TREATISE ON FUEL' SCIENTIFIC AND PRACTICAL P.Y ROBERT GALLOWAY M.R.I.A., F.C.S. VICE-PRESIDENT OF THE INSTITUTE OF CHEMISTS OF GREAT BRITAIN, HONORARY MEMBER OF THE CHEMICAL SOCIETY OF THE LEIGH UNIVERSITY, U.S. AUTHOR OF "THE STUDENT'S GUIDE IN THE HIGHER BRANCHES OF CHEMISTRY," " A MANUAL OF QUALITATIVE ANALYSIS" NIVERSITY WITH ILLUSTRATIONS TRUBNER & LONDON CO., LUDGATE 1880 (All rig)its reserved > HILL 3f 39elucatr tjjis OTork TO THE LADIES AND GENTLEMEN I HAVE HAD THE PLEASURE OF INSTRUCTING DURING MY TWENTY-THREE YEARS' RESIDENCE IN DUBLIN. THEY HAVE LARGELY CONTRIBUTED TO THE PLEASURES OF MY LIFE BY THE ZEAL AND EARNESTNESS WITH WHICH THEY SECONDED MY EFFORTS, AND BY THE HEARTY KINDNESS AND SYMPATHY THEY HAVE EVER SHOWN ME ; AND I AVAIL MYSELF OF THE OPPORTUNITY OF THANKING THEM, AND WISHING THEM EVERY HAPPINESS AND SUCCESS. ROBERT GALLOWAY. PREFACE. THE Lectures I gave on Fuel in the Royal College of Science, Dublin, form the basis of this book. The book is intended for the use of Students in the Higher Schools and Colleges of Science, as well as for Manufacturers. I believe both Students and Manufacturers will find it a useful one; no doubt some who consult it may think that some branches of the subject, which have been omitted, ought to have been introduced ; other branches have necessarily come under my consideration in preparing the work for the press ; but I thought it desirable not to ex- tend the book to an undue length, and to avoid what is technically termed book-making. I am indebted to my friend and former Student, Mr. C. C. Hutchinson, for the excellent drawings ; b vi ii Preface. and for the revision and extension of the " Mathe- matical Formulae/' my late friend and Student, Mr. C. C. Bateman, LL.D., so kindly prepared for my " Second Stepin Chemistry. " I am also greatly indebted to Mr. Hutchinson for assisting me in reading the proofs. EGBERT GALLOWAY. DUBLIN, November, 1879. CONTENTS. CHAPTER I. Fuel Substances. The Physical and Chemical Properties of Various Kinds of Fuel. Classification of Coal generally adopted. The Gases occluded in Coal, Weathering of Coal. Spontaneous Ignition of Coal .... pp. 123 CHAPTER II. Methods for determining the Heating Power of Fuel. Calorific Power. The Mode of Calculating the Calorific Power of Fuel from its Elementary Composition. The Unit of Heat. Andrews', Favre and Silberman's, Ure's, and Thompson's Calorimeters. Calorific Intensity : Affected by the Nature and Quantity of the Combustion Products, &c. The In- tensity may be calculated from the Elementary Compo- sition of the Fuel. Formulae for the Calculation of the Calorific Intensity. Exercises on the Heating Power of Fuel pp. 2457 CHAPTER III. Theoretical Heating Power of Fuel never obtained in Practice. The Calorific Intensity Deduced from the Elementary Composition of the Fuel not accurate. How the Elements are combined, and their state of Condensation in Coal not known. Evidence adduced that the Organic Elements are arranged differently in different Coals. The Nitrogen may be a Heat Producer, Gruner's Industrial Classification of Coal pp. 58-75 x Contents. CHAPTER IV. Pyrometers, the Principles on which they have been Con- structed. Description and Illustration of Siemens' Electric Resistance Pyrometer pp. 7684 CHAPTER V. Siemens' Regenerative Gas Furnace. Its Advantages. The Gas Producer. The Construction and Working of the Producer. The Construction and Working of the Fur- nace pp. 85-98 CHAPTER VI. Technical Examination and Analysis of Coal. Orsat's Gas Apparatus, its Description and Use . . . pp. 99-130 APPENDIX A. What is Coal? pp. 131, 132 APPENDIX B. Extinction of a Fire in a Coal Mine by means of Carbonic Anhy- dride pp. 132-134 APPENDIX C. The Names and Chemical Formulas of the Substances Formed in the Destructive Distillation of Coal . . . pp. 134-136 ILLUSTRATIONS DRAWN TO SCALE. Ure's Calorimeter . p. 33 Thompson's Calorimeter 35 Modification of Favre and Silberman's 73 Siemens' Pyrometer Elevation So ,, Plan 81 ,, Tube containing Platinum Resist- ance Coil 82 ,, Gas Producer 87 ; , Reheating Furnace, showing Valves and Flues 92 ,, Longitudinal Section . 94 Orsat's Gas Apparatus 116 OF THE UNIVERSITY A TREATISE ON FUEL. CHAPTER I. Fuel Substances. The Physical and Chemical Properties of various kinds of Fuel. The Classification of Coal generally adopted. The Gases occluded in Coal. Weathering of Coal. Spontaneous Ignition of Coal. THE different substances which are practically employed for the production of heat are termed fuel ; they consist of woody tissue in an unaltered or an altered form ; or they are substances derived from it by natural or artificial means. Wood is unaltered woody tissue, containing, in addition, water and inorganic substances ; the latter con- stitute the ash. Peat is woody tissue slightly altered, and the different varieties of coal are still more altered forms of it. Peat and coal contain, like wood, variable proportions of ash and water, in addition to the organic or combustible portion. These different altered forms of the tissue have been brought about by natural operations. Other forms of fuel are products obtained from wood or B Conversion of Wood into its altered forms by artificial processes, as charcoal, coke, liquid and gaseous hydrocarbons, &c. Liquid and gaseous hydrocarbons are also produced from coal by natural means. WOOD, when submerged and exposed to a certain temperature, and brought in contact under these conditions with the small amount of oxygen con- tained in the water, absorbs a portion of that ele- ment, carbonic anhydride (C0 2 ), marsh gas (CH 4 ), and water are formed by the oxidation. We may, from a knowledge of these facts, explain theoretically the conversion of wood into peat, lignite and the other varieties of coal. In the passage of the wood into these other forms of fuel the proportion of carbon, as shown in the following equations, decreases less relatively than the hydrogen and oxygen ; and the oxygen decreases more rapidly than the hydrogen^ so that the proportion of the latter element in excess of the quantity required to form water with the oxygen keeps increasing as the change of the tissue progresses, Until anthracite, the ultimate product of the conversion, is reached. It is considered that of the hydrogen in the fuel it is only the excess quantity that is available as a source of heat. The Germans apply to the excess quantity the term disposable hydrogen; as this is a suitable term, it is employed in this work. ( i) 4C M H 48 2S (wood) +120 = 4 C M H S 8 (peat) + 2 4 CH 4 + 32 CO, + 4H 2 0. Peat and Coal. (2) 4 C 34 H 48 0, 2 4 4 = 4C 27 H i8 O r (lignite) 4 (3) 4C 34 H 4S O 22 + 8 O = 4C 26 H 20 2 (cannel coal) + (4) 4C 34 H 4S 22 + i oO = 2 C 40 H 16 O (anthracite) + 2 4 CH 4 + 3 2C0 2 + 3 2H 2 0.* These equations are taken from the late Dr. Miller's work on Organic Chemistry ; the formulae given are empirical ; that for wood is founded upon an analysis of oak ; the formula for pure cellulose, the organic tissue of wood, is somewhat different, being C 12 H 20 O 10 ; it contains, as shown by the formula, no disposable hydrogen. It may be >*Cs well to observe that in all fuel containing oxygen, as well as carbon and hydrogen, the proportion of hydrogen may be sufficient or more than sufficient, but never less in quantity, than is required to form with the oxygen water. The preceding views with regard to the trans- formation of wood into coal are purely theoretical. The following Table, taken from Dr. Percy s work on fuel, is more instructive ; it exhibits the gradual passage of vegetable matter into anthracite, or that variety of coal which consists almost wholly of * The conversion of wood into coal may take place, according to Bischof, in four different ways, viz : (1) By the production from the wood of C0 2 and CH 4 (2) By the C0 2 and H 2 O (3) By the CH 4 and H 2 O (4) By the C0 2 , CH 4 , and H 3 B 2 Charcoal and Coke. carbon ; the proportion of that element is estimated in the Table at the constant amount of iooi Illustration of the Gradual Passage of Woody Tissue into Anthracite. ( Wood average of 26 [ varieties . . . Carbon. Hydrogen. Oxygen. Disposable Hydrogen. 100 12'lS 83-07 I -80 Peat IOO 9^5 55^7 2-89 ( Lignite aver age of 15 \ varieties 100 8-37 42-42 3-07 ( Ten Yard Coal of I Staffordshire Basin IOO 6-12 21-23 3'47 Steam Coal . . . IOO 5*91 18-32 3-62 ( South Wales Coal \ Pentrifelin . . IOO 475 5-28 4-09 {Anthracite from Penn- sylvania, U.S. . IOO 2-84 l ! 74 2*63 Charcoal and coke are fuels produced artificially, they consist essentially of carbon, but they contain some hydrogen and oxygen ; also nitrogen, sulphur, and the inorganic matter (ash) of the substances from which they were prepared. Charcoal is ob- tained by charring or carbonising wood ; peat also yields a charcoal, and coke is obtained by a like process from coal. By the charring, the water and the gaseous products (formed) are expelled ; the charcoal or coke contains more carbon than the Composition of Fuels. o> O b N b r>- N co -too a 1 ^\ \ ^ ^3 p ON r* P f* *P 5 P 02 IH-i IO t*^ O^ b "M b b * s o s. p f- M o oo *M b V* V* b c~v 1 IO ' VO VO M ON CO O KC 3 O Tt- io CO t^ 00 co ^ CO 1 *2 Hydrogen. ' 1 :l io LO M io oo O ^O \O vO s . 10 10 io ro >- * 10 t^ 10 M Tj- O Tj- O OO 10 O M rf" O LO vo \O OO OO OO ON - o >- '5 "> &2 020 ^ ? ?r " ^ P M M M M M " M tx. ^ ..... 13 1 o ^ ^ r: 3 n3 *o -g t, 1 1 .f ^ 1 j2 S c -g ^ f PH pq O O O <1 Amount of Water fuel from which it was obtained, and it has, weight for weight, a higher calorific value, as we shall hereafter explain, than the original fuel. Coal loses on an average in coking one-third in weight, and increases one-tenth in bulk. THE PHYSICAL AND CHEMICAL PROPERTIES OF VARIOUS KINDS OF FUEL. WOOD. Carbon, hydrogen, oxygen, and ash are* the constituents of wood ; it also contains water; when recently felled it contains a large quantity, which varies in amount with the nature of the tree, the part of the tree, the season of the year at which it was felled, and, in trees of the same kind, with the place of their growth. When it becomes perfectly air-dried, it contains from 18 to 20 per cent, of moisture ; a point of great importance in its employment as fuel, as will be seen in the portion of the work devoted to the calorific power of fuel. Another matter of great importance as regards its value as fuel, is the small quantity of disposable hydrogen it contains. * Cellulose, the organic tissue of wood, contains, as shown by its formula, no nitrogen ; but as the sap of all plants contains albumen and other nitrogenous matter, there must be from this source a small amount of nitrogen present in wood, and also a correspondingly small amount of sulphur in addition to the sul- phur which exists as sulphate in the ash. Wood Contains. TABLE Showing the percentage of Water in different kinds of Fresh- cut Wood. Name of Wood. Water. Name of Wood. Water. Hornbeam ... 18-6 Pine 70/7 Willow . . . . 26'0 Red Beech . . -, ' O -/ / 397 Sycamore . . . 27-0 Alder . ,.'.;. j ..,;. 4i'6 Mountain Ash . . 28-3 Aspen . ;, . 437 Ash . . . 28 7 Elm . . . , . 44' c Birch .... / 30-8 Red Fir . . . 7 T-t J 45' 2 Wild Service Tree 32-3 Lime Tree . . . 47-1 Oak ... 34/7 Italian Poplar . 48-2 Pedicle Oak . . OT" / 35'4 Larch .... T^ 48-6 White Fir . . . 37'i White Poplar . . 50-6 Horse Chesnut . 38-2 Black Poplar . . 5i' Proportion of <9// 2 in Wood at different Periods of the Year. Woods. At the end of January. At the end of April. Ash 28-8 ^8-6 Sycamore .... 33-6 40-3 Horse- Chesnut 40*2 47-1 White Fir .... 5 2 7 61*0 Water and Ash in Wood. Difference in the Desiccation of Barked and Unbarked Wood by exposure to air. Barked Stems Unbarked Stems Loss per cent, of the original weight of the Wood. July. 34'53 0*41 August. 3877 0-84 September. 39'34 0*92 October. 39-62 0-98 Amount of Water expelled from Air-dried Wood at Gradually Increasing Temperatures. Water expelled from 100 parts of REMARKS. Wood. Between 200 and Temperature of Dessication. Oak. Ash. Elm. Walnut, 225 there is slight decomposition, and water alone is not evolved The state 125 C. 15*26 1478 I5'32 !5'55 ment, in works on Chemistry, that 150 C. I7"93 16-19 iyo2 J 7'43 wood contains a given quantity of 175 c. 32-13 21'22 36-94 2I'OO OH 2 can only be exact in so far as 200 C. 35'So 27V 33-38 41-77 they indicate the degree of desicca- 225 C. 44"3i 33-3* 40-56 36-56 tion. The amount of ash in wood varies between 0*2 and 5 per cent., according to the kind of wood and the nature of the ground upon which the tree has grown ; it usually amounts to one per cent. The specific gravity of all woods, it is found, is nearly Its Specific Gravity. the same, when the determinations are so made that the pores are completely deprived of air and filled with water. Specific Gravity of different kinds of Wood, Name of the Wood. Specific gravity. Percentage of Water. Freshly felled. Air dried. Fresh felled. Air dried. Common Oak . 1*0754 07075 34-7 16*64 Pedicle Oak . 1-0494 0-6777 35*4 White Willow . 0-9859 0-4873 5'6 Beech 0-9822 0-5907 39-7 18-56 Elm .... 0*9476 0-5474 44'5 18-20 Hornbeam . 0-9452 0-7695 186 Larch . . . 0-9205 0-4735 48-6 Scotch Fir . . 0-9121 0-5502 397 Sycamore 0-9036 0-6592 27-0 18-63 Ash .... 0*9036 0-6440 28-7 Birch .... 0-9062 0*6274 30-8 I9-38 Mountain Ash . 0-8993 0-6440 28-3 Fir .... 0-8941 '555o 37-i 17*53 Silver Fir . . 0-8699 0-4716 45"2 Wild Service 0-8633 0-5910 32-3 Horse- Chesnut . 0-8614 o'5794 38-2 Alder . . . 0-8571 0-5001 41*6 Lime .... 0-8170 0-4390 47'i 18-97 Black Poplar . 07795 0-3656 51-8 Aspen . . . 07654 0-4302 43 '7 Italian Poplar . 0-7634 0-3931 48-2 i9'55 Ground Willow o7 r 55 0-5289 6o'o PEAT. This fuel varies in composition and tex- ture according to the extent of the decomposition or decay of the vegetable matter it is derived from, io Water and Ash in Peat. has undergone. When air-dried its specific gravity ranges from 0*25 to 0*9, or even to above 1*0. When fresh from the bog it may contain, if fibrous, 90 per cent, of water, of which from 50 to 70 per cent, is removed by air-drying ; the proportion of water is considerably less in the denser kinds. In samples of black turf taken from a depth of twelve feet in the bog, and three or more from the bottom of the bog ; and samples of red turf taken from within three feet of the surface which Mr. li. Mallett, F.R.S., experimented on some years ago in Ireland ; he found that when air-dried they each lost on being further dried for four days in a stove or kiln, at a temperature of 180 F., or thereabouts, the following percentages of water : the black, 34*8 per cent. ; and the red, 19 per cent. The black turf, therefore, when air-dried retains nearly twice the moisture in proportion to its weight that red turf does the former holding about one- third, and the latter about one-fifth of their re- spective weights of moisture. Both sorts of turf, after being thus dried, were left exposed to the air under cover of a roof for a period of at least five weeks in the months of October and November. The specimens were afterwards weighed to see how much water they had reabs orbed. The black turf had reabsorbed 7*14 per cent., and the red 4*87 per cent. ; the black had, therefore, only reabsorbed about Its Value as Fuel. 1 1 one-fifth of the water it had lost in kiln-drying, and the red had reabsorbed about one-fourth. The ash peat contains is not in all cases wholly derived from the plants from which the peat has been produced, a part has been deposited in it from the water which has percolated it ; the quantity is therefore variable. The average proportion is from i to 2 per cent., but it may vary from i to 30 per cent. Peat cannot be economically substituted for coal where the price of the latter is, as in Great Britain, relatively low ; its bulky nature, the large amount of water it retains, even after being thoroughly air-dried, renders the carriage of it costly and reduces its available heating power. It is a more costly fuel in these countries than coal, if the quantity of each of the two fuels that would be required for a given amount of work were compared. COAL. This is by far the most important of the substances used as fuel. What is coal ? might appear to the public a very absurd question to ask. Nevertheless, whether the mineral called boghead cannel is, or is not, a coal gave rise to a remarkable trial, which took place at Edinburgh in 1853 before the Lord Justice- General and a special jury, an abstract of which is given in Appendix A. It is difficult, as was proved at that trial, to frame a precise definition of the term coal either in a com- 1 2 On what the Value of Coal as mercial or scientific sense. This arises from the fact that the substances, classed under the term coal, are altered vegetable matter in various stages of alteration and decomposition, varying from lignites, some of which resemble wood and peat, up to anthracite, which contains 90 per cent, or more of carbon, and which might be regarded from its chemical composition as coke naturally produced ; hence the substances which are termed " coal" differ very much from each other both in physical and chemical characters. The real value of a coal for fuel depends on its calorific power, and on certain accessory properties, as for instance its greater or less cohesiveness, the proportion and the chemical character of the ash, and whether the coal cakes or not under the influence of heat. It consists of, in varying pro- portions, carbon, hydrogen, oxygen, nitrogen, sulphur, the incombustible or inorganic portion (ash) and water. The water may be expelled at a temperature slightly above 100 ; the nitrogen ranges pretty constantly between i and 2 per cent. It is derived no doubt from the nitrogenous matter which existed in the sap, &c., of the original plant. The sulphur may exist in the ash as a sulphate, but it exists frequently in the largest amount in combination with iron, in the form of iron pyrites (FeS 2 ), and it exists no doubt to a small extent as a constituent of the organic portion of the coal, Fuel Depends. 