Apparatus. The same as in the last experiment. A small piece of amalgamated zinc, however, will be better than the whole strip.
261. Directions. (A) Twist one end of the clean copper wire around the small piece of amalgamated zinc ([Fig. 82]). Hold one end of the wire in the hand and dip the combination into the acid. What takes place? Watch the surface of the copper, remembering that each, alone, was not acted upon by the acid ([Exp. 108]).
(B) Use the clean iron wire in place of the copper wire, and repeat (A). Watch the surface of the iron.
(C) With a string or thread tie a small piece of well amalgamated zinc to the carbon rod ([Fig. 82]), then dip the combination into the acid. Watch the surface of the carbon.
262. Discussion. While amalgamated zinc is not rapidly dissolved by dilute sulphuric acid, a vigorous[104] action of some kind takes place when it is in contact with another metal or with carbon in the acid. The bubbles of hydrogen that are liberated do not seem to come from the zinc; they appear to grow, in the fluid, directly at the surface of the copper, iron, or other metal used with the zinc. This shows that something besides the mere dissolving of a metal takes place.
Can we arrange our apparatus so that we can get some useful results from this action?
EXPERIMENT 110. To study the construction of a simple Voltaic or Galvanic cell.
Apparatus. A narrow strip of zinc (No. 60), amalgamated as directed in [§ 257]. (An amalgamated zinc rod (No. 74) may be used in place of the strip); a narrow strip of sheet copper (No. 67); the tumbler of dilute acid of [Exp. 108]; a flexible copper wire about 2 feet long, with spring connectors (No. 54) attached to its ends. (See Electrical Connections, [§ 226].)
