336 DR. MEYER WILDERMAN ON THE CHEMICAL STATICS AND DYNAMICS OF 
§ I. The Experiments of Becq.uerel and Minch ix. The Phenomena Observed, by 
Becquerel and Minchin are not Surface Phenomena , but their Combinations 
form Inconstant Galvanic Cells under the Action of Light. Polarisation. 
Becquerel was the first to show that when two metallic plates are immersed in a 
liquid, and one is exposed to light while the other is kept in the dark, an E.M.F. is 
created. 
Which now is the nature of this E.M.F. \ Becquerel’s and Minchin’s (more 
especially the latter’s) experiments brought to our knowledge peculiar facts, which 
all seemed to indicate that the above phenomena are surface phenomena, and strongly 
to oppose the author’s conception of such systems as galvanic cells. What were now 
these observations of Becquerel and Minchin ? According to Becquerel : “ by 
depositing on one of the Ag plates a thin layer of iodide, obtained by the action ol 
the vapour of iodine at the ordinary temperature and then exposing this plate to 
light, it was found that it took positive electricity from the liquid. With a thick 
layer of iodine on the surface of the Ag, there is on the contrary a current the 
inverse of the proceeding, i. e ., the plate exposed to light took negative electricity ; 
further, “ whilst with precipitated chloride and bromide of silver placed on plates of 
platinum there is always produced a current of the same sense, the exposed plate 
being positive; with a layer deposited on Ag there is an effect depending upon the 
thickness of this layer.” “ These two inverse facts indicate that there should 
necessarily be a thickness of layer for which the electric effect is almost nothing ” 
(‘La Lumiere,’ vol. II., p. 129). Minchin again observes (‘Phil. Mag.,’ 1891, 
XXXI., p. 207) with AgCl, AgBr in collodion an E.M.F. in the opposite direction to 
that of Agl in gelatine (p. 200). 
The observations of Minchin with metallic plates seem to be still more inexplicable. 
He tells us of “a very curious case on inversion of the current produced by light 
observed with silver plates immersed in water containing eosine in solution (p. 211), 
or in alcohol containing naphthalene red (p. 212); the E.M.F. is sometime in one, at 
others in the opposite direction.” He made the same observation with “ bismuth in 
water” (p. 213). In “nearly every cell used with tin plates the exposed plate 
was positive to the unexposed; but after a time, varying from a few minutes to a 
few hours, it was found that this positive current died out and was replaced by an 
apparently stronger current, in which the exposed plate was negative, &c.” The 
results were similar with the “ sensitive ” cells which lie obtained by exposing a 
compound of tin deposited on tin plates (obtained by acting on tin plates (alloys) 
with nitric acid and nitrate of ammonia and afterwards heating them till a white 
precipitate—the greater part evidently Sn0 2 —was formed on them) to light, while 
another tin plate without deposit is kept in the dark, both plates being immersed in 
methyl alcohol. He draws the conclusion that “ if the deposit is not uniform, some 
parts of the plate give on exposure to light positive, others negative E.M.F.’s,” and 
