Question 38.-What size of steam pipe would you lay from the receiver to a 30-inch cylinder engine?

The maximum velocity of the steam in the main steam pipe should not exceed 100 feet per second. The piston speed of the engine is not given, but taking it at 300 feet per minute, the size of pipe for a single cylinder engine would be found thus:-A 30-inch diameter cylinder has an area of 706 86, therefore 300 x 706.86 = 6.7 inches, or say 6 *7854

100 X 60 = 35°343 area in inches, and √ 35'343 inches in diameter. With a double-cylindered engine it would be 300 × 706·86 × 2

= 70·686 area in inches, and 70-686

*7854

100 X 60

= 9487 inches, or say 9 inches in diameter. If the engine is a compound one, only the size of the high-pressure cylinder need be considered in estimating the size of the steam pipe.

Question 39.-In a colliery where engines were working, and having 1,800 horse-power, what boilers would you consider necessary?

1800

200

diameter.

= 9 + 1 = 10 Lancashire boilers 28 feet long and 7 feet 6 inches

Question 40.-What height and size of chimney would you construct for such range of boilers?

10 × 5 = 50 feet area = say 8 feet diameter at the base, and to be well proportioned the chimney should be 25 times the diameter in height 8 × 25 = 200 feet high.

=

Question 41.-What is the nominal horse-power of a Lancashire boiler whose length is 30 feet and diameter 6 feet?

Question 42.-Are boilers better calculated to resist pressure lengthwise or crosswise, and in what proportion?

A common cylindrical boiler is twice as strong to resist pressures acting lengthwise than to resist pressures crosswise, and for this reason all the horizontal seams should be double riveted.

Question 43.-How much stronger are boilers having double-riveted plates than those having single-riveted plates?

Double riveting weakens the plates about one-fourth, single riveting about one-half, therefore double-riveted boilers are stronger in the proportion of about 3 to 2.

Question 44-Find the bursting strength of an iron cylindrical boiler 6 feet in diameter, and made of -inch plates, with double-riveted joints. 5 x 21 x 2240 × 69

6×12

=225'4 lbs.

per square inch.

At most collieries railways are required, but the circumstances of each must decide what railways shall be made. Siding room for full and empty trucks

sufficient for the day will be required, but in laying out, regard will of course be had to the intervals between the trains and the output of the colliery. It is not necessary to say more of this here, nor is it necessary to explain the different forms of wagon in use, as these vary much in different districts. Coke ovens and coal-washing machinery, briquette and brick-making machines are in use in some districts, and form part of the surface arrangements; but as these subjects are adjuncts to mining, and a knowledge of them not absolutely necessary for a student to pass an examination in mining, it is not necessary that they should be treated here.

At collieries which supply gunpowder or other explosives, it will be necessary to remember the provisions of the Explosives Act, and to erect the gunpowder magazine in accordance with legal requirements. The written approval of H.M. Inspector should always be obtained both as to plans and position before erection.

A ventilating-fan and a pumping-engine may also possibly form part of the surface erections, but more will be said of these under the heads of Ventilation and Drainage.

CHAPTER VII.

TIMBERING AND WALLING.

The kind of Timber used at Collieries-Storing it Underground-Method of fixing Props and Lids-Temporary Props and Lids-"Dog" for drawing Props-"Sets" of Timber and their fixing in Main Roadways-Timber for Collars-Sills under Props-Timbering for a bad Roof, where the Floor and Sides are good-Lagging-Timbering for a bad Roof and Side, the other Side and Floor being good-Timbering for a bad Roof and Sides, with a good Floor-Timbering for a bad Roof, Floor and Sides - Lagging of Trees and Brushwood-Sizes of Timbers and their distance apart-" Cogs or "Chocks". Methods of Timbering in France-Notching the Timber-Cast-Iron Props-Wrought-Iron and Steel Supports-Storing the Timber on the Surface-Creosoting as a means of preserving Timber from Decay-Customs as to Setting and Drawing the Timber-Walling the Main Roads from the Shaft-Material used in Walling-Semi-circular arched Roadway-Invert under Side Walls-"Horse-shoe" Arch-Elliptical Arch for Roadway-Process of building Arches-Necessity of removing all Timber, and tightly packing behind the Walls of Arches -Packing the Top and Sides with Sand.

TIMBERING is the cheapest way of securing roads, regard being had to first cost only; but if the roads are used a number of years, and the cost of maintenance is taken into account, walling may be a much better and cheaper plan.

The timber used at collieries to support the roof and sides is chiefly pine, fir, and oak. The sizes vary from 4 to 12 inches in diameter, the size and arrangement depending upon the material to be supported and the excavation itself. Where used to support the roof only, the timber requires very little preparation. It is cut into suitable lengths at the surface, sent into the pit, and, in accordance with the Mines Act, 1887, for the convenience of the workmen who have to timber the working places, a proper supply must be kept stored near at hand.

