Before considering the quality of these coals, I will, for better understanding, make some Different kinds of coal described.prefatory statements in regard to the character of coals generally. Charcoal has greater purity than mineral coals usually have, because there is nothing in the charcoal except what naturally belongs to the woody matter. Mineral coal, however, having been buried in water, mud, and sand, must, almost of necessity, have some mixture of foreign matter, either slate, which is simply hardened mud; silica, which may have been derived from sand; iron and sulphur, some of which may have been in the wood, but most of it, probably, introduced in solutions; to which should be added, unexpelled oxygen, which is not only useless as fuel, but which combines with a portion of the contained hydrogen, and forms water in the substance of the coal.
The proportion of ash in coals of the same class is usually determined by the amount of slate in the coal, in addition to the mineral matter which belonged originally to the vegetable material from which the coal was formed. In the pure state, the proportion of ash increases as the transformation of woody fibre goes on from peat to anthracite.
The chemical changes in coal beds.It is worth while to note what are the changes which take place in the vegetable matter during the process. It may be described in a word as a progressive loss of oxygen, and by this loss the coal becomes richer, for the reason just given. The deoxidizing process is carried on by means of chemical changes in the substance of the coaly matter. The oxygen combining with a certain proportion of the carbon, forms carbon di-oxide, or carbonic acid gas; and a certain other portion, combining with hydrogen, forms water. Both of these are volatile in their character, and gradually escape. Another loss is effected by the combination of hydrogen and carbon, forming marsh gas. We have deadly proof that these combinations are in progress in all coal mines by the occurrence of "choke-damp" and "fire-damp," which are the miners' names for these gases.
Deficient nomenclature.Unfortunately, we have no settled nomenclature for the varieties of coal, excepting the broad names lignite or brown coal, bituminous coal, and anthracite. Even the term "bituminous" is scientifically inaccurate, there being, in fact, no bitumen in any coal. But it is applied to such coals as contain more oxygen and volatile combustible matter and water than anthracite, and less of these elements than lignite. The term lignite is made to include a great variety of substances, covering the lignites of the Juro-Trias of James River (Dutch Gap), which retain not only the structure, but the appearance of decaying wood; the lignites of the State of Mississippi, which are of the same geologic age as those of the Rocky Mountains, but which, owing to their watery and crumbly character, are unfit for market; the lignites of the Grand and Moreau rivers of Dakota, which are reported to have no commercial value; the lignites of Bozeman, Montana, which are really valuable, but soon break down into chips and grits; the lignites of Green River, Wyoming, which are firm, bright, lump coals; and the lignites of King County, Washington Territory, many of which are hard, bright, steam and shipping coals. And when brought to the laboratory, it is found that chemically these lignites vary even more than they do optically.
This want of a varied nomenclature is to be regretted, because it sometimes handicaps a good coal with an inferior name.Lignite an unsuitable name for the coals of Washington Territory. It is only of late that the Laramie or Cretaceous coals of Washington Territory have been divided into lignites, bituminous coals, and anthracites. These grade into each other so insensibly that it would be impossible to classify them sharply. None of the lignites which I saw were as low in grade as the typical lignite. The woody structure was quite discernible in some samples of the Franklin coal, and less in the Newcastle and Green River; but in respect to the two latter, I could not with the naked eye discern more of the woody structure than I have seen in some of the West Virginia coals, which belong to the Carboniferous period. I sat by fires of Newcastle and neighboring coals for a month, and observed no unusual amount of smoke, and no peculiar odor. By analysis, these coals show a larger percentage of oxygen than the typical bituminous coal, but decidedly less than is found in the brown coal of Germany, or in some of the lignites of Montana. They need a new name. Their heating power is not so great as that of the bituminous coals of the same region. Their streak and powder are less black, and their fracture more conchoidal, but not decidedly so.
The bituminous coals have the usual cubical fracture. The Wilkeson readily breaks down into small cubes. The lignites are black and lustrous. They come out as lumpy as ordinary coal, and, when exposed to weather, do not break up into powder and grits like ordinary lignite. This is true, at least, of the Newcastle coal.
The coking quality not general in these coals, but found in some.The coking quality of these coals cannot be determined by calculating the proportion between the fixed carbon and the volatile, combustible matter. I am not sure that Professor Fraser's fuel ratio tables are a safe guide in any case. So far as now known, only a few of the Washington Territory coals can be made into good coke. On this point, however, we have only laboratory and rough field tests, excepting at the Wilkeson mines, where twenty-five ovens were turning out a superior quality of coke, as proved by every test save the use of it in high furnace stacks, in which there had been no opportunity for trial. It is claimed by many persons that seams on Green River, Skagit, Yakima, and Snoqualmie will furnish good coking coal. The coal on Snoqualmie Mountain, near Hop Ranch, has not been studied, but it certainly has the external characteristics of good coking coal, and Mr. Peter Kirke made a rough trial of it in an earth-pit with decidedly encouraging results.
Somewhat similar coal is found on Raging River, but where opened, so much slate was interleaved with the coal that washing would be necessary before use. More will be said hereafter with regard to these coals; but the remark may be repeated here in respect to the entire Puget Sound basin, that much additional examination is necessary before its coals will be fully understood. The variations in character of these are not owing entirely, or even chiefly, to their relative ages, but also to the conditions to which they have been subjected, especially in respect to heat. This metamorphic agency has acted not only in the body of the Cascade Mountains, but all through the coal-fields, where faults, flexures, and intrusive rocks have occasioned changes in the original condition of the coal-beds, giving results along the whole scale of metamorphism from lignite to anthracite.
Analyses of Washington Territory coals.I here introduce (on the opposite page) a table of analyses made in Washington City from representative samples of Washington Territory coals and lignites selected by Mr. Bailey Willis during the examination which he made of this field for the Census Bureau, and found in Vol. XV. of the Census Reports.