Popular Science Monthly 



415 



how costly, had to be relegated to the junk 

 heap. Today, it can be repaired easily and 

 perfectly by the use of thermit with a 

 trifling expenditure. In the photograph be- 

 low will be seen the thermit process in opera- 

 tion at the Brooklyn Navy Yard 



Greater even than the heat ^£ 

 of thermit in the temperature 

 scale is that attained with 

 the flame formed by the 

 combustion of the 

 gases, oxygen and 

 acetylene, in the pro- 

 portion of 1.7 vol- 

 umes of the former 

 and 1 volume of the 

 latter. In the apex of 

 the cone of a flame so 

 produced, a tempera- 

 tureof sixty-three hun- 

 dred degrees Fahren- 

 heit is realized. The 

 hydrogen, which is freed 

 from the acetylene, sur- 

 rounds the flame and pre- 

 vents a loss of heat and 

 confines it to a small space. 

 By a suitablyconstructed 

 blowpipe, this little flame 



Using the electric arc to weld together 

 the parts of a large motor armature 



the use of thermit would be impractical. 



To go further in the explanation of 



methods for attaining high temperatures, 



we must introduce electricity — 



the greatest heat-creating power 



that science commands. 



What the Electric 

 Arc Has Done 



For those who are 

 not familiar with the 

 theory of the elec- 

 tric arc, a brief ex- 

 planation of its op- 

 eration will be 

 given. If two car- 

 bon rods, maintained 

 at a sufficiently high 

 difference in voltage, 

 are made to touch and 

 then quickly withdrawn, 

 an arc will be formed. 

 When the rods are brough t 

 into contact, a spark is 

 produced hot enough to 

 vaporize a small portion 

 of carbon, which fills the 

 gap with carbon vapor. 



is used to great advantage even by a com- The carbon vapor thus liberated reduces the 

 paratively unskilled workman for the quick electrical resistance of the gap from many 

 repair of small, broken castings where thousand ohms to a few hundred. 



An electric furnace of the arc type pouring- out part of its three-ton charge of molten steel, which 

 has reached a temperature of 3600° Fahrenheit through the affinity between oxygen and alu min u m 



