70 THE COLLIERY GUARDIAN. July 9, 1915. CURRENT SCIENCE AND TECHNOLOGY. Boring Through Clay. In the Oesterreichische Zeitschrift, W. Petrascheck deals with some of the properties of clays encountered in boreholes, and the difficulties to which they give rise. Prominent amongst these is a tendency that strata situated between hard and heavy beds will be projected into the hole, and the remedy is to create artificially a chemical deposit on the walls of the borehole, in the nature of a flux, or, in more serious cases, the injection of cement. This blocking of the hole, however, can occur, independently of all pressure, solely through contact with water. This leads the author to consider the action of water upon clay or marl. It is generally recognised that the resistance of strata diminishes when they are saturated with water, and this phenomenon is specially to be observed in the case of clay shales, clays, and marl. Cores obtained from boreholes, which can easily be broken in the hand when moist, acquire great solidity when dry. A simple experiment will show what takes place in the borehole. If a fragment of clay is placed at the bottom of a glass of water, it will first give off a shower of fine particles; then the fragment will break up, and the debris falls to the bottom, and gradu- ally dissolves. At the end of from two to four hours the solid block will be transformed into a bed of mud. Clays, however, have colloidal properties which give rise to remarkable phenomena in the presence of saline solutions. If a fragment of clay or shale be placed in a saturated saline solution it does not dissolve. Either it remains intact, or simple fissures are produced which do not affect the general cohesion of the fragment; immer- sion for a day or a week will not result in any change. Furthermore, fragments that have remained for several days in such a solution lose even the capacity to disin- tegrate in water, and immersion for 24 hours will serve to diminish it considerably. Constant results were obtained from tests made with clays of widely different character. As salts, the author employed magnesium chloride, calcium chloride, magnesium sulphate, ammo- nium chloride, and sulphate of ammonia. The results obtained in one experiment were as follow :— After Water. XSjd. 4U. W a v6T. Intact 1 hr. At the end of half-an - hour the mass was ' disintegrated 4 hrs. 1 day 2 days 3 „ 10 „ The fragment broke into small pieces,... which, however, re-... „ mained compact ...Intact . Apparent disin- tegration. ,, ...Partial ditto. ,, ...In small pieces. ,, .. .Disintegration. With basic lyes from the soda lime process, or with solutions of alkaline carbonates, the clay broke down even more rapidly than with pure water. Another experiment directs attention to the action of saline solutions on the colloidal matters existing in clay. If there be added to the salt a mixture of fine clay and water, the particles will be found to agglomerate in lumps. Since the salts which formed the basis of these tests are in common use, its seems practicable to employ them in the form of injections in boreholes, where beds of this nature have to be passed through. Indeed, this suggestion has been the subject of an Austrian patent (No. 62058, G. Wobsa, Hanover). The process will evidently not provide a remedy in borings where the strata have already been acted upon by water and re-consolidated, but in virgin ground it may be found to be effective. It is observed that subsequent injection of ordinary water will not bring about the disintegra- tion of strata consolidated by a means of a saline solution. The Impregnation of Mining Timber. An account of some experiments in regard to the treat- ment of mining timber with creosote was published some time ago by M. Joseph Wuillot, of Mariemont. These tests, carried out at the Reunion, Placard, St. Arthur, Ste.-Henriette, and Placard St. Eloi pits, extended over a period of 11 years. It was found that creosoted timbers placed in 1900 in the Ste.-Henriette pit, in a damp situa- tion, were in an excellent state of preservation in 1910, whilst oak timbers had in the same period been replaced on two occasions. In a dry situation in the Reunion Colliery, the oak timbers lasted longer — about four years — whilst the creosoted pine timbers had about twice that age. It is noted that where for some reason the creosoted props had to be shortened, the cores were rapidly affected in the neighbourhood of the bare sections. The actual saving is difficult to estimate, but the author gives the following tentative figures :— Size of props. Creosoted timber. Price of complete set. Oak timbers. Price of three sets plus cost (4fr.) of setting same. Saving per set. M. Cm. Fr. Fr. Fr. 1’60x52 5-52 13-72 8-20 2’00x56 8’10 19-48 11-38 2 20x58 9-37 22-54 1297 The cost of impregnation by the Gerlache process works out at 4-02 fr., 5-85 fr., and 6-93 fr. per set, according to size, in which case the saving would be 9-70fr., 13-43 fr., and 15-61 fr. respectively. Shot-Firing from the Surface. In the Colliery Engineer Mr. Clark B. Carpenter describes the use at the Hamilton Mine, in Kansas, of an electric firing device operated from outside. The system depends upon the action of a so-called spark box for its success. The operation of the plant