igio.] THE ENERGY OF CARBON. 51 



cracked it is, of course, impossible to say. Neither is it possible 

 to be certain as to the voltage corresponding to the observed reading 

 of 0.015 ampere. The resistance of the ammeter and lead wires 

 together was less than one ohm, and the uncertainty lies in the 

 resistance of the hot metal and the contacts with it. The electrodes 

 were about 15 cm. apart, and the crucible had a diameter of some 

 25 cm., so that, although the temperature was high, the resistance 

 must have been very small. One ohm would probably be a liberal 

 allowance. Assuming a total resistance of two ohms in circuit, 

 the voltage would have been 0.03. 



On general principles, we should expect that any such voltage 

 would be very small. That there is any liberation of energy at all 

 when carbon dissolves in melted iron indicates that the act of solu- 

 tion is, at least in part, chemical, and points to the existence of a 

 new carbide of iron, stable at high temperatures, and of a simpler 

 molecular formula and greater energy content than the well known 

 carbide Fe,C, which is stable only below a red heat, just as CO 

 stands between COo and free carbon and oxygen. Now the heat 

 of formation of Fe^C is not known, but its energy content must be 

 but little less than that of its constituents in a free state ; and con- 

 sequently the margin of liberated energy at the formation of the 

 hypothetical simpler carbide must be extremely small. 



Further experiments on this matter are in progress. 



