoves, are so arranged as to condense the water formed by the combustion of the gas, and the makers gravely assure the public that this removes all deleterious products. The popular idea of a deleterious product is something that has an offensive taste or smell, or that in a very short space of time seriously affects the health, and if this view be accepted then the makers of these stoves have a modicum of truth in their statement, as the condensing water removes some of the products of the combustion of the sulphur in the gas, and where the gas used is exceptionally foul this prevents a certain amount of discomfort. The ventilation of our rooms, however, is never too perfect during the periods that necessitate the use of the gas stove, and the fact cannot be got away from that each cubic foot of gas burnt forms THE USE OF COAL GAS FOR HEATING AND POWER. 211 half a cubic foot of carbon dioxide, none of which is taken up by the condensing water. This gas more- over is discharged near the floor of the room, and being fairly cooled before leaving the stove mingles with the air in the lower portion of the room instead of rising, as the products from an exposed flame do, straight to the ceiling space. A long series of experiments was made upon the relative efficiency of a number of gas stoves which experience had shown to be the ones most in demand by the public. To make any such determinations of value it was necessary that the experiments should be carried out with every care as to exactitude in measurement of the gas consumed and of the increase in temperature, and yet to have the condi- tions such as would be found in practice. The room selected for the experiments was 17 feet 4 inches by 15 feet 7 inches, and 11 feet 1 inch high, giving a cubical capacity of 3,032 cubic feet. It had three windows and one door, the latter being opened twice in the hour to allow the observer to pass in and out during the test, this and all other opera- tions being conducted in such a way as to make the tests strictly comparative. All stoves with flues tested were fitted exactly as they would be arranged when fixed by an experienced fitter, i.e., the opening of the fireplace was closed by a metal plate through which the elbows from the gas stoves passed, and the thermometers were arranged in different parts of the room, so as to give the temperatures at various distances from the stove from the floor level and at each two feet up to the ceiling. In testing these stoves the gas supplied to them was carefully measured by an accurate meter, and the tempera- tures in the room were taken every hour over a period of five hours. Two tests were in this way taken of each stove, but only one test was taken on each day, so as to p 2 212 LIQUID AND GASEOUS FUELS. allow the temperature of the walls and atmosphere of the room to reach its normal condition again. The tests for each stove were found to differ but little among them- selves, and the results taken were the mean of two sets of tests. The conditions aimed at in the tests were that the stoves should raise the temperature of the room at least 6 F. above the outer air temperature in the first hour, and that there should be a total increase of 13 F. in five hours, every care being taken to so select the time of experiments as to elimi- nate any differences in outside temperature likely to invalidate the tests. The first tests made were to ascertain the proportion of heat lost owing to the form of stove used. When a room is being warmed by any form of stove, heat is lost by 1. Hot products of combustion and unburnt products of incomplete combustion going up the flue. 2. Absorption of heat by the walls of the room. 3. Hot air removed by ventilators and cool air brought in. 4. Leakage from doors and windows. The last three factors of loss are due to the room itself and will act practically equally with solid or gaseous fuel, whilst the amount of heat escaping up the chimney is largely dependent upon the construction of the stove. It was found that with the flueless stoves, as might be expected, the whole of the heat was utilised, and that it did not in the least matter whether the gas was burnt in a flat flame or a bunsen burner near the floor level, or whether it was consumed in a regenerative or condensing stove of the most costly and complicated pattern ; in all cases the result was the same, and if the user does not mind hot foul air and injury to his health a few bunsen burners on the floor is the most effective form of stove that can be used. With all the flueless stoves the test conditions were HE USE OF COAL GAS FOE HEATING AND POWEE. 213 satisfied with a consumption of 70 cubic feet of gas in the 5 hours, or 14 cubic feet per hour. It is this high efficiency that accounts for the popularity of this class of stove, but it cannot be too strongly urged upon the public to use them only in halls, passages, or workshops, where ample ventilation can be relied upon, and never under any condition to admit them to the dwelling rooms of a house. The second class of stove, which did the main portion of the heating by radiant heat, and which from the hygienic standpoint is undoubtedly the best, was next tested, and it was found that in order to get the desired result with the best stoves of this class, the gas consumption had to be raised to 40 cubic feet per hour, or 200 cubic feet in the five hours. This result, which was amply verified by check experi- ments, showed such an enormous waste of heat that careful tests were made to see how the heat was being distributed, and it was found that with this class of stove only 35 per cent, of heat found its way into the room, the remainder escaping up the chimney, 49 per cent, as heat in the pro- ducts of combustion and draught through the grate, and 15 per cent, as unconsumed products of incomplete combustion. The last class of gas stoves, in which by air chambers, regenerators, and other devices the heat escaping from the incandescent area in the front of the stove is utilised to heat air supplied to the room before the products escape to the chimney, were, as might be expected, found to be the most variable, the worst needing a gas consumption of over 30 cubic feet per hour, and the best 16 cubic feet per hour to fulfil the standard requirements. Having in this way determined the amount of gas required by the various classes of the gas stove, it was necessary to find how much coal would be used under 214 LIQUID AND GASEOUS FUELS. normal conditions to give the same thermal results in the test room. Consuming bituminous coal in a grate of the ordinary construction, and of the kind used in certainly 90 per cent. of our homes, it required an average of 7 Ibs. of coal per hour to raise the temperature to the same extent as with the gas stove. We must not lose sight of the fact, how- ever, that with the newest and best forms of open grate using solid fuel, the coal consumption can be reduced from 7 Ibs. to 4 Ibs. per hour to give the same effect. It is now possible to contrast the cost of heating by means of coal and coal gas respectively per hour. Coal Gas at 2s. per 1,000. Coal at 18s. 6d. per ton. Gas Cost Coal Cost c. ft. Pence. Pounds. Pence. Eadiating stove 40 0'96 Ordinary stove 7 0-7 Radiating and regenerative . 16 0-38 Newest forms . 4 0-4 Flueless stoves . 15 0-36 So that for all practical purposes the best form of gas stove is as cheap with gas at 2s. per thousand as the old forms of coal stove. The initial consumption of coal to give the necessary increase in temperature is greater than with gas ; and the saving in waste of fuel secured by being able to turn off the gas when the temperature is too great, or when the fire is done with, practically obliterates the difference in cost even with the radiating gas stove, when intermittent and not continuous heating is required ; whilst with rooms used only for an hour or two in the day, gas is cheaper than coal as a fuel. It must always be borne in mind that the radiating gas THE USE OF COAL GAS FOE HEATING AND POWEK. 215 stove, although it utilises only 35 per cent, of the heat of the gas in warming the room, yet like the even more wasteful coal fire, does its work in the right way, and is a powerful factor in ventilation by causing a strong up-draught in the chimney. The great fault with most of the stoves on the market is the high gas consumption, many of them using from 30 to 50 cubic feet of gas per hour, and this, by unduly swelling the consumer's gas bill, creates a prejudice against the use of gas as a fuel ; but there is an immense future for a good stove consuming 12 to 15 feet per hour, and advances are being made in this direction. In constructing gas stoves, care must be taken not to cool the products of combustion too far before they dis- charge into the flue, as if the temperature is reduced below the boiling point of water, although a slight increase in heat is obtained, water is condensed, and taking up the sulphur oxides produced from the carbon disulphide vapour in the gas forms a highly corrosive liquid, which rapidly eats away the metal work of the connecting flue to chimney, and corrodes the iron work of the back of the stove. Gas cookers are daily becoming more firmly established, and the early prejudices against them having been over- come by experience their convenience and economic advantages are leading to their almost universal adoption ; but where they are extensively used a ventilating shaft with a good up-draught should be in connection with a hood a few feet above the stove, as there is one phase in the use of gas fuel which should never be overlooked, and that is, that if a cold substance, metal or non-metal, be placed in a flame, whether it be luminous or non-luminous, it will be observed that there is a clear space in which no combustion is taking place formed round the cool surface, and that as the body gets heated this space gets less and 216 LIQUID AND GASEOUS FUELS. less until, when the substance is at the same temperature as the flame itself, there is contact between the two. Moreover, when a luminous flame is employed in this experiment the space still exists between the cool body and the flame ; but you also notice that the luminosity is decreased over a still larger area, although the flame exists. This means that in immediate contact with the cold body the temperature is so reduced that the flame cannot continue burning, and so is extinguished over a small area ; whilst over a still larger space the temperature is so reduced that it is not hot enough to bring about decomposition of the heavy hydrocarbons, with liberation of carbon to the same extent as in the hotter portions of the flame. Inasmuch as when water is heated or boiled in an open vessel the temperature cannot rise above 100 C., and as the tempera- ture of an ordinary flame is over 1,600 C., it is evident that the burning gas can never be in contact with the bottom of the vessel, or in other words the gas is put out before combustion is completed, and the unburnt gas and products of incomplete combustion find their way into the air and render it perfectly unfit for respiration. The portion of the flame which is supposed to be the hottest is about half an inch above the tip of the inner cone of the flame, and it is at this point that most vessels containing water to be heated are made to impinge on the flame ; and it is this portion of the flame also which is utilised for raising various solids to a temperature at which they will radiate heat. In order to gain an insight into the amount of con- tamination which the air undergoes when a geyser or cooking stove is at work the composition of the products of combustion was determined, and also of the unburnt gases escaping when a vessel containing water at the ordinary temperature is heated to the boiling point by a THE USE OF COAL GAS FOR HEATING AND POWEE. 217 gas flame, the vessel being placed, in the first case, half an inch above the inner cone of the flame, and in the second at the extreme outer tip of the flame. GASES ESCAPING DURING CHECKED COMBUSTION. Bunsen Flame. Luminous Flame. Inner. Outer. Inner. Outer. Nitrogen Water vapour Carbon dioxide 75-75 13-47 2-99 79 17 14-29 5-15 77-52 11-80 4-93 69-41 19-24 8-38 Carbon monoxide . 3-69 nil. 2-45 2-58 Methane 0-51 0-31 0-95 0-39 Acetylene 0-04 nil. 0-27 nil. Hydrogen 3-55 0-47 2-08 nil. 100-00 100-00 100-00 100-00 These figures are of the greatest interest, as they show conclusively that the extreme top of the bun sen flame is the only portion of the flame which can be used for heating a solid substance without liberating deleterious gases. The best forms of geyser and other heaters of water in quantity are those in which the combustion of the flame is completed out of contact with the surface to be heated, and the hot products of completed combustion used to do the heating. The internal combustion engine, in which the fuel may be either sprayed hydrocarbons, volatilised hydrocarbons, or gases, has made such enormous strides forward during the past quarter of a century that it threatens the very existence of the steam engine ; but unfortunately, although coal gas forms the ideal fuel for use in this direction, it cannot compete in price with producer gas as at present made in suction plants for gas engines of large size ; but 218 LIQUID AND GASEOUS FUELS. in cramped manufacturing districts in a big city, and for engines not exceeding 100 H.P., there is so little room available for a producer that coal gas more than holds its own, and the consumption for power purposes now bulks largely in the use of coal gas ; whilst if the cost of its production could be reduced so as to bring the selling price for power down to the 1/1 per thousand charged for power purposes in Sheffield, or the I/- of Widnes, it would enter into brisk competition with the true fuel gases owing to the convenience of having it as a constant supply. With the Sheffield gas 600 British Thermal Units can be relied upon, and, as Mr. Dugald Clerk points out, with gas of this thermal value a good modern gas engine will give 3 b.h.p. per hour at the cost of Id. for gas used. CHAPTER VIII. WATER GAS. The history of water gas The European water gas plant The intro- duction of carburetted water gas Thermal considerations in the manufacture of water gas Blow and run processes Dellwik water gas Chemical actions taking place in the generator The application of water gas The Kramers and Aarts process Carburetted water gas The early forms of plant The Lowe process and its recent modifications The Humphreys -Glasgow system The poisonous properties of water gas Carburetted water gas as a diluent and enricher of coal gas Blue gas as an adjunct to coal gas works Various methods by which it is used Auto-carburetting " Methane-hydrogen." THE history of nearly all commercial processes shows us how rarely success is at once attained, the skeleton cupboard of the manufacturer containing many gruesome records of hard-fought struggles and failures before the discovery of some small alteration in the process has elevated it from the depths of mediocrity to the heights of success ; and history affords no better illustration of this than the present position of water gas. The latter half of the eighteenth century, which was so rich in scientific discovery, saw the first recognition of the fact that when steam is passed through red hot carbon in any of its many forms, an inflammable gas is produced. This discovery is generally attributed to Fontana, and the fact was certainly well known to Lavoisier and the brilliant band of scientists whose labours will ever render this period one of the most notable in scientific history, but it was not until 1824 that any attempt was made to adapt the action to commercial requirements. In this year 220 LIQUID AND GASEOUS FUELS. Mr. Ibbetson conceived the idea that the volume of illuminating gas could be largely increased by passing steam through the red hot coke left in the retorts after the carbonisation of the coal had been completed, the gas so produced passing on and mingling with the coal gas. It was soon found, however, that the temperature of the carbonaceous matter was too low, and that the large quantities of carbon dioxide produced utterly ruined the illuminating power of the coal gas; and although Ibbetson's process has been patented many times since that date, the same cause has always led, and mast alway lead, to failure. The reason for this is that at a high temperature the action of the steam upon the carbon is to yield a mixture of equal volumes of carbon monoxide and hydrogen, both inflammable gases, whilst the action which decomposes the steam also rapidly reduces the temperature of the carbon, and the moment this falls below a certain point, if the quantity of steam be kept constant, carbon dioxide begins to appear in the place of carbon monoxide, and as this is the most fatal of any known gas to the development of light in flames which owe their luminosity to the separation of carbon particles, its presence in any large quantity must of neces- sity ruin the quality of the coal gas with which it is mixed. The value of water gas for all purposes depends upon the carbon dioxide being kept down to the lowest limits com- mercially possible, and its average composition may be taken as Hydrogen 51'89 Carbon monoxide .... 40*08 Carbon dioxide ..... 4*80 Methane . . . . . . 010 Nitrogen 3'13 100-00 the figures given being the average of many analyses. WATEE GAS. 221 Six years after Ibbetson's experiment, Mr. Donovan attempted to make carburetted water gas as a substitute for coal gas, and did so by passing steam through coke heated to a high temperature in a retort, and passing the resulting water gas into a second chamber, where it was brought in contact with crude hydrocarbons, such as tar or naphtha- lene. Failure attended this attempt, and also many others which were made during the next twenty years, but in 1849 another important step towards success was obtained by Gillard, who at Narbonne introduced a sort of cupola furnace for the manufacture of water gas, and adopted the entirely new idea of raising the temperature of his carbona- ceous fuel by blasting it with air instead of heating it in a retort fired from without ; having raised the fuel to incandescence by its own partial combustion, he then shut off the air and passed steam through the fuel, until the temperature was so reduced as to necessitate a fresh blowing up by air. It is this process of " blow and run " which has since been employed in all the water gas processes which have had any claims to success. After Gillard's time numerous other attempts were made to introduce water gas processes, but nothing of importance was done until 1875, when Lowe and Tessie du Motay in America inaugurated the present carburetted water gas systems. Fuel gas had long been used in metallurgical operations, and had been produced in various forms of apparatus by blowing air through a bed of incandescent fuel, an operation which yielded an impure mixture of carbon monoxide with the residual nitrogen from the air, having the average composition Nitrogen . . . . . .64*5 Carbon monoxide .... 29*0 Carbon dioxide ..... 4*0 Hydrogen ...... 2*5 222 LIQUID AND GASEOUS FUELS. As this usually contained only some 30 per cent, of combustible matter, its heating power was very low, and attempts had been made to improve its composition by usingjsoft coal instead of coke, or by mixing a little steam with the air before passing it into the fuel. It was not un- natural, therefore, that as processes for the manufac- ture of water gas appeared to be nearing a com- mercial status of success attempts should be made to utilise this valu- able heating gas for fuel purposes, as by its aid great intensity of heat could be obtained, its heating value being four times as WATER-GAS GENERATOR FIG. 37. "European " water gas generator. great as the air- coke fuel gas, and from two to three times as great as the improved fuel With this object in view several Continental works set up plant on the "blow and run " principle, the most successful being the form adopted by Messrs. Schultz, Knaudt, and Company at Essen, who employed the gas largely and suc- cessfully for welding tubular boilers and lighting by incandescent devices. WAT UK GAS. 223 The form of apparatus installed by them, which is still in use, consists of what is practically a cupola furnace lined with firebrick, and with a constriction a short distance above the hearth, the firebrick being protected at this point by a water-cooled ring, the usual size of the generator being about 20 feet in height and 7 feet in diameter. An air blast is admitted below the water-cooled ring, and by blasting for about 10 minutes, the ignited fuel is raised to incandescence. The air blast is then cut off, steam is admitted above the top of the fuel, and passing down through it, becomes converted into water gas, which escapes by the same opening as that through which the air blast was admitted, this being opened and closed by means of a water-cooled valve slide of such construction that it is impossible for any explosive mixture of water gas and air to to be formed. The water gas passes on to the purifiers, which remove sulphuretted hydrogen and carbon dioxide, and the gas is then stored in the gas holders. The fuel is fed into the generator by means of an orifice at the top, which is closed by a cone ; the whole of the steam, air, and water gas pipes being governed by an arrangement which renders any explosive mixture impossible. Hearing of the success of this installation, Mr. Samson Fox, after having the process investigated, acquired the British rights to the patents covering this and the other processes then in use, and erected an installation at the Leeds Forge in 1887, which was started in 1888, and proved as successful for the particular class of work done there as it had been at Essen. This was followed by the exploitation of water gas and the events of 1889 in connection with it, but any chance which water gas had of being made a general success was entirely swamped by the public disgust at the jobbery in connection with the flotation of the water gas companies, and this feeling being accentuated by a deplorable accident at the Leeds Forge consequent on a leakage of the 224 LIQUID AND GASEOUS FUELS. highly poisonous gas, this chapter in its history ended in disastrous failure and heavy loss to the public. In the meantime, however, events in the gas world had gradually been opening up a field for water gas as an auxiliary to coal gas. Up to the year 1889 the extra candle power needed to enrich a poor coal gas up to the parlia- mentary standard of illuminating power was obtained by adding to the original coal about 3 per cent of cannel coal for each extra candle with which the gas was to be endowed, and as the price of cannel ruled high this enrichment was somewhat costly. In 1887, 1888, 1889, the price of cannel rose to such a pitch that it was costing the gas companies something like 3d. per thousand per candle to bring the gas up to the standard requirements, and evidence was not wanting that this figure might be largely increased if some other method of enrichment were not obtainable. It was then that the idea of using cheap grades of oil for decompo- sition into oil gas for