at the Hamilton Mine is as follows :—There are two leads of No. 10 B. & S. copper wire extending into the mine, and one common wire or return. One lead wire goes to the east side and the other to west side. The common wire splits at the bottom into two wires, one to the east and the other to the west side. The lead wires and the common wires are conducted through an iron conduit down the shaft, and are connected to a three-pole switch located about 30 ft. from the shaft bottom. Another 6 ft. flexible gap switch is located some 120 ft. further in the mine. These two switches are to serve as pro- tection from lightning, as well as to prevent the prema- ture firing of shots during the day while the miners are in the mine. A copper ground wire, which extends through the entire mine, serves as a protection from accumulated static charges. From this gap switch the wires extend to the east and west sides of the mine. The wires are carried on insulators for a part of the distance, but for a large part of the way they are allowed to rest on the floor, with pieces of slate to protect them from the cars, and to keep them from coming loose. The ground wire is generally carried under the head of one of the rails, and is connected to each of the spark boxes by a switch beneath the box. The spark box is the controlling factor in this system. It is a mechanical device which controls the passage of the firing current, and insures that the shots connected to the box nearest the shaft, on either side of the mine, shall be fired first, and that each box shall operate in turn. This consists essentially of a spark box solenoid A, which raises and drops the plunger F, depending on whether the current is or is not passing through it; the trigger G; the lead wires H into the box D, out of the box to the shooting circuit, and I, to the next box; the common wire E; the conducting lever B; and the con- necting plates C and J. In shooting position, the arrangement of the parts is as shown by the accompany- ing drawing. The current enters through the lead wire H, flows through the part B, through J, and out through D. A shunt is run from D to the solenoid and back to the common wire E; B is held against J by a spring not shown in the drawing. When shooting, the current is turned on, the solenoid is excited and pulls up the plunger F, allowing the trigger G to fly out, pulling B around into a position such that when the circuit is broken, the base of the plunger in falling will hit B, and press it down against C, thus making the connection to the next box. The solenoid, being connected to the wires of the shooting circuit, is not again excited when the circuit is again closed. The path of the current in Spark Box. i i i *0) i Lead Wire fn Common W/re_____ LeadWire to ttexf 6or the new position of things is H to B to C and out through I. The trigger G projects outside the box after firing, and must be pushed back to its original position before the box can be operated again. This protects the shot- firer from a premature shot. The spark boxes are located along the main east and west entries. One box supplies each front and back entry on either side of the main entry. . The lead wire and the common wire are covered by the same insulation so that the insulation must be cut in order to connect the room wires. The shots are fired in the evening after all the men have been checked out of the mine. It is the duty of the shot-firer to fire the shots as well as to see that there are no men in the mine, and also that the wiring, spark boxes, and other apparatus are in good order. Before firing the shots he must go through the mine and con- nect the shot wires to the spark boxes, and at the same time throw out the ground switch beneath each box. He then comes to the shaft, throwing in the 6 ft. flexible gap switch and the three-pole switch, and comes to the surface, where he starts the dynamo, tests the circuit, and fires the shot. The shots are tested by passing a current from a single dry cell through the circuit supplied by each spark box, before the shots supplied by that box are fired. The shots are fired alternately on the east and west sides of the mine. After completing the firing, the shot-firer goes imme- diately into the mine, pulling the three-pole switch and the 6 ft. flexible gap switch, and then he goes to each spark box, and disconnects the firing wires and throws in the ground wire switch. This completes his duty, unless he notices any fall of rock, or, in extreme cases, fire, and these he should report when he reaches the top. The common ground wire through the mine was made necessary by the fact that a good ground could not be obtained in the mine. When the apparatus was first installed there were two or three premature explosions, the cause of which was hard to explain, but which was finally attributed to the accumulation of static charges on the spark boxes and the lead wires. Thereupon the ground wire, which is an uninsulated copper wire, trolley wire size, was installed. The boxes are connected to this ground wire by a switch beneath the boxes. The wire is grounded at the top of the shaft. It has proved abso- lutely satisfactory, and there have been no further premature explosions. Current of 20 to 30 amperes at 175 volts is used. It