Hydrogen 34,135 Carbon 7,990 Sulphur 2,263 Phosphorus 5,747 Zinc 1,301 Iron 1,576 Tin 1,233 Olefiant Gas 11,900 Alcohol 7,016 165. There are other methods, besides combustion, by which chemical combination takes place. When, for instance, we plunge a piece of metallic iron into a solution of copper, we find that when we take it out, its surface is covered with copper. Part of the iron has been dissolved, taking the place of the copper, which has therefore been thrown, in its metallic state, upon the surface of the iron. Now, in this operation heat is given out--we have in fact burned, or oxidized, the iron, and we are thus furnished with a means of arranging the metals, beginning with that which gives out most heat, when used to displace the metal at the other extremity of the series. 166. The following list has been formed, on this principle, by Dr. Andrews:-- 1. Zinc 2. Iron 3. Lead 4. Copper 5. Mercury 6. Silver 7. Platinum --that is to say, the metal platinum can be displaced by any other metal of the series, but we shall get most heat if we use zinc to displace it. We may therefore assume that if we displace a definite quantity of platinum by a definite quantity of zinc, we shall get a definite amount of heat. Suppose, however, that instead of performing the operation in one step, we make two of it. Let us, for instance, first of all displace copper by means of zinc, and then platinum by means of copper. Is it not possible that the one of these processes may be more fruitful in heat giving than the other? Now, Andrews has shown us that we cannot gain an advantage over Nature in this way, and that if we use our zinc first of all to displace iron, or copper, or lead, and then use this metal to displace platinum, we shall obtain just the very same amount of heat as if we had used the zinc to displace the platinum at once. 167. It ought here to be mentioned that, very generally, chemical action is accompanied with a change of molecular condition.