ELECTROLYSIS OF SECONDARY COMPOUNDS. 
15 
pitated, and from the metal deposited) as before the experiment. An equivalent of 
sulphuric acid was set free at the zincode, but the quantity of the copper solution in 
the cell continued the same as at the commencement. Copper thus appeared to 
refuse to exchange with itself in electrolysis. 
Sulphate of zinc afforded results exactly similar. 
{a. h.) That the diaphragm itself did not throw any obstruction in the way of such 
transfer we satisfied ourselves, by varying its substance, from membranes to porous 
earthenware ; but this was put out of all doubt in the following manner. A long 
siphon tube reversed was filled with a strong solution of sulphate of copper, and two 
strips of copper were made the electrodes of the battery ; the action proceeded very 
slowly, but after a long time the liquid in the platinode limb of the apparatus became 
sensibly lighter-coloured, while that in the zincode became darker ; the oxysulphion 
disengaged at the latter point had dissolved the copper of the zincode, which, how- 
ever, had no power to pass to the platinode, to replace the metal which had there 
been deposited. 
The preceding experiments bear closely upon an observation familiar to persons 
engaged in electrotyping on the large scale, viz. that the solution around the plati- 
node becomes impoverished, and at last nearly deprived of copper. 
As it appears to be thus established, that in the electrolysis of complex electrolytes, 
the metals which are capable of decomposing water at ordinary temperatures, or 
whose oxides are largely soluble in water, are susceptible of transference in the vol- 
taic circuit from the zincode to the platinode, whilst those which are not marked by 
this strong affinity for oxygen remain stationary ; we were anxious to ascertain to 
which class ammonium belongs. 
(a. c .) The apparatus was charged with a solution of muriate of ammonia (NH 4 Cl) 
of known strength throughout ; 35*5 cubic inches of hydrogen were collected from the 
platinode ; the zincode liquid was yellow and smelt strongly of chlorine. By careful 
neutralization with muriatic acid, it was ascertained that an equivalent quantity of 
ammonia had been disengaged in the platinode cell, and by precipitation of the 
chlorine with nitrate of silver, from the liquid thus neutralized, we found that the 
solution contained the same amount of chlorine as before the experiment ; the 
amount of ammonium in combination with it, must, therefore, have remained un- 
changed : it had received no addition by transfer from the zincode side. The results 
of the experiment were perfectly clear and decisive. 
(, a.d .) In an experiment which was made in the same manner with microcosmic 
salt (NaO, NH 4 0, HO, P 2 0 5 ), the sodium travelled to the platinode, but the whole 
of the ammonium remained in the zincode cell. Here a polybasic acid was used, and 
yet results similar to those with a monobasic acid obtained. We have still further 
evidence that the nature of the acid does not appear to be connected with this tra- 
velling of the base, from the fact, that when the double tartrate of soda and ammonia 
