As has been already noted, chemical action produces heat. Conversely, if we apply heat to the cell we greatly increase its chemical action. We have also noted that chemical action produces an electric current, but unless the current is allowed to flow through some external channel like a closed circuit of wire the chemical action is greatly restrained or entirely checked. [Illustration: Fig. 150] In a glass tumbler I put a rod of pure zinc (Fig. 150, _Zn_), and an electric light carbon, _C_. A short wire, _a_, was arranged for connecting the two externally. In the tumbler was put some water with about one tenth its volume of sulphuric acid. No chemical action was evident until the wire was touched to the zinc, closing the circuit. Then bubbles of hydrogen gas gathered upon the surface of the carbon rod, and clung to it very tenaciously. We lifted out the carbon rod and rinsed off the bubbles in another tumbler of water, and then returned the carbon to its place in the cell. The experiment was repeated many times, and each time no bubbles of hydrogen, which is in this case the sign of the chemical action, appeared until the circuit was closed for the flow of the electric current. Incidentally it should be said that the amount of hydrogen produced by the chemical action is a measure of the amount of electric current produced. Incidentally also it should be said that the bubbles of hydrogen clinging to the carbon rod check and almost stop both the chemical action and the production of electric current when the circuit is closed. If now we put in sodium bichromate to use up the hydrogen as fast as it is produced we may have a continuous current whenever the circuit is closed. Chemical action does not entirely cease in this cell when the circuit is opened. But if two cells are prepared, and one is left with its circuit closed while the other remains with its circuit open, it will be found that the zinc disappears and the acid is used up in the closed cell in a short time, while these remain not greatly changed for a long time in the cell on which the circuit is open. No cell will remain forever without chemical action, yet a dry cell which might use up its zinc and ammonium chloride in a few hours if the circuit is closed may be kept idle three or four years, and still be able to furnish electricity enough to ring a bell. Some persons feel defrauded if the author of a book fails to give them all the new words and conventional terms which belong to any subject. For such here is a page or so.