FURNACE REACTIONS UNDER HIGH GASEOUS PRESSURES. 431 



IB fixed the nut (P) in which the screw-gear works. This screw-gear is rotated by 

 means of a cord passing over the pulley W. Thus, when the furnace is being used 

 for very high electric tensions, the feeding gear can be manipulated from a safe 

 distance. This form of insulation has been found to work satisfactorily up to 

 3000 volts. For higher electromotive forces one of the steel feeding rods is removed 

 and replaced by a thick-walled glass tube. The current, which under these conditions 

 is of course very small, is led by a number of fine platinum wires fused through the 

 glass to the electrode, which is supported on the end of this rod. 



With this modification the furnace has been used up to 25,000 volts. 



Gas Preparation and Compression. 



In connection with this research it was necessary to manufacture and compress 

 relatively large quantities of hydrogen, carbon monoxide, ethylene, and nitrogen. 



The question has been dealt with fully in a recent publication to which we must 

 refer those specially interested in this branch of the subject.* 



GENERAL OBSERVATIONS ON THE ELECTRIC ARC UNDER HIGH GASEOUS 



PRESSURES. 



At the time the present research was started very little information was available 

 with regard to the electric arc burnt in a compressed atmosphere, the investigations 

 having been limited to small arcs and pressures of about 15 atmospheres. The belief 

 was then current that it would prove to be impossible to maintain an arc under 

 gaseous pressures of 100 or 200 atmospheres. 



This erroneous conclusion was due to a misconception of the nature of the 

 difficulties which had been encountered by the various workers, t 



For spectroscopical investigations it is necessary to obtain a relatively long arc 

 giving a clear flame between the extremities of the electrodes. Such an arc, it is 

 undoubtedly true, can only be maintained in a dense atmosphere by means of an 

 exceptionally high electromotive force. 



It should nevertheless be clearly understood that even low-tension arcs will burn 

 without difficulty. At ordinary current densities the entire phenomenon is, however, 

 confined to the crater itself, and a projected image of the arc shows merely the 

 outline of the white-hot crater, and only occasionally is a flash of flame visible on the 

 periphery. 



Electrically the arc is still well characterised by its high electromotive force, which 

 instantly disappears if the electrodes are brought into actual contact. 



* BUTTON and PETAVKL, ' Journ. Soc. Chem. Ind.,' 1904, vol. 23, pp. 87 to 93. 



t W. E. WILSON and G. F. FIT/GERALD, ' Roy. Soc. Proc.' 1896, vol. 60, pp. 377-383. 



