FURNACE REACTIONS UNDER HIGH GASEOUS PRESSURlH 435 



production of calcium carbide. With arcs of as much as 500 amperes between 

 the extreme limits of our experiments, i.e., from 0'5 atmosphere up to nearly 

 200 atmospheres, no consistent effect on the voltage which could be ascribed to 

 the influence of gas pressure was apparent. 



A noticeable feature in all the experiments carried out in air is the very rapid rate 

 of burning of the electrodes. 



To take one instance : with 27-millim. carbons and a 30-ampere arc under a pressure 

 of 29 atmospheres the carbon was consumed at a rate of about 6 millims. per minute, 

 which is nearly twenty times as fast as at ordinary pressures.* 



This burning is principally limited to the positive electrode, which in the above 

 experiment was consumed seven times as fast as the negative, the relative rates at 

 ordinary pressures being about as 3 : 1. At a still lower current density the negative 

 carbon shows practically no loss of weight. 



Under the normal conditions of most of our experiments, that is with very high 

 current densities, the combustion becomes very violent. 



The oxygen thus becomes rapidly exhausted and the subsequent feeding required 

 is relatively very small. 



At first carbonic acid is formed which is in turn reduced to carbon monoxide. This 

 reduction occurs also when the arc is run in an atmosphere ot compressed carbonic 

 acid. In the latter case an interesting observation was the separation of flocculent 

 carbon which was seen to be moving rapidly in the convection currents. This 

 phenomenon is observed from the commencement of the experiment. 



The decomposition of the carbonic acid under these conditions is comparatively 

 slow, in one experiment less than half being decomposed by the end of half an hour. 



A somewhat similar process goes on also in non-oxidisiiig gases. Finely divided 

 carbon is deposited in considerable quantities on the cool walls of the enclosure, the 

 weight collected being in fair agreement with the loss from the electrodes. With 

 such gases the atmosphere, however, remained perfectly clear, t 



* B. MONASCH, ' Der elektrische Lichtbogen,' p. 22. 



t In cases in which a hydrocarbon gas atmosphere (.</., coal gas) is employed, the deposition of carbon 

 is augmented by the breaking up of the higher hydrocarbons. 



The following analyses give the constitution of the coal gas before and after a run at about 

 60 Atmospheres, which lasted 36 minutes with a power of about 10 kilowatts, a horizontal arc being 

 employed. In this case both electrodes had increased in weight, the positive by 6, the negative by 



16 grammes : 



Before run. After run. 



Hydrocarbon vapours 1 0-0 



Heavy hydrocarbons 4 2 7 



CO, 2-0 0-6 



CO 15-0 14-7 



CH< 18-0 -i '.* 



H 42-0 41-8 



1-7 0-0 



N (by difference) ... 16- 1 17-3 



100-0 100-0 



3 K 2 



