114 THE PHILOSOPHY OF BIOLOGY 



of starch by a green plant. Generally speaking, 

 chemical activity, that is, the possibility of occurrence 

 of chemical reactions, is a case of the second law of 

 energetics. Energy passes from a state of high to 

 a state of low potential. A chemical reaction will 

 occur if this change of potential is possible. 



In all such changes energy is dissipated. What 

 exactly does this mean ? It means that, generally 

 speaking, the potential energy of chemical compounds 

 tends to transform into kinetic energy ; while differ- 

 ences in the intensity factor of the kinetic energy of 

 the bodies forming a system tend to become minimal. 

 In a mixture of oxygen and hydrogen there is energy 

 of two kinds, (i) potential energy due to the position 

 of the molecules (O and H molecules are separated) ; 

 and (2) kinetic energy of the molecules (which are 

 moving about in the masses of gas) . After. the explosion 

 the potential energy acquired in the separation of the 

 molecules of O and H has disappeared (the molecules 

 having combined to form water), but the kinetic 

 energy has greatly increased, since the explosion 

 results in the formation of steam at high temperature. 

 But now this steam radiates off heat to adjacent 

 bodies, or becomes cooled by direct contact with the 

 envelope which contains it. The energy of the explo- 

 sion is therefore distributed to the adjoining bodies, 

 and the temperature of the latter becomes raised. 

 But these again radiate and conduct heat to other 

 bodies, and in this way the heat generated becomes 

 indefinitely diffused. 



The general effect of all physico-chemical changes 

 is therefore the generation of heat, and then this heat 

 tends to distribute itself throughout the whole system 

 of bodies in which the physico-chemical changes occur. 

 The energy passes into the state of kinetic energy, 



