1825.1 Electro-chemicai Tfie^ t^^X:MMU^i Pfiknomena. 26j 



with a' ^mitraVy electricity in tli6 di^solViK^liqmd of the other* 

 The two constituent molecules of the water becoming thus libe- 

 rated, act in each solution at the instant they separate in an 

 opposite manner on the elements of the salts, like the two poles 

 of the pile ; the oxygen repels the acid, which, on the contrary, 

 is attracted by the hydrogen, but it attracts the alkali, and \vith 

 it determines to the hydrogen of the other solution, with which 

 it re-forms water, whilst the alkali combines with the iicid that it 

 finds there, and produces a new salt. ., ^-"qoi,-- - 



■' It is th^ change, therefore, between the principles bf the 

 Bfidecules of the water which determines that of the elements of 

 the salts. This change also takes place, as is well known, when 

 wa:ter is decomposed bv the voltaic pile, and it is in like manner 

 by these means that it favours the disunion, with the assistance 

 of that instrument, of the elements of compounds which it holds 

 fti solution. Ilius it is observed that the decomposition of saline 

 e'Otnpounds is always accompanied by that of the water. ,, 



io It follows from what has been said, that tvvo sahne solutions 

 cannot exist together v/ithout an exchange ensuing between the 

 elements of the two salts; this is contrary to the opinion hitherto 

 eritertained. It has been supposed that the exchange does not 

 tske place unless an insoluble salt which precipitates be formed, 

 atid Berthollet attributed the decomposition to the insolubility 

 itself. But it has been justly remarked, that the force of cohe- 

 sion to which the insolubility is owing has no effect till the 

 decomposition has taken place, and consequently cannot be the 

 cause of it. Hence it is only a secondary cause, which renders 

 it permanent and manifest, whereas otherwise it is continual aild; 

 latenti- — •■•■ ■ • ■ ■ ^ ■ ; \. ■- • ; -;'| 



There are phenomena which prov^ ^iH^'V^atiiy of this tatehlfc* 

 action between two sahne solutions, in which no precipitate is 

 fornied,'^s in the action of the carbonates of potash and soda on 

 insoluble salts. The decomposition is never complete, but 

 always stops at a certain point, although a portion of the car- 

 bonate still remains in solution. This arises from the formatioil' 

 dfca-soluble salt by the union of the alkaline base and the acid" 

 <rfithte)Jinsoluble salt, whose quantity continually increases with 

 tiife jjrdgvess'^of the decomposition. The phenomena mentioned 

 above are then developed between the two salts in solution, ^.hd 

 thi^-iMecipi'ocal action opposed that of the alkaline carbonate on 

 the. insoluble salt. It at the same time renders that which ihU 

 soluble salt resulting from the decomposition would exert 6n 

 the* insoluble salt, also derived from the same source, impo'ssibiy? 

 for in tlie decomposition of sulphate of barytes, for instance, iy£ 

 carbonate of potash, the soluble sulphate that is formed, mighE 

 Qfteii th« separation of this carbonate, decompose that of the 

 bak^lebxilWit^oi^ijs decomposition is also'U^^Vf'ifttidttria^e^W 



