THE METROPOLITAN COLLIERY. 157 



curved sheet iron shield (Fig. 90) (a) is hinged at its upper 

 end in such a manner that it presses against the coal in the 

 skip, which it keeps in place until the skip is almost reversed; 

 being on a hinge this shield can adjust itself to the height 

 of the coal above the sides of the skip, and swings back 

 into place as soon as the skip passes it. At the bottom of 

 this curved sheet is hinged a flat piece of sheet iron (b) to 

 guide the. coal on to the screen, the free end sliding up and 

 down on the screen according to the distance the shield i* 

 pushed out of the perpendicular. In this way the coal may be 

 tipped quickly, and still be retained in the skip till upside 

 down, when it is delivered on to the stationary screen with the 

 least possible shock. There is a brake connected with the tip- 

 pler, because it is found that by its use the coal spreads, and is 

 better screened when eased down than when dumped in one 

 heap ; in the latter case the coal tends to slide down bodily r 

 which does not give the slack sufficient chance to pass between 

 the bars. 



The main screens just separate the coal into round coal 

 and slack. The slack is raised in a bucket elevator to two- 

 shaking screens worked together by means of an eccentric. 

 The upper screen has a half inch mesh, and the lower three- 

 sixteenths of an inch. It was found that the dust was separ- 

 ated better by getting rid of the larger pieces first. The over- 

 size from each screen is mixed and sold as "nuts" for use in 

 boilers fed by mechanical stokers. The slack that passes 

 through the bars of the main screens is collected in the box 

 of the billy-fair-play, and weighed by a large spring balance 

 before being discharged through the movable bottom. 



The mouth of the pit is protected by a sliding gate at each 

 entrance to the cage, which gates are lifted by the cage as it 

 ascends, and is lowered as it descends. To reduce the jar, the 

 shaft gate falls on rubber buffers. In order to steady the cage 

 and keep it in position, as it approaches the surface, angle 

 irons are fixed to guide the corners of the cages, also pieces of 

 bar iron at either end. 



Electric signals are employed : for these Leclanche bat- 

 teries are used with relays. 



Near the main shaft is a nest of eleven Lancashire boilers 

 imported from England, nine of which are fitted with the Mel- 

 drum system of forced draft. 



The Cambrian safety lamp is the one used by the miners r 

 in these is burnt a mixture of three Darts of colsa oil to one part 

 of kerosene. This is found to be more sensitive than the colsa 

 oil alone, and does not crust the wick so much. The object de- 

 sired is to obtain a serviceable and at the same time a sensitive 

 oil With colsa alone, one cannot determine less than three- 

 per cent, of gas in the atmosphere; while with kerosene, 



