It will be noticed that these lines do not cross the straight line and the current therefore does not reverse but flows in one direction only. When a single cell of rectifier is used on the 110 volt current supply, it should be placed in series with a lamp bank or a step-down transformer so that the current is reduced to lower voltage. Figure 54 shows how to connect a storage cell in series with a single cell of rectifier and a lamp bank so that the storage cell may be recharged from the alternating current. A step-down transformer will be found more efficient and not quite so wasteful of current as a lamp bank. The rectifier and the storage cell are simply connected in series with the secondary of the step-down transformer in order to secure this result. [Illustration: FIG. 54.—Circuit showing how a Single Cell of Rectifier should be connected in series with a Lamp Bank to Recharge a Storage Cell. A is the Aluminum Plate and L the Lead or Iron Plate.] [Illustration: FIG. 55.—Diagram showing the Difference in Current after it has been passed through a Single Cell or Rectifier and after passing through a Four-Cell Rectifier.] The negative pole of the storage cell must always be connected to the aluminum electrode of the rectifier. The series of little curved lines at the bottom of Figure 53 which represent the alternating current after it has been changed into direct current by the action of the rectifier, have a space between each two, showing that there are periods during which no current flows but that the current is intermittent and made up of a number of short impulses. One-half of the alternating current is therefore really wasted. It is possible, by means of four cells of rectifier, to so connect them that "both halves of the alternating current wave are utilized" and the spaces are filled up as shown in the lower part of Figure 55. [Illustration: FIG. 56.—Diagram showing how a Four-Cell Rectifier is connected. The Alternating Current Source is connected to C and D. The Direct Current is taken off at A and B. The Electrodes marked A, A, A, A are the Aluminum Electrodes. L, L, L, L may be Lead or Iron.] The current which would normally be in a reverse direction, and therefore below the straight line, has been completely reversed so that it flows in the same direction as that above the line. Figure 56 shows how to connect four cells of rectifier in order to secure this result. An electrolytic rectifier composed of cells approximately 5 x 7 inches, as described, will not efficiently handle a current of over two to two and one-half amperes. A four cell rectifier will operate to the best advantage on a voltage over 50, and for that reason it is always best to use a lamp bank or step-down transformer in connection with it.