Electrolysis of Secondary Compounds, 247 



through the arrangement until 48 cubic inches of hydrogen 

 had been collected from the platinode, and 23'5 cubic inches 

 of oxygen from the zincode (about one equivalent in grains), 

 when the process was stopped. The platinode solution was 

 perfectly colourless with a very slight deposit of copper upon 

 the platinode, amounting only to 0*1 grain. It was evaporated 

 to dryness in vapour of ammonia, and the residue was per- 

 fectly white sulphate of potassa, which weighed 21 grains. 

 It was entirely soluble in water: and ammonia did not pro- 

 duce the slightest blue colour in its solution. The liquids of 

 the zincode and connecting tubes together required 51 grains 

 of dry carbonate of soda to neutralize the free acid. Now, it 

 will be observed, that the sulphate of potassa was only one 

 grain less than a quarter of an equivalent, which, considering 

 the nature of the processes by which these quantities were de- 

 termined, will appear a very near approximation ; and we may 

 take the results of the electrolysis to have been as follows : — 

 For one equivalent of force as measui'ed by the gases evolved 

 at the zincode and platinode, half an equivalent of oxysulphion 

 of potassium (sulphate of potassa) was decomposed (as mea- 

 sured by the quarter equivalent potassium transferred), and 

 half an equivalent of oxysulphion of hydrogen (aqueous sul- 

 phuric acid) : for it will be observed, as most remarkable, 

 that the quantity of copper transferred was perfectly insigni- 

 ficant. 



Upon the view of the principle of electrolysis hitherto com- 

 monly admitted, viz. definite decomposition with equivalent 

 and opposite transfer of the elements or radicles of the com- 

 pound to the opposite electrodes of the battery, these results 

 were sufficiently perplexing : but our perplexity increased as 

 we proceeded ; and it was not till after we had expended an 

 incredible amount of labour in testing different hypotheses of 

 various resistances and opposing forces, supposed to be deve- 

 loped in these complicated cases, that we thought of question- 

 ing the principles themselves. These abortive attempts we 

 shall not, of course, obtrude upon the Society, but proceed to 

 select such experimental evidence as may be sufficient to esta- 

 blish, in as concise a manner as possible, the conclusions to 

 which we have arrived. 



{t.) A solution of stdphate of alumina and potassa (alum) 

 (AI2 O3, 3SO3) 4- (KO, SOg) was subjected to exactly the same 

 treatment as the preceding double salt, and the results were 

 precisely similar. 48 cubic inches of hydrogen were collected 

 from the platinode. When ammonia was added in excess to 

 the solution in the platinode cell no precipitate was produced, 

 which proved the absence of alumina. Evaporated to dry- 



