Charging. — Where gunpowder is used it is made up in pellets of the requisite diameter, each weighing four ounces. The pellets are made with a hole through their centre, into which the fuse should be placed. The end of the fuse, which should be cut with a slope, is doubled and drawn back tight, as shown in Fig. 75. A sufficient quantity of gunpowder to do the required work is gently pushed to the back of the hole. The pellet carrying the fuse is inserted, and after being pushed home, the hole is stemmed, as already described. The length of fuse to be used will depend on the time required to retreat to a place of safety. Under any circumstances the fuse should reach a few inches beyond the mouth of the hole, which should be stemmed out to the very mouth.

When squibs are used, the pellets of gunpowder are first pushed back into the hole, then the pricker is inserted and pushed back so as to overlie the charge. The stemming is now pushed in about the pricker until the hole is filled. The pricker is now withdrawn and the squib put into the opening thus left.

In preparing to charge with a high explosive a clean-cut end of the fuse is gently inserted into the detonator until the powder core reaches the detonating compound. The copper tube is then crimped tightly round the fuse by means of a pair of pliers constructed for the purpose. Care must be taken while performing this operation to see that no pressure is exerted by the pliers on the bottom part of the detonator which contains the detonating compound. High explosives are made up in sticks or cartridges of various sizes to suit different conditions, each stick being enclosed in a paper wrapping. Before fitting the fuse and its attached detonator into the stick of explosive, called the primer, which goes on the top of the charge, the paper covering is unwrapped from one end. A hole is then made in the explosive by means of a piece of wood shaped like a pencil. The detonator is pushed about two-thirds of its length into this hole and the paper gathered together and tied round the fuse with a piece of string (Fig. 76). When the hole is in damp or wet ground it is advisable to smear the junction of the detonator and fuse with tallow to prevent a possible misfire caused by the damp penetrating to the detonating compound. After the necessary amount of explosive has been pushed gently to the back of the hole, the primer containing the detonator with the fuse attached is next inserted. Stemming is now commenced, the first six inches of stemming material being pressed in carefully ; after this greater force can be used in ramming in the remainder.

Fuse. — As used in coal mines fuse consists of a central core of mealed gunpowder inclosed in two or more layers of prepared yarn and surrounded with waterproofed tape. For wet work the outer covering is made of guttapercha.

It is usually made to burn at the rate of about two feet per minute, and it is extremely desirable that this rate should not vary more than about ten per cent, for the same fuse. It is quite possible to get considerable flame from ordinary fuse, and for this reason it is not safe to use it in fiery mines.

When blasting in fiery mines is necessary, the explosive charge is fired by means of an electric current acting on a specially made detonator. These detonators are similar to those already described, but they contain two insulated copper wires, held in position by a plug of sulphur or bitumen. The ends of these two wires are connected by a very fine piece of high-resistance wire. When current is passed through this wire, it heats it to redness, and thus causes the ignition of the detonating compound. A section showing the various parts of an electric detonator is given in Fig. 77.

The current to fire the detonator is obtained from a battery, or more commonly from a small magneto designed for the purpose of shot firing.

Handling Detonators. — It is well to remember that the fulminate of mercury used in detonators is an extremely sensitive substance and explodes with great violence. For these reasons the detonators should be handled with the utmost care. They should not be allowed to fall nor be struck against any hard substance. They ought not to be left on the floor nor in any place where they might be trampled on, and on no account should any attempt be made to pick out the composition. Small as the amount of explosive appears to be, there is more than enough in the weakest detonator to smash the hand that holds it into pulp should it be so held. They should be stored by themselves in a dry place, and kept well out of contact with other explosives until such times as they are actually to be used. Care must also be taken to see that they are not exposed to undue heat. They are usually packed with dry sawdust, which should be shaken out or removed by light tapping before the fuse is inserted.

Explosives Order. — The Coal Mines Act 1911 enacts that all explosives must be provided by the mine owner and the price, if any, charged by the owner to the workman. Rules to control the distribution, handling, and firing of explosives are laid down in an Order (No. 953) issued in 1913. These rules must be familiar to all persons whose duty it is to use explosives in the mine, and they ought to be carefully followed out as they have been framed with the object of lessening risk.

Tubs. — In the early days of coal mining the coal was conveyed from the face to the shaft in baskets, which were then carried by women. With the gradual increase in the depth to which coal was worked, it became necessary to work larger areas from each shaft, and the conveyance of the coal became more important because of the longer distances it had to be carried underground. This gave rise to the employment of small wagons run upon a track, and as a means of conveyance it has gradually developed. At first the wagons (also called tubs, hutches and corves) were moved entirely by manual labour, but now we find horses and mechanical haulages largely employed for this work. The removal of the coal from the face of the workings to some suitable station underground is still frequently done by lads or young men, especially in thin seams. Since this method is much more costly per ton-mile than horse or mechanical haulage, its use is limited to short distances near the face, where there would be some difficulty in adopting any other method.

The wagons or tubs are generally of rectangular shape, their length being from one and a quarter to one and a half times their width. The depth of the body depends largely on the height available underground, the size as a whole being determined by the thickness and inclination of the seam where they arc to be used, together with the circumstances under which they will be handled.

