THE AGE OF STEEL 



From what has been said it will be seen that in this 

 open- pit mining the steam engine and steam locomo- 

 tive still play a conspicuous part; but in the other forms 

 of iron mining, electric or compressed-air motors 

 are used, as much better adapted for underground 

 work. In the Lake Superior region, where everything 

 is done by the most modern methods, the use of horses 

 and mules for hauling purposes is practically unknown. 



The cars used for hauling the ore are of peculiar 

 construction. The latest types are built of steel with 

 a carrying capacity of fifty tons of ore, and are so 

 made that by simply knocking loose a few pins their 

 bottoms open and discharge the ore into the receiving 

 bins on the wharves, or into the chutes leading to the 

 waiting boats. 



A perennial problem in iron mining, whether sur- 

 face or subterranean, just as in all other kinds of 

 mining, is the removal of accumulations of water, some 

 of these mines filling at the rate of from twenty-five 

 to thirty thousand gallons an hour. But an equally 

 important problem is that of removing moisture from 

 the ore itself. Obviously every additional pound of 

 moisture adds to the cost and difficulty in handling, and 

 inasmuch as this ore must be transported a distance of 

 something like a thousand miles, necessitating three 

 or four handlings in the process, the aggregate amount 

 of wasted energy caused by each ton of water is enor- 

 mous. It has been found that at least ten per cent of 

 the moisture may be dried out of the ore before shipping, 

 and that the ore does not tend to absorb moisture again 

 under ordinary circumstances once it has been dried. 



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