Mance: Quarry Industry of Southern Indiana 59 



Power. The power machinery used thruout the stone belt 

 consists of engines, boilers, stacks, feed pumps, and water heaters. 

 In most of the mills electrical equipment and air compressors 

 are also included. The first p!ece of apparatus to be considered 

 is the boiler. 



Boilers, altho of many types, can be classed under two main 

 heads, as follows: Fire-tube boilers, in which the water is con- 

 contained in a cast-iron shell, and tubes extend lengthwise thru 

 this shell to conduct the hot gases from the furnaces to the stack; 

 and water tube boilers in which the water is in the tubes and the 

 hot gases from the furnace are forced to pass back and forth 

 across and among the tubes by means of baffle plates. In the 

 smaller power plants the fire-tube boiler is most widely used on 

 account of its lower first cost, cheaper foundations, and easier 

 attention, etc. As the size of the plant increases the water- 

 tube boiler tends to replace the fire-tube boiler on account of its 

 longer life, greater overload capacity, quicker steaming, and 

 greater safety. The disadvantages of the two types can be 

 summed up as follows: Fire-tube boilers are liable to leak at 

 the ends of the tubes; they fluctuate rapidly in the pressure sup- 

 plied; they are not easily examined; and it is necessary to reduce 

 the pressure as time goes on. Water-tube boilers have small 

 steam space, are not easily cleaned, and are liable to prime. 



Another type of boiler that is very efficient but not much 

 used in quarry work is the internally fired boiler, known as the 

 Scotch Marine boiler. These boilers give a greater evaporation 

 of water per pound of fuel burned than either of the types above 

 mentioned. They cost less for foundations, and, altho higher in 

 first cost, soon make up for this in the lower fuel consumption 

 during service. 



The most satisfactory all-round boiler for a quarry or mill 

 equipment and the one that is used almost exclusively in 

 this district is the well-known horizontal return-tubular boiler. 

 The most widely used makes are the Atlas, Chandler Taylor, 

 and the Erie City boilers. They range in size from 40 horse- 

 power up to 200 horse-power, with pressure allowances from 75 

 pounds up to 125 pounds per square inch, according to the age 

 of the boiler. 



The boilers as a rule show the results of hard usage, due mainly 

 to two causes: First, there is a tendency to overload a boiler 

 where it is furnishing steam for steam pumps or drills. The 

 boiler is usually pushed to furnish steam for as many pieces of 



