272 Prof. Oliver Lodge on the Seat of the 
17. Let us therefore endeavour to suppress further qualms, 
and calculate a series of metal-air contact-forces from the 
heats of combustion ; remembering that all we have to do, in 
order to convert heats of combustion per dyad gramme- 
8 
equivalent into volts, is to divide by ee that is by 
46,000. 
But the decision as to what numbers we shall take to repre- 
sent heats of combustion is a matter of some difficulty, for 
not only do the numbers obtained by different observers for 
the same reaction differ, sometimes considerably, but it is not 
obvious when different oxides are formed which of them we 
are to consider as most applicable to the case of the Volta 
experiment. Perhaps one should take the most common or 
stable oxide ; perhaps, seeing that no combination is supposed 
actually to occur, and since the metal is, so to speak, in excess, 
it is most reasonable to take the lowest oxide which the sub- 
stance will form. It may be that the data are not known for 
this ; it may even be that they have only been obtained for 
the hydrate instead of for the oxide. 
I must therefore do the best I can, and quote several 
numbers wherever there is obvious doubt. I imagine that 
J. Thomsen’s are the most reliable when they are available. 
But it must be remembered all through, that since it is only 
the tendency to chemical action which is the cause of the Volta 
effect, whereas combination-heats are obtained by permitting 
or causing the combination to actually occur, the numbers 
obtained by calculation are not likely to be quite right; and 
they may be expected to err on the side of excess, the calcu- 
lated number being higher than the actual value if directly 
observed. 
Energy of Combination of Metals with Oxygen. 
The Mean 
; Heat of} come Ex- ee 
Metal. Molecule. Authority. forma- | seduced! treme probable | 
tion. io Volts. values. | value. 
Thomsen ....-..-. 85430 | 1-85 
Joule serene a 77000 | 1:66 
VAIL enters ic Zn,O Andrews: (sac. stecn 84825 | 1:84 
Favre and Sil- Jee 
tatty ad } 83915 | 1:82 
Zn,O,H,O Thomsen ..seceo-- 82600 
Sn,O Andrews.......... 67100 | 1:46 
Ti Sn,O,H,O Thomsen ......... 68090 
eres 3(Sn,0,) Andrews.........++. 67680 
nO,O BY bao iwtnmnasnte ns 69584 
