732 



the central one having the highest intensity, and the tension dimi- 

 nishing in the successive zones surrounding the innermost, till it 

 became inappreciable in the one most remote ; the author considers 

 this condition of the cloud to be analogous to that of the battery- 

 above described, and the phenomena of the former to receive com- 

 plete illustration from the experimental results obtained with the 

 latter. 



January 20, 1848. 



GEORGE RENNIE, Esq., Treasurer, in the Chair. 



" On the Heat disengaged during Metallic Substitutions." By 

 Thomas Andrews, M.D., M.R.I. A., Vice-President of Queen's Col- 

 lege, Belfast, &c. Communicated by Michael Faraday, Esq., D.C.L., 

 F.R.S. &c. 



In a paper which was published in the Philosophical Transactions 

 for 1844, the author deduced from the experimental inquiry there 

 recorded the general law, that when one base displaces another from 

 any of its neutral combinations with an acid, the heat evolved or 

 abstracted is always the same, whatever that acid element may be, 

 provided the bases are the same. Extending a similar inquiry to 

 salts with metallic bases, he establishes, as the result of the investi- 

 gation of which an account is given in the present paper, the ge- 

 neral principle that when an equivalent of one and the same metal 

 replaces another in a solution of any of its salts of the same order, 

 the heat developed is, with the same metals, constantly the same, 

 the expression of a solution of the same order " being understood 

 to mean a solution in which the same precipitate is produced by the 

 addition of an alkali, or, on one view of the composition of such 

 salts, in which the metal exists in the same state of oxidation. The 

 metallic salts, in the precipitation of which by other metals the 

 evolved heat was ascertained, were those of copper precipitated by 

 zinc, iron or lead ; of silver, precipitated by zinc or copper ; and of 

 lead, mercury, and platinum precipitated by zinc : and the acid ele- 

 ments were either the sulphuric, hydrochloric, acetic or formic acids. 

 From the last series of experiments the author deduces, that if three 

 metals A, B, and C, be so related that it is capable of displacing B 

 and C from their combinations, and also B capable of displacing C, 

 then the heat developed in the substitution of A for C will be equal 

 to that developed in the substitution of B for C ; and a similar rule 

 may be applied to any number of metals similarly related. 



January 27, 1848. 



GEORGE RENNIE, Esq., Treasurer, in the Chair. 



" On Galvanic Currents existing in the Blood." By James New- 

 ton Heale, Esq., Licentiate of the Royal College of Physicians, and 