1 3 being derived from the albuminous bodies which were present in the sap of the plant. Some coals contain only I per cent, of ash, others contain such a large amount as to be unfit for fuel, and to become transformed into bituminous shales. The ash in many coals has not been solely derived from the original plants, but has been carried and deposited in the coal, during its formation, by water and other agencies. Its colour is sometimes white, and at other times red. The redness is due to an excessive quantity of iron pyrites in the coal ; the iron, during the burning of the fuel, becoming converted into ferric oxide (Fe 2 3 ). The com- bustibility and value of the coal depends not only upon the amount, but also on the nature, of the ash it contains ; iron pyrites, for example, in burning corrodes and destroys the fire-bars. A ferruginous and calcareous ash is fusible, and con- sequently incrusts and sticks to the furnace-bars under the form of slag and clinker, thus impeding the combustion, and requiring also an extra expenditure of manual labour from the stoker;* argillaceous, or siliceous ash, on the other hand, remains pulverulent, and impedes the combustion much less than the ferruginous and calcareous ash. * Sometimes a bed of clinker is expressly formed, and made to serve an important purpose. Thus in furnaces in South Wales and some other localities such a bed is ingeniously used as a sub- stitute for a grate, on which small and inferior coal may be profit- ably consumed. 14 Classification of Coal. The comparative freedom of the ash from phos- phorus is of great practical importance in iron smelting. The minor varieties of coal are numerous ; fully a hundred different kinds, it is said, are sent into the London market. The more important kinds may be divided into the four following classes : 1. Lignite, or brown coal. 2. Bituminous coal. 3. Cannel coal. 4. Anthracite.* LIGNITE. Geologists apply this term to those carboniferous minerals which occur in later deposits than the true coal measures. They have frequently the structure of wood, but many of them are free from ligneous texture. They vary in physical characters, from that of the more compact peats to that of the bituminous coals ; they therefore present a great variety of aspects ; " some, being almost as hard as true coal, are known as ' stone coal ;' others, being distinctly woody, are known as 'wood coal;' some, again, consisting of thin layers like compressed leaves, are called 'paper coal ;' whilst soft earthy varieties have received the name of ' peat coal. ' ' They differ from true coals * The industrial classification by M. L. G rimer is given in Chapter III. Properties of the Different Kinds. 1 5 in the large proportion of moisture they contain. When they are first raised they contain as much as 40 per cent., and even after long exposure to the air they may contain from 15 to 20 per cent., and if deprived of this water by desiccation,* they will, if subsequently left exposed to the air, reabsorb the amount they lost in this respect resembling wood. No analyses of this kind of fuel should be accepted which does not indicate the proportion of water. The sp. gr. of the different varieties ranges from i ' i to about i '4. Their colour varies in shade from brown to black, and in lustre from dull to shining. The amount of ash they contain varies from i to 50 per cent. ; in most cases, however, it is not less than 5 and seldom above 10 per cent. Iron pyrites is very frequently, if not always, present in lignites. Lignite is generally non-caking that is, its powder, when heated to redness in a close vessel, does not yield a coherent coke ; varieties of it have been found so rich in resin as to cause it to cake from that cause alone. BITUMINOUS COAL. This variety is the most valuable and most abundant of the English coals, and it constitutes the bulk of the immense coal- fields of North America. It occurs above the old red, and beneath the new red, sandstone, in what * The water is expelled from lignite on exposing it to 100 C. or somewhat higher temperature. 1 6 Properties of the geologists have termed, from its presence, the "coal measures." The term bituminous has been applied to this variety of coal, not from the coals of this class containing any bitumen, but because, like bitumen, they burn with a more or less smoky flame. That they contain no bitumen is proved by their insolubility, as only a mere trace dissolves, in benzole, ether, and like solvents in which natural bitumen dissolves. By some writers the term bituminous is used to denote the matter which is volatilised when a coal is heated to red- ness in a close vessel, and in that sense it is syno- nymous with volatile matter, both terms being employed indiscriminately. Flaming, as Dr. Percy remarks in his work on fuel, would not be a bad substitute for the word bituminous. The passage of bituminous coal into anthracite is as gradual as that of lignite into the bituminous kind, so that there is no precise line of demarcation between these classes of coal. Hence in the class bituminous, many varieties of coal are included, which, in external characters, and ultimate chemical composition, differ widely from each other. " The character of coals of the bituminous class may be summed up as follows :- They are easily frangible, and opaque, except in thin slices ; dull, shining, or fatty in lustre ; black or brown-black in mass, but brown when in the state of fine powder ; some soil the fingers, and others do not ; they are variable Different Kinds. 1 7 in hardness, even, conchoidal, or uneven, in fracture, frequently breaking into pieces more or less cubical or rhombic ; they generally exhibit cleavage, due to bedding or pressure, but never crystalline struc- _ture ; they generally contain only a small proportion of_j^ater. In open fire-places, or in furnaces of ordinary construction, they burn with a more or less smoky flame ; and when heated to redness in a close vessel, they leave a solid, carbonaceous, more or less coherent coke, which contains the fixed inorganic matter, or ashes." (Percy.) The most important practical classification of bituminous coals is the divison of them into caking or coking coals, and non-caking or free-burning coals. Caking coals, when heated to the degree at which they decompose, partially fuse, and become pasty ; gaseous matter is evolved, which burns with a bright flame, and the non-volatile matter swells and forms a spongy mass. The fine powder of such coal yields, when heated to redness in a close vessel, a pretty firmly coherent mass of coke. In the quality of caking there may be every degree from slight fritting or sintering to almost complete fusion. The caking is due to a portion of the con- stituents of the coal, under the influence of heat, forming coal-tar, which, on becoming charred, cements the non-volatile particles into a solid mass. Some coals lose the property of caking after c 1 8 Properties of the exposure to the air, and in some cases the caking of a coal depends on the manner in which it is heated, and the degree of heat to which it is subjected. Caking coal is inapplicable for many furnace operations, in consequence of the caking ; as it becomes agglomerated in the furnace into a mass so compact as to be in a greater or less degree impervious to air; in which case the fire, if the fuel was not kept pervious to air by stirring, would soon be extinguished, and stirring in many cases would be quite impracticable. For its employment in such operations, it requires to be previously converted into coke, or mixed with non-caking coal. Non- caking or free-burning coal does not, in burning, cake or sinter together in any sensible degree ; and when heated in close vessels in a state of fine powder, yields a feebly coherent or powdery coke. A fire supplied with coals of this description remains open, the air penetrating freely the burning mass. CANNEL OB P ABBOT COAL. This is a variety of bituminous coal ; it is called cannel, a corruption, it is said, of candle, from its property of burning with a clear flame, like a candle ; and parrot (in Scotland) from its property of splintering, or flying off with a loud crackling sound, when flat fragments of it are placed upon the surface of the fire. It does Different Kinds. 19 not soil the fingers, is brown or black, and of glistening fracture. There are varieties which are susceptible of a fine polish; common jet, for example, is a variety of cannel coal. This class of coal con- tains a large quantity of disposable hydrogen ; it is therefore especially valuable in the manufacture of gas. Boghead cannel or Torbane mineral is of a dull brown colour ; its sp. gr. is about 1*184. It yields on heating about 70 per cent, of volatile matter, and from 18 to 25 per cent, of an aluminous ash, usually containing from 6 to i o per cent, of carbon ; the coke or residue retains the form of the coal. This mineral, which formed the subject of the trial already referred to, is very valuable for the manu- facture of paraffin, paraffin oils, and gas, on account of the very large percentage of volatile hydrocarbons it yields. The sp. gr. of bituminous coal varies from i '2 to i '5. This variety of coal, fresh from the pit, loses, after its exposure to the air, a portion of its moisture, retaining according to its nature from i to 12 per cent. ; artificially dried, it reabsorbs moisture from the air. On an average this kind of coal leaves less ash than brown coal or turf, but more than wood. ANTHRACITE. This variety is found in the lowest portion of the carboniferous strata. It is much more difficultly combustible than the other kinds of C 2 2o Gases Occluded in Coal. coal ; it contains 90 per cent, or more of carbon ; it does not sinter in the least degree ; it yields but a small portion of volatile matter ; it burns almost without flame and with a steady red glow, giving out great heat. Some varieties decrepitate con- siderably. It is very compact ; in powder, as well as in lump, its colour is deep black. THE GASES CONTAINED (OCCLUDED) IN THE PORES or COAL. Coal almost always contains in its pores a variable quantity of gas, the nature and pro- portion of which differs with the different varieties of coal. The bituminous coals of the South Wales basin contain very little, and that little is almost exclusively carbonic anhydride. Steam coal of South Wales frequently contains a very large quantity of marsh gas, which is evolved to a great extent after it has been raised ; it, therefore, not unfrequently happens that the coal in a ship's ho]d, for example, gives out so large a quantity that the air becomes highly explosive. Cannel coal contains a more complex hydrocarbon, ethane (C 2 H 6 ), than marsh gas. Jet contains hydrocarbons of higher molecular weight than ethane, whereas the gas contained in the pores of anthracitic coal consists almost exclusively of marsh gas. This class of coal yields by far the largest volume of gas : "i Ib. of some anthracites will give off nearly a couple of gallons of gas." The gas in lignite consists almost entirely Weathering of Coal. 2 1 of carbonic anhydride, mixed with a small quantity of carbonic oxide (CO) and nitrogen. In a vacuum, especially at a gentle heat, the gas is readily disengaged from the pores of coal. WEATHERING OF COAL. By the term " weather- ing" of coal is meant the change which coal under- goes on exposure to the air. The weathering is due to the absorption of oxygen from the air, which combines with a portion of the carbon and a portion of the hydrogen of the coal ; in the one case forming carbonic anhydride and in the other water, whilst another portion of oxygen enters into com- bination with the coal, or some constituent of it. The state of this combination is unknown. If coal contains iron pyrites, the oxidation of this sulphur compound also takes place. It is stated by those who have investigated this subject, that the oxidation of coal free, or nearly free, from iron pyrites, is impeded rather than pro- moted by the presence of moisture in the air ; but that the oxidation of pyrites in coal is increased by the presence of moisture. Heat favours the oxidation in both cases. Very little is known as to the conditions favour- able or unfavourable in coal as regards weathering, with the exception that iron pyrites in the coal greatly assists its decay ; and when present in con- siderable quantities may render the coal, owing to 22 The Spontaneous the disintegration which occurs from its oxidation, comparatively worthless after the fuel has been exposed for some time to the influence of the air. SPONTANEOUS IGNITION or COAL. Closely con- nected with the weathering is the spontaneous ignition of coal, which also proceeds from oxidation. When the oxidation of the fuel takes place rapidly, the temperature of the air surrounding the coal becomes, of course, from the generation of heat, increased, and will continue to increase as the oxidation goes on ; and as the oxidation is pro- moted by increase of temperature, so will the oxi- dation increase with the temperature. The igni- tion of coal undergoing oxidation is, therefore, very liable to take place unless the heated atmosphere around the coal is continually removed by cooler currents of external air. " The first unequivocal sign of incipient combustion is a peculiar smell, termed ' fire-stink' by the colliers, which appeared to me to be precisely similar ho that which is pro- duced by distilling coal at the lowest temperature at which decomposition commences. I came to the con- clusion that such incipient decomposition had begun, and conceived that it was due to the heat developed by the oxidation of accumulated finely divided coal, just as in the well-known case of a heap of oiled rags." (Percy.) Dr. Percy believed, and Bichter's experiments, so far as they have been carried out, confirm the opinion, that coal most Ignition of Coal. 23 liable to spontaneous ignition is not that which contains most iron pyrites ; therefore, the spon- taneous ignition of coal is due to the heat de- veloped by atmospheric oxidation of the organic substances of coal, and not to that resulting from the oxidation of iron pyrites. * One of the Inspectors of Mines, Mr. Galloway, has shown that the coal-dust in the atmosphere of a coal mine largely contributes to its explosive character. * See Appendix B. CHAPTER II. Methods for determining the Heating Power of Fuel. Calorific Power. The mode of calculating the Calorific Power of Fuel from its elementary composition. The unit of Heat. Andrews', Favre and Silbermaris, C/re's, and Thompson's Calorimeters. Calorific Intensity : affected by the nature and quantity of the combustion products, fyc. The Intensity may be calculated from the elementary composition of the Fuel. Formulae for the Cal- culation of the Calorific Intensity. Exercises on the Heating Power of Fuel. OF the elementary constituents of fuel, only the carbon and hydrogen* enter into union with the oxygen of the air, and therefore these are the only elements in the fuel which contribute to the generation of heat ; further, if the fuel contains oxygen, this constituent must be considered as if already combined with its equivalent quantity of hydrogen in the fuel. That quantity of hydrogen is therefore considered to be ineffective for the gene- ration of heat, and it is only the hydrogen which * The constituents of iron pyrites will each enter into union with oxygen, but as this mineral is a foreign, and not a natural, substance of coal, we do not take their ' union with oxygen into consideration. Calorific Power. 2 5 is in excess of that amount, and which we have already termed disposable hydrogen, which is effec- tive. The meaning of the terms CALORIFIC POWER, or, as it is sometimes called, the absolute heating power, and CALORIFIC INTENSITY, or pyrometric heating power, must now be explained ; and how or by what means the calorific power and calorific intensitv of fuels are determined. / CALORIFIC POWER. The absolute amount of heat which any substance evolves in burning cannot be ascertained, but the relative amounts evolved by equal weights of different substances can be accurately determined. This is accomplished by transferring the heat emitted by the combustion to a third body, and determining the number of thermornetric degrees a given weight of this third body is raised in temperature by different sub- stances. We thus arrive at the relative amounts of heat they evolve in the act of combining with oxygen; the quantity of heat thus estimated is termed the calorific power of the substance. The calorific power is not affected by the rapidity or slowness with which the combustion takes place ; it remains constant under these varying conditions. Some of the early experimenters on the calorific power of substances employed ice as the third body, and from the amount of ice liquefied, they measured the amount of heat ; the apparatus em- 26 Heat Developed by the ployed, they termed a calorimeter. There is an objection to ice, on account of the difficulty of collecting the whole of the water produced by the liquefaction of the ice. Rumford, therefore, sub- stituted water for ice, and although many im- provements have since been made on Rumford's method as regards the form of apparatus employed in the experiments, and corrections in the calcula- tion of the results, water is still all but universally employed as the third body.