so exceedingly bad, in comparison with what they could be made, and were made by Fliegner.

I think it is a mistake to take only the pressure in the bustle-pipe. What I should want to know in such a case would be the difference in pressure between the blow-pipe and the inside of the furnace, which can be easily determined by the use of a U-gauge, filled with mercury and arranged about as shown on the accompanying rough sketch, Fig. 1, the outer tube being filled with water above the mercury to above the top of the hose before screwing the nipple into the T. This would give direct readings of differences of pressure, which are very much more desirable than those of small differences in large pressures, taken from gauges which may or may not be accurate. The nicest form of U-gauge for this job is the annular one, in which one pressure takes effect in the central tube and the other in the annular space. This makes the difference extremely easy to measure, and compensates for any error in holding the gauge plumb, etc.

Another thing which occurs to me is, that, as a result of the high velocity of the entering blast, the suction effect on the open end of the tube will give an appreciable error, to avoid which, the test-tube should be plugged on the end and its side drilled full of small holes with rounded edges.

If you make any more tests of this kind, these two changes, in my opinion, would render your work much easier, and your results more accurate.

I suppose everybody will be at first inclined to reject, as due to errors of observation, the indication given by the experiments you report, that the pressure inside the furnace is higher than that at the tuyeres. But this is not necessarily true. The high velocity of the air-jet may be transformed back into pressure inside the furnace; in fact, that is what its velocity is for. This point also can be determined with the differential guage by using two concentric pipes, the outer one of which reaches to the nose of the tuyeres, and the other to any desired distance beyond that, in the furnace.

I have taken in the past a great deal of interest in this subject; aud I shall be glad to see your paper published, for the discussion that it ought to bring out. This would be all the more valuable if it should induce you, or some one else, to make more extended and accurate tests, in which the friction in the bustle-pipe and stocks was eliminated. The ordinary formula for the flow of air enables us to design bustle-pipes so that there need be no appreciable loss of pressure when they are clean; and, in a case of this kind, such an unnecessary loss only tends to becloud the value and diminish the interest of the investigation.

I beg to express my thanks to this friendly critic, whose suggestions possess the highest value for me; and I may be permitted to add that, even if my paper should receive no other discussion, this one result of its publication will, in my judgment, justify the wisdom of that invitation of our Secretary (quoted in its first paragraph) which encouraged me to write it.

The Coal-Fields of the United States.

BY MARIUS R. CAMPBELL AND EDWARD W. PARKER, WASHINGTON, D. c.

(New Haven Meeting, February, 1909.)

DESCRIPTION.

ACCORDING to the estimates prepared by the U. S. Geological Survey, the area underlain by workable coal-beds in the United States is 496,776 sq. miles. Of this total area, 480 sq. miles contain the entire anthracite coal-fields of Pennsylvania. The bituminous coal-fields are estimated to be contained in areas aggregating 250,051 sq. miles. The grade of coal between bituminous and lignite, and which is designated by the Geological Survey as "sub-bituminous," is estimated to be contained within areas aggregating 97,636 sq. miles, while the areas containing lignite aggregate 148,609 sq. miles. The coal-fields are divided, for the sake of convenience in classification, into six main provinces, as follows:

1. The Eastern Province, containing the anthracite coal-fields of Pennsylvania and the bituminous coal-fields of the Appalachian region-namely, those of western Pennsylvania, Ohio, Virginia, West Virginia, Kentucky, Tennessee, Georgia, Alabama, and small outlying areas in North Carolina.

2. The Interior Province, containing the bituminous coal-producing regions of Michigan, Illinois, Indiana, western Kentucky, Iowa, Kansas, Missouri, Oklahoma, Arkansas, and Texas.

3. The Gulf Province, containing the lignite-areas of Alabama, Mississippi, Louisiana, Arkansas, and Texas.

4. The Northern or Great Plains Province, containing the lignite and sub-bituminous areas of North and South Dakota, eastern Montana, and northeastern Wyoming.

5. The Rocky Mountain Province, containing the bituminous and sub-bituminous areas of western Montana and western Wyoming, Colorado, Utah, and New Mexico.

