DEFECTS OF COMMON ACID BATTERIES. 35 



was used as the electrode, and the quantity of black matter 

 obtained, and the quantity of copper dissolved to yield that pro- 

 duct: for the analysis indicates an amount and diversity of im- 

 purities in copper that has never hitherto been thought of. Both 

 the number and the proportions are startling. 



Another source of weakness to the electric current, and which 

 affects more or less all batteries of whatever construction, arises 

 from the action of the acid upon the zinc. The more freely this 

 action is allowed to proceed the more constant and powerful is the 

 battery. The acid in combining with the zinc forms a salt, which, 

 if it adhered to the surface of the plate, would soon stop further 

 action ; but this salt being soluble in water, is dissolved from the 

 surface of the plate as soon as formed, allowing a new surface to be 

 exposed. But water can only dissolve a certain quantity of the salt, 

 and its power of dissolving decreases as it approaches to the limit of 

 saturation : hence there is a constant tendency to a decrease of 

 power in the battery, and if means be not taken to withdraw the 

 salt of zinc formed, the battery will continue to decrease in power, 

 till at length it ceases to act. But long before the battery ceases to 

 act, the presence of sulphate of zinc manifests itself in several ways, 

 neutralizing the efficacy of the battery. The zinc salt, as it dis- 

 solves from the plate, being heavier than the acid solution, falls to 

 the bottom ; hence in a very short time the solution is formed of 

 strata of different densities, and this induces a galvanic action be- 

 tween the lower and upper portions of the plates, both copper and 

 zinc, and accounts for the deposition of zinc on the bottom part of 

 the plates, as above referred to. This local galvanic action between 

 the bottom and top part of the zinc plate is sometimes so great when 

 the battery has been long in action, as to double the thickness of 

 the zinc plate at bottom, while the part near the surface of the solu- 

 tion is nearly penetrated by the acid ; and when a battery is formed 

 of a number of pairs, the terminal zincs are those most effected, the 

 one forming the negative terminal or pole more so than the other. 

 We have found a deposition of 6-J ounces of zinc upon the two lower 

 inches of a plate terminal, which measured, in the solution, six 

 inches by five, the battery having been in operation but eighteen 

 hours. When this occurs, the quantity of electricity circulating 

 through the battery is very small. Although this evil may not 

 proceed to the extent of having quantities of zinc deposited upon 

 the bottom part of the plates, still the tendency to deposition which 

 every one who employs a battery must have observed, as also the 

 more rapid action of the acid on the upper parts of the plates, shews 

 that the action of the acid over the surface of the plate is very irre- 

 gular, and consequently the quantity of electricity must be irregular 

 in the same degree. 