the enrichment of coal gas and the utilisation of the vapours of petroleum spirit for the same purpose arose, the employment of oil having one great advan- tage over cannel, and that was that the deteriorating effect of the cannel on the coke was done away with. In 1889 an American named Van Steenburgh came over to England and erected in the Humphries Hall at Knights- bridge a plant for the manufacture of what he called "carburetted hydrogen," which consisted in a water gas cupola with an arrangement for injecting low flash point oil on the top of the incandescent fuel, which gave with great rapidity a large volume of 22 to 24-candle gas. This was visited by several of our leading gas managers, who were immensely struck with the rapidity of make and saving of labour, which made this method of producing gas an ideal one for coping with sudden demands upon the capacity of a gasworks, such as are created by fog, and also for serving as a useful stand-by in case of labour troubles. Hearing that WATEE GAS. 225 various forms of water gas apparatus were being employed in the States, Mr. G. C. Trewby, of the Gas Light and Coke Company, went to America and investigated the different sys- tems in use there, and on his return to England had erected at Beckton a generator for carburetting water gas on what was known as the improved Lowe system. This resulted in the adoption in many works of the gaseous mixture which up to that time had been looked upon as a rival. At the present moment at least one-fifth of the gas supply to London north of the Thames consists of carburetted water gas, whilst most of the large towns in the country have followed the lead of the metropolis. At this point it will be well to consider the economic conditions which up to 1896 prevented pure water gas from coming into general use whilst when carburetted it achieved so remarkable a success. In the formation of water gas the perfect decomposition would be represented by the equation C + H 2 = H 2 + CO 12 18 2 28 A unit weight of hydrogen in burning to water gives out 34,500 calories, and as 2 units burn to form 18 of water, the heat evolved during its production will be 34,500 X 2 = 69,000 calories ; when the 18 units weight of water is again decomposed, this amount of heat will be again absorbed. In this case, however, the water has had to be converted into steam, and so contains an amount of heat equal to the latent heat of steam plus the heat used to raise it to the boiling point. It has been seen that the latent heat of steam is 536 calories per unit of water, and to allow for the heat necessary to bring it up to the boiling point, this is generally called 600. In the present case we are dealing with 18 units of water as steam, so the heat present in it will be 600 X 18 = 10,800 calories, and the extra heat L.G.F. Q 226 LIQUID AND GASEOUS FUELS. used up in decomposing the 18 units weight of water will be 69,000 - 10,800 = 58,200 calories. The water having been decomposed, the oxygen of it is available to burn the 12 units of carbon to carbon monoxide, and as in doing this one unit of carbon emits 2,489 calories, the 12 will yield 2,489 X 12 = 29,868 calories. If this be deducted from the previous heat deficit, we have - 58,200 + 29,868 - 28,332 or a shortage of 28,332 for the 12 units of carbon, or 2,361 for one. If the units be taken as pounds, we see now that 1 Ib. of carbon in decomposing 1/5 Ib. of steam to hydrogen and carbon monoxide uses up 2,361 calories. In order to obtain this amount of heat we may burn 1 Ib. of carbon to carbon monoxide by an air blast, and so obtain 2,489 calories, so that theoretically it should be possible to get the required balance of heat by burning half the fuel by an air blast to producer gas, and by a steam jet converting the remaining half to water gas. In practice, however, the loss of heat taking place from the escape of the hot producer gas, radiation, etc., necessi- tates the air blast being continued until a far higher pro- portion of the carbon in the fuel has been consumed, and by this process, instead of 50 per cent, of the carbon of the fuel being converted into water gas, the actual amount is nearer 30 per cent. In making water gas by such processes as those employed at Essen and the Leeds Forge, fuel in the cupola is first raised to incandescence by the combustion of a portion of it under the influence of an air blast, an operation giving as a gaseous product the so-called air-coke gas, an analysis of which has already been given. WATER GAS. 227 Before the temperature of the fuel has been raised to a sufficient point to enable 1,000 cubic feet of water gas to be made by steam injection, no less than 4,000 cubic feet of the air-coke or producer gas have to be formed, and this quantity contains over 44 Ibs. of carbon taken from the fuel. The 1,000 cubic feet of water gas are then made and contain a little over 15 Ibs. of carbon, so that the production of the 1,000 cubic feet of water gas means an expenditure in round numbers of 60 Ibs. of carbon. These figures are calculated from the analyses of the water gas and producer gas, but they are amply verified by the fact that if the percentage of carbon in the coke be taken in pounds per ton and be then divided by 60, and multiplied by 1,000, figures will be obtained which will come within a few cubic feet either way of the actual yield of water gas obtained from the particular quality of coke. What that means is shown in the following table : Percentage of Carbon in Coke. Pounds per Ton. Water Gas from a Ton of the Coke. 84 1859-2 Cubic feet. 30,986 85 1904 31,733 87 1948-8 32,480 90 2016 33,600 92 2060-8 34,346 95 2128 35,466 100 2240 37,333 In practice, results of several years' working with this type of generator at the Leeds Forge give an average of 34,000 cubic feet per ton of coke. Some observers have given lower figures than these, but that has been due to coke from coal containing a consider- able percentage of cannel forming a large proportion of the fuel used, as with a dirty and crumbly coke a longer blow has to be made in order to obtain the required temperature. J 2 228 LIQUID AND GASEOUS FUELS. A thousand cubic feet of water gas contain as the combustible constituents Hydrogen 2'75 Ibs. Carbon monoxide . . .30 Ibs. and the thermal value will be represented by (2-75 X 34,500) + (30 x 2,435) = 167,925 calories. The thermal value, however, of the 60 Ibs. of carbon used in making the water gas would be 8,137 X 60 = 488,220 calories. In other words, the water gas formed has only just about 30 per cent, of the heating value of the carbon from which it has been formed, and this loss of 70 per cent, of the calorific value rendered the use of water gas as made by the old European process impossible, save for special purposes. When, however, the air-coke or producer gas can be at once led away and burnt whilst hot for any purpose, another 223,328 thermal units will be produced, bringing the total calorific value of the two gases up to nearly 80 per cent, of the value of the carbon used in generating them. If these conditions could have been satisfied, there is no doubt that water gas would have long ago been highly successful, but inasmuch as the producer gas is four times greater in volume than the water gas made, and as the gases are produced intermittently and not continuously, the problem of utilising both of them was an almost insur- mountable difficulty, as if storage had been provided for the producer gas, the gas holder room required would have been enormous, whilst allowing it to cool down would have rendered it hardly worth burning. In some few installa- tions a portion of the producer gas has been successfully used in firing boilers and other work of the same character, WATER GAS. 229 but the difficulties before enumerated were so great that at the time they practically killed the general utilisation of water gas for fuel purposes. When the manufacture of carburetted water gas was first successfully carried out by Lowe and Tessie du Motay, it became at once apparent that the producer gas, the loss of which had crippled all water gas processes, could be utilised for raising chambers filled with chequer brickwork to a high temperature in order to decompose the oils to yield the oil gas which, mixed with the water gas, rendered the latter luminous. It was in this way, by making the car- buretted water gas plant a perfect heat machine, that its greatest success was achieved, as in raising the fuel to incandescence the producer gas, with all its heat in it, was at once burnt with a fresh supply of air in the superheating chambers, the practical loss of heat taking place through- out the whole apparatus being reduced to a minimum. In all the attempts to make water gas which had seen the light up to 1896, the raising of the fuel to incandescence had practically always been obtained by using the air blast in so deep a bed of fuel that the carbon monoxide and residual nitrogen of the air formed the chief resultant products, and it must be remembered that when 1 Ib. of carbon combines with oxygen to form carbon monoxide, as when forming producer gas, only 2, 489 calories are developed, whilst if air be present in sufficient quantity to burn the carbon direct to carbon dioxide, the amount of heat which is evolved is 3'27 times as great, i.e., 1 Ib. of carbon gives 8,137 calories. A process was devised by Mr. Carl Dellwik, in which this fact was utilised by the adjustment of the air supply, and by keeping the level of the incandescent fuel in the generator at a nearly constant height. Under these conditions the producer gas ceases to exist as a by-product, and the gases from the blow consist merely 230 LIQUID AND GASEOUS FUELS. of the ordinary non-combustible products of complete com- bustion, carbon dioxide and nitrogen, the result being that double the quantity of water gas can be made per pound of fuel than was before possible, and the extra heat generated minimises the period of blowing, and enables runs or times of steaming to be continued far longer than before. In the old "European" process it was necessary to blow for nearly ten minutes to bring the fuel bed up to the right temperature, whilst the period during which the incan- descence was sufficiently great to decompose the whole of the volume of steam used, limited steaming to four or five minutes, whereas in the Dellwik process, the period of blow- ing rarely exceeds two minutes, and it is possible to steam for from seven to ten, according to the condition of the fuel. When the author first examined this process, his previous experience in water gas making led him to believe that this procedure must inevitably form a considerable amount of carbon dioxide in the water gas, but analysis soon showed that this was a mistake, as the crude gas collected in the holder proved to be of excellent quality. The following analyses of samples taken at intervals during the process of making bear this out i. ii. in. Hydrogen . . . 52*43 50*09 52*76 Carbon monoxide . 38*30 39*95 37*50 Carbon dioxide . . 4*73 5*38 4*08 Oxygen . . . 0*74 1*22 0*46 Nitrogen . . . 8*80 3*36 5*20 As 5 per cent, of carbon dioxide in the unpurified gas may be looked upon as a fair average when using the old " European " process, these results are distinctly good. In order to make quite sure that no mistake was being made, analyses were taken during a series of runs, when it was found that the average came out at 4*58, the highest being 4*9 and the lowest 4*2. WATEE GAS. 231 In the old process it is found that for the first two or three minutes, whilst the temperature of the fuel is very high, the reaction in the generator may be regarded as being C + H 2 = CO + H 2 but as the temperature of the fuel gets lower and lower, the action more and more nearly approaches to C + 2 (H 2 0) = CO-2 + 2 H 2 . Experiments, however, show that whereas the first product of the decomposition of the steam by the carbon is carbon monoxide and hydrogen, if the fuel is so far cooled as only to admit of the decomposition of a portion of the steam, the excess of steam oxidises the carbon monoxide into carbon dioxide, and the secret of the low carbon dioxide in the gas made by the Dellwik process, in spite of the long period of steaming, is that instead of allowing the steam to blow into the fuel in large volumes, its flow is so regulated that even at the extreme end of the run there shall be no excess of steam to oxidise the carbon monoxide to dioxide. An exhaustive series of tests was made with the apparatus at Warstein in Westphalia, and it was found that the com- pletion of combustion during the period of blowing, claimed by the inventor, undoubtedly took place, as is shown by the following analyses made of the products of combustion given off during a blow. These analyses are confirmed by thirteen other analyses of the carbon dioxide in the blow gas, which yielded from 18*6 to 15*1 per cent, of carbon dioxide, instead of the 5 to 8 found in the "European" producer gas Carbon dioxide . . . 17'9 18'8 Carbon monoxide . . .1*8 I'O Nitrogen .... 78'6 79'5 Oxygen . . . T7 0*7 100-0 100-0 232 LIQUID AND GASEOUS FUELS. The generator consists of a sheet-iron shell, lined with fire-brick, which contains the fuel, coke'; below the grate level is the valve for the air blast, whilst steam can be admitted either at the top or bottom of the generator. The WATEK GAS. 233 water gas is provided with two outlets, one at the top and the other at the bottom, connected by a three-way valve. A central stack valve, geared with the air blast valve, allows the products of the "blow" to pass away, and through it the fuel is fed into the generator. In practice, the gene- rator is filled to the proper level with coke, which is blown up to vivid incandescence with the air blast, the products passing off through the central stack. "When the right temperature is attained the air is cut off, the central valve being simultaneously closed, and steam is admitted at a carefully regulated rate which, passing either up or down- wards through the coke, is decomposed into water gas. The gas escapes at either of its outlets into a scrubber, where it meets with a stream of water trickling over the coke ; this cleanses and washes the gas, which is then stored in a holder. When the temperature of the fuel has fallen to a point at which carbon dioxide is formed in excess, the steam is shut off, and the fuel again raised to bright incandescence by the air blast. The introduction of the Dellwik process for making water pas revolutionised its employment as a fuel. With the old European process, in spite of the production of water gas being only an average of 34,000 cubic feet of gas per ton of coke, it offered such enormous advantages in the welding of corrugated boiler flues as to lead to its adoption at the Leeds forge and at Essen for this purpose, whilst now, on the Continent especially, water gas is being largely employed in many manufacturing operations, more particularly in those processes where intense local heat is required, as in the welding of boiler plates and tubes for various purposes. In the welding of large tubes from plates, not only is the speed of working three to five times as great as with the previous system of coke firing, but there is no waste of time in waiting for the fire to attain the necessary temperature after renewing the fuel, there is no ash or fuel to handle, 234 LIQUID AND GASEOUS FUELS. and the supply can be cut off immediately the work is done : all these factors meaning increased comfort for the work- men and economy in labour. Water gas has also been applied to the process of steel making, and the results attained have been very successful, FIG-. 39. Welding boiler furnace with water gas. showing a considerable economy in fuel consumption as well as a higher production rate, owing to the quicker working. The quality of the steel made in the open hearth furnace heated by water gas is excellent, and fully equals the best crucible steel. As an example of the economy and speed of the operation, it is stated that the consumption of gas required to melt a charge amounted to only 750 cubic WATEE GAS. 235 feet of water gas per hundredweight of steel. For the casting of large objects, the use of gaseous fuel permits of several furnaces being heated at once to the same tem- perature, and in a far more simple manner than with solid fuel. Besides proving successful in connection with the manu- facture of iron and steel, and the working of these metals, such as welding, annealing, chain making, etc., water gas is steadily gaming ground in other industrial processes, such as glass melting, glass blowing, enamelling, etc., and in fact for all the processes to which gaseous fuel can be put. By generating the gas at a central station in a works and distributing it in pipes to the various departments where it is required, a considerable saving in the handling of fuel can be effected, as with solid fuel it would have to be carried round to the different places, which means labour and waste. For the generation of power, water gas can be successfully used in internal combustion engines without any trouble from pre-ignition by simply regulating the degree of com- pression, a consumption of 30 to 35 cubic feet per horse- power per hour being the average amount used ; and by employing small engines at the various points where power is required, all drawing gas from the central generating station, the distribution of power is much cheaper than in the case of steam, as all shafting and belting for transmission are done away with. Water gas was used by Gillard as early as 1839 for lighting, by burning it under pressure for heating a small platinum mantle, but it was not a success, as the sur- face of the metal soon became eroded by the action of the carbon monoxide, and was also acted on by the iron car bony 1, a gaseous compound of iron and carbon monoxide, traces of which are always present in water 236 LIQUID AND GASEOUS FUELS. gas, and which breaks up in the water gas flame, deposit- ing iron oxide on anything heated in it for any length of time. Later on, when the " European " process was working at Essen, the town and works were lighted with water gas used in conjunction with the Fahnehjelm comb, which was introduced in 1883, and consists of a comb of fine rods of magnesia, set in a metal back, which is fixed at the requisite height above a flat flame burner consuming water gas, and which gave a light of 4*3 candles per cubic foot of gas con- sumed. Its light - giving pro- perties and endurance were afterwards improved by Dellwik, who dipped the comb in dilute chromic acid before using. With an ordinary in- candescent mantle, water gas gives a splendid light when burnt in an argand FIG. 40. Fahnehjelm comb. burner of proper con- struction, and the author has obtained a light of 19 candles per foot when using it in this way. Many observers contend that it has only a low illuminating power, because the gas has a calorific value of only 300 to 320 B.T.U. as against 620 in coal gas, but this mistake has arisen from using it in an ordinary incandescent burner, whereas water gas being non-luminous and easily oxi- dised requires no previous admixture with air. A water gas flame is hotter than a non-luminous coal gas flame, because a much larger volume has to be burnt in the same WATER GAS. 237 space to give a flame of definite size, and it is the temperature of the flame that governs the light given by the mantle. When the mantle is used with water gas alone the light given by the mantle soon falls, owing to the deposit of iron compounds on the fabric, but this can be avoided by washing the water gas in a scrubber with strong sulphuric acid. Another water gas process in use at several works on the continent, and an installation of which the author believes is being made at the Uxbridge Gas Works, is that known as the " Kramers and Aarts" process. The novelty in this apparatus consists of having two generators with a regen- erating chamber filled with chequer brickwork behind them, so that when the coke in the generators is being raised to incandescence by the air blast, any carbon monoxide that it may contain can be burnt by an extra air supply in the regenerating chamber to heat the chequer work, so that the products escaping up the chimney consist of the products of complete combustion only, and the heat which they con- tain is further utilised to raise the temperature of the extra air required for the combustion in the generator. When the right temperature of the fuel in the generators has been attained, steam is blown in at the bottom of the first gene- rator, the steam being in excess : the resulting mixture of hydrogen, carbon monoxide, carbon dioxide, and steam is then passed through the regenerators, where it is highly heated, and traverses the second generator, entering at the top and passing downwards through the coke. By this arrangement the carbon dioxide produced by the excess of steam in the first generator gets reduced to carbon monoxide, whilst any excess of steam is also decomposed into hydrogen and carbon monoxide. Inasmuch as in this generator the hottest portion of the fuel will be at the bottom, where the air blast has come more thoroughly in 238 LIQUID AND GASEOUS FUELS. contact with it, the gases finally leave the mass of fuel at the point of highest temperature. It is well known that when steam is forced in a contrary direction to that in which the air blast has been driven through the generator, the proportion of carbon dioxide is always less than when the steam passes in the same direc- tion as the air blast, and this principle has been used in many forms of generator. The author has no personal experience of the " Kramers and Aarts " process, but it is claimed that this alteration in the method of production increases the efficiency of the process. The apparatus, how- ever, is considerably more complicated than that of the Dellwik plant. Many generators have been devised for the manufacture of carburetted water gas, and in these the gas is rendered luminous by admixture with the vapours of various grades of oil after and during manufacture. The processes can be divided into two classes: (a) continuous processes, in which the heat necessary to bring about the interaction of the carbon and steam is obtained by performing the operation in retorts externally heated in a furnace : and (b) inter- mittent processes, in which the carbon is first raised to incandescence by an air blast. When the air blast is cut off steam is admitted until the temperature falls too low for the action, when the air is again admitted. The process therefore consists of alternate " blows " and "runs." The first class of processes has never been commercially successful, and the best of the intermittent processes, and the one which is now employed everywhere, is the one originally devised by Lowe, and which has undergone many improvements and modifications. In this apparatus the coke or anthracite is heated to incandescence by an air blast in a generator lined with fire brick, and the producer gas thus formed passes on to the superheaters, which are WATEK GAS. 239 chambers filled with chequer brickwork, and more air is admitted to ensure its combustion. By this means the superheater is raised to a high temperature. When