Remarks on the Galvanic Battery. 137 



DanieWs Battery. — The battery originally constructed by 

 Daniell consisted of a copper cylinder 6 inches high and 

 3J inches in diameter, with a porous cell or ox-gullet pass- 

 ing through the centre, in which was suspended a rod of 

 zinc 6 inches in length, and ^ inch in diameter. The 

 porous cell passed through the bottom of the copper cylin- 

 der and the end was connected with a glass siphon, bent 

 in such a manner that the top was on a level with the 

 surface of the liquid. The battery was excited with a sa- 

 turated solution of sulphate of copper and water acidulated 

 with sulphuric acid. When fresh water and acid was 

 poured in the top of the porous cell, an equal amount of 

 liquid was forced out from the bottom through the siphon. 

 It was intended by this arrangement to maintain at all 

 times the same strength of acidulated water about the zinc. 

 After this battery came in general use, porous clay cells 

 were substituted for the membranous bag, and the siphon 

 was discarded. 



Hill's Battery. — As many of our experiments were made 

 with Hill's modification of Daniell's battery, a description 

 of its peculiarity is deemed necessary. This battery con- 

 sists of a glass jar, with a sheet of copper placed in the 

 bottom and a disk of zinc, perforated in the centre, sus- 

 pended horizontally near the top. Protected copper wires 

 are attached to the zinc and copper forming the two poles 

 of the battery. When thus arranged the jar is tilled with 

 a solution of s. z., 1 after which a few crystals of s. c. are 

 dropped in through the orifice in the zinc, and lie on the 

 copper plate. If the liquid is not agitated the copper will 

 lie in a solution of s. c. and the zinc in a solution of 5. z., 

 so long as the specific gravity of the latter is less than 36° 

 B. The intervening liquid s. z. acts as a protection in the 

 same manner as the porous cell in Daniell's battery. 



1 The following abbreviations are used : q. Quantity of electricity flowing 

 in tbe external circuit ; s. c. sulphate of copper ; s. z. sulphate of zinc. 

 [Trans. vi.~] 18 



