CHEMISTRY. 511 



Chemical Reactions in the Leclanche Ceil. — Dr. Edward Divers has 

 presented the following reactions : Zinc is slowly acted upon by a solu- 

 tion of ammonium chloride, and crystals of zinco-diammonium-chloride 

 are formed 5 this is decomi>osed by water alone into an insoluble and a 

 soluble portion, probably as shown in this equation : 

 3Zn (NH3 Cl)2 + 2 OH2 = 2 HO Zn NHj CI + (CI H4 N)^. Zn (NH3 Cl)2 



Zinco-diammonium-chloride dissolved in solution of ammonium chlo- 

 ride acts gradually on artificially prepared hydrogen manganite, H2 O4 

 Mn2, causing manganese to go into solution, and the precipitation of 

 zinc on the manganite, probably thus : 



(NH3 Cl)2 Zn -f H2 04Mn2 = 2 NH4 CI + Zn O4 Muz 



These experimental facts lead the author to the following theory of 

 the action of the cell: 



Primary action: — Formation of hydrogen manganite and zinco- 

 diammonium-chloride. 



+ 



Mn2 O4 + 2 HNH3 CI + Zn 



become Muj O4 H2 -f (NH3 Cl)2 Zn. 



Secondary actions, causing polarization. — The hydrogen manganite acta 

 locally upon the zinco-diammonium (chloride solution, and forms zinc 

 manganite and ammonium chloride ; this proceeds more rapidly by gal- 

 vanic action when the cell is at work, thus : 



— + 



Mn2 O4 -f Zn {NH3 Cl)2 + Zn 

 become Muz O4 Zn (NH3 Cl)2 Zn. 



The zinc manganite and the hydrogen manganite by coating over 

 the manganese dioxide, protect it from the primary action of the am- 

 monium chloride and zinc, and thus cause polarization of the cell. 



Secondary actions, causing depolarization. — The ammonium chloride 

 dissolves manganous and zinc oxides out of the manganite, the manga- 

 nous oxide liberating ammonia: 



Mn, O4 Zn -f 4 CI H4 N = Mn 0^ + 2 OH^ + Cl^ Mn + (NH3 CI), Zn + 



2NH3. 



The manganous chloride dissolves in the presence of the free ammonia 

 as a double chloride of manganese and ammonium. By the solution of 

 these oxides the manganese dioxide of the manganite becomes active 

 again. The depolarizing action proceeds slower than the polarizing, 

 and therefore the battery requires to be left un circuited, in order to 

 recover its full power after use. {Chem. Neics, XI.VI, p. 259.) 



Atomic Weights of the Elements. 



Carbon. — Roscoe has redetermined the atomic weight of carbon by 

 the direct combustion of the diamond. If O = 15.96, he obtained as a 



