This process of depositing metals upon the surface of solids by an electric current is called _electroplating_. Everyone has seen _electroplated_ articles such as silver plated knives, forks, and spoons, and nickel-plated rods, handles, etc. _Copper electrotype_ plates such as are used in printing school books are made by this process. In practical electroplating a solution of the metal to be deposited is placed in a tank; across the top of this tank are placed copper rods to act as conducting supports. From one of these rods, the cathode, objects to be plated are hung so as to be immersed in the liquid. From other rods, the anodes, are hung plates of the metal to be deposited. These are dissolved as the current deposits a coating upon the articles, thus keeping the solution up to its proper strength. (See Fig. 261.) [Illustration: FIG. 262.--The current is carried through the solution by ions.] =281. Electrolysis.=--A solution from which a deposit is made by an electric current is called an _electrolyte_. The plates or other objects by which the current enters or leaves the electrolyte are called the _electrodes_. The electrode by which the current enters is called the _anode_ (_an_ = in) while the electrode by which it leaves is the cathode (_cath_ = away). The process by which an electric current decomposes a solution and deposits a substance upon an electrode is called _electrolysis_. The _current_ always flows within the cell from _anode to the cathode_. (See Fig. 262.) The metal goes with the current and is found deposited upon the cathode. =282. Theory of Electrolysis.=--The action going on in an _electrolytic_ cell has been carefully studied. The _theory of electrolysis_, which is supported by much experimental evidence, supposes that many of the molecules in a _dilute_ solution of a substance "split up" into two parts called "ions," one ion having a positive, the other a negative charge. In a dilute solution of sulphuric acid, the _positive_ ion is of hydrogen, while the _negative_ ion is the (SO_{4}) or sulphion. These ions bearing electric charges are believed to be the _carriers of the electric current_ through the electrolyte. The positive ions move with the current from the anode to the cathode, while the negative ions apparently are repelled by the cathode and appear upon the anode. Evidence of the accumulation of the two kinds of ions at the two electrodes is furnished by the _electrolysis_ of water, described below.