When the solution in a rectifier becomes hot it will not operate as efficiently as when cold. The solution becomes exhausted after a certain amount of usage and requires renewal. This condition will be indicated by the failure of the rectifier to operate properly. The old solution should then be thrown away and the jars and electrodes washed and cleaned thoroughly before the new solution is poured in. [Illustration: FIG. 57—A Complete Four-Cell Rectifier connected together and Mounted in a Tray.] CHAPTER V. HOW TO BUILD A STEP-DOWN TRANSFORMER FOR REDUCING THE 110 VOLT A. C. FOR EXPERIMENTAL PURPOSES. A Step-Down Transformer will reduce the 110 volt alternating current to a low voltage. These low voltage currents are still alternating but will operate almost all sorts of direct current apparatus with the exception of permanent magnet type motors which are now practically obsolete. A suitable step-down transformer may be used to operate electrical toys, such as small fans, motors and miniature electric railway trains, ring bells, light small lamps, operate spark coils, etc., in fact the different uses are practically unlimited, depending only upon the ingenuity of the experimenter. [Illustration: FIG. 58.—Details of the two different Pieces of Sheet Iron used in building up the Core. Sufficient of each piece are required to form a pile of each three-quarters of an inch thick.] A step-down transformer cannot be used to recharge storage cells or for electro-plating unless the current is first passed through a rectifier. A transformer is both in principle and construction really very simple. It consists simply of two coils of wire wound around an iron core. One coil consists of many turns of fine wire and is connected to the 110 volt alternating current. This coil is called the *primary*. The other coil consists of a smaller number of turns of larger wire and is called the *secondary*. The lower voltage currents are obtained from the secondary. The first step to take in making a transformer is to procure some sheet iron of the sort used for making stove pipes. It is called stove pipe iron. This iron will have to be cut into a number of pieces like A and B in Figure 58. The exact shape and dimensions are most easily understood from the illustration. A somewhat resembles a three-pronged fork, while B is simply a strip 2 5/8 inches long and 1/2 inch wide. [Illustration: FIG. 59.—The Method used in piling up the Strips to Assemble the Core.] A sufficient quantity of each piece will be required to make a pile three-quarters of an inch thick when tightly compressed.