466 THE COLLIERY GUARDIAN. August 28, 1914. upon the position in which it is to be placed. Obviously, signboards that must be read from a distance should be larger, in size and lettering, than those to be read at close range. For general use underground signboards should be about 3 ft. long and 1 ft. wide. In close places, however, it would be advisable to make them smaller. They may be made of wood alone, wood covered with sheet tin, iron, or copper, or of solid sheet copper or steel. The background may be painted white. However, white enamel finish is better, as it may be more readily cleansed. The lettering may be in black. Stencils for letters or complete sign patterns may be made with little trouble from stiff cardboard. Tin or copper stencils are more expensive, but they will last a long time. Stencils and enamelled steel signboards are procurable at small cost from various manufacturing companies. An excellent signboard is made of rolled steel, and has the colours of the background and letter- ing fused. MISSFIRES IN SINKING SHAFTS.* By K. Jentsch. It is only in rare instances that missfires are due to defects in the electrical appliances used for shot-firing, though they are liable to fail as the result of rough handling, or if employed for firing a larger number of shots at a time than their capacity warrants. Ordinary insulated cables, too, are very reliable—more so, indeed,, than those protected by a sheathing of steel wire, these latter being liable to fractures of the copper core when the freely-suspended length exceeds about 1,000 ft., apart from the greater difficulty experienced in locating injuries in reinforced cables, which are also very troublesome to handle on account of their heavy weight. Insufficient insulation of the wires in the igniters is one of the most frequent causes of missfires, and it is desirable to test the resistance of each igniter before use, so that only such as possess approximately equal resistance (in the first decimal place) will be used together. Since a definite time elapses before the platinum wires of the igniters begin to glow and ignite the charge, it follows that, if any of the igniters have a greater resistance than the others, they will glow and fire their charges the soonest, and, the circuit being destroyed by the exploding charges, the other charges will not be fired at all. Fig. 1.—Wrong Way to Join Wires. Figs. 2 and 3.—Two Correct Methods of Joining Wires. When fuses and electrical time firing are practised in wet shafts, the condition of the fuse should be carefully examined, owing to its tendency to crack during storage, and permit access of water which extinguishes the fuse. Cheap fuses with only a single covering layer are often badly made, the powder being soft and mealy and liable to burn out at the sides in defective spots. Moreover, these fuses are easily crushed in the operation of stemming, thus causing delayed shots and missfires. Weak detonators will not give rise to real missfires, only to imperfect detonation, the charge fizzling, instead of exploding, and liberating injurious nitrous fumes. A No. 3 detonator is sufficient for dynamite, though Nos. 5 to 6 are mostly used; safety explosives requires a more powerful detonator, such as No. 8. Again, provided the shot-firer does his work properly, there can be no danger of missfires resulting from the absence of fulminate in any of the detonators, or from frozen cartridges. Improper Treatment of the Explosives and Firing Appliances.—The sawdust, with which the detonators are filled to protect them from moisture, must be care- fully shaken out before the fuse or igniter is fitted on, otherwise there is risk of the detonator and charge not being fired, although the fuse has acted properly. Owing to the susceptibility of the igniters, fuses and detonators to moisture, it is necessary to make water- tight connections, preferably by covering the joints with gutta-percha or tallow. In charging the shot-holes, any sludgy water in the hole is liable to get between the cartridges and stop the propagation of the ignition ; and since this risk increases with the time consumed in charging and stemming the holes, it is desirable that the operation should be shortened by employing a sufficient number of men to do the work. In very wet and sludgy shafts (e.g., in the hunter sandstone), metallic shells to hold the cartridges should be used, these being inserted in the holes as soon as the drilling tool is removed, care being also taken to wedge them in, so as to prevent them being forced out by an upward rush of water. To avoid the risk of distortion, it is advisable to slip the cartridges into the shell beforehand. Of course, the use of such shells is disadvantageous from another point of view—namely, that the effect of the shot is impaired by the fact that the cartridges are not in direct contact with the sides of the hole. Injury to the cable may result in short circuiting between the two wires, so that only a portion of the current reaches the bottom of the shaft, and is, there- fore, too weak to fire a large number of shots at a time. Such injuries may be detected by connecting the ends of the two wires to a glow lamp, and noticing whether the latter becomes fully incandescent at once. The injuries,if any, will generally be near the bottom endof the cable, this being the portion most exposed to the effects of the firing. To prevent loss