Thus, in coals containing similar quantities of carbon, those of the north of England and in Scotland, for instance, the analytical results, acquired by Dr. Thomson, prove that the relative quantities of hydrogen, carbon and azote, materially differ. Again, external properties and characters must likewise be consulted. The structure and texture of the coal, the density, the mode in which it burns in the fire, swells or decrepitates, and other phenomena must be attended to. We have seen, for example, that some of the English coals possess so strong a tendency to melt, cement, and coke, as to form a hollow fire, and cannot be used in iron works without previous coking; while other coals, even such as possess ten to twenty per cent. more of bitumen, swell but little; and although their fragments cohere in the fire, they do not change their form and bulk, even in the process of coking. There is yet another mode which has been employed to compare, with still greater delicacy, the respective qualities and composition of these combustibles. This is by means of the relative proportions of carbon and gaseous matters, ascertained more completely than is exhibited in the usual form of analysis. For a knowledge of these results, and some others that we propose to introduce, we are indebted, in great measure, to the work of M. Pelouze on gas.* 66 "All the compact coals, even the fattest, the most coking, the most inflammable-in a word, those which the English designate by the name of close-burning coal," and which yield to distillation a coke, always more or less abundant, dense, and of better quality than those of the light coals— ought to be avoided for the manufacture of gas. But among the eligible coals, how many distinctions still remain to be made. We are often astonished to find that the lightest coal-that which leaves the least residuum after its combustion-above all, that which possesses characters entirely bituminous; which kindles rapidly, and gives out a fine and elongated flame, yields much less gas to distillation than some other variety of the light coals which possess the same apparent characteristics, or which were even far from promising as much. We are acquainted with a great number of analyses of coal, made at various periods; but all at a time when the science of the analysis of organic bodies had made little advances. Besides, the only object of those analyses was that of stating the respective proportions of coke, or de-bituminized coal, and the incombustible residuum which the coke yielded by a complete incineration. Little attention was given to determining the component parts of the bituminous portion. Mr. Richardson has devoted himself to researches in the laboratory of Professor Liebig, at Giesen. He has examined the English coals. We give the results of his analyses, the more willingly that his examinations have been directed to the produce in coke, and to the elements of the bituminous portion. British Bituminous Coals. With the certain means that chemists possess, now-a-days, for analysing organic substances, such a work, published by a person so competent in these matters, ought to inspire confidence. Now we see that in the bituminous portion of the coals assayed by Mr. Richardson, the proportion of oxygen varies from 14.54 for 6.33 of hydrogen, to 5.50 for 5.31 of hydrogen. There is, therefore, reason to think, that in the distillation of the first variety, * Traité de l'éclairage au Gaz, avec 24 planches, par Pelouze Pere, Paris, 1839. in consequence of the formation of water, there would remain very little hydrogen for the production of gas for illumination; while the second variety would have yielded a much more abundant result of carbonated hydrogen gas. At the same time that Mr. Richardson was operating at Giesen, M. Reynault, an aspiring mining engineer, was devoting himself at Paris to similar researches, with much assiduity. We give below the principal results which he has obtained. European Bituminous Coals. Analysis per cent., the earthy residuum being previously abstracted. The results show the mean of three different assays for each species of coal. Localities. Carbon. Hydrogen. Oxygen. 2nd 66 66 1. Coal of Alais, basin, No. 23, mine of Rochebelle, France, 5. Coal of Epinac, basin No. 11, 6. Coal of Blanzy, No. 10, 7. Cannel Coal of Lancashire, 8. Coal of Commentry, basin No. 13, 9. Coal of Rive-de-Gier, 66 Belgium, 86.49 No. 20, Grande-Croix, 10. 66 66 66 Rassaud, We remark how much the proportions of oxygen in relation to hydrogen, vary, even in their most extended limits: and if we admit that the abundance of the first is injurious to the production of gas for lighting, all the uncertainty which is generally observed in the result of the manufacture is explained. Many of the coals comprised in the preceding table are defective by an absolute want of hydrogen; but several others, even those rich in hydrogen, by the association of that with a too strong proportion of oxygen, which in the distillation of coal disengages itself with the hydrogen, both being in a nascent state, are found in conditions favorable to combination; that is to say, to the production of water, to the detriment of the quantity of illumina 2. Coaly Anthracite of Rolduc, near Aix-la-Chapelle, Belgium, 92.85 3. Anthracite of Mayenne, 4. 