TBANSACTIONS OF SECTION G. fSS 



engines of late years have been the trip gear, by means of which the steam 

 communication between the high- and low-pressure cylinders is automatically 

 stopped in case of accident, and the consequent cushioning of the steam in the high 

 pressure cylinder brings the engine gradually to rest without shock ; and also the 

 pausing gear, by means of which a definite interval between the strokes is obtained. 

 In heavy lifts, this is of great advantage, by giving time for the valves to settle 

 down to their seats at the end of each stroke, which minimises wear and tear, and 

 it also enables the engine, when running at one or two strokes a minute, to make 

 a brisk stroke and then pause, thus obviating the disadvantage of water slipping 

 back through the valves, which is always the case when an engine makes a very 

 slow stroke. 



Another type of engine, which is increasing in favour, is the hydraidic engine 

 at the bottom of the shaft, actuated by a steam engine at the top, on a similar 

 principle to that introduced many years ago by Lord Armstrong for working the 

 machinery in docks. This system possesses the advantage of occupyino- the 

 minimum of space either at the pit top or in the shaft, and the power can be ap- 

 plied at any point iu the pit without the inconvenience which attends the actua- 

 tion of pumps by spear rods at any other point than at the bottom of the shaft. A 

 plant of this kind has been working at Marseilles for some years, raising 1,700 

 gallons per minute 311 feet high, with an accumulator pressure of forty-two atmo- 

 spheres. 



On leaving the carriage the trams of coal are weighed, and the coal is then 

 tipped on to the screen, where it is cleaned and divided into the necessary number 

 of saleable sizes (which is usually regidated by the quality of the coal ), and then 

 placed in the trucks for transportation. Considerable improvements have recently 

 been made in our screening apparatus, which is probably due, partly to the 

 increased proportion of dirt or dross found in some of the seams now worked, 

 and partly to the necessity of having a more improved and effective apparatus, 

 having regard to the increased cost of working the coal, and consequently to its 

 increased value. The improvements in this direction have taken the form chiefly 

 of travelling belts, moving at a slow speed in lieu of the ordinary falling screen. 



At the docks also, the machinery for placing the coal on board ship has been 

 greatly improved, so as to prevent breakage, one of the most recent improvements 

 being the movable tip, w^hich can be adjusted to suit the varying sizes of ships. 

 Some of these tips are made on the principle of the jib crane, the coal being tipped 

 from the truck into large iron boxes, which are lowered into the ship's hold, and 

 the coal dropped out of the bottom of the box. Others are fitted with what might 

 be termed an auxiliary crane, by which the coal is lowered in boxes into the ship's 

 hold, the truck being, first of all, placed on a cradle, which is raised by hydraulic 

 rams to the necessary height, when it is tipped to such an angle as to cause the 

 coal to run out of the truck through a shoot, extending over the ship's hatchway, into 

 what is termed the anti-breakage box. The box being filled is then lowered into 

 the ship's hold, but its use is discontinued as soon as a sufficient quantity of coal 

 has been loaded to form a cone sufficiently large to prevent further breakage. The 

 anti-breakage box is then swung out of the way, and the coal allowed to slide from 

 the shoot on to the cone, and into the hold where it is trimmed into position. 



Summarising the po.sition of mechanical science, as applied to our coal-mining 

 industry in this country, it may be observed, that there is a general awakening 

 to the necessity of adopting, in the newer and deeper mines, more economical 

 appliances. 



It is true that it would be impracticable, and probably unwise, to alter much of 

 the existing machinery, but, by the adoption of the best-known types of electrical 

 plant, and air compression in our new and deep mines, the consumption of coal per 

 horse-power would be reduced, and the extra expense, due to natural causes, of 

 producing minerals from greater depths would be substantially lessened. The 

 consumption of coal at the collieries in Great Britain alone probably -exceeds 

 10,000,000 tons per annum, and the consumption per horse-power is probably not 

 less than 6 lbs. of coal, and it is not unreasonable to assume that, by the adoption 

 of more efficient machinery than is at present in general use, at least one-half of the 



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