Testing the Atmosphere of Mines at Kolscheid near Aachen. By KAETHER. (Zeitschrift für das Berg-, Hütten- und Salinen-Wesen, 1889, p. 116.) The object of these experiments was to determine how the height of the barometer influenced the composition of mine-atmospheres. In the ventilating shaft a gasometer was placed, which was arranged to fill in about twelve hours. By this means an average sample was obtained. Readings of the barometer were taken at midday and midnight, and samples morning and evening. The determination of marsh gas and carbonic-acid gas, were made with Coquillon's "Grisometer." This apparatus, briefly described, consisted of an arrangement of three glass tubes communicating with each other; one containing a solution of sodium hydrate, the other fitted for electrically acting on the gas, and the third graduated for measuring the diminution of volume during the experiments. A known volume of the sample and air, having been introduced into the measuring tube, are brought into contact with the solution of sodium hydrate, which dissolves the free carbonic acid gas, the following reaction taking place: CO2+ 2 Na OH = Na2 CO2 + H2O 2 2 The diminution of volume having been measured, the gas is admitted into the electrifying tube and exposed to the action of a glowing spiral of paladium wire. The marsh gas is decomposed as follows: : The resulting gases are again treated with the solution of sodium hydrate, when the newly formed carbonic acid gas is dissolved. From the second diminution of volume the quantity of marsh gas is estimated. The results obtained by this process are accurate enough for all practical purposes, and compare favourably with the more exact analysis made by Winkler's method as shown below. Graphite-mining in Bohemia. By A. PALLAUSCH. (Berg- und Hüttenmann. Jahrbuch der k.k. Bergakademien, Leoben, 1889, p. 95.) The graphite district of South Bohemia, in the neighbourhood of Przisnitz and Eggetschlag, extends over an area 14 miles long and 10 miles wide. The graphite occurs in the form of lenticular or irregular deposits embedded in gneiss. The beds vary in thickness from a few inches to more than 20 yards. In one mine as many as five parallel beds have been observed. The graphite is usually rendered very impure by admixed gneiss, kaolin, and iron pyrites. Both hard and soft varieties are met with, the purest containing 80 to 95 per cent. of carbon. The Author traces the history of the mining industry from the year 1767, when mining operations were commenced by the peasants, until 1811, when Prince Schwarzenberg began mining on a large scale. In 1888, in addition to the Prince's mines, the only ones in active operation are those of Porak Brothers and of the Mugrau Company. The largest and deepest of Prince Schwarzenberg's mines works the so-called Florian bed, which has been explored for a length of more than 600 yards by means of four shafts varying in depth from 144 to 262 feet. Workings are now being carried on at the fourth, fifth, and sixth levels, headings being driven across the deposit so as to form pillars 20 yards apart. Beginning at the lowest point, these are worked on both sides by over-hand stoping. The excavations, which require to be supported by strong timbering, are then filled in. The soft graphite obtained with the pick is at once sorted into three classes. The best variety, characterized by its softness, purity, intense black colour, and metallic lustre, and the second variety are brought to the surface in boxes holding 44 lbs. The third variety and the hard graphite are transported in mine-trucks. The treatment of the graphite from the different mines varies according to the quality of the mineral. The two best classes, brought in boxes from the mine, are taken into a well-lighted sorting-house, where each piece is broken and carefully freed from impurities (kaolin, iron ochre, and pyrites). The graphite is then dried on a steam-heated boiler-plate, and packed in barrels ready for the market. Other classes of soft and hard graphite are refined. The mineral is crushed in a roller-mill with excess of water, and the resulting mud is passed through six separating tanks, 5 feet long by 31 feet broad by 31 feet deep, and thence through a number (usually eighteen) of depositing tanks, 20 feet long, 31 feet broad, and 5 feet deep, until the graphite slime attains a given. height. When the slime has settled and become compact, the supernatant water is drawn off, and the slime is