KLISHA MITCHELL SCIENTIFIC JOURNAL 41 



seemed to me an interesting- mathematical relation but noth- 

 ing- more. That was ten years ag-o. Today, I am willing- to 

 say that the phase rule offers the rational basis for the classi- 

 fication of phenomena in inorg-anic chemistry and that it is 

 perhaps the most valuable instrument of research that we 

 possess. In view of the fact that probably ninety-nine per 

 cent of the inorganic chemists make no use of the phase rule, 

 these may seem rather bold statements. I am going to try to 

 justify them. We will consider the phase rule first as a basis 

 of classification and then as an instrument of research. 



There are two criteria by which we may judg-e a method of 

 classification. It must cover the whole ground and the divis- 

 ions must be rational and not arbitrary. Our first division of 

 the subject is by components. We consider separately sys- 

 tems composed of one, two, three, four or more components. 

 Under each of these divisions we make further sub-heads 

 depending- on the number of phases. Thus under one-com- 

 ponetit systems we should take up first one-phase systems 

 and should discuss the genera] and specific properties and 

 characteristics of g-ases, liquids and solids. When consider- 

 ing- the specific properties of specific substances, these sub- 

 stances can be taken in an order based on the Periodic Law. 

 In the one-phase one-component systems and in all the other 

 divisions we can arrang-e our material, in so far as is desirable, 

 according- to the Periodic Law. Under two-phase one-com- 

 ponent systems, we classify liquid and vapor or boiling-point 

 phenomena, solid and vapor or sublimation phenomena, liquid 

 and solid or freezing-point phenomena, solid and solid or allo- 

 tropic phenomena. Under three phases we describe such phe- 

 nomena as the freezing-point of water, the equilibrium 

 between monoclinic sulphur, rhombic sulphur and vapor or 

 melt. Under this same heading comes the general question 

 of monotropic and enantiotropic forms. .While chemical act- 

 ion appears to be excluded in one-component systems, such 

 polymerized vapors as acetic acid, sulphur and nitrogen diox- 

 ide introduce changes involving the law of definite and multi- 



