Mr. Chairman:-
By the valuation of coal is meant the estimation by experiment of its value as a calorific agent, and it will be admitted that the discovery of some method which will readily give accurate and reliable results, and which will enable us to avoid the costly and prolonged test of actual use—a test which may involve great waste and prove very vexatious—is a great desideratum.
In valuing a coal the estimation of the calorific power is of the first importance, yet there are other characteristics of the fuel to be considered, which will render it more or less suitable for the use to which it is to be put, and which should not be overlooked in an examination of and in deciding upon its fitness. These are the nature of its ash, the readiness with which it burns, the presence of sulphur, and, when the coal is for naval use, the loss by attrition; and in this paper it will be the aim, after briefly stating the properties and composition of coal, and describing some of the means proposed for estimating its calorific power, to allude to the methods employed in the estimation of these secondary properties.
Since the heat developed by a fuel depends upon the union of the carbon, hydrogen, and other combustible constituents which it contains, with the oxygen of the air, and since also the heat produced by the combustion of measured quantities of each of these substances in oxygen has been determined with great accuracy, it would appear a simple thing to determine the calorific power of a coal by subjecting it to an elementary analysis and calculating from the weights of the elementary substances obtained the heat produced by its combustion; and this method has been followed to a considerable extent in the past, but it has been found in practice to give very erroneous results,-some of the sources of which we will consider.
We have in coal a substance whose composition is very variable and very complex; but, as we have no proximate analysis of coal, it is not possible to make this directly apparent, and therefore we must prove the truth of the statement in another way. The following table gives the results of the ultimate analysis of several varieties of coal, and exhibits the variability in its ultimate composition.
| Lesmahagow, Parrot Coal, Miller | Wigan Channel, Vane | Coking Coal, Newcastle, Richardson | 10 Yard, Wolverhampton, Vane | Newport Steam, Miller | S. Wales Anthracite, Vane |
Sp. Gr. | 1.251 | 1.276 | 1.280 | 1.278 | 1.309 | 1.392 |
Coke, per cent. | 43.3 | 60.36 | -- | 59.21 | 75.10 | 92.10 |
Carbon | 73.44 | 80.07 | 86.75 | 78.57 | 81.47 | 90.39 |
Hydrogen | 7.62 | 5.52 | 5.24 | 5.29 | 4.97 | 3.28 |
Nitrogen | 11.761 | 2.12 | 6.61 | 1.84 | 1.63 | .83 |
Oxygen | 8.08 | 12.88 | 5.23 | 2.98 | ||
Sulphur | 1.145 | 1.50 | -- | .39 | 1.10 | .91 |
Ash | 6.034 | 2.70 | 1.40 | 1.03 | 5.51 | 1.61 |
An ultimate analysis, however, gives us little real knowledge of the character of a coal, for, as a few experiments will show us, the substances we have determined do not exist wholly in an elementary condition in it. Let us first examine the coal by subjecting a weighed quantity in a confined space to the action of a rarefied atmosphere and heat. We shall find that a considerable amount of gas is evolved from the coal, that this gas is a mixture of compound gases, and that in our ultimate analysis we have estimated their constituents as simple substances. The following table gives the results of some of Mr. Thomas' analyses made in the way described: -
| C.C. of gas from 100 grms., evolved at 100o | Percentage Composition of Gas | |||||
CO2 | CO | CH4 | C2H6 | O | N | ||
Lignite, Bovey | 114.3 | 96.74 | 2.80 | -- | -- | -- | 0.46 |
Cannel, Wigan | 250.6 | 9.05 | -- | 77.19 | 7.80 | -- | 5.96 |
Jet, Whitby | 30.2 | 10.93 | -- | C4H10{ | 86.90 | -- | 2.17 |
Bituminous coal, S. Wales | 55.9 | 36.42 | -- | -- | -- | 0.80 | 62.78 |
Semi-bituminous, S. Wales | 73.6 | 12.34 | -- | 72.51 | -- | 0.64 | 14.51 |
Steam coal, S. Wales | 218.4 | 5.46 | -- | 84.22 | -- | 0.44 | 9.88 |
Anthracite, S. Wales | 555. | 2.62 | -- | 93.13 | -- | -- | 4.25 |
If, in addition to this, we heat the coal in closed vessels, out of contact with the air, if the coal be other than anthracite we shall find that in addition to the gases evolved, as given above, the coal will yield a large number of substances, solid, liquid, or gaseous, which exist already formed in the coal, or which are produced by the action of heat on substances existing in the coal, and there will be left behind a mass of coke. We may thus prove the complex composition of the coal, but our methods of analysis do not yet admit of our estimating these constituents.
