Electromotive Forces in the Voltaic Cell. 359 
. Chapter V. Suggestive. Page 
25. Discussion of Sir William Thomson’s contact-electricity limit to 
the size of atoms, from the new standpoint.....7.........06. 309 
26. Suggested mode of ascertaining the heat of formation of brass or 
am ON rae tae faa Vues Sins 5) 4.chs) 9 sep etn, Sony ona cup a od otal AIOE ERE 360 
27. Attempt to determine size of atoms from heats of amalgamation 
and thermoelectric data. Possible mode of measuring latent 
heats of liquefaction for metals at ordinary temperatures...... 361 
28. Consideration of limit of thinness of a metal sheet exposed to 
air, and estimate of molecular dimensions therefrom.......... 3638 
Size of Atoms. 
25. I may now claim to have accomplished my task, and 
terminate this long paper; but there are several interesting 
points which arise in connection with Sir W. Thomson’s 
deduction of a limit to the smallness of atoms from contact 
data, and these I may be permitted to indicate. Indeed it 
evidently becomes a question whether or not his argument 
remains quite valid if the chemical-strain view be taken of 
Volta’s force. 
Let us then inquire whether any modification has to be 
made in Sir Wm. Thomson’s argument, if the hypothesis set 
forth in this paper be adopted. He says (virtually), Take a 
number of plates of zinc and copper of specified thickness, 
arrange them alternately like the leaves of a book with the 
covers doubled right back, and then shut the book. Directly 
they touched at one edge they became oppositely electrified 
and attracted each other, and therefore did work as they 
approached. By making the leaves numerous and thin 
enough, and shutting them up close enough, any required 
amount of work can be thus done with given quantities of 
metal, provided the thin plates retain the same properties as 
masses of metal possess; z. e. provided they are not only a 
few atoms thick. So far there is no possible objection; but 
_ Sir William proceeds to consider the attraction as depending 
on the affinity of zinc for copper, and the work he requires of 
his plates is that evolved in the formation of brass. But if 
we regard the attraction as depending on the difference of 
combustion energies, Zn/O—Cu/O, we must, to keep the 
charge constant, not only take the plates several atoms thick, 
but we must suppose films of air of sufficient thickness to 
preserve their normal activities in the way of chemical strain 
to be shut up with the plates. Given these, the amount of 
work he has calculated would certainly be done in shutting 
the book, and a corresponding amount of heat generated. 
But would this heat have anything to do with the making of 
brass? So far as I can see, nothing whatever. 
