IDEAS OF PHYSICAL CHEMISTRY 13 



he cannot go. As soon as he has found something in which 

 he can detect nothing heterogeneous, which he is unable by 

 any known means to divide, he stops at what he calls the 

 elementary atom. 



You will notice that this is by no means a positive defi- 

 nition by which we deny to our imagination the right of 

 subdividing our atom or of dissociating our element. We 

 merely ask for better proof than that of instinct, before we 

 allow the inferences that are to be drawn from such a further 

 subdivision to affect our treatment of the subject. The testi- 

 mony which we present in favor of the homogeneity of our 

 ultimate element is purely negative: we have found no hetero- 

 geneity. For example, we take this piece of rock; to the 

 geologist, it presents itself as a unit, granite. The lithologist 

 sees in it a composite mass of quartz, feldspar, and mica, 

 which again are individuals for his eye. But for the chemist, 

 feldspar is highly complex: he can isolate from it, silicon, 

 oxygen, potassium, aluminium, magnesium, iron, and possi- 

 bly other elements. No means have yet been devised so 

 subtle as to subdivide these elementary substances. 



Recognizing such as our simple substances, we find that 

 each has certain properties of its own, which serve to dis- 

 tinguish it from the rest, and which cannot be transferred 

 from it to one of its fellows. The ancient and mediaeval 

 alchemists regarded these elements as composites, contain- 

 ing in different proportions those principles of Aristotle to 

 which we have already referred. To them, therefore, it 

 seemed perfectly logical, that by addition or subtraction of 

 some quality-bearing principle, one metal could be converted 

 into another. It is only because we have, by carefully con- 

 ducted experiments, found the metals to be homogeneous, 

 toward all the agencies which we know, that we have come 

 to another conclusion, and ridicule the idea of their mutation. 