of time, the cable should be tested after each blast, and repaired before the next * Gluckauf. one is ready for firing, the test being, of course, repeated just before use, to detect any short circuiting that may have arisen in the meantime. Imperfect connection at the ends of the wires is a frequent source of missfires. Fig. 1 shows a form of connection particularly liable to give bad results, whilst figs. 2 and 3 illustrate the proper way to connect the wires, by twisting the ends together for a length of about 2 in. They should first be scraped clean, to remove the oxidised or dirty outer skin and give a good contact of metal to metal. In very wet shafts these joints should be protected by slip-on sleeves filled with paraffin wax or other soft insulating material, to prevent loss of current by leakage in contact with the wet shaft sole or water. Care must also be taken to prevent bare or imperfectly-insulated wires from crossing one another. The men must also be careful not to break any of the wires when leaving the bottom of the shaft, as this would lead to the danger of partial missfires when the shots are fired in groups. Finally, the practice of firing instantaneous and time- fuse shots at the same time should be avoided, since the first named may pull the detonators out of the time-fuse shots and cause them to missfire. Unsuitable Current.—It is erroneous to suppose that a relatively high tension is necessary to give a high quantity of current in electrical shotfiring; for excessive tension may lead to short circuiting, and so defeat its own object, whilst Lisse has stated that excessive amperage may fuse the platinum wires of the igniters before they have had a chance to glow. The author has not been able to confirm this statement, but finds that missfires are more frequent with a magneto machine than with a lighting current. This is probably due to the fact that the shot-firing machine requires more care and attention than are always given in the rough-and- ready work of shaft sinking, and besides needing a skilled operator, will not fire more than a certain number of shots at a time, missfires resulting when attempts are made to overload the machine. On the other hand, current of insufficient voltage will be too weak to fire the shots. In the case of, say, 20 shots in series, the line resistance will be 20 times that for a single shot. If divided into two circuits the resistance of the line decreases to one quarter, and the amperage increases four-fold, the length being halved and the section doubled. Hence, a current that would be too weak under the first-named conditions may be strong enough in the second case. Opinions differ as to the minimum amperage for shot-firing, some regarding 2 amperes as sufficient, whereas Humann proposes 5 amperes as the minimum for one igniter. A good deal, however, depends on the resistance of the platinum wires. The internal resistance of the source of current must also be taken into consideration, this being low with series coupling and high with parallel coupling. Series coupling of the shots gives the best guarantee against partial missfires; but is not applicable in all cases, and has sometimes to be replaced by coupling in parallel groups (figs. 4, 5 and 6). In these circumstances uniform distribution of current must be provided, or missfires will result. According to Kirchhoff’s law, the distribution of a current in a number of circuits is in inverse ratio to their resistance. Thus, in shotfiring, the circuit with the smallest number of shots (say 5) will receive the largest amperage, and that with the greatest number (say 10) the lowest. The consequence will be Fig. 4. Thirty charges coupled up in series. Fig. 5. Two groups of 15 charges in parallel connection. AN , J 7; Fig. 6. Parallel connec- tion : 3 groups of 10 charges. that one-third of the total current will be distributed among 10 shots in the latter case, as compared with two-thirds of the current among five igniters in the former. It is therefore desirable to make the groups as uniform in number as possible, and not merely according to the kind of shot-hole ; otherwise the shots round the edge of the shaft bottom will be liable to missfire. In such event, however, the danger is not very great, since the detonators are not rendered useless, and therefore the shots can be fired later. Frequency of Missfires.—Missfires may be divided into three classes: those in which the igniter fails to act; those in which the igniter is useless, but the detonator remains intact; and those in which the detonator does not ignite the explosive properly, if at all (whether through being too weak, or the cartridges frozen, damp or in imperfect contact, or again through the shot-hole being prematurely destroyed by another shot.) Where time ignition is the rule, missfires of the last-named class will be more frequent than when instantaneous firing is practised. Missfires due to faulty grouping will not occur where the shots are coupled up in series, though in the latter case a weak machine may fail to fire certain of the shots provided with igniters of low resistance. It has been stated that, in favourable circumstances, the proportion of missfires, with elec- trical shotfiring, sometimes amounts to 6 per cent., whilst in very wet shafts as many as 80 per cent, of the shots may fail to go off. The chief cause is to be found m an unsuitable grouping of the