BY DR. HARE. 
211 
75. I will, in the next place, consider the phenomena 
observed by Professor Daniell, when solutions of potassa 
and sulphate of copper, separated by a membrane, were 
made the medium of a voltaic current. 
76. Of these I here quote his own account. Philoso- 
phical Magazine and Journal, Vol. 17, p. 172: — 
" A small glass bell, with an aperture at top, had its mouth closed 
by tying- a piece of thin membrane over it. It was half filled with a 
dilute solution of caustic potassa, and suspended in a glass vessel con- 
taining a strong neutral solution of sulphate of copper, below the sur- 
face of which it just dipped. A platinum electrode, connected with the 
last zinc rod of a large constant battery of twenty cells, was placed in 
the solution of potassa; and another, connected with the copper of the 
first cell, was placed in the sulphate of copper immediately under the 
diaphragm which separated the two solutions. The circuit conducted 
very readily, and the action was very energetic. Hydrogen was given 
off at the platinode in a solution of potassa, and oxygen at the zincode 
in the sulphate of copper. A small quantity of gas was also seen to 
rise from the surface of the diaphragm. In about ten minutes the lower 
surface of the membrane was found beautifully coated with metallic 
copper, interspersed with oxide of copper of a black color, and hydrated 
oxide of copper of a light blue. 
" The explanation of these phenomena is obvious. In the experi- 
mental cell we have two electrolytes separated by a membrane, through 
both of which the current must pass to complete its circuit. The sul- 
phate of copper is resolved into its compound anion, sulphuric acid + 
oxygen (oxysulphion,) and its simple cathion, copper: the oxygen of 
the former escapes at the zincode, but the copper on its passage to the 
platinode is stopped at the surface of the second electrolyte, which for 
the present we may regard as water improved in its conducting power 
by potassa. The metal here finds nothing by combining with which it 
can complete its course, but being forced to stop, yields up its charge 
to the hydrogen of the second electrolyte, which passes onto the plati- 
node, and is evolved. 
"The corresponding oxygen stops also at the diaphragm, giving up 
its charge to the anion of the sulphate of copper. The copper and oxy- 
gen thus meeting at the intermediate point, partly enter into combina- 
tion, and form the black oxide; but from the rapidity of the action, 
there is not time for the whole to combine, and a portion of the copper 
remains in the metallic state, and a portion of the gaseous oxygen es- 
