The zinc cup of the particular cell which we were examining appeared to be intact, and we proceeded to dig out the black powder. Its black colour is due to the manganese dioxide. Ammonium chloride is white. We lifted out the carbon rod and scraped the zinc cup clean. The binding posts attached to both the zinc cup and the carbon rod were left intact. Into the zinc cup we now poured a tumblerful of water and added about a quarter of its volume of hydrochloric acid, setting the whole into a large bowl to guard against disaster. Bubbles of gas were formed rapidly, causing the liquid to effervesce as a tumbler of soda water would do. We inverted an empty tumbler over the cup so as to collect this gas. In about two minutes we lifted the tumbler, still holding its mouth downward, and brought a lighted match to it. There was a flash and the contents burned with a pale-blue flame. Some of the zinc had united with some of the hydrochloric acid and set free hydrogen gas, which is one of the constituents of the acid. This is typical of chemical actions. Something similar takes place between the ammonium chloride and the zinc. Three interesting things occur in this experiment: 1. Chemical action, just described, is produced. 2. Heat is produced. This was very evident when we took the zinc cup up in our hands. It was as hot as though boiling water had been put into it. 3. An electro-motive force is produced. This we showed by connecting one end of a piece of copper wire to the binding post of the zinc cup and the other end of the wire to an electric bell. Another wire ran from the bell to the carbon rod. When the carbon rod was lowered into the acid the bell rang. Within ten minutes holes began to appear in the side of the zinc cup. The acid contents began to flow out into the bowl, and not long after the zinc fell to pieces. After fifteen or twenty minutes the action began to grow less. The acid was being used up as well as the zinc. If enough acid is added the zinc will wholly disappear. We have chosen substances which would produce striking results in this experiment, but the same sort of thing is going on about us continually. One summer by the seashore I fastened a brass plate upon my boat with two screws--one of brass and one of galvanized iron. The plate was attached below the water line so that it might be acted upon by the salt water. Within three weeks the head of the galvanized iron screw had entirely dissolved, while the brass screw was as good as ever. A galvanized iron screw near by but not in contact with the brass was still in as good order as ever. I had simply made an electric battery cell out of the ocean by dipping into it zinc and brass in contact. A most interesting relationship exists between the three kinds of activity in the cell, which have been mentioned, viz.: (1) chemical action; (2) production of heat; (3) production of electric current.