176 ^ NEW YORK STATE MUSEUM 



The side walls of the furnace are first built up to a hight of 

 about 4 feet. Pieces of sheet iron are then placed at a distance 

 of about 4 inches from the inner ends of the carbon terminals in 

 such a way as to keep the mixture from coming in contact with 

 the latter. The mixture is then thrown into the furnace till it is 

 rather more than half full. A semicircular trench, having a radius 

 of 10% inches and extending from end to end of the furnace, is 

 now formed, the bottom of the trench being a little above the 

 level of the bottom row *of carbons. Into this trench is intro- 

 duced the core, which has been carefully weighed, so that the 

 amount required to make the core of the right size is used. One 

 of the furnaces at Niagara Falls requires about 1100 pounds of 

 " new core," that is to say, core which hais come directly from 

 the bins, or about 850 pounds of " old core," or core which has 

 already been used in the furnace. The reason for this difference 

 in weight will appear later. All the core having been emptied 

 into the trench, the top is rounded off neatly by hand, so that, 

 when finished, we have a solid cylinder 21 inches in diameter and 

 about 14 feet long, composed of small pieces of coke and extend- 

 ing from the sheet iron plate at either end of the furnace. 



The next operation is to make the connections between the core 

 and the terminals. This is done by packing finely ground coke 

 into the spaces between the ends of the carbons and the pieces 

 of sheet iron, after which the walls are built up to a hight of 

 about 5 feet, the pieces of sheet iron removed, and more mixture 

 thrown in and heaped up to a hight of about 8 feet. 



All that is required now to make carborundum is the 

 electric current. 



After the circuit has been closed in the transformer room, no 

 apparent change occurs in the furnace for about half an hour. 

 Then a peculiar odor is perceived, due to escaping gases, and, 

 when a lighted match is held near the furnace walls, the gas 

 ignites with a slight explosion. When the current has been on 

 for three or four hours, the side walls and top of the furnace 

 are completely enveloped by the lambent blue flame of carbon 

 monoxid gas, formed by the combination of the carbon of the 

 coke with the oxygen of the sand. During the run of a single 

 furnace 5 J tons of this gas are given off. At the end of four or 

 five hours the top of the furnace begins to subside gradually, 

 and fissures form along the surface, from which pour out the 

 yellow vapors of sodium. Occasionally the mixture on the top 

 of the furnace is not sufficiently porous to allow the rapid 

 escape of the gases. The result is that the latter accumulate 

 until the pressure is so great that, at some weak point in the 

 mixture above, a path is forced open and the gases rush out 