the fuel and superheater are sufficiently hot, the air blast is cut off and steam blown through the generator, forming water gas, which meets the enriching oil at the top of the first superheater, called the carburettor, and then passes on to the fixing chambers, where the hydrocarbons are rendered permanent gases. The chief advantage of this apparatus is that a comparatively low temperature can be used for fixing, owing to the large amount of surface for superheating, which to a great extent does away with deposition of carbon. This plant is the only one which has proved successful in this country; and practically all forms of water gas apparatus are now founded upon the same set of actions. Several other types of carburetted water gas producers have from time to time been introduced in England, but without result. In the Springer plant, the superheater and fixing chambers were placed above the water gas generator, an oil heater and vaporiser being also employed. As in the Lowe plant, an air blast raised the fuel to incandescence, the producer gas being used to heat the superheaters and fixing chambers. Steam was then admitted down through the fuel, and the resulting water gas was partly led back again to the fixing chamber and partly to the oil vaporiser, where it helped to distil the crude oil and returned with the vapour to the fixing chambers, where the oil vapours were converted into permanent gases. Making the steam pass down through the fuel after it has been raised to incan- descence was also to be found in the Loomis plant, and, as we have seen, a great advantage is thus gained, as the fuel is hottest where the air blast enters, and by passing the water gas through the hottest portion of the fuel, the percentage of carbon dioxide is kept down. The Flannery WATER GAS. 241 apparatus was only a slight modification of the Lowe. As the gas left the generator the oil was fed into it, and the mixed gases and vapours passed into a D-shaped retort placed in the top of the generator, where the oil was volatilised and fixed in the superheater, in presence of the water gas. The chief feature of the Van Steenburgh plant was that the top of the fuel formed the superheater, so that no fixing arrangement was required, but in all these forms of apparatus far too much oil tar was formed, owing to insuffi- cient superheating of the oil vapour. The modification of the Lowe plant, which is most widely used at the present time, is that known as the " Humphreys and Glasgow " carburetted water gas plant. In this system the fuel is blown up to incandescence by an air blast in the generator, and the producer gas so formed is burnt in the carburettor and superheater, which are heated up by the combustion to the necessary temperature for decomposing the oil. When the fuel in the generator is sufficiently heated, the air blast is shut off, and steam is blown through it, the water gas passing to the top of the carburettor, where it meets the oil, and both are carried down through the carburetter, the oil being thoroughly " cracked" in its passage. In the superheater the oil vapours and water gas are subjected to another heating, which has the effect of finishing the conversion of the oil vapours into permanent gases. The mixed gases, after being subjected to washing, scrubbing and condensing, are ready for distribution as carburetted water gas. The great objection to carburetted water gas in Europe has always been the high percentage of carbon monoxide, which constitutes from 26 to 30 per cent, of the carburetted gas, and which, as has been before pointed out, is one of the most virulent gaseous poisons known. The composition of the mixture will of course vary with the proportion of oil gas mixed with the water gas, but the L.G.F. B 242 LIQUID AND GASEOUS FUELS. quality most used for enriching coal gas is from 20 to 22 candle gas, and has the approximate composition : Hydrogen . . . . . 37*20 Saturated hydrocarbons . . - 18*88 Unsaturated hydrocarbons . . 12*82 Carbon monoxide . . . , 28*26 Carbon dioxide . . . . 0*14 Oxygen . . . . . 0*06 Nitrogen . . . . . 2*64 100*00 So that the dilution of water gas by oil gas may be said to reduce the average percentage of carbon monoxide to 28, but with the exception of a short period in one of the divisions of Liverpool, carburetted water gas alone has never been distributed in this country, although in America about thirty of the largest companies send it out as a domestic supply. In Great Britain it is almost entirely used to enrich and augment the supply of coal gas, and the amount added depends largely upon local circumstances, the table on top of p. 243 showing the maximum and average percentages put into the coal gas in some of the more important towns. So that under ordinary conditions of working it is safe to say that 20 to 50 per cent, of carburetted water gas is added to the coal gas supply. The whole question of what quantity shall be permitted hinges on the percentage of carbon monoxide present in the mixture, and this should be kept down to a point that will prevent such small leakages as are possible in a dwelling room from being actively injurious or endangering life. It must be remembered that coal gas itself contains a certain proportion of carbon monoxide, the quantity being dependent upon the composition of the coal and upon the WATER GAS. 243 Town. Maximum. Average. Bath . 40 10 Belfast 50 30 Birkenhead 64 36 Birmingham . 24 Blackburn . 33 Bridlington 25 Brighton . . 42-79 22-25 Colchester . 20 Coventry . . 44 28 Hastings . 33 Hornsey . . 36 Liverpool . . 50 London (north of the Thames) 2025 Middlesborough 33 Norwich .... 36 - Preston 50 30 Southend .... 45 Southport .... 26 Swansea .... 25 Taunton . . . 40 Tottenham 50 Winchester 30 conditions of temperature and exhaust in the retorts. It has been found that the presence of combined oxygen in coal gives rise during carbonisation to the formation of oxides of carbon, and M. Ste. Claire-Deville, from a long series of experiments on 59 different kinds of coal, established the following relations : In Coal. In Gas. Percentage of Oxygen. Carbon Dioxide, per cent. Carbon Monoxide, per cent. 5 to 6-5 1-47 6-68 6-5 7-5 1-58 7-19 7-5 9 1-72 8-21 9 11 2-79 9-86 11 12 3-13 11-93 R 2 244 LIQUID AND GASEOUS FUELS. The presence of oxygen also in large percentage in the coal generally means a high yield of volatile hydrocarbons, hence a gas of high illuminating power ; but such coals are rather avoided by the gas manager, as they are high in price and ruin the coke. High retort temperatures also seem to have an effect in increasing the percentage of carbon monoxide. In an analysis of gas by Mr. Lewis T. Wright, it is shown that whereas a Derbyshire caking coal yielded 8'72 per cent, of carbon monoxide when distilled at a dull red heat, the same coal yielded 13*96 per cent, of this gas at a bright orange heat. A heavy exhaust would also tend in the same direction, as any trace of air leaking into the retort would form the monoxide. With the coals mostly used, however, from the Newcastle and Durham districts, the average percentage of carbon monoxide rarely exceeds 4 to 5 ; and it is now possible to gain* an idea of the quantity that might be allowed in the mixture sent out as illuminating gas. There is no danger of poisoning by such mixtures during the daytime, as the smell of the gas attracts attention to the danger long before the gas reaches a serious proportion ; nor is it any good considering the cases of large leaks, as from broken mains or torn down fittings, for there would always be the risk of fatal results whether the gas was coal gas only or a mixture of coal and water The real risk is during sleep from such leakages as might be produced by leaky joints or partly re- turn ing a loose tap when putting out the gas. Such a leak would practically never be a serious one, as if it were, it would be detected before the occupant of the room could get to sleep. The author's own view is that practical safety is assured as long as the percentage of carbon monoxide in the gas supply does not exceed 16 to 17. In the Departmental WATER GAS. 245 Committee's Keport on this subject in 1899, they recommend " that the proportion of carbon monoxide in the public gas supply at night should be regulated to 12 per cent., or such greater amount as the Department may consider advisable " ; and in the body of their report they say : " In some cases 12 per cent, of carbon monoxide in the gas supplied might be proper, in others 16, or perhaps 20. ... With the present condition of gas supply, 20 per cent, is the highest proportion of carbon monoxide that should be allowed, and this percentage should be used only under special circumstances." The views of the authorities in London are that the amount of carbon monoxide in the gas distributed should not exceed 16 per cent., and the Legislature is always so chary of doing anything to hamper unnecessarily a great industry, that the limit is not likely to be fixed below this point ; indeed, as coal gas per se may contain up to 12 per cent., fixing anything lower than 16 would be practically prohibiting the use of a valuable adjunct to gas manufacture. Taking, for the sake of calculation, the allowable limit as 16 per cent., this would mean that an ordinary coal gas containing 5 per cent, of carbon monoxide might have its bulk increased by carburetted water gas until the mixture contained 52 of coal gas and 48 of carburetted water gas, whilst if blue water gas were used the limit would be reached when the mixture contained 66 of coal gas to 34 of blue water gas ; in other words, to 100 volumes of coal gas one might add 92 of carburetted water gas, or 51'5 of blue water gas, before reaching the limit of 16 per cent, of carbon monoxide in the mixture. Where the desire is to provide a high candle-power gas such processes as the Humphreys and Glasgow system of making carburetted water gas are by far the best method of enrichment that can be employed, but the introduction of the incandescent mantle has wrought such a change in the 246 LIQUID AND GASEOUS FUELS. conditions of gas consumption that the parliamentary standard governing the illuminating power of gas has been relaxed, and the attention of the gas manager is now largely devoted to giving a gas supply of fair heating value at as cheap a rate as possible, so as to fit it not only for illuminating but fuel purposes. Looked at from a common-sense point of view the incan- descent mantle will be seen to be merely a method of enrichment. Instead of increasing the illuminating power of a flame by crowding into the gas more and more hydro- carbons, which, during combustion, are capable of separating carbon particles, the incandescence of which would increase the amount of light emitted by the flame, and pro rata the amount of heating with the mantle, the flame is charged with incombustible particles of far greater light emissivity than the carbon possesses, and they do their work without that increase in the temperature of the atmosphere insepa- rable from the other processes. It is therefore the introduc- tion of the incandescent mantle and the improvements which are possible in its construction which really give the possibilities to the gas of the future. Taking now the enriched, or, as some now prefer to call it, the adulterated 16-candle gas as supplied during the nineties, the light which can be obtained from it is entirely dependent upon the burner in which it is consumed. This may be stated as in table on opposite page. In considering the value given to the gas by these burners, it is seen that, according to the method by which it is burnt, the consumer may obtain anything from 35 candles down to less than one candle per cubic foot of gas. It must also be borne in mind that the burners employed in these tests were all good, well-made burners, giving the best duty that could be obtained from them, whilst an examination of the burners used in consumers' houses shows that in most cases any antiquated and corroded burner is considered WATEE GAS. 247 LIGHT EMITTED PER CUBIC FOOT OF 16- CANDLE GAS CONSUMED PER HOUR. Burner. Candle Units. Incandescent (high pressure) 30 to 35 (Kern) 20 25 ,, (ordinary) . 14 ,, 19 Regenerative . 7 ,, 10 Standard Argand 3-20 Ordinary Argand 2-90 Union jet flat flame, No. 7 2-44 6 2-15 5 1-87 4 1-74 3 1-63 2 1-22 1 0-85 0-59 good enough at which to burn the gas, and the very people who are loudest in their complaints as to the quality of the gas are those who most disregard the method of its consumption. It is quite clear that under such conditions as these the supply of gas of a high candle power is simple waste of money, and it is manifestly unfair that the consumer of average intelligence, who is willing to utilise the benefits given by the incandescent mantle, should have to pay for a quality of gas only rendered necessary by the inertia of those who decline to march with the times. Water gas is the only gaseous product cheap enough and sufficiently rich in calories to use in admixture with coal gas as a combined heating and illuminating gas, and a number of experiments have been made to ascertain the effect of merely mixing together coal gas and water gas in bulk. In practice, if a 16 per cent, limit was fixed by Parlia- ment for the carbon monoxide in the gas, it would be 248 LIQUID AND GASEOUS FUELS. manifestly unwise to approach the limit too closely, as during a press of work owing to fog or other causes that threw a strain on the resources of the works, a slight want of uniformity in mixing might hring the percentage above the limit. In these experiments 40 volumes of blue water gas were added to 100 of coal gas, which would give 28'5 per cent, of water gas in the mixture, and bring the carbon monoxide up to about 14 per cent. The gases were measured through a meter before mixing, and the resulting mixture was tested for calorific value in a Junker's calori- meter. The blue water gas used was purified from carbon dioxide, and had a calorific value of Calories per cubic foot B.T.U. 80*0 gross 73-4 net 320-0 293-6 , The results obtained are shown in the following table : Illuminating value of coal gas Coal gas . . . . . 17-6 16-0 15-3 15-1 Thermal value of coal gas Calories gross . . ... 172-0 159-9 158-8 149-9 ,, net , . . . , , 155-3 143-8 142-0 134-6 B.T.U. gross . / . 688-0 639-6 632-0 579-6 ,, net . . ~ . 621-2 575-2 568-0 538-4 Mixture Calories gross . . . . . . 146-0 135-6 136-8 129-1 ,, net 131-7 122-8 123-2 116-7 B.T.U. gross . . , 584-0 542-4 547-2 516-4 ,, net . , , . . 526-8 491-2 492-8 466-8 Percentage reduction in thermal value Gross . . . 15-1 15-2 13-4 13-9 Net . . . . 151 14-6 13-4 13-3 This table shows that, given an ordinary gas coal such as we. should in practice use, yielding 10,000 cubic feet per ton of a 15 to 16-candle power gas, it may have added WATER GAS. 249 to the 10,000 cubic feet 4,000 cubic feet of blue water gas, with a reduction of only 13 to 15 per cent, in thermal value. The experiments made by Mr. Patterson and others show that the reduction in candle power is practically propor- tional to the volume of water gas added, as one would expect, so that the candle feet per ton of coal carbonised would be practically the same whether they were present in 10,000 cubic feet of coal gas, or 14,000 cubic feet of the mixture. Instead, however, of mixing the blue water gas with the coal gas, a distinct advantage is to be gained by passing the gas into the foul main. This is done at several places in Germany, notably at Erfurt, and it is found that a distinct gain in candle power is obtained owing to the water gas becoming, to a slight extent, carburetted with benzol vapour present in the hot gas, which, if allowed to cool, would be taken up by the tar. The saving is found by less benzol being required to bring the gas up to a given candle power when the mixture is made in this way, than when, as is done in some other places, the water gas is enriched by benzol, and is then afterwards mixed in with the coal gas. In utilising water gas for the dilution of coal gas it is possible, however, to make it perform a far more important function than that of merely increasing the volume. As has been pointed out, one of the weakest points in the manufacture of coal gas is to be found in the process of carbonisation, which has undergone little or no change since the earliest days of the gas industry. When the coal is placed in the hot retort, evolution of gas at once com- mences with great rapidity, and, working with a five hours' charge, the largest proportion and the richest portion of the coal gas is evolved during the first three hours. The general course of the reactions is well shown in the 250 LIQUID AND GASEOUS FUELS. following table of results, found by Mr. Lewis T. Wright in his studies on carbonisation : Time of Observation (Seconds). Percentage of Total Gas. Average Retort Temperature. Candle Power per 5 c. ft. 30 12-3 1,108 21-8 60 26-1 1,212 202 90 38-9 1,200 17-7 120 , 52-6 1,292 14-8 150 65-8 1,315 13-5 180 78-6 1,360 11-7 210 86-5 1,435 10-7 240 92-6 1,531 7-1 270 96-4 1,613 5-1 300 100-0 1,671 3-8 In a lecture given before the Incorporated Institution of Gas Engineers, in 1900, the author suggested that, instead of using water gas merely as a diluent, it should be made a factor in the distillation itself. He proposed that a stream of water gas should be passed through the crown of the retort during the process of carbonisation, so as not only to hurry the newly-born hydrocarbon gases out of contact with the hot walls of the retort, but also by diluting them to prevent the secondary reactions which were so important a factor in the production of tar from taking place, and by so doing to save many of the important lighting and heating constituents from destruction. This process, which has for some reason been dubbed " Auto-carburetting," is now in use in a few English works and a large number of Continental ones, and is giving excellent results, and should prove of considerable value in the attempts of the gas manager to provide a cheap gas fit for both heating and illuminating purposes. The financial position of a gas works largely depends upon the market which can be obtained for the coke and other WATER GAS. 251 by-products, and where the demand for this is limited it is a very great advantage to the gas manager to be able to keep up the coke by for the GAS OUTLET COKING DOOR ANNULAR SPACE price of his utilising it manufacture of either blue or carburetted water gas, and it would manifestly be a still greater advantage if the excess of tar could also be dealt with on the works. In order to meet this object Mr. C. B. Tully has devised a plant for use in small gas works, in which, instead of carburetted water gas being made with oil in the ordinary way, tar is utilised for this pur- pose. Ever since the manu- facture of coal gas attained to a position of importance, attempts have been made to utilise the tar produced from it for reconversion into gas, but all efforts in this direction have been , ., FIG. 42. " Methane-hydrogen ' plant. more or less failures, owing to the difficulty of again breaking up into gaseous CLINKERING DOOR 252 LIQUID AND GASEOUS FUELS. products the complex hydrocarbons and naphthalene present in it, whilst the large amount of free carbon and pitch has been an insurmountable difficulty, as when a temperature sufficiently high to effect the decomposition into permanent gases has been attained, the yield of free carbon and heavy pitch has been so great as to choke everything up. Mr. Tully has got over this difficulty by making a gene- rator in which the fuel column is nearly double that found in a carburetted water gas generator, and three times more than that in a blue water gas generator. It is the lower portion only of this which is raised to incandescence by an air blast introduced through openings in the lower part of the generator. About midway up the firebrick lining nostrils connect with a flue passing entirely round the generator and opening into a stack pipe which is closed at the top by a snift valve. In this way the incandescent portion of the fuel is maintained at a definite height, as the products of the "blow" pass away through this flue, whilst the upper portion of the fuel is only raised to a moderate temperature. When the necessary incandescence of the fuel has been attained, the air blast is shut off and the snift valve closed, and the exhauster is started. At the same time tar is injected into the fuel from the clear space below a projecting ring in the firebrick lining between the flue and the air injectors, and steam also is turned on at the bottom of the generator ; this is directed upon the clinker and serves to break it up, and then passing upwards is converted into water gas. The tar gets broken up into carbon and gaseous products containing a large proportion of methane, and these mingling with the water gas formed from the steam, pass upwards through the generator. The carbon is filtered out by the cool charge above, and is used up as the fuel gradually sinks into the zone of combustion. The gas which finally leaves the generator is a mixture of hydrogen, carbon monoxide, and methane, with a very small WATER GAS. 253 percentage of carbon dioxide. From the generator the gas passes through the scrubber into the condenser to the exhauster, which forces it into the holder. Methane-hydrogen, as the gas is called, differs from water gas in many respects ; it burns with a yellow instead of a blue flame, due to the large volume of methane present, and the percentage of carbon monoxide is very much less. An analysis of methane-hydrogen made from coal gas tar gives the following result : Carbon dioxide ..... 2*8 Carbon monoxide . . . .28*8 Unsaturated hydrocarbons . . . 0*8 Saturated hydrocarbons . . . 19*2 Hydrogen 42*4 Oxygen ' . 