SINGLE PAIR OF PLATES. 



25 



a wire be attached to each, and their opposite ends are placed in a 

 little dilute acid in another vessel, the same action will take place 

 between the zinc and copper as when they were in contact ; but in 

 this instance, the ends of the two wires which dip into the vessel 

 containing acid will undergo a change : the one attached to the zinc 

 will give off a quantity of hydrogen gas, while the one attached to 

 the copper, supposing it to be also copper, will rapidly, dissolve. 

 The copper and zinc, with the acid in the first vessel, constitutes a 

 battery of one pair. The second vessel with acid, in which the wires 

 are placed, is termed the decomposition cell. 



2. When zinc and copper, placed in dilute sulphuric acid, are brought into con- 

 tact, gas may be seen escaping from the copper. 



3. Zinc and copper, placed in dilute acid, may be connected by a wire, when the 

 same effects are produced as in the first case. 



4. Or they may be connected by putting the wires into a liquid, such as acid and 

 water, &c. 



Best kind of Zinc. The zinc used for the battery should be 

 milled or rolled zinc, not thinner than ^th of an inch, otherwise the 

 waste will be very great ; for amalgamated zinc, when it becomes 

 thin, is so tender and brittle, that the utmost care cannot preserve it 

 whole. The best thickness for the zincs, when their size is upwards 

 of four inches square, is ^th of an inch ; but if under this size, |-th 

 to T 3 ^th of an inch is the proper thickness. Cast plates of zinc should 

 not be used, as they are negative to rolled zinc, and give less electri- 

 cal power : they are so porous that no amalgamation will protect 

 them from the action of the acid " local action," as it is termed, 

 which is not only a waste of zinc and acid, but prevents to a great 

 extent the production of the quantity of electrical force which the 

 surface of the zinc in use is calculated to give. 



Amalgamation of the Zinc Plates. The amalgamation of zinc is 

 a process exceedingly simple ; nevertheless, if care be not taken, a 

 very great loss in mercury and zinc is soon effected. A stoneware 

 pan is best to use, and should be sufficiently capacious to allow the 

 zinc plate to lie flat within it : a mixture of eight parts water, and 



