FURNACE REACTIONS UNDER HIGH GASEOUS PRESSUBiB. 439 



As the reaction proceeds, the pressure in the furnace, due to the evolution of carbon 

 monoxide, rises rapidly and the fused carbide collects upon the bed of carbon and 

 soon accumulates sufficiently to come in contact with the end of the electrode. The 

 sharp drop of the electromotive force thus produced serves to indicate that the time 

 has arrived to raise the carbon slightly. 



There is no difficulty in maintaining these smothered arcs even at the highest 

 pressures, and the regulation of the power is quite a simple matter. Currents of some 

 500 amperes have frequently been employed in the course of this work and maintained 

 as long as desired. 



It is very noticeable that, contrary to experience with such arcs when maintained 

 at atmospheric pressure, the upward rush of the gases through the finely divided 

 charge causes very little* displacement of material. For a given rate of reaction the 

 velocity of the gas currents is of course roughly in inverse proportion to the working 

 pressure. At high pressures, therefore, the gaseous products of reaction rise at 

 a relatively slow speed and percolate through the mixture without disturbing it. 

 When, on the other hand, the enclosure is evacuated the projection of the material is 

 very marked and causes considerable trouble. 



An extremely low consumption of the carbon electrodes is characteristic of these 

 enclosed furnaces, the deterioration of the electrodes being so slight that they can be 

 repeatedly used In general practice the loss in weight of the electrodes is an 

 important question and in favourable cases is still between 1 and 3 per cent, of the 

 output of carbide. The consumption in ordinary furnaces on a laboratory scale is still 

 larger, whereas in the present experiments the loss has always been so small as to be 

 hardly appreciable. 



We may therefore conclude that the corrosion is not due to the dissociation of the 

 lime as suggested by GIN,* but is to be ascribed to atmospheric oxidation. 



A summary of the more important experiments will be found in Table III., 

 whereas Table IV. gives the detailed observations referring to one typical can. 



Before discussing these results it may be well to consider briefly the mechanism of 

 the chemical reaction upon which the formation of the carbide depends. 



It is generally stated that carbon first commences to react readily with lime when 

 the latter reaches its melting point, the production of carbide below this temperature 

 being limited and of little practical importance.! ' " 



In a careful investigation of ROTHMUNDJ it has however been shown that a definite 

 equilibrium exists at about 1600 C., as represented by the equation 



CaO + 3C^ 



the reaction tending to go from right to left at higher, from left to right at lower 



* G. GIN, ' Z. fiir Elektrochemie,' 1902, vol. 8, p. 397. 



t H. MOISSAN, 'Comptes Rendus,' 1904, vol. 138, pp. 243-245. 



| V. ROTHMUND, ' Z. fur anorg. Chemie,' 1902, vol. 31, p. 136. 



