70 PHYSICS OF MATTER 



or in which the interactions between different kinds of matter result 

 in the formation of a substance different from either of the constitu- 

 ents; and that phase of biology which is concerned with the study 

 of the living cell and of the simplest conditions under which matter 

 exhibits the phenomena of life. 



It might have been said that physics deals with those phenomena 

 exhibited by and through matter when molecular groupings of atoms 

 are not disturbed, while chemistry deals with the phenomena of the 

 formation and breaking-up of the molecules. But such a statement 

 is based upon a theory of the structure of matter which in itself calls 

 for explanation, and therefore the previous statement is preferred as 

 being more general and avoiding the theoretical assumptions that 

 are involved in those just given. 



If it is asked what constitutes a particular kind of matter, why, 

 for instance, water-vapor is said to be the same substance as water 

 in the liquid form, it may be said that it is because one can be wholly 

 transformed into the other, each is homogeneous, and remains un- 

 changed in its properties during the transforming, and the trans- 

 formation is unique. 



Professor Ostwald has recently given a most interesting statement 

 of the criterion by which a substance or chemical individual may 

 be recognized without the need of any atomic hypothesis. We may 

 summarize his presentation thus: Where two substances are com- 

 bined as in solution, there will be one and only one proportion be- 

 tween the quantities of the substances for which, on change of state, 

 such as evaporation or crystallization, the vapor or crystals will 

 have the same composition as the remaining substance, while with 

 a greater or less proportion of either ingredient, there will be a change 

 of concentration with change of state. When such a combination 

 retains this property under widely different conditions of tempera- 

 ture and pressure, it is known as a chemical individual or definite 

 compound. If under no circumstances it can be broken up into two 

 phases which differ in constitution, it is called an element. 



Ostwald remarks, "The possibility of being changed from one 

 phase into another without variation of the properties of the residue 

 and of the new phase is indeed the most characteristic property of 

 a substance or chemical individual, and all our methods of testing 

 the purity of a substance, or of preparing a pure one, can be reduced 

 to this one property." 



But returning to our classification, it is seen that physics, chemis- 

 try, and biology are the three fundamental natural sciences, each 

 having as its primary object not the mere arrangement and classi- 

 fication of phenomena, but the formation of such a concept of matter 

 in those relations with which it deals, that the varied facts of obser- 

 vation appear as natural and inevitable consequences. 



