Royal Society, 463 



from the infiltration of water, the author found that the application 

 of this method gave the following results, namely, that the soil at the 

 depth of a foot is subject to an annual, and, in light soils, to a diurnal 

 variation, regulated in its amount by the relative intensity of the solar 

 rays, and the quantity of radiation, depending, of course, on the state 

 of the atmosphere, and the degree of shelter afforded to the sur- 

 face. 



February 25. — " On the Electrolysis of Secondary Compounds." 

 By John Frederic Daniell, Esq., D.C.L., For. Sec. U.S., and Profes- 

 sor of Chemistry in King's College, London ; and W. A. Miller, M.D., 

 Demonstrator of Chemistry in the same College. 



The authors of this paper have further prosecuted the inquiry into 

 the phenomena of electrolysis, commencing from the point to which 

 it had been carried by Professor Daniell in his papers published in 

 the Philosophical Transactions for 1839 and 1840. He had there 

 shown, that in the electrolysis of neutral saline solutions, if the metal 

 is one of those which do not decompose water at ordinary tempera- 

 tures, it is precipitated in the metallic state at the platinode ; but if 

 it belong to the class of those which, at ordinary temperatures, do 

 decompose water, then an equivalent of the oxide is liberated at the 

 platinode, while an equivalent of hydrogen makes its escape in the 

 gaseous form from the same electrode ; the acid, in both cases, being, 

 at the same time, liberated at the zincode, accompanied by an equi- 

 valent proportion of oxygen. On comparing these results with those 

 of an independent voltameter included in the same circuit, it was 

 found that a certain definite proportion of the force which resolves 

 a single equivalent of a simple electrolyte into its anion and cation, 

 produces the resolution of a full equivalent of a complex electrolyte 

 into a simple metallic cation and a compound anion. When ammonia- 

 cal salts in solution were thus decomposed, ammonia, with an equiva- 

 lent of hydrogen, was liberated at the platinode ; while the acid, with 

 an equivalent of oxygen, was evolved, as before, at the zincode, 



Experimental evidence was thus obtained in support of two im- 

 portant theories ; namely, the ammonium theory advanced by Ber- 

 zelius ; and the binary theory of salts propounded by Davy ; in which 

 latter theory, all saline compounds are regarded as being formed on 

 the type of the salts of the hydro-acids. This binary composition of 

 salts is, in the present paper, proved to exist, not only when the salts, 

 previously held in solution by water, are decomposed by the voltaic 

 current, but also when the fused anhydrous salt is electrolysed : for 

 example, metallic silver in crystals is deposited upon the platinode, 

 when fused nitrate of silver is included in the circuit. 



On examining, by the current, the monobasic, dibasic, and tri- 

 basic phosphates, the authors found that there were three distinct 

 modifications of the acid transferred. From the monobasic phos- 

 phates there was obtained the metaphosphoric acid ; from the dibasic 

 salts, pyrophosphoric acid ; and from the tribasic salts, the ordinary 

 phosphoric acid was set free at the zincode. The acids were trans- 

 ferred into weak alkaline solutions and recognised by their appro- 

 priate tests. The view entertained by Professor Graham of the 

 composition of these salts is therefore completely confirmed. 



