BOX CAGES.
There is another mode of raising coal from deep' shafts, that may be commendable in some cases. The plan is to dispense with cars and cages in shafts and substitute for them a simple box of boiler-plate, which may hold five tons, more or less. This box does not leave the shaft, but the coal is dumped from the cars into the box at the bot tom of the shaft, and on arriving at the top the box is emptied by a contrivance into the shutes of the breaker. This mode may be advantageous where deep shafts are sunk on small seams and where large cars cannot be made use of. In seams of from four to six feet, cars which carry more than from one to two tons of coal cannot be made use of, and where the dips of seams are over 20° large cars cannot be conveniently used : therefore in such cases the box cages may be available, and r much greater amount of coal raised than could be done in one shaft if the cars were raised with the coal. The
difference in weight on the engine would not be materially altered, but the load to be carried by the rope would be much less.
The box would not weigh more than one ton, or with four tons of coal 11,200 pounds: consequently, the size of the rope would be decreased from two inches to one and a half inch diameter, the weight of which is about four pounds to the foot, or 4000 pounds to the 1000 feet, instead of 7000 pounds : the weight, therefore, to be lifted.by the rope is 15,200 pounds instead of 25,000, as when the car and cage are lifted with the coal, and the load on the engines 12,960 pounds instead of 16,000 pounds.
A smaller shaft can also be made to answer the purpose, in case the boxes are used in place of the cars and cages, since the former would occupy one-half less space than the latter. This mode is in use at the Pioneer colliery at Ashland.