However, our ultimate analyses have shown that carbon is the most important element present, and it is probable that it exists to a large extent in the coal in a free state. Let us consider what would result if we were to estimate the calorific power of the carbon present from a simple determination of the percentage of free carbon. Carbon is one of the elementary substances which exists in several allotropic or unlike states. In all of these its chemical properties are precisely the same, though its physical properties are widely different. These differences are believed to be due to the difference in the arrangement of the atoms in the molecules. Among other differences Favre and Silbermann have found that their heats of combustion differ considerably, increasing inversely as the density, as the following table, embodying their results, shows.
Substance | Product | Units of Heat | Density |
Wood charcoal | CO2 | 8080 | 1.500 |
Gas-retort carbon | CO2 | 8047 | 1.885 |
Native graphite | CO2 | 7797 | 2.300 |
Artificial graphite | CO2 | 7762 |
|
Diamond | CO2 | 7770 | 3.530 |
"These figures point to the conclusion that the heat of combustion of an elementary substance depends not only on its chemical constitution but also upon its physical state before combustion. It varies not only with the nature of the atoms but also with the manner in which they are grouped together. We cannot deduce the calorific power of graphite from that of charcoal, nor that of the diamond from either. If, then, the mere fact that a substance is composed of pure carbon is not sufficient to determine its heat of combustion, it is not reasonable to suppose that the like information can be acquired in the case of so complex a substance as coal, by a calculation based only on a knowledge of the quantities of carbon, hydrogen and oxygen which it contains." These substances exist in the coal in a state of combination, the compounds of the various elements being mixed together. Hence, when they are burned these compounds must be broken up before they can unite with the oxygen of the air, and, as a general rule, heat is absorbed by the analytical process, and consequently the true heat of the combustion of the coal will be less than the calculated result. Should the compounds, however, be of such a nature that their decomposition is attended with an evolution of heat, the true heat will be greater than the calculated.
Another source of error is due to the fact that the calorific power of hydrogen was determined when that substance was in the gaseous state. Now hydrogen would certainly exist in the coal in a solid or liquid state, and, during the process of combustion, would be converted into 1,t gas. We know that if a solid or liquid is converted into a gas, heat is absorbed. "Therefore, even if the assumption that the 'available' hydrogen is not combined with any of the other elements present in the coal were correct, the calculations themselves would be open to objection, since the hydrogen in its conversion to the gaseous state would absorb heat. Hence, in assuming that the calorific power of solid hydrogen is, like that of gaseous hydrogen, 34,462 units, we commit an error, the existence of which we are certain of, while we are totally ignorant of its magnitude."
Experimental proofs are not wanting to confirm the doubts which theory suggests as to the accuracy of this method of calculation. Two physicists, Scheurer-Kestner and C. Meunier, have made a long series of experiments on the heat of combustion of coal. They analyzed numerous specimens, calculated their calorific power by the ordinary rules, and then made direct experiments to determine their heat of combustion. A comparison of the numbers obtained by calculation and observation proved that they did not agree. Thus in the case of two coals, one from Ronchamp and the other from Creusot, which contained almost precisely the same proportions of carbon, hydrogen, and oxygen, the calorific powers, instead of being identical, were 9,117 and 9,622 respectively. The difference between the real and calculated calorific powers amounted in some instances to as much as fifteen per cent. In the case of two specimens of coal from England, and several from France, the calculated heat of combustion was too small. In that of six kinds of brown coal from France and Germany it was too large, while experiments on several different coals from Russia proved that in these cases the discrepancies between calculation and experiment were comparatively unimportant. It is evident then, that in order to determine the calorific power of a coal with precision we must resort to direct experiments, and that we cannot trust to the calculations based on the elementary composition of the coal. To determine this factor with accuracy we must use the delicate calorimeters employed by the physicist, and at the same time estimate the amount of incombustible matter present. But such precise results are not necessary for the examination of coal for use in the generation of steam; coarser methods will yield results which are sufficiently accurate for this purpose, some of which we will consider.
