_II. The mass of any substance deposited by a current of uniform intensity is directly proportional to the time the current flows._ These laws have been used as a basis for defining and measuring the unit of current flow, the _ampere_. (See Art. 264.) =286. Instances of Electrolysis.=--(a) Medicines, especially those containing a mineral substance, are sometimes introduced into the human body by electrolysis. (b) Water and gas pipes are sometimes much weakened by the effects of electric currents in the earth, especially return currents from street railways. Such currents use the metal pipes as a conductor. At the place where the current leaves the metal and enters the ground, it removes metallic ions from the pipe. This process continuing, the pipe becomes weakened and at length breaks. (c) _Copper_ is purified by the use of electric currents that remove the copper from ore or from other metals and deposit it upon electrodes. _Electrolytic_ copper is the purest known. (d) _Aluminum_ is obtained by the use of large currents of electricity that first heat the material used until it melts and then deposit the metal from the fluid material by electrolysis. These results are called chemical effects of the current since by the use of electric currents substances are changed chemically, that is, they are separated into different chemical substances. Important Topics 1. Electrolysis, electroplating, anode, cathode, ion. 2. Theory of electrolysis--evidence: (a) electrolysis of water; (b) conductivity of acid and water. 3. Laws of electrolysis. 4. Practical use of electrolysis. Exercises 1. A dynamo has an E.M.F. of 10 volts. What is the resistance in the circuit when 20 amperes are flowing? 2. How much silver will be deposited in an hour by this current? 3. Name five objects outside of the laboratory that have been acted upon by electrolysis. How in each case? 4. Why is table ware silver plated? Why are many iron objects nickel plated? 5. How is the electrolysis of water pipes prevented? 6. Two grams of silver are to be deposited on a spoon by a current of 1 ampere. Find the time required. 7. How long will it take to deposit 20 g. of silver in an electroplating bath if a current of 20 amperes is used? 8. If 1000 g. of silver are deposited on the cathode of an electrolytic reduction plant in 10 minutes, what is the current intensity employed? (2) THE STORAGE BATTERY AND ELECTRIC POWER =287. Differences Between Voltaic and Storage Cells.= Voltaic cells in which electric currents are produced by the chemical action between metal plates and an electrolyte are often called _primary batteries_. In voltaic cells one or both plates and the electrolyte are used up or lose their chemical energy in producing the current and after a time need to be replaced by new material, the _chemical energy_ of the electrolyte and of one of the plates having been _transformed_ into electrical energy.