Most of the product is shipped to the large manufacturing cities of the middle west, where it is used for steam as well as fuel; a very large amount also is sent down the Ohio in barges to the lower Mississippi River. The spot value of bituminous coal varies from $0.80 to $1.60 per ton; the product of the Pacific coast mines, however, is from $3 to $5. The output of the mines of the United States aggregates about two hundred and forty million long tons yearly, and this is about one-third of the world's product. For many years there has been an export trade to Canada, the West Indies, Central and South America, amounting in 1900 to 8,000,000 tons. Within a few years, however, the decreased cost of mining due to machinery, and the low rates of transportation to the seaboard has developed an export trade to Russia, Germany, and France. [Illustration: COAL] A small amount of coal is imported into the United States. A superior quality of Australian coal finds a ready market in Pacific coast points as far north as San Francisco, and large quantities of Nanaimo, B.C., coal are sold in Oregon, Washington, and California. A small quantity of the "slack" or waste of the Nova Scotia mines is imported to Boston to be made into coke. The Canadian fields supply a considerable part of the coal used in Montana. =Coke and Coal-Tar Products.=--In the manufacture of iron and steel a fuel having a high percentage of carbon free from volatile matter is essential. The great cost of wood charcoal forbids its use, and so a charcoal made from soft coal is used. Fat coal is heated in closed chambers until the volatile matter is driven off. The product is "coke"; the closed chamber is an "oven." The ovens are built of stone or fire-brick, in a long row. They are usually on an abrupt slope, so that the coal can be dumped into the top, while the coke can be withdrawn from the bottom, to be loaded into cars. About three thousand one hundred and forty pounds of coal are required to make a short ton of coke; from three thousand to five thousand cubic feet of illuminating gas, together with varying amounts of coal-tar and ammonia, are driven off and generally wasted. In a few instances "scientific" ovens are in use for the purpose of saving these products; but in the coal-mining regions such devices are the exception and not the rule. The great waste of energy-products in the manufacture of coke is partly offset by the employment of refuse and slack, which could not be otherwise used.