is probable that not more than 50 to 75 volts is neces- sary to produce sufficient pressure to overcome the resistance of the firing circuit; 0-4 ampere is sufficient to explode a fuse; while 0-9 ampere is sufficient to work a box. THE GERMAN AND AUSTRIAN COAL AND IRON TRADES. We give below further extracts from German periodicals that have reached us, showing the course of the coal and iron trades in Germany and Austria :— The brown coal producers of mid-Germany having raised the price of briquettes by 1 mk. per ton from June 15, the coal merchants’ associations have advanced the price of best briquettes from 83 pf. to 90 pf. per cwt. from July 1. The Galvanised Sheet Iron Sales Association has raised the price of galvanised sheets by 20 mk. per ton from June 14, so that the cost to wholesalers is now 68-20 mk. net, ex Oberhausen or Morgenroth. Smaller purchasers will have to pay 75-80 mk., according to quantity and the state of the freight market. The Vereinigungsgesellschaft Rheinische Braunkohlen- bergwerke m. b. H., Cologne, has acquired mining rights for brown coal over an area of 4,134,204 sq.m. at Geilenkirchen. Rhenish-Westphalian Iron Market. At the end of J une nearly all the iron works were fully- occupied with war orders; and since the number of workmen had been considerably reduced by further drafts for the army, female labour was introduced into many departments. Prisoners of war have also been tried in many places, but not with great success, owing to their unwillingness to work. In the pig iron market business is very active, enormous quantities of material (high-grade iron, in particular) being wanted for making shells. The deliveries are about 60 per cent, of the participation, and are probably not capable of any appreciable increase. High-grade pig is almost com- pletely consumed in the home market, whilst the lower grades find a good sale among neutrals. In semis, business is about the same as before, but prices were recently advanced for the third quarter of the year, and now run:—Basic pig, 102-50 mk. per ton; blooms, 107-50 mk.; billets, 115 mk.; and plate bars, 117-50 mk. —all with an additional 15 mk. for open hearth material. The chief export market, Italy, is now closed. Scrap is easier, owing to the large quantities produced in the manufacture of shells; and as most users are covered for some time ahead, they are not eager to make new purchases. The railway sales have also thrown a good deal of scrap on the market, and weakened prices further. Girders and sections are quiet, owing to the stagnation in the building trade, and no recovery is expected, though a little more business is doing with neutrals. The increased cost of production has forced prices up, so that girders now cost 130 mk. ex Dieden- liofen, with the usual rebates. Bar iron is in active request, chiefly for war purposes, merchants having laid in heavy stocks, which they must dispose of before buying further. The basis price for ordinary basic hoop iron (mild steel) for the third quarter is 145 mk. ex Oberhausen; but higher rates are paid for quick delivery. Owing to the scarcity of brass, various articles for army use are now being made of hoop iron or steel—detonating caps for shells having, for some time past, been made in this way, instead of from copper or brass. The Hoop Iron Union has put up prices for the third quarter to 160 mk. ex Oberhausen for ordinary basic iron, with the usual additions, and a supplement of 20 mk. for open hearth metal. The cold rolling industry is engaged almost exclusively on war orders, and is well occupied. The plate market continues very favourable, the mills being unable to fill all the incoming orders by the dates required. Prices have an upward tendency, about 150-155 mk. being obtained for heavy plate, and 170 mk. and over for fine plate. Pipe manufacturers are also very busy, both on army orders and for neutral countries, the latter finding it very difficult to obtain supplies from any other belligerents. The union is to be prolonged until the end of August, pending a con- sultation for its renewal for a longer period. No sales are being made, except for early delivery. The wire market is also favourably situated, the works being able to dispose of their restricted output at once. Rough rolled wire of ordinary basic material costs 145-150mk., but large contracts at lower prices, from early in the year, are still running. The export trade is suffering from the prohibition, but permits are obtainable in most cases, and large consignments have been forwarded to neutrals. Drawn bare wire costs 160 mk.; galvanised, 200 mk.; and wire rods, 170 mk. per ton, as basis prices for the home district, with the usual additions. Makers of barbed wire have as much as they can do to supply the army. German Iron Ore and Iron Prices. Siegerland spathic and brown ironstone, 18-50 mk. per ton; roasted ore, 25-50mk.; Nassau red ironstone, 20-50 mk.; haematite pig iron, 115 mk.; foundry pig I., 94 mk.; III., 89 mk.; spiegeleisen, 98-50 mk.; steel pig, 88-50 mk.; cupriferous steel pig, 102 mk.; Luxemburg foundry pig III., 74-50 mk.; basic Bessemer steel ingots, 102-50 mk.; blooms, 107-50 mk.; basic open hearth blooms, 127-50 mk.; billets, 115 mk.; plate bars, 117-50mk.; iron sections, 130 mk.; bars, 140 mk •