66 of South Wales, France, 93.56 of La Mure, Dep. of Isere, We here perceive that the anthracites are absolutely wanting in hydrogen, independently of the consideration of oxygen. It explains then very well why this species of combustible is the least convenient substance for the manufacture of illuminating gas."* The results, according to the English engineer, Luke Herbert, obtained from a series of experiments made upon each of the three classes of English bituminous coals, and in each case by the distillation of one ton of the coal, are as follows: 11,600 English cubic feet of gas. 1. Cannel coal of Lancaster produced 2. Coal of Newcastle, (Hartley mine,) 3. Coal of Staffordshire, best quality, By experiments on a similar scale to the last, were obtained the following results: do. The gas obtained possessed an illuminating power much inferior to that from the coal of the first class; but there was much coke of good quality. In this class the series terminates with the drier and less adhesive coals, called "open burning coals." Those of this kind are preferred by blacksmiths because they better bear the blast of the bellows. ADAPTATION OF DIFFERENT VARIETIES OF COAL TO THE PURPOSES OF STEAM NAVIGATION. There has been recently published a very elaborate report, of 607 pages, "to the Navy Department of the United States, on American coals applicable to steam navigation and to other purposes, by Prof. Walter R. Johnson." It includes two hundred and one tables, prepared by the author with unusual care and under peculiar advantages, and furnishes the results of a long series of experimental investigations conducted at Washington. Our space precludes our quoting extensively from this voluminous document; but we cannot refrain from selecting the following table of the relative degree of evaporative power of different coals under similar or uniform bulks. We select this table, at the suggestion of the author, in preference to that which exhibits "the order of evaporative power under equal weights." He remarks that coal, "when sold by weight and used on shore, the weight per Pelouze on Gas. cubic foot is a point of little moment. Space for stowage is easily obtained. But in steam navigation, bulk, as well as weight, demand attention; and a difference of twenty per cent., which experiment shows to exist between the highest and the lowest average weight of a cubic foot of different coals, assumes a value of no little magnitude. This is obviously true, since, if other things be equal, the length of a voyage must depend on the amount of evaporative power afforded by the fuel which can be stowed in the bunkers of a steamer, always of limited capacity." ADAPTATION OF COAL TO STEAM POWER. We learn, through various channels, that the Lords of the Admiralty, in England, have taken up the subject of coal, not solely as relates to its economic working and consumption, but with reference to the probable quantities absolutely workable in Great Britain, the most economic methods of combustion, and the chemical properties and combinations of coal. An inquiry was announced as in progress, in the close of 1846, in reference to the value of coals for the use of the British steam navy. It is designed not merely to ascertain, by chemical analysis, the constituents of different sorts of coal, but, by an extensive series of comparative experiments, to determine their practical applicability. With this object in view, it is announced that steam boilers and furnaces have been erected at the Engineering College at Putney, and the examination is intrusted to Sir Henry de la Beche and Dr. Lyon Playfair, and those associated with them. The editor of the Mining Journal remarks,* "our beds of coal have been the undoubted production of ages; and, vast as they are, it appears the height of the ridiculous to assert, that they are inexhaustible. Every succeeding year brings its increasing consumption, not simply of tons, but of millions; and perhaps there is no other question in the range of political economy that deserves so much patient investigation, and no body of men so highly competent to the task as the gentlemen alluded to." General View or Table of the relative density of different species of Coal and Anthracite, at various parts of the World. In a previous page we took occasion, by means of the requisite tables, to exhibit the relative amounts of carbon and volatile matters which exist in the principal bituminous coals of England, Scotland, Wales, Belgium, France, and the United States of America; and hence to show their comparative adaptation to the manufacture of iron. The following table offers another method of making useful comparisons of the bituminous and non-bituminous combustibles in various parts of the world, by means of their respective specific gravities and weights per solid cubic yard, in pounds, avoirdupois. |