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wood. The main development in recent years has been in the selection of suitable machinery and proper co-ordination of the different parts of the plant, and particularly in the designing of a retort which could be rapidly charged and discharged, and which would insure that the steam penetrated all parts of the wood without forming channels through it. Of the many retorts suggested, some are horizontal, charging through the top and discharging at one end; some are vertical, with various devices, more or less successful, for opening a large discharging door at the bottom; some use either a horizontal or vertical retort in which a cylindrical basket is placed containing the charge; and some have even attempted a continuous operation by charging and discharging all the time by mechanical devices; others still have used the idea of a retort hung on trunnions turned up to be charged and turned over for discharge; and others a horizontal retort with mechanical discharging device. At least two plants have attempted to use the system of running cars into retorts, something like the method used in “hard wood" distillation.

Many patents have been taken out covering the direction the steam moves in the retort, whether down or up, the introduction of the steam at various levels, and the agitation of the charge during the run; but the value of all these points is still doubtful. The time required for steaming out spirits of turpentine by this method varies from 1 to 12 hours in different plants. Yields vary from 6 to 25 gallons per cord, depending on the quality of "light wood" and the character of the plant, a fair average being from 12 to 15 gallons. When steam distillation is properly operated and the product is suitably refined, it would appear that the spirits of turpentine produced should not differ in any appreciable way from the old process spirits of turpentine or gum spirits of turpentine, the low temperature preventing action on the wood, just as in the case of the material which exudes from the tree in the old process.

There are now perhaps 80 plants in the United States for recovering spirits of turpentine from "light wood," and from mill waste. The writer is fairly familiar with the operations of about 50, and very intimately acquainted with from 12 to 15. The products from the various plants vary not only on account of different methods employed in the plants, but mainly because the attempt is not made to produce material of a perfectly uniform standard; and in cases where this is attempted the standards of different plants are different. When success has been attained along the line of standardizing the various methods of manufacturing, a spirit of turpentine produced in this way should be not at all inferior to gum spirits of turpentine; in fact, it should be superior on account of its uniformity.

After the wood has been treated by the steam process, it remains in almost exactly the condition in which it entered the retorts, excepting that the spirit of turpentine has been removed. A part of this refuse is used for fuel. The disposition of the remainder is a serious problem, because it can

not be destructively distilled in the ordinary retort without agitation on account of its poor conducting power. Some fairly successful attempts have been made to utilize it for manufacturing a low grade of paper, and for recovering the resinous material, but most of these attempts are still in the experimental stage. The point which has been definitely proven is that no destructive distillation can be attempted in the same retort that is used for distilling off the spirits of turpentine.

Gas Engines Run by Gases from Copper Furnaces.

The Mansfield Company of Germany has for some time past been utilizing the blast-furnace gases from the copper furnaces at the Krughütte works for direct consumption in gas engines. The blast-furnace gas has a heating power of 650 calories per cu. m.—the proportion of carbon monoxide being 21.65 per cent—and as the volume of gas amounts to about 21,000 cu. m. per hour the available power from this source, when used in gas engines, is between 4,400 and 4,500 horsepower. Owing to the lessened output when any of the furnaces have to be cleaned and also owing to variations in the calorific power of the gas, the mean of 2,700 horsepower is all that can be depended upon. The furnaces are connected up to two gas mains one about 62 inches diameter, the other 391⁄2 inches-either of which can be disconnected for cleaning or repairs. Before reaching the engines the gas has to be freed from dust, for which purpose it is passed through counter-current washers; these consist of spiral blades, rotating at a peripheral velocity of about 165 feet per second. In passing through the apparatus the gas is brought into intimate contact with water, which is sprayed by the action of the blades and forced in the opposite direction to the flow of gas. After being dried, the gas, which now contains only about 0.003 gm. of dust per cu. m., against 17 gm. in its original condition, is led to a gas-holder capable of storing 18,000 cu. ft., whence it passes to the engines. These are two in number, each of 1,300 horsepower, a third engine of equal capacity being in course of erection. Each motor is of the twocylinder class, with fly-wheel mounted on a common shaft between the halves, and each develops 1,300 horsepower when running at 125 revolutions and driven by gas of the above mentioned calorific power. The cylinders are water-cooled, the effluent water being pumped up into a cooling tower and thence returned to the supply tanks. The fly-wheels constitute the rotors of the three-phase Siemens-Schuckert generators, developing 1,080 kw. at 3,000 volts tension.-The Mining Journal.

HOW LONG WILL OUR COAL SUPPLY MEET THE INCREASING DEMANDS OF COMMERCE?'

The story is told in that moveth mountains.

By EDWARD W. PARKER.

U. S. Geological Survey.

Canada of an old lady whose faith is of the kind She lived some distance from the beaten paths of commerce, and modern methods of heating and lighting were unknown to her. But one day her son, who had been "to the city," brought home with him a kerosene lamp and a can of oil. She naturally inquired what the oil was and whence it came, and on learning that it was petroleum or rock oil, she commanded her son to take it back-she would have none of it. She could not understand the wickedness of men who were stealing from the Lord the fuel that He had stored in the world for the purpose of consuming it when the time should be no more.

We are not called upon to interpret in what manner the promise of the destruction of the world by fire shall be brought about, but certain it is that man is consuming, at an enormous rate, not only the combustible material stored beneath the surface of the ground, but we are told by Mr. Pinchot that the forests that formerly seemed inexhaustible, will have been practically destroyed by the middle of the present century, if the present rate of destruction continues. The use of wood for fuel is not so great proportionately to-day as it was a century ago, but other demands upon the forests have taken its place. A recent report of the Forest Service states that the present annual consumption of fire wood is about 100,000,000 cords, valued at $350,000,000, and that the total forestry consumption represents about 20,000,000,000 cubic feet, worth nearly $1,100,000,000. The consumption for lumber has increased more rapidly than the population. My reason for referring in this paper to the forest destruction will be shown later.

