_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.) [Illustration: Fig. 83.] =263. Directions.= (A) Holding the amalgamated zinc strip in one hand and the copper strip in the other (Fig. 83), dip them into the acid, but do not let them touch each other. Note any chemical action. (B) Touch the copper and zinc together, _below_ the surface of the acid. Watch the copper. (C) Separate the lower ends of the strips, then touch them together _above_ the acid. Anything still happen to the copper? (D) Slip one spring connector with the attached wire upon the zinc strip, then stand the strips in the tumbler, so that they can not touch each other. Now touch the copper strip with the free end of the wire, at the same time watching the copper. (E) Raise the wire from Cu, touch it to Cu again, and repeat several times until you are sure that something takes place every time the wire touches Cu. _=264. The Electric Current.=_ Something must happen in or through the wire, and it can only happen when the two metals are joined in some way. This peculiar, invisible action in the wire is called the _electric current_, and such an arrangement is called a _Galvanic cell_. _=265. Source of the Electrification.=_ When two different metals are placed in acid they are electrified unequally by chemical action. Each has a higher potential than the acid, but their potentials are not the same. This electrification tends to pass from the place of higher to the place of lower potential, and the conducting wire allows this transfer to take place. As the difference of potential is kept up by the continued chemical action, the current is continuous, and not simply instantaneous, as in discharges of frictional electricity. As heat is produced by the burning of coal, so electrification is produced by the chemical burning of zinc. Chemical energy is the source of electrification in the Galvanic cell, just as muscular energy was the source of the electrification in the experiments with frictional electricity.