Thomson has devised a calorimeter which has sometimes been used for determining the calorific power of coal. It consists of a thin, copper cylinder placed inside another, of similar material, which is perforated with holes at the bottom and furnished with a stopcock at the top. The coal to be examined is finely powdered and mixed with ten to twelve times its weight of a mixture of three parts of potassic chlorate and one of potassic nitrate, and this mixture, which will burn out of contact with the air, is then placed in the inner cylinder and the whole submerged under a known weight of water. As the mixture burns, the hot gases bubble up through the holes and warm the waters, until the combustion is completed, when the stopcock is opened and the water flows in to fill the vessel. The heat of combustion is deduced from the elevation of temperature of the vessel and water. The quantities of coal and water employed are so adjusted as to make the calculation extremely simple. It has been shown, however, by Dr. Percy, that there is an error in this method, due to the fact that the bubbles of gas which escape are not completely cooled when passing through the water, and that the loss of heat on this account is not unimportant. I have not as yet given much thought to this form of calorimeter; but it would seem an easy thing to overcome, by some simple mechanical device, the fault which Dr. Percy has pointed out, and thus secure a useful, though not a precise instrument.
A more practical method among those of a less refined and delicate nature is that of Berthier. This depends upon the fact that carbon, when heated in the presence of litharge, reduces the litharge in accordance with the following reaction,
2PbO+C = CO2+2Pb
and, calculating from the known atomic weights of carbon and lead, we find that for every gram of carbon present, thirty-four and five-tenths (34.5) grams of lead will be obtained. Berthier proposed to perform the experiment by heating the coal, in a finely-divided state, in a crucible, with about forty times its weight of litharge, and continuing the process at a red beat, for some time. The crucible was then allowed to cool; it was then broken, the button of lead extracted, washed, dried, and weighed, and on the above equation the weight of carbon calculated. Suppose we find that a given sample yields 25 grams of lead; then the heating power is 25/34.5 of that of pure carbon, or assuming that 1 kilogram of carbon raises 7,900 kilograms of water 1°C., 1 kilogram of the sample of coal is capable of raising 5,724 kilograms of water 100. To estimate the evaporative power by this method. we have simply to divide the number of units of heat obtained by 537, the units of heat necessary to vaporize 1 kilogram of water at 100°C.
Many objections to this process have been raised, but it seems to me as unobjectionable as any that have been devised. Among other objections it is urged that hydrogen may be present in the coal to a greater extent than the oxygen necessary to combine with it to form water, and that this free hydrogen, if we may so term it, will reduce a part of the lead, and that by assigning the whole to the carbon very serious errors may be introduced. On the other band, it may be said that according to the reaction, -
PbO+2H = H2O+Pb
one part of hydrogen will reduce 103.5 parts of lead, while one part of carbon reduces 34.5 parts of lead, or 3:1; but at the same time the units of heat produced by the hydrogen are to those produced by an equal weight of carbon as 4.265:1. Now, as the hydrogen is in the solid condition, some heat will be absorbed in converting it into a gaseous form: therefore, in valuing the coal for purchase, when this error exists it will be in the right direction. In using the method, however, I have found a source of error which has led me to modify the details of it. When a crucible is used it is placed in a furnace where it is difficult to manage, and there is great danger of the reducing gases of the furnace reaching the litharge. Hence, instead of the crucible I employ an iron tube, or gas pipe. Into a piece of gas pipe (ungalvanized) one inch in diameter and one foot long, a plug, tightly fitting, is screwed at one end, and a second piece of pipe, one half inch in diameter and three feet long, is screwed at the other. One gram of the coal to be examined, finely powdered, is now mixed with about forty times its weight of litharge, and poured into the tube and covered with a small quantity of litharge. The tube is then placed in the furnace under a boiler, the open end extending out six inches, and allowed to remain there until Upon placing the finger over the open end no pressure is felt. The process does not occupy over ten minutes. The tube is then removed, the closed end rapped sharply on the hearth to cause all the molten lead to descend, and it is then placed in a vise. In the meantime a small box is lined with plaster of Paris for the reception of the lead. This is placed under the tube and the plug is removed and the lead allowed to run into the box. During this operation the tube is rapped with a hammer to facilitate the escape of the molten lead. After the tube is cooled it is frequently found that some of the metallic lead has been caught in the thread, but it is easily got out. Care must, however, be taken not to mistake fused litharge for metallic lead. The lead which is now collected is washed, dried, and weighed, and the calculation made as above. It is found that after a tube has been used two or three times it gives more constant results than at first.
The following determinations, made in this laboratory, prove that this process gives closely agreeing results. for each experiment.
