VIIl—ON THE SUPERFICIAL TENSION OF FLUIDS AND ITS 
POSSIBLE RELATION TO MUSCULAR CONTRACTIONS. By G F. 
FITZGERALD, M.A., F.T.C.D. 
[Read June 17, 1878.] 
I 
Some of the latest contributions to the subject of the superficial tension of fluids 
are due to Mr. Lippmann’s very remarkable researches into the connexion between 
surface tension and the difference of electrical potential at the contact of dissimilar 
fluids.* In connexion with these the lately published experiments of Messrs. 
Ayrton and Perry (see Proc. R. Soc., vol. xxvii., p. 196) are of great interest, and 
their conclusions are especially gratifying to me because some years ago, in the 
spring of 1875, I made some experiments, which seemed to me to show that much 
of the observed electromotive force of contact was accompanied by chemical action. 
{remark in a note I took on Friday, 19th March of that year, on some experiments 
made with varnished zinc and copper condensers “. . . ; . . there always 
seemed an electromotive force in the air near the Zn . . . . . not like 
contact theory, for it resuscitated itself after bringing the poles to the same poten- 
tial” Similarly Messrs. Ayrton and Perry consider that the electromotive force of 
contact of dissimilar substances is accompanied, in most cases, at least, by chemical 
action of some kind, although the amount is so small as to escape the ordinary 
means of analysis. Now, it seems to me that this sort of chemical attraction, which 
only culminates in chemical action in some cases, may be used to explain superficial 
tensions generally, and M. Lippmann’s results. For instance, if we suppose the 
superficial tension to depend upon this chemical attraction, we can easily see how it 
is aflected by the direction of the current passing from one surface to the other ; 
for we know, by the phenomena of electrolysis, that the direction of the current 
alters, and even reverses, the character of this chemical attraction, Similarly 
Professor C. Maxwell mentions in his article on Capillarity, in the last edition of the 
Encyclopedia Britannica, that when a mercury surface is being extended there exists 
an accompanying electrical displacement. Sir W. Thomson, in his method of 
calculating the effective size of molecules by means of the observed difference of 
electrical potential on contact of zinc and copper, assumes that the actual chemical 
attractive forces are measurable by means of the attraction of the zinc and copper 
plates. From exactly similar premissesT propose calculating the superficial tension 
of a fluid. We require to know the electrical distribution corresponding to the 
contact of dissimilar substances, and I shall assume each molecule to be charged 
with that known quantity which passes when an electro-chemical equivalent is pro- 
* Annales de Chimie et Physique, 5" Serie, Vol. XIL., p. 265. 
R 