6. The Pacific Coast Province, containing the areas of Washington, Oregon, and California.

During the last few years the Survey geologists have worked in all of these coal-areas, and have also been making careful estimates as to the quantity of coal contained in the beds when mining first began. In making these estimates care has been taken to ascertain how much of the supply is easily available, and how much is either not available under present miningand market-conditions, or is available with extreme difficulty. According to these estimates, the quantity of coal contained within the known area of the United States, when mining first began, was 3,076,204,000,000 tons. Of this quantity a little less than two-thirds, or 1,922,979,000,000 tons, is considered as coal that is easily accessible or minable under present conditions, while slightly more than one-third, or 1,153,225,000,000 tons, is considered as non-minable under present conditions, or accessible with extreme difficulty. It should be remembered, however, that the quantity of coal given above as easily accessible includes the lignites and sub-bituminous coals of the Western States, of which approximately 530,000,000,000 tons, while easily accessible, cannot be considered available under present conditions, or those which may be anticipated in the near future. This reduces the original supply of easily accessible and available coal to approximately 1,392,979,000,000

tons.

The areas of the different provinces aud the quantity of coal contained therein, when mining first began, are shown in Table I. TABLE I.-Tonnage (Short Tons) by Provinces and Accessibility.

The distribution of this original supply of coal, according to grades and accessibility, is shown in Table II.

TABLE II.-Tonnage (Short Tons) by Grades of Coal and

bituminous.... 250,531 1,176,727,000,000 505,730,000,000 Sub-bituminous 97,636 356,707,000,000 293,450,000,000 389,545,000,000 354,045,000,000

Lignite

Total...

148,609

496,776 1,922,979,000,000 1,153,225,000,000

1,176,727,000,000

216,252,000,000

1,392,979,000,000

The first mining of coal in a commercial way, in the United States, was in what is known as the Richmond Basin, a small area in the eastern part of Virginia. Small quantities of coal had been mined here in the latter part of the eighteenth century, and it was also in the latter part of the eighteenth and the beginning of the nineteenth centuries that efforts were being made to introduce anthracite coal for fuel-purposes. The first actual records of the production of Virginia coal were in 1822, in which year it was reported that 54,000 tons were mined. In 1820 (two years before) 365 long tons of anthracite coal, or one ton for each day of the year, had been shipped to distant markets. From these small beginnings of less than a century ago the production of coal has increased until in 1907 the total output of anthracite and bituminous coal approximated 500,000,000 tons. In 1837 the coal-production of the United States reached, for the first time, a total exceeding 1,000,000 tons, the output being reported from four States only, Pennsylvania, Virginia, Kentucky, and Illinois, although Maryland also was producing a small quantity of coal at that time. In 1840 the production amounted to a little more than 2,000,000 tons, the output being reported from 13 States. Ten years later, in 1850, the production amounted to 7,000,000 tons; in 1860 it was more than 14,000,000 tons; in 1870, more than 33,000,000 tons; in 1880, more than 70,000,000 tons; in 1890 it approximated 160,000,000 tons; in 1900 it was nearly 270,000,000 tons, and in 1907 it was 480,000,000 tons. The aggregate production to the close of 1907 has amounted to 6,865,097,567 short tons.

Up to the close of 1845 the total production of coal in the

United States was 27,700,000 short tons, and since that time the drain on the supply has practically doubled with each decade. The total production to 1845, and decennially since that time, was:

It is estimated that for every ton of coal mined and sold half a ton is lost or wasted, so that the total production of 6,865,097,567 short tons to the close of 1907 represents an exhaustion of 10,200,000,000 tons, or 0.3 per cent. of the total original supply, or 0.7 per cent. of the coal which is easily accessible and available under present conditions. The total supply of easily accessible and now available coal left in the ground at the close of 1907 was 1,382,780,000,000 short tons.

Table III. shows the production of coal annually from 1846 to 1907; also, the average annual production by progressive decades for the same length of time, the latter having been prepared in order to eliminate minor variations due to abnormal conditions. The average annual increase in coal-production, figured from the average of progressive decades, is 7.36 per cent., and for the last five progressive decades-1894 to 1903 to 1898 to 1907-the rate of increase has been above the average.

DURATION OF SUPPLY.

The total reserve of easily accessible and now available coal is estimated at 1,382,780,000,000 tons. The assumption that a constant output has been reached would be utterly unwarranted. On the other hand, the adoption of the flat rate of annual increase of 7.36 per cent. would involve the improbable assumption that the marvelous record of the past and present will be maintained in the future, and that the production will continue to approximately double every decade. Using the waste-allowance, on the basis of this constant rate of increase