Coaling of Wood by Superheated Steam. FR. ELFSTRÖM.

(Teknisk Tidskrift, Stockholm, 1905, General section, pp. 289-91.)

Several years' management of charcoal works in the neighbourhood of Umeå in Sweden, for the dry distillation of tar, oils, and turpentine in the coaling of pine stumps, led the Author to observe the wastefulness of the common process, which occupied 5 days and nights; and he decided upon trying to improve it by introducing superheated steam direct into the coaling retorts. In the first attempt with a primitive arrangement, foot-lengths of 3-inch plank were completely coaled in 2 hours by the exclusive use of superheated steam; and the oils thereby obtained were of excellent quality, superior to any previous yields. The next step was to course the superheated steam through a row of retorts, whereby the steam and gases evolved from the wood in the first retort were carried forwards collectively into the next, and so on in continually increasing quantities into the last. The greater part of the heat is required for evaporating the water out from the wood; but the steam need not be so highly superheated for this purpose as for the subsequent coaling of the wood. The main steam-pipe is therefore provided with branches and stop-valves, enabling the hottest steam to be admitted into the retort in which the coaling is nearest being completed; the last retort in the series, freshly charged with cold wood, utilizes the accumulation of cooler steam that reaches it from the whole of the preceding retorts. The firing of the superheaters is so managed that the coaling is completed in the successive retorts in equal intervals of time, thus enabling the work to be carried on continuously with the smallest staff of workmen. With ten large retorts connected in series, each of 20 to 30 cubic metres capacity (say 700 to 1,000 cubic feet), coaling is completed in 12 to 20 hours, according to the quantity of moisture in the wood; drawing and charging take 4 to 5 hours; whence each retort can be worked off once in 24 hours. For slaking the charcoal, ordinary saturated steam is admitted for an hour into the finished retort, wherein it becomes superheated sufficiently for passing on into the intervening superheater, which raises it to the full temperature for completing the coaling in the next retort. Then a little water is played for half an hour into the cooling retort, carrying off thence a large quantity of heat to be utilized; and for an hour longer a fine spray only is showered upon the charcoal, which can then be drawn without risk of firing and without injury in handling. On their way to the superheater the mixed steam and gases from the finished retort are led through boiling water in a covered tank, in which the heavy oils, boiling at 200° to 250° C. (390° to 480° F.), become condensed, while the lighter turpentine goes forwards with the steam into the superheater without sustaining any deterioration. The condenser, which is almost self-acting, requiring scarcely any attention, constitutes one of the most important novelties in the plan.

The advantages of this new mode of coaling are:-the time is reduced from 5 days and nights to 18 or 20 hours; the yield of oil is increased about 17 per cent., and is of so much better quality that it fetches from 25 to 50 per cent. higher price; the consumption of fuel for firing, when working on a large scale, is reduced to a fraction of what it was before, and does not exceed 15 per cent. on the charcoal obtained; moreover for this purpose woodman's chips and saw-mill refuse can be used advantageously.

A complete range of retorts for producing about 1,200 heaped chaldrons of charcoal per annum (3,600 chaldrons English) costs about 8,000 kronor (£444), which would be redeemed in less than a year by the saving effected as compared with coaling in heaps. Working expenses would be from 1.25 to 1.50 kr. per heaped chaldron (say 54d. to 7d. per English chaldron) of charcoal made. A charcoal factory on this plan was erected early in 1905 at a sawmill in the neighbourhood of Sundsvall, where the foregoing statements are confirmed.

A. B.

Continuous Carbonizing of Wood-Waste.

(Stahl und Eisen, Düsseldorf, 1905, p. 1381.)

The Rhenish Wood Distillation Company, of Düsseldorf, has introduced a method of utilizing wood-waste, such as sawdust, shavings, spent dye wood, etc., by a system of rapid carbonization with condensation of the volatile products, the uncondensable gases being also utilized in supplying part of the heat required for the distillation. The plant, which is entirely automatic, includes (1) a dryer, (2) a pre-heater, (3) a rotatory retort, (4) a charcoal separator and cooler, (5) cooling and condensing arrangements for the distillates, and (6) a fire-place for the retort, besides rectifying arrangements for the further treatment of the by-products. The retort, 13 feet long and 3 feet 3 inches in diameter, provided with a system of rotating arms for passing the wood to be charred continuously through it, is placed below the heater, which is fed with waste by a screw conveyor, the dried and slightly heated wood being pressed forward by a pair of rotating paddles which deliver in a broad even layer to the retort. The latter is heated by a coke fire, and is provided internally with a shaft carrying spirally-arranged blades rotating in the opposite direction to the retort itself, which prevent the adhesion of particles of wood to the heated wells, and move the finished charcoal continuously forward to the delivery screw-carrier, contained in a water-cooled channel. The volatile products pass through the pre-heater into a system of condensing tubes, the flow being maintained by an exhaust fan, the condensed gas going back to the fire-place of the retort. The carbonizing process is completed in 15 minutes, each retort being capable of heating 10 to 12 tons of material in 24 hours. The volatile products make up at about 50 per cent., and the charcoal 23

to 25 per cent., of the charge. The crude distillate from coniferous wood contains 20 per cent. by volume of tar, and 80 per cent. of crude wood vinegar, which, by further treatment, gives 90 per cent. of clean vinegar, containing 6 per cent. of acetic acid, and 10 per cent. of residual tar from the still.

The yield of methyl alcohol is 1 per cent. of that of the crude vinegar. The products therefore obtained from 100 parts of pine wood shavings are

The heating value of the charcoal obtained, if used for boiler-firing, is fully equal to that of the same waste wood when burnt directly in the damp state.