* It has been ascertained by experiment, that one part by weight of carbon, when it combines with oxygen sufficient to form the compound carbonic anhydride (C0 2 ), evolves heat sufficient to raise the temperature of 8080 parts by weight of water i Centigrade ; this is usually expressed by saying that the calorific power of carbon is 8080, or that carbon evolves 8080 units of heat during its con- version into C0 2 . Favre and Silberman found by experiments that one gramme of carbonic oxide (CO), in its con version into C0 2 , evolved 2403 units of heat ; consequently, the amount of CO which contains one gram of carbon will evolve 5607 units. In the preceding paragraph we have seen that one gram of carbon, in its conversion into C0 2 , evolves 8080 units ; therefore, one gram of carbon, in its conversion * Becently Bunsen has re-employed ice as the third body in certain calorific experiments. Oxidation of Certain Bodies. 2 7 into CO, will evolve (80805607)2473 units ; this is less than one-half the heat it, the GO, evolves in its conversion into C0 2 . A probable explanation is, that in the conversion of carbon into carbonic oxide (CO), some of the heat generated by the combination is rendered latent by the passage of the carbon from the solid to the gaseous state. Whatever may be the reason, the student will not fail to observe the great loss of heat and waste of fuel which takes place when the carbon becomes only converted into CO and not into CO 2 . It has also been ascertained by experiment that i part by weight of hydrogen, when it combines with 8 parts by weight of oxygen, water being- produced, evolves heat sufficient to raise the tem- perature of 34,462 parts by weight of water i C.; the calorific power of hydrogen is therefore stated to be 34,462. With the aid of these data, the calorific power of fuel may be calculated from its chemical composi- tion ; but before illustrating this by examples, the student must know what thermal unit is employed for determining the calorific power of bodies. UNIT or HEAT. The unit of heat, or the thermal unit, chosen for comparison, is not everywhere the same. In France the one selected is the quantity of heat necessary to raise the temperature either of one kilogramme of water, or one gramme of that 28 Unit of Heat. liquid, from o to i C. This latter unit is frequently employed in England, but not universally; i Ib. of water, from o to iC. is employed, and sometimes i Ib. of water, one Fahrenheit degree between the temperatures of 50 and 60 F. What unit weight of water is selected is imma- terial,* although it is most desirable that one standard be universally adopted ; but it has hitherto been considered not immaterial what portion of the thermometric scale was selected, as the specific heat of water was considered to increase slightly as the temperature increased beyond its point of greatest density. But Hirn, in recently investigating this subject, has arrived at the conclusion that the specific heat of water does not exhibit any irregularity near its point of maximum density, but merely changes somewhat more quickly below than above that point. If the elements of a fuel consisted of carbon and hydrogen only, it would only be necessary to multiply the weight of each of the elements in one part by weight of the fuel by their respective calorific values, and add the products together. * Whatever unit weight for water is adopted, the same unit weight must be adopted for the substance whose calorific power has to be determined ; thus, if a kilogramme of water is employed, a kilogramme of the substance whose calorific power is to be deter- mined must also be employed. And the unit of heat, or that quantity of heat which raises the temperature of the unit weight of water i, will vary of course according to the thermometric scale employed. Calorific Power. 29 Thus, for the sake of illustration, suppose a fuel contained in 100 parts 8571 of carbon and 14*29 of hydrogen ? 0*8571 x 8080 + 0*1429 x 34462 = 1 1849*99 One part by weight of this fuel would, therefore, evolve in burning, the carbon being all converted into C0 2 heat sufficient to raise 1 1849*99 parts by weight of water from o to i C. If the fuel contained oxygen as well as carbon and hydrogen, it would be necessary, as previously noticed, to deduct from the total quantity of hydrogen the amount necessary to combine with the oxygen in the substance, and to account, as available for evolving heat, only the remainder of the hydrogen, the disposable hydrogen, with the carbon. For example, a sample of peat has the following percentage composition : Carbon . . . .61-53 Hydrogen . . . . 5*65 Oxygen . . . .32*82 100*00* As oxygen combines with hydrogen in the pro- portion of 8 to I, the number representing the amount of oxygen divided by 8 will give the * The ash and nitrogen of the peat have been omitted, as they were not material for the purpose of illustration, and it is assumed that all the carbon becomes converted in the burning into CO. 30 The Different Kinds of number representing the quantity of hydrogen which will combine with the oxygen ; thus, 32*82 -r-8 = 4*io : now, 5*65 4*10 = 1*55, the amount of disposable hydrogen ; consequently 0*6153 x 8080 + 0*0155 x 34462 = 5471*3 is the calorific power of the peat. One part by weight of this peat would, therefore, raise 5471*3 parts by weight of water from o to i C. The calorific power of various bodies is given in my work, " The Student's Guide in the Higher Branches of Chemistry/' and also a description of the apparatus employed by Dr. Andrews in this difficult field of research, together with a reference to the apparatus and methods employed by M. Favre and Silberman in a like investigation. The apparatus employed by Andrews and that employed by Favre and Silberman would be unsuit- able, if correct, for determining the calorific power of fuel for commercial purposes ; but I have found they are unsuitable for coal even in the most deli- cate scientific investigations, as no constant quan- tity of the products from its combustion can in them be obtained. The modification proposed by MM. Kestner and Meunier of Favre and Silberman's apparatus for the determination of the heating power of coal will be noticed in Chapter III.; we shall in this only notice the two calorimeters (Ure's and Thompson's) Calorimeters. 3 1 that are suitable, and sufficiently exact, for technical purposes : the latter is to be preferred in most cases.* lire's calorimeter in Fig. 1 is founded on the same principle as the one employed by Rumford, but somewhat improved. It consists of a large copper bath (a), capable of holding 100 gaUons of water. It is traversed four times, backwards and forwards, in four different levels, by a zig-zag horizontal flue or flat pipe (#), which is nine inches broad, and one deep, ending in a round pipe at (c), which passes through the copper bath, and there receives the top of a small black-lead furnace (d) ; this furnace contains the fuel ; the crucible is surrounded, at the distance of one inch, by a second, and this is surrounded by a third, crucible ; the stratum of inclosed air between the crucibles serving to prevent the heat from being dissipated. A pipe (e), from a double cylinder bellows, enters the ash-pit of the furnace at one side, and sup- plies a steady but gentle blast, to carry on the combustion, kindled at first by half an ounce of red-hot charcoal. So completely is the heat, which is disengaged by the burning of the fuel, ab- sorbed by the water in the bath, that the gases * A method by Berthier is frequently described at considerable length in books. The method consists in estimating the calorific power of coal by the amount of litharge it reduces. I found long ago that this method is perfectly unreliable, and therefore it is use- less to describe it. 32 Ures Calorimeter. discharged at the exit orifice (/), have usually the same temperature as the atmosphere. The copper bath weighs 2 Ibs. per square foot ; it is on an average 5^ feet long, \\ wide, 2 deep, and if broad. Including the zig-zag tin-plate flue, and a rim of wrought-iron,it weighs altogether 8 5 Ibs. Since the specific heat of copper is to that of water as 94 to 1000 Ibs., the specific heat of this vessel is equal to that of 8 Ibs. of water, for which, therefore, the proper correction is made by leaving 8 Ibs. of water out of the 600 or 1000 Ibs. used in each experiment. The heating power of the fuel is measured by the number of degrees of temperature which 600 or looolbs. of water are raised by it; deducting the 8 Ibs. from the amount for the specific heat of the copper. When the object is to determine the latent heat of steam or other vapours, they may be introduced through the top orifice (/), the latent heat being deducted from the elevation of temperature of the water in the bath, which is calculated from the liquid discharged into a graduated glass placed under the outlet (C). In this case the furnace is of course removed. The apparatus devised by Mr. Lewis Thompson, is one for determining the calorific power of coal and other combustibles. The combustible, of what- ever nature, is burnt in oxygen evolved from an oxidising mixture. The latent heat of steam is Ures Calorimeter. 33 34 Lewis Thompson s taken to be equal to 967 F.; admitting this to be the latent heat of steam, it follows that if 967 parts of water are heated i o F. , as much heat has been evolved as would evaporate ten parts of water having a temperature of 2 1 2 F. ; the thermometer in this way indicating the number of parts of water capable of being evaporated by the fuel. The experiment is conducted in the following manner : Thirty grains of an average sample of coal, or other fuel, in a state of very fine powder, are very intimately mixed in a mortar with from 300 to 360 grains of a mixture, which must be perfectly dry and in a state of fine powder, composed of 3 parts by weight of potassic chlorate, and i of potassic nitrate ; the mixture is afterwards intro- duced into the narrower copper cylinder (a, Fig. 2), which forms the furnace ; the bottom of the cylin- der must be occasionally tapped as the mixture is introduced, but the mixture must not be compressed more than is necessary. A cotton fusee (a little cotton wick which has been prepared by dipping it in a solution of nitre and then drying it and which acts as a slow match) not more than half an inch in length is placed in the centre of the mixture to the extent of half its length, and is fixed by pressing the mixture around it, the cylinder is then placed in its seat on the brass base (b). A copper cylinder (c) with a copper tube fitted with a stop-cock (d) is called the inclosure, it is per- Calorimeter. 35 FIG. 2. THOMPSON'S APPAKATUS FOB DETERMINING THE HEATING POWER OF FUEL. Scale, 3 Inches to a Foot. A, Glass cylinder graduated to hold 29,010 grains of water. (a) Furnace in which coal mixture is burned. (b) Base for holding the furnace and inclosure. (c) Inclosure, copper cylinder with tube. (d) Stop-cock for exit of air from interior of inclosure after combustion. (e) Holes in bottom of inclosure for exit of combustion products. (/) Spring (of which there are three) for retaining inclosure on base. (fj) Wider furnace for combustion of coke, anthracite, &c. D 2 Mode of Using forated at the bottom with a number of small holes at (e) to allow the gases produced by the combus- tion to pass through the water, and thus transfer the heat of combustion to the water ; when the inclosure (c) is fitted over the furnace (a), the latter being seated on the base (6), the springs (/) of the base clasp the sides of the inclosure ; when the furnace and inclosure are thus joined and im- mersed in the water, the water is excluded from, or admitted to, the interior of the inclosure according as the stop-cock is shut or opened. A glass cylinder (J.) holds, when filled up to the graduated mark, 29,010 grains, the temperature of the water is determined by a delicate thermometer, which ought to be immersed in it for a few minutes before noting the temperature ; the temperature of the water ought not to be above 60 F. at the commencement of each experiment. THE MODE OF CONDUCTING THE OPERATION. The temperature of the water having been deter- mined and the thermometer withdrawn, and the fur- nace, containing the mixture and fusee, being seated on the base, the fusee is lighted, the inclosure, the stop -cock being closed, is then fixed over the fur- nace, and the apparatus is let down to the bottom of the graduated glass cylinder; this part of the operation must be quickly performed so as not to allow the mixture to become ignited before the immersion, otherwise the experiment fails, and the Thompsons Calorimeter. 37 operator's hands and face are in danger of being burnt. A minute or so after the immersion the wick burns down to the mixture, its combustion then commences, and when it ceases the stop-cock is opened,* and the apparatus (furnace and inclosure) and the thermometer, which must now be rein- troduced into the water, are moved gently up and down in, not out of, the water, which causes the water within and without the inclosure, and at every depth, to acquire the same temperature. When the thermometer indicates that the tem- perature of the water has become stationary, that is, that the water at different depths is of a uniform temperature, the temperature is instantly noted, and the number of the thermometric degrees to which the water has been heated, represents the quantity of water which would be converted into steam from a temperature of 2 1 2 F. If, foT ex- ample, the temperature of the water has been raised 10 F., we learn that the sample of fuel under examination would be capable of converting ten times its weight of water into steam, since every grain of the fuel has been burnt in the midst of 967 grains of water ; and if the latent heat of * Attention should be paid to the state of the exit tube of the inclosure at the conclusion of the combustion. If on opening the stop-cock, air does not freely issue, a pointed wire must be intro- duced to clear it. 38 Mode of Using steam be taken at 967 F., then if 967 grains of water be raised 10 F., sufficient heat has been generated to boil off i o grains of water from 2 1 2 F. , this then represents the evaporative power of the fuel ; and pounds or tons can, of course, be substi- tuted for grains. As part of the heat generated by the fuel is absorbed by the copper of the apparatus, this amount must be added to every calorific result obtained.* The amount of heat absorbed by the copper is found by multiplying the weight of the copper part of the apparatus by its specific heat, this product gives the weight of water, which, in respect to absorption of heat, would be exactly equivalent to the weight of the copper. Dr. Percy has found that by inclosing the lower part of the inclosure within a larger metallic cylinder, perforated all over with small holes, so that the escape of the gases from the water was retarded, the experimental results were notably higher ; thus, in comparative experiments upon a Welsh steam coal, it was found that its theoretical evaporative power was raised by this addition from 14*41 to 1 4 '96 Ibs. of water. The colder the water employed, the smaller will be this loss of heat, owing to the gases being more thoroughly cooled, In testing coke, anthracite, or other difficultly * The amount to be added is generally determined by the maker of the instrument. Thompson s Calorimeter. 39 combustible substance, the wider furnace (g) must be used, and the mixture must be allowed to remain loose and uncompressed in the furnace ; but in the case of bituminous coal, &c., the narrower furnace (a) is employed. It is seldom, however, that coke or anthracite is completely burnt, even in the wide furnace, the only plan then is to collect the un- burnt particles on a tared filter,* and after having washed the particles on the filter free from all soluble salts, the filter and contents must be dried at 212 F., and, when perfectly dry, weighed ; the quantity of ash and carbon the unburnt portion contains must then be determined, and from the total quantity of carbon and ash in the fuel em- ployed the carbon in the unburnt portion and the relative quantity of ash must be deducted. We thus arrive at the quantity of the fuel burnt, and hence can determine its evaporative power. The unburnt portion of the carbon and the ash is determined by burning the filter and the coal in a porcelain crucible, previously weighed, until the carbonaceous matter is perfectly consumed. When the crucible is cold, it is again weighed ; the weight of the crucible deducted from the weight of the crucible and ash gives the quantity of the latter * The filter is first dried in the water or air bath at 212 F., then placed in a stoppered weighing tube, and tube and filter weighed ; the same plan is followed when the filter and unburnt portion of the coal has to be dried and weighed, care being taken to employ the same stoppered weighing tube. 40 Thompsons Calorimeter. substance ; this again deducted from the unburnt portion of the fuel gives the carbonaceous matter it contained. I have found it advisable in burning difficult combustible substances not to let down the appa- ratus (inclosure, furnace, &c.) to the bottom of the glass vessel at first, but just to let that portion of the inclosure surrounding the furnace to dip beneath the surface of the water until the combustion com- mences, and then to let it down to the bottom. In determining the heating power of peat by this method, I have found it necessary to mix 1 5 grains of it with a like weight of a good bitu- minous coal, the heating power of which has been previously very accurately determined. After the heating power of coal or other fuel has been determined, the sulphur that was present in the coal may be estimated by precipitating the sulphuric acid, into which it has been converted, by baric chloride, and determining the amount of baric sulphate in the usual manner. In employing this method for estimating the amount of sulphur in tar, it is necessary to add an equal weight of sugar to the tar, otherwise it does not deflagrate satisfactorily. When wax, spermaceti, and other fusible sub- stances are tested, they require to be in the first place mixed or fused with about three times their weight of manganic oxide (Mn0 2 ) or cupric oxide Calorific Intensity. 