0'2 Nitrogen 5*8 while the gas, owing to the quantity of the hydrogen and methane present, has a satisfactory thermal value. The plant has been in use for some time at Truro and at the gas works at Swindon belonging to the Great Western Kailway, and it has been found on extended working to give excellent results. CHAPTEK IX. POOE FUEL GAS. Incomplete combustion The principle of the gas generator Thermal considerations Bischof generator Siemens and his work Air-producer gas Blast furnace gas Dowson or semi- water gas The Dowson type of generator Anthracite as a fuel, and the considerations governing the size used The composition of Dowson gas Mond gas, and its production The Buire- Leucauchez generator The growth of the internal combustion motor Suction gas plant The Berrier suction generator Pintsch suction plant Dowson suction plant The adoption of the suction plant and gas engine for marine purposes The Emil Capitaine plant The use of bituminous coal for suction plant, and the troubles to be overcome The Duff-Whitfield generator The Boutillier plant. THE poorest in heat value, but for many purposes the most valuable as fuel, is the so-called generator or producer gas, formed by the incomplete combustion of carbon in a limited supply of air, and consisting of a mixture of com- bustible carbon monoxide and the residual nitrogen of the air. The small yellowish and blue flames which play over the top of a coal or coke fire that has burnt clear, show the principle of its formation ; the coke freed from all volatile matter merely emits the glow of incandescence in its com- bustion, but the small flame flickering above it marks the combustion of a secondary product. The draught in the chimney caused by the air and gases above the fire becom- ing heated and expanded and rushing upwards, draws in more air from the room, some passing above the fire, some through it. As the latter portion comes in contact with the POOR FUEL GAS. 255 incandescent fuel at the bars or grate of the stove, air is in excess, and complete combustion takes place, carbon dioxide being produced ; this, together with the residuum of the air, is drawn forward by the draught of the chimney through the red-hot fuel, and the carbon dioxide, parting with one half its oxygen to a further portion of carbon, yields a double volume of carbon monoxide, so that for every cubic foot of carbon dioxide that passes through the red-hot mass of carbonaceous matter, two cubic feet of the monoxide are produced, and reaching the surface of the fuel, there meet air streaming direct to the chimney, and being at a tem- perature above its ignition point, burn with the oxygen, giving the flickering flame, and re-forming carbon dioxide, which together with the residual air and nitrogen passes up the chimney. Now close in the space above the fire grate so that all air drawn in by the chimney draught must pass through the red-hot fuel, when a gas producer is obtained, and the mix- ture of carbon monoxide and nitrogen may be lighted, if desired, at the mouth of the chimney pot. It is quite clear that the flame burning on the chimney stack cannot give as much heat as the solid fuel and flame burning in the open grate, and one can gain an idea of the sort of loss taking place by calculation from the data already given (page 226). In order to simplify the problem, let us suppose we are dealing with pure carbon and oxygen, instead of coke and air. By the calorific data already given A unit weight of carbon burning to carbon dioxide gives 8,137 calories. A unit weight of carbon burning to carbon monoxide gives 2,489 calories. A unit weight of carbon monoxide burning to the dioxide gives 2,435 calories. Taking a pound for our unit, we see then that if we burn it 256 LIQUID AND GASEOUS FUELS. completely in our grate, 8,137 calories or 14,652 B.T.U. will be evolved. If, however, only half the required oxygen be used, and carbon monoxide is formed, supposing this to be possible, only 2,489 calories or 4,212 B.T.U. would be generated on the grate, but combustible carbon monoxide would be obtained. Taking the equation as Carbon. Oxygen. Carbon monoxide. 2 C + 2 = 2 CO 24 32 56 if 24 Ibs. of carbon give 56 Ibs. of carbon monoxide, then 1 Ib. of carbon gives 2*33 Ibs. When 1 Ib. of carbon mon- oxide burns to carbon dioxide, 2,435 calories are obtained, so that the 2'33 X 2,435 = 5,673'5 calories available when the carbon monoxide burns. We have therefore in the combustion of 1 Ib. of carbon generated 2,489 calories on the grate 5,673 ,, in the gas or a total of 8,162 (The discrepancy between 8,162 and 8,137 calories is due to small errors in the thermal values as determined experimentally.) So that the difference between completely burning the solid carbon in the grate or producing gas from it is that in the first case we get the whole of the heat developed locally, whilst in the second case we get a little under 30 per cent, of the heat developed on the grate of the pro- ducer, and over 70 per cent, available in the gaseous fuel ; a large amount of this loss, however, can be saved if the gas can be burnt close to the generator, and before it has time to cool. POOE FUEL GAS. 257 1 -V- 1 1 1 ,1 1 1 1 Where the heating work to be done demands great local intensity, then the solid fuel completely burnt in a furnace would be the best to employ ; but for very many operations the use of the solid would be so wasteful as to make it worth while to sacrifice the 30 per cent, of the heat in converting the remainder into gas, the ease and economy of the application of which will generally make up for the initial loss, and in many cases lead to a very large saving. The introduction of the gas producer probably dates back to 1839, when Bischof devised a simple form of generator, in which a chimney draught drew air in through the firegrate of a furnace, and the gases escaping at the outlet were utilised for gas firing. The most important epoch in the history of the rise of producer gas was when in 1857 Siemens FIG. 43. Bischof generator. invented his system of regeneration, in which chambers of chequer work were heated to a high temperature by the products of combustion escaping from the furnace, the heat being afterwards utilised to raise the temperature of the air and fuel gas, which by their combustion gave the heat in the furnace. Used in connection with this recuperating device a gas producer showed such economy and developed such high temperatures that it revolutionised many manufacturing processes. L.G.F. s 258 LIQUID AND GASEOUS FUELS. In the first generators made on this system Siemens, like Bischof, used the draught of a chimney to draw the air through the incandescent fuel, and adopted the ingenious device of making the flue that gave the draught also a syphon, which, as the gas cooled and increased in weight, flowed down to the furnace. The slow flow of air that could be obtained in this way, however, was a draw- back, and the idea soon arose of increasing the rapidity of combustion in the generator by means of an air blast pro- duced by a blower or a centri- fugal fan. When made by any such processes as those originated by Bischof and Siemens, in which air and incandescent FIG. 44. Siemens producer. fuel alone are employed, the only variations in the com- position of the gas will be those arising from differences in the fuel used and the rate of flow of air. Where coke is the fuel used the composition of the gas will approximate to Per cent. Carbon monoxide .... 29*0 Carbon dioxide . . . . . 4*0 Hydrogen . . . . . .2*5 Nitrogen 64*5 100-0 the trace of hydrogen being formed from moisture in the fuel. Such a gas is of very low calorific value, a cubic foot only giving about 19 calories, or 72 B.T.U. When, however, slack is employed, as is the case with POOE FUEL GAS. 259 nearly all producers on a large scale, the hydrocarbons in the coal improve the composition and thermal value, a typical analysis of a Siemens gas made with slack approximating to Per cent. Carbon monoxide .... 22*6 Carbon dioxide 4*4 Hydrogen 7*8 Methane 1*5 Nitrogen 63'7 100-0 with a thermal value of 32 calories, or 125 B.T.U. per cubic foot. Blast furnace gas, until lately allowed to burn to waste at the mouth of the furnaces in which the reduction of iron from its ores is carried out, is a gas of much the same character as the air-producer gas, and is now collected and used for steam raising and other fuel purposes, such as heating the blast. In order to collect the gases, the mouth of the blast furnace is generally closed by means of a bell cone, which, whilst allowing the feeding of fuel and ore into the furnace, closes it against escape of gas, whilst ducts open into the upper throat of the furnace and conduct away the gases, in many cases liquid by-products being condensed from the gas before it is burnt. The composition of such gas will vary considerably, but its average analysis will not differ much from the following : Per cent. Carbon monoxide . . . 27*71 Carbon dioxide 8*62 Hydrogen 1'34 Nitrogen 62'33 100-00 s 2 260 LIQUID AND GASEOUS FUELS. Its thermal value is, if anything, less than coke-producer gas, averaging 18 calories, or 70 B.T.U. The introduction of a blast to the gas producer at once caused an undue rise of temperature above the firebars, and led to serious trouble from clinkering and destruction to the iron grate, and attempts were then made to introduce air by means of a steam injector, as it was even then recog- nised that steam had a powerful influence in reducing temperature, and thus preventing, or at any rate diminish- ing, clinkering, whilst the production of an increased volume of hydrogen in the resulting gas increased to a valuable extent the thermal efficiency of the gas produced. Such gas is a varying mixture of generator or producer gas with water gas, and is generally known as " Dowson gas," owing to the fact that at the commencement of the eighties it was J. E. Dowson who first perfected the method of making the mixed gas, and devised a practical apparatus for its production, although it had been used on the con- tinent some years before, and Joshua Kidd had taken out a patent for increasing the value of the producer gas by passing steam as well as air through the fuel. The thermal advantages of such a process are manifest : it has been seen that the formation of producer gas by the passage of air through a bed of incandescent carbonaceous fuel is an exothermic action, heat being developed, whilst the production of water gas by passing steam through the heated fuel is endothermic, i.e., absorbs heat, and it is clear that if the passage of air and steam could be so regulated that the one action generated as much heat as the other absorbed, the fuel in the generator would be kept at a constant temperature, and a gas of fairly uniform composition would be obtained. Assuming, for the sake of simplicity, that we are dealing with pure carbon and oxygen, the conversion of 1 Ib. of carbon into carbon monoxide would evolve 2,489 calories POOR FUEL GAS. 261 (p. 59), whilst the conversion of 1 Ib. of carbon into water gas by the decomposition of steam would use up 2,361 calories (p. 226). One might imagine that if in a producer one half the carbon was burnt to producer gas by air, and the remaining half made into water gas by steam, a fail- balance of temperature would be established. Any such theoretical considerations are, however, entirely futile, as they presuppose that the whole of the heat generated by the combustion of the carbon by air can be utilised for supplying that required for the formation of the water gas, whilst in practice the heat escaping in the products, lost in radiation, and from many other causes, necessitates a considerably larger proportion of air to steam. Gas made in this way shows a considerable increase in thermal efficiency, owing to the increase in the percentage of hydrogen present, whilst these forms of apparatus give an advantage over air producers owing to the thermal actions in the generator using up a certain proportion of the heat as it is generated ; but it must be clearly borne in mind that for a given weight of fuel used in the generator, the heat units available in the gas formed must always be less than the amount which could have been generated by the direct combustion of the fuel, the advantage of gasifying the fuel being in ease of application, cleanliness, and ability to concentrate the heat at the desired spot. Very many forms of generator for the production of this semi- water gas have been devised, and in this country those most used are the Dowson, Wilson, Dawson, Mason, and Duff, whilst for making the mixed gas on a very large scale the Mond plant is the most economical, owing to the recovery of ammonia formed from the nitrogen in the fuel used. Plant of the Dowson type is mostly installed for power purposes, and for use in the gas engine it is essential that the gas should be scrubbed free from tar vapour and dust, 262 LIQUID AND GASEOUS FUELS. and should be delivered to the engine at atmospheric temperature : to ensure efficiency, the fuel to be employed in the producer is generally selected according to the purpose for which the gas is to be used. With the Dowson type of generator anthracite is the usual fuel, as the amount of tar produced by its combustion is small, and the quality of the gas good. The anthracite is generally screened at the colliery, the standard sizes being regulated according to the size of mesh through which it will pass. Will pass . . . 5 in. mesh. . 2J - ,, . If . f Size of Coal. Will not pass Large 5 in . mesh. Cobbles . 3 ? ) Nuts (French) . If 5 5 ,, (German) ) ) Peas f J J Duff or slack . t All sizes down to peas can be used, but for the best working the size should be governed by the diameter of the generator, and this becomes still more important when the anthracite is used for water gas making, as is often the case in America. When the anthracite is fed into the generator it packs most closely in the centre throughout the whole depth of fuel, and is loosest around the sides, with the result that in making gas both the air and steam show a tendency to work up near the walls of the generator, and there is a want of uniformity in the action, the central portion of the fuel in the generator being rendered partially inactive. With a large generator "nuts " might render as much as 30 per cent, of the fuel inoperative, whilst "cobbles " would reduce the inactive zone to 10 per cent, of the total. It must be remembered, however, that the surface of fuel exposed, and the resistance to air blast and steam are also important factors, and the smaller the coal the greater will POOR FUEL GAS. 263 be the surface and the less the space left for the passage of the gases, and this also requires proper adjustment. An idea of the difference made to these factors by the size of the anthracite may be gathered from the following table. Clearance in per- Surface of fuel ex- Size of Coal. centage of generator posed per cubic foot space. of generator space. Large . . 47 per cent. . 7 sq. feet. Cobbles . .46 10 Nuts (French) .44 .22 The smaller sizes can only be used in small generators, and slack or duff is a fatal drawback, as it chokes the air spaces between the pieces of coal, and forces the blast and steam to form channels, which, exposing too small a surface of incandescent fuel to the rapidly flowing gases, leads to the production of a gas of unsatisfactory composition. The Dowson generator consists of an iron shell lined with fire brick, in which the fuel rests upon fire bars below which the air is injected by a steam gas jet. The fuel is introduced at the top by means of a closed feed, and the gas is drawn off from the top of the generator, and after passing a hydraulic seal, goes through two scrubbers to free it from ash, dust, and tar vapour, and is then ready for use. The average of a number of analyses gives as the composition of the gas the following results : Per cent. Hydrogen 18'19 Methane . . . . . . 1-40 Carbon monoxide .... 25*17 Carbon dioxide ..... 5*98 Nitrogen 49'26 100-00 264 LIQUID AND GASEOUS FUELS. The calorific power ^is 42 calories, or 163 B.T.U. In practical working it is riot easy to maintain the gas of quite such high thermal value, as the clinker formed in FIG. 45. Dowson generator. the generator disturbs the results, and the calories per cubic foot gradually fall, until just before clinkering the value of the gas may be as low as 38 calories, or 150 B.T.U. The make, with a generator of this description, approximates to 80 cubic feet per pound of anthracite POOE FUEL GAS. 265 consumed in the generator. The form of Dowson generator now used as a suction plant is shown in Fig. 45. FIG. 40. Moncl generator. In the Dowson and other producers of this type the steam, generally superheated, is the motive power that 266 LIQUID AND GASEOUS FUELS. draws in the air necessary to keep up the thermal condi- tions in the generator, but in several other systems the steam and air are fed independently to the generator, and the most important of these is the Mond process, designed in the first place to recover the nitrogen present in slack, which is done by using such an excess of steam in the generator that the temperature is kept down, and the nitrogen converted into ammonia by the hydrogen liberated from the steam. The excess of steam present oxidises a large proportion of the carbon monoxide produced into carbon dioxide, which is present in the gas in considerable quantities, and this reduces its calorific value, but it con- tains a larger proportion of hydrogen, the high thermal value of which makes it a valuable power gas, whilst the process necessary for the recovery of the ammonia ensures its being well cleansed. Cheap bituminous slack is automatically fed in charges of 8 to 10 cwts. into a bell shaped casting that forms a con- tinuation to the feeding hopper, and which enters the generator for some little distance. Here the freshly intro- duced slack remains a short time, and undergoes a process of distillation, the hydrocarbon gases and tar vapours having to pass downwards through the body of hot fuel in the generator before they can escape, the vapours being in this way converted into fixed gases. The body of the generator is lined with fire brick, and at the bottom is a basket fire grate of inclined fire bars sloping down into a water seal for the removal of ashes and clinker. The generator has a double lining, and the mixture of air and steam passes in and down between the two casings, in this way keeping down the temperature of the inner lining, and at the same time heating the feed. The proportion of steam used is very large, being about 2J Ibs. for every pound of fuel gasified, and this excess POOR FUEL GAS. 267 serves the dual purpose of keeping the temperature below the point at which the ammonia formed by the com- bination of the nitrogen and hydrogen would again be decomposed, and also, by preventing caking and clinker- ing in the fuel, facilitates the automatic working of the plant. Leaving the generator, the producer gas, containing still an excess of steam, passes at a temperature of about 450 C. to the regenerator, consisting of a series of double tubes, where the hot gases, flowing through the inner tube, heat up the air and steam mixture flowing through the outer tube on their way to the generator. The gas then passes through the washer, a chamber in which rotating paddle-wheels throw up a fine spray, which cools the gas to 90 C. (194 F.), and so cooled it passes up a tower in which the gas is washed by 4 per cent, sulphuric acid, the ammonia being converted into ammonium sulphate, which remains in solution, and is continuously withdrawn and replaced by fresh acid. The gases, now cooled to 82 C., pass on to a cooling tower, where cold water condenses some of the remaining water vapour from it, and reduces the temperature to 61 C., at which it leaves the plant. The water, heated by cooling the gas, then flows down a third tower, up which the air feed for the generator, driven in by a blower, is passing, and saturates it with water vapour, and the moistened air, being further heated in the regenerator, passes on to the generator. The quantities and temperatures are so arranged that for every ton of slack fed into the generator about 2j tons of steam and 3 tons of air are blown in, and about 160,000 cubic feet of gas are obtained per ton of fuel, with about one ton of ammonium sulphate for every 28 tons of fuel consumed, about 23 tons being gasified and 5 used for producing the extra steam required. 268 LIQUID AND GASEOUS FUELS. The composition of the Mond gas approximates to Per cent. Hydrogen ...... 24'8 Methane 2*3 Carbon monoxide .... 13*2 Carbon dioxide ..... 12*9 Nitrogen ...... 46*8 100-0 The thermal value of the gas is usually about 38 calories or 150 B.T.U., so that, in spite of the cooling effect of the 13 to 16 per cent, of carbon dioxide found in it, the increase in the quantity of hydrogen and methane suffices to bring the calorific value up to as high a value as is found in a semi-water gc^s. The specific gravity of the gas is about 0'8. The complication in the plant needed for the ammonia recovery, which is the profit-earning part of the plant, renders it unfitted for installations of less than 4,000 h.p., and to give the best results it should work continu- ously. As this production is far beyond the needs of any but a few of the largest works, Parliamentary powers have been obtained for distributing the gas as a fuel supply in South Staffordshire over an area of some 120 square miles, the gas being sent out from the works through a 3 ft. main under a pressure of 10 Ibs. per square inch. By using a battery of generators the gas can be kept constant in pro- duction, and gas holders for storage dispensed with, the trunk mains really forming a storage chamber for the gas under pressure. It is supplied to the consumer through a reducing valve, which cuts down the pressure to that most suitable for the work in which it is to be employed. Another type of semi- water gas generator is the " Buire- Leucauchez." In this system no external source of steam 270 LIQUID AND GASEOUS FUELS. is employed, but a thin stream of water is allowed to trickle on to highly-heated iron plates below the generator grate, and being evaporated by the radiant heat, is caught up as steam by the air blast and carried into the bed of incandescent fuel. When poor fuel gas first forced its way into notice it was entirely as a heating agent chiefly for steam raising ; then came the adaptation of it to metallurgical and manufactur- ing processes, brought about by the introduction of the regenerative system by Siemens; and finally it has achieved its great success in the direct production of power by the internal combustion engine. The last thirty years have seen the rise of the gas engine from the early forms of the Otto and Langen type, which was limited in size to about three h.p., and certainly showed no sign of being a bantling, that in less than thirty years would grow into a power producer that would rend the supremacy from the steam engine as a source of motive power. The gas engine has even grown out of its name, and has now assumed the more ambitious title of " internal combustion motor " in order to enable it to cover the use of not only those gases rich in calories, such as coal, oil, and water gas, but also the poor producer and semi-water gases, and even petroleum vapour, alcohol, benzene, and atomised oil. Up to 1879 no fuel but coal gas was used in the gas engine, but in that year Dowson showed that it was possible to use the gas now commonly known by his name, and as the engine was gradually improved in construction, and the problems to be solved in its use became clearer, so modifications were made that led to the present compression type of engine and its further improvement, until now an indicated efficiency is claimed for it of over 30 per cent., whilst the size of the engine has grown from the original 3 b.h.p. Otto engine of 1876 up to 2,000 b.h.p.'s, and for POOR FUEL GAS. 271 many phases of power work the steam engine has practically passed away. When it was realised that the large percentage of incom- bustible nitrogen in theDowson gas was not an insuperable objection to its use in the gas engine, small generators of that type were largely employed for the production of the cheap semi-water gas for engines of moderate horse power. In attempting to further simplify the form of such generators the idea was revived of drawing the air or air and steam into the bed of incandescent fuel, instead of driving it in, but in place of using the suction of a flue to do this, as Bischof and Siemens had done in the earliest forms of generator, the attempt was made to use the suction in the engine cylinder, caused by the thrust of the piston, not only to draw gas from the generator to the combustion chamber of the engine, but also to draw air and steam into the fuel in the generator, so that the engine in its working should bring about the make of gas needed to continue its action. So arose the suction generator, which has so largely increased the use of the gas engine. The first of this type of generator was made, the author believes, by M. Leon Berrier in 1894, who fitted a suction pump to the side of the engine cylinder ; the pump being driven by the fly-wheel, sucked gas from the generator and compressed it into the engine cylinder, whilst the lowering of pressure in the generator sucked air and water vapour into the fuel, and made a fresh charge of gas. The first plant of this type that the author saw was near Berlin, in 1895, at Messrs. Pintsch's works, in which steam was generated by the heat of the gas passing to the engine in an external vaporiser, and was drawn under the grate of the generator and carried into the fuel by the air sucked in, whilst after passing through a scrubber, a purifier and a regulating valve, the gas travelled on to the com- bustion chamber of the engine. Since then many forms of 272 LIQUID AND GASEOUS FUELS. suction generators have been devised, differing mainly in small details only, but tending to the simplification of the plant. FIG. 48. Pintsch suction plant As an example of the latest type the Dowson suction plant, shown in section in Fig. 49, may be taken. In this plant the anthracite peas forming the fuel are placed in the container, which holds sufficient to last for several hours, POOE FUEL GAS. 273 and pass by gravity into the body of the generator as the fuel in it burns low. Water supplied at the right rate from FlG. 49. Dowson suction plant. a circular drip pipe, fed by a bird fountain, trickles on to a column of broken brick or iron in a chamber in the top lining of the generator, whilst air entering the vaporising chamber mingles with the steam, and the two then are L.G.F. T 274 LIQUID AND GASEOUS FUELS. sucked down below the bars at the bottom of the generator and pass upwards through the fuel : being there converted into gas, it passes through a water seal and coke scrubber to the engine. This form of plant has many advantages, not the least being the small stand-by loss when not at work, and low cost of repairs. The average fuel consumption is one pound of anthracite per brake h.p. hour, so that with anthracite at 20s. per ton, the b.h.p. only cost about O'l of a penny. Tests of the gas made in a Dowson suction plant by Mr. Ballantyne give the composition as being Per cent. Hydrogen . . , . . . 