Coal | Wt. Lead | Calorific Power |
Lee Wilkesbarre (anthracite) | 31.60 | 7235 |
Lee Wilkesbarre (anthracite) | 31.65 | 7247 |
Lee Wilkesbarre (anthracite) | 31.09 | 7099 |
Lee Wilkesbarre (anthracite) | 31.13 | 7128 |
Newburgh Orrel (bituminous) | 31.61 | 7238 |
Newburgh Orrel (bituminous) | 31.26 | 7158 |
Lao-ping (Chinese) (bituminous) | 27.10 | 6206 |
Lao-ping (Chinese) (bituminous) | 27.46 | 6288 |
Lao-ping (Chinese) (bituminous) | 27.27 | 6290 |
Lao-ping (Chinese) (bituminous) | 27.10 | 6205 |
Lignite | 23.60 | 5404 |
Lignite | 23.19 | 5311 |
Lignite | 23.97 | 5489 |
Lignite | 23.29 | 5457 |
Lignite | 23.58 | 5400 |
Lignite | 23.55 | 5393 |
Peat | 22.75 | 5209 |
Peat | 22.63 | 5182 |
Peat | 22.42 | 5135 |
All but the last four of these analyses were made by Lt. Charles Belknap, U. S. N., Instructor in Physics and Chemistry. The last four were made by Cadet Eng. A. T. Woods, U.S.N.
In order that the process should give reliable results, it is essential that the litharge should be pure. If, as was the case with Johnson's experiments, the litharge contains minium the results will be too low. As some experimenters have found it difficult to obtain constant results with litharge, Mitchell has proposed the use of the ordinary carbonate of lead, but I am disposed to believe that this would be an unwise change, as the composition of the carbonate exhibits greater variations than that of the litharge. It has been said of Berthier's process that in the Admiralty investigation the results exhibit a variation often amounting to a virtual contradiction of the simultaneous results of direct combustion; but Johnson, on the other hand, gives results, to be cited farther on, in which the evaporative power, as determined by experiment, and the results of the litharge test closely agree. It may, however, be urged with some degree of fairness that too small a sample of the coal is taken for examination for us to be able to draw any useful conclusions as to the properties of the mass of the coal from the results; but this argument is equally valid when used against any laboratory process, such as the ultimate analysis, or the determination of the calorific power by a calorimeter; yet if care has been used in selecting lumps of the coal which represent the average character, and then these lumps are finely powdered and intimately mixed, any part of this will fairly represent the average quality of the mass; or we may follow the course prescribed for the assay of an iron ore. Break up in an iron mortar forty or fifty pounds of the coal into pieces that will pass through a sieve with one-half inch meshes. Thoroughly mix the fine and the coarse. Now break up about ten pounds of this mixture so that it will pass through a sieve with one-fourth inch meshes. Mix well: take one pound of this and pulverize until it will pass through a sieve of sixty meshes to the linear inch. Mix well: take out fifty grams, pulverized in agate mortar and pass through muslin bolting cloth. Of course in the analyses given the whole of this course of procedure was not followed, as we sought only to test the accuracy of the method by concurring results and not to analyze the coal.
L. Gruner has also arrived at the conclusion that the calorific power of a coal cannot be accurately determined by its elementary analysis. He holds that a more correct estimate of the heating power of a coal is obtained by determining the average amount of coke which it yields. The higher the yield of coke the greater is the heating power, but this heating power does not diminish in the same ratio as the yield of coke; thus for a decrease in the yield of coke from 80.4 to 59 per cent., the heating power diminishes only from 9622 to 8215. In using the percentage of coke as an estimate of the value of the coal Gruner conflicts with other investigators who hold that it is an uncertain guide, since wide differences have been found in the evaporative power of different coals which possessed an equal average 'amount of fixed carbon. From the consideration of the amount of coke it will be seen that he is led to a system of classifying coals which is almost identical with Johnson's published in 1844.
He groups the different kinds of coal arbitrarily in five classes, as follows, though there is no distinctly marked division between any two.
