436 MESSRS. R. S. HUTTON AND .1. E. PKTAVKI, ON KI.KCTKTC 



The interesting results thus obtained with regard to comhustion led us to carry out- 

 some experiments on the oxidation of electrodes of other materials, the production of 

 an atmosphere free from oxygen and the oxides of carbon being also of considerable 

 practical importance for the further work we had in view. A priori one would be led 

 to believe that copper, iron, or aluminium when heated and fused in highly compressed 

 air (100 atmospheres) would not only rapidly fix the available oxygen, but would do 

 so with sufficient intensity to make the combustion self-supporting. 



Repeated attempts were made to produce this result, a summary of which will be 

 found in Table II. (p. 452). 



Briefly speaking, we may say that with an iron bar maintained for one hour at a 

 bright red heat and then partially melted by means of a current rising to 1000 amperes, 

 the percentage of oxygen fixed was hardly appreciable. 



A similar result was obtained in the case of copper, whereas even aluminium melted 

 in the arc at a pressure of 26 atmospheres only oxidised on the surface, the well-known 

 tenacity of the oxide films being sufficient to prevent the rapid combustion of the 

 metal. 



The negative results thus obtained led to some experiments being carried out with 

 oxygen. 



An arc was struck between two iron bars of 1^-inch diameter, surrounded by 

 oxygen at 1 5 atmospheres pressure ; as soon as the temperature reached a bright red 

 heat, a vivid combustion commenced on the positive electrode and continued quite 

 steadily, although the current was then cut off.* After the combustion had proceeded 

 a short time the pressure was gradually reduced, the combustion ceasing when the 

 pressure had fallen to about 5 atmospheres. A length of some 5 inches of the bar had 

 by this time been consumed, the loss of weight being 535 grammes, the loss on the 

 negative electrode being only 15 grammes. The product of the reaction was collected 

 in a crucible placed for this purpose under the arc, and on analysis proved to be 

 magnetic oxide (Fe 3 O 4 ). 



It is worthy of note that although the partial pressure ot the oxygen in the 

 experiments previously referred to was considerably above that required in the case 

 of the pure gas, the combustion was not merely insufficient to maintain the temperature 

 required for continued combustion, but even with the assistance of the arc the total 

 iron burnt was almost negligible. The result is due probably to the high effective 

 heat conductivity which is characteristic of compressed gases, the evolution of heat 

 due to oxidation being, in the diluted gas, insufficient to overcome this cooling 

 effect.! 



It was thought also that oxygen might easily be removed from the atmosphere by 

 the introduction of successive small quantities of hydrogen, care being taken to always 



* E. FRANKLAND, ' Journ. Chera. Soc.,' 1864, vol. 17, pp. 52-55, describes an interesting case of the 

 combustion of iron, in compressed oxygen. 



t J. E. PETAVKI, 'Phil. Trans.,' A, vol. 197, pp. 229-L'54, 1901. 



