62 MR. J. P. JOULE ON THE LIFE AND WRITINGS 



cient for the exhibition of most electro-magnetic experiments." 

 Mr. Sturgeon was prepared to meet with this remarkable fact, 

 having early in 1827 constructed several dry electric columns, 

 in which zinc roughened on one side was the only metal em- 

 ployed. The importance of employing rolled instead of cast 

 zinc for voltaic batteries was thus made evident. 



The second fact to which I shall allude, as developed in 

 this pamphlet, is the great advantage to be derived from 

 amalgamating the zinc plates of a voltaic battery. Sir 

 Humphrey Davy, in his Bakerian Lecture for 1826, an- 

 nounced that amalgamated zinc is positive relatively to pure 

 zinc, without, however, drawing any conclusion regarding 

 the construction of voltaic batteries. Mr. Kemp, in 1828, 

 published in Professor Jameson's Journal, the account of a 

 battery in which the positive metal consisted of liquid amal- 

 gam of zinc. Mr. Sturgeon appears, however, to have been 

 the first person who introduced the use of amalgamated plates 

 of zinc. After pointing out the method of amalgamating the 

 plates, by first dipping them in a solution of sulphuric acid, 

 and then immersing them in mercury, or spreading mercury 

 over them with a piece of rag, he says, " were it not on 

 account of the brittleness and other inconveniences occasioned 

 by the incorporation of the mercury with the zinc, amalgama- 

 tion of the surfaces of the zinc plates in galvanic batteries 

 would become an important improvement; for the metal 

 would last much longer, and remain bright for a considerable 

 time, even for several successive hours, — essential consider- 

 ations in the employment of this apparatus. Notwithstanding 

 the inconveniences, however, the improvement afforded by 

 amalgamating the surfaces of zinc plates becomes available 

 in many experiments ; for the violent and intense chemical 

 action which is exercised on zinc by a solution of sulphuric or 

 muriatic acid, with the consequent evolution of heat, and 

 annoying liberation of hydrogen, have no place when the 

 plates are amalgamated ; the action is tranquil and uniform, 



