318 Royal Society. 



&c. By Jolm Frederic Daniell, Esq., F.R.S., Professor of Chemistry 

 in King's College, London*. 



The discovery of definite electro-chemical action naturally suggests 

 the inquiry into the relative proportion of that part of a voltaic cur- 

 rent, which, in the case of its decomposing a saline solution, is car- 

 ried by the elements of the water, and that part which is carried by 

 the elements of the saline compound, and into the definite relations, 

 if any such there be, subsisting between the two electrolytes so de- 

 composed. This question was the origin of the investigation which 

 forms the subject of the present letter. The power which the author 

 employed in this experimental inquiry was that of a small constant 

 battery of thirty cells, six inches in height, with tubes of earthen- 

 ware, charged in the manner he has described in his former commu- 

 nications to the Society. The result of the first experiment evidently 

 indicated that the decomposition of one equivalent of water was ac- 

 companied by the decomposition of an exact equivalent of sulphate 

 of soda. The author then endeavours to ascertain whether the power 

 of the current is equally divided between what had hitherto been re- 

 garded as the two equivalent electrolytes. The first experiments 

 he made in order to determine this point seemed to lead to the ex- 

 traordinary conclusion, that the same current which is just sufficient 

 to separate an equivalent of oxygen from an equivalent of hydrogen 

 in one vessel, will at the same time separate an equivalent of oxygen 

 from one of hydrogen, and also an equivalent of sulphuric acid from 

 one of soda in another vessel. 



The author then examines the remarkable phenomena relative to 

 the transfer of matter from one electrode to the other without the 

 decomposition of the transported compound ; a phenomenon which 

 was first observed by Mr. Porret in glass cells divided into two com- 

 partments by a diaphragm of bladder. 



Having observed that the products of electrolyzation cannot be 

 kept long separate in their respective cells, on account of the ulti- 

 mate mixture of the liquids on the platinode side of the diaphragm, 

 the author was led to construct an apparatus by which this evil is 

 remedied much more perfectly, and to which he gives the name of 

 the double diaphragm cell. It consists of two cells, formed of two 

 glass cylinders, with collars at their lower ends, fitted by grinding 

 to a stout glass tube bent into the form of the letter U, and firmly 

 fixed on a wooden post. The current transmitted by this double 

 cell is more retarded than when passing through the single cell, on 

 account of the greater distance of the electrodes ; but it answers its 

 intended purpose of stopping the transfer of the liquid even in the 

 case of saline solutions, and there is still sufficient conducting power 

 to render it powerfully effective. Experiments were then made to 

 ascertain whether in the electrolysis of the dilute sulphuric acid any 

 transfer of the acid takes place ; from which the author concludes 

 that during the electrolysis of an equivalent of water, a portion of 

 acid passes over from the platinode to the zincode ; and possibly an 



* See p. 312. ante. 