41 (CuO) in fine powder, which serves to regulate the combustion. Sulphur requires no such pro- vision, but may be burned safely with six times its weight of the chlorate mixture. Dr. Frankland has employed this apparatus for determining the calorific values of different sub- stances used as food. CALORIFIC INTENSITY. If the heat generated by the combustion be transferred to the combustion products, as is the case in the ordinary burning of fuel, the calorific intensity or pyrometrical heating power of the fuel or other combustible is obtained. The difference between the calorific power and the calorific intensity will perhaps be more clearly per- ceived if we illustrate the difference by examples. The calorific power carbon is, in its conversion into carbonic anhydride (C0 2 ), 8080, that is, as we have already explained, the heat generated during the combustion of one part by weight of carbon will raise 8080 parts of water 1 C.; or will heat one part of water from o to 8o8oC.; or will raise 3*67 parts of water from o C. to =2202 C. Now 3*67 3' 6 7 parts of C0 2 are produced by the combustion of one part of carbon, and if the heat produced by the combustion be transferred, not to ivater,&s is the case in determining the calorific power ,l*\it to the product of combustion (CO 2 ) as takes place in the burning of fuel or other combustible in pure oxygen, or in air 42 How the Calorific Intensity the temperature of the C0 2 would be 2202 C., if its specific heat were the same as that of water, but this is not the case. The specific heat of C0 2 is 0*2164, taking water to equal ro ; the temperature of the CO 2 will consequently be in the inverse ratio, or 3x8o8o =Iol83 C 1 1 x 0*2164 this is the pyrometrical heating power, or calorific intensity of carbon in its conversion into CO 2 , when it is burnt in pure oxygen. The student will be aware that 3 parts of carbon combine with 8 parts of oxygen to form 1 1 parts by weight of C0 2 . The calorific intensity is affected by the nature and quantity of the combustion products ; it is also influenced by the temperature of the air or oxygen wdth which the substance is supplied ; by the amount of water the substance contains ; the rapi- dity with which the combustion is effected and this will be modified by the state of division and porosity of the substance ; by the greater or less pressure under which the combustion takes place. The calorific intensity of a fuel may be estimated by the pyrometer,* or may be calculated theoreti- cally from its elementary composition. A descrip- tion of the best form of pyrometer is given in Chapter IV. ; the method by calculation will be the one at present described. * Thermometers can only be employed to measure temperatures under 600 F. Instruments employed to measure higher tempera- tures are termed pyrometers. may be Determined. 43 The calorific intensity of a simple combustible body is obtained by dividing its calorific power by the product of the relative weight of its combustion pro- duct into the specific heat of that product. It has already been shown by calculation what the calorific intensity of carbon is when converted into C0 2 , when that element is burnt in pure oxygen. We will now see (ist) what is the calo- rific intensity of carbonic oxide (CO) when con- verted into C0 2 ; and (2nd) the calorific intensity of hydrogen when converted into H 2 O, when these substances are burnt in an atmosphere of pure oxygen. ist. The calorific power of CO is, as has been already stated, 2403 ; its calorific intensity is 7072*9 ; thus i'57 x 1*57 being the amount of C0 2 formed by the com- bustion of one part of CO ; and o'2i64 is the^ specific heat of C0 2 . 2nd. In determining the calorific power of hydro- gen, the compound produced (H 2 O) is at first in the state of vapour (steam), but becomes con- densed ; the heat estimated in the calorimeter is, therefore, the heat of combination including the heat rendered latent in the steam. But in deter- mining the calorific intensity of this element the latent heat has to be deducted, because, as the 44 Determination steam does not become condensed in the combus- tion, as in the calorimeter, its latent heat will therefore not become available, and must, conse- quently, in calculating the calorific intensity of hydrogen, be deducted from the calorific power of that element. Now, one part by weight of water (the product of the oxidation of hydrogen) at iooC., to be transformed into steam of that temperature, must for that conversion absorb or abstract 537^ of sensible heat, which becomes, and remains, latent as long as the water continues in the state of steam. One part by weight of water at 100 C. requires, as just stated, in order to be converted into steam at iooC 537C. ; "a further correction has also to be made for the difference between the specific heat of water (=i) and that of steam ( = 0*4805) from o C. to 100 C., because in the computation of temperature the initial temperature is assumed to be o C. This difference is (i *o 0*4805) x 100 = 5 1 '95 thermal units, which must also be subtracted. The sum of these two numbers is 537 + 51 '95 = 588*95, which is the number of thermal units to be deducted for one part by weight of steam produced ; and since for one part by weight of hydrogen nine parts by weight of steam are produced, it is neces- sary to subtract 588*95x9 = 5300*55 from the number representing the calorific power of hydro- gen found by experiment in the calorimeter. The number left by subtraction must then be divided of the Calorific Intensity. 45 by the number obtained by multiplying the weight of steam produced by the specific heat of the steam, in order to ascertain the theoretical maximum tem- perature resulting from the combustion of hydrogen in pure oxygen," &c., 34462-5300-5^ Q Gt 9x0-4805 Although the calorific power of carbon (8080) is much less than that of hydrogen (34462), yet, as shown by the examples given, its calorific in- tensity (10183) is much greater than that of hydrogen (6743). The reason of carbon exceeding hydrogen in calorific intensity is due, as will have been observed, to three causes ist, the specific heat of aqueous vapour is about twice as great as that of CO 2 ; 2nd, i part of hydrogen produces 9 parts of water, whilst one part of carbon produces only 3*67 pares of C0 2 ; 3rd, the amount of heat in he latent state carried off by the steam. The calorific power of a substance is the same, whether burnt in pure oxygen or in atmospheric air ; but the calorific intensity is much greater when the substance is burnt in oxygen, than when burnt in air ; because the nitrogen, which takes no part in the combustion, absorbs a certain amount of heat, and thus lowers the temperature. The calorific intensity of a simple combustible in air is therefore obtained by dividing its calorific power by the sum of the products of the relative weight of its com- 46 Determination bustion product into its specific heat, and the pro- duct of the weight of nitrogen (in the air required for the combustion of the substance) into its specific heat. We find, for example, the calorific intensity of i part of carbon in the following way : For every i part by weight of oxygen contained in air, there are 3 '3 5 of nitrogen; now 3 ? parts of oxygen are required to convert 3* parts of carbon into C0 2 ; there are associated with the o parts of oxygen in the air 26*8 parts of nitrogen, and the specific heat of nitrogen is 0*244. We find the calorific intensity when the carbon is burnt in air to be 2717 "6 C. ; thus ^3x8080 r- n Q - = 2717-6 C. II X 0'2 I 64 + 26-8XO-244 Paradoxical as it might at first appear, the calo- rific intensity of carbonic oxide (CO) is greater than that of carbon when burnt in air. It will be seen that it is due to the lesser amount of air the carbonic oxide requires for its combustion; thus 2 43 -= 2982=0. 1-57x0-2164+1-91 xo'244 In substances containing oxygen it is necessary, as has been before observed, to deduct from the total quantity of hydrogen the quantity necessary to combine with the oxygen in the substance, and to account as available for raising the temperature only the remaining hydrogen, the disposable hydro- gen, with the carbon. The quantity of water which of the Calorific Intensity, 47 is formed by the combustion of the hydrogen by the oxygen in the fuel, as well as that formed by the combustion of the hydrogen by the oxygen of the air, will require to be evaporated, and will, therefore, diminish the available heat. It is sometimes important to know, not only the calorific power of a given weight of any parti- cular fuel, but also the calorific power of a given volume of the fuel say, a cubic foot. This is obtained by multiplying the calorific power of a given weight of the fuel by the weight of a cubic foot. FORMULAE FOR THE CALCULATION OF THE " CALO- RIFIC INTENSITY," OR " PYROMETRICAL HEATING EFFECT," OF FUEL FROM ITS ELEMENTARY COM- POSITION. CARBON BURNED in pure oxygen j , JT_ | Calorific power or absolute heating effect ( of carbon. _ ( Weight of carbon used (referred to I any unit of weight). Weight of oxygen required for the c=- complete combustion of c, weight of carbon. s= Specific heat of carbonic anhydride. r_ I Calorific intensity of the combustion I products in degrees Centigrade. Hence _ (No. of heat units produced byburn- . mg carbon. 48 Formula for the Calculation T , K x f No. of heat units transferred to the 1 (c4 |c) s = ( combustion products. /. /(c + fc) s = Kc. yes us. EXAMPLE. Determine the calorific intensity of one gramme of carbon burned in pure oxygen Here -/T=8o8o and 8=0*2164. ... /= 3x8o8o c CARBON BURNED in atmospheric air. Since there is contained in the quantity of air required for the complete combustion of the carbon a quantity of nitrogen equal to 8^93 times the weight of the carbon consumed, the calorific inten- sity will be diminished by the cooling effect of this quantity of nitrogen r>. . _ f Nitrogen present in air requisite to con- ~ I vert the C into C0 2 , s'= specific heat of nitrogen. Hence (2) /(V 1 cs.+8'93cs / )=Kc. Kc e(ys+8'93 8 ') ns + 26'8s' EXAMPLE. Determine the calorific intensity of one gramme of carbon burned in air ( ne arly). of the Calorific Intensity. 49 CARBON BURNED in atmospheric air (water being present). In this case the absolute heating effect will be further diminished by the quantity of heat which becomes latent in the conversion of the water into steam. A further correction must also be made on account of the difference between the specific heat of water and that of steam, because in the cal- culation of temperature the initial temperature is assumed to be o C. Thus (i 0.4805) x 100 will be the thermal quantity required to be deducted for this difference of specific heat /Weight of water present (unit of weight Letw=j as before). This also represents the 1 weight of steam produced. 537 C. latent heat of steam. s"= specific heat of steam. (i s") x 1 00 = correction for difference of specific heat. Hence ,No. of heat units pro- (3) JEc-{(i-&")x 100 + 537} duced by the com- bustion. No. of heat units trans- bustion products, in cluding also steam. E 50 For mules for the Calculation . r Kc 537w (i s") x 100 w EXAMPLE. Calculate the absolute heating effect of 4 grammes of carbon in the presence of i gramme of water, s" = o> j_ 8080x4 537 x i (10.4805) x 100 _ 4[V x 0.2 1 64 + 8.93x0. 2440] +0.4805 HYDROGEN BURNED in pure oxygen. Let h= weight of hydrogen burned. k=its calorific power. 9h= weight of steam produced by the com- bustion of the weight h of hydrogen. B"=8pecific heat of steam. In this case, as the water produced is in the state of vapour, its latent heat must be deducted, and also the same correction made for the difference of specific heat. Hence (4) /x.9hs"=kh-{ 0.5195x100 + 537} x 9 h. 9hs" 9s" EXAMPLE. Determine the calorific intensity of the combustion of one gramme of hydrogen in pure oxygen. - 9x0.4805 HYDROGEN BURNED in atmospheric air. \ As one part by weight of oxygen is mixed, in of the Calorific Intensity. 5 1 atmospheric air, with 3.35 parts by weight of nitro- gen, the weight of nitrogen, mixed with the eight parts by weight of oxygen, required for the con- version of one part by weight of hydrogen into water=8 x 3.35 = 26.8. Hence from (4) M /= k ~53QQ.55 9s" + 26.8s' EXAMPLE. Calculate the calorific intensity of the combustion of one gramme of hydrogen in air - 34462-5300.55 9 x 0.4805 + 26.8 x 0.244 CARBON AND HYDROGEN burned in pure oxygen. From (i) and (4) we have of heat units produced by the burning of the compound. M _ f No: of heat units transferred { to combustion products. Hence (6) /- K c+h(k-53Q0.55) V cs + 9hs" EXAMPLE. Calculate the calorific intensity of the combustion of 4 grammes of marsh gas (CH 4 ) in pure oxygen. Here c=3 grammes and h i gramme. V x 3 x o. 2 1 64 + 9 x 0.4805 E 2 52 Formula for the Calculation CARBON AND HYDROGEN, burned in atmospheric air. In this case the number of heat units absorbed by the nitrogen will be expressed from (2) and (5) / (8.93 cs' + 26.8 hs') Hence Kc + h (k-53oo.55) V cs -f 9hs" + (8.93 cs' + 26.8hs') Kc + h (k-5300.55). c (V s + 8.938') 4-h (26.8s' EXAMPLE. Calculate the calorific intensity of the combustion of 4 grammes of marsh gas (CH 4 ) in atmospheric air. T= 8080x3 + 34462-5300.55 3 (v x.2i64 + 8.93 x.244) + 26.8 x .244 + 9 x .4805 = 2699 C. CARBON, HYDROGEN, AND OXYGEN BURNED in atmospheric air. The oxygen is assumed not to be present in the substance in a greater ratio than would be requisite to convert the whole of the hydrogen into water ; and it may be in less proportion. If h' be taken to represent the amount of hydrogen which com- bines with the oxygen present in the fuel, then the amount of hydrogen available for raising the temperature, " the disposable hydrogen," will be denoted by h-h'. Let D=h-h' ; then formula (7) becomes of the Calorific Intensity. 53 c(v s + 8.93s')+D /=_ Kc + D(k- 5300.55) c (v 8 + 8.93 s') + 26.8 D s' + 9 h s" EXAMPLE. Calculate the calorific intensity of 100 grammes of an anthracite coal of the follow- ing percentage composition : Carbon 94.05, hydro- gen 3.38, oxygen 2.57. Here h' = ^p=o.32 and therefore = 3.38-0.32 = 3.06. Hence 8080x94.05 + (34462 -5300. 5) 3.06 T 94.05 {V x 0.2164 + 8. 93 x 0.2440} +26.8x = 2701 C. 3.06 x 0.2440 + 9 x 3.38 x 0.4805 If a solid body which is unaltered by the com- bustion be present, as the ash in coal, its weight multiplied by its specific heat must be added to the divisor. The quantity of heat lost by the presence of ash in coal is so insignificant that the results are but very slightly affected if the ash be left out of the calculation. If ash be present let ;r=its weight and S=its sp. heat ; then (8) becomes /J r | Kc + D (k- 5300.55) _ CARBONIC OXIDE BURNED in pure oxygen. Let 7*= the calorific power of carbonic oxide (CO). y= weight of CO burned. i. 57y weight of CO 2 produced by the combustion of y. 54 Formula for the Calculation Hence Tj No. of heat units produced by the burning of CO. 7(1.5 7y ) s = No. of heat units transferred to combustion products. = Ty ' 1.57x7x8 1.57x3 EXAMPLE. Calculate the calorific intensity of one gramme of CO burned in pure oxygen : T=2 4 3 . 1.57x0.2164 CARBONIC OXIDE BURNED in atmospheric air. One part by weight of CO requires for its con- version into CO 2 0*57 parts by weight of oxygen ; there is associated with this amount of oxygen in air i '9 1 parts by weight of nitrogen. Hence T (u) /= 1.57 s+ 1.91 s EXAMPLE. Calculate the calorific intensity of one gramme of CO burned in air. 1.57 x 0.2164 + 1.91 x 0.2440 FORMATION OF CARBONIC OXIDE DURING THE BURNING OF FUEL IN AIR. If in the burning of fuel some of the carbon be converted only into CO, the absolute heating effect will be diminished, because, as has been already noticed, one gramme of carbon in its conversion of the Calorific Intensity. 55 into CO evolves only 2473 heat units, whereas that weight of carbon in its conversion into CO. evolves 8080 heat units. Suppose in example (8) some of the carbon to be transformed only into CO, the formula becomes as follows : Let c= weight of carbon converted into CO. -* c= weight of oxygen required to convert c weight of carbon into CO. s= specific heat of CO. 7r=the calorific power of the carbon converted into CO. k __ {weight of nitrogen associated in air with I 3 c weight of oxygen. Hence (!2)/=- EXAMPLE. Calculate the calorific intensity of i oo grammes of the anthracite coal given in example (8). Supposing only 80 per cent, of the carbon to be converted into C0 2 the remaining 14.05 per cent, being converted into CO. Here K=2473 and y=o.2479. Hence ^8080x80 + 2473x14.05 + 3.06(34462-5300.55) 80 { V x 0.2164 + 8.93 xo.244o} +26.8 x 3.06x0.2440 + 9x3.38 x 0.4805 + -i- x 14.05 x 0.2479 + 4.46 x 14.05 x 0.2440 56 Exercise on the Heating EXERCISES. 