261 



fact, equivalent to an increase of temperature, to solution, or to any 

 of the other circumstances which are known to be capable of adding 

 to the force of the affinities inherent in the substances themselves. 



Some very curious cases of interference with this action of platina 

 and other metals are next described. Thus, small quantities of car- 

 bonic oxide, or olefiant gas, mixed with the oxygen and hydrogen 

 gases, totally prevent the effect in question 5 while very large quan- 

 tities of carbonic acid, or nitrous oxide gas, do not prevent it: and 

 it is remarkable, that the former of these gases do not affect the me- 

 tallic plates permanently; for if the plates be removed from those 

 mixtures, and put into pure oxygen and hydrogen gases, the combi- 

 nation of these elements takes place. 



The author concludes by some general notice of numerous cases 

 of physical action, which show the influence of certain modifications 

 of the conditions of elasticity at the external surface of gaseous 

 bodies. 



The seventh series, which is a continuation of the subject of the fifth, 

 namely, electro-chemical decomposition, commences with a prelimi- 

 nary exposition of the reasons which have induced the author to intro- 

 duce into this department of science several new terms, which appear 

 to be required in order to avoid errors and inaccuracies in the state - 

 ment both of facts and theories. As a substitute for the term pole, 

 and with a view to express also a part of the voltaic apparatus to 

 which that name has never been applied, although it be identical with 

 a pole in its relation to the current, the author proposes to employ 

 the term electrode. The surfaces of the decomposing body, at which 

 the positive current of electricity enters and passes out, are denomi- 

 nated respectively the eisode and the erode. Bodies which are de- 

 composable by the electric current are called electrolytes, and when 

 electro -chemically decomposed, they are said to be electrolyzed : the 

 substances themselves, which are evolved in such cases, being called 

 zetodeSjWnd the terms zeteisode and zetexode being applied, accordingly 

 as the substance passes in one direction or the other. The propriety 

 and the advantage of employing these new terms, the author observes, 

 can be properly appreciated only by an experience of their uses and 

 applications in the exposition of the theory of decomposition given 

 in the fifth series of these inquiries, and of that of definite electro- 

 chemical action advanced and supported in the present paper. 



The first section of this paper is occupied w r ith the consideration of 

 some general conditions of electro-chemical decomposition. It has 

 been remarked, that the elements which are strongly opposed to each 

 other in their chemical affinities are those most readily separated by 

 the voltaic pile ; and the discovery of the law of conduction, explained 

 in the fourth series, has led to a great augmentation of the number 

 of instances which are in conformity with this general observation : 

 but it is here shown, that the proportion in which the elements of a 

 body combine has great influence on the electro-chemical character 

 of the resulting substance ; and that numerous instances occur where, 

 although one particular compound of two substances is decomposable, 

 another is not. It appears, that whenever binary compounds of simple 



o 



