LEWIS. THE LAW OF PHYSICO-CHEMICAL CHANGE. 60 



<// = «//, and P= P' 



in equation (29). Therefore the total area A reckoned algebraically 

 must equal zero. That is, the two areas on the two sides of the line of 

 constant pressure P must be equal. This is the well-known principle 

 of Maxwell. 



Summary. 



(1) The equation of Clausius for vapor pressure is simplified. 



(2) The meaning and utility of a new quantity, the escaping tendency, 

 or fugacity, are explained. 



(3) The influence of temperature and pressure upon fugacity is ex- 

 pressed in simple equations. 



(4) A simple, general equation, which embraces every possibility of 

 the change of state of any simple substance, is proposed. 



(5) This equation rests upon the conception of the intensity and 

 capacity dimensions of energy. 



(6) This equation is verified as applied to the influence of pressure on 

 fugacity. 



(7) This equation is verified as applied to the influence of temperature, 

 if a new quantity, instead of entropy, is regarded as the capacity dimen- 

 sion of heat. 



(8) This equation is verified for the influence of surface tension. 



(9) This equation is verified for the influence of electrical potential. 



(10) A method is offered by which the fugacity may be found from 

 the vapor pressure. 