1. Calculate the calorific intensity of ether (C 2 H.) 2 O in oxygen gas and in atmospheric air. 2. Calculate the calorific intensity of alcohol, C 2 H 5 HO in oxygen gas, and in atmospheric air. 3. A caking coal from Northumberland was found to have the following percentage composi- tion : Carbon 80.54 Hydrogen , 4.76 Oxygen 14.70 100.00 Determine from these numbers its calorific intensity in air, assuming that all the carbon is converted into carbonic anhydride. 4. A non-caking coal from South Staffordshire wa,s found to have the following percentage com- position : Carbon . ,: |i .... 78.46 Hydrogen . 4.96 Oxygen ....... 16.58 100.00 Determine its calorific intensity from these num- bers, assuming that one-half the carbon is con- verted into carbonic oxide, and the other half into carbonic anhydride. Power of Fuel. 5 7 5. A cannel coal from Tyneside was found to have the following percentage composition : Carbon 87.86 Hydrogen . ... . . . 7. Oxygen . '.-.. . . . . Nitrogen . ..... . . 100 ^w Determine its calorific intensity from these bers, assuming that all the carbon is converted into carbonic anhydride. 6. An anthracite from South Wales was found to have the following percentage composition : Carbon . . . . . . . 94.05 Hydrogen . '. / r . '. . 3.38 Oxygen . \ . V . . ' '. 2.57 100.00 Determine its calorific intensity from these num- bers, assuming that 25 per cent, of the carbon is converted into carbonic oxide and the rest into carbonic anhydride. 7. Determine the pyrometrical heating power of a cubic foot of the coals named in each of the pre- ceding exercises, taking the specific gravity of the coal in Exercise 3 to be 1.26 ; that in Exercises 4 and 5 to be 1.28 ; and that in 6 to be 1.35. CHAPTER III. Theoretical Heating Power of Fuel never obtained in Practice. The Calorific Intensity deduced from the Elementary Com- position of the Fuel not Accurate. How the Elements are combined and their state of Condensation in Coal not known. Evidence adduced that the Organic Elements are arranged differently in different Coals. The Nitrogen may be a Heat Producer. Gruner's Industrial Classification of Coal. BEFORE proceeding to show that the method for determining the theoretical calorific intensity of coal from its elementary composition by calculation is imperfect, we will allude to the difference between the theoretical heating power and the practical results. Owing to several causes the total theoretical heat- ing power of fuel is never obtained in practice : i st, the fuel is scarcely ever fully consumed, a part escapes combustion by passing off in the form of combustible gases and smoke, and another part remains mixed up with the ash ; 2nd, there is a loss of heat by radiation and also by conduction, the loss by conduction not only occurs through the materials of the furnace, but also from the gaseous Theoretical Heating Power. 59 products and excess of air which carry with them a considerable portion of the heat into the chimney and air, and also some of the heat is conducted away by the ash which falls through the grate. In calculating the calorific intensity, the theoretical amount of air required for the combustion of the fuel is employed, but this is never obtained in practice, it requires, in order to approach theory, the most favourable circumstances such as properly arranged furnaces, the adjustment of the fuel and of the air supplied to it ; this latter requires skill and constant attention on the part of the fireman ; a large excess of air is generally allowed to pass through the fire, which carries away a considerable amount of heat, and the loss from this cause is very much greater than is generally supposed ; further, if any of the carbon becomes converted only into carbonic oxide (CO), it has been shown by examples already given that a great loss of heat will occur. Another portion of the heat is lost by the water present in, and that formed by the burning of, the fuel. It is for this reason that the practice of charring has been adopted. By the charring the whole of the water the fuel contains and also almost all that would be produced from the hydrogen it contains is expelled; there consequently remains an artificial fuel of higher calorific power than the natural one from which it was derived. The charring is, of course, attended with a loss of 60 Theoretical Heating Power carbon in the form of C0 2 , of CO, and of hydro- carbons. The loss of heat in a furnace, due to the ad- mission of a greater amount of air than is necessary for the complete combustion of the fuel, may be illustrated by an example. On page 48 it was found that the calorific intensity of carbon burned in air was 2718 C. when the theoretical amount of air for its combustion was supplied. Taking the formula given for this calculation, we see that the exact weight of air needed for the combustion of c weight of carbon is (8 + 26.8)-; then if any excess of air pass through the furnace the formula will.be modified thus : Let a = specific heat of air. x = a number expressing the excess of air passing through, in terms of the amount theoretically required. Then the heat carried away by this excess of air is 34-8 x f x x x a ; if twice as much air passed through as was needed x would equal i ; if three times as much x = 2 and so on. The formula then becomes : " 3K EXAMPLE. Determine the calorific intensity of carbon burned in air when double the amount of air than is necessary for its combustion is supplied. Here #=i and a = o. not obtained in Practice. 6 1 3 x 8080 r _. = ii x 0.2164 + 26.8 x 0.2440 + 34. 8 x 0.2377 = 1410 C. The loss of heat in this case is therefore : 2718 1410= 1308 C. or 48 per cent, of the heat possible to be obtained. Then, again, high temperatures control both the combination of substances and the continuance of the combination of substances that have already combined; thus, at the temperature of 2500 C. oxy- gen and hydrogen will not enter into union, and carbonic anhydride is resolved into carbonic oxide and oxygen at about ioooC. ; there is, therefore, a limit to combination (combustion), for it ceases at & point which has been laid down by St. Glair Deville at 2500 C., and which has been called by him the point of dissociation, and the combustion also does not take place below a certain tempe- rature. It really only takes place between the limits of temperature of about 3 1 5 C. and 2 500 C. The time required for the combustion of the fuel, and consequently for the evolution of heat, depends upon its state of division and aggrega- tion, and upon its chemical composition. If the fuel be thrown on the fire in* large pieces, it burns slowly, and a large proportion of the heat generated is absorbed. If it be wood that is employed, and instead of being burnt in the form of large logs, it be first divided into shavings, the combustion will 62 Theoretical Heating Power be so rapid that a large proportion of the heat will, for all useful purposes, be lost. This arises from the greater facility with which the air comes in contact with it when in the form of shavings. If, however, the fragments are still further reduced in size, the smallness of the particles, and the close con- tact existing between them, excludes the entrance of the necessary supply of air ; and for this reason it is extremely difficult to obtain any available heat, either from saw-dust, or very finely-divided coal. But in determining the value of a fuel, not only must the state of division, but also the state of aggregation be taken into account ; thus, par- ticular qualities of charcoal, coke, and anthracite may have the same calorific power, and yet differ remarkably in their manner of burning. " Of the three, charcoal, being very light and porous, ignites most easily, and in a given volume contains the least combustible matter ; and accordingly, under the same conditions, it is most quickly consumed. Coke also contains less combustible matter in a given volume, and, except when prepared at high tempe- ratures, is more easily ignited than anthracite.* * "It is obvious that, on this account, anthracite is not adapted as a fuel for ordinary steam-boiler furnaces ; but by the following simple contrivance it may be advantageously employed in these furnaces. The ash-pit is kept filled with water, and deep fish-bellied bars are used, of which the lowest parts nearly, if they do not actually, touch the water- Steam is necessarily evolved from the surface of the water, and enters the fire-place along with the air which sustains combustion. On passing through the incandescent not obtained in Practice. 63 The practical effect of these differences in the manner of burning will be well understood by experimenting on the three kinds of fuel in a common casting-furnace about one foot square and from two to three feet deep. If an attempt is made to heat a large crucible in such a, furnace by means of anthracite, it will be found that the bottom becomes heated to whiteness before the top is hardly red-hot ; whereas, by the use of coke, the temperature is not so excessive at the bottom, but is more equally diffused through the furnace. The effect of anthracite as a fuel is the rapid pro- duction of an intense heat confined to a space not extending beyond a few inches above the base." (Percy.} The imperfections attending the method for determining by calculation the theoretical calorific intensity of coal may be classified under two divi- sions ; the second is the most important of the two. anthracite, it is decomposed, with the formation of the combustible gases, carbonic oxide and hydrogen, which are afterwards burned under the boiler at a distance from the fire, by the admission of a suitable supply of air from without- The decomposition of the steam causes a considerable diminution of temperature within the fire-place, but there is no permanent loss of heat, as, on the subse- quent burning of the combustible gases derived from the steam, the heat absorbed in the first instance is again given out and econo- mised ; there is, so to speak, only a transference of heat from the fire-place to a distance. The bars do not become sufficiently heated to burn rapidly away. The fire-place should be enclosed above by a fire-brick arch, as no part of the boiler should be unprotected above the solid fuel." Dr. Percy's " Metallurgy." 64 Combination of the Elements i st. The calculation is based upon the quantity of carbon and hydrogen the coal contains ; the methods we adopt at the present time for esti- mating the different elementary constituents of coal are imperfect, as will be explained in the chapter on the " analysis of coal ;" but although the numbers obtained are not in some cases abso- lutely correct by reason of our imperfect methods, they are in most cases sufficiently exact for all practical purposes. 2nd. In calculating the calorific intensity, we assume that the calorific power of the carbon and hydrogen, in this complex chemical compound, coal, is the same as when these elements are in their free or uncombined state ; it is further assumed, in making the calculation, that the oxygen in the coal is, as though it were, in combination with hydrogen, and therefore, in regard to that portion of the hydrogen in the coal, it is considered to be ineffective as regards the generation of heat. It has been established by the researches of Favre and Silberman that the calorific power of carbon, like its sp. heat, varies with its density; the calorific power as determined by M. Favre and Silberman, and the sp. heat as determined by M. Regnault for the different forms of carbon, is here given : in Coal not known. 65 Calorific Power. Sp. Heat. Wood charcoal . . . 8080 ... 0.24150 Coke from gas retorts . 8047 ... 0.20360 Native graphite . > ., 7797 0.20187 Graphite from blast) ^ Q ^^ furnaces . . ) Diamond ... . . 7770 ... 0.11687 We are entirely ignorant as regards the density of carbon as it exists in coal, we cannot, therefore, know its proper calorific value; it is possible that its density is different in different varieties of coal, still less do we know the proper calorific value of the hydrogen in coal ; it can scarcely be the same when existing as a constituent of a solid body as when it exists in its free gaseous state. From the experiments made on the calorific power of substances, it is known by experi- ment that the calorific power of a compound is in general less than the calorific power of its elements in their uncombined state ; and that whatever may be the calorimetric effect of any chemical change, whether it be one of combination or one of decomposition, the calorimetric effect of the reverse change is equal and opposite ; if, for instance, the formation of a chemical compound is attended with an evolution of heat, their separa- tion is attended by the disappearance of an equal quantity of heat; therefore the heat produced by the combustion of such a compound must be less, 66 The Elements united differently : : by the amount absorbed in the separation of its elements, than the combustion of those elements in their uncombined state. It has been further ascertained that the calorific power of isomeric compounds varies like the elements with their density; for example, the calorific power of the hydrocarbons belonging to the olefiant gas series (C n H 2n ) diminishes as their molecular condensa- tion increases, and for each addition of C n H 2D into the molecule, Favre and Silberman infer, from their experiments, that there is a decrease of 3 7. 5 units. Berthelot has shown that when carbon and nitro- gen unite to form cyanogen, an absorption of heat takes place ; an absorption likewise takes place in the formation of the amides, hydrocyanic acid, and other compounds. If the nitrogen in coal is com- bined with some of the carbon, an absorption of heat would most probably take place when they united ; if so, the heat will be evolved on their separation ; consequently, the nitrogen compound will be, as well as the carbon and hydrogen, a heat producer. As we neither know how the elements are com- bined nor their state of condensation in coal, the results obtained in calculating the calorific inten- sity from its elementary composition can at best be only approximations to the truth. * That the organic * MM. Scherrer-Kestner and Meunier have found by experiment that coals, excluding lignites, give a higher calorific power by the calorimeter than the calorific power deduced by calculation. in different Coals. 67 elements are differently arranged in different coals appears proved, for it has been ascertained by experiment that different varieties of coal having almost exactly the same percentage composition as regards their organic elements have been found to yield different quantities of coke and to vary considerably in calorific power ; and so far as inves- tigations have yet proceeded in this direction, the calorific power, with some few exceptions, in- creases and diminishes with the amount of coke the coal yields.* This is at least true, M. Gruner observes, for coals properly so-called, but not always for anthracites and lignites ; he believes that the proximate analysis furnishes an image more true of the essential properties of coal (calorific power, agglomerating power, and ash) than the ultimate analysis of it ; and as the proximate method exacts much less time and experimental ability, is in all cases more preferable in an industrial point of view. As a further illustration that the organic elements are arranged differently in different coals, it may be noticed that caking and non-caking coals may have the same elementary composition ; therefore, the property of caking must depend upon the proximate constitution of the coal, and riot upoi* its elementary composition. * In a few of the exceptions the coal which yielded the least coke had the highest calorific power, and in some other cases when they yielded the same amount of coke they had different calorific powers. F 2 68 Gruner s Classification Gruner* divides coals, excluding lignites, into five classes. Although the characters of each class are different, it will be seen from the Table we give that the passage from one class to another is, as is the case in most natural classifications, gradual. The percentage amounts of the organic consti- tuents, as shown by the Table, are comprised between the following numbers : Carbon 75 to 93 Hydrogen 4 to 6 Oxygen, including nitrogen 3 to 1 9 As regards the nature and appearance of the coke, the extreme types, ist and 5th classes, approximate most closely, but they differ widely, as regards the quantity they yield of it, and volatile matter, and of their inflaming powers. The ist class yields from 55 to 60 per cent, of coke, and from 40 to 45 of volatile matter, they inflame readily, and burn with a long smoky flame ; the 5th class yields from 82 to 93 per cent, of coke, and from 10 to 18 per cent, of volatile matter, they inflame with difficulty, and burn with a short flame of feeble durability, and almost without smoke. The combustibility and length of flame depends upon the amount of the volatile matter the coal yields ; but these properties also depend to some * " Ponvoir Calorifique et Classification des Homlles." Par M. L. Gruner, Ann. des Mines, 1873, i^ 169. I have availed myself of some of the valuable matter in this Paper.- R. G. of Coals. 