The Romance of Modern Chemistry

NATURES BUILDING MATERIAL particles of sulphur can be dissolved out by using a suitable liquid. The reader will therefore see that it is a comparatively easy matter to separate the components of a mechanical mixture. Suppose now that some of the iron-sulphur mixture is put in a tube and that the tube is heated by a flame at one end. Something of importance obviously takes place, for the contents of the tube above the flame begin to glow vigorously and are raised to a white heat. Even if the tube is no longer heated externally, the flame being re- moved, the glowing continues until the zone of incan- descence has passed right through from one end of the iron-sulphur mixture to the other. This extraordinary display of energy is evidence that the iron and sulphur are combining chemically, and if the product is examined when it has cooled, it will be found that a new substance with entirely different properties has indeed been pro- duced. There are no iron particles now to be attracted by the magnet, and no liquid can be found which will extract the sulphur and leave the iron behind. The iron and sulphur particles are no longer lying side by side , they have united and coalesced to form a compound sulphide of iron the properties of which are quite different from those of iron and sulphur. Countless other illustrations might be cited of the fundamental difference between a mere mixture of two elements and a chemical compound of the two. A familiar case is gunpowder. This is a mechanical mixture of sulphur, carbon, and nitre, and it is only when the gunpowder is fired that the real chemical process begins. This pro- cess results in the production of a number of new sub- stances—gases—absolutely different from the original constituents of the gunpowder. 34