transferred to a tank, provided with a stirrer, and thence is forced by pumps at a pressure of 6 atmospheres into large filter-presses. Each press is emptied three to four times in twelve hours and yields 396 to 529 lbs. of graphite in tabular cakes containing 20 per cent. of moisture. These cakes are finally dried by being exposed to heated air at a temperature of about 190° Fahrenheit for twentyfour to thirty hours. Two drying-rooms are used, each holding 20 tons, so that while the drying operation is in progress in one, the other is cooled, emptied, and refilled with moist graphite. When the weather is favourable the cakes are dried in the sun. The selling price of the pure graphite varies from £1 10s. to £20 per ton, and that of the refined product from 168. to £8 per ton. The production of graphite in Prince Schwarzenberg's works, in 1888, amounted to 6,753.5 tons, valued at £17,850. The total production of the district has increased from 7,129 tons in 1880 to 11,790 tons, valued at £23,470, in 1888. B. H. B. Mining and Metallurgy in Australia. By H. A. GORDON. (Mining Machinery and Treatment of Ores in Australian Colonies. Reports on Mining Machinery at the Melbourne Exhibition; on Mining and Plants for the Reduction and Treatment of Ores in the Australian Colonies; and on Processes adopted in America for Treatment of Auriferous and Argentiferous Ores. Wellington, New Zealand, 1889.)1 At the request of the Minister of Mines for New Zealand, the Author visited the Melbourne Exhibition and the Australian colonies, and reported on the machinery best adapted for working the mines of New Zealand and for reducing the various ores. In his report, which is illustrated with one hundred and fifty-eight drawings, the subjects are dealt with under the following heads: crushing and pulverizing machinery, ore-concentrators, chlorination, rock drills, water augers, steam-boilers, pumping-machinery, mineral railways, new explosives, machinery at the Mount Bischoff tin mine, Broken Hill mine and works (where the plant is a duplicate of the ore-dressing machinery used at Lake Superior and Anaconda copper mines, in the United States), zinc desilverization process at the Dry Creek smelting works, Adelaide, and a description, abstracted from Prof. T. Egleston's work on the metallurgy of gold, of the processes used for extracting metals from the ore at the Boston and Colorado works, in the United States. There is also an Appendix, containing a report by Prof. W. C. RobertsAusten on the Freiberg metallurgical process. Although the quartz-reduction mills, and other machinery reported on, are new to Australia, they have already been described in the English technical journals. The Mount Bischoff tin mine 2 is situated on the western slope of Mount Bischoff, forty-nine miles from Emu Bay, Tasmania. The tin ore appears to be confined to a basin, 1,400 feet in diameter. The plant at the mine comprises one stone-breaker, seventy-five heads of 1 The original is in the Library of the Institution. 2 Transactions of the Mining Association and Institute of Cornwall, vol. ii., 1888, p. 51. The ore stamps, thirty classifying pyramidal boxes, thirty jiggers, seventeen Kayser buddles, twenty-three single- and twelve doubleconvex revolving-tables. The whole of the works are lighted up with electric glow-lamps. The quantity of clean ore produced during the first half of 1888 amounted to 1,266 tons. from the mine is conveyed to the stone-breaker, and thence to the stamping-battery, where it is stamped until it passes through a grating having 144 to 169 holes to the square inch. The ore is then classified, the classification being effected for the coarser and richer ore by revolving trommels, or by a series of reciprocating screens, one above the other, and for fine sands by self-acting classifying boxes. There are two sets of these boxes for every five heads of stamps, one for the coarse material and one for the fine sand. From the bottom of the pyramidal boxes, the sand passes through a 1-inch gas-pipe to the jiggers. These are furnished with screens and bedding suitable for the fineness of the material that enters them. The bedding consists of crop-tin, the thickness depending on the quality of the material treated. For rich ore the bedding is thin, but for poor sand a thicker layer is required. The speed of the jiggers varies from 60 to 220 strokes per minute. Ore passing through a 144-mesh requires 144 to 160 strokes per minute, whilst that passing