Sept. 17, 1885 | 
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 ex- 
hibits 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,, SOs°OH,—not Aydroxides. 
recent times, in discussing questions of this kind, we have perhaps 
often been led to attach too much importance 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 Prof. 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 Zez- 
dency 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 in air. 
Prof. I odge, if I understand his argument, appears to assume 
that the air effects are in some 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 ;resence of products of dissociation, but probably 
to a very unnecessary extent. Recent investigations to which 
T have alluded show that there are other factors of extreme im- 
portance: 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 zie/ently attacks platinum at low temperature-, 
it is wethout action wpon it at temperatures between about 300° 
and 1300°, but then agai begins to act upon it, the action be- 
coming violent at 1600° to17c0°. I have little doubt that the 
action at Jow 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 tem- 
peratures consists of other than diatomic molecules.1 Assuming 
Prof. 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 Prof. Lodge will not uni- 
formly 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 constituent atoms ; for example, in 
all probability, oxygen stuff has a higher absolute 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 Prof. 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 hope- 
less view that Prof. Lodge and others seem to hold regarding 
the possibility of settling the important question of pure contact 
versus chemical action by appeal to experiment. I may also 
point out that according to my hypothesis it is possible that the 
metals may exert a considerable attraction for each other, 
especially those having monatomic molecules :? many alloys are 
* This conclusion would also lead me to disbelieve entirely in the explana- 
tion which Clausius has given of electrolysis. 
? Assuming that the heat absorbed in raising the temperature of a solid is 
mainly expended in overcoming intermolecular attraction, the high ‘‘ atomic 
heat” of metals may be regarded as evidence that their molecules powerfully 
_ attract each other, and hence that their molecular composition is relatively 
simple ; and on this view the ‘‘atomic heat” of carbon and of a number of 
other non-metals and of some metalloids is low owing to the extent to which 
the “‘affinity ” of the atoms is, as it were, exhausted in the formation of 
their molecules. Comparison of the ‘‘molecular heats” of chlorides and 
In 
NATORE 
471 
undoubtedly compounds ; possibly not a few are compounds of 
the ‘‘ molecular aggregate” class.! 
To return now for but a few moments to the subject of 
chemical change and its intimate connection with electrical 
phenomena. One application I would make of the views here 
put forward would be to explain the superior activity of bodies 
in the wascent state, and in particular of nascent hydrogen. 
Briefly stated, I believe it to consist in the fact that nascent 
hydrogen is hydrogen in circuit—hydrogen in electrical contact 
with the substance to be acted upon. The experiments of 
Faraday and of Grove afford the clearest evidence that in order 
to bring about action between hydrogen and oxygen at ordinary 
temperatures it is merely necessary to make them elements in a 
voltaic circuit. The difference in the effects produced by 
“nascent hydrogen” from different sources is, I imagine, 
attributable to the variations in E.M.F., which necessarily attend 
variations in the constituent elements of the circuit. 
It is not so easy, however, as yet to explain some of the 
changes which take place at high temperatures. Mr. Dixon’s 
experiments have proved that a mixture of carbonic oxide and 
oxygen is non-explosive, but that explosion takes place i- 
moisture be present, the velocity of the explosive wave dependf 
ing upon the amount of water present. When the mixture of 
the two gases is ‘‘ sparked,” change takes place, but only in the 
path of the discharge. Mr. Dixon considers ‘* that the carbonic 
oxide becomes oxidised at the expense of the water, the hydrogen 
set free then becoming reoxidised. M. Traube, who in a series 
of papers has called attention to the importance of water in 
promoting oxidation, has suggested that the oxygen and carbonic 
oxide together act on the water, forming hydrogen peroxide and 
carbonic acid: CO + 20H, + O, = CO(OH), + H,O,; and 
that the peroxide then reacts with carbonic oxide to form car- 
bonic acid: CO + O,H, = CO(OH),. The carbonic acid, of 
course, is resolved into carbon dioxide and water (Berichze, 1885, 
p. 1890). Traube actually shows that traces of hydrogen peroxide 
are formed during the combustion. It appears to me that the 
water may exercise the same kind of action as it (or rather dilute 
sulphuric acid) exercises in a Grove’s gas battery, and that its 
hydrogen does not become free in any ordinary sense. The pro- 
duction of hydrogen peroxide is not improbably due to a 
secondary simultaneous change. 
Unlike a mixture of carbonic oxide and oxygen, a mixture of 
hydrogen and oxygen is violently explosive. If we assume that 
in both cases the reacting molecules are electrolysed by the very 
high E.M.F. employed, and that the atoms then combine, it is 
difficult to explain the difference in the results. Does it arise 
from the fact that hydrogen is an altogether peculiar element ? 
Or are we to attribute it to an influence which water itself exer- 
cises upon the formation of water from hydrogen and oxygen— 
as in the Grove gas battery? It is noteworthy that the velocity 
of the explosive wave in electrolytic gas, according to Berthelot 
and Vielle, is a close approximation to the mean velocity of 
translation of the molecules in the gaseous products of combus- 
tion calculated from the formula of Clausius (H. B. Dixon, 
Phil, Trans., 1884, p. 636). And this is also true of mixtures 
of carbonic oxide and oxygen, and of nitrous oxide and oxygen 
with hydrogen. May we therefore assume, as the velocity 
corresponds with that of the products, that the water exercises 
the important office of inducing change throughout the mass, 
and not that the hydrogen is peculiar? I am tempted here to 
suggest that perhaps the ‘‘induction” observed by Bunsen and 
Roscoe in a mixture of chlorine and hydrogen is due to the 
occurrence of a change in which a something is produced which 
then promotes reaction between the two gases. I here assume 
that there would he no action between the pure gases. 
If I have allowed myself to flounder in among these difficult 
questions, it is not because I feel that I am justified in speaking 
similar compounds with those of the oxides lends much support to this view, 
as we have reason to believe that the chlorides—which have high ‘“‘ molecular 
heats ””—are of relatively simple molecular composition, and that the oxides 
—which have low “‘ molecular heats”—are of relatively complex molecular 
composition. 
* ‘The study of alloys from this point of view will probably furnish inter- 
esting results. It is noteworthy that the contact difference of potential of 
brass is less than that of copper, and much less than that of zinc, with the 
same solution, in all the cases quoted by Ayrton and Perry ; thus— 
Zinc Copper Brass 
Alum... = —"536 volt. —"127 chi —"org 
Sea salt —"565 5, —"475 —"435 
Sal ammoniac —"637 4, —*596 —"348 
It is especially important to examine the copper-tin alloys, which vary in 
electrical conductivity in so remarkable a manner, 