69 extent upon the quality and quantity of the ash. We see by the Table that the coke commences becoming compact when the carbon reaches 80 per cent., and the oxygen and nitrogen fall below 15 per cent., and these proportions serve as the boun- dary between dry and fat coal. As the oxygen diminishes, the coal becomes more friable, less sonorous, blacker, and less dense. The brightness and agglomerating power increases with the amount of hydrogen. These different properties are notably modified by the inorganic substances ; the density and hardness increases with the amount of ash, but the brightness diminishes with its increase. The coals of the ist class are hard, compact, and sonorous to blows ; their colour is rarely pure black, and in all cases their powder is brown. The coals of the 2nd class are in general hard and com- pact, but in a less degree than those of the ist class, but they are more brilliant in colour and of a deeper black ; they also yield a less proportion of gas, but it possesses a greater illuminating power. The coals of this class are employed in the manufacture of gas, and where a short, vivid, and rapid fire is required, not a moderate, uniform, and sustained heat. The coals of the 3rd class are black, of vivid brilliancy, a little hard, the structure more or less platy; they burn with a shorter and less smoky flame than those of the ist 70 Gruner's Classification and 2nd class. By reason of their fusion and agglomeration into a compact mass in the fire they are rendered eminently suitable for the forge. The coals of the 4th class are almost always friable, they inflame with difficulty, and burn slowly with a short and very little smoky flame; they yield of all classes the best coke, but they require to be carbonised immediately on being brought up from the pits. The coals of the 5th class are black and are habitually furrowed with striae ; it is difficult to burn them in the grate, and, from the small quantity of volatile matter they yield, they are not suitable for the generation of steam and other purposes where a different heat is required, but are well adapted for purposes where a localised tem- perature is required. In the Table the ash and water have been deducted, and the coals are made to consist conse- quently of carbon, hydrogen, and oxygen only; this is done in order to compare the calorimetric and experimental heating powers of coal having nearly the same proportion of the organic constituents, but which varied in the quantity of ash and water. The real calorific power was determined by the calorimeter, the evaporative power by the amount of water evaporated in practical operations.' 55 ' The numbers given with respect to the heating powers, * The Table gives the amount of water at o C. vaporised at 1 12 C. per kilogramme of the pure coal burnt. of Coals. I Ijg ^: til o ^, 'I Ft 9 HI 00 o O !& 2 vo CO - o ^ " ** 8-2 O O ON"*" ^ 00 *** o r* o is ON ON . r Wi 72 Description of the Apparatus and the amount of coke and volatile matter yielded ; and the percentage composition of the organic con- stituents are calculated upon the pure coal that is, coal free from ash and moisture ; the experi- ments and analyses were made with coal in the ordinary state, but from the results obtained it was calculated what the results would have been if the coal had been pure ; this was done in order to compare coals having organic constituents in similar proportion. It may be as well to state that the Table is a union of the results given by Gruner in two Tables. It has been made evident in this chapter that it would be most desirable for practical, as well as for scientific, purposes that a process should be devised for determining with minute exactness the calorific power of coal, so that by the results obtained by this method of examination, and those derived by the exact analysis, &c., the state of condensation of the carbon in every coal, and the proximate composi- tion of the coal, could be arri ved at. An investigation with this important object in view I commenced some time ago, aided by my friend and former student, Mr. C. C. Hutchinson, but for the present we have been compelled to abandon it. We tried the apparatus employed by Kestner and Meunier with a like object in view, but we found that it gave results that were not of that degree of exactness required for such an of Kestner and Meunier. 7 3 investigation. The apparatus (Fig. 3) is a modi- fication of Favre and Silberman's, and it is described here, as it may be the means of inducing others to take up this most important investigation. The following is an outline of the description Kestner and Meunier give for the method of using it. They state that they found it expedient after many trials: 1 . Not to use more than half a gramme of coal. 2. For certain coals to employ 60 parts of oxygen and 40 parts of nitrogen, instead of pure oxygen. 3. To give sufficient velocity to the current of gas to maintain vivid combustion. FIG- 3. (a) Cup or basket of platinum containing the powdered coal. (b &') Platinum wires suspending the basket. (c d] Tube conveying the current of oxygen. 4. Lastly, to replace the basket or cartridge 74 Description of the Apparatus employed by Favre and Silberman by another apparatus which allows of burning a powdered body, and of weighing without loss the ashes pro- duced. These conditions have been realised, they state, thanks to the use of a very delicate thermo- meter and of a platinum apparatus (Fig. 3). It consists of a platinum capsule a and three wires b,b,b of the same metal, with a tube c,c, whose lower end opens in the centre of the circumference formed by the rim of the capsule. The upper end of the tube fits in the nozzle of an oxygen blow- pipe which passes through the stopper of the com- bustion chamber, so that the gas on arriving at c flows to the centre of the combustible mass con- tained in the capsule. All the joints of the chamber were luted with melted caoutchouc. The coal for determination and the ash which remains after combustion are each weighed in the capsule. Combustion is set up by means of a particle of wood charcoal weighing less than a milligramme, which is introduced through the opening for the blow-pipe. As only a small amount of coal was em- ployed, a thermometer so delicate had to be employed that the errors of observation were in- finitesimal. The elevation in temperature of the water of the calorimeter did not in general exceed one degree of the ordinary thermometer. As a strong current of gas had to be employed of Kestner and Meunier. 75 they found that the absorption of the carbonic anhydride was not sufficiently complete without employing a number of Liebig's potash bulbs ; they avoided this inconvenience by using soda lime, in place of potash, which absorbs CO 2 very rapidly. They did not succeed in completely burning the carbon. After each operation the bottom and sides of the capsule remained coated with a layer of that body. This observation shows that it was not completely successful in the hands of the inventors. 7 6 CHAPTER IV. Pyrometers, the Principles on which they have been Constructed. Description and Illustration of Siemens' Electric Resistance Pyrometer. MANY forms of pyrometers have been invented, but few of them are satisfactory in their indications. We shall, therefore, simply state the principles upon which they have been constructed, describing only in detail the one which is the most perfect. The principles involved in the construction of the various forms of this heat-measurer may be classified thus : 1 . Change in the volume of bodies. 2. Change in the chemical or molecular state. 3. Transformation of energy. 4. Transmission of energy. To the first class belong those instruments in which the change of volume of a body, solid or gaseous, is made the subject of observation ; the expansion or contraction following some connected law and being a function of the temperature. The pyrometers of Daniell and of Wedgewood Pyrometers. 77 are illustrations of this method; in the former the ex- pansion of a bar of platinum is the indicating agent; in the latter, the contraction of a block of fire-clay. To the second class belong those forms of the instrument which depend upon chemical or mole- cular changes. Begnault devised a gas or hydrogen pyrometer for measuring the variable temperatures of furnaces, but since the discoveries of Graham and Deville that iron is permeable to hydrogen at a red heat, the apparatus is regarded as inaccurate.* Lamy invented one in which he employed the decom- position of calcic carbonate and the increase of pressure of the liberated carbonic anhydride in a closed vessel as the indicator. The pyrometer invented by Siemens, and which is illustrated and described further on, is an example of a change in the molecular state of .a body. The third class comprises those instruments in which the energy of heat is converted into an electric current ; which is measured. The instru- ment, the thermopile, is placed either in the furnace itself, exposed to radiation, or its face is placed in contact with some good conducting body. The fourth class embraces those instruments in which advantage is taken of some agent for the transmission of heat from the source to some form of thermometer. This is accomplished either by a bar * Ann. Ch. Phys. [3] Ixiii. 42, 78 Description of Siemens of metal, one end of which is placed in the furnace, and to the other end is attached an accurate ther- mometer ; or else the heat passes through an orifice in a screen and is concentrated by a lens upon the bulb of a thermometer at a given distance from the source of heat. Another modification is to employ an infusible body of known weight and specific heat. It is placed in the furnace and sub- sequently removed to a calorimeter, containing a known weight of water; this process is exactly similar to the determination of specific heat by the method of mixtures. SIEMENS' ELECTRIC PYROMETER, which we shall now describe, " is the only kind which is service- able, and can be recommended." (Wemhold.) The principles involved in the construction of this instrument, and its application to the measure- ment of temperatures, are : ist. The increase in resistance to the passage of an electric current through a conductor when that conductor is heated. 2nd. That if two circuits or conductors be offered for the passage of an electric current, the amount of current passing through each branch is inversely proportional to the resistance offered in each separately. From numerous experimental re- searches Siemens has deduced a law which he believes expresses the functional relations which exist between the increase of resistance and the in- Electric Pyrometer. 79 crement of temperature in a given conductor. This law he expresses by the accompanying formula : Let II = the resistance of the circuit, T = the temperature, computed from the absolute zero, or from 2 7 2. 8 5 C. a j3 y = coefficients which vary for each metal. Then E = a jT+p T + y. Substituting the experimental values of a, /3, y in the case of platinum the formula becomes E, = 0.039369 V T + 0.002 1 6407 T o. 24127. This law has been applied in Siemens' instrument by employing a divided circuit through which an electric current is passed. In one branch is placed a standard resistance coil ; in the other the platinum spiral to be heated in the furnace. The hotter the spiral becomes the greater its resistance becomes, and the greater is the ratio between the intensities of the current in the two branches. This is measured by each circuit current passing through a voltameter tube, both tubes being placed side by side each other upon a scale. The ratio of the amounts of water decomposed in each gives the relative resistances in each circuit ; hence the resist- ance of the platinum coil is obtained, and by com- paring this with its known resistance at o C. and by the use of the formula given above the tempera- ture of the furnace is obtained. The instrument consists of two distinct parts, the voltameter for measuring the current, and its 8o Description of Siemens connections, shown in Figs. 4 and 5, and the wrought iron tube, &c., shown in Fig. 6. The current from the battery enters at the binding screw (a) ; when FIG. 4. ELEVATION. SIEMENS' PYROMETER. VOLTAMETER AND CONNECTIONS. SCALE \\ INCHES TO A FOOT. Electric Pyrometer. 81 the commutator (b) closes the circuit, the current passes along the wire (e) through the cable and the central insulated wire (/) in the heating tube E, FIG. 5. PLAN. CA and B) Voltameter tubes. (C and D) Reservoirs for supply of tubes. (a) Binding screw by which current enters. (6) Commutator. (e) Binding screw and wire of the undivided current. (k) Standard resistance coil. (1) (m) and (n) Binding screws for return current. (h') and (t') Wires leading through cable to insulated wires in the heating tube, (r) and (s) Weighted levers for pressing rubber pads on the end of voltameters. (M) and (v) Weights for end of levers. G 82 Mode of Using FIG. 6. f SIEMENS' PYROMETER TUBE CONTAINING PLATINUM RESISTANCE COIL. SCALE \\ INCHES TO A FOOT. E, Wrought iron tube. F Porcelain cylinder upon which is wound a platinum spiral. / h, i, Platinum wires insulated in pipe-clay. the Pyrometer. 83 Fig. 6. The enlarged section shows the platinum spiral wound upon a cylinder of porcelain F ; on arriving at the point (g) two passages are open to the current ; one to return through the wire (A), into which it is short circuited without passing- through the spiral, back along the continuation of (A) in the cable through the standard resistance coil (k) and from there by the wires shown, through the voltameter tube A, thence to the binding screws (/) and (m) back to the battery. The second passage open to the current at the point (g) is to pass through the platinum coil to the insulated wire (i), which joins the extreme end of the coil at (p), along the cable to the binding screws through the voltameter B and as in the case of A. t *v V Jj] The two voltameter tubes are upper end by india-rubber pads kept levers (r and s), which have weights (u and v) at their ends. At their lower ends they are connected by pieces of flexible rubber tubing with the reser- voirs (C, D), which slide in vertical grooves, so that the gas generated in each tube can be brought to the atmospheric pressure by adjusting the water level in the reservoirs to the same height as that in the tubes. The instrument is used as follows : The end of the wrought iron tube is plunged into the furnace as soon as it has attained the maximum tempera- G 2 84 Pyrometer. ture, the commutator is turned to complete the battery circuit. The current passes through the circuit as just described and some of the acidulated water in each voltameter is decomposed. As soon as one of them is about half-filled with gas, the current is stopped and the gas in each tube is brought to the atmospheric pressure by adjusting the reservoirs C and D and the volume of gas in each is read. The voltameter may be made ready for the next experiment by raising the reservoirs and then pressing the upper part of the weighted levers (r and s) together ; this allows the column of water in the flexible tube to force the gas out by raising the pads. When the tubes are completely refilled and all the gas expelled the levers are allowed to drop. During the experiment the commutator is employed to reverse the direction of the current about every half-minute, in order to avoid the polar- ization of the voltameter electrodes. The wires attached to the voltameter are of stout copper, but in the interior of the wrought iron tube platinum wires are substituted for them on account of the high temperature to which they are submitted. A Table is supplied with each instrument to facilitate the conversion of the readings into tem- peratures. CHAPTER V. Siemens' Regenerative Gas Furnace. Its Advantages. The Gas Producer. The Construction and Working of the Producer. The Construction and Working of the Furnace. IT has already been shown that in ordinary fur- naces there is a great loss of heat and waste of fuel, consequently , many inventors have endea- voured in a variety of ways to burn fuel more economically in manufacturing operations. The most philosophical and successful of these inven- tions is the furnace devised by Mr. C. W. Siemens. The defects of ordinary furnaces, which have been already noticed, are greatly obviated in Mr. Siemens' furnace, and therefore a greater amount of the heating-power of fuel is utilised. In addi- tion to this a class of fuel, such as slack, breeze, peat, sawdust, &c., which could not be advantage- ously burned in an ordinary furnace, can be econo- mically employed in that of Siemens'. The advantages are briefly effected as follows : ist, by transforming the fuel used into gaseous 86 Construction and Working products; 2nd, by mixing the gases thus pro- duced with, as near as is practicably possible, the amount of air requisite for their complete combus- tion; 3rd, by burning the gaseous fuel directly in contact with the substance to be operated upon by the heat ; and, 4th, by the heat of the com- bustion products, which in the ordinary process of burning is wasted, being stored up and utilised to raise the temperature of the gaseous fuel before it is burned in the combustion-chamber. This utilisation of the heat of the combustion products constitutes the process of " regenera- tion," -that is, the retransference of the waste heat of the combustion products to the hearth of the furnace. The description of the furnace will be divided into two parts: ist, the Gas Producer; and, 2nd, the Furnace proper, with the Regenerators. GAS PRODUCER. Fig. 7 represents one of these producers for the transformation of a solid into a gaseous fuel. It consists of a rectangular chamber built of fire-brick, and usually placed below the level of the ground; one side of this (6) is inclined at an angle of 45 to 60. The lower part of this sloping side consists of an iron grate (c), with horizontal bars, for the admission of air to the incandescent fuel ; the lower side of the furnace is formed by the fire-bars (d). By means of the water-pipe (e) a limited quantity of water is of the Gas Producer. I e 8 88 Construction and Working supplied to the floor (/) of the chamber beneath the fire-bars. Suppose the furnace to be lighted and the neces- sary amount of fuel to be supplied through the self-closing hopper (#), the air passing through the grate (c) and coming in contact with the incandes- cent fuel forms first carbonic anhydride (C0 2 ), which as it passes upwards through the layers of heated fuel is converted into carbonic oxide (CO) ; at the same time some of the fuel resting on the incline (b) undergoes destructive distillation, there is thus formed a certain amount of hydrocarbons. By the radiation of heat from the grate and fire-bars the water on the floor (f) is vaporised, and ascends and passes into the furnace where it is decomposed by some of the heated fuel, carbonic oxide being formed and hydrogen set free ; thus further increas- ing and adding to the heating power of the gaseous fuel, thus 2 H 2 O + C 2 = 2 CO + 2 H 2 . The gaseous mixture thus obtained passes up through the openings (g) and up the perpendicular brick uptake (A), and enters the wrought iron " cooling-tube' ' (i). Here the gaseous mixture, which on leaving the furnace was of a temperature between 300 and 430 C., is cooled down to about 1 00 C. ; the mixture, from the cooling, contracts and becomes denser, thereby establishing a pre- ponderating weight to the descending gaseous of the Gas Producer. 