CHAPTER VI 



ELECTROLYTES, NON-ELECTROLYTES AND 

 COLLOIDS 



Since electrolytes in dilute aqueous solution are usually largely 

 dissociated, it is with the ions that we have most to do. Many 

 of the ions are elements and their properties may be predicted 

 from their places in the periodic system. In Fig. i, curve III, 

 the atomic weights of the elements are plotted on the abscissae 

 and the atomic volumes on the ordinates. There are a number 

 of U-shaped curves. At the tops of the arms are, Li, Na, K, 

 Rb and Cs. These are the alkali metals and are arranged in 

 order of their properties. The first spaces going down the left 

 hand slopes indicate F, CI, Br and I. These are the halogens 

 arranged in the order of their properties, forming the most im- 

 portant monatomic anions in life processes. We find Be (above 

 B), Mg, Ca, Sr and Ba occupying the first places down the right 

 hand slopes. This is the alkaline earth series. The last three 

 are arranged according to their physiological properties, but Mg 

 sometimes behaves as an alkaline earth metal, sometimes as an 

 alkali metal. It is peculiar also in its physical properties, 

 MgS0 4 , for instance, being very poorly dissociated. The inter- 

 mediate elements of the first and second curves, C, N and O and 

 Si, P and S, form many of the compound ions. 



The most important anions may be arranged according to their 

 effect on the thermodynamic properties of water as a solvent in 

 the following lyotrope series : CNS, I, (Br, N0 3 ), CI, CH 3 COO, 

 S0 4 , HP0 4 , Tartric, Citric. They decrease the compressibility 

 of water from left to right. Those to the left decrease, and 

 those to the right increase the viscosity of water. They increase 

 the saponification of esters by bases from left to right and the 

 reverse is true of the hydrolysis of esters by acids. They in- 

 crease the surface tension of water from left to right. The 

 electrolytic solution tension increases from left to right. The 



