(B) Join the cells in parallel and take the reading, using the same external resistance as in (A). (C) Increase the external resistance by adding coils of wire or 2 metres of No. 28 G-s wire and repeat (A) and (B). What does the experiment show? (D) Take the reading with 1 cell and large external resistance. _=368. Best Arrangement of Cells.=_ It will be seen by experiments that with a given number of cells the strongest current is produced when they are arranged so that the internal resistance of the battery nearly equals the external resistance of the circuit. When the external resistance is small, the internal resistance may be kept down by joining the cells in parallel; and, although the E. M. F. is also kept small, the value of C will be larger than it would be with a larger internal resistance and a larger E. M. F. When the external resistance is large, the internal resistance can be made large by joining the cells in series. The advantage comes, however, from having a large value of E. A large resistance can not hold back a current of large E. M. F. By joining the cells in series the value of E is made large, and the value of C becomes large even though there is an increased internal resistance. (See Elementary Electrical Examples.) CHAPTER XXI. CHEMICAL EFFECTS OF THE ELECTRIC CURRENT. _=369. Chemical Action and Electricity.=_ We have learned that the electric current is produced, in the cell, by chemical action. There is a definite relation between the chemical action and the current produced. We are now to study the changing of electrical energy back, again, to chemical energy. [Illustration: Fig. 112.] _=370. Electrolysis=_ is the name given to the process of decomposing chemical compounds by passing the electric current through them. The compound decomposed is the _electrolyte_. Fig. 112 shows a tumbler of liquid (electrolyte) through which the current is to pass in the direction of the arrow. Two carbon plates, A and C, are in the liquid, and are joined to the source of electricity. The current enters at A (_anode_) and leaves at C (_cathode_). [Illustration: Fig. 113.] =EXPERIMENT 147. To study the electrolysis of water.= _Apparatus._ The two simple cells (§ 275) joined in series (§ 364), although two Daniell or two dry cells will be better. A tumbler of water containing a few drops of sulphuric acid to make the water a conductor. Two pieces of sheet copper will serve as the electrodes. The galvanoscope may also be put into the circuit as in Fig. 113. =371. Directions.= (A) Allow the current to pass, and note (1) whether gas is set free at both electrodes, A and C, and (2) at which the quantity of gas is the greater. If very little gas is produced use more cells. (B) Remove A and C from the liquid, to remove the gas, then watch the action of the needle of G V as the water is again decomposed.