The subject assigned to me for this meeting by your distinguished secretary is, "How Long Will the Supply of Coal Meet the Increasing Demands of Commerce?" The question is one to which, of course, no accurate reply could be given, for the answer is predicated upon the determination of one unknown and unascertainable quantity, and that is the rate of increase which the demands of commerce will take. Other and scarcely less important factors also enter into the solution of the problem. Among these may be mentioned the improvement which must be brought about in (1) the methods of mining, assuring a greater percentage of recovery from

'Read before the tenth annual session American Mining Congress, Joplin, Mo.

the mines and a larger proportion of usable fuel and less waste and inferior coal (by inferior coal I mean slack coal or fines, which are sold at low prices, or not at all); (2) processes for using economically the slack or lowgrade coal; (3) more efficient methods of combustion, which will increase output of energy per unit of fuel consumed; (4) the utilization of other forces of nature, which will, to greater or less extent, diminish the drain upon our coal supplies. Much is already being done and more will be done in the development of better methods in the mining, preparation and utilization of coal. The government, through the technologic branch of the United States Geological Survey, is spending thousands of dollars in the way of scientific investigation of fuel utilization, and although this work is of recent inauguration, having had its inception at the Louisiana Purchase Exposition, highly valuable results have been obtained, and these are being published and gratuitously given to the public as fast as they can be compiled and published. I shall not attempt to go into these, as I understand you are to have a paper by Prof. Joseph A. Holmes, under whose direction this work is being conducted. I will only mention the fact that one of the results accomplished during the exposition period was the demonstration that producer gas for power purposes could be made from bituminous coal and lignites with an increase of from 200 to 300 per cent over the efficiency obtained from a steam power plant. It is significant, too, that when one of the gas-engine manufacturers was approached with a proposition to install one of his engines as a working exhibit at the St. Louis Exposition, the proposition was declined because of want of belief that producer gas from bituminous coal could be so used. I speak from personal knowledge on this "oint, for I did the approaching. One of the coals successfully used at this exposition plant was a California black lignite or sub-bituminous coal, containing 8 per cent sulphur. I am informed by Prof. Fernald, in charge of the producer gas investigations of the technologic branch, that 66 2-3 per cent of the power represented by the installation of producer-gas plants during the last year are for using bituminous coal, while 80 per cent of the number of plants are designed for anthracite.

As to the utilization of other forces, the development in the harnessing of water courses which has been made possible through the long distance transmission of power by electricity is one of the wonders of the present time. The great Susquehanna river is being dammed at McCalls Ferry, Pa., for the purpose of sending power electrically to Baltimore and Philadelphia, two cities 100 miles apart. The power of Niagara Falls is being utilized to a great extent already, and it is a momentous question as to whether we can better afford to permit what remains to be used for power or to preserve it as one of nature's art works. Is it better to use it for utilitarian purposes or its beauty and grandeur? I am sufficiently uncommercial to hope for the latter.

As to the interesting demands of commerce on our coal supply, our

only method of forming an opinion on this point is from what has preceded (as Patrick Henry once remarked, "We have no way of judging of the future but by the past"). And our past, so far as coal mining is concerned, presents an interesting history. I have prepared and present here a chart which illustrates better than I can tell in figures the rapid, almost phenomenal, growth of our coal mining industry. It shows the total production of coal in the United States for each 10 years to the close of 1905. Each decade shows an output approximately double that of the preceding one, which means that the production in each 10 years has been equal to the production up to the beginning of that decade. How long can or will this continue? Let us prolong the curve as it would show for the future if this history were to continue. I have done this on another chart, which is on a scale of about one-eighth of the one showing our record in the past. It will be noticed that while the production has approximately doubled, there is a decreasing ratio in the percentage of increase during each decade. For instance, the total production of coal from the earliest times to the close of 1845 was nearly 28,000,000 tons. In the decade for 1846 to 1855, inclusive, the production was something over 83,000,000 tons, or practically three times the total production to the beginning of that decade. In the 10 years ending in 1865, the total production was 174,000,000 tons, an increase of about 70 per cent over the total production for the beginning of that decade, but this was the period in which the civil war occurred, and coal mining, like all other industries, suffered a relapse. Moreover, the records of production for that period are incomplete, and it is possible that the actual tonnage was more than we have recorded. In the 10 years from 1866 to 1875, the total production amounted to nearly 420,000,000 tons, and it was in this decade that the wonderful development in the coal mining industry began. The production for this 10 years was two and one-half times that of the preceding 10 years, and was 35,000,000 tons in excess of the total production up to the beginning of the decade. In the following decade (that ending in 1885) the production was again somewhat more than doubled, but not in the same proportion as in the preceding 10 years. The production in the decade ending in 1895, was 87 per cent larger than that of the preceding one, and was over 30,000,000 tons in excess of the total production to the close of 1885. In the 10 years from 1896 to 1905, this country produced 2,832,403,000 tons, an increase of 78.5 per cent over the preceding 10 years.

If we can assume that the production will continue to increase with the decreasing percentage ratio, the production for the decade ending in 1915 would be 60 per cent over that of the decade ending in 1905, and the total production for the 10 years would be 4,530,000,000 tons, or an average of 453,000,000 tons a year. (Our production last year was 414,000,000). In the next 10 years there would be an increase of 54 per cent and the production for the 10 years would amount to something over 6,600,000,000

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