that can be obtained with a rope drive, but where the pitch is steep enough the smooth direct-connected drive probably gives as good results as can be obtained by using a rope drive with a jerk inserted. However, where the pitch is between 3 and 8° it is very probable that a much greater capacity can be obtained with a rope drive, which can give a jerk or a quick stop that will tend to move the coal forward by its own momentum. It is unfortunate that direct comparison can not be made between the two systems of drive under the same conditions; but, as far as the writer knows, the two systems are not at work in the same colliery. Each colliery visited employs either direct-connected or rope drive alone.

In its present form the shaking chute is not as flexible as it can be made. To make a bend or to shift the chute, tearing down and rebuilding are necessary, but this feature will probably be overcome soon. The lack of flexibility has prevented application of the chute to longwall mining methods, but doubtless before long it can be successfully used on longwall faces.

SHAKING-CHUTE MINING WITH INDIVIDUAL DRIVE AT NATALIE COLLIERY

Transportation of coal from the working face to the haulage roads is always a problem when a single roadway runs up a room. Only one car is then available for the miner to load, and until this car is removed and replaced by another the loading of coal must halt in that working place. If cars could be delivered in trips that would permit continuous loading, the daily output of each man employed could be greatly increased.

If the room-and-pillar method of mining is used in thin beds, the height of the mine car often necessitates brushing of the roof or taking up the bottom to permit clearance. This extra labor sometimes becomes very expensive and often makes the mining of a thin bed too costly.

To avoid both of these difficulties, the Colonial Collieries Co. at its Natalie colliery has adopted shaking chutes that operate successfully in a coal bed about 30 inches thick. The chutes have the double advantage of being installed without top being taken down or bottom taken up and of presenting to the miner who is loading the coal an end that is free from coal. As fast as the coal is loaded into the shaking chutes by shoveling, it is carried down the room by the chute. These chutes work successfully on pitches of 3 per cent and more.

Mining methods.—This system of removing the coal from the working face in the room makes it possible to confine the mine cars to the main haulage roads only. One or more cars can be delivered to chute for loading. A whole trip of cars can thus be loaded from one or more shaking chutes without having a locomotive or mule shift the cars until all are loaded. The loaded cars can then be made up into a trip and hauled to the nearest parting. There the locomotive can pick up a trip of empties for return to the working places, go back, pick up the trip of loaded cars at the parting, take it to the foot of the shaft or slope, pick up a trip of empties there, and return with it to the parting. With this system comparatively little time may be lost in loading the mine cars, particularly if the parting is near the working places. In fact, the only time lost is that required for the locomotive to make up its trip of loaded cars, to

Figure 34.—Details of construction of shaking chutes

take them to the parting, pick up the trip of empty cars, and place the cars in the gangway at the room necks. As the haulage system is kept in constant use, no time is lost in waiting for the mine cars to be loaded.

Types of chutes used.—Two kinds of shaking chutes are used at this colliery. The chutes themselves are identical in construction, and consist of steel plates of No. 6 sheet iron bolted to 3 by 6 inch timbers along the sides, as Figure 34 shows. Each section is made so that one end fits into the end of the adjoining section, and the sections are bolted together. Each section is 14 to 16 feet long and the chute is hung from an iron pipe or bar by a chain every 14 to 16 feet. Another form of construction for shaking chutes, made entirely

Operating data.—The essential difference between the two types of shaking chutes is in the drive. Some are driven by electric motors that have a 10-horsepower input to the motor, which delivers 4 horsepower to the shaker. These motors run at 870 revolutions per minute.

The diagram, Figure 36, shows that a worm gear is used to reduce the speed of the motor and to drive the connecting rod, which is connected to the bottom of the first section of the chute. The ratio of reduction is 11.6 to 1. An outfit of this sort costs about $800

The second type of drive uses compressed air. (See fig. 37.) A small compressed-air cylinder is directly connected to the bottom of the shaking chute, and the stroke of the piston gives a 6-inch movement to the chute. An outfit of this character costs about $150.

The air cylinder requires approximately 17 horsepower, but delivers only 4 horsepower to the shaking chute. Translating the power required into kilowatt hours for each day of six hours shows that

the electric drive consumes 45 kilowatt hours and the air drive 78 kilowatt hours. Two men using 1 shaking chutes can a load as many as 15 "cars, of a capacity of a 95 cubic feet each, "during a shift. In 3 the section visited by I the writer four shakTS ing chutes — two % driven by compressed ° air and two by elec3 tricity—were in use. a The average produc

0 tion from this section £ was 36 cars a day, or M 9 cars for each shak

C

1 ing chute. One loader » is required on the jl gangway for every

1 two shaking chutes; « therefore 10 men are

2 employed for every z 36 cars of coal loaded, ° making 3.6 cars per M man.

'" In installing the * chutes, bottom is taken ° up to provide places a for the electric or 2 compressed-air drive, S as it is advisable to § keep the chutes as [ near the floor of the « working places as g possible. Bottom is g taken up in the gangways that the cars will be low enough for the shaking chutes to load directly into