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MESSRS. R. S. HUTTON AND J. E. PKTAVEL ON ELECTRIC 



these high current densities the apparent resistance of the arc under pressure remains 

 positive just as at atmospheric pressure. 



An entirely different type is obtained in an oxidising atmosphere, and in this case 

 alone are the results comparable with the well-known conditions of the ordinary 

 open arc. 



In fig. 10, E, the E.M.F. of a 150-atmosphere arc of about 2 millims. length is given 

 and compared with measurements made at atmospheric pressure, the positive carbon 

 being 41 millims., the negative 27 millims. diameter. 



Fig. 10. Curves of the electromotive force and current of the arc in various compressed gases. 



The data refer to the conditions existing while a fair proportion of the oxygen was 

 still present ; the arc then shows a bright flame which, if the electrodes are fed up 

 rapidly and with regularity, can be easily maintained. Here again the increased 

 voltage observed is due principally, as shown by other experiments, to the first 10 or 

 15 atmospheres. 



For the purpose of general comparison, few data on large current arcs being 

 available, a number of measurements were made with an open arc burning at 

 atmospheric pressure between carbons (positive 41 millims., negative 27 millims.) and 

 maintained at a constant length of 8 millims. The curve thus obtained is recorded in 

 fig. 10, A. 



Finally it should be mentioned that, in the course of the chemical work to be 

 described, constant use has been made of " smothered " arcs, as, for instance, in the 