Distinguishing Property | Elementary Composition: | Elementary Composition: | Elementary Composition: | Relation of O/H | Residue of Coke on Distillation | Appearance of Coke. |
Dry coal, burning with a long flame | 75 to 80 | 5.5 to 4.5 | 19.5 to 15 | 4:3 | 0.50-0.60 | Powdery, or slightly caked |
Bituminous coal with long flame, or gas coal | 80 to 85 | 5.8 to 5 | 14.2 to 10 | 3:2 | 0.60-0.68 | Fused, but deeply seamed |
True bituminous coal, or smithy coal | 84 to 89 | 5 to 5.5 | 11 to 5.5 | 2:1 | 0.60-0.74 | Fused, but tolerably compact |
Bituminous coal with short flame, or coke coal | 88 to 91 | 5.5 to 4.5 | 6.5 to 5.5 | 1 | 0.74-0.82 | Fused; compact; very slightly seamed |
Anthracite coal | 90 to 93 | 4.5 to 4 | 5.5 to 3 | 1 | 0.82-0.90 | Powdery |
The length of the flame depends on the amount of volatile matter; the combustibility of the coal on the nature of the ash. If the ash contains iron and lime, a slag forms; if it contains alumina and silica, it remains in a powdery form, which is more favorable to the combustion of the coal. The first class, dry coal with long flame, is used for making coke. The Sp. Gr. is about 1.25. The color is usually brownish. A proximate analysis gives—
Coke | Ammoniacal liquor | Tar | Gas |
50-60 | 12-5 | 18-15 | 20-30 |
Volatile matter. 50-40 per cent.; Calorific power, 8200-8300. As soon as the carbon exceeds 80 per cent. and the oxygen is under 15 per cent., this class of coals begins to coke on heating.
(2) Bituminous coal with long flame (gas coal).—The coke obtained from this coal is always caked together. The coal itself is hard, the fracture laminated. The Sp. Gr. is 1.28-1.30. Color, pure black, with strong luster. Proximate composition—
Coke | Ammoniacal liquor | Tar | Gas |
60-68 | 5-3 | 15-12 | 20-17 per cent |
Volatile matter, 40-32 per cent.; Calorific power, 8500-8800.
(3) True Bituminous, or "Smithy Coal." —Color, pure black, with high luster; brittle, with laminated fracture. Fuses when burning, leaving the coke in a compact cake. Sp. Or. 1.3. Proximate analysis—
Coke | Ammoniacal liquor | Tar | Gas |
68-74 | 3-1 | 13-10 | 16-15 per cent |
Volatile matter, 32-26 per cent.; Calorific power, 88,000-9300.
(4) Bituminous coal with short flame, or "Caking coal."—This class exhibits the same properties as the previous one; its luster, however, is not so great. It is very brittle, and although it is termed dure in France, this means that it does not burn away quickly. It does not contain much volatile matter, and is consequently difficult to kindle. Sp. Gr. 1.30-1.35. Proximate composition—
Coke | Ammoniacal liquor | Tar | Gas |
74-82 | 1-1 | 10-5 | 5-12 per cent |
Volatile matter, 26-18 per cent.; Calorific power, 9300-9600. One kilogram of this coal evaporates 9.75 kilograms of water.
(5) Anthracite Coal.—This coal forms the link to pure anthracite. It is black, and shows dull streaks. Its cohesion is slight, but increases the nearer it approaches the character of pure anthracite. Sp. Gr. 1.35-1.40. Proximate composition—
Coke | Ammoniacal liquor | Tar | Gas |
82-90 | 1-0 | 5-2 | 12-8 |
Volatile matter, 18-10 per cent.; Calorific power, 9200-9500. One kilogram, calculated without ash, evaporates 9.15 kilos of water; but as it usually contains 10-11 per cent of ash, its real evaporative poweris 8.12 kilos.
C. Hilt likewise regards the yield of coke, together with the amount of ash, as of especial importance in the valuation of coal. He gives a classification of coals according to the ratio between the quantities of bitumen and coke which they yield when ignited in a covered crucible.
| Bitumen : Coke |
| 1:2 to 1:9 |
| 1:9 to 1:5.5 |
| 1:5.5 to 1:2 |
| 1:2 to 1:1.5 |
| 1:1.5 to 1:1.25 |
| 1:1.25 to 1:1.1 |
If the bitumen or volatile matter be expressed in terms of ash free coke we have –
Bitumen
No. 1 contains 5 to 10 pr. ct.
No. 2 contains 10 to 15.5 pr. ct.
No. 3 contains 15.5 to 33.3 pr. ct.
No. 4 contains 33.3 to 40 pr. ct.
No. 5 contains 40 to 44.4 pr. ct.
No. 6 contains 44.4 to 48 pr. ct.
