Page:Popular Science Monthly Volume 91.djvu/431

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Popular Science Monthly

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��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 If two car- bon rods, maintained at a sufficiently high difference in voltage, are made to touch and then quickly withdrawn, an arc will be formed.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

�� �