TRANSACTIONS OF SECTION B. 961 
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‘the mere mechanical interposition of the neutral molecules of the sclyent—in the 
manner suggested by Kohlrausch—but by the actual attraction exercised by these 
molecules upon the negative ion in virtue of the affinities of the negative radicals. 
One result of increased attention being paid to the investigation of problems 
such as I have indicated will probably be that we shall be called upon to 
abandon some even of our most cherished notions. I would suggest, for 
example, that it may become necessary to regard nitrogen peroxide not as 
a mixed anhydride of nitrous and nitric acids, but as a compound of two 
NO, groups; its conversion into nitrite and nitrate affords no proof of its 
constitution, as chlorine peroxide, ClO,, which exhibits no tendency whatever 
to combine with itself, also yields both chlorite and chlorate. A greater 
shock may result from a conviction arising that not only carbon dioxide, 
but sulphur dioxide, and perhaps even sulphur trioxide, dissolve in water, forming 
hydrates—SO,OH,, SO,,OH,—not hydroxides. In recent times, in discussing 
questions of this kind we have perhaps often been led to attach too much import- 
ance to the argument from analogy; it is not improbable that, especially in the 
case of compounds other than those of carbon, chemical change involves change in 
structure more frequently than we are apt to believe. 
It is possible that a precise estimate of what, for want of a better name, I have 
spoken of as residual affinity, may sooner or later be obtained, if the view Professor 
Lodge has propounded in his paper ‘ On the Seat of the Electromotive Forces in a 
Voltaic Cell’ be correct, that the cause of the volta effect is the tendency to chemical 
action between the bodies in contact ; that, for example, chemical strain at the air- 
contacts is the real cause of the apparent contact-force at the junction of two metals 
inair, Professor Lodge, if I understand his argument, appears to assume that the 
air effects are insome way dependent on the presence of ‘ dissociated oxygen atoms.’ 
I think this is probably an entirely unnecessary assumption; of late years, no 
doubt, it has been the fashion to attribute the occurrence of changes of various 
kinds to the presence of products of dissociation, but probably to a very un- 
necessary extent. Recent investigations to which I have alluded show that there 
are other factors of extreme importance: for example, that water must be present 
in order to render a mixture of carbonic oxide and oxygen explosive. Again, the 
observations of V, Meyer and Langer have shown that, whereas chlorine violently 
attacks platinum at low temperatures, it is without action upon it at temperatures be- 
tween about 300° and 1,300°, but then again begins to act upon it, the action becoming 
violent at 1,600° to 1,700°. I have little doubt that the action at low temperatures 
is dependent upon the presence of moisture ; if it were due to dissociated chlorine 
atoms, the action should increase with rise of temperature without break. In 
short, I see no reason to assume that oxygen at ordinary temperatures consists of 
other than diatomic molecules.!_ Assuming Professor Lodge's view to be correct, the 
strain exists in virtue of the attraction which the oxygen molecules exert upon the 
metal molecules. On this assumption, I can well understand that the method 
of calculation followed by Professor Lodge will not uniformly lead to satisfactory 
results. The ‘heat of combination’ is not necessarily a measure of ‘ affinity.’ The 
values are in all cases algebraic sums of a series of values, scarcely one of 
which is known, and, as I have already pointed out, the affinities of the 
molecules are by no means always of the same order as the affinities of the con- 
stituent atoms: for example, in all probability, oxygen-stuff has a higher abso- 
Jute affinity than sulphur-stuff; chlorine-stuff a higher absolute affinity than iodine- 
stuff, yet iodine and sulphur compounds, more often than not, seem to exhibit more 
residual affinity than chlorine and oxygen compounds. So that, from Professor 
_Lodge’s point of view, chlorine would have the higher and iodine the lower contact 
values ; whereas, from my point of view the reverse might often be the case. I 
point this out because it appears to me that we here have an opportunity of testing 
the question experimentally, and seeing that it is possible practically to prevent 
chlorine from attacking metals by excluding moisture, I do not take the hopeless 
' } This conclusion would also lead me to disbelieve entirely in the explanation. 
_ which Clausius has given of electrolysis. 
1885. 3Q 
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