86 



fall that represents to a large degree a complete waste and the fact that they 

 are suitable for this line of manufacture should certainly be a means of utiliz- 

 ing a large quantity of this discarded material. 



Table 55a. Wood for Mine Rollers, year ending June, 1912. 



SPRAGS. 



This is a second division of this industry which deserves special attention, 

 not that it represents a commodity that is important in the amount of wood 

 consumed nor economically prominent in the operation of large factories and 

 the use of skilled labor, but because it serves to illustrate the tendency in 

 Pennsylvania towards waste utilization. 



A sprag is a cylindrical wooden commodity pointed at each end, about 21 

 inches long, ranging in thickness from 2^ to 31 inches and is used in coal 

 mining operations for checking and regulating the speed of a mine car as it 

 runs in and out of the laterals leading to the shafts. The speed of the car 

 is checked by locking one of its wheels. This occurs when the sprag, having 

 been cast between the spokes of the rotating wheel, strikes against the car 

 still. 



Mine cars are not equipped with brakes like freight cars and upon the 

 sprag often depends the safety of the car and more often a train when run- 

 ning downgrade. Sprags must therefore necessarily be very strong and many 

 companies are particular in the specifications of their orders for manufactur- 

 ing them. Small sprags of not proper thickness are a slight economy, if any, 

 as the frequent breakages entail considerable waste. Also the species of 

 wood used for making them, if not of the requisite strength, hardness, and 

 durability, would in nowise pay in service the expenses of making the sprags. 



This industry excludes the softwoods and a number of soft hardwoods, like 

 aspen, yellow poplar, basswood, etc. Chestnut is not; suitable owing to lack of 

 sufficient strength, though if easily available and very cheap, it is used to a 

 limited extent. The most practical sprag woods, listed according to amounts, 

 are given in Table 55b following: 



