TABLE OF CONTENTS. 



CHAPTER PAGE 



I. INTRODUCTION i 



Definition of Electric Arc X 



Appearance of Arc 3 



Discovery of Arc 5 



II. ARC IN AIR BETWEEN CARBON ELECTRODES 8 



Relation Between Potential Difference, Current and Length 



of Arc 9 



E.M.F. Required as Distinct from Voltage of Arc 16 



Hissing Arc 21 



Fall of Potential in Different Parts of Arc 22 



Counter E.M.F. of Arc 25 



Meaning of "Resistance of Arc" 28 



"Negative Resistance" 31 



"Forward E.M.F." 33 



Residual E.M.F 35 



Temperature of Arc 40 



Variation in the Temperature of the Arc 44 



Effect Produced by Cooling Electrodes 46 



Size of Anode Crater 48 



Enclosed Arc 49 



Miscellaneous 50 



III. ARC IN AIR BETWEEN OTHER SUBSTANCES THAN CARBON. . . 53 



Flaming Arc 54 



Arc Between Metals 6r 



Arc Between Oxides 67 



Magnetite Arc 67 



Arc Between Electrolytes 69 



Arc Between Unlike Electrodes 69 



IV. ARC WITH PRESSURES GREATER OR LESS THAN ATMOSPHERIC 



PRESSURE AND IN OTHER GASES THAN AIR 73 



Arc with Pressures Greater than One Atmosphere 73 



Arc with Pressures Less than One Atmosphere 74 



Carbon Arc in a Vacuum 75 



Metal Arc in a Vacuum 81 



Arc in Other Gases than Air 83 



vii 



