THERMODYNAMIC AL SYSTEM OF GIBBS 101 



equation 



2mhC1 + 2MO2 — MH20 + MCI2 > 



and this is evidently the relation between the /x's in a gaseous 

 mass containing all four components. In this case we may- 

 observe that if the gram were taken as the unit mass of aU four 

 substances, the relation between the components would be 

 (approximately) 



73 @a + 16 ©6 = 18 ©ft + 71 ©,, 



where <Sa, ®6, ©*, ®z represent one gram of hydrogen chloride, 

 oxygen, water and chlorine, respectively; and (84) would take 

 the form 



73 Ma + 16 Mb = 18 Mk + 71 Mr, 



or, 



73 Ha + 16 jUb = 18 Hk + 71 Hi, 



where the value of /x for each substance is that in a part of the 

 system in which it is present as an actual component. 



Again, the four substances magnesium chloride, potassium 

 sulphate, magnesium sulphate, potassium chloride, may be 

 regarded as components of a solution made by dissolving mag- 

 nesium chloride and potassium sulphate in water, since the last 

 two may be formed out of the first two according to the equation 



MgCl2 + K2SO4 = MgS04 + 2KC1. 



K the units of quantity of the four substances are the quantities 

 represented by the symbols MgCl2, K2SO4, MgS04 and KCl, 

 (84) takes the form 



-^MgCla + -^K2S04 = -^MgSO* + 2 M^Ch 



so that the potentials in the solution are related by the equation 



/^MgCh + MK2SO4 — MMgSO* + 2 mkci- 



Gibbs shows that if there are r independent relations similar 



