1348 THE COLLIERY GUARDIAN December 31, 1915. suffer, particularly if they are a little insensitive to start with—which is not at all uncommon. In speak- ing of sensitiveness, I mean, of course, sensitiveness to the impulse of a detonator. Supposing we had two 6 ft. holes, one charged with insensitive and the other with sensitive gelatine, the chances are that the deto- nation of the insensitive would be incomplete, and that a plug, or even two, might be left at the bottom of the hole. The sensitive explosive would, of course, be com- pletely detonated. Moreover, an insensitive explosive responds very quickly to bad charging. What I mean is this : that supposing from some cause or other—say, a badly-drilled hole—it is difficult to get the cartridges into actual contact with one another by means of the tamping rod; in other words, there is an actual air gap between individual plugs. A good sensitive explosive will easily bridge the gap on detonation, but an insensi- tive one may not do so, and the result is obvious. You may ask how sensitiveness is attained and regulated, 'but my reply is that this is a very valuable trade secret. This much I may say, however, that the use of a larger detonator is to an extent a corrective. “ Bad charging ” (d) has already been referred to under .insensitiveness. An air gap is occasionally quite unavoidable, and I am of the opinion that sometimes sufficient care is not always taken to squeeze the cart- ridge home. To get the best results, the cartridges should be in actual contact. Let me repeat again that during all the experience of Mr. Waters and myself with holes actually charged up by us, we have had neither a misfire, nor, let me add, have we ever had a partial explosion. Nowadays, one hears little of interposed cartridge of sand tamping — a practice which is very wrong. Some 10 or 11 years ago, somewhat elaborate experiments were made at the Langlaagte Deep with interposed tamping, but misfires could not be got. I now realise that the explosive then used was sensitive enough to overcome 'the “ inert gap,” but it would be different in many cases to-day. Damp Detonators. I have now to consider the effect of damp detonators (e). It is, of course, well known that detonators do deteriorate very badly when stored in a damp atmo- sphere, and manufacturers are insistent on this point. I assume that everyone connected with mining knows how detonators are packed, but for the sake of those who are not so connected, I may say that the top portion of each detonator is filled with coarse sawdust, which has to be removed by tapping before the fuse is inserted. This is not always effected without patience, and a grain or two of sawdust left behind will easily prevent the spit of the fuse reaching the detonating composition. This may in turn cause a misfire, with all the attendant dangers. Now, I do not wish to minimise the danger of storing detonators underground, but I do believe that with the class of detonators supplied to this market, these dangers are exaggerted. Some experiments were carried out at Leadville, U.S.A., viz. :— With fresh detonators there was complete detonation; 24 hours underground, incomplete detonation, i.e., a portion of the charge left in hole unexploded; 48 hours underground, incomplete detonation, with red fumes, showing that some of the charge had burned; 72 hours underground, cap exploded without detonating the charge at all; 144 hours underground, cap did not explode. Now, no particulars are given about these detonators, or about the explosives, but these results were so remark- able that I determined to imitate them with Nobel’s ordinary detonators as supplied to this market, and Modderfontein blasting gelatine. I strongly suspect that in the experiments quoted, the sawdust had been removed from the detonators, so, notwithstanding the fact that this would be highly unpractical, I decided to do the same. Detonators with and without their saw- dust were exposed for varying periods to an atmosphere saturated with moisture at a temperature round about 75 degs. Fahr. It would take too long to detail the experiments now, and, as a matter of fact, they are not quite complete yet, but quite sufficient is known to warrant certain definite conclusions. Detonators without sawdust, after three days’ exposure, behaved quite normally. On the fourth day there was a weakening, which gradually increased. After the third it would have been unsafe to use them. Right up to the 10th day, no deterioration could be detected in detonators with sawdust, but from the fourth day onwards great difficulty was experienced in removing the sawdust. Now, the effect of sawdust remaining in the detonator has already been referred to, but the experiment showed clearly that this and not the dampness was the real danger, so that it really comes back to the same thing, viz., that it is unsafe to store detonators underground for longer than a very limited period. It would be both simple and inexpensive to make it compulsory to have’ a special airtight box containing, say, two boxes of detonators permanently fixed inside the box which is intended to contain the fuse and detonators only. Stored in this manner, detonators should keep in perfect con- dition for months. Exudation of Nitro-Glycerine. So far my remarks on sensitiveness have had a clear and definite meaning, but there is another form of the same thing to which I wish to direct particular attention. The other kind of sensitiveness which I have in mind is due to exudation of nitro-glycerine. Normal well-made gelatinous explosives stand a great deal of rough handling, and they are fairly impervious to friction when enclosed in a wrapper. If this were not so, the accident rate would be appalling. When they exude nitro-glycerine, and the nitro-glycerine gets to the out- side of the wrapper—which is not at all uncommon—it is a very different story. Not only is the explosive in this