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of “ions”, or electrons, protons and neutrons etc.-forming that atom. The settings, dispositions and movements of these ions etc. inside an atom fix up or determine the quality, nature, characteristics and all other properties of that particular element of which that atom is the final and indivisible elementary constituent. One, two or any number of atoms of one variety or of various kinds of atoms of different elements, may constitute a molecule of a particular substance, All molecules of any substance are in close contact together. Many substances may be mixed together. Due to perpetual vibrations and other motions, a number of ions or electrons etc, leave a particular molecule and penetrate in the neighbouring molecules, and so on; and to fill up the gap of the previous molecules, ions etc. flow from other molecules in contact. So a flow of these ions or electrons etc. go on inside the substance. If the incoming and the out going ions etc. are the same the substance remains the same. But as soon as the exchanges of these ions etc. become different, due to various reasons then the substance changes to some other substance, due to the change in its internal structure of molecular settings and atomic
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