222 PROFESSOR DANIELL ON THE ELECTROLYSIS OF SECONDARY COMPOUNDS. 
gas adhering to the surface of the electrode, and is much more consistent with, what 
we now know to be the fact, the immediate deposit of the metallic cathion upon the 
platinode without the intervention of the gas. I had also remarked, at times, without 
being able to account for it, that the texture of the copper was spongy and little co- 
herent. 
The beautiful application of this observation by Professor Jacobi and Mr. Spencer 
to the formation of fac-similes of medals and other volta-types, as I have proposed to 
call them, has made us better acquainted with the minutest details of this kind of 
precipitation ; and every one who has attended much to the process, must have ob- 
served that, in conducting it in the usual way, after the same solution has been a 
long time in use, the deposit of compact copper became mixed with copper in a loose, 
pulverulent state, which can be brushed off the mould with the fingers, and greatly 
interfered with the beauty of the result. This arises from the accumulation of acid 
in the solution from the decomposed sulphate; and I have no doubt that oxisulphion 
of hydrogen being thus formed, the current is divided between it and the oxisulphion 
of copper ; and that the pulverulent copper is owing to the secondary action of the 
hydrogen disengaged from the former upon the solution. 
Experiment 40. — I have from the first prevented this injurious effect in Mr. Spencer’s 
process, by making the precipitation in a separate cell, containing the sulphate of 
copper, connected with two or three cells of the constant battery by a copper zin- 
code ; by this arrangement the copper was dissolved at the zincode as fast as it was 
deposited at the platinode, and the accumulation of acid prevented. 
I shall now only trouble you with a brief account of two or three more experi- 
ments, the results of which throw some additional light upon the electrolysis of 
secondary compounds. 
Experiment 41. — I was anxious to ascertain in what manner the carbonates would 
conduct themselves as electrolytes, and particularly the relation which they would 
exhibit to the oxalates. For this purpose the carbonates of potassa, soda, and am- 
monia were subjected to the voltaic action in the double diaphragm tube, the zincode 
cell of which was sometimes connected with a Liebig’s tube, for the purpose of ab- 
sorbing the carbonic acid ; and carbonic acid and oxygen were found to be given off 
in equivalent proportions to the alkali and hydrogen at the platinode ; proving these 
salts to be oxicarbions of potassium, sodium, and ammonium respectively. 
Experiment 42. — Oxalate of ammonia, treated in the same way, yielded nothing at 
the zincode but carbonic acid, and ammonia with hydrogen at the platinode. When 
the constitution of the oxalic acid is remembered, this result will be very intelligible; 
for 
Oxalic acid. Carbonic acid, 
(2 C + 3 O) + O = 2 (C + 2 O), 
the one equivalent of oxygen being quite sufficient to convert the one equivalent of 
oxalic acid into two equivalents of carbonic acid. 