89 matter in the wrought iron downtake (j), which forces the current of gas forward through the main flue on to the furnace. A slight excess of pressure over the atmosphere is also produced, which exercises the following beneficial effects : ist, the gaseous mixture passes into the furnace with a slight outward pressure ; 2nd, any leakage of air into the main gas flue is thereby prevented; the leakage would be injurious, as it would be attended with the for- mation of explosive mixtures. From the down- take the gaseous fuel proceeds into the brick flue (&) which leads to the Regenerative Furnace. The movable iron plate (/) acts as a damper for the greater or less communication of this block of gas producers with the main flue, several sets of producers being frequently used, in connection with one flue, so as to afford a constant and steady supply of gas. The tarry matter produced is deposited in the tar- well (m) during the passage of the gaseous mixture to the main flue. The openings (n) in the arched roof of the producer, and which are fitted with covers and stoppers, are for the purpose of testing the gas by allowing it to escape and then igniting it ; and also for the introduction of iron bars necessary for the removal of the clinkers, &c., formed in the furnace. The following is the percentage composition of 9O Gas Producer. the gas from the producers according to analyses made at St. Gobain :* Hydrogen . . from 4 to 1 1 per cent. Carbonic oxide 15 to 19 Carbonic anhy-) , , dride . . I ^ to 7 Nitrogen . . ,,75 to 63 The hoppers (a) are kept continuously filled with fuel, and are covered with an iron plate so as to prevent the escape of gas on introducing fresh fuel into the body of the producer. When the producer is constructed to utilise very small coal, or poor fuel, the water-pipe (e) is replaced by a steam blast, by which means a mixture of air and steam is blown into the pro- ducer. According to the capacity, each furnace converts from one to three tons of fuel into gas per day. REGENERATIVE REHEATING FURNACE. The special application of the Regenerative Gas Furnace we shall describe, is that form of it employed for reheating iron or steel. The furnace consists of three parts the VALVES, the REGENERATORS, and the HEATING CHAMBER. Fig. 9 is a longitudinal section through the body of the furnace showing the REGENERATORS and HEATING CHAMBER. In Fig. 8 * Orsat's apparatus described in the next Chapter affords a ready means of determining the amount of CO and C0 2 in the gaseous fuel. Regenerative Gas Furnace. 91 is shown a section of the valve arrangement by a plane parallel to, and situated in front of, the plane of section of Fig. 9. For the regulation of the admission of the currents of gaseous fuel and air into the furnace, and their reversal, two valve chambers containing valves worked by a system of levers are required. The one shown in section in Fig. 8 is the one for the admission of air ; it con- tains a regulating valve (a) and a reversing valve (b). Behind this and separated from it by a par- tition is a similar chamber containing a reversing valve, and in connection with the short tube (c) which communicates with the main flue, the end being closed by a regulating valve (d). The reversing valves (b) are worked by two inde- pendent levers, one of which is shown at (e), with the rods and levers in connection with it. The regulating valves (a) and (d) are worked by two independent screw standards, one of which is shown at (/). To avoid confusion in the drawing this system of rods and levers has been indicated by dotted lines only. The construction and work- ing is as follows : The pit in which the valve- chambers are placed is covered in with iron plating (g), in which are openings for the admission of air ; the air thus entering passes through the valve (a), and takes the direction to the left indicated by the arrow into the flue (Ji). The gas entering from the main flue into the oblong iron tube (k) passes Construction and Working FIG SIEMENS' EEHEATING FURNACE SECTION, SHOWING VALVES AND FLUES. SCALE \ INCH TO A FOOT. ( A) The valve-chamber made of cast iron. (a) Air regulating valve. (6) Air reversing valve. (c) Short iron tube through which the gaseous products pass into the gas valve-chamber similar to A, and containing gas re versing valve like (6). (d) Gas regulating valve. (e) Hand lever for reversing the air valve (&), another behind this similarly connected for reversing the gas valve. (/) Screw standard connected as shown by dotted lines for working the regulating valve (a), another behind it working the regulating valve (d). (g) Iron plating for cover of pit. (h) Air flue leading to regenerator, (i) Partition behind which is gas flue to regenerators. (&) Square tube communicating with main gas flue. (p 1 ) Flue communicating with chamber (I 1 ). (q 1 ) Partition behind which is a flue communicating with chamber (mf). r) Exit flue leading to chimney stack. of the Gas Fitrnace. 93 through its regulating valve (d), the short pipe (c), its own valve-chamber, and emerges into a flue behind the brick partition (i), separating it from the air flue. Passing along their respective flues, the air and eras ascend from their continuations A' o and i' in Fig. 9 into the REGENERATORS () and (ra). These two chambers are constructed of a number of horizontal layers of fire-brick, the openings in the one set being opposite a brick in the other and vice versd the currents of gas and air have thus to pass through in a zigzag course, their contact with a large amount of surface is hereby ensured. Passing up through these layers they emerge into the heating chamber B by the flues n and a. The air emerging at (n) being denser than the gaseous fuel emerging at (6) sinks and diffuses into it so that a thorough intermixture occurs. On being kindled at these openings the mixture burns with a moderate calorific intensity, the flame passing directly over the hearth of the chamber B. The products of combustion pass away to the right through (n') and (o 1 ) into the Regenerator (/') and (m') , here they pass over the large cooling surface of brick divisions and are deprived by the brick surface of a large amount of heat, conse- quently they emerge into the flues (p) and (q) at a much lower temperature than on leaving the hearth of the furnace. Entering (p f ) and the flue behind 94 Construction and Working FIG. 9. SIEMENS' KEHBATING FURNACE LONGITUDINAL SECTION. SCALE \ INCH TO A FOOT. (h'} Continuation of flue (h) in Fig. (8). (i r ) Continuation of flue behind (i) in Fig. (8). (I) and (m) Regenerating chambers. (w) and (o) Entrance flues for the air and gas. B The heating chamber. (n f ) and (o') Flues similar to (w) and (o). (I'} and (m') Regenerating chambers. (p) Flue in connection with (p'). (q) Flue in connection with that behind partition (2 73 Proximate Composition. Water . . . . 0*76 Volatile matter . . . 35*97 Fixed carbon (coke) . . 57' 11 Ash . . . . . 6* 1 6 100*00 H2 Analysis Amount of sulphur in the coke 2*288 in the vola- tile matter . . . 3*026 Percentage of nitrogen . 0*43 V. WIGAN CANNEL COAL. Specific gravity A _. . *jj 1*284 Proximate Composition. Water :: . , t * . . 0*82 Volatile matter ' , : . %t 36*09 Fixed carbon (coke) .; . 61*02 Ash .- : ' /. f i J-'. . , . 2*07 100*00 Amount of sulphur in the cok e 0*639 in the vola- tile matter . . . 0*543 I*l82 Percentage of nitrogen . 1*42 The Carlisle is, what is termed by gas manufac- turers, a dirty coal ; the gas produced from it will of Coal. 1 1 3 require, on account of the large quantity of sulphur compounds it must contain, the largest quantity of purifying material to remove them. The Newcastle Pelt on Main will yield a larger amount of nitro- genous compounds than the other four coals. The Boghead Coal, from the larger amount of volatile matter it yields than the other four, will yield the largest amount of gas. HEATING POWER. The determination of the heating power has been described in Chapter II. ULTIMATE ANALYSIS OF COAL. For the determination of the elementary organic consti- tuents in coal the student is referred to works on quantitative analysis like that of Fresenius for the processes to be adopted ; we will merely remark that only 3 grains of anthracite, and from 5 to 7 grains of bituminous coal ought to be employed ; more correct results are obtained by employing these quantities than larger amounts. The nitrogen is determined by Will and Varen- trapp's method ; about 1 5 grains of the coal should be employed for this latter estimation. Errors in the Ultimate Analysis of Coal. "When coal contains much inorganic matter, especially iron pyrites, the usual method of calcu- lating its composition from the data obtained in the process of organic analysis maybe erroneous in a sen- sible degree. The ashes left by incineration are esti- I 1 14 Errors in the ultimate mated as inorganic matter, and the proportion of oxygen is found by subtracting the sum of the carbon, hydrogen, nitrogen, and ashes, from the amount of the dry coal subject to analysis. By incineration, the iron of the pyrites is converted into ferric oxide, and the sulphur, in a greater or less degree, into sulphuric anhydride (S0 3 ), which may remain in combination with any bases in the ashes such as lime capable of forming a sulphate not decomposable at a red heat. Supposing the whole of the sulphur of the sulphide to be retained in this state in the ashes, for one part by weight of iron pyrites there would be an increase of one part by weight due to oxygen derived from the air during incineration. The whole amount of this error, provided no correction be made, would fall upon the oxygen. It is not asserted that the whole of the sulphur is oxidised, or that the whole quantity of the oxidised portion is retained as a sulphate in the ashes, but that a considerable por- tion of a stable sulphate may be produced during incineration will appear from analyses of coal and coal ashes. " It is certain that the alumina in the ashes must, either wholly, or in great measure, exist in combina- tion with silica as clay ; and clay holds water in com- bination which cannot be expelled except at a tem- perature far more than sufficient to decompose coal. Hence, during the process of the organic analysis Analysis of Coal. 1 1 5 of the coal, the water in the clay will be expelled, and so occasion an error of excess in the deter- mination of the hydrogen. This source of error has been pointed out by Regnault. " Calcic carbonate is sometimes present in coal in very appreciable quantity, in which case carbonic anhydride would be evolved during the organic analysis, and so an error of excess would be caused in the determination of the carbon. " There is, lastly, another source of error which may result from the absorption of oxygen during the drying of the coal preparatory to combus- tion." (Percy.) ANALYSIS OF GASEOUS MIXTURES. The appa- ratus to be described is one invented by M. Orsat of Paris. It is adapted for a rapid and sufficiently accurate estimation for industrial purposes of furnace gases namely, carbonic oxide, carbonic anhydride, oxygen, and nitrogen. The apparatus consists of a cylinder, A B, drawn down at both ends, and open to receive a gra- duated tube of such size that every division will represent half a cubic millimetre. The space be- tween the two is filled with water, in order to have the tube, and consequently the gas, which is being analysed, at a constant temperature, and thus avoid corrections for dilatation. This graduated tube communicates at A, with a horizontal capillary tube provided near its extremity with a stop-cock i 2 n6 Description of Or sat' s FIG. 10. ORSAT'S APPARATUS FOR THE ANALYSIS or FURNACE GASES. A B graduated tube for measuring the gas. C stop-cock for admission of gas. D aspirating bottle. E absorbing cylinder containing potash. F n ammonia and copper solution. e and/ marks to show the height of solution. G stop-cock for potash cylinder. H }> )? copper solution cylinder. I stop-cock for expulsion of gas. K tube for admission of water to tromp. L water tromp. M exit tube of tromp. m and n zero marks of cylinders. N admission tube for gas. flexible rubber tube, joining graduated tube and aspirator. P stop-cock for admission of air into cylinder F. Gas Apparatus. 117 C, through which the gases to be analysed are introduced into the apparatus. At B it is connected by means of an india-rubber tube O, with an open- ing near the bottom of the bottle D, which serves to produce a current of gas into the graduated tube when it is lowered, and forces the gas .out of it when it is raised. The capillary tube A C is con- nected by two branches H and G, each of which has its own stop-cock, with two bell jars placed in cylinders E and F, which contain the absorbent liquids. The cylinder E is filled up to the mark c with a solution of caustic potash of 1*357 sp. gr. In the bell glass a bundle of tubes open at both ends are placed. When the gas enters that vessel the pressure forces part of the liquid into the cylinder, uncovering the tubes wet with the potash solution, thus presenting to the gas such an amount of surface contact that the absorption is almost in- stantaneous. A bent tube in the cork provides for the necessary admission of air. In order that all the joints may be perfectly air-tight, the corks, E, F, A, B, are covered with sheet india-rubber, or corks of that material are employed. The bell jar in cylinder F contains a roll of copper wire gauze, which must be slightly conical in shape and reach to the top of the jar. An ammoniacal solution composed of two-thirds by volume of a cold saturated solution of ammonic chloride and 1 1 8 Mode of using Or sat' s one-third of commercial ammonia is introduced into F. The solution is colourless when prepared, but soon becomes blue in contact with the copper. As it absorbs oxygen very rapidly the communication with the air is effected by means of a stop-cock, P, which must only remain open while the cylinder F is in use. The liquids in the cylinders must have free access to the bell jars. The tubes m and n must almost touch the stop- cocks, and the rubber connections must be made t]Q;ht by binding them with two or three turns of copper wire and twisting the ends together. The aspirator D is filled (all the stop -cocks being opened) with water, acidulated with 5 or 6 c. c. of hydrochloric acid until, it resting on its support, the liquid stands in the graduated tube at 100. The object of the acid is to overcome the tension of the ammoniacal vapours, and to neutralise the alka- lies when by accident they enter the capillary tubes. How TO USE THE APPARATUS. Before com- mencing the analysis of any gaseous mixture, the apparatus must be freed from air or other gaseous matter it may contain. This is accomplished by successively filling the graduated tube with gas and afterwards expelling it through the stop-cock I. This process is conducted in the following manner: The cock C is shut and I opened, the aspirator D is then raised till the liquid is just on the point of Gas Apparatus. 