2. Ions: hydrogen, positive: sulphion, negative.
3. Current, where and how produced, direction, illustration.
4. Polarization: cure, local action, cure.
Exercises
1. Write in your own words an account of the production of an electric current by the simple voltaic cell. Use sketches.
2. Which plate has the higher potential? How is it produced?
3. Would you expect to get an E.M.F. by forming a cell of two copper plates? Why?
(3) Practical Voltaic Cells
248. Advantages of Voltaic Cells.—Many forms of voltaic cells have been devised. Several of the more common of these will be described and their electro-chemical action explained.
At the present time voltaic cells are employed only where small currents are needed, such as for electric bells and induction coils. Where more than a small amount of current is required, the dynamo and the storage battery have generally taken their place as sources of electric current.