About the year 1842 Prof. W. R. Johnson began, under the auspices of the Navy Department, a series of experiments to determine which, among our many varieties of coal, was best adapted to and most economical for the purposes of the navy. Similar investigations were also subsequently undertaken by Dr. Lyon Playfair and Sir Henry de la Beche with the British coals. In both these researches the following principles were stated as governing the end sought.
1st. The fuel should burn so that steam may be raised in a short period, if this be desired; in other words it should be able to produce a quick action.
2nd. It should possess high evaporating power—that is, be capable of converting much water into steam with a small consumption of coal.
3d. It should not be bituminous, lest so much smoke be generated as to betray the position of vessels of war when it is desirable that they should be concealed.
4th. It should possess considerable cohesion of its particles so that it may not be broken into small fragments, by the constant attrition which it may experience in the ship.
5th. It should combine a considerable density with such mechanical structure that it may be easily stowed away into small space—a condition which in coals of equal evaporative values often involves a difference of more than twenty per cent.
6th. It should be free from any considerable quantity of sulphur, and it should not progressively decay, both of which circumstances render it liable to spontaneous combustion.
Great importance was attached to the determination of the evaporative power which was accomplished by burning weighed quantities of coal under a boiler of known dimensions and measuring the quantity of water evaporated. Of course, at the same time the area of the grate surface, of the combustion chamber, of the heat absorbing surface and the length and area of the flues were also known. The conditions under which the experiments were conducted were apparently like those which exist in practice, and promised to lead to positive results, yet the results given in Johnson's Report in 1844, and the• British series of reports, concluded in 1851, after showing that no fixed relation exists between the calorific power as calculated from the results of analysis and the evaporative power of the coal, also "prove, by the very differences which they exhibit, that the only trustworthy method of determining the value of a fuel for steam purposes is that of practical experiment under the boiler in which it is to be used, and where several tons and not pounds are consumed." The results of such experiments cannot, however, be considered as applying to furnaces and boilers dissimilar to those actually used. The conditions attending the advantageous combustion of coal resemble those which obtain for the combustion of coal gas for illuminating purposes. To obtain the highest photometric power for a given gas, a certain form of burner, number of apertures, rate of flow, and length of chimney are found essential, and these are determined by experiment. To get the maximum effect with a gas from another source, some or all of these conditions must be varied. For this reason, and others which might be given, notwithstanding the conclusions of the Admiralty's Board, the results of laboratory experiments which are conducted under similar conditions for different coals cannot but be of value in deciding the fitness of a fuel for the purpose to which it is to be applied.
In the English experiments, besides the determination of the evaporativepower, Berthier's litharge test was applied, and the loss by attrition was also estimated. "This factor, which is of extreme importance in - steam navigation, becomes reduced the more the cleavage of the coal or the shape of the fuel approaches the form of a cube. In order to attain at least a relative idea of the waste occasioned by transport, i.e., of the attrition of the individual pieces of coal against each other, and the conversion of unbroken coal into dust, unfit for use, which is occasioned by the motion of the vessel, the various specimens were rotated in a drum for the same length of time, and the dust thus produced separated and weighed." The subjoined table shows some of the results of the British investigation. 1. No. pounds of water at 100°C. converted into steam by one pound of fuel. 2. Ditto after deducting portions of coke contained in ash. 3. Theoretical evaporative power in pounds of water at 1000, as calculated from litharge test. 4. Weight of coal per cubic foot of stowage in pounds. 5. Ditto per solid cubic foot deduced from specific gravity. 6. Percentage loss by equal amount of attrition.
