Prof. Daniell on the Electrolysis of Secondary Compounds. 319 



equal portion of water also passes over from the zincode to the plati- 

 iiode. These experiments appear to confirm the results previously 

 obtained ; namely, that one fourth of an equivalent of sulphuric 

 acid passes from the platinode to the zincode for every single equiva- 

 lent of a compound vvhich has been electrolyzed by the current. 



The axithor then proceeds to examine the follovv^ing question, viz. : does 

 the acid during its transfer, in the case of the mixed acid and water, 

 or do the acid and the alkali, in the case of the saline solution, con- 

 vey any portion of the current which effects the simultaneous de- 

 composition of the water in both instances ? He next investigates 

 the action of the voltaic current on the aqueous solution of the chlo- 

 rides, as the simpler constitution of this class of salts promised to 

 throw some light on the nature of the electrolysis of secondary com- 

 pounds. 



The results of all these experiments tend to the establishment of 

 the fundamental principle, that the force which is measured by its 

 definite action at any one point of a circuit cannot perform more 

 than an equivalent proportion of work at any other point of the same 

 circuit ; and that the current, which is measured by its electrolysis 

 of an equivalent of simple chloride of lead, cannot at the same time 

 be sufficient to electrolyze an equivalent of chloride of sodium, and 

 an equivalent of water, at the same electrodes. The sum of the 

 forces which held together any number of ions, in a compound elec- 

 trolyte, could, moreover, only have been equal to the force which 

 held together the elements of a simple electrolyte, electrolyzed at 

 the same moment in one circuit. 



In applying these principles to the electrolysis of the solution of 

 sulphate of soda, water seems to be electrolyzed, and at the same 

 time the acid and alkali of the salt appear in equivalent proportions 

 with the oxygen and hydrogen, at their respective electrodes. It 

 cannot be admitted, that after the decomposition of the water there 

 is any excess of force applicable to the decomposition of the salt ; 

 but it must be concluded that the only electrolyte which yields is 

 the sulphate of soda, the ions of which, however, are not the acid 

 and alkali of the salt, but an anion, composed of an equivalent of 

 sulphur, and four equivalents of oxygen and the metallic cathion, 

 sodium. From the former, sulphuric acid is formed, at the anode, 

 by secondary action, and the evolution of one equivalent of oxygen ; 

 and from the latter, soda at the cathode, by the secondary action of 

 the metal, and the evolution of an equivalent of hydrogen. The for- 

 mation of these secondary electrolytes, and compound anions and 

 cathions, will probably furnish the key to the explanation of many 

 of those decompositions and recompositions, to which the presence 

 of water is necessary, such as those of nitric acid on the metals, and 

 the formation of Schoenbein's circuit*: but the author reserves for a 

 future opportunity the examination of this hypothesis, as weU as of 

 the general question. 



* See Dr. Schcenbein's papers in Lend, and Edinb. Phil. Mag., vol. ix. 

 p. 63, and several subsequent volumes. 