Tubs are constructed either entirely of wood, or of light steel plates forming a body which is fitted to an underframe of wood. There is an increasing tendency to use steel in their construction in order to prevent small coal passing through the joints of the wood cleading, as it does when the body is of wood. This small coal is shaken out along the haulage roads and ground into fine dust by the passing traffic, thus creating a source of danger should the mine be dry.

Steel wheels are used, and should be of as large diameter as circumstances will allow. When running in sets or rakes the tubs are coupled together by couplings attached to each end of a strong metal drawbar, which is securely bolted to the frame of the tub

In most cases the tubs for use in thin seams have a carrying capacity of from 9 to 10 cwts., and weigh from 4 to 4½ cwts. when empty. Tubs for use in seams over 4 feet thick may hold from 10 to 20 cwts. or even more, their tare (empty weight) increasing with the capacity. A patent tub with adjustable end, made by the Butterley Co., is shown in Fig. 78. The capacity of a tub may be found by calculating the volume of the box in cubic feet and multiplying by 48. This will give the weight of coal that it will contain in pounds, since 1 cubic foot of broken coal weighs approximately 48 pounds.

Track. — Where possible the main levels should be given a slightly rising grade, about 1 in 130. This ensures good drainage and makes haulage easier because of the slight inclination in favour of the load. The gauge of the track is fixed to meet the conditions of the mine, and may be anything from 20 to 42 inches, or in exceptional cases even more. A broad gauge keeps down wear and tear, while a narrow one makes the negotiation of curves easier. It is desirable, however, to avoid curves wherever possible.

The Mines Act requires a clear space of two feet at one side of the road if the road is used as a travelling road and the speed of the haulage is in excess of three miles per hour.

All roads on which mechanical haulage is used must be provided with refuge holes at intervals of not more than 10 yards. If the gradient does not exceed 1 in 20, and a two feet space is provided, or if the speed of haulage is not more than three miles an hour, the intervals may be extended to not more than 20 yards. On roadways where the haulage is worked by animal power, refuge holes must be provided at intervals of not more than 25 yards.

The rails in common use belong to three distinct classes: (a) Flange rails, (b) Bridge rails, and (c) Flat rails. Sections of these are shown in Fig. 79. Flange rails are used for the most part on main roads, and arc joined together by means of fish-plates and bolts and secured to sleepers of wood or steel. When wood sleepers are used the rails are fastened to them by dogs or spikes. When the sleepers are of steel the rails are fastened to them by clips.

Bridge rails are generally used near the face or where the traffic is light. When laid to form a track, the ends are butted together, and fastened to wood sleepers by plate nails.

Flat rails are not extensively used, but have an advantage where light tubs are employed on grades of 1 in 5 or steeper, as the tendency for loose grit to lie on them causes greater friction and allows the tub to be brought down a fairly steep grade by the aid of sprags.

The weight of the rail, irrespective of its shape, depends on the nature of the traffic, but there is nothing gained by using rails of too light a section. On main haulage roads rails weighing from 24 to 50 lbs. per yard may be used, whereas in side roads near the face 10 lbs. per yard may be ample. The lengths vary from 4 feet to 18 feet or more, the longer lengths being used on main roads, the shorter on side roads.

The sleepers to which the rails are attached are best made from good timber, and are all the better of being treated with creosote before use. They are placed under the rails at intervals of from 2 to 3 feet.

On all main roads it is necessary to provide for traffic being diverted to and from the various parts of the workings. This is done by placing points and crossings in the track where branches diverge. (See Fig. 80.) On main roadways where the traffic is heavy, the crossings are usually formed by cutting and bending the rails, as is done in the case of railway track. For lighter work a cast-iron crossing is often used, but it is difficult to get a straight, well-fitted connection between them and the rails, besides they soon work loose and require constant attention.

Rails, crossings, and sleepers should be removed at once from abandoned roads and carefully stacked in some safe and accessible part of the mine. The too common practice of leaving the track lying in abandoned roads until it is required elsewhere, frequently leads to loss and occasionally to accidents, as an abandoned road is rarely examined or secured to the same extent as a working one; and no excuse should be furnished for entry into such places.

Haulage. — The haulage of coal from the working face to the bottom of the shaft may be carried out in two or more stages. It is customary to describe those haulages which start from the pit-bottom and run to some terminal point in the workings as main haulages, while the subsidiary systems that feed them are described as secondary haulages. The tubs containing the coal are first brought out from the various side roads, often by manual power, and collected at some suitable point. They may then be removed from that point by horses or by some mechanical appliance to the terminus of the main haulage. After being transferred to the main haulage, they are conveyed by it to the shaft bottom.

In haulage the load may have to be moved (a) along the strike or level course, in which case the only resistance to be overcome is the friction of the tub itself and the further frictional resistances between its wheels and the track; (b) uphill against the force of gravity, in which case the work consists of overcoming the force of gravity as well as the frictional resistance; (c) downhill with gravity in favour of the load, in which case only the friction has to be overcome. This may be entirely overcome by gravity, or it may simply be diminished to the extent of the aid afforded by gravity, the gradient being the determining factor of whether a tub will run by itself or not.