15*2 Methane . . . . . 1*2 Carbon monoxide . . . .21*0 Carbon dioxide ..... 8*2 Oxygen 0'2 Nitrogen . . . . . . 54.2 The fuel used was anthracite "peas," and its thermal value was 35*3 calories or 137'7 B.T.U per cubic foot, and as a rule the thermal value of the suction gas is about ten per cent, below that of gas made in the pressure plant. The latest development in the use of the gas engine and suction plant is in the direction of adapting it for marine purposes, and this is due to Herr Emil Capitaine, who not only played a leading part in developing the marine motor, but has devoted many years to adapting the gas engine for the propulsion of vessels. On a small scale this has now been successfully accom- plished, and a sixteen ton gas motor launch, named after the inventor of the system, Emil Capitaine, took part in the reliability trials for motor boats held in the Solent POOE FUEL GAS. 275 in 1905, and attained an average speed of ten miles per hour for ten hours on a consumption of 412 Ibs. of anthracite, this weight including the stand-by losses of the generator. Several tugs, barges, and other vessels fitted on the same principle are in use on the Continent, and a gas motor FIG. 50. Capitaine suction plant. barge, fitted by Messrs. Thornycroft, in the spring of 1906, made an extended tour of the English canals, the engine being under weigh for forty days, whilst to demonstrate the possibility of making marine gas engines of considerably higher horse power, Messrs. William Beardmore are con- structing sets of engines of 500 and 1,000 h.p., to work with gas producers on a 7,000 ton cargo steamer. As has been pointed out, one of the greatest essentials in T 2 276 LIQUID AND GASEOUS FUELS. using gaseous fuel for power is that it should be clean and free from tar or dust, which might give rise to choking in the valves and glands of the engine, and in the suction plants used with land engines coke scrubbers are employed, which would occupy far too much space for marine work. In the suction plant devised by Capitaine for his small power engines, the bulky coke scrubber is done away with, and the gas leaving the generator is first made to give up as much of its heat as possible to the ingoing air and steam in a double tube regenerator, and then passes on to a small tower, in which it is washed and further cooled by very fine sprays of water, which form, with the tar and dust, a fog in the gas, which is got rid of by passing the gas through a centrifugal machine running at a high speed ; this throws out the moisture and impurities, and leaves a clean gas to be sucked out by the engine. In order to start the generator a fire is lighted, and the anthracite having been fed in, air is blown in by a hand- driven fan until the gas produced will burn properly at a test cock ; this will take nearly half an hour with a generator of the size needed to supply 50 to 100 h.p. As soon as the gas is sufficiently good to burn, the engine is started by compressed air, and after a few strokes begins to run automatically. With large engines and producers a small oil motor is used for blowing up the fuel in the generator to the right temperature and starting the engine. The size of the generator is of course governed by the horse power required, the area of the fire grate necessary being 0*05 square feet per h.p., as against 0*2 square feet in an ordinary steam boiler consuming 15 Ibs. of coal per square foot of grate area. The composition of the gas is much the same as with an ordinary suction plant, an analysis of the gas POOR FUEL GAS. 277 from the Capitaine generator using anthracite as a fuel being Per cent. Hydrogen 14 Methane ...... 1 Carbon monoxide . . . . .25 Carbon dioxide ..... 6 Nitrogen 54 100 The constant and rapid changes in speed of a marine engine when entering a crowded waterway is a serious trouble, as after working for some time at a slow speed, the fire in the generator gets dull, and if the full load is then put on, and a large charge of air and steam is drawn into the fuel, a poor gas results until the temperature has recovered itself. The floor space occupied by the suction generator and engine for the larger powers may be taken as half a square foot per h.p., which compares favourably with the space taken up in vessels of the mercantile marine using steam power, although of course considerably above that possible in the service or in fast liners. The superficial area of engine and boiler space in various vessels is shown in the table on p. 278. As regards weight, the suction plant and gas engine com- pare favourably with steam, giving the same power at three- quarters the total weight of the steam plant. It is clear that if the marine gas engine is to be used for big powers, and is to take a place on ocean-going steamers, the fuel used in the generator cannot be restricted to anthracite or coke : it must be a fuel like bituminous coal, which can be obtained at any port, and although such cleansing processes as those adoped by Capitaine answer perfectly with a clean anthracite, directly a bituminous 278 LIQUID AND GASEOUS FUELS. coal comes to be used, coke scrubbers and elaborate con- densing apparatus become a necessity for getting rid of the tar vapours and other products of the decomposition of the hydrocarbons from the coal. As we have seen in the Mond and some other processes, bituminous slack is the fuel used, but at once a complicated plant for the recovery of the by-products becomes a necessity. Such plants could never be employed afloat, and until a really successful ss. Deutsch- land. ss. Konig Wilhelm der H.M.S. King Alfred. ss. Celtic. ss. Duke of Cornwall. H.M.S. Juno. ss. Indian. Grosse. Total i.h.p. . 38,900 30,000 30,000 13,000 5,520 9,830 2,120 Highest mean speed in knots . 23-51 22-79 23 16 19-75 20 10-75 Superficial area of engine and boiler space per i.h.p., sq. feet 0-425 0-42 0-346 0-96 0-405 0-44 0-949 Total weight of machinery in tons . 5,670 4,460 2,575 2,975 612 904 455 I.h.p. per ton of machinery . 6-35 6-71 11-65 4-37 9-02 10-88 4-66 bituminous coal generator has been devised, which will give a gas so clean as to require but very little treatment between the generator and engine, the problem of high power marine gas engines for big ships will remain unsolved. There have been many attempts to construct generators that will do this, but there are several factors which have prevented any of them being completely success- ful when employing the wide range of qualities in coal which have to be faced, and many of the generators for which, success has been claimed have had their weak points made manifest when it has been attempted to use them for POOR FUEL GAS. 279 a highly bituminous caking coal of the kind met with in many foreign ports. A generator can be made to deal with any non-caking coal, but directly the caking varieties are employed, the fuel swells and arches of coke are formed in the generator, FIG. 51. Duff-Whitfield plant. which produce cavities in the fuel, clinker, and other troubles that at once interfere with anything like uniformity in the composition of the gas or working in the generator, whilst if this trouble is overcome, the question of the destruction or elimination of the tar remains, and an idea of what that means is shown by the hundreds of failures in the gas industry to convert tar into permanent gas. A description of two of the most successful generators 280 LIQUID AND GASEOUS FUELS. using bituminous coal will give an idea of the general lines upon which inventors are working in their attempts to solve these difficulties. In the Duff-Whitfield generator, the hydrocarbon gases and tar vapour formed by the distillation of the coal freshly FIG. 52. Boutillier suction plant. fed into the generator are led by a pipe from the space at the top of the fuel, and are discharged into the incandescent mass just above the entering air, which, being the hottest point in the fuel bed, tends to decompose them, and before reaching the exit port these vapours have to traverse a considerable depth of heated fuel, which as far as possible completes the action. In the Boutillier plant, the generator is under-fed by a POOE FUEL GAS. 281 spiral stoker, which supplies the coal to the bottom of the generator, and the gas and tar distilling out have to pass up through the whole bed of incandescent fuel, which, as in the case of the Duff-Whitfield arrangement, is supposed to affect its complete decomposition. In these days of rapid engineering advancement it is never safe to dogmatise with regard to future developments, but the author's own feeling with regard to the marine gas engine is that it will be a success up to a few thousand horse power, but that it is doubtful if we shall ever see our monster liners and battleships developing the enormous power used by means of gaseous fuel burnt in any of the present forms of gas engine, the difficulties being to sufficiently cleanse the gas from tar without using up too much space for scrubbers and washers, and with the present forms of engines to sufficiently vary the speeds without the risk of stopping the engine. If these troubles were once thoroughly got over the economy of the suction gas plant would soon ensure its introduction on a very large scale. In a paper read early in 1907 before the Manchester Association of Engineers, Mr. A. V. Coster quoted figures showing the economy of gas engines over steam, each plant giving 1,400 i.h.p. on 200 days' steaming. In the case of gas the cost of fuel was 1,350, whilst with steam it amounted to 3,375 a saving in favour of gas of 2,025, whilst the weight of the gas plant was only 267 tons as against 373 tons with steam as the motive power. The necessity of a perfectly clean gas from the suction plant arises from the fact that regularity in running is dependent on keeping the valve seats free from tar, and scrubbing the gas with spray seems the most effective method of doing this, a 20 b.h.p. plant using from 2,000 to 3,000 gallons of water per week for ten hours a day working. 282 LIQUID AND GASEOUS FUELS. The consumption of fuel in a gas suction plant during the time gas is not being made, known as " the stand-by loss," is far lower than with any form of steam engine, generally only amounting to about one-seventh. In some recent trials of small plants the following results as to full consumption were obtained, the plants being from 15 to 20 b.h.p. :- Using anthracite as a fuel Full load : I'l Ibs. per b.h.p. hour. Half load : 16 Water : 1 gallon per b.h.p. hour at full load and at half load. Using coke as fuel Full load : 1*3 Ibs. per b.h.p. hour and 1J gallons of water. In all cases fuel needed for starting is included. CHAPTEE X. THE FUEL OF THE FUTURE. Comparison of the thermal values of our fuels : Solid, liquid, and gaseous The internal combustion engine as a measure of efficiency with gaseous fuel The future of the fuel question The life of our liquid fuel supply The era of gaseous fuel The utilisation of the peat deposits of the world Modern methods of making peat a valuable fuel The calorific value of peat briquettes as compared with other fuels The problem of the future The fixation of solar energy and its regeneration by combustion Fermentation and the production of alcohol from vegetation Alcohol as a fuel Denaturated or methylated spirit : Its calorific value Alcohol or petrol as a source of power in the motor engine. HAVING reviewed the various fuels and the way in which they are employed, it will be well to now collect and con- trast the data available with regard to their calorific value, so as to obtain a clearer idea of their relative value in thermal units as apart from their intrinsic value practice. in AVERAGE THERMAL VALUE OF FUELS. Calories. British Thermal Units. Coal- Newcastle . 8,446 15,203 Welsh 8,402 15,123 Lancashire ..... 8,113 14,602 Derbyshire ..... 8,120 14,616 Anthracite 8,677 15,619 284 LIQUID AND GASEOUS FUELS. AVERAGE THERMAL VALUE OF FUELS continued. Calories. British Thermal Units. Coke Oven coke ..... 8,020 14,436 Gas Coke 7,900 14,226 Peat 30 per cent, water 3,000 5,400 20 ... 4,000 7,200 10 ... 5,000 9,000 5 ... 5,500 9,900 Wood- Ash 4,711 8,480 Beech ...... 4,774 8,591 Birch 4,771 8,586 Elm 4,728 8,510 Fir 5,035 9,063 Oak 4,620 8,316 Pine . ... 5,085 9,153 Charcoal . ... 8,137 14,646 LIQUID FUEL. Petroleum (fuel) American . . 10,904 19,627 Russian ..... 10,800 19,440 Texas 10,700 19,242 Caucasus ..... 10,340 18,611 Borneo 10,461 18,831 Burmah 10,480 18,864 Petroleum spirit ('684) 11,624 20,923 Shale oil ...... 10,120 18,217 Blast furnace oil. 8,933 16,080 Heavy tar oil 8,916 16,050 Alcohol absolute 7,184 12,931 10 per cent, water 6,400 11,520 20 . . 5,700 10,260 methylated .... 6,200 11,160 THE FUEL OF THE FUTUEE. GASEOUS FUELS. 285 Natural gas ... . 12,008 21,615 Coal gas (London, 16 c.p.) 10,666 19,220 Water gas ... . . 4,430 7,980 Mond gas ... . 1,402 2,525 Dowson gas ... . 1,310 2,353 Suction-plant gas 1,200 2,160 Air-coke gas . . . 540 972 Blast-furnace gas 528 951 In this table the calories represent the number of kilos of water raised 1 C. by the combustion of 1 kilo of the fuel, whilst the British thermal units represent the number of pounds of water raised 1F. by the combustion of 1 Ib. of the fuel. In the case of the gaseous fuels the calorific value is determined per cubic foot burnt, and is then calculated from the specific gravity of the gas to heating value per pound. British Thermal Units. Cubic feet per pound at 60 P. Per cubic foot, gross. Per pound. Coal gas (16 c.p. London) 31 620 19,220 Water gas ..... 26-6 300 7,980 Mond gas ..... 16-4 154 2,525 Dowson gas 15-9 148 2,353 Suction-plant gas .... 16 135 2,160 The calorific value of a fuel tells us exactly how many heat units can be developed from a given weight by com- bustion, but it affords us no clue as to how much of that heat we can translate into mechanical work, the latter operation being dependent upon the degree of perfection in the heat engine we employ for the conversion, and often 286 LIQUID AND GASEOUS FUELS. proves a more important factor than the heating value of the fuel. The classic researches of Joule showed us that 778 foot- pounds were equal to 1 British Thermal Unit, and we know that 38,000 foot-pounds per minute are equal to one horse power, and it follows that, on the assumption that we are oo ooo using a theoretically perfect motor, ' or 42*42 British 778 Thermal Units per minute will give one horse power. The perfect motor has not yet however been attained, and the percentage ratio of the attained to the theoretical is generally spoken of as the efficiency of the engine, and is best expressed in efficiency per brake horse power. This factor is determined by experimentally finding the thermal units per minute developed by the fuel and the brake horse power, when 42 42 X gives the B.T.U. per minute per b.h.p. percentage efficiency per brake horse power, and the ratio of the true value of fuels as a source of power can be arrived at by taking their maximum efficiency as obtained in practice and seeing how that percentage of their utilised heating value compares one with the other. B.T.U. utilised, Fnpl British Thermal Efficiency per Ib. x 1 U61. Units, per b.h.p. B.T.U. x Efficiency per Ib. 100 Coal (steam engine) . 14,800 8'6 1273 Coal (turbine) .... 14,800 12-0 1776 Oil (in Diesel engine) 19,440 32-0 6220 Petrol . ... 20,923 22-0 4603 Alcohol . ... 11,160 38-0 4241 Coal gas . ... 19,220 25-0 4805 Mond gas . ... 2,525 26-0 656 Dowson gas 2,353 26-0 612 Suction gas 2,160 26-0 562 Blast-furnace gas 951 25-6 243 THE FUEL OF THE FUTURE. 287 The factors in the internal combustion motor which make for high efficiency are to be found not only in the engine itself, but also in being able to employ high compression of the explosive mixture, a cool cycle, and proper proportioning of the combustible and air. The conversion of the heat units of a solid fuel like coal into mechanical work means having first to convert them into steam, and then utilise the steam in the steam engine, a process so wasteful that with a good type of boiler and condensing engine only about 8J per cent, of the theoretical value of the heat units in the coal is converted into power, which the turbine increases to 12 per cent., whilst with a liquid or gas the internal combustion motor offers a con- version so far more economical that it is small wonder that steam as a source of power is looked upon as doomed. The great advantages in weight of fuel employed however are somewhat tempered by cost, as for instance in the case of coal and oil, because although a pound of oil in the best type of engine gives five times as much power, oil of the necessary quality could not be obtained in bulk under 4d. per gallon, and it is the cost sheet which to the user is the true test of efficiency. In the following table the approximate cost per b.h.p. is given Consumption per b.h.p. Cost of Fuel. Pence per b.h.p. Coal 2 Ibs. 18s. 6d. per ton 0-2 Oil (sp. gr. -8) Petrol (sp. gr. '7) . 0-4 0-55 4d per gallon Is. 0-2 0-94 Methylated spirit . 0-6 2. 1-75 (sp. gr. -82) Coal gas . 16 cub. ft. 2s. per 1,000 cub. ft. 0-4 Power gas lib. 20s. per ton o-i (anthracite) 288 LIQUID AND GASEOUS FUELS. The future of the fuel question is one that always must be fraught with the deepest interest. There is not the slightest doubt that with regard to fuel, the world is in the position of a man who is living on his capital, and although the end may be long delayed it is bound to come sooner or later. The question of the life of our coal supplies is one that has occupied an enormous amount of attention, and is being very fully dealt with by a Koyal Commission, which has already issued a warning note : " Vast as are the avail- able resources, it must be borne in mind that a large per- centage of them are of inferior quality, or are contained in deeper and thinner seams, which cannot be worked at the present cost." We may take 236 million tons of coal as representing the quantity annually raised in this country, and it is interesting and instructive to note the uses to which it is applied, the figures quoted being those compiled by the Koyal Commission on Coal Supplies : Factories . . '. . 22*97 per cent. Domestic .... 13*87 Iron and steel manufacture 12*17 ,, Mines 7'80 Gas works .... 6*50 ,, Kailways .... 5*63 ,, Potteries, brickworks, glass- works and chemical works 2*16 ,, Metal and minerals . . '43 ,, Coasting steamers . . '87 ,, Steamers over seas . . 7*25 ,, Exported .... 20'35 Of the total coal supply of the country about 52 million tons 'are annually used for the production of power, and THE FUEL OF THE FUTUEE. 289 although in the best forms of triple expansion engines worked by the most economical forms of boiler it is possible to get the consumption of coal down to 2 Ibs. per horse- power hour, the average consumption is a little over 5 Ibs., as an examination of the engines in the factories through- out the country reveals all kinds, from the most modern to beam engines erected in the first half of the last century, and if all these ancient steam wolves were relegated to the scrap heap and replaced by steam turbines, and where possible by internal combustion engines fed either by coal gas or suction-plant gas, the average consumption could easily be reduced to 1J Ibs. per horse-power hour. The question of the probable future supply of liquid fuel is still less encouraging. As long ago as 1886 Professor J. P. Lesley, addressing a meeting of the Institute of Mining Engineers in Pittsburg, said : " I am no geologist if it be true that the manufacture of oil in the laboratory of Nature is still going on at the hundredth or the thousandth part of the rate of its exhaus- tion. And the science of geology may as well be abandoned as a guide if events prove that such a production of oil in Western Pennsylvania as our statistics exhibit can continue for successive generations. It cannot be. There is a limited amount. Our children will merely and with difficulty drain the dregs. I hold the same opinion respecting natural gas, and for the same reasons, with the difference merely that the end will certainly come sooner and be all the more hastened by the multiplication of the gas wells, and of the fireboxes and furnaces to which it is led." This has proved to be true with regard to the natural gas, whilst, although statistics show that the output of oil is increasing, an analysis of the returns indicates that this is due to increase in the number of wells, and not to any increase in natural supply, the oil-bearing wells being L.G.F. u 290 LIQUID AND GASEOUS FUELS. extremely short-lived, and the rapid multiplication of new wells using up at an alarming rate the available area over which the oil is found. Under these conditions it is impossible to resist a glance forward to the period when, our capital being exhausted, we are driven to search out fresh means of developing the heat energy upon which commercial supremacy is so absolutely dependent. As our present supply of solid and liquid fuel becomes less and less, there will be an intermediate period in which fuel substances hitherto neglected will be pressed into service, whilst feverish economy will take the place of the prodigal waste which at present characterises our use of existing fuels. The use of steam as a motive power will grow less and less before the conquering strides of the internal combus- tion motor, and where it is used it will be in the turbine and not in the reciprocating engine. This period also will see great advances in the centralisation of power production, and in no case will this be more marked than in the manu- facture of gas, which, made in coke ovens at the colliery, will be distributed under pressure over great distances, the gas being not a high power illuminating gas but a mixture of the coal gas from the coal and water gas from all the coke that is not required for metallurgical purposes, the mixture having 8 to 10 candle power, and between 400 and 500 B.T.U.'s per cubic foot, with a selling price of under Is. per thousand, and will be used for illumination with the incandescent mantle, heating in the gas stove, and power in the gas engine. This period will also see the utilisation of the vast deposits of peat, and the rapid commercial development of those countries in which it is to be obtained. An idea of the general distribution and quantity of peat likely to be available may be gathered from the following THE FUEL OF THE FUTURE. 