The granular carbon may be had by crushing up some old battery carbons. The parts given in both of the above formulas are proportioned so that they may be measured by bulk and not by weight. An old teaspoon or a small cup will make a good measure. Each one of the zinc shells should be filled in this manner. After they have all been filled, clean off the top edge of the zinc and pour the remaining space in the cell full of molten tar or pitch so as to seal it over. Solder a small binding-post to the top edge of the zinc to facilitate connection. Then wrap the cells in several thicknesses of heavy paper to prevent them from short circuiting, and they are ready for use. A small hole bored through the sealing material after it is dry will provide a vent for the escape of gases. *Recharging dry cells* is a subject that interests most experimenters. Dry cells very often become useless before the zinc shell is used up or the chemicals are exhausted, due to the fact that the water inside of the cell dries up and the resistance therefore becomes so great that it is practically impossible for the current to pass. The life of such cells may be partially renewed by drilling several holes in the cell and permitting it to soak in a strong solution of sal ammoniac until some of the liquid is absorbed. The holes should then be plugged up with some sealing wax in order to prevent evaporation. An old dry cell may be easily turned into a "wet" cell by drilling the zinc full of holes and then setting it in a jar containing a sal ammoniac solution. The battery should be allowed to remain in the solution. *Wet batteries* are very much easier to make than dry batteries and are capable of delivering more current. They have the disadvantage, however, of wasting away more rapidly, when not in service, than dry cells. The Leclanche cell is the type generally first attempted by most experimenters. *Carbon plates* for making such a battery are most easily and cheaply obtained from old dry cells. About the only way that a dry cell can be broken open is with a cold-chisel and a hammer. Care must be taken, however, in order not to break the carbon. Ordinary jelly-glasses make good jars for small cells. Fruit-jars may be used for larger batteries by cutting the tops off so that the opening is larger. The carbon plate contained in a dry cell is usually too long for a jar of this sort and must be broken off before it can be used. The lower end is the one which should be broken because the top carries a binding-post, with which connections can be made. A small hole is bored in the carbon rod at a distance from the bottom equal to the height of the jar which is to be used. [Illustration: Fig. 59.—A Zinc-Carbon Element, made from Heavy plates.]