Egg Coal will pass through 2¾-inch mesh screen. Stove Coal will pass through 2-inch mesh screen. Chestnut Coal will pass through 1⅜-inch mesh screen. Pea Coal will pass through ¾-inch mesh screen. No. 1 Buckwheat Coal will pass through ½-inch mesh screen. No. 2 Buckwheat Coal will pass through ¼-inch mesh screen. No. 3 Buckwheat Coal will pass through ⅛-inch mesh screen. Hard coal of stove and chestnut sizes are those most commonly used for domestic heating, because they are well suited for furnaces and heating stoves. Of the two sizes chestnut coal is most largely used and on account of the greater demand, the price for this size is usually somewhat in advance of the others; at the same time the smaller sizes--pea and buckwheat coals--are less in price for the same grade of coal. Under conditions that will permit their use the latter coals are an economical form of fuel. =Bituminous or soft coal= represents the chief fuel of commerce. The market prices of these coals are determined largely by reason of their reputation as desirable fuel. The variations in price depend on the physical qualities, rather than on the amount of heat evolved in combustion. The compositions of coals vary markedly in different localities and often in the same locality several grades are produced. It sometimes happens that from different parts of a mine the coal will differ very much in heat value. Bituminous coals are roughly classified as coking and free-burning. The former is valuable for gas manufacture and for production of coke. The coking coals fuse on being heated, allowing the volatile portion to escape; and when the gas has been all distilled, the residue is coke. When used for gas making, the volatile portion forms the illuminating gas. When burned in a furnace, the gases from soft coal burn with a yellow flame and usually with considerable smoke. The classification of bituminous coals differ somewhat in the East from that of the West. Eastern bituminous coals are commonly graded: A. Run-of-mine coal = unscreened coal as taken from the mine. B. Lump coal = that which passes over a bar screen with 1-1/4-inch openings. C. Nut coal = that which passes through a bar screen with 1-1/4-inch openings and over one with 3/4-inch openings. D. Slack = all that which passes through a 3/4-inch bar screen. Western bituminous coal: E. Run-of-mine coal = the unscreened coal as taken from the mine. F. Lump coal--divides as 6-inch, 3-inch and 1-1/4-inch according to the diameter of the mesh through which the pieces pass the screens. G. Nut coal--varying from 1-1/4-inch size to 3/4-inch in diameter. H. Screening = all coal which passes a 1-1/4-inch screen including the dust.