50 On the Replacement of Metals in a Voltaic Cell. [Nov. 25, 



lected in 14 minutes ; a similar volume required 15 minutes, and so on, as 



in the subjoined Table. 



Time required. 



First measure 14 minutes. 



Second ,, 15 „ 



Third „ 16 m. 50 sec. 



Fourth „ 17 „ 40 „ 



Fifth „ 19 „ 20 „ 



After 20 hours 25 minutes. 



After some time a white precipitate formed, the product of the action 

 of the potassium hydrate and magnesium chloride, which increased in 

 amount. The evolution of gas continued until the whole of the magne- 

 sium immersed had disappeared. 



Sodium Chloride. 



Similar experiments were made with a neutral solution of chloride of 

 sodium containing 5 per cent, of salt. Judging by one experiment with 

 the divided-cell arrangement, the sodium salt was decomposed somewhat 

 more quickly than the potassium salt, as might be anticipated. 



Volta, in his original pile, employed a solution of common salt as the 

 exciting liquid. It seems to have been generally assumed, at least in late 

 years, that it is the water alone that is decomposed ; but as a matter of 

 fact the plates become alkaline. 



Ammonium Chloride. 

 On employing a 5-per cent, solution of ammonium chloride, free ammo- 

 nia and hydrogen were obtained at the platinum plate. On causing the 

 platinum to dip into a little mercury during the reaction the mercury in- 

 creased in bulk, owing to the formation of the so-called ammonium 

 amalgam. 



Chlorides of Metals of the Alkaline Earths. 



The chlorides of barium, strontium, and calcium are easily decomposed 

 by magnesium in connexion with platinum. The hydrates pass into the 

 liquid until it is saturated, when they precipitate. Of course hydrogen 

 escapes at the same time from the platinum plate. 



Other Combinations. 

 As might be expected, these actions are not confined to chlorides. The 

 sulphates and nitrates of potassium and sodium give similar results in the 

 magnesium connected with platinum, an alkaline hydrate always appearing 

 against the platinum plate. 



If one metal in conjunction with another more electro-negative than 

 itself will decompose the salt of a more positive metal in aqueous solution, 



