may occur, however, renders important the installation of proper ventilating appliances. In but two or three mines are fans employed to secure a proper circulation of air within the mine. Ordinarily an air shaft with a fire pot suspended at its base is deemed sufficient. The inadequacy of this method in some of the larger mines, where the entries are long and the amount of powder burned is large, is manifest in the heavy air and a smoke lingering long after a discharge.

Blasting in Lignite.-Powder is generally used for shooting in mines, though dynamite proves effective in the open pit. Under favorable conditions, as in the mine at Lehigh, a six-foot hole is drilled, and in this three pounds of FF powder brings down on average three tons of lignite.

the

THE FUEL VALUE OF THE LIGNITES OF NORTH DAKOTA

The fuel value of a given lignite will vary considerably with. conditions under which and the purpose for which it is used. In one connection it may be esteemed highly and in another not at all. Out of this fact grows the diversity of opinion in regard to a number of well known lignites of the state. A lignite whose value as a steam coal is very high may not prove suitable for certain kinds of stoves. An actual case will serve well for illustration. In two localities lignite from seams that are high in ash, due to admixture of clay are thought well of for heating purposes, because the clay enables them to stand up well and prevents slacking. Judged by ordinary standards these lig. nites are very inferior. These recognized standards are: The amount of fixed carbon and the percentage of ash that the lignite contains; the result given by the calorimeter, and amount of water which a given amount of lignite will evaporate. Of the three tests the last is the most satisfactory. The lignites have been tested in accordance with these, as well as in a variety of practical ways, and a brief statement of results is proposed in this chapter.

Chemical Properties of the Lignites.-Coal in all of its forms, as well as peat, is derived from vegetable tissue which is composed of carbon, hydrogen and oxygen. When not exposed to the atmosphere, and hence free from ordinary decay, these three chemical elements tend to rearrange themselves, part of the carbon uniting with part of the oxygen to form carbon dioxide (CO2), another part uniting with part of the hydrogen to form the inflammable gas (CH4), while other parts of the oxygen and hydrogen combine to form water The proportion of the carbon entering into these combinations is lower than that of the other elements, and as these gases escape the percentage of carbon remaining uncombined grows higher. Conditions, there

fore, which favor the formation and escape of these gases, favor the formation of a coal which is high in uncombined or "fixed" carbon.

Conditions which favor the formation and escape of the gases formed by the decay of wood out of ordinary contact with the atmosphere are: Pressure, heat, folding and erosion of the containing strata, which allows the escape of the gases, and time, which is necessary for the chemical transformation, ordinarily slow.

In accordance with these conditions, coal in the older formations and in regions of tilted strata often contains a very high percentage of fixed carbon and is classed as anthracite. Where the formation is young but the region one of tilted strata, and of crushing, bituminous coals are common; whereas coal which, in the geological sense of the term, is recent, and forms part of a horizontal series that has not been subjected to great pressure. folding, is nearly certain to have a comparatively low percentage of fixed carbon. These are practically the conditions under which the lignites are found.

or

Fixed Carbon.-The average amount of fixed carbon in twenty-six samples of North Dakota lignite analyzed in 1909, when thoroughly dried, was 52 per cent. Sixty samples analyzed this year, after thoroughly drying, gave 51.21 per cent of fixed carbon. Compilations given in a former report of this Survey* show, for forty-one samples of West Virginia bituminous coal, 67.16 per cent of fixed carbon; for twenty-two samples of the better grades of semibituminous dry coals of Maryland, 75.99 per cent, and for twenty-six samples of dry bituminous coal from Pennsylvania, 67.97 per cent. Judged by the fixed carbon alone the heating power of one ton of North Dakota lignite is worth 76 per cent of a ton of West Virginia bituminous; 65.9 per cent of Maryland semibituminous, and 74.4 per cent of Pennsylvania. bituminous. These figures show that the North Dakota lignites. rank far above the coals that are the average representatives of this class.

Comparing the lignites of North Dakota with the product of the west interior coal fields, which includes Iowa, Missouri and Kansas, with respect to fixed carbon, the lignite appears to be

*First Biennial Report, E. J. Babcock, pp. 81, 82, 83.