of the Voltaic Pile. 131 



particles of a metal must contract more suddenly than those 

 of any other substance, heat will be imparted to surrounding 

 bodies, and to that part of the metal which has not been 

 equally exposed to the heat-making body, with greater rapidity. 

 Thus, conducting power appears to depend upon the particles 

 of the conductor being nearer each other, thereby producing 

 a more rapid contraction after being heated. 



Capacity for heat appears, then, to be the consequence of 

 the greater want of* attraction between the particles of the sub- 

 stance than of a conductor; for if a substance possessing a 

 greater capacity do expand by exposure to a higher tempera- 

 ture, yet by exposure to a lower temperature, it will, owing to 

 the greater want of attraction, unlike the metals, not contract 

 in the same sudden manner they do, and therefore cannot be so 

 powerful a conductor. Thus, owing to the greater mutual 

 attraction between the particles of a conductor, metals possess 

 the least capacity for heat of all the forms of matter. In water 

 these two powers are more equally blended than in any other 

 body ; it possesses a greater conducting power than any other 

 fluid of equal density, and has a great capacity for heat. It 

 exists in three forms, solid, fluid and gaseous, at a less varia- 

 tion of temperature than any other fluid compounds, and, by 

 the action of heat alone, differs from all others in being unal- 

 terable in composition. 



The Voltaic pile consists of a number of series, generally 

 about 200, arranged in the form of a pile ; each series con- 

 siting of zinc, silver or copper, both about the size of a half 

 crown, and cloth of the same size moistened with some saline 

 or acid solution, as of nitre, common salt, or sal ammoniac, 

 sulphuric, nitric or muriatic acid. This apparatus is vari- 

 ously arranged for the sake of convenience, but the principle 

 is still the same ; as by arranging the plates of the two metals 

 soldered together cross-ways in a wooden trough, and filling 

 the interstices with the saline or acid solution ; if the hands 

 moistened be applied to each extremity of the pile, a shock 

 will be perceived. 



If two platina wires, one in contact with the zinc extremity, 

 the other with the copper extremity, be connected by means 

 of a small piece of charcoal, the charcoal will be ignited. 



If the wires be immersed in the same portion of water, 

 oxygen will be given off at the positive wire, that connected 

 with the zinc extremity; and hydrogen gas at the negative 

 wire, that connected with the copper extremity. 



If the wires be introduced into strong acid solutions, oxy- 

 ■j* n separates at the positive wire, and the inflammable com- 

 ponent at the negative wire. Strong saline solutions are 



It 2 acted 