291 table, showing the areas of peat bogs in various European countries, whilst in Canada and America the supplies are even more vast. Sweden. . . . 5,198,500 hectares. Norway . . . 1,600,000 Denmark . . . 81,000 Finland . . . 7,400,000 Kussia (in Europe) . 38,000,000 Ireland. . . . 475,000 Germany . . . 2,837,000 In a drained "settled" bog the content of dry peat fibre is about 12 J per cent. One hectare is 2'47 acres, thus containing 1,250 tons of peat per metre of depth of bog. A bog with an average depth of 2J metres will consequently give 3,125 tons of peat (calculated as dry fibre) per hectare. In all processes for the preparation of a useful fuel from the enormous peat deposits of the world the trouble has been to find a method by which the large quantity of water held by the raw peat could be economically reduced to a percentage that would make the peat a fuel of sufficiently high calorific value to compete with the other solid fuels. The raw peat as won from the bog contains anything up to 88 per cent, of water so firmly held by the fibre that pressure, centrifugal wringing, and other mechanical means are unable to eliminate any considerable percentage, whilst to evaporate by artificial heat the 80 to 88 per cent, of water would use more fuel than would be left, the result being that air-drying has been the only possible method to employ to get rid of at least part of the moisture in the peat. Air-drying, however, necessitates time, space, and, above all, dry atmospheric conditions, the latter being rarely met with in the humid districts in which the peat bogs are u 2 292 LIQUID AND GASEOUS FUELS. found, and the result has been that the practical output of peat fuel has been very small, whilst the thermal value has been so low that it has had no market where other forms of fuel were obtainable. It has now been found that when peat, as obtained from the bog, is pulped into a homogeneous mass and heated under pressure to a temperature between 150 and 180 C. it ceases to hold the water in the same way as before, with the result that it can be mechanically wrung or pressed out of the peat, whilst the residue on slightly warming can be moulded into briquettes having a considerably higher calorific value than any previously made, whilst chemical actions just started in the tissues of the peat cause the exudation of small quantities of hydrocarbons of the nature of paraffins, which, on pressing the warm peat residue in a briquetting machine, cause the fibres to bind together into a dense ebonite-like mass having a specific gravity of 1*28 with a good non-absorbent surface. The author has tested both laboratory-made medallions and briquettes made in this manner on a commercial scale for calorific value in the Mahler Bomb, with the following results : Medallion = 5,744 calories = 10,337 B.T.U. Briquettes = 5,136 = 9,245 Peat briquettes have been made for some time in both Sweden and Canada, the process generally being to take the raw peat with its contained water, amounting to between 80 and 90 per cent, of the mass, air-dry the moisture down to 50 per cent., disintegrate and dry by artificial heat down to 15 to 20 per cent, of moisture, pulverise and mould hot into briquettes. The ordinary peat briquettes made by such a process have a calorific value below 4,000 calories, the most often quoted figure being 3,802 calories, given by a determination THE FUEL OF THE FUTURE. 293 made by the Koyal Chemical Institution of Berlin, and the great superiority of this type of briquette in thermal value is entirely due to the more thorough elimination of water during the process of manufacture. The importance of eliminating the water may be seen from the following analyses of moisture in peat, and the calorific value of the samples as determined by the Bomb : Percentage of Moisture Calorific in the Peat. Value. 26-0 3,246 22-0 3,802 21-0 4,115 16-0 4,331 15-0 4,490 12-0 . 4,832 7-37 5,136 6-12 5,489 5-9 5,744 If these figures be plotted diagrammatically it will be seen that it is practically correct to say that each 10 per cent, of moisture present in the peat reduces the thermal value by 1,000 calories. A black peat medallion, which gave a calorific value of 5,744 calories, was made in the laboratory by the wet car- bonising process at a temperature of 180 C., which means a pressure of nearly 10 atmospheres, or 150 Ibs., on the square inch, and contained 5*9 per cent, of moisture ; whilst a peat briquette made by the same process and which had a thermal value of 5,136 calories, and had been made on a commercial scale at a temperature of 155 C., contained 7*37 per cent, of moisture. In order to gain a clear conception of the fuel value of the peat briquettes, it will be well to contrast their thermal value with other forms of fuel. 294 LIQUID AND GASEOUS FUELS. Eight thousand four hundred calories may be accepted as fairly representing the run of English coals, whilst the average of the German coals would be nearly 1,000 calories less, i.e., 7,400. It is not, however, the best samples of coal which are Effect of Moisture on the Thermal Value of Peat. 6000 5000 4000 3000 10 20 Percentage of Moisture. FIG. 53. 30 always exported, so that it would be probably fair to take 8,000 calories as a heat standard. Taking now the peat briquettes at 5,136 calories, the K-I O* ratio to ordinary coal will be - = 0'64, or approximately oOOO two-thirds the value, weight for weight, of coal. The briquettes, however, would have a considerable advantage in stowing over coal, owing to their packing THE FUEL OF THE FUTUEE. 295 close ; a ton of briquettes will occupy 30 cubic feet, whilst the average stowage value of the Newcastle coal would be 43 to 45 cubic feet, or one-third greater, so that bulk for bulk the briquettes would represent just about the same heating value. It is not, however, with high grade English coal that the peat briquette comes into competition at present as a fuel, but with brown coal and lignite, which, on account of the high moisture and ash contained in them, rarely have a heating value much exceeding 4,000 calories and often below 3,000. Such coal, however, is often made into briquettes, in which a good deal of the moisture is driven off, which increases their calorific value, and it is with these brown coal briquettes that the peat briquettes will come most largely in competition. These brown coal briquettes are mostly made in Germany, and taking seven well-known brands, the calorific values range from 4,323 calories to 5,098, the average of them all being 4,959 calories, or 8,926 British Thermal Units. So that the peat briquettes made by this process are fully equal to the best brown coal briquettes in thermal value, and far superior to them in ash and sulphur. The peat briquettes burn with a clean, bright combus- tion, which can easily be regulated so as to be practically smokeless, and as they are not brittle the loss from break- age is very small. These properties make the briquettes an ideal fuel for the house and for many manufacturing operations, and their adoption on a large scale would do much towards cleansing the air of our big towns from the smoke nuisance due to the use of bituminous coal. There is another point in drawing comparisons between different kinds of fuel based on their calorific value that must not be overlooked, and that is the amount of air 296 LIQUID AND GASEOUS FUELS. needed for complete combustion. This, in the case of peat, is less than with coal, the result being that, in practice, so sharp a draught not being required, the heat of the peat is better utilised, and in working results the peat will often in steam raising more than hold its own with coal of a considerably higher thermal value. The peat, however, will not last for ever, and a time must be reached when a world, bankrupt in fuel, has to face one of the greatest problems that can be formulated, and then the work of ages long past will be utilised, and the memory of the work of men like Priestley, Sausaure, Helmholtz, and many others will help to a solution of this all-important question. We have seen that, no matter what the source of our oil supplies may be, all other forms of fuel at any rate are of vegetable origin, and \ve have also seen (p. 24) the wonder- ful cycle in Nature by which the balance of animal and vegetable life is kept constant, the energy derived from the sun being the determining factor which enables plant life to feed on the products of animal life, so revivifying the atmosphere as to make the living world a possibility. The more one studies this marvellous action, the more clearly does one see that the whole energy of the world is sunlight, that the vibrations of life are just as dependent upon the sun's rays as the growth of the plant, the only difference being that the plant has the power of absorbing and fixing a certain proportion of the energy flooded down upon it, whilst the living animal has to derive its energy second- hand from the vegetation and, in the higher grades of life, from the flesh that fed on it. In the same way, in combustion we see that the heat we derive from our coal, our peat, or wood, is simply energy which, during the life of the plant, has been rendered latent in doing the chemical work of breaking up carbon dioxide and water vapour, and storing the carbon in combination THE FUEL OF THE FUTUBE. 297 in the cellulose in such a form that, on burning back to carbon dioxide once more, the energy is again liberated as the heat and light which had its origin in the sun's rays, although thousands of years may have elapsed since those rays fell on the growing vegetation that afterwards formed our coal fields. Life without light is impossible, and both vegetation and animal at once deteriorate as soon as it is to any extent withdrawn. It is no false impulse that makes us yearn for sunny climes ; sun is life, and the sun's energy during countless ages has been stored up in the fuel beds of the world, and having squandered these, when we find ourselves bankrupt in our powers of heat production, it is to the sun again that we must turn. When we take stock of our sources of energy we find that we can employ gravity, muscular force, or the heat of combustion to generate power, but if we go still further back we find the energy of the sun behind them all. Without the sun the circulation of water in Nature would cease, and gravity would not help us much without water power ; cut off vegetation, and muscular power, deprived of vegetable and animal food, ceases ; cut off light, and the world returns to a lifeless mineral mass. As far as our knowledge goes, it is vegetation, and vegeta- tion only, that has the power of storing sun energy in such a form that it can be reproduced and converted into power when we require it, and the extent to which this action takes place is but limited, Helmholtz having calculated that of the energy exerted by the sun's rays on any area of growing vegetation about one fifteen-hundredth is fixed in doing chemical work, but small as this fraction is, it is an important asset in the future of the world, and although gravity employed as water power generated by cataracts and tides will be an important source of power, it is to the growing plant that we must turn for the main supply of energy generated in the fuelless world of the future. 298 LIQUID AND GASEOUS FUELS. It is quite clear that existing conditions would render impossible the conversion of vegetation into any of the forms of fuel to which we are accustomed, as, apart from the fact that the vegetation that formed our coal measures grew under entirely abnormal conditions, the conversion of the cellulose into peat, lignite, and coal is an operation which requires a combination of time, temperature, and pressure impossible now to attain, whilst, save to a very limited extent, timber even takes too long in its growth to be more than an insignificant adjunct. After careful con- sideration of every possible method by which growing vege- tation could be rapidly converted into available fuel for the generation of heat, we are forced to the conclusion that fermentation will be the only practical solution of the problem. Of the many forms of cellulose produced by the growing plant, starch is one of the most important, as it possesses an organised structure and is essential to the germination of the seeds. It is found in abundance in potatoes, wheat, and rice, an idea of the composition of which can be obtained from the following analyses : Potatoes. Wheat. Rice. Starch 20-2 60-8 83-0 Water 75-9 12-1 5-0 Gluten 10-5 6-0 Albumen 2-3 2-0 Dextrin and sugar 10-5 1-0 Woody fibre 0-4 1-5 4-8 Oily matter 0-2 1-1 o-i Mineral matter . 1-0 1-5 o-i 100-0 100-0 100-0 During germination a remarkable substance called " diastase " is formed, which has the power of inducing THE FUEL OF THE FUTUEE. 299 the conversion of starch into dextrin and maltose, which, when fermentation is started by the addition of a small quantity of yeast, is converted into alcohol. During this action 95 per cent, of the grape sugar is split up into alcohol and carbon dioxide, 4 per cent, forms succinic acid, whilst about 1 per cent, is used up by the yeast in its growth. Although grain contains such a larger proportion of starch than potatoes, the latter will always be the more economical source of fuel alcohol, as the crop per given area is much larger. For instance, an acre of land will yield about 12J cwts. of grain, equal to 8J cwts. of starch, but from the same ground you could get 125 cwts. of potatoes, yielding 22 cwts. of starch. A ton of potatoes yields from 25 to 28 gallons of absolute alcohol, or up to 30 gallons of 90 per cent, spirit, and this would mean that potatoes would have to be grown in such quantities as to sell at 20s. a ton l if the methylated spirit was reduced to Is. a gallon. It must, however, be remem- bered that excise restrictions very much increase the cost of production, whilst the Government charges for supervision and denaturation amount to about 5d. per gallon, and that when the day comes that sees the world dependent on alcohol fuel, such restriction will be swept aside or reserved for potable alcohol. The beetroot sugar industry has made great strides for- ward in France, and beetroot molasses is a cheaper source of alcohol than even potatoes, whilst still later experiments show that wood sawdust can be made so generous a source of alcohol that over 50 gallons of 90 per cent, alcohol per ton can be obtained from it, and, when the great demand for alcohol as a fuel arises, it will be found that vegeta- tion in all its forms will by proper treatment yield to 1 In Ireland, in a good season, potatoes cost 35s. to 40s. per ton wholesale. 300 LIQUID AND GASEOUS FUELS. fermentation and give us the means of regenerating the solar energy that caused its growth. For years past in both Germany and France the import- ance of keeping labour on the land and preventing over- crowding in the cities has led to the Governments of those countries doing all in their power to encourage the produc- tion of industrial alcohol, and in Germany especially State aid has not been spared to develop agriculture in this particular direction, and when we desire to know the value of alcohol as a fuel, we find that our own meagre experi- ments are entirely overshadowed by the work which has been done on the Continent. If we are to judge a fuel entirely by its calorific value, alcohol would prove itself but a poor substitute for the hydrocarbons derived from shale or petroleum, but, as has been pointed out on several occasions, there is a factor quite as important as calorific value, and that is the ease with which calories can be converted into work, and the use of alcohol and petrol respectively in the internal combustion motor is as good an example of this as could be cited. If we take the calorific value of alcohol as given by various observers, we are struck by the wide differences in the figures determined by them, and when one determines the value by experiment, one finds that the determination presents several difficulties. In the Bomb the difficulty of exact weighing with a volatile liquid and the formation of a trace of aldehyde during burning introduce errors, whilst if we vaporise and determine the calorific value in the Junker calorimeter, it is difficult to obtain a sufficiently high rate of combustion with accurate weighing to give true results. Another source of error, of course, is that the so-called "absolute alcohol," unless most carefully prepared, may contain a considerable percentage of water. The molecular heat of combustion of ethylic alcohol, as determined by Faure and Silbermann, was 330,450, THE FUEL OF THE FUTUEE. 301 which would give 7,183*7 calories per unit, whilst determi- nations in the Mahler Bomb give 6,950 calories, so that we shall not be far from the truth in taking 7,000 calories, or 12,600 B.T.U., as the thermal value of absolute alcohol, whilst methylated alcohol in the calorimeter gives a heating value of 6,200 calories, or 11,160 B.T.U., which is further Sp. Grav 7900 7950 8000 8050 8/00 8/50 8200 8250 8300 8350 8400 8450 8500 8550 8600 8650 8700 8750 8800 8850 8900 8950 9000 9050 '4 s f ^^ Percentage Alcohol by volume. Absolute \ 5 \ v \ 95 /o 90% -85% 80% 75% 70% V s \ V ^ i ^ \ s < \ >^ ^v s N I \ s KK/ s^ S 65 /o 7000 6500 6000 5500 5000 4500 4000 Alcohol- Calories Gross. FIG. 54. Alcohol curve. reduced when 20 per cent, of water is present to 5,450 calories, or 9,810 B.T.U. Taking the values determined for alcohol with known percentages of water and plotting them diagrammatically, a line is obtained which will give the calorific value for any per- centage of alcohol, and this may be approximately obtained by taking the specific gravity of the sample by means of the hydrometer and by reference to a specific gravity table. It is, however, the denaturated or methylated spirit that we must take into consideration, as it is the only form of 302 LIQUID AND GASEOUS FUELS. alcohol which at present, and probably for a long time to come, will be available for industrial purposes. This form of alcohol is, as a rule, 90 per cent, spirit, to which has been added something sufficiently foul in smell and taste to prevent even the most hardened drinker from attempting to use it as a beverage. In England this is done by mixing with the spirit 10 per cent, of methylic alcohol, or wood naphtha (CH 4 0), which has a lower thermal value than the ordinary, or ethylic alcohol (C 2 H 6 0), the calorific value of pure wood naphtha being 5,307 calories, or 9,552 B.T.U. Taking now the methylated spirit with its thermal value of 6,200 calories, let us see how it compares as a source of energy with those at present in use. As before pointed out, it is the internal combustion motor that at present must be taken as the index of success in the generation of energy, and in this field of utility alcohol at once comes into competition with petrol, which from the advent of automobilism has occupied the pride of place. Taking the thermal value of the two liquid fuels, alcohol seems to have but little chance as a competitor i Calories. Britishjhermal Petrol (sp. gr. '684) \ .' 11,624 20,923 Methylated spirit . . 6,200 11,160 the calorific value of the spirit being not much more than one-half that of the petrol. When, however, they come to be tested directly one against the other in practice, the difference practically nearly disappears, and in experiments made with a pair of eight horse-power engines, one designed for alcohol and the other for petrol, the consumption was : Petrol . . . 340 grams per horse-power hour. Methylated spirit . 373*5 THE FUEL OF THE FUTURE. 303 the efficiency calculated for the petrol being only 16*5 per cent., whilst for the alcohol it rose to 28 per cent. Moreover, it must be borne in mind that an enormous amount more work and experience has been brought to bear upon the petrol motor than has been devoted to alcohol motors, and there is very little doubt that when attention becomes more concentrated on the use of alcohol it will be found far more fitted than petrol for a motor fuel. The fact that it is possible to attain so much higher an efficiency from alcohol is due to two sets of factors first, the greater ease with which complete combustion can be obtained, and the smaller proportion of air needed as compared with petrol ; and secondly, the fact that with alcohol far higher compression and a comparatively cool cycle is possible, conditions which are amongst the most important in fuel economy. Taking first the question of combustion, we have seen that a good petrol may for all practical purposes be looked upon as hexane, C&H.U, as it is a mixture of this with the lower and next higher members of the group in proportions which give about this composition. The complete combustion of this compound will be represented by : C 6 H 14 + 19 = 6 C0 a + 7 H 2 2 vols. 19 vols. so that two volumes require 19 volumes of oxygen, and as oxygen constitutes 20*9 per cent, of the atmosphere, we can take the amount of air required as - . or one volume will require 45*45 volumes of air. So that in a petrol motor this would mean that for complete combus- tion there should be not more than 2J per cent, of petrol 304 LIQUID AND GASEOUS FUELS. vapour in the mixture entering the combustion chamber, whilst practice has led to generally 1J times the theoretical proportion of air being admitted, so that the petrol vapour is diluted with about 68 times its volume of air, four-fifths of which is inert nitrogen, taking no part in the action, but tending to hinder and retard the combustion; indeed, under ordinary pressure, such a mixture would not burn, much less explode. The compression of this mixture before explosion can only be taken to something like 80 Ibs. per square inch, owing to the risk of premature ignition, and the explosion then takes place with such rapidity that the diluting action of the nitrogen present prevents anything like complete combustion taking place, and the low efficiency and stench of the petrol motor is the result. With completed combus- tion the products would be simply carbon dioxide and water vapour, whilst the atmosphere of the London streets since the advent of the motor 'bus needs no analysis to show what is taking place. Compounds like the members of the paraffin group that go to form petrol, are highly susceptible to change from rise of temperature, and the heat generated by the compression already brings about a certain amount of change, otherwise there would be no risk of pre-ignition, as we know that a temperature of 1,200 C. is needed to ignite the mixture at atmospheric pressure, and at the moment of explosion such portions of the hydrocarbon as do not happen to be in contact with the necessary oxygen for their combustion, owing to the hindering action of the inert nitrogen, undergo changes, some simple, some complex, which result in the products of combustion containing not only the products of complete combustion and the product of incomplete com- bustion, carbon monoxide, but considerable quantities of hydrocarbons, such as ethane, propane, and acetylene, formed by the heat at the moment of explosion on the THE FUEL OF THE FUTUEE. 