shots, and in failure to handle the shotfiring machine properly ; but the percentage of missfires from this cause should not exceed about 1 per cent, on the average. The best manner of clearing up missfires when once these have occurred depends on the kind of missfire to be dealt with. If they merely result from failure of ignition, the simplest remedy is to fire them off again. When the detonators are intact, though the igniters have become useless, the charge should be left in the hole, and any fresh holes bored near by must be arranged so that the drills will not strike the existing charge. Shots which merely fizzle, without actually exploding, are dangerous on account of the poisonous gases given off, but if the men clear out as soon as the disagreeable fumes are perceptible no serious risk is likely to be incurred. Imperfect shots, due to slow combustion of the detonating cartridge, or the presence of sludge between the cartridges in the shot hole, are harmless, inasmuch as the detonators are no longer present. The cartridges may therefore be taken out of the holes and used over again. Finally, the presence of fragments of explosive charges in the debris, in the case of time fuse firing, is not so dangerous as might be supposed. The detonators will not be present, and since even ordinary dynamite cannot be exploded by a stroke from a pick or shovel the risk is actually small. OBITUARY. Death of Lord Merthyr of Senghenydd. It is with very great regret that we have to announce the death, which occurred yesterday, at Newbury, Berkshire, of Lord Merthyr, better known as Sir William Thomas Lewis. We cannot speak now of the full debt which South Wales and the mining industry owed to this great captain of indus- try. To do so would fill many columns of the Colliery Guardian. Lord Merthyr was bom at Merthyr Tydfil on August 5, 1837, his father being engineer of the Plymouth Iron Works at that place. His schooldays began when he was seven, and ended when he was 12 J. He was then apprenticed under his father, and worked 12 hours a day, but he made a point of walking two miles after work every evening to the school of a Mr. Williams. In 1855 he was engaged as assistant to the chief engineer to the Bute estate, whom he succeeded in 1867. Lord Merthyr was more prominently identified than any other man with the develop- ment of the South Wales mineral field in collieries, railways, and docks for the last 50 years. At the close of the strike in 1875, Lord Merthyr induced the Coal Owners’ Association to agree to the adoption of the principle of a sliding scale for the control of miners’ wages. This was the first attempt at practical conciliation in the affairs of employers and work- men in the South Wales coalfield, and it secured for South Wales for many years a period of settled trading conditions unprecedented in its history. When the great strike occurred in South Wales in 1898, Lord Merthyr still clung to the sliding scale principle, and its abolition led him for a period to dissociate himself from the other masters in the coalfield. Lord Merthyr’s services in the cause of industrial peace were very valuable, too, in 1900, when he was success- ful in settling the Taff Vale Bailway strike in August of that year. Soon afterwards he submitted a scheme for the for- mation of boards of arbitration for the prevention of railway disputes to the boards of the Taff Vale, the Bhymney, the x A. • Barry, and the Cardiff railway companies, but only the last- named company accepted the principle, and tae proposal was dropped. No less devoted was he to the cause of philanthropy and the alleviation of suffering among the miners and their families in South Wales, and the Mon- mouthshire and South Wales Miners’ Provident Society, which was founded in 1882, owed to him its origin and success. Lord Merthyr was knighted in 1885, received a baronetcy in 1896, and was created a baron in 1911. He had received a fair share of the honours of his profession, being elected, when only 26 years of age, an Associate of the Institution of Civil Engineers, becoming a Member at 30. In the same year he was appointed president of the South Wales Institute of Engineers. In 1880 he was elected president of the Mining Association of Great Britain, in 1910 he was elected president of the Iron and Steel Insti- tute, in succession to Sir Hugh Bell, and in the same year acted as president of the Institution of Mining Engineers. Lord Merthyr was a member of the Boyal Commission on Coal Supplies and Trade Union Commission. In latter years he was a moving spirit in the organisation of mining educa- tion in the Principality. He was an incessant worker, and seemed almost incapable of fatigue. He was chairman of the International Coal Company and of the Lewis Merthyr Consolidated Collieries Limited. The disaster at the Universal Colliery, owned by the last-named company, may not unreasonably be held to have hastened his death. He was also trustee for the debenture holders in Messrs. Burn- yeat, Brown and Company and the Bhymney Iron Company. Lord Merthyr, who was left a widower in 1902, leaves two sons and six daughters, and is succeeded in the title by his eldest son, the Hon. Herbert Clark Lewis, who married in 1899 Elizabeth Anna, the elder daughter of the late Major- General B. S. Couchman, of the Madras Army. Their son, William Brereton Couchman, born in 1901, now becomes heir to the barony.