state sensitive to friction, but it is dangerously so. No gelatinous explosives should show exudation three months after storage, otherwise there is something wrong with the manufacturing end. Long journeys by rail or wagon cause, or at least help on, exudation, because the irregular vibratory or shaking effect exercises pressure on the lower cartridges of the packet or case, and all gelatinous explosives tend to exude nitro-glycerine when gentle pressure is exerted. Then rapid alterations of temperature assist in the same direction. All of these causes can, to an extent, be overcome by increasing the percentage of collodion cotton, but it is just in respect of this very necessary adjustment that so many manufacturers fail. Explosives which show exudation on the outside of the wrapper should never be used. They should simply be returned to the maker. I am certain that exudation has caused many unexplained accidents. It is precisely for this reason that I deprecate the use of tamping rods sheathed with copper or any other metal. Tamping rods should be of wood alone. But the danger does not end with the charging. Exuding explosives may leave a smear of nitro-glycerine along the hole, and they may even leave a smear on the explosive itself. Naturally, the risk is increased if the cartridge is broken across to insert the detonator. When the burning fuse gets down to the hole, conditions may thus have been created which will give not a bad imitation of a so-called running fuse. This is not theory, but fact, as has been demonstrated. I have already referred to the danger of making the bottom cartridge—or, for that matter, any other cartridge but the top one—the “ primer,” but in order to set the matter at rest once and for all, lengthy series of experiments were carried out. It would take too long to detail the experiments, so I shall merely give the conclusions, which are very definite. It must be remembered, however, that the explosives supplied to this market are wrapped in two kinds of wrapper, viz., parchment and paraffined paper. The wrapping, for most of -the cartridge, is double, but slight differences in the diameters of the cartridges may make this wrapping treble or single ply at the overlap. In order to imitate mining conditions as nearly as possible, the cartridges in some cases were charged into a steel tube of suitable diameter, and tamped with sand in the usual manner. It was found :— (a) That ignition seldom, if ever, takes place from side spitting of the fuse, unless it has been very badly abused. The amount of abuse which fuse can stand will be referred to later. (b) That when ignition does take place it is caused by the heat of the smouldering fuse. Smouldering always takes place, no matter how good the fuse, and its effects are most marked about 2 in. behind the point where the powder core is burning. (c) Unwrapped explosive in direct contact with fuse is always ignited. This indicates the great danger of breaking cartridges. (d) Paraffined wrappers offer more resistance to the igniting effect of fuse than parchment. (e) When the contact of the fuse is at the single ply ignition takes place more readily than at double ply, i.e., at the overlap. (/) Exudation enormously increases the risk of ignition. Accidents not infrequently take place through attempting to force a cartridge into a hole which is in reality too small for it. When such a cartridge is in an exuding state, the risk of an explosion is very great indeed. In this connection, the Modderfontein factory has for a number of years put a number of 1 in. size cart- ridges into every 10 lb. packet. The smaller size cartridges are, of course, used for the bottom of the hole. The practice, it is hoped, will soon become universal. When on the subject of sizes, I might suggest that it is high time we adopted definite standards of length and diameter of cartridges. The matter is not so simple as it looks, but standardisation is badly wanted. Re-blasting. I next quote the text of a note handed me by Mr. W. Waters:—‘‘I frankly confess that the dangers of re-charging and re-blasting holes or sockets of holes while the rock is hot from the original blast are not fully appreciated by miners. When a cut has completely failed to break, the miner knows that time must be lost, and resigns himself to the state of affairs. He, in this instance, usually waits long enough for the rock to cool down, this cooling down being assisted by the hose-pipe water. What I wish to call special attention 'to is the common practice of cleaning out the bottom of a cut— which may be broken fairly w’ell, but not quite clean. The miner in this instance usually re-charges either one or two of the cut hole sockets with from two to four cartridges, and lights up same when firing the ‘ round,’ these socket holes being arranged to explode before the ‘ easers.’ As mentioned above, when the cut com- pletely fails at the first blast, the miner resigns himself to the loss of time. When, how’ever, he finds that the cut has come fairly well at the first blast, and only requires a few plugs to clean it out, he is often in a hurry to blast his round, and thus, we fear, re-charges the cut sockets before the rock has sufficiently cooled down. The exploding heat required for blasting gelatine and gelignite is roughly about 400 degs. Fahr., and it may take some seconds, or even minutes, before the explosive in these socket holes heats up to the exploding point. Thus the miner may be lighting up his last holes, namely, the ‘ lifters,’ or perhaps be just walking away from the face, when the cut sockets prematurely explode. The usual reason assigned for such an acci- dent is a ‘ running fuse.’ I think otherwise.” Cantridges, as we all know, are frequently found among the broken rock, and this is particularly notice- able in the coal mines. Dynamites, owing to their want of “ cling,” do not hold the detonator well, so it is liable to get detached from the primer. This is one of the principal reasons for the finding of unexploded cart- ridges, but another is “ cut out ” shots, which are difficult to avoid, unless the fuse is extraordinarily regular. Now, some years ago certain manufacturers introduced coloured wrappers in order to render the cartridges more conspicuous. It would be very interest- ing to know how the claims for the coloured wrappers work out in practice. Of course, in coal mines it is very difficult to pick out unexploded cartridges under- ground, consequently a large number are caught on the surface belt. It is generally known that nitro-glycerine explosives freeze at 8 degs. Cent., and when in that state they are very dangerous indeed, and will easily explode when touched with a pick or shovel. In colder countries, particularly in Canada, accidents from this cause are very common, notwithstanding the fact that explosives are invariably thawed in an approved apparatus before use. The perfect “ cheesa ” stick has still to be made. A reliable stick should have the following properties — ! (a) It should burn with a good strong flame without ejecting bits of incandescent material. (5) The flame should be strong enough to keep alight when the charges detonate. (c) It should not be put out by a few drops of water. t (d) It should not go out when dropped from, say, a height of 3 ft. on its long axis. (e) It should comply with the Government speci- fication with regard to nitrous oxides. These tests do not appear to be very stringent, but they have so far proved very difficult of attainment, and failure of any one may lead to serious accidents. Teste of Fuses. Undoubtedly a good many accidents are caused by fuse, but, on the whole, the fuse now being supplied to this market is of excellent quality, and is fairly free from such gross defects as “interruption of powder core” and “side spitting.” It is also sufficiently waterproof for all our local conditions, and some of these are extra- ordinarily severe. Now, just at this stage, let me say that, though I have had hundreds of thousands of coils tested under all sorts of severe conditions, I have never come across a so-called “ running ” fuse, or anything the least like it. In order to see if burning speed could be influenced by harsh treatment, a certain well-known brand of fuse was subjected to the following tests. These tests were carried out specially for this paper :— (a) It was hammered almost flat. (b) It was hammered almost flat, turned on its edge, and again hammered flat. (c) It was drawn into numerous tight knots. (d) It was drawn into numerous tight knots, hammered flat, and untied. (e) It was twisted strongly in the direction opposite to its natural twist. It was found that in no instance was the burning speed affected in the slightest degree. I have not carried out these experiments to show that fuse can with safety first of all be used for tying up bundles, picks, and jumpers, and then afterwards be used as fuse, but •to show what an amount of abuse it really can stand— but the practice is dangerous. Fuse should be treated with the greatest care, for all varieties cannot withstand these drastic tests, but even the ordinary practice of tying up “ miner fashion ” puts a very severe strain on it. It is not generally realised how severe on the fuse covering our climate is. Owing to the absence of moisture in the atmosphere, the waterproof coating tends to become dry and crack. This of itself'tends to side spitting, but if it is used as parcel twine before it is used as fuse, this tendency will become accentuated. The general test to which fuse is subjected is to immerse a coil in a bucket of water with the ends pro- jecting, leave it there from two to 24 hours, then see whether it will burn through. Most fuse will survive this ordeal, but the only way to really try it out is to subject it to tests which are the exact counterpart of practice. It is not generally known that fuse burns slower at this altitude than at sea level, and I have often wondered whether miners unconsciously allow for this in the deep levels. Panama Fuel Depots.—The Acting British Consul at Colon has forwarded a copy of a circular, issued by the Governor of the Panama Canal, giving an outline of the policy decided upon by the Canal Administration in regard to applications by coal and fuel oil companies for the establishment of private coal and oil depots on the Isthmus. While the United States Government is establishing plants for supplying coal, fuel oil, etc., to shipping, it is not intended to prevent private interests from selling coal and fuel oil to shipping. Coal and fuel oil may be brought into the canal zone by individuals and com- panies without the payment of duty, unless such coal or fuel oil is disposed of for use outside the canal zone, and within the territory of the Republic of Panama. The Government plants are being laid out so as to afford ample wharf room, and to provide ample modern coal and oil handling machinery, and, so far as coal is concerned, a certain area at each plant has been set aside for the private storage of coal, which will be served by the Government’s coal handling machinery with the same"convenience as the area occupied by the Government coal pile. The Canal Administration will reimburse itself for cost of plant, etc., at rates apportioned among all who use these facilities. On account of lack of storage space and coal handling machinery, no arrangements can be made that will permit individuals and companies participating in Panama Canal coal business prior to the completion of the permanent plants. The Cristobal plant will be completed early in 1916, and the Balboa plant next July. As regards fuel oil, the Government installations are completed, including cribs, oil handling plants, pipe lines, manifolds, etc. Applications can be made at any time for the lease of lots in the tank farms at Mount Hope and Balboa.