I remember when I mixed the sulphuric acid with water that I learned to pour the acid into the water and not the other way around. Spatterings of sulphuric acid are not good for hands or clothes. With this solution I filled the jar almost to the top and then hung over the edge a sort of a crow's foot shape of cast zinc. The zinc reached down into the sulphuric acid solution. There was a binding post on it to which a wire could be connected. This wire and the one which came from the plate of copper at the bottom were the two terminals of the battery. We called the wire from the copper "positive" and the one from the zinc "negative." Now we shall see why and how the battery worked. The molecules of sulphuric acid dissociate in solution just as do those of copper sulphate. When sulphuric acid molecules split, the sulphate part goes away with two electrons which don't belong to it and each of the hydrogen atoms goes away by itself but without its electron. We call each a "hydrogen ion" but you can see that each is a single proton. In the two solutions are pieces of zinc and copper. Zinc is like all the rest of the metals in one way. Atoms of metals always have lonely electrons for which there doesn't seem to be room in the game which is going on around their nuclei. Copper as we saw has two lonely electrons in each atom. Zinc also has two. Some metals have one and some two and some even more lonely electrons in each atom. What happens then is this. The sulphate ions wandering around in the weak solution of sulphuric acid come along beside the zinc plate and beckon to its atoms. The sulphate ions had a great deal rather play the game called "zinc sulphate" than the game called "hydrogen sulphate." So the zinc atoms leave their places to join with the sulphate ions. But wait a minute! The sulphate ions have two extra electrons which they kept from the hydrogen atoms. They don't need the two lonely electrons which each zinc atom could bring and so the zinc atom leaves behind it these unnecessary electrons. Every time a zinc atom leaves the plate it fails to take all its electrons with it. What leaves the zinc plate, therefore, to go into solution is really not a zinc atom but is a zinc ion; that is, it is the nucleus of a zinc atom and all except two of the planetary electrons. Every time a zinc ion leaves the plate there are left behind two electrons. The plate doesn't want them for all the rest of its atoms have just the same number of protons as of electrons. Where are they to go? We shall see in a minute. Sometimes the zinc ions which have got into solution meet with sulphate ions and form zinc sulphate molecules. But if they do these molecules split up sooner or later into ions again. In the upper part of the liquid in the jar, therefore, there are sulphate ions which are negative and two kinds of positive ions, namely, the hydrogen ions and the zinc ions.