305 hydrocarbon vapours, and it is these products added to those from the lubricants that give the noisome stink which is the chief drawback to the autocar, or at any rate the chief cause of its unpopularity amongst the general public. It has been shown by M. Sorel that in many cases in the petrol engine 82 per cent, of the hydrogen and 42 per cent, of the carbon present in the petrol is wasted owing to such secondary reactions. If we take the petrol as being CeHu, then its percentage composition will be Carbon 83'7 Hydrogen ... . 16'3 100-0 so that as 16 ' 3 * 82 = 13-04, and 83 ' 7 ^ 42 = 35 . 15> 100 100 the total amount used in the actual explosion would be Carbon 83'7 35'2 = 48'5 per cent, available Hydrogen 16'3 13'0 = 3'3 and the thermal value of the proportion used would be 5,085 calories instead of 11,624. With alcohol, however, we do not find the same difficulty in getting approximately complete combustion, when once the mixture of vapour and air is made. Taking in the first place absolute alcohol, we find that its completed combustion may be represented by the equation : C 2 H 6 + 3 2 = 2 C0 2 + 3 H 2 2 vols. 6 vols. 100 X S so that the air required will be - - = 14'3 vols. per Z0*y vol. of alcohol vapour, or roughly one-third the amount needed by the petrol, and it is fairly easy with this more L.G.F. x 306 LIQUID AND GASEOUS FUELS. moderate proportion to attain an approximation to complete combustion, more especially as double the compression possible with petrol can be used. Where combustion with alcohol is incomplete, the products are aldehyde, acetic acid, and carbon monoxide, and it seems probable from the work of Dr. Trillat that there are three distinct stages of combustion in the engine cylinder, which are largely dependent upon the existing temperature Temperature. I. 200 to 400 C. C 2 H 6 + = C 2 H 4 + H 2 (Ethaldehyde) II. 400 to 500 C. C 2 H 6 + 2 = C 2 H 4 2 + H 2 (Acetic acid) III. above 500 C. C 2 H 6 + 3 2 = 2 C0 2 + 3 H 2 When it was first proposed to use alcohol instead of petrol in the internal combustion engine, it was prognosticated that the formation of acetone and acetic acid would cause such rapid corrosion and destruction of the valves and metal work as to render its use impossible, but the experi- ence gleaned by experiment in both France and Germany shows that with a little thoughtful care all trouble due to this cause can be so minimised as to be practically of no importance. There is no doubt but that the use of methylated alcohol or wood naphtha for denaturating the alcohol tends to the production of acetone and other acetic compounds of a more or less corrosive tendency, and on the Continent, when industrial alcohol has been required for power purposes, denaturation by benzene and pyridine bases and colouring by aniline dyes has been largely employed. One's first idea is that if alcohol could be enriched in thermal value by admixture with some hydrocarbon of high calorific value with a vaporising point so close to that of alcohol that we could rely upon their vaporisation taking THE FUEL OF THE FUTUEE. 307 place pro rata during carburetting, then it seems probable that the ease of burning of the alcohol might help the combustion of the hydrocarbon, and lead to a higher efficiency being developed. It would not do to use a mixture of petrol and alcohol, as they do not dissolve in each, other, and the petrol is far more volatile than methylated spirit, but benzene answers admirably for the purpose, and has been tried in conjunc- tion with alcohol in all proportions up to a mixture of equal parts. Benzene, as we have seen (page 98), is one of the first products of the distillation of coal tar, and is now obtained in enormous quantities on the Continent, and to a limited extent also in this country, from the recovery plants fitted to coke ovens in which the metallurgical coke is produced. This hydrocarbon has the formula C 6 H 6 , and is only a little less volatile than petrol, one pound giving 4*5 cubic feet of vapour measured at normal temperature and pressure. Like all the volatile hydrocarbons, there is a certain amount of variation in the determinations of its calorific value, which according to Thomsen is 10,1O2 calories, or 18,188 British theimal units, but the value as determined in the Bomb is generally approximately 9,880 calories, or 17,780 British thermal units. The commercial benzene is sold as 90 per cent, or 50 per cent, benzol according to the percentage distilling at the boiling point of water. Like petrol, it evolves inflammable vapour, even at the freezing point, and as regards danger in storage and use, is for all practical purposes the same as petrol, and can be perfectly well used in its place for motors. The experiments made with alcohol carburetted with benzene were highly satisfactory, and indeed the mixing of the hydrocarbon with the alcohol seemed to get over certain troubles as to temperature of carburation, which in many of x 2 308 LIQUID AND GASEOUS FUELS. the experiments with alcohol, when the ordinary form of carburettor was used, had shown themselves, and also showed a certain economy ; but M. Cheveau has found that even when mixed with the alcohol the tendency to undergo changes other than combustion, owing to decomposition and other causes, although it gives increased power, leads to a less efficiency than can be obtained with alcohol alone, and that a mixture of equal volumes of benzene and alcohol in experiments made by him on a 16 b.h.p. motor working at 180 revolutions gave an efficiency of 32 per cent., whilst with 90 per cent, alcohol alone he obtained an efficiency of 38 per cent. Benzene could never form a permanent carburettor for use with alcohol, as its present low price is entirely depend- ent on the demand for it for the production of aniline colours being more than satisfied by the amount condensed from the coke ovens, and before this source for it was utilised the benzene from coal tar fetched as high as 15s. per gallon, whilst now it can be obtained at Is., but if any large demand for it arose for use in the internal combustion engine, the price must again quickly rise to a prohibitive limit. In any case benzene could only have been used as a carburettor for alcohol whilst raw fuel, such as coal, was plentiful, and would disappear as soon as the natural fuel supplies failed : it is to alcohol, and alcohol alone, to which posterity will have to turn for a fuel, and the sooner this fact is recognised, and the full force of experiment is turned on to the problems of the alcohol motor, the better. The advantages of alcohol alone as a fuel are so great that it seems a pity that Government restrictions should render it practically impossible as an economical fuel. The motor boat and the submarine will undoubtedly play an important part in the coast warfare of the future, but alcohol would be the only fuel available if our foreign supplies were cut off. THE FUEL OF THE FUTURE. 309 Moreover, the safety of alcohol as compared with petrol in not forming an explosive atmosphere at ordinary tem- peratures, the power of extinguishing it when on fire by water, and the fact that it only consumes one-third the amount of air for a given power make it a far better liquid fuel than petrol for use in a submarine. A point which is greatly in favour of the use of alcohol in the motor, as compared with all other liquids yielding inflammable vapours, is that when mixed with air in the cylinder there is a greater range of composition over which the mixture is explosive than is found with any of the others. The effect of compression upon the range of mixtures of vapour and air which are explosive has never been deter- mined, but the effect is probably fairly constant with all such mixtures, so that the explosive range of various hydrocarbons and air will probably vary to much the same extent under compression in the cylinder as they do under atmospheric pressure. Alcohol vapour mixed with air is explosive at atmospheric pressure when the percentage of vapour is 4 per cent., and continues explosive until there is more than 13*6 per cent, present, so that the mixture may contain any percentage between these limits and still explode, whilst with other inflammable vapours the quantity is as follows : Explosive Percentage. Range. Alcohol . . .4-0 to 13'6 9-6 Ether. . . . 2'9 7'5 4'6 Benzene . . . '2*7 6'3 3'6 Petrol ... 2 5 3'0 The value of this extra range must be manifest when one considers the difficulty of getting an exact mixture of vapour and air in the cylinder. 310 LIQUID AND GASEOUS FUELS. A few years ago (1903) petrol could be obtained in bulk below 9d. a gallon, which meant that it was being sold below cost price, whilst now it has risen to a considerably higher figure, and the price will probably be forced up until other carburetted material is brought into competition with it. These fluctuations in price are largely dependent upon the supply of petrol being in a few hands : most of that derived from American oil is needed in America, whilst Russian oil yields but a small percentage of the most volatile spirit. The result is that the bulk of the English supply comes from less prolific and equally well controlled sources. The fact that the petrol supply can be so manipulated by the great oil rings makes it all the harder to introduce a competitor like alcohol, as directly alcohol began to com- mand the market, ifcs use could be killed by dropping the price of petrol, or by the demand causing a rise in price of alcohol, and an excellent illustration of this is to be seen in the use of alcohol in Germany. The production of alcohol there is State-aided, and everything that can be is done to make its use a success. In 1901 there was a very prolific crop of potatoes, and an enormous quantity of spirit was made, the price falling in 1902 and 1903 to Sd. and 9d. a gallon. Under these con- ditions alcohol motors and engines became a technical success, and an enormous number were put upon the market. In 1904, however, there was a failure of the potato crop, and a consequent rise in the price of alcohol to Is. 3d. a gallon, at which figure it became more expensive than petrol as a motor fuel, and its use for this purpose at once dropped to a very small percentage of the output. The fact that in Germany there is an import tax on petrol made competition easier for alcohol, but in a country like our own, with no tax on petrol, and alcohol so ham- pered by State regulations as to be practically doubled in price, no competition can arise between them until the THE FUEL OF THE FUTUKE. 311 gradual exhaustion of the petrol supplies renders its price prohibitive. In America the Department of Agriculture in 1906 instituted an inquiry as to the possibility of using alcohol as a substitute for petrol for motors, and in order to make the experiments as exhaustive and authoritative as possible, placed the experimental work in the hands of Professor C. E. Lucke, of Columbia University, and Mr. S. M. Woodward. These gentlemen issued on March 1st, 1907, a preliminary report on the subject, dealing with the use of alcohol in internal combustion engines not specially designed for its use. The conclusions they arrived at, so far, are (1) Any engine on the American market to-day, operating with gasoline or kerosene, can operate with alcohol fuel without any structural change whatever, with proper manipulation. (2) Alcohol contains approximately 0'6 of the heating value of gasoline, by weight, and in the Department's experiments a small engine required 1*8 times as much alcohol as gasoline per horse-power hour. This corre- sponds very closely with the relative heating value of the fuels, indicating practically the same thermal efficiency with the two when vaporisation is complete. (3) In some cases carburettors designed for gasoline do not vaporise all the alcohol supplied, and in such cases the excess of alcohol consumed is greater than indicated above. (4) The absolute excess of alcohol consumed over gaso- line or kerosene will be reduced by such changes as will increase the thermal efficiency of the engine. (5) The thermal efficiency of these engines can be improved when they are to be operated by alcohol, first, by altering the construction of the carburettor to accom- plish complete vaporisation, and, second, by increasing the compression very materially. 312 LIQUID A.ND GASEOUS FUELS. (6) An engine designed for gasoline or kerosene can, without any material alterations to adapt it to alcohol, give slightly more power (about 10 per cent.) than when operated with gasoline or kerosene, but this increase is at the expense of greater consumption of fuel. By alterations designed to adapt the engine to new fuel, this excess of power may be increased to about 20 per cent. (7) Because of the increased output, without correspond- ing increase in size, alcohol engines should sell for less per horse-power than gasoline 1 or kerosene 2 engines of the same class. (8) The different designs of gasoline or kerosene engines are not equally well adapted to the burning of alcohol, though all may burn it with a fair degree of success. (9) Storage of alcohol and its use in engines is much less dangerous than that of gasoline, as well as being decidedly more pleasant. (10) The exhaust from an alcohol engine is less likely to be offensive than the exhaust from a gasoline or kerosene engine, although there will be some odour, due to lubricat- ing oil and imperfect combustion, if the engine is not skilfully operated. (11) It requires no more skill to operate an alcohol engine than one intended for gasoline or kerosene. (12) There is no reason to suppose that the cost of repairs and lubrication will be any greater for an alcohol engine than for one built for gasoline or kerosene. (18) There seems to be no tendency for the interior of an alcohol engine to become sooty, as is the case with gasoline and kerosene. (14) With proper manipulation there seems to be no undue corrosion of the interior due to the use of alcohol. (15) The fact that the exhaust from the alcohol engine 1 Petrol. 2 OIL THE FUEL OF THE FUTURE. 313 is not as hot as that from gasoline or kerosene engines seems to indicate that there will be less danger from fire, less offence in a room traversed by the exhaust pipe, and less possibility of burning the lubricating oil. This latter fact is also borne out by the fact that the exhaust is smokeless. (16) In localities where there is a supply of cheap raw material for the manufacture of denaturated alcohol, and which are at the same time remote from the source of supply of gasoline, alcohol may immediately compete with gasoline as a fuel for engines. (17) If, as time goes on, kerosene and its distillates become scarcer and dearer by reason of exhaustion of natural deposits, the alcohol engine will become a stronger and stronger competitor, with a possibility that it may in time entirely supplant the kerosene and gasoline engines. (18) By reason of its greater safety and adaptability to the work, alcohol should immediately supplant gasoline for use in boats. (19) By reason of cleanliness in handling the fuel, increased safety in fuel storage, and less offensiveness in the exhaust, alcohol engines will, in part, displace gasoline engines for automobile work, but only when cost of fuel for operation is a subordinate consideration. In this field it is impossible to conveniently increase the compression because of starting difficulties, so that the efficiency cannot be improved as conveniently as in other types of engines. (20) In most localities it is unlikely that alcohol power will be cheaper or as cheap as gasoline power for some time to come. APPENDIX. TABLE OF ELEMENTS. Elements. Symbol. Atomic Weight. Specific Heat. = 16 H=l Aluminium . Al 27-1 26-9 0-219 Antimony Sb 120-2 119-3 0-049 Argon . A 39-9 39-6 Arsenic . As 75-0 74-4 0-083 Barium . Ba 137-4 136-4 Bismuth Bi 208-5 206-9 0-030 Boron . B 11 10-9 0-254 Bromine Br 79-96 79-36 Cadmium Cd 112-4 111-6 0-054 Cassium . Cs 132-9 131-9 0-048 Calcium Ca 40-1 39-8 0-180 Carbon . C 12-00 11-91 variable Cerium . Ce 140-25 139-2 0-044 Chlorine Cl 35-45 35-18 Chromium Cr 52-1 51-7 0-104 Cobalt . Co 59-0 58-56 0-103 Columbium . Cb 94 93-3 Copper . Cu 63-6 63-1 0-093 Erbium . Er 166 164-8 Fluorine F 19 18-9 Gadolinium . Gd 156 155 Gallium . Ga 70 69-5 0-079 Germanium . Ge 72-5 71-9 0-074 Glucinum Gl 9-1 9-03 Gold Au 197-2 195-7 0-032 Helium . He 4 4 Hydrogen H 1-008 1-000 Indium . In 115 113-1 Iodine . I 126-9 125-90 0-054 Iridium . Ir 193-0 191-5 0-032 Iron Fe 55-9 55-5 0-112 Krypton Kr 81-8 81-2 Lanthanum . La 138-9 137-9 0-045 316 APPENDIX. TABLE OF ELEMENTS continued. Elements. Symbol. Atomic Weight. Specific Heat. = 16 H = 1 Lead . Pb 206-9 205-35 0-031 Lithium Li 7-03 6-98 0-940 Magnesium . Manganese Mg Mn 24-36 55-0 24-18 54-6 0-245 0-122 Mercury Hg 200-0 198-5 0-033 Molybdenum Mo 96-0 95-3 0-066 Neodymium . Nd 143-6 142-5 Neon Ne 20 19-9 Nickel ... Ni 58-7 58-3 0-109 Nitrogen N 14-04 13-93 Osmium Os 191 189-6 0-031 Oxygen . . O 16-00 15-88 Palladium Pd 106-5 105-7 0-059 Phosphorus . P 31-0 30-77 0-202 Platinum Pt 194-8 193-3 0-032 Potassium K 39-15 38-86 0-166 Praseodymium Pr 140-5 139-4 Radium . Rd 225 223-3 Rhodium Rh 103-0 102-2 0-058 Rubidium Rb 85-5 84-8 Ruthenium . Ru 101-7 100-9 0-061 Samarium Sm 150-3 148-9 Scandium Sc 44-1 43-8 Selenium Se 79-2 78-6 0-084 Silicon . Si 28-4 28-2 0-165 Silver . Ag 107-93 107-12 0-056 Sodium . Na 23-05 22-88 0-293 Strontium Sr 87-6 86-94 Sulphur. S 32-06 31-83 Tantalum Ta 183 181-6 Tellurium Te 127-6 126-6 0-048 Terbium Tb 160 158-8 Thallium Tl 204-1 202-6 0-032 Thorium Th 232-5 230-8 0-027 Thulium Tm 171 169-7 Tin Sn 119-0 118-1 0'0n2 Titanium Ti 48-1 47-7 0-112 Tungsten W 184 182-6 0-034 Uranium U 238-5 236-7 Vanadium V 51-2 50-8 0-115 Xenon . Xe 128 127 Ytterbium Yb 173-0 171-7 Yttrium Yt 89-0 88-3 Zinc Zn 65-4 64-9 0-093 Zirconium Zr 90-6 89-9 0-066 APPENDIX, 317 Drachms. 10= 266= 7,168= Oz. 1 16 448 0(125= 28,672= 1,792 WEIGHTS AND MEASURES. AVOIRDUPOIS WEIGHT. Lbs. 0039= 0626= 1 = 28 Qrs. 000139= 00223 = = -0357 = = 1 = = 112 =40 = I 573,440=35,840 =2,240 =80 =20 Cwts. 000035= 000558= 00893 = 25 = =1 Ton. French Grammes. 00000174= 1-771846 28-34954 453-59 12,700 000028 = 000447 = 0125 = 05 = 50,802 =1,016,048 LONG MEASURE. Ins. Feet. Yards. Fath. Poles. Furl. Mile. Fr ench Metre 1= 083= 02778= 0139= 005 = -000126= 0000158= 0254 12= 1 333 = 1667= 0606= 00151 = 0001894= 3048 36= 3 1 5 = 182 00454 000568 = 9144 72= 6 2 1 = 364 0091 001136 = 1-8287 198= 16J 5 = 2| = 1 = -025 = 003125 = 5-0291 7,920= 660 = 220 =110 = 40 =1 := 125 = 201-16 63,360=5,280 =1 ,760 =380 =320 =8 =1 =1 ,609-315 MEASURE OF CAPACITY. Pints. 1 8 16 64 512 2,560 5,120 Galls. 125 1 2 8 64 320 640 Cubic ft. 02 1604 3208 1-283 10-264 51-319 102-64 Litres. 5676 4-541 9-082 36-32816 290-625 1,453-126 2,906-25 1 gallon = 277i cubic in. = -16 cubic ft. = 10 Ibs. dist. water = 4 '543458 litres. 1 cubic ft. = 6-2321 gallons. 1 grain = -064799 gramme. 1 Ib. avoir. = '453593 kilogram. USEFUL DATA. 1 Ib. avoir. = 16 oz. = 7,000 grains = 453-59 grammes = 1-21527 Ib. troy. 1 Ib. troy = 12 = 5,760 = 373-242 = 0*82285704 Ib. avoir. 1 oz. avoir. = 437-5 grains = 28'35 grammes = 0-9114583 oz. troy. 1 cubic cent. = -0610270734 cubic in. = '282 fl. drms. = '00176 pint = '0352 fl. oz. 1 cubic ft. = 28315-3 c. c. = 6-2321 gallons = 28-3153 litres = 997-1364 fl. oz. = 49-8568 pints. 1 gallon = -16046 cubic ft. = 277-274 cubic in. = 4-54346 litres. 1 cubic in. = 16-386 c. c. = 4-616 fl. oz. = '0164 litre = -02885 pint. 1 litre = -03531 6 cubic ft. = -220096 gallon = 61-0270 cubic in. = 1'761 pint. 1 fl. oz. = 28-396 c. c. = 1-7329 cubic in. 1 pint = 567-919 c. c. = '020057 cubic ft. = 34'659 cubic in. = '567920 litre. 1 gramme = '002204 Ib. = -03527 oz. = 15'432348 grains. 318 APPENDIX. TABLE FOR CONVERTING DEGREES OF THE CENTIGRADE THERMOMETER INTO DEGREES OF FAHRENHEIT'S SCALE. Centigrade. Fahrenheit. Centigrade. Fahrenheit. Centigrade. Fahrenheit. 90 130 40 104 170 338 85 121 45 113 175 347 80 112 50 122 180 356 75 103 55 131 185 365 70 94 60 140 190 374 65 85 65 149 195 383 60 76 70 158 200 392 55 67 75 167 205 401 50 58 80 176 210 410 45 49 85 185 215 419 40 40 90 194 220 428 35 31 95 203 225 437 30 22 100 212 230 446 25 13 105 221 235 455 20 4 110 230 240 464 15 +5 115 239 245 473 10 14 120 248 250 482 5 23 125 257 255 491 32 130 266 260 500 +5 41 135 275 265 509 10 50 140 284 270 518 15 59 145 293 275 527 20 68 150 302 280 536 25 77 155 311 285 545 30 86 160 320 290 554 35 95 165 329 295 563 To convert F. to C. To convert C. to F. C '. X 9 + 32 = TABLE OF THE CORRESPONDING HEIGHTS OF THE BAROMETER IN MILLIMETRES AND ENGLISH INCHES. Milli- English Milli- English Milli- English metres inches. metres inches. metres inches. 720 _ 28-347 724 28-504 728 28-662 721 28-386 725 28-543 729 := 28-701 722. 28-425 726 28-583 730 28-740 723 = 28-465 727 = 28-622 731 = 28-780 APPENDIX. 319 TABLE OF THE CORRESPONDING HEIGHTS OB' THE BAROMETER ETC. -continued. Milli- metres = English inches. Milli- metres = English inches. Milli- metres - English inches. 732 28-819 747 29-410 762 30-000 733 28-858 748 29-449 763 30-039 734 28-898 749 = 29-488 764 = 30-079 735 28-937 750 29-528 765 30-118 73(5 28-976 751 = 29-567 766 = 30-158 737 29-016 752 29-606 767 30-197 738 29-055 753 29-645 768 30-236 739 29-095 754 29-685 769 30-276 740 29-134 755 29-724 770 30-315 741 29-174 756 29-764 771 30-355 742 29-213 757 29-803 772 30-394 743 29-252 758 29-843 773 30-433 744 29-292 759 29-882 774 30-473 745 29-331 760 29-922 775 30-512 746 = 29-370 761 = 29-961 TABLE OF THE TENSION OF AQUEOUS VAPOUR EXPRESSED IN INCHES OF MERCURY, AT 32 F., FOR EACH DEGREE F. BETWEEN AND 100. Temp. Inches of Mercury. Temp. F. Inches of Mercury. Temp. F. Inches of Mercury. Temp. Inches of Mercury. 