442 MESSRS. R. S. HUTTON AND .T. E. PETAVEL ON ELECTRIC 



factors which must be taken into account : firstly, the thermal loss, which increases as 

 the hot zone widens out, and, secondly, the variation of the average temperature 

 of the furnace, the effect of which will superpose itself upon the actual gas evolution 

 and thus augment the pressure readings. Apparently these two factors counter- 

 balance each other. 



From the analysis of the furnace gas [see Table IV. (3)] a re-absorption of carbon 

 monoxide is clearly indicated. The fall of pressure after the end of the run cannot 

 of course form the criterion, as its amount will vary with the distribution of 

 temperature in the furnace. The considerable decrease in the percentage of the 

 carbon monoxide can, however, only be ascribed to re-absorption, and the results are 

 thus so far in agreement with those of the observers mentioned above. 



That this absorption is not due entirely to physical causes is shown clearly by 

 comparison with a similar series of analyses carried out in the case of carborundum 

 (Table VII). 



There is little doubt that the graphitised surface of the ingot, referred to in a 

 preceding paragraph, is a result of the recombination of the carbon monoxide. The 

 instant the power is cut off, the temperature of the molten mass begins to fall rapidly, 

 and it is during this period that the back reaction chiefly occurs. As soon as the 

 product has frozen, further attack is limited, for the ingot of carbide is of a very 

 compact and impermeable texture, and is protected by the graphite film. 



Such a " skin reaction " would doubtless become predominant were the experiments 

 carried out on a few grammes of material, but when dealing, as we are here, with 

 larger quantities, the total loss is too small to influence appreciably the result. This 

 is shown by the fact that the yield is not increased when the carbon monoxide is let 

 off immediately upon stopping (cf. Table III., C 26). 



The further question, as to whether the presence of an atmosphere of carbon 

 monoxide during the run has an unfavourable effect on the efficiency of the process, 

 is also answered in the negative by a comparison with furnaces operated at 

 atmospheric pressure, but otherwise under identical conditions. 



These unexpected results called for more detailed study, and a number of 

 experiments were undertaken in which provision was made for carrying away the 

 carbon monoxide as soon as it was formed. The first method which suggested itself 

 was to remove the gaseous products of reaction by dilution with some inert gas, 

 which was alternately introduced and discharged, the pressure in the furnace being 

 made to fluctuate between two fixed values. The record of such an experiment 

 with coal gas will be found in Table III. (C 22), showing, if anything, a decreased 

 yield. 



A more efficient method of washing out the carbon monoxide was then devised. 

 A hollow carbon electrode was brought into use, and during the entire run a constant 

 stream of pure hydrogen was injected directly into the reaction zone of the furnace. 

 The current of gas was also maintained during the cooling, the quantity of gas 



