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 power is 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. 4.-Coking gas coal, 1: 1.5 to 1 : 1.25 1: 1.25 to 1 : 1.1 5.-Flint coal (young), yielding much gas, 6.-Gas coal, If the bitumen or volatile matter be expressed in terms of ash free coke we have— Bitumen. to 10 pr. ct. Bitumen. pr. ct. No. 4 contains 33.3 to 40 No. 6 contains 44.4 to 48 No. 1 contains 5 No. 2 contains 10 to 15.5 pr. ct. No. 3 contains 15.5 to 33.3 pr. ct. 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 Bêche 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 * Ding. Pol. Jour., CCVIII. 424. ; 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 evaporative power, 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 100°, 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. Slieverdagh, Mean of three patent fuels, 9.46 9.70 13.84 58.25 | 85.79 | 68.5 9.40 10.60 16.40 57.43 | 83.85 | 46.5 9.35 9.66 16.72 60.17 81.11 49.3 10.14 11.80 | 15.64 | 53.22 82.72 56.2 7.47 8.04 14.31 55.70 82.35 | 57.5 10.21 10.64 16.68 53.30 78.81 45.0 9.79 9.99 14.70 50.50 82.60 | 54.0 7.08 7.10 13.77 49.80 79.67 | 85.7 8.46 8.67 15.15 54.6078.61 | 64.0 7.56 7.69 15.12 55.00 | 78.61 63.0 7.40 7.91 14.85 | 54.25 80.48 69.7 7.30 7.66 13.20 52.50 77.99 65.7 9.85 10.49 16.21 62.80 99.57 74.0 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. 8 11 10 8 7 Penn. anthracite, 1 natural coke of Va., 10.537 32.157 Md. and Penn. free-burning coals, Va. bituminous, Foreign and western highly bituminous, 10.877 31.736 9.523 28.194 8.710 27.740 33.520 32.040 29.830 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 car91.955 31.464 bon is to that of the lead produced as follows: 83.393 XC x=28.534, which may be considered as identical with that obtained by experiment. where 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. NOTE―The calorific power given by Scheurer, Kestner and Meunier were determined by experiment with Favre & Silbermanns calorimeter. The data given by Gruner are also the results of experiments. |