0-0439 19 0-1027 38 0-2291 57 0-4653 1 0-0459 20 0-1073 39 0-2381 58 0-4822 2 0-0481 21 0-1121 40 0-2475 59 0-4997 3 0-0503 22 0-1171 41 0-2571 60 0-5178 4 0-0526 23 0-1223 42 0-2672 61 0-5364 5 0-0551 24 0-1278 43 0-2775 62 0-5556 6 0-0576 25 0-1335 44 0-2882 63 0-5755 7 0-0603 26 0-1395 45 0-2993 64 0-5959 8 0-0630 27 0-1457 46 0-3108 65 0-6170 9 0-0659 28 0-1522 47 0-3226 66 0-6388 10 0-0689 29 0-1589 48 0-3349 67 0-6612 11 0-0721 30 0-1660 49 0-3476 68 0-6843 12 0-0753 31 0-1733 50 0-3607 69 0-7081 13 0-0788 32 0-1810 51 0-3742 70 0-7327 14 0-0823 33 0-1883 52 0-3882 71 0-7580 15 0-0861 34 0-1959 53 0-4026 72 0-7841 16 0-0899 35 0-2038 54 0-4175 73 0-8109 17 0-0940 36 0-2119 55 0-4329 74 0-8386 18 0-0982 37 0-2204 56 0-4488 75 0-8671 320 APPENDIX. TABLE OF THE TENSION OF AQUEOUS VAPOUR continued. Temp. F. Inches of Mercury. Temp. F. Inches of Mercury. Temp. F. Inches of Mercury. Temp. Inches of Mercury. 76 0-8964 83 1-1274 89 1 -3652 95 1-6457 77 0-9266 84 1-1643 90 1-4088 96 1-6971 78 0-9577 85 1 -2023 91 1-4537 97 1 -7498 79 0-9898 86 1-2413 92 1-4998 98 1-8039 80 1-0227 87 1-2815 93 1-5471 99 1-8595 81 1 -0566 88 1-3228 94 1 -5958 100 1-9170 82 1-0915 BOILING POINT AND LATENT HEAT OF WATER UNDER VARYING PRESSURES. Pressure. Boiling Point. Latent Heat. 1 atmosphere 212 Fahr. 966 thermal units. 2 249 940 3 273 923 4 291 910 5 306 900 . 6 319 891 WEIGHT AND VOLUME OF GASES. Weight. Volume. Per Cubic Per Cubic Per Kilo. Per Pound Metre in Foot in in Cubic in Cubic Kilos. Pounds. Metres. Feet. Air 1-2^318 0-08073 0-773 12-385 Nitrogen 1-25616 0-07845 0-796 12-763 Oxygen . . . 1-4298 0-08926 0-699 11-203 Hydrogen 0-08961 0-00559 11-160 178-83 Carbon dioxide . . . 1-9666 0-12344 0-508 8-147 Carbon monoxide 1-2515 0-07817 0-800 12-800 Carbon vapour. 1-0727 0-06696 0-932 14-930 Aqueous vapour 0-8047 0-05022 1-242 19-912 Sulphurous acid 2-8605 0-1787 0-349 5-596 Ethylene 1-2519 0-07814 0-799 12-797 Methane 0-7155 0-044H6 1-397 22-391 Acetylene .... 1-1900 0-07428 0-840 13-456 Benzol 3-3333 0-208 0-303 4-808 Ethane 1-3415 0-08565 0-746 11-950 APPENDIX. 321 5 B x . s a ^Jt*OO(5OSgOaOpH'*t.OOO>g'*t>g -+ Ci ri r: OJ 3^ cs M n 5 b C DP 03 g ^ t - 00 ss - tO <^ r- CC SS ^H tO CO GO 03 2 + i*Hi-4C4Ct:'aDAO>OO>-4i-H i **e, GCOOGOOOGOGOCOobcOOOCOOCaOOCOOQOo6o6GO S w a ^H CD ^ O- O CO CO C5 C^ lO QO ^H -^ l> O CO CO C^ "^ H" "02 S ~ 1? i i s S s s s 25 & tCj-H x g H x^" S2OeNGOCoS?^?OiO ftcMGOCOS?5oS2S 03 SI + OOi-H^HCSfMCO-^-^iOOCOCOt^t^COOSS^OO J 1 1 1 ^ I' OOaOQOCCQOQOQOCOQOCOGOOOQOQOQOQOGOGOGOGO O co 1 - ,O o iJ t> ft M CO -* " " ^* 1O CO t^ 00 O O O O O O O C^ C5 C^ O O wi Ci 3~ fc O H S 03 x o osioocowaocociOOco^aoco^iOOcofNoo 03 O O S J Cs Si' O C O O O O O O O C- C' C O 'C O O O O t^t^aCOOOCOOQOOOGOQOGCOOGOCOGOOOQOGOOOOO 03 g EM [2 .O^^COOOO^^COOOOCM^COOOO^^COCO PQ *" O -^ >b cb b- H L.G.F. 322 APPENDIX The British Thermal Unit is the amount of heat required to raise 1 Ib. of pure water 1 F., or from 39'1 F. to 40-1 F. The Large Calorie (French Unit) is the amount required to raise 1 kilogram of water through 1 C. The Small Calorie (Scientific Unit} is the amount of heat required to raise 1 gramme of water from C. to 1 C. The Pound Centigrade Unit is the amount of heat required to raise 1 Ib. of water from O c C. to 1 C. British Thermal Unit. Large Calorie. Small Calorie. Pound Centigrade Unit. Foot-pounds. B.T.TL Ca. Ca. Ib. C.U. 1 0-252 252 0"555 778 3-9682 1 1,000 2-2046 3,080 0-003968 o-ooi 1 0-002046 3-08 1-8 0-4536 453-6 1 1,397 QUANTITY OF Am EEQUIRED FOE THE COMBUSTION OF FUELS. Composition. Carbon. Hydro- gen. Oxygen. Nitrogen. cu. m. cu. ft. Coke . 98-0 0-5 10-09 162-06 Coal, anthracite . 95-4 2-2 1-8 0-5 9-01 144-60 bituminous . 87-0 5-0 4-0 . 8-93 143-40 coking . 85-0 5-0 6-0 . . 8-68 139-41 ,, cannel . 84-0 6-0 8-0 8-79 141-07 smithy . 77-0 5-0 15-0 7-67 123-15 Charcoal 90-0 2-0 8-53 133-90 Lignite . 71-0 5-0 19-0 . . 7-02 112-43 Peat, dry 58-0 6-0 30-0 . 5-75 92-36 Wood, dry . 50-0 6-0 42-0 1-0 4-57 73-36 Petroleum 85-0 14-0 1-0 10-76 172-86 Natural gas . 68-7 22-5 1-0 6-2 14-20 227-93 Coal gas 58-0 23-7 1-4 3-8 14-51 233-06 Water gas 34-0 5-9 43-0 3-4 3-16 50-70 Producer gas 1-0 5-0 21-0 69-0 72 11-56 Air per Kilogram. Pound. BIBLIOGRAPHY. Adams . Altukhov Andreev Aydon . Barff . Batty . Bell . Benson . Best . Bickford Bloomer Booth . Boyd . Brannt . Buerk . Clark . Dudley . LIQUID FUEL. Liquid Fuel .... Heating Furnaces with Oil and its Residue. Oil and its Products Liquid Fuels .... Petroleum as Fuel Petroleum Residues as Fuel for Smelting Furnaces. Petroleum Oil Fuel Petroleum Fuel for Boilers . The Science of Burning Liquid Fuel. Petroleum Vapour Burners . Petroleum Fuel Liquid Fuel and its Com- bustion. Petroleum, its Development and Uses. Petroleum, its History and Uses. Petroleum as a Fuel at Sea . Petroleum as a Source of Emergency Power for War- ships. Fuel Oil Jour. Soc. Arts, 1868, vol. xvi., 432. Tekhnik.,1883, No. 18, 8. Promischl, i., p. 227. 1864. Proc. Inst. Civ. Eng., liii., p. 177. 1878. Jour. Soc. Arts, xxviii., p. 761. 1880. Polyt. Review, 1876, p. 51. London. 1902. Gorn. Jurn., 1886, iv., p. 364. Eng. Min. Jour., Ixxvii., 771. 1904. Horseless Age, ix., 632. 1902. St. Petersburg. 1888. London. 1903. London. 1895. London and Philadel- phia. 1895. Iron Age, 1878, No. 24. Proc. U. S. Nav. Inst, ix., 798. 1883. Jour. Franklin Inst., cxxvi., 81. 1888. Y 2 324 BIBLIOGEAPHY. Dvorkovitz . Edwards Flannery Gulischambarov . Hodgetts Kamenski Kent . . . Lewes . . Lucke . . Nicol and Gravell Nobel . North . Orde . Oven Paul . Phillips Poole- . Eedwood Petroleum and its Uses Liquid Fuel for Naval Pur- poses. On Liquid Fuel for Ships Petroleum as Fuel Petroleum Heating of Steam- ships, Locomotives, etc. Liquid Fuel .... Petroleum Eesidues as Fuel for Steamship Boilers. Steam Boiler Economy . Oil as Fuel .... Liquid Fuel Combustion The Use and Transport of Liquid Fuel. On the Extended Use of Oil Kesidues in Furnaces with- out Spraying. Oil Fuel . Petroleum, its Power and Uses. Liquid Fuel .... Liquid Fuel for Steamships Firing with Petroleum Kesi- dues. On Liquid Fuel . The Composition of Fuel : the Value of Natural Gas. Fuels, their Analysis and Valuation. The Calorific Power of Fuels Petroleum and its Products . Trans. Inst. Min. Eng., xxvii., 495. 1904. Jour. Amer. Soc. Nav. Eng,, vii., 144. 1895. Trans. Inst. Nav. Arch., xliv., 53. 1902. Gorn. Jurn., 1880, ii., 251. St. Petersburg. 1894. Trans. Civ. Mech. Eng. Soc., 1888-9,63. 1889. Zap. Imp. Kuss. Techn. Obsch., iv., 2, 452. 1870. New York. 1901. Petr. Kev., viii. 1903. Trans. Amer. Soc. Mech. Eng., xxiii., 483. 1902. Trans. N.E. Coast Inst. Eng. Shipbuild., iii., 27. 1887. Moscow. 1882. London. 1905. London. 1905. Trans. N.E. Coast Inst. Eng. Shipbuild., xvii., 41, 69, 85. 1901. Proc. Inst. Mech. Eng. 1902, 417. Zap. Odesk. Otd. Imp. Kussk. Techn. Obsch., Jan.-Feb., 27. Jour. Soc. Arts., xvi., 400. 1868. Harrisburg. 1887. London. 1892. New York. 1901. London. 1906. BIBLIOGRAPHY. 325 Richardson Rowland Samuel . Selvvyn . Tarbutt Teleczinski Thwaite Tweddle Urquhart Versenev Williams Williston Ayrton . Ayrton and Perry Carnegie Petroleum as Steam Fuel On the Use of Petroleum as Steam Fuel. Liquid Fuel .... Petroleum as Steam Fuel Fuel Oil .... Liquid Fuel .... Petroleum as Steam Fuel Liquid Fuel .... Liquid Fuel .... Petroleum and its Use as a Domestic and Commercial Fuel. Liquid Fuel .... Crude Petroleum and its Products as Fuel. On the Use of Petroleum Refuse as Fuel. Supplementary paper . Apparatus for Burning Crude Petroleum. The Management of Petro- leum-fired Boilers. Fuel, its Combustion and Economy. Liquid Fuel for Power Purposes. GASEOUS FUEL. De 1'emploi des moteurs a gaz pour la production d'elec- tricite". The Gas Engine Indicator Diagram. Natural Gas Fuel . Jour. Roy. United Serv. Inst., ix., 70. 1865. Chem. News, xi., 39. 1865. Jour. Soc. Arts, xvi., 504. 1868. Engineering, v., 60. 1868. Jour. Franklin Inst., clvi., 139. 1903. Jour. Soc. Arts, xlvii., 384. 1899. Jour. Roy. United Serv. Inst, ix., 62. 1865. Trans. Inst. Nav. Arch., ix., 88. 1868. Trans. Soc. Eng., 1886, 193. Lemberg. 1 870. London. 1887. Eng. Min. Jour., Ixviii. 1899. Proc. Inst. Mech. Eng., 1884, 36. Ibid., 1889. 36. Engineering, xxiii., 9. 1877. Moscow. 1891. London. 1879. Eng. Mag., xxv. 1903. Revue Industrielle, Oct.5, 1881. Electrician, Dec. 10, 1881. Proc. Phys. Soc., July, 1894. Phil. Mag., July, 1894. Jour. Iron and Steel Inst., 1885, i., 168. 326 Clerk Donkin Dowson Elliott . Engineer Engineering Humphrey Jenkin . Kennedy Meyer . N orris . Perry / Robinson Schottler Thwaite Witz -. BIBLIOGRAPHY. Kecent Developments in Gas Engines. The Gas and Oil Engine Gas, Oil and Air Engines On the Economical Effect of using Cheap Gas for Gas Motors. The Production and I7se of Gas for Heating and Motive Power. Cheap Gas for Motive Power . Gas Power compared with Steam Power. Gaseous Fuel .... Gas Power for Electric Lighting. Gas Power .... Gas Power .... Gas Power .... Producer Gas Gas and Petroleum Engines . Dowson's Gas as a Motive Power. Gas Engines .... The Mond Gas - Producer Plant and its Application. On Gas and Caloric Engines . Possible and Impossible Eco- nomies in the Utilisation of Energy. Versuche an der 160 pferdigen Kraftgasanlange mit Koks- generatoren des Gas und Wasserworks zu Basel. The Otto Cycle Gas Engine . The Steam Engine and Gas and Oil Engines Gas and Petroleum Engines . Die Gasmachine . Gaseous Fuel Moteurs a Gaz Proc. Inst. C. E. 1896. London. 1897. London. 1896. Brit. Assoc. 1881. Jour. Soc. Arts. 1882. Proc. Inst. C. E. 1883. Proc. Inst. C. E. 1887. Brit. Assoc. 1888. Proc. Inst. C. E. 1893. Trans. Gas Instit. 1893. Trans. Inst. Min. Eng. 1898. Proc. Cleveland Inst. Eng. 1899. London. 1906. London. 1898. Nov. 2, 1883. March 26, 1886. Proc. Inst. C. E. 1897. Forrest Lecture, Inst. C. E. 1884. Proc. Roy. Inst. 1893. Zeitschrift des Vereins Deutscher Ingenieure. Berlin. 1896. London. 1896. London. 1899. London. 1890. Brunswick. 1899. London. 1889. Vols. i., ii., iii. Paris. 1892, 1895, 1899. INDEX. A. ABEL flash-point apparatus, 93 Acetylene, 175 Advantages of oil fuel, 130 Air, composition of, 6 impurities in, 6 minor constituents of, 6 Air-producer gas, 43 Air to gas in burners, ratio of, 192 Alcohol, 299 advantages of as a fuel, 303 as a fuel, 100 calorific value of, 300 combustion of, 305 denaturated, 302 enriched, 306 for motors, 311 manufacture, 299 methylated, 302 produced during fermenta- tion, 299 American oil, 85 Ammonia, fixed, 154 free, 154 liquor, 154 Animal to vegetable life, relation of, 24 Anthracite, 32 composition, 32 size for generators, 262 Applications of water gas, 233 Area required for suction plant, 277 Ascension pipe, 145 Atoms, 52 Atomic weight, 54 Atmospheric condensers, 146 burners, 190 Auto-carburetting, 249 Aydon, Wise and Field's oil burner, 117 B. BAKU oil district, 68 Barff's oil furnace, 115 Batswing burner, 178 Bench of retorts, 149 Benrier's generator, 271 Benzene, 307 Bischof 's generator, 257 Bituminous coal, 38, 144 Blast furnace gas, 46, 259 oil, 99 Bomb, Mahler, 65 Boutillier generator, 280 Briquettes, peat, 292 British Thermal Unit, 59 Buire-Leucauchez generator, 268 Bunsen burner, 189 . air and gas ratio in, 192 cause of non-luminosity, 198 temperature of, 205 328 INDEX. Burners, gas, batswing, 178 bunsen, 189 cockscomb, 178 duty of, 247 incandescent mantle, 180 regenerative, 179 union jet, 178 Burners, oil, 108 Aydon, Wise and Field, 117 Holden, 120 Korting, 117 Orde, 121 Eushden and Eeles, 120 Swensson, 117 C. CALORIE, 58 Calorific value, 60 calculated, 60 determined, 64 Calorimeters, 64 Fischer. 71 Junker, 74 Mahler, 65 Simmance-Abady, 80 Thompson, 71 Thomson, 69 Candle power to calories, relation of, 184 Cannel coal, 166 Capitaine suction plant, 274 Carbon, 55 Carbon dioxide, 13 and animal life, 25 and vegetation, 26 in combustion, 12 properties, 13 Carbon monoxide, 14 toxic character of, 15 Carburetted water gas, 45 composition, 242 Flannery, 239 Humphreys -Glasgow, 241 Kramers and Aarts, 237 Loomis, 239 Lowe, 238 Springer, 239 Van Steenburgh, 234 Carburetting coal gas, 167 Cavendish, experiments of, 4 Cellulose, 27 calorific value of, 59 Charcoal, 29 Checked combustion, 14 in stoves, 215 Chlorophyll, 26 Choke damp, 35 Clowes' flame-cap test, 105 Coal, 32 calorific value of, 281 composition of, 34 formation of, 32 gas given off by, 35 hydrogen in, 33 oxygen in, 33 varieties of, 32 Coal gas, 141 as a fuel, 182 calorific value, 183 carburetting, 167 composition, 164 enrichment, 166 manufacture, 141 purification, 156 Coal gas and coal, relative cost of, 206, 214 Coal tar, 97 Cockscomb burner, 178 Cohesion, 51 Coke, 37 INDEX. 329 Coke gas, 43 Combustion, 8 complete, 12 heat of, 60 nature of, 8 products of, 12 rapid, 12 slow, 12 Composition of air-producing gas, 43, 221 carburetted water gas, 242 coal gas, 164 coke gas, 43 Dowson gas, 263 Mond gas, 268 natural gas, 46 producer gas, 43, 221 semi- water gas, 45 suction gas, 274 water gas, 44, 220 Condensers, atmospheric, 146 Cooking stoves, 215 Creosote, 99 Crude oil, 88 D. DANGERS of water gas, 244 Decay of vegetation, 30 Dellwik water gas, 229 Denaturated alcohol, 302 Density of gases, 52 Determination of calorific value, 58 Diastase, 298 Distillation of wood, 29 Dowson gas, 260 Dowson suction plant, 273 Duff-Whitfield generator, 280 Durr liquid fuel system, 115 Duty of gas burners, 247 E. EAMES' liquid fuel system, 115 Eeles' oil burner, 120 Elements, 48 Energy from the sun, 296 Engines, gas. 217 Enrichment of coal gas, 166 Equations, 53 European water gas process, 222 Evaporative value, 63 Explosions in coal mines, 35 F. FAHNEHJELM comb, 236 Fermentation, 298 Fire, 8 Fire damp, 35 Fischer calorimeter, 71 Flame, 16 bunsen, 190 chemical actions in, 174 luminous, 173 non-luminous, 180 Flame cap test, Clowes, 105 Eedwood, 105 Flash point, 92 Abel apparatus for, 93 Pensky - Marten apparatus for, 94 Flueless stoves, 206 Fog, 121 Fuel, 24 Fuel gas, 221 poor, 254 Fuel oils, 84, 137 composition, 42 suitability of, 137 Fuels, thermal value of various, 281 330 INDEX. Furnace, liquid fuel, 132 Eames, 115 Foote, 113 Nobel, 112 Richardson, 111 Sims and Barff, 115 Furnace, regenerative, 149 space, 132 G. GAS, blast furnace, 46 calorific determination of, 74 coal, 141 Dowson, 260 generator, 254 Mond, 266 natural, 46 oil, 168 producer, 221 semi-water, 260 Siemens, 258 suction, 273 water, 44, 219 Gas, coal, 141 composition, 164 enrichment, 166 manufacture, 141 purification, 156 Gas coal, 144 liquor, 154 oven, 172 tar, 97 Gas engines, 217 Gaseous fuel, 42 Gas from blast furnace, 46 coke, 43 slack, 43 Gas generators, 255 Berrier, 271 Bischof, 257 Boutillier, 280 Gas generators contd. Buire-Leucauchez, 268 Capitaine, 274 Dowson, 263 Duff-Whitfield, 280 Mond, 266 Pintsch, 271 principle of, 255 Siemens, 258 Gas stoves, efficiency of, 211 Gassing, 15 Generator gas, 254 Graphite, 33 H. HEAT of combustion, 60 of formation, 60 radiant, 124, 207 radiated in a furnace, 124 theory of, 50 units, 59 Heating by coal gas, 214 Heavy oil, 99 Holden oil burner, 120 Humphreys -Glasgow plant, 241 Hydrocarbons, 56 Hydrogen, 47 combustion of, 47 in coal, 33 Hydraulic main, 146 IGNITION point, 9 Illuminating power in relation to calories, 184 Illuminating power of coal gas flames, 166 Illuminating power of coal gas burners, 247 Illuminating power of oil lamps, 111 INDEX. 331 Impurities in air, 6 coal gas, 156 Incandescence, temperatures of, 16 Incandescent mantle, 181 Incomplete combustion, 14 products of, 14 Internal combustion motors, 217 J. JUNKER calorimeter, 74 K. KORTING oil burner, 117 Kramers and Aarts water gas process, 237 L. LAMP oil, 90 Lamps, illuminating value of oil, 111 Latent heat of steam, 61 Lavoisier's work on combustion, 8 Lebon, 142 Le Chatelier thermo-couple, 202 Leeds forge, 222 Lignite, 32 Lime, purification by, 160 manufacture of, 162 Limestone, 162 Liquids, calorific determination of, 74 Liquid fuel, 84, 137 comparative values of, 137 for locomotives, 123 for steamships, 132 in the navy, 133 United States experiments, 134 Liquid fuel systems Aydon, Wise and Field, 117 Diirr, 115 Eames, 115 Foote, 113 Holden, 118 Korting, 117 Nobel, 112 Orde, 121 Eichardson, 111 Kushden and Eeles, 120 Simms and Barff, 115 Swensson, 117 Liquor, ammoniacal, 154 Lloyd's regulations for oil fuel, 100 Lowe water gas process, 238 Luminosity of flame, 173 M. MAHLER bomb, 65 for liquids, 74 for gases, 74 Marine suction plant, 274 Matter, three states of, 49 Methane, 35 calorific value, 60 in mines, 35 Methane -hydrogen gas plant, 251 Methylated alcohol, 302 Mineral oil, 84 Mixing water gas with coal gas, 172 Molecular weight, 54 Molecule, 52 Mond gas, 266 Motors, internal combustion, 217 N. NATURAL gas, 46 Navy, use of liquid fuel in the, 133 332 INDEX. Nitrogen, 7 in coal gas, 155 properties, 7 Nobel's troughs, 112 Non-luminosity in flames, cause of, 194 O. OBJECTIONS to carburetted water gas, 241 Oil, 84 combustion of, 88 composition of American, 88 Russian, 88 consumption in furnace, 126 crude, 88 early history of, 84 fields, 87 fuel, 84 in America, 84 in Eussia, 86 lamps, 108 production of, 41 shale, 96 theories of formation of, 40 wells, 84 Oil burners Aydon, Wise and Field, 117 Holden, 118 Korting, 117 Orde, 121 Rushden and Eeles, 120 Swensson, 117 Oil fuel, 84 comparative values of, 137 for locomotives, 123 for naval use, 133 Oil gas, 168 for enriching, 168 Paterson's, 168 Young's, 169 Orde's oil burner, 121 Ostatki, 90 Oven gas, 172 Oxygen, 7 consumption of, 26 in combustion, 8 in coal, 145, 243 properties, 7 P. PEAT, 30, 291 briquettes, 292 calorific value of, 293 compared with coal, 294 Pensky-Marten apparatus, 94 Pentane, 102 Petrol, 102 combustion of, 305 Petroleum, 84 products of, 89 Phenoloid, 99 Pintsch suction gas plant, 271 Poisoning by carbon monoxide, 15 Priestly's work, 3 Producer gas, 221 Products of combustion, 12 in gas stoves, 209 in motors, 304 Purification of coal gas, 160 R. RADIANT heat, 124, 207 Radiation of heat in a furnace, 124 Rapid combustion, 11 Ratio of gas to air in a bunsen burner, 192 Redwood's flame-cap test, 105 Regenerative burner, 179 furnace, 149 retort firing, 149 stoves, 206 INDEX. 333 Regulations, Lloyds', for oil fuel, 100 Kelation of animal to vegetable life, 24 illuminating power to calories, 184 Kesiduum, 90 Respiration, 25 Retorts, coal gas, 148 Retort charging machine, 150 Revivification, 163 Richardson's furnace, 111 Rushden and Eeles' oil burner, 120 Russian oil, 86 S. SAFETY lamps, 36 Saturated hydrocarbons, 56 Scrubbers, 146 Semi-water gas, 45 Shale oil, 96 Siemens gas, 258 regenerative furnace, 257 Simms and Barff oil furnace, 115 Sloping retorts, 150 Slow combustion, 12 Smithell's tube, 199 Smoke, 17 Solar distillate, 169 Source of illuminating power, 173 Space required for suction plant, 277 Starch, 298 Steam for oil burners, 126 latent heat of, 61 raising by liquid fuel, 130 Stoves, 206 efficiency of gas, 211 cooking, 215 flueless, 206 regenerative, 206 Suction plant, 271 Berrier, 271 Boutillier, 280 Buire-Leucauchez, 268 Capitaine, 274 Dows*on, 273 Duff-Whitfield, 280 Pintsch, 271 Sulphur in coal gas, 158 products of combustion, 158 Sun as the source of energy, 296 Swensson oil burner, 117 Symbols, 53 T. TAR, 97 coal, 97 composition, 98 Temperature of bunsen flame, 205 of incandescence, 16 measurement of, 202 Thermal conditions in gas gene- rator, 255 Thermo-couple, 202 Theory of heat, 50 formation of oil, 40 Thompson calorimeter, 71 Thomson calorimeter, 69 U. UNITED STATES experiments, 134 Union jet burner, 178 Unsaturated hydrocarbons, 57 V. VAN STEENBURGH water gas, 224 Vapour of petrol, 102 Vegetation, growth of, 27 in relation to animal life, 24 Vertical retorts, 148 334 INDEX. W. WARMING rooms, 207 Washers, 160 Water gas, 43, 219 applications, 233 carburetted, 224 composition, 220 calorific value, 228 Dellwik, 229 formation of, 225 history of, 219 Humphreys -Glasgow, 241 Kramers and Aarts, 237 lighting by, 235 Water gas contd. Lowe, 238 mixed with coal gas, 172, 242 blue, 248 Van Steenburgh, 224 Water in combustion, 61 Weight of gases, 54 Welsbach mantle, 181 Wood, 28 calorific value, 28 charcoal, 29 distillation of, 29 mineral matter in, 29 moisture in, 28 naphtha, 30 BRADBURY, AGNEW, & CO. LD., PRINTERS, LONDON AND TONBR1DOE. A SELECT LIST OF STANDARD WORKS PUBLISHED BY ARCHIBALD CONSTABLE & CO. LTD. INDEX. 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The Nature Student's Note Book* By REV. CANON STEWARD, M. A., and ALICE E. MITCHELL. Containing Nature Notes, Diary, Classification of Plants, Trees, Animals, and Insects in detail. Interleaved with writing paper. Foolscap 8vo. 25. net. The Bird: Its Form and Function* By C. WILLIAM BEEBE, Curator of Ornithology of the New York Zoological Park, etc. ; Author of " Two Birdlovers in Mexico." With over 370 Illustrations chiefly Photographed from Life by the Author. Demy <\.to. Price 145. net. Pall Mall Gazette. " This book is no common one. We heartily recom- mend the book for both old and young. We have here a valuable scientific resume of the latest knowledge, biological, physiological, anatomical, concern- ing birds in general and species in particular, presented in language popular in the best sense, easily intelligible to those who have had no laboratory or museum training, and illustrated by nearly 400 plates and figures." ( 14. ) Natural History, etc. (continued). 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Authorised Translation from " Die Naturlichen Pflanzenfamilien," by F. L. SCRIBNER and E. A. SOUTHWORTH. With Illustrations and Glossary. Demy Svo. IDS. 6d. net. ( 15 ) A Series of Technical Dictionaries in Six Languages. ENGLISH. GERMAN. FRENCH. SPANISH. RUSSIAN. ITALIAN. EDITED AND COMPILED BY MESSRS. DEINHARDT AND SCHLOMANN. With many Illustrations, Formula, etc. In this series each volume treats only of one special branch of Technical Industry. With each word, term, or item, so far as it is possible, a diagram, formula, or symbol is given, so that error or inaccuracy is almost impossible. The volumes are designed of small size for the convenience of pocket use. VOLUME I. (Ready.} Price 55. net, cloth; 75. 6d. net, leather. The Elements of Machinery and the Tools most frequently used in Working Metal and Wood. VOLUME II. (Ready.) Electrical Plants and the Transmission of Power. Electrical Machinery and an Appendix dealing with Electric Tramways. 255. net. VOLUME III. (Shortly.} Steam Boilers and Steam Engines* d t VOLUME IV. (In Preparation.} Hydraulic Machinery; Turbines, W T ater Wheels, Suction Pumps, Centrifugal Pumps, etc. VOLUME V. - (In Preparation.} Hoisting and Conveying Machinery* VOLUME VI. (In Preparation.} Small Tools and Machine Tools* VOLUME VII. (In Preparation.} Railway and Railway Engine Construction* VOLUME VIII. (In Preparation.} Structural Ironwork, Bridge Construction, etc* VOLUME IX. (In Preparation.} Metallurgy. VOLUME X. (In Preparation.} Architecture, Building, etc* VOLUME XI. (In Preparation.} Naval Construction, etc* Each Volume may be purchased singly. ( 16 ) THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO 5O CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. AUfc 1 f* 1OJ m 18 1941 29AprM Qt Jl* tf^ \w> REC'D i n MAV n -I %^. 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