Fig. 75.
Fig. 76 shows a chemical meter, a part of the current passing through a jar containing zinc plates and a solution of zinc sulphate. Metallic zinc is dissolved from one plate and deposited upon the other. The increase in weight shows the amount of chemical action which is proportional to the ampere hours. Knowing the relation between the quantity of current that can pass through the solution to that which can pass through the meter by another conductor, a calculation can be made which will give the current used. A lamp is so arranged that it automatically lights before the meter gets to the freezing-point; this warms it up to the proper temperature, at which point the light goes out again.
Fig. 76.
CHAPTER VII.
CHEMICAL EFFECTS OF THE ELECTRIC CURRENT.
79. Electrolysis. It has been seen that in the voltaic cell electricity is generated by chemical action. Sulphuric acid acts upon zinc and dissolves it in the cell, hydrogen is produced, etc. When this process is reversed, that is, when the electric current is passed through some solutions, they are decomposed, or broken up into their constituents. This process is called electrolysis, and the compound decomposed is the electrolyte. (See "Study," § 369, etc., with experiments.)
Fig. 77.