HEAT DISSIPATION AT ELECTRODES OF SHORT ELECTRIC ARC 943 



sipated after an arc = 1.25. We identify w^ and w- with the numbers so 

 designated in Table I. When the value of wq is taken from the table we im- 

 plicitly assume that the electrical spreading resistance at the contact is so 

 much larger than the rest of the resistance of the electrode wires that sub- 

 stantially all of the heat wo is generated in the spreading resistance and not 

 along the wires. With this assumption we obtain, 



^ = 0.765 

 rj = 0.282 

 d = 0.580. 



The final result of the experiment is represented by the number 6 = .58 

 which means that a metal vapor arc between activated platinum electrodes dis- 

 sipates 58 per cent of its energy upon the positive electrode and 42 per cent 

 upon the negative electrode. This result differs only slightly from w^/{w^ -f- 

 w-) = 0.577, the difference being the correction due to resistive heat de- 

 veloped equally in the two electrodes. For the inactive electrodes we ob- 

 tain w+/(w+ + W-) = 0.572 which is in close agreement, and it too must 

 differ only slightly from the value which would be obtained if data were 

 available for making the correction due to resistive heat. 



Reliability of Results 



The fact that the experiments account for only rj = 0.765 of the total 

 energy need not be disturbing. It seems most likely that an inaccurate 

 value for the thermal conductivity of the platinum wires and imperfect 

 geometry of the wires account for this. The low resistance of the thermo- 

 couple circuits does not affect the indications of temperature difference 

 which they give. 



The large corrections of line 2 in columns 1 are highly uncertain as one 

 sees readily by inspection of the corresponding curves of Fig. 3. If these 

 corrections were taken to be zero one would obtain d = 0.556. It certainly 

 seems unlikely that for inactive platinum electrodes can be less than this 

 value. 



Interpretation 



There are previous observations upon closure arcs between inactive elec- 

 trodes which must be correlated with the results of these measurements 

 There are no corresponding earher data upon active electrodes. 



A single closure arc between inactive platinum electrodes produces a 

 pit on the positive electrode having a volume which is comparable with 

 that to be expected if all of the energy of the arc is dissipated upon that 

 electrode and is used there in melting and vaporizing metal with all of the 