The usual manner of supporting the roof in the working places is by means of single props (called "posts," "trees," &c.), having short lids or caps (in Somersetshire called "traps ") on the top. If these props are cut from the tops of old trees, they are spongy in texture, and less durable than when cut from the lower portions of young trees. The bark should always be left on them, as it helps to preserve the wood.

In fixing props, the workman with one hand holds the lid under the roof requiring support, whilst with the other he moves the top of the prop, the bottom of which rests on the floor, until it touches the lid, which is firmly held by the post, while the latter is driven well under the lid by means of a sledge-hammer. The post should be upright if the seam lies flat; if not, the prop will not be upright, but at right angles to the floor and roof, or, as the roof will sink a little notwithstanding the prop, the latter may be set in a direction which deviates slightly from the perpendicular between floor and roof towards the vertical. A single prop and lid is sometimes though not often fixed in the main roadways as well as the working places. Fig. 161 shows a single prop and lid. At times it is required to fix a single prop and lid for a temporary or passing purpose.

For instance, where a double row of "chocks" is used in Longwall workings, as a protection to a continually advancing face, the back row is often taken down and re-fixed in front of that which was previously the front row. Each of these chocks

should have temporary single props and lids, placed round it to protect the workman while in the act of taking out the chocks. These temporary single props may afterwards be withdrawn, and to facilitate the after removal, when fixing them a short sill is placed on a few inches of rubbish, the prop and lid being placed over the sill (see Fig. 162). These props are afterwards safely removed and recovered by means of a "dog." Fig. 163 shows a "dog" for drawing props, as

used at the Lundhill Colliery, Yorkshire. It is an iron bar 3 feet long, with one end shaped in the form of a hook, as shown in the sketch. Five inches from the hook end is a chain with two links and a hook about 6 inches long. The " dog" is used with a piece of half-inch long-linked chain 6 feet or more in length, with a hook at the end of it. The chain is passed round the prop to be drawn, and hooked into a link. The other end of the chain is put into the hook at the end of the "dog" chain. Another prop is used as a fulcrum, the point of the lever is pressed against this, and the prop is drawn out. The length of the chain must be such as to allow the timber-drawer to be safely clear of the falling roof consequent on the withdrawal of the post.

Usually the main roadways are secured by "pairs" or "sets" of timbers, as shown in Figs. 164, 167, 168, 169 and 170, Figs. 164, 167 and 169 being front elevations, and Figs. 168 and 170 side elevations of roadway. These consist of a

C.M.H.

head-piece or "collar," which is held up in position next the roof by two props, reaching from the floor to near each end of the "collar."

It requires two timbermen in large roadways to fix this timber, and if the roof is very bad it may require more.

The collar, having been placed where required, is held there temporarily by a prop from the floor to the middle of the collar. Holes or notches are prepared beforehand in the floor at the sides of the road. One end of a prop is now placed in one of these notches, and the other is brought under the collar, where it is driven sufficiently to be quite firm. The other prop is treated similarly, and the two props may afterwards be alternately tightened by being more firmly driven under the collar, after which the middle prop is removed. As seen on the drawings, these props instead of being vertical when in position are slightly inclined

at the top towards the centre of the roadway. The object of this is to strengthen the support. The distance of these props from each other on the floor of the road is often regulated by the gauge of the way and the size of tub or tram having to pass between them; if made the same distance apart at the top and bottom, the weight of the incumbent strata would be more likely to break the collar in the centre than when the props are slightly inclined towards each other at the top, thereby reducing the length of collar between the supports.

Sometimes the "collars" consist of slabs of wood or "flats" sawn into suitable lengths, as shown in Fig. 164, but as this kind of collar will not bear much weight without breaking, more frequently trees with the bark left on exactly the same as the props are used. In other cases they are split down the middle, so as to form two halfround pieces, and where this is so the splitting should be done by cleavage, because sawing slightly weakens the piece by dividing the fibres. Where space is not important, however, it may be found more economical to select slightly Fig. 166.-TIMBERING A ROADWAY. larger timbers and saw them, the larger size compensating for the loss of strength resulting from sawing. Where these half-round pieces are used as "collars," the flat portion should be laid next the roof, in order to cover as large a surface as possible. Whatever the collar is, care must be taken to ensure its bearing against the roof.

If the latter has an even surface, there will not be much difficulty in this, but in other cases the irregularity of the roof presents obstacles to true contact between it and the collar.

In fixing the props which support the collars, they are placed sometimes with the smaller ends downwards, and sometimes with the smaller ends upwards, but if the floor is strong the smaller ends should be downwards.

If the floor is very soft, the pressure from above causes the props to sink, and the larger ends should be downwards. In some cases this will not be sufficient to prevent the sinking, and advantage may be derived from placing a sill under the foot of each prop. The size of sill will be determined by experience.

Roadways having a strong floor and sides, but a bad roof, do not require the "sets" of timber just described. In these no props will be required, as the sides of the roadways are notched sufficiently for the insertion of the collars, which thus