Kind of Fuel | 1 | 2 | 3 | 4 | 5 | 6 |
Welsh - |
|
|
|
|
|
|
Jones & Co. Anthracite | 9.46 | 9.70 | 13.84 | 58.25 | 85.79 | 68.5 |
Ward’s Fiery Vein | 9.40 | 10.60 | 16.40 | 57.43 | 83.85 | 46.5 |
Graigola | 9.35 | 9.66 | 16.72 | 60.17 | 81.11 | 49.3 |
Duffryn | 10.14 | 11.80 | 15.64 | 53.22 | 82.72 | 56.2 |
Pouty Pool | 7.47 | 8.04 | 14.31 | 55.70 | 82.35 | 57.5 |
Ebbro Vale | 10.21 | 10.64 | 16.68 | 53.30 | 78.81 | 45.0 |
Bedwas | 9.79 | 9.99 | 14.70 | 50.50 | 82.60 | 54.0 |
Scotch - |
|
|
|
|
|
|
Dalkeith Jewel | 7.08 | 7.10 | 13.77 | 49.80 | 79.67 | 85.7 |
Wallsend Elgin | 8.46 | 8.67 | 15.15 | 52.60 | 78.61 | 64.0 |
Fardel Splint | 7.56 | 7.69 | 15.12 | 55.00 | 78.61 | 63.0 |
Grangemouth | 7.40 | 7.91 | 14.85 | 54.25 | 80.48 | 69.7 |
English - |
|
|
|
|
|
|
Broomhill | 7.30 | 7.66 | 13.20 | 52.50 | 77.99 | 65.7 |
Park End, Sydney | 8.52 | 8.98 |
| 54.44 | 80.05 | 55.0 |
Irish - |
|
|
|
|
|
|
Slieverdagh | 9.85 | 10.49 | 16.21 | 62.80 | 99.57 | 74.0 |
Mean of three patent fuels | 9.27 | 9.66 | 15.44 | 66.48 | 70.66 |
|
From the examination of this table and a comparison of columns 2 and 3 it will be seen that the litharge test occasionally gives results at variance with those obtained by the evaporative test, but as a rule they are concurrent. When the results disagree it would be interesting to know what results are actually obtained in practice.
The results obtained by Johnson are more concurrent, and are exhibited in the following table, together with the results of M. Baudin by the litharge method:
No. of specimens assayed | Nature of coals | Evaporative power, by experiment | Lead reduced by 1 of combustible |
8 | 7 Penn. anthracite, 1 natural coke of Va. | 10.537 | 32.157 |
11 | Md. and Penn. free-burning coals | 10.877 | 31.736 |
10 | Va. bituminous | 9.523 | 28.194 |
8 | Foreign and western highly bituminous | 8.710 | 27.740 |
3 | French anthracites |
| 33.520 |
3 | Free-burning coals |
| 32.040 |
3 | Bituminous coals |
| 29.830 |
3 | Highly bituminous |
| 27.586 |
Prof. Johnson believed the lead-reducing power of the coal to depend on the carbon constituent, and cites the following instances in support of this view: The ultimate analysis of Cambria county, Penn., coal gave 91.955 per cent, of carbon, and experiment showed its lead-reducing power to be 31.464. Again, ultimate analysis showed Clover Hill, Va., coal to contain 83.393 per cent, of carbon, and this on experiment yielded 28.527 parts of lead. Now the ratio of the percentages of carbon is to that of the lead produced as follows: 91.955/83.393=31.464/x where x=28.534, which may be considered as identical with that obtained by experiment.
Important experiments upon the evaporative power of American coals and of the evaporative efficiency of different boilers and furnaces have been carried on for some years and are still being pursued by a board of Engineers of the Navy, under the direction of Chief Engineer B. F. Isherwood, and it is probable that, as our data accumulate, we may be able to discover some closer relation between the results of experiment and those of use; but the value of these results would be greatly enhanced if the fuels employed were also subjected to analysis, and their calorific powers determined by the various methods suggested, for we might, from the data thus collected, be able to effect the complete solution of the problem stated at the opening of this paper. The presence of sulphur in coal may sometimes be detected by simple inspection; for as it frequently exists in the form of iron pyrites, these, or the rust produced by the weathering of the crystals, may generally be readily observed. Sometimes these crystals may be so finely disseminated through the mass that they cannot be seen, or the sulphur may be present in another form. A rough way for detecting the sulphur may then be used, Which is as follows: The powdered coal is fused in an iron vessel with twice its volume of carbonate of soda. The fused mass, when cold, is then placed on a bright silver or copper surface, and moistened with water. If sulphur is present the metallic surface will be blackened by the formation of a film of sulphide. To make sure that the carbonate contains no sulphur it must first be fused and tested in the same way. I have now in hand some experiments by which I hope to test for sulphur at the same time that I am making the lead test, the results of which will be given later.
The nature of the ash, the readiness with which the coal burns, and the determination of the amount of ash, are factors which are only to be obtained by the combustion of the coal. The process usually followed, of burning the weighed coal in a weighed iron vessel, is correct in principle, but of course as conducted in the laboratory the errors incident to the corrosion of the iron when heated are avoided by the use of noncorrosive material. In every way, too, the process used there is more delicate: yet the process used in the engine-room gives fair results.