1884.] On the Electrolysis of Dilute Sulphuric Acid, Sfc. 217 



We found that the closeness of the packing could be so nicely 

 adjusted as scarcely to allow mechanical admixture of the fluids, on 

 the one hand, or electrical endosmose on the other. In our experi- 

 ments we varied the current density, and, unlike Bourgoin (" Annales 

 de Pharmacie," vol. xv), found that the increase of sulphuric acid 

 in the positive compartment per equivalent of hydrogen set free 

 decreased along with the decrease in the current density. The 

 strength of acid was 4*2 per cent. The results are set out in the 

 annexed table. 



Current in 

 milli-amperes. 



Time in hours. 



Increase of sulphuric acid 

 in positive compartment 

 for one part ol hydrogen 

 set free. 



32 -8 



20 



9-17 



33 -4 



6 



9 5 



72-3 



2 5 



10-3 



72-7 



2 



9-4 



106 



2 



11 



117 



2-5 



10-5 



215 



15 



12-05 



220 



1 



12 -04 



229 



2 



12-31 



It is necessary also to bear in mind the remarkable phenomenon 

 called by the Germans "Wanderung der Ionen." Daniell long ago 

 described an experiment in w r hich he placed dilute sulphuric acid in 

 the positive compartment and a solution of sulphate of copper in the 

 negative. He found that when 15*5 grs. of copper had been depo- 

 sited on the negative electrode there were 23 grs. of sulphuric acid in 

 the same compartment. Now, as 15' 5 grs. of copper are equivalent 

 to 24 grs. of sulphuric acid, and as Bourgoin's formula allows for the 

 formation of only half an equivalent of sulphuric acid, that is 12 grs., it 

 is evident that there was a considerable accumulation of that substance 

 unaccounted for. In two similar experiments made with our apparatus, 

 we obtained for 0'147 and 0*125 grm. of deposited copper respectively 

 0*209 and 0*180 grm. of free sulphuric acid. The half equivalents 

 would be 0*114 and 0*097 grm. respectively. The excess of acid in 

 all these cases is due to the "unequal transference of the ions." If 

 both compartments had been filled with sulphuric acid, some similar 

 transference would doubtless have taken place, in addition to what is 

 expressed in Grotthuss' chain of decomposition. 



We conclude, therefore, from our own results, as well as from those 

 of previous experimenters, that the method employed is incapable of 

 determining whether it is HoSO^ or some hydrate which yields to the 

 current. 