119 entering the capillary tube ; I is then shut and C opened and D lowered ; the gas to be examined passes into the apparatus and fills the graduated tube. This volume of the gas is then expelled as before by closing C and opening I and raising D. When this has been done two or th apparatus may be considered to be from all foreign gaseous matter. v ^1 ]? #r If the tube conveying the gas be of extreme length to effectually strument of gas in the manner described would be a lengthy operation, and, therefore, to save time and labour it is better to use the tromp L. To do this a funnel is attached to the extremity of the tube K, and placed under a small stream of water, which need only be a few centimetres in height. The water runs into the tube L, and is discharged at M, and in its passage produces a strong aspiration. By keeping C and I open the gas may be rapidly drawn out of the apparatus. It requires about one and a half litres of water to draw out a litre of gas, the quantity varying a little according to the height of the fall of water. The next thing to be done is to bring the absorbent liquids to the zero marks m and n in the respective vessels ; this must, of course, be done for each vessel separately. All the cocks but G having been closed, the aspirator D must be slowly lowered ; the potash solution in E will rise, and when it I2O Mode of using Or sat\ reaches zero, m, the connection tube must be nipped firmly between the finger and thumb so as to completely close it ; as D is replaced on the stand, G is at the same time closed. The stop- cocks H and F are next opened, all the others remaining closed, and the absorbent liquid in F is brought to the zero mark n as in E, and when D is replaced on the stand H and F are shut. Some practice and caution are required in order to guard against passing the zero point, and thus forcing the absorbents into the capillary tube. The sample of gas to be analysed is now taken ; for this purpose the cock I is opened, all the others being shut, D is then slowly raised until the water in the graduated tube stands at the zero point ; I is then closed, D replaced on the stand and C gradually opened ; the liquid in the graduated tube comes to equilibrium at 100, the tube having become filled with the gas ; C is then closed. Should the pressure exceed or be lower than that of the atmosphere, it is advisable in the first instance to take a little more than 100 c. c., and after a few minutes to partially open I, so as to establish an equilibrium and bring the volume to 100 c. c., when this is done I is shut ; and G is opened and D raised till the liquid stands very nearly at the zero point in the measuring tube ; the gas has now been forced into the bell jar containing the potash solution ; by alternately raising and Gas Apparatus. 1 2 1 lowering D, a perfect exposure of all the gaseous particles to, and renewal of, the absorbing fluid is effected. The raising and lowering should be re- peated at least three times, and oftener when the solutions have been for some time in use. The last time the gas is to be passed into E, the liquid in the graduated tube must be brought exactly to the zero point ; D is lowered, and the stop-cock G quickly closed, so that the liquid in the bell jar stands exactly at the zero point m. If D be now placed alongside of the tube A B in such a way that the liquid in it and the measuring tube are brought to precisely the same level, the gas is under its original, atmospheric, pressure, and we ascertain the diminution it has undergone. This diminution represents the volume of those gases present in the original gaseous mixture which have been absorbed by the potash ; in furnace gases this wiU. be due to carbonic anhydride (CO 2 ). If sulphurous anhydride (S0 2 ), sulphuretted hydro- gen, and chlorine be present, they will also be absorbed. Sulphurous anhydride can be deter- mined in the presence of carbonic anhydride by employing a solution of potassic bichromate in sulphuric acid, or a solution of potassic perman- ganate, as an absorbent prior to passing the gaseous matter into the potash solution. After the estimation of the C0 2 , the gas is passed into the vessel F, all the free oxygen and 122 Method of carbonic oxide are absorbed by its solution ; the operation is carried on, and the amount absorbed ascertained, exactly as described with regard to E. The quantity of gas unabsorbed will be the amount of nitrogen present in the gas. Generally speaking the two gases, oxygen and carbonic oxide, do not exist in furnace gases in the presence of each other ; but if they do occur to- gether, their relative proportions can be deter- mined by a simple calculation. If it should be thought necessary to directly determine the amounts of each of these two gases, it may be accomplished by employing a third cylinder containing either pyrogallate of potash or sticks of phosphorus for the absorption of the oxygen, prior to absorbing the carbonic oxide by the ammonia copper solution. As before stated, the respective amounts of each, when they are both absorbed in the same solution, can be readily calculated if the air has been the only source of the oxygen. The clue for this calculation is furnished by the relation existing between the amount of nitrogen and that of the other products. In the formation of carbonic anhydride the volume produced is equal to the oxygen used ; consequently if the gas analysed contains only nitrogen, oxygen, and carbonic anhy- dride, the mixture will have the same volume as the original air. The volume, therefore, of the nitrogen \ Calculation. 123 present in the 100 c. c. of gas used will be 79 c. c., whilst the sum of the oxygen and carbonic anhy- dride will be 21 c. c. Now, in the formation of carbonic oxide the volume of this gas formed is double that of the oxygen required for its produc- tion ; consequently for every 79 c. c. of nitrogen present in the air used, there will be a volume of oxygen and carbonic oxide greater than 2 1 c. c. ; the more carbonic oxide formed the greater the increase in volume ; therefore for every 100 c. c. of air used we shall have more than 100 c. c. of combustion products, if carbonic oxide be one of the products. Knowing the volume of nitrogen present the question may be solved as follows : Let n= volume of nitrogen found. x=sum of volumes of oxygen and carbonic anhydride. y= volume of carbonic oxide. Hence y _ ( oxygen which went to form carbonic 2 ( oxide. y _ ( total volume of atmospheric oxygen ^\, \" < 2 ( used during air combustion. The volume of mixed gases operated on is 100 c. c. (i) /. x + y + n = 100. Since 100 parts of air contain 21 of oxygen and 79 of nitrogen, we have 21 _ ( oxygen associated with n parts of 79 i nitrogen for the combustion. 124 Method of Hence: n = x + From (i) we have x = 100 y n 21 y /. n = 100 y n + *- 79 2 Hence: (2) 100 n=79oo ^ Substituting in this formula the value found for 11, we readily arrive at the volume of carbonic oxide present, and deducting this amount from the total volume absorbed by the ammoniacal copper solution, we also have the oxygen present. EXAMPLE. 100 c. c. of gas lost in volume 5 c. c. in the first cylinder, and after passing from the second cylinder, the gas measured 70 c. c. ; find the amount of carbonic oxide and oxygen respec- tively present : From the formula (2) we have 70 y IOO X 70 = 79OO i-2-x 2 v = 9 x 2 = 2278 c. c. of CO. 79 The absorption in second cylinder was 95 70 = 25, and the oxygen present is 25 2278 = 2-22. Percentage composition of the mixture : Carbonic anhydride (observed) . 5 'oo Nitrogen ... 70 'oo Carbonic oxide . (calculated) . 2278 Oxygen ... 2*22 lOO'OO Calculation. 1 2 5 As the apparatus is intended for industrial in- vestigations, it is of course desirable to have as few calculations as possible. To accomplish this desirable object Fichtet prepared the following Tables, so that when both carbonic oxide and free oxygen are present the amounts may be sought in the Tables. Table I. gives the increase of volume of 100 c. c. of air when i c. c. to 42 c. c. have been transformed into carbonic oxide (CO). Table II. gives the amount of oxygen and carbonic anhydride together, the volume of CO, and the quantity of air required for its formation ; this latter Table is the one most required. TABLE I. Increase in 100 c. c. of Air when any of the Oxygen is transferred into CO. N. 0. CO. Final volume. 79 21'00 100*00 79 20-50 ... i IOO-50 79 20'00 2 loroo 79 ... 19-50 ... 3 101-50 79 19-00 ... 4 I02'00 79 ... 18-50 ... 5 I02-50 79 18-00 ... 6 I03-OO 79 ... 17-50 ... 7 ... I03-50 79 17-00 8 I04-00 79 16-50 9 104-50 79 16-00 ... 10 I05-00 126 Tables employed for N. 0. CO. Final volume. 79 ... 15-50 ... 1 1 ... I05-50 79 ... 15-00 12 106*00 79 ... 14-50 ... 13 106-50 79 ... 14*00 14 107-00 79 ... 13-50 ... 15 ... 107-50 79 ... 13-00 ... 16 108*00 79 ... 12-50 17 ... 108-50 79 ... I2'00 18 109-00 79 ... II'5O 19 109-50 79 ... II'OO 20 IIO'OO 79 ... IO-50 21 110*50 79 ... lO'OO 22 111*00 79 ... 9-50 ... 23 111*50 79 ... 9'00 24 112*00 79 ... 8-50 ... 25 112*50 79 ... 8-00 ... 26 ... II3-00 79 ... 7-50 ... 27 ... II3'50 79 ... 7-00 28 II4-OO 79 ... 6-50 29 ... II4-50 79 6-00 30 115*00 79 ... 5-50 ... 31 ... II5-50 79 ... 5-00 32 I I 6*OO 79 ... 4-50 ... 33 116-50 79 ... 4-00 34 II7-00 79 ... 3-50 "... 35 ... II7-50 79 ... 3-00 ... 36 I I 8*OO 79 ... 2-50 37 118-50 79 ... 2.OO ... 38 II9-OO Calculating the Results. 127 N. 0. CO. Final volume. 79 ... 1-50 ... 39 ... IIQ-SO 79 ... I '00 ... 40 I20'00 79 ... 0-50 ... 41 ... I20-50 79 ... O"OO ... 42 121-00 TABLE II. Number of c. c. of CO produced by the Combustion of Carbon in Air, and the corresponding quantities of Nitrogen, in 100 c. c. of Gas to be Analysed. N. O and C0 2 together. CO. Quantity of air necessary to produce the CO. 79-00 21 O'OO ... lOO'OO 78-605 ... 20-395 ... I -00 ... 99-50 78-2I ... 19-79 2*00 99*00 78-00 ... I9-47 2-53 ... 9874 77-8I5 ... I9-I85 ... 3'oo ... 98-50 77-42 ... 18-58 4-00 ... 98-00 77-025 ... I7-957 ... 5*oo ... 97-50 77'OQ ... I7-94 5-06 ... 97*47 76-63 ... I7-37 6-00 ... 97-00 76-I35 ... 16-865 . 7-00 ... 96-50 76-OO 16-40 7-60 ... 9^25 75^4 ... 16-16 8-00 ... 96'00 75-405 ... I5-595 ... 9-00 ... 95-50 75-05 ... 14-95 lO'OO ... 95-00 75-00 ... 14-87 10-13 ... 94-94 74^55 ... I4-345 ... I I 'GO ... 94-50 74-26 ... 13-74 12-00 ... 94*00 1 2 8 Tables employed for N. 74-00 and C0 2 together. ... I3-34 CO. 12-66 Quantity of air necessary to produce the CO. ... 93-67 73-865 ... I3-I35 ... 13-00 ... 93-50 73'47 ... 12-53 14-00 ... 93-00 73-075 ... II-925 ... 15-00 ... 92-50 73-00 ... II'Sl 15-19 ... 92-41 72-68 ... II-32 1 6-00 92-OO 72-286 ... IO-7I4 ... 17-00 ... 9I-50 72-00 ... 10-28 17-72 ... 91-14 71-89 io- 1 1 18-00 91-00 7^495 9-505 ... 19-00 ... 90-50 71-10 8-90 20-00 9O'OO 7I-OO ... 8-75 ... 20-25 ... 89-88 70-705 8-295 ... 2I'OO ... 89-50 70-31 7-69 22-00 89*00 70-00 7'2i 2279 ... 88-61 69-925 ... 7-085 ... 23-00 ... 88-50 69-52 6-48 24-00 ... 88-00 69-125 ... 5-875 ... 25-00 ... 87-50 69-00 5-68 25-32 ... 87-34 68-73 5-27 26-00 ... 87-00 68-235 4-765 ... 27-00 ... 86-50 68-00 4-15 27-85 ... 86-08 67-94 4-06 28-00 ... 86-00 67-505 3-495 ... 29-00 ... 85-50 67-15 ... 2-85 ... 30-00 ... 85-00 67-00 2-62 30-58 ... 84-81 66-755 2-245 ... 31-00 ... 84-50 Calculating the Results. 129 N. 66-36 and C0 2 together. 1*64 CO. 32-00 Quantity of air necessary to produce the CO. 84-00 66'QO I '09 32-91 ... 83-55 65-965 ... 1-035 .-. 33-00 ... 83'50 65-67 ... 0'33 34-00 83-00 65-29 O'OO 3471 ... 82-65 To illustrate the use of Table II. we will suppose that i oo c. c. of a gas is to be analysed. It is passed through E, a diminution of 5 '5 c. c. in the volume takes place, due to the absorption of the CO 2 . The remainder of the gas(ioo 5 '5 =94*5) is then passed through F ; after this has taken place 69 c. c. of gas remains unabsorbed, which gas is nitrogen ; therefore 25*5 c. c. of gas has been absorbed in F, which represents the carbonic oxide and oxygen together. On referring to Table II. we find that 69 of nitrogen corresponds to 25*32 of carbonic oxide ; therefore the oxygen the gas contained was 0*18 c. c. as 25 '5 25-32=0*18. The volume of air required for the formation of 2 5 '3 2 c. c. of CO is, as we learn from the Table, 87*34 c. c. The following was, therefore, the composition of the 100 c. c. of the gas : N . . . 69*00' observed. CO . . . 25*32 taken from the Table. CO 2 ... 5*50 observed. . . . . 0*18 difference. 100*00 K 130 Orsat's Apparatus. The errors that may occur in the results obtained by this apparatus are of no importance in industrial investigations ; the one of most importance arises from the unequal solubility in water of the different gases operated upon. This may be avoided in scientific investigations by substituting mercury for the acidulated water. It is only necessary to vary the absorbent liquids to make the apparatus applicable for the estimation of most gases. 131 APPENDIX. A, WHAT is COAL ? " The owners of an estate at Torbanehill, in the county of Linlithgow, had granted a lease of the whole coal, ironstone, lime- stone, and fire-clay contained within it, except copper and any other minerals whatsoever than those above specified ; and it should be remarked that the true coal measures of geologists were proved to exist under the same estate. In the course of working, the lessees extracted a combustible mineral of great value as a source of coal gas, and realised a large profit by the sale of it as gas coal. The lessors, thereupon, denied that the mineral in ques- tion was coal, and disputed the right of the lessees to work it. At the trial there was a great array of scientific men on each side, including chemists, botanists, geologists, and microscopists ; and of practical gas engineers, coal viewers, and others, there were not a few. On the one side it was maintained that the mineral was coal, and on the other it was a bituminous schist. The evidence, as might be supposed, was most conflicting. The 132 What is Coal? judge, accordingly, ignored the scientific evidence altogether, and summed up as follows : ' The question for you (the jury) to consider is not one of motives, but what is this mineral ? Was it coal in the language of those persons who deal and treat with that matter and in the ordinary lan- guage of Scotland ? because to find a scientific defi- nition of coal after what has been brought to light within the last five days is out of the question. But was it coal in the common use of that word, as it must be understood to be used in language that does not profess to be the purest science, but in the ordinary acceptation of business transactions reduced to writing ? Was it coal in that sense ? That is the question for you to solve, for you to determine.' The jury found that it was coal. Subsequently to this trial the same mineral was pro- nounced not to be coal by the authorities of Prussia, who accordingly directed it not to be entered by the custom-house officers as coal." (Percy.} B. Mr. Goldsworthy Gurney in the beginning of the year 1851 employed carbonic anhydride as an ex- tinguisher of combustion on a gigantic scale. The object of the experiment was to extinguish a fire in a colliery, about seven miles from Stirling, which A Fire extinguished in a Mine. 133 had raged for about thirty years over an area of twenty-six acres. A sum of 1 6,oool. was expended in surrounding the fire with a puddle-wall, to pre- vent its extending to other workings. The wall took five years to build, the workmen being fre- quently driven back, and obliged to recommence at a greater distance from the fire. After its com- pletion it required constant attention, for if the fire had once passed it would have been very diffi- cult to have again surrounded it. It cost the Earl of Mansfield, the owner of the property, in consequence, about 2Ool. a-year in keeping it repaired. The fire being thus, as it were, corked and bottled up, ought to have become extinguished for want of air to support the combustion. But as no part of the fire mine was deeper than twenty fathoms, and as some of it ran at no great distance below the surface, it obtained a sufficient supply of air from without, as well as through the leakages in the puddle-wall, to maintain a smouldering, volcano -like existence. Mr. Gurney had not only to extinguish the fire, but he had also to accomplish what was quite as difficult, the cooling down of the mine, so that when the air was admitted the coal should not re- ignite. He obtained the carbonic anhydride by passing air through an immense coke fire in a brick furnace ; this gas, along with the nitrogen of the air, was forced through the furnace along an iron 134 Destructive Distillation cylinder down the shaft, and through a steam jet into the mine ; water in the form of the finest spray was also driven along with the gas. After having blown in about 8,000,000 cubic feet of the gas at the rate of about 7000 cubic feet per minute, it was found by exit of the gas through the leakages and shafts that the mine was fully charged with it. At the end of three weeks the fire was extin- guished, the mine during that time having been kept fully charged with the gas. Fresh air was then admitted by the jet. After a time the action was reversed, the air charged with moisture being thus drawn out. The air that was drawn out gradually decreased at the rate of about 6 a day. After about one month's operations, the down- cast shaft was uncovered, and the temperature of the mine was found to be about 98 F. C. The following Table gives the names of the con- stituents and their composition which have been discovered in the gaseous, liquid, and solid pro- ducts formed in the destructive distillation of coal ; they may be classed in reference to their illumi- nating properties under the following heads : of Coal. o UH & -3 CQ - ' 5 S ! s c? W O ^J 5 o J ? o 2 Jtt ac O 3 5 Q r S r S T. C? r? 6 * ig =3 136 Distillation of Coal. 1. The combustible non-illuminating consti- tuents. 2. The illuminating hydrocarbons. 3. The non-essential constituents as regards illumination. 4. The impurities. The members of the first-class are hydrogen and carbonic oxide ; they amount to from 30 to 60 per cent, of coal gas. The specific gravity of the hydrocarbons varies from O'553 (air=ro) to 6*635. THE END. PRINTED BY BAI.LANTYNE AND HANSON LONDON AND EDINBURGH THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL PINE 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. SEP 21 1942 LD 21- UNIVERSITY OF CALIFORNIA LIBRARY