52 PRESIDENTS ADDRESS—SECTION A. 
they must, then the phenomena of charge must appear. Let us 
take two plates of platinum and place the silver or chlorine, or 
even the chloride of silver, between the plates, and by some 
means persuade the chloride to decompose into atoms of chlorine 
and silver, or the molecules of silver into atoms of silver, or the 
molecules of chlorine into atoms of chlorine. Then I consider 
that if the layer of substance is thin, the platinum plates will be 
found to be charged—if work has had to be done in forcing the 
decomposition. In fact, just as in electrolysis, or by the appli- 
cation of electric force atoms in the “third” state—if I may so 
express it—cannot be got into molecules without producing the 
phenomena of charge, so if once in molecules they cannot be 
brought to “third” state atoms without suffering a defect of 
something—which becomes sensible by the charging of the plates. 
Let some silver chloride placed between platinum plates be elec- 
trolysed into silver and chlorine, then small layers of these 
substances (really free) will appear on the plates. Then remove 
the undecomposed silver chloride entirely and bring the plates 
together with pressure. Suppose that recombination into silver 
chloride results from this pressure, Then between the time 
when there were molecules of silver and molecules of chlorine, 
and the time when there were molecules of silver chloride, there 
will have been by all chemical experience atoms of silver and 
atoms of chlorine. During this separation they will have (by the 
application of external work) to undo from the electrodes what 
was done during electrolysis—if one of the plates retained the 
charge (say positive) which it got during electrolysis, that charge 
will disappear. If the charge has been lost beforehand, then the 
plate will appear negatively charged. A corresponding charge 
will appear at the other elecrode. Both electrodes will thus be 
charged. I was led to these speculations by attempting to find 
an explanation of the ultimate course of the effects produced by 
rubbing bodies together, or, in other words, the ultimate course 
of action of a frictional electric machine. I was struck in the 
first place by the fact that most substances, which we know from 
hereditary experience, to lend themselves best to the construction 
of electric machines are very complex molecularly. Probably 
much more so than the general run of so-called chemical com- 
pounds. Some, like sulphur, are capable of allotropic modifi- 
cations ; some, like sealing wax, defy precise chemical description ; 
some, like metals, are in a transition state of combination with 
gases condensed on their surfaces; others, like silica, are in 
unknown combination with water, as in quartz crystals—our old 
friend “electrical amalgam” is as indefinite as most amalgams. 
Fused quartz, I find, is not particularly easily electrified, but 
even it must have its gas layer. 
Now, there are many cases in chemistry of actual and undoubted 
chemical change being brought about, directly or indirectly, by the 
