THOMPSON. — ON THE EQUILIBRIUM OF THE SYSTEM. 437 



protected by silica tubes, was lowered through the window in the tower 

 into the crucible and the furnace heated without pumping out the air. 

 There was no lid on the crucible in this experiment. The results are 

 given in Table III. 



It is seen that without the lid and with no charge in the crucible 

 the temperature is quite constant, which would be improved, if any- 

 thing, when the charge is in the crucible and the lid in position. 



The carbide used in the following experiments was made from Merk's 

 lime and Acheson graphite powder in the form of turnings from 

 graphite electrodes. Carbide was made by heating a mixture of the 

 two in an arc furnace consisting of a graphite electrode and graphite 

 crucible. By the loss in weight method 10 it analyzed 78 per cent 

 pure. The impurities must have been carbon and lime which were not 

 harmful for these experiments. 



The first experiments were carried out at from 1700° to 2000°, but 

 no consistent results could be obtained. After a run at these temper- 

 atures it was found that the walls of the furnace were always lined 

 with a white powder, whether lime and carbon were heated alone or 

 when carbide was in an atmosphere of carbon monoxide. It was 

 found when carbide was heated in carbon monoxide to about 1800° 

 only graphite was left in the crucible and the white powder was formed 

 on the walls. When carbide was heated alone in a vacuum the walls 

 of the furnace were lined with a thin sheet of calcium, which easily 

 peeled off and took fire when brought in contact with moisture. 

 Graphite was left behind in the crucible. These two facts taken 

 together show that calcium reduces carbon monoxide according to the 

 equation : 



Ca -f CO = CaO + C. 



Therefore, if carbide is to be produced, it must either be below the 

 temperature where it breaks up into its elements, or the velocity of 

 the reaction 



CaO + 3 C = CaC 2 + CO 



must be greater than the velocity of the preceding reaction. The 

 latter is evidently the state of affairs in the manufacture of carbide, 

 but equilibrium measurements could hardly be made under this 

 condition. 



10 Lunge, Chemische-technische Untersuchungs Methoden, 5te Auflage, 

 Band II, 711. The drying tube contained a layer of P2O5 besides one of 

 Ca Cl 2 , which the escaping gas had to pass first. 