Hand-Hammer Drills.

H. B.

(Engineering and Mining Journal, New York, 26 August and 9 September, 1905, pp. 362 and 450.)

Among recent developments and improvements in mining engineering and mining machinery, not the least important is the introduction of the hand-hammer drill. The need for a machine to

do what this is designed to perform was urgent. Its field of usefulness lies principally in narrow veins and places difficult of access; but it will be found serviceable in drifting and stoping generally, and for squaring up development work and breaking up blocks and boulders.

The hammer-drill is a development of the pneumatic hand-riveter, well known in machine-shop practice. From this was evolved the plug-drill, extensively used for small shallow holes in quarrying. The new drills of this type, however, which are now attracting much attention, are designed for regular mining work. They are of simple construction and are very light, weighing only from 15 lbs. to 20 lbs. The working parts are few and are easily kept in order. A section through the working parts of a Murphy drill, one of the newest designs, is shown. It is used with a solid piece of drill steel cored for the passage of the exhaust. The machine strikes 2,000 blows per minute. The temperature of the bit is kept down by the exhaust air, which also keeps the hole clear, and thereby makes the high speed practicable. A dust-catcher is provided to keep down the flying particles. The air-consumption of this class of drill is comparatively large, about 20 cubic feet a minute, and the greatest depth of hole is 3 feet. The speed of boring in fairly hard quartz is fully 1 inch a minute. As no time is lost in changing position, the hand

hammer drills are found in practice to compare favourably with a 21-inch machine-drill on short holes. Perhaps the most expressive statement as to the ease of operating a hammer-drill is contained in the directions given with the Murphy machine, viz. :-"Slip the shank of the drill-steel in the end of the drill; place the bit against the rock; hold firmly; turn on the valve, and let her go." The two difficulties to be overcome in these machines are connected with the hole extending longitudinally through the bit, through which the air is exhausted. In very dry rock the dust blown out of the hole may become a nuisance; and in wet soft ground the hole becomes clogged.

G. G. A.

Large Water-Hoist.

(Engineering an 1 Mining Journal, New York, 30 September, 1905, p. 588.)

The largest automatic water-hoisting plant in America, and probably in the world, was recently put into operation by the Lackawanna Company in Keyser Valley, near Scranton, Pa., U.S.A. The immense scale on which this project has been undertaken and the originality and completeness of the design have caused wide interest in the work. The volume of water to be dealt with is very large. Two huge "buckets," each of a capacity of 17 tons of water, are hoisted by an 800-HP. electric motor. As it takes but one minute to fill a bucket and to hoist it to the top of the shaft, the quantity raised in 24 hours is nearly 6 million gallons. When the descending bucket reaches the water at the foot of the shaft, two valves in the bottom open to admit it, closing again as soon as the water reaches a certain level. While this bucket is filling the other slowly ascends to the head-frame at the top of the shaft. A lever on the outside of the bucket, connected with the valves in the bottom, comes into contact with a timber on the head-frame, thereby opening the valves. The water then flows out in two big streams, one on each side of the shaft, into concrete reservoirs, whence it is led away through a flume. The length of time the buckets are at rest is regulated by mechanism in the hoisting-room. Notwithstanding the great weight to be lifted, and the large dimensions of the machinery, all works with ease and regularity. One man is employed to oil and attend to the motor, while another watches the buckets, only, however, to act in case of accident.

G. G. A.

Borax Deposits of California. G. E. BAILEY.

(Mining World, Chicago, vol. xxiv., 1906, pp. 4-5.)

The American borax deposits are situated in California in two systems of dry-lake beds; and when the borax industry started, the supply was obtained by working the crusts taken from the surface of Death Valley and other similar dry lakes. About 15 years ago, however, it was discovered that the beds of still older dry lakes of early Tertiary age contained richer deposits than those being worked, and since then nearly all the borax produced, about 46,000 tons annually, has come from these older beds of colemanite (borate of lime) near Daggett. The process of concentrating colemanite is to roast it, the rich borates falling into a powder while the accompanying minerals are not affected. The powder is converted into borax by boiling with sodium carbonate. Boric acid was formerly made by boiling the crude material with sulphur, forcing in steam, and leaching out the solution which was purified by frictional crystallization. The Blumenberg process has superseded this. In it sulphur is burned in large iron muffles, air being forced into the muffle at a pressure of 9 lbs. to the inch. The gases from the muffle pass up through the vats, 30 feet in height, containing the crushed material. The vats are then filled with water, and liquids leached into outdoor vats covering several acres. When the liquid reaches the first vat it is white, and contains sulphur-lime compounds formed in the dark, but the action of sunlight soon causes a precipitation of sulphide of lime. The clear solution of boric acid is then drawn off and passed through a series of vats until sufficiently concentrated by evaporation to crystallize readily. As the vats are in the Mohave desert, where there is a constant dry wind and high temperature, the process of evaporation is rapid.

B. H. B.

Static Electricity in Ore-Dressing. W. C. SWART.

(Engineering and Mining Journal, New York, 26 August, 1905, p. 351.)

The use of static electricity is now past the experimental stage. After five years of successful working under varied conditions of ordinary mining practice, the electrostatic ore separator may be regarded as having established itself as an efficient and reliable machine. Very important progress has been made in the application of these machines. At first they were used only for ores of which the constituent particles differ widely in conductivity. But other processes have recently been developed, and machines are now made to utilize, for the purpose of separation, other electrical properties of matter. The electrostatic capacity of the ore particles has been made to play an important part; but perhaps the most interesting of these new processes is that which depends for its