through a 169-mesh requires 200 to 220 strokes. Two forms of buddle are employed, one for the slimes and one for coarse sand. The latter is termed a Kayser buddle. In principle it is similar to the ordinary buddle. It is, however, provided with revolving arms, carrying the scrapers, hinged near the centre, underneath the main arms, whilst the outer extremity is held in position by a screw. The hinged arm may be raised or lowered to the exact height required. Instead of the brushes of the ordinary buddle, the Kayser buddle has scrapers. It is 20 feet in diameter, and concave in shape. The mixture of water and sand is distributed at the periphery by eight gas-pipes. The heavy sulphides remain, while the light sand passes down the bottom of the buddles, and is discharged over the circular riffle at the centre. One buddle will concentrate the ore from ten heads of stamps, 8 cubic feet of water being required per minute. For the treatment of slimes, the convex table is used, and has proved the best concentrator for the purpose. In this case, the process is continuous. The proper working of the table, however, depends largely upon the construction, particularly upon the even and smooth surface of the sixteen equal sections of wood of which it is composed. Recently, tables with a 1-inch coating of Portland cement have given great satisfaction. The convex tables have a diameter of 16 feet, and an inclination of 1 in 12. In the tables recently erected, two are built on one shaft. B. H. B. Gold-Mining in Transylvania. By E. THILO. (Berg- und Hüttenmannische Zeitung, 1889, p. 125.) The gold-mining centres of Transylvania are the towns of Brád, Abrudbanya (the Auraria major of the Romans), and Zalatna (Auraria minor). Mining is here carried on under great difficulties. The mines are situated at considerable distances from the railway, the roads are bad, wood is scarce and dear, and the water-supply is defective. In the vicinity of Brád, some beds of lignite occur, but the fuel is of poor quality. Gold is widely distributed throughout the region, but rarely in payable quantities. The gold in the ore seldom amounts to 19 dwt. per ton. The ore is treated in primitive stamping batteries. An overshot water-wheel drives six or twelve rectangular wooden stamps, 4 feet 6 inches to 6 feet 6 inches in length. The shoes are of iron, or, in some cases, of basalt. The mortar-boxes are of wood, lined with iron or basalt. The ore is shovelled into the mortarbox, and stamped while a stream of water runs through. The muddy water passes out either into a sump, where the heavy particles sink, or over an inclined plane covered with blankets, that serve to retain the gold. Most of the gold remains in the mortar-box, and the process is ocasionally interrupted in order to put the stamped residue through a hand-sieve. The fine material that passes through then proceeds to a primitive concentrator, consisting of an inclined table, having a surface of 10 square feet, over which water slowly flows, and on which the material is continually shovelled up against the stream until all the particles of gangue are washed away. Below this concentrator there is another inclined table, covered with blanket, to catch any particles of gold that escape. The material thus caught is treated again, and the gold is finally separated out of the concentrates on a wooden vanning shovel. The stamping process is very slow, twelve stamps treating only 4 tons in a week. The loss of gold, however, is very slight, and notwithstanding the constant handling of the material, the treatment is remarkably inexpensive, not more than 10d. being paid for stamping a ton of ore, and 18. for washing the pulverized material. The total cost per ton thus amounts to 18. 10d. The cost of the stamps is less than £20. Owing to want of water, they can rarely be worked for more than six months in the year. More scientific methods are adopted at the larger works. At the Government works at Vöröspatek, and at the works of the Ruda Company at Brád, the ore is treated in Tyrol amalgamation mills, and at Vulkoj an American stamp battery, with Frue vanners, has been erected. The cost of stamping at Vulkoj amounts to 68. per ton. In recently designing a mill for this district, the Author selected for comminuting the ore the Jenisch falling-ball mill, a machine that has been found to answer admirably for pulverizing basic slag. He is thus enabled to treat 30 to 40 tons of ore in [THE INST. C.E. VOL. XCIX.] 2 K |